摘要:

Anahst, February, 1979 143 SHORT PAPERS Spectrophotometric Determination of Dequalinium Chloride in Pharmaceutical Preparations C. P. Leung and S. Y. Kwan Government Laboratory, Oil Street, North Point, Hong Kong Keywords : Dequalinium chloride determination ; spectrophotonaetvy ; picric acid Dequalinium chloride [decamethylenebis(4-aminoquinaldinium chloride)] is a quaternary ammonium compound with antibacterial and antifungal properties. It is commonly used in the form of lozenges and paints for the treatment of infections of the mouth and throat. The compound is described in the British Pharmacopoeia1 and the method of assay therein is based on non-aqueous titration with perchloric acid in 1,4-dioxan. There are no official methods of assay for preparations containing dequalinium chloride.The usual amount of dequalinium chloride in lozenges is 0.25mg and a method of assay has not hitherto been developed for the accurate determination of such small amounts. Picric acid has been used for the spectrophotometric determination of residual quaternary ammonium cations2 ; the coloured complex formed is extracted into chloroform and the absorbance is measured at 365 nm. Picric acid has also been used for the determination of some cationic surfactant$ ; the extractant is 1,2-dichloroethane and the absorbance is measured at 375 nm. In the proposed method a complex is formed from picric acid and dequalinium chloride at pH 5-9. The yellow complex is extracted into 1,2-dichloroethane and the absorbance measured spectrophotometrically at the maximum, at 342 nm.The proposed method has been applied successfully to the determination of dequalinium chloride in lozenges (0.25mg) and paint (0.5% m/V). For paint, an alternative direct ultraviolet absorption method has also been found to be applicable as the only excipient in the paint is propane-1,2-diol, which does not show ultraviolet absorption in the range 220- 350 nm. For identification purposes and for detection of other related compounds in the sample, a thin-layer chromatographic method has also been proposed. Experimental Apparatus Sjbectrophotometer. A Pye Unicam, Model SPSOOO, spectrophotometer was used. Reagents Picric acid solution, 0.12% mlV in water. Bztfer solution, PH 7. Dilute 250 ml of 0.2 M potassium dihydrogen orthophosphate and 150 ml of 0.2 M sodium hydroxide to 1 1 with water.Acidi$ed iodoplatinate solution. Dissolve 0.25 g of hexachloroplatinic(1V) acid hexa- hydrate (H2PtC1,.6H20), 5 g of potassium iodide and 2 ml of hydrochloric acid (sp. gr. 1.16) in sufficient water to produce 100 ml. Procedures Spectrophotometric determination of dequalinium chloride with picric acid Transfer an amount of powder equivalent to 0.25 mg of dequalinium chloride into a 100-ml separating funnel, add 20 ml of water, 20 ml of pH 7 buffer solution and 1 ml of picric acid solution. Extract the solution with three 15-ml portions of 1,2-dichloroethane and filter each extract through a Determination in lozenges. Weigh and powder 20 lozenges.144 SHORT PAPERS Analyst, Vol. 104 small pledget of cotton-wool into a 50-ml calibrated flask.Adjust to the mark with the same solvent and measure the absorbance at 34% nm in a 1-cm cell against a blank solution prepared in the same way but omitting the sample. Calculate the amount of dequalinium chloride present in the sample by reference to a calibration graph prepared by applying the same procedure to 5.0-20.0-ml volumes of a standard solution of dequalinium chloride containing 0.02 mg ml-1, each aliquot being diluted to 20 ml with water before addition of the buffer solution and picric acid. Determination in paint. Dilute a volume of sample equivalent to 10 mg of dequalinium chloride to 1 1 with water. Pipette 20ml of the dilute solution into a 100-ml separating funnel and proceed as described above for lozenges. 0.4 ca ff 0, 2 0.2 Direct ultraviolet absorption method for determination of dequalinium chloride in paint Dilute a volume of sample with water to a drug concentration of 0.01 mg ml-1.Measure the absorbance at 326 nm concomitantly with ti standard solution of dequalinium chloride containing 0.01 mg ml-1. - - Identification of dequalinium chloride by thin-layer chromatography Shake an amount of powdered lozenges equivalent to 0.25 mg of dequalinium chloride with 2 ml of 95% V/V ethanol in a stoppered centrifuge tube. Centrifuge, then spot 0.04 ml of the supernatant liquid on to a 0.25-mm silica gel G plate. IdentiJcution in paint. Spot a volume of paint containing 5 pg of dequalinium chloride on to a silica gel G plate. Spot on to the plate a volume of standard solution equivalent to about 5 pg of dequalinium chloride, and develop the plate using either of the following mobile phases: (i) butan-1-01 - glacial acetic acid - water (3 + 1 + 1) ; (ii) 2-methylpropan- 1-01 - glacial acetic acid - water - acetic anhydride (2 + 1 + 1 + 1). IdentiJcation in lozenges.Locate the spots on the plate by spraying with acidified iodoplatinate solution. Results and Discussion The yellow complex extracted into 1,2-dichloroethane exhibits maximum absorption at 342 nm. The colour was found to be stable for at least 1 h. Beer’s law was obeyed over the concentration range 2-14 pg ml-l in 1,2-dichloroethane. The effect of variation of pH on the developm.ent of colour is shown in Fig. 1. The colour is stable over the pH range 5-9. Solutions buffered at pH 7 were used throughout the work.1 I I I -_J 0 2 4 6 8 1 0 1 2 1 4 PH Fig. 1. Effect of pH on development of colour of complex formed from dequalinium chloride and picric acid.February, 1979 SHORT PAPERS 145 However, the coloured com- plex was found to be only partially soluble in chloroform and quantitative extraction of the complex was, therefore, not possible. Lozenge 1 and the paint were British-made products and lozenges 2 and 3 were different batches of a local (Hong Kong) product. The local product was manufactured with overages of dequalinium chloride of 10% for lozenge 2 and 5% for lozenge 3. The results obtained are given in Table I. Chloroform was examined as a possible extraction solvent. The method was applied to two brands of lozenges and to one brand of paint.TABLE I DETERMINATION OF DEQUALINIUM CHLORIDE IN COMMERCIAL PREPARATIONS Amount of drug Recovery I L > (amount found/ Preparation Labelled Found* labelled amount), yo Lozenge 1 . . . . 0.25 mg 0.260 (&0.001) mg 104.0 (f0.4) 0.280 (&0.002) mg 112.0 (f0.8) Lozenge 2 . . . . 0.25 mg Lozenge 3 .. . . 0.25 mg 0.266 (fO.001) mg 106.4 (f0.4) Paint . . .. . . 0.5% m/V 0.553 (&0.002)% m/V 110.6 (f0.4) 0.550 ( f. 0.000) % nz/ V t 110.0 (-J=O.O)t * Mean of 10 determinations; values in parentheses are standard deviations of individual t Result obtained from direct ultraviolet absorption method. results. The accuracy of the method was tested by adding known amounts of dequalinium chloride to the samples and carrying out analyses before and after addition.Recoveries of dequali- nium chloride added to the samples are listed in Table 11. These experiments indicated a maximum error of about &2%. TABLE I1 RECOVERY OF ADDED DEQUALINIUM CHLORIDE FROM PREPARATIONS Amount of dequalinium chloride/pg Preparation Added Recovered* Recovery, yo Lozenge 1 . . .. 200 201.1 (f1.2) 100.6 (f0.6) Lozenge 2 . . .. 100 100.4 (f0.8) 100.4 (f0.8) Lozenge 3 . . .. 100 99.9 (f0.6) 99.9 (k0.6) 200 200.5 (31.0) 100.3 (f0.5) Paint . . .. .. 100 100.7 (f0.7) 100.7 (f0.7) I A I 200 202.2 (k2.0) 101.1 (kl.0) 200 202.4 (k2.0) 101.2 ( f l . O ) * Mean of 10 determinations; values in parentheses are standard deviations of individual results. Recovery experiments were also performed on a mixture prepared in the laboratory according to the formula used by the local manufacturer: Dequalinium chloride .. .. 5 mg Lactose . . .. .. . . 4.7 g Acacia gum . . .. .. . . 0.9 g Sucrose . . .. .. . . 13.1 g The recovery was found to be 101.2% (average of 10 determinations), with a standard devi- ation of 1.0%. Thin-layer chromatography served for both identification of dequalinium chloride and146 SHORT PAPERS Analyst, Vol. 104 establishing the absence of other related compounds. No quaternary ammonium com- pounds, other than dequalinium chloride, or amines were detected in the samples. The colouring matter present in the two brands of lozenges tested was Sunset Yellow FCF [C.I. 15985 (1956), E.E.C. No. Ello], which was found not to interfere in the determination. The other common excipients encountered in dequalinium chloride lozenges are sucrose, lactose and acacia gum, and in paint the solvent is propane-1,2-diol. All of these substances were also found not to interfere in the proposed method of assay for dequalinium chloride. The authors thank Dr. A. J. Nutten, Government Chemist of Hong Kong, for permission to publish this paper. References 1. 2. 3. “British Pharmacopoeia 1973,” HM Stationery Office, London, 1973, p. 143. Sloneker, J. H., Mooberry, J . B., Schmidt, P. E., Pittsley, J. E., Watson, I?. R., and Jeanes, A., Sheiham, I., and Pinfold, T. A., Analyst, 1969, 94, 387. Analyt. Chem., 1965, 37, 243. Received June 2nd, 1978 Accepted September 18ih, 1978

ISSN:0003-2654    

DOI:10.1039/AN9790400143

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

146 SHORT PAI'ERS Analyst, Vol. 104 Spectrophotometric Determination of lsoprenaline Sulphate and Methyldopa Using Chloranil Mohamed A. Korany and Abdel-Aziz M. Wahbi Faculty of Pharmacy, University of Alexandria, Alexandria, Egypt Keywords : Isoprenaline sulphate determination ; amethyldopa determination ; chloranil reagent ; spectrophotometry ; charge-transfer complex The official methods1 for the determination of isoprenaline sulphate and methyldopa are based on measurement of the colour produced when these compounds are treated with iron salts in the presence of an alkaline buffer. Other spectrophotometric methods based on the use of sodium molybdate,2 4-nitrobenzenediazonium chl~ride,~ thiosemicarbazide4J and sodium hexanitritocobaltate(III)6 have also been reported. Feigl' and Feigl et aZ.8 reported that chloranil (tetrachloroquinone) forms coloured condensation products with primary and secondary aryl amines, amino acids, phenols and naphthalene.Birks and Slifking reported that some amino acids form n - T charge-transfer complexes with chloranil in aqueous ethanol (50% V/V) buffered at certain pH values. Al-Sulimany and Townshendl0 described a procedure for the determination of various amino acids using chloranil. Recently, Al-Ghabsha et aZ.ll investigated the reaction of chloranil with a wide range of arnines and described a method for their determination. This paper deals with the use of chloranil for the spectrophotometric determination of isoprenaline sulphate and methyldopa. Experimental Apparatus Beckman double-beam spectrophotometer, Model 24.Reagents ChZoraniZ soZutiort. Bufer solution, pH 9. A 0.05 M solution of d.isodium tetraborate. Prepared drug solution. Dissolve 20 mg of methyldopa or isoprenaline sulphate in 20 ml of 0.1 M hydrochloric acid. Neutralise with 0.05 M disodium tetraborate solution to pH 7 and dilute to 100 ml with water in a calibrated flask. A saturated solution of clhloranil in ethanol.Febraary, 1979 SHORT PAPERS 147 General Procedure and Preparation of Calibration Graph Pipette 1-5-ml aliquots of the prepared drug solution into a 25-ml calibrated flask. exactly 5 ml of chloranil solution and 2 ml of 0.05 M disodium tetraborate solution. and dilute to volume with water. tetraborate solution and 5ml of chloranil solution and dilute to 25ml with water.both solutions in a water-bath at 65 "C for 30 min. at 354 nm for isoprenaline sulphate and 358 nm for methyldopa. Add Mix Prepare a blank solution using 2 ml of 0.05 M disodium Heat Measure the absorbance in 1-cm cells Procedure for Tablets Extract an accurately weighed amount of the powder, equivalent to about 100 mg of isoprenaline sulphate or methyldopa, with 0.1 M hydrochloric acid by washing through a filter-paper into a 100-ml calibrated flask. Dilute the extract to the mark with 0.1 M hydrochloric acid. Pipette 20 ml of this solution into a 100-ml calibrated flask, neutralise with 0.05 M disodium tetraborate solution to pH 7 and dilute to the mark with water. Proceed as described under General Procedure using 2 ml of the final neutral solution.Calculate the amount of isoprenaline sulphate or methyldopa from the appro- priate calibration graph. Weigh and powder 20 tablets. Results and Discussion Chloranil, in aqueous alcoholic solution buffered a t pH 9, reacts with isoprenaline and methyldopa to form complexes with maximum absorption at 354 and 358 nm, respectively. The absorbances of the complexes were found to be stable for 1 h. Under the described experimental conditions, a linear correlation was obtained between absorbance, Alcm, and concentration, C, of isoprenaline sulphate and methyldopa over the range 0.2-1 mg per 25 ml. On extrapolation to zero concentration, the graphs have a small positive intercept on the absorbance axis. The two linear equations were found to be A,,, = 0.022 + 0.710 C for isoprenaline sulphate and Alcm = 0.024 + 1.104 C for methyldopa.The small positive intercept in these two equations may have originated from a minor non-specific side-reaction of the phenolic groups in the alkaline buffer used. The apparent molar absorptivities for isoprenaline sulphate and methyldopa were found to be 4.9 x lo3 and 6.6 x lo3 1 mol-l cm-l, respectively. The relative standard deviation for the determination of 0.448mg of isoprenaline sulphate and 0.460mg of methyldopa were 0.50 and 0.92%, respectively (five separate determinations). Chloranil solution in ethanol is yellow, but it slowly becomes violet when added to disodium tetraborate solution of pH 9. The absorbances of the blank solution against solvent (alcohol - buffer solution) at 354 and 358 nm were found to be 0.710 and 0.527, respectively.The violet colour was developed equally in the blank and test solutions. However, in view of these relatively high absorbance readings the use of a double-beam spectrophotometer is preferable in order to obtain precise results. The reaction mechanism can be explained by analogy with the reaction of adrenaline and noradrenaline with chloranil.ll According to the suggestions of Al-Sulimany and Townshend,lo and El-Ghabsha et d.,ll it is assumed that the reaction involves the formation TABLE I DETERMINATION OF ISOPRENALINE SULPHATE AND METHYLDOPA Tablet Isoprenaline sulphate (20 mg per tablet) Me th yldopa (250 mg per tablet) * Results expressed deviation. IN COMMERCIAL TABLETS Fraction of nominal content, yo* Proposed method Official method f A -I .. 100.0 &- 0.9 100.7 f 0.6 .. 99.4 f 0.7 100.5 f 0.5 as mean of six separate determinations f standard148 SHORT PA.PERS Analyst, Vol. 104 of a molecular complex between the primary aliphatic amine of methyldopa or the secondary aliphatic amine of isoprenaline sulphate with a :reaction product of chloranil at pH 9. The method has been applied to the determination of isoprenaline sulphate and methyl- dopa in purchased tablets. In the absence of any knowledge of the composition of the excipients and fillers in the tablets, the results obtained were compared with those obtained by using the official methods1 Concordant results were obtained on using both methods (Table I). This agreement indicated that tablet fillers and excipients did not interfere in the proposed method. The official methods suffer from the disadvantage that the colour produced is based on the phenolic group of the compounds and requires the use of elaborate buffer solutions.It should be emphasised that the present method can be applied to any compound with an -NH, or -NH- group but it can only be applied to tablets containing one amino com- pound. 1 . 2. 3. 4. 5 . 6 . 7 . 8. 9. 10. 1 1 . References “British Pharmacopoeia 1973,” HM Stationery Office, London, 1973, pp. 257 and 304. Hamekoski, J., and Kivinen, A., Farmaseuttintn Aikak., 1966, 75, 225; Analyt. Abstr., 1968, 14, Kolodziejska, T. P., Acta Pol. Pharm., 1969, 26, 519; Analyt. Abstr., 1971, 20, 1252. Khalil, S . K. W., and Salama, R. B., J . Pharm. Pharmac., 1974, 26, 972. Salama, R. B., and El-Obeid, H. A., Analyst, 1976, 101, 136. Wahbi, A. M., Abdine, H., Korany, M. A., and Abdel-Hay, M. H., J . ,4ss. 08. Analyt. Chem., 1978, Feigl, F., “Spot Tests in Organic Analysis,” Seventh Edition, Elsevier, Amsterdam, 1966, pp. 249 Feigl, F., Gentil, V., and Stark-Mayer, C., Mikrochim. Acta, 1957, 350. Birks, J. B., and Slifkin, M. A., Nature, Lond., :L963, 197, 42. Al-Sulimany, F., and Townshend, A., Analytica Chim. Acta, 1973, 66, 195. Al-Ghabsha, T. S . , Rahim, S. A., and Townshend, A., Analytica Chim. Acta, 1976, 85, 189. 7102. 61, in the press. and 407. Received April 26th, 1978 Accepted June 30th, 1978

ISSN:0003-2654    

DOI:10.1039/AN9790400146

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

148 SHORT PA.PERS Analyst, Vol. 104 Spectrophotometric Determination of Microgram Amou n t s of H yd roq u i none, Pyrog a I I ol and Resorcinol Q. S. Usmani, M. M. Beg and 1. C. Shukla Department of CherPzistry,~Urciversity of Allahabad, Allahabad, India Keywords : Hydroquinone determination ; pyrogar!lol determination ; resorcinol determination ; spectrophotometric microdetermination ; sodium carbonate Advances in polyhydroxyphenol chemistry are a result of the development of new experi- mental techniques, especially methods for detection and determination of these compounds. Small-scale procedures are valuable for establishing the concentration and the constitution of polyhydroxyphenols in plant products. Various spectrophotometric and colorimetric rneth~dsl-~ have been reported for the small-scale determination of polyhydroxyphenols.A spectrophotometric method6 has been developed for the determination of catechol, :resorcinol and phloroglucinol with the use of potassium iodate in dilute nitric acid. In this investigation hydroquinone, pyrogallol and resorcinol were determined spectro- photometrically, after heating with sodium carbonate solution in a boiling water-bath for about 15 min. The method is convenient and precise.February, 1979 SHORT PAPERS Experimental Reagents 149 All reagents were of AnalaR grade. Sodium carbonate solution, 0.5% mlV. Sample solzdion. Stock solutions of hydroquinone, pyrogallol and resorcinol were pre- pared by dissolving accurately weighed amounts of the samples in distilled water in 100-ml calibrated flasks.Aliquots of these solutions were used to give a range of 0.5-250 pg. Apparatus meter using 1-cm matched silica cells. Absorbance measurements were carried out with a Beckman, Model DU, spectrophoto- Preparation of Calibration Graph Aliquots of solution containing 5-250 pg of the polyhydroxylphenol were transferred into different stoppered test-tubes and 5 ml of 0.5% sodium carbonate solution were added to each. The tubes and contents were thoroughly shaken and placed in a boiling water-bath for about 15min. The reaction mixture in each tube was then cooled and transferred quantitatively into a 25-ml calibrated flask and diluted to the mark with water. The absorbance of hydroquinone, pyrogallol and resorcinol solutions were measured at 320, 340 and 440 nm, respectively, and plotted against concentration of the phenol.Results and Discussion The absorbance is proportional to the concentration over the range 5-100 pg of hydro- quinone, 5-50 pg of pyrogallol and 20-200 pg of resorcinol. The Beer - Lambert law is not obeyed outside these ranges although colours are produced at a lower concentration of the samples. Determinations of the concentrations of unknown samples of hydroquinone, pyrogallol and resorcinol were carried out by measuring the absorbance and reading off the concentra- tion from a calibration graph (Fig. 1). Results obtained with different concentrations of the phenols are shown in Table I. The determination of other mono-, di- and trihydroxyphenols has not been possible with this method.The determination of hydroquinone, pyrogallol or resorcinol by this method was not possible if more than one of these compounds was present in the same solution. The presence of carbohydrates (glucose, galactose, etc.) was the only interference investigated. In the presence of these compounds the colour developed was not constant. Amount of compound in final solution/yg Fig. 1. Graph of absorbance versus amount of com- pound in final solution. A, Hydroquinone; B, pyro- gallol; C , resorcinol. For wavelengths used see Table I.150 SHORT P.4PERS Analyst, Vol. I04 It is thought that the development of a yellow colour on heating the sample with sodium carbonate is caused by the oxidation of the polyhydroxyphenols to the corresponding quinones. This opinion is supported by examination of the ultraviolet spectrum of the oxidation product from hydroquinone, which is found to be the same as that of $-benzo- quinone .On passing a slow stream of oxygen through the solution, while heating in the water-bath, it was found there was no effect on either the time required for the development of the colour or the absorbance. The sensitivity and the range over which the Beer-Lambert law was obeyed was also unaffected. However, under oxygen-free conditions it was observed that the colour did not develop even after heating the reaction mixture for a long period in a boiling water-bath. Hence, the atmospheric oxygen is sufficient for the development of the colour under the proposed reaction conditions. Moreover, without the use of sodium carbonate the atmospheric oxygen alone does not give a constant colour within the described reaction time. The effect of oxygen was investigated.TABLE I DETERMINATION OF HYDROQUINONE, PYROGALLOL AND RESORCINOL Compound Hydroquinone . . .. WITH SODIUM CAREiONATE SOLUTION Range of validity Amount Wavelength/ of Beer’s law/ taken/ nm Pg Pg 320 5-100 5 Pyrogallol . . .. 340 Resorcinol . . .. 440 5-50 40 80 7 28 49 20-200 30 120 180 Absorbance 0.360 0.360 0.365 0.720 0.730 0.730 1.140 1.140 1.190 0.245 0.240 0.240 0.720 0.730 0.720 1.20 1.20 1.25 0.105 0.105 0.110 0.205 0.215 0.205 0.280 0.280 0.275 Standard deviation 0.55 0.97 1.14 0.83 0.41 1.66 1.90 1.46 1.09 The use of other alkaline reagents such as sodium hydrogen carbonate, ammonia solution and sodium hydroxide gave similar colours under the described reaction conditions. With the use of sodium hydrogen carbonate the sensitivity of the method is much lower than that with sodium carbonate. The colour developed with ammonia and sodium hydroxide is not constant even after 30 min and the absorbance continues to increase with increase in reaction time.February, 1979 SHORT PAPERS 151 References 1. 2. 3. 4. 5. 6. Bishop, L. R., Mitt. VersStr. GarGew., Wien, 1971, 25, 165. Roncero Vazquez, A., Duran Maestro, R., and Constante Graciani, E., Grasas Aceit., 1971, 22, 371. Grant, J. W. D., and Joshbhai Patel, C., Analyt. Biochem., 1969, 28, 139. Korenman, I. M., Ganiana, V. G., and Kurina, N. V., Tr. Khirn. Khim. Tekknol., 1968, (2), 140. Thielemann, H., 2. Chemie, Lpz., 1969, 9, 464. Beg, M. M., Usmani, Q. S., and Shukla, I. C., Analyst, 1977, 102, 306. Received December 9th, 1977 Amended July 6Ch, 1978 1 Accepted July 31st, 1978

ISSN:0003-2654    

DOI:10.1039/AN9790400148

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

February, 1979 SHORT PAPERS 151 Simple Procedure for the Determination of Total Carbon and its Radioactivity in Soils and Plant Materials R. C. Dalal Ufiiversity of New England, Armidale, N.S. W. 2351, Australia Keywords : Soil organic carbon determination; plant carbon determination; I4C radioactivity measurement; chromic acid digestiolz Carbon in soil and plant materials can be determined by wet- and dry-combustion methods.lS2 In both instances, soil and plant carbon is converted into carbon dioxide, absorbed in alkali and determined either by titration against a standard acid or by weighing. These methods involve large apparatus, are expensive and time consuming, and therefore cannot be adapted to the routine analysis of a large number of samples. This paper describes a simple pro- cedure for the simultaneous determination of total carbon and its radioactivity.Experiment a1 A wet-combustion method modified from that developed for the measurement of the radioactivity of leaves treated with carb0n-14~~~ was used. The digestion apparatus con- sisted of a McCartney bottle (id. 22 mm, capacity 28 cm3) with an aluminium screw-cap fitted with a 2.5 mm thick neoprene seal, and a test-tube (id. 13 mm, capacity 8 cm3). The digestion mixture, modified from that of van Slyke and Folch,s was prepared by dissolving 25 g of chromium trioxide in 100 cm3 of concentrated sulphuric acid - ortho- phosphoric acid (2 + 1). This mixture was heated to 145-150 "C, then cooled and tightly stoppered to prevent the absorption of moisture from the atmosphere. A suitable amount of soil (particle size less than 0.15 mm) or plant material, containing less than 10 mg of carbon, was weighed into a McCartney bottle and 5 cm3 of chromic acid digestion mixture were added rapidly.With the aid of forceps the test-tube, containing 5.0 cm3 of 0.4 M sodium hydroxide solution, was lowered into the bottle, which was immedi- ately stoppered tightly. Appropriate blanks were prepared simultaneously. The bottles were autoclaved at 121 "C and approximately 105 kPa for 1 h, then left overnight at room temperature. The test-tube was removed from the bottle, its outside washed free of acid and the sodium hydroxide solution was transferred into a graduated tube (capacity 36 cm3, length 150 mm) fitted with a C19/17 Quickfit or similar stopper.The volume was made up to 10.0 cm3 with carbon dioxide free distilled water and the tube was stoppered. For the purpose of measuring radioactivity when the soil or plant samples were labelled with carbon-14, 1.0cm3 of the sodium hydroxide solution from the stoppered tube was transferred into a 20-cm3 glass scintillation vial. After adding 10 cm3 of scintillation solution [a mixture of toluene (2 volumes), containing 5 g of 2,5-diphenyloxazole (PPO) and 0.1 g of 1,4-bis(5-phenyloxazo1-2-yl)benzene (POPOP) per litre, and Triton X-100 (1 vol~me)~], the vial was capped tightly and shaken. A stable, clear, homogeneous emulsion was formed at room temperature and, after storage overnight in the dark, the sides of the vial were wiped to remove any smudges or radioactive contaminants and counting was carried1 52 SHORT PAPERS Analyst, Vol.104 out in an ambient-temperature liquid scintillation counter. The counting efficiency, calcu- lated by spiking the mixture with [l%]hexadecane of known specific activity, was found to be 74%. The radioactivity measured was corrected for the background and efficiency and the total and specific activity of the sample were calculated, For the determination of the total carbon in the samples, 1 cm3 of saturated barium chloride solution and 0.05 cm3 of 1% phenolphthalein solution (prepared in ethanol) were added to the remaining 9.0 cm3 of the sodium hydroxide solution in the tube (10.0 cm3 if no radioactivity measurements were required.). The mixture was titrated against 0.10 M hydrochloric acid until the colour of the solution changed from red to colourless.By using a magnetic stirrer and titrating under reflected light, the end-point in the titration was reproducible. Alternatively, the sodium hydroxide solution can be titrated to pH 8.3 using an automatic titrator or by the procedure suggested by Bundy and Bremner.' From the volume of 0.10 M hydrochloric acid used for the titration of the sample and the blank, the amount of organic carbon in the sample can be calculated. 1 cm3 of 0.10 M hydrochloric acid = 0.60 mg of carbon Results and. Discussion The chromic acid digestion mixture oxidised all of the carbon in glucose, benzoic acid (benzenecarboxylic acid), hydroquinone (1,li-dihydroxybenzene) and adenine (6-amino- purine) (Table I).There was no significant effect on the oxidation of the carbon in these compounds or soil and plant samples if the proportions of concentrated sulphuric acid and orthophosphoric acid in the acid mixture were changed from 2 + 1 to 3 + 2. However, if the amount of chromium trioxide was decreasfed below 20 g per 100 cm3 of the acid mixture, adenine was not completely oxidised. TAE;LE I CARBON CONTENTS OF GLUCOSE, BENZOIC ACID, HYDROQUINONE AND ADENINE Carbon content determined f 1 Amount taken Percentage of theoretical Sample (dry mass)/mg mg value Glucose . . .. .. 20.0 7.90 & 0.02 98.8 Hydroquinone . . .. 15.5 9.68 f 0.03 98.7 Benzoic acid . . ,. 15.0 10.22 f 0.05 99.0 Adenine .. .. .. 20.0 8.82 f 0.03 99.3 The operation from the addition of the chromic acid digestion mixture to the closing of the McCartney bottle prior to autoclaving should not take more than 10 s, during which period the loss of carbon even from glucose did not exceed 2%.The loss of carbon from organic compounds and soil and plant materials was reduced and the period of operation was extended to 20 s when the chromic acid. digestion mixture was cooled to 4 "C, which reduced the rate of reaction in comparison with that at room temperature (20 "C). TABLE I1 EFFECT ON RECOVERY OF CARBON OF THE AMOUNT OF SOIL AND PLANT MATERIALS USED Amount (dry mass) I Sample mg Soil . . .. 250 500 750 1000 1500 2 000 Plant material . . 10 16 20 25 Carbon content -7 mg 0.985 0.394 2.040 0.408 3.045 0.406 4.050 0.398 5.820 0.388 6.921 0.346 2.882 38.8 5.835 38.9 7.820 39.1 9.662 38.6 Percentage of the maximum carbon content 96.5 100.0 99.5 97.5 95.1 84.8 99.2 99.5 100.0 98.7 Leas t-square difference (P = 0.05), yo ] 2.5 1 JFebruary, 1979 SHORT PAPERS 153 Studies on the effect of the size of the soil samples showed that the carbon recovery was low when the carbon content of the sample did not exceed 1 mg or the amount of soil taken exceeded 1 g (Table 11).No significant effect on the amount of plant material per sample was observed. However, the amount of carbon per sample preferably should not exceed 10 mg. When the soil was mixed with carbon-14 labelled plant material, the recoveries of total carbon and carbon-14 activity were complete (Table 111). Hence both total carbon and its radioactivity in soil and plant samples can be measured simultaneously.TABLE I11 RECOVERY OF CARBON FROM SOIL MIXED WITH "C-LABELLED PLANT MATERIAL 14C activity* f A \ Recovery of carbon Sample % Bq Rq per mg C % oh Soil ( 1 8) . . . . 0.406 f 0.012 - - - - Total Specific 7-7 Carbon content, activity/ activity/ Total C, 1*C activity, Plant material (20 mg) . . . . 39.10 f 0.77 215 & 3 27.5 f 0.3 - - Soil -i- plant material7 , . . . 0.446 & 0.012 10.7 & 0.2 2.4 -f 0.05 101.8 f 2.0 99.5 f 1.9 * Each carbon-14 activity measurement was repeated a t least four times and counted to a t least lo4 t 500 mg of plant material were mixed with 500 g of air-dried soils; 1 g of sample was taken for deter- counts per sample with a counting efficiency of 74%. mination of carbon. In the wet-digestion methods of Walkley - Blacks and S~hollenberger~ for the determination of organic carbon in soil, iron(I1) and oxides of manganese interfere.l The presence of the former leads to over-estimates and of the latter to under-estimates of the organic carbon content of soils.l0 These interferences are eliminated in the present procedure because the carbon oxidised from the sample is measured directly.Organic carbon can be determined in calcareous soils after the carbonates have been removed by treatment with sulphuric acid - iron(I1) sulphate solution1 and the samples oven dried at 105 "C. However, as in all other wet-combustion methods, chloride ions interfere.l Interference from small amounts of chloride ions (up to 4 mg of C1- as KC1 or NaC1) was reduced by adding 2.5% of mercury(I1) oxide or silver(1) sulphate to the acid digestion mixture. When amounts of organic carbon in 17 soils varying from 0.30 to 14.42% were deter- mined by the present procedure and by the Walkley - Black method,l the results were closely correlated [equation (l)] .The regression equation .. .. .. (1) y = 1.21% - 0.03 . . .. 1' = 0.997, P (0.001, wherey and x are the percentages of organic carbon in the soils deter- mined by the present procedure and by the Walkley - Black method, respectively, showed that the present procedure determined 21% more organic carbon than the Walkley - Black method. Assuming that the present method measured the total organic carbon in these soils, the recovery of organic carbon by the Walkley - Black method was 100/1.21 = 83%, which falls within the range of values reported by Allison.ll However, this procedure needs to be calibrated with the dry-combustion proceduref for the determination of total carbon in soils.Conclusion The present method can be used for the routine analysis of soil and plant samples for carbon and carbon-14 radioactivity measurements. For the determination of organic carbon in samples that contain carbonates, pre-treatment of the samples with sulphuric acid - iron(I1) sulphate solution is required. Iron(I1) and oxides of manganese do not interfere.154 SHORT PAPERS Analyst, VoL. 104 The interference by small amounts of chlorides (up to 4 mg of C1- per sample) can be reduced by adding mercury(I1) oxide or silver(1) sulphate to the digestion mixture, although samples that contain large amounts of chloride ions should be pre-treated in order to remove chlorides.12 The financial assistance provided by the Australian Meat Research Committee is gratefully acknowledged. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. References Allison, L. E., i n Black, C. A., Editor, “Methods of Soil Analysis,” Agronomy Series 9, Part 2, Bottner, P., and Warembourg, F. R., PI. Soil, 1976, 45, 706. Shimshi, D., J . ExpZ Bot., 1969, 20, 381. McWilliam, J. R., Phillips, P. J., and Parkes, R. R., Tech. Pap. D i v . PI. I n d . C.S.I.R.O. Aust., Van Slyke, D. D., and Folch, J., J . Bid. Chew., 1940, 136, 509. Turner, J. C., Int. J . APpl. Radiat. Isotopes, 1968, 19, 557. Bundy, L. G., and Bremner, J. M., Proc. Soil Sci. SOC. Am., 1972, 36, 273. Walkley, A., and Black, I. A., Soil Sci., 1934, :57, 29. Schollenberger, C. J., Soil Sci., 1945, 59, 53. Walkley, A,, Soil Sci., 1946, 63, 251. Allison, L. E., Proc. Soil Sci. SOC. A m . , 1960, 24, 36. Jackson, M. L., “Soil Chemical Analysis,’’ Prentice-Hall, Englewood Cliffs, N. J., 1958, p. 215. American Society of Agronomy, Madison, Wisc., 1965, p. 1367. No. 3, 1973. Received June 28th, 1978 Accepted September l l t h , 1978

ISSN:0003-2654    

DOI:10.1039/AN9790400151

出版商:RSC    

年代:1979

数据来源: RSC

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154 SHORT PAPERS Analyst, VoL. 104 Determination of Lead in Columbite Concentrates by Atomic-a bsorption Spectrometry After Sulphide Separation C. Chow Geological Survey Laboratory, P.O. Box 1015, Ipoh, West Malaysia Keywords : Lead determination ; columbite coizcentrates ; atomic-absorption spectrometry ; sulphide separation Spe~trographic,l-~ chromatographic5 and polarographic6 methods have been used to d eter mine lead in niobium and tantalum metal anld their oxides. In the determination of lead in columbite concentrates by atomic-absorptilon spectrometry, the problem arises that the ore is not completely decomposed by common acids. Further, niobium and tantalum compounds are easily hydrolysed, especially in the presence of mineral acids, forming white precipitates of hydrated earth acids that coprecipitate lead, and this often leads to low results. It was found that if potassium pyrosulphate7 was used to decompose the ore and the melt leached with tartaric acid, the dissolved lead could be precipitated as sulphide, using copper sulphide as collector.After filtering the mixture of lead sulphate and lead sulphide and dissolving it in concentrated hydrochloric and nitric acids, lead was determined by atomic- absorption spectrometry. Experimental Instrumental A Varian Techtron AA4 instrument was used with the following settings : wavelength, 217.0 nm; lamp current, 5 mA; slit width, 200 pm; and air - acetylene flame (air pressure, 15 p.s.i.g.; acetylene pressure, setting 3 on the flow meter). A standard ASL hollow-cathode lamp was used as the line source.February, 1979 SHORT PAPERS 155 Reagents All reagents were of analytical-reagent grade.Potassium fiyrosulp hat e. Standard lead solutions, 1000 and 100 pg ml-l. Copper solution. Prepare the 1000 pg ml-l solution by dissolving 0.3197 g of anhydrous lead nitrate in 200ml of distilled water. Prepare the 100 pg ml-l solution by dilution. Dissolve approximately 0.2g of metallic copper in a mixture of about 6 drops of concentrated nitric acid and 4 ml of concentrated hydrochloric acid. Dilute to 200 ml with distilled water. Dissolve 100 g of L(+)-tartaric acid in distilled water, filter the solution into a 1-1 calibrated flask and dilute to volume with distilled water. Tartaric acid solution, 10% m/V. Procedure Weigh accurately 0.25g of columbite sample (less than 200 mesh) into a silica crucible.Add about 8-10 g of potassium pyrosulphate and fuse the mixture for about 45 min in a low to medium Bunsen-burner flame. Cool the melt and extract it into 50 ml of 10% m/V tartaric acid solution by boiling with continuous swirling until the melt is completely dissolved. Dilute the resulting solution to 200 ml with distilled water, add 5 ml of copper solution and pass hydrogen sulphide through the solution for about 15min. Add some ashless paper pulp, filter through Whatman No. 40 (11-cm) filter-paper and wash with water saturated with hydrogen sulphide. Transfer the residue into a porcelain crucible and ignite it a t low heat until all of the carbon has been burnt away. Dissolve the residue by warming it gently in the porcelain crucible with 5-10 drops of concentrated hydrochloric acid followed by 3-4 drops of concentrated nitric acid (if the sample contains bismuth, use 3 ml of con- centrated hydrochloric acid in order to prevent hydrolysis of the bismuth).Filter the solution through Whatman No. 40 filter-paper into a 100-ml calibrated flask, wash with distilled water and dilute to volume with distilled water. Measure the absorbance a t 217.0 nm against a blank prepared in the same manner as the sample. Preparation of Calibration Graph Transfer by pipette 1-10-ml aliquots of standard 100 pg ml-l lead solution into a series of silica crucibles and evaporate the solutions to dryness on an asbestos sheet on a hot-plate. Fuse the residue with 8-10 g of potassium pyrosulphate and then follow the method described under Procedure.Interferences Elements likely to be present in columbite samples were investigated for their inter- ference effects. Errors corresponding to less than about twice the standard deviation found for the determination of lead in pure solutions were considered to indicate the absence of interference effects. Known amounts of diverse ions were added to 500pg of lead. Results and Discussion The lead content in the samples examined had not been determined previously. The additions method was used in the analyses. Two portions of columbite sample, each of 0.25 g, were weighed accurately into two silica crucibles, one of which contained a known amount of standard lead that had previously been transferred by pipetting in a standard lead solution and evaporating to dryness in the silica crucible on an asbestos sheet on a hot- plate.The sample solution was prepared according to the method described under Procedure. As shown in Table I, the recovery of lead was satisfactory. No interference was observed in the presence of 140 mg of niobium, 50 mg of tantalum, zinc, tin(II), calcium, manganese(II), tungsten, cadmium, copper(I1) or iron(III), 30 mg of titanium(IV), 5 mg of cobalt, nickel or chromium(VI), or 2 mg of strontium, bismuth(III), arsenic(II1) or mercury(I1). However, 2 mg of antimony(II1) or barium could not be tolerated.156 SHORT PAPERS TABLE I Analyst, Vol. 104 RECOVERY AND DETERMINATION OF LEAD IN COLUMBITE SAMPLES All results are averages of duplicate determinations.Lead found in sample/ Sample reference Pg 682(1)232 .. .. 326 326 325 325 682(1)L108 . . .. 425 425 682(1)195 .. . . 260 260 682(1)L85 .. .. 525 525 682(1)L91 .. .. 498 498 Lead added to sample/ Pg 100 200 500 200 200 1508 1501 - - - - - Total lead Lead found/ recovered/ Pl.g Pg 430 105 535 210 830 330 625 200 450 190 665 140 655 157 - - - - - - - - - - Error, % t 5 + 5 +1 0 - 5 - 6.7 t 4 . 7 - - - - - The atomic-absorption spectrometric metho’d described is simple and rapid. By carrying out a preliminary sulphide separation niobium and tantalum are removed from the matrix, together with relatively large amounts of potassium pyrosulphate and tartaric acid. Acknowledgement is made to the Director-General of the Geological Survey, Malaysia, for permission to publish this paper. References 1. 2. 3. 4. 5. 6. 7. Chandola, L. C., and Venkatasubramaniam, R.., 2. Analyt. Chem., 1973, 266, 127. Grekova, I. M., and Nazarenko, V. A., Zav. Lab., 1969, 35, 537. Laib, R. D., and Lykins, J. D., Appl. Spectrosc., 1968, 22, 539. Zakharov, E. I., Lipis, L. V., and Petrov, K. E., Zh. Analit. Khim., 1959, 14, 135. Strelow, F. W. E., and van der Walt, T. N., Analyt. Chem., 1975, 47, 2272. Kolthoff, I. M., and Elving, P. J., “Treatise on Analytical Chemistry,” Part 11, Volume 6, Inter- Kolthoff, I. M., and Elving, P. J., “Treatise on Analytical Chemistry,” Part 11, Volume 6, Inter- Received June 12th, 1978 Accepted August 14th, 1978 science, New York, 1964, p. 374. science, New York, 1964, p. 217.

ISSN:0003-2654    

DOI:10.1039/AN9790400154

出版商:RSC    

年代:1979

数据来源: RSC

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SHORT PAPERS Analyst, Vol. 104 Direct Determination of Calcium, Magnesium and Zinc in Lubricating Oils and Additives by Atomic-absorption Spectrometry Using a Mixed Solvent System Zsuzsa Wittmann Hungarian Oil and Gas Research Institute, Veszpve'm, Hungary Keywords : Lubricating oil analysis ; calcium determination ; magnesium determination ; zinc determination ; atomic-ab.sorption spectrometry Continued interest in the testing of lubricants has centred on the various additives used and the determination of their metallic constituents. There are some spectroscopic methods for the determination of calcium, magnesium and zinc salts in oils in which an organic solvent is used as a medium for spraying directly into the flame. Alternatively, preliminary ashing to remove organic matter followed by dissolution of the residue in a mineral acid may beFebruary, 1979 SHORT PAPERS 157 more suitable, but this takes a longer time. The use of organic solvents was studied in this work and the results are compared with those obtained by established methods.Since the work of Allan1s2 and Robin~on,~ organic solvents have been used to increase the sensitivity of atomic-absorption determinations. In addition, the use of organic solutions offers a rapid means of analysis in comparison with conventional atomic-absorption spectro- metric techniques. The most widely used simple solvent is 4-methylpentan-2-one but xylene, cyclohexane, 2,2,4-trimethylpentane and others have also been applied. The use of mixed solvent systems as homogeneous solvents has become more widely used recently.Inorganic salts can be used in these solvent systems as standards instead of the much less readily available, more expensive and less stable organic metal salt solutions. Cyclohexanone - butan-1-01 - ethanol - concentrated hydrochloric acid - water (10 + 6 + 4 + 1 + 1 ) 4 5 5 and 95 parts of 2-methylpropan-2-01 - toluene (3 + 2) plus 5 parts of water6 as both oil- and water-compatible mixed solvent systems and aqueous inorganic salt solutions as calibration solutions were applied by Holding and co-workers. Inorganic salt standards dissolved in dimethyl sulphoxide and a mixed solvent (toluene - glacial acetic acid, 7 + 3 V/V) were used by Guttenberger and Harold' for the determina- tion of different metals using an air - acetylene flame. The atomic-absorption determination of calcium, magnesium and zinc in fresh and used lubricating oils and additives in an air - acetylene flame using inorganic salt standards and a mixed solvent system is described in this paper.Experimental Holding and co-workers' mixed solvent system^^-^ were tried, but with some additives stable solutions were not obtained. Some other mixed solvents, such as toluene or benzene - propan-2-01, methanol or ethanol - water (1 + 3 + 1) and aqueous inorganic salts were also tried as calibration solutions and proved to be good solvents. However, the results were sometimes erratic, because the standards and samples had dissimilar structures. Even the addition of strong mineral acids, e.g., concentrated hydrochloric acid, could not eliminate the system errors of 20-40% relative.A clear-burning flame was obtained with Guttenberger and Harold's mixed solvent system (toluene - glacial acetic acid, 7 + 3 V/V)7 if a lean gas mixture containing very small amounts of fuel (close to the point of extinction of the flame) was used. Inorganic salt standards were dissolved in methanol or ethanol, which are more readily available than dimethyl sulphoxide (used by Guttenberger and Harold7). The following mixed solvents were tried: toluene or benzene - propan-2-01, methanol or ethanol (I + 4 or 1 + 9). These solvents gave a clear-burning flame and seemed suitable for the determina- tion of calcium, magnesium and zinc. However, systematic errors of 2040% relative were noticed. Toluene - glacial acetic acid (1 + 4) had excellent burning characteristics, a low spectral background and good solvent properties for lubricating oils and additives.The addition of glacial acetic acid to the solvent resulted in the elimination of the systematic errors. Apparatus zinc hollow-cathode lamps was used. acetylene flame under the conditions given in Table I. An MOM, Model 190A, atomic-absorption spectrophotometer with calcium, magnesium and The determinations were carried out in an air - Stock Solutions Dissolve appropriate amounts of calcium chloride (CaC1,.2H20), zinc acetate [Zn(CH3C00),.2H,0] and magnesium acetate [Mg(CH3C00),.2H,0] in ethanol to give metal concentrations of 500, 500 and 100 pg ml-l, respectively, and standardise the solutions by complexometric titration.Standard Solutions Add 0.0, 0.1, 0.2, 0.3 and 0.4 ml of the 500 pg.ml-l ethanolic zinc stock solution, 0.0, 0.2, 0.4, . . . and 1.2 ml of the 500 ,ug ml-l ethanolic calcium stock solution and 0.0, 0.2, 0.4,158 SHORT PAPERS Analyst, Vol. 10P TAB:LE I OPERATING CONDITIONS Condition Calcium Zinc Magnesium Wavelength/nm . . . . 422.7 213.8 285.2 Lamp current/mA . . .. 4 4 2.5 Slit width/mm . . .. 0.04 0.04 0.03 Scale expansion . . .. 6x l x 1 x Burner heightlmm . . . . 7 5 5 0.6 and 0.8 ml of the 100 pg ml-l ethanolic magnesium stock solution to 100-ml calibrated flasks, Calibration solutions were prepared for the concentration ranges 0.1-2 pg ml-1 of zinc, 0.25-6 pgml-l of calcium and 0.05-0.8 pg ml.-l of magnesium. Tests were made of the effect of potassium acetate as an ionisation suppressant on the calibration solutions.Linear calibration graphs were obtained, as shown in Fig. 1. Add 20 ml of toluene to each flask and dilute to volume with glacial acetic acid. Zn-- I I I I I 1 .o 1.5 2.0 Mg tr 0.2 0.4 0.6 0.8 I _I. 0 0.5 I I Concentration/pg ml-' Fig. 1. Calibration graphs: x , with alkali metal salt; 0, without alkali metal salt. Sample Solutions mately 0.3 mg of calcium, 0.1 mg of zinc and 0.05 mg of magnesium. and stir the solution. acid and dilute to volume with glacial acetic acid. Weigh into a 50-ml beaker an amount of lubricating oil or additives containing approxi- Add 20 ml of toluene Transfer the solution into a 100-ml calibrated flask with glacial acetic Results anti Discussion It is evident that there are certain factors (solvent, inter-element effects, etc.) that can be subject to severe interference, the magnitude of which is dependent on the solvent used.When toluene and glacial acetic acid mixed solvents were used the interferences that result in differences between standards and samples were removed. Potassium acetate was added as an ionisation suppressant to the mixed solvent. However, the effects of the ionisation suppressant on sensitivity were negligible. No inter-element effects were found in the determination of calcium and magnesium. Similarly to organic solutions, organophosphakes had no effect on the determination of these elements when mixed solvents were used, as has been established for organic solvents by Holding and Matthews.5 According to our experience, the addition of ethanol (maximum concentration 1.5% V/V) to the mixed solvent with the standards caused no interference.February, 1979 SHORT PAPERS 159 I 1 L .d 0.1 0.2 0.5 1 .o 1.5 2.0 Oil concentration, % V/V Fig. 2. Effect of oil on absorbance: A, 1.0 pg ml-1 of zinc; B, 2.0 pg ml-1 of calcium; C, 0.2 pg ml-1 of magnesium. The effects of increasing amounts of oil in the mixed solvent at a constant metal concentra- tion on the absorbance are shown in Fig. 2. The results indicate that the addition of oil to the mixed solvent system during calibration is not necessary. Different types of lubricating oils and additives were examined in order to compare the results of the determination of metals by three different techniques : direct determination by atomic-absorption spectrometry, atomic-absorption spectrometric determination after ashing and determination by chemical methods.The results of the comparative determinations are given in Table 11. TABLE I1 COMPARISON OF RESULTS OF ANALYSES FOR CALCIUM, MAGNESIUM AND ZINC IN LUBRICATING OILS AND ADDITIVES Found, % ntlm Sample Element number Calcium . . .. 1 2 3 4 Zinc . . .. 10 11 12 13 14 15 16 17 18 Magnesium . . 19 20 21 22 Other elements of interest present - P P P Mg Mg Mg, Zn, p Ca, Mg, p P P P P, Ba P, Ba P, Ba P, Ba, unknown P, Ba, unknown Ca, Zn, P Ca Ca Ca * t = complexometric titration after ashing; g analysis; 1 = literature value. 1 Established methods* 15.20 (t, g) 4.70 (t) 5.90 (t) 2.70 (t) 10.60 (t) 6.75 (t) 1.41 (1, t) 5.30 (t) 1.65 (1, t) 2.70 (t) 7.80 (t, p) 0.075 (t) 0.056 (p) 0.061 (t) 0.039 (t) 0.031 (t) 12.00 (t) 3.60 (g) AAS on aqueous solution after ashing 11.90 15.05 4.65 5.85 2.80 10.60 6.70 1.40 - \ AAS using organic mixed solvent system 11.95 15.20 4.7 5.85 2.75 3.65 10.65 6.72 1.40 - 5.40 - 1,66 2.65 2.70 7.85 7.85 - 0.075 0.056 0.056 0.061 0.060 0.039 0.040 - 0.030 0.86 (1, t) 0.87 0.87 0.50 (t) 0.51 0.49 0.25 (t) 0.26 0.25 - 0.04 0.04 gravimetric analysis after ashing ; p = polarographic160 SHORT PAPERS Analyst, Vol.104 The relative standard deviations calculated for ten replicate measurements were 1.5% for zinc a t the 1.0 pg ml-l level, 2.0% for calcium at the 3.0 pg ml-l level and 1.5% for magnesium at the 0.5 pg ml-l level. References 1 . 2. 3. 4. 5. 6. 7. Allan, J . E., Nature, Lond., 1959, 184, 1195. Allan, J. E., Spectrochim. Acta, 1961, 17, 467. Robinson, I . W., Analytica Chim. Acta, 1960, 23, 479. Holding, S. T., and Noar, J. W., Analyst, 1970, 95, 1041. Holding, S. T., and Matthews, P. H. D., Analyst, 1972, 97, 189. Holding, S. T., and Rowson, J. J . , Analyst, 19175, 100, 465. Guttenberger, J., and Harold, M., 2. .4naZyt. Chenz., 1972, 262, 102. Received Jaizuary 31st, 1978 Accepted July 13th, 1978

ISSN:0003-2654    

DOI:10.1039/AN9790400156

出版商:RSC    

年代:1979

数据来源: RSC

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SHORT PAPERS Analvst. Vol. 104 Spectrophotometric Determination of Iron by Synergistic Extraction with lsonitrosobenzoylacetone and Pyridine B. J. Desai and V. M. Shinde Department of Chemistry, Shivaji University, Kolhap ur 416 004, India Keywords : Synergistic iron extraction ; ivon determination; spectropkotometry ; alloy analysis ; isonitrosobenzoylacetone Isonitrosobenzoylacetone (H-INBA) has been used €or the extractive spectrophotometric determination of palladium and ruthenium.l In this paper we describe a simple method for the synergistic extraction of iron(I1) from an aqueous solution a t pH 4 by using H-INBA in combination with pyridine. The extracted blue complex is suitable for the spectrophoto- metric determination of iron at 590 nm. Experimental Apparatus Absorbance measurements were made 011 a Zeiss, Model 738636, spectrophotometer, using 1-cm silica cells and pH measurements were made on a Philips pH meter (precision t Y Pel - Reagents Standard iron(I1) solution, 5 mg ml-1.Prepared by dissolving 3.51 g of analytical-reagent grade ammonium iron(I1) sulphate in 100ml of distilled water containing 1% of sulphuric acid and standardised titrimetrically.2 Soh tions of lower concentration (50 pg ml-1) were prepared by appropriate dilutions of the stock solution. Equal volumes of 0.8 M pyridine in benzene and 0.25% m/V H-INBA in benzene. Extraction solution. Sodium thiosulphate solution, 2.5% m/V. Sodium hydroxide solution, 1 M. Hydrochloric acid, 1 M. All other reagents were of analytical-reagent grade. General Procedure To an aliquot of solution containing 50 pg of iron(I1) add 1 ml of 2.5% aqueous sodium thiosulphate solution in order to prevent atimospheric oxidation of the iron and adjust the pH of the solution to 4, in a total volume of 25 ml, with 1 M hydrochloric acid or 1 M sodiumFebruary , 1979 SHORT PAPERS 161 hydroxide solution.Transfer the solution into a separating funnel and shake with 10ml of extraction solution (5 ml each of 0.25% H-INBA and 0.8 M pyridine solutions in benzene) for 2 min. After separation of the phases measure the absorbance, a t 590 nm, of the organic layer against a reagent blank prepared in the same manner and calculate the iron content from a calibration graph obtained by following the above procedure. The calibration graph gave a straight line over the range 20-120 pg of iron per 10 ml of organic phase, indicating that Beer's law is obeyed over this range.Results and Discussion The absorption spectrum of the iron(I1) - INBA complex extracted with pyridine at pH 4.0 Addition Pyridine thus exerts a syner- is shown in Fig. 1. of pyridine caused quantitative and rapid extraction of iron. gistic effect on the extraction of the iron(I1) - INBA complex. In the absence of pyridine the complex was not extracted. 460 540 620 700 Wavelengthhm Fig. 1. Absorption spectrum of complex from 50 pg of iron(II), ti ml of 0.25% H-INBA in benzene and 5 ml of 0.8 M pyridine in benzene, measured against reagent blank. The extraction of the iron(I1) - INBA - C,H,N complex commences at pH 3, becomes quantitative between pH 3.8 and 4.4 and then gradually decreases (Table I).The optimum pH range is therefore between 3.8 and 4.4 In all later work the pH of the aqueous solution was adjusted to 4 in order to ensure quantitative extraction of the complex. The complex is stable for 36 h. The Sandell's sensitivity of the colour reaction is 0.014 pg cm-2 (at 590 nm) with a molar extinction coefficient of 3.79 x lo3 1 mol-l cm-l. TABLE I DISTRIBUTION RATIO OF IRON(II) - INBA - PYRIDINE COMPLEX BETWEEN BENZENE AND AQUEOUS SOLUTION AS A FUNCTION O F PH Fifty micrograms of Fe(I1) extracted into 5 ml of 0.25% H-INBA and 5 ml of 0.8 M pyridine in benzene. Amount of iron extracted PH into benzene, % 3 19.86 3.4 63.23 3.6 83.81 3.8-4.4 100.00 4.6 91.18 4.8 88.22 5 85.29 6 72.06 7 59.24 Distribution ratio (D) 0.61 4.29 12.94 25.84 18.73 14.50 6.44 3.63 co162 SHORT PAPERS Analyst, Vol. 104 The concentrations of H-INBA and pyridine were varied from 0.05 to 0.25% and from 0.1 to 1 M, respectively.It was found that a single extraction with 5 ml each of 0.25% H-INBA and 0.8 M pyridine is sufficient for quantitative extraction of 20-120 pg of iron. The graph of log D (distribution coefficient) 'O~:YSUS log C (H-INBA concentration) a t constant pyridine concentration has a slope of 1.73. Similarly, the graph of log D veyszGs log C (pyridine concentration) at constant H-INBA has a slope of 2.3. Hence the probable composition of the extractable species is Fe( I NBA),.2C6H,N. This composition is analogous to that formed in other synergistic extractic~ns.~-' The extraction reaction, therefore, can be expressed as Fe(H,O),,+ + 2H-INBA f Fe(INBA),.2H20 + 2H+ + 4H20 Fe(INBA),.2H20 + 2C,H,N + Fe(INBA),.2C6H,N + 2H20 Solvents such as toluene and xylene can also be used for the extraction of iron.Similarly, other bases such as /3-picoline can be used as a substitute for pyridine. The precision of the method was checked by measuring the absorbance at 590 nm of six samples each containing 20, 40, 50 and 60 pg of iron. The standard deviation of the mean absorbance was found to be 0.003 1 for 50 pg of iron. The coefficient of variation was 0.93%. The results in Table I1 show that tbe precision of the method is satisfactory. PRECISION OF THE METHOD Amount of Mean absorbance Standard Coefficient of ironlpg (6 determinations;) deviation variation, yo 20 0.135 0.001 5 1.17 40 0.27 0.001 5 0.58 50 0.34 0.003 1 0.93 60 0.405 0.003 5 0.87 Separation and Determination of Iron in Synthetic Mixtures Iron is found in association with other metals such as chromium, molybdenum, tungsten, manganese, nickel, copper, lead, cobalt, zinc, vanadium, aluminium and titanium in aluminium-, cobalt-, nickel-, titanum- and zinc-based samples.The proposed method for the spectrophotometric determination of iron in synthetic mixtures is made more specific by selective extraction of iron(II1) with 4-methylpent-3-en-2-one (mesityl oxide)* from a 5 M hydrochloric acid solution. To iron (5 mg), and the cations mentioned above, in a 10-ml flask is added an adequate amount of concentrated hydrochloric acid t o give the desired acid concentration ( 5 ~ ) in a total volume of 10 ml.The solution is then. extracted for 2 min with 10 ml of pure mesityl oxide. This transfers only iron into the organic phase and other cations remain in the aqueous phase. After the separation of the two phases, iron is removed from the organic phase by extraction with two 20-ml portions of water, and these are combined and diluted TABLE 111 DETERMINATION OF IRON IN SYNTHETIC MIXTURES All results are the means of 3 determinations. Composition of the mixturelnig Fe, 5; Mn, 0.6; W, 0.5 . . .. .. .. Fe, 6 ; Cu, 1; Zn, 1; Pb, 0.5 . , .. .. Fe, 5; Mn, 0.5; Ni, 1; Cr, 0.5; Cu, 2; Mo, 1 . . Fe, 6 ; Al, 5 ; V, 0.6 . . .. .. .. Fe, 5; Al, 1; Cu, 1; Mo, 0.5 . . .. .. Fe, 6 ; Cu, 1; Mn, 0.5; Ti, 1; Zn, 3; Ni, 1; Cr, 0.5 Fe, 5; Ni, 1; Cu, 1; Mn, 0.5; Co, 2; Cr, 0.5; V, 0.5 Amount of iron recovered, yo .... 99.12 .. .. 98.80 .. I . 98.8 .. .. 99.12 .. .. 99.12 .. .. 98.8 .. .. 98.57 Relative error, yo 0.88 1.20 1.20 0.88 0.88 1.20 1.43February, 1979 SHORT PAPERS 163 to 50 ml. An aliquot of this solution containing 50 pg of iron is taken and iron is spectro- photometrically determined as described under General Procedure. Ions such as uranium, palladium, ruthenium(III), gold(III), EDTA, citrate, tartrate and phosphate also do not show any interference. The results of the analysis of seven synthetic mixtures are shown in Table 111. The recovery of iron is greater than 98.9%. Determination of Iron in Steel, Copper-based Alloy and Aluminium Alloy Two steel samples (NBS 33 b and c ) , one brass (NML 41) and one aluminium alloy were dissolved9 and then the proposed method was applied to the separation and determination of iron.The results obtained are shown in Table IV. TABLE IV ANALYSIS OF STANDARD SAMPLES Iron content, yo A Composition, elements other than Relative Sample iron, yo Declared Found error, yo C, 2.24; Si, 2.0; P, 0.11; S, 0.03; Rln, 0.64; Ni, 2.24; Cr, 0.61; 1 33 b* Mo, 0.40 . . .. .. . . 91.7 92.0, 92.0, 91.0 0.10 Mn, 0.86; Ni, 1.98 .. . . 91.0 91.2, 91.2, 91.4 0.21 33 c* C, 3.31; Si, 1.88; S, 0.06; P, 0.11; 41 Rrasst Pb, 2.35; Zn, 40.65; Cu, 56.9 . . 0.009 0.0088, 0.0086, 0.009 2.22 Aluminium alloy Ni, 2.12; Mn, 1.7; Cu, 4.0; * Sample from the National Bureau of Standards. t Sample from the National Metallurgical Laboratory.remainder A1 . . .. . . 0.03 0.031, 0.030, 0.028 3.33 Conclusion The proposed method for the spectrophotometric determination of iron is simple and rapid. A scheme for the separation of iron from manganese, copper, zinc, lead, nickel, chromium, molybdenum, tungsten, aluminium and vanadium has been reported. The results are accurate and the wide applicability of the method has been demonstrated by the satisfactory analysis of a variety of samples. The authors thank the CSIR (New Delhi) for providing a fellowship to one of them (B. J. D.). References 1. 2. 3. 4. 5. 6. 7. 8. 9. Desai, B. J., and Shinde, V. M., Mikrochim. Acta, in the press. Vogel, A. I., “Text Book of Quantitative Inorganic Analysis,” Third Edition, Longmans, London, Testa, C . , Analytica Chim. Acta, 1961, 25, 525. Akaiwa, H., Kawamoto, H., and Hara, M., Analytica Chim. Acta, 1969, 43, 297. Oi, N., J . Chem. SOG. Japan, 1954, 75, 1067. Patil, S. P., and Shinde, V. M., 2. Analyt. Chem., 1973, 265, 349. Patil, P. S., and Shinde, V. M., Mikrochim. Acta, 1977, 1, 151. Shinde, V. M., and Khopkar, S. M., Sep. Sci., 1969, 4, 161. Patil, P. S., and Shinde, V. M., Analyst, 1978, 103, 79. 1957. Received June 21st, 1978 Accepted September 6th, 1978

ISSN:0003-2654    

DOI:10.1039/AN9790400160

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

164 SHORT PAPERS Analyst, Vol. 109 Potentiometric Method for the Rapid Determination of Sulphate in the Presence of Chromium(V1) R. Prasad* Inco Europe Limited, European Research and Development Centre, Wiggin Street, Birmingham, B 16 OA J Keywords: Sulphate determination; barium ion-selective electrode; chrom- ium( V I ) ; potentiometry Control of the ratio of chromium(V1) to sulphate is essential for the effective working of chromium(V1) - sulphuric acid electrochemical systems, such as those used for the colouring of stainless steel or the deposition of chrorniurn, requiring rapid and frequent determinations of sulphate, if the optimum properties of the chromium bath are to be maintained. Widely used methods in industry depend on the principles reported by Willard and Schneidewindl and Richards and Parker,2 although it has long been realised that these time-consuming procedures must be followed exactly if reliable results are to be obtained, as these precipita- tion procedures are susceptible to both positive and negative errors.An application of a barium(I1) ion-selective electrode is described that permits the rapid determination of sulphate in the presence of chromium(V1). Ascorbic acid is used to reduce chromium(V1) and to complex chromium(II1). The sulphate ions are then determined by titrating with barium(I1) perchlorate. The end-point is determined by following the course of the titration potentiometrically using one of the recently reported electrodes3,* that are selective to barium(I1) ions as the indicator electrode, in combination with the saturated calomel electrode.Experimental All of the reagents were of analytical-reage:nt grade. L-ASCOY~~C acid. Sodium hydroxide solution, 30% m/V. Barium(II) perchlorate solutions, 0.05 and 0.02 M in water - propan-2-01 (3 + 1). Propan-2-01, Reagents Apparatus It was used with the following cell system: Hg - Hg2C12, saturated KCl I sample solution I membrane, 10-2 M BaCl,, AgCl- Ag. The barium(I1) ion-selective electrode was constructed as described by Jaber et al.3 and was used in combination with the calomel electrode. Measurements were made with a pH meter with a precision of k l . 0 mV. Procedure Take an aliquot of the sample containing not more than 40-50 mg of either chromium(V1) or chromium(II1) and not less than 2-3 mg of sulphate ions. Dilute to about 100 cm3 and add about 0.5 g of ascorbic acid.When this has dissolved, adjust the pH to about 3.5 with 30% m/V sodium hydroxide solution and a.dd about 20 cm3 of propan-2-01. Titrate the solution potentiometrically with the appropriate barium(I1) perchlorate solution, previously standardised against standard sulphuric acid. If the amount of chromium exceeds 50mg, remove the excess by adjusting the pH of the aliquot to about 10 with sodium hydroxide solution and swirling for about 2-3min with the appropriate amount of silver(1) benzoate [l g of chromium(V1) requires 5 g of silver benzoate]. Filter, wash the precipitate with 2-3 portions, each of 15 cm3, of water and add the washings and the filtrate to about 50cm3 of a strong cation-exchange resin * Present address : Rachho Pharmaceuticals and.Chemicals, 104-A Vishal Bhawan, 95 Nehru Place, New Delhi-110019, India.Fe bmary , I 9 79 SHORT PAPERS 165 (H+ form) in a beaker and percolate for about 5min to remove silver and sodium ions. Filter and wash the resin with water into a 150-cm3 tall-form beaker, add 0.5 g of ascorbic acid and continue as described above. Results and Discussion It was observed that the response of the electrode did not follow the Nernst equation, giving a slope of approximately 20 mV instead of 29 mV at 20 "C for a ten-fold change in barium-ion activity. However, preliminary titration of sulphuric acid at a pH of about 3.5 in propan-2-01- water gave reproducible results (h0.02 cm3 of both titrants for 2-60 mg of sulphate ions).The precision and accuracy of the sulphate determinations deteriorated sharply in the presence of chromium(II1). Although several commonly cited reductants were used in order to reduce chromium(V1) to chromium(II1) and overcome possible inter-ion interference, the results were always low and erratically irreproducible (Table I). These discrepancies were ascribed to the slow dissociation of a chromium(II1) - sulphate complex in a slightly acidic environment, preventing the complete precipitation reaction between sulphate and barium(I1) ions. TABLE I EFFECT OF CHROMIUM(III) ON THE DETERMINATION OF SULPHATE Method of reducing chromium(V1) to . . chromium (111) Hydrochloric acid - acetic acid - ethanol Hydrochloric acid - ethanol . . .. .. Acetic acid - ethanol .. .. .. .. Ethanol .. .. . . .. .. Hydrogen peroxide . . . . .. .. Sodium nitrite . . .. .. .. .. Amount of sulphate/mg Theoretical potentiometry I A -i Found by .. 7.77 5.25 3.96 4.36 .. 7.77 5.47 0.42 .. 7.77 3.42 5.91 .. 7.77 3.49 5.14 .. 7.77 6.35 4.13 .. 7.77 4.95 3.75 Accurate recovery of sulphate, however, was achieved when L-ascorbic acid was used as a reducing agent (Table 11). It is tentatively assumed that after reducing chromium(V1) to chromium(III), identified by the redox titration, the L-ascorbic acid (or its oxidation product, dehydroascorbic acid) complexes with chromium( 111) ions and thus prevents any complex formation between Cr3+ and SO,2- ions. This assumption is supported by the work of TABLE I1 REDUCTION AND MASKING OF CHROMIUM WITH ASCORBIC ACID Amount of chromium/mg 10 10 20 20 20 20 20 40 40 50 Amount of ascorbic acid/mg 50 150 220 250 300 200 200 400 500 500 Amount of sulphate/mg -h-----7 Found by the Theoretical proposed method* 2.35 2.35 2.35 2.35 2.35 2.35 2.35 2.35 2.35 2.35 6.70 6.70 7.77t 7.96 9.40 9.35 9.40 9.45 11.75 11.72 * Mean of three measurements.t Gravimetric measurement.166 SHORT PAPERS Analyst, Vol. 104 0 1 2 3 4 5 6 Tit rant vol u me/cm3 Fig. 1. Potentiometric titration of 6 mg of sulphate in the presence OC 40 mg of chromium(VI), with 2 x &I barium(I1) perchlorate. Piibil and VeselS;,5 who used ascorbic acid to mask chromium(II1) in calcium - EDTA titrations. A typical potentiometric titration curve obtained by the described procedure is presented in Fig.1. Iron and nickel ions atnd excess of ascorbic acid did not interfere in the determination of sulphate by the proposed potentiometric method (Tables I1 and 111). A sharp decline in the electrode performance was noted when the aniount of chromium(V1) and/or chromium(II1) was in excess of 50mg. Elucidation of this observation could not be attempted owing to the absence of chemical data on the chromium - ascorbic acid system and selectivity coefficients of the barium electrode in such a mixed system. TABLE I11 DETERMINATION OF SULPHATE IN THE PRESENCE OF CHRORIIIUhl(VI) Amount of sulphate/ mg r 7 Found gravi- Found by the 2- Theoretical metrically proposed method 7.77 8.07 8.03 7.93 8.03 7.90 7.83 7.96 8.06 13.84 14.00 13.79 13.80 43.68 44.13 44.67 38.10 37.10 38.22 37.20 37.25* 36.91 24.12 24.69 24.03 24.69 24.64 * After recrystallising the preceding precipitate, in sulphate were determined by gravinietry.Amount of other ions presentlmg Iron, 2.24, and ammonium, 0.72 Nickel. 9.28 Nickel, 12.0 Iron, 4.2, and ammonium, 0.72 which 38.22 mg ofFebmary, 1979 SHORT PAPERS 167 Table 111 records some of the results showing the acceptable precision and accuracy of the proposed procedure, which can be completed in about 10min compared with the much longer time required for the gravimetric procedure.6 The author is indebted to Inco Europe Limited for permission to publish this paper. References 1 . 2. 3. 4. 5. 6. Willard, H. H., and Schneidewind, R., Trans. Am. Electrochem. SOC., 1929, 56, 333. Richards, T. W., and Parker, H. G., Proc. Am. Acad. Arts Sci., 1895196, 31, 67. Jaber, A. M, Y., Moody, G. J., and Thomas, J. D. R., Analyst, 1976, 101, 179. Guggi, M., Pretsch, E., and Simon, W., Analytica Chim. Acta, 1977, 91, 107. Pfibil, R., and Veself, V., Talanta, 1961, 8, 565. “Chromium Plating,” Robert Draper Ltd., London, 1954, p. 488. Received March 31st, 1978 Accepted September 20th, 1978

ISSN:0003-2654    

DOI:10.1039/AN9790400164

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

FebrNary, 1979 SHORT PAPERS 167 Determination of Thiocyanates by Thermal Decomposition of Silver Thiocyanate A. Cyganski and T. Majewski Institute of General Chemistry, Technical University, ul. Zwirki 36, 90-924, Ld&, Poland Keywords : Thiocyanate determination ; thermal decomfiosition of silver thio- cyanate ; halide and thiocyanate determinatiofi Thiocyanates, in the form of silver thiocyanate, cannot be determined by most methods in the presence of other anions that form insoluble precipitates of silver salts, but they can be determined by thermal analysis as silver thiocyanate in the presence of halogen anions. Alternatively, a thiocyanate and either an iodide, a bromide or a chloride can be deter- mined. The method is relatively simple; the apparatus required is a furnace fitted with temperature control equipment in which a silica vessel containing a porosity 4, sintered-glass crucible and precipitate can be heated. Thermal Decomposition of Siver Thiocyanate Experimental A PparatzGs The thermal decomposition studies were carried out using a derivatograph (MON OD 102/ 1500 "C) with a-alumina as the inert substance.Other operating conditions were : Tmax. 1000 O C , heating-rate 5 "C min-l, differential thermal analysis (DTA) sensitivity 1/20, thermogravimetric (TG) sensitivity 200 mg, differential thermogravimetric (DTG) sensitivity 1/15 and mass of sample 250 mg. The X-ray diffraction analysis of the sinters produced by heating silver thiocyanate was carried out with a DRON-1 X-ray analyser using copper radiation and a nickel filter.The intensites of the reflections were measured with a scintillation counter. Diffractograms were recorded with an automatic recorder for 28 angles from 2 to 70". Thermal analysis Fig. 1 shows thermal curves for silver thiocyanate. Four transformations are represented on the DTA curve, two exothermic ones caused by loss of mass and two endothermic ones. An exothermic transformation follows immediately after the first endothermic peak.168 SHORT PAPERS Analyst, Vol. 104 Study of sinters from silver thiocyanate In order to examine the course of the reactions, sinters from the silver thiocyanate under investigation were prepared under conditions similar to those of the derivatographic deter- mination. Weighed samples of the salt (250 ing) were heated at a rate of 5 "C min-l to the temperatures determined from the thermal analysis curve, i.e., 280 and 600 "C.The loss in mass of each sinter was verified by comparison with the values from the TG curve. Chemical analysis The amount of sulphur in sinters was determined by fusion with sodium peroxide and sodium carbonate. Sulphates were deterimined after dissolving the product in hot dilute hydrochloric acid (1 + 5). Silver was determined by dissolving the sinters in hot dilute nitric acid (1 + l), evaporating the solution to dryness, dissolving the residue in water and determining silver as silver chloride. Sulphur dioxide was absorbed in 0.1 M tetrachloromercurate(II), [HgCl,] 2-, solution. Carbon dioxide was determined gravimetrically by absorption in Ascarite.Nitrogen was determined by the Dumas method, Korbl'sl reagent being used as an auxiliary oxidant. The composition of the gaseous products obltained at 600 "C was also determined. X - m y difraction analysis In Fig. 2 the X-ray diffraction pattern of silver thiocyanate and of its sinters obtained at 280 and 600 "C is presented. X-ray diffraction, patterns of silver thiocyanate and its sinters were made. DTG B C D T A j & ' , I 200 400 600 800 Temperatu re/O C Fig. 1. Thermal curves for silver thiocyanate; A, 280 "C; B, 600 "C; and C, 900 "C. O 28 Fig. 2. X-ray diffraction patterns of silver thiocyanate (a) and its sinters prepared at 280 "C (b) and 600 "C ( c ) . Results and Discussion The first exothermic transformation at 280 "C corresponds to the reaction 5AgSCN + 20, = 214gCN.3AgSCN + 2S0, .. .. * . (1) This reaction is indicated by the loss in mass, the content of sulphur in the sinter and especially by the amount of sulphur dioxide formed (Table I).February, 1979 SHORT PAPERS TABLE I DETERMINED AND CALCULATED COMPOSITION OF THE PRODUCTS FORMED DURING DECOMPOSITION OF SILVER THIOCYANATE AT 280 " c 169 Calculated values for- A Determined I 1 Parameter value, yo 3AgCN.3AgSCN, % AgCN.AgSCN, yo Mass loss . . .. 8.56 8.09 9.67 Ag content . . . . 69.74 70.72 71.95 S content . . . . 11.76 12.61 10.69 SO, content . . . . 14.85 15.54* 19.307 * SO, content calculated according t o equation (1). 7 SO, content calculated according t o equation (2). The AgCN.AgSCN compound was described by Duval.2 This compound was formed in accordance with the reaction 2AgSCN + 0, = AgCN.AgSCN + SO, .. .. - * (2) The calculated mass loss corresponding to the formation of the compound is 9.67y0, the sulphur content is 10.69% and the amount of sulphur dioxide released is 19.30%. The determined figures are 8.56, 11.76 and l4.85%, respectively (Table I). A compound of the general formula xAgCN.yAgSCN is probably formed during thermal decomposition of silver thiocyanate; x and y can vary, depending on the conditions under which the sinters are obtained, e.g., during thermal decomposition of Bi(SCN) a compound of the formula Bi(CN),.5Bi(SCN) was formed.2 The second transformation corresponds to the formation of silver sulphide at approxi- mately 600 "C, according to the equation 2(2AgCN.3AgSCN) + 60, = 5Ag,S + SO, + 5C0, + 5N, . .- (3) By adding equations (2) and (3) an equation for the decomposition of silver thiocyanate at 600 "C is obtained: 2AgSCN + 20, = Ag,S + SO, + 2C0, + N, Such a course for the reaction is proved by mass loss [28.00% as found on the TG curve, 27.73% as calculated from equation (4)], the presence of Ag,S, found diffractometrically, and the composition of gaseous products. The determined sulphur dioxide content is 19.15y0 and that calculated from equation (4) is 19.30%. The corresponding figures for carbon dioxide and nitrogen are 25.10 and 26.52y0, and 8.23 and 8.44y0, respectively. A by-product of the reaction is silver sulphate, formed as a result of oxidation of the sulphide. The increase in mass, occurring at 620 "C, is caused by the formation of silver sulphate.The presence of this compound was established diffractometrically (Fig. 2). Subsequent mass loss occurring at 850 "C is caused by the decomposition of silver sulphate and forma- tion of metallic silver. The peak occurring on the DTA curve at 970 "C corresponds to the melting-point of silver. This reaction is indicated by the presence of 4.12% of sulphate in the sinter. Determination of Thiocyanates Experimental Principle Silver thiocyanate was decomposed by heating at 600 "C and the sulphur dioxide formed was absorbed in sodium tetrachloromercurate(I1) solution when the following reaction occurred4 : [HgC1J2- + 2S0, + 2H20 = [Hg(S0.J2l2- + 4H+ + 4C1- . . - (5)170 SHORT PAPERS Analyst, Vol. 104 The liberated hydrochloric acid was titrated with 0.1 M sodium hydroxide solution and the amount of SCN calculated according to equation (4).Apparatus Furnace Jitted with temperature control. Rotameter. Bubblers to absorb liberated gases. Reagents and 11.7 g of sodium chloride in water and dilute to 1 1. Sodium tetrachloromercurate(II) solution, 0.1 M. Nitric acid, dilute (1 + 2). Silver nitrate solution, 0.1 M. Sodium chloride solution, 0.1 M. Potassium bromide solution, 0.1 M. Potassium iodide solution, 0.1 M. A mmonium thiocyanate standard solution, 0.1 M. Sodium hydroxide standard solution, 0.1 M., Dissolve 27.2 g of mercury( 11) chloride Procedure One millilitre of nitric acid (1 + 2) was added to 150 ml of the neutral solution containing thiocyanates and, possibly, halogen anions.The solution was heated to boiling and then, with stirring, 0.1 M silver nitrate solution was added dropwise. The solution containing the precipitate was maintained at the boiling-point for 3 min and then cooled and kept in the dark until the precipitate had settled. The precipitate was filtered through a porosity 4, sintered-glass crucible, washed with water, then with ethanol and dried. The crucible and contents were placed in a fused silica vessel through which a current of air (10 1 h-l) could be drawn, and the vessel and contents placed in a crucible furnace. The air, after leaving the silica vessel, was passed through three bubblers, each containing 25 ml of 0.1 M sodium tetrachloromercurate(I1) solution. If the amount of thiocyanate taken was more than 85.26 mg the number of bubblers was increased to four.The temperature of the furnace was increased to 600 "C while maintaining the flow of air. The solution from the bubblers was then transferred into a 250-ml conical flask and titrated with 0.1 M sodium hydroxide solution, using methyl red as indicator. T.ABLE I1 DETERMINATION OF THIOCY ANATES BY THERMAL PROCEDURE Amount of thiocyanatelmg Taken Found Error, yo 113.4 112.7 - 0.6 85.03 85.31 - 0.3 56.42 55.6 - 1.4 28.34 28.2 -0.5 14.17 14.25 -0.6 5.67 5.62 - 1.0 T.ABLE I11 DETERMINATION OF MIXTURES OF THIOCYANATES AND IODIDES Amount of thiocyanatelmg Amount of iodidelmg - - Ratio of Taken Found Error, % Taken Found Error, yo SCN to I 5.69 6.64 -0.87 12.68 12.75 +0.55 1 : 2.23 14.22 14.35 +0.91 126.8 125.8 -0.78 1 : 8.9 28.45 28.20 -0.87 126.8 128.8 + 1.56 1 : 4.45 56.91 56.42 - 0.86 126.8 128.2 + 1.10 1 : 2.23 85.27 83.98 + 1.51 253.7 258.0 + 1.69 1 : 2.97February, 1979 SHORT PAPERS 171 The results of the determination of thiocyanates are shown in Table 11.Table I11 gives the results of the determination of thiocyanates by the thermal method and iodides by weighing silver iodide and silver thiocyanate. Table IV gives the results of determinations of thiocyanates in the presence of chlorides, bromides and iodides. TABLE IV DETERMINATION OF THIOCYANATES IN THE PRESENCE OF CHLORIDES, BROMIDES AND IODIDES Amount of thiocyanate/mg Amount of halogen in samplelmg n - r \ Taken Found Error, % c1 Br I 17.07 17.03 - 0.23 8.8 19.07 31.7 56.91 56.05 - 1.51 17.71 39.9 63.4 68.29 67.15 - 1.6 35.42 79.9 126.9 85.36 84.25 - 1.3 35.42 79.9 126.9 Conclusion The proposed method is the first thermal method described for the determination of thiocyanates. Thiocyanates, in the presence of chlorides, bromides and iodides, can be determined satisfactorily. It is also possible to determine thiocyanates and one of the halogen anions from the amount of sulphur dioxide produced on heating silver thiocyanide and determination of the mass of the precipitate containing silver thiocyanate and silver halide. It is relatively simple. References 1. 2. 3. 4. Korbl, J., Mikrochim. Acta, 1956, 1705. Duval, C., “Inorganic Thermogravimetric Analysis,” Elsevier, Amsterdam, 1953. Cyganski, A., Roczn. Chem., 1977, 51, 869. West, P. W., and Gacke, G. C., Analyt. Chem., 1956, 28, 1816. Received March 13th, 1978 Accepted July 26th, 1978

ISSN:0003-2654    

DOI:10.1039/AN9790400167

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

172 Analyst, February, 1979, Vol. 104, pp. 172-173 Communication Material f o r publication as a Communication must be on a n urgent matter and be of obvious sciemtific importance. Rapidity of publication i s enhanced if diagrams are omitted, but tables and formulae can be included. Communications should not be simfile claims for pviority: this facility for rapid publication is intended for brief descriptions of wort? that has progressed to a stage at which it i s likely to be valuable to workers facad with similar problems. A fuller paper may be offered subsequently, if justified by later work. Manuscripts aye not subjected to the usual examination by referees and inclusion of a Communication i s at the Editor's discretion. Selective Determination of Arsenic( 1111) and Arsenic(\/) by Atomic-absorption Spectrophotometry Following Arsine Generation Keywords : Arsenic( 111) and arsenic( V ) sdective determ,ination ; atomic- absorption spectrophotometry ; hydride generation The development of a method for the selective determination of arsenic(II1) and arsenic(V) a t the parts per billion (log) level in water is required.In a direct method for the selective determina- tion of arsenic(II1) and arsenic(V) by atomic-absorption spectrophotometry, Aggett and Aspelll determined arsenic(II1) by maintaining a pH of 4-5, and total arsenic by evolution from 5 M hydrochloric acid by the hydride evolution technique with sodium tetrahydroborate(II1). Normally the determination of arsenic in water is carried out on samples adjusted to about pH 1 by the addition of hydrochloric acid immediately after collection to stabilise the solution from possible adsorption to metal hydroxides.Therefore, although the above method is simple and precise, great care is required in adjusting the pH to 4-5. Thus, it is desirable to develop a method for determining arsenic(II1) in the presence of arsenic(V) a t a higher acidity. In the study of arsine generation for atomic-absorption spectrophotometry using sodium tetra- hydroborate(III), the selective evolution of arsine from arsenic(II1) has been found to take place in 0.25 M hydrochloric acid solutions of both arsenic(II1) and arsenic(V) containing appropriate amounts of zirconium(1V) and potassium iodicle. A simple and rapid method is described for the differential determination of arsenic(II1) and arsenic(V) a t the parts per billion level in water utilising this phenomenon.Experimental Apparatus arsenic measurement unit, was similar to that described previously.2 of argon. Reagents water. The atomic-absorption equipment, including a long absorption tube (60 x 1.2 cm i d . ) and Nitrogen was used instead Zirconium solution, 20 mg ml-l. Potassium iodide solution, 20% m/V. Sodium tetrahydroborate(III) solution, 5% m/ V in 0.1 M sodium hydroxide solution. This was prepared by dissolving zirconium oxychloride in Procedure for the Determination of Arst:nic(III) Arsine was generated by injection of 1 ml of sample solution that contained less than 100 ng of total arsenic. A calibration graph was constructed using 0.25 M hydrochloric acid solutions containing 4 mg ml-1 of zirconium(IV), 2% of potassium iodide and 0-100 ng ml-l of arst:nic(III).Procedure for the Determination of Total Arsenic The procedure used was identical with that for the determination of arsenic(III), with the exception that the sample solution was replaced with a 2 M hydrochloric acid solution containing 1% of potassium iodide. The procedure was similar to that published recently.2COMMUNICATION 173 Results and Discussion In the presence of more than 1 nig nil-l of zirconium(1V) at an acidity of less than 2 M hydro- chloric acid, the conversion from arsenic(V) to arsine is more selectively suppressed than that from arsenic(II1) , although arsenic(II1) is partly prevented from being converted into arsine. If 2% of potassium iodide is added after addition of 3-5 mg ml-l of zirconium(1V) in 0.25 M hydrochloric acid, arsenic(II1) is quantitatively recovered and can be determined selectively in the presence of arsenic(V) a t a level of less than 100 ng ml-1 as total arsenic. By this method it is possible to determine arsenic(II1) in the presence of arsenic(V) up to a ratio of arsenic(V) to arsenic(II1) of 6: 1 a t a level of 50 ng ml-l of arsenic(II1) without interference from the arsenic(V).The absorbance begins to decrease slightly from 60 min after addition of potassium iodide in the presence of zirconium(1V). Therefore, it is necessary to measure the absorbance from between 5 and 50 min after the addition of potassium iodide. The determination of total arsenic is carried out on a solution in 2 M hydrochloric acid con- taining 1% of potassium iodide. The amounts of arsenic(V) are calculated from the difference between total arsenic and arsenic(II1) results. The results for the recovery of arsenic(II1) and arsenic(V) in mixtures containing known amounts of standard arsenic(II1) and arsenic(V) are shown in Table I. TABLE I RECOVERY RESULTS Arsenic added/ng ml-' 7 7 A s ( W 4"db"' 0 20 20 20 40 20 60 20 80 40 20 40 40 60 60 40 80 20 40 60 20 Arsenic found/ng ml-1 ----7 As(II1) Total As A;AV) 21 40 19 20 61 41 22 80 58 21 100 79 40 60 20 40 80 40 40 99 59 60 81 21 60 100 40 79 100 21 1 100 References Aggett, J., and Aspell, A. C., Analyst, 1976, 101, 341. Nakashima, S., Analyst, 1978, 103, 1031. 1. 2. Institute for Agricultural and Biological Sciences, Okayama University, Kurashiki-shi, Okayanta 710, Japan Received December 4th, 1978 Susumu Nakashima

ISSN:0003-2654    

DOI:10.1039/AN9790400172

出版商:RSC    

年代:1979

数据来源: RSC