摘要:

520 SHORT PAPERS [Analyst, VOl. 91 SHORT PAPERS Determination of Cyclamate in Soft Drinks by Gas Chromatography BY M. L. RICHARDSON AND P. E. LUTON (John & E. Sturge Ltd., Lifford Chemical Works, Kings Norton, Birmingham 30) A GAS-CHROMATOGRAPHIC procedure has been published by Rees for the determination of sodium cyclamate in soft drinks,l but we have had difficulty in applying this method to soft drinks obtained from several sources. According to Beck2 if the acid content of a solution is greater than that corresponding to pH 0-65, cyclamic acid is formed which, unlike sodium cyclamate, is soluble in the solvents involved in the procedure and hence is discarded by the solvent extraction steps. We have confirmed Beck’s observations, and have also shown that as the organic acid content of these samples varies (often considerably), this must be taken into account, otherwise erroneously low cyclamate values are obtained. In the procedure described by Rees, the cyclohexene produced by the nitrite reaction is determined as a basis for calculating the sodium cyclamate content of the sample.Other products, such as monochlorocyclohexane, cyclohexanone and cyclohexanol (see Fig. 1) are also formed, and this stresses the importance of rigid standardisation in preparing solutions for gas chromato- graphic evaluation, to ensure that thc amount of cyclohexene produced is reproducible. In our modified method, the test solution is acidified with sulphuric acid in preference to hydrochloric acid before i t is reacted with sodium nitrite and this precludes the formation of monochlorocyclohexane.Feig13 also reports that a reaction product is cyclohexanol. The proposed procedure has been applied to three random samples of soft drinks and sodium cyclamate values of 0.30 (0.31), 0.49 (0.50) and 0.21 (0.21) per cent. kvere obtained; values in parenthesis were obtained when the same saniples were analysed by (see ,Vote). Te m pe r a t u r e p r o g r a m me base-line change an alternative method Fig. 1. Gas chromatography showing peaks of: A, cyclo- hexene ; B, monochloroc yclohexane ; C, cyclohexanone ; D, c yclohexanol METHOD APPARATUS- Pye 104 Series model 14 gas chromatograph with flame ionisation detector. Column, 5 ft-10 per cent. polyethylene glycol 400 on 100 to 120-mesh Celite. Carrier gas-45 nil per minute of argon.Hydrogen-45 ml per minute.August, 19661 SHORT PAPERS Air-500 ml per minute. Attenuation-1 x 103. Initial period-3 minutes at 50” C. Temperature programme--16” C per minute to 50” to 120” C. Final period-20 minutes. Chart speed-30 inches per hour (Speedomax W recorder). 52 1 REAGENTS- Sulphuric acid, 10 N. Sodium cyclamate solution, 0-20 per cent. w/v, aqueous. Z i n c acetate solution--Add 21.9 g of zinc acetate dihydrate and 3 nil of glacial acetic acid to Potassium ferrocyanide solution, 10.6 per cent. wlv, aqueous. Light petroteurn, boiling range 30” to 40” C-Analysis by the conditions above should give no peaks corresponding to benzene or cyclohexene. If peaks are obtained, re-distil the light petroleum and collect the fraction distilled a t 30” to 35” C.Light petroleum solution-Add enough benzene (about 2 drops) to 50 nd of the light petroleum, so that on analysis of a l-pl sample with the conditions given above, a benzene peak is obtained, 4 to 5 inches high. water and dilute the solution to 100 ml. Sodium nitrite, 0.5 M. PROCEDURE- Transfer by pipette, 2 nil of sodium cyclairiate solution (0-20 per cent.), 18 nil of water, 2 ml of sulphuric acid (10 N ) , 1 nil of light petroleum solution and 1 ml of sodium nitrite solution into a 25-ml calibrated flask. Stopper the flask, shake the contents for a few seconds and release the stopper carefully. Continue this process for a further 3 minutes until there is no sign of effervescence on releasing the stopper. Add water if required, so that the solvent enters the neck of the flask.By means of a 1-pl syringe, transfer a 1-pl sample of the light petroleum solution to the top of the column and record a chromatogram. Repeat the above process with 4, 6 , 8 and 10 ml of cyclamate solution and 16, 14, 12 and 10 ml of water, respectively. Plot a graph of the area of the cyclohexene peak relative to that of the benzene peak against the concentration of sodium cyclamate. ANALYSIS OF COMMINUTED ORANGE DRINKS- Transfer by pipette, an aliquot of comminuted orange drink containing less than 50 mg of sodium cyclamate (preferably about 25 mg) into a 100-ml beaker, add water to produce a volume of about 40m1, adjust the pH to 0.95 to 1.05 with sulphuric acid and transfer the solution to a 50-ml calibrated flask.Add 1 ml of zinc acetate solution and 1 ml of potassium ferrocyanide solution, shake the mixture well and dilute to the mark with water. Filter the solution through a Whatman No. 90 filter-paper and extract a portion of the filtrate with three 50-ml aliquots of chloroform, and then twice with 25-ml portions of light petroleum. Transfer by pipette, 20 ml of the final aqueous solution, 1 ml of light petroleum solution and 1 ml of sodium nitrite solution to a 25-ml calibrated flask and then complete the determination as described under “Procedure” from “Continue this process” to “record a chromatograni.” Calculate the area of the cyclohexene peak, relative to that of the benzene peak and, by means of the calibration curve, determine the concentration of sodium cyclamate in the original comminuted orange drink. Note-We, however, consider this procedure to be lengthy and it involves the use of expensive instrumentation; in view of this we recommend the much simpler direct procedure described in the following paper (Analyst, 1966, 91, 522). We thank the Directors of John 2% E. Sturge Limited for permission to publish this paper. REFERENCES 1. Rees, D. I., Analyst, 1965, 90, 568. 2. Beck, K. M., Fd Technol., 1957, 11, 156. 3. Feigl, F., “Spot Tests in Organic Analysis,” Sixth Edition, Elsevier Publishing Co., Amsterdam, Received December 3rd, 1965 1960, p. 542.

ISSN:0003-2654    

DOI:10.1039/AN9669100520

出版商:RSC    

年代:1966

数据来源: RSC

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522 SHORT PAPERS [AIzaZyst, Vol. 91 The Determination of Cyclamate in Soft Drinks by Titration with Sodium Nitrite BY M. L. RICHARDSON AND P. E. LUTON (John & E. Sturge Ltd., Lifford Chemical Works, Kings Norton, Birmingham 30) THE present recommended method is based on the reaction- the end-point of which is determined electrometrically. The British Pharmacopoeia 1963l prescribes this reaction for the assay of a number of drugs containing the -NH- grouping, such as benzocaine, dapsone, procaine hydrochloride and suramin. The National Formulary XI12 also uses a similar procedure, but in its First Supplement deletes the use of the electrometric end-point leaving starch - iodide paper as the method of end-point detection. This deletion was carried out so that the analyst is directed to perform the procedure in only one manner, that is, no alternative procedures may be stated in the National Formulary.2 The starch - iodide external indicator procedure has also been recommended for the cyclamate content of comminuted drink^,^ but owing to other constituents present has proved suitable only as a rough check.The proposed method is, however, much simpler and quicker than that earlier described by Rees4 and modified by ourselves.6 -NHSO,- + NO,- -+ + N2, RECOVERIES Various volumes of sodium cyclamate solution (5.00 ml of sodium cyclamate solution c 4.76 ml of 0.1 M sodium nitrite solution) were added to 100 ml of a comminuted drink containing the usual amounts of benzoic acid and saccharin and the solution then acidified with 5 ml of 5 N hydrochloric acid.Recoveries were as follows. Volumes of cyclamate Volume of 0.1 N solution added, sodium nitrite added, Recovery, ml ml per cent. 0 5 15 25 - 0 4-72 99.1 14-45 102.0 23-20 98.3 REPRODUCIBILITY Percentage w/v of Number of Coefficient of variation, Drink sodium cyclamate determinations per cent. A 0-2 1 B 0.38 C 0-58 D 0.29 4 3 3 3 4.5 1.5 < 1.0 < 1.0 EXPERIMENTAL APPARATUS- Titration vessel-Fit a 150-ml beaker with two similar platinum-wire electrodes of 1 mm diameter and 5 cm long, wound in a helix of 0.6 cm diameter and 1 cm long. The electrodes should be about 2.5 cm apart. Clean the electrodes, when necessary, by immersing them for about 30 seconds in boiling concentrated nitric acid containing 0-5 per cent. iron(m) chloride, and then rinse thoroughly in distilled water.l Polarising potential-The circuit is as described in the British Pharmacopoeia1 ; the polarising potential should be adjusted to give the maximum galvanometer response as indicated in Fig.1, which also shows the effect of too high and too low polarising potentials. We found that a polarising voltage of 40 mV was suitable, but stress that the voltage depends on the size, shape and geometry of the electrodes. REAGENTS- Hydrochloric acid, 5 N. Sodium nitrite, 0.1 M-Standardise against sulphanilic acid.'August, 19661 SHORT PAPERS 523 I 0.1 M sodium nitrite, ml - Fig. 1. Selection of polarising potential: curve A, voltage too high (by 10 mV); curve B, voltage ideal; curve C, voltage too low (by 10 mV) PROCEDURE- Transfer 100 ml of comminuted drink to a 150-ml beaker, add 5 ml of 5 N hydrochloric acid, and mix with a magnetic stirrer. Place the electrodes in position and titrate with 0.1 M sodium nitrite solution in suitable increments (in the region of the end-point these should not be greater than about 0-1 ml of titrant), recording the galvanometer readings for each addition. Plot a titration curve and deduce the end-point by extrapolation. Calculate the sodium cyclamate present. Note-The burette jet must be kept below the level of the solution being titrated. We thank the Directors of John & E. Sturge Ltd. for permission to publish this paper. REFERENCES 1. 2. 3. 4. 5. British Pharmacopoeia 1963, p. 1024. National Formulary XII, 1965, p. 68, 362. “Sucaryl Sweetener in Soft Drinks : Technical Information,” &4bbott Laboratories Ltd. Rees, D. I., Analyst, 1965, 90, 568. Richardson, M. L., and Luton, P. E., Did., 1966, 91, 520. Received December 3rd, 1965

ISSN:0003-2654    

DOI:10.1039/AN9669100522

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

August, 19661 SHORT PAPERS 523 The Determination of Ethanolamine and Serine in Phospholipids BY A. J. DE KONING* (Fishing Industry Research Institute, University of Cape Town, Rondebosch, Cape Town, South Africa) THE quantitative analysis of phospholipids is frequently based on the determination of the products they yield on hydrolysis, e . g. , choline from lecithins and sphingomyelins, and ethanolamine together with serine from cephalins. Several methods for the determination of ethanolamine and serine are described in the literature. For instance, periodate oxidation has been described by Dittmer, Feminella and Hanahan,l and paper-chromatographic determinations have been studied by Levine and Chargaff2 and also by Magee, Baker and Th~mpson.~ The paper-chromatographic procedures proved unreliable in our laboratory.This paper describes the determination of ethanolamine (100 to lOOOpg) and serine (100 to 500 pg) by their separation on a cation-exchange resin, and subsequent colorimetric determination with ninhydrin. It is essentially Moore and Stein’s procedure4 applied to a phospholipid hydrolysate and its accuracy is better than 10 per cent. * Present address : University of Basutoland, Bechuanaland and Swaziland, P.O. Roma, via Maseru, Basutoland, Southern Africa.524 SHORT PAPERS [Analyst, VOl. 91 METHOD REAGENTS- Ethanolanzine-British Drug Houses Ltd. laboratory reagent (assay not less than 99 per cent.). Re-distil in L~UCUO (b.p. 64" C a t 4 mm pressure), nLo 1.4538, (value quoted in the literature,5 1.4539). Serine-DL-Serine, obtainable from the California Foundation for Biochemical Research, served as standard compound.Found : carbon, 34.35 per cent. ; hydrogen, 6-77 per cent. ; C,H,O,N requires carbon, 34.29 per cent.; hydrogen, 6.72 per cent. Stock solution of ethanolanzine and serine-Prepare a solution containing 2.22 mg of ethanolamine and 0.71 mg of serine per ml in N hydrochloric acid. Citrate buffer solutions of pH 3-25, 5.0 and 5.28-These solutions were prepared in 5-litre volumes, adjusted if necessary to the required pH with hydrochloric acid or sodium hydroxide, and stored a t 0" C. Dissolve 105 g of citric acid, 41 g of sodium hydroxide and 52 ml of concen- Dissolve 525 g of citric acid and 200 g of sodium hydroxide in 5 litres of water; Dissolve 122 g of citric acid, 72g of sodium hydroxide and 34ml of concen- Before use, boil the buffer solution for 10 seconds and add 5 ml of Brij solution (prepared by dis- solving 35 g of Brij 35, obtainable from the Atlas Powder Company, in 100 ml of water) per litre. To the buffer of pH 5-28 add 1 g of the disodium salt of EDTA per litre. Cation-exchange resin-The ion-exchange resin used was Ambcrlite C.G.120, type 2 (Fisher Scientific Company). A long column (120 x 0.9 cm) was used for serine and a short column (30 x 0.9 cni) for ethanolaniine determinations. The columns were jacketed and operated a t 50" C. Before use, the columns were washed with 0-2 N sodium hydroxide and then with the appropriate buffer solution (about 25 ml for the short column and 100 ml for the long column).Ninhydrin-Dissolve 2.0 g of ninhydrin (Merck's AnalaR reagent) in 50 nil of Cellosolve and mix with 50 ml of citratc buffer solution of pH 5.0 containing 80 mg of tin(I1) chloride (anhydrous Merck's AnalaR reagent). Store the reagent under nitrogen in a dark bottle and use within 6 hours of preparation. (a) pH 3.25. (b) pH 5.0. (c) pH 5.28. trated hydrochloric acid in 5 litres of water; trated hydrochloric acid in 5 litres of water. PROCEDURE- About 600 mg of a phospholipid was hydrolysed with 25 ml of 2 N hydrochloric acid in a sealed ampoule a t 120" C for 24 hours. The ampoule was opened and the solution filtered. The residual tar was thoroughly leached with hot water and poured into the same filter. After evaporation of the filtrate on a steam-bath, the material was dissolved in 25-0 ml of water in a calibrated flask.Ethanolamine and serine were determined in l-ml and 3-ml aliquots, respectively. DETERMINATION OF ETHANOLAMINE- The hydrolysate containing 100 to 1000 pg of ethanolamine was placed on to the short column and cluted a t 50' C with a citrate buffer of pH 5-28. Fractions of 2 nil were collected with an automatic fraction-collector. Tubes 30 to 80 were treated with 4ml of the ninhydrin solution and the colour was developed a t 100" C for 20 minutes. After appropriate dilution with an iso- propanol- water (3 + 7) mixture, the optical density of the colour was read in an Evclyn colori- meter a t 565 nip. Under the conditions described, ethanolamine was eluted in tubes 50 to 60; the extra tubes served to obtain a blank value for the ninhydrin colour.The optical densities were plotted against tube number, and ethanolamine was determined quantitatively by comparing the peak area with that of a known amount of ethanolaniine, or more conveniently, by means of the optical density factor (see below). Also, a known amount of ethanolamine was usually added to the phospholipid and the percentage recovery determined. DETERMINATION OF SERINE- The hydrolysate containing 100 to 500p.g of serine was eluted on the long column with the citrate buffer of pH 3.25 a t 50" C. Fractions of 1 nil were collected, and tubes 90 to 140 were treated with 2 ml of the ninhydrin reagent and analysed as described for ethanolamine. A serine percentage recovery test was also included.August, 19661 SHORT PAPERS 525 TREATMENT OF A STANDARD MIXTURE- Five ml of the stock solution, i.e., a mixture of 11.10 mg of ethanolamine and 3.55 mg of serine was “hydrolysed” with 25 ml of 2 N hydrochloric acid at 120” C for 24 hours.The reaction mixture was evaporated to dryness and dissolved in 25.0 ml of water in a calibrated flask as des- cribed above. An aliquot of 1 ml was taken for the preparation of a standard ethanolamine chromatogram, and of 2 nil for a serine chromatogram. The optical density factors of ethanolaniine and serine were found by the following expression- c (optical densities- blanks) mg of substance i.e., the optical density per mg of substance. hydrolysate may be readily calculated by means of these factors. The amounts of ethanolamine and serine in a DISCUSSION AND RESULTS The quantitative determination of ethanolamine and serine in phospholipid hydrolysates is complicated by the fact that the phospholipids often contain small amounts of polypeptide im- purities.6 Either rigorous purification of the phosphatide before hydrolysis is necessary, or ethanol- amine and serine must be completely separated from other ninhydrin-reacting substances in the hydrolysate.Accordingly, serine was eluted with the buffer of pH 3-25 on the long column which separates it adequately from its nearest honiologues, threonine and glutamic acid. This treatment also separated serine completely from phosphoryl ethanolaniine and 2-aminoethyl phosphonic acid, compounds which are ninhydrin-reactive and present in hydrolysates of certain phospho- lipid~.~~*~S It should be emphasised here that this separation is not achieved with the short column as described by Dittmer et aZ.l Ethanolamine was treated as a basic amino-acid and was eluted from a short column with the buffer of pH 5-28.The position of ethanolaniine was between histidine and arginine when a mixture of basic amino-acids was separated on this column. Ammonia emerged just after etharlol- amine and formed a double peak with it, Large quantities of ammonia were formed when the TABLE I RECOVERY OF ETHANOLAMINE AND SERINE ADDED TO PHOSPHOLIPIDS Percentage present & Sample amine Serine Ethanol- Hake flesh .. . . 1.60 0-34 Hake liver . . . . 1.83 0.39 Rock lobster (hepato- pancreas) . . . . 1.93 0.36 Rock lobster (roe) .. 1-74 0.10 Percentage added r- amine Serine 1-53 0.32 - 0.10 Ethanol- 0.50 1.05 0.66 - Total percentage determined & arnine Serine 3-07 0-69 - 0-47 Ethanol- 2.42 1.42 2.58 - Percentage recovery - amine Serine 98 105 96 Ethanol - - 100 101 108 - phospholipid mixture was hydrolysed with 6 N hydrochloric acid a t 120’ C (cf. Dittmer et aZ.l). Under our hydrolytic conditions, uiz., 2 N hydrochloric acid a t 120’ C, ammonia formation was negligible. Tablc I shows the results obtained in the analysis of several marine phospholipids. Percentage recovery tests of ethanolamine and serine indicate that thc accuracy of the present method is within 10 per cent. 1. 2. 3. 4. 5. 6. 7. 8. 9. REFERENCES Dittmer, J. C., Feminella, J . L., and Hanahan, D. J., J . Biol. Chenz., 1958, 233, 862. Levine, C., and Chargaff, E., Ibid., 1951, 192, 466. Magee, W. L., Baker, R. W. R., and Thompson, R. H. S., Biochim. Biophys. Acta, 1960, 40, 118. Moore, S., and Stein, W. H., J . Biol. Chem., 1954, 211, 893. Hodgman, C. D., Editor, “Handbook of Chemistry and Physics,” Fortieth Edition, The Chemical de Koning, A. J., Biochim. Riophys. Acta, 1964, 84, 467. Crone, H. D., and Bridges, R. G., Biochem. J . , 1963, 89, 111. Rouser, G., Kritchevsky, G., Heller, D., and Lieber, E., J . Auner. Oil Chem. SOC., 1963, 40, 425. de Konig, A. J., Natuve, 1966, 210, 113. Received August 24th, 1966 Rubber Publishing Co., Cleveland, Ohio, 1968, p. 976.

ISSN:0003-2654    

DOI:10.1039/AN9669100523

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

526 SHORT PAPERS [Analyst, VOl. 91 The Paper Chromatography of Some Purines, Pyrimidines and Imidazoles BY M. N. KHATTAK, N. T. BARKER AND J. H. GREEN (Department of Nuclear and Radiation Chemistry, University of New South Wales, Kensington, Sydney, Australia) QUANTITATIVE determination and separation of various hydroxypurines, amino-hydroxypyrimi- dines and two imidazoles have been attempted by using paper-chromatographic techniques. Few other methods are applicable for their separation. During experiments on the radiation decomposi- tion of nucleic acid constituents the opportunity arose to study the chromatographic behaviour of a number of rather rare compounds. About 24 solvents were tried, and of these the 7 solvent systems which were found more efficient were used. €2, values, absorption maxima and the percentage recoveries of the compounds were found.EXPERIMENTAL COMPOUNDS- The pyrimidines and the three purines (2-hydroxy, 8-hydroxy and 2,8-dihydroxy) were kindly supplied by Professor Adrian Albert, Australian National University, Canberra. Purine,G-hydroxy- purine (hypoxanthine) , 2,6-dihydroxypurine (xanthine) and 2,6,8-trihydroxypurine (uric acid) were commercial products (obtained from British Drug Houses Ltd. and L. Light Laboratories Ltd.). 4-Amino-5-imidazole carboxamide was obtained from Calbiochem (U.S. A.) and 4-amino-5-imidazole carboxamidine was prepared by heating adenine in glacial acetic acid in a sealed tube a t a high temperature.l All the solvents used for developing were analytical-reagent grade. Propanol and butanol were re-distilled in an all-glass apparatus under an atmosphere of nitrogen.DEVELOPING SOLVENT SYSTEMS- The systems used in the investigations, each being freshly prepared, were as given below- (2) butanol- water (86 + 14),2 (ii) propanol- water (77 + 23),3 (iii) butanol- propionic acid - water (43 + 27 + 30),4 (iv) t-butanol- ethyl methyl ketone - formic acid - water (40 + 30 + 15 + 15),5 (v) t-butanol- ethyl methyl ketone - ammonia (15 N) - water (40 + 30 + 10 + 20),5 (vi) isopropanol - hydrochloric acid (10 N) - water (65 + 18.4 + 16-6),8 (vii) ammonium bicarbonate (16 per cent.). APPARATUS- Strips of Whatman No. 1 chromatographic paper (10 x 50 cm) were cut to allow up t o 40 cm for movement of the solvent. A Shandon 20-inch rectangular chromotank 2130 was used throughout the work.An ultraviolet lamp (Philips No. 92123) enclosed in a light-tight box which had a circular hole covered by a Chance glass filter (maximum transmission a t 250 mp) was used to detect the ultraviolet absorbing or fluorescent spots in the chromatograms. Micro-pipettes (Misco type) were used for spotting the solutions on the paper. PROCEDURE- to 1 0 - 4 ~ were applied a t 3-cm intervals on the paper strips. Optimum amounts were up to 5Opg in the spots, each of which had a maximum diameter of 5 mm. All the chromatograms were developed by uni-dimensional descending technique a t room temperature (20" to 25" C), and after development, the chromato- grams were dried by hanging in a fume-hood for 1 hour. Some were further dried in a large oven a t 5OOC. Uric acid spots were not visible in ultraviolet light; however, by spraying the paper with Folin - Ciocalteu's reagent, their positions were found.The marked areas were cut and eluted in a known volume of 0.1 N hydrochloric acid or 0.1 N ammonia solution. The eluates were filtered, and the concentrations were measured in a Beckman DU spectrophotometer at the appropriate A,,,. in 1-cm silica cells. Solutions of the pure compounds a t concentrations of The separated spots were located in the ultraviolet light and marked.August, 19661 SHOKT PAPERS 527 RESULTS AND DISCUSSION The absorption maxima and percentage recoveries are given in Table I. R, values (the mean of 5 experiments reproducible to i0.01) are shown in Table 11, with absorption or fluorescence i n ultraviolet light.There is a gradual lowering of I?, values in the purines. It is to some extent related to the solubilities of these compounds. Purine itself is highly soluble, but when a group (especially hydroxyl) enters a t the 2-position, the resulting product is less soluble. LVhen all the three positions (2, G and 8) are occupied, the compound is completely insoluble. The fact that the R,; values cf tlicse substances are the lowest could be due to their low solubilities. The variations in the RI; values of the pyrimidines and iniidazoles could be explained similarly in terms of the structures and solubilities of these compounds. The results of the chromatographic studies reported in this paper have been used in the identification and measurement of the products formed in the y-radiolpsis of de-aerated aqueous solutions of various nucleic acid constituent^.^^^ TABLE I .4 HSO R PT I 0 N hl A S I 51 A AN I) PE KC E K T ,-ZG E REC OV E K I E S OF <I 0 R.1 PO U N U S C H RO MAT OG R APH E D Compounds Group A- Purine .. . . .. . . .. 2-Hydroxypurine . . . . . . 6-Hydroxypurine (Hypoxanthine) . . 8-Hydroxypurine . . . . . . S,&Dihydroxypurine (Xanthine) . . 2,s-Dihydroxypurine . . . . .. G,8-Dihydroxypurine . . . . . . 2,G,S-Trihydroxypurine (Uric acid) . . 4,5-Dianiino-2-hydroxypyrimidine . . 4,5-Diamino-6-hydroxypyrimidine . . 4,5-Diainino-2,6-dihydroxypyrimidine Grotip R- 2,4,5-Triaminopyrimidine . . . . 4,5,G-Triaminopyrimidine . . . . Gvoup C- 4-Amino-5-imidazole carboxainidine 4-Xmino-5-i1niclazole carboxamide .. .. . . . . . . . . . . . . . . . . . . .. . . . . . . .. . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . Amax.,* m p 260 264 248 280 268 310 267 260 305 257 260 268 263 287 269 Recovery,* per cent. 9 8 95 95 96 80 85 SG 75 so 85 A0 65 65 i 0 S3 * Average of three expriments. TABLE Ii C o m po u n tl s ( 2 ) 3-Hyclroxypurine . . . . . . . . 16 (i-Hydroxypurine (Hypoxantliine) . . 25 S-Hydroxypurinc . . . . . . . . 33 J,G-Dihydroxypurine (Xanthine) . . . . 22 2,tbDihydroxypurine . . . . . . 14 A,8-Dihydroxypurine . . . . . . 30 c ; l o l r p ‘4 -- l’urinc . . . . . . . . . . 60 2,6,8-Trihydroxypurine (Uric acid) . . 5 4,5-Diamino-2-hydroxvpvrimidine . . 7 3,4-Diamino-G-hydroxypyrimid inc . . G 4,S-Diarnino-2,6-dihydro~~p~rimidinc , .0 C V O Z ( ~ B- ?,4,5-Triaminopyrimidine . . . . . . 10 4,5,6-Triami nopyrimidine . . . . . . 11 (;r.onp c- 4-r2mino-5-imiclazole carboxamidine . . 16 4-.!mino-5-imidazole carboxamide . . 23 (ii) 75 3 7 54 (i 3 60 27 3 3 17 31 20 5 33 3 .‘i 22 34 (io) 60 37 5 0 54 32 30 26 14 27 32 6 23 37 42 57 66 40 41 51 37 33 35 23 7 40 5 36 53 35 SS (i) i) (i0 41 41 4 f 43 40 35 2,” 6 3 0 G 3 0 38 41 58 42 zlbsorption 80 Absorption 60 Absorption .?G .4bsorption 35 ilbsorption 60 Fluorescence 40 Absorption 40 -- 4 Fluorescence 60 Fluorescence ~- Fluorescence 55 Fluorescence G4 Fluorescence G2 Absorption $0 Absorption528 1. 2. 3. 4. 5. 6. 7. 8. 9. SHORT PAPERS [Analyst, VOl. 81 REFERENCES Cavallieri, L. F., Tinker, J. F., and Brown, G. B., J . Amer. Chem. Soc., 1949, 71, 3976. Smith, J., and Markham, R., Biochem. J . , 1949, 45, 294. Korn, E. D., Charalampons, F. C., and Buchanan, J . M., J . Amer. Chem. SOC., 1953, 75, 3610. Goodman, M., U.S. Atomic Energy Commission, Report N o . UCRL-1961, September, 1952, 67. Fink, K., Cline, R. E., and Fink, R. H., Analyt. Chem., 1963, 35, 3, 389. Ekert, B., and Monier, R., Nature, 19G0, 188, 309. Hems, G., Archs. Biochem. Biophys., 1959, 82, 437. Khattak, M. N., and Green, J. H., Aust. J . Chem., 1965, 18, 1847. , , Int. J . Radiat. Biol., in the press. -- Received May 28th, 1363

ISSN:0003-2654    

DOI:10.1039/AN9669100526

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

528 SHORT PAPERS The Determination of Total Sulphur in [Analyst, VOl. 81 Soil and Plant Material BY I . A. CHAUDHRY AND A. H. CORNFIELD (Chemistry Department, Imperial College of Science and Technology, London, S . W.7) WHEN many samples of soil or plant material need to be analysed for their total sulphur content, bomb methods and apparatus with combustion trains are hardly suitable. Simple digestion and combustion procedures, in which many different reagents are used, have also been described. Among these reagents have becn oxidising salts, with or without acid, peroxides and sodium bi~arbonate.1~2~~~4 The authors tried most of these reagents and found that the highest values for total sulphur in a number of soils were obtained by using the magnesium nitrate - nitric acid method .4 Potassium chlorate3 usually gave slightly lower total sulphur values.Sodium peroxide, hydrogen peroxide, potassium perchlorate and sodium bicarbonate gave very low values. In the original magnesium nitrate - nitric acid method4 a relatively low combustion tempera- ture (350" C) is used and a long combustion period (overnight) is required, presumably to ensure complete oxidation. In a preliminary test on 3 soils it was found that when a 3-hour combustion period a t either 350" or 550" C was used, total sulphur values were lower than with combustion overnight a t 350" C. The magnesium nitrate was replaced by potassium nitrate, which, used like the magnesium nitrate with nitric acid, was then tested. I t was found that the latter method (potassium nitrate - nitric acid) gave the highest values for total sulphur and that a 3-hour com- bustion period gave as high values as overnight combustion.The results obtained for 10 soils that varied in texture from sands to clays by using (i) the proposed method (potassium nitrate - nitric acid and 3-hour combustion at 550" C), (ii) the mag- nesium nitrate - nitric acid method and combustion overnight a t 350" C4 and (iii) the potassium chlorate method (3-hour combustion a t 550" C)3 are shown in Table I. A turbidimetric method, TABLE I COMPARISON OF RESULTS OF TOTAL SULPHUR DETERMINATIONS FOR 10 SAMPLES OF AIR-DRIED SOlL Total sulphur found, per cent.,* by- Potassium nitrate - Magnesium nitrate Soil texture nitric acid method nitric acid method Sandy . . . . . . . . 0.096 0.092 Sandy .. . . . . . . 0.037 0.034 Sandy loam . . . . . . 0.061 0.057 Loam . . . . . . . . 0.032 0.028 Loam . . . . . . . . 0.105 0.101 Loam . . . . . . . . 0.098 0.096 Silt loam . . . . .. , . 0.033 0.029 Silt loam . . .. . . . . 0.046 0.043 Clay loam . . . . . . . . 0.019 0.015 Clay .. . . .. . . 0.074 0.068 Range of coefficicnt of variation. . Mean coefficient of variation . . 2.19 per cent. 3-79 per cent. Mean . . .. .. 0.0801 0-0563 0 to 5.6 per cent. 1.5 to 10 per cent. * Each result is the mean of duplicates. 1 Potassium chlorate method 0.087 0.03 1 0-054 0.029 0.094 0.089 0-025 0-038 0.014 0.068 0.0529 3.0 to 10 per cent. 5-85 per cent.August, 19661 SHORT PAPERS 529 based on those described by Butters and Chenery4 and Massoumi and C~rnfield,~ was used to determine sulphate in the digests.With every sample of soil the potassium nitrate - nitric acid method gave higher values for total sulphur than the magnesium nitrate - nitric acid method. In addition, the range of the coefficients of variation, and its mean, were lower for the former method. The potassium chlorate method usually gave the lowest total sulphur values. TABLE I1 RECOVERY OF SULPHUR FROM SOIL SAMPLES Recovery of 500 pg of sulphur added as methionine to soil samples* Original Methionine sulphur recovered, sulphur in soil, c-------A------, Soil No. Oxidant per cent. CLQ per cent. Potassium nitrate - nitric acid. . Magnesium nitrate - nitric acid Potassium chlorate . . . . Potassium nitrate - nitric acid. . Magnesium nitrate - nitric acid Potassium chlorate .. .. Potassium nitrate - nitric acid. . Magnesium nitrate - nitric acid 2 { 3 4 - 1Potassium chlorate . . .. 0.0445 0.0441 0.0439 0.109 0.104 0.108 0.062 0.059 0.058 490 467.5 460 502.5 455 457.5 495 472.5 445 98 93.6 92 100.5 91 91.5 99 94.5 89 Potassium nitrate - nitric acid. . 0.083 485 97 Magnesium nitrate - nitric acid 0.082 475 95 Potassium chlorate . . . . 0.079 460 92 * Each result is the mean of duplicates. Coefficient of variation, per cent. 1.44 2.26 3.07 0.70 1-55 2-31 1.43 0.78 1.59 1-45 1.48 3-07 Table I1 shows recoveries of known added amounts of sulphur (in the form of methionine) from four of the soils. For potassium nitrate - nitric acid, recoveries ranged from 96 to 101 per cent. (mean 98.6 per cent.); for magnesium nitrate - nitric acid, 90 to 96 per cent. (mean, 93.5 per cent.); and for potassium chlorate, 88 to 94 per cent.(mean, 91 per cent.). I t is seen, there- fore, that potassium nitrate - nitric acid is a better reagent than the other two for determining total sulphur in soils. The potassium nitrate - nitric acid method was also tested as a procedure for determining total sulphur in plant materials. Table 111 shows that there was complete recovery of methionine sulphur added to 4 plant materials. TABLE I11 RECOVERY OF SULPHUR FROM PLANT MATERIALS Recovery of 500pg of sulphur added as methionine to plant material with the potassium nitrate - nitric acid method* Original Mcthionine sulphur recovered, Coefficient sulphur found, r------u 7 of variation, per cent. per cent.Plant material per cent. CLg Dwarf peas . . . . 0.275 495 99 1.42 Oat straw . . . . . . 0.14 492.5 98.5 0-7 1 Hay . . . . . . 0.17 497.5 99.5 0.7 1 Young grass . . . . 0.355 500 100 0-0 * Each result is the mean of duplicates. Details of the potassium nitrate - nitric acid method for digesting soils and plant materials are described below. METHOD REAGENTS- Fuming nitric acid. ,Vitric acid, 25 per cent. v/v-Prepare from analytical-reagent grade nitric acid. Digesting solution-Dissolve 100 g of AnalaR potassium nitrate in 600 ml of distilled water. Add 350 ml of concentrated nitric acid and dilute to 1 litre.530 SHORT PAPERS [L4nazysf, 1'01. 91 PROCEDURE FOR SOILS- Weigh 1 g of the soil (air-dried and ground to pass a 0-6-mm sieve) into a 50-ml tall beaker. Add 10 ml of the digesting solution and evaporate to dryness on a steam-bath.Place the beaker in an electric furnace, heat to 550" C and maintain a t this temperature for 3 hours. After cooling, add 5 ml of 25 per cent. nitric acid v/v, and again digest the contents for 1 hour on a steam-bath. Extract the soluble salts Ivith distilled water and filter the solution through a ll'hatman No. 42 filter-paper. Llilute to a known volume and take a suitable aliquot of the filtrate for the turbidi- metric determination of sulphate. PKoCELlURL FOR PLANTS - \Veigh accurately 150 to 200mg of finely ground plant material into a 50-ml tall beaker. Add 3 ml of fuming nitric acid, cover the beaker with a watch-glass and set aside for 15 minutes. \Vash the watch-glass and add the washings to the beaker. Evaporate the contents to dryness on a steam-bath. Then add 10 ml of the digesting solution and proceed as described under soils. I t was found that blank values with potassium nitrate were as low as those when magnesium nitrate (prepared from Specpure magnesium) was used. I~EFE REX c E s An appropriate blank is always run with each batch of determinations. 1. Bardsley, C. E., and Lancaster, J . D., P'YOC. Sozl Scz. SOC. Anzeu., 1960, 24, 265. 2 . ;2idinyan, R. Kh , Pochiwedetiie, 1957, 49. 3. Saalbach, E., Kessen, G., and Judel, G. K , L a d w Forscli , 2962, 15, 6. 4. Butters, B., and Chenery, E. M., :Inalyst, 1959, 84, 239. 5 . Massoumi, X., and Cornfield, A . H , I h i d , 1963, 88, 321. Received Jaizuary 4th, 1966

ISSN:0003-2654    

DOI:10.1039/AN9669100528

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

530 SHORT PAPERS [L4nazysf, 1’01. 91 A Simple Colorimetric Finish for the Johnson - Nishita Micro-distillation of Sulphur BY G. A. DEAN (Conmoizwea!th Scieiztific aiid Ipidustrial Research Organization, Divisioii of Soils, Lir.L4 . Regional Laboratory, Nedlands, Westerii .4 ustralia) THE usual methylene-blue finish for the routine micro determination of sulphur in soils and plants by the Johnson - Nishita distillation method is somewhat tedious and often too sensitive1 unless a very small sample is taken, which results in sampling difficulties. No suitable reagent giving a sensitive colour on direct absorption of hydrogen sulphide could be found, and a procedure based on a colloidal metal sulphide2 was eventually developed. The method is suitable for determining amounts of sulphur up to 200 pg, and Johnson - Nishita units designed for the methylene-blue finish may be used without modification.PRINCIPLE- volume of N sodium 1ij.drosidc. do not interfere. to givc colloidal bismuth sulpliide in acetate buffer containing 1 per cent. gelatin. precautions or further operations are necessary. 1-cm cells a t 400 mp, or a t a longer wavelength if a lower sensitivity is required. sulphide in acetate buffer was described by Field and Ol~lach.~ HYDROGEN SULPHIDE ABSORBENT- A solution of N sodium hydroxide was found to be an extremely efficient absorber for hydrogen sulphide, allowing high nitrogen flow-rates and hence short distillation t i n ~ e s . ~ For example, when 1000 p g of sulphur, as sulphate, were digested for 10 minutes in a standard Johnson - Nishita distillation unit5 with a nitrogen flow-rate of 500 nil per minute, a second N sodium hydroxide absorber collected only 0.4pg of sulphur, and less than 4pg were distilled from the unit in the next 30 minutes.The hydrogen sulpliidr generated by the Johnson - Nishita digestion is absorbed in a measured A n intermediate wash is unncccssary as traces ol reducing agent This sodium hydroxide is mixed u I t 1 1 a measured volume o f bismuth reagent KO special The clear yello\v-brown colour is measured in Some advantages o f using bismuth are given by Boltz.2 The first use of colloidal bismuthAugust , 19661 SHORT PAPERS 53 1 Air oxidation in aerated N sodium hydroxide a t 20" C was found to be independent of sulphide concentration between 0 and a t least 3 p.p.ni., and was about 0.07 p.p.m.per hour, which, in the present method, is equivalent to a decrease in optical density of 0.001 in 5 minutes. Hence no special precautions are required during the transfer. When the final bismuth - acetate buffer solution was used as the absorbent instead of sodium hydroxide, recovery of 100p.g of sulphur was 78 per cent. COLOUR DEVELOPMENT- Full optical density was reached immediately after mixing, and in diffused daylight was stable for a t least 3 days. The optical density and absorption maximum were independent of temperature of mixing (sodium hydroxide a t 20" C, bismuth reagent between 0" and 50" C), age and rate of addition. Colloid protection was excellent; the solutions were clear and sparkling and were unaffected by boiling. Gum arabic gave results similar to gelatin, but some samples caused slow oxidation of the bismuth sulphide and hence fading of the colour by about 1 per cent.per hour. -4ir oxidation of the alkaline sulphide is prevented by the use of nitrogen. s E K S ITIVI T Y Absorption maximum occurred betwecn 360 and 365 mp, but traces of iodide from the Johnson - Nishita reducing agent caused slight interference (no intermediate wash was used ; the reducing agent was as recommended by Gustafsson3). At 400 mp, sensitivity to sulpliide was decreased by one-fifth but interference from iodide was ncgligible. A t 400 m p an optical density of 0.01 in a l-cm cell was equivalent to 1.8 pg of sulphur in 30 nil, or about one-sixth the sensitivity of methylencl b1ue.l In agreement with previous ob~ervations,~ Beer's law was obeyed up to an optical density of a t least 1.4 (250 pg of sulphur in 30 nil).At 480 mp the sensitivity was about one-half of that a t 400 nip. I'RECISION Hydrogen sulphide in pi sodium hydroxide was added directly in 20-nil aliquots to 10-nil aliquots of bismuth reagent ; the a\rerage optical density and standard deviation were- Solution A\ . . . . . . 0.298 + 0.0012 (0.39 per cent., 9 determinations) Solution B , . . . . . 0.933 0.0021 (0.22 per cent., 5 detcrminations) The over-all mechanical precision (excluding that of the spectrophotometer, a 'I-nicani SPBOO), calculated from the observed precision of the component operations, was j 0 . 1 5 per cent. For 8 calibration curves, each determined on a different day with standards of 50 and 100p.g distilled in the usual manner, Beer's law was obeyed to a standard deviation of 0.55 per cent., the same as the calculated niechanical precision, and the standard deviation of the slope from the mean was 3 per cent., or about the same ab for niethylene blue.The main source of errm is therefore the distillation rather than the finish. If the order of addition was reversed, the optical density was somewhat higher but less precise, and was critically dependent on the rate and manner of addition. For example, with solution B above, the average optical density and standard deviation for four determinations were 1.040 &0-014 (1.4 per cent.). When tubes were re-used after rinsing with water, no significant inter- ference from adsorbed traces of bismuth could be detected.Reversing the order of addition simplifies the procedurc but the results are too dependent on technique to justify its use without previous tests. REAGEKTS- 31 E TH 0 11 The amounts given are sufficient for 100 analyses. Biswzzith yeagent-This is 1500 p.p.ni. of bismuth and 1 per cent. gelatin in 4 N acetic acid. Heat 2 g of analytical-reagent grade bismuth subnitrate or 3.4 g of analytical-reagent grade bismuth nitrate pentahydrate in 230 nil of glacial acetic acid until dissolved, filter if necessary through a \%7hatman No. 50 filter-paper, cool, add 30 g of gelatin dissolved by warming in about 500 ml of watcr, and dilute to 1000 nil. l h e reagent is stable indefinitely. Sodizinz h j d m x i d e , s-Dissolve 80 g of sodium hydroxide in 2 litres of water.PROCEDURE- Provide the outlet of the Johnson - Sishita distillation unit with a suitable receiver, such as a 6 x J-inch test-tube, with the outlet tube reaching to the bottom. Transfer 20 nil of pi sodium532 SHORT PAPERS [Analyst, Vol. 91 hydroxide by pipette* into the dry receiver and distil hydrogen sulphide in the usual manner with a nitrogen flow-rate of between 500 and 600ml per minute for 15 minutes. During this time place 10 ml of bismuth reagent by pipette into any suitable dry vessel such as a 6 x 1-inch test-tube. Detach the receiver and pour the solution into the bismuth reagent, allow a few seconds’ drainage, and mix it thoroughly. Measure the optical density at 400 mp against a reagent blank solution.After use, steam the receiver vigorously for 5 to 10 seconds and drain for 1 minute; the combined action of the steam and residual sodium hydroxide keeps the receiver perfectly clean from run to run indefinitely. Alternatively, provided tests have shown that a reversed order of addition gives acceptable results (see above), with a pipette run 10 ml of bismuth reagent directly into the receiver by using a rigidly standardised technique, mix thoroughly and measure the optical density as above. After use, rinse thoroughly with water and allow to drain: steaming is unnecessary. Treat standards containing 0 to 200 p g of sulphur in a similar way. Beer’s law is obeyed. RESULTS Ground pine-needle samples of 100 mg, ashed according to the method of Steinbergs et ~ l ., ~ were analysed by a Johnson - Nishita distillation unit with various finishes. The mean percentage of sulphur found and standard deviations were- By methylene blue . . . . .. . . 0.0885 & 0.0024 (9) 0.0882 & 0.0012 (6) . . By bismuth sulphide { ~ ~ ~ t ~ ~ $ ~ , ?& m i . . 0.0877 & 0.0024 (16) The figures in parenthesis are the number of determinations. DISCUSSION The present finish has been used in this laboratory for many hundreds of plant analyses. Compared with the methylene-blue finish it is quicker, more convenient and gives identical results. With a bank of 12 units a distillation occupied 35 minutes from start to start, excluding the time required for colour measurement. If duplicate receivers are used the time would be decreased.The procedure given is suitable for up to 200pg of sulphur, or more if the wavelength is increased, and up to 1470 p g can be tolerated before the theoretical capacity of the bismuth reagent is exceeded. Even at this concentration no flocculation occurs on standing overnight, and the sulphur is readily determined by transferring an appropriate aliquot to 30 ml of reagent blank solution. However, such large amounts of sulphur may not be distilled comp1etely.j It is important to keep the nitrogen flow-rate above 500 ml per minute: a t 300 ml per minute recovery of sulphur from standard plant samples was 82 per cent. REFERENCES 1 . Gustafsson, L., Talanta, 1960, 4, 227. 2. Boltz, D. F., Editor, “Colorimetric Determination of Nonmetals,” Interscience Publishers Inc., 3. 4. Gustafsson, L., Talanta, 1960, 4, 236. 5. 6. * The USC of an autopipette is indispensable in routine work. New YorB and London, 1958, p. 270. Field, E., and Oldach, C . S., I n d . Engng Chem., Analyt. E d n , 1946, 18, 665. Johnson, C. M., and Nishita, H., Analyt. Ckem., 1952, 24, 736. Steinbergs, A,, Iismaa, O., Freney, J. R., and Barrow. N. J., Analytica Claim. Acta, 1962, 27,158. Received February 14th, l9G6 In this work Daffert type autopipettes were used.

ISSN:0003-2654    

DOI:10.1039/AN9669100530

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

532 SHORT PAPERS [Analyst, Vol. 91 The Oxidation of Hydroxylamine in Sodium Hydroxide in the Presence of Copper(I1) BY J. H. ANL)ERSON* (Long ,4 shton Research Station, University of Bristol, Somerset) THE oxidation of hydroxylamine to nitrous oxide a t pH 8 by copper(I1) salts in air produces traces of nitrite.l No nitrite is formed, however, from the spontaneous decomposition of hydrogen hypo- nitrite, HN202-, to nitrous 0xide.l It was suggested1 that copper(I1) oxidised hydroxylamine to a transient intermediate, which contained a single nitrogen atom and which was represented by * Present address : Fisons Pharmaceuticals Ltd., Holmes Chapel, Cheshire.August, 19661 SHORT PAPERS 533 the hypothetical compound, nitroxyl, (NOH) ; this might deconipose to nitrous oxide with great speed and only small amounts might be further oxidised to nitrite. Partington2 states that copper(I1) oxidises solutions of hydroxylamine in sodium hydroxide to nitrous oxide.In the present work a nitrogenous gas, but no nitrite, is produced in the absence of air; in the presence of air appreciable amounts of nitrite are produced, suggesting that the oxidation involves two steps. ME THO D s Reagents used were as previously described.l Changes in the volume of gases, resulting from the oxidation of hydroxylamine in air or under nitrogen, were measured by performing the reactions a t 30" C in double side-arm Warburg flasks in the previously described manner.l The flasks con- tained 200pmoles of sodium hydroxide, and copper sulphate and additions as shown in Table I.Reactions were started by adding 5 pmoles of hydroxylammonium chloride from the side-arm, bringing the total volume to 2.5 ml. The hydrogen cyanide vapour used for inhibiting certain reactions was derived from 0.2 ml of a suspension of 10 per cent. calcium hydroxide in 0-7 M calcium cyanide3 held on filter-paper in the centre well. Nitric oxide was determined by oxidation with a solution of alkaline permanganate placed in a ~ide-arm.~ The gas produced in the absence of air was calculated as nitrous oxide. After the stated period of reaction, samples were spun in a centri- fuge to remove the precipitates of copper hydroxide and were then analysed as previously des- ~ r i b e d . ~ ? ~ Gas analysis was performed with the model MS. 2H mass spectrometer (Associated Electrical Industries).The reactions (volume 2.5 ml) were performed under reduced pressure in Thunberg tubes.' These were cooled to -60" C to reduce the vapour pressure of water, and were evacuated with a rotary vacuum pump until a pressure of 0-4mm of mercury was attained. After tem- perature equilibration a t 30" C the reaction was initiated by adding hydroxylammonium chloride from the side-arm. When the oxidation was complete, the tube was cooled to -60" C and the gas was allowed to expand into the chamber of the mass spectrometer. Hyponitrite does not decompose under these conditions. RESULTS OXIDATION OF HYDROXYLAMINE IN THE ABSEKCE OF AIR- Warburg experiments performed under nitrogen showed that a suspension of 100 pmoles of copper(I1) hydroxide in the presence of 1 millimole of sodium hydroxide oxidised 10 pmoles of hydroxylammonium chloride to 5.3 pmoles of nitrous oxide (or nitrogen).The reaction was complete in 20 minutes, and yellow copper(r) hydroxide was formed. The gas probably accounted for the hydroxylamine nitrogen added, because no nitric oxide was formed and no hydroxylamine, nitrite or hyponitrite was found in the residual reaction mixture. When the gas (produced under reduced pressure) was analysed in the mass spectrometer, masses 44 and 30 were detected, showing the presence of nitrous oxide and of the nitrosonium ion, NO+, which is formed by the destruction of nitrous oxide under these conditions. Negligible amounts of nitrogen were found other than that of residual air. These were determined by measuring the niass-32 peak (oxygen).Experiments performed under reduced pressure with 5 pmoles of hydroxylamine in the presence of 1 millimole of sodium hydroxide showed that the recovery of hydroxylamine was 90 per cent. after 1 hour. When small amounts of copper(I1) were added (12.5 and 125 mpmoles) the recoveries of hydroxylamine (86 and 81 per cent., respectively) were slightly decreased. h-o nitrite was formed. Possibly the small disappearance of hydroxylamine was caused by a nietal-ion impurity (in the sodium hydroxide) which was reduced by the oxidation of hydroxylamine to nitrous oxide, and oxidised by the reduction of hydroxylamine to ammonia. The impurity might be replaceable by copper. Kitrite (2.5 pmoles), which was added to the reactions in the presence and absence of copper, was quantitatively recovered after 1 hour and did not decrease the recoveries of hydroxylamine.These findings suggest that the lack of production of nitrite from hydroxylamine and an excess of copper(I1) in the absence of air does not arise from the reduction of nitrite by copper(1) or hydroxylamine. As nitrite is formed from hydroxylamine and copper in air, the reaction would seem to involve two steps: (u) the oxidation of hydroxylamine by copper(I1) to an intermediate which spontaneously decomposes to gas; ( b ) the oxidation of the intermediate to nitrite by oxygen. STABILITY OF HYPONITRITE- Sodium hyponitrite (7 pmoles) in the presence of 1 millimole of sodium hydroxide did not form nitrous oxide or nitrite when 30 pmoles of copper(1r) were added in the absence of air, or534 SHORT PAPERS [AutaZyst, Vol.9 1 when 2.5 pnioles of copper(I1) were added in the presence of air. nitrite is not an intermediate in the conversion of hydroxylaniine to nitrous oxide or nitrite, OXIDATION OF HYDROXYLAMIKE I N THE PRESENCE OF AIR- The observed decrease in gas volume (calculated as oxygen) associated with the oxidation of hydroxylamine in air (Table I ) was not cqual to the theoretical uptake caIculated as oxygen, These results show that hypo- TABLE I THE PRODUCTS OF THE COPPER-CATALYSED OXIDATIOS OF HYIIROXYLAILIINE Periods of reaction: group A, 16 hours; group R, 6 hours. Lkcrease -Amount Time in gas Hiydroxyl- of copper required for volume, amine Nitrate formation, sulphate attaining calculated disap- Sitrite pmoles added, stationary as pmoles pearance, formation, (-*--, Group m pmoles Aklditions readings of oxygen pmoles pmoles Found Calculated - G hours - 10 minutes Cyanide 25 Cyanide 16 hours - - - 60 minutes - 20 minutes - 10 minutes r o (.! A J 1.25 6.2 1.9 4.9 6.9 3.6 5-2 4.2 1.9 2.0 2.3 1.3 1.9 1.3 3.5 3.1 2.2 2.4 2-8 0.0 0.0 8.4 2.4 3.3 1.5 0.8 1.1 0.3 0.7 0-0 0.0 - - in accordance with equation ( 1 ) , from the nitrite production.In certain experiments, however, nitrate was produced in amounts which were almost equal to those calculated by multiplying the difference between the observed and theoretical decreases in gas volume by the factor 2/3 derived from equation ( 2 ) . The hydroxylamine that Lvas not accounted for as nitrite and nitrate was prob- ably converted to nitrous oxide, which u-as not determined.The production of this gas from hydroxylamine, according to equation (3), does not involve a change in the volume of gases. The contraction in volume that resulted from the greater solubility of 1 pniole of nitrous oxide compared with that of 1 pmole of oxygen was calculated to be approximately 0.1 pniole of oxygen. This was small and was not taken into account when calculating the nitrate formation. KH,OH + 0, = KO2- + H,O + H+ . . . . - * ( 1 ) NH,OH + 140, = NO,- + H,O + Hf . . . . . . (a) L?NH,OH + 0, = K,O + 3H,O . . . . . . . . (3) Table 1 shows that 5 pmoles of hydroxylamine present with 0.2 millimole o f sodium hydroxide disappeared completely in 6 hours forming 2-0 pnioles of nitrite and 2.4 pmoles of nitrate (group A ) .\Vhen a small amount of copper(rr) (25 mpmoles) was added, the oxidation of hydroxylamine to 2.3 pnioles of nitrite was complete in 10 minutes and no nitrate was formed (group A ) . Cyanide inhibited the oxidation of hydroxylamine in the presence, or absence, of copper(II), and nitrite (and nitrate) were formed (group A ) . These results suggest that the nietal- ion impurity is reduced by the oxidation of hydroxylamine and oxidised by oxygen. In these respects the impurity is probably replaceable by copper. Cyanidc probably binds the metal ions. Increasing the amount of copper added from 1.25 to 12-5 mpmoles increased the rate of oxida- tion o f hydroxylaniine but decreased the formation of nitrite plus nitrate from 4-3 to 2.2 pmoles (group B).These findings suggest that the formation of nitrous oxidc was increased. DISCUSSION Latinier7 states that alkaline conditions favour the decomposition of hydroxylaniine to nitrous oxide and ammonia. The decomposition studied in the present work is oxidative, but i t is always possible that small amounts of ammonia were formed in the presence and absence of air by the reduction of hydroxylamine with a reduced metal-ion impurity or copper(1). The analysis performed with the mass spectrometer showed that the gas produced by the quantitative oxidation of hydroxylaniine with an excess of copper(r1) in the absence of air contains nitrous oxide. Possibly the hypothetical compound, nitroxyl, is the intermediate from which the nitrous oxide is spontaneously formed, as indicated by equation (4).. . . - (4) 2 (NOH) = N,O + H,O . . . .August, 19661 SHORT PAPERS 535 As nitrite is produced from hydroxylamine and copper(1r) in air, the oxidation would seem to involve two steps. The first step would be the oxidation of hydroxylamine to nitroxyl by copper(r1) according to equation (5). As solutions of hyponitrite in sodium hydroxide are stable, it seems unlikely that hyponitrite is an intermediate of the conversion of nitroxyl to nitrous oxide. The second step is apparently the oxidation of nitroxyl to nitrite. Probably the reaction requires molecular oxygen as indicated by equation (6) and does not involve copper(r~) as oxidant. NH20H + ~ C U ( I I ) = (NOH) + ~ C U ( I ) + 2 H f . . . . . . ( 5 ) (NOH) + 4 0 2 = NO2- + H+ .. . . . . * * (6) The oxidation of copper(1) by oxygen may produce peroxide. This would oxidise nitrite to nitrate. The finding that increasing the copper concentration decreased the yield of nitrite plzcs nitrate (group B, Table I) may be compared with previous results1 in which increasing the copper con- centration from 1 to 1 0 0 0 p ~ a t pH 8 increased the rate of oxidation of 1 mM hydroxylamine to nitrous oxide, but only about 5 per cent. of the hydroxylamine was converted t o nitrite. Possibly a high concentration of hydroxyl ions is required for the oxidation of nitroxyl to nitrite. I thank Dr. K. 1%’. Dunning for helpful discussions of the typescript, and Dr. R. Clampitt for performing the analysis with the mass spectrometer. REFERENCES 1. 2. 3. 4. 5. 6. 7. Anderson, J. H., Analyst, 1964, 89, 357. Partington, J. R., “General and Inorganic Chemistry,” Second Edition, Macmillan and Co. Ltd., Robbie, W. A., Meth. Med. Res., 1948, 1, 307. Anderson, J. H., Biochem. J., 1965, 94, 236. - , Ibid., 1964, 91, 8. - , Analyst, 1963, 88, 494. Latimer, W. M., “The Oxidation States of the Elements and their Potentials,” Second Edition, Received August 31st, 1965 London, 1951, p. 554. Prentice Hall Inc., New Jersey, 1952, p. 07.

ISSN:0003-2654    

DOI:10.1039/AN9669100532

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

August, 19661 SHORT PAPERS 535 Limits of Sensitivity of Detection of Aluminium in Amorphous and Crystalline Aluminium Oxide by X-ray Diffractometry BY C. J. TOUSSAINT AND G. VOS (Euratom, Chemistry Department, Analytical and Mineral Chemistry Section, Ispra, Italy) IT is frequently necessary to know the limit of detection that can be obtained in quantitative determinations by X-ray diffraction, but few results have been published. Recent work on the Iiniit of sensitivity of silicon in lithium fluoride and tungsten' and of structural constituents in metallographic samples2 are examples. During research on the determination of aluminium in sintered aluminium powders, we made a study of the minimum detectable amount of aluminium in an aluminium oxide matrix with two types of diffractometer, one with a curved crystal monochromator, the other with a filter to eliminate the Kp radiation.Assuming that the diffraction line is free from interference, the limit of detection of a crystalline phase in a mixture of powders generally depends on: the absolute intensity of the particular diffraction maximum from the crystalline phase; the mass absorption coefficient of the matrix ; and an instrumental factor (type of diffraction technique and equipment, experimental conditions). EXPERIMENTAL Two different types of diffractometers were used. One was the CGK* diffractometer, equipped with a curved quartz monochromator in front of the reflection specimen, proportional counter and de-mountable X-ray tube with copper anode. The applied voltage and beam current were 45 kV and 15 mA, respectively.The other was the Philips diffractometer with sealed-off copper tube, proportional counter, nickel filter (to eliminate copper K p radiation) and pulse-height analyser. * Compagnie G6nCrale dc Radiologie : Paris, France.536 SHORT PAPERS [AnaLyst, VOl. 81 Further instrumental parameters were slit divergence and scatter 1 ’, receiving slit width 0.2 mm. Excitation conditions were 40 kV and 20 mA, and 50 kV and 20 mA (fine focus or normal focus tube). The (1 11) reflection of aluminium has been chosen as analytical line. The minimum composition detectable may be defined as that concentration which yields an intensity equal to three times the standard deviations of the background intensity. Thus- 3-cdB7 Limit of detection = -- P.T where P = intensity of the peak in counts per second. B = intensity of the background in counts per second. T = counting time in seconds. C = percentage weight of aluminium. The limits of detection were determined with a counting time of 100 seconds. The intensity of the peak was obtained from a sample containing 0.5 per cent. of aluminium, while the back- ground was measured with pure aluminium oxide samples. RESULTS AND DISCUSSION The limits of detection are given in Table I. As well crystallised aluminium gives strong reflections and the mass absorption coefficient of the matrix is only 28 cni2 per g (copper KJ, aluminium can be determined to about 0.0080 per cent. in crystalline aluminium oxide. In un- favourable circumstances, a matrix of amorphous aluminium oxide in which the broad halo of TABLE I LIhlITS O F DETECTION OF ALURIINIUM I N CRYSTALLINE 4ND AMORPHOUS ALUMINIUM OXIDE FOUSD BY UIFFEKENT X-RAY DIFFRACTOlIETER TECHNIQUES -\pparat us Diffractometer with monochromator, tube load Bi5 watts Diffractometer with filter- ( a ) Fine focus tube, tube load 800 watts .. .. ( b ) Normal focus tube, tube load 1000 watts . . ( a ) Fine focus tube . , . . .. .. . . (b) Normal focus tube . . . . . . . . . . Diffractometer without filtcr- Limits of detection Matrix amorphous, Matrix crystalline, aluminium oxide aluminium oxide A 7 -? 0.0550 per cent. 0.020 per cent. 0-0480 0.0270 Not determined 0~0100 0.0360 Not determined 0,0220 0.0080 diffraction emanating from the amorphous regions occurs a t about the same wavelength as the aluminiuni (1 11) reflex, therefore giving rise to high background counting rates, limits of 0.03 per cent.can be attained. In Fig. 1 are shown diffractometer traces of an amorphous aluminium oxide sample containing 0.5 per cent. of aluminium under different experimental conditions. The most unfavourable results were obtained with the diffractometer equipped with the crystal monochromator. As the two diffractonieters used were of a different type i t is impossible to give a quantitative cxplanation. It is interesting to note that Parrish and K ~ h l e r , ~ with the same type of apparatus and for the usual type of measurements, obtained results of the P / B ratios that were about the same, when they compared a quartz crystal monochromator placed behind a transniission specimen with the pulse-height discrimination method.In certain circumstances, however, such as when the analytical line lies in the lowangle region, the crystal monochromator should give better results. The influence of the total power applied to the X-ray tube has considerable influence on the sensitivity. The poor results obtained with the CGR diffractonieter arise from this, as the maximum power that could be applied was only 675 volts. On examination of Table I, we conclude that this plays an important r61e. Eliminating the filter gave only a slight increase in the sensitivity. In conclusion, we believe that with modern X-ray diffractometer apparatus, limits of detection between 0.1 and 0.01 per cent. under similar conditions can be obtained.August, 196G] SHORT PAPERS 537 I I I 39 37 35 33 20 A = Without nickel filter B = With nickel filter C = Pure aluminium oxide with nickel filter Fig. 1. X-ray diffractometer traces of an amorphous aluminium oxide sample containing 0.5 per cent. of aluminium. Instrumental parameters : copper radiation, fine focus tube, 40 kV and 20 mi\, scanning speed 4' pcr minute REFERENCES 1. 2 . Iiudielka, H., hldller, H., .Irck. Eisenhz2tlWes., 1963, 34, 181. 3. Parrish, \I7., and Taylor, J., Int. Symp. X-Ray Microsc., No. 2, Stockholm, Elsevier, Amsterdam, 1960, 458. Parrish, \V , liohler, T. R., RPU. S c i e z t . Instmm., 1956, 27, 795. Received -4 z i p s t 131h, 1965

ISSN:0003-2654    

DOI:10.1039/AN9669100535

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

538 ANALYTICAL METHODS COhIhIITTEE [Analyst, 1701 91 Analytical Methods Committee REPORT PREPARED BY THE MEAT PRODUCTS SUB-COMMITTEE Nitrogen Factor for Kidney THE Analytical Methods Committee has received the following Report from its Meat Products Sub-committee. The Report has been approved by the Analytical Methods Committee and its publication has been authorised by the Council. REPORT The Meat Products Sub-committee of the Analytical Methods Committee responsible for the preparation of this Report was constituted as follows: Dr. S. M. Herschdoerfer (Chairman), Mr. S. Back, Mr. P. J. Cooper (appointed 1965), Mr. P. 0. Dennis, Mr. J. R. Fraser (resigned 1965), Mr. H. C. Hornsey, Dr. A. J. Kidney, Mr. T. McLachlan, Dr. R. A. Lawrie, Dr. A. McM. Taylor and Mr. E. F. Williams, with Mr.P. W. Shallis as Secretary. In the course of its investigations on the nitrogen factors of different types of meat the Sub-committee has already reported on pork,l beef,2 chicken,3 liver,* veal5 and turkey.6 Two reports were also issued on the nitrogen content of rusk The Sub-committee has now completed its determinations of the nitrogen content of kidneys and its findings are summarised in Fig. 1. In a similar way as for the various types of meat, kidneys have a variable nitrogen content. On the other hand, it was interesting to note that there was very little difference between the mean values for the kidneys of the three species examined by the Sub-committee. The over-all weighted mean was 2.69 per cent. RECOMMENDATION The Sub-committee recommends an average factor of 2.7 for use in the analysis of kidney products. REFERENCES 1 . 2. 3. 4. 6. 7 . 8. 3. Analytical Methods Committee, Analyst, 1961, 86, ,557 -, I b i d . , 1963, 88, 422. -, Ibid., 1963, 88, ,583. ~~ , Ibid., 1964, 89, 630. -, Ibid., 1965, 90, 256. -, I b i d . , 1961, 86, 560. __ , I b i d . , 1965, 90, 579. -, I b i d . , 1965, 90, 581.OX KIDNEYS (fresh) I I - I __-__- I I 1 I I I I 1 1 OX KIDNEYS (frozen) N o . of samples 14 25 LAMB KIDNEYS (fresh): 12 PIG KIDNEYS (fresh) : 12 (2 kidneys from same carcase minced) (8 to I2 kidneys minced) Range Mean 2.48-2'93 2.7 I 2'26-3.07 2.69 2.46-2.98 2.67 24 1-2.90 2.67 Fig. 1 . Nitrogen contents of kidneys from different species. Horizontal lines represent tlie range of nitrogen contents, short vertical lines indicate the average values cn w CD

ISSN:0003-2654    

DOI:10.1039/AN9669100538

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

540 ANALYTICAL RIETHODS COMMITTEE ;Analyst, IroL 91 Analytical Methods Committee REPORT PREPARED BY THE FISH PRODUCTS SUB-COMMITTEE Nitrogen Factor for Cod Flesh THE Analytical Methods Committee has received the following Report from its Fish Products Sub-committee. The Report has been approved by the Analytical Methods Committee and its publication has been authorised by the Council. REPORT The Fish Products Sub-committee was appointed by the Analytical Methods Committee in 1963 and its constitution is: Dr. S. $1. Herschdoerfer (Chairman), Dr. J. H. Bushill (deput17- Mr. W. C. A. Wise), Dr. C. L. Cutting, Mr. J. R. Fraser (resigned June, 1965), Mr. B. J. Hasberry (deputy--Mr. D. J. Ward), Dr. W. T. Little, Dr. J. A. Lovern, Mr. T. McLachlan and Mr. P. J. Cooper (appointed August, 1965), with Mr.P. L!:. Shallis as Secretary. The Sub-Committee’s terms of reference are : “ ( a ) To establish the essential characteristics of fish and differences in these characteristics caused by decomposition or other changes; ( b ) To recommend methods for determining the amount of fish present in food products.” Cod is the fish used most frequently as an ingredient in manufactured products-fish fingers, fish cakes, fish pastes, etc.-and the Sub-committee examined the available methods for determining the fish content, expressed as cod, of such products. It was considered at the time that a method based on the nitrogen content of the fish was the most promising one, and accordingly a search of the relevant literature was carried out and arrangements were also made for analyses to be carried out in a number of laboratories.In a paper on “Seasonal Variations of Fat, Water Solubles, Protein and Water in Cod Fillets,” Dambergsl reported the results obtained in monthly analyses of samples of muscles of medium-size Kova Scotia inshore cod (Gadus morrhzia L.). He observed that the protein content of the muscles reached a maximum in October to Yovember and then gradually diminished to a minimum in May. This cyclic variation was observed in all parts of the fillets, i.e., the head, middle and tail sections. Similar observations had been made on Sorth Sea cod by Tronside and Love,2 who concluded that the variations in protein were influenced by the spawning effort and by starvation during the winter months. The Sub-committee arranged to examine head, middle and tail sections of fillets as well as whole fish, to compare results obtained on freshly caught fish and on fish purchased in markets and to investigate as far as possible fish from different fishing grounds.The sampling instructions issued to all participating laboratories were that the fish should be filletted, the skin removed from the fillets and then the whole, or the appropriate portions, of the fillets should be minced and the minced flesh thoroughly mixed before the sample was removed for analysis. Details of the determination of moisture by vacuum drying at 70” C and of the determination of nitrogen by the Kjeldahl method with mercuric oxide as catalyst were also issued to all participating laboratories.540 ANALYTICAL RIETHODS COMMITTEE ;Analyst, IroL 91 Analytical Methods Committee REPORT PREPARED BY THE FISH PRODUCTS SUB-COMMITTEE Nitrogen Factor for Cod Flesh THE Analytical Methods Committee has received the following Report from its Fish Products Sub-committee.The Report has been approved by the Analytical Methods Committee and its publication has been authorised by the Council. REPORT The Fish Products Sub-committee was appointed by the Analytical Methods Committee in 1963 and its constitution is: Dr. S. $1. Herschdoerfer (Chairman), Dr. J. H. Bushill (deput17- Mr. W. C. A. Wise), Dr. C. L. Cutting, Mr. J. R. Fraser (resigned June, 1965), Mr. B. J. Hasberry (deputy--Mr. D. J. Ward), Dr. W. T. Little, Dr. J. A. Lovern, Mr. T. McLachlan and Mr. P. J. Cooper (appointed August, 1965), with Mr.P. L!:. Shallis as Secretary. The Sub-Committee’s terms of reference are : “ ( a ) To establish the essential characteristics of fish and differences in these characteristics caused by decomposition or other changes; ( b ) To recommend methods for determining the amount of fish present in food products.” Cod is the fish used most frequently as an ingredient in manufactured products-fish fingers, fish cakes, fish pastes, etc.-and the Sub-committee examined the available methods for determining the fish content, expressed as cod, of such products. It was considered at the time that a method based on the nitrogen content of the fish was the most promising one, and accordingly a search of the relevant literature was carried out and arrangements were also made for analyses to be carried out in a number of laboratories.In a paper on “Seasonal Variations of Fat, Water Solubles, Protein and Water in Cod Fillets,” Dambergsl reported the results obtained in monthly analyses of samples of muscles of medium-size Kova Scotia inshore cod (Gadus morrhzia L.). He observed that the protein content of the muscles reached a maximum in October to Yovember and then gradually diminished to a minimum in May. This cyclic variation was observed in all parts of the fillets, i.e., the head, middle and tail sections. Similar observations had been made on Sorth Sea cod by Tronside and Love,2 who concluded that the variations in protein were influenced by the spawning effort and by starvation during the winter months.The Sub-committee arranged to examine head, middle and tail sections of fillets as well as whole fish, to compare results obtained on freshly caught fish and on fish purchased in markets and to investigate as far as possible fish from different fishing grounds. The sampling instructions issued to all participating laboratories were that the fish should be filletted, the skin removed from the fillets and then the whole, or the appropriate portions, of the fillets should be minced and the minced flesh thoroughly mixed before the sample was removed for analysis. Details of the determination of moisture by vacuum drying at 70” C and of the determination of nitrogen by the Kjeldahl method with mercuric oxide as catalyst were also issued to all participating laboratories.August, 1966j NITROCEK FACTOR FOR COD FLESH 541 The results obtained in the period January, 1964, to September, 1965, are summarised in Figs.1 and 2. Laboratory No. of results I 16 2 71 3 18 4 99 5 33 6 58 Over-all mean 295 * - I 0 I . 2.0 2.2 2.4 2% 2.8 3.0 3.2 3 . 4 Total nitrogen, per cent. Fig. 1. Means, normal limits (95 per cent.) and ranges of results from different laboratories, January, 1964, to September, 1065 These results were submitted to a statistical analysis to determine the average percentages of nitrogen, their normal limits of variation and to establish how much of this variation was due to the causes listed below- A. B. C. Differences between fish of different sizes. D. E. Differences between fishing grounds. Differences between seasons of the year.Differences between parts of the fish analysed. Differences between fresh, stored and frozen fish. The over-all mean value for the nitrogen content of cod flesh on 295 samples was 2.871 per cent., with a standard deviation of 50.137. I>ISCLTSSIOS OF RESI'LTS (a) A seasonal variation in the nitrogen content was confirmed in the samples examined, although it was noted that these periods were somewhat different from those reported bj- Dambergs. ( b ) As expected, no difference was found between the left and right sides of fish. The head portion had a higher and the tail portion a lower nitrogen content than the middle port ion. (c) The size of the fish does not appear to have any significant influence on the nitrogen content of the flesh.(d) Fresh fish examined within a few hours of capture and also pre-rigor, had a higher than average nitrogen content, whereas fish kept on ice for 10 to 12 days had a lower than average nitrogen content. (e) The apparent influence of the fishing grounds was indicated by the higher nitrogen levels observed in cod from Iceland and the Faroes and the lower nitrogen content of cod of distant-water origin. Lower figures can also be due to the loss of nitrogen on prolonged storage in ice.542 BOOK REVIEWS [Analyst, 1 7 0 1 . 91 RECOMMENDATION After due consideration of all the relevant data the Sub-committee recommends that an average nitrogen factor of 2.85* should be used in the analysis of cod products. ACKNOWLEDGMENT The Sub-committee thanks those listed below for their help and communications- Birds Eye Foods Ltd. British Food Manufacturing Industries Research Association. J. Lyons & Co. Ltd. Ministry of Technology, Torry Research Station. Ross Foods Ltd. Unilever L t d. REFEKENCES 1. 2. * The Sub-committee has followed the usual practice of the Meat Products Sub-committee in recom- Dambergs, N., J . Fish. Res. B d Canada, 1964, 21, 703. Ironside, J. I. M., and Love, R. M., J . Sci. Fd Agric., 1958, 9, 597. mending an average nitrogen factor expressed to the nearest 0.05 per cent.

ISSN:0003-2654    

DOI:10.1039/AN9669100540

出版商:RSC    

年代:1966

数据来源: RSC