摘要:

576 Analyst, September, 1966, Vol. 91, p p . 556--582 The Determination of Boron in Mild Steel BY T. S. HARRISON AND W. D. COBB ( A P ~ l e b y - ~ ~ o d i i 7 ~ h a i i i Steel Company, Ceizfval Laboratory, Scunthorpe, Lincolnshive) ,4 method of controlling the reaction between acetic anhydride and water to permit the development of the boron - curcumin complex without the previous separation of iron is described. The effect of other elements in amounts normally found in mild steel has been examined. The method has been applied to a series of British Chemical Standards and also to commercial samples. THE purpose of this work was to try and adopt Hayes and Metcalfe'sl curcumin colour procedure so as to be able to make a direct determination of boron in the presence of iron, thus giving a method for the determination of boron in mild steel that would be suitable for routine batch work.To test the colour procedure in the presence of iron, additions of 10 N sodium hydroxide were made to 5-ml aliquots of sulphuric acid (20 per cent. v/v) containing iron and boron so as to nearly neutralise all of the acid. These solutions were evaporated to dryness on a steam-bath and the Hayes and Metcalfe colour procedure was then applied. Not all the iron salts went into solution when the curcumin - acetic acid reagent was added, and the final colours produced had approximately one third of the intensities of those found with the Hayes and Metcalfe procedure. These tests were useful in that they suggested that iron did not interfere positively with the curcumin - boron reaction.Whereas Hayes and Metcalfel found that their colour procedure could tolerate the introduction of up to 0.25 ml of water, their direct procedure based on a 0.25-ml aliquot was not sufficiently sensitive or practical for our purpose. In order, therefore, to increase the sensitivity without resorting to the preliminary separation of boron by distillation, a means had to be found of permitting an adequate sample fraction to be taken and at the same time restricting the amount of water present in the colour procedure. Acetic anhydride has been used to eliminate small volumes of water, and Crawley2 used hydrochloric acid to catalyse the reaction between them. As it was anticipated that any volume taken would contain sulphuric acid (20 per cent.v/v), it was thought that the addition of hydrochloric acid might not be required. Tests proved this to be correct. It was also confirmed that an explosive reaction could occur, and that an addition of glacial acetic acid gave a more controlled reaction. Before the addition of acetic anhydride, it was found advisable to keep the temperature of the solutions below 20" C, because at higher temperatures the reaction was more violent. Tests showed that an excess of acetic anhydride resulted in greatly reduced optical densities due to boron (e.g., when applying colour procedure A with 6 ml of acetic anhydride), and so the amounts of acetic anhydride used in the experimental colour procedures A and B were calculated to allow for less than 0.1 ml of water to remain in solution. It was found that by substituting a 50 per cent.acetone - water solvent for the ethanol used in Hayes and Metcalfe's procedure to extract the curcumin - boron complex, a filtration stage was avoided. COLOUR PROCEDURES COLOUR PROCEDURE A- To a 1-ml aliquot in a polythene bottle add 2 ml of glacial acetic acid at room temperature. Add 4 ml of acetic anhydride. Mix the contents, stopper the bottle and immerse the lower half of it in water until the reaction has taken place (about 30 seconds). Cool to room tern- perature. Add 3 ml of the curcumin - acetic acid reagent, mix the liquids and add 4 ml of sulphuric acid- acetic acid reagent. Mix them again, and allow them to stand for the specified period of time. Extract the solutions with a 50 per cent.acetone - water solvent. Transfer the solutions to 100-ml calibrated flasks and measure the optical density as indicated in Table I.HARRISON AND COBB 577 COLOUR PROCEDURE B- To a 2-ml aliquot in a polythene bottle add 10 ml of glacial acetic acid and cool to below 20” C. Add 8.5 ml of acetic anhydride and, after the reaction has taken place (almost im- mediately), stopper the bottle and cool it to room temperature. Continue as in colour procedure -4 from “Add 3 ml of curcumin - acetic acid reagent.” TABLE I TIME REQUIRED FOR THE FORMATION OF THE BORON - CURCUMIN COMPLEX WITH VARYING BASE SOLUTIONS, WITH AND WITHOUT IRON Optical density corrected for the blank. Obtained by taking the indicated aliquot from the following solutions through the colonr procedure A or €3 I h > Standing No iron.2 gof iron, time allowcd 75 Pg 75 pg for the No iron. 2 g of iron, 2 g of iron, of boron of boron No iron. 1 g of iron, 2 g of iron, formation of 150 p g 150 pg 75 pg +2mlHC1 +2ml HCl 75 pg 75 pg 75 pg the boron - of boron of boron of boron (conc.) (conc.) of boron of boron of boron complex, diluted diluted diluted diluted diluted diluted diluted diluted minutes to 100 ml to 100 ml to 50 ml to 50 ml to 50 ml to 100 ml to 100 ml to 100 ml curcumin + H,SO& + H$O& + H2SO4 +.&SO,, -kH,SO,, -k.H$04, + H2SO4, +.H~SO~P I h 7 I h \ l-ml aliquot through colour procedure A 2-ml aliquot through colour procedure B 15 0.730 0.676 - 0-715 0-771t 0.579 0.548 0.672 30 0.807 0.778 - 0.799 0.834t 0.738 0.710 0.714 0.79 1 60 0.810 0.809 - 0-815 0-839 0.798 0.806 0.813 0.804 - 0.825* - I 0.781 0.785 0.804 0.810 - 0*826* - - 0.799 0.808 0.809 0.819 - 0.829t - - 0-793 0.811 0.819 120 0.803 0.796 - - 0.793 0-816 0.816 - - - - - 0.802 0.804 0.809 - - - - - 0.799 0.806 0.806 - - - - I 0.804 0-809 0.819 1 80 0.780 - 0.790 - - 0.786 0-804 0.810 - - - - - - 5 0.520 0.411 - 0.817t - - - - - - - - - - - 0,797 0.784 * Solutions filtered after extraction with 50 per cent.acetone - water solvent. t Salts were slow to dissolve. A series of tests was carried out (Table I) to find the time required for the formation of the boron complex consistent with a suitable form of base solution. As a result of these tests, colour procedure B was adopted for the final method given under Experimental. The graph was found to be linear up to 1.6 pg per 100 ml for a 4-cm cell.This is equivalent to a range of up to 0.0040 per cent. of boron. COLOUR STABILITY- (18 hours) showed a loss of up to 4 per cent. in optical density owing to boron. The final coloured solutions were found to be stable for 3 hours. Overnight standing EXPERIMENTAL PRINCIPLE- is developed in the presence of the iron, and is measured photometrically. REAGENTS- After the elimination of water from the sample solution, the boron - curcumin complex Acet0n.e - water solvent-Mix equal volumes of distilled water and acetone, AnalaR. Curcumin - acetic acid reagent-Dissolve 0.5 g of curcumin in 400 ml of glacial acetic acid, AnalaR, with warming and stirring. Sulphuric acid - acetic acid reagent-Cautiously add, with cooling and stirring, 200 ml of sulphuric acid (spgr. 1-84) that has been tested for low boron content, to 200 ml of glacial acetic acid, AnalaR.Dilute s.ulphuric acid (20 per cent. 71/71). Glacial acetic acid, AnalaR.,578 HARRISON AND COBB: DETERMINATION OF BORON I N MILL) STEEL rd?LdySt, VOl. $11 Acetic anhydride, AnalaR. Sodium carbonate, anhydrozts, AszalaR. Hydrogen peroxide, 5 volztme, AnalaR. Iron(I1) solz.dion--Dissolve 10 g of boron-free iron in 200 ml of sulphuric acid (20 per cent. v/v). Cool, dilute to 250ml with sulphuric acid (20 per cent, v/v) and filter. (5 ml of solution = 0.2 g of iron.) NoTE-A~~ of the reagents are stable and stock solutions may be kept. APPAR.4TUS- Boron- free glassware. Polythene bottles-100-nil capacity fitted with polythene stoppers.Photo-electric absorptiometer-The Spekker is a suitable instrument used in conjunction with a mercury lamp, Ilford No. 605 colour filters and Calorex H.503 heat filters. PREPARATION OF THE SAMPLE SOLUTION- Transfer 2 g (Note 1) of the sample to a 100-ml conical flask and add 40 ml of sulphuric acid (20 per cent. v/v). Insert an air condenser (Note 2) and digest on a water-bath at 80" C until the reaction ceases. Cool, rinse the condenser with sulphuric acid and filter through a small paper-pulp pad that has been previously washed with sulphuric acid of the same strength. Collect the filtrate in a 100-ml calibrated flask and wash the pad with a little sulphuric acid. Transfer the pad to a platinum crucible, sprinkle with 0.2g of sodium carbonate, dry and ignite at a low temperature to remove carbon.Cool, and cautiously add sulphuric acid until the fused mass has dissolved, keeping the crucible covered with a polythene cover. Filter the solution through a small paper-pulp pad that has been previously washed with sulphuric acid into the same calibrated flask and wash with sulphuric acid. Dilute to the mark with sulphuric acid and mix (Note 3). Add 1 ml of hydrogen peroxide. Add 1 g of sodium carbonate and fuse at a temperature of 1100" C. ADOPTED COLOUR PROCEDURE- Transfer a 2-ml aliquot of the sample solution to a dry polythene bottle, add 10 ml (Note 4) of glacial acetic acid and cool to below 20" C. Hold the base of the bottle under cold water and add 86ml of acetic anhydride. Stopper the bottle and allow the reaction to take place (this occurs almost immediately) and then cool to room temperature.Add 3 ml of curcumin - acetic acid reagent, mix and add 4 ml of sulphuric acid - acetic acid solution. Mix the contents and leave them for 1 hour (Note 5). Extract the solution with the 50 per cent. acetone-water solvent and transfer to a 100-ml calibrated flask, making up to the mark with 50 per cent. acetone - water. Measure the absorption of the clear solution with an absorptiometer, with Ilford No. 606 colour filters and H.503 heat filters in the appropriate cell, Deduct the value for the blank obtained by taking boron-free iron through the procedure, and obtain the boron content by reference to the calibration graph. CALIBRATIOX- with water. StaNdard boron solution (A) -.Dissolve 0.2857 g of boric acid in water and dilute to 500 ml (1 ml of solution = 100 pg of boron.) Standard boron solution (B)-Dilute 50 ml of solution ( A ) to 250 ml with sulphuric acid (25 per cent.v/v>, giving a final acidity of 20 per cent. v/v. (1 ml of solution = 20 pg of boron.) To solutions of 2 g of boron-free iron in 20 per cent. v/v sulphuric acid contained in 100-ml Dilute to the graduation marl; with sulphuric acid and mix. Transfer a 2-ml aliquot to a dry polythene bottle and continue according to the adopted Prepare calibration graphs by plotting the optical density due to boron against the boron calibrated flasks add measured amounts of boron solution (B) as indicated by Table 11. colour procedure. concentration for each cell size.September, 19661 HARRISON -4ND COBB: DETERMINATION OF BORON I N MILD STEEL TABLE 11 ADDITIONS OF BORON SOLUTION (23) Boron Boron solution equivalent, (B), ml Pi? 0.5 10 1-0 20 2-0 40 3.0 60 4.0 80 6.0 120 8.0 160 12.0 240 16-0 320 Nil Nil Boron equivalent, per cent.0*0005 0.001 0.002 0.003 0.004 0-005 0.008 0.012 0.016 Nil Cell size, 4 4 4, 2 4, 2 4, 2, 1 2, 1 1 1 4, 2, 1 CXl 2J XOTES- 1. The range of the method may be increased by reducing the sample weight. 2. 3. A suitable form of condenser is a 30-inch length of glass tubing, internal diametcr 3 mm, carrying a one-hole rubber bung to fit the 100-ml conical flask. If it is desired to determine the insoluble portion separately, treat the extract from the fusion as a separate determination and add 5 ml of iron@) solution to both blank and samples before making up to 100ml with sulphuric acid.All additions for the colour procedure must be accurately measured by burette. The standing time may be increased to 2 hours to suit individual requirements. 4. 5. DISCUSSION THE USE OF HYDROGEN PEROXIDE TO AID SOLUTION OF INSOLUBLE CARBIDES- It was found that the addition of hydrogen peroxide to a solution of steel in sulphuric acid (20 per cent.) resulted in an increased blank value. The volume of hydrogen peroxide added, however, had to be kept to a minimum so that the final acidity remained close to 20 per cent. v/v. Tests were carried out on 2 g of steel that contained 0.5 per cent. of molybdenum, to ascertain the minimum amount of hydrogen peroxide required to effect a solution of the insoluble carbides.It was found that 1 ml of a 5-volume solution was sufficient, giving an increase in the blank, when measured in a 4-cm cell, of less than 0.02 optical density. THE SEPARATE DETERMINATION OF INSOLUBLE BOROX- tion resulted. An addition of iron(I1) was found to overcome this interference. When insoluble portions containing vanadium were treated separately, a brown coloura- CALIBRATIONS- A series of calibrations was made, and the results are detailed in Table 111. Boron, CLg 10 20 40 60 70 so 130 160 240 320 Boron equivalent, per cent. 0.0005 0.001 0.002 0.003 0.0035 0.004 0.006 0-008 0.012 0.010 TABLE IIP CALIBRATIONS Optical density nzi?zzis the blank I 7 -----A. --- 4-cm cell 2-cm cell l-cm cell ----- 7 * f-----T A, A2 B Cl c2 CI c2 Cl c2 0.115 0-103 0.109 0.111 0.113 - - - - 0.226 0-212 0-219 0.219 0.223 - - - - 0-438 0.415 0.434 0-421 0.435 0.214 0.222 I - 0.648 0.616 0.657 0.628 0-654 0-316 0.332 - - 0.761 0.758 0.751 0.754 0.762 0.376 0-382 L - 0.577 0.878 0.848 0.879 0.S83 0.443 0.444 0-226 0.225 - - - - I 0.642 0-635 0.328 0-324 - - - - - 0.863 0.865 0.434 0-435 - - - - - - - 0-628 0.632 - - - - - - - 0.850 0-8G1580 HARRISON AND COBB: DETERMINATION OF BORON I N MILL) STEEL [~4?2a&St, VOl.(31 Calibrations A, and A, were obtained by taking 2-g portions of boron-free iron together with the boron fractions, dissolving and treating according to the full procedure given under Experimental. Calibration B was carried out by taking 0.2-g portions of boron-free iron, in solution, together with the boron fractions and adding 1 g of sodium carbonate, making the solution up to 100ml with sulphuric acid and taking 2-ml aliquots through the adopted colour procedure given under Experimental.Calibration C, was carried out according to the calibration procedure given in the same section. Calibration C, resulted from taking further 2-ml aliquots from the C, solutions but allowing 2 hours’ standing time for the formation of the boron - curcumin complex. The results show that the simplified calibration procedure finally adopted would serve for both soluble and insoluble determinations. A comparison of C, with C, shows that the standing time allowed for the formation of the boron -curcumin complex may be varied between 1 and 2 hours to suit individual requirements.TErE EFFECT O F OTHER ELEMENTS- Synthetic tests were carried out to study the effect of other elements on the determination of total boron by the method. The element under investigation, together with 2 g of boron-free iron and the equivalent of 0*0020 per cent. of boron, was taken through the full procedure.* Further synthetic tests were carried out on the basis of a separate insoluble determination. The element under investigation was fused with 1 g of sodium carbonate, extracted with sulphuric acid and added to 0.2 g of boron-free iron and the equivalent of 0.0020 per cent. of bor0n.t The method is free from interference from elements at the levels likely to be encountered in mild steels. SAMPLES- method described on two separate occasions.with the certificate value. Total boron was determined on a series of mild steel B.C.S. standards, by using the The results shown in Table IV are compared TABLE IV RESULTS OBTA41NED WITH B.C.S. MILD STEEL STANDARDS, COMPARED WITH CERTIFICATE VALUES U.C.S. No. 273 375 277 326 327 328 329 330 Total boron, per cent. Certificate value Direct curcumin 0.002 0~0020 0.0020 09001 0~0010 0~0000 < 0.001 0~0001 0*0001 0.001 0.00 10 0~0010 0.003 0*0020 0.0021 0.004 0.0037 0.0037 0.00s 090078 0.0076 0.007 0.0064 0.0064 w-- 7 * The results showed no interference from 2 per cent. of manganese, 1 per cent. of molybdenum, chromium, copper and silicon, or 0.5 per cent. of niobium, titanium, vanadium, nickel, tungsten, zirconium, tin, phosphorus, cobalt, zinc, magnesium, lead and tantalum, or 0.1 per cent.of beryllium, arsenic and antimony. 7 The results showed no interference from 1 per cent. of silicon, molybdenum and chromium, or from 0-5 per cent. of vanadium, titanium and tungsten. All the recoveries were between 0.0018 and 0.0020 per cent. of boron. ,411 the recoveries were between 0.0018 and 0.0020 per cent. of boron.September, 19661 HARRISON AND COBB 581 Soluble and insoluble boron determinations were carried out on a series of steel plate and pit samples (Table V) from Fortiweld quality steels. The results for the distillation procedure were obtained on aliquots taken from the same sample solutions obtained for the direct procedure. The quinalizarin values were those obtained on a routine basis. TABLE V RESULTS FOR A SERIES OF PLATE AND PIT SAMPLES OF FORTIWELD QUrlLITY STEELS Sample No.1 > - 3 4 5 (i 5 S 9 Boron, per cent. Soluble Insolublc Total Soluble Insoluble Total Soluble Insoluble Total Soluble Insoluble Total Soluble Insoluble Total Soluble Insolu bIe Total Soluble Insoluble Total Soluble Insoluble Total Soluble Insoluble Total Distillation curcumin Direct curcumin Routine 0*0008 0.0012 0.0011 0.001 1 0-001 1 0.0023 0.0023 0.0023 0.0023 0.0025 0,0035 0.0034 0.0034 0,0034 0.0033 0.0024 0.0032 0.0029 0.0030 0.0028 0~0010 0~0010 0.0009 0.001 1 0.0008 0-0032 0,0042 0.0039 0.0039 0.0039 0.0015 0.00 19 0.0017 0.00 18 0.001 6 0.0019 0.0019 0.0017 0*0019 0.0013 0.0038 0-0036 0,0035 0.0035 0.0028 ,-A-, quinalizarin w - l 0.0022 0.001s 0*0040 0.0014 0-0027 0.0041 0.0025 0*0010 0.0035 0.0028 0.0009 0.0037 0.002 1 0.0015 0.0036 0.002s 0.0003 0.0031 0.002 1 0*0018 0.0039 0.001 3 0.0026 0.0039 0-0025 0.00 13 0.0038 0.0028 0*0011 0.0039 0.002 1 0.001 8 0.0039 0.0029 0+0005 0.0034 0.002 1 0.0016 0.0037 0.0014 0.0022 0.0036 0.0024 0.00 10 0.0034 0.0027 0.0009 0.0036 0.0020 0.0014 0.0034 0.0028 0.0004 0.0032 0.0020 0.0017 0.0037 0.0012 0.0024 0.0036 0.0024 0.00 13 0.0037 0.0026 0.001 1 0.0037 0-0019 0*0017 0.0036 04027 0*0005 04032 0.0018 0-0017 0.0035 0-0008 0.0020 0.0028 0.0017 0.001 1 0-0028 0*0018 0.0008 0.0026 0.0014 0.0014 0.0028 0,0022 0.0003 0.0025 CONCLUSIONS A method for the determination of boron in mild steel has been described. The elements in amounts normally found in mild steel have been shown not to interfere. The method is suitable for routine batch work. We thank Messrs. 0. S. Bell and W. W. Foster for their co-operation, and the Directors of The Appleby-Frodingham Steel Company for permission to publish this paper. REFERENCES 1. Hayes, M. R., and Metcalfe, J., Armlyst, 1962, 87, 956. 2. Cra-wley, R. H. A., Ibid., 1964, 89, 749. Received Seflteitaber 9th, 1965

ISSN:0003-2654    

DOI:10.1039/AN9669100576

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

682 ,4?zalyst, September, 1966, Vol. 91 , fib. 582-586 Distillation Method for Determining Total Carbon in Sodium BY V. M. SINCLAIR, J. L, DRUMMOND AND A. W. SMITH (Dounreay Experimental Rencfor Establishsne.szt, Uizited Kingdom A tomic E9zergy A zrthoritjf, T~UYSO, Caithqzess, Scotland) h procedure is described for measuring total carbon in sodium by the removal of the alkali metal by distillation, combustion of the residue in oxygen and manometric determination of the resultant carbon dioxide. It has been shown by radio-tracer techniques that there is no loss of carbon from the sample during the distillation stage, and that recovery of various forms of carbon is essentially complete. The coefficient of variation of a single determination a t the 20 p.p.m. level is about 10 per cent.The bias is believed to be less than 10 per cent.; the average blank value is about 1.5 p.p.m. of carbon. A DISTILLATION method by Walker and Francel for the determination of “free” carbon in sodium has been published. A related procedure has been developed concurrently at Doun- reay for determining total carbon in sodium and sodium - potassium allo~7~. The main differences from Walker and France’s method are considered in this paper. EXPERIMENTAL APPARATUS- Silica crucibles (1-8 cm i.d. x 4 cm kti,gh)-The silica tubing must be washed with water before fabrication of the crucibles. It must not be touched with bare hands before glass- blowing, or the surface of the silica will be adversely affected. Immediately before use the crucibles should be re-washed with water, dried at 120” C, and ignited at 800” C in oxygen for 10 minutes, or until the carbon dioxide blank is negligible.Oxygen in >-, ‘E A = Valve B = O-rings C = Glove-box D = Distillation pot E = Sample crucibles and holder F = Perspex lid To Air pump in - To pumps /L /M G = Molecular-sieve trap H = Sliding furnace J = Silica combustion tube K = First trap L = Second trap M = Manometer Fig. 1. Transfer glove-box and combustion apparatusSINCLAIR, DRUMMOND AND SMITH 583 DistiLlatioqt $ot-The stainless-steel distillation pot is similar to that described by Walker and France,l but with 3 of the 6 bolts retaining the top replaced by fixed studs for attaching the pot to the roof of the transfer glove-box (see Fig. 1). The pot, cold-finger and a nickel support to hold 4 crucibles must be washed thoroughly with dilute nitric acid and dried a t 120" C before use.Sam$Ziizg a d distillation rigs-The sampling and distillation rigs are similar to those described by Walker and France.l The cold-finger of the distillation pot is cooled with water for sodium or with a solid carbon dioxide - methanol mixture for sodium - potassium alloy samples. I t has been shown by direct measurement that the sodium temperature during a distillation was about 350" C with the furnace at a temperature between 600" and 650" C. The crucible temperature rose to a maximum of about 400" C after all the sodium had been distilled. Combztstioiz vig--One end of the combustion tube protrudes into the inert-gas filled transfer box shown in Fig.1, which is used for unloading the crucibles from the distillation pot under carbon dioxide free conditions. The combustion furnace operates at 800" to 900" C, and the carbon dioxide produced is separated and determined in a conventional manometric apparatus. PROCEDURE- Prepare the samples and carry out the distillation as described by Walker and France.l After cooling the pot at the end of the distillation, connect the top of the pot to the underside of the Perspex lid of the combustion rig glove-box, replace the lid on the box, and purge the box with argon. Disconnect the lower half of the distillation pot inside the box, and remove the crucibles to a storage vessel in the box. Carry out a blank combustion on the empty apparatus to ensure that the apparatus blank is less than 2 pg of carbon.Load a sample crucible from the glove-box into the cold end of the Combustion tube and evacuate the apparatus to less than torr. Isolate the combustion tube from the vacuum pumps, admit oxygen to a pressure of about 70cm of mercury, and move the pre-heated furnace into position surrounding the crucible. After the apparatus has been at 800" C for 10 minutes, slowly evacuate the apparatus through an efficient trap cooled in liquid nitrogen to less than torr, and continue the combustion under vacuum for a further 10 minutes to complete the decomposition of any sodium carbonate, either from the original sample or that formed during the combustion. Isolate the cold-trap, and substitute a solid carbon dioxide - methanol trap for the liquid nitrogen.At the same time, cool a second small trap in the gas-measuring system with liquid nitrogen to transfer the carbon dioxide but not moisture. Warm to room temperature, and measure the carbon dioxide pressure in a convenient volume. Repeat the combustion with the other sample and blank crucibles. Calculate the weight of carbon in each, deduct the blank value, and relate to the weight of sample obtained from the known volume of the sample crucibles. RESULTS AND DISCUSSION Consideration has been given to the possible sources of error by which carbon might be lost or gained. DISTILLATION STAGE- and 10-5 In the distillation stage the temperature of the liquid metal is raised to between 350" 400" C, and the sodium is distilled on to the cold-finger under a pressure of less than torr.During this distillation carbon could distil as an unknown, volatile, sodium - carbon species, or be lost as gases such as carbon monoxide or carbon dioxide as a result of reactions such as- Na,O + C + 2Na + CO . . .. .. . . (i) Na,C03 + 2Na + 2Na,0 + CO . . .. * . . . (ii) Na,CO, $ Na,O + CO, . . .. .. . . (iii) (NaCO), species + xNa + xC0 . . .. .. . . (iv) The gas could either escape or be gettered by the distilling liquid metal. These reactions were studied under the time and temperature conditions prevailing during the distillation stage.584 [And%Jst, vol. $11 (i) Carbon and sodium oxide reaction-From thermodynamic considerations, the equili- brium partial pressure of carbon monoxide at 400" C for the reaction between sodium oxide and free carbon should be very low. However, towards the end of a sodium distillation, any carbon monoxide or sodium produced by this reaction could be removed from the system by pumping or by transfer to the cold-finger; the reaction could proceed irreversibly.Possible losses of carbon monoxide were therefore examined both in a static system with evacuated sealed tubes and under distillation conditions, In the static system, samples of sodium oxide were mixed with carbon-14 labelled elemental carbon, both with and without free metallic sodium present. After heating to about 400" C for several hours, the carbon-14 activity of the gas was measured. The results in Table I confirm that the amount of carbon monoxide found was insignificant. SINCLAIK, DRUMMOND AND SMITH : DISTILLATION METHOD TABLE I REACTIONS OF SODIUM OXIDE AND CARBON Excess sodium Carbon added, Yes 600 No 600 Yes 600 Yes 600 No GOO Y e s 600 present r*g Oxygen added, Carbon in gas, Clg Pug - <0*5 290 <0*5 1450 <0*6 2000 < 0.5 3500 < 0.5 4000 < 0.5 In similar experiments under distillation conditions in a glass and silica rig, any gas evolved was collected continuously and counted for carbon-14, and also the distilled sodium from the cold-finger was dissolved and analysed for carbon-14. The amounts of carbon-14 found were always less than 0.1 per cent.and less than 3 per cent. of that added, respectively. (ii) Sodium carbonate and sodium reaction-The change in free energy calculated for the reaction between sodium carbonate and sodium is +32 K cal., and therefore the equilibrium partial pressure of carbon monoxide should be negligible.To confirm by experiment that no significant amount of carbon monoxide was evolved even during cdntinuous pumping, sodium metal was added to known amounts of sodium carbonate labelled with carbon-14 and distilled off. The amounts of carbon-14 in the gases evolved during distillation of the sodium and in the sodium distillate, shown in Table 11, suggest that there is no appreciable loss of carbon from a distillation residue arising from a reaction of sodium and sodium carbonate. TABLE I1 SODIUM - SODIUM CARBONATE REACTION Sodium added, g 2 1 1 1 I 1 Sodium carbonate added, PE: 800 900 300 26 160 73 Carbon in gas, Carbon in distillate, per cent. per cent.<1 3 1 2 <1 3 <1 3 (1 1 < 1 ( 1 (iii) Decomposition of sodium carbonate-Results given by Preston and Turner2 for the thermal decomposition of sodium carbonate indicate that the amount of carbon dioxide lost from sodium carbonate on pumping a t 400" C is small. The loss of carbon by this route is therefore negligible; this is again confirmed by the results in Table 11. (iv) Decomposition of sodium carbonyl-The nature of sodium carbonyl species in liquid sodium is uncertain. However, specimens of hexasodium hexacarbonyl were prepared as described by Miller,3 and the dissociation pressure of the carbonyl was measured over the range 600" to 800" C. Extrapolation to distillation temperatures, viz., 350" C, suggested that the pressure of carbon monoxide would be low and that loss would be negligible.To check this hypothesis some carbon-14 labelled sodium carbonyl was prepared in a large excess of sodium to give a carbon content of about 10 p.p.m. A sample of this sodium was distilled, and it was found that about 97 per cent. of the carbon-14 was present in the residue, with only 3 per cent. in the distillate and less than 1 per cent. in the evolved gas.September, 19661 FOR DETERMINING TOTAL CARBON IN SODIUM 585 (v) Loss of carbon transferred from steel-Although the most probable forms of carbon in sodium have been covered, it is possible that unidentified forms, present in the liquid metal, could be lost during the distillation procedure. To guard against this possibility, 2 specimens of iron containing iron carbide labelled with carbon-14 were prepared by dissolving carbon-14 in molten iron and cooling.These were suspended in low temperature filtered sodium contained in 2 stainless-steel cans (type 1S.S.l) and heated at 600” C for 24 hours. Analysis of samples of the can showed that significant amounts of carbon-14 had transferred from the carburised specimens to the stainless-steel container. Samples of the sodium were distilled, and the gas produced during the distillation, the distilled sodium and the residue were all examined for carbon-14. The results in Table I11 show that a significant amount of carbon-14 was found only in the residue. TABLE I11 LOSS OF CARBON TRANSFERRED FROM STEEL per cent. per cent. per cent. Carbon-14 in residue, Carbon-14 in distillate, Carbon-14 in gas, 99 <1 <1 99 2 <1 MEASUREMENT OF BLANKS- A positive error could be caused in results by the distillation procedure if carbon was picked up by samples at any stage of the procedure.The “blank” for the method was there- fore measured by regularly placing empty crucibles alongside sample crucibles throughout the whole procedure, and measuring the carbon in these. The reproducibility of this blank effectively sets the lower limit for determination. Initial results were discouraging in that very high carbon blanks were occasionally obtained, corresponding to about 10 to 20 p.p.m. of carbon in the sample. Some effort was therefore devoted to tracing the source of the carbon and eliminating the trouble. It was found that up to 0.5 ml of carbon monoxide plus carbon dioxide was evolved from the steel distillation pot during a distillation, and that these gases were largely “gettered” by the sodium distillate.Attempts to eliminate these gases only showed that they were probably not the main cause of the high blanks. The preparation of the sample crucibles from silica tubing was more critical, because the surface of the silica appeared to become reactive to sodium vapour and to adsorb carbon dioxide from the atmosphere if it was touched with bare hands and then ignited. Following the precautions outlined in the Experimental section, it was found possible to obtain blanks equivalent to 1 to 2 p.p.m. of carbon. RECOVERY OF CARBON- graphite and as carbonate) to samples of low-carbon sodium. given in Table IT.:, were satisfactory. The full analytical procedure was checked by adding known amounts of carbon (as The recoveries of carbon, TABLE IV CARBON RECOVERY FROM THE COMPLETE METHOD Form of carbon Oxygen content of sodium, Carbon added, Recoveries, p.p.m.p.p.m. per cent. Graphite . . . . . . 1000 30 to 3000 85 to 95 Carbonate . . . . . . 10 to 20 3 to 100 94 to 9s Graphite . . . . . . 10 to 20 2 to 10 90 to 120 PEIWORMANCE OF THE METHOD- Although these studies have been concerned primarily with sodium, a limited amount of work has indicated that the method is applicable to samples of sodium - potassium alloys containing up to 30 per cent. of potassium. The method has been in routine use for some hundreds of samples of sodium and sodium - potassium alloys over a period of 4 years, and has operated without serious trouble apart from occasional high blanks.Over the past year, the blank level has varied between 0.5 and 5 p.p.m. with an average of 1.5 p.p.m. These blanks are realistic, because the empty crucible follows all stages of the method alongside the sample crucibles. I t has been shown586 SINCLAIR, DRUMMOND AND SMITH that the blanks near 5 p.p.m. were usually caused by contamination during sampling; it is essential that sampling stations are kept scrupulously clean and that strict attention is given to the careful handling of sample crucibles. Duplicate determinations on routine samples have shown that near the 20 p.p.m. level of carbon, the coefficient of variation of the complete procedure is about 10 per cent. All the evidence available to date suggests that the method is probably accurate to within 10 per cent. The operator time for the analysis of 3 samples and 1 blank (or 2 samples and 2 blanks) is about 6 hours. The total elapsed time is about 12 hours. CONCLUSIONS It has been confirmed that distillation is a suitable technique for the separation of sodium from samples for carbon determination, and Walker and France’s procedure for determining free carbon has been extended to determine total carbon, irrespective of its nature. The method has been used with samples as large as 10 g of alkali metal, and hence low levels of carbon down to 1 or 2 p.p.m. can be determined. I t would seem feasible to increase the amount of sample taken and to extend the method to even lower limits should this be required. REFERENCES 1. 2. 3. Miller, H. C., U.S. Patent 2,858,194, 1958. Walker, J. A. J., and France, E. D., Analyst, 1965, 90, 228. Preston, E., and Turner, W. E. S., J . SOC. Glass Techizal., 1934, 18, 182. Reccivcd Janzta~y 31st, 1966

ISSN:0003-2654    

DOI:10.1039/AN9669100582

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

A~talyst, September, 1966, Vol. 91, p p . 587-590 587 The Use of Diphenylcarbazone for the Determination of Microgram Amounts of Lead BY N. TRINDER (Ministry of Agriculture, Fisheyies and Food, National Agricultural A dvisory Service, Kenton Bar, Newcastle upon Tyne 3) The conditions necessary for extracting the crimson diphenylcarbazone - lead complex into xylene from an aqueous cyanide solution have been examined. A procedure is described for the spectrophotometric determination of lead isolated by means of diphenylthiocarbazone. FEW organic reagents have been proposed for the colorimetric determination of very small amounts of lead. Diphenylthiocarbazone (dithizone) has been used almost exclusively since it was introduced by Fischer.l Dithizone was first used as a means of isolating lead from organic material,2 and its extension to colorimetric determination soon f~llowed.~ The nature of dithizone is such that for the determination of lead in complex mixtures it is necessary to adopt a double extraction procedure, first isolating the lead and then determining it with a weaker solution of dithizone.This procedure has the obvious dis- advantage that metals giving a coloured dithizonate at the first extraction may again give a dithizonate at the second extraction unless special precautions are taken. Bismuth is especially troublesome in this respect and, to obviate interference, a preliminary extraction with a diethyldithiocarbamate solution may be neces~ary.~ Nevertheless , no satisfactory complementary reagent to dithizone has so far emerged.Diphenylcarbazone is known to give a red colour with lead,5,6,7 but attempts to use this reaction for the spectrophotometric determination of lead have so far been unsu~cessful.~ 9' This lack of success is probably caused by the number of compounds (for example, iron salts and citrates) that inhibit the development of the lead complex, preventing the use of the reagent on complex mixtures. Diphenylcarbazone is useful, therefore, only for solutions from which interfering agents have been removed and can be considered solely as complementary to an isolating reagent. EXPERIMENTAL In the presence of lead, diphenylcarbazone imparts a bright crimson colour to the solvent layer when a weakly alkaline solution is shaken with an aromatic hydrocarbon, amyl acetate or carbon disulphide.Other metals produce similar colours, but in the presence of cyanide, diphenylcarbazone is virtually specific for lead. The optimum conditions for developing the colour were determined with a Unicam SP600 spectrophotometer and 1-cm light path cuvet tes. CHOICE OF SOLVENT- A number of solvents, in particular benzene, toluene and xylene, were tried, and xylene was found to be the most satisfactory. The blank colour (pale orange) due to the diphenyl- carbazone was minimal with xylene, and this solvent was less objectionable to use than either toluene or benzene. REAGENT STRENGTH- The reagent blank increased arithmetically over the range 0.01 to 0.05 per cent. w/v of diphenylcarbazone in xylene. Under the conditions described in the method (given below) , the optical density at 525 mp was about 0.065 for each 0.01 per cent.of diphenylcarbazone. Maximum production of colour in the presence of lead was at 0.02 per cent. Above this concentration there was no increase in colour due to lead.588 TRINDER: USE OF DIPHENYLCARBAZONE FOR THE [A?ZdySt, VOl. $11 SEXSITIVITY OF REAGENT- The lead complex gave maximum optical density at 525 mp, and the molar extinction coefficient for a 1-cm light path at this wavelength was about 72,000 if the colour was read 15 minutes after development. After 2 hours this had increased to about 74,000 and after 20 hours (overnight refrigeration) to about 82,000, After subtraction of the reagent blank, Beer's law was obeyed over the range of 0.4 to 2.0 pg of lead per ml.The optical density was 0.35 for each pg of lead per ml of solvent when the colour was read after 15 minutes. S;TAHILIT17 OF THE LEAD - DIPHENYLCAKBAZONE COMPLEX- ?'he complex dissolved in xylene is stable for at least 20 hours at 20" C if kept over aqueous potassium cyanide containing an excess of diphenylcarbazone. Once transferred by pipette into a cuvette the complex begins to fade slowly after 5 minutes or more. Readings should, therefore, be taken expeditiouslv after pipetting or the colour should be read in the preparation tube (see below). EFFECT OF POTASSIUM CYANIDE- Maximum optical density of the lead complex was obtained over the pH range 9.5 to 10.4 in the aqueous phase. This represented the addition of 0.25 to 0-5 ml of 20 per cent. potassium cyanide solution to 3 ml of 1 per cent. nitric acid, The value of the reagent blank fell as more cyanide was added, and the addition of 0-35 ml of 20 per cent.potassium cyanide solution was considered to be the best compromise (pH 9.9). There was a progressive reduction in the intensity of the lead complex colour as the pH of the aqueous phase rose above 10.4. EFFECT OF AMMONIA- The procedure outlined below involves the addition of excess potassium cyanide to a weak solution of nitric acid. Some workers might consider this a potential hazard, so the effect of first neutralising the acid with ammonia was studied. It was found that ammonia, in excess, slightly diminished the intensity of the lead complex, but the intensity of the colour was not affected when the acid was just neutralised.1XTERFEIZENC.E DUE TO BISMUTH- In the presence of nitrate or acetate, and in the absence of chloride, up to 10 pg of bismuth per ml of solvent did not reduce the colour due to the lead- diphenylcarbazone complex. At a solvent concentration of 1OOpg of bismuth per ml the bismuth was pre- cipitated in the aqueous layer and some interference with the lead colour occurred. In the presence of nitrate, bismuth from 1 to 100 pg per ml of solvent caused a slight but constant increase in the reagent blank. The optical density due to these amounts of bismuth was 0.025, fading to 0.005 after 2 hours. This increase is thought to arise from an impurity in the reagent, but different batches of diphenylcarbazone have not been tested to confirm this. STABILITY OF REAGENT IN XYLENE- A 0.02 per cent.w/v solution of diphenylcarbazone in xylene stored for 9 months at room temperature in an amber glass bottle gave a constant optical density with 2-0 pg of lead per ml of solvent during this period. The reagent blank, however, rose by 13 per cent. during the 9 months. METHOD APPARATUS- Observations should be made with a Unicam SP600 spectrophotometer or similar instrument. Tubes for the development of the lead - diphenylcarbazone colour must be rinsed with diluted nitric acid (5 volumes of nitric acid, sp.gr. 1.42, to 95 volumes of water) immediately after use. R E AGE N TS- (i) F O R THE ISOLATION OF LEAD- See the report of Analytical Methods Committee of the Society of Analytical Chemistry on thc determination of lead.4September, 19661 DETERMINATION OF MICROGRAM AMOUNTS OF LEAD 589 The following reagent is also required.Dithixone solution, 0.05 per cent. w/v-Dissolve 0.05 g of diphenylthiocarbazone in 100 ml of benzene. Store in a refrigerator above the freezing point of benzene in an amber glass bottle. (ii) I’OK THE DETERMINATION OF LEAD- All reagents, including water, should be free from lead. Nitric acid, 1 per cent. v/v-Mix 1 volume of nitric acid, sp.gr. 1.42, with 99 volumes Bismuth witrate solution-Dissolve 0-023 g of bismuth nitrate, Bi(N0J3.5H,0, in 100 ml Nitric acid reagent-Mix 1 volume of nitric acid, sp.gr. 1.42, 1 volume of bismuth nitrate Diphezzylcarbazone solGtion, 0.02 per cent. w/v-Shake 0.1 g of diphenylcarbazone with Filter through a So. 1 Whatman filter- If a shaker is not available, heat 0.1 g of diphenyl- Potassiz~m cyanide solution-Prepare a 20 per cent.w/v solution in water. Use after Ammonia solution, 20per cent. v/v-Mix 1 volume of ammonia (spgr. 0.88) with 4 volumes of water. of 1 per cent. nitric acid. solution and 98 volumes of water. This reagent contains 1 pg of bismuth per ml. 500 ml of xylene in a vibratory shaker for 1 hour. paper into a dry amber glass bottle. carbazone with 500 ml of xylene on a water-bath until all the solid material has dissolved. 2 days or low results may be obtained. of water. Standard lead solzttiom- A. and dilute to 1 litre. B. 10 pg of lead). C. and dilute to 100 volumes with 1 per cent. nitric acid (1 ml contains 2pg of lead). I). acid (1 ml contains 2 pg of lead).Dissolve 1.60g of lead nitrate crystals in water, add 10ml of nitric acid (sp.gr. 1.42) Dilute 1 volume of solution ,4 to 100 volumes with 1 per cent. nitric acid (1 ml contains Mix 1 volume of bismuth nitrate solution with 20 volumes of standard lead solution €3 Dilute 20 volumes of standard lead solution B to 100 volumes with 1 per cent. nitric Xylene-This should be suitable for histological purposes and free from sulphur. PROCEDURE- Isolation of lead-Extract the lead into 0.05 per cent. dithizone solution under conditions similar to those described under method A in the Report of the Analytical Methods Com- mittee of the Society for Analytical Chemistry on the determination of lead.4 Shake the solution vigorously, discard the aqueous layer, and spin the benzene layer containing the lead dithizonate in a centrifuge at 3000 r.p.m. Transfer the cleared benzene to a funnel containing a small cotton-wool plug. Transfer by pipette a suitable volume of the filtered benzene (containing up to 8pg of lead) to a dry 15-ml centrifuge tube.Determination of lead i n the absence of bismuth-Add 4 ml of 1 per cent. nitric acid. Shake the tube vigorously, then spin it in a centrifuge for 1 minute at 3000 r.p.m. Draw off the benzene layer to waste. Transfer by pipette 3 ml of the aqueous layer into a centrifuge tube. Add 0.35 ml of 20 per cent. potassium cyanide solution to the tube. (Alternatively, add 0.15 ml of 20 per cent. ammonia solution, mix, and add 0.2 ml of 20 per cent. potassium cyanide solution.) Mix the solutions and add 3 ml of 0.02 per cent.diphenylcarbazone solution. Spin the solution in a centrifuge for 1 minute at 3000 r.p.m. After a standard interval of time, transfer the solvent layer by pipette into a 1-cm cuvette and read the optical density at 525 mp within 5 minutes. Compute the lead concen- tration from a calibration graph of 1.0 to 6-0pg of lead by using standard lead solution D. Determifiation of lead in the pyesence of bism5tth-Either read the optical density 2 hours after preparing the lead - diphenylcarbazone complex, or use 4 ml of nitric acid reagent (containing bismuth) to remove the lead from the benzene layer instead of 4 ml of 1 per cent. nitric acid. Read the optical density 15 to 30 minutes after development of the colour. Prepare a calibration graph with the standard lead solution C instead of solution D.Shake the tube vigorously 40 times.590 TRINDER [Afzazyst, Vol 91 DISCUSSION It is necessary to spin the solution in a centrifuge and filter the benzene layer containing the lead dithizonate to prevent small amounts of citrate remaining in the solvent phase after extraction. Full recovery of lead was not obtained until this step was introduced. The procedure adopted for the determination will depend on the time factor, the possi- bility of bismuth being present and the reactivity to bismuth of the batch of diphenylcarbazone used. At least 9 pg of bismuth per ml of solvent can be present if the method for the deter- mination of lead in the presence of bismuth is used. Precise details of the extraction of the lead dithizonate are not given because the procedure will vary according to the nature of the material under test-indeed, in some circumstances the use of benzene as the solvent for dithizone may not be suitable, and it may be necessary to investigate the possibility of some other solvent, e g . , carbon tetrachloride. REFERENCES 1. Fischer, H., Angew. Chem., 1929, 42, 1025. 2. 3. 4. 5. Cazeneuve, &I. P., C.R. Hebd. SLa+zc. Acad. Sci., Paris, 1900, 130, 1478. 6. 7. Allport, N. L., and Skrimshire, G. H., Analyst, 1932, 57, 440. Fischer, H., and Leopold, G., Angew. Chem., 1934, 47, 90. Analytical Methods Committee, Analyst, 1959, 84, 127. Vasserman, E. S., and Suprunovitsch, I. B., Ukr. Khim. Zh., 1934, 9, 330; Brit. Chew. ,4bstv., A , Evans, B. S., A.rzalyst, 1939, 64, 2. 1935, 352. ICeceivccl 3 l c r ~ t ZUh, 1986

ISSN:0003-2654    

DOI:10.1039/AN9669100587

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

Analyst, September, 1966, Vol. 91 591 SHORT PAPERS Polarographic Determination of 0.01 to 0.10 per cent. of Bismuth in Lead BY J. BASSETT AND J. C. H. JONES* (Chemistry Department, Woo1wiCk Polytechnic, London, S. E . 18) THE accurate determination of low concentrations (0.01 to 0.10 per cent.) of bismuth in lead is of importance to manufacturers, because the presence of this element can affect various properties of lead, e.g., corrosion resistance and creep characteristics. The need for a rapid, reliable method prompted the present study of the application of polarography to this determination. Several polarographic procedures have been reported in which the bulk of the lead is removed by precipitation either as the sulphate1g2 or as the ~ h l o r i d e . ~ , ~ These methods are lengthy and, as our own studies of the removal of lead as lead sulphate have indicated, may entail the loss of bismuth due to its adsorption on the precipitate.Pfibil and Matyskas have described an amperometric method for the determination of bismuth in lead that does not require any prior chemical separation. A similar base electrolyte of lead nitrate and nitric acid is used in the rapid polarographic method described in the present paper. The lead sample is dissolved in nitric acid, sodium tartrate added and the pH adjusted to between 1.1 and 1.3 by the addition of ammonia. The polarographic wave obtained (E = -0.01 volts, against an S.C.E.) with an aliquot of the solution is due to copper and bismuth. The addition of EDTA to a second aliquot complexes bismuth so that the polarographic wave now obtained is due to copper only.The difference in wave heights is proportional to the concentration of bismuth. METHOD APPARATUS- A Tinsley single-unit pen recording polarograph (Mark 19) was used. All pH measurements were made with a Pye universal pH meter. The rate of flow of mercury and the drop time of the capillary were 4-131 mg per second and 3.2 seconds, respectively. REAGENTS- All reagents should be of analytical-reagent grade. Nitvic acid, 50 per cent. v/v, aqueous-Prepare from concentrated nitric acid, sp.gr. 1.42. Nitvic acid, 20 per cent. v/v, aqueous-Prepare from 50 per cent. v/v aqueous nitric acid. Sodium tartrate solution, 25 pev cent. w/v, 'aqueous. Gelatin solution, 0.25 per cent. w/v, aqueous. Disodiuvn ethylenediarninetetra-acetate (EDTA ) .Puve lead-Obtainable from Associated Lead Manufacturers. Puve bismuth-Obtainable from Johnson, Matthey & Co. Ltd. Standavd bismuth solution-Dissolve 0-5000 g of pure bismuth in 200 ml of 50 per cent. nitric acid solution, and make up to 500 ml with water. 1 ml E 0.0010 g of bismuth. PROCEI)ITRE- - To 5 g o f sample in a 100-ml beaker add 40ml of 20 per cent. nitric acid and heat until dissolution of the sample is complete. Cool the solution, add 2-0 ml of sodium tartrate solution and adjust the pH to between 1-1 and 1.3 by the dropwise addition of concentrated ammonia from a burette (approximately 3 ml is required), The solution should be stirred vigorously during this stage to dissolve the white precipitate that is initially formed. Transfer the solution to a 50-ml graduated flask, add 2.0 ml of 0.25 per cent. gelatin solution and dilute to the mark with water.* Present address : Associated Lead Manufacturers, 7 Wadsworth Road, Greenford, Middlesex.592 SHORT PAPERS [AnaZyst, Vol. 91 By pipette, transfer 20 ml of the solution to a polarographic cell and de-oxygenate by bubbling hydrogen through i t for 10 minutes. Record the polarogram (A) from $-0.20 to -0.30 volts against an S.C.E.; the reduction of lead ions begins a t -0.30 volts against an S.C.E. Dissolve 0-05 g of EDTA in a second 20-ml aliquot, de-oxygenate the solution and again record the polaro- gram (B) from + O m 2 0 to -0.30 volts against an S.C.E. Measure the wave heights, h, and h,, obtained a t a half-wave potential of -0.01 volts against an S.C.E.in polarograms A and €3, respectively, and find the bismuth concentration from the difference in wave heights (hl-lz2). C.\I.,IBRATION- Add 0.50, 1-0, 2.0, 3-0, 4.0 and 5.0 ml of standard bismuth solution to separate 5-g samples of pure lead contained in 100-ml beakers (this corresponds to 0.01 to 0.10 per cent. of bismuth). Prepare the solutions and record the polarograms in the absence of EDTA as described under Procedure. Plot wave heights (Ei = -0.01 volts against an S.C.E.) against concentration of bismuth. RESULTS The method was applied to a number of synthetic samples, each containing 5 g of pure lead and a small amount of added impurity. The results (Table I) show that no interference occurs in the presence of these other elements which are normally found in commercial grades of lead.TABLE I ~ ~ E T I < R M I S A T I O N OF BISMUTH I N THE PKESEXCI': O F OTHER ELEMENTS impurity adclcd 0.060~0 Copper. . 0.010% Copper. . 0.050% Silver . . 0.050y0 Iron . . 0.050% Zinc . . 0.050% Cadmium O.OIO~o Tellurium 0.010% Selenium 0.0507& Nickel . . 0.050y0 Arsenic 0.050% Tin . . 0-0500;, Antimony Bismuth Bismuth added, found, Form of added impurity per cent. per cent. . . Copper(I1) chloride . . . . * . . . . . lron(m) chloride . . . . . . . . . . . . Silver nitrate . . . . . . . . . I . . Zinc nitrate . . . . . . . . . . . . Cadmium nitrate . . . . . . . . . . Tellurium dissolved in nitric acid . . . . . . Selenium dissolved in nitric acid . . . . . . Nickel chloride .. . . . . . . . . Lead sample containing 0-05y0 arsenic . . . . Lead sample containing 0.05% antimony. . . . Lead sample containing 0.05% tin. . . . 0.060 0.060 0.050 0.050 0.050 0.050 0-050 0.050 0-050 0.050 0.050 o.ot50 0.059 0.060 0.050 0-051 0.050 9.050 0-048 0.048 0.052 0.050 0.053 0.051 Relativc error, per ccnt. -2 0 0 4-2 0 0 -4 -4 4- 4 0 +6 +a The reproducibility of the method was investigated with 5-g samples of pure lead to which the equivalent of 0.05 per cent. of bismuth had been added as a known volume of standard bismuth solution. The standard deviation calculated from the results of 11 determinations was 0-002 per cent. DISCUSSION With a con- ventional polarograph, the lower limit of bismuth concentration that can be determined is about 0.005 per cent. The use of a cathode-ray polarograph would probably enable the method to be applied a t lower concentrations of bismuth, e.g., 0.001 per cent., but the analysis of samples containing a high copper-to-bismuth ratio (e.g., 0.10 per cent. of copper and 0.001 per cent. of bismuth) would not be satisfactory by this method as bismuth is found from the difference in wave heights. We thank Dr. A. I. Vogel, Head of the Chemistry Department, Woolwich Polytechnic, for his interest, and one of us (J.C.H. J.) thanks the Directors of Associated Lead Manufacturers for enabling him to undertake the present research. REFERENCES The method described is rapid and can be completed in about 30 minutes. 1. Zotta, M., Gazz. Chimico Ital., 1945, 78, 143. 2. 3. 4. 5. Cozzi, D., Analytira Chim. Ada, 1950, 4, 204. Pletenev, S. A., Aref'eva, T. V., Tal, E. M., and Dubovitskaya, E. I., %nu. Lab., 1946, 12, 38. Conradi, G., and Kopanica, M., Chemist Analyst, 1963, 52 (l), 11. Pribil, R., and Matyska, B., ChemickL Listy, 1950, 305. Reccivcd Febr7iary Znd, 1966

ISSN:0003-2654    

DOI:10.1039/AN9669100591

出版商:RSC    

年代:1966

数据来源: RSC

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September, 19661 SHORT PAPERS 593 The Photometric Determination of Excess of Cadmium in Cadmium Oxide BY IT. J. NORMAN (Azistralian Defence Scientific Service, Defence Standards Laboratories, Department of Supply, -1 delaide) CADMIUM oxide is considered to be a degenerate n-type semi-conductor,l in which the donors arise either from impurities or excess of interstitial cadmium.2 From the results of precision measurements of lattice parameters of samples of doped cadmium oxide, Cimino and Marezio:3 inferred an excess of cadmium of the order of 0.01 per cent. A photometric method developed by the author4 for determining the excess o f zinc in zinc oxide has been applied to the determination of excess of cadmium in cadmium oxide. The method, which is based on the reduction of dichromate, gives good reproducibility, and is sensitive to 0.1 p.p.m.of excess of cadmium by weight. METHOD The apparatus and reagents required, and the calibration and analytical procedure used for determining excess of interstitial cadmium in cadmium oxide are identical with those specified in the author’s paper4 for determining excess of zinc in zinc oxide except for the following motli- fications- (1) Use 10 ml of acid mixture in place of 20 ml. (2) Add 4.0 g of cadmium oxide instead of 5.0 g of zinc oxide. (3) In the preparation of the blank solution (iii), dilute the 10 ml of acid mixture with 25 1111 of water before adding the 4.0g of cadmium oxide. NOTE- For samples of cadmium oxide in which the excess o f cadmium exceeds 30 p.p.m., a pro- portionately smaller sample weight may be taken, provided that the amount of acid mixturc used is correspondingly reduced.RESULTS The results of analysis of three samples of cadmium oxide by this method are shown in ’I’able I. Samples A and B were analytical-reagent grade cadmium oxide. Sample C was prepared by dissolving high purity spectrographic grade cadmium metal in analytical-reagent grade acid and precipitating it as the carbonate. The cadmium carbonate was ignited for 5 hours at 600” C. TABLE I RESULTS BY THE PROPOSED METHOD Optical density of blank solution . . = 0.980 Optical density of “ignited reference” . . = 0.096 Nct optical density . . .. . . = 0-884 (equivalent to 25 ml of 0.0001 N dichromatc) Reference, Equivalent Colour, Equivalent Excess of net optical dichromate, net optical, dichromate, (a - b), cadmium,* Sample density a ml density bml ml p.p.m. A (4.0g) 0.740 21.0 0-064 1-9 19.1 26.9 0.746 21.2 0.091 2-6 18.6 26.2 0.742 21.1 0.079 2.3 18.8 26.5 0-812 23.1 0.44 1 12.5 10.6 14.9 0-799 22.7 0.432 12.3 10.4 14.7 0.879 24-9 0.176 5.0 19.9 56.1 0.885 25-0 0.205 5.9 19.1 53.9 B (4.0 g) c (2.0 g) This paper is published by permission of the Chief Scientist, Australian Defence Scientific Service, I3epartment of Supply, Melbourne, Victoria, Australia. REFERENCES 1. 2. 3. 4. Received Janiiavy 17th, 1 %ti * For a sample weight of 4.0 g of cadmium oxide, the excess of interstitial cadmium, in p.p.m. by Lamb, E. F., and Tompkins, F. C., Trans. Faraday Soc., 1962, 58, 1424. Colin, Y., and Fourrier, C., C.R. Hebd. Se‘a?zc. Acad. Sci., 1962, 254, 4453. Cimino, A., and Marezio, M., Physics Chem. Solids, 1960, 17, 57. Norman, V. J., Analyst, 1964, 89, 261. weight, is given by the expression 1.41 (a-b).

ISSN:0003-2654    

DOI:10.1039/AN9669100593

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

594 SHORT PAPERS [Analyst, Vol. 91 The Refractive Index of Aqueous Perchloric Acid BY J. R. McLEAN AND G. S . PEARSON (Ministry of Aviation, Rocket Propzdsion Establishment, Westcott, AyZesbury, Bucks) PEKCHLORIC acid (nominal 72 per cent.) is used in laboratory experiments at this Establishment in research into the combustion mechanism of solid propellents containing ammonium perchlorate. 192 The acid used is the commercially available analytical-reagent grade, which is specified to be 71-0 to 73-0 per cent. w/w. It is necessary to check each bottle of acid supplied to ensure that it does contain 71.0 to 73.0 per cent. acid, as it has been reported3 that nominal 72 per cent. acid can be as low as 65 per cent. Conventional analysis by titration is inconvenient because it requires special care, as 72 per cent.perchloric acid is hygroscopic. Refractive-index measurements offer a rapid and convenient check on the perchloric acid concentration. Values of the refractive index are available in the literature of acid concentrations from 0 to 20 per cent.,4 and from 50 to 70 per cent.5 However, a marked discrepancy was observed between the present measurements and the literature values over the 50 to 70 per cent. range, hence the refractive index was determined for the complete range from 0 to 72 per cent., and the reliability of the present results established by using perchloric acid from several sources. EXPERIMENTAL Yerchloric acid was obtained from 5 different sources: Hopkin and Williams Ltd. (Esses, England), AnalaR grade 72 per cent.; Eastman Kodak Co.(Rochester, N.Y.), 72 per cent.; Merck AG. (Darmstadt, Germany), guaranteed reagent, 70 per cent.; Merck Suprapur, 70 per cent. ; and G. E'. Smith Chemical Co. (Columbus, Ohio), C.P. vacuum distilled, 72 per cent. The Hopkin and Williams acid was diluted with de-ionised, distilled water to make up solutions of nominal concentration of 10, 20, 30, 40, 50, 60, 62.5, 65, 67.5 and 70 per cent. of acid. These solutions were analysed by titration against N sodium hydroxide, with phenolphthalein as indicator. Titration against 0 . 1 ~ sodium hydroxide was not satisfactory and gave consistently low values. This was attributed to weighing errors and water absorption. The refractive index was measured on an Abbi: refractometer maintained at 20" and 30" C.The refractometer was washed and allowed to dry thoroughly between readings. The refractive indices of AnalaR grade chloroform and carbon tetrachloride, and also of de-ionised, distilled water were determined at the same time as the acid refractive indices. RESULTS AND DISCUSSION The refractive indices for a range of perchloric acid concentrations from 0 to 72 per cent. (Hopkin and Williams acid) are presented in Table I, together with the values obtained for the TABIS I REFRACTIVE INDICES OF AQUEOUS PERCHLORIC ACID, (Hopkin and Williams Ltd. AnalaR grade) Refractive index Per cent. w/w 0.00 9-73 20.05 30.75 40.3 1 50.28 60.08 62-81 64-00 68.52 70-06 72.62 Chloroform* . . . . Carbon tetrachloride* . r 20" c 1.3330 1.3395 1-3470 1-3580 1.3680 1.3813 1.3953 1-4034 1.4054 1.4129 1-4151 1.4190 1.4445 1.4601 30" C 1.3320 1.3381 1.3452 1.3559 1.3665 1.3800 1.3960 1.4010 1.4028 1.4103 1.4130 1.4159 1.4390 1.4450 * AnalaR specifications of n:o for chloroform and carbon tetrachloride are 1.4440 to 1.4450, and 1.4600 to 1.4610, respectively.September, 19661 SHORT PAPERS 595 refractive indices of water, chloroform and carbon tetrachloride.concentrated acid from the five sources are presented in Table 11. line plot. The refractive indices of the These give a good straight TABLE I1 REFRACTIVE INDICES OF CONCENTRATED PERCHLORIC ACID Per cent. w/w Refractive (by analysis) index a t 20” C Source 72.59, 72.65 1-4 193 Hopkin and Williams AnalaR grade 72.55, 72-59 1.4193 Eastman Kodak 69.52, 59.52 1.4153 Merck Suprapur 69-88, 69-88 1.4156 Merck guaranteed reagent 70.68, 70.72 1.4170 G.F. Smith Chemical Co. ‘The literature values4 from 0 to 20 per cent. are in reasonable agreement with those reported here. However, those obtained by Smith and Lamplough5 (also made with an Abb6 refractometer) with 50 to 70 per cent. acid are higher than the values we obtained by about 0.5 per cent., corres- ponding to a change of acid concentration of 4.5 per cent. in the range 50 to 70 per cent. It is concluded that the previous values reported5 for the refractive index of 50 to 70 per cent. acid are in error. This error may have arisen from an impurity in the acid used, or an error in the titration of the acid. In the present work, perchloric acid from 4 widely separated sources has been used and consistent results have been obtained. Further, refractive indices measured for chloroform, carbon tetrachloride and water are in excellent agreement with literature values, thus showing that the refractometer was not displaying a systematic error.I t is therefore believed that the present results are reliable and can be used as the basis of a rapid analytical method for checking the concentration of aqueous perchloric acid. It is to be noted that the cement used in the refractonieter must not be a litharge - glycerine cement, because this produces a dangerously explosive compound with perchloric acid.6 An inert cement such as polythene must be used. ~XEFERENCES I . The Combustion Institute, Pittsburgh, Pennsylvania, 1965, p. 1365. 2. Cummings, G. A. McD., and Pearson, G. S., Combust. Flame, 1964, 8, 199. 3. 4. 5. 6. Cummings, G. A. McD., and Hall, A. R., “Tenth International Symposium on Combustion, 1964,” Levy, J. B., J . Phys. Chem., 1962, 66, 1092. Wagner, “Tabellen zum Eintauchrefraktometer,” Fourth Edition, VEB Carl Zeiss, J ma, 1955. Smith, G. F., and Lamplough, C. E., Chemist Analyst, 1952, 41, 7. 9. Saf. Summ. Ass. Brit. Chem. Mfrs, 1962, 33, 20. Received F;ebvirnv~ 3rd, 1966

ISSN:0003-2654    

DOI:10.1039/AN9669100594

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

September, 19661 SHORT PAPERS 595 Semi-quantitative Determination of Organophosphorus Insecticides by the Ring-oven Technique with Preliminary Thin-layer Chroma tograph y BY I. PEJKOVIC-TADIC, M. B. CELAP, T. J . JANJIC (Imtitute of Chemistry, Faculty of Science, University of Belgrade, 16 Studentski fvg, Relgvadc) AND S . LJ. VITOROVIC (Iitsfitute for -4pplication of Nuclear E7tergy in Agriculture, Veferinary and Foresfry, Zemizii, 15 Karanjska, Yugoslavia) THIS paper describes a method for the semi-quantitative determination of four organophosphorus insecticides in mixtures : Raytex (fenthion), diazinon, Guthion (azinphosmethyl) and malathion. The insecticides were first individually determined with the Weisz ring oven and the following mean deviations were obtained: Baytex, 1-8 per cent.: diazinon, 3-9 per cent. : Guthion, 3.2 per cent.; and malathion, 3.4 per cent. (Table I).596 SHORT PAPERS [Analyst, Vol. 9 L TABLE I DETERMINATION OF INDIVIDUAL INSECTICIDES ON THE RING OVEN Baytex 7-Y Present, Found, Pg Per 4 Ilg Per P' 2.50 2.50 2.50 2.50 2-50 2.66 3.00 2.95 3.00 3-00 3.00 3.08 Diazinon ---L- 7 Present, Found, PLg Per P' PFLg Per Pl 25.0 25.0 25-0 26.6 25.0 26.6 30.0 28.3 30.0 30.0 30.0 31.5 Guthion /--A_--- 7 Present, Found, 2-50 2.66 2.50 2.66 2-50 2.50 3.00 3.00 3.00 3.10 3-00 3.10 PLg Per P1 CLg Per Malathion r-.-L- 7 Present, Found, Pg Per 4 P.g Per P1 6.00 5.00 5.00 5-16 5.00 5.32 6-00 6-66 6.00 8-00 6.00 5.66 Mixtures of the four insecticides were then analysed. After chromatography of their solution on silica-gel G layers, the separated insecticides were scraped into a sintered-glass funnel mounted above the oven, washed into the ring zone and determined as above.The deviations from the calculated values mere as follows : Baytex, 5.5 per cent. ; diazinon, 5.5 per cent. ; Guthion, 5.6 per cent.; and malathion, 6.1 per cent. (Table 11). TABLE I1 ANALYSIS OF INSECTICIDE MIXTURKS Concentration of insecticide present, pg per pl Mixture Baytex Diazinon Guthion hlalathion 2-50 25.0 2.50 5.00 I 2.50 25.0 2.50 5.00 2.50 25.0 2.50 5.00 3-00 30.0 3.00 6.00 I1 3.00 30.0 3.00 6.00 3.00 30.0 3.00 6-00 I A - Concentration of insecticide found, pg per pl Baytex Diszinon Guthion Malathion A I 7 _-____ 2.66 24. 1 2.25 4.50 2.66 22-5 2-33 5.00 2-66 24.1 2.50 4.50 2-83 28-3 2.83 6-32 2-91 31.6 2.83 5.66 3-1 6 31.6 2-83 5.66 EXPERIMENTAL I< I N G -OVEN METH o I) - Standard scales were prepared by spotting 1, 2, 4, 6, 8 and 10pl of stock solutions of the appropriate insecticide in chloroform (Baytex, 0.1 per cent.; Guthion, 0.1 per cent. ; malathion, 0.2 per cent. ; and diazinon, 1 per cent. w/v) on to the 5.5-cm diameter filter-paper (Schleicher and Schiill No. 58g2) by means of a 10-pl micro-pipette. The substance was then washed with 0.5 ml of chloroform. The paper was air-dried, sprayed with palladium(I1) chloride reagent1 (a 0-5 pei- cent. aqueous solution acidified to pH 3 with two to three drops of concentrated hydrochloric acid) and washed with two 0.5-ml portions of 0.05 N hydrochloric acid. After thorough washing with water, the paper was dipped into ammonium .sulphide solution for 30 seconds and dried in an oven a t 105" C for 10 minutes.Stable brown rings on a straw-coloured background were obtained. Tn the same manner 3 coloured rings were prepared for each insecticide to be determined and their intensities compared with those of the standard scale; the amounts present (Ca) were then calculated by the expression- 1zy Ca = CS- %a where C, is the concentration of the standard solution, na the volume of sample solution, and ns the volume of standard solution used in the matching ring. COhIBIN.\'TION OF THE RING OVEN WITH THIN-LAYER CHR0M.~TOGRAPHl7-- A micro-pipette was used to transfer 1, 2 and 3p1 of chloroform solution of the insecticide mistnre I or T T to an air-dried 0.2-mm thick silica-gel G chromatoplate (20 x 20 >( 0.5 cm).The mobile phase, consisting of hexane and acetone (4 + l ) , was allowed about 30 minutes for a frontal migration of 14 cm, and the plate was then taken out of the jar (32 x 20 x 10 cm). At the margin of the plate a guide mixture containing 2 p1 of the mixture I or I1 was run in parallel andsprayed with palladium(I1) chloride reagent. The R, values were: diazinon, 0.50; Baytex, 0-41 ; malathion, 0.2'3; and Guthion, 0.14. The areas of the samples were lightly marked with a spatula and they werc then scraped quantitatively from the plate into the funnel (porosity G4). Each lot of scrapingsSeptember, 19661 SHORT PAPERS 597 was washed with about 1 ml of chloroform on to the round filter-paper and the insecticide deter- mined as above. The standard rings were obtained by carrying aliquots of solutions of the individual insecticicles through the same chromatographic treatment. RESULTS A mixture of organophosphorus insecticides Raytex, diazinon, Guthion and malathion was analysed by using thin-layer chromatography in combination with the Weisz ring oven. The determinations performed with 10 to lOOp,g o f the insecticide had a deviation of *5.6 per cent. from the calculated value. REFERENCE 1. I%iumlcr, J . , and Ilippstcin, S., Hrlv. Cliiin. Actn, 1961, 44, 1162. Received Noveiizbev 26tl1, 1965

ISSN:0003-2654    

DOI:10.1039/AN9669100595

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

September, 19661 SHORT PAPERS 597 Comments on “The Effect of Nitrilotriacetic Acid Impurity on the Stnndardisation of Solutions of Ethylenediaminetetra-acetic Acid” BY IC. G. MONK ( U. K..4 .E..1., .-I tonaic W e u p o m Research Establishment, A Ider?nasto)i, Bevkslzire) THE observations reported in the paper concerned’ are of great importance to those people working with EIITA titrations, and it is possible that much of the large amount of work published on the subject over the last 15 years has been affected, to some degree, by the presence of unknown amounts of NTA in the EDTA used. Unfortunately, the paper contains certain errors and it is the purpose of this note to draw attention to them in the hope of avoiding future confusion. The logK’s and logK,’s a t pH 19 (KH is the conditional stability constant), which are of relevance to the present discussion, are listed below.They are all taken or calculated from results compiled by Wilson and Wilson.2 Complex LogIY LO~KII at pH 10 Zinc - EDTA . . . . . . . . 16.5 16.0 Zinc - NTA . . . . . . . . 10.6 10.4 Zinc - Solochrome Black T . . . . - 11.4 Cadmium - EDTA . . . . . . 16.5 16.0 Cadmium - NT-2 . . . . . . 9.8 9-6 I t is clear that the logKH’s of the NTA and EDTA complexes are sufficiently different t o produce the two inflections in a potentiometric titration curve of zinc or cadmium that the authors have observed. However, the authors’ assumption, a t the bottom of p. 212, “that the two successive end-points are due to EDTA and NTA, respectively,” is clearly wrong. The first end- point corresponds to the complexation of the last traces of metal ion by the total EDTA and NTA added.However, because EDTA gives the more stable complex, the shape of the inflection is governed by the NTA - metal ion equilibrium, and the first end-point is essentially due to NTA. Further titration results in decomposition of the metal - NTA complex by EDTA, the second inflection corresponding to the completion of this process, a t which stage all the metal is present as the EDTA complex. The second inflection is therefore an EDTA end-point, the shape of the curve being modified by the presence of some NTA. The titration is analogous to that of a strong base by a mixture of strong and weak acids. Calculation of the molarity of the solution from the volume used up to the first end-point gives the total NTA and EDTA concentration, while the concentration of EDTA alone may be calculated from the total volume used up to the second inflection.Deductions by the authors on pages 213 and 215 concerning titrations with visual indicators are also in error as they are based on the erroneous conclusions from the potentiometric titrations. In the authors’ Fig. 1, the ordinate y is equal to- Complexometric normality of solution found by titration against metal M Complexometric normality of solution found by titration against zinc a t pH 10598 SHORT PAPERS [Analyst, Vol. 91 Values of y greater than 1 can only be the result of a greater response of the indicator to NTA in the titration of M than in the titration of zinc at pH 10.It will be noticed that y is, in fact, greater than 1 for most of the metals titrated, and is particularly high for bismuth and cadmium. If the authors’ contention were true that Solochrome Black ‘I‘ detects the EDTA end-point in the titration of cadmium and the NTA end-point in the titration of zinc, then values of y for cadmium would be less than 1 and the graph would slope downward from left to right. The values of y may be compared with the ratio- Total (EDTA + NTA) normality of solution = Y __ EDTA normality of solution If EDTA (molecular weight, 372.2) contains x per cent. of NTA (molecular weight, 191.1), The corresponding values of x, i’ and 3’ in the titrations of bismuth and 100 + 0 . 9 5 ~ . 100 - x then Y = cadmium are given below. x . . .. . . 0.26 0.60 0.75 1.00 . . . . 1.0049 1.0098 1.0147 1.0197 1 (bismuth) . . 1.0041 1.0095 1.0140 1.0172 v (cadmium) . . 1-0048 1.0089 1.0134 1.0169 The maximum value attainable by y a t each level of x is represented by Y , and would occur if the precise NTA end-point were being detected in the titration of M and the precise EDTA end-point were being detected in the titration of zinc a t pH 10. In fact, these figures do show that y approaches Y quite closely in the titration of bismuth, and somewhat less so in the titration of cadmium. It is clear, therefore, that catechol violet is an effective indicator for NTA in the titration of bismuth, that Solochrome Black T does not respond appreciably to NTA in the titration of zinc a t pH 10, and that the latter indicator does respond fairly well to NTA in the titration of cadmium.In the penultimate sentence of the Discussion, therefore, “EDTA” should be replaced by “NTA,” and vice z‘ersu. All the above deductions have been checked by titrations with NTA alone. The bismuth end-point obtained by using catechol violet is nearly as good with NTA as with EDTA. At pH 10, the titration of cadmium with NTA, with Solochrome Black T as the indicator, gives an end-point that is not very good, but which could probably be detected with a precision of 1 to 2 per cent. under optimum conditions. With zinc, under the same conditions, no end-point at all occurs; the solution becomes progressively bluer as excess of NTA is added, but only by virtue of mass-faction. Even with a several-fold excess of NTA the colour retains a violet tinge. This is to be expected, as the first set of figures shows that the complex between zinc and Solochrome Black T is more stable than that with NTA. The stability constant of the cadmium - Solochrome Black T complex is not available, but we may infer that i t is considerably less than that of the cadmium - NTA complex. 12EFERENCES 1. 2. Farrow, R. N. P., and Hill, 12. G., AIzaZyst, 1965, 90, 210. Wilson, C. L., and Wilson, D. W., “Comprehensive Analytical Chemistry,” Elsevier Publishing Co., Received Decembev 12th, 1965 Mr. K. N. P. Farrow and Mr. A. G. Hill agree with Mr. Monk’s comments, but feel that they do not Amsterdam, London, New York and Princeton, 1960, Volume lB, pp. 167 and 169. affect the main aspect of the paper.

ISSN:0003-2654    

DOI:10.1039/AN9669100597

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

598 SHORT PAPERS [Analyst, Vol. 91 A Simple Multi-purpose Titrimeter BY W. JENNISON AND &I. L. CLARK ( U . F<.A .1<.-4 ., -4 nalyfical Group, Dounreay Exfierimenfa1 Reactor Establishment, Thurso, Caithness, Scotland) AN inexpensive titrimeter has been designed for dead-stop, constant-current, photo-electric and potentiometric titration with any electrode system except glass. This instrument may also be a general-purpose galvanometer. Although of simple construction, the design may be of interest to others as the total cost of the components is less than &lo, and the instrument can be built in a few hours. There is negligible short-term drift and a minimum of maintenance is required. The batteries used have shelf-life and no fault has developed after two years of continuous use.September, 19661 SHORT PAPERS EXPERIMENTAL DESCRIPTION OF INSTRUMENT- 599 Two transistors are arranged as a common-emitter difference-amplifier mounted in an alu- minium block and are so matched that they are independent of the resistance of the source to be measured.This amplifier has an input resistance of about 1.2 megohms for voltage measurement and 25,000 ohms for current measurement. A maximum sensitivity of 1.0 volt or 1.0 pA for full-scale deflection is obtained, but sensitivity controls that are normally off can be used to shunt the amplifier as required (Fig. 1). For calibration purposes, a voltage derived from B4, KG and R7 can be fed through R3 to the detector input by depressing the push-switch (PS). A mark inscribed on the meter a t 81 per cent.of full-scale deflection allows the detector to be set up to read 0 to 3 PA or 0 to 1-25-volt full scale. Five ranges are provided by the selector- switch and, when not in use, this switch is left in the “off” position, the “Set-mV” potentiometer a t zero, the “Set-scale” potentiometer a t maximum resistance, and the cell terminals disconnected. Set zero RI$ ~ Scale $R2 b il TI T 2 ’ Sensitivity control Scnsitivity control 0 .-- / Off Photo-electric Constant voltage Constant current Fig. I . Iliagram showing circuit for instrument I’H OTO-T< LE CT R IC TIT I3 AT ION- Lincarity of photocell response is normally unimportant in this type of titration, and the input resistance o f the detector is varied in inverse proportion to the light falling on the cell.The selector-switch is turned to the “Photo-electric” position and a photo-voltaic-cell assembly with filter is connected. With the cell disconnected, the “Set-zero” potentiometer is adjusted to give zero on the meter scale. The cell is then connected, and the meter deflection is adjusted to a suitable value by the sensitivity controls. If light transmission through the titration solution is expected to rise a t the end-point, the controls should be adjusted to give a meter deflection of 25 per cent. o f full scale. Conversely, if the transmission is to fall, the meter is set to full-scale deflection. A titration may now be performed.600 SHORT PAPERS [Analyst, Vol. 91 TITRATION AT CONST.\NT vor2*r.kGE, DEAD-STOP TIT~L~TION- With the selector-switch in the “Constant voltage” position a known potential of 0 to 125 millivolts is impressed across the input terminals in series with the detector.The “Set-zero” potentiometer is adjusted, and the cell terminals are connected to the instrument. For dead-stop titrations, the sensitivity controls may be used to set the meter needle to full scale, whereas, in amperometric titrations of the “kick-off” type the sensitivity controls are switched off. The titrations may now be performed while observing the change in current between additions of titrant. ‘rITI2,iTION -\T C0NST.INT CURRENT (POLARISED SLECTR0DES)- With the selector-switch in the “Constant-current Set” position the push switch is depressed and the meter needle is adjusted to give full-scale deflection by using the “Set-scale” potentiometer.The push-switch is released, the cell containing the solution to be titratecl is connected across the instrument input terminals, and the meter zero is re-set. Finally, the selector-switch is moved to the “Constant-current Read” position, a polarising current of 2 ,uA flows through the cell, and the titration may be performed while observing the potential differences between additions o f titrant. The meter reads 0 to 1.0 volt. P O T EN T I 0 MET It I C TIT RAT I 0 N S- The selector-switch is put to the “Potential” position, the meter necdle is set on zero, and If a scale of 0 to 2.5 volt is required, the sensitivity After calibration the appropriate electrode combination the meter calibration is made as above. controls can be adjusted accordingly.is connected across the input terminals and the titration is performed. Appendix COMPONENTS LIST H11 = 1.5-volt Exide T.20 batteries = 15-volt Exide DH.521 battery -= 1.35-volt Mallory RM.3K Mallory cell B, l34 M = 0 to 25 microammeter (internal resistance 1500 ohms) Set zero = 1000-ohm, 2-wa tt, wire-wound Potentiometer Scale = 10,000-ohm, 2-watt, wire-wound potentiometer Sensitivity control (Coarse) = 25,000-ohm, 2-watt, C.T. potentiometer with “on - off” switch Sensitivity control (Fine) = 1000-ohm, 2-watt, wire-wound potentiometer Set mV = 100-ohm, 2-watt, wire-wound potentiomctcr Kl = 1800-ohm, Q-watt resistor R, = lSOO-ohm, +-watt resistor R3 = 6S0,OOO-ohrn and 56O,OO0-ohm, :-watt resistors in series, with a tolr.1-ai1c.c K4 = 6.8-megohm, +watt resistor with a tolerance o f 1 per cent. R, = 1000-ohm and 100-ohm, :-watt resistors in series, with a tolerance o f R, = 1000-ohm, ;-watt resistor with a tolerance of 1 per cent. R, = 330-ohm, Q-watt resistor with a tolcrancc o f 1 per cent. of 1 Fer cent. 1 per cent. TI = OC75 T2 = o c s 5 PS -- D.P.S.T. push-button switch spring-loaded “off” Receivcd .lTuj, 6th, I!)65

ISSN:0003-2654    

DOI:10.1039/AN9669100598

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

600 SHORT PAPERS [Analyst, Vol. 91 Some Anomalous Results given by Phase-solubility Analysis BY J. V. WILKINSON AND J . S. WRAGG (Analytical Developmevtt Gvoup, Standavds Department, Boots Piwe Drug Co. Ltcl., Station Street, Nottiizghanz) IN the accounts of phase-solubility analysis, given by Carratt, Johnson and Iiing,l Higuchi and Connors,2 Mader3 and O ~ t c h , ~ each author has indicated some of the conditions in which the method is likely to fail. In all instances, it has been pointed out that the components of the solute must not form a solid solution, neither must they be present in the ratio of their solubilities. However, Higuchi is alone in emphasising that the most serious limitation to the application o f phase-solubility analysis is the condition that the solubility of each component must not be affected by the presence of the other components.September, 19661 SHORT PAPERS 601 When samples of an insecticide of commercial quality were recently examined by phase- solubility analysis, total impurity contents were obtained that were more than twice those found by gas - liquid chromatography, infrared spectrophotometry and isotope-dilution analysis.To investigate this occurrence, several mixtures were prepared containing the pure insecticidal com- pound together with known amounts of some of the impurities likely to be present in the com- mercial material, and these mixtures were assayed by the phase-solubility method. EXPERIMENTAL PKE PA KATI ON OF hi IXTU RES- Amounts of the insecticide, 3,5-di-t-butylphenyl methylcarbamate, (butacarb, I), were purified by re-crystallisation from light petroleum. Mixtures of known composition were prepared by adding to this re-crystallised material known amounts of 2,5-di-t-butylphenyl methylcarbarnate, 11, 3,5-di-t-butylphenol, 111, and 3-t-butylphenyl methylcarbamate, IV, each of which had also been purified by re-crystallisation.O.CO.NH.CH, 0. CO. NH . CH, 0 H O.CO.NH.CH, I I t-C4H9 I I A pj' PI P /I/\ t-C4Hg /" t-C,H, t-C,Hg A/( /\/ t-C4H9 t-C*H, t-CdH, I I1 I11 IV Prepare the mixtures by heating I to a temperature just above its melting-point of 100" C, and adding one or more of 11, 111 and IV with stirring; continue stirring until the mixture has com- pletely crystallised, When cool, grind the mixtures in a mortar. Mixture 1 2 3 4 5 6 7 8 TABLE I COMPOSITION OF PREPARED MIXTURES Percentage by weight Re-crystallised insecticide I 82 95 96 91 91 95 90 80 Impurity I1 15 5 5 5 - - Impurity Impurity I11 IV - 5 10 20 The compositions of the mixtures are shown in Table I.Two batches of re-crystallised in- secticide (I) were used in the preparation of these mixtures; the first batch was used in mixtures 1 to 4, and the second was used in mixtures 5 to 8. PHASE-SOLUBILITY PROCEDURE- The technique described by Garratt was used in the phase-solubility determinations. In each instance, the equilibration temperature was 31" C and, except where otherwise stated, the period of equilibration was from 10 to 14 days. The solvents used were hexane, cyclohexane, methanol - water (5 + 2) and methanol - water (3 + 1).To determine the solution concentration, the solvent was removed a t room temperature under a stream of nitrogen and the residue dried at 100" C to constant weight. After the assay of one of the process samples by phase-solubility analysis the solid phases were separated from the solution phases, washed with a limited amount of solvent and dried. The solid phases were examined by thin-layer chromatography on silica gel with hexane - t-pentyl alcohol (9 + 1) as the solvent. After drying, the chromatograms were sprayed with 5 N sodium hydroxide solution in methanol - water (1 + l), heated at 100" C for 5 minutes, cooled and then sprayed with a 0-5 per cent. w/v solution of 2,6-dichloro-~-benzoquinone-4-chloroimide in methanol. The solid phases were then combined and themselves assayed by the phase-solubility method.602 SHORT PAPERS [Analyst, Vol.91 RESULTS The results of assaying two process samples of the insecticide, the two re-crystallised samples of the insecticide and the prepared mixtures are shown in Table 11. TABLE I1 RESULTS OF PHASE-SOLUBILITY ANALYSIS Sample Proccss samplc I* Process sample 2, solid phases . . Re-crystallised insecticide I uscd to prepare mixtures 1 to 4 . . . . . . 2 . . . . . . 2 . . . . . . 2 . . . . . . 3 . . . . . . 3 . . . . . . 4 . . . . . . 4 . . . . . . lie-crystallised insecticide I used to prepare mixtures 6 to 8 . . . . . . Mixture 5 . . . . . . 6 . . . . . . 7 , . . . . . 8 . . . . . . .. . . . . . . . . c i . . Mixturc 17 . . . . . . Equilibration period, days Solvent 5 Hexane 10 Hexane 21 Hexane 10 21 Hexane LO Hexane Methanol - water (3 + 1) 10 14 14 14 14 14 14 14 Hexane Methanol - water (5 f- 2) Hexane Hexane Methanol - water (5 + 2 ) Cyclohexane Hexane Methanol - water (5 + 2) Hexanc Methanol - water (5 + 2 ) 14 14 14 14 14 Methanol - water (5 + 2) Methanol - water (5 + 2) Methanol - water (5 + 2) Methanol - water (5 + 2) Methanol - water (5 + 2) Percentage w/w of total compounds other than I & added found - 32.2 - 3 2 4 - 33.0 - 17-6 - 23.3 - 0.0 - I 18 5 5 5 4 4 9 9 2.0 0.6 38.7 11.7 6.1 9.7 12.5 4.0 22.8 11.2 - 0.0 9 11.5 5 5.5 10 11.2 20 23.0 * SampIe assayed for I by infrared = 88 per cent., and by isotope dilution = 86.6 per cent.Sample assayed for I by isotope dilution = 82.2 per cent. A typical phase-solubility diagram is shown in Fig.1. When the impurities are present in sufficient concentration, the diagrams show changes of slope. This is illustrated in Fig. 2. r^ 2 & z w 6 0 0 1 40 ;? 2 0 - 0 3 v, .- LI - 0 50 I00 I50 50 I00 I50 System concentration, mg per g l’hase solubility of mixture 4, with System concentration, mg per g Phase solubility of mixture 1 , with 17ig. 1. Fig. 2. hcsanc a s solvent hexane as solvent No impurities were detectable in the solid phases after the assay of process sample 2, either when they were re-assayed or when they were examined by thin-layer chromatography. DISCUSSION The following points arise from a consideration of these results- (;) When hexane mas used as the solvent, the contents of total impurity were more than When the more polar soIvent methanol - water (5 + 2) was used, the twice those expected.results were still higher than theory, though only by 10 to 20 per cent.September, 19661 SHORT PAPERS 603 A probable explanation of these results is that complexes are formed between the principal compound, I, and the other components of the solute. These complexes are probably the result of hydrogen bonding, though a simple 1 to 1 complexing would not fully explain the results when hexane was used as solvent. Such complex formation would be a reversible process and the position of the equilibrium would be influenced by the polarity of the solvent. The effect of complex formation on a phase-solubility determination would be to increase the apparent pro- portion by weight of the other components.The recovery of solute from the tube below saturation point each time was satisfactory. The solid phases were found to consist of pure I. The point we particularly wish to make is one that we consider has not been adequaiely stressed by previous authors ; when a substance is assayed by phase-solubility analysis with a given solvent, it is possible for the results to be in error, because of the formation of complexes, without the phase-solubility diagram giving any warning of the situation. While complex formation may be revealed by a change of solvent to one of different polarity, the use of a. rela- tively polar solvent will not guarantee accurate results. It follows that, in any system where complex formation is a possibility, it is advisable to perform recovery experiments on suitable mixtures of known composition. We thank Dr. 11. A. Peak for his helpful advice and the provision of the compounds, and 1)r. T. I. Watkins and Mr. M. W. Raker for the assays by the isotope-dilution method. (ii) None of the phase-solubility diagrams showed any abnormality. REFERENCES 1. Garratt, D. C., Johnson, C. A., and King, R. E., J . Pharm. Pharmac. SuppZ., 1963, 15, 206T. 2. Higuchi, T., and Connors, K. A., “Advances in Analytical Chemistry and Instrumentation,” 3. Mader, W. J., “Organic Analysis,” Interscience Publishers, New York and London, 1954, Volume 2, 4. Outch, IV. T., Azisf. J . Pkarm., 1961, 42, 1277. Interscience Publishers, New York, London and Sydney, 1965, Volume 4, p. 117. p. 253. Received Febrzinrzp 212d, 1966

ISSN:0003-2654    

DOI:10.1039/AN9669100600

出版商:RSC    

年代:1966

数据来源: RSC