摘要:

542 NOAKES: THE DETERMINATION OF SELENIUM The Determination of Selenium and Tellurium in Copper BY F. D. L. NOAKES A description is given of a new method for determining selenium and tellurium in copper that is slightly more accurate and considerably more rapid than previously published methods. The main difference from other methods is the initial precipitation of selenium and tellurium from the nitric acid solution of the sample after complete removal of nitrous oxides by means of a solution of stannous chloride in strong hydrochloric acid. This avoids the tedious procedures hitherto used to remove nitric acid. After separation, the selenium and tellurium may be determined gravimetrically or, as preferred by the author, by the volumetric methods described. In two appendices, the preparation of standard solutions of selenium and tellurium are described. In this connection, experiments showing the rate and degree of oxidation of quadrivalent selenium to hexavalent selenium by bromine and by nitric acid and the subsequent precipitation of the selenium are outlined.[Vol. 76 SEVERAL methods for the determination of selenium and tellurium in copper have already been published. They involve rather lengthy procedures and do not always give concordant results. With the proposed volumetric method it is possible to determine selenium in 29 hours, and selenium and tellurium in 3 i to 4 hours, or in slightly less time if the method described as “routine volumetric” is used.Sept., 19511 AND TELLURIUM I N COPPER 543 In the previously published methods, the solution of the sample and the preliminary separation of the selenium and tellurium from the copper require considerable time.Challis1 and Evans2 used nitric acid, either alone or with the addition of bromine, for the solution of the sample, followed by evaporation to fumes with sulphuric acid. This evaporation must be carried out slowly to avoid loss by “bumping.” Experiments described in Appendix I show that with certain methods of precipitation an apparent loss, due in fact to oxidation of part of the selenium to the hexavalent state, may occur when solutions containing bromine are used. Treatment with nitric acid and bromine has been used, and the long evaporation with sulphuric acid has been avoided by collecting the selenium and tellurium in an iron precipitate by a “basic acetate” method.The results for this method of precipitation were more consistent than those for direct precipitation with a m m ~ n i a , ~ , ~ , ~ but they still tended to be slightly low. The initial precipitate may be purified effectively by means of sodium hypophosphite,l but this does not seem to be necessary when volumetric methods are used. In general, the author found that the volumetric methods of Berg and Teitelbaum6 and Evans2 were more rapid and accurate than gravimetric methods. Although the end-point of the tellurium titration is not easy to distinguish, these methods were adopted. The sulphur dioxide separation of selenium from tellurium as described by Lenher and Kao5 gave satisfactory results and was used with the addition of an improved collector for the selenium precipitate.In the proposed method the sample is dissolved in nitric acid and the bulk of the nitrous oxides formed are removed by boiling. After neutralisation, the remaining nitrous oxides are decomposed by the addition of a reagent such as urea, sodium azide or hydrazine hydro- chloride. The solution is then decolorised by the addition of a strong reducing agent and the selenium and tellurium are precipitated by adding an excess of the reagent. Many reducing agents were tried, but only stannous chloride in hydrochloric acid solution, as recommended by Schoeller,’ proved wholly satisfactory. Sodium formaldehyde sulphoxylate was found to precipitate selenium completely in a form that is easily filtered, but under all the acid conditions tried tellurium was incompletely precipitated.The use of the sulph- oxylate is therefore limited to the separation of selenium. The hydrochloric acid solution of stannous chloride, when added to the solution containing .selenium, tellurium and copper, brings about the precipitation of the selenium and tellurium as copper selenide and copper telluride. The mixture should not be allowed to stand for more than 30 minutes before being filtered, nor should the temperature be allowed to rise over 70” C as, if so, a violent reaction takes place with intense frothing. The treatment of the precipitate follows closely the procedure described by Evans2 and by Pollard.8 RECOMMENDED METHOD REAGENTS- of water. chloric acid. chloride and shake well.acid, sp.gr. 1.46 to 1.49. Hydrochloric acid (1 + 1)-Dilute hydrochloric acid, sp.gr. 1.18, with an equal volume Hydraxine hydrochloride-Dissolve 15 g in 100 ml of a 10 per cent. v/v solution of hydro- Stannous chloride-Add hydrochloric acid, sp.gr. 1.18, to an excess of solid stannous After settling, pour off the supernatant liquid and warm until clear. Bromine - hydrobromic acid mixture-Add 10 ml of bromine to 100 ml of hydrobromic Sulphur dioxide solution-Saturate hydrochloric acid, sp.gr. 1.18, with sulphur dioxide. Sodium salicylate-Dissolve 12 g in 100 ml of water. Potassium cobalticyanide-Dissolve 10 g in 100 ml of water. Potassium iodide-Dissolve 4 g in 100 ml of water. Gum arabic solution-Dissolve 1 g of gum arabic or gum acacia in 100 ml of water.Standard sodium thiosulphate solution, 0.05 N-This strength is for use with more than Dissolve 12.5 g of crystalline sodium thiosulphate per litre of water. Standard sodium thiosulphate solution, 0.01 N-This strength is for use with less than Dissolve 2.5 g of crystalline sodium thiosulphate per litre of water. 0.005 g of selenium. 1 ml of solution = 0.001 g of selenium. 0.005 g of selenium. 1 ml of solution = 0.0002 g of selenium.544 NOAKES: THE DETERMINATIOX OF SELENIUM [Vol. 76 Standardisation-The solutions of sodium thiosulphate are conveniently standardised against a solution containing 0-001 g of selenium per litre. Dissolve 0.25 g of pure selenium in 2ml of fuming nitric acid and evaporate to dryness on the steam-bath. Dissolve the residue in water and dilute to 250 ml in a graduated flask. Five millilitres of this solution, after addition of potassium iodide solution, may be directly titrated with thiosulphate or, preferably, the selenium may be precipitated with sulphur dioxide after addition of 30 ml of hydrochloric acid, sp.gr.1.18. The precipitate is then treated as described for the assay. (See also Appendix I, p. 546.) Standard iodine solution, 0.01 N-Dissolve 3 g of potassium iodide and 2.55 g of iodine (See Appendix 11, p. 547.) Standardisation-This solution is conveniently standardised against 0.01 N arsenious 1 ml of 0.01 N arsenious oxide = 0.0012692 g of in 2 litres of water. 1 ml of solution = 0@00319 g of tellurium. oxide, starch being used as indicator. iodine. PROCEDURE- Dissolve 5 to 20g of sample in 20ml of water and 20ml of nitric acid, if necessary adding more nitric acid.Boil the solution for 2 minutes to remove the bulk of the nitrous oxides and then add a solution of sodium hydroxide until a faint permanent precipitate is formed. Re-dissolve the precipitate by the dropwise addition of concentrated nitric acid and add an excess of 4 to 5 drops. Add 10 ml of hydrazine hydrochloride solution and 20 ml of hydrochloric acid, sp.gr. 1.18. Reduce immediately by adding stannous chloride soluton until the pale precipitate first formed is completely re-dissolved and then add 1 ml in excess. Warm the solution to about 60" C, but not above 70" C, and do not allow to stand longer than 30 minutes. The solution should now be cleax, with the selenium and tellurium collected in a coagulated black precipitate.Filter the precipitate with gentle suction on an asbestos pad in a Gooch crucible and wash the precipitate and the original beaker five times with hydrochloric acid (1 + 1). Dissolve the precipitate into the original beaker with two 5-ml portions of bromine - hydro- bromic acid mixture, previously warmed to 30" C, washing with hydrochloric acid (1 + 1) between the additions. Finally, wash the pad with hydrochloric acid (1 + 1) until the washings are colourless. Dilute the solution to 100 ml with hydrochloric acid (1 + l), add crystals of sodium hypophosphite until the bromine is destroyed and warm gently until precipitation of the selenium and tellurium commences. Add a further 3 g of sodium hypophosphite and warm the solution to 50" C.Allow to stand at 50" C for 30 minutes to ensure complete coagulation of the precipitate. Wash the pad and beaker five times with hydrochloric acid (1 + 1) and finally twice with hydrochloric acid, sp.gr. 1.18. Dissolve the precipitate through the pad with 1 to 2 ml of bromine - hydrobromic acid mixture and wash with hydrochloric acid, sp.gr. 1-18, until the washings are colourless. Dilute the filtrate and washings to 50 ml with hydrochloric acid, sp.gr. 1.18, and add about half a gram of powdered kieselguhr to act as a collecting agent. Add hydrochloric acid, saturated with sulphur dioxide, slowly until the bromine colour is discharged and then rapidly add 20 ml or a suitable excess. Warm to about 30" C and agitate until the red precipitate of elemental selenium is coagulated.Filter on an asbestos pad with suction and wash four times with hydrochloric acid, sp.gr. 1.18, twice with hydrochloric acid (1 + 1) and twice with cold water, collecting all the washings in the same flask as the filtrate. Treat the precipitate as described below under "Selenium titration" or, if preferred, gravimetrically, after repeating the precipitation with sulphur dioxide. Boil the filtrate to remove the bulk of the sulphur dioxide and then add bromine water until a faint colour persists for 2 minutes. Reduce the acidity to about 50 per cent. by the addition of water. Add crystals of sodium hypophosphite until precipitation commences and then add 3 g in excess. Bring the solution to the boil and allow to stand for 20 minutes to coagulate the tellurium.Filter, with suction, on an asbestos pad and wash five times with hydrochloric acid (1 + 1). Treat the precipitate as described below under "Tellurium titra- tion" or, if preferred, gravimetrically, after repeating the sodium hypophosphite precipitation. Place a 100 or 150-ml glass-stoppered bottle under the Gooch crucible containing the selenium precipitate and pour 1 to 2 ml of bromine - hydrobromic acid mixture on to the Filter, with suction, on an asbestos pad. SELENIUM TITRATION-Sept., 19511 AND TELLURIUM I N COPPER 545 pad, covering the crucible at once with a watch glass. Allow to stand for 2 to 5 minutes, remove the watch glass, wash it with water and then wash the pad with water until the volume of solution and washings is 50 ml.Add the asbestos pad to the contents of the bottle, insert the glass stopper and shake vigorously. Add 2 ml of hydrochloric acid, sp.gr. 1.18, and 2 to 4 ml of sodium salicylate solution and shake. Then add 2 ml of potassium cobalticyanide solution, 5 ml of potassium iodide solution and 4 ml of carbon tetrachloride. Shake well and allow to stand for 1 minute. Titrate with the appropriate strength of thiosulphate solution until the iodine colour is reduced to a pale straw-yellow, shaking well between additions; then add 2 ml of a freshly boiled starch solution and continue the titration to a pale pink end-point. (A mark on the receiving bottle facilitates this.) Add more salicylate if the solution and suspension are not quite white. TELLURIUM TITRATION- Dissolve the precipitate from the pad with 1 to 2 ml of bromine - hydrobromic acid mixture and wash with the minimum amount of hydrochloric acid (1 + l), collecting the solution and washings in a small beaker.Evaporate to dryness on the steam-bath until the hydrochloric acid is completely removed. Treat the residue with 5 ml of phosphoric acid, sp.gr. 1.75, and 5 ml of gum arabic solution. Shake well and allow to stand until clear. Transfer to a 250-ml conical flask with 50 ml of water, add 2 ml of potassium cobalticyanide solution and 2 g of sodium hypophosphite. Dilute the cold solution with 150 ml of water and titrate with 0.01 N iodine solution until the colour changes to a pale straw. Add 10ml of benzene and continue the titration until a pink colour appears in the benzene, taking care to shake vigorously after each addition of iodine.Heat to brisk boiling and allow to cool. ROUTINE VOLUMETRIC METHOD The procedure may be simplified if a volumetric method is to be used for routine analyses. The precipitate from the stannous chloride separation is filtered, washed with hydrochloric acid, sp.gr. 1.18, and dissolved in bromine - hydrobromic acid mixture. The selenium and tellurium are then separated as previously described with sulphur dioxide but without the purification of the stannous chloride precipitate with sodium hypophosphite. The addition of potassium cobalticyanide solution during the titration prevents any interference from the small amounts of copper that may be present (Evans2). DISCUSSION OF RESULTS By the longer of the two methods described the author has made determinations of selenium alone in 24 hours and of selenium and tellurium in 34 to 4 hours.The range of samples studied was from about 0.001 to 0.1 per cent. of the elements determined. Lower amounts may be determined by taking several 20-g samples and combining the precipitates. The use of very dilute thiosulphate solutions for the selenium titration is not to be recom- mended, as the end-point becomes indistinct. Typical results are shown in Table I. Numerous tests have been carried out with this method on synthetic solutions. TABLE I TYPICAL RESULTS FOR SYNTHETIC SOLUTIONS Selenium Tellurium Weight of I A \ r A \ copper taken, added, found, added, found, 20 0.001 0*0010 0.00095 0.00 10 20 0.01 0.0098 0.0095 0-0089 10 0.03 0.0296 0.0190 0-0187 5 0.10 0.0980 0.095 0-0944 g % % % % Both the “long” and “short” volumetric methods described have also been used for the analysis of numerous samples of copper with satisfactory results.I t was found that results obtained by the slightly longer method did not differ appreciably from those obtained by the “routine” method and the author therefore adopted the shorter procedure for most of his work.546 NOAKES : THE DETERMINATION OF SELENIUM pol. 76 In conclusion, the author wishes to express his thanks for the advice and help he has received from the British Non-Ferrous Metals Research Association and their chief chemist, Mr. B. W. Drinkwater, from Dr. W. B. Pollard and from Mr. E. W. Yeoman, in whose laboratory at the Royal School of Mines this work was carried out.APPENDIX I STANDARD SOLUTION s OF SELENIUM During the early stages of the work it was found that if solutions of selenium in bromine - hydrobromic acid mixture were allowed to stand, the results of determinations of selenium content by direct titration with thiosulphate after the addition of potassium iodide solution became progressively lower with the lapse of time. This was not so if fuming nitric acid was used to dissolve the selenium initially. Hence it. appeared that in the presence of bromine - hydrobromic acid mixture there is either a loss of selenium or selenium is converted into a form that does not liberate iodine from potassium iodide. To confirm these conclusions, experiments were made as follows- (1) A solution was made by dissolving 0-25 g of selenium in bromine - hydrobromic acid mixture and diluting to 250 ml with water.(2) A second solution was made by dissolving 0.25 g of selenium in fuming nitric acid and diluting to 250 ml with water. Of each of these solutions, 5-ml samples were taken and the selenium was precipitated and titrated with thiosulphate as in the assay. 5 ml of solution (1) required 4.75 ml of thiosulphate. 5 ml of solution (2) required 4.70 ml of thiosulphate. (a) A 50-ml sample of solution (1) was placed in a 50-ml glass-stoppered bottle and the stopper sealed with paraffin wax. ( b ) A 50-ml sample of solution (2) was treated as (a). (c) A 50-ml sample of solution (1) was placed in a 100-ml bottle and the neck was left open but loosely plugged with glass wool to keep out dust.(d) A 50-ml sample of solution (2) was treated as in (c). (e) The remainder of solution (1) was allowed to stand in the original stoppered graduated flask. (f) The remainder of solution (2) was treated as in (e). These six solutions and the original sodium thiosulphate solution were kept in a dark cupboard for six weeks. At the end of that time, two 5-ml portions of each were taken, one being titrated direct with the thiosulphate and the other titrated after precipitation of the selenium with sulphur dioxide in hydrochloric acid of sp.gr. 1.18 as described in the paper. The following results were obtained- Portions of solutions (1) and (2) were then treated as follows- Sodium thiosulphate used ml ml r-r-.Test solution Direct titration, After precipitation, U 1.20 4.90 b 4.75 4.90 c 3-90 5.10 d 4.80 5.20 e 1-30 4.90 f 4.70 5-10 Two further portions of solutions (e) and (f) were treated with sulphur dioxide in hydro- chloric acid (1 + l), and the selenium precipitated from solution (e) required only 0.90 ml and that from solution (f) 4.10 ml of thiosulphate. The slightly higher figures obtained after precipitation compared with the tests carried out before the solutions were stored are probably due to deterioration of the thiosulphate solution, although a check showed this to be slight. In experiments (c) and (d) evaporation of the solutions accounted for an apparent increase in the selenium content. These tests indicate that there is no loss of selenium during solution but that selenium is gradually oxidised to the hexavalent state by bromine in hydrobromic acid solution and,Sept., 19511 AND TELLURIUM I N COPPER 547 possibly, to a very slight extent, by the nitric acid.That the oxidation is chiefly due to the presence of bromine is confirmed by the very much lower state of oxidation found in solution (c) where the conditions of the experiment permitted evaporation of bromine, the solution becoming colourless after a few days. These experiments confirm the suggestion by Evans2 that oxidation with bromine might in part go beyond the quadrivalent stage. Pollards has shown that this oxidation is negligible if the solutions are treated soon after oxidation with the bromine, but the author found that oxidation can be detected if the solution isallowed to stand for even a few hours.For example, 5ml of a fresh solution of pure selenium in bromine - hydrobromic acid mixture required 4.75 ml of sodium thiosulphate solution when titrated direct and gave a sharp end-point; 5 ml of the same solution titrated under the same conditions but 4 hours later required only 4-60 ml and gave a very unsatisfactory end-point. As a further check, several tests were made with a solution of sodium selenate (Sev'). These showed that- 1. Sulphur dioxide precipitates selenium completely from solutions of selenium"' in hydrochloric acid, sp.gr. 1.18. 2. Sulphur dioxide does not precipitate selenium from solutions of selenium"' in hydro- chloric acid (I + 1). 3. Sodium hypophosphite precipitates selenium rapidly from solutions of seleniumVL in hydrochloric acid, sp.gr.1.18, but only very slowly from solutions in hydrochloric acid (1 + 1) unless the solution is boiled. From the boiling solution of the stronger acid the selenium is precipitated in the black modification. 4. Sodium formaldehyde sulphoxylate does not precipitate selenium from a solution of seleniumV1 in dilute nitric acid and after the addition of urea, etc. 5. Selenium present in the hexavalent condition does not liberate iodine from potassium iodide under the conditions of the selenium titration. 6. Stannous chloride precipitates selenium from a solution of seleniumv1 in hydrochloric acid, even in the presence of nitric acid, etc., as in the method described, if the solution is warm, but not if cold. It is therefore necessary that selenium solutions containing bromine should be treated at once, unless precipitation by stannous chloride or by the method of Lenher and Kao5 is to follow, The dissolution of copper containing selenium and tellurium is usually complete without the addition of bromine. APPENDIX I1 STANDARD SOLUTIONS OF TELLURIUM Standard solutions of tellurium can be made by dissolving appropriate weights of tellurium oxide in hydrochloric acid, sp.gr. 1.18, but dilution must not be effected by adding water alone as tellurium hydroxide will be gradually precipitated by hydrolysis. Dilution with hydrochloric acid (1 + 1) may be used, but the presence of so much chloride in the standard solution is not always convenient. The author dissolved tellurium dioxide (TeO,) in the nzinimzm amount of a strong solution of sodium hydroxide and then diluted with water. Such a dilute solution is stable and has no appreciable effect on glassware. REFERENCES 1. Challis, H. J. G., Analyst, 1942, 67, 186. 2. 3. Keller, E., J . Anzer. Chew. SOC., 1897, 19, 771. 4. 5. 6. 7. 8. r C T ~ ~ ~ ~ ~ ~ ~ RHODESIA Evans, B. S., Ibid., 1942, 67, 346. Browning, P. E., and Flint, W. R., Amer. J . Sci., 1909, 28, 12. Lenher, V., and Kao, C. H., J . Amer. Chem. SOC., 1925, 47, 769. Berg, R., and Teitelbaum, M., Chem. Zeit., 1928, 52, 142. Schoeller, W. R., Analyst, 1939, 64, 318. Pollard, W. B., Ibid., 1946, 71, 221. P.O. Box 137 KITWE February, 1951

ISSN:0003-2654    

DOI:10.1039/AN9517600542

出版商:RSC    

年代:1951

数据来源: RSC

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548 DWYER AND GIBSON : THE MICRO-ESTIMATION OF IRON WITH [Vol. 76 The Micro-Estimation of Iron with Triphenylmethylarsonium Thiocyanate BY F. P. DWYER AND N. A. GIBSON A new reagent, triphenylmethylarsonium thiocyanate, is recommended for the colorimetric estimation of iron in the presence of cobalt, nickel and chromium. The procedure is suitable for a range of 1 to 10 pg of iron per ml. The coloured iron complex has been isolated. MANY reagents have been suggested for the micro-colorimetric estimation of iron and they have been critically evaluated by Wenger and I>uckert,l who recommend three for ferrous iron and five for ferric iron. Those recommended for ferrous iron, viz., o-phenanthroline, a :a'-dipyridyl and dimethyl glyoxime, all suffer serious interference by cobalt and nickel.Of those recommended for ferric iron , viz., pyramidone, salicylic acid - 5-sulphonic acid, acetyl acetone, barium isonitrosothioglycolate and potassium thiocyanate, the last named is that most widely used. Although the thiocyanate test for iron has been known for some time, and was suggested as a quantitative test in 1890 by Kruss and Moraht,, the composition of the substance responsible for the red colour in aqueous solution is still in doubt. The following formulae have been suggested: Fe(CNS),' (Schlesinge?) , Fe(CNS)" and Fe (CNS),' (Bent and French*) and Fe( Fe(CNS) s) (Schlesinger and van Valkenb~rgh~). The red compound formed with triphenylniethylarsonium thiocyanate can be isolated easily, and has the formula (Ph,MeAs),(Fe(CNS),). This supports the work of Schlesinger and van Valkenburgh.The arsonium ferrithiocyanate complex has a low water solubility, but is soluble in chloroform, acetone, ethylene dichloride and o-dichlorobenzene. In the proposed method, an aqueous solution of the ferric salt is treated with triphenylmethyl- arsonium chloride and ammonium thiocyanate solutions. After extraction of the complex with o-dichlorobenzene, the iron is estimated colorimetrically. The absorption spectrum in o-dichlorobenzene closely resembles that obtained by Woods and Mellod on treating a ferric salt with ammonium thiocyanate in 60 per cent. acetone, both having the absorption maximum at 478mp. The chief disadvantages of the thiocyanate method as usually applied are the sensitivity of the colour to excess of thiocyanate ion, its dependence on the amount of sulphate ion and certain other ions present and the instability of the ferrithiocyanate complex.As an extraction technique is used in the present work, the colour is virtually independent of the amount of thiocyanate ion added, provided the aqueous solution is saturated with respect to the quarternary arsonium thiocyanate. TABLE I This is shown in Table I. EFFECT OF AMOUNT OF THIOCYANATE ION USED Solution containing 100 pg of iron in 10 ml Ammonium thiocyanate used Iron found, Pi3 1 ml of 2 per cent. solution . . .. .. .. 91.2 1 ml of 5 per cent. solution . . .. .. .. 99.0 1 ml of 25 per cent. solution . . .. .. .. 100.0 5 ml of 25 per cent. solution . . .. .. .. 102.0 1 ml of 10 per cent. solution . ... .. .. 99.6 For the same reason, as shown in Table 111, the test solution can be normal with respect The most serious disadvantage of the thiocyanate method is the rapid fading of the colour, This is owing to the reduction Suggested methods for The first is the addition of potassium to sulphate ion without exceeding a 1 per cent. reduction in reading. stated by Sandell' to be about 10 per cent. in 10 minutes. of the ferric iron by thiocyanic acid or its decomposition products. overcoming this disadvantage fall into three categories.Sept., 19511 TRIPHENYLMETHYLARSONIUM THIOCYANATE 549 persulphate (Stokes and Gains), which produces a yellow precipitate that has to be eliminated by the addition of mercuric thiocyanate. The second is extraction by solvents (Stokes and Cains, Bernhard and Dekter,s VanossilO) ; Sandell' states that although extraction techniques increase the sensitivity, the stability is poor.The third method is addition of acetone (Woods and Mellon6), but the density of colour is very dependent on the amount of acetone present, and large errors can be introduced by evaporation of the solvent. Moreover, many salts are insoluble in aqueous acetone and their precipitation would cause further errors. In the present work the solution rarely faded by 1 per cent. in less than 3 hours, and was often stable to this extent for 24 hours. The greatly increased stability of the ferrithio- cyanate complex in o-dichlorobenzene is probably related to the low polarity of this solvent. Beer's law is not obeyed perfectly, but the agreement is rather closer than that obtained by the usual thiocyanate method.PREPARATION OF TRIPHENYLMETHYLARSONIUM FERRITHIOCYANATE, (Ph,MeAs),(Fe(CNS),)- Triphenylmethylarsonium chloride, 55 ml of a 5 per cent. solution, was treated with ammonium thiocyanate, 50 ml of a 20 per cent. solution, and sufficient water (800 ml) to keep the triphenylmethylarsonium thiocyanate in solution ; to the mixture was added slowly a solution of ferric alum containing 1-06 g in 50 ml of 2 per cent. sulphuric acid. The fine red precipitate that separated was coagulated by stirring and, after filtration, washed with 0.01 N sulphuric acid. The compound was recrystallised from 100ml of acetone by the addition of 1600ml of 0.01 N sulphuric acid and 40 ml of 20 per cent.ammonium thiocyanate solution. Melting-point, 124' C. -4mzZysis-Calculated for (Ph,MeAs),(Fe(CNS),) : Fe = 4.08% ; As = 16.34% ; C = 55.31%; H = Found: Fe = 4.10%; As = 16.39%; C = 55.26; H = 4.06%; N = 6.22%. 3.98%; N = 6.14%. PROCEDURE- In a small separating funnel put 5 ml of o-dichlorobenzene, b.p. 180" to 183" C, and then from a pipette add 10 ml of test solution, which should contain between 1 and 10 pg of iron per ml and have a pH of 1 to 2. To this add 1 ml of 2 per cent. triphenylmethylarsonium chloride solution and 1 ml of 25 per cent. ammonium thiocyanate solution. Shake out the arsonium ferrithiocyanate with the o-dichlorobenzene and filter through a KO. 2 sintered-glass filter. To the aqueous layer add 1 ml of 2 per cent. triphenylmethylarsonium chloride solution and extract twice with 1 ml of o-dichlorobenzene. Repeat this once more, then wash combined filtered extracts into a 25-ml graduated flask and compare with a blank solution in a Spekker absorptiometer, using 0 6 c m cells, heat absorption filters H503 and blue Spectrum filters No.602. Calculate the amount of iron in the solution by reference to a calibration curve prepared by treating a series of known solutions of iron in the same way. Extract the aqueous layer with a further 1 ml of o-dichlorobenzene. RESULTS- Results covering the whole range suggested are shown in Table 11, the average mean deviation being 0-5 per cent. or better, and the maximum deviation rarely exceeding 1 per cent. TABLE I1 RESULTS OF APPLYING THE PROCEDURE TO 1O-ml SAMPLES CONTA41NING 1 TO 1opg OF IRON PER MILLILITRE Four samples taken at each concentration Iron taken, 1 *oo 2-00 4.00 6.00 8-00 10.00 PLg Per ml Iron found Minimum, Maximum, 0.99 1.00 1.99 2.01 3.99 4.02 6.00 6-00 7.99 8.01 9.90 10-12 .- tG Per ml Pg Per ml Mean deviation, PLg Per ml 0.003 0.01 0.01 0.00 0.01 0-03 Mean deviation, 0.3 0.5 0.3 0.0 0.1 0.3 %550 DWYER AXD GIBSON [Vol.76 INTERFERENCE- Anions-As has already been pointed out, sulphate in concentrations up to normal can be present without interference. Nitrate and chloride ions can be present in concentra- tions up to normal, but concentrations of nitric acid above 0.1 N oxidise the thiocyanate to give an opalescent solution and so lead to a high result, while similar concentrations of hydrochloric acid give a low result.The interference by hydrochloric acid was noted by Kriiss and Moraht2 and ascribed to the formation of the FeCl,”’ ion by Schlesinger and van Valkenlj~rgh.~ It is more probably due to the formation of FeCI,’, as (Ph,MeAs)(FeCl,) can be isolated under similar conditions. Sulphuric acid up to a concentration of normal can be present, but above this concentration, the peak of the absorption spectrum becomes lower and moves towards longer wavelengths, being 486 mp for 5 N sulphuric acid. These results are summarised in Table 111. TABLE I11 INTERFERENCE BY IONS ADDED TO 100 p g OF IRON IN 0.01 N SULPHURIC ACID Concentration of added reagent 2 N N 0-5 N 0.2 N 0.1 N 0.01 N HzSO,, Pg 97.8 (Colour change) 100.0 99.1 100.2 100-3 100.0 HCl, Pg (Colour change) 94.6 97.8 99.3 99.6 Iron found after addition of- (Rapid 98.9 98.9’ decomp.) (Slight decomp.) - - - 96.3 - - 101.8 100.0 100.0 101.1 100.2 99.5 98.5 100.0 100.0 Fluoride, oxalate and pyrophosphate forrn colourless complexes with the iron and therefore must be absent.Iodide, nitrite, sulphite and thiosulphate act as reducing agents, while dichromate oxidises the thiocyanate ion. Cations-A major advantage of this method is the fact that chromium and nickel salts do not form complexes and are not extractable. Test solutions of iron are unaffected by a thousandfold concentration of chromium and nickel. Cobalt gives an analogous blue compound, but the absorption maximum is so far from that of iron that the concentration of cobalt can be 20 times that of iron without an increase of more than 1 per cent.in the absorptiometer reading for iron. Silver and mercurous ions give insoluble thiocyanates and will be removed in the filtration. Antimonous, cadmium, mercuric and zinc: ions form colourless complexes, but this Copper forms an analogous compound of similar colour and must be absent. It is hoped to extend this work to the estimation of cobalt and copper. The iron and cobalt complexes can be readily separated by chromatographic means, difficulty can be overcome by the use of greater amounts of the reagents. and this will be investigated later. RE FE RE NCE s 1. . Wenger, P., and Duckert, R., Helv. Cham. Acta, 1944, 27, 757. 2. 3. 4. 5. 6. 7. 8. 9. Kruss, G., and Moraht, H., Ann., 1890, 260, 193. Schlesinger, H. I., J . Amer. Chem. SOC., 1941, 63, 1765. Bent, H. E., and French, C . L., Ibid., 1941, 63, 568. Schlesinger, H. I., and van Valkenburgh, H. B., Ibid., 1931, 53, 1212. Woods, J. T., and Mellon, M. G., Ind. Eng. Chern., Anal. E d . , 1941, 13, 551. Sandell, E. B., “Colorimetric Determination of Traces of Metals,” Interscience Publishers Inc. Stokes, H. N., and Cain, J. R., J . Amer. Chem. SOC., 1907, 29, 409. Bernhard, A., and Dekter, I. J., Science, 1932, 75, 517. 10. Vanossi, R., Anales SOC. Quim. Argentina, 1941, 29, 48. New York, 1944, p. 264. CHEMISTRY DEPARTMENT UNIVERSITY OF SYDNEY March, 1951

ISSN:0003-2654    

DOI:10.1039/AN9517600548

出版商:RSC    

年代:1951

数据来源: RSC

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Sept., 19511 NOTES 551 ERRORS IN WEIGHING CAUSED BY ELECTRIC CHARGES DEVELOPED IN SILICA CRUCIBLES ON HEATING THE possibility of the occurrence of error caused by an electrostatic charge on an object being weighed has long been recognised. On an ordinary balance the presence of such a charge is usually betrayed by erratic movements of the beam. We have recently observed that errors of this kind may pass undetected with an aperiodic balance. A silica crucible, ignited in an electric muffle furnace a t 1000” C and cooled over anhydrone, was weighed on an air-damped aperiodic balance with a “projected scale” reading to 100 mg. On adding the fractional weights necessary to bring the scale into use, a point was reached at which the highest scale reading was exceeded by a distance corresponding to an excess weight of about 2mg.On addition of 100mg to the weights already in the pan, however, the balance came to rest in a position well below the zero reading of the scale. That is to say, the addition of the 100-mg weight caused an abnormally large deflection of the beam. The balance was found t o operate normally when the crucible was replaced by brass weights. On repeating the weighing of the crucible, the original effect was observed to have diminished but not to have disappeared. The same effect could be observed to a greater or less degree in the weighing of all silica crucibles that had been ignited and cooled in the manner described above (see Table I, crucibles Nos. 1 and 2). Crucibles that had been handled, even momentarily, and replaced in the desiccator showed a much smaller effect when weighed after 10 or 15 minutes (see Table I, crucibles Nos.3 and 4). TABLE I CONSECUTIVE WEIGHINGS OF FOUR IGNITED AND COOLED SILICA CRUCIBLES (a) Weighed by normal procedure . . ( b ) Weighed under counterpoised nickel crucible (screened) . . a - b .. .. .. (c) Weighed by normal procedure ( d ) Weighed, screened, after C - d .. .. .. (e) Weighed by normal procedure (f) Weighed, screened, after a second after “earthing” . . .. .. “earthing” . . .. .. .. after a second “earthing” . . “earthing” . .. .. .. e - j .. .. .. Crucible No. 1 12.3286 g 12.3354 g - 6.8 mg 12.3340 g 12.3356 g - 1.6 mg 12.3339 g 12.3356 g - 1.7 mg Crucible No. 2 12.1 185 g 12.1256 g -7-1 mg 12.1246 g 12.1260 g - 1.5 mg 12.1240 g 12.1260 g - 2.0 mg Crucible No.3 9.4154 g 9.4161 g - 0.7 mg 9.4158 g 9.4163 g - 0.5 mg 9.4158 g 9-41 60 g - 0.2 mg Crucible No. 4 14-2995 g 14.2988 g + 0.7 mg 14-2994 g 14.2988 g + 0.6 mg 142994 g 14-2988 g + 0.6 mg It was found that the error could apparently be completely eliminated by covering the crucibles, on the balance pan, with an inverted counterpoised nickel crucible. (Presumably, any other metal screening device would have served the purpose equally well.) By stroking the edges of the crucible with an earthed copper wire, the effect could be reduced, there being, usually, a slight persistence of the effect. Exposure of the crucibles to ultra-violet light for 1 minute was apparently without effect. Consistent weighings were, however, always obtained when the crucibles were screened as described.That a charge existed on the crucibles could be demonstrated by bringing an earthed wire into the vicinity of a crucible on the balance pan in apparent equilibrium at the correct crucible weight, when it appeared lighter or heavier by as much as 50 to 100 mg, according as the wire was held above or below a certain point. The same effect was observed when other objects were brought near the crucible, the greatest response being elicited by another crucible that had been ignited and cooled in the manner described. It is probable that the first-observed anomalous behaviour of the balance was due to the fact that when the crucible was near the base of the balance it was attracted towards it electrostatically and that, on adding 100mg t o the right-hand pan, the crucible, moving away from the base, experienced a rapidly decreasing attraction, according to the well-known inverse square law.It would therefore appear to be much lighter in its final than in its initial position.552 NOTES [Vol. 76 The importance of the phenomenon, from the analyst’s point of view, is that (i) the existence of a small electric charge on an object being weighed may pass unnoticed when an aperiodic balance is used and many introduce a considerable error into the weighing and that (ii) the charge developed on silica under the conditions described can be dissipated only with difficulty. It is suggested that a charged object can be weighed accurately by screening it, on the balance pan, with a suitable counterpoised metal cover.Experience of the balance used suggests that the weighings recorded are correct to about k0.2 mg. The weights of the crucibles when screened (b, d and f) may, therefore, be regarded as constant. The effect of handling the crucibles is to reduce the apparent error to about one-tenth of its initial magnitude. Even after earthing the crucibles (c and d) a small but real effect persists. From the weighings of crucible No. 4 it appears that a positive error is possible, but no other example of this effect has been observed. Table I shows results of tests with four different “vitreosil” crucibles. SCOTTISH CO-OPERATIVE WHOLESALE SOCIETY LIMITED CEREAL LABORATORIES REGENT MILLS GLASGOW, C.3 A. W. ARMSTRONG December, 1950 CONFIRMATORY TEST FOR ETHYL ALCOHOL IN BLOOD AND URINE FOR the quantitative estimation of alcohol in blood and urine, the method due to Kozelka and Hinel has been found satisfactory over a period of years.For legal purposes, however, it is desirable to confirm the presence of ethyl alcohol by chemical tests. The method devised by Gettler and Seige12 is ideal for this purpose in that the alcohol is isolated in the pure state and can be identified by the usual tests and produced in court if necessary. The quantity of sample required for the foregoing method2 is at least 100 ml, but as the majority of specimens examined in this laboratory, submitted by the Police under the Road Traffic Act, rarely exceed one fluid ounce, it was necessary to find a means of identification applicable to a small amount of sample.Attempts were made to oxidise the alcohol to acetic acid for subsequent identification. This was found impracticable owing to the difficulty of obtaining the acetic acid in sufficient concentration to give a reliable test. However, when the alcohol was oxidised to acetaldehyde the aldehyde was easily separated and identified. Procedure-Transfer 2 to 5 ml of urine or blood. by means of a pipette into a 200-ml distillation flask and add 5 ml of N sulphuric acid and for blood samples 15 ml of 10 per cent. sodium tungstate solution and 2 drops of a 2 per cent. suspension of DC “Antifoam” A* in warm liquid paraffin. Distil and collect 5 ml of distillate in a 20-ml hard-glass Pyrex tube. Add 2 ml of 2 per cent. potassium dichromate solution to the distillate, followed by the careful addition of 5 ml of con- centrated sulphuric acid.Close the tube with a rubber stopper, wrap in a cloth as a protection against breakage, and shake for approximately 1 minute. Cool, transfer to a distillation flask (at this stage the odour of acetaldehyde will be detected if alcohol was originally present), add a few millilitres of water, distil and collect 4 to 5ml of distillate in a test tube. Add to the distillate 2 drops of a 5 per cent. aqueous solution of phenol and carefully run 2ml of concentrated sulphuric acid down the side of the tube. An orange -yellow colour or precipitate at the interface of the two liquids indicates the presence of acetaldehyde. Form- aldehyde gives a bright crimson colour under the same conditions IHehner).As most of the specimens examined in this department have an alcohol content of between 120 and 400 mg. of ethyl alcohol per 100m1, usually only 2 to 5ml of sample are required for the test. The method is not specific for ethyl alcohol, as n-propyl alcohol and its higher homologues also yield some acetaldehyde on oxidation. But where the quantity of specimen is insufficient for the isolation and subsequent identification of the alcohol, the above test confirms the presence of ethyl alcohol beyond all reasonable doubt, especially in cases of contravention of the Road Traffic Act. It is of interest to note that with a specimen containing 8 mg of methylated spirits a reddish - orange band was produced, showing that the presence of a small quantity of methyl alcohol in ethyl alcohol can easily be detected.* Obtainable from Albright and Wilson Ltd., London. The minimum amount of ethyl alcohol detectable by this method is 6 mg.Sept., 19511 MINISTRY OF FOOD 553 The author is indebted to Mr. A. R. Jamieson, City Analyst, for permission to publish this note. REFERENCES 1. 2. Kozelka, F. L., and Hine, C. H., Biochem. J., 1919, 18, 101; Ibid., 1919, 19, 737; Ind. Eng. Chem., Gettler, A. O., and Seigel, H., Amer. J. Clin. Path., 1937, 7, 85. -4nal. Ed., 1941, 13, 903; Analyst, 1942, 67, 174. CORPORATION CHEMIST’S AND CITY ANALYST’S DEPT. 20, TRONGATE GLASGOW, C.1 R. S. WATSON February, 1951 THE PRESERVATION OF AMINO-ACID PARTITION CHROMATOGRAMS As suggested by Clegg,l the fading of amino-acid paper strip chromatograms developed with ninhydrin2 can be inhibited by washing the dried papers with ether, drying, dipping them in a suitable preserving varnish, and re-drying.The varnishes that have been used are- (1) “Necol” label varnish adhesive 310-4326 (I.C.I.), diluted with an equal volume of ethyl acetate. (2) Label varnish (B.D.H.) diluted with an equal volume of acetone. (3) Collodion (transparent strips) as a 5 per cent. solution in acetone. All three preserve the ninhydrin colours, but (2) and (3) leave a pale yellow wash over the “Necol” varnish, which leaves no extraneous colour, has previously been found suitable The life of the colours is extended for at least several weeks, and this applies to the various In particular, the yellow spot from proline These results suggest that the fading is due mainly to atmospheric oxidation and that a paper. for use as a varnish under tropical conditions. abnormal colours3 given by certain amino-acids. loses its tendency to turn purple. similar technique might prolong the life of paper strip chromatograms of sugar^.^ REFERENCES 1. 2. 3. 4. Clegg, D. L., Anal. Chem., 1950, 22, 48. Consden, R., Gordon, A. H., and Martin, A. J. P., Biochem. J., 1944, 38, 224. Atkinson, R. O., Stuart, R. G., and Stuckey, R. E., Analyst, 1950, 75, 447. Brown, F., Hirst, E. L., Hough, L., Jones, J . K. N., and Wadman, H., Nature, 1948, 161, 720. THE BRITISH DRUG HOUSES LTD. GRAHAM STREET LONDON, N.l H. W. ADAM R. G. STUART February, 1951

ISSN:0003-2654    

DOI:10.1039/AN9517600551

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

Sept., 19511 MINISTRY OF FOOD 553 Ministry of Food STATUTORY INSTRUMENTS* 1951-No. 1135. The Feeding Stuffs (Manufacture) (Amendment) Order, 1951. Price 3d. This Order, which came into operation on J u l y lst, 1951, amends the Feeding Stuffs (Manufacture) Order, 1950 (S.I., 1950, No. 1988; Analyst, 1951, 76, 119), by prescribing formulae for two compounds known as “National Cattle Food No. 6 (Dairy)” and “National Cattle Food No. 7 (Feeding).” - No. 1160. The Cream Order, 1951. Price 3d. This Order, which came into operation on J u l y lst, 1951, reimposes the prohibition on the manufacture and supply of cream except under licence and the obtaining of cream except from the holder of a licence. It also restricts the serving of clotted cream by catering establishments to a specified area, namely, the counties of Cornwall, Devon, Dorset, Gloucester, Somerset and Wiltshire, and imposes a maximum price for clotted cream, except when supplied as part of a meal by a catering estab- lishment in the specified area.* Obtainable from H.M. Stationery Office. Italics indicate changed wording.554 MINISTRY OF FOOD [Vol. 76 - No. 1196. The Food Standards (Edible Gelatine (Order, 1951. Price 3d. This Order, which comes into operation (a) as respects sales by the manufacturer of edible gelatine, on the 1st day of August, 1951; (b) as respects sales by wholesale, on the 1st day of November, 1951; (c) as respects sales by retail, on such date as the Minister of Food may by Order appoint should be read with the Food Standards (General Provisioni) Order, 1944, as amended (S.R.G. O., 1944, Nos. 42 and 654; Analyst, 1944, 69, 49 and 247), and prescribes a standard for gelatine f o r human consumption, as follows- STANDARD FOR EDIBLE GELATINE Edible gelatine shall be clean wholesome protein which- The standard for edible gelatine shall be as follows:- (a) is obtained by extraction from collagenous material ; (b) is free from objectionable taste and offensive odour; (c) dissolves completely in warm water to give a clear or translucent colloidal solution which sets to a jelly when cooled to and maintained a t 60” F; In the case of edible gelxtine sold, offered or exposed for sale by retail, a 3 per cent. solution shall set as aforesaid: Provided that where edible gelatine sold, offered or exposed for sale by retail is clearly and conspicuously described as being of low setting strength on a label (which includes directions for use) marked on or securely attached to the wrapper or container in which i t is so sold, offered or exposed for sale, a solution made up in accordance with the directions for use shall set as afore- said ; ( d ) yields not more than 3-25 per cent.by weight of ash; (e) contains in each million parts by weight not more than two parts by weight of arsenic (expressed as arsenic), seven parts by weight of lead, thirty parts by weight of copper, one hundred parts by weight of zinc. FOOD STANDARDS COMMITTEE THE Minister of Food has approved for publication the following Report of the Food Standards Committee’s Metallic Contamination Sub-committee recommending that no exception need be taken to the presence of traces of copper in foods in amounts not greater than those set out below.The Report is as follows- REPORT ON COPPER The Food Standards Committee has considered and adopted a Report by its Metallic Contamination Sub-committee in respect of the limits of copper in foods. “1. I n pursuance of their terms of reference, the Metallic Contamination Sub-committee submit a Report on Copper in foods and beverages. “2. Copper differs from the majority of trace elements in that it is a physiological constituent of plant and animal life. In plants it plays an important part in cell respiration; in the blood of vertebrate animals the formation of haemoglobin cannot take place unless traces of copper are present.On the other hand, copper is an active oxidation catalyst and if present in milk or butter to the extent of about 2 parts per million (p.p.m.) it activates some form of breakdown in the fat thereby imparting a tallowy flavour and impairing the keeping qualities of butter; copper accelerates the destruction of ascorbic acid ; copper salts in quite small amounts inhibit the action of pepsin and trypsin; and inorganic copper compounds are highly toxic to unicellular organisms such as algae. It is not possible to say with any precision what is the amount of copper required daily by the human organism but the information a t our disposal suggests that the daily amount required by an adult is from 1 to 2 mg, a quantity which would usually be supplied in a normal diet.“4. A t the other extreme when copper salts are present in sufficient concentration they are strongly astringent and irritating to the stomach. The medicinal dose of copper sulphate other than as an emetic is from 16 to 120 mg. In the light of present knowledge it is not possible to assess the risk to health which may arise from the consumption of foods with an unusually high copper content. The presence of quite harmless amounts of copper can, however, render many foods and beverages unpalatable. “5. Our primary concern is to protect the consumer against the sale of foods with a copper content greatly in excess of the nutritional needs of the human organism. This hazard is not likely to arise unless food is processed under conditions conducive to copper contamination ; verdigris could, for example, be a serious source of contamination.We are satisfied that the consumer will be adequately protected by proposing limits consistent with good commercial practice. “6. We have received analytical data from the Government Chemist, the British Food Manufacturing Industries Research Association, the Port Medical Officers of Health, the National Association of Cider The Report is in the following terms- “3. The existence of chronic copper poisoning has not been established.Sept., 19511 MINISTRY OF FOOD 555 Makers, the Institute of Brewing and food manufacturing firms, and after examination of the figures we recommend the classification of foods and beverages and the limits shown below- (1) Beverages other than wines, beer and cider (2) Wines, beer and cider .. (3) Foods not scheduled below (4) Scheduled foods- Chicory, dried or roasted Cocoa powder . . .. Coffee beans . . . . Colourings . . .. Flavourings . . .. Edible gelatin . . .. Pectin, solid or liquid Tea . . . . .. Tomato ketchup . . Tomato purCe . . .. Yeast and yeast extract .. .. . . .. . . .. .. .. .. .. .. .. .. .. .. .. .. .. I . .. .. .. .. .. . . .. .. .. .. .. .. I . .. .. .. . * .. .. .. .. .. .. .. .. .. .. .. .. . . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 2 p.p.m. 7 p.p.m. 20 p.p.m. 30 p.p.m. 70 p.p.m. calculated on the fat free substance 30 p.p.m. 30 p.p.m. (on dry colouring matter) 30 p.p.m. 30 p.p.m. (already prescribed) 30 p.p.m. 150 p.p.m. (provisional) 50 p.p.m. on the dried total solids (already prescribed) 100 p.p.m.on the dried tomato solids 30 p.p.m. “7. A provisional limit of 150p.p.m. has been recommended for copper in tea in view of reports from the Tea Research Institute for Ceylon on the treatment of a disease known as blister blight, which is seriously affecting tea estates. Control measures involve the use of copper fungicides and a t the experi- mental stage it is impossible to avoid a high degree of contamination. We understand that it may be possible to work to a lower limit when further experience of methods of control has been gained and the limit of 150 p.p.m. might be reviewed after one year, In the meantime we are satisfied that no exception need be taken to the importation of tea containing not more than 150 p.p.m. of copper.Only a fraction of the copper in the leaf is soluble and in view of the proportion which the weight of the infusion bears to the weight of the leaf, the copper content of the infusion would not substantially exceed the limit of 2 p.p.m. which we have recommended for beverages. “8. Milk is outside our terms of reference, but in our view there is no reason to assume that copper would be present in liquid milk in excess of the limit of 2 p.p.m. proposed for other beverages. “9. We have not attempted to prescribe limits for composite foods containing one or more of the scheduled foods in addition to foods not scheduled; and recommend instead that where a scheduled food is used in the preparation of any other article of food not being a beverage ready-to-drink, due allowance should be made for the additional amount of copper necessarily introduced by the use of the scheduled food.In view of the higher natural copper content of certain animal and vegetable products, e.g., shell fish and crustacea, offals, etc., we have not proposed specific limits for these articles; but recommend that the sale of such articles containing copper in excess of 20p.p.m. should be permitted if i t can be shown that such copper is of natural occurrence. I t will be apparent that, from the public health standpoint, copper is in a different category from arsenic and lead and we have felt justified in recommending limits of copper content which ought not to present any problem for the food manufacturer. We do not suggest that these limits should be embodied in a Statutory Order immediately. There is room for further enquiry into the physiological function served by copper. Finally, analytical tests for copper in foods have hitherto only been undertaken by a few food manufacturing concerns and there is need for more comprehensive data. For these reasons we suggest that whilst there may be occasion, as in the case of edible gelatin and tomato ketchup, to prescribe limits for a few foods which are particularly liable to copper contamination, the question of imposing comprehensive statutory limits might be reviewed in a year’s time in the light of experience.” The members of the Metallic Contamination Sub-committee are Mr. G. G. Barnes (Chairman), Professor G. R. Cameron, Dr. L. E. Campbell, Professor S. J . Cowell, Dr. J. M. Johnston, Dr. W. P. Kennedy, Dr. G. W. Monier-Williams, Dr. J. R. Nicholls, Dr. G. Roche-Lynch, Mr. G. Taylor and Mr. B. W. Smith (Secretary). June 30t12, 1951 “10. “11. The spoilage of food by copper contamination also calls for further research.

ISSN:0003-2654    

DOI:10.1039/AN9517600553

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

556 THE ACTIVE PRINCIPLES OF PYRETHRUM FLOWERS [Vol. 76 The Active Principles of Pyrethrum Flowers Consultative Committee on Insecticide Materials of Vegetable Origin REPORT OF THE STANDING SUB-COMMITTEE ON METHODS OF ANALYSIS OF VEGETABLE INSECTICIDES ON THE WORLD-WIDE COLLABORATIVE ANALYSIS OF PYRETHRUM FLOWERS, 1948-49* A REPORT has been published recently by the Colonial Products Advisory Bureau (Plant and Animal) on a scheme of collaborative analyses designed to determine a number of factors concerned with the accuracy of the determination of the active principles of pyrethrum flowers. Pyrethrum belongs to the genus Chrysanthemum of the family Compositae. A few species of the genus possess insecticidal properties and one, Chrysanthemum cinerarii folium Vis. (synonym, Pyrethrum cinerariae foliuwz) is the most important commercially.The insecticidal properties of pyrethrum are due t o two groups of esters, known collectively as “pyrethrins,” which are con- centrated in the flower heads with by far the greatest amount located in the achenes. In 1924, Staudinger and Ruzicka succeeded in isolating from pyrethrum flowers two principles exhibiting insecticidal activity. They showed these to be esters formed by the combination of a keto- alcohol, pyrethrolone, either with a mono-carboxylic acid or with the mono-methyl ester of a dicarboxylic acid. Both acids were shown to be cyclopropane derivatives. These esters were named pyrethrin I and pyrethrin I1 respectively. Subsequently, Staudinger and Harder proposed two methods for their determination in the flowers.One, which they designated the acid method, is of considerable importance, since it is the foundation on which most of the modern methods are based. Briefly, the acid method consisted in extracting the flowers with petroleum ether, liberating the carboxylic acids from the extract by hydrolysis and estimating the two acids after separating them by steam distillation (pyrethrin I acid being volatile and pyrethrin I1 acid non-volatile) and then calculating the pyrethrin I and pyrethrin I1 from the amounts of each acid obtained. This method was further developed by Seil and has been widely used in this country and in the U.S.A. A variant of it, devised by Ripert, has been used mainly on the Continent. Later, the mercury reduction method was developed by Wilcoxon and by Holaday.This method depends on the fact that the monocarboxylic acid, after hydrolysis of the pyrethrins as in the Seil method, can be separated by extraction with light petroleum and estimated by its reducing action on Denighs reagent; the dicarboxylic acid is estimated as in the Seil method. The mercury reduction method has been adopted as an official R.O.A.C. method. * Published by the Colonial Products Advisory Bureau (Plant and Animal), Imperial Institute Building, London, S.W.7. Price 4s.Sept., 19511 THE ACTIVE PRISCIPLES OF PYRETHRUM FLOWERS 557 It was soon recognised that exact determination of the pyrethrins was no simple matter on account of the difficulty of securing complete separation from inactive substances contained in the complex extract removed from the flowers by solvent extraction.It was evident that the chemical methods so far evolved yielded results that were indicative only of the relative richness of the samples tested and did not record the absolute values of pyrethrins I and 11. A great deal of practical experimental work was carried out by a number of workers in an effort t o prevent, as far as possible, the inclusion of inactive substances as “pyrethrins.” In the United Kingdom a study of the analytical methods for pyrethrum flowers had been conducted for a number of years by the Sub-committee on Methods of Analysis of Vegetable Insecticides under the Imperial Institute Consultative Committee on Insecticide Materials of Vegetable Origin. -4s the result of their practical investigations, and those of other official bodies and of individual workers, it was considered that the existing methods should be modified in a number of respects. In 1946 it was decided that practical collaboration on an international basis was desirable if any universal agreement was to be reached on pyrethrum analysis. ,4s the result of the favourable response t o an approach made to pyrethrum analysts throughout the world, the Sub-committee were able to proceed to the practical application of their plans.It was decided that the scope of the investigation should be limited to the analysis of two samples of ground pyrethrum flowers by the Seil, Ripert and mercury reduction methods. The Sub- committee considered that, if concordance of results was to be obtained, the methods to be used must be drawn up in great detail.To this end they asked Dr. Seil to revise his method with the co-operation of the Chemical Analysis Committee on Insecticides of the National Association of Insecticide and Disinfectant Manufacturers, U.S.A. At the same time, arrangements were made with Monsieur Ripert for the revision of his method by his chief assistant, Mlle. S. Gerhardstein, whilst the Sub-committee undertook the revision of the mercury reduction method in conjunction with Jfr. J. J . T. Graham of the Production and Marketing Administration, United States Depart- ment of Agriculture. It was decided that the three revised methods should be employed for the analysis 01 one sample of flowers that had been stored for four years, and another sample of flowers that had recently been harvested.It was also agreed that statistical help would be required in planning the experiment and in carrying out an analysis of the results, so that the maximum amount of information might be derived from the investigation. Details of the methods lvere despatched, with the two samples, with the request that analytical work should commence on June 15th, 1948, and that the experiments should be carried out in the random order indicated on an enclosure with cach pair of samples. I n all 42 reports were received. They were submitted to statistical analysis by the Department of Statistics, Rothamsted Experi- mental Station. It is clear from the statistical examination of the results that the investigation failed to differentiate decisively betwecn the Seil arid mercury reduction methods as rcgards concordance of results. On the other hand, it showed that the Ripert method yielded less concordance than the other two methods.Thcre is no doubt that the mercury reduction method gave consistently higher results for both pyrcthrin I and pyrethrin I1 than the Sell method. The Ripert method yieldcd consistentll- lower values for pyrethrin I than either of the other two methods, while the values for pyrethrin I1 were too inconsistent for comparison with the results obtained by the other two methods. It was not possible to obtain definite evidence to show that there was any regular correlation between the values obtained by the Seil and mercury reduction methods either for pyrethrin I or pyrethrin 11.To obtain this information, it would be necessary t o carry out deter- minations on a greatcr number of samples. The most important fact that emerged from the work was the magnitude of the inter-laboratory standard error obtained under the very strict conditions laid down for the test. IVhile the standard error of a determination by any one individual was rather less than 5 per cent. by both the Seil and mercury reduction methods, thc standard error for comparison betwcen laboratories was of the order of 10 per cent. for pyrethrin I and pyrethrin I1 separately, the values being rather smaller for total pyrethrins. Repetition of the analyses by the same workers in the same laboratories did not reduce substantially the differences between laboratories.The experiment has shown that neither the Seil nor the mercury reduction method is capable of giving the concordance with which they have been generally credited and that, even if the complete absence of sampling error can be assumed, a difference of 0.3 between Seil or mercury Ry April, 1948, work on the modifications of the three methods had been completed.558 T H E ACTIVE PRISCIPLES OF PYRETHRUM FLOWERS [Vol. 76 reduction determinations as carried out by two laboratories cannot be regarded as significant for flowers containing between 1.0 and 2.0 per cent. total pyrethrins. The Ripert method was not considered to merit further consideration. There seems no doubt that the present chemical methods leave much to be desired both from the experimental aspect and also as a means of assessing the relative insecticidal effectiveness of pyrethrum flowers, extracts or preparations. LaForge and his associates have shown that pyrethrolone is not a homogeneous compound, but is a mixture of two keto-alcohols, pyrethrolone and cinerolone. The esters of the latter keto-alcohol have been named cinerins.Recently, several homologues of pyrethrin I and cinerin I have been synthesised. Insecticidal evaluation of these esters has shown that toxicity is mainly dependent on the nature of the unsaturated side-chain of the keto-alcohols and to a lesser estent on the stereo-chemistry of the components. I t has become necessary, therefore, to regard “pyrethrin I” and “pyrethrin 11” as groups of esters characterised only by their acid component, which in each is esterified with more than one keto-alcohol.This later conception of the active principles of pyrethrum flowers as a mixture of esters that are not all of the same insecticidal value has increased the difficulties of obtaining a satisfactory evaluation of pyrethrum flowers. I n order to obtain a true assessment of the insecticidal value of pyrethrum, i t would therefore appear necessary to devise a method that will determine each oi the biologically-active principles in the pure state by physical, chemical or biological means, or by a combination thereof. A large amount of work has been carried out in these three fields, but there is no evidence t o show that a successful working method is yet in sight. IVhile the search for an absolute method will continue, the question arises whether the present empirical methods can be further improved.In this connection it must be noted that, since the collaborative work was begun, several papers on the analysis of pyrethrum have been published, notably by hiitchell and his ~ o - w o r k e r s , ’ ~ ~ ~ ~ giving practical evidence of errors in the present methods and suggesting means for improvement. With effect from the 1st of April, 1949, the scientific and technical activities of the Imperial Institute were transferred to the Colonial Office, and the Plant and Animal Products Department of the Institute is now known as the Colonial Products Advisory Bureau (Plant and Animal). The Sub-committee that published this report will continue to function under the new organisa- tion. \Vhile there are other problems that the Sub-committee will have t o consider, attempts to improve methods of pyrethrum analysis will be continued. Suggestions by individual workers will be examined and adopted, if they prove acceptable; while a t the same time original collaborative work will continue among the members and also, if possible, on a wider basis. This Report deserves careful study by all those interested in the evaluation of pyrethrum flowers or extracts. The Sub-committee responsible for it is to be congratulated on the planning of the experimental work and presentation of the results. REFERENCES 1 . 2. 3. Mitchell, \V., Tresadern, F. H., and \Vood, S X., Analyst, 1918, 73, 484. Mitchell, \Y., and Tresadern, F. H., ./. SOC. Chenz. I n d . , 1949, 68, 221. Campbell, A., and Mitchell, \V., J . Scz. Food Agrzc., 1950, 1, 137. H. E. COOMBER I\-. MITCHELL

ISSN:0003-2654    

DOI:10.1039/AN951760556b

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

558 THE ACTIVE PRISCIPLES OF PYRETHRUM FLOWERS [Vol. 76 Book Review THE VITAMIN B COMPLEX. By F. A. ROBIXSOS’, M.Sc., LL.B., F.R.I.C. Pp. xi + 658. London: During the last 20 years, few fields of nutritional research have been more fruitful than the study of the vitamin B complex. This study continues to produce results of great interest to chemists, biologists and clinicians. The members of the vitamin B complex show extreme chemical diversity, but most of them are known to exert a fundamental and highly specific influence on the life of all organisms, ranging from bacteria to men. In the present volume, Mr. Robinson provides the most comprehensive sun-ey of the subject that has yet appeared. The physical, chemical and biological properties of each factor, as well as methods for its extraction from natural sources, synthesis and estimation, are discussed.Bibliographies a t the end of each section cover the literature up to the end of 1949. Altogether over 3300 references are listed. Chapman and Hall Ltd. 1961. Price 60s.Sept., 19511 PUBLICATIONS RECEIVED 559 The absence of references for 1950 is noticeable in the chapters on new factors, such as vitamin B,,, and several statements on the properties of this vitamin will need to be modified in the light of recent knowledge. Unfortunately the time taken at present to issue a book of this nature and the current spate of papers on vitamin B,, make such lapses unavoidable. The vitamin B complex has presented the analyst with an exceptionally wide range of problems, some of which (cf. Analyst, 1951, 76, 58) are still without a satisfactory solution. Various biological, microbiological, chemical and physical methods have been proposed for the estimation of each factor: they are here reviewed critically, but no practical details are given, so that it is necessary to consult the original literature for such information. The extensive references help one to do this. This volume promises to become a standard reference book and can be recommended for the library of all persons interested in the R group of vitamins. J. E. PAGE

ISSN:0003-2654    

DOI:10.1039/AN9517600558

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

Sept., 19511 PUBLICATIONS RECEIVED 559 MICROCHEMISTRY GROUP A JOINT Meeting of the Group with the Liverpool and North-Western Section of the Royal Institute of Chemistry will be held at 7 p.m. on Thursday, October 18th, 19.51, in the Chemistry Lecture Theatre of the University of Liverpool. The following papers will be presented and discussed : “ Some of the Principles of Quanti- tative Microscopical Analysis,” by J. G. A. Griffiths, B.A., Ph.D., F.K.I.C.; “Some Kew and Simple Techniques for the Application of Fluorescence Microscopy,” by J. King, O.B.E., F.R.I.C. ; “Applications of Polarisation Microscopy in Chemical Practice,” by N. H. Hartshorne, M.C., M.Sc., Ph.D., F.R. I.C. The meeting will be preceded by visits to Messrs. Lever Brothers, Port Sunlight, Ltd., and to Messrs. J. Bibby & Sons, Ltd. Members of the Xorth of England Section of the Society are cordially invited to participate in both the meeting and the visits. REPORT OF THE ANALYTICAL METHODS COMMITTEE THE Report of the Meat Extract Sub-committee, “Analysis of Meat Extract,” reprinted from The AnaZyst, June, 1951, 76, 329-333, is now available from the Secretary, Miss D. V. Wilson, 7-8, Idol Lane, London, E.C.3; price to members 1s. 6d. and to non-members 2s. 6d.

ISSN:0003-2654    

DOI:10.1039/AN951760559b

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

REPORTS OF THE ANALYTICAL METHODS COMMITTEE OBTAINABLE FROM THE SECRETARY The Reports of the Analytical Methods Committee listed below may be obtained direct from the Secretary, Society of Public Analysts and Other Analytical Chemists, 7-8, Idol Lane, London, E.C.3 (not through Trade -Agents), a t the price of 1s. 6d. t o members of the Society, and 2s. 6d. t o non-members. Remittances must accompany orders and be made payable t o “Society of Public Analysts.” Milk Products Sub-committee : Report Xo. 1. Report Xo. 2. Report So. 3. Report S o . 4. Analysis of Condensed Milks (1). -Analysis of Condensed Milks (2). Analysis of Sweetened Condensed Milk in which the Sucrose has altered during Determination of \Vater, of Total Solids and of Fat in Dried Milk. Storage. Out of p i n t .Report. Sub-committee on Dirt in Milk. Report on the Determination of Total Solids in Fresh Liquid Milk. Essential Oil Sub-committee : Determination of Dirt in Milk. Report No. 1. Report No. 2. Report No. 3. Report Xo. 4. Report KO. 5 . Report NO. 6. lieport So. 7. Report Xo, 8. Determination of Cineole in Essential Oils. (2) Camphor Oil. (3) Other Oils. Report S o . 9. Report So. 10. Report S o . 11. Report S o . 12. Report KO. l?. Report So. 14. Solubility Test for Ceylon Citronella Oil. (Gratis.) of Arsenic, Lead, etc. in Food Colouring Materials): Estimation of Cineole in Essential Oils. Physical Constants (1). Physical Constants (2). Interim Report on the Determination of .4cetylisable Constituents in Essential Oils. Determination of Phenols in Essential Oils.Determination of Citral in Lemon Oil. Determination of Solubilities. Determination of Carvone and Menthone. Determination of Citronellal. Determination of -4ldehydes other than Citronellal. Determination of Ascaridole. Determination of Esters. (1) Cajuput and Eucalyptus Oils. Out of print. (Addendum to Report S o . 13, Gratis.) Metallic Impurities in Foodstuffs Sub-committee (formerly Sub-committee on the Determination Report S o . 4. Determination of Zinc. Sub-committee on the Determination of Unsaponifiable Matter in Oils and Fats and of Un- saponified Fat in Soaps: Report So. 1. Report KO. 2. Report KO. 3. Report 30. 4. Report No. 5 . Report KO. 6. Determination of Unsaponifiable matter in Oils and Fats. Determination of Unsaponified Fat in Soap.Out of print. Determination of Free Alkali in Soaps. Determination of Free Alkali and Silica in Silicated Soaps. Determination of Rosin in Soaps. Determination of Phenols in Soaps. Poisons Sub-committee appointed to investigate Methods of Assay for Various Substances appearing in the Poisons Schedules of the Poisons Regulations, 1935: Report So. 1 . Report So. 2. Report So. 3. Report S o . 4. Report So. 5 . Report So. 6. Report on the Determination of Fluorine in Foods. .Addendum to above Report. (Gratis.) -Assay of Lobelia (Lobclia Influla). .Assay of Gelsemium. Assay of Aconite. Assay of ’L’ohimba. .Assay of Jaborandi. -Assay of Ephedra and of Ephidrinc in Sasal Sprays. Fluorine in Foods Sub-committee : Sub-Committee on Vitamin Estimations. Sub-committee on Vitamin Estimations. Carotene Panel : Microbiological Panel : Report on the 31 icrobiological Assay of Riboflavine and Nicotinic Acid. The Determination of Carotene in Green-Leaf Material. Part 1. Fresh Grass. gub-Committee on Vitamin Estimations. Aneurine Panel : The Chemical Assay of h e u r i n e in Foodstuffs. Tragacanth Sub-Committee : Report So. 1. Report S o . 2 . Evaluation of Powdered Tragacanth. Evaluation of Flake Tragacanth. Soapless Detergents Sub-committee : Esaminat ion of Detergent Preparations.

ISSN:0003-2654    

DOI:10.1039/AN9517600560

出版商:RSC    

年代:1951

数据来源: RSC