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JANUARY, 1968 THE ANALYST Vol. 93, No. I 102 A Sequential Scheme for the Determination of Several Fall-out Nuclides in Water BY F. M. BATHIE AND B. A. BURDEN (Ministry of Technology, Laboratovy of the Government Chemist, Covnwall House, Stamford Street, London, S.E.1) A method is described for the sequential separation and measurement of fall-out nuclides of ruthenium, molybdenum, tellurium, antimony and tin in water. The nuclides, together with added carriers, are separated from 10 litres of sample by precipitation and solvent-extraction methods, and are counted on a low background anti-coincidence p-counter. Chemical recoveries of added carriers range from 46 per cent. for antimony to 66 per cent. for molybdenum. The limits of detection range from 0.02 to 0.08 pico- curies per litre.THIS paper describes a sequential separation scheme for the fall-out nuclides of ruthenium, molybdenum, tellurium, tin and antimony in a single sample of water. Several sequential schemes1 9293,4 have been published that deal with various combinations of fall-out nuclides, but do not include nuclides of tellurium, tin and antimony. The method by Osmond, Owers, Healy and Mead5 and Osmond, Evett, Arden, Lovett and Sweeny6 that deals with strontium, caesium, barium and cerium nuclides has been extended in this laboratory to include nuclides of manganese, zirconium, yttrium and rare earths.' This latter scheme, and the one described in this paper, thus provide a means of examining water for all of the fall-out nuclides with a half-life greater than about 3 days, except iodine-131 and silver-111.Several methods exist8 for determining any one of the five elements discussed in this paper, but the present method was developed primarily for use with drinking waters, in which the activities are very low. Large volumes of water are therefore required, and it is more convenient to use a sequential separation scheme. The volume of water that can be used is limited both by the hardness of the water and the volatility of ruthenium. Thus, evaporation of water under acidic conditions may lead to loss of ruthenium, and under alkaline conditions large amounts of water solids are precipitated, particularly from hard waters. It was found convenient to precipitate ruthenium from a 10-litre sample, and subsequently concentrate the supernatant liquid by evaporation before determining the other elements in the sequential scheme.EXPERIMENTAL An outline of the separation scheme is given in Fig. 1, but decontamination steps for individual nuclides are not shown; the numbers in parentheses are those referred to in the text. The 10 litres of water containing carriers for the five elements are treated with sodium hypochlorite solution to oxidise the ruthenium and ensure exchange between carrier and fall-out activity. Ruthenium is oxidised to perruthenate ion, Ru0,-, and possibly some ruthenate ion, RuO,2-. It is reduced to ruthenium(1V) by addition of ethanol and, on boiling the slightly alkaline solution, the flocculent hydroxide precipitates and settles out fairly rapidly, thus enabling the clear supernatant liquid to be siphoned off.With hard waters, some water solids will also be deposited at this stage, and may carry down some of the tellurium, antimony and tin; the precipitate will also contain any insoluble matter originally present in the sample. Rain water, for example, often contains organic and siliceous solids in suspension. This insoluble material accompanying the ruthenium hydroxide precipitate is rendered soluble by fusion with alkali, separated from the ruthenium, and returned to the main solution before the separation of the remaining four elements. The fusion converts the ruthenium to sodium ruthenate, which, although water-soluble, is easily reduced to the 0 SAC; Crown Copyright Reserved. 12 BATHIE AND BURDEN: A SEQUENTIAL SCHEME FOR THE [Auta&St, VOl.93 insoluble hydroxide. Ruthenium, therefore, appears in both the aqueous and acidic extracts of the fused melt, and is precipitated from both, as the hydroxide, and the precipitates are combined. Reduction to ruthenium metal with magnesium and acid effectively separates this element from tin and antimony, but some tellurium may still be associated with it. This is, however, separated in the next stage when ruthenium tetroxide is extracted with carbon tetrachloride. The ruthenium is finally precipitated as the metal with magnesium and acid for chemical-yield determination and counting. In an attempt to obtain more durable counting sources for ruthenium, some experiments were carried out on electroplating of this element from solutions of ruthenium nitrosyl ~hloride.~ Adherent and lustrous deposits were only obtained, however, when the thickness of the deposit was less than 1 mg per cm2; thicker deposits tended to flake off the cathode.The low background anti-coincidence counters in use in this laboratory can only accept sources of l-inch diameter, which limits the amount of carrier that can be used during the separation. The electroplating was, therefore, abandoned, but it may offer some advantages where a low-background counting system is available that will accept large area sources. The remaining four elements are separated after evaporating the acidified sample to a few hundred millilitres. Molybdenum is first precipitated with benzoin a-oxime, and is centrifuged, together with some water solids deposited during the evaporation. The insoluble material, which may contain some tin and antimony deposited during the evaporation, is rendered soluble by fusion with alkali and, after separation of molybdenum, is added to the main tin and antimony fraction.Molybdenum is re-precipitated with benzoin a-oxime, re-dissolved, and decontaminated by iron(II1) hydroxide scavenges. It is finally precipitated with 8-hydroxyquinoline for counting and chemical-yield determination. Tellurium is precipitated next by reduction to the metal with hydrazine and sulphur dioxide. The technique used for the decontamination of this element is basically that reported by Meinke.10 Tin and antimony are precipitated together as sulphides, and are decontaminated by two tellurium metal and two lead sulphide scavenges.These elements are separated by extracting the antimony into 2-ethylhexan-1-01 and light petroleum from concentrated hydrochloric acid, as described by Orlandini, Wahlgren and Barclay.ll In this extraction the antimony, after oxidation to the quinquivalent state, is extracted to better than 99 per cent. and tin is extracted to about 9 per cent. The contamination of the antimony by tin is reduced by washing the solvent phase several times with hydrochloric acid; antimony is finally precipi- tated with 8-hydroxyquinoline for chemical-yield determination and counting. Tin is further purified by extraction into isobutyl methyl ketone, and is finally precipitated with cupferron and ignited to tin(1V) oxide, in which form it is weighed and counted.The time taken to complete the above separation and purification scheme averages 5 days, which includes 1 day for evaporating 10 litres to 600 ml on a 1200-watt boiling-ring. The average chemical recoveries of added carriers are given in Table I. TABLE I AVERAGE CHEMICAL RECOVERY OF ADDED CARRIERS Fraction .. . . Ruthenium Molybdenum Tellurium Antimony Tin Recovery, per cent. . . 60 66 63 46 49 Range . . .. .. 30 to 60 40 to 90 40 to 80 30 to 60 20 to 60 RECOVERY OF ADDED RADIONUCLIDES- As a check, recovery experiments were carried out by adding known amounts of radio- nuclides to simulated water samples. The samples were processed by the method, and the count-rates of the final sources were corrected for decay and chemical recovery. The radio- nuclides used were ruthenium-106 (half-life 1 year), molybdenum-99 (half-life 67 hours), tellurium-132 (half-life 78 hours), antimony-124 (half-life 60 days) and tin-113 (half-life 118 days).Chemical forms of these species were as follows: ruthenium-106, as ruthenium trichloride ; molybdenum-99, as ammonium molybdate ; tellurium-132, as sodium tellurite; antimony-124, as antimony trichloride; and tin-113, as tin(1V) chloride. The antimony and tin nuclides, although not fission products, were used for convenience. The latter nuclide decays by electron capture to indium-113m (half-life 104 minutes), which emits a 0-393-MeV y-photon. When the tin sources had been prepared, the daughter was allowed to grow to equilibrium before counting in a y-spectrometer. The other four nuclides were counted inJanuary, 19681 DETERMINATION OF SEVERAL FALL-OUT NUCLIDES IN WATER 3 a /3-counter, and for tellurium, the daughter, iodine-132 (half-life 2.3 hours), was allowed to come to equilibrium before counting.The results are listed in Table 11. As it is im- possible to match the chemical forms of the active species used in these experiments with those present in fall-out, the results of the recovery experiments given in Table I1 are not, in themselves, conclusive evidence of complete recovery of the fall-out nuclides in a sample. Sample 1 2 3 4 TABLE I1 RECOVERY OF ADDED RADIONUCLIDES FROM SIMULATED Ruthenium-106 Molybdenum-99 - - Added, Found, Added, Found, counts counts Re- counts counts Re- Per per covery, per per covery, minute minute per cent.mmute minute per cent. 3608 3456 95.8 9610 9154 95.3 3516 3560 101.3 39,960 38,390 96.1 3588 3420 95.3 9860 9345 94-9 3646 3460 95.0 40,250 38,880 96.6 TABLE I I-contilzwed Antimony-124 r Added, Found, counts counts Re- per per covery, Sample minute minute per cent. 1 7672 8108 105.7 2 7072 7257 94.6 3 7672 7313 95.3 4 7672 7740 100.9 WATER SAMPLES Tellurium-132 P Added, Found, counts counts Re- Per minute minute per cent. 4710 4337 92.1 3380 3435 101.6 4425 4224 95.6 11,125 11,660 104.7 per covery, Th-113 Added, counts mmute 3335 3330 3252 2978 per Found, counts Per minute 3160 3247 3035 333.4 Re- covery, per cent. 94.5 97.5 102.5 101.9 Samples 1, 2 and 3 were drinking waters containing 100, 40 and 20 mg of calcium per litre, respectively.Sample 4 was rain water. RADIOCHEMICAL PURITY OF COUNTING SOURCES- To ascertain the level of contamination of each of the final counting sources by other radionuclides, several decontamination experiments were carried out. Simulated water samples, with known amounts of possible contaminants present, were processed by the method. The final sources were counted and decontamination factors calculated in the normal way from the ratio of count-rate added to the count-rate found in the sources. Contaminants used included a mixture of fission products containing strontium-90 - yttrium-90, cerium-144 - praseodymium-144, promethium-147, caesium-137 and zirconium-95, and a solution of radium D.E.F. (lead-210, bismuth-210 and polonium-210). The extent of contamination of the ruthenium and tin sources by tellurium-132, antimony-124 and molybdenum-99, and of the ruthenium, molybdenum, tellurium and antimony sources by tin-113, was also deter- mined.The results are listed in Table 111. The decontamination factors are in excess of 2 x 103, except for the antimony source contaminated with tin-113, when a figure of 230 was obtained. This was considered adequate in this instance, as the fission yields of the two fission-product nuclides of tin, tin-123 and tin-125, are relatively low. TABLE I11 DECONTAMINATION FACTORS Decontamination factor from- telluriurn-133, antimony-124 and Fraction molybdenum-99 tin-113 Ruthenium . . 3 x 10s >8 x lP Molybdenum . . - >8 x 108 Tellurium . . - >8 x 108 Antimony .. - 2-3 x lo2 Tin . . .. 4 x 104 - * The mixed fission products contained strontium-90 - promethium-147, caesium-137 and zirconium-95. mixed fission products* 3 x 106 2 x 106 3 x 106 3 x 106 1 x 107 yttrium-90, cerium-144 - radium D.E.F.2.2 x 108 >2 x 106 1.7 x 104 1 x 104 2.3 x 108 praseodymium- 1444 APPARATUS- BATHIE AND BURDEN : A SEQUENTIAL SCHEME FOR THE METHOD [Analyst, Vol. 93 A low background (about 1 count per minute) anti-coincidence /3-counter was used. Perspex $her-stick, 16 mm i.d. In frared lamps. Centrifuges. REAGENTS- Molybdenzzlm, tellurium and antimony carrier solutions-Prepare solutions of analytical- reagent grade ammonium molybdate, telluric acid and antimony potassium tartrate in water containing 10 mg of molybdenum, tellurium and antimony, respectively, per ml of solution.Ruthenium carrier solution-Dissolve ruthenium trichloride in a few millilitres of hydro- chloric acid and dilute with water to prepare a solution containing about 10 mg of ruthenium per ml of solution. Standardise the solution by precipitating the metal with magnesium and acid, as described in the Method, and by using a sintered-glass crucible for filtration and weighing. Count a portion of the ruthenium metal in a /3-counter to determine the level of ruthenium-106 present in the carrier solution. (Most commercial sources of ruthenium contain this nuclide.) Tin carriw solution-Heat sodium stannate with a few millilitres of hydrochloric acid and dilute with water to prepare a solution containing about 10 mg of tin per ml of solution. Standardise the solution by precipitation with cupferron (ammonium salt of N-nitrosophenyl- hydroxylamine) and ignition to tin(1V) oxide, as described in the Method.Lead, zirconium and iron carrier solutions-Prepare solutions of lead nitrate, zirconyl chloride and iron(II1) chloride in water containing about 5 mg of lead, zirconium and iron, respectively, per ml of solution. The strength of these solutions need not be accurately known. 8-Hydroxyquinoline solution-Dissolve 4 g of 8-hydroxyquinoline in a few millilitres of glacial acetic acid and dilute with 100 ml of water. Add 6 N ammonia solution until the solution becomes turbid and then glacial acetic acid until clear. This solution is stable for about 2 months, if kept cool. Sodium polysulphide solution-Dissolve 100 g of sodium sulphide and 8 g of sodium hydroxide in the minimum amount of water.Dissolve 3 g of sulphur in the hot solution, dilute to 200ml and filter. Cupferron solution-Prepare a 10 per cent. w/v solution of the ammonium salt of N-nitrosophenylhydroxylamine in water immediately before use, and filter. Benzoin a-oxime solution, 2 9er cent. w/v in ethanol. Sodium hydrogen suZ9hite solution-Saturate 5 per cent. w/v sodium hydroxide solution with sulphur dioxide gas. Sodium hyjbochlorite solutiow-Use a solution containing 10 per cent. of available chlorine. Potassium iodate solution, 7 per cent., aqueous. Poly(viny1 acetate) (Gelva) solution, 5 9er cent. w/v in methalzol. 2-Ethylhexan-1-01, 5 per cent. v/v in light petroleum (boiling range 80" to lOO"C)-EqUili- brate by washing with concentrated hydrochloric acid. Isobutyl methyl Ketone-Equilibrate by washing with 6 N hydrochloric acid.PROCEDURES FOR PRELIMINARY SEPARATIONS RUTHENIUM SEPARATION- To 10 litres of sample in a 12-litre flask add the following carriers: 10 mg of molybdenum and antimony, and 20mg of ruthenium, tellurium and tin. Add 10ml of sodium hypo- chlorite solution, mix and allow to stand for 30 minutes. Add 100ml of ethanol, followed by 50 per cent. sodium hydroxide until the solution is slightly alkaline (about pH 9 to 10, with universal indicator paper). Boil to coagulate the ruthenium precipitate, cool and allow it to settle overnight. Siphon off the bulk of the supernatant liquid (1) into a second flask and complete the separation by centrifuging the last few hundred millilitres in a 250-ml centrifuge jar. Wash the ruthenium (and any precipitated water solids) with water into a nickel crucible, add 5 ml of hydrofluoric acid and evaporate to dryness under an infrared lamp.Cool and add a further 5ml of hydrofluoric acid, and again evaporate to dryness.January, 19681 DETERMINATION OF SEVERAL FALL-OUT NUCLIDES IN WATER Dlscard. 5 Insoluble Solubler Ru02(2) I Dissolve in HCI. Add to Ru fraction (3) Sample + Ru, Mo, Sb, Sn and Te carriers i Oxidise with NaOCI. Add CzHsOH I I 1 Te lnsol u ble RuO2 + water solids I Fuse with Na2CO3 - Na202. Leach with water I fraction Reducd acidity Tellurium-I25m Organic’iayer (4) Aqueous layer -+ Ru fraction I 1 I Ruthenium-103 Ruthenium- 106 Sb I ,Soluble ( I ) I fraction Sn fraction I Extract with isobutyl methyl ketone Organic layer Aqueous layer A I Evaporate to 500ml., Add benzoin a-oxime Soluble (5)- Hydrazi j e + SO; Insoluble (7) Soluble (8) with NH40H. Pass HzS 1 S b A + SnS. Soluble rejected I Dissolve in HCI and oxidfse with KMn04. Extract with 2- ethyl hexan- 1 - 0 1 I lnsolu ble Mo + water solids Fuse with NazCO3. Leach with water I A Any insoluble Soluble Treat with HCI 1 F, Benzoin +-Soluble Insoluble asxime Discard. -A t--- Soluble Insoluble Mo benzoin a-oximate (6) I Mo fi - Molyb< iction mum-99 Mix the residue with five times its volume of anhydrous sodium carbonate and fuse over a Meker burner. When the initial reaction has subsided, add 2 to 3 g of sodium peroxide in portions, and fuse for a further 5 minutes. Cool and extract the melt with hot water.Centrifuge the solution and transfer the supernatant liquid into a beaker, and precipitate ruthenium hydroxide (2) from this aqueous extract by adding a few millilitres of ethanol. Heat the precipitate to coagulate it, centrifuge and add the supernatant liquid to (1). Treat the insoluble matter from the aqueous extract of the melt with the minimum volume of concentrated hydrochloric acid and heat it in a water-bath. Centrifuge it and transfer the supernatant liquid into another tube. If any insoluble matter remains, add 2ml of concentrated hydrochloric acid and heat in a water-bath. Add 10ml of water, centrifuge the mixture, and combine the supernatant liquid with the previous acidic extract ; discard any further insoluble matter.To the acidic extract add a few millilitres of ethanol, followed by 50 per cent. sodium hydroxide until ruthenium (and nickel) hydroxide (3) is precipitated. Heat to coagulate the precipitate, centrifuge it and add the supernatant liquid to (1).6 BATHIE AND BURDEN: A SEQUENTIAL SCHEME FOR THE [Arta@d, VOl. 93 Dissolve each of the ruthenium precipitates (2) and (3) in 2 ml of concentrated hydro- chloric acid and, while warming, combine them in a single tube by using the minimum amount of water. Then reduce the ruthenium to the metal by careful addition of magnesium turnings, until there is excess of magnesium present. Dissolve this excess of magnesium by dropwise addition of concentrated hydrochloric acid, centrifuge the mixture and add the supernatant liquid to (1).Wash the ruthenium metal with hot water, adding the washing to (1). Add 5 ml of sodium hypochlorite solution and a few drops of 50 per cent. sodium hydroxide solution to the metal, and heat it in a water-bath for a few minutes, with occasional stirring. Allow the solution to cool, add a further 5 ml of sodium hypochlorite solution, and wash it into a 100-ml separating funnel with 10ml of water. Add 20ml of carbon tetrachloride, followed by concentrated hydrochloric acid, until the colour of the aqueous phase changes to a pale yellow; shake the solution for a few minutes and allow the phases to separate. Transfer the organic layer to a second separating funnel and repeat the extraction of the aqueous phase with a further 10 ml of carbon tetrachloride.When the phases have separated, add the aqueous phase to (1). Wash the combined organic extracts with 20 ml of water, adding the washing to (1) , and repeat this step twice more. Retain the carbon tetrachloride layer (4) for ruthenium purification. MOLYBDENUM SEPARATION- To the main solution (1) add concentrated hydrochloric acid until it is acidic and then 10 ml in excess. Evaporate the solution to low volume on a boiling-ring, wash it into a 1-litre beaker with water to give a volume of about 500 ml, add 30 ml of concentrated hydrochloric acid and cool the solution in ice - water. Add 10 ml of bromine water, followed by 10 ml of benzoin a-oxime, while stirring, and allow to stand in the ice-bath for 20 minutes, with occasional stirring. Centrifuge the molybdenum benzoin a-oximate ( j h s any precipitated water solids) in a 250-ml centrifuge jar, and retain the supernatant liquid (5) for separation of tellurium, tin and antimony. Wash the solids into a nickel crucible with water and evaporate to dryness under an infrared lamp.Then add 10ml of 40 per cent. hydrofluoric acid and again evaporate to dryness. Mix the residue with five times its volume of sodium carbonate and fuse it over a Meker burner. Cool the melt and extract it with hot water; centrifuge the solution. Dissolve any insoluble material in concentrated hydrochloric acid and add it to the main solution (5). To the aqueous extract, add 1 mg of iron carrier, centrifuge the solution and discard the iron(II1) hydroxide, transferring the supernatant liquid into a beaker, acidifying it carefully with concentrated hydrochloric acid, and boiling to remove carbon dioxide.Add a few millilitres of bromine water, cool the solution in an ice-bath and add 5 ml of benzoin oc-oxime to precipitate the molybdenum; centrifuge it and add the supernatant liquid to the main solution (5). Wash the precipitate with water, centrifuge it and add the washing to (5) , retaining the molybdenum precipitate (6) for purification. TELLURIUM SEPARATION- Evaporate the main solution (5) to about 250 ml. Add about 5 g of hydrazinium dichloride and bring the solution to the boil; saturate it with sulphur dioxide gas for 15 minutes. Boil the solution to coagulate the tellurium metal, and filter it through filter-paper pulp; retain the precipitate (7) for tellurium purification, and wash the filtrate (8) into a 1-litre beaker.TIN AND ANTIMONY SEPARATION- Reduce the acidity of filtrate (8) to about 0.2 N by adding ammonia solution (with indicator paper), and heat the solution to boiling. Pass hydrogen sulphide gas through the solution for 15 minutes, and allow the precipitate to settle for at least 2 hours, but preferably overnight. Pass hydrogen sulphide gas through the solution again for 15 minutes, and then centrifuge it in a 250-ml centrifuge jar; discard the supernatant liquid. Wash the precipitate into a 40-ml centrifuge tube with hydrogen sulphide water, centrifuge it, and discard the supernatant liquid. Add 5ml of concentrated hydrochloric acid, boil off the hydrogen sulphide, centrifuge the mixture and transfer the supernatant liquid into another tube.Wash the insoluble matter with 15 ml of hot water, centrifuge it and add the supernatant liquid to the previous acidic extract ; discard the insoluble matter, which is mainly rutheniumJanuary, 19681 DETERMINATION OF SEVERAL FALL-OUT NUCLIDES IN WATER 7 sulphide. Add 10 mg of tellurium carrier and about 1 g of hydrazinium dichloride, heat the solution in a water-bath, and pass sulphur dioxide gas through it. Centrifuge it and transfer the supernatant liquid into another tube. Add a further 10mg of tellurium carrier, heat the solution in a water-bath, and again pass sulphur dioxide gas through it. Centrifuge it and filter the supernatant liquid into a beaker; boil off sulphur dioxide and wash the solution into a centrifuge tube.Reduce the acidity to about 0.2 N with ammonia solution, and pass hydrogen sulphide gas through the solution. Centrifuge it to collect the tin and antimony sulphides, and discard the supernatant liquid; wash the precipitate with hydrogen sulphide water and discard the washing. Treat the tin and antimony sulphides with a few millilitres of sodium polysulphide solution plus a few drops of 50 per cent. sodium hydroxide, and heat them in a water-bath; dilute to 20 ml with water. Centrifuge and discard any insoluble matter (ruthenium sulphide). Add 5 mg of lead carrier and centrifuge it, then add a further 5 mg of lead carrier, centrifuge it again, and filter the supernatant liquid into another tube; discard the lead sulphide. Add 2 ml of glacial acetic acid and heat the solution in a water-bath to coagulate the precipitate.Centrifuge it to collect the tin and antimony sulphides and sulphur, and discard the super- natant liquid. Add 2 ml of concentrated hydrochloric acid to dissolve the tin and antimony sulphides, and boil off hydrogen sulphide. Then add 10 ml of water, centrifuge it, and transfer the supernatant liquid into another tube. Treat the sulphur again with 2 ml of concentrated hydrochloric acid, boil, dilute with 10 ml of water, centrifuge it and discard the sulphur, transferring the supernatant liquid into the first acidic extract. Pass hydrogen sulphide gas through the solution to precipitate tin and antimony sulphides, centrifuge to collect the precipitate, and discard the supernatant liquid.Add 2ml of concentrated hydrochloric acid to the precipitate and boil off hydrogen sulphide. Then wash the solution into a 100-ml separating funnel with 10 ml of concentrated hydrochloric acid, add about 40 mg of potassium permanganate and 10 ml of 2-ethylhexan- 1-01 and light petroleum, and shake the funnel for 10 minutes; allow the phases to separate and transfer the aqueous layer into a second separating funnel. Extract the aqueous phase with a further 5ml of 2-ethylhexan-1-01 and light petroleum, and combine this with the first organic layer. Then extract the combined organic layers with 5 ml of concentrated hydrochloric acid (adding a further 40 mg of potassium permanganate), and combine this with the first aqueous layer. Retain the organic layer (9) for antimony purification and the aqueous layer (10) for tin purification. PURIFICATION AND ISOLATION OF ELEMENTS- Ruthehm-Extract the ruthenium from the carbon tetrachloride (4) into 10 ml of 3 M sodium hydroxide solution to which just sufficient sodium hydrogen sulphite solution has been added to decolorise the carbon tetrachloride layer.Wash the aqueous layer into a centrifuge tube with about 10ml of water. Heat the solution in a water-bath and add 1 ml of ethanol to precipitate ruthenium hydroxide; centrifuge to collect the precipitate, and discard the supernatant liquid. Dissolve the precipitate in 3ml of concentrated hydrochloric acid by warming, and reduce it to the metal, as before, by careful addition of magnesium turnings. Wash the precipitate first with hot water and then with ethanol, discarding the washings.Make a slurry of the precipitate with ethanol, and filter it on a filter-stick through two tared Whatman NO. 42 papers (21 mm in diameter). Dry the papers in an oven at 80" C, keeping the source paper flat with a metal ring. Cool and weigh, and calculate the chemical recovery, assuming that both papers gain or lose the same weight. Mount the source on a planchet with a few drops of Gelva solution and count, both normally and through a 200mg per cm2 aluminium absorber. Molybdenzcm-Transfer the molybdenum benzoin a-oximate precipitate (6) into a beaker with a few millilitres of fuming nitric acid, add 1 ml of 60 per cent. perchloric acid and heat the solution under an infrared lamp. When charring occurs, add a few millilitres of fuming nitric acid and continue heating.When the wet combustion is complete, evaporate to dryness, cool and dissolve the residue in concentrated ammonia solution. Wash the solution into a centrifuge tube with 10 ml of water, warm and add 1 mg of iron carrier; centrifuge it and discard the iron(II1) hydroxide, transferring the supernatant liquid into a beaker. Then8 [Analyst, Vol. 93 add 10 ml of water, neutralise with dilute sulphuric acid, adding a few drops in excess, heat to boiling and add 5 ml of 8-hydroxyquinoline solution. Filter on a filter-stick and wash with hot water. Dry the papers in an oven at 105" C, with the source paper kept flat, as described for ruthenium. Cool, weigh and calculate the chemical recovery (the precipitate contains 23.05 per cent.of molybdenum). Mount the source on a planchet with a few drops of Gelva solution and count. Re-count, at intervals, for several half-lives of molybdenum-99. TeZZztrizw+-Transfer the filter pulp, containing tellurium metal (7) into a beaker and wet combust it with fuming nitric and perchloric acids. Evaporate to dryness, dissolve the residue in 5 ml oE concentrated hydrochloric acid, and evaporate to dryness. Dissolve the residue in 5ml of concentrated hydrochloric acid, and wash the solution into a centrifuge tube with 15 ml of water. Add about 1 g of hydrazinium dichloride, heat the solution in a water-bath and pass sulphur dioxide gas through it ; centrifuge it and discard the supernatant liquid. Add a few drops of concentrated nitric acid and evaporate the solution nearly to dryness; cool and dissolve the residue in a few drops of concentrated hydrochloric acid.Dilute it to 15 ml with water and neutralise with 6 N ammonia solution, adding 1 ml in excess. Heat the solution in a water-bath and add 1 mg of iron carrier; centrifuge it and discard the iron(II1) hydroxide, transferring the supernatant liquid into another tube. Add 5 ml of concentrated hydrochloric acid, followed by about 1 g of hydrazinium dichloride. Heat the solution in a water-bath and pass sulphur dioxide gas through it to precipitate tellurium metal. Centrifuge it and discard the supernatant liquid; wash the precipitate with water and discard the washing. Add a few drops of concentrated nitric acid to the precipitate, heating to dissolve it, wash the solution into a beaker with concentrated hydrochloric acid and evaporate it to dryness.Dissolve the residue in 5ml of concentrated hydrochloric acid and again evaporate to dryness. Dissolve the residue in 5 ml of concentrated hydrochloric acid and wash it into a centrifuge tube with 15 ml of water. Add about 1 g of hydrazinium dichloride, heat the solution in a water-bath and pass sulphur dioxide gas through it to precipitate tellurium metal; centrifuge it and discard the supernatant liquid. Wash the precipitate with water and discard the washing . Make a slurry of the precipitate with water and filter it on a filter-stick, washing the precipitate successively with water and ethanol. Dry the papers in an oven at 80" C , as described for ruthenium.Cool, weigh and calculate the chemical recovery. Mount the source on a planchet with a few drops of Gelva solution and count, both normally and through a 5 mg per cm2 aluminium absorber. When fresh fission products are present, re-count the source, at intervals, until the tellurium-132 - iodine-132 has decayed away. Antimony-To the 2-ethylhexan-1-01 - light petroleum phase (9), add 10 ml of concen- trated hydrochloric acid and 40 mg of potassium permanganate, and shake it for 10 minutes; allow the phases to separate and discard the aqueous layer. Repeat this step twice more. Extract the antimony from the organic layer by shaking it for 10 minutes with 20ml of water; allow the phases to separate and transfer the aqueous phase into a centrifuge tube.Pass hydrogen sulphide gas through the solution and centrifuge it to collect the antimony sulphide, discarding the supernatant liquid. Add 3 ml of concentrated hydrochloric acid and, after boiling off hydrogen sulphide, with stirring, add 15 ml of water, followed by 5 ml of 8-hydroxyquinoline solution and 2 ml of 25 per cent. ammonium acetate solution. Then add 6 N ammonia solution, dropwise, until antimony 8-hydroxyquinolinate is precipitated. Centrifuge it and discard the supernatant liquid; wash the precipitate with cold water until the washings are colourless. Make a slurry of the precipitate with water and filter it on a filter-stick. Dry the papers in an oven at 105" C, keeping the source paper flat, as described for ruthenium. Cool, weigh and calculate the chemical recovery (the precipitate contains 21.97 per cent.of antimony). Mount the source on a planchet with a few drops of Gelva solution and count, both normally and through a 12 mg per cm2 aluminium absorber. When fresh fission products are present, re-count the source, at intervals, until antimony-127 has decayed away. Tin-Dilute the aqueous phase (10) to twice its volume with water, add 20 ml of isobutyl methyl ketone and shake the mixture for 10 minutes; allow the phases to separate and transfer the aqueous layer into a second separating funnel. Extract the aqueous layer with a further 10 ml of isobutyl methyl ketone, and wash the combined organic layers with 10 ml BATHIE AND BURDEN: A SEQUENTIAL SCHEME FOR THEJanuary, 19681 DETERMINATION OF SEVERAL FALL-OUT NUCLIDES IN WATER 9 of 6 N hydrochloric acid and discard the washing.Extract the tin from the organic layer by shaking it for 10 minutes with 25 ml of water; allow the phases to separate and transfer the aqueous layer into a centrifuge tube. Pass hydrogen sulphide gas through the solution €or 15 minutes to precipitate the tin sulphide, centrifuge it, and discard the supernatant liquid. Add 3 ml of concentrated hydro- chloric acid, boil off hydrogen sulphide, with stirring, then add 20 ml of water and 5 ml of fresh cupferron solution, and allow the mixture to stand for 30 minutes, with occasional stirring. Filter it on a Whatman No. 30 paper and, after washing with water, transfer the paper to a silica crucible, dry and ignite the precipitate to tin(1V) oxide.Cool, make a shmy with ethanol, and filter it on a filter-stick. Wash the precipitate with ethanol and dry it in an oven at 80” C, with the source paper kept flat, as described for ruthenium. Cool, weigh and calculate the chemical recovery. Mount the source on a planchet with a few drops of Gelva solution and count, at intervals. CALCULATION- by the equation- The concentration, A,, of any nuclide in a water sample at the time of sampling is given 1 1 1 1 1 1 A , = C x x - x - x - x - x - picocuries per litre, x Y D v 2.22 where C = counting rate in counts per minute, corrected for lost counts and background, E = fractional counter efficiency for the nuclide counted, X = self-absorption correction factor, Y = fractional chemical recovery, D = decay factor for the time interval between sampling and counting for the V = volume of sample in litres.particular nuclide counted, and Where the nuclide is easily available as a standardised solution, a graph should be prepared relating counter efficiency with source weight. The terms E and X in the above equation are, therefore, combined in a single figure for these nuclides. At the present time this can be done for ruthenium-103, ruthenium-106 and molybdenum-99. For the other nuclides, efficiences were obtained from a general calibration graph relating counter efficiency for a 20-mg source with the maximum #3-energy of the particle. The counter efficiency for a 20-mg source of any nuclide is found by summing the individual efficiencies for each /3-particle, multiplied by the fraction each particle contributes to the total radiation. With the nuclides tellurium-125mJ tellurium-127m and tellurium-l29rn, which decay by isomeric transition, the emitted particle is a mono-energetic electron. For a normal #3-particle spectrum, the “average” energy is about one third of the maximum #3-particle energy.It was assumed, for the purpose of obtaining the counter efficiency, that the conversion electrons were equivalent to a normal /%particle of three times their energy. For nuclides, the efficiency of which is found in this way, the count-rates must be corrected for the self-absorption that occurs in the material of the source. Non-standardised solutions of the nuclides may be used for this purpose, as it is only necessary to plot a graph of relative counts against source weight and normalise the curve to give a self-absorption factor of unity at a source weight of 20 mg.This is possible for tellurium-132 - iodine-132, antimony-125 and tellurium-l25m (the last by separating the tellurium-l25m from an aged solution of antimony-125). For the other tellurium nuclides, a sample of tellurium metal was irradiated in a reactor. This gives many nuclides but, after allowing for decay, the predominant activities are those of tellurium-l27m, tellurium-127 and tellurium-l23m. A solution of these activities was used to prepare a self-absorption curve that could be used for the isomeric pairs tellurium-127m - tellurium-127 and tellurium-129m - tellurium-129, as these have similar p-energies. A curve for tin-123 was prepared by using strontium-89 in the form of strontium oxide, as these two nuclides have similar maximum p-energies (tin-123 = 1.42 MeV and strontium-89 = 1.48 MeV), and strontium oxide and tin(1V) oxide (the counting form of the tin source) have similar average atomic numbers (strontium oxide = 23, and tin(1V) oxide = 22).POSSIBLE NUCLIDES PRESENT IN THE PURIFIED SOURCES- The purified ruthenium source will contain ruthenium-106 (half-life 1 year), with its daughter, rhodium-106 (half-life 30 seconds), in equilibrium. In fall-out less than a year old10 BATHIE AND BURDEN: A SEQUENTIAL SCHEME FOR THE [Analyst, Vol. 93 ruthenium-103 (half-life 40 days) will also be present. These are resolved by making use of the widely differing @energies of rhodium-106 and ruthenium-103 (ruthenium-106 has a maximum /3-energy of 0.039 MeV, which is too weak to count in an end-window Geiger counter).The transmissions of mthenium-106 - rhodium-106 and ruthenium-103 through a 200 mg per cm2 aluminium absorber are measured for these nuclides. Count-rates for each of these nuclides present in a sample source may then be found by simultaneous equations, and substituted separately in the above equation. The only active fission-product nuclide of molybdenum, of sufficient half-life to be found in fall-out, is molybdenum-99 (half-life 67 hours), and this would only be found in fall-out of recent origin. The tellurium source may contain a complex mixture of nuclides , including tellurium-125m (half-life 58 days) , the isomeric pairs tellurium-127m - tellurium-127 and tellurium-129m - tellurium-129 (half-lives 105 and 33 days, respectively), and, in fall-out of recent origin, tellurium-132 (half-life 78 hours).If the last is present, it is easily identified because its daughter, iodine-132 (half-life 2.3 hours), grows in after the final tellurium precipitation, so that the count-rate rises to a maximum after a few hours. The two nuclides in transient equilibrium then decay with a half-life of 78 hours, so that by following the count-rate for a few weeks the count from this pair may be separated from that from the remainder of the tellurium nuclides. Distinguishing between the two isomeric pairs tellurium-127m - tellurium-127 and tellurium-129% - tellurium-129 is difficult, as there is no large difference between half-life or /3-energy.In this laboratory no attempt has been made to distinguish between the two. In fall-out more than 2 years old, the only tellurium nuclide present would be tellurium-125m (half-life 58 days), the daughter of antimony-125 (half life 2-8 years). This nuclide may be distinguished from the two isomeric pairs by its considerably lower transmission through an aluminium absorber of 5 mg per cm2 (about 30 and 85 per cent., respectively). The antimony source will contain antimony-125 and, in recent fall-out, antimony-127 (half-life 94 hours) may be present. The latter decays to tellurium-127 (half-life 9-4 hours) in about 80 per cent. of its disintegrations, so that when this nuclide is present the count-rate rises at first, and then the two nuclides, in transient equilibrium, decay with the half-life of antimony-127.The remaining 20 per cent. of disintegrations decay to tellurium-127m (half-life 106 days), which appears, together with the supported amount of tellurium-127, in the “tail,” after the resolution of the decay curve. Also present in the “tail” (apart from counts from antimony-125 itself) are counts from tellurium-125% (half-life 58 days), produced in about 30 per cent. of the disintegrations of antimony-125. To obtain an accurate figure for antimony-125 it is, therefore, necessary to re-dissolve the antimony source when anti- mony-127 has decayed away, and to remove tellurium activities by scavenging with tellurium carrier. Two nuclides of tin may be found in fall-out, tin-123 (half-life 129 days) and tin-125 (half-life 9-63 days) , which are easily resolved by decay measurements.The purified antimony is then mounted and a count taken. RESULTS The sensitivity of detection of the various nuclides for a 10-litre sample, by using a counter with a background count-rate of 1 count per minute, is given below. Ru then- Ruthen- Molyb- Tellur- Tellur- Antim- ium-103 ium-106 denum-99 ium-129 ium-126m ony-I26 Tin-123 Limit of detection, picocuries per litre 0.08 0.02 0.06 0.02 0.06 0.06 0.02 These results were calculated from a count equivalent to three standard deviations of a background count of 3000 minutes’ duration. Chemical recoveries were as listed in Table I. A time interval of 5 days between sampling and counting was assumed. Several drinking waters12 have been examined radiochemically by using this procedure in conjunction with that developed by Wood and Richards.’ This work was carried out for the Ministry of Housing and Local Government, and the object was to account for all of the radioactivity present by comparing the total /%activity (directly determined, and ex- pressed as though all of the radiation was from strontium-90), with the sum of the individually measured nuclides, again calculated as strontium-90.The results are shown in Table IV. Samples of rain water collected on the roof of this laboratory have also been analysedJanuary, 19681 DETERMINATION OF SEVERAL FALL-OUT NUCLIDES IN WATER 11 TABLE IV COMPARISON OF THE SUM OF INDIVIDUALLY DETERMINED RADIONUCLIDES IN Figures expressed as strontium-90 in picocuries per litre DRINKING WATERS WITH THE TOTAL p-ACTIVITY DIRECTLY DETERMINED Sum of individual Sample nuclides Total /?-activity Manchester (October, 1962).. .. .. 20.3 21.4 Belfast (May, 1963) . . .. .. .. 104.1 99.6 Cardiff (May, 1963) ., .. * . .. 29.8 28.2 Belfast (August, 1964) . . .. .. 35.1 38.6 Cardiff (September, 1964) . . .. . . 13.1 11.6 Manchester (June, 1966) . . .. . . 11.1 10.7 Leeds (December, 1966) . . .. .. 8.9 8.9 London (May, 1966) .. .. .. 7.0 6-2 Pwllheli (July, 1966) .. .. .. 9.7 10.6 London (March, 1964) . . * . .. 9.1 9.7 by the proposed method. A sample collected between November 4th, 1966, and November 7th, 1966, containing fall-out from the fourth Chinese nuclear test of October 27th, 1966, and a second sample collected between January 6th, 1967, and January 12th, 1967, contahing fall-out from the fifth Chinese nuclear test of December 28th, 1966, gave the results indicated in Table V.The nuclides determined in rain water after the fifth Chinese test include three pairs of the same elements, ruthenium-103 - ruthenium-106, tellurium-132 - tellurium-129m and antimony-127 - antimony-125. As the date of the explosion is known (December 28th, 1966), it is possible to compare the ratio of each pair of nuclides with the theoretical figure TABLE V ACTIVITY OF LONDON RAIN WATER Nuclide Ruthenium-103 . . Ruthenium-106 . . Molybdenum-99 . . Tellurium-132 . Tellurium-129m . . Antimony-127 . . Antimony-126 . . Tin-126 . . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .... Sample collected November 4th to November 7th, 1966, picocuries per litre 4.7 f 0.4 0.79 f 0.08 19.9 f 0.6 13.2 f 0.4 0.61 4 0-08 0.98 f 0.10 Sample collected January 6th to January 12th, 1967, picocuries per litre 1210 f 20 24.0 f 3.0 1660 f 50 3170 f 30 112 f 2 n.d. 173 f 6 7.7 f 0.3 a d . 29.1 f 0.4 The figures are calculated to 00.00 hours, November Bth, 1966, for the first sample and to 00.00 hours, January 7th, 1966, for the second. The limits are based on counting statistics only (90 per cent. confidence limits). n.d. = not detected. for several possible nuclear fuels. It is first necessary, however, to determine the contribution (for the longer-lived nuclides) of fall-out from previous tests. An approximate estimate was obtained from the antimony pair, as the ratio of activities of antimony-127 to antimony-125 is virtually independent of the nuclear fuel for fission neutrons.By using an average value for this ratio, the amount of “old” antimony-125 was calculated. The contribution of “old” rutheniurn-106, ruthenium-103 and tellurium-129m in the rain water was then calculated from the measured activities in the previous rainfall, the level being significant only for ruthenium-106. The corrected ratios of ruthenium-103 - ruthenium-106 and tellunum-132 - teIlurium-129wz are compared in Table VI with the theoretical ratios for fission of uranium-235, TABLE VI COMPARISON OF OBSERVED AND THEORETICAL RATIOS FOR FISSION BY FISSION NEUTRONS Observed ratio, December Theoretical ratio, calculated from r \ calculated to fission yields18 A Nuclide pair 28th.1966 Uranium-236 Uranium-238 Plutonium-239 Ruthenium-103 - ruthenium-106 . . 71.1 77.1 22.3 9.24 Tellurium- 132 - tellurium- 129m. . .. 253 237 236 150 Antimony-127 - antimony-126 . . .. - 552 626 62912 BATHIE AND BURDEN uranium-238 and plutonium-239 by fission neutrons, showing that agreement is good for uranium-236 fission. PILE-IRRADIATED URANIUM- A sample of uranium oxide was irradiated in the BEPO reactor at Harwell for 3 days at a thermal neutron flux of about 10l2 neutrons per cm2 per second. A weighed portion of the uranium was dissolved in acid in the presence of carriers, and the solution added to 10 litres of drinking water and passed through the experimental procedure described earlier. The object was to compare experimentally observed fission yields with figures quoted from the literature. The activity of strontium439 was measured and used as a monitor for determining the thermal neutron flux by using a fission yield of 4.79 per cent.The results are listed in Table VII. TABLE VII FISSION YIELDS FOR THERMAL-NEUTRON IRRADIATION OF URANIUM-235 Fission yield, per cent. Nuclide Ruthenium- 106 Ruthenium- 103 Molybdenum-99 Tellurium-132 . . Tellurium- 129m Antimony-127 . . Antimony-126 . . Tin-125 .. .. Sample 1 Sample 2 .. . . 0.38 0.40 .. .. 2*6* 2*8* .. . . 6.04 6.46 .. . . 4-36 - .. . . 0.16 I .. . . 0.11 0.13 .. . . 0.031 0.026 .. . . 0.011 0.012 * Figures obtained by y-counting. - 3 Literature 0~38’~ 3.014 6.0614 4.714 0.17’6 0.1 416 0.01 314 0.02114 We thank Dr. D. I. Coomber for his helpful advice, and the Government Chemist, Ministry of Technology, for permission to publish this paper. 1. 2. 3. 4. 6. 6. 7. 8. 9. 10. 11. 12. 13. 14. 16. REFERENCES Crouch, E. A. C., and Cook, G. B., J. Inorg. Nucl. Chem., 1956, 2, 223. Welford, G. A., Collins, W. R., Morse, R. S., and Sutton, D. C., Talanta, 1960, 5, 168. Buchtela, K., and Lesigang, M., Radiochimica Ada, 1963, 1, 208. Boni, A. L., Analyt. Chem., 1960, 32, 699. Osmond, R. G., Owers, M. J., Healy, C., and Mead, A. P., U.K. Atomic Energy Authority Report, A.E.R.E., R.2899, Hamell, 1969. Osmond, R. G. D., Evett, T. W., Arden, J. W., Lovett, M. B., and Sweeny, B., U.K. Atomic Energy Authority Report, A.E.R.E., AM.84, Harwell, 1961. Wood, R., and Richards, L. A., Analyst, 1966, 90, 606. U.S. Academy of Sciences, Nuclear Science Series, NAS-NS 3038 (1961), 3033 (1961) , 3023 (1960), 3029 (1961), 3009 (1960), U.S. Department of Commerce, Washington, D.C. Griess, J. C., J. Electrochem. Soc., 1953, 100, 429. Meinke, W. W., U.S. Atomic Energy Cornmission Report, AECD, 2738, Berkeley, California, 1949. Orlandini, K. A., Wahlgren, M. A., and Barclay, J., Analyt. Chem., 1965, 37, 1148. “Radioactivity in Drinking Water in the United Kingdom,” 1962, 1963, 1964 and 1966 results, Report by the Ministry of Housing and Local Government, Scottish Development Department, Ministry of Health and Social Services, Northern Ireland, Welsh Office, S.O. Code No. 75- 100-0-62 to 75-100-0-66, H.M. Stationery Office, London, 1963, 1964, 1966 and 1966, respec- tively. Rangarajan, C., Mishra, V. C., Lalit, B. Y., Gopalakrishnan, S., and Sadasivan, S., “Fission Products Data and its Application in Studying Fallout from Nuclear Weapon Tests,” AEET.209, Government of India Atomic Energy Commission, Bombay, India, 1965. KatkofT, S., Nucleonics, 1960, 18 (ll), 201. Hageboe, E., J. Inorg. Nucl. Chem., 1963, 25, 615. Received April 27th, 1967

ISSN:0003-2654    

DOI:10.1039/AN9689300001

出版商:RSC    

年代:1968

数据来源: RSC

摘要:

Analyst, January, 1968, Vol. 93, &5. 13-19 13 Heterocyclic Azo Dyestuffs in Analytical Chemistry Part I. The Ligand Properties of 2-(2-Pyridylazo)-l-naphthol and its Sulphonated Analogues BY R. G. ANDERSON* AND G. NICKLESS (Department of Inorganic Chemistry, School of Chemistry, The University, Bristol 8) The preparation, from 2-hydrazinopyridine and the respective 1 , 2-naph- thaquinones, of 2-( 2-pyridylazo)-l-naphthol (a-PAN) and its derivatives con- taining sulphonic acid groups in positions 4 to 8 of the naphthalene ring, respectively, is described. The metal-complexing properties of the dyes are discussed in relationship to the position of the sulphonic acid group, and compared with those of 1-(2-pyridylaz0)-2-naphthol @-PAN). The dye with the sulphonic acid group in position 8 appears to be the most promising colorimetric reagent.All the new dyes are shown to be superior indicators to /3-PAN for the complexometric titration of copper. ~-(%PYRIDYLAZO)-~-NAPHTHOL (p-PAN) was first proposed as an analytical reagent in 1955 by Cheng and l3ray.l Since then it has been used in the complexometric and colorimetric determination of many metals, particularly in conjunction with solvent extraction pro- cedures.293 The dye is noted for its high sensitivity, the stability of its complexes, and the characteristic colour changes produced on chelation. It , therefore, seemed worthwhile to us to study other pyridylazonaphthol derivatives, and, in particular, those containing sulphonic acid groups, which can be used in purely aqueous media. A variety of other pyridylazonaphthol dyes has been studied with a view to use in analytical chemistry.In particular, sodium 2-pyridyldiazotate has been coupled with a-naphth~l,~ 2,7-dihydro~ynaphthalene,~ chromotropic acid,6 H-acid,6 2,3-dihydroxynaphtha- lene-6-sulphonic acid (6,7-dihydroxynaphthalene-2-sulphonic acid)' and 8-hydroxyquinoline.8 The resultant dyes have found limited applications in analytical chemistry. However, the reactions of sodium 2-pyridyldiazotate with phenols and naphthols are, in general, slow, and the diazotate fails to react completely with many phenolic substances. We have shown9 that 2-hydrazinopyridine reacts smoothly with 0- and 9-benzoquinone to give two pyridineazo dyestuffs not available by conventional synthetic procedures.This reaction has been used to prepare 2-(2-pyridylazo)-l-naphthol (a-PAN), an isomer of p-PAN, and its derivatives containing sulphonic acid groups in positions 4 to 8 of the naphthalene ring, respectively, and to study their possible analytical usefulness. / HO I HO a-PAN @-PAN EXPERIMENTAL Spectroscopic and potentiometric measwements-The techniques used to measure the stability constants and visible spectra of the complexes have been described previou~ly.~ All measurements were made in 60 per cent. aqueous methanolic solutions at an over-all ionic strength of 0-1 M and a temperature of 25" C for potentiometric or 20 & 2" C for spectro- scopic methods. Solutions of all dyes containing sulphonic acid groups were standardised by the technique of spectrophotometric titration before use.1° 2-(2-PyridyZazo)-l-na~hthoZ (a-PA N)-2-Hydrazinopyridine was prepared by the method of Fargher and Furness,ll and 1,Znaphthaquinone by the method of Fieser.l2 A 3.2-g sample of 1,2-naphthaquinone was dissolved in 200ml of 60 per cent.aqueous methanol and a * Present address: Department of Chemistry, The University, Leicester. 0 SAC and the authors.14 ANDERSON AND NICKLESS : HETEROCYCLIC A20 [ANalyst, Vol. 93 solution of 2-2g of 2-hydrazinopyridine in 40ml of G M hydrochloric acid added. When the resulting solution was neutralised with ammonia solution an 84 per cent. yield of a-PAN was precipitated. The product, a red - brown powder melting at 102" to 104' C, was found by thin-layer chr~matographyl~ to be homogeneous. (Found: carbon, 72-1 per cent. ; hydrogen, 4.6 per cent.; nitrogen, 16.7 per cent.Calculated for Cl,HllN30: carbon, 72.3 per cent.; hydrogen, 4-4 per cent.; nitrogen, 16.9 per cent.) A sample of the copper complex was prepared by heating together equimolar amounts of copper chloride and a-PAN in ethanol. The complex was precipitated from the solution as a dark, copper-coloured powder. (Found: carbon, 52-4 per cent.; hydrogen, 3.2 per cent.; nitrogen, 11.8 per cent. Calculated for CU.C~,H,~N,O.C~: carbon, 51-9 per cent.; hydrogen, 2.9 per cent; nitrogen, 12-1 per cent.) 1-(2-Pyridylazo)-2-naphthoZ (P-PAN)-A commercial sample was obtained from Hopkin and Williams Ltd., and was standardised by spectrophotometric titration before use.lO 2-(2-Pyridylazo)-l-na~hthol-4-sul~honic acid (a-PA N-4.S) , [4-hydroxy-3-(2-pyridyZazo)- naphthalene-1-sulphonic acid]-A solution containing 1.1 g of 2-hydrazinopyridine in 20 ml of water was added to a solution containing 2.6 g of sodium 1,2-naphthaquinone-4-sulphonate and 12 ml of 72 per cent.perchlolic acid in 100 ml of water. The resulting orange precipitate was dissolved in sodium hydroxide solution, filtered and re-precipitated with hydrochloric acid. a-PAN-4S was thus found by thin-layer chromatography to be an orange - red homogeneous powder.13 (Found: carbon, 52.3 per cent. ; hydrogen, 4.1 per cent. ; nitrogen, 12.6 per cent. Calculated for Cl,HllN,0,S.H20: carbon, 51.9 per cent.; hydrogen, 3.8 per cent. ; nitrogen, 12-1 per cent.) 2- (2-Pyridylazo) -1-naphthol-5-sulPhonic acid (a-PA N-5S), [5-hydroxy-6- (2-pyridy1azo)- nap ht hulene- 1 -sztl$honic acid] -2-Amino- 1 -naphthol-5-sulphonic acid (6-amino-5-hydroxy- naphthalene-1-sulphonic acid) was prepared as follows : benzene diazonium chloride was coupled with sodium 1-naphthol-5-sulphonate (5-hydroxynaphthalene-1-sulphonate) in weakly alkaline conditions.The resulting dye was dissolved in sodium hydroxide solution and reductively cleaved with sodium dithionite. The aniline produced was removed and the solution neutralised with hydrochloric acid, when a 72 per cent. yield of the amine was precipitated. A 0.98-g sample of potassium dichromate was dissolved in 2 M hydrochloric acid and 2.4 g of 2-amino-1-naphthol-5-sulphonic acid (6-amino-5-hydroxynaphthalene-1-sulphonic acid) added , which dissolved to give a solution of 1,2-naphthaquinone-5-sulphonic acid (5,6-naphthaquinone-l-sulphonic acid).2-Hydrazinopyridine (1.1 g) in water (20 ml) was then added to the quinone solution, when an immediate orange precipitate of dye was formed. This was purified via its sodium salt and was found by thin-layer chromatography to be homogeneous.n (Found: carbon, 52.7 per cent.; hydrogen, 3.7 per cent.; nitrogen, 11.8 per cent. Calculated for C,,H,,N,O,S.H,O: carbon, 51.9 per cent. ; hydrogen, 3.8 per cent. ; nitrogen, 12-1 per cent.) Although we tried to take melting-points the sulphonic acid reagents decomposed, presumably by losing the azo-nitrogens. Thus in this work we have found it impossible to take melting-points of any of the sulphonic reagents. The other sulphonated dyestuffs were prepared in exactly analogous ways, starting from the appropriate sodium naphthol snlphonate.All were orange-to-yellow dyes that were found to be homogeneous by thin-layer chromatography on cellulose.15 2-(2-Pyridylazo)-l-naphthol-6-sulphonic acid (a-PA N-6s) , [5-hydroxy-6-(2-$yridylazo)- naphthalene-2-sulphonic acid]-This was prepared from sodium 2-naphthol-6-sulphonate (6-hydroxynaphthalene-2-sulphonate) . (Found : carbon, 50.6 per cent. ; hydrogen, 3.7 per cent. ; nitrogen, 11.1 per cent. Calculated for Cl,HllN30,S.l&H20: carbon, 60.6 per cent.; hydrogen, 3.9 per cent.; nitrogen, 1143 per cent.) 2-(2-PyridyZazo)-l-na~hthol-7-sul~honic acid (a-PA N-7s) , [8-hydroxy-7-(2-pyridylazo)- naphttCtalene-2-suZphonic acid]-This was prepared from sodium 2-naphthol-7-sulphonate (7-hydroxynaphthalene-2-sulphonate) .(Found: carbon, 49-7 per cent. ; hydrogen, 4.0 per cent. ; nitrogen, 11-1 per cent. Calculated for C,,H,,N,0,S.2H20: carbon, 49.3 per cent. ; hydrogen, 4.1 per cent.; nitrogen, 11.5 per cent.) 2-(8-Py~idylaxo)-l-na~hthol-8-sul~honic acid (a-PAN-8S), [8-hydroxy-7-(2-pyridylazo)- naphthalene-1-sul~lzonic acid]-This was prepared from sodium 2-naphthol-8-sulphonate (7-hydroxynaphthalene-l-sulphonate) . (Found : carbon, 48.3 per cent. ; hydrogen, 4.2 perJanuary, 19681 DYESTUFFS IN ANALYTICAL CHEMISTRY. PART I 15 cent. ; nitrogen, 10.5 per cent.. Calculated for Cl5H,,N,O4S.2~H,O : carbon, 48.1 per cent. ; hydrogen, 4.3 per cent.; nitrogen, 11-2 per cent.) For the sulphonic acid derivatives, water is always present when the dyestuffs are formed, as described here, from aqueous solutions.We have tried therrnogravimetric studies to elucidate the actual number of water molecules, but the whole thermogravimetric analysis pattern is complicated not only because of the loss of water but also because of the loss of nitrogen through decomposition. These two losses occur in the same temperature region. The solvents used in the thin-layer chromatography were- (1) Fifty millilitres of 40" to 60" C light petroleum, 50 ml of diethyl ether and 5 ml of absolute ethanol. (2) Sixty millilitres of butanol, 20 ml of absolute ethanol and 20 ml of 2 M ammonia solution. (3) Forty millilitres of isopropyl alcohol, 80 ml of ethyl methyl ketone and 30 ml of 0.88 ammonia solution.RESULTS AND DISCUSSION 1,2-Naphthaquinone has been shown to give azo dyes of a-naphthol exclusively on reaction with aromatic hydrazine deri~atives.l*~~~ At various values of pH the visible spectra of a-PAN and of its complexes show a close similarity to those of its sulphonated derivatives, but are distinct from those of B-PAN. The amine produced from the reduction of the sodium mono-phenylhydrazone of 1,2-naphthaquinone-4-sdphonate was found by infrared spectro- photometry to be identical with that produced from the reduction of 2-phenylazo-l-naphthol- 4-sulphonic acid (4-hydroxy-3-phenylazonaphthalene-l-sulphonic acid) but to be different from l-amino-2-naphthol-4-sulphonic acid (4-amino-3-hydroxynaphthalene-1-sulphonic acid). a-PAN and P-PAN were found by thin-layer chromatography to be different compounds.Furthermore, we have found that 1-(2-benzothiazolylazo)-2-naphthol-6-sulphonic acid [5-(2-benzothiazolylazo)-6-hydroxynaphthalene-2-sulphonic acid] and 1,2-naphthaquinone mono-( 2-benzothiazolylhydrazone)-6-sulphonic acid are different compounds. On the basis of the evidence given below it is seen that azo dyes of l-naphthol only were obtained. We have previously described the use of both /3-PANlg and a-PAN and its sulphonated derivatives17 as chromatographic spray reagents. /%PAN was noted for its high sensitivity, giving pink, violet and green colours against a yellow background with many metal ions. a-PAN was found to be similar to /3-PAN in sensitivity, but it was noticed that the back- ground colour was orange - red, and the metal complexes had violet, blue and green colours.a-PAN-6S and a-PAN-7S were slightly less sensitive than a-PAN, whereas a-PAN-4S, a - P A N 6 and a-PAN-8S were more sensitive. It was noted that the spots contrasted particularly well when a-PAN-4S was used as a spray reagent. The visible spectra and acid-dissociation constants of the dyes are contained in Tables I and 11. In these tables, and in the ensuing discussion, reference to a cation, neutral molecule or anion of a sulphonated dye is made without regard to the sulphonic acid group, as this group remains ionised under nearly all normal experiment a1 conditions. All the dyes show hypsochromic and bathochromic shifts on protonation and ionisation, respectively. Table I and Fig. 1 show that the spectra of a-PAN and its sulphonated deriva- tives are essentially similar but distinct from those of /?-PAN.In general, /3-PAN is seen to TABLE I VISIBLE SPECTRA OF THE DYES Cation Neutral molecule (PH - 0) (PH - 6 ) Amax., mp E x 10-8 Amax., m p Q x r 1 8-PAN .. 425 16.2 470 17.2 a-PAN . . 460 14.8 482 16-8 a-PAN-4S .. 465 16-8 477 19.1 a-PAN-5S . . 463 16.6 485 19.1 a-PAN-6S .. 465 16-3 492 19-2 a-PAN-7S .. 465 16.6 487 19.1 a-PAN-8S .. 468 14-7 488 17.3 Anion r 495 13.2 514 21-6 498 20.9 610 22-3 513 22-5 61 2 22-4 632 22.3 (PH - 13) Amax., m p E x16 ANDERSON AND NICKLESS : HETEROCYCLIC AZO [Analyst, Vol. 93 Wavelength, mu Wavelength, mu Fig. 1. Absorption spectra of (a) u-PAN and (b) p-PAN, concentration lo-%, at A, pH 0; B, pH 6; C, pH 13; and D, the nickel (11) complex [1:1] at pH 9 absorb at somewhat shorter wavelengths than a-PAN.Further, although pK,, is about the same for both dyes, pKoH is considerably lower for a-PAN than it is for /3-PAN. This fact has a considerable effect on the behaviour of the two dyes in analytical chemistry. However, there is also a considerable variation in the bathochromic shift produced on ionisation among the sulphonated derivatives of a-PAN. This shift is smallest for CC-PAN-~S, about the same for a-PAN-5S, a-PAN-6S and a-PAN-7S, larger again for a-PAN and very large for a-PAN-8s. This trend is best considered by comparing the bathochromic shifts observed on passing from the cation to the anion. If the magnitude of this total batho- chromic shift is compared with the magnitude of pKNH or pKoH or better, log PZH (the sum TABLE I1 ACID-DISSOCIATION CONSTANTS OF THE DYES P-PAN .... .. U-PAN .. .. .. u-PAN-4S .. .. .. a-PAN-5S .. .. .. a-PAN-6S . . .. .. u-PAN-~S .. .. .. a-PAN-8S . , .. .. * Determined spectrophotometrically. ~ K N E PKOH 2.32* 12.00* 2*29* 10-00* 243* 8-63t 248* 9-13? 2*86* 10.447 2.39* 9-11? 2.46* 9-09? t Determined potentiometrically. 5 Fig. 2. Bathochromic shift (Av) plotted against log fig for the equilibrium, RH,+ + R- + 2H+, for various PAN derivativesJanuary, 19681 DYESTUFFS IN ANALYTICAL CHEMISTRY. PART I 17 of pKN, and pKoH), exactly the same relationship is noticed, the only exception being the pKNH of a-PAN, which is low. If log /3f is plotted against the shift in wavelength or fre- quency involved in removing two protons from the molecule (see Fig.2), a definite, if em- pirical, relationship between the two can be seen for /I-PAN, or-PAN and its sulphonated derivatives. Thus, the magnitude of the frequency shift is directly related to the ease of protonation, or the basicity, of the Ligand. Tables I11 and IV summarise results relating to the spectra and stability constants, respectively, of the metal complexes of the dyes. The copper complex of a-PAN is seen to absorb at longer wavelengths than does that of p-PAN. With the nickel and zinccomplexes there are shoulders to the main peaks that lie at longer wavelengths for the a-PAN complexes and at shorter wavelengths for the p-PAN complexes. These two facts explain why the complexes of a-PAN appear to be more blue in colour than those of /%PAN.As a result of the greater acidity of the hydroxyl group in a-PAN, it was found that the copper complex of a-PAN is thermodynamically considerably less stable than that of /3-PAN. It is observed that for a-PAN and its sulphonated derivatives the peak wavelengths for the metal-complex spectra are lowest for or-PAN-4S, about the same for a-PAN-SS, cc-PAN-GS, or-PAN-7S and a-PAN, and highest for a-PAN-8s. It is also observed that the log K, values for the metal complexes are qualitatively directly related to the bathochromic shift involved in passing from the cation to the 1 : 1 complex. Thus exactly the same behaviour was observed with the ligands on chelation as on ionisation. This is not unexpected, as the more basic a ligand is, normally the more stable are its chelates, assuming that steric and other effects are constant.I t would be unwise, however, to draw any hard and fast conclusions concerning TABLE I11 SPECTRA OF THE METAL COMPLEXES Zinc( 11) * Amax., mP P-P-4N . . 545 514 a-PAN .. 545 CX-P~~N-~S . . 528 - a-PAN-5S . . 543 - a-PA4N-6S . . 545 - a-PAN-7S . . 543 - K-PAN-~S . . 589 555 x 10-3 22.6 20.8 25.2 26-0 23.2 25-1 26.0 27.1 28-2 - - - - Copper( 11) - mp e x ~ O - ~ 650 20.8 566 21.2 555 22.6 567 22.5 570 22.3 569 22.0 582 22.4 Zinc( 11) Copper( 11) Nickel( 11) Cobalt (111) Palladium(II1 Amax., - - I - - - - - - - - - Nickel (11) Palladium (I I) * -7 mp E x1O-3 mp E xlOp3 552 18.6 - - 519 18.6 - 548 22.0 - 563 41.8 650 11.5 532 45.8 612 12.9 580 41.2 - - 547 46.1 631 9.1 582 42.6 675 8.9 549 45.3 630 10.7 579 41.8 670 9.5 547 45.5 628 10.6 592 43.3 703 12.5 556 43-8 652 13.1 Amax., Amax., - - - 1:1 a t p H 9 - 1: 1 at pH 5 - 1:2 at pH 9 - l : l a t p H 5 - 1:1 a t p H 5 Nickel(I1) - a-PAN and /?-PAN - 1 : 1 at hH 9 TABLE IV STABILITY CONSTANTS OF THE METAL COMPLEXES Copper (11) * log Kl p-PAN... . 17.0 IX-PAN.. . . 14.6 a-PAN-4S . . 13.8 a-PAN-6S . . 14-3 a-PAN-7S . . 14-5 a-PAN-8S . . 15.7 wPAN-~S . . 14.6 - - - 8-6 8.5 17.1 8.8 8.7 17.5 9.2 8.1 17.3 8.9 7.9 16.8 9.9 7.6 17-4 * Determined spectrophotometrically. t Determined potentiometrically. Cobalt (111) * Amax., mp E x ~ O - ~ - - - - - - 615 11.5 583 12.8 635 9-1 598 10.6 635 10.5 603 11.9 630 10.8 598 12.2 653 10.2 612 11.6 - - - 5.9 6.1 11.9 6.0 6.5 12.5 6.2 6-5 12-7 6.2 5-8 12.0 8.3 6.2 14.518 ANDERSON AND NICKLESS : HETEROCYCLIC A20 [Analyst, Vol.93 log K1 and the bathochromic shift discussed above, because the former refers to the reaction of the anion with the metal cation, for which the wavelength change involved is more or less the same for each dye. Nevertheless, as far as analytical applications are concerned, it is the shift from the cation or neutral molecule that is of greater interest. The relationship between complex stability and position of the sulphonic acid group discussed above cannot be applied to the log K, values, as these are abnormally small for a-PAN-7s and a-PAN-8S, because of the steric effects encountered in trying to pack two ligand molecules around one metal atom. It has thus been shown that the order of basicity of a-PAN and its sulphonated deriva- tives, with respect to proton dissociation and metal-complex formation, is as follows- a-PAN-4S < a-PAN-5S = a-PAN-7s < a-PAN-6S < a-PAN < a-PAN-8S (The results show that a-PAN-6S is slightly more basic than a-PAN-5s or a-PAN-7s.) The charge distribution in the 1-naphthol molecule is such that electron-withdrawing substituents will have a maximum acid-strengthening effect on the hydroxyl group if they occupy positions 2 or 4 or, to a lesser extent, 5 or 7 of the naphthalene ring.The sulphonic acid group is just such a group, and this explains why a-PAN-4S is the most acidic ligand, a-PAN-6S is slightly more basic than a-PAN-5s or a-PAN-7S, and all four ligands are more acidic than a-PAN itself.To explain the high basicity of a-PAN-8S, one must consider the sulphonic acid group itself. In position 8 of the naphthalene ring, it is close enough to the hydroxyl group for the sulphonic oxygen atoms to shield the hydroxyl proton, possibly with the formation of a weak hydrogen bond, and thus raise its acid-dissociation constant. For the same reason, a high electron density around the phenolic oxygen atom causes it to form stronger bonds with metals. Through internal hydrogen-bonding, this trend of basicities is also transmitted to the heterocyclic nitrogen atom, thus enhancing further the difference in chelating power of these ligands. All the complexes of the sulphonated dyes have molar extinction coefficients that are close to those of a-PAN and slightly higher than those of /3-PAN.As a colorimetric reagent, therefore, a-PAN-8S seems to be the most promising of the new dyes, because of its high pKoH value, the high stability of its complexes and the large bathochromic shift produced on chelation. Perhaps the most familiar use of /3-PAN is as an indicator for the direct complexometric titration of copper with EDTA.2 Further, excess of EDTA may be back-titrated with standard copper solutions by using P-PAN as indicator, and the copper complex of /I-PAN has also been used as an indicator for the titration of metals that form only weak complexes with /I-PAN. The end-point of the complexometric titration of copper with /&PAN is slow because of the small difference in stability between the copper - P-PAN complex and the copper - EDTA complex18 (log K, = 18*3), and also because of the insolubility of the copper - /%PAN complex.Heating of the solution and the addition of organic solvents have been recom- mended to produce a faster colour change at the end-point.19 With a-PAN and its sulphonated derivatives, however, not only is the gap in stability larger, but there is also the possibility of forming water-soluble copper - indicator complexes. It was to be expected, therefore, that these dyes would be better indicators for the titration of copper. Further, although the copper complexes of these dyes are less stable than that of /I-PAN, because of the greater acidity of the dyes, chelation was found to take place at about 0.2 pH units lower than Copper solutions (0-01 M) were titrated directly against EDTA at a pH of 4.5 to 6.0 first with /3-PAN and then a-PAN and its sulphonated derivatives as indicators.All the dyes of 1-naphthol gave faster colour changes of from blue - violet to green at the end-point than /3-PAN, and it was, therefore, concluded that the new dyes were an improvement on /I-PAN for the titration of copper. The difference between the stability of the zinc - /3-PAN complex20 (log K, = 11.2) and the zinc - EDTA complexl8 (log K1 = 16.1) is large, and the titration of zinc with P-PAN as indicator is satisfactory. With a-PAN and its sulphonated derivatives the gap in stability is even larger still, and, in this case, displacement of the metal from the indicator complex begins to occur before the end-point is reached.As a result, the end-point becomes less easy to see if the solutions are more dilute than about 0.1 M, and consequently /%PAN is considered to be the best indicator for the titration of zinc. with p-PAN.January, 19681 DYESTUFFS IN ANALYTICAL CHEMISTRY. PART I 19 The dye produced from the reaction of sodium 2-pyridyldiazotate with l-naphthol has been studied as an analytical reagent for metal ions.* The dye gives sensitive colour changes with a wide range of metals and forms extractable complexes of high stability with copper and zinc. This dye has been assumed to be 4-(2-pyridylazo)-l-naphthol. A slightly impure sample was prepared by condensing 2-hydrazinopyridine with 1,4-naphthaquinone. The metal-complexing reactions of this dye were found to be most undistinguished and quite unlike those reported for the dye prepared from l-naphthol.As a chromatographic spray reagent, the compound gave colours only with metals in groups VIII and Ib of the Periodic Table, and these were of a low sensitivity. It was a yellow dye with a pKNK value of 4.0 in 50 per cent. aqueous methanol, as opposed to the value of 2.54 in 50 per cent. aqueous dioxan found for the dye prepared from the diazotate. Further, 4-(2-pyridylazo)-l-naphthol failed to give the distinctive green complex with cobalt, produced by all the other pyridylazo- naphthol dyes. D. Betteridge (in a private communication) has subsequently shown by infra- red spectroscopy that the dye obtained by Betteridge, Todd, Fernando and Freisefl was, in fact, identical with the 2-(2-pyridylazo)-l-naphthol described in this paper.The dye has recently been suggested as an extractive indicator in the titration of EDTA with copper.21 1. 3. 4. 6. 8. 9. 10. 11. 12. 13. 14. 15. 16. > Y. 3. r- 4 . 17. 18. 19. 20. 21. REFERENCES Cheng, K. L., and Bray, R. H., Analyt. Chem., 1955, 27, 782. Anderson, R. G., and Nickless, G., Analyst, 1967, 92, 207. Busev, A4. I., and Ivanov, V, M., J . Analyt. Chem., USSR, 1964, 19, 1150. Betteridge, D.. Todd, P. K., Fernando, Q., and Freiser, H., Analyt. Chem., 1963, 35, 729. Sommer, L., 2. analyt. Chem., 1960, 171, 410. Sommer, L., and HniliCkovA, M., Naturwissenschaften, 1958, 45, 544. HniliEkovP, M., and Sommer, L., 2. aizalyt. Chem., 1960, 177, 425. Busev, A. I., Ivanov, V. M., and Talipova, L. L., Zh. Analit. Khim., 1963, 18, 33. Anderson, R. G., and Nickless, G., Analytica Chim. Acta, 1967, 39, 469. Pease, B. F., and Williams, M. B., Analyt. Chem., 1959, 31, 1044. Fargher, R. G., and Furness, R., J . Chem. Soc., 1915, 107, 691. Fieser, L. F., Org. Synth., 1937, 17, 68. Pollard, F. H., Nickless, G., Samuelson, T. J., and Anderson, R. G., J . Chromat., 1964, 16, 231. Zincke, Th., and Bindewald, H., Bey. dt. chem. Ges., 1884, 3026. Kamel, M., and Amin, S. A., Indian J . Chem., 1964, 2, 232. Pollard, F. H., Nickless, G., and Jenkins, H., in West, P. W., Macdonald, A. M. G., and West, T. S. , Editors, “Analytical Chemistry 1962 : The Proceedings of the International Symposium, Birmingham, in Honour of Fritz Feigl,” Elsevier Publishing Company, Amsterdam, London and New York, 1963, p. 160. Pollard, F. H., Nickless, G., and Anderson, R. G., Talanta, 1966, 13, 725. Schwarzenbach, G., and Freitag, E., Helv. Chim. Acta, 1951, 34, 1503. Cheng, K. L., Analyt. Chem., 1958, 30, 243. Corsini, A., Yih, I. Mai-Ling, Fernando, Q., and Freiser, H., Ibid., 1962, 34, 1090. Retteridge, D., Talanta, 1966, 13, 1497. Received June 14th, 1967

ISSN:0003-2654    

DOI:10.1039/AN9689300013

出版商:RSC    

年代:1968

数据来源: RSC

摘要:

20 AnaEyst, January, 1968, Vol. 93, fi$. 20-25 Heterocyclic Azo Dyestuffs in Analytical Chemistry Part 11. The Ligand Properties of 2-( 2-Pyrimidylazo)-l-naphthol and its Sulphonated Analogues BY R. G. ANDERSON* AND G. NICKLESS (Department of Inorganic Chemistry, Scltool of Chemistry, The University, Bristol 8) The preparation, from 2-hydrazinopyrimidine and the respective 1,2-naph- thaquinones, of 2- (2-pyrimidylazo) - 1 -naphthol and its derivatives containing sulphonic acid groups in positions 4 to 8 of the naphthalene ring, respectively, is described. The metal-complexing properties of the dyes have been studied, and they are critically compared with their pyridyl analogues as analytical reagents. The dyes produce larger bathochromic shifts on chelation, and form complexes of lower stability.These two facts indicate that the dyes should be capable of higher selectivity than their pyridyl analogues. They are found to be better indicators for the titration of copper and better chro- matographic spray reagents than their pyridyl analogues. IN Part I of this series,l we discussed the use of pyridineazo dyestuffs in analytical chemistry. Azo dyestuffs containing other heterocyclic ring systems have been studied to a lesser extent, but this work has been mainly confined to thiazolylazo and benzothiazolylazo dyestuffs.2 These dyes differ from their pyridyl analogues in that they possess lower pKA values and consequently form less stable complexes. Further, these dyes and their anions have more intense colours than their pyridyl analogues, and the colour contrast produced on chelation is not as pronounced.The dyes, however, are easily prepared by coupling the diazotised aminothiazole with the appropriate phenol or naphthol. The synthesis of pyridineazo dyestuffs by the diazo-coupling reaction is complicated by the low reactivity of sodium 2-pyridyldiazotate, and many phenols and naphthols fail to couple at all. We have simplified this problem to a certain extent by showing that 2-hydrazinopyridine reacts readily with a range of quinones to produce some pyridylazo dyestuffs not available by the normal diazo-coupling reacti0n.l~~ The applications of this reaction have now been extended to the preparation of a series of 2-pyrimidylazo dyestuffs corresponding to the pyridylazo dyestuffs described previous1y.l The metal-complexing properties of these two series of dyes have been critically compared from an analytical point of view.HO HO 2-(2-PyridyIazo) -1-naphthol 2-( 2-Pyrimidylazo) -I-naphthol (a-PAN) (a-MAN) EXPERIMENTAL Spectroscopic and fiotentiometric measurements-The techniques used in these measure- ments have been described previ~usly.~ With the exception of the pK,, determinations and measurements of the spectra of the protonated forms of the ligands, all measurements were made in 50 per cent. aqueous methanolic solutions at an over-all ionic strength of 0.1 M and a temperature of 25" C for the potentiometric, or 20" 2" C for the spectroscopic methods. 0 SAC and the authors. *Present address : Department of Chemistry, The University, Leicester.ANDERSON AND NICKLESS 21 Because of the low pK,, values of the dyes, these were determined spectrophotonietrically in aqueous solutions containing calculated amounts of perchloric acid.In these cases, obviously, the ionic strength was greater than 0.1 M. The spectra of the protonated forms of the dyes, for which the pH had to be less than 0, were measured under similar conditions. All solutions of the dyes were standardised by spectrophotometric titration, before use. 2-(2-Pyrimidylaxo)-l-naphthoZ (a-MA N)-2-Chloropyrimidine was prepared by the method of Kogon, Minin and Overbergefl and converted to 2-hydrazinopyrimidine by the method of Shirakawa, Ban and Yoneda.6 1,ZNaphthaquinone was prepared by the method of Fieser.7 The 4.7-g sample of quinone was dissolved in 600 ml of 50 per cent.aqueous methanol, to which were added 30ml of concentrated hydrochloric acid and a solution of 3.3g of 2-hydrazinopyrimidine in 30ml of water. On dilution with water, a 70 per cent. yield of an amorphous red precipitate of dye, melting at 149" to 150" C, was formed. This was found by thin-layer chromatography to be homogeneous.* (Found : carbon, 63.7 per cent. ; hydrogen, 4.4 per cent. ; nitrogen, 20.5 per cent. Calculated for C,,HloN,O.H,O: carbon, 62.7 per cent.; hydrogen, 4.5 per cent.; nitrogen, 20.9 per cent.) A sample of the copper complex was obtained by mixing equimolar alcoholic solutions of copper chloride and a-MAN, and collecting the precipitate formed. This was insoluble in organic solvents but was moderately soluble in water to give a violet solution containing chloride ions.(Found: carbon, 48-3 per cent.; hydrogen, 2.9 per cent.; nitrogen, 16.1 per cent. Calculated for Cu.C,,H,N,OCI: carbon, 48.3 per cent. ; hydrogen, 2.6 per cent. ; nitrogen, 15.6 per cent.) 2-(2-Pyrimidylazo)-l-naphthol-4-sul~honic acid (N-MAN-~S), [4-hydroxy-3-(2-pyrinzidyZ- azo)-naphthaEene-l-suZphonic acid]-A solution of 4-4 g of 2-hydrazinopyrimidine in 80 ml of water was added to a solution of 10.4g of sodium 1,2-naphthaquinone-4-sulphonate in 25ml of hydrochloric acid and 300ml of water. The orange precipitate produced was recrystallised from water to give a 63 per cent. yield of a-MAN-4S, and was found to be homogeneous by thin-layer chromatography.8 (Found : carbon, 45.0 per cent. ; hydrogen, 3.4 per cent.; nitrogen, 15.3 per cent. Calculated for C,,H,N,O,S.Na.H,O: carbon, 45.4 per cent.; hydrogen, 3.0 per cent.; nitrogen, 15.1 per cent.) The other sulphonated derivatives of a-MAN were prepared in exactly the same way as their pyridine analogues1 by using 2-hydrazinopyrimidine, with the exception that they were recrystallised from water. All were obtained as orange crystalline solids, soluble in water, and found to be homogeneous by thin-layer chromatography. 2-(2-Pyrimidylazo)- 1-naphthol-7-sulphonic acid (a-MAN-7s) [8-hydroxy-7-( 2-pyrimidylazo)-naph thalene-2-sul- phonic acid] decomposed on recrystallisation and therefore the crude dye was used, the solutions being standardised by spectrophotometric titration before use. 2-(2-Pyrimidylaxo)-l-na~hthoL5-suZ~honic acid (a-MA N-5S), [5-hydroxy-6- (6-pyrimidyl- azo)-naphthalene-l-su&honic acid]-(Found : carbon, 50-0 per cent' ; hydrogen, 3.2 per cent.; nitrogen, 16.0 per cent. Calculated for Cl,H,,N,0,S.QH20: carbon, 49.5 per cent. ; hydrogen, 3.2 per cent.; nitrogen, 16.5 per cent.) 2-(2-Py~imidyZazo)-l-na~hthoZ-6-suZ~honic acid (a-MAN-6s) , [5-hydroxy-6-(2-pyrimidyl- azo)-na~hthalene-2-suZ~honic acid]-(Found : carbon, 48.1 per cent. ; hydrogen, 3.7 per cent. ; nitrogen, 15.9 per cent. Calculated for C,,H,,N,O,S.H,O: carbon, 48.3 per cent. ; hydrogen, 3-5 per cent.; nitrogen, 16.1 per cent.) 2-(2-Pyrimidylazo)-l-na~hthol-7-szd~honic acid (a-MAN-7S), [8-hydroxy-7- (2-Pyrimidyl- azo)-na;hhtJzalene-2-sulphonic acid]-(Found, uncrystallised : carbon, 42-5 per cent.; hydrogen, 4.1 per cent.; nitrogen, 14.5 per cent. Calculated for C,,HloN4O,S.3~H,O: carbon, 42.7 per cent.; hydrogen, 4.3 per cent.; nitrogen, 14.3 per cent.) 2-(2-Pyrimidylazo)-l-na$hthoZ-&suZ$honic acid (a-MAN-8S), [8-hydroxy-7-(2-fiyri.;upzidyZ- azo)-naj!4thaZelze-l -s~Z~zCoutic acid]-(Found : carbon, 48.3 per cent. ; hydrogen, 3.8 per cent. ; nitrogen, 15.5 per cent. Calculated for C1,HloN,O4S.H2O: carbon, 48.3 per cent. ; hydrogen, 3.5 per cent. ; nitrogen, 16.1 per cent.) The metal complexes of a-MA N-4s-These were prepared by mixing together aqueous solutions of dye and metal salt in the molar ratio 2 : 1, from which the complex precipitated, generally immediately. Ammonia solution was added to the manganese, calcium and magnesium complexes in order to obtain a high enough pH for chelation to take place.22 Ion Zn(I1) .. Ni(I1) . . Mn(I1) .. Pb(I1) . . Mg(I1) . . Cu(I1) . . Eg\ :: UO2Z+ . . ca(1I) * . ANDERSON AND NICKLESS : HETEROCYCLIC A20 TABLE I COMPLEXES OF a-MAN-4S Found, per cent. C H 38.6 2.9 40.5 2.3 38.2 3.4 40.2 2.9 36.4 2.2 40.3 3.1 32.0 1.7 26.1 2-4 42-4 3.1 38-2 3.4 7 N 12-9 13.2 12.6 13.2 12.7 13-6 10.9 8.9 16.1 13-2 Calculated, per cent. - C H N 38.4 3.0 12.8 41.0 2.5 13.2 38.1 3.2 12.7 39.7 2.9 13.3 37.1 2.2 12.4 40.1 2.9 13.4 32.9 1.5 10.1 26-7 2.2 8.6 42-6 3.2 16.0 38.2 3.6 12.7 [AIzlalyst, VOl. 93 Formula NiL.3H20 CoL.2H20 PdL.H,O MnL.2H20 PbL.H,O UOBL.3Hz0 MgL.2H20.+NH, CaL.4H20 In cases where water or ammonia molecules are given in Table I, then the presence of water or ammonia was proved.However, as mentioned in Part I of this series, the assignment of the actual number of molecules is extremely difficult. Again , all these complexes were tested by thin-layer chromatography and their homogeneity proved. The complexes were washed free from all reagent and dried under extremely reduced pressure. 1-(2-PyrimidyZazo)-2-lza~lztlzoZ (/I-MAN)-This was prepared by the oxidative coupling method of Hiinigg in which 0 6 5 g of 2-hydrazinopyrimidine and 0-75g of naphthol were dissolved in the minimum amount of methanol, to which was added 2.5 ml of concentrated ammonia solution (sp.gr. 0.88) in 12.5 ml of water. When a solution of 7.5 g of potassium ferri- cyanide in 25 ml of water was added a dirty yellow precipitate formed, which was soluble in organic solvents to produce a yellow solution that turned orange - red when alkali was added and violet - red when copper chloride was added.Thin-layer chromatographya showed that the major component had an R, value similar to that of 1-(2-pyridylazo)-2-naphthol. It was assumed that the major component was /3-MAN, which was responsible for the colour reactions with alkali- and metal-containing solutions. RESULTS AND DISCUSSION For the reasons stated previously,l it is obvious that all the pyrimidylazonaphthol dyes obtained from quinones were derivatives of l-naphthol. Further, thin-layer chromato- graphy,* in addition to other results discussed below, shows that the impure sample of /I-MAN obtained was a different compound from a-MAN. The use of these dyes as chromatographic spray reagents has been described previously.1° /I-MAN gives pink, violet and green colours with metals against a yellow background.The colours are not as bright as those of 1-(2-pyridylazo)-2-naphthol, probably because the dye was not pure. The dye was also seen to be slightly more sensitive in its reactions towards metals in groups IIa and IIIa. However, with a-MAN and its sulphonated derivatives, the differences between the two heterocyclic ring systems are very much more evident. The dyes produce violet, blue and green colours with metals as before, but the background colour is orange - yellow, as opposed to the orange - red colour of the pyridylazo dyes. This manifests itself in a greatly improved colour contrast on chelation with these new dyes. Further, the sensitivities of these dyes towards metals in groups IIa and IIIa are considerably greater than those of the pyridylazo dyes.As chromatographic spray reagents, therefore, the pyrimidylazo dyestuffs are strikingly superior to their pyridyl analogues. In particular, a-MAN-4S was found to be the most sensitive spray reagent of all of those studied. Tables I1 and I11 contain results relating to the spectra and acid-dissociation constants of the dyes. Like their pyridyl analogues, all these dyes undergo hypsochromic and batho- chromic shifts on protonation and ionisation, respectively. However, the pyrimidylazo dyes absorb at lower wavelengths in acid and neutral solutions and at higher wavelengths in alkaline solution, with the net result that there are larger bathochromic shifts on passing from the cation or neutral molecule to the anion. (In the Discussion, references to cation, neutral molecule or anion are made without regard to the sulphonic acid group that is present as the sulphonate anion under most normal experimental conditions.) Further, theJanuary, 19681 DYESTUFFS IN ANALYTICAL CHEMISTRY.PART I1 TABLE I1 VISIBLE SPECTRA OF THE DYES 23 Cation (pH < 0 in water) & a-MAN .. 455 9.4 a-MAN-4S .. 445 11.9 a-MAN-5S .. 447 11.9 a-MAN-6S .. 452 11.8 a-MAN-7S .. 449 12.0 a-MAN-8S .. 448 10-7 Amax., m p t x Neutral molecule (PH 5) & Amax.. m p x lo-* 469 11-6 462 14-7 468 14-1 473 14.1 470 14.3 470 12.8 Anion - 623 25-1 508 25.1 523 27.1 527 27.1 523 27.0 53 1 25.8 (PH 13) Amax., mp E x TABLE 111 ACID-DISSOCIATION CONSTANTS OF THE DYES a-MAN .... ;:g ;.% m-MAN-4S.. . . 0-58* 8*41t a-MAN-5s.. . . 0.87* 8.877 a-MAN-6S . . . . 0-89* 8.91 t a-MAN-7s.. . . 0.87* 8.667 a-MAN-%. . . . 1-17* l O * l O t * Determined spectrophotometrically. t Determined potentiometrically. magnitude of the bathochromic shifts follow approximately the same order, with regard to the position of the sulphonic acid group, as those of their pyridyl analogues,1 but the corre- lation, however, is not quite as good. The shift is small for a-MAN because of a high peak wavelength for the cation, and the peak wavelength of the anion of a-MAN& is not as high as would be expected, as it is about the same as that of its pyridyl analogue. The acid-dissociation constants of the pyrimidylazo dyestuffs are all uniformly lower than those of their pyridyl analogues to the extent of about 1-5 units in PKFH.and 0.3 units- in pKoH. The lower PKNH values are to be expected from the relative basicities of the un substituted heterocycles, (pKN, = 5-23 for pyridine and 1-30 for pyrimidinell), and this effect is also present to a smaller extent in the pKoH values. The correlation between basicity and position of the sulphonic acid group is exactly the same as that found for the pyridylazo dyestuffs,l (with the added factor that pKoH for a-MAN is now in place) and presumably, therefore, is due to the same causes. TABLE IV SPECTRA OF THE METAL COMPLEXES Zinc( I I) * Amax., m p E X ~ O - ~ U-MAN .. 543 24.9 x-MAN-~S.. 529 27.0 - - a-MAN-5s.. 541 27-4 a-MAN-6s..544 20.9 a-MAN-7s.. 542 27.1 a-MAN-8s.. 551 27.4 - - - - - Copper( 11) * Amax., m p z X ~ O - ~ 564 19.5 556 22-1 565 22-3 669 22.5 567 21.8 676 21.4 - - - - - - - - Nickel (I I) * Amax., m p t x ~ O - ~ 544 21-4 572 40.6 535 47.0 583 39.0 547 47.2 583 41.1 548 46.7 585 39.1 547 45-1 582 34.6 652 40.6 Cobalt( 111) * L b X . , m p t X ~ O - ~ 633 9-6 590 11.8 645 9.1 606 11-2 648 9.1 607 11.1 650 8.4 604 10-2 058 7.1 617 8-9 - - Palladium(I1) - m p E x10-s 670 11.2 621 13.3 690 10.2 640 12.9 696 10.0 642 12.6 693 9-6 642 11-9 710 11.0 655 13.0 Amax., - - zinc (11) - 1: 1 at pH 9 Copper(I1) - 1 : l a t p H b Nickel (I I) - 1:2 at pH 9 Cobalt (111) - 1 : l a t p H b Palladium (11) - 1: 1 at pH 6 Nickel(I1) - u-MAN (only) - 1 : 1 at pH 924 ANDERSON AND NICKLESS : HETEROCYCLIC A20 TABLE V STABILITY CONSTANTS OF THE COMPLEXES [Analyst, Vol.93 Copper (11) * Zinc( 11) t Manganese(I1) t f A L \ I \ W K l W K l W K , LogK1 h g K 2 - - U-MAN . . 13.6 - - - a-MAN-4S . . 12-6 7.7 7-1 14.8 5.3 4.9 10.2 a-MAN-5S . . 13.0 7.9 7-8 15.7 6-3 5.3 10-6 u-MAN-GS . . 13.2 8.1 7.8 15.9 5.8 5-2 11.0 a-MAN-7S . . 12.9 7.7 7.0 14.7 5.7 5.3 11.0 * Determined spectrophotometrically. t Determined potentiometrically. a-MAN-8S . . 14.3 9.2 6-3 15.6 7.5 5.7 13.2 Tables IV and V summarise results relating to the spectra and stability constants of the metal complexes. The zinc, copper and nickel complexes absorb at about the same wave- length as their pyridyl analogues, while the cobalt(II1) and palladium complexes absorb at higher wavelengths.However, all the pyrimidylazo dyes show larger bathochromic shifts from the cationic or neutral forms on complex formation than their pyridyl analogues. This is the most striking difference between the dyes and is obviously a definite asset to their use in any form of analysis when a colour change on chelation is exploited. Further, the spread in peak wavelengths for different metals is larger, and this implies the possibility of greater selectivity in colorimetric analysis. The positions of the peak wavelengths of the complexes are directly related to the basicities of the ligands, as are also the bathochromic shifts, with the two exceptions observed for the ionisation of the ligands, namely, those due to the high peak wavelength for the protonated form of a-MAN, and the relatively small bathochromic shifts produced on chelation with or-MAN&.The larger bathochromic shifts produced on complex formation with the pyrimidylazo dyes are thought to be the direct result of the larger shifts produced on removing the hydroxyl proton. The anion thus produced would be expected to have a larger resonance energy if a pyrimidine ring was present- The stabilities of the complexes are all uniformly lower than those of their pyridyl analogues. This is to be expected from the lower basicities of the ligands, but it is felt that the differences in stabilities between the two series is smaller than would be expected if the bonds between the three chelating ligand atoms made equal contributions to the over-all stabilities of the chelates.Thus, the heterocyclic nitrogen atom would appear to contribute less to the formation of the complexes than the other atoms. It was found that chelation with zinc and manganese took place at about 0.5 of a pH unit higher with the pyrimidylazo dyes than with the pyridylazo dyes, and with copper, at about 0.2 of a pH unit lower. It would thus appear that the initial pH values required for chelation with different metals are more widely separated with these new dyes. This means that they should be capable of greater selectivity, by careful pH control, in their applications in analytical chemistry.January, 19681 DYESTUFFS IN ANALYTICAL CHEMISTRY. PART 11 25 The relationship between metal-complex stability and position of the sulphonic acid group is the same as that observed with the pyridylazonaphthol dyes.l (Log K, for the manganese complex of a-MAN-4S was found to be lower than that for the a-MAN-5S complex, but the difference was less than the experimental error.) Again, therefore, the electronic and steric effects, discussed previously with respect to the pyridylazo dyes,l would appear to apply equally to their pyrimidyl analogues.It has been shown1 that the pyridylazo derivatives of l-naphthol are better indicators for the complexometric titration of copper than l-(2-pyridy1azo)-%naphthol, as a direct result of their lower basicity. As the pyrimidylazo dyes are less basic still, it was felt that they ought to be even better indicators. Copper chloride solutions (0.01 M) were titrated against a 0.01 M EDTA solution at a pH of from 4.5 to 6.0, with the new dyes as indicators.The end-points, from blue - violet to bright green, were sharp, reproducible and quickly attained, and as indicators for copper the pyrimidylazo dyes were, in fact, found to be considerably better than their pyridyl analogues. Back-titrations with copper solution were equally satisfactory. Of the new dyes, ,&MAN was the least satisfactory, giving a more sluggish end-point than the a-naphthol dyes. No quantitative work was carried out on this dye, because of its impure nature, but it is assumed by analogy with the pyridylazo dyes,l that the end- point reaction is slower, because the dye forms a more stable copper complex. The pyrimidyl- azo dyes were also used for the titration of zinc, but were found to be less useful in this respect than their pyridyl analogues because the EDTA attacked the weakly bound metal - indicator complex before the true end-point, which thus became difficult to see if the solutions were more dilute than about 0.1 M.A series of solid metal complexes of a-MAN-4S was prepared by mixing an aqueous solution of the dye with an aqueous solution of a divalent metal salt in the molar proportions 2 : 1. Invariably a 1 : 1 complex was precipitated, and in no case was a 2 : 1 complex formed. This is thought to be because, with a divalent metal ion, as soon as one ligand molecule is attached, the net charge on the complex is zero, although there is likely to be a large dipole moment present because of the charge separation between the sulphonate group and the central metal atom.In conclusion, it has been found that the pyrimidylazo dyes possess several advantages over their pyridyl analogues as analytical reagents. The dyes were observed to be more soluble in water and more sensitive as chromatographic spray reagents, particularly towards metals in groups IIa and IIIa. They produce larger and more varied bathochromic shifts on chelation, thus increasing their usefulness, particularly with regard to selectivity, in colorimetric and other forms of analysis. The complexes are less stable, and there is alarger variation in initial pH for chelation with the pyrimidylazo dyes. This also means thatit should be possible to make them more selective as colorimetric or complexometric reagents. They are better indicators for the complexometric titration of copper. The main drawback at present to the use of these dyes in analysis is the high cost of preparing them. If this could be overcome, then there should be considerablepossi- bilities of developing them as reagents with a more selective action than the well known 4-(2-pyridylazo)resorcinol and 1-(2-pyridylaz0)-2-naphthol. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. REFERENCES Anderson, €2. G., and Nickless, G., Analyst, 1968, 93, 13. -- , Ibid., 1967, 92, 207. Pease, B. E., and Williams, M. B., Analyt. Chem.. 1959, 31, 1044. Kogon, I. C., Minin, R., and Overberger, C. G., Org. Synth., 1955, 35, 34. Shirakawa, K., Ban, S., and Yoneda, M., J. Pharm. Soc., Japan, 1953, 73, 598. Fieser, L. F., Org. Synth., 1937, 17, 68. Pollard, F. H., Nickless, G., Samuelson, T. J., and Anderson, R. G., J. Chromal., 1964, 16, 231. Hiinig, S., U.S. Patent No. 2,832,764, 1958. Pollard, F. H., Nickless, G.. and Anderson, R. G., Talantu, 1966, 13, 725. Albert, A., Goldacre, R., and Phillips, J., J . Chem. Soc., 1948, 2240. NOTE-ReferenCe 1 is to Part I of this series. , , Analytica Chim. Acta, 1967, 39, 469. -- Received June 14fh, 1967

ISSN:0003-2654    

DOI:10.1039/AN9689300020

出版商:RSC    

年代:1968

数据来源: RSC

摘要:

26 Afid’st, January, 1968, Vol. 93, pj5. 26-27 An Improved Silver Reagent for Use in the Walden Silver Reductor BY M. A. SALAM KHAN AND W. I. STEPHEN (Chemistry De$avtment, The University, P.O. Box 363, Birmingham 15) The preparation and use of silver-impregnated pumice granules in the silver reductor is described. This material possesses advantages over the conventional chemically precipitated silver and is equally effective for the reduction of iron(II1) and copper(I1) in solution. WHILE investigating the formation of hydrogen peroxide in metallic reductors,l some difficulty was experienced with the conventional silver reductor containing chemically precipitated silver metaL2 The finely divided silver readily forms a compact mass in the column; this impedes the flow of solution through the column, and the application of reduced pressure is necessary for the attainment of practically useful flow-rates.Smith and CagleS recognised this difficulty in the operation and regeneration of the silver reductor, and recommended the use of an electro-deposited silver in the form of “silver-tree” type aggregates. Although their method is effective in producing a highly crystalline silver of low apparent density that does not readily compact in the column, it is not practicable in that it requires unusually high electrical energies (60 to 80 amp2res at 6 volts) and pure silver anodes and platinum cathodes. A simpler method has been the use of a granular material as an inert substrate on which silver metal can be deposited. Granular pumice, which is inert to reducing substances and resistant to attack by hydrochloric acid, has been found effective.The porous nature of the material allows it to absorb an appreciable volume of silver nitrate solution which, after drying, can be decomposed to metallic silver and oxides of nitrogen, by heating to a tem- perature of about 500” C. In the preparation described below, the granulated material was found to contain between 50 and 55 per cent. of silver metal (by extraction with nitric acid and precipitation of silver chloride). When filled into a conventional glass reductor column, the silverised pumice allows a free flow of solution through the bed of reductant, the rate of which can now be controlled by means of the stop cock on the reductor. The column is first activated by passing 2 N hydrochloric acid through the bed of reductant.The efficacy of the silver - pumice reductant has been compared with that of the normal silver reductant in two typical reductor experiments, the determinations of iron(II1) and copper(I1). Provided that the same pre- cautions to avoid formation of hydrogen peroxide and re-oxidation of the reduced solutions are observed, results from the two types of reductor are in close agreement (maximum difference is 0.2 per cent.). This modified silver reductant possesses other advantages over the copper-precipitated material. It appears to need less frequent regeneration (about 40 determinations against the 20 to 25 determinations with the conventional reductor), probably because the silver chloride formed from the reduction is less firmly held on the granules of pumice than on the surface of silver metal, which in the precipitated form is soon covered by a layer of silver chloride.Regeneration of the reductant is best effected by passage of chromium( 11) chloride solution through the column (Huffmann’s process) .* It is easier to prepare and handle than the copper-precipitated material, and, as it contains little more than 50 per cent. of silver, it is obviously a cheaper reagent. Although the new reagent has not been exhaustively tested as a reductant for cations other than Fe3+ and Cu2+, there is no reason to suppose that it cannot be used for the reduction of V5+, UO,a+ and MOO?-, for which ions the conventional Walden reductor has been successfully applied.0 SAC and the authors.SALAM KHAN AND STEPHEN 27 PREPARATION OF SILVER - PUMICE REDUCTANT- Dissolve 200 g of silver nitrate in 200 ml of distilled water contained in a 400-ml beaker, and add, in small amounts, 100 g of thoroughly washed pumice, granulated to a size of about 10 mesh. Pour off the surplus liquid, transfer the pumice granules to an evaporating basin and dry them in an air-oven at 110" C. Return the still hot granules to the beaker and pour the remaining silver nitrate solution over them. Remove the granules and dry, as before. Repeat the process until all of the silver solution has been absorbed. Heat the dry granules at 500" C in a muffle furnace, which has a suitable means for the extraction of fumes, until the evolution of nitrous fumes has ceased and all the silver nitrate has decomposed (about 1 to 13 hours).Allow the granules to cool to room temperature and wash them on a suitable sintered-glass filter funnel with distilled water to remove any soluble silver salts. Fill the 2-cm diameter reductor column to a height of 25 cm with the granular material and keep the column of reductant covered with distilled water. A sample of the dried material should be assayed for its silver content, by boiling it with dilute nitric acid, and extracting the granules with distilled water until free from silver ions. The silver solution is then treated with an excess of chloride ions and the precipitate of silver chloride is collected, dried and weighed in the usual way. The material should contain between 45 and 65 per cent. of silver. We are grateful to Professor R. Belcher for his encouragement with this work. REFERENCES 1. 2. Salam Khan, M. A., and Stephen, W. I., Analytica Chim. Acta, 1968, in the press. Walden, G. H., Hammett, L. P., and Edmonds, S. M., J. Amer. Chem. Soc., 1934,56, 67; see I. M. Kolthoff and R. Belcher, "Volumetric Analysis," Volume 111, Interscience Publishers Inc., New York, 1967, p. 14. Smith, G. F., and Gagle, F. W., Analyt. Ckem., 1948, 20, 183. Huffman, E. H., I d . Engng Chem. Analyt. Edn, 1946, 18. 278. 3. 4. Received June 22nd, 1967

ISSN:0003-2654    

DOI:10.1039/AN9689300026

出版商:RSC    

年代:1968

数据来源: RSC

摘要:

28 Analyst, January, 1968, Vol. 93, $9. 28-33 Analytical Evaluation of Gestogens in Oral Contraceptives BY G. R. KEAY (City Laboratories Service, Shortley Road, Coventry) Oral contraceptive preparations are now manufactured and prescribed on a large scale, and the public analyst has a duty to ensure that a chemically satisfactory product is supplied. A scheme has been devised that will enable all of the ingredients, both progestogenic and oestrogenic, of the preparations a t present available in this country to be identified and assayed. The active ingredients are separated from the tablet excipients by solvent extraction, the solution is evaporated and the residue identified by using infrared spectrophotometry and thin-layer chromatography. Assay of the ingredients involves the use of ultraviolet spectrophotometry.A few excep- tions were found to this general scheme and these have been successfully overcome by suitable modifications. THE group of sex hormones referred to as gestogens consists of those that constitute the steroid fraction of the oral contraceptive tablet. This steroid content is composed of a member of the oestrogenic or follicle-stimulating hormones, together with a much larger concentration of progestogen or corpus luteum secreted material. The most potent of all oral oestrogens is ethinyloestradiol which, with its 3-methyl ether, mestranol, may be regarded as a semi-synthetic steroid, containing the benzenoid nucleus in the structure. Either of these two compounds may be found as the powerful oestrogenic component in the variety of proprietary oral contraceptives.The earliest known synthetic progestogen was the 17-ethinyltestosterone, known as ethisterone, but this has been largely replaced by more potent compounds in recent years. Djerassi, Miramontes, Rosenkranz and Sondheimerl investigated derivatives of 19-nor- testosterone, which itself proved to be the least hazardous of the compounds examined, and these derivatives are now widely used. Among common oral progestogens are norethisterone (17-ethinyl-19-nortestosterone) and its acetate, and norethynodrel, which differs only in the position of a double bond. In modern proprietary oral contraceptives, progestogens are usually present at dose levels between 1 and 5 mg, whereas the ethinyloestradiol or mestranol component rarely exceeds 0.1 mg, and is frequently present at half this level.Some proprietary products are so compounded that the oestrogenic hormone is present alone in several of the tablets, the remaining month’s supply containing both oestrogen and progestogen. Analytically the problem presented to the public analyst is fundamentally one of ensuring that the dispensed medicament contains the labelled ingredients and thus conforms with the quantitative declaration. Because of the extremely close relationship to each other of members within each class of compound, the method of quantitative assessment must, if possible, be also one of identification. In those tablets containing both oestrogen and progestogen, the method applied must enable the minor oestrogenic constituent to be accurately determined.Lastly, the sample size submitted for analysis is severely limited, so that any method that is devised must, if possible, be such that little more than about two tablets are sufficient for an assay. The available analytical literature dealing specifically with this class of compound is scarce and, while it is appreciated that individual manufacturers may be fully conversant with methods of assay for their particular material, the public analyst is somewhat at a disadvantage in having the responsibility on behalf of the public of ensuring that such proprietary products from any manufacturers are of the correct composition. 0 SAC and the author.KEAY 29 The following three basic analytical techniques were used in evolving a scheme of analysis that would satisfy the above requirements.Ultraviolet spectrophotometric examination. Thin-layer chromatography. Infrared spectrophotometry. The scheme evolved consists of solvent extraction of the active ingredients, followed by identification by using thin-layer chromatography or infrared spectrophotometry. The active ingredients in all instances but one are then quantitatively determined by ultraviolet spectrophotometry . Only two oestrogens, mestranol and ethinyloestradiol, occurred in all of the tablets examined, and these differ from one another only by the substituent on the 3 carbon atom. The similarity between these oestrogens requires their previous identification by thin-layer chromatography before determination. Wavelength, rnp Fig.1. Ultraviolet absorption curve of mestranol in methanol Both give similar ultraviolet spectra with a main peak at about 280mp, followed by another peak on the shoulder at about 288mp (Fig. 1). As can be seen from Fig. 1, the slope of the main peak absorption is re-joined at about 290 mp. The main peak was subject to some interference from the progestogens present so that the shoulder peak was used for the determination of the oestrogen, except when it was known that no progestogen was present. The height of the shoulder peak was found to be proportional to concentration, which enabled it to be used for determining the oestrogen content. EXPERIMENTAL REAGENTS- ,411 reagents should be of analytical-reagent grade whenever possible. A ntimony trichhride . Carbon tetrachloride.Chloroform. Cy clo hexane . Ethyl acetate. Hydrochloric acid, 20 per cent. VIV. Methanol. Potassium bromide. Silica gel G-Obtainable from E. Merck and Co. Inc.30 KEAY: ANA4LYTICAL EVALUATION OF GESTOGENS IN ORAL CONTRACEPTIVES [Afia&St, VOl. 93 APPARATUS- Calibrated jhsks, 10 and 100 ml-These were made of low-actinic glass. Thin-layer plates, 20 x 5 em. Thin-layer spot remover-See Fig. 2. Ultraviolet light source-A mercury vapour lamp was used. PREPARATION OF THIN-LAYER PLATES- Prepare a slurry of 30 g of silica gel G mixed with 60 ml of water, and coat plates to give an absorbent thickness of 300 p. Activate the plates by heating a t 110" C for 30 minutes. PROCEDURE- Weigh an amount of the powdered tablets equivalent to about 6 mg of progestogen and transfer it into a 100-ml calibrated flask with 50ml of chloroform.Shake the mixture continuously for 30 minutes. Make up to volume with chloroform, mix and filter. Use this solution for identification and assay of the steroids. IDENTIFICATION- Thin-layer chromatography-Evaporate an aliquot of the chloroform solution to dryness and dissolve the residue in 1 ml of a solution of chloroform - methanol (1 + 1 v/v). Place a spot of this solution, at least 25 ply on the thin-layer plate at a distance of 2 cm from the base of the plate. A solution containing authentic steroids, in the proportion encountered in the tablet under examination, was also spotted on the same plate. Develop the plate in the solvent system cyclohexane - ethyl acetate (1 + 1 v/v) until the solvent front is within 1 cm of the top of the adsorbent, thus giving a development run of about 16 cm.Dry the plate at 100" C for 10 minutes and spray, while still warm, with a saturated solution of antimony trichloride in chloroform. Observe the spots produced both in daylight and under ultra- violet light. It was found that although the colours faded fairly rapidly in daylight, they remained fairly stable under ultraviolet light for at least 24 hours. The method is essentially that of Golab and Layne.2 The results obtained are shown in Table I. TABLE I DETECTION OF GESTOGENS AFTER SEPARATION BY THIN-LAYER CHROMATOGRAPHY Oestrogens- Progestogens- Ethinyloestradiol . . Mestranol . . .. Chlormadinone acetate Norethisterone . . Norethynodrel . . Ethynodiol diacetate Megestrol acetate .. Lynoestrenol .. RF .. 0.54 .. 0.68 .. 0.42 .. 0.47 .. 0-56 .. 0-70 I . 0.74 .. 0.40 Spot under Spot in daylight ultraviolet light Purple Violet Yellow Orange Pale yellow Yellow Violet Red Purple Purple Red Pink Red - violet but turns Lime Virtually colourless Pale yellow to blue - grey INFRARED SPECTRA- Progestogens-Evaporate an aliquot of the chloroform solution directly on to powdered potassium bromide. Compound the resultant homogeneous mass into a disc of suitable thickness, with a pressure of 15 tons on the ram and a vacuum of less than 2 cm of mercury. Record the spectrum and compare against a standard spectrum. Oestrogens-Because of the small amount of oestrogen compared with progestogen, the oestrogen must first be separated and concentrated by means of thin-layer chromatography.Evaporate an aliquot of the chloroform solution to dryness and dissolve the residue in 1 ml of chloroform - methanol (1 + 1 v/v). Place duplicate spots of solution, at least 50 pl, on thin-layer plates and develop, as before, with cyclohexane - ethyl acetate (1 + 1 v/v). Dry at 100" C for 10 minutes. Mask off a portion of plate containing one of the spots and spray the exposed portion, while still warm, with a saturated solution of antimony trichloride in chloroform. Remove the located oestrogen spot from the unsprayed portion of plate byJanuary, 19681 KEAY: ANALYTICAL EVALUATION OF GESTOGENS IN ORAL CONTRACEPTIVES 31 means of the extractor (see Fig. 2). Extract with chloroform and evaporate the chloroform solution directly on to powdered potassium bromide.Compound into a disc, as before, and record the spectrum. The infrared spectra obtained exhibit maxima only at the same wavelengths as authentic specimens of gestogens prepared in a similar manner. A = Suction head B = Filter tube, with porosity C = Receiver tube 3 sinter Fig. 2. Apparatus for removal of spot from thin-layer plate ULTRAVIOLET ASSAY- Progestogens-Transfer by pipette a 20-ml aliquot of the chloroform solution into a 100-ml calibrated flask. Evaporate it to dryness by using a current of air. Dissolve the residue in methanol and make up to 100 ml. Measure the extinction of the solution at the maximum, with l-cm silica cells and methanol as blank. If norethynodrel is present it must be isomerised to norethisterone.Add 1 ml of 20 per cent. v/v hydrochloric acid to the residue dissolved in 40 ml of methanol. Allow the solution to stand for 1 hour at room temperature and make up to 100 ml. Measure the extinction of the solution at the maximum, with l-cm silica cell and methanol as blank. Table I1 gives determined values for progestogens. TABLE I1 DETERMINED VALUES FOR PROGESTOGENS Progestogen Wavelength of maximum extinction, mp E,l:m Lynoestrenol . . . . . . .. 200 Norethynodrel (isomerised) . . .. 240 Norethisterone . . .. .. .. 240 Norethisterone acetate . . .. .. 240 Chlormadinone acetate . . .. .. 285 Megestrol acetate.. .. .. .. 289 300 670 560 506 510 650 Oestrogens present alone or with a Progestogen showi.pzg a maximztm at lower than 250 mp- Evaporate a 50-ml aliquot of the chloroform solution, containing about 200 pg of oestrogen, to dryness in a current of air.Dissolve the residue in methanol and make up to 10 ml in a calibrated flask. Measure the extinction of the resulting solution in a 1-cm silica cell at the following wavelengths : mestranol, 285, 287.5 and 290 mp; and ethinyloestradiol, 286, 288.5 and 291 mp. The content of mestranol in milligrams per tablet is given by the expression- and the content of ethinyloestradiol in milligrams per tablet by- where Y is the average tablet weight in grams and W is the weight in grams of sample taken. Oestrogens firesent with a pyogestogen showing a maximum in the region 280 to 290 mp- Evaporate 50 ml of the chloroform solution to dryness and dissolve the residue in 1 ml of chloroform - methanol (1 + 1 v/v).Place 0.5 ml of this solution on to a thin-layer plate at a distance of 2 cm from the base of the plate. Place a spot of standard oestrogen alongside32 KEAY: ANALYTICAL EVALUATION OF GESTOGENS IN ORAL CONTRACEPTIVES [Analyst, Vol. 93 and develop, as before, but with the solvent cyclohexane - ethyl acetate - carbon tetrachloride (2 + 2 + 1 v/v). Remove the plate, dry and heat at 100" C for 10 minutes. Mask off the portion of the plate containing the sample. Locate the standard spot by spraying with a saturated solution of antimony trichloride in chloroform. Remove the area from the plate containing the untreated sample spot with the extractor and extract oestrogen from the silica gel with methanol.Make the extract up to 10 ml with methanol. Prepare a blank by extracting a band of similar size from the plate containing no steroids. Measure the extinction of the solution in a l-cm silica cell at the same wavelengths as given above. The calculation of oestrogen content is as previously outlined, but the result must be multiplied by 2. After thin-layer separation, or when the tablet is composed of oestrogen alone, the concentration is found by measuring the extinction of the methanol solution at the maximum, at about 280mp. Ethinyloestradiol is soluble in 0.1 N sodium hydroxide and the wavelength of maximum extinction shifts from 280 to 300 mp. The measurement of the extinction of 0.1 N sodium hydroxide solution, at the maximum, provides an alternative means of assay of ethinyl- oestradiol, and also differentiates it from mestranol.Determined values for oestrogens are shown in Table 111. Oestrogen TABLE I11 DETERMINED VALUES FOR OESTROGENS Wavelength of maximum Solvent extinction, m p E;%& Mestranol (main peak) . . .. .. Methanol 279 Mestranol (shoulder peak) . . . . Methanol 287.6 Ethinyloestradiol (main peak) . . . . Methanol 281.5 Ethinyloestradiol (shoulder peak) . . Methanol 288.5 Ethinyloestradiol .. .. .. 0.1 "aOH 298.5 82 14-4 89 11.4 81 THIN-LAYER ASSAY- A solution of ethynodiol diacetate in methanol showed no peaks in the ultraviolet and gave complete absorption below 210 mp. This substance was therefore determined by thin- layer chromatography as follows. Evaporate an aliquot of the chloroform solution to dryness and dissolve the residue in a known volume of methanol - chloroform (1 + 1 v/v).Spot on to a thin-layer chromato- graphic plate, at a distance of 2 cm from the base of the plate, an aliquot of the sample solution containing about 10 pg of ethynodiol diacetate. Alongside this spot place standard spots in the range 8 to 12 pg. Develop the plate with cyclohexane - ethyl acetate (1 + 1 v/v) until the solvent front is 1 cm from the top of the plate. Dry the plate at 100" C for 10 minutes. While still warm, spray with a saturated solution of antimony trichloride in chloroforni. From the intensity of the spot colours, calculate the ethynodiol diacetate content of the sample. RESULTS Table IV summarises the results obtained by using the method described to determine mestranol recovery from a base made up of purified talc, magnesium stearate, lactose and starch.TABLE IV RECOVERY OF MESTRANOL FOR TABLET BASES Mestranol added, pg Recovered, pg 0 125 250 500 1000 - 126 248 486 1006 In Tables V and VI the results obtained by using the methods described to determine progestogens and oestrogens in proprietary preparations are summarised.January, 19681 KEAY: ANALYTICAL EVALUATION OF GESTOGENS IN ORAL CONTRACEPTIVES 33 TABLE V RESULTS FOR THE DETERMINATION OF PROGESTOGENS IN COMPOUNDED TABLETS Norethisterone . . .. Norethisterone acetate . . Norethynodrel . . .. Chlormadinone acetate . . Megestrol acetate .. Ethynodiol diacetate . . Lynoestrenol .. .. Nominal content, mg per tablet .. 2.0 2.0 .. 2.6 3-0 4.0 .. 2.6 2.6 2.5 5-0 6.0 ..2.0 .. 4-0 1.0 .. 1.0 1.0 2.0 .. 2.5 6.0 TABLE VI Found, mg per tablet 2-19 2.18 2-60 3.10 3.80 2.30 2.33 2-56 4.70 4.83 2-05 3.70 1.01 1-00 1.00 2.00 2-70 6-36 RESULTS FOR THE DETERMINATION OF OESTROGENS IN COMPOUNDED TABLETS Nominal content, Found, Oestrogens pg per tablet pg per tablet Mestranol . . .. .. .. 76 77 75 72 75 70 80 78 80 81 100 98 100 100 100 97 100 94 100 100 100 91 1 00 95 100 97 100 99 160 144 Ethinyloestradiol .. .. 50 60 50 46 50 48 60 46 100 108 100 108 DISCUSSION Examination of samples of sixteen proprietary oral contraceptives gave analytical results that were all within 10 per cent. of the declared ingredient value. This was considered to be a reasonable tolerance for the techniques used, although a 10 per cent. deficiency would be regarded with somewhat more concern than a 10 per cent. excess. A deficiency of this magnitude was not found, and recovery experiments and standard additions showed the accuracy of the methods used to be better than 5 per cent. The amount of sample used for the complete analysis was four tablets, and this was found to be sufficient for all stages of the scheme. I express my thanks to the pharmaceutical companies that have supplied authentic substances for reference purposes, and to Coventry Corporation, in whose laboratories the work was carried out, for permission to publish this paper. REFERENCE 1. 2. Djerassi, C., Miramontes, L., Rosenkranz, G., and Sondheimer, F., J . Amer. Chem. Soc., 1964, Golab, T., and Layne, D. S., J . Chrontat., 1982, 9, 321. Received February 2nd, 1967 76, 4092.

ISSN:0003-2654    

DOI:10.1039/AN9689300028

出版商:RSC    

年代:1968

数据来源: RSC

摘要:

34 Analyst, January, 1968, Vol. 93, $$. 34-38 Enzymatic Detection of Ten Organophosphorus Pesticides and Carbaryl on Thin-layer Chromatograms: An Evaluation of Indoxyl, Substituted Indoxyl and 1-Naphthyl Acetates as Substrates of Esterases BY C. E. MENDOZA*, P. J. WALES, H. A. McLEOD AND W. P. McKINLEY (Research Laboratories, Food and Drug Directorate, Departmest of National Health and Welfare, Ottawa 3 Ontario, Canada) An enzymatic inhibition method sufficiently sensitive and reproducible for detecting ten organophosphorus pesticides and carbaryl resolved by thin-layer chromatography is described. Reproducible detection of nanogram amounts of these pesticides is achieved with a 450-p thick gel layer, steer-liver homo- genate as source of esterase, and indoxyl or substituted indoxyl acetates (5-bromoindoxyl, 5-bromo-4-chloroindoxyl and 5-bromo-6-chloroindoxyl acetates) as substrates, the esterase and substrate spray solutions being used at a pH of about 8.The coloured products of enzymatic hydrolysis of these substrates are stable and intense ; white spots indicated the sites of pesticides that inhibited the enzyme. Spots persist for days when the amounts present are >l ng of parathion; >2ng of carbophenothion ; > 5ng of azinphos-methyl, diazinon, ethion, malathion and parathion-methyl; 2 20 ng of caxbaryl, Trithiona-methyl and mevinphos ; and > 1 OOng of disulfoton. Carbophenothion and disulfoton are also detected at the 1 ng level and carbaryl, at 5 ng; however, the spots produced disappear within a few hours. Unsatisfactory results are obtained with l-naphthyl acetate as substrate, and with bovine and sheep sera as sources of esterase.ENZYME inhibition reactions have been applied in paper and thin-layer chromatography to detect some organophosphorus pesticides1 s2s3s4 and ~arbamates.~ The substrate l-naphthyl acetate was used with bovine-liver esterase in paper chromatography to detect organophos- phorus pesticides,l s2 and indoxyl and 1-naphthyl acetates were tested with re-constituted dried horse-blood serum in thin-layer chromatography. A change in pH was the criterion used in another method4 to detect cholinesterase-inhibiting insecticides on thin-layer chromato- graphic plates coated with cellulose. Acetylcholine chloride was used as the substrate for human plasma esterase, with bromothymol blue as the pH indicator.Several light re-spray- ings of substrate - indicator solution gave maximum definition of spots; nevertheless, the spots remained unstable. Non-enzymatic methods utilising the reaction of specific moieties in pesticides were even less sensitive than the enzymatic methods in detecting carbay15 and organophosphorus This study was initiated because of the problems we encountered with the l-naphthyl acetate reaction, problems reported with the pH rneth~d,~ and because of the insensitivity of the non-enzymatic methods.6s6s7,* s 9 ~ 1 O ,l1 Other investigators used indoxyl acetate in colori- metry12 and fluorimetryls of cholinesterases and substituted indoxyl acetates in histochemistry of esterases.14 Thus we evaluated indoxyl, substituted indoxyl and l-naphthyl acetates as substrates for the enzymatic detection of ten organophosphorus pesticides and carbaryl ; the factors investigated were the amount of pesticides, pH of esterase and chromogenic solutions, thickness of silica-gel layers and sources of esterases.0 SAC and the authors. p&icides.6,7 9 8 ,9 ,10,11 * National Research Council of Canada postdoctorate fellow, 1965-67.MENDOZA, WALES, MCLEOD AND MCKINLEY 35 EXPERIMENTAL APPARATUS- Chromatographic tanks, 28 x 7 x 26 cm. Glass plates, 20.5 cm2. Sfway-bottles, 50-ml round tyee, No. 130.01 or 130.02-Obtainable from Research Special- Vir Tis@ or all-glass tissue homogenisers. Thin-layer applicator and accessories-Obtainable from Desaga, Heidelberg, West Microsyringes with square-tip needles, 25-pLObtainable from The Hamilton Co., Inc., Bromine $ask-A I-litre Erlenmeyer flask fitted with a wash-bottle fl ow-tube was used.ties Co., Berkeley 7, California, U.S.A. Germany. Whittier, California, U.S.A. REAGENTS- Indoxy1 acetate. 5-Bromoindoxyl acetate. 5-Bromo-4-chloroindoxyl acetate. 5-Bromo-6-chloroindoxyl acetate. These chemicals are obtainable from Sigma Chemical Co., St. Louis 18, Missouri, U.S.A. PESTICIDE STANDARDS- The names of the pesticides used are those approved by the Committee on Insecticide Terminology of the Entomological Society of America.16 Purity is expressed as a percentage. Azinphos-methyl (Guthion), 93.0 per cent. Carbaryl, 99.7 per cent. Carbophenothion (Trithion), 94.6 per cent. Diazinon, 95.8 per cent.Disulfoton (Disyston), 96.8 per cent. Ethion, 95.0 per cent. All of the pesticides were dissolved in hexane, with co-solvent acetone for azinphos- methyl, carbaryl and parathion-methyl, and all of the solvents were glass-distilled. Weight per volume concentrations of pesticides were prepared so that 10-pl aliquots contained the amounts given in Table I, but were not corrected for impurities in the standards. Malathion, 99-5 per cent. Parathion-methyl, 99.5 per cent. TrithionB-methyl, 99.0 per cent. Mevinphos a-isomer (Phosdrin) , 60.0 Parathion, 98-8 per cent. per cent. PROCEDURES- Prefiaration of liver homogenate-Use livers from 1 to 2-year old steers, and keep the livers and the glassware in an ice-bath while preparing the homogenate. Grind liver tissues devoid of vascular vessels and membranes, and homogenise 3 g of the ground liver with 27 ml of water in an all-glass homogeniser, or 20 g of ground liver with 180 ml of water in a VirTis@ homogeniser. Spin the combined homogenate in a centrifuge at 2000 r.p.m.for 20 minutes at room temperature, and collect and transfer the supernatant liquids into 13 x 100-mm test- tubes. Seal the tubes with plastic sheet and quickly freeze them in an acetone - dry ice bath; store the tubes at -20" C. Before using the homogenate for pesticide detection, test for esterase activity; thin-layer chromatographic plates sprayed with homogenate should turn intense blue when treated with the 5-bromoindoxyl acetate spray solution. Preparation of 1-naphthyl acetate spray solution-Prepare a solution as described by McKinley and Johal,2 or as outlined by McManus and Mowry,lG modifying the latter as follows.Dissolve 1 g of naphthyl acetate in 50 ml of acetone and add 50 ml of water (solution A). This solution keeps indefinitely in a refrigerator. Prepare, shortly before use, a solution of 20 mg of Fast blue RR in 15 ml of phosphate buffer solution and add 15 ml of water (solution €3). Mix 2 ml of solution A with solution B just before spraying. Preparation of indoxyl and substituted indoxyl acetates spray solution-Dissolve the sub- strate (15mg of indoxyl acetate, 15mg of 5-bromoindoxyl acetate, 1Omg of 5-bromo-4- chloroindoxyl acetate or 10 mg of 5-bromo-6-chloroindoxyl acetate) in 5 ml of absolute ethanol before use (solution C).36 MENDOZA, WALES, MCLEOD AND MCKINLEY [Analyst, Vol.93 Mix 4-0 ml of 0-05 M tris(hydroxymethy1)aminomethane buffer solution, 5.0 ml of 2.00 M sodium chloride, 0.2 ml of 1-00 M calcium chloride and 3.8 ml of water to make 13 ml of solution, or proportionately for a large volume (solution D). Prepare a solution of potassium hexacyanoferrate(II1) and hexacyanoferrate(I1) , 0.05 M with respect to each (solution E). Mix, immediately before spraying, 13ml of solution D with 2ml of solution E and thoroughly mix the resulting solution with solution C; this 20-ml spray solution is sufficient for two plates. Thin-layer chromatographic $Zates-Shake thoroughly for 1 minute a mixture of MN- Kieselgel G-HR@ and water (1 + 2 w/v) in a stoppered flask and spread the slurry 250 or 450-p thick on acetone-rinsed glass plates.As soon as the layer gels, place the plates in a vertical position in an oven at 110" C for 1 hour; store the plates in an air-tight box. Before spotting, scrape the gel off the edges of the plate, about 1-5cm from the top, 0.3 cm from the bottom, and 0.5 cm from the sides, to ensure an even solvent front and to prevent loss of gel when in contact with the solvent. With a 25-4 syringe apply the pesticides to the plate 2.5 cm from the bottom of the gel. Spot a constant volume (10 p1) of different concentrations to evaluate the substrates, various amounts of pesticides, pH values of spray solutions and two thicknesses of the gel layer. Development o j the plntes-Equilibrate each tank with 100 ml of 15 per cent. acetone in hexane for about 10 minutes.Chromatograph the plates in this tank until the solvent front reaches the line previously drawn 15 cm from the origin. Air-dry the plates for about 5 minutes and expose them to bromine; yellowing of the plates indicates over exposure. Use a gentle flow of nitrogen to push the bromine cloud out of the storage flask. Bromine converts the thiophosphates into active inhibitors and, as it may inhibit the enzyme, allow the excess to dissipate for 20 minutes. Spray the appropriate enzyme solution gradually and evenly over the plates, making the gel just thoroughly wet. Allow the plates to dry for 20 minutes at room temperature. Spray the chromogenic substrate solution in the same manner; the colour develops in 1 to 30 minutes. RESULTS AND DISCUSSION SENSITIVITY TEST BY THIN-LAYER CHROMATOGRAPHY- Table I shows the amounts of carbaryl and ten organophosphorus compounds enzymati- cally detected on a 450-p thick silica-gel layer, with steer-liver homogenate (1 volume) in 0.05 M tris(hydroxymethy1)aminomethane buffer solution (pH 8-32) (2 volumes) and 5-bromoindoxyl acetate spray solution made with the same buffer solution.Although 1 ng of carbaryl, carbophenothion, disulfoton, and parathion were tested, the smallest amount studied for the other pesticides was intentionally limited to 5 ng. Spots persisted when the amounts present TABLE I SENSITIVTTY TEST ON THIN-LAYER CHROMATOCRAMS WITH 5-BROMOINDOXYL ACETATE AND ESTERASES FROM STEER LIVER* Amount spotted, ngt A I 3 Chemicals . . . . 800 400 200 100 80 50 20 10 8 5 2 1 Azinphos-methyl Carbophenothion Diazinon ..Disulfoton . . Ethion . . .. Malathion . . Parathion-methyl Trithion@-meth yl Mevinphos .. Parathion . . Carbaryl .. * (+) = detected: (u) = unstable or spot disappeared after a few minutes; (0) = not detected; t Constant volume (10 pl) was used for each spot. (-) = not tested.Fig. 1. The eHcct of thickness of silica-gel layer on the detection of 10 organophosphorus pesticides (left, 450 p, and right, 250 p), with 5- bromo-4-chloroindoxyl acetate as substrate for steer-liver esterase, and both spray solutions a t pH 8.32. (Phosdrin is mevinphos; Trithion, carbophenothion ; Disyston, disulfoton ; Guthion, azinphos-methyl. Labels on the bottom of the plates: top row = micrograms of pesticide standards multiplied by 1 x l O F , e.g., Spot No.1 is represented by 8 x pg of mevinphos; b , bottom row = spot numbers.) [To face p. 36A B C Fig. 2 . Thin-layer chromatogram with five substrates for steer-liver esterase to detect organophosphorus pesticides, with 450-p thick silica-gel layer. (Labels on the bottom of each thin-layer chromatographic plate : top row = micrograms of pesticide standards multiplied by 1 x e.g. Spot No. 1 (A) is represented by 2 x 10-2pg of Guthion; bottom row = spot numbers. Thin-layer chromatographic plates at right side: A, top plate, was sprayed with 5-bromoindoxyl acetate; B, middle plate, was sprayed with 5-bromo-4-chloroindoxyl acetate, at pH 8.32 ; C, bottom plate, was sprayed with 1-naphthyl acetate solution at pH 7; Spot Xos. 1 , Phosdrin, i.e., mevinphos ; 2, malathion ; 3, diazinon ; 4, Trithionm-methyl; 5, Trithion or carbophenothion; 6, Disyston or disulfoton; 7, ethion; 8, parathion; 9, methyl parathion ; 10, Guthion or azinphos-methyl) To fuce p.371January, 1968j ENZYMATIC DETECTION OF TEN ORGANOPHOSPHORUS PESTICIDES 37 were >l ng of parathion; 2 2 ng of carbophenothion; >5 ng of azinphos-methyl, diazinon, ethion, malathion, and parathion-methyl ; >20 ng of carbaryl, TrithionB-methyl and mevinphos ; and >lo0 ng disulfoton. Carbophenothion and disulfoton were also detected at the 1 ng level and carbaryl, at 5 ng; however, the spots disappeared within a few hours. The levels of organophosphorus pesticides used in the subsequent experiments were based on this test and on the possibility of applying this method in pesticide residue analyses.EFFECT OF GEL THICKNESS- Intense backgrounds and well defined spots were consistently obtained when the gel layer was 450-p thick, but not when 250-p thick (Fig. 1). The substrates 5-bromoindoxyl and 5-bromo-4-chloroindoxyl acetates were used in this test. Each substrate solution was prepared with 0-05 ivi tris(hydroxymethy1)aminomethane buffer (pH 8-32), and liver homo- genate (1 volume) was diluted with the same buffer solution (2 volumes). CONPARISON OF INDOXYL AND SUBSTITUTED INDOXYL ACETATES- To compare the sensitivity of detection with indoxyl, 5-bromoindoxyl, 5-bromo-4- chloroindoxyl and 5-bromo-6-chloroindoxyl acetates, the same amounts of each organophos- phorus pesticide were chromatographed on 450-p thick silica-gel layers.Liver homogenate (1 volume) diluted with 0.05 M tris(hydroxymethy1)aminomethane buffer (pH 8-32) (2 volumes) and substrate solution, made with the same buffer solution, were sprayed on to thin-layer chromatographic plates. Indoxyl and substituted indoxyl acetates detected nanogram amounts of ten organo- phosphorus compounds and carbaryl resolved on thin-layer chromatograms (Fig. 2, top and middle plates). Indigo compounds produced by the hydrolysis of the substrates gave coloured backgrounds, leaving the sites of inhibition by pesticides as white spots; the colours produced were blue for indoxyl and 5-bromoindoxyl acetates, turquoise for 5-bromo-4-chloroindoxyl acetate and pink for 5-bromo-6-chloroindoxyl acetate.These backgrounds were stable and the spots lasted for months. 5-Bromo-4-ch1oroindoxy1, 5-bromoindoxyl and indoxyl acetates produced more intensely coloured backgrounds than 5-bromo-6-chloroindoxyl acetate ; an intense colour is preferred because it delineates more distinctly the sites of enzyme inhibition. Both indoxyl and Ei-bromo- indoxyl acetates produced a blue centre in the disulfoton spot; although this peculiarity is not understood, it may be used as a criterion for the presence of disulfoton. Unlike 5-bromo-4- chloroindoxyl acetate, 5-bromo-6-chloroindoxyl acetate produced well defined spots for mevinphos and diazinon, and it consistently gave stable spots for disulfoton. COMPARISON OF TWO PREPARATIONS OF ~-NAPHTHYL ACETATE SPRAY SOLUTION- The preparation of I-naphthyl acetate spray described here gave the same background intensity as that of McKinley and Johal.2 Both gave unsatisfactory analyses of ten organo- phosphorus pesticides at the levels detected by the indoxyl acetates.Spots corresponding to the organophosphorus compounds at nanogram levels were not clearly defined (Fig. 2, bottom plates) ; therefore, confirmation of pesticides based on these spots was not reliable. Unsatisfactory results were obtained when 1-naphthyl acetate was tested with two gel thicknesses, phosphate buffer solutions (pH 5.3 and 7.19), B.D.H. buffer solution (pH 7.0) and two homogenate dilutions (1 volume of homogenatej5hs 2 or 6 volumes of buffer solution2). 1-Naphthyl acetate was not tested at pH 8.32 because of its rapid hydrolysis to naphthol, which readily coupled with Fast blue RR.EFFECT OF PH- The pH values were chosen to cover the range 5 to 9 and the same tris(hydroxymethy1)- aminomethane buffer solution was used to make each pair of homogenate and substrate sprays. Solutions of 5-bromoindoxyl acetate made with 0-05 M tris(hydroxymethy1)amino- methane buffer were used with liver homogenate (1 volume) in the same buffer solution (2 volumes) on 450-p thick silica-gel layer. A t pH 8.32 and 9.10, 5-bromoindoxyl acetate gave intense and uniform blue backgrounds; the sites of enzyme inhibited by pesticides were white and well defined. However, at pH 7.19, this substrate produced a speckled background and indistinct spots. At pH 5-30, it exhibited very pale and uneven backgrounds; the sites of enzyme inhibition were either invisible or barely discernible.This enhancement of indigo dye production at higher pH agrees with previous findings.l5J7 Characteristic responses were observed for each substrate.38 MENDOZA, WALES, MCLEOD AND MCKINLEY SHEEP AND BOVINE SERA AS SOURCES OF ESTERASES- The sera (1 volume) were diluted with 0.05 M tris(hydroxymethy1)aminomethane buffer (pH 8-32) (1, 3, 4 or 6 volumes) ; 5-bromoindoxyl acetate solution was made with the same buffer solution. These sera were unsatisfactory for detecting the resolved pesticides because only minute amounts of indigo compound were hydrolysed from 5-bromoindoxyl acetate sprayed on thin-layer chromatographic layers, 450-p thick. Sera diluted with B.D.H. buffer solution (pH 7.0) likewise produced only faint backgrounds when used with the l-naphthyl acetate spray solution of McKinley and Johal.2 CAUSES OF, AND REMEDIES FOR, FAILURES IN THE DEVELOPMENT OF THE BACKGROUND Unreactive oxidising solution-Re-spray the plate with 2 ml of the oxidising solution diluted with 13 ml of 0.05 M tris(hydroxymethy1)aminomethane buffer (pH 8-32).Insuficient amount of enzyme on plate-Re-spray with homogenate solution, diluted as before. Two tubes of homogenate diluted as specified are sufficient to spray two plates. Insu$cient amount of szcbstrate on plate-Re-spray with the same substrate; 20 ml are usually adequate for two plates. Inadequate dissi$ation of excess of bromi.pze-This cannot be remedied. Thin gel Zayer-The gel layer should be about 450-p thick.Inadequate spray-bottle-That listed under Apparatus has a fine orifice and is recom- mended; sprayers that work solely on the creation of a vacuum around the orifice are un- satisfactory. CONCLUSION Ten organophosphorus pesticides and carbaryl can be detected with precision in nano- gram amounts by using indoxyl or substituted indoxyl acetates as substrate for steer-liver esterase. Spray solutions, with pH values not lower than 8, produced intensely coloured backgrounds and well defined spots; the intensity of the colours and the definition of the spots were enhanced by using a 450-p instead of a 250-p thick silica-gel layer. The technique used in this experiment is being developed as a method for the analysis of pesticide residues in plant materials. We are indebted to Mrs. C. R. Sherwood for technical assistance in certain phases of the work, to Mr. B. Korda and Mr. H. Baird for photography, and to Dr. K. A. McCully, Dr. J. B. Rogers and Dr. K. Murray for their critical review of the manuscript. COLOURS- 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. REFERENCES McKinley, W. P., and Read, S. L., J . Ass. Ofl. Agric. Chem., 1962,45, 467. McKinley, W. P., and Johal, P. S., Ibid., 1963,46, 840. Ortloff, R., and Franz, P., 2. Chemie, Lpz, 1965, 5, 388. Menn, J. J., and McBain, J. B., Nature, 1966,209, 1351. Chiba, M., and Morley, H. V., J . Ass. Ofl. Agric. Chem., 1964,47, 667. MacRae, H. F., and McKinley, W. P., Ibid., 1961, 44, 207. Kovacs, M. F., jun., Ibid., 1964, 47, 1097. Watts, R. R., Ibid., 1965,48, 1161. Stanley, C. W., J . Chromat., 1964, 16, 467. Barney 11, J. E., Ibid., 1965,20, 334. Irudayasamy, A., and Natarajan, A. R., Analyst, 1966, 90, 503. Gunther, J., and Ruff-Sondermeier, D., Nuturwisseraschajtera, 1965, 52, 540. Guilbault, G. G., and Kramer, D. N., Analyt. Chem., 1965,37, 120. Holt, S. J., irt Danielli, J. F., Editor, “General Cytochemical Methods,” Academic Press, Inc., New York, 1968, Volume 1, p. 376. Kenaga, E. E., Bull. Ent. SOC. Amer., 1966, 12, 161. McManus, J. F. A., and Mowry, B. W., “Staining Methods, Histologic and Histochemical,” Harper and Row, Publishers, New York, 1960, p. 172. Gehauf, B., and Goldenson, J., Analyt. Chem., 1957,29, 276. Received May 19th 1967

ISSN:0003-2654    

DOI:10.1039/AN9689300034

出版商:RSC    

年代:1968

数据来源: RSC

摘要:

Analyst, January, 1968, Vol. 93, p$. 3941 39 Determination of Aldrin Residues in Vegetables by the Chemical Conversion of Aldrin to Dieldrin BY KOIDU NOREN (Department of Food Hygiene, National Institute of Public Health, Stockholm, Swedm) The determination of aldrin in certain samples of vegetables by gas chromatography has proved to be difficult, as peaks from impurities interfere. To eliminate this disadvantage a method was developed in which aldrin was converted to dieldrin and the amount of dieldrin determined by gas chro- matography. VARIOUS clean-up procedures have been described for use in the determination of chlorinated pesticide residues in plant material by gas chr~matography.~ ,293949596 In this laboratory, the method generally used is based on the procedure of Mills.g In some determinations, however, this method failed to eliminate an impurity that interfered with the gas-chromatographic determination of aldrin. This impurity has also been noted by Goodwin, Goulden and Reynolds,f and by Burke and Guiffrida' using their method for extraction and clean-up.To overcome this problem, Goodwin, Goulden and Reynolds compared gas - liquid chromato- graphy on non-polar and polar stationary phase. Also, separation by liquid - solid chrom- atography (hexane - aluminium oxide) was carried out successfully. Hamence, Hall and Caverly3 treated the sample with chlorine, converting the aldrin into a derivative that could easily be separated from the impurity by gas chromatography. The derivative had about the same retention time as of-DDT, which made it unfit for quantitative determinations in the presence of 09'-DDT. For the purpose of evolving a quantitative method in which most of the common chlorinated pesticides could be separated and determined on the same column by gas - liquid chromatography and electron-capture detection, a procedure has been developed by which aldrin is converted to dieldrin without affecting other chlorinated pesti- cides present.The conversion has also been confirmed by thin-layer chromatography. METHOD Homogenise 1 kg of vegetable, then extract 100.0 g of the homogenised material with 90ml of hexane plus 50 ml of isopropyl alcohol and repeat the extraction with 90ml of hexane plus 20 ml of isopropyl alcohol. Shake the combined extracts with 600 ml of water to remove isopropyl alcohol.Transfer the hexane layer quantitatively to a 200-ml gradu- ated flask and make up to the mark with hexane. Evaporate 50*00ml of the extract, which corresponds to 25.0 g of sample, at reduced pressure at 35" C to 1 to 2 ml, and transfer to a pre-wetted chromatographic column, of 2-cm diameter, containing 15g of Florisil and a 4-cm high layer of anhydrous sodium sulphate. (Before use activate the Florisil for 24 hours at 600" C ; after cooling add 2 per cent. of water and mix carefully.) Elute the pesticides with 150 ml of light petroleum (boiling range 35" to 60" C) - diethyl ether (80 + 20). Evaporate the eluate at reduced pressure at 35" C to 15 ml, transfer the residue quantitatively to a 25-ml graduated flask and make up to the mark with the solvent. Analyse by gas chromatography.This method has been used for lindane, aldrin, chlordane, dieldrin, up'-DDT andpp'-DDT. If the chromatogram indicates the presence of aldrin in the sample, a simple procedure is carried out in which the aldrin is oxidised by peroxyacetic acid at 65" C to the 6,7-epoxy derivative (dieldrin). The reaction mixture is washed with sodium hydrogen sulphite solution to remove the oxidising agent and then with sodium carbonate solution to remove the acid.8 0 SAC and the author. The dieldrin formed in this way is analysed by gas chromatography.40 APPARATUS- KOIDU N O R ~ N : DETERMINATION OF ALDRIN RESIDUES IN [Analyst, Vol. 93 CONVERSION OF ALDRIN TO DIELDRIN Separating funnel-125-ml capacity. Graduated $asks-25 and 100-ml capacity.Water-bath, 65" C. Magnetic stirrer-This is equipped with polyethylene-covered stirring bar. Evaporator. Gas chromatograph-Wilkens Aerograph HyFi 600, equipped with an electron-capture detector, was used. Column-Pyrex glass, Q inch x 5 feet, packed with 5 per cent. DC-11 on Chromosorb W silicone grease, 60 to 80 mesh. Temperature of column-195" C. Temperature of injectio~-210" C. Temperature of detector-195' C. Recorder-Texas instrument, model PWS-IMVG-05-A 25-BT. The gas flow-rate was 75 ml of nitrogen per minute. Benzene, redistilled. Hydrogen peroxide, 30 per cent. w/v, analytical-reagent grade. Glacial acetic acid, analytical-reagent grade. SuZphuric acid, analytical-reagent grade. Sodium hydrogen sul$hite solution, 10 per cent. wlv, aqueous.Sodium carbonate solution-Prepare a saturated aqueous solution. Anhydrous sodium swtphate-Heat overnight at 450" C. PROCEDURE- Gently evaporate 25.00 ml of the cleaned extract, corresponding to 25-0 g of sample, to 0.5 to 1 ml, at reduced pressure at 35" C. A rotating evaporator connected to a water pump was used. Transfer the residue to a 100-ml graduated flask with 25ml of benzene. Add 2-0 ml of hydrogen peroxide, 1.0 ml of glacial acetic acid and 1.0 ml of sulphuric acid. Place the flask in a water-bath at 65" C. Equip the flask with a magnetic stirrer. Stopper the flask and allow to react for 3 hours, with stirring. Then transfer the mixture to a 125-ml separating funnel. Rinse the flask with small portions of benzene and collect the benzene in the separating funnel.Wash the benzene layer by shaking with 25 ml of sodium hydrogen sulphite solution. Allow to separate, and discard the aqueous layer. Repeat the washing with 25 ml of saturated sodium carbonate solution and with 25 ml of water until neutral. The benzene layer is passed through a chromatographic column, of 2-cm diameter, containing 2.5 cm of anhydrous sodium sulphate. Rinse the separating funnel with small portions of benzene and transfer to the column. Elute the column with an additional 10 to 15ml of benzene. Evaporate the collected benzene to 15 to 20 ml at reduced pressure at 35" C. Transfer the benzene extract quantitatively to a 25-ml graduated flask and make up to the mark with benzene. Examine this solution by gas chromatography. TABLE I REAGENTS- RECOVERY OF DIELDRIN FROM ALDRIN ADDED TO THE SAMPLE BEFORE THE EXTRACTION OF THE MATERIAL WITH HEXANE - ISOPROPYL ALCOHOL AND SUBJECTION TO THE PROCEDURE FOR CLEAN-UP WITH FLORISIL AND CONVERSION OF ALDRIN TO DIELDRIN Dieldrin Recovery, Aldrin added, Theoretical, Found, Sample p.p.rn.p.p.m. p.p.m. per cent. Y Carrots .. .. . . 0.050 0-052 0.044 85 0.010 O.OIO4 0.009 1 88 0.010 0-0104 0-0086 83 Potatoes .. . . 0*030 0.052 0.044 85 0-050 0-052 0.046 88 0.050 0.052 0.041 79 0.010 0.0104 0.0081 78 Meanvalue .. .. 84 Cabbage .. . - o*ofjo 0.052 0.043 83January, 19681 VEGETABLES BY THE CHEMICAL CONVERSION OF ALDRIN TO DIELDRIN 41 TABLE I1 RECOVERY OF DIELDRIN FROM THE CONVERSION OF ALDRIN TO DIELDRIN The concentrations are given before and after the conversion procedure Before conversion Aldnn, r-n, Sample p.p.rn. p.p.m.Cabbage .. . . 0~0090 0 0-050 0 0.050 0 0-056 0 0.062 0.011 Potatoes . . . . 0.042 0 0.046 0.021 0.046 0 Carrots . . . . 0*0090 0.01 1 After conversion Dieldrin, theoretically from -7 Found, From aldrin, aldrin, p.p.m. p.p.m. p.p.m. 0.0086 0.0086 0.0094 0.051 0.05 1 0.052 0~0200 0.0090 0.0094 0.047 0.047 0.052 0.055 0.055 0-057 0.079 0-068 0.065 0-044 0.044 0.044 0-062 0-04 1 0.047 0.046 0.046 0.048 Dieldrin Mean value . . Recovery, per cent. 91 98 96 90 96 105 100 87 96 . 95 RESULTS The method has been applied to samples of carrots, cabbage and potatoes. Recovery experiments have been carried out with addition of standard solutions of aldrin to the material before the first extraction of the plant material, and before the conversion procedure.Average recovery of dieldrin from the over-all procedure was 84 per cent. (Table I). In the conversion of aldrin to dieldrin 95 per cent. of the theoretical amount of dieldrin was recovered (see Table 11). Other chlorinated pesticides that may be present in the sample, e.g., lindane, heptachlor, chlordane, o$'-DDT and $$'-DDT, were not affected by this procedure and were recovered to 88 to 101 per cent. from samples of carrots (see Table 111). The sample solution is suitable for further analysis, e.g., by thin-layer chromatography. TABLE I11 RECOVERIES OF SOME CHLORINATED PESTICIDES ADDED TO SAMPLES OF CARROTS BEFORE TO THE PROCEDURE FOR CLEAN-UP WITH FLORISIL AND CONVERSION OF ALDRIN TO DIELDRIN THE EXTRACTION OF THE MATERIAL WITH HEXANE - ISOPROPYL ALCOHOL AND SUBJECTION Pesticide Added, p.p.m. Recovery, per cent. Lindane .. .. .. 0-050 91 Heptachlor . . .. .. 0.050 101, 98 Chlordane . . .. .. 0.050 88, 94 op'-DDT .. .. .. 0.10 91, 98 PP'-DDT .. .. .. 0.50 89, 94 REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. Goodwin, E. S., Gulden, R., and Reynolds, J. G., Analyst, 1961, 86, 697. McKinley, W. P., c O 5 , D. E., and McCully, K. A., J. Ass. OJf. Agric. Chem., 1964, 47, 863. Hamence, J. H., Hall, P. S., and Caverly, D. J., Analyst, 1965, 90, 649. Jones, L. R., and Riddick, J. A., Analyt. Chem., 1952, 24, 669. Mills, Paul A., Onley, J. H., and Gaither, R. A., J. Ass. Ofl. Agrzc. Chem., 1963, 46, 186. Mills, Paul A., Ibid., 1959, 42, 734. Burke, J., and Giuffrida. L.. Ibid., 1964, 47, 326. McKinney, R. M., and Pearce, G. W., J. Agric. Fd Chem., 1960, 8, 456. Received March 281h, 1967

ISSN:0003-2654    

DOI:10.1039/AN9689300039

出版商:RSC    

年代:1968

数据来源: RSC

摘要:

42 Analyst, January, 1968, Vol. 93, j$. 42-49 Determination of Trace Amounts of Copper, Zinc and Magnesium in Animal Feeds by Atomic-absorption Spectrophotometry BY A. G. ROACH,* P. SANDERSON AND D. R. WILLIAMS (Central Laboratories, R. Silcock 6. Sons Ltd., 56 Derby Road, Liver9ooE 20) An automated method for the determination of copper, zinc and mag- nesium in animal feeding stuffs by atomic-absorption spectrophotometry is described. Samples are prepared by a dry-ashing method that permits a rapid, accurate and economic assessment of these elements. Analyses are carried out at a rate of 60 samples per hour, with a maximum coefficient of variation of 4 per cent. for each element. THE accurate definition of the essential nutrients in both raw materials and compound feeding stuffs is necessary to achieve optimum performance in animals.This includes the definition of the macro nutrients, such as protein and oil, and the micro nutrients of both inorganic and organic origin, all of which play an important r81e in animal growth and production. The r6le of essential trace inorganic elements in the p.p.m. range in animal nutrition has received, and is receiving, close attention, as it is established that animal performance can be improved by achieving the correct balance between such elements. A notable example is in pig nutrition, in which closely controlled levels of copper and zinc have shown marked improvements in liveweight gain. Similarly, magnesium is of particular importance to high performance dairy cows. Deficiencies of magnesium in the diet can lead to disorders, such as hypomagnesemia.The definition of the inorganic-element content of animal feeding stuffs depends on the precise knowledge of the contribution from the natural content of each raw material, together with that added in the form of inorganic salts. It follows, therefore, that accurate and rapid routine analysis of raw materials is essential for successful formulation and control of products. A basic problem in the analysis of animal feeding stuffs for inorganic elements is the satis- factory destruction of the organic matter, without loss of the volatile inorganic components. For good recoveries in the determination of copper , Gorsuchl recommended a wet-oxidation procedure for the destruction of organic matter, while the Analytical Methods Committee of the Society for Analytical Chemistry2 recommend a dry-ashing technique for the successful analysis of zinc and magnesium.The wet-oxidation procedure is long and time consuming, and limits the number of analyses that can be undertaken in a given time. A simpler, faster method that would allow determinations of several elements to be carried out on one prepared sample would be preferred. HighS indicated that a modified dry-ashing method could limit the loss of volatile compounds, and Middleton4 compared a wet-oxidation method with a dry-ashing technique for the determination of copper in plant materials, with results for each method in good agreement. To extend the work by Middleton, recovery experiments were carried out in this labora- tory to compare results obtained by using the two methods on several animal feeding stuffs. It was found that, under strictly controlled conditions, the dry-ashing technique gave results that were comparable with those obtained by using the wet-oxidation procedure.Several colorimetric reagents were evaluated for the determination of copper, the most successful of which were diethyldithiocarbamate2 and 2,2’-diq~inoly1.6,~ s 7 The evaluation of methods for the determination of zinc in feeding stuffs showed the dithizone titrimetnc method to be the most suitable. For magnesium, the complexometric method with EDTA8s9s10 suffers interference from phosphorus, and the titan yellow dye absorption method has a high variability. * Present address: John Tyzack & Partners (Selection) Ltd., 10 Hallam Street, London, W.l.0 SAC and the authors.ROACH, SANDERSON AND WILLIAMS 43 These analytical methods have their limitations when applied to the analysis of animal feeding stuffs. The complex make-up of high performance diets, with twenty or more different raw materials, provides a wide range of inorganic elements, including calcium, phosphorus, magnesium, iron, copper, zinc, manganese and cobalt, which are present in amounts varying from about 1 p.p.m. to 3 per cent. This complexity often gives rise to interferences that in- herently affect the accuracy and reproducibility and, together with the lengthy nature of the test, make it difficult to carry out a large number of analyses to a desired precision. Comment is made later of the statistical evaluation of the methods in our laboratory.A review of the theoretical and practical applications of atomic-absorption spectroscopy has recently been published by Lockyer.11 Atomic-absorption techniques were applied successfully by Walshl2 and Russell, Shelton and Walsh13 for the analysis of physiological fluids and, recently, were applied by Allanl49l59ls and Davidl7,ls for the determination of several inorganic elements in soil, although for very low levels of copper it was necessary to concentrate with an organic complexing reagent to bring the concentration into a range suitable for determination. In the determination of inorganic elements in animal feeding stuffs, the application of atomic-absorption techniques offered the following advantages over the available classical chemical methods : high specificity for the element being determined; negligible interference from other inorganic elements; high sample throughput ; and economic employment of staff.Additional equipment, including a Technicon sampler unit and a recorder, made it possible to analyse samples at the rate of 60 per hour. APPARATUS- potentiometric recorder were used. EXPERIMENTAL A Unicam SP90 atomic-absorption spectrophotometer and O to 10-mV Servoscribe Co@er, zinc and magnesium hollow-cathode lamps. Propane gas. Acetylene gas. ,4 ir compressor and stabiliser. Technicon sampler Mark I I . All of the reagents used were of analytical-reagent grade. Aqua regia-To 50 volumes of concentrated hydrochloric acid add 25 volumes of con- Standard cupper solzdion-Dissolve 250mg of copper foil in a small volume of concen- Evaporate to dryness and dissolve the residue in concentrated hydro- Evaporate the solution to dryness, then make the residue up to 1 litre, so Standard zinc solution-Dissolve 200 mg of zinc foil in dilute hydrochloric acid and make Standard magnesium solzttion-Dissolve 100 mg of magnesium foil in dilute hydrochloric REAGENTS- centrated nitric acid and 25 volumes of distilled water.trated nitric acid. chloric acid. that the solution contains 250pg per ml of copper. up to 1 litre so that the solution contains 200 pg per ml of zinc. acid and make up to 1 litre so that the solution contains 100 pg per ml of magnesium. DESIGN OF EXPERIMENTS- The experiments were designed to evaluate methods of sample preparation, and to compare the performance of the instrumental method, based on atomic absorption, with the existing chemical methods for determining each element.SAMPLE PREPARATION- ( a ) Copper, by wet oxidation-A selection of animal and vegetable materials used in animal feeding stuffs was treated as follows. Two grams of finely ground sample (passing a B.S.S. 60-mesh sieve) were weighed into a 100-ml Kjeldahl flask and wet oxidised with 20ml of concentrated nitric acid and 3ml of concentrated sulphuric acid, with a final treatment with 2ml of perchloric acid. The solution was diluted and made up to 1OOml in a graduated flask. The colour complex formed between copper and 2,2'-diquinolyl was measured spectro- photometrically at 550 mp in pentyl alcohol.44 ROACH, SANDERSON AND WILLIAMS : DETERMINATION OF TRACE [Analyst, VOl.93 Copper (150 p.p.m.) was then added to each raw material and the complete procedure repeated. (b) Copper, by dry ashiutg-The same samples as in (a) above, including those with added copper, were treated as follows. A 2-g sample was weighed into a 3-inch silica evaporating dish and placed on a hot-plate for half an hour until the sample had charred. Ashing was completed in about half an hour at 450" 2 20" C in a Selas gas-fired muHe with an Ether, Type 900, temperature controller. Care was taken to ensure that the sample did not burst into flames when placed in the hot muffle. The ash was extracted into aqua regia, as described in the paper by Middlet~n.~ To determine the recovery of copper by the proposed ashing method, 15 p.p.m. of copper were added to each raw material (this level was near the natural copper content of the material); 150 and 1400 p.p.m.were also added to a mixed feed to assess the recovery of copper at levels normally encountered in animal feeding stuffs. Zinc, by dry ashing-The selection of animal and vegetable materials, for which recoveries of copper were determined, was also used for testing the recovery of zinc. Zinc was added at two levels of 15 and 150 p.p.m. to each material. Two-gram samples were ashed at 450" t 20" C, after charring, and zinc determined by using the dithizonate titrimetric method. A mixed feed was then made up similar to that for the copper recovery experiment. Zinc recoveries were determined at two levels of 150 and 1400 p.p.m.of sample by using the same method. Magnesium-Two-gram samples of raw materials were ashed at 450" & 20" C, after charring, as for copper and zinc, and analysed by the atomic-absorption method. Additions of magnesium (0.50 per cent.), equivalent to the background levels found, were made so that the recoveries of magnesium were determined. ATOMIC ABSORPTION- The Unicam SP90 atomic-absorption spectrophotometer has a single-beam monochroma- tor with a wavelength range of 210 to 770mp. The output from the instrument can be read directly from a calibrated meter or recorded on a suitable recorder. To facilitate rapid change-over between elements, a triple lamp-turret attachment is used so that while one lamp is in use, two others can be warmed up.Scale-expansion facilities on the photo- multiplier circuit allow the scale to be increased 4-fold, so that low concentrations can be determined with a satisfactory precision, without the need for chemical concentration. The compressed air is supplied by a suitable compressor fitted with stabiliser and filters, and the fuel supply obtained from cylinder storage. A Technicon Mark I1 sampler has been incorporated into the analytical system to achieve a uniform throughput of samples and a constant volume of solution available for each determination. Details of the operating conditions for each element are given below in Table I. TABLE I SP90 OPERATING CONDITIONS Wavelength, mp . . .. . . .. Slit width, m p . . * . .. .. Air pressure, p.s.i. .. . . .. .. Air ffow-rate, litres per minute . . .. Propane pressure, p.s.i. . . .. .. Acetylene pressure, p s i . . . * . .. Propane flow-rate, ml per minute . . .. Acetylene flow-rate, ml per minute Lamp current, mA . . .. .. .. .. Copper 324.8 0.2 38 4.5 10 370 - - 4.9 Zinc 213.9 0.4 38 4.6 10 360 10 - c Magnesium 285.2 0.1 30 5.0 9-2 - - 1400 4.0 STANDARD SOLUTIONS- Three sets of standard solutions were made so that five levels in the range 0 to 1Opg of copper, 0 to 4 pg of zinc and 0 to 2 pg of magnesium per ml were obtained. Samples were analysed at the rate of 60 per hour, which resulted in about 2ml of solution being aspirated through the atomiser to obtain a satisfactory response. To assess the variability at each level of concentration, replicates were measured in random order of concentration.January, 19681 AMOUNTS OF COPPER, ZINC AND MAGNESIUM IN ANIMAL FEEDS 45 TEST SAMPLES- Samples of animal feeding stuffs were dry ashed and diluted when necessary to the concentrations required for analysis.These were analysed with the atomic-absorption spectrophotometer and by manual techniques, by the 2,2'-diquinolyl colorimetric method for copper, the dithizonate titrimetric method for zinc and the EDTA titrimetric method for magnesium. During the analysis of test samples, standard solutions were introduced at regular intervals to ensure that the instrument was operating with a constant sensitivity and to allow calibration graphs for calculation of results to be plotted. DISCUSSION SAMPLE PREPARATIOX- Copper-For a single sample to be used for copper, zinc and magnesium determinations it was necessary to ensure that a dry-ashing technique would give the same results for copper as the existing wet-oxidation procedure.Table I1 shows the results obtained by using both techniques of sample treatment. TABLE I1 COMPARISON OF WET-OXIDATION AND DRY-ASHING SAMPLE PREPARATION PROCEDURES FOR DETERMINATION OF COPPER Natural copper level, p.p.m. + 150 p.p.m. of copper HNO, - H,SO, - HClO, 450" & 20" C HNO, - H,SO, - HClO, 450" & 20" C Natural copper level, p.p.m. A A I 5 r \ Wet oxidation with Dry ashing at Wet oxidation with Dry ashing at Material Rice bran extract .. 9.3 8.2 146.1 151.6 Groundnut meal extract. . 20.4 23.2 162-9 176.7 Meat meal .. .. 12.3 18.7 157.4 171.6 Pollards .. .. .. 17-5 17-7 159.8 170.7 Fish meal . . .. .. 6.9 5-3 151.7 147-7 Wheat . . .. . . 5.9 5.3 154.9 148.2 Barley . . .. .. 5.5 6.3 144.8 147-5 Soya meal .. .. 26.2 28.4 164.2 179.2 A Student's t-test on the differences obtained at both levels of copper showed no significant difference (P > 0.05). This compares well with Middleton's results,* which gave no significant difference for the two methods when certain plant materials were analysed. TABLE I11 COPPER RECOVERIES BY DRY ASHING Material Rice bran extract . .. Groundnut meal extract . . Meat meal . . .. .. Pollards . . .. . . Fish meal . . .. .. Wheat .. .. .. Barley . . * . .. Soya bean extract . . .. Mixed feed I .. .. Mixed feed I1 . . .. Background copper, p.p.m. 10.2 21-2 21-7 11-3 9.0 6-5 4.0 18.3 9.0 7-8 Added copper, p.p.m.15-0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 153.4 1332 Total copper found, p.p.m. 23.7 36.0 39.8 27-8 23-0 19.7 18.0 34.6 153.0 1374 Percentage recovery 94 93 104 102 83 98 93 108 103 95 Recovery experiments for the dry-ashing procedure are shown in Table 111. Apart from fish meals, which give low recoveries, the general performance is satisfactory. Zim-The recovery of added zinc with the dry-ashing technique is shown in Table IV. The results indicate that the performance of this sample preparation technique was com- parable with that reported for copper. Magnesizlm-Good recoveries (Table V) were obtained by using the same sample preparation technique.46 ROACH, SANDERSON AND WILLIAMS : DETERMINATION OF TRACE [A%fZ&St, VOl.93 TABLE IV ZINC RECOVERIES BY DRY ASHING Material Rice bran extract . . .. Groundnut meal extract . . Meat meal . . .. .. Pollards . . .. .. Fish meal . . .. .. Wheat .. .. .. Barley . . * . . . Soya meal extract . . .. Mixed feed I .. .. Mixed feed I1 .. .. Background zinc, p.p.m. 66.0 56.3 102.5 81.8 106.5 42.5 37.3 71.8 53.7 46-5 Added zinc, p.p.m. 40 40 40 40 40 40 40 40 191.2 1487 Total zinc found, p.p.m. 94.3 93.0 144.3 120.8 146.3 82-8 78.8 108.5 244.7 1433 Percentage recovery 96 92 105 98 100 101 104 92 101 96 The results show that by using Middleton's method4 and ensuring that care was taken during the ashing process, good recoveries were achieved for each element, even a t the extreme levels that would normally be encountered. The results show that it is possible to use a common solution prepared from a dry-ashed sample to carry out each determination.A similar procedure reported by Roach19 is used for preparing samples for calcium and phos- phorus determinations by the Technicon AutoAnalyzer, so that when copper, zinc, calcium and magnesium determinations are required, a single ashing is sufficient. TABLE V MAGNESIUM RECOVERIES BY DRY ASHING Tota! Background Added magnesium magnesium, magnesium, found, Material per cent. per cent. per cent. Rice bran extract . . Groundnut meal extract Meat meal . . .. Pollards . . . . Fish meal . . .. Wheat .. ,. Barley . . . . Soya meal extract . . Mixed feed I .. Mixed feed I1 . . .. . . . . . . .. .. .. .. .. .. 0.53 0.28 0.15 0.40 0.22 0.1 1 0.1 1 0.17 0.33 0.34 0.45 0.46 0.45 0-46 0.45 0-45 0.46 0.46 0.30 0.80 0-95 0.73 0.58 0.85 0.65 0.55 0.55 0.63 0.64 1.16 Percentage recovery 93 100 96 100 96 98 98 102 97 103 ATOMIC ABSORPTION- Standard solutions-The instrument performance with standard solutions is shown in Table VI.For the determination of copper the most suitable concentration range for the instrument was 0 to 10 pg per ml. Replicate analyses at five concentrations of copper showed a maximum coefficient of variation of 2.3 per cent. The sensitivity of atomic absorption for the determination of zinc was greater than for copper, and hence a narrower range of concentration (0 to 4pg per ml) was necessary for optimum performance. The performance for zinc was satisfactory, with a coefficient of variation of 3.7 per cent.For magnesium, the concentration range is 0 to 2 pg per ml, with a maximum coefficient of variation of 1.5 per cent. RAW MATERIALS AND MIXED FEEDS- Copfier-Inspection of Table VII shows that the coefficient of variation on test samples was of the same order as that reported for standard solutions. The mean results of several replicates were comparable with the results obtained with the 2,2'-diquinolyl colorimetric reagent, which had been evaluated in this laboratory to give a performance of 8 per cent. coefficient of variation for levels of copper in feeding stuffs up to 1500 p.p.m. Russell and Hart,* in recovery experiments for copper in gelatin, recorded a variation of 36 per cent. for several colorimetric methods, including 2,2'-diquinolyl, neocuproine, biscyclo- hexanone oxalyldihydrazone and zinc dibenzyldithiocarbamate.January, 1968] AMOUNTS OF COPPER, ZINC AND MAGNESIUM IN ANIMAL FEEDS 47 24 0 n 8 p: i2 rl 2 M z W z 0.1 n c? 0 2 I4 R L crc 0 ITABLE VIII COMPARISON OF THE ATOMIC-ABSORPTION AND MANUAL DITHIZONE TITRIMETRIC METHODS FOR THE DETERMINATION OF ZINC Samples of raw materials Manual dithizone ti trime tric method Atomic- absorption method Concentration of zinc, pg per ml of solution Mean concentration of zinc, pg per ml of solution Coefficient of variation (6 results) Samples of animal feeding stuffs Rice Meat and A I bran 1 2 3 4 5 6 2-98 2-96 2.98 2.98 3.44 3.28 2-93 2.90 2-85 2-86 3.12 3.10 1.0 1.3 0.7 1.0 1.3 1.2 TABLE IX COMPARISON OF THE ATOMIC-ABSORPTION AND MANUAL EDTA TITRIMETRIC METHODS Samples of animal feeding stuffs I A \ 7 extracted 3.16 1.32 3-00 1.49 0.8 0.8 bone meal 2.58 2.08 1.2 FOR THE DETERMINATION Pollards Barley 5-88 1.74 5.66 1-61 0.9 2.0 OF MAGNESIUM Samples of raw materials A I \ 1 2 3 Rice bran extracted Manual EDTA titrimetric Concentration of magnesium, Concentration of magnesium, pg per ml of solution 1.40 0.81 0.40 0.69 pg per ml of solution 1.42 0.85 0.48 0.69 Coefficient of variation 1.4 2.0 1.6 1.6 t (4 results) method A tomic-absorption method Meat and bone meal 1.32 1.23 2.2 Groundnut extracted Barley 0.77 0.60 0.83 0.67 2.7 2.1January, 19681 AMOUNTS OF COPPER, ZINC AND MAGNESIUM IN ANIMAL FEEDS 49 The atomic-absorption method was as good as, and in many instances better than, our existing manual technique for copper, and results were comparable with those published for other colorimetric techniques.The SP90 spectrophotometer has scale-expansion facilities that allow samples of very low levels of copper to be measured. The 2,2’-diquinolylcolori- metric method for comparable low levels of copper requires a concentration stage. Zinc-Table VIII shows the results of the atomic-absorption determination of zinc com- pared with the manual dithizone titrimetric procedure. The results with the atomic-absorption method for animal feeds were similar to those obtained with standard solutions of zinc. Magnesium-The results in Table IX show good agreement between the two methods, and it is seen that the variability of the atomic-absorption method on test samples was similar to that obtained with standard solutions.The coefficient of variation is lower than 4.0 per cent. that was established for the EDTA complexometric method in this laboratory. For the titan yellow dye absorption method higher mean values with a higher coefficient of variation (13.6 per cent.) were obtained in a comparison with EDTA. Depression of absorption of magnesium by sulphate, aluminium and phosphate has been reported, but Allan16 and Willis20 have shown that the use of strontium or lanthanum salts is not necessary to counteract phosphate interference at low concentrations. As the materials we analyse generally contain 0 to 5 per cent. of magnesium and less than 2 per cent. of phosphorus, a large dilution is necessary to obtain the magnesium concen- tration in the range 0 to 2 pg per ml.The phosphate concentration is then too low to have an effect on the absorption of the magnesium, thus making the addition of lanthanum or strontium salts unnecessary. The speed of analysis, despite one dilution stage, together with its accuracy, makes the atomic-absorption method much to be preferred. CONCLUSIONS Accurate and rapid methods of analysis are necessary for adequate control of raw materials and compound feeding stuffs to be maintained. Our existing manual techniques were slow, required skilled techniques, and were vulnerable to interference from the wide range of elements that is encountered in animal feeding stuffs. Atomic-absorption spectroscopy lends itself to a rapid, accurate and interference-free method of analysis.Its reproducibility and accuracy have been shown to be better than, or as good as, those of existing colorimetric methods. By adopting a dry-ashing technique, which had a low loss of the elements concerned, it was possible to use one solution to measure copper and zinc, with one dilution stage for magnesium. In addition, the same solution was used for calcium determinations with an AutoAnalyzer, which reduced the work necessary for preparation of samples. The authors thank the Directors of R. Silcock & Sons Ltd. for permission to publish this paper, and Mr. J. B. Seed for assistance with the experimental and analytical work. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. REFERENCES Gorsuch, T. T., Analyst, 1959, 84, 135. Analytical Methods Committee, “Determination of Trace Elements, with Special Reference to Fertilisers and Feeding Stuffs,” W. Heffer & Sons Ltd., Cambridge, 1963, p. 3. High, J. H., Analyst, 1947, 72, 60. Middleton, K. R., Ibid., 1966, 90, 234. Breckenridge, J. G., Lewis, R. W. J., and Quick, L. A., Can. J. Res., 1939, 17, 258. Russell, G., and Hart, P. J., Analyst, 1958, 83, 202. Tuck, B., and Osborn, R. M., Ibid., 1960, 85, 105. Patton, J., and Reeder, W., Analyt. Chem., 1956, 28, 1026. Lewis, L. L., and Melnick, L. M., Ibid., 1960, 32, 38. Analytical Methods Committee, up. cit., p. 24. Lockyer, R., i n Reilley, C. N., Editor, “Advances in Analytical Chemistry and Instrumentation,” Walsh, A., Spectrochim. Acta, 1955, 7 , 108. Russell, B. J., Shelton, J. P., and Walsh, A., Ibid., 1957, 8, 317. Allan, J. E., Analyst, 1961, 86, 530. -, Spectrochim. Acta, 1961, 17, 459. -, Analyst, 1958, 83, 466. David, D. J., Ibid., 1958, 83, 665. Roach, A. G., “Automation in Analytical Chemistry,” Proceedings of the Technicon 5th Inter- Willis, J. B.. Analyt. Chem., 1961, 33, 556. Received June 17th, 1966 Interscience Publishers Inc., New York, 1964, p. 1. -, Ibid., 1960, 85, 496. national Symposium, London, 1965, p. 137.

ISSN:0003-2654    

DOI:10.1039/AN9689300042

出版商:RSC    

年代:1968

数据来源: RSC

摘要:

50 Analyst, January, 1968, Vol. 93, @. 50-65 Spectrophotometric Determination of Selenium with 2-Mercaptobenzothiazole BY B. C. BERA AND M. M. CHAKRABARTTY (Reseamh and Control Laboratory, Durgapur Steel Plant, Durgapur 3, West Bengal, India) A rapid, sensitive and selective spectrophotometric method has been developed for the determination of micro amounts of selenium. This method is based on the absorptiometric measurement of the stable yellow colour formed by the reaction of selenium(1V) with 2-mercaptobenzothiazole in strong hydrochloric acid solution (more than 6.5 M). At 370 mp, Beer’s law is obeyed from 1 to 7 pg of selenium per ml, the optimum range being from 3 to 6pg. The sensitivity and molar absorptivity at 370 mp are 0.008 ,ug per cm2 and 9480, respectively. The yellow product conforms to a stoicheiometry of 1:4 between selenium and the ligand.A 10 to 12-fold excess of tellurium(1V) can be tolerated. Interference by iron(II1) and copper(I1) are eliminated by extraction. The method has been successfully applied to the determination of selenium in various samples. THE spectrophotometric determination of traces of selenium is generally based on two types of reaction.lS2 One type involves the reduction of selenium(1V) to elemental selenium, often with the simultaneous production of a coloured oxidation product. In the other, a coloured or fluorescent piazselenol is formed when selenium( IV) reacts with an aromatic o-diamine. The 3,3’-diaminobenzidine method3 is based on the second type. Its selectivity has been improved by masking or by prior extraction of ~elenium,~ but vanadium(V) and reducing agents such as tin(II), iodide and ascorbic acid interfere; the reproducibility of this method is also influenced by temperature and light.6 However, it has been extensively used for the photometric determination of selenium in a large variety of samples.6 The 2,3-diamino- naphthalene method’ is twice as sensitive (sensitivity 04032pg of selenium per cm2) as the 3,3’-diaminobenzidine method, but Sb3+, Sn2+, Cu2f and NOs- interfere, and 2 hours are required for full development of colour.An indirect approach involving the oxidation of phenylhydrazine 9-sulphonic acid by selenious acid, coupling of the oxidation product with 1-naphthylamine, and measurement of the colour of the azo dyestuff has been reported.8 This method is more sensitive (sensitivity 0.002 pg of selenium per cm2) than the 2,3-diamino- naphthalene method, but the coupling reaction is sensitive to small pH variations, and Ag+, Pt4+, Vs+, Co2+, C?+, oxidising and reducing agents interfere.Tellurium( IV), bismuth( 111) and copper(I1) interfere in the determination of selenium with 2-mer~aptobenzimidazole,~ which is almost as sensitive (sensitivity 0@07 pg of selenium per cm2) as the 3,3’-diamino- benzidine. In the procedure based on the use of 2,2’-dianthrimide,1° heating for 5 hours at 90” C is required for development of the colour. Moreover, Bi3+, Co2+, C$+, Fe2+, Hg2+, Ni2+, Pb2+, Sn2+ and NO,- interfere. Several other colorimetric methods are described in the literature, but they are either insensitive or have various limitations relating to development of colour and to their applicability in the analysis of typical materials.2-Mercaptobenzothiazole, a widely used precipitant ,l1 has been used for the gravirnetric,l2 amperometricl3 and spectroph~tometricl~ determination of palladium, and for the spectro- photometric determination of osmium.16 A preliminary investigation into the analytical potentialities of several heterocyclic thiols revealed that this reagent reacts with selenious acid in strong hydrochloric acid solution (more than 6.5 M), producing a yellow colour or precipitate, depending on the concentration of selenium. Although the colour formed with microgram amounts of selenium is not intense visually, it absorbs strongly in the near ultra- violet regon.The purpose of the present study was to investigate the feasibility of this colour reaction for the determination of traces of selenium. The proposed method, as described below, is simple and compares favourably with the accepted diaminobenzidine method in sensitivity and selectivity. Moreover, with the present 0 SAC and the authors.BERA AND CHAKRABARTTY 51 method the colour develops rapidly and rigid control of pH is not required. A 10 to 12-fold excess of tellurium can also be tolerated. Iron(II1) and copper(I1) are eliminated by extracting their cupferron complexes with chloroform. The method has been successfully applied to the determination of selenium in various synthetic samples. APPARATUS- spectrophotometer, with 1-cm cells.MATERIALS- Standard selenium solution-Selenium dioxide was purified by the sublimation met h0d.l Prepare a stock solution of selenious acid by dissolving 3-5166 g of the purified selenium dioxide in 500 ml of water containing 5 ml of concentrated hydrochloric acid. The solution was standardised gravimetrically by precipitating elemental selenium with hydroxylaminel" and found to contain 5-00 mg of selenium per ml. Prepare more dilute solutions by appro- priate dilution. 2-Mercaptobertzothiazole reagent solution-Prepare a 0-1 per cent. w/v solution of 2-mer- captobenzothiazole in 50 per cent. v/v aqueous ethanol. The solution remains stable for at least 8 hours, but on further storage it slowly undergoes decomposition, even under refrigeration, and was, therefore, prepared fresh daily.Diverse ions-Prepare solutions of diverse ions from analytical-reagent grade salts. GENERAL PROCEDURE- A suitable aliquot of the stock solution of selenious acid, containing 25 to 175 pg of selenium, was placed in a 25-ml calibrated flask, to which were added 15 ml of concentrated hydrochloric acid (about 12 M) and 4 ml of reagent solution. The volume was made up to the mark with 2~ hydrochloric acid and the mixture was allowed to stand for at least 10 minutes to attain room temperature. The absorbance was read at 370mp against an appropriate reagent blank. EXPERIMENTAL Absorbance measurements were made with a Jouan (Pans) "Graphi-Spectral" recording % 470 Wavelength, mu Fig. 1. Absorption spectra of the selenium colour system and the reagent in 7-5 f 0.2 M hydrochloric acid: curve A, selenium (4 pg per ml) and reagent (4 ml of 0.1 per cent.solution) against blank; curve B, selenium (2 pg per ml) and reagent (4 ml of 0-1 per cent. solution) against blank; curve, C reagent (4 ml of 0-1 per cent. solution) against water RESULTS AND DISCUSSION SPECTRAL CURVES- The absorption spectra of the selenium compound and the reagent in 7.5 M hydrochloric acid demonstrate that the absorbance decreases continuously from 350mp, as shown in Fig. 1. The absorbance of the reagent is negligible at 370 mp and above, but varies, although52 BERA AND CHAKRABARTTY: SPECTROPHOTOMETRIC DETERMINATION [Alzdyst, Vol. 93 to a small extent, with the degree of acidity. All absorbance measurements were finally carried out at 370 mp, and appropriate reagent blanks were always used to compensate for any change in their absorbances.EFFECT OF HYDROCHLORIC ACID- In alkaline or neutral media, selenious acid does not react with the reagent, but, on standing for over 1 hour, reduction to elemental selenium occurs. Strongly acidic solutions favour the formation of a yellow colour. In concentrations of hydrochloric acid below 4 M, the solution is nearly colourless. The absorbance of the colour system at 370mp attains a maximum in 6 . 5 ~ hydrochloric acid and remains constant up to 1 0 ~ . Sulphuric acid in this range of molarity produces less colour, and nitric acid oxidises the reagent. All absorbance measurements were carried out in 7.5 & 0.2 M hydrochloric acid. Sexa- valent selenium at this level of acidity is completely reduced to the quadrivalent state.EFFECT OF REAGENT- At least 14-fold molar excess of the reagent over the concentration of selenium is required to ensure full development of colour. For example, at least 3ml of 0.1 per cent. reagent solution are necessary with 100p.g of selenium in a final volume of 25ml for maximum development of colour to occur. No change in absorbance is produced with larger amounts. However, as the reagent is sparingly soluble in a strongly acidic medium, the use of more than 8 ml of the reagent solution should be avoided. EFFECT OF TEMPERATURE- The effect on the colour system of temperatures between 25" and 90" C was studied by using a water-bath. The absorbance remains constant up to about 60°C, and then decreases, possibly because of loss of some of the selenium as the volatile tetrachloride.Moreover, prolonged heating, even at 60" C, favours liberation of elemental selenium. STABILITY OF THE COLOUR- constant for at least 6 hours. CALIBRATION, REPRODUCIBILITY AND SENSITIVITY- Six samples, each of ten different concentrations, were taken and selenium was deter- mined, as described under General procedure. The precision, expressed as standard deviation from the mean of each of the ten series of determinations, is shown in Table I. The calibration graph follows Beer's law in the range of 1 to 7 pg of selenium per ml of the solution, and the optimum range, as evaluated by Ringborn's procedure,17 is from 3 to 6pg. The sensitivity18 and molar absorptivity of the colour system at 370 mp are 0.008 pg per cma and 9480, respectively. The absorbance of the colour system attains a maximum within 10 minutes and remains TABLE I CALIBRATION AND REPRODUCIBILITY SeIenium concentration, Range of measured Average absorbance Pg Per ml absorbances of six samples 0.05 0-042 to 0.048 0.046 1.00 0-118 to 0.124 0- 120 2-00 0.242 to 0.260 0.244 3-00 0.362 to 0.372 0.366 4.00 0.478 to 0.488 0.484 6.00 0.594 to 0.606 0.800 6-00 0.710 to 0.724 0.716 7.00 0.824 to 0.836 0.832 7.60 0.864 to 0-878 0.870 8.00 0-916 to 0.930 0-924 Standard deviation f 0.003 &0*003 f 0.003 f 0.004 f 0.004 f 0.006 f 0.006 f 0.008 f0.008 ,tO*OlO EFFECT OF DIVERSE IONS- Selenium is determined in the presence of foreign ions, except iron(II1) and copper(II), exactly as described under General procedure.The tolerance for foreign ions is taken as the largest amount that causes the actual absorbance by the selenium to deviate by less thanJanuary, 19681 OF SELENIUM WITH 2-MERCAPTOBENZOTHIAZOLE 53 2 per cent. Ions such as Fe2+, Sn2+, SOS2- and I-, which reduce selenium(1V) to elemental selenium, interfere and should be absent. Arsenic(III), antimony(II1) and tungsten(V1) do not interfere in the presence of citrate or tartrate, but bismuth(II1) interferes. Ions such as Co2+, Ni2+, CrS+, VS+ and Te*+ do not react with the reagent, but interfere because of their own absorbance. However, the adverse effects of moderate amounts of these ions (q., 40 pg per ml of C$+ or Ni2+) can be overcome by taking into account the absorbance of the sample in the absence of the reagent.Tellurium(V1) slowly liberates chlorine from hydrochloric acid of the proposed molarity and interferes. Silver(1) and gold(III), which are precipitated by hydrochloric acid and by the reagent, respectively, and platinum metals, which react with the reagent, interfere. However, palladium(I1) can be separated by extracting its dimethylglyoxime complex with chlorof~nn~~ before the determination of selenium. Iron(II1) and copper(I1) are separated by extraction as their cupferrates with chloro- form20s21 before development of the colour. Large amounts of chromium(II1) and nickel(I1) can be removed by extraction of the blue perchromic acid with ethyl acetate,22 and by extraction of the dimethylglyoxime complex with chlor~forrn,~~ respectively.For 4 pg of selenium per ml, the tolerance limits of the diverse ions (pg per ml) are as follows: EDTA, acetate, oxalate, citrate and tartrate, 2000; PO:-, 1500; F-, 400; A13+ and Zn2+, 200; Cd2+ and Pb2+, 100; W6+, Th4+ and Ti4+, 80; Mo6+ and Hg2+, 60; Sb3+, AsS+ and Pd2+, 40; and Us+, 20. DETERMINATION OF SELENIUM IN THE PRESENCE OF TELLURIUM(IV)- As stated earlier, selenium can be determined in the presence of 10 to 12-fold excess of tellurium(1V) by correcting the absorbance of the selenium colour system for the absorbance of the sample itself, before colour development. The method, as given under GeneraI procedure, is otherwise followed in the usual way. Typical results are given in Table 11. DETERMINATION OF SELENIUM IN THE PRESENCE OF IRON(III) AND COPPER(II)- Procedzcre-A suitable aliquot of a synthetic sample containing Se&, FeS+ and Cu2+ was placed in a 50-ml separating funnel and the acidity adjusted to about 0-1 M with respect to hydrochloric acid.One millilitre of chilled, freshly prepared 4 to 5 per cent. cupferron solution was added and, after mixing, the solution was extracted twice with 10-ml portions of chloroform and the organic phase rejected. The acidity of the aqueous phase was then raised to about 1.0 M and, after adding 1 ml of cupferron solution, the mixture was extracted at least three times with 10-ml portions of chloroform to remove the excess of cupferron. The aqueous phase was transferred into a small beaker, warmed on a water-bath to drive off the dissolved solvent, and the solution made up to 10 ml.A suitable aliquot (4 ml or less) of this solution, containing 25 to 175 pg of selenium, was placed in a 25-ml calibrated flask, 15ml of concentrated hydrochloric acid (about 1 2 ~ ) and 4ml of reagent solution were added, and the volume made up to the mark with 2 M hydrochloric acid. The mixture was allowed to stand for at least 10 minutes to attain room temperature and the absorbance read at 370 mp against a reagent blank. Typical results for the recovery of selenium from various mixtures are recorded in Table 11. TABLE I1 DETERMINATION OF SELENIUM IN SYNTHETIC SAMPLES Amount present, pg Selenium A I 3 found, Selenium Tellurium Iron Copper Pg I00 100 100 100 150 400 400 400 400 600 1000 - 1250 - 1600 - 2000 - 1500 - 4000 4000 - 4000 - 6000 - 8000 - 6000 - 101.0 - 101.8 - 103.0 - 105.5 - 152.5 4000 402.5 4000 396-8 6000 396-0 8000 389.6 6000 593.6 Relative error, per cent.+ 1.0 + 1.8 + 3-0 + 5.5 + 1.6 + 0-6 - 0.8 - 1.0 - 2.6 - 1.054 BERA AND CHAKRABARTTY : SPECTROPHOTOMETRIC DETERMINATION [AnabSt, VOl. 93 NATURE OF THE REACTION PRODUCT The yellow solid product formed by the reagent with milligram amounts of selenium could not be isolated, as, during filtration, slow liberation of elemental selenium was observed. Mole fraction o f Se4+ Fig. 2. Continuous variation study with equimolar solutions of selenium and reagent: curve A, 6 x 1 0 - 4 ~ ; curve B, 2.6 x 1 0 - 4 ~ Three different methods, such as the method of continuous variation as modified by Vosburgh and Cooper,% the molar ratio method26 and the slope ratio method,26 were used to determine the stoicheiometry of the reaction product in solution in 7.5 & 0.2 M hydro- chloric acid.The results of these studies, as represented in Figs. 2, 3 and 4, establish that selenium reacts with 2-mercaptobenzothiazole in the ratio of 1 to 4. This finding is in accordance with the observation by Busev2' that 2-mercaptobenzimidazole, a nitrogen hetero- analogue of the 2-mercaptobenzothiazole ligand, reacts with selenium( IV) in the ratio-ofyl to 4. 1- 1 I 1 I I I L 2 4 6 --+ Moles of reagent/moles of Se4+ Fig. 3. Molar ratio plots. Final %oncen- M ; curve tration of selenium: curve A, 1 x B, 6 x 10-SM Concentration of variable component x 10-5M Fig. 4. Slope ratio plots. Final concentra- tion of fixed component (in excess) 7-6 Y M : curve A, selenium varying; curve B, reagent varyingJanuary, 19681 OF SELENIUM WITH 2-MERCAPTOBENZOTHIAZOLE 55 Dr.R. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. The coloured complex can be readily extracted into chloroform and carbon tetrachloride, but the sensitivity is reduced considerably. It can be partially extracted into ethyl methyl ketone and pentyl acetate, but cannot be extracted into diethyl ether, benzene or toluene. Extraction with solvents, such as butyl, isobutyl and isopentyl alcohols, does not give distinct separation of the phases. The authors are grateful to the Council of Scientific and Industrial Research, New Delhi, for awarding a fellowship to B.C.B.They are also indebted to the General Manager, Durgapur Steel Plant, for providing all facilities, and to Dr. G. P. Chatterjee, Dr. H. N. Ray and K. Dutta for their interest and encouragement. REFERENCES Boltz, D. F. , Editor, “Colorimetric Determination of Nonmetals, ” Interscience Publishers Inc., Kolthoff, I. M. , and Elving, P. J., Editors, “Treatise on Analytical Chemistry, ” Interscience Hoste, J., and Gillis, J., Analytica Chim. Acta, 1955, 12, 158. Cheng, K. L., Analyt. Chem., 1956, 28, 1738. Iwasaki, I., Kishioka, A., and Yoshida, U., Bunseki Kagaku, 1961, 10, 479; Chem. Abstr., 1963, Broad, W. C., and Barnard, A. J., jun., Chemist Analyst, 1961, 50, 124. Lott, P. F., Cucor, P., Moriber, G., and Solga, J., Analyt. Chem., 1963, 35, 1159.Kirkbright, G. F., and Yoe, J . H., Ibid., 1963, 35, 808. Busev, A. I., and Huang, M. T., Zh. Analit. Khim., 1962, 17, 1091. Langmyhr, F. J., and Dahl, I., AnaZytica Chim. Acta, 1963, 29, 377. Welcher, F. J., “Organic Analytical Reagents,” D. Van Nostrand Company Inc., New York; Majumdar, A. K., and Chakrabartty, M. M., 2. analyt. Chem., 1958, 162, 96. -- , Ibid., 1959, 20, 379. B e r i B. C., and Chakrabartty, M. M., Micraclzem. J., 1966, 11, 420. Vogel, A. I., “A Text Book of Quantitative Inorganic Analysis, including Elementary Instru- Ringbom, A,, 2. analyt. Cham., 1935, 115, 332. Sandell, E. B., “Colorimetric Determination of Traces of Metals, ” Third Edition, Interscience Furman, N. F., Mason, W. B., and Pekola, J. S., AnaZyt. Chem., 1949, 21, 1325. Kolthoff, I. M., and Elving, P. J., op. cit., p. 157. Brookshier, R. K., and Freund, H., Analyt. Chem., 1951, 23, 1110. Hall, A. J., and Young, R. S., Analyst, 1946, 71, 419. Vosburgh, W. C., and Cooper, G. R., J . Amer. Chem. Soc., 1941, 63, 437. Yoe, J. H., and Jones, A. L., Ind. Engng Chem. Analyt. Edn, 1944, 16, 111. Harvey, A. E., and Manning, D. L., J . Amer. Chem. Sac., 1950, 72, 4488. Busev, A. I., Talanta, 1964, 11, 485. New York and London, 1958, p. 312. Publishers Inc., New York and London, Part 11, Volume 7, 1961, p. 182. 58, 6184. Macmillan & Co. Ltd., London, Volume IV, 1948, p. 109. -- , , Analytica Chim. Acta, 1959, 20, 386. mental Analysis,” Third Edition, Longmans, Green & Co. Ltd., London, 1961, p. 508. Publishers Inc., New York, 1959, p. 80. -, oP. cit., p. 712. Received May l l t k , 1966

ISSN:0003-2654    

DOI:10.1039/AN9689300050

出版商:RSC    

年代:1968

数据来源: RSC

摘要:

56 Analyst, January, 1968, Vol. 93, $@. 56-58 Separation of Low Concentrations of Halogen from Some Luminescent Materials and Elemental Sulphur by a Modified Oxygen-f lask Method BY F. J. DE BOER AND J. VISSER (Philips Research Laboratories, N . V . Philips’ GloeilamfienfaArieken, Eindhoven, The Netherlands) A separation method for low concentrations of halogen from some luminescent materials and elemental sulphur is described, which is based on a modified oxygen-flask method. Relatively large samples can be burned and, in this way, halogen at the p.p.m. level can be determined by any suitable method. The combustion of sulphur can serve as a concentration method for determining other impurities. THE determination of a trace of halogen in luminescent materials and elemental sulphur is a difficult problem, especially in the p.p.m.range. The main elements present in the compound interfere with the analysis1 and it is necessary to remove them. In this paper we report on a modification of the well known oxygen-flask method,2J with which we have, for several years, obtained good results. The procedure is simple, free from contamination, and the blank is low because oxygen is the main reagent. The modification to the apparatus made it possible to burn a large amount of cadmium sulphide, zinc sulphide or selenide and elemental sulphur in the oxygen atmosphere and to determine halogen in this way at the p.p.m. level. EXPERIMENTAL APPARATUS AND METHOD- The apparatus consists of a wide-mouthed 500-ml conical flask with a ground-glass stopper through which pass two platinum electrodes of I-mm diameter, the ends of which are bent upwards.The flask is fitted with an oxygen inlet tube of 2-mm bore, with a stopcock. Fig. 1. Details of the quartz vessel The pressure of the oxygen is controlled by a bubbler device filled with mercury. A platinum wire of 500-mm length and 0.5-mm diameter is wound round the outside wall and the bottom of a cylindrical quartz vessel (30-mm diameter, 15 mm in height), as shown in Fig. 1. This wire is held in place by ten grooves in the vessel, and each end is formed into a loop. The 0 SAC and the authors.DE BOER AND VISSER 57 vessel can be suspended from the electrodes, thus making electrical contact. The length of these electrodes should be adjusted so that the vessel is situated at, or near, the centre of the flask.The current to the electrodes is supplied from a variable low-voltage transformer (20 volts, 30 amp&res), with an ammeter connected in series (see Fig. 2). P tat i n u m electrodes Fig. 2. Details of the apparatus The stopper, with the quartz vessel suspended from the electrodes, is placed in a clamp, and the vessel is heated electrically at 800" to 900" C in air for about 5 minutes. The weighed sample is placed in the quartz vessel after cooling. The vessel must be handled only with tweezers. A platinum wire (about 50 mm in length, 0.1 mm diameter), making contact with both electrodes, is carefully buried in the sample. The flask is charged with a suitable halogen-free absorption solution3s4 and flushed with oxygen for a few minutes.The stopcock is closed, the stopper, with the quartz vessel in place, is inserted into the flask and secured with metal springs, and the flask immersed up to the neck in a cooled water-bath. By passing a small current through the platinum wires, the thin wire starts glowing and the sample is ignited. There is a large consumption of oxygen which lowers the oxygen pressure in the flask. Initially, the current is too low to heat the quartz vessel significantly, but, by raising the current gradually to about 12 amperes, the thin platinum wire fuses and the vessel is heated to a temperature of 900" C. This heating is necessary to ensure complete conversion of the sample and to release all of the halogen. After the vapours have been absorbed, careful addition of oxygen is required with continued heating.It can be made by turning the stopcock. This addition must be repeated once or twice, depending on the amount of sample, which may vary from 0.1 g to several grams. After the combustion is complete, the flask is left to cool for about half an hour. The pressure in the flask is brought up to atmospheric pressure, and the stopper, with the quartz vessel, is removed. The halogen present in the absorption solution can be analysed by any suitable method. NEPHELOMETRIC DETERMINATION OF CHLORIDE- The absorption solution used is 10 ml of water with a few drops of formic acid to convert chlorine into chloride. As some batches of hydrogen peroxide and sodium forrnate2 contained traces of chloride, formic acid was preferred.To obtain chloride-free formic acid, a mixture of formic acid and water (1 + 1) is distilled in a quartz apparatus with a small volume of silver nitrate. PROCEDURES58 DE BOER AND VISSER After combustion of sulphide samples, the absorption solution is heated with nitric acid and silver nitrate by Lamb's method.6 Silver chloride is determined with the E.E.L. nephelometer . If large amounts of sulphide are burned, the considerable amount of sulphuric acid thus formed interferes with the nephelometric method. Chloride can easily be separated by heating the absorption solution, until it nearly fumes, in a 50-ml conical flask fitted with a distillation head. The latter consists of a ground-glass stopper with side-arm and inlet tube. The chloride is distilled as hydrochloric acid in a current of nitrogen and received in a test-tube containing 1 ml of water.After a few combustions, a platinum film may be found to have formed on the surface of the absorptioi? solution and the walls of the flask. Samples containing selenide give red selenium in the combustion flask. In both cases, the nephelometric determination of chloride is interfered with. All the chloride can be distilled, as previously described. In the case of selenide samples, however, some chloride-free sulphuric acid must be added. In the combustion of elemental sulphur, sulphur dioxide is formed. This can be easily expelled by boiling. Sensitivity of the nephelometric chloride determination is about 0.2 pg in 10 ml. PHOTOMETRIC DETERMINATION OF BROMIDE- The absorption solution is about 50ml of water.By adding organic material to the sample (we prefer three drops of isopropyl alcohol), the total bromine is converted into hydrobromic acid during combustion. Sulphur dioxide can be expelled by boiling, and hydro- bromic acid is determined by using a modified method by Pohl,6 in which bromide is converted into bromine with chloramine-T. The bromine reacts with fluorescein to give eosin (tetra- bromofluorescein), and the optical density of the red eosin is measured photometrically at 525mp. Chloride and traces of chlorine do not interfere. Sensitivity of the bromide determination is about 0.1 pg. PHOTOMETRIC DETERMINATION OF IODIDE- The absorption solution is 10 ml of water. If chloride is expected in the sample, a few drops of formic acid are added.If necessary, sulphur dioxide is expelled by boiling and the iodide converted into iodate with bromine. The iodine liberated from the iodate solution gives six times the amount of iodine in the original sample when excess of iodide is added, according to the following reaction'- 10,- + 51- + 6H+ - 31, + 3H,O. The iodine is extracted into chloroform and the optical density measured at 510mp. Sensitivity of the iodide determination is about 0.3 pg. DISCUSSION The following determinations have been carried out on the original materials: chloride 0.1 to 300 p.p.m. in zinc sulphide, cadmium sulphide, zinc selenide and sulphur; bromide, 10 to 30 p.p.m. in doped cadmium sulphide; and iodide, 10 to 30 p.p.m. in doped cadmium sulphide. It was not necessary to determine the halogens in the presence of other halogens. The sulphides were prepared with chloride-free hydrogen sulphide. We have determined 002pg of chloride in samples of zinc sulphide weighing 2g. The amounts brought to combustion varied from 0.1 to 2 g, depending on the halogen content, but it is possible to bum larger amounts. Luminescent materials, such as zinc or cadmium telluride, do not ignite at all. It is possible that this combustion method for sulphur can serve as a concentra- tion method for the determination of other impurities. REFERENCES 1. 2. Schbniger, W., Mikrochim. Actu, 1955, 123; 1956, 869. 3. 4. 5. 6. 7. Malur, J., 2. analyt. Chem., 1965, 211, 324. Macdonald, A. M. G., AnaZyst, 1961, 86, 3. Childs, C. E., Meyers, E. E., Cheng, J., Laframboise, E., and Balodis, R. B., Microchem. J., 1963, Lamb, A. B., Carleton, P. W., and Meldrum, W. B., J. Amer. Chem. Soc., 1920, 42, 251. Pohl, F. A., 2. analyt. Chem., 1966, 68, 149. Crouch, W. H., jun., AnaZyt. Chem., 1962, 34, 1698. 7, 266. Received July loth, 1967

ISSN:0003-2654    

DOI:10.1039/AN9689300056

出版商:RSC    

年代:1968

数据来源: RSC