摘要:

Analyst, September, 1979, Vol. 104, $9. 853-859 Polarographic Determination of Some Linear Alkylbenzene Sulphonates 853 J. P. Hart and W. Franklin Smyth Chemistry Department, Chelsea College, Manresa Road, London, S W3 6 L X and B. J. Birch Unilever Research, Port Sunlight Laboratory, Port Sunlight, Wzrral, Merseyside, L62 4XN The linear alkylbenzene sulphonate content of sewage samples has been determined by an indirect polarographic method. ICecoveries made on sewage samples spiked with between 25 and 100 pg of 4-phenyldodecane sulphonate ranged from 82.0 to 104.1%, respectively, showing the method t o be reliable when concentrations were of the order of 0.5 pg ml-l or greater. This was also confirmed by recoveries made on tap water. Keywords : Linear alkylbenzene sulphonate determination ; polarography Linear alkylbenzene sulphonates (LAS) are anionic surfactants commonly used in the detergent industry and are normally assayed at low concentration levels by a spectrophoto- metric method following extraction of a methylene blue complex into ch1oroform.l-3 Re- cently, there has been a necessity to investigate other methods that possess greater selectivity and sensitivity.A.c. polarographic methods have been tried,4-6 but have been found to be non-selective and non-specific. This paper describes a systematic study of the nitration of structurally different LAS prior to differential-pulse polarography of the resulting nitro derivatives. The sensitivity and selectivity of the method have been evaluated and the method has been applied to determination of LAS in sewage and tap water.Experimental Reagents and Chemicals These were methanol, butan-2-one, ethyl acetate, dichloromethane, fuming nitric acid, concentrated sulphuric acid and 0.2 M, 10% and 507’ m/V sodium hydroxide solution. A stock Britton - Robinson (BR) solution, composed of a mixture of 0.04 M boric acid, 0.04 M acetic acid and 0.04 M orthophosphoric acid, was prepared in distilled water. Buffer solutions of various pH were prepared by the addition of 0.2 M sodium hydroxide solution to aliquots of this solution. The LAS examined (synthesised by Palmer Research Ltd., Mostyn, Clwyd) had the structures given in Table I. TABLE I STRUCTURES OF LAS EXAMINED All reagents were of analytical-reagent grade. Compound X Y ? 1-Phenyldecane sulphonate .. . . . . H 1-Phenyltridecane sulphonate . . . . H 1-Phenylpentadecane sulphonate . . . . H 2-Phenyltetradecane sulphonate . . . . CH, 3-Phenylpentadecane sulphonate . . . . C2H5 4-Phenyldodecane sulphonate . . . . C,H7 7-Phenyltridecane sulphonate . . . . C,H,, 7-Phenyltetradecane sulphonate . . - C6Hl3 I Y -c-x Instrumentation All pH measurements were made using an EIL, Model 23A, pH meter incorporating a glass indicator electrode, saturated potassium chloride - calomel reference electrode and a temperature compensator.854 HART, SMYTH AND BIRCH POLAROGRAPHIC DETERMINATION Analyst, Vol. 104 Polarography was carried out with a PAR, Model 174A, Polarographic Analyser operated in the differential-pulse mode, and polarograms were recorded on an Advance HR2000 X - Y recorder.A three-electrode system was used for polarography and consisted of a saturated potassium chloride - calomel reference electrode, a platinum counter electrode and a dropping-mercury electrode. The dropping-mercury electrode had the following characteristics : outflow velocity m = 1.57 m g l , drop time t = 4.3 s at the potential of the saturated potassium chloride - calomel electrode and at a mercury pressure h = 68 cm in 1 M potassium chloride solution. For the Polarographic Analyser the controlled drop time was 0.5 s with a modulation amplitude of 50 mV, scan speed -5 mV s-l and low pass filter 0.3 s. The usual start potential was about -0.4 V. Experimental Techniques Nitration at the micro level with fuming nitric acid - concentrated sulphuric acid (25, 37.5, 50 a& 75% V / V ) Approximately 10 mg of the LAS, accurately weighed, were dissolved in 100 ml of methanol.Further dilution was carried out to give a final concentration of about 20 pg ml-l and 2 ml of this solution were pipetted into a ground-glass centrifuge tube. The tube was heated on a steam-bath until the solvent had completely evaporated, then 0.5 ml of the nitration mixture (25, 37.5, 50 or 75% V/V fuming nitric acid- concentrated sulphuric acid) was added. After 30min the tube was removed from the steam-bath and 9.5ml of distilled water were added carefully. The contents of the centrifuge tube were transferred into the polarographic cell, two 5-ml volumes of distilled water were used to wash the tube and these washings were also added to the polarographic cell.A 10% solution of sodium hydroxide was used to adjust the pH of the mixture to 12.0 and, after de-aeration for 10 min with nitrogen, polarography was carried out. Blanks were prepared by treating 0.5ml of the nitration mixture only. Nitration at the micro level with fuming nitric acid Approximately 10 mg of LAS were accurately weighed into a 100-ml calibrated flask and made up to the mark with methanol. After further dilution with methanol as above, 2 ml of this solution were pipetted into aconical centrifuge tube and evaporated to dryness on a steam- bath. Nitrations were then carried out at 0, 30 and 100 "C, using various amounts of fuming nitric acid for times varying from 1 min to 1 h. The nitric acid was blown off with a stream of nitrogen and the residue dissolved in the appropriate volume of BR buffer, pH 12.0.Blanks were prepared by evaporating 2 ml of methanol to dryness and carrying out the above procedure. Calibration graphs and response factor for LAS nitrated at the micro level with fuming nitric acid Approximately 10 mg of LAS were accurately weighed into a 100-ml calibrated flask and made up to the mark with methanol. Aliquots of stock solution were diluted to 25 ml with methanol in calibrated flasks, and 2 ml of these solutions were pipetted into 10-ml conical centrifuge tubes. After evaporation on a steam-bath, the tubes were allowed to cool and transferred into a water-bath thermostatically controlled at 30 "C. Nitration was carried out using 0.1 ml of fuming nitric acid and, after 15 min, excess of acid was blown off with nitrogen.The residue was taken up in 5ml of BR buffer, pH 12.0, and after shaking vigorously for 2 min the solution was transferred into the 25-ml pear-shaped cell. Nitrogen was passed through the solution for 10 min to de-aerate it, then the polarogram was recorded using the differential-pulse mode. The peak current was measured and graphs of i, (PA) versus concentration of LAS (pg ml-l) in the final buffer solution were constructed. Sewage and Tap Water Analysis The sewage sample (50 ml) was measured into a 100-ml beaker and allowed to evaporate completely to dryness. Care was taken to ensure that the sample did not "spit," by removing the beaker from the gauze when only a few millilitres of solution remained and carefullySeptember, 1979 OF SOME LINEAR ALKYLBENZENE SULPHONATES 855 swirling the liquid around the bottom of the beaker.The heating and swirling action was continued until the beaker was completely dry, then it was allowed to cool to room tempera- ture. The beaker was washed with two 5-ml portions of methanol and the washings were transferred into a Pyrex test-tube (about 13 x 1.5 cm). Several anti-bumping granules were added and the tube was carefully immersed in an oil-bath at 85 "C. Only the lower 2-3 cm were initially immersed in the oil until the methanol began to boil steadily. When evaporation was complete, the tube was removed from the oil-bath and allowed to cool. This last procedure was performed on 50-ml aliquots of sewage, to which had been added various amounts of the LAS chosen as a standard, viz., 4-phenyldodecane sulphonate.A set of known solutions containing the standard LAS (approximately 5-250 pg) were also prepared for the construction of a calibration graph. Nitrations were carried out with fuming nitric acid at 30 "C for 15 min, evaporation of the nitric acid and dissolution of the residue in 5 ml of BR buffer solution, pH 12. The tubes were stoppered and shaken for 1 min, then the contents were filtered into the polarographic cell. The solutions were de-aerated for 10 min with oxygen-free nitrogen and polarographed. A blank was obtained by treating 10ml of methanol in the same way as the methanol extracts of sewage residues. Aliquots of laboratory tap water (50 ml) were measured into 100-ml beakers and to all, except one, was added 1 ml of standard 4-phenyldodecane sulphonate (concentration of the standard varied from approximately 5 to 50 pg ml-1).The remainder of this procedure was identical with that described for sewage. Results and Discussion Nitration at the Micro Level with Fuming Nitric Acid - Concentrated Sulphuric Acid Nitrations were performed on micro amounts of LAS (approximately 30 pg) using 25, 37.5, 50 and 75% V/V fuming nitric acid - concentrated sulphuric acid, as described under Experimental. Differential-pulse polarography of the nitro derivatives was carried out at pH 12 and the most suitable nitration was with 37.5% V/V fuming nitric acid - concentrated sulphuric acid at 100 "C for 30 min. Nitration at the Micro Level with Fuming Nitric Acid In an effort to improve the over-all sensitivity of nitration, fuming nitric acid was incorporated as the nitrating agent.This could be blown off after nitration and thus avoided the use of sodium hydroxide for pH adjustment. The residue could be conveniently taken up in the supporting electrolyte of choice, which was found to be BR buffer, pH 12. Fig. 1 shows the differential-pulse polarograms of 7-phenyltridecane sulphonate nitrated at 0, 30 and 100 "C with 0.1 ml of fuming nitric acid for 30 min. The sizes of the reduction peaks for temperatures of 0 and 30 "C were comparable, indicating that the yield of nitro derivative was the same in both instances. A small peak occurred at potentials more positive than the main reduction peak, and was probably due to slight dinitration.This small peak increased significantly in size for nitrations carried out at 100 "C. The product obtained from nitra- tion at 100 "C gave a broader second peak than the product obtained at either 0 or 30 "C. This is probably due to the formation of both mononitro and dinitro products a t the highest temperature. For analytical purposes a single peak is, of course, better than two incompletely resolved peaks, so that a nitration temperature of 30 "C was preferred, nitric acid being more easily evaporated than at 0 "C. To determine the optimum reaction time, LAS was treated with 0.1 ml of fuming nitric acid at 30 "C for times ranging from 5 to 60 min. After evaporating off excess of fuming nitric acid, polarography was carried out in BK buffer, pH 12.From the graph of peak current vcysus time for 2-phenyltetradecane sulphonate using the above conditions, the nitration reaction was found to be complete after 15 min and this was also found for the other LAS Initial experiments were carried out to determine optimum temperature and time.856 HART, SMYTH AND BIRCH : POLAROGRAPHIC DETERMINATION Analyst, Vol. 104 c-f 100 mV I Fig. 1. Differential- pulse polarograms of nitration of 7-phenyl- tridecane sulphonate in BR buffer (pH 12). Nitrations carried out a t A, 0 "C; B, 30 "C; and C, 100 "C. Concentration (with respect to LAS) = 4.33 pg ml-l and starting potential -0.40 V. examined. Fig. 2 shows differential-pulse polarograms of several different LAS types, and two further compounds, benzoic acid and phenol, after nitration at 30 "C for 15 min using 0.1 ml of fuming nitric acid.Equimolar amounts of phenol did not give rise to differential- pulse polarographic peaks in the vicinity of the LAS reduction peak, whereas benzoic acid Fig. 2. Differential- pulse polarograms of the nitro derivatives of three LAS compounds and two standard compounds; sup- porting electrolyte BR buffer (pH 12) and starting potential -0.4 V. A, 20.2 pg of sodium ethyltridecyl benzene sulphonate; B, 17.8 pg of sodium hexa- heptyl benzene sulpho- nate; C, 10.0 pg of sodium pentadecyl benzene sul- phonate; D, 266pg of phenol; E, 20 pg of benzoic acid; and F, blank of nitration mixture. Fig. 3. Differential- pulse polarograms of: A, nitro derivatives of a mixture of 2 pg ml-1 of 1-phenylpentadecane sulphonate and 5 pg ml-' of 7-phenyltetradecane sulphonate ; and B, blank of nitration mixture.Starting potential -0.4 V.September, 1979 OF SOME LINEAR ALKYLBENZENE SULPHONATES 857 would be expected to cause some interference. Using these milder conditions, only one major peak was obtained and indicated that mononitration was the prevalent route. Between 5 and 50 pg of LAS were nitrated and, after evaporation, the residues were taken up in 5 ml of buffer solution and polarographed. Table I1 gives E , values and the slopes of the calibra- tion graphs. The coefficient of variation was determined for phenyldecane sulphonate on six replicate determinations at 5 and 50 pg, and the values were found to be 8.2 and 7.9%, respectively .TABLE I1 DIFFERENTIAL-PULSE POLAROGRAPHIC DATA FOR LAS NITRO DERIVATIVES This procedure was then employed to construct calibration graphs. I N BR BUFFER, pH 12.0 Compound l-Phenyldecane sulphonate . . . . l-Phenyltridecane sulphonate . . . . l-Phenylpentadecane sulphonate . . . . 2-Phenyltetradecane sulphonate . . . . 4-Phenyldodecane sulphonate . . . . 7-Phenyltridecane sulphonate . . . . 7-Phenyltetradecane sulphonate . . . . 3-Phenylpentadecane sulphonate . . . . Slope of cali- pA pg-l ml E P I bration graph/ V us. S.C.E. - 0.67 -0.67 -0.66 -0.72 -0.73 - 0.74 -0.73 -0.74 0.017 0.016 0.016 0.008 0.010 0.011 0.009 0.010 Thus, LAS can be assayed at the micro level (5-50 pg) using fuming nitric acid at 30 "C for 15 min. The latter method gives rise principally to mononitro derivatives with dinitra- tion as a minor reaction pathway, as evidenced in the polarograms. The LAS mononitro derivatives gave E , values differing by about 50 mV between the nitro derivatives of LAS types with and without a phenyl group in the 1-position. This is illustrated in Fig.3 for a solution containing the nitro derivatives of l-phenylpentadecane sulphonate and 7-phenyl- tetradecane sulphonate. Using this method, therefore, LAS, with a phenyl group in the l-position, can be qualitatively differentiated from LAS with a phenyl group attached to other chain positions. However, quantitative measurements are not possible without curve resolution techniques, because the peaks are only partially resolved.* This method was then applied to the determination of LAS in sewage and tap water.Sewage Analysis The samples of sewage examined were collected from three different sources and designated detergent-free, normal and dosed. In the first type, most of the anionic surfactant, con- sisting of some complex mixtures of LAS species had been removed by treatment, in the second the sewage was untreated and in the last LAS was added to the sewage stream. Using the method outlined under Experimental, sewage residues were nitrated, and differential-pulse polarograms of the three types of sewage are illustrated in Fig. 4. All of the sewage samples gave a reduction peak that occurred at the same potential as for the nitro derivative of a standard LAS (4-phenyldodecane sulphonate), i e . , -0.74 V. Sewage samples were collected over a period of several days and submitted to both the polarographic and methylene blue procedures.In the methylene blue procedure, as is usual, the calibra- tion graph was constructed from known solutions of Manoxol OT. The polarographic method was found to be suitable for the determination of LAS with reasonable specificity. This is indicated by the results shown in Table I11 where, in general, the spectrophotometric method gave higher results, probably because the methylene blue pro- cedure gives a total anionic surfactant content, the so-called MBAS value, whereas only surfact- ant species or other organic compounds with a benzene ring would be likely to interfere in the polarographic method. Even then the E , values of the derivatives of these species would not necessarily coincide with those of LAS nitro derivatives.As shown earlier, benzoic acid and phenol did not interfere significantly. Gas-chromatographic methods would be expected to have greater selectivity than the polarographic method described above, but the former are often more time consuming. while of interest, has little practical importance. * It should be noted that the l-isomer does not occur in commercial LAS samples; hence this observation,858 HART, SMYTH AND BIRCH POLAROGRAPHIC DETERMINATION Analyst, Vol. 104 4- c * * 200 mV 200 mV Fig. 4. Differential-pulse polarograms of nitrated sewage residues and blanks of A, surfactant-free sewage; B, normal sewage; C, dosed sewage ; Supporting electrolyte BR buffer (pH 12) and initial nitration mixture.D, blank; and E, blank. potential -0.3 V. Samples of sewage were spiked with known amounts of 4-phenyldodecane sulphonate and subjected to polarographic LAS analysis, and the recovery of added standard was calculated. These results are presented in Table IV. Tap Water Analysis In order to determine the limit of detection for the method described for sewage, a tap water sample in which the LAS concentration was expected to be low was used as described under Experimental, varying amounts of 4-phenyldodecane sulphonate being added to 50-ml aliquots. After evaporation, extraction and nitration, polarography was performed in BR buffer, pH 12. Fig. 5 shows the differential-pulse polarograms of some of the nitrated residues. Tap water gave a broad peak, which masked the reduction peak derived from less than 11.2 pg of LAS.Recoveries of LAS were calculated for the tap water samples spiked with 22.4, 33.6 and 44.8pg of 4-phenyldodecane sulphonate per 50ml. A base line was constructed to the TABLE I11 LAS CONTENT OF SEWAGE DETERMINED BY SPECTROPHOTOMETRIC AND POLAROGRAPHIC PROCEDURES Day of sampling Source of sample* 1 Sewage stream A B C 2 3 A B C A B C Concentration/pg ml-1 Spectrophotometric Polarographic method method 2.9 0.6 0.8 1.9 42.0 2.9 I A 3 16.8 0.3 67.0 1.4 69.3 22.3 4.3 12.0 77.5 0.2 1.4 2.9 * Sewage stream A = detergent-free sewage; B = normal sewage; C = dosed sewage.September, 1979 OF SOME LINEAR ALKYLBENZENE SULPHONATES 859 TABLE IV RECOVERIES OF LAS FROM SEWAGE STREAMS, A, B AND c WHERE A IS DETERGENT FREE, B IS NORMAL AND c IS DOSED WITH SURFACTANT Source of sample Sewage stream A A A B B B C C C Amount addedlpg 25 25 25 100 100 100 150 150 150 Amount found/& Recovery, 21.3 85.2 20.5 82.0 22.2 88.8 95.2 95.2 104.1 104.1 91.5 91.5 141.3 94.2 146.7 97.8 149.0 99.3 % * Average of three determinations.shoulders on each peak, and the peak heights measured to this. Recoveries were found to be 80, 88 and 91% in order of increasing LAS concentration. The lower value indicates the difficulty in constructing a true base line when the peak heights of the LAS nitro derivative are comparable only to the peak resulting from tap water alone. Some improvement in recovery was achieved by subtracting the residual current from the total height of the peaks. The recoveries based on this method were 85.2, 90.6 and 92.3% in the same order of LAS concentration as given above. I D I I b o " Fig. 5. Diff erential-pulse polarograms of tap-water residues after nitration. A, Blank; B, tap water; C, tap water + 11.2 pg of LAS; and D, tap water + 22.4 pg of LAS. Polarography was per- formed in BR buffer (pH 12) using an initial potential of -0.3 V. One of us (J. P. H.) thanks Unilever for the support of a CASE award. References 1. 2. 3. 4. 5. 6. Longwell, J., and Maniece, W. D., Analyst, 1955, 80, 167. Webster, H. L., and Halliday, J., Analyst, 1959, 84, 552. Fairing, J . D., and Short, F. R., Analyt. Chem., 1956, 28, 1827. Linhart, K., Tenside, 1972, 9, 28. Buchanan, G. S., and Griffith, J . C., J . Electroanalyt. Chein., 1963, 5, 204. Kambara, T., and Hasebe, K., Bunseki Kagaku, 1965, 14, 491. Received January 19th, 1979 Accepted April 2nd. 1979

ISSN:0003-2654    

DOI:10.1039/AN9790400853

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

860 Analyst, September, 1979, Vol. 104, $9. 860-864 Determination of the Amino Acid Contents of Coalworkers' Lungs After Correction for Blood, Fat, Dust and Collagen Roy Loxley Health and Safety Executive, Safety i n Mines Research Establishment, Red Hill, Shefield, S3 7HQ The amino acid contents of dust-affected coalworkers' lungs, complicated pneumoconiotic lesions, the remainder of the lungs from which the lesions had been removed and dust-free control lungs have been determined. The results have been corrected for blood, dust, fat and collagen content, but no significant differences between dust-free and dust-affected lungs were found. The residual amino acid results, after correction, closely resembled the results for glycoprotein extracted from human lung pleura and aorta.Keywords : Amino acid determination ; coalworkers' lungs ; human lung analysis ; pneumoconiosis Coalworkers' pneumoconiosis is caused by inhaled coal dust that is retained in the lungs. The progress of the disease can be monitored by a series of X-ray pictures, and grades of pneumoconiosis have been devised by Liddell and Lindars.l In some cases the disease is complicated by the formation of lesions. These lesions were thought to be fibrosed and the condition of complicated pneumoconiotic lesions (CPL) was called progressive massive fibrosis (PMF). It was thought that a complete amino acid determination of coal dust affected lungs and dust-free control lungs might reveal differences in their composition that could be related to the progress of the disease.A comprehensive bank of formalin-fixed whole and partial lungs that had been minced, dried and ground to homogeneous powders was available at the Safety in Mines Research Establishment, and analytical methods designed specifically for formalin-fixed samples have been developed by Bergman2 and Bergman and L ~ x l e y . ~ * ~ For the work described here, four dust-free control lungs (Control), four CPLs (CPL), the four lungs from which the CPLs had been removed (Rest) and four simple pneumoconiotic lungs without reported cornplica- tions (Simple) were analysed for the amino acid content. The results were corrected for dust, blood, fat and collagen. A suggestion that a coalworker's CPL gave a result similar to that of fibrin, after correction for collagen, was made by Wagner,5 but he gave no supporting evidence.Methods Samples were taken of four disease-free control lungs, four simple pneumoconiotic lungs with varying dust content, four complicated pneumoconiotic lungs with the CPLs removed and the four CPLs that had been separately minced, dried at 105 "C and ground to pass through a 100-mesh sieve. Samples of the dried ground material were hydrolysed with 6 N hydrochloric acid and aliquots of the diluted hydrolysate were taken for hydroxyproline determination. The method of Bergman and Loxley3 was used, in which the hydroxy- proline was oxidised by chloramine-T to a product that, when coupled with 4-dimethylamino- benzaldehyde, produced a red colour suitable for colorimetric determination. Additional aliquots of each diluted hydrolysate were evaporated to dryness on a rotary evaporator and re- dissolved in a citrate buffer.The amino acid contents were determined after separation on Aminex resin. The method of Atkin and Ferdinand6 was used for Control 1, CPL 5, Rest 5 and Simple 9; a modified version of this method' was used for the remainder. The blood content of the samples was determined by hydrolysing the haemin of the haemoglobin with hydriodic acid in acetic acid after pre-heating with phenol to remove the effects of formalin fixation. The pyrroles produced were then coupled with 4-dimethyl- aminobenzaldehyde to produce a red colour, which was measured c~lorimetrically.~ Crown Copyright.LOXLEY 861 A double-digestion procedure was used to determine the dust content of the lungs.The lung tissue was dissolved in acetic and formic acids and the insoluble residue was weighed.2 The fat content of the lungs was assumed to be represented by the loss in mass of a 5-g sample after a triple ethanol - diethyl ether (3 + 1) extractionJ8 followed by a triple chloro- form - methanol (3.7 + 1) extra~tion.~ The residue was given a final rinse with benzene to reduce the risk of explosion and consequent loss of sample during the drying at 105 "C. The volume of each extractant was 40ml and the residue was separated at each stage by centrifuging for 20 min at 3000 rev min-l. Calculations The major components of human blood are haemoglobin (71y0), albumin (19%) and globulin (lo%), according to Geigy.lo The amino acid composition of average blood was calculated from the equations given for haemoglobin by Huntsman and Lehmann,ll for albumin by Saifer and Palo12 and for globulin by Tristram and Smith.13 The dry mass of a sample of blood increased by 15% after treatment with formaldehyde, and so each individual amino acid content of the average blood was decreased by 15% in order to obtain the amino acid content in formalin-fixed blood.The dry mass of fat-, blood- and dust-free minced human lung increased by 15% after formalin fixation; the mass of collagen was assumed to increase by a similar amount. Hence, the amino acid content of formalin-fixed human lung collagen was obtained by decreasing by 15% the individual amino acid contents given in the analysis of fresh human lung collagen (120 "C extract) .14 The calculated hydroxyproline content of formalin-fixed human lung collagen was ll.6yo and this figure was used to convert the hydroxyproline, found in the samples by the Bergman and Loxley method, into the formalin-fixed collagen content.The amino acid results for the formalin-fixed lung samples were corrected for dust, fat and formalin-fixed blood to give the amino acid results for the uncontaminated fat-free lung samples. The sum of the corrected amino acids in each sample was decreased by 15% in order to convert into unhydrolysed protein and increased by 15% in order to allow for formalin fixation. Thus, the formalin-fixed protein contents, shown in Table I, were the same as the amino acid totals. An example of this calculation is as follows: let the amount of an amino acid K in a lung sample be A%, the formalin-fixed blood content of the sample Byo, the dust content of the sample D%, the fat content of the sample F%, the amount of K in formalin-fixed human haemoglobin X y o , the amount of K in formalin-fixed human albumin Yyo and the amount of K in formalin-fixed human globulin 2%.The content of amino acid K in blood, fat and dust-free formalin-fixed tissue is 100 [A - 0.01B (0.71X + 0.19Y + O.lOZ)] % 100 - B - D - F This formula was then corrected for the amino acids contributed by the formalin-fixed collagen, to give the amino acid composition of the unaccounted part of the lung samples. If the formalin-fixed collagen content of the sample is Cyo, and the amount of the amino acid K in formalin-fixed human lung collagen is Wyo, the amount of K in formalin-fixed collagen, blood, dust and fat-free tissue is 100 [A - 0.01B (0.71X + 0.19Y + 0.102) - O.OlCW] YO 100 - B - C - D - F Results and Discussion Control sample 4 had a sodium chloride content of 12.8y0, owing to the method of formalin fixation used with that lung.This contaminant has been entered under Dust for convenience. The results given for blood, dust and fat are similar to those obtained for about 300 lung samples in our collection, and show typical individual, as well as group, variations. The sum of the three components constituted a major portion of each sample's analysis and thus affected the accuracy of all corrected results. Table I shows the results of analyses of the formalin-fixed lung samples.862 LOXLEY: DETERMINATION OF AMINO ACID CONTENTS OF COALWOKKERS’ Analyst, Vd.104 The formalin-fixed collagen results (Table I), corrected for blood, dust and fat, show no significant variations due to dust. However, the CPL results tended to show a small decrease compared with the corresponding Rest results. The results obtained by Nagelschmidt ct al.15 tended to show a higher figure for the CPLs compared with the corresponding Rests, but no correction for blood had been made. The blood content of a CPL is always less than the corresponding Rest and so a correction of Nagelschmidt et al.’s results for blood would reduce or even reverse the tendency, and thus give a closer agreement with the results in Table I. TABLE I RESULTS FOR FORMALIN-FIXED LUNG ANALYSIS Sample Control 1 .. Control 2 . . Control 3 . . Control 4 . . CPL 5 . . CPL 6 . . CPL 7 . . CPL 8 . . Rest 5 . . Rest 6 .. Rest 7 .. Rest 8 . . Simple 9 . . Simple 10 . . Simple 11 . . Simple 12 . . . . . . . I . . . . .. . . .. . . . . . . , . . . . . . . Blood, 28.3 56.7 7.5 36.5 8.2 10.5 10.9 16.5 24.3 21.7 18.5 29.9 12.2 22.3 35.3 12.7 Yo Dust, Yo - - 0.6 12.8* 15.8 13.4 17.5 16.7 5.8 8.8 8.0 7.9 9.2 10.6 13.1 23.7 Fat, 7.2 9.1 17.6 19.0 7.4 16.4 14.3 11.9 7.2 11.4 7.7 11.5 8.9 8.4 10.2 6.6 % Collagen, 29.6 34.7 28.6 24.6 25.2 40.8 20.2 25.1 27.2 33.7 32.2 36.0 27.1 19.6 33.5 35.9 %t Total protein, 56.9 77.8 81.1 75.5 79.8 82.7 71.8 67.9 84.7’ 75.4 73.8 67.5 88.5 71.7 75.0 81.0 Yo t * Sodium chloride (see text). t Results after correction for blood, dust and fat.The blood-, dust- and fat-corrected total amino acid contents of the samples, which are the same as total formalin-fixed protein, are shown in Table I. According to Blackburn,16 the acid hydrolysis conditions used completely destroy tryptophan and partially destroy cystine, serine and threonine. Gruber and Mellon17 add tyrosine (completely destroyed) and glutamic acid, histidine and lysine (partially destroyed) to the list when formalin-fixed material is used. Keutmann and Pottsl* confirmed that methionine is partially destroyed in the hydrolysis process. It was difficult to assess the total loss of amino acids during hydrolysis but a figure of 10% was assumed, which was made up of tyrosine (5%) and tryptophan (3y0), the remaining 2% being assumed to be contributed by the partially destroyed amino acids.The total amino acid content, i.e., Total Protein in Table I, was between 78 and 99% when the assumed 10% loss was added t o the figures given, with the exception of Control 1. These totals showed no significant variation due to the presence of dust. The individual amino acid results corrected for blood, dust, fat and collagen are shown in Table 11. The low recoveries of histidine, lysine and methionine were not unexpected, because the losses of these amino acids, due to partial destruction, were concentrated in the residual figures, especially in the samples with a high blood content and high total contami- nants. The negative values were neglected in calculating the total and average amino acid compositions. Control 1 was excluded from calculations because it appeared to be totally different from the other Controls.Neither the individual amino acids nor their totals showed any significant variation due to dust. Even the results for the CPLs were not significantly different from those for the lungs from which the CPLs were extracted. Wagner5 suggested that a coalworker’s CPL had an amino acid composition similar to that of fibrin, after correction for collagen content. An extensive literature search failed to produce the amino acid composition of fibrin, but results for fibrinogen, which undergoesSeptember, 1979 LUNGS AFTER CORRECTION FOR BLOOD, DUST AND COLLAGEN 863 TABLE I1 AMINO ACID RESULTS FOR SAMPLES AFTER CORRECTION FOR BLOOD, DUST, FAT AND COLLAGEN The results are percentages, the figures in parentheses being the negative values that were neglected in calculating the total and average amino acid composition.Sample Aia Arg Asp Glu Gly His Ileu Leu Lys Met Phe Pro Ser Thr Val Tota Control 1 .. 5.3 1.4 5.9 8.7 3.8 (-3.3) 1.4 2.8 0.7 0.2 (-0.6) 6.1 3.5 2.2 (-0.9) 42.0 Control 2 .. 8.9 4.2 8.2 9.4 7.7 (-3.6) 2.8 8.3 (-9.1) (-0.5) 4.3 6.4 2.2 2.7 4.7 69.8 Control 3 . . 7.3 4.4 7.5 11.0 6.5 0.8 2.0 7.8 2.7 1.1 4.1 5.8 3.8 3.6 6.3 74.7 Control 4 . . 6.4 2.9 8.4 12.5 5.4 (-7.9) 3.3 8.1 (-1.2) 0.3 5.4 5.1 3.7 3.3 5.1 69.9 Average . . . . 7.5 3.8 8.0 11.0 6.5 0.3 2.7 8.1 0.9 0.5 4.6 5.8 3.2 3.2 5.4 71.5 CPL 5 . . . . 5.9 4.4 9.1 11.5 5.6 0.3 3.4 7.5 2.0 1.8 4.1 5.6 4.6 3.5 4.4 73.7 CPL 6 . . . . 6.2 3.9 8.2 11.7 7.6 (-0.5) 3.3 6.9 1.1 1.1 3.8 5.2 4.4 3.8 4.9 72.1 CPL 7 .. . . 4.5 4.6 7.7 10.3 4.7 0.2 3.1 6.6 2.8 0.6 3.6 3.8 4.1 3.8 4.7 65.1 CPL 8 . . . . 4.6 3.8 6.8 9.4 4.4 (-0.9) 2.8 5.8 1.6 0.5 2.9 4.2 3.6 3.4 4.5 58.3 Average .. _ . 5.3 4.2 8.0 10.7 5.6 0.1 3.2 6.7 1.9 1.0 3.6 4.7 4.2 3.6 4.6 67.3 Rest 5 . . . . 7.4 3.2 9.6 13.6 7.5 (-0.6) 3.2 8.7 0.4 1.7 3.8 7.5 5.4 3.8 4.0 79.8 Rest 6 . . .. 6.4 3.2 7.6 10.1 6.3 (-2.0) 3.5 7.2 (-0.7) 0.6 3.7 5.4 3.3 3.3 4.9 65.5 Rest 7 . . . . 5.6 3.7 7.3 10.1 4.9 (-1.5) 3.0 6.5 1.9 0.5 3.1 4.4 3.8 3.5 4.5 62.8 Rest 8 . . . . 5.4 3.5 6.7 8.9 5.0 (-5.3) 2.9 5.9 (-2.7) (-0.1) 2.7 1.9 3.2 3.0 3.8 52.9 Average .. .. 6.2 3.4 7.8 10.7 5.9 - 3.2 7.1 0.6 0.7 3.3 4.8 3.9 3.4 4.3 65.3 Simple 9 . . 7.9 3.3 11.1 13.8 7.7 (-0.3) 2.9 9.8 1.0 1.7 4.7 5.8 5.9 4.6 5.4 85.6 Simple 10 .. 7.2 2.3 8.3 10.5 5.4 (-0.6) 1.8 8.9 (-1.9) (-0.4) 4.9 3.9 3.0 4.0 6.1 66.3 Simple 11 . . 4.8 3.9 8.1 12.2 4.7 (-2.4) 3.2 5.5 (-3.5) 0.5 3.1 8.9 3.6 3.2 3.7 65.4 Simple 12 . . 6.4 4.4 8.1 10.0 5.7 0.7 3.1 7.2 2.5 0.9 3.6 5.3 4.0 3.6 5.7 71.2 Average . . . . 6.6 3.5 8.9 11.6 5.9 0.2 2.8 7.9 0.9 0.8 4.1 6.0 4.1 3.9 5.2 72.4 minor modifications when converted into fibrin, have been published by Geigy.lo The difference between the total amino acid contents of fibrinogen and fibrin has been estimated at less than 3% by Ferdinand19 and as the peptides lost during the conversion would probably have been trapped in the clotted fibrin, and thus register in the analysis, the amino acid results for fibrinogen were used for comparison. The average amino acid results listed in Table I1 were corrected to give their content in pure protein, assuming a loss in content of 10% due to the conditions of hydrolysis that were used.The corrected figures are shown in Table I11 together with the results for fibrinogen for comparison. The only resemblances between the corrected amino acid results and fibrinogen were in the glutamic acid, isoleucine and phenylalanine contents. A much closer agreement was found when the same amino acid results were compared with the glycoproteins extracted by John and Thomas20 from human aorta and pleura, which are also shown in Table 111. The agreement was even better when a correction for about 10-15y0 elastin was made, based on the surplus alanine, glycine, proline and valine, the prominent amino acids of elastin.After elastin correction only lysine, arginine and histidine were more than 15% outside the range covered by the two glycoproteins. The lysine and histidine results were expected to be low because their partial destruction was magnified by large blood corrections when their residual amounts were calculated. TABLE I11 COMPARISON OF THE AVERAGE RESIDUAL AMINO ACID CONTENTS OF THE SAMPLES WITH FIBRINOGEN AND LUNG GLYCOPROTEINS Sample Ala Arg Asp? Glu*t Gly His Ileu*t Leu? Lys Met? Phe*t Pro Sert Fibrinogen . . .. 3.7 7.8 13.1 14.5 5.6 2.6 4.8 7.1 9.2 2.5 4.6 5.7 7.0 Control . . . . 9.4 4.8 10.1 13.9 8.2 0.4 3.4 10.2 1.1 0.6 5.8 7.3 4.0 CPL . . . . . . 7.1 5.6 10.7 14.3 7.5 0.1 4.3 9.0 2.5 1.3 4.8 6.3 5.6 Rest . . .. .. 9.5 5.2 10.8 14.8 9.0 - 4.9 9.8 0.9 3.1 5.0 7.3 6.0 Simple ... . 8.2 4.3 11.1 14.4 7.3 0.2 3.5 9.8 1.1 1.0 5.1 7.4 5.1 Aortaglycoprotein . . 6.4 7.1 10.4 14.1 6.7 2.7 4.2 8.8 7.4 0.9 4.4 6.4 5.9 Pleuraglycoprotein . . 5.8 6.9 10.9 15.4 5.7 2.4 4.0 9.4 7.7 1.5 4.6 5.8 5.8 * Similar result to fibrinogen. t Similar result to glycoprotein. Thrf Val? 6.1 4.1 4.0 6.8 4.8 6.1 5.2 6.6 4.8 6.4 5.1 6.1 5.1 5.7864 LOXLEY If methods of determining formalin-fixed elastin and glycoprotein were available, correc- tions for these components could be made, but the errors that could arise in calculating the results for what appear to be relatively minor components of our samples would be so large that the final residual amino acid results would be very inaccurate. Another way of isolating the differences due to dust retention in human lungs would be to separate the samples into fractions by physical and chemical properties and thus concentrate any differences into individual fractions.Modifications to some of the major components may take place during the various separation stages but this would not be a serious problem if the changes are not the reverse of the processes caused by the presence of the dust. Conclusions No significant difference was found in the blood, dust, fat and collagen corrected amino acid determinations of the controls, CPLs, the lungs from which the CPLs had been extracted and the simple pneumoconiotic lungs. The corrected results of the analyses were similar in content to the glycoproteins extracted from human pleura and aorta.The splitting of the formalin-fixed lungs into fractions separated by physical and chemical properties is proposed as an alternative to correcting for contaminants, as a means of isolating differences between dust-affected and control lungs, with particular emphasis on the CPLs. The author thanks Dr. William Ferdinand of the Department of Biochemistry, Sheffield University, who kindly provided the amino acid determinations. This paper is published by permission of the Director of Research and Laboratory Services, and Head of the Safety in Mines Research Establishment, Health and Safety Executive. References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. Liddell, F. D. K., and Lindars, D. C., BY. J . Ind. Med., 1969, 26, 89. Bergman, I., Analyt. Chem., 1966, 38, 441. Bergman, I., and Loxley, R., Analyst, 1969, 94, 575. Bergman, I., and Loxley, R., Analyt. Chem., 1971, 43, 1204. Wagner, J . C., Ann. N . Y . Acad. Sci., 1972, 200, 401. Atkin, G. E., and Ferdinand, W., Analyt. Biochem., 1970, 38, 313. Atkin, G. E., and Ferdinand, W., J . Chromat., 1971, 62, 373. Bloor, W. R., J . Biol. Chem., 1914, 17, 377. Talvitie, N. A., and Brewer, L. W., A m . Ind. Hyg. Ass. J . , 1962, 23, 58. Geigy, J. R., “Documenta Geigy Scientific Tables,” Fifth Edition, Geigy, Bask, 1956, pp. 304, 313 Huntsman, H., and Lehmann, R. G., “Mans Hemoglobin,” North-Holland, Amsterdam, 1974, p. 68. Saifer, A., and Palo, J., Analyt. Biochem., 1969, 27, 1. Tristram, G. R., and Smith, R. H., Adv. Protein Chem., 1963, 18, 227. Rickert, W. S., and Forbes, W. F., Expl Geront., 1972, 7, 387. Nagelschmidt, G., Rivers, D., King, E. J., and Trevella, W., BY. J . Ind. Med., 1963, 20, 181. Blackburn, S., “Amino Acid Determination. Gruber, H. A., and Mellon, E. F., Anal-yt. Biochem., 1968, 26, 180. Keutmann, H. T., and Potts, J. T., Analyt. Biochem., 1969, 29, 175. Ferdinand, W., personal communication. John, R., and Thomas, J., Biochem. J.. 1972, 127, 261. and 315. Methods and Techniques,” Edward Arnold, London, 1968, p. 17. Received February 28th, 1979 Accepted April 6th, 1979

ISSN:0003-2654    

DOI:10.1039/AN9790400860

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

Analyst, September, 1979, Vol. 104, pp. 865-872 865 Naphthidines and o-Dianisidine as Redox Indicators in Titrations with N-Bromosuccinimide H. Sanke Gowda, R. Shakunthala and U. Subrahmanya Department of Postgraduate Studies and Research in Chemistry, Manasa Gangotri, University of Mysore, Mysore, India The optimum conditions for the successful use of naphthidine, 3,3’-dimethyl- naphthidine, 3,3’-dimethylnaphthidinedisulphonic acid and o-dianisidine as indicators in macro- and micro-titrations of hexacyanoferrate(II), iron(II), hydroquinone, metol and ascorbic acid with N-bromosuccinimide have been established. The indicators give a very sharp reversible colour change a t the equivalence point and have advantages over the existing redox indicators. Hydrazinium sulphate and hydroxylammonium chloride have been determined indirectly.Anhydrous hexacyanoferrate(I1) and iron(I1) are suggested for the standardisation of N-bromosuccinimide solutions. Keywords : Naphthidine and o-dianisidine indicators ; N-bromosuccinimide and hexacyano ferrate (II) standardisation In a recent paper, six N-substituted phenothiazine indicators1 were proposed for titrations with N-bromosuccinimide (NBS). Also, the compounds naphthidine (N) , 3,3’-dimethyl- naphthidine (DMN) and 3,3’-dimethylnaphthidinedisulphonic acid (DMNS) have been used as redox indicators in dichrometry,2-6 cerimetry7 and vanadametry,8 and o-dianisidine (ODA)9 has been recommended for the titration of iron(I1) with potassium dichromate. This paper describes the development of new methods for the standardisation of NBS solutions and for the determination of macro- and micro-amounts of hexacyanoferrate( 11) , iron( II), hydro- quinone, metol, ascorbic acid, hydrazinium sulphate and hydroxylammonium chloride with NBS, using N, DMN, DMNS and ODA as indicators.Experimental and Results Reagents Prepare 0.1% m/V solutions of N, DMN and DMNS by use of the procedure described by Belcher et aZ.5 and also a 0.1% m/V solution of ODA in 0.5% sulphuric acid. Store all of the solutions in amber-glass bottles. Dissolve 2.23 g of NBS in 100 ml of boiled distilled water in a 500-ml calibrated flask and dilute the solution to the mark. Prepare the solution just before use and standardise it iodimetrically.1° Prepare pure anhydrous potassium hexacyano- ferrate(I1) from AnalaR potassium hexacyanoferrate(I1) trihydrate.ll Dissolve 18.415 g of the pure anhydrous salt in boiled distilled water and dilute the solution to 11.Check the normality of the solution by titrating it against standardised cerium(1V) sulphate solution, using iron(I1) 1 ,lo-phenanthroline perchlorate as indicator.12 Dissolve an appropriate amount of recrystallised AnalaR ammonium iron(I1) sulphate in 0.5 M sulphuric acid and standardise this solution against standard potassium dichromate solution.13 Arsercic(III) solution, 0.025 M. Recrystallise AnalaR arsenic(II1) oxide and then prepare a standard solution.l4 Potassium hexacyano ferrate(I1I) solution, 0.1 M. Purify AnalaR potassium hexacyano- ferrate(II1) and prepare a standard solution.15 Prepare and standardise the solutions of hydroquinone,16 metol,17 ascorbic acid,18 hydra- zinium sulphate,lg hydroxylammonium chloride20 and sodium thiosulphate21 by the accepted methods. Prepare other working solutions by suitable dilution of the standardised stock solutions.Indicator solutions. N-Bromosuccinimide solution, 0.025 M. Hexacyanoferrate(1I) solution, 0.05 M. Iron(II) solution, 0.05 M.866 Procedures Standardisation of NBS solution against hexacyanoferrate(II) Take 20ml of 0.02-0.05 M hexacyanoferrate(I1) solution and 0.2 ml of 0.1% N, DMN, DMNS or ODA and dilute them to 40 ml with sufficient acetic acid to give an acidity of 0.4 M (2 M when N is being used as the indicator) at the end-point. Titrate the mixture against 0.01-0.025 M NBS solution to the appearance of a reddish-brown colour.For the standardisation of 0.002 5-0.005 M NBS solutions, transfer 10 ml of 0.005-0.01 M hexacyano- ferrate(I1) solution and 0.05 ml of 0.1% N, DMN, DMNS or ODA to a flask and dilute the mixture to 25 ml with acetic acid in order to give the concentration described above. Then titrate the solution against NBS to the appearance of a pink or orange - red colour. The results are presented in Table I. SANKE GOWDA et al. : NAPHTHIDINES AND O-DIANISIDINE Analyst, Vol. 104 Standardisation of NBS solution against iron (11) Dilute 20ml of 0.02-0.05 M iron(I1) solution and 0.2 ml of 0.1% ODA to 40ml with orthophosphoric acid in order to give an acid concentration of 2 M at the end-point. Titrate the mixture with 0.01-0.025 M NBS (proceeding slowly near the end-point) to the appearance of a red colour.For the standardisation of 0.0025-0.005 M NBS solutions, mix 10 ml of 0.005-0.01 M iron(I1) solution and 0.05 ml of 0.1% ODA, dilute the mixture to 25 ml with orthophosphoric acid of sufficient strength to give the above acidity and titrate the mixture with NBS (again proceeding slowly near the end-point) to the appearance of an orange - red colour. The results are given in Table I. TABLE I STANDARDISATION OF NBS SOLUTION Strength of NBS solution found by- r iodimetric method/M 0.02534 0.025 12 0.021 44 0.01230 0.01008 0.005 038 0.004 804 0.002 542 0.002 428 0.002 234 arsenic( 111) hexacyanoferrate( 11) method/M method/M 0.02543 0.025 32 0.025 22 0.025 14 0.021 48 0.021 46 0.01242 0.012 32 0.010 14 0.010 10 0.005 042 0.005 034 0.008 41 8 0.004 808 0.002 548 0.002 544 0.002446 0.002422 0.002 244 0.002 238 iron (I I) method/M 0.025 36 0.025 18 0.021 46 0.012 30 0.010 12 0.005036 0.004 8 12 0.002538 0.002428 0.002 236 Titration of hydroquinone Take 20 ml of 0.01-0.025 M hydroquinone solution and 0.1 ml of 0.1% N, DMNS or ODA (not ODA if the medium is hydrochloric acid) and dilute the mixture to 40 ml with sufficient sulphuric, hydrochloric or orthophosphoric acid .to give an acidity of 0.6 M at the end-point.Titrate the mixture with NBS to the appearance of a red or orange - red colour. In the titration of 0.002 5-0.005 M hydroquinone solution, dilute 10 ml of hydroquinone and 0.05 ml of the indicator to 25 ml with the acid to give the above acidity and titrate against 0.002 5-0.005 M NBS solution.Titration of metol Transfer 20 ml of a 0.01-0.025 M solution of metol and 0.1 ml of 0.1% ODA solution to a flask and dilute to 40 ml with sulphuric, hydrochloric, acetic or orthophosphoric acid to give a concentration of 0.3 M sulphuric or hydrochloric acid or 0.6 M acetic or orthophosphoric acid at the end-point. Titrate the mixture with NBS to the appearance of a reddish-brown colour. In the titration of 0.005 M metol solution, dilute 10 ml of metol and 0.05 ml of 0.1% ODA to 25ml with the acid to give the above acid concentration and titrate with NBS to the appearance of an orange - red colour.September, 1979 AS REDOX INDICATORS WITH N-BROMOSUCCINIMIDE 867 Titration of ascorbic acid Mix 20 ml of 0.01-0.025 M ascorbic acid solution and 0.1 ml of 0.1% N, DMN, DMNS or ODA (not DMN in sulphuric or orthophosphoric acid media) and dilute the mixture to 40 ml with sufficient sulphuric, hydrochloric, acetic or orthophosphoric acid to give 0.4 M sulphuric, hydrochloric or orthophosphoric acid or 0.7 M acetic acid at the end-point.Titrate the mixture with 0.01-0.025 M NBS solution to the appearance of a pink or orange - red colour. In the micro-titration of ascorbic acid solution, dilute an aliquot of 0.025 M ascorbic acid solution and 0.05 ml of 0.1% N, DMNS or ODA to 25 ml with orthophosphoric acid in order to obtain an acidity of 0.5 M at the end-point and titrate with 0.002-0.005 M NBS solution. Determination of ascorbic acid in vitamin C tablets and injection Transfer a known amount of well powdered vitamin C tablets containing about 100mg of ascorbic acid into a 100-ml calibrated flask.Dissolve the powder in doubly distilled water and dilute the resulting solution to the mark. Filter the solution if there is any turbidity. With vitamin C injection solution, dilute a known volume of the injection solution with doubly distilled water to 100 ml so that 1 ml of the diluted solution contains about 1 mg of ascorbic acid. Transfer an aliquot of the solution and 0.05 ml of N, DMNS or ODA into a flask and dilute to 25 ml with orthophosphoric acid in order to give an acidity of 1 M at the end-point. The results of the assay are given in Table 11. Titrate the mixture with 0.005 M NBS. TABLE I1 DETERMINATION OF ASCORBIC ACID IN VITAMIN C TABLETS AND INJECTION Amount of ascorbic acid (quoted) /mg 500 500 Citrative (Pharmed) .. 500 Sukcee (IDPL) . . . . 500 Chewcee (Cyanamid) . . 500 Calcium 10% (Sandoz) + vitamin C (Sandoz) . . 500 Tablet or injection Celin (Glaxo) . . . . 100 Redoxon (Roche) . . . . 200 Vitamin C tablets (Medicaids) 100 Amount of ascorbic acid found by- r iodimetric method/mg NBS method/mg 99.11 99.06 500.9 501.0 200.05 200.05 501.5 501.5 93.92 93.89 504.3 504.4 500.5 500.4 494.8 494.2 504.5 504.5 Determination of hydraxinium sulphate Take an aliquot of 0.01 M hydrazinium sulphate solution, a two-fold excess of 0.1 M potassium hexacyanoferrate(II1) solution and 10 ml of 7 N sodium hydroxide solution and dilute the mixture to 35 ml. Next neutralise the sodium hydroxide with sulphuric acid.Add 0.2 ml of 0.1% N, DMN, DMNS or ODA and dilute the mixture to 50 ml with acetic acid to give an acid concentration of 0.4 M (2 M for N) at the end-point. Then titrate the hexacyanoferrate(I1) produced with NBS to the appearance of a reddish-brown colour. Allow the mixture to stand for about 3 min. Determination of hydroxylammonium chloride Add a two-fold excess of 0.1 M hexacyanoferrate(II1) solution and 15 ml of borax - boric acid buffer solution (8 g of borax and 4 g of boric acid per 100 ml of water) to a suitable aliquot of 0.025 M hydroxylammonium chloride solution and dilute the mixture to 40 ml. Allow the mixture to stand for 30 min. Add 0.2 ml of N, DMN, DMNS or ODA and sufficient acetic acid to give a concentration of 0.4 M (2 M for N) at the end-point and titrate the hexacyanoferrate( XI) produced with NBS.The average indicator correction was found to be 0.02 ml of 0.01 M NBS for 0.2 ml of 0.1% indicator solution in titrations with 0.025 M NBS and 0.02 ml of 0.0025 M NBS for 0.1 ml of 0.1% indicator solution in titrations with 0.002 M NBS. The results of the determinations of hexacyanoferrate(II), iron( 11), hydroquinone, metol, ascorbic acid, hydrazinium sulphate and hydroxylammonium chloride are presented in Table 111.868 SANKE GOWDA et al. : NAPHTHIDINES AND O-DIANISIDINE Analyst, Vol. 104 TABLE I11 DETERMINATION OF HEXACYANOFERRATE(II), IRON(II), IRON(III), HYDROQUINONE, METOL, ASCORBIC ACID, HYDRAZINIUM SULPHATE AND HYDROXYLAMMONIUM CHLORIDE WITH NBS USING N, DMN, DMNS AND ODA INDICATORS Substance Substance taken/mg found*/mg 209.10 208.70 104.60 104.90 70.52 70.43 9.24 9.27 5.21 5.23 2.67 2.69 1.15 1.16 Hexacyanoferrate (11) - Iron (11)- 56.16 56.24 27.84 27.81 18.24 18.28 9.62 9.59 5.14 5.12 2.43 2.42 1.08 1.07 Iron (111)- 52.82 52.91 25.34 25.37 8.43 8.41 4.22 4.20 2.51 2.49 1.14 1.13 Hydroquinone- 56.12 56.22 27.84 27.88 18.78 18.80 9.46 9.48 4.79 4.81 2.83 2.85 1.24 1.25 Relative error, yo - 0.19 + 0.23 -0.13 +0.22 + 0.38 + 0.75 f0.87 + 0.14 -0.11 -0.31 - 0.39 -0.41 - 0.93 + 0.22 +0.17 + 0.12 - 0.22 - 0.47 -0.80 -0.88 $0.18 + 0.14 +0.11 +0.21 + 0.42 +0.71 t 0 .8 1 Standard deviation/ mg 0.089 4 0.094 8 0.021 0 0.014 1 0.022 8 0.031 6 0.006 3 0.026 1 0.022 8 0.023 7 0.025 3 0.031 6 0.0190 0.005 5 0.022 8 0.025 2 0.026 8 0.028 4 0.0200 0.0109 Substance taken/mg 89.92 46.94 17.66 8.29 5.51 2.92 1.19 Metol- Substance found*/mg 90.11 47.06 17.69 8.31 5.53 2.94 1.20 A scorbic acid- 87.62 87.72 43.82 43.85 17.48 17.46 9.77 9.79 4.01 4.02 2.24 2.25 1.25 1.26 Hydrazinium sulphate- 32.98 32.92 26.62 25.55 16.44 16.49 8.84 8.87 4.28 4.26 2.03 2.04 1.48 1.49 Relative error, yo +0.21 + 0.26 +0.17 + 0.24 + 0.36 + 0.69 f0.84 + O .l l + 0.07 +0.12 + 0.21 f0.25 + 0.45 +0.80 -0.18 - 0.26 + 0.31 + 0.34 + 0.49 + 0.68 - 0.47 Hydroxylammonium chloride- 0.021 0 34.44 34.46 + 0.06 0.0224 24.32 24.35 t 0 . 1 2 0.022 8 18.86 18.88 +O.ll 0.0385 9.48 9.51 + 0.32 0.0443 5.62 5.64 + 0.36 0.026 1 2.44 2.45 +0.41 0.032 6 1.38 1.39 + 0.73 Standard deviation1 mg 0.022 4 0.026 1 0.026 8 0.0155 0.0338 0.036 8 0.0506 0.0452 0.014 2 0.023 7 0.040 5 0.034 1 0.052 2 0.032 2 0.021 9 0.0290 0.032 3 0.0189 0.021 9 0.026 1 0.0089 0.033 2 0.0472 0.0189 0.0328 0.063 2 0.051 0 0.012 7 * Average of six determinations.Discussion N, DMN, DMNS and ODA undergo a two-electron oxidation to a red or violet intermediate, which is believed to be a diradical dication.22 The coloured intermediate is reduced to the original form of the indicator by hexacyanoferrate(II), iron(II), hydroquinone, metol or ascorbic acid. The formal redox potentials of N,7 D M N , 6 DMNS6 and ODA23 have been reported to be 922, 776, 838 and 849 mV, respectively. Standardisation of NBS with Hexacyanoferrate( 11) IodimetriclO and a r ~ e n i c ( I I 1 ) ~ ~ methods are the only titrimetric methods that have been proposed for the standardisation of NBS solutions.The iodimetric method involves the use of starch indicator, which has several disadvantage^,^^ while the arsenic(II1) method employs the irreversible methyl red indicator, which is destroyed by the first drop of NBS in excess at the equivalence point. The authors have now developed a simple but accurate method for the standardisation of NBS solutions against hexacyanoferrate(I1). The use of pure anhydrous potassium hexacyanoferrate( 11) as a standard substance has assumed greater importance because it has the advantage of a high reaction mass and it can easily be obtainedSeptember, 1979 AS REDOX INDICATORS WITH N-BROMOSUCCINIMJDE 869 in a very pure state.ll I t reacts with NBS instantaneously in acetic acid at room temperature (27 "C) to form hexacyanoferrate(III), succinimide and bromide ion.The reaction is quantitative, involving a two-electron change. In the standardisation of NBS solution with 0.02-0.05 M hexacyanoferrate(II), N, DMN, DMNS and ODA indicators give very sharp and correct end-points in 2 4 , 0.25-2, 0.25-3 and 0.2-5 M acetic acid solutions, respectively. N, DMN and DMNS give sluggish end- points at lower acidities and premature end-points at higher acidities. ODA gives sluggish end-points a t lower acidities and larger titration values at higher acidities. All of the four indicators change colour from emerald green to reddish brown or orange - red at the equiva- lence point. The stabilities of the end-point colours of N, DMN, DMNS and ODA are 8, 15, 15 and 10-15 min, respectively, in the titration of 0.02-0.05 M hexacyanoferrate( 11) solutions and 3, 10, 8 and 5-8 min, respectively, in the titration of 0.005-0.01 M hexacyanoferrate(I1) solutions.Influence of Indicator Concentration At least 0.1 ml of 0.1% N, DMN, DMNS or ODA is necessary in a total volume of 60 ml for efficient indicator action in the titration of 0.02-0.05 M hexacyanoferrate(I1) solution. More than 0.5 ml of 0.1% N, DMN and DMNS or 0.3 ml of ODA causes sluggish and over- shot end-points. For the titration of 0.005-0.01 M hexacyanoferrate( 11) solution at least 0.05 ml of the indicator is necessary in a total volume of 35 ml. Concentrations higher than 0.2 ml of N, 0.5 ml of DMN or 0.3 ml of DMNS or ODA give sluggish and overshot end- points. The sensitivity of the indicators decreases in the order ODA > DMNS > N > DMN.The proposed method has been used successfully for the determination of the hexacyano- ferrate(I1) present in commercial samples of potassium hexacyanoferrate( 11) crystals. The results given in Table I11 compare favourably with those obtained with the cerium(1V) sulphate method.12 Standardisation of NBS with Iron( 11) Vulterin26 titrated NBS in 10-13.5 M orthophosphoric acid containing osmium(VII1) oxide catalyst against iron(I1) potentiometrically. The investigation of this potentiometric titration yielded erratic results, which prompted the authors to study the direct titration of iron(I1) with NBS solution. Mohr's salt [ammonium iron(I1) sulphate] has the advantage of a high reaction mass but has the disadvantage of being impure.Its solution was standardised against primary standard potassium dichromate and was used for the standardisation of 0.002 5-0.025 M NBS solutions. In the titration of 0.005-0.05 M iron(I1) solution with NBS solutions only ODA gives a sharp colour change, from colourless to orange - red, at the equivalence point at 1.8-2.7 M orthophosphoric acid concentrations. The indicator gives sluggish end-points at acid concentrations lower than 1.8 M and premature end-points at concentrations higher than 2.7 M. The end-point colour of ODA is more stable for the titration of higher concentra- tions of iron(I1) in higher concentrations of orthophosphoric acid. For example, in the titration of 0.05 M iron(I1) solution, the end-point colour is stable for about 15 min in 1.8 M orthophosphoric acid and 60 min in 2.7 M acid.In the titration of a 0.005 M iron(I1) solution the orange - red colour is stable for 6 min in 1.8 M orthophosphoric acid and 30 min in 2.7 M acid. Influence of Indicator Concentration At least 0.05 ml of 0.1% ODA solution in a total volume of 60 ml is necessary for satis- factory indicator action in the titration of 0.02-0.05 M iron(I1) solution. Higher con- centrations of the indicator (greater than 0.2 ml) give sluggish and premature end-points. In the titration of 0.005-0.01 M iron(I1) solution, 0.05 ml of ODA is required in a total volume of 35 ml. The method of standardisation of NBS with iron(I1) has been usefully employed in the determination of iron in iron(I1) salts and iron(II1) salts, after reduction with tin(I1) chloride in the well established manner, as mercury(I), mercury(I1) and tin(1V) chlorides do not interfere in the functioning of ODA indicator.The results given in Table III compare well with those obtained with use of the dichromate method.27 More than 0.1 ml gives sluggish and premature end-points.Analyst, Vol. 104 870 Comparison of Standard Substances Inspection of the results contained in Table I shows that satisfactory agreement exists among four methods of standardisation. The titrations were carried out against the three primary standard substances arsenic(III), hexacyanoferrate( 11) and potassium dichromate indirectly through the agency of a standardised ammonium iron(I1) sulphate solution and a standardised sodium thiosulphate solution.The average molarity values fall within a range only slightly greater than 1 part per thousand. It is of interest to note that the arsenic(III), hexacyanoferrate(I1) and iron(I1) used in this work were titrated against a solution of cerium(1V) sulphate according to the established procedures and were found to give concordant results. Thus, it was found that excellent internal consistency existed between the various standard substances, indicating the validity of the proposed standard methods. SANKE GOWDA et al. : NAPHTHIDINES AND 0-DIANISIDINE Titration of Hydroquinone In the titration of hydroquinone with NBS, potassium iodide - starch indicator2* does not function. NBS oxidises hydroquinone to quinone instantaneously in sulphuric, hydrochloric or orthophosphoric acid media at room temperature, the reaction involving a two-electron change.N, DMNS and ODA give a colour change from light yellow to reddish brown or orange - red at the equivalence point in the titration of 0.01-0.025 M hydroquinone solution. N gives sharp end-points in 0.25-3 M sulphuric acid or 0.5-3 M orthophosphoric or hydro- chloric acid, DMNS in 0.25-2.5 M sulphuric acid or 0.5-3.0 M orthophosphoric or hydro- chloric acid and ODA in 0.5-3 M sulphuric acid or 1-3 M orthophosphoric acid. The stability of the end-point colour depends upon the nature and concentration of the acid. The end- point colour of N is stable for about 2-6 rnin in sulphuric or hydrochloric acid and 5-15 min in orthophosphoric acid. The end-points with DMNS are stable for 2-5 rnin in hydrochloric acid, 5-10 min in sulphuric acid and about 10 rnin in orthophosphoric acid.The orange - red colour of ODA is stable for 2-7 min in sulphuric acid and 4-5 rnin in orthosphosphoric acid medium. All of the three indicators function well in the titration of 0.0025-0.005 M hydroquinone solution a t the acid concentration described above with a sharp and reversible colour change from almost colourless to pink or orange - red. The end-point colour is stable for 2-5 min. Influence of Indicator Concentration A certain concentration of indicator, 0.1-0.75 ml of 0.1% DMNS, 0.1-0.3 ml of 0.1% N or 0.1-0.5 ml of 0.1% ODA solution, is necessary in a total volume of 60 ml for correct indicator action in the titration of 0.01-0.025 M hydroquinone solution.Higher concentra- tions of the indicator give sluggish and overshot end-points. In the titration of 0.0025- 0.005 M hydroquinone solution, 0.05-0.15 ml of 0.1% N or DMNS or 0.05-0.2 ml of 0.1% ODA indicator is required in a total volume of 35 ml. Higher concentrations of the indicator give sluggish end-points. The results presented in Table I1 compare favourably with those obtained by use of the cerium (IV) sulphat e met hod. l6 DMNS and ODA are more sensitive than N in this titration. Titration of Metol Metol, (N-methyl-9-aminophenol sulphate) is quantitatively oxidised to N-methyl-p-quinon- imine with the loss of two electrons. In the titration of a 0.005-0.025 M solution of metol, only ODA gives a sharp colour change at the end-point (from light yellow to orange - red) in 0.25-1.5 M sulphuric acid, 0.25-2 M hydrochloric acid, 0.5-3 M orthophosphoric acid or 0.5-5 M acetic acid.Sluggish and overshot end-points are obtained at higher acidities. At least 0.05 ml of 0.1% ODA solution is necessary for correct indicator action in a total volume of 60 ml. The titration results presented in Table I11 compare favourably with those obtained potentio- metrically with cerium(1V) sulphate s01ution.l~ The orange - red colour is stable for 35-60 s. More than 0.3 ml of ODA gives sluggish and overshot end-points.September, 1979 AS REDOX INDICATORS WITH N-BROMOSUCCINIMIDE 871 Titration of Ascorbic Acid NBS oxidises ascorbic acid quantitatively to dehydroascorbic acid in an acidic medium at room temperature ; this oxidation involves a two-electron change.The optimum conditions have been developed for the use of N, DMN, DMNS and ODA indicators in the titration of ascorbic acid with NBS. All of the above four indicators, in the titration of 0.01-0.025 M ascorbic acid solution, give a sharp and reversible colour change from colourless to pink or orange - red at the end- point. The use of N yields stoicheiometric results in 0.25-2.5 M sulphuric acid, 0.5-5 M acetic acid and 0.25-3 M hydrochloric or orthophosphoric acid; use of DMN yields stoicheio- metric results in 0.25-2 M hydrochloric acid and 0.5-4 M acetic acid; use of DMNS yields stoicheiometric results in 0.25-1.5 M sulphuric acid, 0.25-3 M hydrochloric or orthophosphoric acid and 0.5-5 M acetic acid; and the use of ODA yields stoicheiometric results in 0.25-2 M sulphuric or hydrochloric acid, 0.25-3 M orthophosphoric acid and 0.5-5 M acetic acid.The stability of the end-point colour depends upon the nature and concentration of the acid. The end-points obtained with N, DMNS and ODA in a sulphuric acid medium are stable for 8, 10 and 15-25min, respectively, those with N, DMN, DMNS and ODA in hydrochloric acid are stable for 3, 10, 7-10 and 20-40 min, respectively, while the pink or orange - red colours of N, DMNS and ODA in orthophosphoric acid are stable for 4-10,lO-15 and 2040 min, respectively. In an acetic acid medium the end-point colour of N, DMN, DMNS and ODA is stable for 2-5, 10, 10-20 and 20-50 min, respectively. All of the four indicators give sluggish and premature end-points at higher concentrations of the acids.Below 0.25 M concentrations of sulphuric, hydrochloric or orthophosphoric acid and a 0 . 5 ~ concentration of acetic acid sharp end-points are not obtained. It is found that at least 0.05 ml of 0.1% N, DMN, DMNS or ODA is needed for a satisfactory colour change in a total volume of 60 ml. More than 0.3 ml of N, 0.7 ml of DMN, 1 ml of DMNS and 0.5 ml of ODA give sluggish and overshot end-points. Milligram amounts of ascorbic acid can be determined by titrating ascorbic acid with 0.0025 M NBS solution in a medium of orthophosphoric acid because the increased potential of the ascorbic acid - dehydroascorbic acid couple in orthophosphoric acid gives protection to the ascorbic acid against atmospheric oxidation.Furthermore, orthophosphoric acid complexes any heavy metal cations present, which might catalyse the atmospheric oxidation of ascorbic acid. N, DMNS and ODA give sharp and correct end-points in the titration of ascorbic acid with 0.0025-0.005 M NBS solutions in 0.25-4 M orthophosphoric acid. The pink or orange - red colour of N, DMNS or ODA is stable for 3-7, 5-8 and 14-20 min, respectively. Above 4 M acid premature end-points are obtained. Volumes of 0.05-0.15 ml of 0.1% N, 0.05- 0.3 ml of 0.1% DMNS or 0.05-0.2 ml of 0.1% ODA are necessary in order to obtain a sharp colour change in 35 ml of solution. The results presented in Table I11 compare favourably with those obtained by use of the iodate method.lS For this titration, ODA and DMNS are recommended as being the most sensitive indicators in all four acid media. Applications of the Ascorbic Acid Titration The titration of ascorbic acid with NBS has been employed successfully for the determina- tion of ascorbic acid in vitamin C tablets and injections.The interference of some of the substances likely to be present in vitamin C tablets and injections was studied. Amounts up to 0.1 g of oxalic acid, 1.75 g of tartaric acid, 2 g of citric acid, 2 g of sucrose or dextrose and 0.75 g of starch do not interfere in the determination of 5 mg of ascorbic acid in an orthophosphoric acid medium. The results of the assay of vitamin C tablets and injections presented in Table I1 compare favourably with those obtained by the iodimetric method.29 Applications of the Hexacyanoferrate(I1) Titration The titration of hexacyanoferrate(I1) with NBS has been used in the determination of hydrazinium sulphate and hydroxylammonium chloride, which are quantitatively oxidised to nitrogen and water at room temperature (27 "C) by a 2-6-fold excess of hexacyanoferrate(II1) in 2 - 2 .5 ~ sodium hydroxide solution in about 3 min and in boric acid- borax buffer in872 SANKE GOWDA, SHAKUNTHALA AND SUBRAHMANYA about 30 min, respectively. One mol of hydrazinium sulphate consumes 4 mol of hexacyano- ferrate(II1) while 1 mol of hydroxylammonium chloride consumes 1 mol of hexacyano- ferrate( 111). Hydrazinium sulphate and hydroxylammonium chloride have been determined from the amount of hexacyanoferrate(I1) formed in the reaction. The results of the deter- mination of hydrazinium sulphate and hydroxylammonium chloride presented in Table I11 compare well with those obtained with the cerium(1V) sulphate Conclusion The results of this investigation have shown that it is possible to standardise NBS solutions with hexacyanoferrate(I1) solution and standardised iron(I1) solution.N, DMN, DMNS and ODA serve as excellent reversible redox indicators in titrations with NBS. They are superior to starch and methyl red indicators, which are affected by a number of limitations. They have advantages over six recently proposed N-substituted phenothiazine indicators in that they do not require the use of potassium bromide in the titration mixture, they are added at the beginning of the titration and they require a smaller indicator correction.One of us (U. S.) thanks the Council of Scientific and Industrial Research, New Delhi, for the award of a Junior Research Fellowship. 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. 29. 30. References Sanke Gowda, H., and Akheel Ahmed, S., Analyst, 1978, 103, 1148. Belcher, R., and Nutten, A. J., J . Chem. SOC., 1951, 547. Belcher, R., Nutten, A. J., and Stephen, W. I., J . Chem. SOC., 1951, 1520. Belcher, R., Nutten, A. J., and Stephen, W. I., J . Chem. SOL, 1951, 3444. Belcher, R., Nutten, A. J., and Stephen, W. I., J . Chem. SOC., 1952, 1269. Belcher, R., Nutten, A. J., and Stephen, W. I., J . Chem. SOC., 1952, 3857. Sanke Gowda, H., and Shakunthala, R., Analytica Chim. Acta, 1977, 91, 399.Sanke Gowda, H., and Shakunthala, R., Analytica Chim. Acta, 1978, 97, 385. Weeks, M. E., I n d . Engng Chem., Analyt. Edn, 1932, 4, 127. Biltz, H., and Beherens, O., Ber. Dt. Chem. Ges. 1910, 43, 1984. Kolthoff, I. M., and Belcher, R., “Volumetric Analysis,” Volume 111, Interscience, New York, 1957, Belcher, R., and Nutten, A. J ., “Quantitative Inorganic Analysis,” Butterworths, London, 1960, Kolthoff, I. M., and Belcher, R., “Volumetric Analysis,” Volume 111, Interscience, New York, 1957, Kolthoff, I . M., and Belcher, R., “Volumetric Analysis,” Volume 111, Interscience, New York, Kolthoff, I. M., and Belcher, R., “Volumetric Analysis,” Volume 111, Interscience, New York, 1959, Furman, N. H., and Wallace, J. H., J . A m . Chem. SOC., 1930, 52, 1443. Rao, G. G., and Sastri, T. P., 2. Analyt. Chem., 1958, 163, 263. Ballentine, R., I n d . Engng Chem., Analyt. Edn, 1941, 13, 89. Kolthoff, I. M., and Belcher, R., “Volumetric Analysis,” Volume 111, Interscience, New York, 1959, Cooper, S. R., and Morris, J. B., Analyt. Chem., 1952, 24, 1360. Kolthoff, I. M., and Belcher, R., “Volumetric Analysis,” Volume 111, Interscience, New York, 1959, Bishop, E., “Indicators,” Pergamon Press, Oxford, ‘1972, p. 570. Crawford, A. B., and Bishop, E., J . R. Tech. Coll. Glasg., 1950, 5, 52. Berka, A., and Zyka, J., Colln Czech. Chem. Commun., 1958, 23, 402. Kolthoff, I. M., and Belcher, R., “Volumetric Analysis,” Volume 111, Interscience, New York, 1995, Vulterin, J., Colln Czech. Chem. Commun., 1967, 32, 3349. Sarver. L. A., and Kolthoff, I. M., J . Am. Chem. SOC., 1931, 53, 2902, 2906. Barakat, M. Z., Shehab, S. K., and Abdalla, A., J . Am. Pharm. Ass. Sci. Edn, 1960, 49, 360. Barakat, M. Z., Abdel-Wahab, M. F., and El-Sadr, M. M., Analyt. Chem., 1955, 27, 536. Kolthoff, I. M., and Belcher, R., “Volumetric Analysis,” Volume 111, Interscience, New York, 1957, Received November 28th, 1978 Accepted February 27th, 1979 p. 53. p. 367. p. 176. 1959, pp. 41-42. p. 236. p. 463. pp. 230 and 237. p. 208. p. 149.

ISSN:0003-2654    

DOI:10.1039/AN9790400865

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

Analyst, September, 1979 SHORT PAPERS 873 Non-aqueous Tit’ration of Substituted N-o-Tolyl benzohyd roxamic Acids Y. K. Agrawal Pharmacy Department, Faculty of Technology and Engineering, Maharaja Sayajirao University of Baroda, Kalabhavan, Baroda 390 001, India Keywords : Non-aqueous titration ; substituted N-o-tolylbenzohydroxamic acids The preparation and properties of substituted N-o-tolylbenzohydroxamic acids have recently been rep0rted.l These hydroxamic acids are insoluble in water and, hence, their ionisation constants have been determined in a 1,4-dioxan - water medium.2-4 These acids can be titrated in a tnixed aqueous medium with phenolphthalein as the indicator; however, no sharp neutral point is obtained, which leads to unsatisfactory results. In this work the N-arylhydroxamic acids have been titrated visually in a non-aqueous medium with o-nitro- aniline as the indicator.They were also titrated potentiometrically. Experimental Reagents as described e1sewhere.l (boiling range 60-80 “C) and dried over phosphorus(V) oxide, under vacuum, before use. the method of Cundiff and Mark~nas.~ solution of pyrogallol, 2 N sulphuric acid, distilled water and finally the required solvent. formamide (DMF) (pro analysi) were used without purification. Hydroxamic acids. The para-substituted o-tolylbenzohydroxamic acids were synthesised These acids were recrystallised from benzene and light petroleum Tetrabutylammonium hydroxide (0.1 M) was prepared by Nitrogen was passed through a series of towers containing a saturated alkaline Methanol (GR grade, E.Merck), benzene (GR grade, E. Merck) and dimethyl- A 0.1 M solution of o-nitroaniline in methanol was prepared. Tetrabutylammonium hydroxide. Nitrogen. Solvents. Indicator solution. Apparatus National Physical Laboratory certified grade “A” graduated apparatus was used for measurements, including a microburette that was graduated to 0.01 ml. A Systronics digital pH meter and platinum electrodes were used. Procedure A weighed amount of the hydroxamic acid was transferred into a 20-ml titration vessel. The vessel had C10 joints for the burette and nitrogen inlets. A 10-ml aliquot of dimethyl- formamide was added and the contents were stirred by means of a magnetic stirrer. TWO drops of the 0.01 M solution of o-nitroaniline were added and the titration was carried out against 0.1 M tetrabutylammonium hydroxide under an atmosphere of nitrogen. For potentio- metric determinations platinum and calomel (filled with a saturated solution of potassium chloride in methanol) electrodes were used. Results and Discussion The results of the visual titration of substituted N-o-tolylbenzohydroxamic acids are given in Table I.The standard deviations show that they can be titrated with reasonable accuracy. The indicator colour with dimethylformamide as the solvent changes from yellow to red, corresponding to the change from acid to base, for compounds I and I1 (Table I), from yellow to pinkish red for compounds HI, IV and V, from yellow to orange - red for compounds874 SHORT PAPERS Analyst, Vol. 104 TABLE I TITRATION RESULTS FOR THE DETERMINATION OF SUBSTITUTED N-O-TOLY LBENZOHYDROXAMIC ACIDS Relative molecular mass f A 1 Visual method Compound I I1 I11 IV V VI VI I VIII Colour Potentiometric No.of deter- Standard ' Benzohydroxamic acid M.p./"C Solvent* change? Calculated method, found Found minations deviation, N-o-Tolyl-o-fluoro- 130 DMF Y-R 245.26 245.0 246 8 0.90 MeOH LY-R N-o-Tolyl-p-fluoro- 140 DMF Y-R 245.26 245.2 245 10 0.90 N-o-Tolyl-o-bromo- 110 DMF Y-PR 306.17 306.0 307 9 0.80 N-o-Tolyl-m-bromo- 90 DMF Y-PR 306.1 7 306.1 307 9 0.99 MeOH LY-R MeOH LY-R MeOH LY-R MeOH LY-R N-o-Tolyl-p-bromo- 155 DMF Y-PR 306.17 306.1 306 10 0.80 N-o-Tolyl-p-iodo- 140 DMF Y-OR 353.17 353.2 354 10 1.00 MeOH LY-R ~ ~ . _ ~ ~ ~~~~~ N-o-To1 yl-o-ni tro- 150 DMF Y-OR 272.26 272.1 273 10 MeOH Y-OR N-o-Tolvl-m-ni tro- 101 DMF Y-OR 272.26 272.2 271 8 MeOH Y-OR 0.90 1.00 IX N-o-Tolyl-p-nitro- 170 DMF Y-OR 272.26 272.2 271 10 0.99 X N-o-Tolyl-3,5-dinitro- 140 DMF Y-PO 317.26 317.1 316 10 0.90 MeOH Y-OR MeOH Y-OR * DMF, dimethylformamide; MeOH, methanol.t Y, yellow; R, red; OR, orange -red; PR, pinkish red; LY, light yellow; PO, pinkish orange, VI, VII, VIII and IX and from yellow to pinkish orange for compound X. When the dimethylformamide was replaced with methanol, the change was from light yellow to red for compounds I-VI and yellow to orange - red for compounds VII-X. These acids were also titrated potentiometrically using the pH meter and platinum elec- trodes. The platinum electrode was found to be the most satisfactory for the titration of hydroxamic acids in non-aqueous media.TABLE I1 EFFECT OF CARBON DIOXIDE ON APPARENT MOLARITY OF TITRANT Final solution, in DMF, 0.1 M in tetrabutylammonium hydroxide and 0.025 M in carbonate. Hydroxamic acid/M Apparent molarity Molarity change 0.01 0.02 0.05 0.25 0.50 0.089 0.087 0.085 0.079 0.072 0.01 1 0.013 0.015 0.021 0.028 The effect of carbon dioxide on the tetrabutylammonium hydroxide was studied (Table 11). It was observed that the carbon dioxide decreases the apparent molarity of the titrant, indicating the formation of carbonate. I t also became apparent that the change in the apparent molarity was dependent on the amount of acid titrated and the solvent used.6 The error due to carbon dioxide was eliminated by carrying out the titrations in an atmosphere of nitrogen and ensuring that the titrant and solvent were themselves free from carbon dioxide. The author thanks Professor S. M. Sethna, Pro-Vice Chancellor of Maharaja Sayajirao University, Baroda, for the inspiration for this work, and Professor S. K. Banerjee, head of the Pharmacy Department, for providing the facilities, and acknowledges U.G.C., New Delhi, for financial support. References 1. 2. 3. Agrawal, Y. K., J . Chem. Engng Data, 1977, 22, 70. Agrawal, Y . K., and Mudaliar, A., J . Fluorine Chem., 1977, 9, 333. Agrawal, Y . K., Bull. SOC. Chim. Belg., 1978, 87, 831.September, 1979 SHORT PAPERS 875 4. 5. 6. Kucharsky, J., and Safric, L., “Titration in Non-Aqueous Solvents,” Elsevier, New York and Received August 24th, 1978 Accepted March 19th, 1979 Agrawal, Y. K., and Kapoor, H. L., J . Chem. Engng Data, 1977, 22, 159. Cundiff, R. H., and Markunas, P. C., Andyt. Chem., 1962, 34, 584. Amsterdam, 1965, p. 117.

ISSN:0003-2654    

DOI:10.1039/AN9790400873

出版商:RSC    

年代:1979

数据来源: RSC

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September, 1979 SHORT PAPERS 875 Trace Determination of Carbonyl Compounds in Air by Gas Chromatography of their 2,4- Din it rop henyl hyd razones R. A. Smith and 1. Drummond Occupational Health and Safety Division, A lberta Labour, 10 158-103 Street, Edmonton, Alberta, Canada, T6J OX6 Keywords : Trace carbonyl determination ; air analysis ; 2,4-dinitrophenyl- hydrazones ; gas chromatography The analysis of air samples for aldehydes and ketones by the gas-chromatographic (GC) determination of their 2,4-dinitrophenylhydrazine (2,4-DNPH) derivatives has several attractive features. The carbonyl compounds are selectively and efficiently collected by use of gas scrubbers containing an acidic solution of 2,4-DNPH1 and the GC analysis allows the simultaneous determination of many different compounds.Moreover, standard solutions for each of the compounds can be readily prepared gravimetrically from stable crystalline solids. Papa and Turner2 reviewed the literature up to 1972, and the American Public Health Association Intersociety Committee method for benzaldehyde in automobile exhaust1 follows many of their suggestions. Unfortunately, the method involves a lengthy recovery of the 2,4-DNYH derivatives, an awkward and unusual stop flow GC injection technique and apparently has a restricted linear range owing to decomposition of the 2,4-DNPH derivatives in the gas chromatograph. We report here a simplified method for the recovery of the 2,4-DNPH derivatives and analytical conditions that extend the usable range of the analysis for formaldehyde down- wards by a factor of 100.We also investigated the double chromatographic peaks given by certain carbonyl com- pounds, which are taken by some workers as evidence of substantial decomposition during GC analy~is,~ and showed them to be due to syn- and anti-isomeric forms of the 2,4-DNPH derivatives. Experimental Apparatus Gas chromatography was performed using a Hewlett-Packard 5840A gas chromatograph equipped with flame-ionisation detectors. The chromatographic conditions were as follows: column, 1.83m x 2 mm i.d., glass, arranged for on-column injection and filled with 3% OV-1 on 100-120-mesh Gas-Chrom Q pre-tested packing (Applied Science Labs., State College, Pa., USA) ; this column has approximately 1700 theoretical plates; injector tempera- ture, 250 "C; detector temperature, 265 "C; carrier gas, nitrogen at a flow-rate of 30 ml mine'; detector gas flow-rates, hydrogen 30 ml min-l and air 300 ml min-l; the column oven was run isothermally at 195 "C for the analysis of C,-C, carbonyl derivatives and was increased to as high as 250 "C for compounds of higher relative molecular mass.Nuclear magnetic resonance (NMR) spectra were obtained at 60MHz using a Varian A56 6O-MHz spectrometer. Gas chromatography - mass spectrometry was performed using a Hewlett-Packard 5710A gas Chromatograph interfaced to a Hewlett-Packard 5930A mass spectrometer equipped with a Hewlett-Packard 5933A data system.876 SHORT PAPERS Analyst, Vol. 104 Reagents and Materials The 2,4-DNPH was obtained from Aldrich Chemical CO., formaldehyde was obtained as a 37% solution from J.T. Baker and acetaldehyde was purchased from Eastman Kodak. All other aldehydes were synthesised by standard methods in our laboratory, as were the 2,4-DNPH derivatives of all carbonyl compounds used.4 Carbon disulphide was purchased from J. T. Baker. The absorbing solution was prepared by diluting 3 + 1 (V/V) a saturated solution of 2,4-DNPH in 0.1 N sulphuric acid with 0.1 N acid and extracting twice with a volume of carbon disulphide one tenth of that of the acid solution, shortly before use. Standard solutions for GC analysis were prepared by dissolving weighed amounts of the 2,4-DNPH derivatives in known volumes of carbon disulphide containing 200 pg ml-1 of anthracene (from BDH) in the presence of a small crystal of 2,4-DNPH.(The upper limit of solubility of formaldehyde-2,4-DNPH in carbon disulphide is approximately 1 mg ml-1.) Whenever dilutions of the original standard are made a crystal of 2,4-DNPH should be present in the flask. Procedure Air samples were collected using a bubbler containing 15 ml of absorbing solution at a flow-rate of 1 1 min-1. The derivatives were recovered by adding 5.0 ml of carbon disulphide, containing 200 pg ml-l of anthracene, directly to the bubbler, shaking vigorously and after separation of the layers removing the lower carbon disulphide layer by using a Pasteur pipette , Prior to GC analysis the column was conditioned by two 5-pl injections of a 350 pg ml-1 solution, which was repeated if the column had not been used for more than 1 h.l The carbon disulphide solution, which had been separated from the solution in the bubbler, was then injected directly into the gas chromatograph using a conventional technique and the resulting chromatogram was quantified using the method of internal standardisation. Results and Discussion When carbon disulphide is used as the solvent for the 2,4-DNPH derivatives it is noticeable that certain carbonyl compounds give double chromatographic peaks, whereas other deriva- tives give single, sharp peaks.Other workers have noticed this effect (which varies in noticeability both with the solvent and with resolution of the chromatographic column) and have ascribed it to either substantial decomposition of the 2,4-DNPH c o r n p o ~ n d s ~ , ~ or to the existence of syn- and anti-isomeric forms of the derivative^.^ As an analytical method relying on material subject to substantial decomposition is scarcely satisfactory, we sought to clarify the source of the double peaks.We noticed in our work, and could find no evidence to the contrary in other work,2,3,5 that symmetrically substituted carbonyls gave single peaks (such as formaldehyde, acetone, pentan-3-one and heptan-4-one) and unsym- metrically substituted carbonyls gave double peaks, the difference in retention time being approximately proportional to the difference in the number of carbon atoms in the longest side- chains. This observation is consistent with the presence of isomers but not readily explicable in terms of decomposition. Next, we examined the mass spectra of the material present in the two chromatographic peaks given by hexan-2-one.The normalised mass spectra gave identical fragmentation patterns: in particular, both showed molecular ions at m/e 280; this could not occur if one of the peaks was due to a decomposition product but is consistent with the presence of syn- and anti-isomers. Finally, we examined solutions of the derivatives by NMR spectro- scopy for evidence of isomers. Using 1,4-dioxan-d, solutions (which gave similar GC results to carbon disulphide solutions), because of the increased solubility of the derivatives, we were able to observe signals assignable to the syn- and anti-isomers for both acetaldehyde and propionaldehyde derivatives (Table I). The ratio of the peak areas of the signals for the syn- to anti-isomers for acetaldehyde was 2.4 : 1 and propionaldehyde 5.8 : 1, both values being in good agreement with the ratio of the peak areas observed by us in the GC analysis of the dioxan solutions.September, 1979 SHORT PAPERS a77 TABLE I NMR PARAMETERS OF 2,4-DNPH DERIVATIVES OF FORMALDEHYDE, ACETALDEHYDE AND PROPIONALDEHYDE IN 1,4-DIOXAN-d, SOLUTION anti- Isomer syn-Isomer Derivative 6, p.p.m.* JIHz Formaldehyde .. . . 6.71 (d); 7.27 (d) (H-H) 11 Acetaldehyde- Propionddehyde- syn . . .. . . H, 7.10 (9); CH,, 2.04 (d) (H-CH,) 5 atzti . . .. . . H, 7.66 (4); CH,, 2.06 (d) (H-CH,) 5 syn- . . .. . . H, 6.95 (t); CH,, Ob; CH,, 1.24 (t) (H-CH,) 5; (CH,-CH,) 8 anti- . . .. . . H, 7.68 (t); CH,, 2.43 (m); CH,, 1.17 (t) (H-CH,) 5; (CHa-CH,) 8 * d = Doublet, t = triplet, q = quartet, m = multiplet and Ob = obscured. The chemical shifts are in parts per million relative to tetramethylsilane. Based on these three sets of observations we felt confident that the 2,4-DNPH derivatives were not subject to gross decomposition on GC analysis and that the sum of the areas of the two peaks could be used to quantify the chromatogram of a carbonyl compound.We then proceeded to examine the linearity of response using standard solutions prepared as above. The relative response of anthracene (the internal standard) compared with the 2,4-DNPH derivatives of formaldehyde, acetaldehyde and propionaldehyde was measured and found to be constant over the range 10-1 000 pg ml-l. The values found were, within experimental error, the same as reported by Papa and Turner2 and were 2.80 (0.10), 2.70 (0.10) and 2.50 (0.10), respectively (the figures in parentheses are standard deviations).The lowest concentration at which a linear response was found was approximately one hundredth of that reported by Papa and Turner2; apparently the presence of the crystal of 2,4-DNPH in the standard solutions aids in extending the range of analysis, for without it we found reduced response at the same concentrations as Papa and Turner. Finally, we investigated the partition of the derivatives between carbon disulphide and the absorbing solution. In all measurements, using 15 ml of absorbing solution and 5 ml of carbon disulphide over the concentration range 10-1 000 pg ml-l of adduct, we found that at least 97% of the adduct was extracted into the carbon disulphide in a single extraction step. The use of anthracene as an internal standard means that quantitative recovery of the carbon disulphide is not needed, and the recovery of the derivatives from the bubbler for subsequent GC analysis is therefore very quick and efficient. References 1. 2. 3. 4. 5. Katz, M., Editor, “Methods of Air Sampling and Analysis,” Second Edition, American Public Health Papa, L. J., and Turner, L. P., J . Chromat. Sci., 1972, 10, 744. Pias, J. B., and Gasco, L., Chromatographia, 1975, 8 (6), 70. Vogel, A. I., “Practical Organic Chemistry,” Third Edition, Longmans, London, 1961. Kallio, H., Linko, R. R., and Kaitaranta, J., J . Chromat., 1972, 65, 355. Association, Washington, D.C., 1977, p. 336. Received December 12th, 1978 Accepted April llth, 1979

ISSN:0003-2654    

DOI:10.1039/AN9790400875

出版商:RSC    

年代:1979

数据来源: RSC

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878 SHORT PAPERS Analyst, VoZ, 104 Effect of Ammonium Nitrate on the Gas-chromatographic Determination of Some Pesticide Residues in Soils E. G. Cotterill Agricultural Research Council, Weed Research Organization, Begbroke Hill, Yarnton, Oxford, OX5 1PF Keywords : Pesticide residue determination ; soil analysis ; gas chromato- graphy ; a m m o n i u m nitrate In the course of routine measurements of atrazine residues in soil samples containing high levels of ammonium nitrate fertiliser, the response of the gas-chromatographic detector was not constant for standards interspersed with the samples. The peak height but not the peak area increased, suggesting an increase in column efficiency. This effect was studied in order to define it more closely. Experimental Pesticide Solutions Solutions containing 100 pg of analytically pure pesticide in 1 ml of methanol were pre- pared.The herbicides atrazine, simazine, metribuzin, tri-allate and linuron and the insecticide phorate were used. A 10% solution of ammonium nitrate in methanol was prepared and aliquots of it were added to aliquots of pesticide solution to produce solutions containing either 0.2 or 20 ng pl-1 of pesticide to 10 pg pl-l of ammonium nitrate. Chromatography Either a Pye 104 gas chromatograph with a nickel-63 electron-capture detector or a Hewlett-Packard 5750 G gas chromatograph with a nitrogen-specific flame-ionisation detector was used. The Hewlett-Packard instrument was fitted with either a stainless-steel column (1.8 m x 3 mm i.d.) packed with 10% UCW 982 on Chromosorb W AW DMCS or a glass column (1.8m x 4mm i.d.) packed with 2% OV-17 on Chromosorb W HP.The Pye chromatograph was fitted with a glass column (1.5 m x 4 mm i.d.) packed with 5% SE-30 on Chromosorb W HP. On-column injections were made using automatic sample injectors. Volumes of 5 pl of the 0.2 ng pl-l pesticide standard solutions were injected into the Pye and 3 pl of the 20 ng pl-l solutions into the Hewlett-Packard chromatograph. The chromatographic conditions were as follows for both chromatographs : carrier gas, nitrogen at a flow-rate of 40 ml min-l; injector temperature, 240 "C; and detector tempera- ture, 350 "C. The column temperatures used for the pesticides were as follows: atrazine, 210; simazine, 210; metribuzin, 220; tri-allate, 180; chlorpropham, 180; linuron, 160; and phorate, 190 "C.Results and Discussion The effect of ammonium nitrate concentration on the peak height of a 60-ng atrazine standard solution is shown in Fig. 1, the optimum response being at a concentration of approximately 4 pg pl-l. Table I shows the effect of this concentration on the responses of the other pesticides. In every instance the peak height was increased while the peak area remained constant. All of the columns used for this study were aged by repeated sample injections, but had not deteriorated to the point where they would normally be replaced. No values are included in Table I where the chromatographic system was not suitable for the pesticide concerned. When the enhancement of peak height was first observed the stainless-steel column packed with UCW 982 was in use.On changing to the glass column packed with OV-17 the effect disappeared. However, after several hundred injections the effect returned. Injections of standards into the chromatograph fitted with an electron-capture detector also showed peak-height enhancement. These observations, together with the constant peak areas,September, 1979 SHORT PAPERS 879 Fig. 1. Peak height of 60 ng atrazine standard versus concentration of ammonium nitrate. suggested that enhancement was due to an increase in column performance, probably due to the extract. This was confirmed by injecting the column conditioner Silyl8 (Pierce Chemical Co.) on to an aged OV-17 column. The conditioner restored the column performance and removed the enhancement effect.Theoretical plate measurements were made in order to determine the effect of enhancement. A new OV-17 column gave 2190 plates but after ageing gave only 1 140 plates; after enhancement the number of plates was increased to 2070. TABLE I MEAN PEAK HEIGHTS AND PEAK AREAS OF PESTICIDE STANDARDS ON DIFFERENT COLUMNS Results are means of six determinations ; standard deviations are given in parentheses. Column OV- 17 SE-30 UCW 982 A r I Pesticide + NH4N03 Atrazine Simazine Me tribuzin Tri-allate Linuron Phorate + NHdNO, + NH4NO3 + NH4NO3 + NH,NO3 + NH4NO3 - Peak height/ mm 23 (1.7) 34 (3.1) 33 (0.9) 53 (1.0) 33 (1.3) 52 (2:O) 41 (1.9) 63 (0.5) - - 104 (2.0) 190 (3.7) 1 Peak area, arbitrary units 23 (1.7) 24 (1.1) 1-80 (3.2) 186 (3.5) 52 (2.0) 62 (4.2) 63 (0.5) 49 (1.9) - - 125 (2.4) 124 (4.4) Peak height/ mm 8 (0.3) 13 (1.0) 8 (0.4) 13 (0.7) - - 90 (0.0) 122 (2.5) 27 (0.6) 42 (1.0) - - Peak area, arbitrary units 8 (0.3) 8 (1.0) 7 (1.0) a (0.2) 81 (0.0) - - 85 (1.7) 27 (0.6) 29 (0.7) - - t Peak height/ mm 13 (1.2) 20 (2.3) 22 (1.2) 34 (2.3) 49 (1.9) 78 @.7j 27 (1.3) 42 (0.3) - 27 (2.0) 49 (3.6) 1 Peak area, arbitrary units 15 (0.7) 14 (0.6) 121 (0.8) 119 (0.9) 44 (1.7) 46 (1.8) 41 (2.8) 42 (0.3) - - 35 (1.5) 34 (2.5) To check the enhancement effect in the presence of soil extracts, soil was treated with ammonium nitrate at a rate equivalent to 200 kg ha-l.When 50 g of the soil were extracted with 100 ml of methanol using the method of Byast et aZ.,I the concentration of ammonium nitrate in solution after evaporation was about 4pgpl-l.Injections of the treated soil extract increased the peak height of a subsequent 60-ng atrazine standard by 55-65%. No increase occurred following injections of untreated soil extracts. An additional complication was that ammonium nitrate-induced enhancement was short- lived. Fig. 2 shows how consecutive injections of an untreated 60-ng atrazine standard decreased in peak height with time after enhancement had been induced by injection of ammonium nitrate. The calculated regression line shows a correlation coefficient of 0.95.880 SHORT PAPERS Analyst, Vol. 104 Time after injection of fertilizer soil extracdmin Fig. 2. Variation of standard response with time of injection of fertilised soil extract. Conclusions The apparent enhancement of response could lead to large errors in the determination of pesticide residues using the peak-height method of measurement. The magnitude could depend on the frequency of injection of standards. Therefore, when a high ammonium nitrate fertiliser concentration is present in pesticide extracts, peak areas are more likely to e v e accurate values than peak heights.I t is advisable that extracts from soils containing high fertiliser levels should be chromatographed using a freshly conditioned column. When ammonium nitrate is present in the soil in sufficient amounts to cause measurement diffi- culties, its presence in the extract should be avoided by the use of an alternative extraction or partition technique. The author thanks J. A. P. Marsh, who supplied the samples that first showed this phenomenon. Reference 1. Byast, T. H., Cotterill, E. G., and Hance, R. J., “Methods of Analysis for Herbicide Residues,” Second Edition, Technical Report, Agricultural Research Council, Weed Research Organization, Yarnton, 1977, No. 15, 58 pp. Received February 5th, 1979 Accepted March 23rd, 1979

ISSN:0003-2654    

DOI:10.1039/AN9790400878

出版商:RSC    

年代:1979

数据来源: RSC

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880 SHORT PAPERS Analyst, Vol. 104 Spectrophotometric Determination of Iodide Ion Using Palladium and 2-Nitroso-5-diethylaminophenol Shoichi Hamada, Shoji Motomizu and Kyoji Tiiei Department of Chemistry, Faculty of Science, Okayama University, Tsushima-naka, Okayama-shi, Japan Keywords : Iodide determination ; spectrophotounetry ; palladium ; 2-nitroso-5- diethy lamino phenol 2-Nitroso-5-diethylaminophenol (nitroso-DEAP) reacts with palladium(I1) to form a red complex that is soluble in acidic solutions and easily extracted into chloroform. The molar absorptivity of the complex is 2.3 x 1 0 4 1 mol-l cm-l at 540 nm in 2 M sulphuric acid1 and 4.4 x lo4 1 mol-l cm-l at 486 nm in chloroform.2September, 1979 SHORT PAPERS 881 It is well known that iodide ion also reacts with palladium(I1) to form a very stable complex that is insoluble in aqueous solution, and the palladium complex formed with iodide does not decompose in the presence of nitroso-DEAP.In this work, iodide ion was determined indirectly by determining spectrophotometrically the excess of palladium using nitroso-DEAP, after reaction of the iodide ion with palladium(I1) ion. Experimental Apparatus in a cell with a 10-mm path length. A Hitachi Perkin-Elmer, Model 139, spectrophotometer was used to measure absorbances An Iwaki, Model KM, shaker was used. Reagents Prepare a stock solution by dissolving 4.19 g of potassium iodide in water and diluting to 250 ml with water. Standardise the solution by the Volhard method. Dilute the stock solution accurately with water to give working solutions.Palladium(I1) solution. Weigh approximately 1.26 g of palladium(I1) nitrate into a porcelain evaporating dish, add about 20 ml of 12 M hydrochloric acid and evaporate the solution nearly to dryness. Dissolve the residue in 100 ml of 0.5 M hydrochloric acid. Dilute this stock solution with water to give an approximately 5 x 2-Nitroso-5-diethylarninophenol solution. Prepare nitroso-DEAP by nitrosation of the parent compound (m-diethylaminophenol) in acidic aqueous solution with sodium nitrite.3 Recrystallise the crude nitroso compound twice from hydrochloric acid solution. Use an aqueous solution (6 x M) in 0.05 M sulphuric acid. Procedure Pipette up to 5 ml of the solution containing iodide ion into a stoppered test-tube and dilute to 5 ml with water. Add 2 ml of palladium(I1) solution, 3 ml of about 7 M sulphuric acid and 0.5 ml of nitroso-DEAP solution and mix well.After the mixture has been allowed to stand for 5 min, shake it with 5 ml of chloroform for 1 min. Discard the aqueous phase and wash the organic phase with 5 ml of about 2.5 M sulphuric acid by shaking for about 1 min by hand, to remove the excess of reagent. Measure the absorbance of the organic phase at 486 nm. Standard iodide solution. M solution. Other reagents were of analytical-reagent grade. Results and Discussion Effects of Experimental Variables The time necessary for complete formation of the pallahum complex with nitroso-DEAP is about 30s at room temperature. The effect of acidity on the reaction of iodide ion with palladium(I1) ion was examined by varying the concentration of sulphuric acid from 0 to 0.5 M ; no effect of acidity was observed.When iodide solution was added to the solution containing palladium ion and nitroso-DEAP, palladium iodide was not completely formed. Therefore, the palladium solution was added to iodide ion and then the nitroso-DEAP was added to the mixture. In a previous paper,2 the effect of acidity on the extraction of the palladium complex was determined for concentrations of sulphuric acid from 2 to 3 M when 0.5 ml of nitroso-DEAP solution was used. In this work, the same acidity of sulphuric acid and the same volume of nitroso-DEAP were used. Calibration Graph and Apparent Molar Absorptivity The calibration graph with chloroform as reference was a straight line over the range 0 4 x The apparent molar absorptivity calculated from the slope of the graph was 2.1 x lo4 1 mol-l cm-l at 486 nm.This value is almost half that of the palladium - nitroso-DEAP complex in chloroform (4.4 x lo* 1 mol-I cm-l at 486 nm). Hence, Iodide ion reacts almost instantaneously with palladium(I1) ion. The effect of the order of addition of the reagents was examined. M iodide ion.882 SHORT PAPERS Analyst, Vol. 104 1.0 I [ 1-1 /I 0-5 M Fig. 1. Calibration graph at 486 nm. Amount of P d M solution; and amount of nitroso- added, 2 ml of 5.3 x DEAP added, 0.5 ml of 6 x M solution. the composition of the palladium - iodide complex appears to be 1 : 2. in chloroform is illustrated in Fig. 1. to iodide ion was confirmed to be 1 : 2.The calibration graph From the break in the graph, the ratio of palladium(I1) Effects of Diverse Ions The interference of diverse ions was examined by using 5 ml of sample solution con- taining iodide ion (3.22 x The results obtained are shown in Table I. M and silver(I),, mercury(II), thallium(III), platinum(1V) and gold(II1) at concentrations above lo-' M caused negative errors. These interferents are ions that react with either iodide ion or nitroso-DEAP. M) and a test ion. Iridium(IV), tungsten(V1) and nitrite a t concentrations above TABLE I EFFECT OF DIVERSE IONS ON IODIDE ION Maximum tolerable lo-,* Ion concentration/M zii ~ ~ ~ ~ ~ 2 ~ - & , 2 + , A13+, Mn2+, Zn2+, Cr;+, Fe3+, Co2+, Ni2+, Cu2+, Pb2+, F- 10-3* Os(VIII), Zr(IV), Rh(III), Br- 10-4 Ir(IV), W(VI), NO,- 10-6 Ag+, Hg2+, Tl(III), Pt(IV), Au(II1) 10-7 * Maximum tested. Conclusion Iodide ion reacted with palladium(I1) ion and the iodide complex formed was not de- composed by addition of nitroso-DEAP. Thus, the excess of palladium reacted with nitroso-DEAP to form a coloured complex, which was extracted into chloroform. By using this principle, micro-amounts of iodide ion were determined spectrophotometrically. In this method, the sensitivity and selectivity are good: the molar absorptivity is 2.1 x 104 1 mol-1 cm-1 at 486 nm and chloride at concentrations below 10-2 M and bromide at concentrations below Further, the stability and reproducibility of the absorbance at 486 nm are very good. It is expected that the proposed method will be useful in practical applications. M do not interfere. References 1. 2. 3. T6ei. K.. Motomizu, S., and Hamada, S., Bunseki Kagaku, 1978, 27, 668. TBei, K., Motomizu, S., and Hamada, S., Analytica Chim. Acta, 1978, 101, 169. Mohlau, R., Chem. Ber., 1892, 25, 1059. Received February 191h, 1979 Accepted March 19th 1979

ISSN:0003-2654    

DOI:10.1039/AN9790400880

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

September, 1979 SHORT PAPERS 883 Electroanalytical Study of Zinc - L-Citrulline Complex at a Dropping-mercury Electrode K. M. Suyan, S. K. Shah and C. M. Gupta Chemical Laboratories, University of Rajasthan, Jaipur, India Keywords : Polarography ; zinc - L-citrulline complex The importance of amino acids and several other nitrogen-containing compounds has been recognised in the fields of biochemistry and pharmacy.1*2 The complexation behaviour of various metal ions with certain biologically important compounds has recently been investi- gated in our laboratorie~.~-S This paper reports a detailed polarographic investigation of the formation of the zinc - L-citrulline complex in aqueous and mixed aqueous and non- aqueous media. Experimental All of the reagents used were of analytical-reagent grade and all of the solutions were prepared in doubly distilled water.Purified acetonitrile, dimethyl sulphoxide and dimethyl- formamide were used as non-aqueous solvents. Potassium nitrate was employed as a support- ing electrolyte to keep the ionic strength, p, constant at 0.2 M, while Triton X-100 (0.005%) in the final solutions served as the maximum suppressor. The pH of the solution was maintained by 0.1 N solutions of sodium hydroxide and nitric acid. The experimental technique was the same as has been described previously.6 The electrode had the characteristics m = 2.16 mg s-1 and t = 4.2 s (for a 40 cm height of mercury reservoir in 0.2 M potassium nitrate solution at a 1.0-V potential versus S.C.E.). Results and Discussion A single, well defined wave appeared for each solution.The graph of i d versus htR. gave a straight line passing through the origin with a slope of 0.56 & 0.005pAcm-~, indicating the diffusion-controlled nature of the reduction process. The graph of log i / ( i d - i) versus ED.M.E. yielded a straight line, but the resulting slope was not found to be in agreement with the theoretical value for a reversible process, thus indcating the irreversible nature of the reduction process. Effect of pH The polarographic investigation of the zinc - L-citrulline system was carried out systematic- ally over the pH range 4.5-10.5 on solutions 0.5 mM in zinc, 0.018 M in L-citrulline, 0.2 M in potassium nitrate and containing 0.005~o of Triton X-100. The half-wave potential shifts to more negative values with increasing pH and such a cathodic shift suggests the formation of the complex in this pH range.Effect of Ligand Concentration In order to investigate the effect of a change in the ligand concentration, polarograms of 0.5 mM zinc solutions with various concentrations of L-citrulline (0-0.044 M) (p = 0.2 M) were recorded at two different temperatures, 23 1 and 30 -j= 1 "C. The zinc-L- citrulline reduction wave remained irreversible and diff usion-controlled in all of the solutions investigated. The shift in half-wave potential to more negative values, along with a decrease in diffusion current on increasing the L-citrulline concentration, indicated complex formation. The nature of the wave did not change at higher concentrations of L-citrulline.Kinetic Parameters applied in order to determine the kinetic parameters. for a totally irreversible wave (at 25 "C) with E+ greater than -1.0 V 'uersm S.C.E. Further studies on the system were carried out at pH 9.7. The Koutecky' treatment for irreversible waves, as modified by Meites and IsraelI8 was It follows from the treatment that 0.546 log t ) . . .. 0 0542 i ED.M.E. = E& - an where884 SHORT PAPERS Analyst, Vol. 104 (In these equations ED.M.E, and Ei are referred to a normal hydrogen electrode and all of the symbols have their usual significance, as in the original paper of Meites and Israel.8) The kinetic parameters have been calculated by employing equations (1) and (Z), knowing the values of the diffusion constant which are obtainable with the help of the Ilkovic equation.9 The value of an was obtained by equating the slope of the straight-line graph of ED.M,E.veysus log - 0.546 log t [i (id-i)] with 0.0542/an. The intercept of the same graph, when the quantity being plotted as abscissa is equal to zero, gives a value for the parameter E,, defined by equation (2), which is then used to calculate KfPh. The values of an and krPh at various free ligand concentrations are given in Table I. The free ligand concentration was calculated by using the pH of the solution and the pK value of L-citrulline.2 TABLE I KINETIC PARAMETERS FOR ZINC - L-CITRULLINE SYSTEM Concentration of Zn2+ = 0.5 mM, pH = 9.7, p = 0.2 M (KNO,), concentration of Triton X-100 = 0.005%. Free ligand concentration/ M 0.0 0.004 0.008 0.012 0.018 0.024 0.030 0.036 0.044 Temperature 23 "C A r \ - E+ uersus S.C.E./V &/PA un k,Ph/cm s-' 1.005 2.95 1.44 1.56 x 1.175 2.79 1.08 5.28 x 1.185 2.71 1.10 1.60 x 1.218 2.67 1.18 1.74 x 1.221 2.62 1.23 2.27 x 1.230 2.58 1.26 4.45 x 1.238 2.50 1.29 8.97 x 1.241 2.38 1.33 1.53 x 1.243 2.30 1.34 8.98 x Temperature 30 "C f A \ - E+ uersus S.C.E./V &/PA un k&/cm s-l 1.003 3.12 1.44 4.98 x 1.160 2.87 1.10 1.25 x 1.205 2.79 1.10 6.97 x 1.215 2.71 1.11 8.00 x 1.217 2.62 1.12 4.89 x 1.218 2.58 1.15 1.50 x 1.227 2.51 1.24 3.28 x 1.230 2.50 1.26 1.33 x 1.221 2.54 1.20 1.99 x 10-23 Effect of Non-aqueous Solvents Solutions containing 0.5 mM, 0.016 M of L-citrulline and various amounts (0-50y0 V / V ) of dimethyl sulphoxide, dimethylformamide and acetonitrile were subjected to polarography at a constant ionic strength (p = 0.2 M).The investigations of the zinc - L-citrulline system with acetonitrile, dimethylformamide and dimethyl sulphoxide as solvents revealed that the half-wave potential was shifted to more negative values as the organic solvent concentration increased from 0 to 50%. This is a consequence of the energy of the bond between the metal and the organic solvents being slightly greater than the energy of the bond with water.l0s1l As a result, the discharge of an ion containing these solvent molecules in the solvate sheath takes place with greater energy. Addition of increasing amounts of the non-aqueous solvents causes the diffusion current to decrease. The decrease in diffusion current may partly be caused by an increase in the viscosity12 of the medium and partly by ion-pair f0rmati0n.l~ In non-aqueous media with low dielectric constants, electroactive ions are largely converted into neutral species known as ion pairs, and this ion-pair formation must be considerable because a continuous decrease in diffusion current is observed.The value of the slope of the graph of ED.M,E, UCYSZLS [i (id-i)] - 0.546 log t has been found to decrease slightly (Table 11) with increasing concentrations of non-aqueous media. Hence, it can be concluded that the reaction becomes relatively faster and less irreversible in a high concentration of non-aqueous media.14 The investigations of the zinc - L-citrulline system with 1,4-dioxan as solvent gave two ill- defined waves. The polarographic results were processed by the method of Koutecky,' modified by Meites and Israel,8 as was discussed above.The values of rate constant and transfer coefficient are given in Table 11.September, 1979 SHORT PAPERS TABLE I1 VALUES OF KINETIC PARAMETERS FOR ZINC - L-CITRULLINE SYSTEM I N NON-AQUEOUS MEDIA Concentration of Zn2+ = 0.5 mM, concentration of L-citrulline = 0.016 M, p = 0.2 M (KNO,), pH = 9.5. Concentration of solvent solvent, yo V/V Non-aqueous non-aqueous Dimethyl sulphoxide Dimeth ylformamide Acetonitrile . . 0.0 .. 10 20 30 40 50 . . 10 20 30 40 50 . . 10 20 30 40 50 885 -E+ versus S. C. E. /V 1.218 1.253 1.273 1.281 1.285 1.300 1.260 1.272 1.287 1.301 1.315 1.250 1.278 1.288 1.308 1.321 2.30 1.97 1.68 1.48 1.19 1.03 2.05 1.85 1.56 1.39 1.35 2.17 2.01 1.80 1.56 1.48 Slope of log plots/mV 43 39 38 36 36 35 40 39 38 37 37 45 46 47 52 58 un 1.21 1.36 1.44 1.48 1.52 1.52 1.36 1.40 1.45 1.48 1.48 1.20 1.15 1.10 1.03 0.93 k&/cm s-l 5-27 x 10-14 2.02 x 10-17 3.25 x 10-30 2.38 x 2.61 x 1.14 x 1.48 x 1 0 4 7 1.39 x 6.64 x 7.71 x 3.31 x 10-31 1.49 x 1044 2.83 x 10-24 1.25 x 10-23 8.57 x 4.32 x Quantitative Determination and Differentiation of Zinc and Nickel in the Presence of Each Other The conventional gravimetric and titrimetric methods for the determination of zinc and nickel in the presence of each other have been described.l59l6 These methods, being manual, are, relatively, not so accurate and high sensitivity cannot be achieved because of their inherent limitations.The values of the half-wave potentials of Zn2+ (1.005 V veysus S.C.E.) and Ni2+ (1.015 V versus S.C.E.) ions in a non-competing medium (0.2 M potassium nitrate solution) are very close to each other.Therefore, the polarographic waves due to the discharge of Zn2+ and Ni2+ ions in the medium merge with each other and it is not possible to determine zinc in the presence of nickel. The presence of a small amount of L-citrulline (0.03 M) results in a marked separation of the respective reduction waves, thus providing a convenient method for their individual determination; the half-wave potentials of Zn2+ and Ni2+ ions in 0.03 M L-citrulline solution have been found to be 1.307 5 and 1.162 5 V veysus S.C.E. , respectively. The waves resulting from the two complexation reactions are irreversible and diffusion- controlled and the wave height is directly dependent on the concentration of the metal ions in the solution.Some results for the determination of zinc in the presence of nickel are presented in Table 111. TABLE I11 DETERMINATION OF ZINC IN THE PRESENCE OF NICKEL Concentration of Ni2+ = 4 x lo-* M, concentration of citrulline = 0.04 M, concentration of Triton X-100 = 0.005y0, p = 0.2 M (KNO,), temperature = 23 "C. Zinc present/ Zinc found/ rnM mM Error, yo 0.6 0.587 2.2 0.8 0.770 3.7 1.0 0.980 2.0 1.2 1.158 3.5886 COMMUNICATIONS Analyst, Vol. 104 As this is an electroanalytical technique, more accurate results are achieved than with a manual method. This method can also be used for the determination of the zinc and nickel in nickel - silver and silver coins.We thank Professor J. P. Tandon, Head of the Department of Chemistry, University of One of the authors (K.M.S.) is grateful to CSIR, New Delhi, for the Rajasthan, Jaipur. award of a fellowship. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. References Suffet, I. H., and Purdy, W. C., J. Electroanalyt. Chem., 1966, 11, 302. Perkins, D. J., Biochem. J . , 1954, 57, 702. Chaturvedi, D. N., and Gupta, C. M., 2. Analyt. Chem., 1972, 260, 120. Miyan, N., Suyan, K. M., and Gupta, C. M., J . Inst. Chem. India, 1978, 50, 78. Chaturvedi, D. N., and Gupta, C. M., 2. Prakt. Chem., 1974, 3, 503. Suyan, K. M., Sachan, N. P., Shah, S. K., and Gupta, C. M., Indian J . Chem., in the press. Koutecky, J., Colln Czech. Chem. Commun., 1953, 18, 597. Meites, L., and Israel, Y., J. Am. Chem. Soc., 1961, 83, 4903. Ilkovic, D., Colln. Czech. Chem. Commun., 1934, 6 , 498. Shrivastava, 0. N., and Gupta, C. M., Analyst, 1972, 97, 204. Rawat, P. C., and Gupta, C. M., Talanta, 1972, 19, 706. Muller, M., “The Polarographic Method of Analysis,” Chemical Education Publishing, Easton, Schaap, W. B., J. Am. Chem. Soc., 1960, 82, 1837. Migal, P. K., Russ. J . Chem., 1962, 7 , 675. Vogel, A. I., “A Text Book of Quantitative Inorganic Analysis,” Longmans, London, 1968, p. 635. Lingane, J. J ., “Electroanalytical Chemistry,” Second Edition, Wiley-Interscience, New York, Received January 5th, 1979 Accepted March 8th, 1979 Pa., USA, 1951, p. 74. 1958, p. 209.

ISSN:0003-2654    

DOI:10.1039/AN9790400883

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

886 COMMUNICATIONS Analyst, Vol. 104 Com m u n i cati ons Material for publication as a Communication must be on a n urgent matter and be of obvious scientiJic importance. Rapidity of publication i s enhanced i f diagrams are omitted, but tables and formulae can be included. Communications should not be simple claims for priority: this facility for rapid publication i s intended for brief descriptions of work that has progressed to a stage at which i t i s likely to be valuable to workers faced with similar problems. A fuller paper may be ofleered subsequently, i f justified by later work. Manuscripts are not subjected to the usual examination by referees and inclusion of a Communication i s at the Editor’s discretion. Determination of Trace Amounts of Sulphate by Molecular Emission Cavity Analysis Using a Vaporisation System Keywords Hydrogen flame ; molecular emission cavity analysis ; sulphate reduction; tin - orthophosphoric acid The determination of trace amounts of sulphate in high-purity waters by molecular emission cavity analysis (MECA) has been rep0rted.l I t involved the sequential injection of five 30-111 aliquots of sample into a MECA cavity, with the solvent being evaporated between injections, in order to achieve the S, emission intensity required to measure 20-300p.p.b.(parts per log) of sulphate. An alternative MECA technique, involving the conversion of the analyte into a vapour for transfer into the cavity, has been described for a number of elements such as ammoniacal nitrogen2 (conversion into ammonia) and arsenic3 (conversion into arsine) .Sulphide and sulphite can also be determined in this way, by injection into strong acid and transfer of the evolved hydrogen sulphide and sulphur dioxide into a MECA cavity with a stream of nitrogen. TheSeptember, 1979 COMMUNICATIONS 887 more speedy vaporisation of hydrogen sulphide allows these anions to be determined in admixture.4 Conversion of sulphate into a vapour-phase compound, usually hydrogen sulphide, is generally considered to be a difficult process. However, the use of a modified tin - orthophosphoric acid reductant5 has been found to be readily applicable for reducing sulphate to hydrogen sulphide, and is used as the basis of an extremely sensitive MECA vaporisation procedure for the deter- mination of sulphate.Experimental Reagents Preparation of reductant Analytical-reagent grade orthophosphoric acid (density 1.75 g ml-l, 1 200 ml) was partially dehydrated by slowly heating in a heating mantle up to 290 f- 5 "C over 135 min. It was allowed to cool to below 70 "C, and general-purpose reagent tin granules (240g) were added. The mixture was purged with nitrogen via a PTFE tube as it was heated to 290 "C over 70 min t o dissolve the tin. The reagent was allowed to cool before storing in a tightly stoppered glass container. Prolonging the times given for dehydrating the orthophosphoric acid and dissolving the tin results in a reagent that is too viscous to be of use. The procedure should be carried out in a fume hood, because considerable amounts of hydrogen sulphide and other gases are generated during the dissolution of the tin.The evolution of such gases should have ceased by the con- clusion of the procedure. Standard sulfihate solutions sodium sulphate in exactly 1 1 of doubly distilled, de-ionised water. were freshly prepared before use, using the same solvent. Apparatus ponents are the heater, reactor, condenser and MECA detector. A 1000 p.p.m. sulphate solution was prepared by dissolving 4.430 g of analytical-reagent grade Less concentrated solutions The apparatus used for the determination of sulphate is illustrated in Fig. 1. The main com- Cyclone condenser Fig. 1. System for generating hydrogen sulphide from sulphate for MECA (half-scale).888 COMMUNICATIONS Analyst, VoL 104 The heater was made from an aluminium cylinder into which a hole was made to accommodate the vial reactor.Both portions of the cylinder were covered with asbestos insulating sleeves. The heater temperature was controlled by a Variac, and measured by a thermometer or thermo- couple placed in a bore-hole in the bulk of the cylinder. The heater was connected to a rack-and- pinion device, which allowed it to move vertically, in order for it to be quickly and reproducibly positioned around the reactor vial. The reactor consisted of a disposable glass 7.5-ml screw-top vial, which could be attached to the apparatus by a water-cooled screw-thread that forced the top of the vial against a replaceable silicone-rubber seal. The vial holder was fixed in position with respect to the vertical axis of the heater.The nitrogen purge inlet tube was of small-bore (1/16 in i d . ) stainless steel, protected by a PTFE sleeve inside the vial extending almost to the bottom of the vial. Gases were removed by the stream of nitrogen (15 ml min-l) via a PTFE outlet a t the top of the holder. The gases were carried from the reactor to a specially designed glass condenser, which could be disassembled for cleaning. The manner of introduction of the gases and the inverted funnel- shaped outlet tube ensured that water (and possibly reagent) carried over collected on the outer water-cooled walls, and not in the tubing leading to the cavity, where it would dissolve hydrogen sulphide and decrease the signal. The detector, as previously described,2 consisted of a stainless-steel MECA cavity (i.d.4 mm, 0.d. 7 mm), positioned in a hydrogen - nitrogen flame, with flow-rates of 1.8 and 2.8 1 min-1, respectively, in line with an optical system consisting of a collector - focusing lens, diffraction grating (set a t 384nm with a 17-nm spectral band pass) and RCA 1P28 photomultiplier tube. The cavity was water cooled, to maintain i t a t a low temperature in the flame, thus providing very sensitive conditions for generating S, emission, which is measured as a function of time on a chart recorder. Determination of Sulphate (More Than 30 ng) The heater was allowed to reach and maintain a temperature of 300 "C. A 1-ml volume (&lo%) of cold reductant was added to each vial from a burette. Each vial in turn was screwed into the assembly and heated for 1.5 min, to ensure freedom from sulphate (in practice this was usually unnecessary).The vials were capped and allowed to return to room temperature. A known volume (up to 3ml) of aqueous standard or sample solution was injected into the cold reagent, the vial re-attached to the apparatus and heated as before. The gases evolved were carried to the MECA cavity and the S, emission measured as a function of time. The peak area or height was used to determine the sulphate concentration by comparison with the responses of standards of appropriate con- centrations. A series of vials were rinsed with doubly distilled water and dried. Results and Discussion In the system described, the conversion of sulphate into hydrogen sulphide was found to begin at 198 "C. Therefore, no S, emission was observed until the reagent had reached this temperature, and there was a delay before a response appeared on the recorder (Fig.2). The height or area of the peak is a measure of the amount of sulphate in the sample. The calibration graph in both instances over the range 40 ng-5 pg of sulphate has the sigmoid shape characteristic of S, emission measurements (e.g., reference 6) but a linear graph can be obtained from a log - log plot of the same data, the slope of which is about 1.6, typical of MECA S, measurements.' The limit of detection (2,) is 15 ng of sulphate (>5 p.p.b., depending on the volume). The results of the first applications of this method are shown in Table I, where it has been used in conjunction with an oxygen-flask combustion for the determination of sulphur in various organic materials. The results are compared with those obtained by the most sensitive classical method, the 2-aminoperimidine nephelometric method .Q The first five samples are secondary standards, including the NBS orchard-leaf sample, which is not certified for sulphur.In all of the samples analysed, the nephelometric method gave results that were consistently slightly higher than the known values and the results obtained by MECA. This is possibly due to the fact that the nephelometric method is prone to positive errors because of the presence of inter- ferents, such as phosphate, which increase the turbidity. Both methods had similar standard deviations (about 2.5%) but the MECA procedure was quicker and much more sensitive.Thus,September, 1979 COMMUNICATIONS 889 much smaller aliquots were taken from the oxygen-flask solution for MECA than for nephelometry. The sensitivity of the MECA procedure is so high that the sulphate content of distilled or doubly distilled water (about 30 p.p.b.) can be measured directly on a 1-ml sample. 300 I=------ P ,o 200 s E g 100 \ 3 2 CI 0 60 180 300 Time/s Fig. 2. Effect of heating-block tem- perature on hydrogen sulphide generation from sulphate. Block temperatures : A, 290°C; and B, 235 "C. Arrows indicate time when emission starts. TABLE I COMPARISON OF MECA AND NEPHELOMETRIC DETERMINATION OF SULPHUR IN VARIOUS MATERIALS AFTER OXYGEN-FLASK COMBUSTION^ Sulphur found, yo Sulphur content, Sample mass {-*- 7 Sample % * for MECA/mg MECA Nephelometr y Coal dust A .. . . 2.05 11.390 2.1 2.1 Coal dust B . . . . 0.67 13.068 0.66 0.69 NBS orchard leaves . . 0.23 10.207 0.23 0.24 Refined oil A . . . . 0.55 4.815 0.54 0.57 Refined oil B . . . . 0.27 19.540 0.26 0.29 Tallow oil . . . . 0.0034 90-183 0.0033 & 2.5y0t 0.0036 f 2.8y0t Polyurethane . . . . - 3.3-5.2 0.152 f 2.7%t 0.158 f 2.4%t Safflower oil . . . . - 1 1 8- 1 7 3 0.005 5 0.005 7 0.0248 0.025 6 9.300 2.0 10.922 0.65 10.237 0.24 6.792 0.53 17.100 0.27 Crude oil . . . . - 57-76 * Sulphur blank in filter-paper used for combustion of sample = 4.2 pg. t Standard deviation calculated from ten determinations. The technique described has many favourable characteristics. It is extremely sensitive, rapid and easy to operate. Reproducible reductant preparation is easily achieved and, once prepared, the reagent can be stored in a stoppered bottle for months without noticeable change.An aqueous sample (10 pl) was injected into a vial containing the reagent, capped and stored for a t least 1 d without affecting the ultimate response. This allows a large number of samples to be collected over a period of time and run consecutively. The reductant in a vial can be re-used many times, provided that only small (e.g., 10 pl) volumes of sample are used and the reductant is allowed to cool to room temperature between injections.890 COMMUNICATIONS Analyst, Vol. 104 Volumes of water of up to 250 pl injected into the reductant have no effect on the intensity or time of appearance of the sulphate response. Thus, it is possible to obtain a calibration for a desired concentration range by injecting different volumes of a single standard solution.Like- wise, the volume of sample injected can be chosen so that the response falls within a calibration range. For greater volumes of water there is a slight decrease in intensity, possibly because of the slower temperature increase, as evidenced by the longer time for the emergence of the sulphate response. As with many volatilisation systems producing trace amounts of volatile species, continued operation at levels significantly below 1 pg of sulphur results in decreasing and increasingly irregular responses, probably due to adsorption of hydrogen sulphide by the tubing. This is readily avoided by running a more concentrated sulphate sample occasionally during a sequence of analyses.Sulphide, sulphite, thiosulphate and sulphate release a volatile sulphur compound in sequence, each giving a single peak response, as the temperature of the reagent gradually increases. They can therefore be resolved and determined in admixture, especially if a programmed heater temperature control is used. Peroxo- disulphate gives an identical response to sulphate, and thiocyanate gives a similar response to thiosulphate. Few common metal ions have a significant effect, but those which bind sulphide strongly, such as copper, depress the response. Such ions, however, are readily removed from the solution before MECA measurement. A more detailed investigation of this and other aspects of the procedure is in progress. The effect of other compounds has been investigated briefly. The authors thank Mr. J . S. Bedasie for participating in the analysis of the samples in Table I. I. M. A. Shakir thanks the Ministry of Higher Education and Scientific Research, Iraq, for the award of a research scholarship. References 1. 2. 3. 4. 5. 6. 7. 8. 9. Flanagan, J . D., and Downie, R. A,, Analyt. Chem., 1976, 48, 2047. Belcher, R., Bogdanski, S. L., Calokerinos, A. C., and Townshend, A., AnaZyst, 1977, 102, 220. Belcher, R., Bogdanski, S. L., Henden, E., and Townshend, A., Analytica Chim. Acta, 1977, 92, 33. Henden, E., PhD Thesis, Birmingham University, 1976. Kiba, T., Takagi, T., Yoshimura, Y., and Kishi, I., Bull. Chem. Soc. Japan, 1955, 28, 641. Dagnall, R. M., Thompson, I<. C., and West, T. S., Analyst, 1967, 92, 506. Belcher, R., Bogdanski, S. L., Knowles, D. J., and Townshend, A,, Analytica Chim. A d a , 1975, Bedasie, J . S., MSc Dissertation, Birmingham University, 1978. Stephen, W. I., Analytica Chim. Acta, 1970, 50, 413. 77, 53. Received June 21st, 1979 Ronalstan Chemical Consultants, Temple House, New Street, Birmingham, B2 4L.H Department of Chemistry, University of Birmingham, P.O. Box 363, Birmingham , B 15 2T T S. L. Bogdanski lssam M. A. Shakir W. I. Stephen Alan Townshend

ISSN:0003-2654    

DOI:10.1039/AN9790400886

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

890 COMMUNICATIONS Analyst, Vol. 104 Novel Reagent for the Determination of Atmospheric Isocyanate M onorner Concentrations Keywords : Isocyanate determination ; 1- (2-pyridy1)piperazine reagent ; atornospheric pollution ; high-performance liquid chromatography A high-performance liquid chromatographic (HPLC) method for the determination of both ali- phatic and aromatic isocyanates was first devised by Dunlap et al. using N-(4-nitrobenzyl)propyl- amine as the urea-forming reagent (nitro reagent). Subsequent w0rk~9~ indicated serious disadvant- ages associated with the use of this reagent, including oxidation of the reagent both during and after sampling, deterioration of the HPLC column packing by excess of reagent in the samples and its unsuitability for sampling in a reducing atmosphere.These disadvantages appear to stem from the presence of the aromatic nitro group in this secondary amine. Crown Copyright.September, 1979 COMMUNICATIONS 891 We report here the results of initial studies using 1-(2-pyridyl)piperazine as the isocyanate- reactivity entity. It is a stable, high-boiling liquid (boiling-point 283 “C) , completely miscible with water, soluble in a wide range of polar and non-polar solvents and readily available commercially (Aldrich Chemical Co. Ltd., Gillingham, Dorset) . The molecule has negligible steric hindrance a t the -NH position and reaction with isocyanate groups is rapid and exothermic. With aromatic and aliphatic diisocyanates disubstituted ureas are produced, which are not appreciably soluble in water but dissolve readily in cold, dilute mineral acids.More important, these substituted ureas possess significantly higher molar absorptivities than those derived from the nitro reagent, or the corresponding substituted urethanes derived from ethan01.~~~ These higher sensitivities have special importance from a sampling and analytical standpoint in view of the current trend towards lower permissible airborne isocyanate exposures.6 The molar absorptivities and wavelengths of maximum absorbance using dioxan as reference solvent are shown in Table I. This reagent has several significant advantages over the nitro reagent. TABLE I MOLAR ABSORPTIVITIES AND WAVELENGTH OF MAXIMUM ABSORBANCE OBTAINED USING DIOXAN AS A REFERENCE SOLVENT Isocyanate derivative* TDI/nitro reagent TDI/ethanol MDI/nitro reagent MDI/ethanol HDI/nitro reagent TD I / 1 - (2 -P) P MDI/1-(2-P)P HDI/l-( 2-P) P Molar absorptivity/l mol-l cm-l 60 500 31 400 16 500 80 200 46 000 38 500 34 700 16 600 L x .252 248 246 256 252 249 252 275 * TDI = toluene diisocyanate; MDI = methylene bisphenyl isocyanate; HDI = hexamethylene di- isocyanate; 1-(2-P)P = 1-( 2-pyridy1)piperazine. It is apparent from Table I that 1- (2-pyridy1)piperazine-based urea derivatives are eminently suitable for the determination of isocyanates by HPLC. As the reagent is miscible with water, problems associated with column degradation are readily overcome. Alternatively, thin-layer chromatography can be employed to quantify the urea derivatives. Detection might be achieved, for example, by exposing the sample spots to cyanogen bromide and o-tolidine to produce poly- methine dyes.’ In addition to using a solution of 1-(2-pyridyl)piperazine for conventional bubbler sampling, its high boiling-point makes it suitable for use as a liquid coating in adsorption tubes containing glass micro-beads or gas-chromatographic column packings.We thank Dr. P. A. Ellwood for valuable assistance in the preparation of the isocyanate derivatives. References 1. 2. Dunlap, K. L., Sandridge, R. L., and Keller, J., Analyt. Chew., 1976, 48, 497. Vogt, C. R. H., KO, C. Y., and Ryan, T. R., “Modification of an Analytical Procedure for Isocyanates to High Speed Liquid Chromatography,” US Dept. of Health, Education and Welfare, Public Health Service, Centre for Disease Control, National Institute for Occupational Safety and Health, Cincinnati, 1976. “2,4-Toluenediisocyanate (TDI),” Standards Completion Program Failure Report No. S344, US Dept. of Health, Education and Welfare, Public Health Service, Centre for Disease Control, National Institute for Occupational Safety and Health, Cincinnati, 1977. Cox, G. B., and Sugden, K., Analytica Chim. Acta, 1977, 91, 365. Bagon, D. A., and Hardy, H. L., J . Chromat., 1978, 152, 560. “Occupational Exposure to Diisocyanates,” US Dept. of Health, Education and Welfare, Public Health Service, Centre for Disease Control, National Institute for Occupational Safety and Health, Publication No. 78-215, Cincinnati, 1978. Received June 25th, 1979 3. 4. 5. 6. 7. Karrer, P., “Organic Chemistry,” Elsevier, Amsterdam, 1950, p. 807. Health and Safety Executive, Research and Laboratory Services Division, 403 Edgeware Road, London, NW2 6LN Horace L. Hardy Ronald F. Walker

ISSN:0003-2654    

DOI:10.1039/AN9790400890

出版商:RSC    

年代:1979

数据来源: RSC