摘要:

MAY, 1967 Vol. 92, No. 1094 Dioximes THE ANALYST of Large Ring 1,2=Diketones and their Applications to the Determination of Bismuth, Nickel and Palladium BY J. BASSETT, G. B. LETON AND (THE LATE) A. I. VOGEL (Chemistry Department, Woolwich Polytechnic, London, S. E. 18) The preparation of alicyclic vic-dioximes containing 5 to 12 carbon atom rings from the corresponding 1,2-diketones is reported, and their appli- cation to the gravimetric determination of bismuth in the presence of several complexing agents is described. The dependence of complete precipitation of bismuth upon pH, and the effect of foreign ions has been studied. A poly- meric structure is suggested for the bismuth - dioxime compounds. The application of large ring (8 to 12 carbon atoms) vic-dioximes to the gravi- metric determination of nickel and palladium has been studied; the infrared and ultraviolet spectra of the nickel(I1) and palladium(I1) complexes are presented.BISMUTH EARLY attempts1,* to use dimethylglyoxime for the gravimetric determination of bismuth were largely unsuccessful owing to the formation of basic bismuth salts at the high pH required for the complete precipitation. Lott and Vitek3 overcame this difficulty by carrying out the precipitation in the presence of ethylenediaminetetra-acetic acid and of nitrilotriacetic acid; these complexing agents possess the dual function of preventing the precipitation of basic bismuth salts and of masking certain interfering ions. The results were found to be consistent with the formula Bi,O,DMG (where H,DMG is dimethylglyoxime).Lott and Vitek proposed the following structural formula for the bismuth - dimethylglyoxime compound- CH,-C=N-0-Bi=O CH,C = N-0-Bi = 0 The work described here was undertaken so as to study the application of a wider range of vic-dioximes to the gravimetric determination of bismuth and, as far as possible, to ascertain the nature of the bismuth compounds formed. I EXPERIMENTAL PREPARATION OF V~C-DIOXIMES- The vic-dioximes (melting-points are given in parentheses) of the following 1,2 diketones were used: cyclopentane-1,2-dione (216" to 217" C) , cyclohexane-1,2-dione (188" to 189" C) , cyc1oheptane-lJ2-dione (178" to 179" C), cyclo-octane-lJ2-dione (169" to 170" C) , cyclononane- 1,2-dione (177" to 178" C) , cyclodecane-lJ2-dione (189" to 190" C) , cyclo-undecane-lJ2-dione (206" to 207" C) , cyclododecane-lJ2-dione (213" to 214" C) , 3-methylcyclohexane-1 ,2-dione (164" C) , 4-methylcyclohexane-1,2-dione (181" to 182" C) , 4-isopropylcyclohexane-1,2-dione (182" to 183" C) and 4-t-butylcyclohexane-lJ2-dione (202" C).The preparation of the di- ketones, with the exception of 4-isopropylcyclohexane-1,2-dione and 4-t-butylcyclohexane- 1,2-dioneJ has been reported elsewhere.4 The latter compounds were prepared from the corresponding pure ketone^.^ The vic-dioximes were obtained from the diketones by addition of the latter to an ice-cold alkaline solution of hydroxylammonium chloride in the presence of sufficient ethanol to dissolve the diketone. The resulting dioximes were re-crystallised from water or dilute ethanol and finally from benzene.279280 BASSETT et al. DIOXIMES OF LARGE RING l,%DIKETONES [AflabSt, VOl. 92 The purity of the dioximes was established by thin-layer chromatography. About 5 pg of the dioxime in 5 pl of the eluting solvent (benzene - tetrahydrofuran - chloroform, 80 + 15 + 5 v/v) were applied to a silica-gel plate. Each dioxime was found to give only one spot on the resulting chromatogram. The reagent used for precipitating the metal ions was either a saturated aqueous solution of the dioxime or, for the less soluble dioximes, a solution in ethanol or in acetone. EFFECT OF pH- The influence of pH upon the precipitation of bismuth by vic-dioximes was studied by using procedures (a) and (b) as described below. The bismuth nitrate solutions used were prepared by dissolving appropriate amounts of pure bismuth oxide (Johnson, Matthey Specpure) in 1 + 1 nitric acid and diluting to 1 litre.The solutions were standardised by titration with standard EDTA solution, with xylenol orange as indicator,6 and checked gravimetrically by precipitation of bismuth phosphate from homogeneous solution.' The results in Table I were obtained by using 4-methylcyclohexane-1,2-dione dioxime (4-methylnioxime). With procedure (a), precipitation is virtually quantitative in the pH range 11.5 to 12.0. The presence of calcium ions, procedure (b), however, enables bismuth to be precipitated quantitatively at the lower pH range of 9.0 to 10.0. Similar experiments with other alicyclic vic-dioximes indicated that the pH required for quantitative precipitation of bismuth does not vary appreciably with the dioxime used.TABLE I EFFECT OF pH ON THE PRECIPITATION OF BISMUTH Procedure (a)- pH . . .. .. . . 11.0 11.5 11.8 12.0 12.5 Bismuth taken, mg . . . . 100.4 100.4 100.4 100.4 100.4 Bismuth found, mg . , , . 92.2 100.3 100.2 100.7 102.7 Procedure (b)- pH . . .. .. 8.7 9.0 9.3 9.5 9.8 10.0 10.5 11.0 11.5 Bismuth taken, mg . . 102.4 99.5 102.4 99.5 102.4 102.4 102.4 102.4 102.4 Bismuth found, mg.. 94.8 99.2 102.4 99.8 102.1 102.5 104.1 110.1 116.6 MASKING AGENTS- The use of the following complexing agents was studied with procedures (a) and ( b ) : cyclohexanediaminetetra-acetic acid (CDTA), ethylenediaminetetra-acetic acid (EDTA), hydroxyethylethylenediaminetetra-acetic acid (HEEDTA), iminodiacetic acid (IDA), nitrilotriacetic acid (NTA) and propylenediaminetetra-acetic acid (PDTA).The pH required for complete precipitation of bismuth in the presence of these masking agents appears to be related to the stability of the bismuth complex f ~ r m e d . ~ , ~ Thus in the presence of IDA, bismuth was precipitated at a pH greater than 4.0; CDTA was found to complex bismuth so strongly that precipitation did not occur, even at pH 12.0; and HEEDTA interfered with the complete precipitation of bismuth. The most satisfactory masking agents appeared to be EDTA, NTA and PDTA; the optimum values of pH for quantitative precipitation in the presence of these complexing agents are given in Table 11. TABLE I1 OPTIMUM pH FOR QUANTITATIVE PRECIPITATION OF BISMUTH Masking Procedure agent EDTA NTA [$ (4 PDTA (b) Bismuth taken, PH mg 11.5 to 12.0 100.2 9.5 to 10.0 99-6 10.5 to 11.0 99.5 8.5 to 9.0 99.6 11.5 t o 12-0 100.4 9.0 to 9.5 100.4 Bismuth found, mg 100.2 99-7 99.3 99.8 100.3 100.3May, 19671 REAGENTS- AND THEIR APPLICATIONS TO THE DETERMINATION OF BISMUTH METHOD 281 vic-Dioxime solution-Prepare as described under Experimental.Disodium ethylenediaminetetra-acetate (EDTA ) solution, 0.05 M-Dissolve 18.6 g of di- sodium ethylenediaminetetra-acetate dihydrate in water and dilute to 1 litre with water. Calcium chloride solution, 0.5 M-Dissolve 50 g of analytical-reagent grade calcium car- bonate in a minimum volume of dilute hydrochloric acid and dilute to 1 litre with water. All other reagents were of analytical-reagent grade.PROCEDURE (a)- To the bismuth solution containing 50 to 500 mg of bismuth in 100 ml, add sufficient EDTA solution to mask bismuth and the interfering ions present, and adjust the pH to between 7 and 8 with dilute ammonia solution. Add 0.5 to 1 g of potassium cyanide (required only if nickel, cobalt, copper, palladium, zinc, silver, cadmium or mercury are present), followed by sufficient dioxime solution to provide at least a 30 per cent. excess of the reagent. Adjust the pH to 11.5 with 2-5 N sodium hydroxide solution and digest the resulting yellow precipitate, with occasional stirring, for 45 minutes at 60" to 70" C. Filter through a sintered- glass crucible (No. 4) and wash thoroughly with water; wash the precipitates formed with water-insoluble dioximes with hot water followed by ethanol.Dry the precipitate to constant weight at 105" to 110" C and calculate the bismuth content; base the conversion factor on the general formula Bi,O,N,D where D(NOH), is the formula of the dioxime. PROCEDURE (b)- Carry out the initial stages of the determination as for procedure (a) but, after adding the dioxime reagent, add sufficient calcium chloride solution (1 to 2 ml excess) to displace the bismuth completely from its EDTA complex. Precipitate the bismuth by adjusting the pH to 9.5 with 2-5 N sodium hydroxide solution and complete the determination as for procedure (a). RESULTS The results for the determination of bismuth by procedure (a) with nioxime, 4-methyl- nioxime and 4-isopropylnioxime as precipitating reagents are given in Table I11 ; similar results were obtained with procedure (b).These three dioximes formed clean, yellow bismuth precipitates which, unlike the bismuth dimethylglyoximate precipitate, did not "creep" or form films on the walls of the beaker. It is seen that results were satisfactory when the method was applied to solutions containing from 50 to 500mg of bismuth. TABLE I11 DETERMINATION OF BISMUTH BY PROCEDURE (a) Cyclohexane-1,2-dione dioxime (nioxime)- Weight of precipitate, mg . . 70.1 140.2 280.5 351.2 700.9 Bismuth taken, mg . . . . 49-7 99.4 198.7 248.4 496.8 Bismuth found, mg . . . . 49.7 99.3 198.7 248.8 496.5 4-MethyZcyclohexane-1,2-dione dioxime (4-methy1nioxime)- Weight of precipitate, mg . . 71.7 143.7 287.4 359-6 724.8 Bismuth taken, mg .. . . 49.7 99-4 198.7 248.4 501.9 Bismuth found, mg . . . . 49.6 99.4 198.8 248.8 501.4 4-Isop~opylcyclohexane- 1 , 2-dione dioxime (4-isopropylnioxime) - Weight of precipitate, mg . . 78.9 157.8 238.2 316.6 Bismuth taken, mg . . . . 52-3 104.7 157.0 209.3 Bismuth found, mg . . . . 52-2 104.3 157.5 209.3 The water-soluble dioximes of cycloheptane-1 ,2-dione (heptoxime) and cyclo-octane- 1,2-dione (octoxime) gave satisfactory results for bismuth (less than 100 mg) by procedure (b) only. Some typical results are given in Table IV.282 BASSETT et U l . : DIOXIMES OF LARGE RING I,%DIKETONES [Ana&!yst, VOl. 92 TABLE IV DETERMINATION OF BISMUTH WITH CYCLOHEPTANE-1 ,%DIONE DIOXIME Weight of precipitate, mg . . 71.4 142.7 285.4 Bismuth taken, mg . . . . 49.4 98.8 197.6 Bismuth found, mg .. . . 49.4 98.7 197.5 The 9 to 12-membered alicyclic vic-dioximes gave easily filterable precipitates with bis- muth, but the conditions for quantitative precipitation were not discovered during the course of the present work. The effects of foreign ions, added as solutions of their chlorides, nitrates or sulphates, on the precipitation of bismuth by 4-methylnioxime are shown in Table V. The results by procedure (a) are similar to those found by Lott and Vitek3 for dimethylglyoxime; lead, however, interfered even in the presence of tartrate or acetate added as auxiliary complexing agents. With procedure (b) only those foreign ions that form stable cyano complexes did not interfere. Similar trends were observed with nioxime and 4-isopropylnioxime as the precipitating agents.TABLE V INFLUENCE OF FOREIGN IONS ON THE PRECIPITATION OF BISMUTH BY 4-METHYLNIOXIME Foreign ions added Procedure (a)- Pd, Ni, Cu, A1 . . Ba, Sr, Ca, As . . Ba, Mg, Hg, Ag . . Zn, Cd, Pd, Co . . Ca, Sr, Ni, Cu . . Pd, Ca, Zn, Co . . Ca, Sr, Ni, Cu . . Procedure (b)- Zn, Ag, Cd, Hg . . Ba, Al, Mg, Sr . . Ni, Co, Cu, Pd . . As .. .. .. Amount of each foreign ion, mg .. 25 .. 25 . . 25 . . 25 . . 50 . . 25 . . 100 .. 25 .. 25 .. 25 .. 25 Bismuth taken, mg 49.7 49.7 99.4 99.4 94.5 198-7 189.6 100.4 100.4 100.4 100-4 Bismuth found, mg 49.7 49.8 99.4 99.4 94.2 198.9 188.4 100.3 133.6 100.5 102.5 The reproducibility of results obtainable by procedures (a) and (b) was studied by using aliquots of bismuth nitrate solution containing 104.5 mg of bismuth. The results obtained with 4-methylnioxime as precipitating agent are shown in Table VI.Similar values of standard deviation were obtained with nioxime and 4-isopropylnioxime as precipitating reagents. TABLE VI REPRODUCIBILITY OF THE METHODS Bismuth found by procedure (a), mg 104.5, 104-5, 104.5, 104.7, 104.9, 104.6, 104.1, 104.5, 104.5, 104.5, 104.7 Mean = 104.5 Standard deviation = 0.20 Individual values Bismuth found by procedure (b), mg 104.5, 104.3, 104.5, 104.5, 104.3, 104.5, 104.8, 104-4, 104.2, 104.9, 104.3 Mean = 104.5 Standard deviation = 0.22 Samples of the various bismuth precipitates were analysed for carbon, hydrogen and nitrogen; the bismuth content of each precipitate was determined by EDTA titration, with xylenol orange as indicator.The results of these analyses are presented in Table VII. The theoretical values given have been calculated on the basis of the general formula Bi,O,N,D where D(NOH), represents the formula of the vic-dioxime.May, 19671 AND THEIR APPLICATIONS TO THE DETERMINATION OF BISMUTH TABLE VII RESULTS OF MICRO ANALYSES 283 Dioxime Pentoxime .. Nioxime . . . . 4-Methylnioxime . . 4-Isopropylnioxime 4-t-But ylnioxime Heptoxime . . Octoxime . . . . Nonoxime.. .. Decoxime . . .. Carbon, per cent. +- Theory Found . . 10.4 10-6 . . 12.2 12-5 . . 13.9 14.5 . . 17-1 17.6 . . 18.6 18.8 . . 13.9 14.3 . . 1 5 5 15.9 . . 17.1 17.5 . . 18.6 18-05 Hydrogen, per cent. I--- Theory Found 1-05 1.1 1.4 1.5 1.7 1.7 2.2 2.3 2.5 2.45 1.7 1.8 2.0 2-0 2-3 2.35 2.5 2.4 Nitrogen, per cent.7-7 Theory Found 4.9 4.95 4.75 4-2 4.6 4.3 4.4 4.8 4.3 4.9 4.6 5.1 4.5 5.1 4.4 5.0 4.3 5.0 Bismuth, per cent. +-7 Theory Found 72.5 72.0 70.8 70.8 69.2 68-8 66.1 65-7 64.7 64.6 69.2 69-3 67.6 67.6 66.1 66.4 64.7 64.6 The discrepancies between the theoretical and practical results are in some instances somewhat larger than usual; it is suggested that this may be connected with the fact that many of these bismuth compounds decompose violently when heated. DISCUSSION We conclude from the above results that bismuth may be quantitatively determined in the presence of a wide range of foreign ions by using procedure (a) and that the reagents nioxime, 4-methylnioxime and 4-isopropylnioxime are superior to dimethylglyoxime in respect of the properties of the precipitate formed.The modified procedure (b) was suggested by the work of Pfibil and CutalO on the precipitation of pure bismuth hydroxide with ammonia solution in the presence of EDTA and an equivalent amount of calcium nitrate. This procedure enables the quantitative precipitation of bismuth at a lower pH than is required for procedure (a), but interference from foreign ions is more serious owing to the removal of the masking agent (EDTA) by the added calcium ions. A limitation to the determination of bismuth with vic-dioximes in the presence of a complexing agent is the relatively narrow range of pH (about 1 unit) in which the pure compound is quantitatively precipitated (see Table I). The conversion factors used to calculate the results (bismuth found) in the gravimetric determinations were based on the formula3 Bi204N,D where D(NOH), is the dioxime.This formula was also used in calculating the “Theory” values in Table VII. The insoluble nature of the bismuth precipitates both in water and in common organic solvents may, however, indicate a polymeric structure. The observations during preliminary experimental work that cyclohexane-1,3-dione dioxime failed to precipitate bismuth quantitatively and that cyclo- hexane-1,4-dione dioxime did not give a precipitate (in contrast to cyclohexane-1,Z-dione dioxime) are in accord with a polymeric structure in which the bismuth atoms are joined by oxygen bridges. The strain in such a system (1,3- and 1,4-dione dioximes) would increase as the distance between the two oxime groups became greater.Structures I and I1 given below, based on the oximino and nitrone form+ of the oxime group, respectively, are possible polymeric structures that have the composition (Bi,0,N2D)n. 0 t \ C = N / C = N t 0 C’ I c\ 1 I1284 BASSETT et al. DIOXIMES OF LARGE RING l,%DIKETONES [ATZdySt, VOl. 92 Polymeric structures involving bismuth - oxygen bonds are a well established feature of bismuth chemistry.12J3 The infrared spectra of the various dioximes and the corresponding bismuth compounds have been determined as Nuj ol mulls with a Perkin-Elmer Infracord spectrophotometer (model 137), and as potassium bromide discs (concentration about 0.5 per cent.) with a Unicam SP200 infrared spectrophotometer. Some typical spectra obtained with the latter instrument are presented in Figs.1 and 2. The infrared spectra of the other dioximes and bismuth compounds are included in the Ph.D. thesis of Leton.5 Comparison of the various infrared spectra shows, for each pair, that the 0-H band of the dioxime at about 3350 cm-l is absent from the spectrum of the bismuth compound. In the spectra of the nickel(I1) - vic-dioxime complexes the appearance of the 0-H band at about 1775cm-1 has been attributed to hydrogen bonding14; the absence of such a band in the spectra of the bismuth compounds suggests that they are not structurally analogous to the nickel complexes. The effect of deuteration of the bismuth coinpounds was not studied in view of the absence of the 0-H band from their infrared spectra. The bands at about 1540 and 1150 cm-l are also striking features of the infrared spectra of the series of bismuth - vic-dioxime compounds.The band found between 1500 and 1600 cm-l may probably be attributed to the C=N stretching ~ibrati0ns.l~ A possible value for an N + 0 stretching frequency would seem to be between that obtained in pyridine N-oxideslG (about 1250 cm-l) and tertiary amine N-oxides17 (about 950 cm-l). It is therefore suggested that the band found at about 1150 cm-l may be assigned to N -+ 0 vibrations, in accord with structure 11. The infrared spectra of certain of the dioximes and the corresponding bismuth compounds have also been examined, over the range 1300 to 400 cm-l, as Nujol mulls on a Perkin-Elmer infrared grating spectrophotometer, model 337. These studies do not provide any evidence for the assignment of Bi-0 bands in the spectra of the bismuth compounds.NICKEL AND PALLADIUM The study of the application of alicyclic vic-dioximes to the gravimetric determination of nickel and palladium was confined to those possessing 8 to 12-membered carbon rings. These vic-dioximes have not previously been used for the determination of these elements. EXPERIMENTAL STANDARD NICKEL SOLUTIONS- Nickel solutions were prepared by dissolving about 1 g of pure nickel (Mond Nickel Co.) in hot concentrated hydrochloric acid and diluting to 1 litre with water. These solutions were standardised electrolytically by using platinum electrodes and gravimetrically with 4-methylcyclohexane-1 ,2-dione dioxime as the precipitant. Standard palladium solutions-Palladium solutions were prepared by dissolving about 2 g of anhydrous palladium chloride (Johnson, Matthey & Co.Ltd.,) in hot concentrated hydrochloric acid and diluting to 1 litre with water. The solution was standardised gravi- metrically with 4-methylcyclohexane-1,2-dione dioxime. PROCEDURES- The procedure used by Banks and Hooker1* for the gravimetric determination of nickel with 4-methylcyclohexane-1,2-dione dioxime was found to be unsuitable with the 8 to 12- membered alicyclic vic-dioximes. The latter form yellow nickel( 11) complexes, and it was found difficult to observe the appearance of a persistent yellow colour analogous to the pink colour utilised by Banks and Hooker. The following procedure was therefore adopted. Dilute an aliquot of the nickel solution to about 250ml with water and adjust the pH to between 5 and 6 with dilute ammonia solution.Heat the solution to 60" C, add excess of dioxime (not less than 30 per cent.), dropwise with stirring, and digest the resulting precipitate for 45 minutes at 60" to 70" C. Collect the precipitate in a sintered-glass filter- crucible, wash with hot water and with a little ethanol to remove excess dioxime; dry to constant weight at 105" to 110" C. The procedure used for the gravimetric determination of palladium was similar to that described by Banks and Hooker,18 except that the precipitate was washed with hot water followed by a little ethanol.1 Fig. 1. Infrared spectra of (a) cyclopentane-1,2-dione dioxime, and (b) the corresponding bismuth compound I I 5000 4000 3000 2000 1800 1600 1400 1200 I000 800 Wavenumber, cm-' I0 285 Fig.2. Infrared spectra of (a) cyclo-octane-1,2-dione dioxime, and (b) the corresponding bismuth compound286 BASSETT et d. : DIOXIMES OF LARGE RING l,%DIKETONES [A.tza@St, VOl. 92 MEASUREMENT OF ABSORPTION SPECTRA IN CHLOROFORM- Solutions of known concentration were prepared by accurately weighing samples of the solid complex on a microbalance and dissolving them in analytical-reagent grade chloro- form. The solutions were transferred into 100-ml calibrated flasks and diluted to the mark with chloroform immediately before making the absorption measurements. The solutions were rapidly transferred into 0.5-cm cells and the absorption spectra scanned on an automatic recording Unicam SPSOO spectrophotometer. INFRARED SPECTROPHOTOMETRIC STUDY- The infrared spectra of the complexes were recorded as Nujol mulls on a Perkin-Elmer Infracord spectrophotometer (model 137) and as potassium bromide discs (concentration about 0-5 per cent.) on a Unicam SP200 infrared spectrophotometer.RESULTS AND DISCUSSION the 8 and 9-membered alicyclic vic-dioximes are given in Tables VIII and IX, respectively. The results obtained for the gravimetric determination of nickel and palladium with TABLE VIII DETERMINATION OF NICKEL WITH ALICYCLIC V~C-DIOXIMES Cyclo-octane- 1,2-dione dioxime- Weight of precipitate, mg . . 73.5 148.0 167.9 Nickel taken, mg . . . . 11.0 21.9 24.8 Nickel found, mg . . . . 10.9 21-9 24.8 Cyclononane-1,2-dione dioxime- Weight of precipitate, mg .. 76.4 155-0 Nickel taken, mg . . . . 11.0 21.9 Nickel found, mg . . . . 10.6 21.4 TABLE IX DETERMINATION OF PALLADIUM WITH ALICYCLIC V~C-DIOXIMES Cyclo-octane-1,2-dione dioxime- Weight of precipitate, mg . . 25.0 50.6 100.9 125.2 Palladium taken, mg . . 6.0 11.9 24.1 30.0 Palladium found, mg . . 6-0 12.1 24-1 30.0 Cyclononane- 1,2-dione dioxime- Weight of precipitate, mg . . 26.9 55.2 110.0 Palladium taken, mg . . 6.2 12.4 24.7 Palladium found, mg . . 6.1 12.4 24.8 The analyses for nickel and palladium with the 10, 11 and 12-membered alicyclic vic- The nickel and palladium precipitates were analysed for carbon, hydrogen and nitrogen dioximes were, in general, less satisfactory. and some of the results are included in Table X. TABLE X MICRO ANALYSES Formula of Dioxime used complex Cyclo-octane-1,2-dione dioxime .. (C,H,,N202),Ni Cyclononane-l,2-dione dioxime . . (CgH,5N202)2Ni (C,H,,N,O,)*Pd (C9H15N202)2Pd Cyclodecane-1,2-dione dioxime . . (C,,H,7N20,),Ni (C10H17N202)2Pd Cyclo-undecane- l12-dione dioxime ( C11H,,N20,),Ni Cyclododecane-l,2-dione dioxime (C,,H2,N202),Ni Carbon, Hydrogen, Nitrogen, per cent. per cent. per cent. +--7 +- * Theory Found Theory Found Theory Found 48.4 48.5 6.6 6.85 14.1 14.7 43.2 43.1 5.9 5.9 12.6 12.9 50.85 50.6 7.1 7.0 13.2 13-65 45.7 45.5 6.4 6.6 11.85 11-4 53.0 53.4 7.6 7.7 12.4 12.7 47.95 48.1 6.8 6.8 11.2 10.9 54.9 54.6 8.0 7.72 - - 56.6 56.6 8.3 8.22 - -May, 19671 AND THEIR APPLICATIONS TO THE DETERMINATION OF BISMUTH 287 These results indicate that the precipitates are bis-complexes of nickel(I1) and pal- ladium(II), and the conversion factors were calculated on this basis.The most satisfactory of the vic-dioximes studied was cyclo-octane-l,2-dione dioxime which precipitates relatively small amounts of nickel and palladium quantitatively. The yellow precipitates filter easily and can be dried to constant weight at 105" to 110" C for about 1 i hours. The ultraviolet absorption spectra of chloroform solutions of nickel(I1) and palladium(I1) bis-(cyclo-octane-l,2-dione dioxime) are shown in Fig. 3. The values of Am,,. and Emax. Wavelength, rnp Fig. 3. Ultraviolet absorption spectra of A, chloro- form solution of nickel(I1) bis-(cyclo-octane-l,2-dione dioxime) : and B, chloroform solution of palladium(I1) bis-(cyclo-octane-l,2-dione dioxime) (Table XI) indicate the marked similarity exhibited by the series of nickel(I1) - vic-dioxime complexes.Owing to the limited amounts of certain of the dioximes available, the absorption spectra of only two of the palladium complexes were recorded. These values are in accord with the observation of Banks and Barnum,lg that the absorption spectra of chloroform solutions of nickel(I1) and palladium(I1) complexes of vic-dioximes that do not contain aromatic substituents are practically identical. TABLE XI ABSORPTION PROPERTIES OF NICKEL(II) AND PALLADIUM(II) - V~C-DIOXIME COMPLEXES I N CHLOROFORM SOLUTION Complex Nickel(I1) bis-octoxime . . Niclrel(I1) bis-nonoxime . . Nickel(I1) bis-decoxime . . Nickel(I1) bis-undecoxime Nickel(I1) bis-dodecoxime Palladium(I1) bis-octoxime Palladium( 11) bis-decoxime Colour .. Orange - yellow . . Orange - yellow , . Orange - yellow . . Orange - yellow . . Orange - yellow .. Yellow .. Yellow h l a x . , mP 264 332 380 263 333 380 264 335 385 248 263 333 385 245 264 334 384 246 280 246 282 Emax., 1 mole-cm 2-43 x 104 5.78 x 103 4.43 x 103 2.21 x 104 4-90 x 103 3-68 x 103 2.11 x 104 4-69 x 103 3.71 x 103 1-82 x 104 2-17 x 104 4.86 x 103 3.65 x 103 1-09 x 104 1.97 x 104 4-20 x 103 3.36 x 103 1-74 x 104 1-82 x 104 1-27 x 104 1.24 x lo2288 BASSETT et d. DIOXIMES OF LARGE RING I,%DIKETONES [A?Za&St, VOl. 92 The infrared spectra of nickel(I1) and palladium( 11) bis-(cyclo-octane-1 ,Z-dione dioximes) are shown in Figs. 4 and 5 , respectively. The spectra of the series of nickel(I1) complexes with 8 to 12-membered alicyclic vic-dioximes were found to show a marked similarity to each other and to the spectra of the palladium(I1) complexes with the 8 and 10-membered dioximes.I I I400 I000 65 Wavenumber, cm-' Fig. 4. Infrared spectrum of nickel(r1) bis-(cyclo-octane-l,2-dione dioxime) I O!iOOO 4dOO 3d00 2:O 1$00 I400 I000 61 Wavenumber, cm-l Fig. 5. Infrared spectrum of palladium(1r) bis-(cyclo-octane-l,2-dione dioxime) The observed bands were found to be in general accord with the assignments made by Blinc and Hadiil5 on the basis of their study of the infrared spectra of nickel dimethylglyoxime and related complexes. The weak, broad band near 2340 cm-1 reported by Blinc and Hadii, and attributed by them to the OH stretching frequency was, however, apparent only in the infrared spectra of our palladium complexes and was not observable in the spectra of the nickel complexes. The authors' thanks are due to Imperial Chemical Industries for a grant, to Mr. J. W. Betts for the ultraviolet and infrared spectra of the nickel and palladium compounds, and to the United Kingdom - Nigerian Technical Assistance Scheme for a grant to G.B.L.May, 19671 AND THEIR APPLICATIONS TO THE DETERMINATION OF BISMUTH REFERENCES 289 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. Kubina, H., and Plichta, J., 2. analyt. Chem., 1927, 72, 11. Celechovsky, J., and Okak, A., Chemicke' Listy, 1952, 46, 479. Lott, P. F., and Vitek, R. K., Analyt. Chem., 1960, 32, 392. Cumper, C. W. N., Leton, G. B., and Vogel, A. I., J . Chem. Soc., 1965, 2067. Leton, G. B., Ph.D. Thesis, London University, October, 1963. Korbl, J., Pfibil, R., and Emr, A., Chemicke' Listy, 1956, 50, 1440. Ross, H., and Hahn, R. B., Analyt. Chem., 1960, 32, 1690. Selmer-Olsen, A. R., Acta Chem. Scand., 1961, 15, 2052. Miklbs, I., and Szegedi, R., Acta Chim. Hung., 1961, 26, 365. Pfibil, R., and Cuta, J., Colln Czech. Chem. Commun., 1951, 16, 391. Brady, 0. L., and Mehta, R. P., J . Chem. Soc., 1924, 125, 2297. Bannister, F. A., and Hey, M. H., Mines Mag., 1935, 24, 49. SillCn, L. G., Svensk. Kern. Tidskr., 1941, 53, 39. Rundle, R. E., and Parasol, M., J . Chem. Phys., 1952, 20, 1487. Blinc, R., and Hadii, D., J . Chem. Soc., 1958, 4536. Costa, G., and Blasina, P., 2. 9hys. Chem., 1955, 4, 24. Mathis-Noel, R., Wolf, R., and Gallais, F., C . R. Hebd. SBance. Acad. Sci., Paris, 1956,242, 1873. Banks, C. V., and Hooker, D. T., Analyt. Chem., 1956, 28, 79. Banks, C. V., and Barnum, D. W., J . Amer. Chem. Soc., 1958, 80, 4767. Received June 29th, 1966

ISSN:0003-2654    

DOI:10.1039/AN9679200279

出版商:RSC    

年代:1967

数据来源: RSC

摘要:

290 Analyst, May, 1967, Vol. 92, p p . 290-292 A Limit Test for 4-Chloroacetanilide in Phenacetin and its Preparations* A thin-layer chromatographic method is presented that is suitable for use as a limit test for 4-chloroacetanilide in phenacetin. 4-Chloroacetanilide is detectable a t 0.01 per cent., but the test may be made more stringent by suitable adjustment of sample size. The method has been applied on a collaborative basis to samples of phenacetin and to several commonly used tablets containing phenacetin. IT has been suggested that the nephrotoxic action of phenacetin may be caused by impurities, and 4-chloroacetanilide has been particularly referred to in this respect, although the case against it has not been proved conclusively. The monograph in the British Pharmacopoeia 1963, p.580, includes a test, based upon the determination of chloride after reduction, which limits chlorine-containing impurities, expressed as 4-~hloroacetanilide, to about 0.1 1 per cent. It was considered desirable to provide a more specific test, together with a more stringent limit. The British Pharrnaceopoeia Commission appointed an ad hoc group to study the problem, consisting of: Dr. D. C. Garratt (Chairman), Dr. L. E. Coles, Mr. J. Deavin, Dr. G. E. Foster, Dr. A. R. Moss, Mr. R. A. Savidge and Mr. J. S. Wragg, together with members of the Commission’s staff. Published methods available for study were the paper-chromatographic method of the U.S.P. XVI1,l a spectrophotometric method2 and two thin-layer chromato- graphic method^.^,^ During the course of the work a method based on gas chromatography was p~blislied,~ but this was not investigated by the group.The paper-chromatographic method was rejected as, in the opinion of several members, it was extended to the limit of its sensitivity if a standard of not greater than 0.03 per cent. is required. The spectrophotometric method involves total hydrolysis with liydrobromic acid ; 4-chloroaniline produced from any 4-chloroacetanilide present is separated by extraction into cyclohexane from an alkaline medium and determined by measurement of the light absorption at 298 mp with suitable base-line correction. 4-Hydroxyaniline produced from phenacetin remains in the alkaline aqueous phase. This was found to be a sensitive and precise method when used for phenacetin, but it was abandoned because other ingredients of dosage forms and compound preparations are likely to interfere with the procedure.Further, the conditions of hydrolysis did not seem to be sufficiently precisely defined. It appeared that thin-layer Chromatography offered the most promising approach and the published method of Savidge and Wragg3 together with procedures developed in members’ laboratories, were examined. For a method designed as a pharmacopoeia1 limit test for 4-chlor- acetanilide, rather than as a more general test to reveal all possible impurities, it was agreed that the spot caused by this specific contaminant should be compact and well separated from any other spots. It was also agreed that, for such a purpose, a method of treatment that produced a stable visible colour capable of being examined and compared in daylight was to be preferred to one dependent on the use of two ultraviolet light sources that would have to be of the correct type and intensity to give satisfactory results. The method of Savidge and Wragg provides adequate separation of a compact spot but involves the use of ultraviolet irradiation for viewing purposes.A method that appeared to meet the required objectives was developed in the laboratory of Dr. Moss from an original proposal by Fresen,* and was examined in its application to phenacetin and to combinations of phenacetin with other drugs. The method involves a short acid hydrolysis which converts the 4-chloroacetanilide to 4-chloroaniline and part of the phenacetin to j5-phenetidine.After making the hydrolysate ammoniacal, it is extracted * Enquiries relating to this publication should be addressed to The Secretary, British Pharmacopoeia Commission, General Medical Council Office, 44 Hallam Street, London, W.l.BRITISH PHARMACOPOEIA COMMISSION (ad hoc COMMITTEE) 291 with cyclohexane and the extract is subjected to thin-layer chromatography on silica gel with dichloromethane as the mobile phase. 4-Chloroaniline is made visible by diazotisation followed by coupling with N-( 1-naphthy1)ethylenediamine ; some 9-phenetidine is also extracted and similarly made visible. Members applied the method to three samples of phenacetin, one of which was believed to contain very little 4-chloroacetanilide, another, an amount of 4-chloroacetanilide approxi- mating to the limit of 0.03 per cent.that is applied in the United States Pharmacopoeia, and the third, an amount of 4-chloroacetanilide in excess of this limit. Although it was intended that the method should be used as a limit test in which the 4-chloroaniline derived from the sample under test would be compared with a single standard representing the limiting amount, for the purpose of this collaborative examination a series of standards was applied so that estimates of the amounts of 4-chloroacetanilide present could be obtained. It was found that a suitable gradation of colour between successive standards is obtained if amounts equivalent to between 0.02 and 0.08 pg are used. Above this loading the spots are too intense in colour for a clear gradation to be observed.For an accurate assessment of samples that contain amounts of 4-chloroacetanilide outside the normally encountered range, it is necessary simply to adjust the amount of the sample taken for hydrolysis. Results reported on the three samples examined are given in Table I. TABLE I PERCENTAGE OF 4-CHLOROACETANILIDE FOUND I N SAMPLES OF PHENACETIN Laboratory Sample A €3 C D' Phenacetin 1 . . . . <om01 <0.01 <0*01 0.005 Phenacetin 2 . . . . 0.02 0-045 0.02 0-03 Phenacetin 3 . . . . 0-04 0.08 0.07 0.06 0.03 0.03 - 0-05 - - - - Two further samples of phenacetin were then obtained and batches of Compound Acetyl- salicylic Acid Tablets B.P.C., Compound Codeine Tablets B.P. and Soluble Compound Codeine Tablets B.P. were prepared from them.The results obtained are shown in Table 11. TABLE I1 PHENACETIK AND IN TABLETS* PREPARED FROM THEM PERCENTAGE OF 4-CHLOROACETANILIDE FOUND I N TWO FURTHER SAMPLES OF Laboratory 1 Sample A B C D E Phenacctin 4 . . . . . . . . 0.01 <0.037 0.01 Phenacetin 5 . . . . . . . . 0.07 0.05 to 0.06 0.07 Compound acetylsalicylic acid tablets . . 0.07 0.05 to 0.06 0.07 Compound codeine tablets . . . . 0.07 0.05 to 0.06 0.06 Soluble compound codeine tablets . . 0.07 0.05 to 0-06 0.06 (prepared from 5) (prepared from 5) (prepared from 5 ) (prepared from 4) Soluble compound codeine tablets . . 0.01 <0.03t 0.01 < 0.03 t 0.02 0.07 0.06 0.05 0.05 0.04 0.06 0.05 0.05 0.04 0.05 0.04 < 0.037 0.01 * For tablets, the results are expressed in terms of the amount of phenacetin present.i A more precise figure was not determined as these samples readily met the proposed limit of 0.03 per cent. Results, which agreed well with those given above, were also obtained by one laboratory with the method of Savidge and Wragg.3 When applied as a limit test, and assuming 0-03 per cent. to be an acceptable value, all of the laboratories would have accepted phenacetin 4, and the tablets prepared from it, and would have rejected phenacetin 5 and its preparations. In addition to these collaboratively examined samples, many samples of commercially available tablets containing phenacetin were successfully examined in the laboratory of one292 member. These samples represented a wide range of formulations in which phenacetin was present, together with acetylsalicylic acid, caffeine, codeine, phosphate, guaiphenesin, pre- pared ipecacuanha, phenylephrine hydrochloride, phenylpropanolamine hydrochloride and quinine sulphate.The method was also used for paracetamol and paracetamol tablets, and found to be equally applicable. (It is possible for paracetamol to be manufactured by a route involving 4-chloroacetanilide, although this does not appear to be used in practice, at least for material of British origin.) In view of this work, the group recommended that the following method (which sets a limit for 4-chloroacetanilide at a level of 0.03 per cent.) should be used for phenacetin and its preparations. METHOD REAGENTS- BRITISH PHARMACOPOEIA COMMISSION (ad hoc) COMMITTEE Ethanol-As described in the British Pharmacopoeia 1963, p.26, Alcohol (95 per cent.). Dilute hydrochloric acid-As described in the British Pharmacopoeia 1963, p. 367. Strong ammonia solution-As described in the British Pharmacopoeia 1963, Appendix I, Phenacetin-The British Chemical Reference Substance (Note 1). Other reagents and solvents are of analytical-reagent grade. PROCEDURE- To 0.20 g of the sample, or a quantity of powdered tablets equivalent to this amount, add 6 ml of ethanol and 10 ml of dilute hydrochloric acid and boil the mixture under a reflux condenser for 15 minutes. Allow the solution to cool, transfer it to a stoppered cylinder, add 4 ml of strong ammonia solution, mix, and again allow to cool (Note 2). Add 5-0 ml of cyclohexane, shake the mixture for 2 minutes, allow the phases to separate, and use the cyclohexane layer (solution A ) for the test.In a similar way prepare another solution (solution B) by using 0.20 g of phenacetin that is free from 4-chloroacetanilide and 0.06 mg of 4-chloroacetanilide instead of the substance being examined. Spread a layer of a suitable silica-gel adsorbent [Kieselgel G (Merck) has been found to be satisfactory] about 0.25-mm thick on a glass plate, heat at 105” C for 1 hour and allow to cool. Apply separately to the plate, 0.005ml of solutions A and B. Place the plate with one end in a shallow layer of dichloromethane contained in a closed tank, the atmosphere of which is saturated with dichloromethane. Allow to stand until the solvent front has travelled 10 cm beyond the points of application of the solutions, dry the plate in a current of warm air, transfer immediately to a closed glass tank and expose to nitrous fumes for 15 minutes.The nitrous fumes may be generated by the dropwise addition of sulphuric acid (50 per cent. w/w) to a solution containing 10 per cent. w/v of sodium nitrite and 3 per cent. w/v of potassium iodide in a beaker inside the tank. Place the plate in a current of warm air to remove nitrous fumes from the surface and spray evenly with a 0.5 per cent. w/v solution of N-( l-naphthy1)ethylenediamine hydrochloride in ethanol. Allow it to dry and repeat the spraying, if necessary, until maximum colour development is obtained. The purplish blue spot (RF about 0.4) derived from the 4-chloroacetanilide in the chromatogram obtained with the solution B is more intense than any spot of the same R, in the chromatogram obtained with solution A . Any p-phenetidine derived from the phenacetin has an R, of about 0.1 (Note 3). NOTES- the near future. is examined, crystallisation may occur a t this point. be overcome by shaking the solution with cyclohexane, then spinning it in a centrifuge. adsorbent and the degree of activation. p. 898. 1. It is expected that British Chemical Reference Substance, phenacetin, will be available in 2. If the test is applied on a more stringent basis and a larger amount (say 0.5 g) of phenacetin Difficulties arising from this crystallisation may 3. The RF values given are approximate and may vary according to the source of the silica-gel REFERENCES 1. 2. Crummett, W. B., Simek, J., and Stenger, V. A., Analyt. Chem., 1964, 36, 1834. 3. 4. 5. “United States Pharmacopoeia,” Seventeenth Revision, 1965, p. 451. Savidgc, R. A., and Wragg, J. S., J . Pharm. Pharmac., 1965, 17, 60 s. Fresen, J. A., Pharm. Weekbl. Ned., 1964, 99, 829. Koshy, I<. T., Wickersham, H. C., and Duvall, R. N., J . Pharm. Sci., 1965, 54, 1547. Received November loth, 1966

ISSN:0003-2654    

DOI:10.1039/AN9679200290

出版商:RSC    

年代:1967

数据来源: RSC

摘要:

Analyst, May, 1967, Vol. 92, $9. 293-299 293 Salicylideneamino-2-thiophenol-A New Reagent for the Photometric Determination of Tin: Application to the Analysis of Ores, Rocks and Minerals BY G. R. E. C. GREGORY AND P. G. JEFFERY (Warren Spring Laboratory, Stevenage, Herts.) Salicylideneamino-2-thiophenol can easily be prepared by the reaction of 2-aminobenzenethiol with salicylaldehyde. This reagent reacts with silver, copper, molybdenum, tin and several other metals to give coloured complexes, but by a suitable choice of conditions it can be made selective for tin. The tin complex is readily extracted into organic solvents and can be used for the photometric determination of this metal in ores, rocks and minerals. AROMATIC amines condense readily with certain aldehydes to form crystalline compounds known collectively as anils.By suitable choice of aldehyde and amine this reaction can be used to produce compounds with interesting analytical properties. Dagnall, Smith and West ,1 for example, describe the use of salicylidene-2-aminophenol for the fluorimetric deter- mination of aluminium. The reagent was prepared by the condensation of salicylaldehyde with 2-aminophenol. A sulphur analogue of this reagent can be prepared in a similar way from salicylaldehyde and 2-aminothiophenol, which react together to give the compound salicylideneamino-2-thiophenol, I, referred to in this paper by the abbreviation SATP. (-JCH="J-J YYSB ' OH HS ' r(\y'" I -OH I1 This compound I is obtained as colourless needles melting at 133" to 136" C. It is insoluble in water, slightly soluble in dilute acids to give colourless solutions and soluble in alkali hydroxide or carbonate to give yellow solutions.It is generally soluble in organic solvents. Like most anils, SATP tends to hydrolyse in solution, particularly in the presence of acids. Continued heating of the solution results in the formation of a stable yellow phenolic compound, with a marked yellow fluorescence in ultraviolet light, which is thought to be a benzothiazoline, 11. Alkaline solutions of the compound, 11, show a strong blue fluorescence. SATP reacts readily with tin in aqueous solution to give an insoluble yellow complex. The complex can be extracted into immiscible organic solvents to give a bright yellow solution that can be used for the photometric determination of tin.EXPERIMENTAL Salicylideneamino-2-thiophenol can be prepared as follows. Dissolve 10.0 g of salicylaldehyde in 25 ml of chloroform and mix in a 100-ml flask with a solution of 10.25 g of 2-aminothiophenol also dissolved in 25 ml of chloroform. Slowly distil off part of the chloroform by immersing the flask in a water-bath at 67" C. When about half of the chloroform has distilled, a turbidity appears in the flask. Maintain the bath at 67" C for a further 5 minutes, then remove the flask and allow it to cool to room temperature. Filter the solid on to a Buchner funnel and alternately stir with small volumes of chloroform and suck dry until all of the yellow colour has been removed. After re-crystallisation from ethanol, a yield of 5.8 g is obtained.It is important that the temperature is not allowed to rise above 70" C at any stage of the preparation and that heating is not unnecessarily prolonged. An analysis of SATP gave sulphur 13-95 per cent. and nitrogen 6.12 per cent. (theoretical, sulphur 13.98 per cent.; nitrogen 6.11 per cent.).294 GREGORY AND JEFFERY SALICYLIDENEAMINO-2-THIOPHENOL [Analyst, VOl. 92 SATP is soluble in acetone, ethyl methyl ketone and isobutyl methyl ketone, and less soluble in aliphatic alcohols. However, the decomposition of the reagent is extremely rapid in ketonic solution and also in methanol. This decomposition is still appreciable in other alcoholic solutions, but can be considerably retarded by adding ascorbic acid and by avoiding exposure to light. Solutions in ethanol containing ascorbic acid and stored in brown glass bottles are sufficiently stable for use over a period of 8 hours.In neutral aqueous solutions SATP reacts with many cations to give mainly yellow reaction products. Under these conditions V(V), V(IV), Cr(VI), Fe(III), Co(II), Cu(II), Zn(II), Ga(III), Ge(IV), Mo(VI), Ag(I), Cd(II), In(III), Sn(IV), Sn(II), Pt(IV), Au(III), Hg(II), Hg(I), Tl(III), Pb(I1) and U(V1) all react visibly with the reagent. In acid solution at pH 2 the reagent reacts with a reduced number of cations. These are listed in Table I. Most of these reaction products give coloured solutions in organic solvents. TABLE I REACTIONS OF SALICYLIDENEAMINO-2-THIOPHENOL I N ACID SOLUTION, pH 2 I on V(V) V(IV) Cr(V1) Fe(II1) Cu(I1) Ga(II1) Mo(V1) &(I) Sn(1V) Sn(I1) Bi(II1) Pt(1V) Reaction Pale yellow precipitate .. .. Pale blue precipitate . . .. . . Pale yellow precipitate . . .. Green precipitate . . . . .. Pale yellow precipitate . . . . Brown precipitate . . . . .. Yellow colour . . .. . . .. Yellow precipitate . . .. . . Yellow precipitate . . .. .. Pale yellow colour . . .. .. Pale yellow precipitate . . .. Pale yellow precipitate (fading) . . Extraction of complex into isobutyl into xylene methyl ketone Extraction of complex None Colourless Pale yellow* Colourless Yellowt Pale yellow None Faint yellow? Yellow Yellow None None None Colourless Yellow Colourless Yellow* Colourless Yellow Yellow* Yellow Yellow None Pale yellow Transient yellow colours are also given by In(III), Au(III), Hg(II), Hg(1) and Tl(II1).* Partial extraction. t Slight extraction. No reaction has been observed in either neutral or acid solution with the following cations: Li(I), Na(I), Mg(II), Al(III), K(I), Ca(II), Ti(IV), Cr(III), Mn(II), Fe(II), Ni(II), As(V), As(III), Sr(II), Y(III), Zr(IV), Sb(V), Sb(III), Ba(II), the lanthanons, W(VI), Tl(1) and Th(1V). Formation of the tin complex at as low a pH as possible increases the selectivity to tin and also avoids a tendency for tin to hydrolyse from solution. Below pH 2 where there is still a tendency for tin to hydrolyse, both the reagent and the tin complex decompose fairly rapidly. Attempts to keep the tin in solution by complex formation at pH 2 with citric, tartaric or oxalic acids were unsatisfactory, as the presence of these acids also prevented the formation of the tin - SATP complex.However, the addition of lactic acid not only prevented hydrolysis but also permitted the reaction of tin with the reagent. The inclusion of lactic acid also prevented formation of the molybdenum complex. The tin complex, together with excess of reagent, extracts readily into all the common immiscible organic solvents, although the extracted tin complex is not very stable in ketones and alcohols-the yellow colour fading fairly rapidly with time. The use of hydrocarbon solvents, in which the copper, silver and molybdenum - SATP complexes are only slightly soluble, confers greater selectivity towards tin. It was observed, however, that in aliphatic hydrocarbons such as hexane or iso-octane the tin complex gives first a clear yellow solution, then precipitates slowly as the extract ages.This did not occur in benzene, toluene or xylene solution. Because of its lower toxicity and higher flash-point, xylene was the preferred extractant. The use of ascorbic acid to stabilise the reagent solution also reduces iron(II1) to the non-reacting iron(f1) form. The effect of small amounts of these cations can be further reduced by masking with sodium thiosulphate. The thiosulphate ion does not interfere with tin complex formation, but its decomposition in acid solution to give finely divided sulphur limits the amount that can be added. Both copper and silver still interfere to some extent.May, 19671 295 From the absorption curves of the reagent and of the tin complex in the xylene extract, shown in Fig.1, it can be seen that the maximum optical density occurs at 415 mp. There is a relatively small residual absorption due to the extracted reagent. The molar absorptivity, calculated from a calibration, is 16,100. Straight-line calibration graphs indicate that, pro- vided a considerable excess of reagent is present, the Beer -Lambert law is valid up to 50 pg of tin in 10 ml of xylene. A NEW REAGENT FOR PHOTOMETRIC DETERMINATION OF TIN Wavelength, my Fig. 1. Absorption spectrum for A, tin complex measured against reagent blank (50 pg of tin in 10 ml of solution, with 1-cm cells); and B, reagent blank measured against xylene METHOD REAGENTS- Salicylideneamino-2-th~o~henol solution-Dissolve 1 g of ascorbic acid in 100 ml of warm ethanol.Add 0.1 g of salicylideneamino-2-thiophenol and stir until dissolved. Store in a brown glass bottle and prepare freshly each day, 2,4-Dinitrophenol indicator solution-Dissolve 0.25 g of 2,4-dinitrophenol in a mixture of 50 ml of ethanol and 50 ml of water. Sodium hydroxide, about 2.5 N. Lactic acid solution-Mix 20 ml of lactic acid and 80 ml of water. Sodium thiosulphate solution-Dissolve 1 g of sodium thiosulphate pentahydrate in 100 ml Xylene, AnalaR grade. Ti.n(IV) standard stock solution-Weigh accurately about 0-5 g of high purity tin metal into a conical flask. Add 200 ml of concentrated hydrochloric acid, cover with a clock-glass and allow to stand until dissolved (up to 2 days may be necessary). Add 1 ml of 100-volume hydrogen peroxide and dilute to 1 litre with water in a calibrated flask, T i .n ( W ) dilute standard solution-Dilute accurately 25 ml of the stock standard solution to 250 ml with diluted (1 + 9) hydrochloric acid. This solution contains 50 pg of tin per ml. PROCEDURE FOR TIN ORES- Mix intimately a weighed sample of about 0.25 g with 2.5 g of sodium peroxide in a nickel crucible. Heat until just sintered and then bring up to the fusion-point for a few minutes. Allow the melt to cool and dissolve it in 100 ml of 6 N hydrochloric acid. Dilute to 500 ml with water in a calibrated flask. Transfer an aliquot containing not more than 50 pg of tin to a 75-ml, all-glass, stoppered boiling-tube. Add 2 drops of the 2,kdinitrophenol indicator solution and neutralise carefully to a yellow end-point, or to just permanent precipitation of metal hydroxides, if these are present, by adding 2.5 N sodium hydroxide solution.Dilute to about 20 ml with water and add 2 ml of lactic acid solution. Mix and allow the solution to stand until any precipitated metal hydroxides have re-dissolved. Add 1 ml of the sodium thiosulphate solution and mix. Add by pipette 5 ml of the salicylideneamino-2-thiophenol of water.296 GREGORY AND JEFFERY : SALICYLIDENEAMINO-2-THIOPHENOL [ArtaZySt, VOI. 92 solution, shake the tube immediately and allow it to stand for 20 minutes. Extract with exactly 10 ml of xylene, shake the mixture vigorously for 20 seconds and allow the phases to separate. After allowing the solution to stand for 5 minutes, measure the optical density of the organic extract with a spectrophotometer set at a wavelength of 415 mp with a reagent blank solution, prepared at the same time as the sample solution, as reference. CALIBRATION- With a 1-ml semi-micro burette, measure aliquots of the dilute standard tin solution containing 0, 10,20,30,40 and 50 pg of tin into stoppered boiling-tubes.Follow the procedure as described above from the point at which the sample aliquot is transferred to the stoppered boiling-tube. Draw a calibration graph; this should be linear and pass through the origin. DISCUSSION CONSTITUTION OF THE TIN COMPLEX- The mole ratio, the Job and the Harvey and Manning methods all fail when used to investigate the constitution of the complex. This is because no appreciable reaction occurs until the reagent is present in at least a 10-molar excess.The effect of increasing reagent concentration is shown in Fig. 2. 20 40 60 80 100 120 I Reagent to tin, mole ratio 3 Fig. 2. Effect of reagent concentration on the formation of the tin complex The tin complex can be almost quantitatively precipitated by the addition of ethanolic reagent to an aqueous tin solution in the presence of lactic acid at pH 2. The final ethanol concentration should be at least 40 per cent. to avoid co-precipitation of excess of reagent but not above 45 per cent., when the tin complex becomes appreciably soluble. The complex is stable to drying at 110" C. Precipitation of 50 mg of tin by this method gave 241.7 mg of dried complex, corresponding to a reagent-to-tin ratio of 2.00. A titrimetric determination of tin in the dried complex after a wet oxidation gave 19-46 per cent.of tin, corresponding to a reagent-to-tin ratio of 2-16. The complex formed with tin(I1) has an identical absorption curve in xylene solution and the same molar absorptivity to that formed with tin(1V). It is possible that oxidation of the tin(I1) occurs, although this seems unlikely in the presence of ascorbic acid. From Fig. 2 it can be seen that at least a 50-molar excess of reagent must be used to ensure complete formation of the complex. Too great an excess must, however, be avoided or the absorption of the blank becomes excessively high. EFFECT OF TIME AND TEMPERATURE ON THE FORMATION OF THE COMPLEX- Sufficient time must be allowed after addition of the reagent for the insoluble complex to form, but low recoveries are obtained if this period is too protracted.This effect is shown in Fig. 3, from which it can be seen that 20 minutes appears to be the optimum time for measurement to be made. No temperature effect has been found between 5" and 40" C, but above 50" C the complex tends to decompose.May, 19671 A NEW REAGENT FOR PHOTOMETRIC DETERMINATION OF TIN 297 O" t I L . . A 40 20 Time, minutes Fig. 3. Effect of time of standing a t 20" C on the formation of the tin complex STABILITY OF THE EXTRACTED COMPLEX- When measured against the extractant, the optical densities of both the extracted tin complex and the blank first fall slightly and then increase slowly with time. The effect, shown in Fig. 4, is small but, for the most consistent results, it is advisable to take the measurements 5 minutes after separation of the phases.A reagent blank prepared at the same time as the sample must be used as the reference. f 5 0'361 0.35 0 20 40 60 Time, minutes Fig. 4. Effect of time of standing on the extracted complex: A, blank; B, 25pg of tin sample; and C, after correction for the blank INTERFERING IONS- The effect of several possible interferences on the determination of 25 pg of tin is given in Table 11. The most serious interference is that from copper, of which not more than 5 pg can be tolerated. Large amounts of chloride and of sulphate do not interfere. One of the advantages of the proposed method is that, for most materials, a preliminary separation of the tin is not necessary.If a separation is required, the bromide distillation method of Onishi and Sandel12 or the iodide extraction method of Tanaka3 as modified by Newman and Jones4 should prove satisfactory.298 GREGORY AND JEFFERY : SALICYLIDENEAMINO-2-THIOPHENOL [ArtaZySt, VOI. 92 TABLE I1 INVESTIGATION OF INTERFERENCES Tests were made by adding the interfering ion to a solution containing 25 pg of tin Ion added V(V) .. V(1V) . . Cr(V1) . . Cr(II1). . Fe(II1) CO(I1) . . Cu(I1) . . Zn(l1) . . As (I I I ) Mo(V1) A m - . Cd(I1) . . Sb(II1) Hg(II) Pb(I1) . . Bi(II1). . .. .. . . . . .. .. .. .. .. .. . . .. .. .. . . . . Phosphate . . Fluoride . . Several samples have are given in Table 111. .. .. .. . . .. . . .. . . . . .. .. .. . . .. .. . . . . .. Amount added, Pg 1000 100 1000 100 100 25 1000 100 10,000 1000 1000 100 25 5 1000 1000 100 1000 100 1000 100 1000 1000 100 1000 1000 100 1000 1000 500 100 1000 100 Amount of tin recovered, Pi? 26.9 25.5 26.5 25.0 26.4 25.4 21.0 24.0 21-8 25.3 25.0 30.9 27.5 25.4 25.0 27.5 25.0 25.8 25.0 Extract turbid 24.3 25-4 32.0 25-5 250 26.2 25.4 25.3 17.2 23.5 25.0 24.6 24.8 Recovery, per cent.107.5 102.0 106.0 100.0 105.5 101.5 84.0 96-0 87.5 101.0 100.0 123-5 110.0 101.5 100.0 110.0 100.0 103.5 100.0 97.0 102.0 12s.o 102.0 100.0 104.5 102.0 101.0 68.0 94-0 100.0 98.0 99.0 - RESULTS been analysed by the proposed method. The results obtained TABLE I11 COMPARISON OF RESULTS WITH THOSE OBTAINED BY A TITRIMETRIC METHOD Laboratory reference number s 453 s 454 s 455 S 456 s 457 S 451 S 460 S 461 S 462 Tin, per cent.Sample c o 1 o m m ; t r i c Canadian tin ore, tin concentrate . . Canadian tin ore, mill sample . . .. Canadian tin ore, tail sample . . .. Geevor mine, mill sample “A” . . .. Geevor mine, mill sample “B” . . .. Cornish beach sand, composite sample . , Cornish beach sand, No. 1 concentrate.. Cornish beach sand, No. 2 concentrate.. Cornish beach sand, table concentrate . . 45.4 0-62 0.80 0-66 1.02 0.14 21.1 6.0 2.25 45.5 0.37 (0.58) * 0.69 0.66 1.02 0.14 5.97 2.06 20.4 * This result was obtained by X-ray fluorescence analysis. REPRODUCIBILITY OF THE METHOD- Eight replicate aliquots were taken from one sample solution of a tin concentrate (S 453) and the tin complex extracted into xylene as described above. The optical densities recorded were 0-622, 0.624, 0.622, 0.622, 0.615, 0.618, 0.620 and 0.624 (standard deviation 0.003, and the coefficient of variation 0.5 per cent.).Four completely separate determinations of tin on this concentrate gave values of 45.7, 45.2, 45-4 and 45.0 per cent.May, 19671 APPLICATION OF THE REAGENT TO SILICATE ROCKS AND MINERALS- As an extension of this work, attempts were made to determine tin in several silicate materials. Silica was removed by evaporation with hydrofluoric and sulphuric acids and the residue fused with potassium pyrosulphate. After solution of the melt in dilute hydro- chloric acid, the tin present was determined by the procedure described above, except that additional ascorbic acid was added to reduce iron(II1). The results obtained are given in Table IV. A NEW REAGENT FOR PHOTOMETRIC DETERMINATION OF TIN 299 TABLE IV COMPARISON OF RESULTS FOR SOME SILICATES Tin, p.p.m. Sample material with SATY other methods G l , granite . . . . 2.0, 2-8, 3.6 4* JV-1, diabase . . . . 2-9, 3-4 3” T-1, tonalite . . . . 1.2, 1.5 50, 29, 50t * “Recommended vslucs,” Flei~cher.~ t Quoted by Thomas6 The reproducibility of these results is far from satisfactory and further work is clearly indicated before this method can be recommended. CONCLUSIONS Salicylideneamino-2-thioplienol is proposed as a new photometric reagent for deter- mining tin. I t is sufficiently specific to permit the direct determination of the metal in most ores, rocks and minerals without the necessity of a preliminary separation. REFERENCES 1. 2. Onishi, H., and Sandell, E. B., Analytica Chim. Acta, 1956, 14, 153. 3. 4. 5. Fleischer, M., Geochim. Cosmochim. Acta, 1965, 29, 1263. 6. Dagnall, R. M., Smith, R., and West, T. S., Talanta, 1966, 13, 609. Tanaka, K., Japan Analyst, 1962, 11, 332; Analyt. Abstr., 1964, 11, 86. Xewman, E. J., and Jones, P. D., Analyst, 1966, 91, 406. Thomas, JV. I<. L., “Standard Geochemical Sample T-1,” Supplement No. 1, Government Printcr, Received Septenzber 6th. 1966 Dar es Salaam, 1963.

ISSN:0003-2654    

DOI:10.1039/AN9679200293

出版商:RSC    

年代:1967

数据来源: RSC

摘要:

300 Analyst, May, 1967, Vol. 92, $9. 300-304 Determination of Trace Amounts of Magnesium, Strontium and Nickel in Lake-water Samples by Neutron-activation Analysis BY A. G. SOULIOTIS, E. P. BELKAS AND A. P. GRIMANIS (Nuclear Research Center “ Democritos,” Chemistry Department, Aghia Paraskevi A ttikis, Athens, Greece) Neutron-activation analysis has been used to determine magnesium, strontium and nickel in water from eleven Greek lakes. The elements were separated by an isolation procedure (taking up to 30 minutes) ; the magnesium and strontium were determined by y-spectrometry, and the nickel by p-co- incidence counting. The ranges found were 11 to 31 p.p.m. of magnesium, 0.02 to 1.12 p.p.m. of nickel and 0.07 to 0.48 p.p.m. of strontium. NEUTRON-activation analysis is a rapid modern analytical method that is available for most precise analytical work for determining trace elements in different matrices.l ,2 y 3 Because of its high sensitivity and accuracy, neutron-activation analysis has become a useful tool for analytical chemist^.^ to 11 In the past years spectrographic methods had been applied for determining minute amounts of elements in lake waters,12 but these methods or other conven- tional ones were sometimes restricted for some elements because of insufficient sensitivity, the impurity of the reagent or the large reagent blanks.A promising method for determining microgram or submicrogram amounts of elements present in lake water is neutron-activation analysis, which will supply complementary or new information for most trace elements in lake waters.Radioactivation analysis has also been used by several investigators for determining trace elements in water.13y14?15J6 A review of the chemical composition of the river and lake waters of the world has been made.17 Recently 14 trace elements were determined in the Greek lakes by activation analysis.ls Magnesium and strontium (simultaneously) and also nickel were determined in the same lakes by neutron-activation analysis. The half-lives of the nuclides are 9-45 minutes for magnesium-27, 2.8 hours for stron- tium-87m and 2.56 hours for nickel-65. Various competing nuclear reactionslg y2* s 2 1 have been considered, but are found to be insignificant when the levels of the interfering elements, present in the lake waters, have been taken into account.EXPERIMENTAL Materials of analytical-reagent grade were used. Magnesium nitrate carrier solution-Prepare an aqueous solution of magnesium nitrate Staizdard magnesium nitrate solution-Prepare an aqueous solution of magnesium nitrate Manganese chloride hold-back carrier solution-Prepare an aqueous solution of manganese Sodium chlorate, solid. Nitric acid, fuming, 6 N, concentvated, 20 and 50 per cent., aqueous. Sodium nitrate hold-back carrier solution-Prepare an aqueous solution of sodium nitrate Ethanol, absolute. Phenolphthalein indicator, 0- 1 per cent. alcoholic solution. Ammonia solution, concentrated, 2.5 per cent., aqueous. Diammonium hydrogen orthophosphate solution, 25 per cent., aqueous, freshly prepared. REAGENTS- containing 10mg of magnesium per ml. containing 0-2 mg of magnesium per ml.chloride containing 10mg of manganese per ml. containing 10 mg of sodium per ml.SOULIOTIS, BELKAS AND GRIMANIS 301 Hydrochloric acid, 2 N, 3 N and 4 N. Strontium nitrate carrier solution-Prepare an aqueous solution of strontium nitrate containing 10mg of strontium per ml. Standard Strontium nitrate solution-Prepare an aqueous solution of strontium nitrate containing 5 mg of strontium per ml. Barium chloride hold-back carrier solution-Prepare an aqueous solution of barium chloride containing 10 mg of barium per ml. Copper nitrate hold-back carrier solution-Prepare an aqueous solution of copper nitrate containing 10mg of copper per ml. Iron(II1) nitrate hold-back carrier solution-Prepare an aqueous solution of iron( 111) nitrate containing 10mg of iron per ml.Ammonium acetate, 6 M, aqueous. Acetic acid, 6 M. Sodium chromate solution, 1.5 M, aqueous. Sodium carbonate solution, 10 per cent., aqueous. Nickel metal-Supplied by Johnson, Matthey & Co. Ltd., spectrographically pure. Nickel nitrate carrier solution-Prepare an aqueous solution of nickel nitrate containing Benzene. Sodium chloride hold-back carrier solution-Prepare an aqueous solution of sodium chloride Ammonium arsenate hold- back carrier solution-Prepare an aqueous solution of ammonium Potassium sodium tartrate solution, 10 per cent., aqueous. Dimethylglyoxime, 1 per cent. alcoholic solution. Chloro form. IRRADIATION Lake-water samples were stored in polythene bottles. Before irradiation, samples were filtered through a Pyrex funnel with Whatman filter-paper and transferred with a Pyrex pipette into small polythene tubes.In all irradiations the targets were sent to the core of the reactor by a pneumatic transfer system (rabbit). The flux to which targets were irradiated was 2 x lo1% per cm2 per second supplied by the “Democritos” swimming-pool nuclear reactor operating at 1 MW. With magnesium and strontium, a volume of more than 10ml of lake-water sample was placed in the external tube of the specially adjusted polythene via1.22 An amount of more than 1 ml of a mixture consisting of equal volumes of the magnesium and strontium standard solutions was put in the central tube. The irradiation time was 25 minutes. For nickel the target was adjusted in the same manner as above.A volume of more than 10 ml of lake water was transferred by pipette into the external tube. Nickel turnings, 10 mg, were weighed into two small snap-closure polythene vials, which were then inserted in the central tube.23 The irradiation time was 45 minutes. 10mg of nickel per ml. containing 10 mg of sodium per ml. arsenate containing 10mg of arsenic per ml. RADIOCHEMICAL SEPARATIONS24s25s26 MAGNESIUM AND STRONTIUM- After irradiation of the target, 5 ml of the lake-water sample were transferred by pipette (sampling in duplicate) into a 50-ml centrifuge tube containing 1 ml of magnesium and 2 ml of strontium carrier solutions, and 1 ml each of hold-back carrier solutions of manganese, barium and sodium. The solution was cooled in an ice-bath, and 25 ml of cold fuming nitric acid were added. The supernatant liquid was collected in another 50-ml centrifuge tube for isolating the magnesium, while the precipitate was subjected to the strontium isolation procedure.Supernatant liquid-The solution was heated in a water-bath, and a few crystals of sodium chlorate were added. The manganese dioxide precipitate was separated by spinning the solution in a centrifuge. The supernatant liquid was decanted into another 250-ml centrifuge tube, cooled in an ice-bath, and 1 ml of sodium hold-back carrier solution was added. Careful and complete neutralisation of the nitric acid was carried out with concen- trated ammonia solution (about 35 ml) in the presence of phenolphthalein indicator, and 5 ml The precipitate was spun in a centrifuge.302 SOULIOTIS, BELKAS AND GKIMANIS : DETERMINATION OF TRACE AMOUNTS [Auzalyst, Vol.92 of diammonium hydrogen orthophosphate solution were added while stirring and cooling the mixture. The ammonium magnesium orthophosphate precipitate was separated by spinning the solution in a centrifuge for 1 minute at 3000 r.p.m. The ammonium magnesium ortho- phosphate precipitate was dissolved in a few drops of 3 N hydrochloric acid and then trans- ferred into a 50-ml centrifuge tube and cooled in an ice-bath The hydrochloric acid solution was completely neutralised in the presence of phenolphthalein indicator with a few drops of concentrated ammonia solution. To the solution 1 ml of diammonium hydrogen ortho- phosphate solution was added and the ammonium magnesium orthophosphate precipitate was filtered, rinsed with 2-5 per cent.ammonia solution and finally with ethanol. The filter-paper and precipitate were transferred into a culture tube for counting. After counting, the filter-paper and precipitate were transferred into a pre-weighed porcelain crucible and then ignited at 1100" C to magnesium pyrophosphate. (The chemical yield was, on the average, about 65 per cent.) Precifiitate-The precipitates of barium nitrate and strontium nitrate were dissolved in 2 to 3 ml of water. Aliquots of copper, sodium and iron hold-back carrier solutions, 1 ml of each, were added to the solution together with 1 drop of phenolphthalein indicator. Concentrated ammonia solution was added dropwise to precipitate iron as iron(II1) hydroxide scavenger.The supernatant liquid was decanted into another 50-ml centrifuge tube. The ammoniacal solution was completely neutralised with 6 N nitric acid; 2 ml of 6 M ammonium acetate and 1 ml of 6 M acetic acid were added to the solution, which was heated to boiling, and 1 ml of 1.5 M sodium chromate was then added dropwise. The solution was stirred and cooled in an ice-bath. The barium chromate precipitate was separated by spinning in a centrifuge. The supernatant liquid was decanted into another 50-ml centrifuge tube, neutralised with con- centrated ammonia solution (pH 7) and then 10 ml of 10 per cent. sodium carbonate solution were added. The solution was heated to coagulate the strontium carbonate precipitate, which was then filtered with a pre-weighed filter-paper, rinsed with water and then with ethanol.The filter-paper with the precipitate were transferred into a culture tube for counting. After counting they were heated at 110°C. (The chemical yield, on the average, was about 60 per cent.) For the standards a 0-5-ml aliquot was used (sampling in duplicate) and the same analytical steps were followed exactly. The precipitate was separated by spinning the solution in a centrifuge. NICKEL- After irradiation of the target, 5 ml of lake-water sample were transferred by pipette (sampling in duplicate) into a 100-ml beaker containing 1-ml portions of hold-back carriers of sodium chloride and ammonium arsenate and 5 ml of 20 per cent. potassium sodium tartrate. The solution was adjusted to pH 9 with ammonia solution.A standard precipitation of nickel as nickel - dimethylglyoxime was carried out and the nickel - dimethylglyoxime was then extracted into chloroform. The same step was once again repeated with the aqueous phase. The same step was once again repeated in the chloroform layer. The aqueous solution was adjusted to pH 9 with ammonia solution, and a standard precipitation of nickel as nickel - dimethyl- glyoxime was carried out in the presence of the hold-back carriers and tartrate. The nickel - dimethylglyoxime precipitate was rinsed with hold-back carriers (Naf, C1-, As5+) and hot water. The nickel - dimethylglyoxime precipitate was dissolved in hot 4 N hydrochloric acid. After dissolution, the filtered solution was neutralised with ammonia solution and brought to pH 9; a standard precipitation of nickel - dimethylglyoxime was then carried out in the presence of the same hold-back carriers and tartrate.The precipitate was filtered with a pre-weighed filter-paper, rinsed in the same way as before, air dried by suction and counted. After counting it was heated at 110" C. (The chemical yield, on the average, was about 90 per cent.) For the standards, the nickel turnings were transferred into two beakers, 1-ml volumes of 50 per cent. nitric acid were added and then heated until dissolution occurred. The two nickel nitrate solutions were transferred into two 1-litre calibrated flasks and were then diluted to volume. Aliquots of 100p1, taken from solutions in each calibrated flask (sampling in duplicate), were subjected to the same analytical steps as before.Nickel was back-extracted from chloroform with 2 N hydrochloric acid.May, 19671 OF MAGNESIUM, STRONTIUM AND NICKEL IN LAKE-WATER SAMPLES DETERMINATION OF RADIOACTIVITY The radioactivity measurements for magnesium-27 and strontium-87nz were made by using a well-type crystal connected to a single channel analyser to count y-rays at the areas 0-83 MeV and 0.39 MeV, respectively. Because of the presence of nickel-65 a ,&count was made with a Geiger counter connected anti-coincidentally. 303 RE s u LTS IDENTIFICATION AND CONTROL OF RADIOCHEMICAL PURITY OF MAGNESIUM-27, STRONTIUM-87WZ AND NICKEL-65- The isolated precipitates of ammonium magnesium phosphate, strontium carbonate and nickel - dimethylg1yoxime:were subjected to a y-ray spectrometric e~arnination,~' y28 which con- firmed the absence of any y-emitting radionuclide as contaminant.Hal€-life measurements of the isolated radio-elements were also performed by plotting the decay curve on semi-log paper, for each isolated precipitate. The half-life was obtained from the slope of the straight line which was calculated by the method of least squares. Values were found corresponding to those reported in the literat~re.1~ $0 CONCENTRATION OF ELEMENTS DETERMINED- Quantitative results for the magnesium, strontium and nickel content of lake-water samples taken from the surface and depth of the most important Greek lakes have been obtained by radiochemical methods. The results, being the average of at least duplicate analyses, are given in Table I.Samples analysed were collected with a Ruttner water sampler (made of Plexiglass) from the surface and 5 or 15 metres' depth, depending on the maximum depth of each lake. The collection of samples was made at the deepest point, often the centre of the lakes. TABLE I CONCENTRATION OF ELEMENTS DETERMINED IN LAKE-WATER SAMPLES" Lake Aghios Vassiliosi Doiranit . . Ioanninat . . Kastoria: . . Marathon: . . Ostrovon: . . Paralimni $ . . Prespa mikrit Stymphaliss . . Trichonisj . . Volvii .. . . . . . . . . Magnesium 7 h - - 7 Surface Depth 28.3 30.6 19.7 19.8 12.7 10-5 14.5 14.4 13.7 16-9 25.9 27- 1 21.5 25.3 11.2 11.7 13.0 - 10.9 16.2 26.7 23.6 Strontium Nickel 7 h - 7 r.__L 7 Surface Depth Surface Depth 0.07 0.09 0.02 0.09 0.26 0.44 0-66 0.27 0.17 0.17 1.22 0.52 0.10 0.16 0.64 0.76 0.20 0.22 0.09 0.10 0.12 0.09 0.46 0.21 0.16 0.17 0.44 0.74 0-07 0.09 0-93 0.29 0-48 - 0.23 - 0.29 0.40 0.54 0.58 0.15 0.08 0.50 0.57 * Concentrations expressed in parts per million.t Depth of sample collection, 5 metres. $ Depth of sample collection, 15 metres. $ Maximum depth less than 4 metres. Each lake-water sample analysis was performed a t least in duplicate. DISCUSSION The analytical methods proposed involve the use of radiochemical separations, and result in a remarkable radiochemical purity of the isolated precipitates of ammonium magnesium orthophosphate, strontium carbonate and nickel - dimethylglyoxime. Experimental values are reproducible, with a relative error of less than + 2 per cent. From the results given it is apparent that activation analysis with its high sensitivity should play an important r81e in supplying complementary or new information on elements present in microgram or sub- microgram amounts in lakes.The information given by our results in this paper may have, for the elements determined, not only geological but also biological interest. The presence304 SOULIOTIS, BELKAS AND GRIMANIS or absence of some trace elements can affect the eutrophic, oligotrophic or atrophic behaviour of the lake. Determination of the trace elements in a given lake should, therefore, be performed several times a year. We thank Miss M. A. Phoka and Mr. S. C. Archimandritis for their valuable assistance in the 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. present study. REFERENCES Bock-Werthmann, ?V., and Schulze, W., “Activiersungs Analyse, ” A tomkernenergie-Documentation, Beim Gmelin Inslitut, AED-C-14-1, Hahn-Meitner Institut fur Kernforschung, Berlin, 1961. Bock-Werthmann, W., Ibid., AED-C-14-2, Hahn-Meitner Institut fur Kernforschung, Berlin, 1963. , Ibid., AED-C-14-3, Hahn-Meitner Institut fur Kernforschung, Berlin, 1964. Boyd, G. E., Analyt. Chenz., 1949, 21, 335. Leddicotte, G. W., and Reynolds, S. A., Nucleonics, 1951, 8, 62. Leddicotte, G. W., Mullins, W. T., Bate, L. C., Emery, J. F., Druschel, R. E., and Brookbank, W. A., jun., Int. Conf. Peaceful Uses Atom. Energy, Geneva, 1958, 28, 478. Atkins, D. H. F., and Smales, A. A., in Emelkus, H. J., and Sharpe, A.G., Editors, “Advances in Inorganic Chemistry and Radiochemistry,” Academic Press, New York, Volume 1, 1959, p. 315. Leddicotte, G. W., Pure Ap@. Chem., 1960, 1, 61. Meinke, W. W., in “Chemistry Research and Chemical Techniques Based on Research Reactors,” Tech. Rept. Series No. 17, I.A.E.A., Vienna, 1963, 95. Meinke, W. W., Analyt. Chem., 1959, 31, 792. Hutchinson, E. G., Editor, “A Treatise on Limnology,” J. Wiley & Sons, Inc., New York, 1957. Blanchard, R. L., and Leddicotte, G. W., U.S. Atomic Energy Commission Report ORNL-2620, Blanchard, R. I,., Leddicotte, G. W., and Moeller, D. W., Int. Conf. Peaceful Uses Atom. Energy, Leddicotte, G. W., and Moeller, D. W., Rept. C.F.-61-5-118, 1961, p. 32. Selz, J., Haerdi, W., and Monnier, D., Chimia, 1963, 17, 354. Livingston, D. A., Prof. Pap. U.S. Geol. Surv., 440-G, 1963. Grimanis, A. P., Pantazis, G., Papadopoulos, C., and Tsanos, N., Int. Conf. PeacefuE Uses Atom. Strominger, D., Hollander, J. M., and Seaborg, G. T., Rev. Mod. Phys., 1958, 30, 585. Allen, R. A., Smith, D. B., and Hiscott, J . E., “Radioisotope Data,” Second Edition, U.K. Atomic Koch, R. C., “Activation Analysis Handbook,” Academic Press, New York and London, 1960. Belkas, E. P., and Souliotis, A. G., Analyst, 1966, 91, 199. Souliotis, A. G., Analyt. Chem., 1964, 36, 811. Fairhall, A. W., “The Radiochemistry of Magnesium,” U.S. Atomic Energy Commission Report Sunderman, D. N., and Townley, C. W., “The Radiochemistry of Barium, Calcium and Strontium,” Kirby, L. J., “The Radiochemistry of Nickel,” U.S. Atomic Energy Commission Report NAS- Grouthamell, C . E., Editor, “Applied Garnma-ray Spectrometry,” Oxford, London, Edinburgh, Heath, R. L., “Scintillation Spectrometry, Gamma-ray Spectrum Catalogue, ” U.S. Atomic Energy Received June 15th, 1966 , Science, 1955, 121, 86. 1959, p. 78. Geneva, 1958, 28, 511. Energy, Geneva, 1964, 15, 854. Energy Research Establishment Report AERE-R 2938, H.M. Stationery Office, London. NAS-NS-3024, 1961. U.S. Atomic Energy Commission ReFort NAS-NS-3010, 1960. NS-3051, 1961. New York, Toronto, Sydney, Paris and Braunschweig, Pergamon Press, 1960. Commission Report IDO-16408, 1957.

ISSN:0003-2654    

DOI:10.1039/AN9679200300

出版商:RSC    

年代:1967

数据来源: RSC

摘要:

Analyst, May, 1967, Vol. 92, $19. 305-310 305 A Rapid Method for the Determination of Iron in Plant Material with Application of Automatic Analysis to the Colorimetric Procedure BY C. QUARMBY AND H. M. GRIMSHAW (Natural Environment Research Council, The Nature Conservancy, Merlewood Research Station, Gvange-over-Sands, Lancashive) A colorimetric procedure is described for the determination of iron in plant material by using sulphonated 4,7-diphenyl- 1,lO-phenanthroline. The method may be applied directly to the AutoAnalyzer, and gives good and reproducible recoveries over a wide range of added iron. The possibility of low recoveries of iron resulting from the wet digestion of material in the presence of sulphuric acid is discussed. THE accurate determination of iron in biological materials has often proved difficult, even though many colorimetric methods have been described-l This is borne out in a report of the Agricultural Research Council,2 in which identical samples of several plant materials were sent to ten centres for analysis by their own methods.Solution preparation involved wet or dry ashing, and was followed by the use of l,l0-phenanthroline, dipyridyl, potassium thiocyanate or salicylic acid in colorimetric determinations. One centre used direct spectro- graphic arcing of the powdered samples. The results showed large inter-laboratory variations, ranging from 20 to 60 per cent. of the mean, according to the material analysed. Replicate determinations at the same centre of sub-samples of a given material also gave variable results, but were of a smaller range than those from different centres.Subsequent examination showed that plant material is particularly susceptible to surface contamination by iron- bearing dust and soil particles; moreover, the actual distribution of iron within the tissues may vary locally, thus making representative sub-sampling difficult. Differences in the amount of sample taken and in methods of preparation for analysis were also suspected of contributing significantly to the variability of the results. The method described involves the wet digestion of the plant material, with colorimetric determination of the iron by a fully automatic or relatively rapid manual method. It has been shown to give good recovery of a wide range of added iron, and with replicate samples of oak leaf litter gave values varying by less than 2 per cent.of the mean. THE MANUAL METHOD Case3 introduced 4,7-diphenyl-l,l0-phenanthroline, generally referred to as bathophenan- throline,* as an improvement on the well known 1,lO-phenanthroline. However, as this substituted compound is barely soluble in water, it has to be dissolved in ethanol or aqueous ethanol, and the iron(I1) complex is generally extracted into an organic solvent before measurement. This increases the sensitivity of the determination, but the method is tedious when dealing with large numbers of samples. The present method is simpler, and makes use of a sulphonated form of bathophenanthroline as described by Riley and Williams? REAGENTS- All reagents should be of analytical grade.Nitric acid, concentrated, sp.gr. 1.42. Sulphuric acid, concepztrated, sp.gr. 1.84. Perchloric acid, 60 per cent., sp.gr. 1.54.306 [Analyst, Vol. 92 Su@honated bathophenanthroline-Treat 0.4 g of 4,7-diphenyl-l , 10-phenanthroline with 4.0 ml of fuming sulphuric acid (20 per cent. sulphur trioxide). Stir until dissolved, leave to stand for 30 minutes and pour into 400 ml of water. Neutralise the excess of acid with ammonium hydroxide to pH 4 to 5 and make up to 1 litre. QUARMBY AND GRIMSHAW: RAPID METHOD FOR THE Hydroxylammoniwt chloride, 2.5 pey cent. w / v , aqueous. Sodium acetate, 33 pev cent. NaOOC.CH,.3H20 w / v , aqueous. Standard ivon solutions-Prepare a stock solution by dissolving 0.1000 g of clean iron wire in about 10 ml of 10 per cent.sulphuric acid and making the volume up to 1 litre. Dilute 100-fold to give a standard solution containing 1 pg of iron per ml. Colorimetric yeagent- Just before the determination mix sodium acetate, sulphonated bathophenanthroline and hydroxylammonium chloride solutions in the proportions 4 + 3 + 1. INITIAL TREATMENT OF SAMPLE- oven, until sufficiently brittle to be ground. used, taking care that the entire sample passes through the sieve. mesh of 0-4 to 0-7 mm has been found suitable for sample weights of 50 to 500 mg. the ground sample in an oven at 105" C for 3 hours before weighing for digestion. Plant material should be dried at room temperature, or at 40" C in an air-circulated Any suitable knife or hammer mill may be In this laboratory, a Dry PREPARATION OF SAMPLE SOLUTION- Digest up to 0.5 g of the ground vegetation with 1 ml of 60 per cent.perchloric acid, 6 ml of concentrated nitric acid and 1 ml of concentrated sulphuric acid in a 200-ml Kjeldahl flask. Blank digestions are required as a check on possible contamination of the digest acids. Bring to the white fume stage and heat for a further 15 minutes. Normally, on cooling, the remaining liquid should be colourless. Dilute the digest with about 15 ml of water, boil for 10 minutes, filter into a 100-ml calibrated flask and dilute to the mark when cool. PROCEDURE- Transfer by pipette 20 ml of the sample solution containing up to 0.03 mg of iron into a 50-ml calibrated flask. If a smaller aliquot is taken, the acid content should be adjusted to give a final concentration equivalent to 20 ml of 1 per cent.sulphuric acid. Add 16 ml of the colorimetric reagent, dilute to volume, mix thoroughly and read the optical density at 536 mp. Beer's law is obeyed up to at least 0.4 mg of iron per 50 ml, and the colour is stable for at least 24 hours. The standards (0 to 0.03 mg of iron) are transferred by pipette into 50-ml calibrated flasks and the acidity made equivalent to 20 ml of 1 per cent. sulphuric acid. They are then treated as described above. RESULTS AND DISCUSSION Riley and Williams applied the bathophenanthroline method to rocks and minerals that are normally very rich in iron, and they required only 1 ml of sample digest for colour develop- ment. The iron(I1) - bathophenanthroline complex is stable over the pH range 2 to 9, and they found that a sodium acetate buffer at a final concentration of 0 .0 4 ~ was sufficient to maintain the final pH within the required range. Plant materials, however, usually have a relatively low iron content and larger aliquots of the digests are required. Furthermore, the amount of acid remaining after wet digestion may vary slightly. In most of the methods described, the excess acid is neutralised with dilute ammonia solution by using pH papers or a pH meter, and sodium acetate buffer is then added to stabilise the final pH. To improve the speed of the manual method however, and to enable it to be adapted to a fully automatic procedure, it was found possible to prepare a buffer of sufficient strength both to dispense with the neutralisation and to control adequately any variations in the final acidityof the digests.It was found that 8 ml of 33 per cent. w/v hydrated sodium acetate in a final volume of 50 ml was sufficient to buffer 20 ml of 1 per cent. sulphuric acid (the theoretical final acid concentration in the diluted digests) to pH 4-8. This value was chosen as being in the region of maximum buffering capacity of sodium acetate - acetic acid. It was shown that, under these conditions, a final acid concentration in the diluted digest solution of 0-5 to 1.5 per cent. sulphuric acid can be tolerated. These values are considered to be the extremes likely to be met in practice.May, 19671 DETERMINATION OF IRON I N PLANT MATERIAL 307 COLOUR STABILITY- It was shown that under the conditions described, the colour develops fully within 20 seconds and is stable for at least 24 hours.RECOVERY OF IRON FROM DIGESTION FLASKS- Standards prepared directly from stock solution and treated as above gave reproducible results, and good agreement was also found between duplicate determinations on a single digest. However, determinations made on replicate digests often gave widely varying results. To investigate this, appropriate amounts of the iron stock solution were digested as described above. The digest was diluted and immediately filtered into 100-ml calibrated flasks without further heating. After dilution to volume, 20-ml aliquots were taken for the determination of iron. A series of undigested standards was prepared to cover the same range for comparison.TABLE I EFFECT OF DILUTING DIGESTS AND BOILING THEM FOR 10 MINUTES ON THE RECOVERY OF DIGESTED IRON A. Sample digests diluted and filtered directly into flasks < Iron digested, Iron found, mg mg 0.025 0.024 0.050 0.047 0.075 0.055 0.100 0.046 0.125 0.024 0.150 0.039 0.200 0.033 0.250 0.098 7 Recovery, 96 94 73 46 19 26 17 39 % B. Sample digests diluted and boiled before filtering into flasks 7 Iron digested, mg 0.050 0.100 0.150 0.200 0.300 0-400 0.500 1.00 2.00 3.00 4.00 Iron found, mg 0.049 0.096 0-152 0.200 0.304 0.407 0.506 0-99 1.98 2-98 3-98 - Recovery, 98 96 101 100 101 102 101 99 99 99 100 % The results (Table I A) show that the recovery of iron becomes progressively poorer when more than 0-05 mg of iron is digested per flask. Subsequent tests with bathophenan- throline as a spot reagent revealed the presence of iron particles, both in the Kjeldahl flask and on the filter-paper.Further, if more than 0.05mg of iron was digested and washed directly into a calibrated flask without filtering, the aliquot taken for iron determination gave a colour developing gradually with time. Over a period of about 20 hours the optical density approached that given by an undigested iron standard of the same iron content. These results are in agreement with those of Smith and Sullivan,6 who stated that digestion of 100 mg of potassium ferricyanide with perchloric acid - sulphuric acid mixtures resulted in the precipitation of anhydrous iron(II1) sulphate. The present work indicates the low solubility of iron( 111) sulphate in anhydrous sulphuric acid.It was found that dilution of the acid in the Kjeldahl flask with about 15 ml of water, followed by boiling for 10 minutes was sufficient to bring all the precipitated iron into solution. There was no advantage in adding a reducing agent such as hydroxylammonium chloride in an attempt to convert the iron(II1) sulphate to the more soluble iron(I1) salt. Table I B shows that boiling the digest with water before filtering allows full recovery of up to at least 4mg of iron per flask. Comparison with other methods showed that elimination of the neutralisation stage produced a nearly 2-fold increase in the rate at which samples could be analysed. When using semi-automatic equipment for transferring sample solutions and reagents by pipette, colorimetric determinations could be made at the rate of 30 samples per hour.308 APPARATUS- which is fully described elsewhere.7 QUARMBY AND GRIMSHAW: RAPID METHOD FOR THE THE AUTOMATIC METHOD [Analyst, Vol.92 The instrument used for the automatic determination was the Technicon AutoAnalyzer, As the sample solution is filtered before use, and the colour develops fully within 20 seconds /mixing coils i t not Fig. 1. Flow diagram of the AutoAnalyzer as used in the automatic method for determining iron. All pump tubing is in Tygon REAGENTS- These are prepared as described for the manual method with the following exceptions- Hydroxylammonium chloride, 0-5 per cent. WIV, aqueous. Colorimetric reagent-This is not required as the components are added as separate Standard iron solutions-Prepare from the stock solution a series of standards containing reagents. from 0 to 5 p.p.m.of iron, each made up in 1 per cent. v/v sulphuric acid. PROCEDURE- The large 3-ml cups are used. Sampler I1 is fitted with a standard cam to give a sampling rate of 40 samples per hour, with a sample-to-wash time-ratio of 2 to 1 to allow for adequate washing. As a further precaution, a cup containing water is inserted after every third sample. It is preferable to use water for this purpose rather than 1 per cent. sulphuric acid, as the former gives more well defined minima for the construction of the baseline (Fig. 2 ) . Standards, samples and digestion blanks are always run together, and although the blanks give a small peak this should not be greater than that given by the zero standard.In the present work, the reagent blank was found to be caused by iron impurities in the bathophenanthroline, but was not great enough to warrant further purification of the reagent.May, 19671 DETERMINATION OF IRON I N PLANT MATERIAL 309 Time- Fig. 2. A typical recording of the peaks obtained by using calibration standards. The figures above each peak refer to the concentration of iron in the standard in p.p.m. The time interval between successive peaks is 90 seconds RESULTS AND DISCUSSION INTERFERENCES- The interferences in the determination of iron by bathophenanthroline have been reviewed.* It has been shown that chloride, nitrate, sulphate, perchlorate and acetate do not interfere. The metal ions listed that may cause interference are unlikely to be present in plant material in amounts sufficient to have any significant effect.On the other hand, citrate, oxalate, lactate, tartrate, cyanide, sulphide, fluoride, phosphate and pyrophosphate all gave a less intense iron colour. Of these however, only phosphate is expected to remain after the wet digestion described above, and is therefore the only ion in plant material likely to cause interference. It was found with the automatic method that a full recovery of iron was obtained on digesting 0.1 mg of iron with at least 10 mg of phosphate phosphorus, equivalent to 1 p.p.m. of iron and 100 p.p.m. of phosphate phosphorus in the final diluted digest, and that 4.0 p.p.m. of iron could be recovered fully in the presence of up to 50 p.p.m.of phosphate phosphorus. Phosphate phosphorus rarely exceeds 0.3 per cent. in unfertilised plant material, and therefore this ion is unlikely to interfere in the method described, provided the recommended sample weights are not exceeded. Tests confirmed that perchloric acid is without effect at concentrations up to 100 p.p.m. in the final digest. Full recovery of up to 4-0 mg of iron was also obtained in the presence of 10mg of dehydrated silica. Table I1 shows the recovery of iron from six plant materials to which known amounts of iron had been added. The weight of iron digested varies from 0.06 to 0.37 mg per flask, and the final percentage figures for iron are in good agreement. To determine the repro- ducibility of the method, ten sub-samples of oven-dried oak leaf litter were digested as described above, a portion being taken from each digest solution for analysis on the Auto- Analyzer.At a level of 0.044 per cent. of iron, the standard deviation is 0.001 per cent. and indicates the accuracy to be expected of the method under conditions of routine analysis. We are indebted to Mr. S. E. Allen for his help and advice during the course of this work. The sample weights taken were in the range of 225 to 275mg.310 QUARMBY AND GRIMSHAW TABLE rr RECOVERY OF IRON ADDED TO VARIOUS PLANT MATERIALS Type of material and weight digested Heather (Calluna vulgaris) shoots, 500 mg Mat grass (Nardus stricta), 250 mg Pine (Pinus sylvestris) fresh needles, 500 mg Oak (Quercus petraea) fresh leaves, 500 mg Oak (Quercus petraea) leaf litter, 250 mg Acid peat, 50 mg Iron added, mg - - 0.050 0.100 0.150 - - 0.050 0.100 0.150 - - 0.050 0.100 0.150 - - 0.050 0.100 0.150 - - 0.050 0.100 0.150 - - 0.050 0.100 0.150 Total iron found, mg 0.210 0.216 0.261 0.315 0.366 0-062 0.062 0-113 0.166 0.224 0.108 0.119 0.164 0.210 0.260 0.082 0.080 0.137 0-181 0.230 0.1 12 0.112 0.164 0.214 0.264 0.184 0.184 0.235 0.283 0.335 Iron in plant material, percentage dry weight 0.042 0.043 0.042 0-043 0.043 0.025 0.025 0.025 0.026 0.030 0.022 0.024 0-023 0.022 0.022 0.016 0.016 0.017 0.016 0.016 0.045 0-045 0.046 0.046 0.046 0.368 0.368 0.370 0.366 0-370 Percentage recovery of added iron - - 96 102 102 - - 102 104 108 - - 101 97 98 - - 112 100 99 - - 104 102 101 - - 102 99 101 REFERENCES Publishers Inc., New York, 1959, pp.522 to 554. Research Council, London, 1963. 1. Sandell, E. B., “Colorimetric Determination of Traces of Metals,” Third Edition, Interscience 2. “Report of Group on Comparison of Methods of Analysis of Mineral Elements in Plants, Agricultural 3. Case, F. H., J . Org. Chem., 1951, 16, 1541. 4. Smith, G. F., McCurdy, W. H., jun., and Diehl, H., Analyst, 1952, 77, 418. 5. Riley, J. P., and Williams, H. P., Mikrochim. Acta, 1959, 804. 6. Smith, G. F., and Sullivan, V. R., Ind. Engng Chem. Analyt. Edn, 1935, 7, 301. 7. Miiller, R. H., Analyt. Chem., 1958, 30 (l), 53A, 54A, 56A. 8. Johnson, W. C., Editor, “Organic Reagents for Metals,” Hopkin & Williams Limited, Chadwell Received September 22nd, 1966 Heath, Essex, 1964, Volume IT, p. 68.

ISSN:0003-2654    

DOI:10.1039/AN9679200305

出版商:RSC    

年代:1967

数据来源: RSC

摘要:

Analyst, May, 1967, Vol. 92, $9. 311-315 31 1 The Determination of Nitrate in Soil Solutions by Ultraviolet Spectrophotometry BY P. A. CAWSE ( U . K. Atomic Energy Authority, Wantage Research Laboratory, Wantage, Berks.) Ultraviolet spectrophotometric analysis has been applied to the deter- mination of nitrate nitrogen over the 0.5 to 10 p.p.m. range in soil solutions and perfusates in the absence of organic matter, and over the 5 to 50 p.p.m. range in its presence. If necessary, a 4-fold increase in ultimate sensitivity can easily be obtained. Sulphamic acid can be used for the destruction of nitrite which would otherwise interfere, and a short procedure has been suggested for the reduction of severe interference present in extracts from highly organic samples such as peat.The more important nitrification inhibitors used in perfusion experiments are well tolerated. Nitrate contents of soil solutions were measured by the method and gave results in good agreement with the nitrate reduction and ammonia distillation method. V-4RIOUS methods have been proposed for the determination of nitrate in soil solutions, extracts and perfusates. They are mainly dependent on either the reduction of nitrate followed by the determination of nitrite1 and ammonia,2 or the colorimetric measurement of a nitration product formed with reagents such as b r ~ c i n e , ~ chromotropic acid,4 4-methyl- ~mbelliferone,~ phenoldisulphonic acid6 and 2,4-xylenol.' A polarographic method* and the interference of nitrate in the determination of rhenium by a-furildioxime9 have also been suggested.Some of these techniques have the disadvantage of being fairly tedious, while others show non-linear calibration graphs, poor colour stability, low sensitivity and severe inter- ference from chlorides, nitrites and organic matter. The use of strong sulphuric acid in nitration procedures promotes interference from organic compounds in soils. A more simple, reliable and rapid technique was required for the analysis of soil solutions and perfusates. According to Bastian, Weberling and Palilla,lo the absorption spectra of the nitrate ion in 5 per cent. v/v perchloric acid shows a double peak in the 210 and 300-mp regions, and readings at the shorter wavelength are about a thousand times more sensitive. These authors investigated the interference from many anions and cations, and applied the method to the measurement of nitrate in alkaline earth carbonates that had been dissolved in dilute perchloric acid.Although Hoather and Rackhamll carried out the direct determina- tion of nitrate in waters at 210 mp, there appears to be no parallel investigation dealing with the reliability of the method for soils. The work described here was designed to test the suitability of ultraviolet spectrophoto- metry for the measurement of nitrate, firstly in soil solutions extracted by a centrifugation method,12 where the most serious interferences would be expected to come from iron and organic matter, and secondly in soil perfusates where the presence of nitrite or various nitrification inhibitors could cause further errors ; in addition, the interference of boron has not been previously studied.EXPERIMENTAL A good absorption by nitrate can be obtained by the measurement of soil solutions diluted with water, but dilution of aliquots with 5 per cent. v/v perchloric acid was retained as a final step before ultraviolet spectrophotometry; it was found that the presence of acid reduced nitrite interference (from sodium nitrite) and iron interference (from ammonium iron(II1) sulphate) by 73 and 23 per cent., respectively, at 210 mp, compared with water312 CAWSE: DETERMINATION OF NITRATE I N SOIL [Analyst, Vol. 92 alone. The acid also prevented any bacterial action in the samples that could be accumu- lated for at least 1 week at room temperature without variation in optical density.INTERFERENCE AND REMOVAL OF NITRITE- Sulphamic acid has been used for the destruction of nitrite in soil extracts in the micro- diffusion analysis of nitrate.13 The effectiveness of this removal procedure and its influence on nitrate recovery was tested by adding 1 ml of 2 per cent. sulphamic acid to solutions that contained known amounts of nitrate, and 50 pg of nitrite nitrogen. Solutions were shaken and allowed to stand for 2 minutes before making up the volumes to 10ml with 5 per cent. perchloric acid. Absorbance was measured at 210 mp in a Unicam SP500 spectro- photometer with l-cm silica cells. The results were compared with a calibration graph obtained from known amounts of nitrate in perchloric acid, and the recoveries were satisfactory- with 50 pg of nitrite nitrogen added f h \ Nitrate nitrogen taken, pg .. . . 2 4 6 8 10 Nitrate nitrogen found, pg , . . . 1.96 3-91 5.97 7.98 9.95 Recovery, per cent. . . * . . . 98.0 97.8 99.5 99.8 99.5 The absorption spectra of the same concentration of sulphamic acid in perchloric acid was measured in a Unicam SP700 recording spectrophotometer, and showed a large peak at 192 mp. Although readings taken at 210 mp were free from interference because of the sharp decline in the sulphamic acid absorption peak, it would not be advisable to use lower wavelengths. The interference of nitrite was examined by preparing a fresh sodium nitrite standard in quartz distilled water, and measuring the absorption arising from 25 pg of nitrite nitrogen in 10 ml of 5 per cent.perchloric acid. A correction for traces of nitrate present in the nitrite standard was obtained by deducting the reading of a sulphamic acid blank from a nitrite plus sulphamic acid treatment. At a wavelength of 210 mp, 0-55 pg of nitrite nitrogen gave the same optical density as 0.1 pg of nitrate nitrogen, and it would not be advisable to exceed this amount of nitrite in test samples. With some of the soils used in experimental work, whose properties are shown in Table I, there is no interference because only 0.1 or 0.2-ml aliquots of soil solution are required for nitrate analysis, and these particular soils are not prone to nitrite accumulation. TABLE I DESCRIPTION OF ARABLE SOILS USED FOR ANALYSIS Total carbon Soil dry soil, reference Soil origin and description pH percent.1 Black Series, Sonning organic loam . . 7.0 3.5 2 Broad Series, Sonning organic clay loam 7.7 6.6 3 Faringdon light loam . . . . . . 6.3 2.2 4 Grove heavy loam . . . . . . 7.0 3.5 Soil solution, Soil moisture p.p.m. a t extraction, per cent. G i r o d 50 0.06 0.27 62 0.05 0.19 25 0.05 0.13 45 0.05 0.25 INTERFERENCE OF ORGANIC MATTER- One-ml aliquots of soil solutions from the soils described in Table I, and a coloured water extract from moss peat, were decolorised by mixing with 4 ml of alumina cream suspension and spinning in a centrifuge. Faringdon soil gave the most intensely coloured extract, but colour removal had no effect on the ultraviolet absorption spectra; analysis of nitrate by the distillation method of Piper14 gave good agreement with ultraviolet spectrophotometry without any decolorising procedure.The peat extract was an exception, and results consistently exceeded the distillation figures by as much as 120 per cent., probably because of organic matter absorption in the lower ultraviolet region. The interfering substances were completely removed by alumina cream treatment, and results from both methods were almost identical; interference could be conveniently estimated by comparing absorption readings with and without alumina cream reagent.May, 19671 SOLUTIONS BY ULTRAVIOLET SPECTROPHOTOMETRY 313 INTERFERENCE OF IRON(III)- The absorption of iron(II1) ion in perchloric acid solution at 240 mp has been used for quantitative ana1y~is.l~ Interference in nitrate determination was measured at 210 mp with a solution of ammonium iron(II1) sulphate. Aliquots were fumed with 0-5 ml of perchloric acid to expel nitrate, and made up to 10 ml with water; 0.83 pg of iron(II1) gave an absorption equivalent to 0.1 pg of nitrate nitrogen.When 1Opg of iron(II1) was subjected to alumina cream treatment, analysis of the supernatant solution showed that 90 per cent. had been removed, and therefore interference from this element in soil solutions is unlikely. INTERFERENCE OF BORON- A solution of Specpure boric acid in quartz distilled water showed that 16.7 pg of boron gave the same absorption as 0.1 pg of nitrate nitrogen at 210 mp. Vinogradov16 states that the average boron content of soils is 1 x per cent. Water-soluble boron comprises about 10 per cent.of this, so that it is unlikely to interfere. INTERFERENCE OF NITRIFICATION INHIBITORS- Seven inhibitors were dissolved in water at their effective strengths, and 0-2-ml portions were diluted to 10ml with 5 per cent. perchloric acid for test. Aliquots from 0 . 0 0 6 ~ potassium chlorate, 0.001 M ethyl urethane, 0.015 M 2-chloro-6-(trichloromethyl)pyridine and 0.005 M guanidine carbonate did not affect the nitrate absorption spectra. Serious inter- ference was found with aliquots from 0.002 M allylthiourea, 0.005 M DL-methionine and 0.001 M nitrourea. SULPHAMIC ACID AND ALUMINA CREAM TREATMENT OF SOIL SOLUTIONS- The effect of sulphamic acid and alumina cream treatments on nitrate recovery was tested with 0.1 ml of soil solution and 15 pg of nitrate nitrogen, and finally, the effect of 250 pg of nitrite nitrogen and 10 pg of iron(II1) on the analysis of soil solutions was examined.After spinning the alumina cream in a centrifuge, 1 ml of the supernatant solutions was taken for sulphamic acid treatment, then diluted with 5 per cent. perchloric acid for absorption measurement. The results showed that both nitrate recovery and removal of nitrite and iron(II1) were satisfactory. Nitrate nitrogen, pg I A \ Recovery Soil solution + 250 pg Soil alone of nitrate nitrogen per cent. and 10 pg of iron(II1) Soil solution Soil solution + 15 pg of nitrate, of nitrite nitrogen 1 12-55 27-20 97.7 12.00 2 25.45 40.45 100 25-70 3 7.70 22.50 98.7 7.40 4 10.25 24.75 96.7 9-75 METHOD All reagents are of analytical-reagent grade. Ammonia solution, 15 N.Perchloric acid, 70 per cent. wlw. Sulphamic acid solution, 2 per cent. w / v . Alztmina cream-Prepare by dissolving 30 g of potassium aluminium sulphate in 1 litre of water. Filter, and add the filtrate to a mixture of 225 ml of distilled water and 25 ml of ammonia solution. Free the aluminium hydroxide precipitate from sulphate by decanting with water, and finally dilute a suspension of the precipitate to 1 litre. The preparation has a final pH of about 6.8, and should be well agitated during use. Nitrate stock solution-Prepare by dissolving 3-6090 g of potassium nitrate in water and diluting to 1 litre. Nitrate standard solution-Dilute 10 ml of stock solution to 100 ml with water. REAGENTS- 1 ml = 50 pg of nitrate nitrogen.314 CAWSE: DETERMINATION OF NITRATE IN SOIL [Analyst, Vol.92 PROCEDURE- If organic matter interference is present, take a l-ml portion of the sample, which should contain between 5 and 50pg of nitrate nitrogen, and portions of nitrate standard solution to cover this range. Mix with 4 ml of alumina cream and spin in a centrifuge. Take 1 ml of the supernatant fraction in a 10-ml calibrated flask, add 1 ml of sulphamic acid solution, and allow the mixture to stand for 2 minutes. Dilute to 10 ml with 5 per cent. v/v perchloric acid, and measure the absorbance at 210mp with l-cm silica cells. A blank correction is required for small amounts of nitrate in reagents. A second procedure can be used in the absence of organic matter interference, whereby the alumina cream treatment is omitted.In this event, samples should contain 0-5 to 10 pg of nitrate nitrogen. RESULTS The method was compared with a nitrate reduction and ammonia distillation technique without decolorisation of soil solutions. Three replicate determinations were made for each method and good agreement was found for the mineral soils, but decolorisation was essential for a moss-peat extract. The results are shown in Table 11. TABLE I1 NITRATE CONTENT OF SOIL SOLUTIONS Nitrate nitrogen, p.p.m. found by- Soil 1 not decolorised 2 not decolorised 3 not decolorised 4 not decolorised Moss peat not decolorised 1 decolorised . . 2 decolorised . . 3 decolorised . . 4 decolorised . . Moss peat decolorised . . SENSITIVITY AND ACCURACY- An optical density of 0.1 can be nitrate nitrogen diluted to 10 ml with is linear over the range specified in the r 1 ultraviolet technique distillation .. 102.5 103-6 .. 148.5 151.2 .. 81.4 80.1 . . 100,o 100.8 . . 13.9 6.2 . . 101.6 - . . 148.0 - 80-5 - . . 99.4 - .. 6.3 6.0 DISCUSSION . . obtained in l-cm silica cells at 210mp, with 2 p g of 5 per cent. v/v perchloric acid. The calibration graph procedure, and a concentration of 0.5 p.p.m. of nitrate nitrogen in the soil solution is a practical lower limit. If necessary, greate; sensitivity can be achieved by increasing the optical path of the spectrophotometer cells or by reducing the dilution with perchloric acid. By using the full procedure one operator analysed 40 samples in 2& hours, with a standard deviation of +0.0480 pg of nitrate nitrogen on a single sample.With the shorter procedure the standard deviation was &0-0023 pg of nitrate nitrogen. The soils examined gave no interference from organic or inorganic compounds, unlike the peat extract, and it should be noted that a strongly coloured solution is not a reliable indication of the degree of interference to be expected. Soil nitrate is frequently extracted by water at neutral pH, or by saturated calcium sulphate, and according to the calcium interference levels quoted by Bastianlo there would be no problem with the use of 0.2-ml aliquots. Chlorides are also well tolerated, but the use of extractants that increase the solubility of organic matter and iron should be avoided. If nitrite determination is not required on the same extract, it can be more conveniently destroyed by the use of sulphamic acid in the extractant.CONCLUSIONS Ultraviolet absorption can be successfully applied to the determination of nitrate in soil solutions and perfusates; the sensitivity of the method to nitrate is sufficiently pre- dominant to make the effect of interfering elements unimportant. It is a simple, rapid technique, which is suitable for the daily control of perfusion experiments in which large numbers of samples can be involved.May, 19671 SOLUTIONS BY ULTRAVIOLET SPECTROPHOTOMETRY REFERENCES 315 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. Nelson, J. L., Kurtz, L. T., and Bray, R. H., AnaZyt. Chem., 1954, 26, 1081. Richardson, H. L., J . Agric. Sci., 1938, 28, 73. Robinson, J. B. D., Allen, M. de V., and Gacoka, P., Analyst, 1959, 84, 635. Clarke, A. L., and Jennings, A. C., J . Agric. Fd Chem., 1965, 13, 174. Skujins, J. J., Analyt. Chem., 1964, 36, 240. Easthoe, J. G., and Pollard, A. G., J . Sci. Fd Agric., 1950, 1, 266. Buckett, J., Duffield, W. D., and Milton, R. F., AnaZyst, 1955, 80, 141. Skyring, G. W., Carey, B. J., and Skerman, V. B. D., Soil Sci., 1961, 91, 388. Bloomfield, R. A., Guyon, J. C., and Murmann, R. K., Analyt. Chem., 1965, 37, 248. Bastian, R., Weberling, R., and Palilla, F., Ibid., 1957, 29, 1795. Hoather, R. C., and Rackham, R. F., Analyst, 1959, 84, 548. Bowen, H. J. M., and Cawse, P. A., Soil Sci., 1964, 98, 358. Bremner, J. M., and Shaw, K., J . Agric. Sci., 1955, 46, 320. Piper, C. S., “Soil and Plant Analysis,” University of Adelaide, 1950, p. 207. Bastian, R., Weberling, R., and Palilla, F., Analyt. Chem., 1956, 28, 459. Vinogradov, A. P., “The Geochemistry of Rare and Dispersed Chemical Elements in Soils,” Second Received September 30th, 1966 Edition, Consultants Bureau Inc., New York, 1959, p. 26.

ISSN:0003-2654    

DOI:10.1039/AN9679200311

出版商:RSC    

年代:1967

数据来源: RSC

摘要:

316 Analyst, May, 1967, Vol. 92, 99. 316-318 Determination of Terminal Hydroxyl Groups in Polyethyleneoxy Compounds BY K. W. HAN ( Unilever Research Laboratory, Mercatorweg 2, VZaardingen, The NetherZands) The 3,5-dinitrobenzoyl chloride method has been adapted for the semi- micro analysis of hydroxyl groups in polyethylene glycol and non-ionic surfactants of the polyethylene oxide type. The 3,5-dinitrobenzoates are determined colorirnetrically after removal of the excess of acid chloride by column chromatography. By this method 1OOf~g of hydroxyl can be determined with a relative accuracy of 4.5 per cent. Products containing fewer than ten ethylene oxide units per molecule do not respond adequately. Results of the analyses of some technical non-ionic detergents and polyethylene glycol are reported.SEVERAL methods for the determination of hydroxyl groups on a macro or micro scale are known. In the macro method acetic anhydride or phthalic anhydride are used as acylating agent, whereas in a semi-micro method, based on the two-phase titration of anionic surfac- tants,l chlorosulphonic acid is used. No accurate micro or semi-micro methods are available for determining polyethylene glycols and their mono-ethers. Johnson and Critchfield's method2 for determining the hydroxyl group in fatty alcohols on the micro scale has been examined for its applicability to these polyethyleneoxy compounds. In Johnson and Critchfield's method, dinitrobenzoyl chloride is used to esterify the higher alcohol. The excess of reagent is eliminated by acid hydrolysis and the ester is extracted with hexane.The hexane extract is coloured by a strong base, propylene diamine, and the absorbance of the solution measured at 525 nm. As the dinitrobenzoates of polyethylene glycols and non-ionics do not dissolve in hexane, the solvent was replaced with chloroform. This, however, produced high blanks, which were caused by traces of co-extracted dinitrobenzoyl chloride and dinitrobenzoic anhydride. The interference has been reduced by chromato- graphic separation of the ester from all other reaction products after hydrolysis. Separation appeared to be possible by thin-layer chromatography on silica gel G (obtained from Merck), with 0.3-mm layers activated at 120" C for 2 hours. The plates were developed in chloroform, which completely removed the hydrolysis products, leaving a stationary spot of the polyethyleneoxy dinitrobenzoate esters at the start.For column chromatography the silica gel G was replaced by Kieselgel 0.05 to 0.2 mm (obtained from Merck), which was completely de-activated with water. This was necessary to allow the dissolution of the purified ester from the column by dimethylformamide. Instead of pyridine, dimethylformamide was used as solvent in the acylation. It has the same catalytic properties,3 can be dried more easily and is almost odourless. The ester was coloured by anhydrous ethylene diamine, instead of propylene diamine. This did not significantly change the wavelength of maximum absorbance. EXPERIMENTAL REAGENTS- All reagents are of analytical-reagent quality.3,5-DinitrobenxoyZ chloride-This is prepared by reacting 3,5-dinitrobenzoic acid with thionyl chloride.4 The 3,5-dinitrobenzoyl chloride formed is then dissolved in dimethyl- formamide, and this freshly prepared solution is used for the esterification of the terminal hydroxyl group of the polyethyleneoxy compound. Hydrochloric acid, 2 ~ . Chloro forin.HAN 317 Ethylene diamiae-Dehydrate commercial ethylene diamine by adding to it an equal weight of sodium hydroxide pellets and heating the mixture for half an hour at 100” C, occasionally swirling it. After cooling it to room temperature, pour off the liquid and distil the solution at atmospheric pressure. The pure ethylene diamine is collected between 117’ and 118°C. APPARATUS- Dimethyl f ormamide.A Beckman DB spectrophotometer was used for the absorbance measurements. The chromatographic column (200mm long and 14mm in diameter) was packed with Kieselgel 0.05 to 0.2 mm, which is prepared as follows. For each column, 5 g of Kieselgel is dried at 150” C for 2 hours. The material is slurried with distilled water into the column. The column is then flushed with 25 ml of dimethyl- formamide to remove free water and the dimethylformamide is finally removed by washing with 50ml of chloroform. When using the column for the first time, the Kieselgel should be thoroughly purified by passing 5 ml of a 10 per cent. w/v solution of 3,5-dinitrobenzoyl chloride in dimethyl- formamide through it and then washing it with pure dimethylformamide. The absence of the acid chloride in the effluent is ascertained by a spot test with ethylene diamine.After this preliminary purification, the column is de-activated again with distilled water, then flushed with 25ml of dimethylformamide and 50ml of chloroform, as described above. An amount of sample, equivalent to 100 pg of hydroxyl, is dissolved in 2 ml of dimethyl- formamide in a 100-ml stoppered conical flask. One millilitre of a freshly prepared solution of 1 g of 3,5-dinitrobenzoyl chloride in 10 ml of dimethylformamide is added to the sample. The reaction mixture is left at room temperature for 1 hour, then 25 ml of 2 N hydrochloric acid is added, followed by 20.00 ml of chloroform (from a pipette). The flask is stoppered and shaken vigorously for half a minute. After de-gassing, shaking is resumed for half a minute.The layers are allowed to separate and 2-00 ml of the chloroform are transferred (by pipette) to the chromatographic column. The column is eluted with 50 ml of chloro- form, and the effluent containing the by-products is discarded. The purified ester is dis- solved by passing dimethylformamide over the column. The movement of the ester band is observed carefully. The band is collected in a 10-ml calibrated flask. When the effluent fills the flask to the mark, 1 ml of anhydrous ethylene diamine is added, the flask is stoppered and finally shaken. The absorbance of the dimethylformamide solution is measured at 528 nm, against dimethylformamide containing 10 per cent. of ethylene diamine as reference. Correction for impure reagents is made by running a blank.RESULTS AND DISCUSSION Table I gives the results of hydroxyl determinations in some polyethylene glycols and The hydroxyl figures in the column “Hydroxyl added’’ are based on the non-ionics. DETERMINATION PEG-40E0 PEG-11EO PEG-BE0 NP-32E0 NP-28EO NP- 14E0 NP-8-5E0 TA-35EO TA-34EOS TA-8.6EO .. .. .. .. . . . . . . .. .. .. TABLE I OF HYDROXYL GROUPS IN POLYETHYLENEOXY COMPOUNDS* .. .. .. . . .. .. .. .. .. .. H ydroxyl H ydroxyl added, found, Pg Pg 68-0 70.3 (f3-2)t 95-0 92-12 (&4*2) 96.0 30-0 ( 5 1.4) 143.0 146.5 (& 6.6) 105.0 103-0 (54.7) 90.0 58.0 (k2.6) 170.0 54.0 (h2.5) 141.0 142.0 (&6*4) 160.0 158.0 (&7*1) 110.0 48-0 (f2.2) * PEG Polyethylene glycol. NP Nonylphenol. TA Tallow alcohol. Experimental (2s) error. $ PEG-free.Difference, Pg per cent. 2-3 3.4 - 2.8 - 3.0 - 66.0 - 69.0 3.5 2.5 - 2.0 - 1.9 - 32.0 - 36.0 - 116.0 - 68.0 1.0 0.7 - 2.0 - 1.3 - 62.0 - 57.0318 HAN conventional macro method in which acetic anhydride - pyridine solution is used. The spectro- metric results are obtained by using one calibration line determined with nonylphenol-28EO. The 2s error of the results calculated from 20 determinations of known samples is 4.5 per cent. relative. The absolute blank absorbances range from 0.060 to 0.080 (92 observations over a period of a few months). As Table I indicates, the method does not give satisfactory results for polyethylene glycol-5EO. PEG-11EO and higher appear to be determined satisfactorily. With poly- ethylene glycols, the results depend on the size of the reacting molecules. These products are mixtures of adducts of different molecular weight. PEG-5EO is a mixture for which an average of 5 ethylene oxide units per molecule are found. It may be composed, however, of compounds ranging in ethylene oxide number from 1 to about 15. A negative response of the lower members of the range means a partial loss of hydroxyl groups and causes a low result. As for non-ionics, it must be noted that the technical products invariably contain polyethylene glycol as contamination. The low results found for NP-14E0 and NP-8.5EO may, therefore, be caused by an inadequate response of their low molecular polyethylene glycol fractions or by the lower nonylphenol ethoxylates themselves. REFERENCES 1. 2 . 3. 4. Blinkenstaff, R. T., Schaeffer, J. R., and Kathman, G. G., Analyt. Chew., 1954, 26, 746. Johnson, D. P., and Critchfield, F. E., Ibid., 1960, 32, 865. Bosshard, H. H., Rlory, R., Schmid, M., and Zollinger, H., Helv. Chim. Acta, 1959, 176, 1653. Vogel, A., “A Textbook of Practical Organic Chemistry,” Third Edition, Longmans, Green and Co., Received May 26th, 1966 London, 1964, pp. 189 and 262.

ISSN:0003-2654    

DOI:10.1039/AN9679200316

出版商:RSC    

年代:1967

数据来源: RSC

摘要:

Analyst, May, 1967, Vol. 92, pp. 319 319 Precipitation from Homogeneous Solution by Cation Release at Constant pH BY P. F. S. CARTWRIGHT (Department of Chemistry, Sir John Cuss College, London, E.C.3) PRECIPITATION from homogeneous solution by cation release a t constant pH from an iron - EDTA complex has been described by MacNevin and Dunton for the precipitation of hydrated iron oxide.1 They concluded that the method should be applicable to the precipitation of a large number of metal ions. The technique has subsequently been studied in greater detai1,293 and it is now possible to form a clearer picture of the scope of the method. Some of the more important aspects are briefly discussed below. Choice of oxidising agent-MacNevin and Dunton considered several oxidising agents before deciding that hydrogen peroxide was to be preferred.Oxidising agents, such as ammonium per- sulphate and sodium hypochlorite, were found to be too vigorous, while the use of sodium bromate was restricted to acid solution. The complex formed by iron with EDTA is, however, extremely easy to break up by oxidation, despite its relatively high stability constant (Kabs, = 25). Other metals, and in particular bismuth, form complexes that are extremely resistant to attack over certain ranges of pH. Hydrogen peroxide has the advantage that the products of its breakdown are not themselves precipitating anions, but it suffers in that it may be catalytically destroyed by traces of ions in solution, or by first-formed precipitate particles, and its use is frequently restricted to solutions containing stabilising anions, notably the phosphate ion ; this imposes a limitation on the method.Selectivity in sepavation-Hydrogen peroxide is not selective in its attack upon metal - EDTA complexes. All cations present in complexed form are released into solution as their complexes are destroyed. The method is therefore in itself non-selective, and only serves to release all cations a t a slow rate into an initially homogeneous solution. A certain degree of selectivity can be achieved by choosing a pH range at which only one cation forms a precipitate, or by including an anion that will precipitate only one cation. There are few occasions, however, on which these techniques can be applied successfully. t h of in Masking eficiency-It is essential in carrying out precipitation from homogeneous solution lat precipitation should not occur immediately on addition of the precipitating anion to a solution the metal - EDTA complex.Immediate precipitation will occur with all cations over pH ranges which the metal - EDTA complexes have low stability. This can occur in both acidic and alkaline conditions according to the nature of the cation, and imposes a limitation on the choice of pH a t which precipitation can be carried out from homogeneous solution. It is possible that other complexing agents that form stronger complexes than EDTA may offer some assistance, but little use appears to have been made of these agents. Nature of the pvecifiitate-The method frequently results in the formation of denser precipitates that are more readily filtered than those obtained by the direct addition of reagents. Errors caused by absorption and occlusion are also reduced.The method is not always successful, however, and gives gelatinous precipitates, for example, with thorium and zirconium phosphates. Gordon, Salutsky and Willard have similarly reported voluminous precipitates with hydrated thorium oxide.4 CONCLUSIONS The technique of precipitation from homogeneous solution by cation release from metal - EDTA complexes, by oxidation with hydrogen peroxide, is capable of giving good results in certain cases. There are severe limitations to its general application to the precipitation of a wide range of cations, and the selectivity of the method is poor, REFERENCES 1. 2. 3. - , Ibid., 1962, 87, 163. 4. MacNevin, W. M., and Dunton, M. L., Analyt. Chem., 1954, 26, 1247. Cartwright, P. F. S., Analyst, 1961, 86, 688 and 692. Gordon, L., Salutsky, M. L., and Willard, H. H., “Precipitation from Homogeneous Solution,” Received December 19th, 1966 John Wiley and Sons Inc., New York; Chapman & Hall Ltd., London, 1959.

ISSN:0003-2654    

DOI:10.1039/AN9679200319

出版商:RSC    

年代:1967

数据来源: RSC

摘要:

320 Analyst, May, 1967, Vol. 92,pp. 320-323 Analytical Methods Committee REPORT PREPARED BY THE METALLIC IMPURITIES IN ORGANIC MATTER SUB-COMMITTEE The Determination of Small Amounts of Tin in Organic Matter Part I: Amounts of Tin up to 30 pg THE Analytical Methods Committee has received the following Report from its Metallic Impurities in Organic Matter Sub-committee. The Report has been approved by the Analytical Methods Committee and its publication has been authorised by the Council. REPORT The constitution of the Sub-committee responsible for the preparation of this Report was: Mr. W. C. Johnson (Chairman), Dr. J. C. Gage, Dr. T. T. Gorsuch (resigned November, 1966), Dr. R. A. Hoodless, Miss E. M. Johnson, Dr. H. Liebmann, Dr. R. F. Milton, Dr. E. J. Newman and Mr. G.B. Thackray, with Mr. P. W. Shallis as Secretary. INTRODUCTION Tin may be present in organic materials, such as foodstuffs, in concentrations ranging from less than one to several hundred parts per million. The Sub-committee has considered several colorimetric, titrimetric and polarographic methods for the determination of small amounts of tin, and has concluded that no single method could conveniently be adapted to the determination of such a wide range of tin concentrations in organic matter. The Sub- Committee’s investigation has therefore been divided into the examination of methods for determining tin in two separate ranges of concentration. For amounts of tin up to 30pg a colorimetric method based on the reaction of tin(1V) with catechol violet is recommended; the other method under consideration is the colorimetric method involving the use of the zinc complex of toluene-3,4-dithiol for amounts in the range 30 to l5Opg.For amounts above 150 pg a method involving titration of tin(I1) with iodine would undoubtedly prove suit able. METHOD A: FOR AMOUNTS OF TIN NOT GREATER THAN 30pg The method recommended is that of Newman and Jones,l which is based on, but contains modifications of, the procedures of Tanaka2 and Tanaka and Yamayo~hi.~ This method was chosen because it contains a solvent-extraction stage designed for the selective extraction of tin from sulphuric acid solutions such as would be produced from wet oxidations of organic matter. EXPERIMENTAL- In view of the work that had been carried out on behalf of the Analytical Methods Committee by Newman and Jones,l the Sub-committee decided that the usefulness or other- wise of the method could be demonstrated adequately by having its members carry out a simple collaborative test.A sample of orange squash was divided between the collaborating laboratories. Each laboratory determined the tin content of the sample by the recommended method after wet oxidation with nitric and sulphuric acids, or with 50 per cent. hydrogen peroxide and sulphuric acid. Recovery tests were also conducted in which amounts of tin equivalent to 1-0, 2.0 and 10.0 p.p.m. were added to the sample before wet oxidation. The tin was addedANALYTICAL METHODS COMMITTEE 32 1 as portions of the dilute standard tin solution (tin(1V) sulphate) prepared as described under “Method” in the Appendix to this Report.In one laboratory, tin was also added as tin(1V) chloride to find out whether volatilisation losses of tin(1V) chloride could occur during the early stages of the digestion. The results obtained are shown in Table I. The figures for the tin content of the sample are in good agreement and the recoveries of added tin were all satisfactory. It was found by two of the collaborating laboratories during preliminary experiments on the orange squash that reproducible results were obtained only when completely colourless digestates were produced. TABLE I DETERMINATION OF TIN IN ORANGE SQUASH B C Tin added, Laboratory p.p.m. A 0 1.0 5.0 10.0 0 1.0 5.0 10.0 0 0 1.0 1.0 5.0 5.0 10.0 10.0 0 0 0 l*O* 1-o* 1.ot 5*0* 5-O* 5*0t 10-0* 10.0” lO.Of 0 0 1.0 1.0 5.0 5.0 10.0 10.0 0 0 1.0 1.0 5.0 5.0 10.0 10.0 * Tin added as the chloride.t Tin added as the sulphate. Tin found, p.p.m. 2.0 3.0 6.7 10.9 2.2 3-2 6.8 11.9 2.1 2-4 3.3 3.4 7.8 7.8 12.3 12.2 2.3 2.2 2.1 3.3 3.1 3.3 7.0 7.2 7.3 12.5 11.8 12.1 2.7 2.7 3.6 3.6 8.1 7.7 13.6 13.1 2-5 2.3 3.3 3.5 7.0 7.3 11.8 12.6 Tin recovered, pap.m. 1.0 4.7 8.9 - - 1.0 4.6 9.7 - 1-1 1.2 5.6 5.6 10.1 10.0 - 1.1 0.9 1.1 4.8 5.0 5-1 10.3 9.6 9.9 - 0.9 0.9 5.4 5.0 10.9 10.4 - 0.9 1.1 4.6 4.9 9.4 10.2 i The two sets of re&lts quoted were obtained with different supplies of catechol violet. A separate calibration graph was prepared for each.322 ANALYTICAL METHODS COMMITTEE [Analyst, Vol. 92 Appendix RECOMMENDED METHOD FOR THE DETERMINATION I N ORGANIC MATTER OF AMOUNTS OF TIN NOT GREATER THAN 3opg PRINCIPLE OF METHOD- After destruction of the organic matter by wet oxidation with nitric and sulphuric acids,4 nitric, perchloric and sulphuric acids4 or 50 per cent.hydrogen peroxide in the presence of sulphuric acid,5 the residual sulphuric acid is diluted to four times its volume with water to give an approximately 9 N concentration of the acid. Tin is selectively separated from this solution by treating it with potassium iodide and extracting tin(1V) iodide into toluene. Tin(1V) is then returned to aqueous solution by shaking the toluene extract with a solution of sodium hydroxide. After acidification, and removal of free iodine from the solution, the tin( IV) is determined spectrophotometrically as its coloured complex with catechol violet, the solution being buffered to pH 3.8 with acetate.RANGE- For tin contents in the range 1 to 30 pg in the sample taken. APPLICABILITY- The colour reaction between tin(1V) and catechol violet is far from selective. However, Newman and Jones1 have shown that the solvent-extraction step is highly selective or even specific. For the present application, therefore, the recommended method can be regarded as specific. REAGENTS- All reagents should be of analytical grade. Water-Purify glass-distilled water further by passing it through a mixture of strongly Sulphuric acid, approximately 9 N-Cautiously mix 250 ml of sulphuric acid, sp.gr. 1-84, Potassium iodide, approximately 5 M-Dissolve 83 g of potassium iodide in water to Toluene (low in benzene).Sodium hydroxide, approximately 5 N and approximately 0-1 N. Hydrochloric acid, approximately 5 N. Ascorbic acid solution-A freshly prepared 5 per cent. w/v aqueous solution. Catechol violet solution-A 0-05 per cent. w/v aqueous solution. Sodium acetate trihydrate solution-A 20 per cent. w/v aqueous solution. Ammonia solution, approximately 5 N. Tin(1V) stock solution-Dissolve 0.1000 g of pure granulated tin in 20 ml of sulphuric acid, sp.gr. 1-84, by heating until fumes appear. Cool, cautiously dilute with 150ml of water, and cool again. Add 65 ml of sulphuric acid, sp.gr. 1.84, cool, and transfer to a 500-ml calibrated flask. Dilute to the mark with water. acidic cation-exchange resin and strongly basic anion-exchange resin. with 500 ml of water, cool to room temperature, and dilute to 1 litre with water.produce 100 ml. Prepare freshly each day. Prepare freshly each week. 1 ml of solution = 200 pg of tin. Tin(1V) dilute standard solution-Dilute 5.0 ml of tin(1V) stock solution to 100 ml Prepare freshly each day. 1 ml of solution = 10 pg of tin. with water in a calibrated flask. PREPARATION OF CALIBRATION GRAPH- 'Transfer by pipette, or small-capacity burette, suitable volumes of dilute standard tin solution, to cover the range 0 to 30 pg of tin, to a series of 50-ml beakers and treat each as follows: dilute to 7 ml with water, add 1 ml of 5 N sodium hydroxide, and mix. Add 2.5 ml of 5 N hydrochloric acid, mix, add 2-0 ml of catechol violet solution, mix again, and add 5 ml of sodium acetate solution (see Note 1).Adjust the pH of the solution with 5 N ammonia solution to 3.8 A 0.1 units, with the aid of a pH meter. Transfer to a 25-ml calibrated flask, dilute to the mark with water, mix thoroughly, and set aside for 30 minutes. MeasureMay, 19671 DETERMINATION OF SMALL AMOUNTS OF TIN 323 the optical density of the solution in a l-cm cell at a wavelength of 552 mp, with the solution containing no added tin in the reference cell. Construct a graph relating the amount of tin to the optical density (see Note 2). The graph should be rectilinear and pass through the origin. PROCEDURE- Dilute the sulphuric acid solution containing not more than 30 pg of tin to approximately 9 N, cool, and transfer it to a separating funnel. For each 25 ml of solution add 2.5 ml of 5 M potassium iodide, mix, and add 10ml of toluene.Insert the stopper, shake the funnel vigorously for 2 minutes, allow the layers to separate, and discard the aqueous phase. Wash the toluene layer, without shaking it, with 5 ml of a solution prepared by mixing 25 ml of 9 N sulphuric acid and 2-5 ml of 5 M potassium iodide, and discard the washings. The toluene layer will be coloured pink with extracted iodine. Add 5 ml of water to the toluene extract and then 5 N sodium hydroxide dropwise, with shaking, until the toluene layer is colourless. Add 2 drops of 5 N sodium hydroxide in excess (usually a total of 8 to 10 drops is required). Insert the stopper, shake the funnel for 30 seconds, allow the phases to separate, and transfer the aqueous layer into a 50-ml beaker.Shake the toluene layer with 3 ml of 0.1 N sodium hydroxide for 30 seconds, allow the layers to separate, and add the aqueous layer to the contents of the 50-ml beaker. Retain the organic (toluene) phase. Acidify the aqueous solution in the beaker with 2-5 ml of 5 N hydrochloric acid, and decolorise the liberated iodine by the dropwise addition of ascorbic acid solution. Add 2.0 ml of catechol violet solution, and mix. Wash the toluene retained from above, without shaking, with 5 ml of sodium acetate solution. Add the washings to the contents of the beaker, mix, and adjust the pH of the solution to 3.8 0.1 units with 5 N ammonia solution by means of a pH meter. Transfer the solution to a 25-ml calibrated flask, and complete the deter- mination of tin as described above under “Preparation of Calibration Graph.” Calculate the amount of tin present by reference to the calibration graph. ?TOTES- 1. adhered to. 2. prepared. The order of addition of reagents is important, and the stated order should be strictly When a new bottle or batch of catechol violet is used a fresh calibration graph should be REFERENCES 1. 2. Tanaka, K., JaFa, Analyst, 1962, 11, 332. 3. 4. 5. Newman, E. J., and Jones, P. D., Analyst, 1966, 91, 406. TanaBa, K., and Yamayoshi, K., Ibid., 1964, 13, 540. Analytical Methods Committee, Analyst, 1960, 85, 643. __ , “The Use of 50 per cent. Hydrogen Peroxide for the Destruction of Organic Matter,” Ibid., 1967, 92, in the press.

ISSN:0003-2654    

DOI:10.1039/AN9679200320

出版商:RSC    

年代:1967

数据来源: RSC

摘要:

324 Analyst, May, 1967, Vol. 92, pp. 324-325 Analytical Methods Committee REPORT PREPARED BY THE METALLIC IMPURITIES IN ORGANIC MATTER SUB-COMMITTEE The Determination of Small Amounts of Zinc in Organic Matter THE Analytical Methods Committee has received the following Report from its Metallic Impurities in Organic Matter Sub-committee. The Report has been approved by the Analytical Methods Committee and its publication has been authorised by the Council. REPORT The Trace Elements in Fertilisers and Feeding Stuffs Sub-committee of the Analytical Methods Committee recommended, in 1963, a titrimetric dithizone procedure that was generally applicable to the determination in fertilisers and feeding stuffs of up to 100-pg amounts of zinc in the final solution.1 An alternative spectrophotometric procedure suitable for the determination of concentrations of less than 10 p.p.m.of zinc was also given.l As part of its work in investigating methods for determining the more important metals that can appear as impurities in organic matter, this Sub-committee had also to consider the determination of small amounts of zinc. The method recommended by the Trace Elements in Fertilisers and Feeding Stuffs Sub-Committee was therefore examined to ascertain whether or not it could be recommended as being directly applicable to the determination of zinc in organic matter generally. This investigation indicated that, with a few comparatively minor modifications, this method could be recomended by this Sub-committee, and members were of the opinion that these modifications could also, with advantage, be incorporated in the method as published in 1963.The modifications proposed, with reasons for their adoption, are- Method A (titrimetric procedwe) - 1. The pH of the ammonium citrate solution is sufficiently high to allow a little of the dithizone to be transferred to the aqueous phase. It is therefore proposed that after the ammonium citrate solution has been extracted with dithizone, the aqueous phase should be washed with carbon tetrachloride, 2 ml being sufficient to remove any dithizone present. 2. If a little of the ammonium citrate phase is inadvertently transferred to funnel (B) with the dithizone extracts, then the 5 ml of 0.02 N hydrochloric acid may be insufficient to neutralise it and produce a distinctly acid phase, with the consequent danger that all the zinc may not be reverted to the aqueous phase.Care must therefore be taken to ensure that the aqueous solution is distinctly acid when the dithizone extracts are being washed. Method B (spectrophotometric procedwe)- 1. The dithizone extract is obtained from an aqueous solution of pH 4.0 to 4.5, and if any of this aqueous solution has been entrained with the dithizone, treatment with the sodium sulphide solution without first washing the dithizone extract with water will cause decomposition of the sulphide. It is therefore proposed that the dithizone extract should be washed with two 15-ml portions of water before being washed with the sodium sulphide solution.DETERMINATION OF SMALL AMOUNTS OF ZINC RECOMMENDATION The Sub-committee recommends that, after destruction of organic matter by some suitable m e t h ~ d , ~ ? ~ the titrimetric dithizone procedure for up to 1OOpg of zinc in the final solution and the alternative spectrophotometric finish for up to 1Opg of zinc in the final solution previously recommended by the Trace Elements in Fertilisers and Feeding Stuffs Sub-Committee1 are, with the modifications given below, applicable to the determination of zinc in organic matter generally.It is also recommended that these modifications should be incorporated in the method as previously pub1ished.l MODIFICATIONS- 325 Page 35, line 15-After the sentence ending “. . . carbon tetrachloride layer” insert, as a new sentence, “Shake the solution with 2 ml of carbon tetrachloride, and discard the carbon tetrachloride layer.” Page 35, line 22-After the words “0.02 N hydrochloric acid” insert “(ensure that the aqueous layer is acid).” Page 36, line 5-To read “Wash the combined dithizone extracts run off during the titration with two 15-ml portions of distilled water; shake the washed solution for 10 seconds. . . .” REFERENCES 1. 2. 3. Analytical Methods Committee, “Determination of Trace Elements, with Special Reference to -- , Analyst, 1960, 85, 643. -- , “The Use of 50 per cent. Hydrogen Peroxide for the Destruction of Organic Matter,” Ibid., Fertilisers and Feeding Stuffs,” W. Heffer & Sons Ltd., Cambridge, 1963, pp. 34-36. 1967, 92, in the press.

ISSN:0003-2654    

DOI:10.1039/AN9679200324

出版商:RSC    

年代:1967

数据来源: RSC