ISSN:0003-2654    

DOI:10.1039/AN96186FX025

出版商:RSC    

年代:1961

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN96186BX027

出版商:RSC    

年代:1961

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN96186FP121

出版商:RSC    

年代:1961

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN96186BP131

出版商:RSC    

年代:1961

数据来源: RSC

摘要:

JUNE, 1961 THE ANALYST Vol. 86, No. 1023 PROCEEDINGS OF THE SOCIETY FOR ANALYTICAL CHEMISTRY XORTH OF ENGL-4ND AND SCOTTISH SECTIONS X JOIST Meeting of the Sorth of England and Scottish Sections was held at 7.30 p.m. on Friday, April 28th, 1961, in the Central Hotel, l’ictoria Viaduct, Carlisle. The Chair was taken by the Chairnian of the North of England Section, Mr. J. hlarkland, B.Sc., F.R.I.C. The following papers were presented and discussed : “The Determination of Nitrates and the Application of ‘Dead-stop’ Titrimetry,” by A. F. Williams, B.Sc., F.R.I.C. ; “Ion- exchange Resins as Analytical Tools,” by T. R. E. Kressman, HSc., Ph.D., F.R.I.C. The meeting was preceded in the afternoon by a visit to the U.K.A.E.A. Power Station at Chapelcross. WESTERN SECTI( A JOIXT Meeting of the Western Section with the Car( id District Section of the Royal Institute of Chemistry, the South Wales Section and the Food Group of the Society of Chemical Industry was held at 7 p.m.on Friday, April 28th, 1961, at University College, Cardiff, A lecture on “Modern Legislation in Relation to Food Additives” was given by C . A. .$dams, C.B.E., B.Sc., F.R.I.C., Barrister-at-Law. The meeting was preceded in the afternoon by a visit, by courtesy of Rlessrs. P. Leiner (Wales) Ltd., to their Treforest works. The Chair was taken by Mr. S. Dixon, M.Sc., F.R.I.C. MIDLLINDS SECTIOX AKD PHYSICAL METHODS GROUP X JOIST Meeting of the Midlands Section and the Physical Methods Group was held a t 7 p.m. on Wednesday, -April 26th, 1961, in the Main Chemistry Lecture Theatre, The Uni- versity, Edgbaston, Birmingham, 15.The Chair was taken by the Chairman of the Midlands Section, Dr. H. C. Smith, M.Sc., F.R.I.C., Dip.Ed. The following papers were presented and discussed : “Spectrofluorimetry,” by C. A. Parker, B.Sc., Ph.D., F.R.I.C. ; “Tesla-luminescence Spectra,” by R. J. Magee, M.Sc., Ph.D., -4.R.I.C., M.R.S.H. (see summaries below). The meeting was preceded at 3 p.m. by a visit to the Mond Nickel Co. Ltd., Wiggin Street, Birmingham, 16. SPECTROFLUORIMETRY DR. C. A. PARKER recalled that the visible fluorescence of solutions of certain compounds when exposed to ultra-violet light had been used for many years for the determination of such organic materials as vitamins and condensed-ring aromatic hydro- carbons. It had also been used to detect traces of metals‘that could be made to react with a reagent to give a fluorescent compound.The technique could be made much more specific and sensitive by using a modern photomultiplier tube and a spectrometer to analyse the spectrum of the fluorescent light or to isolate specific frequencies of light for excitation of fluorescence. If an ultra-violet detector was used, the method was applicable to a wide range of substances, because many aromatic compounds fluoresced in the ultra-violet region of the spectrum. The range of frequencies at which the band of fluorescent light appeared was directly related to the energy differences between the ground state and the first excited state of the molecule and provided one criterion for identification.The shape of the fluores- cence band was generally independent of the frequency of the exciting light, but asecond 365366 PROCEEDINGS [Vol. 86 criterion for identification could be obtained by plotting its intensity as a function of the frequency of the exciting light (the excitation spectrum). Spectrofluorimetry thus had two advantages over absorption spectrophotometry. First, it provided two charac- teristic spectra instead of one, and second, it was capable of measuring much lower concentrations. It was somewhat less widely applicable than absorption spectrophoto- metry, because not every absorbing substance fluoresced-at least at room temperature. The ideal general-purpose spectrofluoriineter required the use of two wide-aperture spectrometers and was expensive.However, very useful work could be done with a simpler arrangement in which only one spectrometer was used (e.g., the monochromator from a cominercial absorption spectrophotometer) . The technique had been much employed in recent years, particularly in the United States of America, for the determination of low concentrations of compounds of bio- chemical significance. It could also be used in inorganic trace analysis, and the author described some applications from his own experience. TESLA-LUMINESCENCE SPECTRA DR. R. J. MAGEE said that the phenomenon of tesla-luminescence had first been investigated some thirty years ago by workers in the Chemistry Department of The Queen’s University, Belfast. After a few years, however, for reasons unknown, interest in the subject had died out.Recently, with modern methods and a new approach, the field had been re-investigated. This paper gave a report on the progress of these re-investigations. The new developments included a simplified tesla-generator, sample tubes and improved methods for the detection of the spectra obtained. The author gave details of the equipment used and presented the results obtained with a number of organic and inorganic compounds. He discussed the range and possibilities of the technique. MIDLANDS SECTION AND MICROCHEMISTRY GROUP A JOINT Meeting of the Midlands Section and the Microchemistry Group was held a t 7.15 p.m. on Friday, May 12th, 1961, in the Nottingham and District Technical College, Burton Street, Nottingham. The Chair was taken by the Chairman of the Microchemistry Group, Mr.C. Whalley, B.Sc., F.R.I.C. The subject of the meeting was “Automation in the Analytical Laboratory” and the following papers were presented and discussed : “The Scope of Automation in the Laboratory,” by G. Mattock, B.Sc., Ph.D., A.R.I.C. (see summary below) ; “A Colorimeter-type Instrument for the Continuous and Automatic Analysis of Gases in the Parts per Million Range” and “An Automatic Titrimeter,” by M. Akhtar, Ph.D., M.Sc., D.I.C. The meeting was preceded at 2.30 p.m. by a visit to the production factory of Boots Pure Drug Co. Ltd. THE SCOPE OF AUTOMATION IN THE LABORATORY DR. G. MATTOCK stated that the application of automation in the analytical laboratory was primarily intended to reduce the man-hours required for analyses and so to make operations more efficient.In this sense it was not necessarily a requirement that the automatic technique be faster, but it must reduce the time demanded of an operator. In this sense it was justifiable to include newer instrumental methods of analysis, which themselves reduced the time required of the analyst, whether or not the instrument was fully automatic. In the design of automatic instruments, it was neither adequate nor desirable merely to automate traditional methods: the technique used by the instrument must evolve from the requirement that a particular result was to be sought by automatic means, controlled by the acceptable accuracy (not the maximum possible accuracy) and ease of calibration. Further, it was important to emphasise that automation might be only partial to a complete analysis and was only valuable where it could eliminate one of the more time-consuming aspects.Two different groups of automatic apparatus could therefore be identified- (;) those performing a sequence of operations covering the entire analysis of one or several components, starting with the introduction of the untreated sample and ending with a record of the analysis, preferably on a repetitive basis, andJune, 19611 PROCEEDINGS 367 (ii) those performing only a part of the analysis and thus requiring manual Apparatus of type (i) was only economically useful when routine operations were carried out; type (ii) apparatus, while valuable for routine analysis, was also applicable to occasional analyses and was therefore probably of more general value. Continuous analysers performing repetitive determinations on samples auto- matically fed into the apparatus were representative of class (i), and Dr. Mattock discussed them to illustrate how novel analytical principles could be introduced into automatic apparatus. Certain automatic titrators, while performing more orthodox operations, also illustrated class (i). There was a wide variety of apparatus in class (ii). Examples included automatic sampling devices and automatic titrators of set-end-point and curve-recording types. Also to be included were newer instrumental-measurement methods, which by their nature effected a reduction in the time necessary for a complete analysis, e.g., techniques of X-ray fluorescence, photometry and direct electrometric measurement. intervention in intermediate stages.

ISSN:0003-2654    

DOI:10.1039/AN9618600365

出版商:RSC    

年代:1961

数据来源: RSC

摘要:

June, 19611 PROCEEDINGS 367 The Analysis of Commercial Sodium 2,2=Dichloropropionate (Dalapon Sodium Salt) BY D. C. GARKATT” (Standards Departmepit, Boots Pure Drug Co. Ltd., Station Street, Nottingham) Several possible methods of determining the principal constituent of commercial sodium 2,2-dichloropropionate have been investigated and compared, and procedures for determining various impurities have also been established. The methods examined for determining 2,2-dichloropropionic acid include the mercury-precipitation method of Marquardt and Luce, a colorimetric method based on the formation of its 2,4-dinitrophenylhydra- zone and a gas-chromatographic procedure. A COMMERCIAL selective herbicide effective against couch grass (Agropyron repens) consists primarily of sodium 2,2-dichloropropionate together with relatively small amounts of associated chlorinated products and sodium pyruvate ; the common name I “dalapon” has been given to 2,2-dichloropropionic acid.Methods1 ,2 for determining sodium 2,2-dichloro- propionate are based on hydrolysis to pyruvic acid, but the reaction is not quantitative and impurities may also affect the results. Investigation into the reproducibility of any method with these variables is simple, but an assessment of accuracy depends on the purity of standards. In order to study the accuracy of the chemical procedures and t o investigate the quality of standards, it was considered that an alternative method was needed, and gas-chromato- graphic techniques based on the work of Crowshaw3 were developed.With the gas-chromato- graphic methods a complete analysis of standards was possible, and, although the primary object was to assist in the assessment of the chemical techniques, good agreement was found between all methods for commercial products. GAS CHROMATOGRAPHY- The gas-chromatographic methods used were based on the separation of methyl esters of the chlorinated acids. Preliminary runs on esters prepared from commercial samples showed several peaks that were subsequently identified by comparison with samples of pure esters; in order of emergence from the column they were methyl monochloroacetate (MCA), * This paper is published under the name of the head of the department, since many members of the staff contributed to the work recorded and discrimination for authorship would be unfair.368 GARRATT: THE ANALYSIS OF COMMERCIAL SODIUM [Vol. 86 methyl 2-chloropropionate (MCP), methyl dichloroacetate (DCA), methyl 2,2-dichloropro- pionate (2,2-DCP), methyl trichloroacetate (TCA), methyl 2,3-dichloropropionate (2,3-DCP) and methyl 2,2,3-trichloropropionate (2,2,3-TCP).Methyl pyruvate is not resolved and is eluted at the same time as the methyl dichloroacetate. To aid the identification of the components and to provide samples for use in standard mixtures pure esters were separated on a preparative scale under the following conditions- Column length-6 feet. Column diameter-1 inch. Column temperature-100" C. Stationary phase-20 per cent. of Apiezon M on ungraded Celite. Carrier gas-Argon flowing at 600 ml per minute.Flash-heater teqberature-150" C. Detector-Argon ionisation detector with 1700 volts applied. Sample load-Approximately 0.5 g. DETERMINATION OF SODIUM 2,2-DICHLOROPROPIONATE An internal-standard procedure was used and o-xylene was found to be suitable for the purpose, as it was eluted after 2,3-DCP and before 2,2,3-TCP, complete resolution being obtained. To prepare the methyl esters the extracted acids were treated with diazomethane in ether solution. The diazomethane was prepared by Boer and Backer's m e t h ~ d , ~ which is given in the Appendix, p. 372. PROCEDURE- Weigh accurately 1 g of sample into a 50-ml separating funnel, and dissolve in 3 ml of water. Add 10 ml of ether and then 5 ml of 10 per cent. v/v sulphuric acid, and shake the funnel vigorously.Separate the aqueous layer, and extract it with a further 5 ml of ether. Wash the combined ether extracts with 1 ml of water. Add diazomethane solution until the yellow colour persists, indicating an excess of reagent. Filter through paper, wash the paper with ether, and carefully evaporate the ether solution until a volume of about 10 ml is obtained. Cool, transfer to a 20-ml calibrated flask with small amounts of ethanol, add exactly 0.500ml of o-xylene, and make up to volume with ethanol. Treat 0.85 g of standard sodium 2,2-dichloropropionate in exactly the same way for use as a standard, and chromatograph sample and standards under the following conditions- Column length-5 feet. Column diameter4 to 5 mm. Column temperature-94" C. Stationary phase-20 per cent.of Apiezon M on 100- to 110-mesh Celite. Carrier gas-Hydrogen - nitrogen mixture (4 + l), 65 ml per minute. Flash-heater tepperature-150" C. Detector-Thermal-conductivity detector. Sample size-50 p1. Recorder-1 -0-mv full-scale deflection, chart speed 24 inches per hour. Approximate inlet pressure-6 lb per sq. inch above atmospheric. Outlet pressure-Atmospheric. Under these conditions the column characteristics were- Retention volume (methyl 2,2-dichloropropz'onate)--456 ml, Retention volume (o-xylene)-952 ml. From the curves obtained for both standard and sample, measure the areas under the Calculate the 2,2-DCP content of the Mix well. methyl 2,2-dichloropropionate and o-xylene peaks. original sample from the equation- AB SB 2,2-DCP, % = 85 x -l where A = area under 2,2-DCP peak for sample, B = area under o-xylene peak for sample, S = area under 2,Z-DCP peak for standard and B, = area under o-xylene peak for standard.June, 19611 2,2-DICHLOROPROPIONATE (DALAPON SODIUM SALT) 369 DETERMINATION OF IMPURITIES The same sample solution was used as prepared for determining sodium dichloropro- pionate.Standard mixtures of esters were prepared from pure samples, the relative amounts being chosen to cover the concentration range expected in the samples to be assayed. Suit- able amounts of the esters were weighed into 20-ml calibrated flasks each containing 0.500ml of o-xylene and then made up to volume with ethanol. The chromatographic conditions were- Column length-6 feet . Column diameter-4 to 5 mm. Column temperature-100" C.Stationary phase-20 per cent. of Apiezon M on 100- to 110-mesh Celite. Carrier gas-Argon, 35 ml per minute. Flash-heater temperature-150" C. Detector-Argon ionisation detector with 1700 volts applied. Sample size-3 pl. The retention volumes under these conditions were- MCA .. . . . . 165ml MCP.. - . . . . . 209ml DCA.. .. . . . . 331ml 2,Z-DCP . . . . . . 407ml TCA . . . . . . 599ml 2,3-DCP . . * . . 736ml o-Xylene . . .. . . 880ml 2,2,3-TCP . . .. . 1530ml A standard curve for each minor component was prepared by using area ratios, with o-xylene as internal standard. During the run the recorder sensitivity was reduced by a factor of 10 during elution of the o-xylene. The peak area for each component in each standard mixture was measured, and the ratio to the peak area obtained for o-xylene was calculated.From these results standard curves were produced and were found to be reasonably reproducible from day to day. I t was convenient to use two separate instruments, one for determining dalapon and the other for determining impurities. Obviously this is not really necessary, since dalapon and its impurities can both be determined on the same sample by using a suitable standard mixture. CHEMICAL DETERMINATION OF SODIUM 2,Z-DICHLOROPROPIONATE Two basic methods are available. The first depends on hydrolysis to pyruvic acid and formation of a hydrazone, which may be either weighed or extracted and determined colorimetrically. The other depends on hydrolysis to pyruvic acid and simultaneous forma- tion of a mercury complex, which is isolated and allowed to react with potassium iodide, and the liberated base is then titrated.In neither method is the hydrolysis complete; with the colorimetric method it is necessary to treat a standard simultaneously with the samples, but for the mercury method a factor may be employed. COLORIMETRIC HYDRAZONE METHOD- The method is based on formation of the 2,4-dinitrophenylhydrazone after hydrolysis and measurement of its colour intensity after extraction into alkaline so1ution.l s2 The intensity and peak wavelength of the extracted hydrazone were found to vary according to the concentrations and proportions of the sodium carbonate and sodium hydroxide. This point was therefore examined in detail by carrying out determinations on a standard solution of freshly distilled pyruvic acid.With sodium carbonate solution as the extraction medium it was found that peak absorption occurs at 370 mp. The Et2 values of the final solution were obtained from four separate determinations and found to be 2206, 2168, 2180 and 2188. Because of the variation, the effect of the amount of sodium carbonate present in the final solution was examined; the results were- Volume of 20 per cent. w/v sodium carbonate per 200 ml, ml 5 10 15 20 25 E:,%m .. .. .. .. * . .. .. . . 2207 2307 2118 2066 2054370 GARRATT THE ANALYSIS OF COMMERCIAL SODIUM v o l . 86 If sodium hydroxide is added to the sodium carbonate extract the peak absorption shifts to 445mp. Some workers have used the mixed alkalis to determine pyruvic acid, but opinion differs widely on the concentrations required.Work was carried out to determine the optimum nonnalities. Extraction of the pyruvic acid 2,4-dinitrophenylhydrazone into sodium carbonate solution was carried out by the method described below in which two 5-ml portions of 20 per cent. w/v sodium carbonate solution are used, since this volume gave the highest Ei?m values. Different volumes of N or 2 N sodium hydroxide were added to the carbonate extracts, and the solutions were diluted to 200ml and read at the peak wavelength of M5mp after 10 minutes; the results are shown in Table I. TABLE I Ei& VALUES FOK SODIUM CARBONATE EXTRACTS Concentration of measured solution with respect to sodium hydroxide, li 0-05 0.075 0.10 0.13 0-15 0.18 0-20 0.23 0.25 0.30 0-35 0.40 0.45 0.50 0.56 0-60 0.66 0-75 0-80 0.90 1-00 1.20 E:& 1510 1628 1666 1744 1782 1816 1862 1886 1912 1900 1906 1977 1990 2020 2040 2040 2040 2040 2040 2040 2020 1994 Wavelength of peak absorption, mp 440 440 440 440 440 440 445 445 445 445 445 445 445 445 445 445 445 445 445 445 445 445 The stability of the colour developed with the final normality in sodium hydroxide of 0.75 was determined; the results were- Time after adding sodium hydroxide, minutes .. .. .. .. 10 30 60 80 90 100 110 120 Ei& .. .. .. .. .. 2040 2040 2040 2035 2027 2015 2002 1997 With the final normality in sodium hydroxide maintained at 0.75, the volume of 20 per cent. w/v sodium carbonate solution used was varied; the results were- Volume of 20 per cent. w/v sodium carbonate solution, ml .. .. 5 6 8 10 11 12 13 15 Concentration of measured solution with respect to sodium carbonate, N 0.094 0.113 0.151 0-189 0.208 0-227 0.246 0.283 EiZ .. .. .. .. .. 2014 2019 2027 2040 2040 2035 2030 2019 For maximum extinction values of reasonable stability, the normality of sodium hydroxide should fall between 0-55 and 0.90 and that of sodium carbonate between 0.19 and 0.23. It has been demonstrated that variations in laboratory temperature of from 0" to 37" C have no significant effect on the intensity of colour developed. The procedure finally adopted for the colorimetric determination of sodium 2,Z-dichloro- propionate in commercial dalapon sodium salt is described below. PreParation of 2,4-dinitropheny~~ydrazin~ solution-Suspend 1 g of 2,4-dinitrophenyl- hydrazine in 10 ml of 2 N hydrochloric acid.Then add 5 ml of concentrated hydrochloric acid and finally, with agitation, a further 300 ml of 2 N hydrochloric acid. Filter the solution.June, 19611 ~,~-DICHLOROPROPIONATE (DALAPON SODIUM SALT) 37 1 PROCEDURE- Place 150 ml of distilled water and 2 ml of N sodium hydroxide in a 500-ml Erlenmeyer flask, and heat to boiling. Add to the boiling solution exactly 5 ml of a solution prepared by dissolving 1 g of sample in exactly 50 ml of distilled water, cover the flask with a watch- glass, and transfer immediately to an oven at 110" C. After 3 hours remove the flask, cool, and adjust the volume of the solution to 200 ml in a calibrated flask. Transfer 5 ml of this solution to a suitable separating funnel, add 2 ml of 2,4-dinitrophenylhydrazine solution, and mix thoroughly.Add 20ml of toluene, and shake the funnel vigorously for 2 minutes. Remove excess of phenylhydrazine reagent by shaking the toluene with two 5-ml portions of 2 N hydrochloric acid, then remove traces of acid with 15ml of water. Add exactly 10ml of 10 per cent. w/v sodium carbonate solution, and shake the funnel vigorously for 2 minutes. Run the hydrazone into a 200-ml calibrated flask. Repeat the extraction with a further 10-ml portion of the sodium carbonate solution, followed by two washings with water, each of 15 ml, collecting all aqueous phases in the flask. Add 75 ml of 2 N sodium hydroxide, mix, dilute to volume with water, and mix again. Set aside for 10 minutes before measuring the extinction; read in either a 0.5- or 1-cm cell at 445mp within 1 hour of adding the hydroxide solution, and compare the colour with that obtained by treating a sample of pure sodium 2,2-dichloropropionate in the same way.TITRIMETRIC MERCURY-COMPLEX METHOD- The mercury method of Marquardt and Luce for sodium 2,2-dichlor~propionate~ was applied without modification. It should be noted, however, that the precipitated mercury complex may need to be washed with more water (75 to 100 ml) to free it from acid, and it is advisable to test the washings with litmus paper. Set aside for 20 minutes. Remove the aqueous layer when clear, and discard. CHEMICAL DETERMINATIONS OF POSSIBLE IMPURITIES SODIUM PYRUVATE- As small amounts of sodium pyruvate are usually present in commercial samples of dalapon sodium salt, it is necessary to determine the amount, because results obtained by either the colorimetric or the titrimetric method for the principal constituent include this and must be corrected.The pyruvate is conveniently determined by the colorimetric procedure described above, a suitable weight of sample being used and the hydrolysis stage omitted. Marquardt and Luce described methods for the chemical determination of these two impurities, and it was of interest to compare the results with those obtained by gas chromato- The published procedure for the monochloropropionate was followed without alteration, but difficulty was experienced with the determination of the trichloropropionate. The direc- tions given could not be followed clearly, since a number of inconsistencies are apparent in the published text.The method used for trichloropropionate was similar to that given, but 0.5 g of sample and N potassium hydroxide were used. When carried out on laboratory-prepared mixtures with the standard sodium 2,2-dichloropropionate the results were- SODIUM SALTS O F MONOCHLORO- AND TRICHLOROPROPIONIC ACIDS- graphy. 4 Trichloropropionate added, yo . . .. . . 5.6 5.4 2.2 2.2 0.0 Trichloropropionate found, % . . . . . . 6-7 5-5 3.4 3-0 1.6 It is concluded that results obtained for sodium 2,2,3-trichloropropionate by the chemical method are unsatisfactory, and if a determination of this component is required the gas- chromatographic method, which has given good recoveries on standard mixtures, should be used.RESULTS The methods described above were applied to commercial samples of dalapon sodium salt, and comparative results are recorded in Table 11. Table I11 shows comparative results obtained in the routine application of these methods. Some of the samples examined were known to contain a wetting agent and this did not interfere with the methods.372 GARRATT THE ANALYSIS OF COMMERCIAL SODIUM ANALYSIS OF SAMPLES Sodium 2,2-dichloro- propionate plus sodium pyruvate, expressed as sodium 2,2-dichloro- propionate, found by- Sample A B C D r colori- metric method, 82.7, 83.3 70 83.2, 81.6 83.2, 85.0 87.2, 86.4 mercury method, % 83.6, 85.1, 84.2, 84.5, 84.1 83.3, 81.7, 83.5, 84.5, 83.7, 84.6, 83-8, 84-0 85.5, 85.1, 85.8, 86.1, 85-0 86.7, 86-6 D$lUs 88.4, 89.0 87.4, 88-1 3 per cent.of added sodium pyruvate ANALYSIS OF SAMPLES TABLE I1 OF DALAPON SODIUM SALT BY VARIOUS METHODS Sodium 2,2-di- chloropro- pionate found by gas- chromato- graphic method, 82.9 % 85-2 Sodium pyruvate found by colori- metric method, % 0.84, 0.64 0.05, 0.05 [Vol. 86 Sodium 2-mono- chloropropionate found by- Sodium 2,2,3- trichloropropionate found by- I I gas- chromato- mercury graphic method, method, 3-6 3.4 % % 7.5, 6.2 6.8 r 1 gas- chromato- mercury graphic method, method, % % 5-2, 2.9 4.3, 4.2 2.6, 1.1 2-5 84.7 0.15, 4.2, 3.3 3-7, 2.0 0.15 4.1 4.3 87.1 0.13, 3.9, 3.8 3.2, 2.2 0-13 3-2 3.1 86.9 3.31, 3.4, 4.0 2.6, 2.7 3.32 2.7 2.9 TABLE I11 OF DALAPON SODIUM SALT BY VARIOUS METHODS Sodium 2,2-dichloropropionate $us sodium pyruvate, expressed as sodium 2,2-dichloropropionate, found by Sample mercury method, % E F 84-1, 83.1, 84.9, 84.8 G 88.4, 88.4, 88.7 H 84.4, 83.5 J 86.0, 86.1 85.2, 85.3, 84.0, 84.0, 85.9 Sodium 2,2-dichloropropionate found by gas-chromatographic method, 84.3 85-5 88.8 84.2 88.4 % Sodium pyruvate, as pyruvic acid, found by colorimetric method, 0.15 0.05 Negligible 0-03 0.04 % CONCLUSION A gas-chromatographic method for determining 2,2-dichloropropionic acid and the many possible impurities that may occur in commercial samples of dalapon sodium salt has been developed.Results for the main constituent have been compared with those obtained by chemical methods of assay, and, in general, agreement has been found to be satisfactory. The choice of method in any given instance would depend on the information required.If occasional samples are being analysed for 2,2-dichloropropionic acid content then the mercury-precipitation method of Marquardt and Luce is to be recommended. The colorimetric method requires less operator time and therefore offers advantages when many samples are to be examined simultaneously. When fuller information is required about the composition of the sample, the gas-chromatographic procedure is undoubtedly the method of choice. Appendix PREPARATION OF DIAZOMETHANE REAGENTS- absolute ethanol. ether. Solzction A-Dissolve 3.5 g of potassium hydroxide in 5 ml of water, and add 15 ml of Solution B-Dissolve 15 g of N-methyl-N-nitroso-$-toluene sulphonamide in 85 ml ofJune, 19611 2,%DICHLOROPROPIONATE (DALAPON SODIUM SALT) 373 PROCEDURE- Heat solution ,4 in a 100-ml flask on a water bath maintained at 65" C. Connect to the flask a dropping funnel and a double-surface condenser leading into two 250-ml flasks in series, each containing 40 ml of ether and each cooled in an ice - salt mixture. Ensure that the inlet tubes to these flasks dip below the surface of the ether. Add solution B slowly from the dropping funnel so that the rate of addition equals the rate of distillation. After all solution B has been added, add a further 10ml of ether and continue the distillation until a colourless distillate is obtained. Dry the ethereal solution of diazomethane contained in the first receiver for 4 hours with about 5 g of potassium hydroxide pellets, and then filter it through a Whatman No. 1 filter-paper into a suitable container. Fit a calcium chloride drying tube to the container, and store at 0" C. Under these conditions the solution is stable for about 1 week. REFERENCES 1. 2. Roth, H., personal communication. 3. Crowshaw, W., personal communication. 4. 5 . Smith, G. N., Getzendaner, M. E., and Kutschinski, A. H., J . Agvic. Food Chem., 1957, 5, 675. Boer, T. J. de, and Backer, H. J., Rec. Trav. Chzm. Pays-Bas, 1954, 73, 229. Marquardt, R. P., and Luce, E. N., Avzal. Chem., 1959, 31, 418. Received November 8tk, 1960

ISSN:0003-2654    

DOI:10.1039/AN9618600367

出版商:RSC    

年代:1961

数据来源: RSC

摘要:

June, 19611 2,2-DICHLOROPROPIONATE (DALAPON SODIUM SALT) Reactions of Steroids Sulphuric Acid (the with Acetic Anhydride 373 and Liebermann - Burchard Test) BY R. P. COOK (Biochemist~y Department, Queen’s College, University of St. Andrews, Dundee) The intensities of colours developed and the rates of reaction when various steroids (CIS to C,,) dissolved in acetic acid were treated with acetic anhydride and sulphuric acid (the Liebermann - Burchard test) have been investigated ; cholesterol was used as standard. Only certain sterols (C,,, C,, and C,J and some of their derivatives gave a typical blue-green colour. The colour intensities produced , relative to that developed by cholesterol, could be grouped in five classes: (i) zero or slight, (ii) about half, (iii) equal to and either “fast” or “slow acting,” (iv) about twice and either “fast” or “slow acting” and (v) four to six times greater, all being “fast acting.” The nature and conformation of the substituents in positions 3 and 7 of the sterol ring appear to be important.THE Liebennann - Burchard test consists in adding to a sterol, dissolved in a suitable solvent, acetic anhydride containing a small amount of sulphuric acid, when a (usually) blue-green colour develops; a history of the test was given by Dam.l The test, used both qualitatively and quantitatively, is much employed in studies of sterols, particularly with cholesterol. This paper describes the comparative results obtained after testing a number of steroids and their derivatives dissolved in acetic acid, cholesterol (cholest-5-en-3/3-01) being used as an arbitrary standard.Some observations on cholesteryl esters dissolved in chloroform (many are insoluble in acetic acid) are also made. The colours developed after 1-5 (“fast acting”) and 35 minutes (“slow acting”) were observed and measured (cf. paper by Moore and Baumann2).374 COOK: REACTIONS OF STEROIDS WITH ACETIC ANHYDRIDE [Vol. 86 NAMING OF COMPOUNDS The generic name "steroid" is used for compounds containing the perhydrocyclopenteno- phenanthrene nucleus with various substituents attached. In Table I (p. 375), the main headings are- Sterols-These are steroids having a side-chain of eight, nine or ten carbon atoms, always with a hydroxyl group at position 3. In their systematic description, to avoid use of a large number of roots, cholestane has been taken as the parent compound; to this have been added (as prefixes, with the number in the steroid skeleton or in the side-chain) methyl, ethyl or hydroxyl substituents.Stavtols-These are fully saturated sterols. Stevtols-These are sterols having one double bond and one hydroxyl group in position 3. Di~~droxystenols-These are sterols having one double bond and two hydroxyl groups. Stenadi(tri)e72oZs--These are sterols having two or three double bonds and one hydroxyl group. Compounds defined by a page reference to Fieser and Fieser's "Steroids" are described Systematic naming is generally in accordance with I.U.P.A.C. in more detail in that book.3 rules*; the trivial name or names follow the systematic name. METHOD REAGENTS AND C O M P O U N D S All chemicals used were of analytical-reagent grade, and attention was paid to the removal of all but traces of water.The compounds tested were obtained from the sources listed in the Appendix, p. 380. Cholesterol standard-Commercial cholesterol was recrystallised from glacial acetic acid by Fieser's method and then recrystallised from methanol; the purified compound was stored in dark bottles and kept at -15" C. Its melting-point was 149.5" to 150" C in a sealed capillary tube and 148" to 149' C in a Kofler block; its specific rotation, [ ~ r ] ~ ~ " , was -3943" (C = 1.5 in chloroform). PROCEDURE- As only small amounts of certain compounds were available, samples of about 1 mg were accurately weighed in a tared 1-ml calibrated flask on a microbalance (sensitivity 0.01 mg).Glacial acetic acid was then added, with warming if necessary to ensure solution, and the contents of the flask were diluted to the mark. The cholesterol standard was similarly treated. The colour-forming reagent consisted of chilled acetic anhydride (19 volumes) to which was added 1 volume of concentrated sulphuric acid; the reagent was freshly prepared for each test. For the test itself, 1-0 ml of colour-forming reagent was added to 0.5 ml of steroid solution, and the solution was well mixed with a fine glass rod. The colour developed was observed visually after 1.5 and 35 minutes and after 20 hours. The intensity of colour was measured with an E.E.L. colorimeter (Evans Electroselenium Ltd.), the No. 205 red filter being used.2" C in tubes shielded from direct light. Duplicate determinations were always made, and any discrepant values were re-determined. The results were calculated from the optical densities on a weight-to-weight relationship ; the intensity of colour developed after 35 minutes by 0-5 mg of cholesterol was taken as 100. A numerical relationship was found, but, as the compounds had perforce to be tested in small batches over a period of 3 years, it was thought that a system of intensity rating indicating a broad comparative basis was more suitable than a whole-number relationship. With most of the compounds, the relationship is approximately equimolecular, notable exceptions being bi-steroids (see Table I, samples Nos. 54, 55 and 56) and cholesteryl esters.Colour was developed at 20" RESULTS STEROLS AND RELATED COMPOUNDS- to similar studies on certain of the samples have been included. The results for these substances are shown in Table I. For ease of presentation, referencesTABLE I REACTIONS OF STEROLS AND RELATED COMPOUNDS IN THE LIEBERMANN - BURCHARD TEST Sample No. Stanols- 1 2 3 4 5 6 7 8 9 10 Stenols- 11 12 13 13A 14 15 16 17 The notation used for intensity of colour is based on the optical density compared with that developed by 0-5 mg of cholesterol (taken as 100) : 0 = no reaction; S = 10 to 20; 0-5 C = 40 to 60; C = 80 to 140; 2 C = 160 to 240. Intensities greater than 400 are expressed to the nearest whole-number multiple of C. Colours and intensities after 20 hours are given only when stability or intensification was observed; in general, the colours faded to a green-blue of intensity about 0.5 C Compound 5a-Cholestan-3a-01 (epicholestanol) 5a-Cholestan-3 /3-01 (cholestanol, dihydro- 5 P-Cholestan-3a-01 (epicoprostanol) 5 /3-Cholestan-3 /3-01 (coprostanol, copro- 4a-Methyl-5a-cholestan-3 /3-01 4,4-Dimethyl-5a-cholestan-3 p-01 (di- 5a-Cholestane-3/3, 5a-diol 5a-Cholestane-3 /I, 7a-diol 3-acetate 5a-Cholestane-3 /3, 7 /3-diol 3-acetate 5a-Cholestane-3 /3, 5a, 6/3-triol cholesterol) sterol) meth ylcholestanol) Cholest-4-en-3 /3-01 (allocholesterol) Cholest-5-en-3a-01 (epicholesterol) Cholest-5-en-3 /3-01 (cholesterol) Cholesterol hydrate 19-Norcholesta-6-en-3 /3-01 (norcholesterol) 5a-Cholest-6-en-3 p-01 acetate 5wCholest-7-en-3 /3-01 (lathosterol, 5 /3-Cholest-7-en-3/3-01 (coprostenol) A'-cholestenol) Source No. * 9 9 9 6, 13, 22 14, 28 26 4 1 1 11 15 15 See text 6 29 12 9 2 Colour and relative intensity after- 1.6 minutes 36 minutes r - 0 Brown-green; S None None 0 Pale blue; S 0 Green-blue; 0.5 C 0 Green; S 0 Green-blue ; S 1 Blue-green ; C Blue; C Deep blue-green ; 2 C Blue-green ; 2 C None None 0 Green; 2 C 0 Blue-green ; 2 C 0 Green; 2 C 0 Blue-green ; C 0 Blue-green ; C 0 Pink Blue-green ; C Blue; 6 C Blue-green ; C Blue; 6 C Purple; C Purple; C w 6 E Keferencet + U +I Remarks G n 3a axial 3 #I equatorial J 3a equatorial 313 axial Intensifies to about 0.5 C on standing - 3/3 equatorial, 5a axial - 3 #I equatorial, 5a and 6 j? axial 3 #I equatorial - 3 /3 equatorial - greater than for cholesterol - 3 /3 equatorial - 315 axial - w Z 3/3 equatorial, 7a axial I W c 38 and 78 equatorial } w 0 X - cl - 3a axial Intensity about 10 per cent.W 7 38 equatorial 6 - * See Appendix, p. 380. t See reference list, p. 380.TABLE 1 ( c o d . ) Colour and relative intensity after- w 4 b, SamDle Source NO. Compound Stenols 18 19 20 21 22 23 24 25 (c0Tttd.)- 4a-Methyl-5a-cholest-7-en-3 /3-01 (metho- 4a-Methyl-5a-cholest-8-en-3 /3-01 4a-Methyl-5a-cholest-8( 14)-en-3 /?-01 4a-Methyl-5a-cholest-14-en-3 8-01 4,4-Dimethylcholest-5-en-3/3-01 24a-Methylcholest-5-en-3 8-01 (campesterol) 24b-Ethylcholest-5-en-3 /I-01 (/3-sitosterol) 24-Ethylidenecholest-5-en-3 /3-01 (fucosterol) stenol, lophenol) Dihydyoxystenols- 26 Cholest-4-ene-3/3, 6/3-diol 27 Cholest-5-ene-3 /3, 4/3-diol 28 Cholest-B-ene-3/3, 7a-diol 29 Cholest-5-ene-3 /3, 7 /I-diol 30 Cholest-5-ene-S/?, 24b-did 31 Cholest-B-ene-3j3, 25-diol 32 Cholest-5-ene-3/3, 26-diol Sknadi (tvi) ends- 33 Cholesta-5,7-dien-3 j-01 (7-dehydrochole- sterol) 34 Cholesta-5, 22-dien-3 8-01 (22-dehydro- cholesterol) 35 Cholesta-5,24-dien-3 8-01 (24-dehydro- cholesterol, desmosterol) 36 Cholesta-5,25-dien-3 8-01 37 Cholesta-8(9),22-dien-38-01 (zymosterol) 38 24b-Methylcholesta-8( 14) ,22-dien-3 8-01 39 24b-Methylcholesta-5,22-dien-38-01 40 24b-Methylcholesta-6,7,22-trien-3 /3-01 41 24b-Ethylcholesta-6,22-dien-3~-01 42 24b-Ethylcholesta-7,22-dien-3 p-01 ( A8 ( la) -ergos t erol) (brassicasterol) (ergosterol) (stigmasterol) (a-spinasterol) No.* 15, 28 14 14 14 4 1 1 1 21 12 12 12 9 9.24 18 20 3 3 3 1 4 1 20 1 1 1.5 minutes Deep blue; 5 to 6 C Blue-purple; 2 C Blue-purple ; 2 C, Purple; 3 C Blue; 2 C 0 Green; S 0 Dark blue; 6 C Blue; 2 C Blue-green; 6 C Blue; 6 C 0 0 0 Blue; 6 C 0 0 0 Blue-green; C Blue; 2 C Green; S Blue; 6 C 0 Blue; 5 C Remarks 35 minutes Deep purple; 4 t o 5 C Blue-purple; 2 C Purple; 3 C Green-blue ; 3 C Blue-green ; C Green; C Green; C 3/3 equatorial 3 /3 equatorial 3 /3 equatorial 3 /3 equatorial Green; 7 C Green; 2 C Blue-green; 6 C Blue; 6 C Green; C Green; C Blue-green ; C 3 /3 equatorial, 6 /3 axial 3 /3 equatorial, 4 /3 axial 38 equatorial, 70( axial 313 and 78 equatorial 3/? equatorial 3 /3 equatorial 3 /3 equatorial 3 13 equatorial Green; 4 C Blue-green; C Green; 0.5 C Green; C 3 equatorial 3 /3 equatorial 3 /? equatorial Blue-green; C Green-blue; 2 C Green; C Green; 4 C Blue-green; C 3/3 equatorial Blue-green; 2 C 3 8 equatorial Reference? 8 9 - 6 - 10 - cholestenol 6 (for analogues) - 6 6 0 0 0 w * See Appendix, p.380. t See reference list, p. 380.Sample No. Compound 0 x 0 compounds- 43 44 45 46 47 48 49 50 50A 51 Ketols- 52 53 5a-Cholestan-3-one (cholestanone) 5 8-Cholestan-3-one (coprostanone) Cholest-4-en-3-one (A4-cholestenone) Cholest-5-en-3-one (As-cholestenone) Cholest-7-en-3-one (A7-cholestenone) Cholesta-3,5-dien-7-one Cholesta- 4 6 -dien- 3-one 24b-Methylcholesta-4,7,22-trien-3-one (ergosta-4,7,22-trien-3-one) Enol acetate of sample No. 50 Cholest-4-en-6 8-hydroperoxy-3-one ( A4-cholestene-3-one-6 /3-hydroperoxide) Cholest-5-en-3 8-01-7-one (7-oxo(keto) - Cholest-5-en-3 b, 26-diol- 16,22-dione cholesterol) (kryptogenin) Bi-steroids- 64 Cholestenone pinacol 56 3,3-Bis(cholesta-3,5-dienyl) 66 7-Oxocholesteryl acetate pinacol MisGe~~ane0U.s- 57 Cholest-5-en-3 p-thiol (thiocholesterol) 68 Cholesteryl methyl ether 69 Dicholesteryl ether 60 “Isocholesterol” 61 4,4,14-Trimethy1cho1est-8-en-3 /3-01 ( As-lanosterol, dihydrolanosterol) TABLE I (contd.) Colour and relative intensity after- Source f A \ No.* 1.5 minutes 35 minutes 9 None None 6 Purple: 4 C Blue-green; 4 C 4 0 Pale green; S 4 0 Apple green; 0.6 C 4 Fluorescent green; Intense fluorescent 2 c green; 2 C 4 Fluorescent green ; Intense fluorescent 0.5 C green; 2 C 9 None None 4 None None 4 None Red-yellow fluores- cence; S 4 Purple: 2 C Blue-green; 3 C 4 Purple; C Dark blue; 2 C 4 Green; 0.6 C Ydlow; s 19 0 Blue-green; 2 C 6 0 Blue-green ; C 7 None None 6 Yellow-green Yellow-green fluorescence fluorescence 1 Yellow-green Yellow-green fluorescence fluorescence Remarks Referencet I I - - I - Colour constant after 18 hours - Multiply by 2 for molar comparison - - - Mixture of trimethylsterols - - 3 (p.235) 11 (preparation and structure) - - - - - 3 (p. 364) - * See Appendix, p. 380. t Sep reference list, p. 980.378 [Vol. 86 OTHER STEROIDS- Representative steroids only were tested, but particular attention was paid to available compounds having a A5, 3/3-01 configuration (i.e., 3/3-hydroxyld-en). The sources of these samples are listed in the Appendix, p. 380. Oestrogens-These have eighteen carbon atoms and are described on p. 463 of v steroid^."^ Some samples of oestrone, oestradiol and oestriol from sources Nos.16 and 25 tested under the standard conditions gave an immediate eosin-like fluorescent colour that later faded to yellow, but other samples gave negative results. With the latter, it was observed that a colour could be produced by adding excess of concentrated sulphuric acid. Androgens-These have nineteen carbon atoms and are described on p. 519 of e steroid^."^ 17/3-Hydroxyandrost-4-en-3-one (testosterone) from source No. 17 gave no colour ; 3p- hydroxyandrost-5-en-17-one (dehydroepiandrosterone) from source No. 15 gave a pale yellow ; androst-5-ene-3P, 17a-diol (source No. 15) gave an immediate deep red, changing after 30 minutes to yellow-brown ; androst-5-ene-3/3,17/3-diol (source No. 15) gave no colour.Gestagens-These have twenty-one carbon atoms and are described on p. 566 of steroid^."^ Pregn-4-ene-3,20-dione (progesterone ; source No. 17) and its main reduction products gave pale yellow colours, as did the 3/3,5-en compounds 3P-hydroxypregn-5-en-20-one and pregn- 5-ene-3/3,20P-diol (source No. 15). Corticoids-These have twenty-one carbon atoms and are described on p. 603 of “Steroids.”3 No reaction was obtained with cortisol, cortisone and corticosterone from source No. 17. No samples of corticoids having 3/3-hydroxyl-5-en structure were available for testing. Cardenolides-These have twenty-three carbon atoms and are described on pp. 736, 752 and 754 of v steroid^."^ Those tested were from sources Nos. 5 and 23 and had the 5/3-con- figuration; the positions of the hydroxyl substituents are given after the trivial names, and the colours are those obtained after 30 minutes.Digitoxigenin (3/3,14-dioi), yellow; digoxi- genin (3a,12a,14-triol), pale green; gitoxigenin (3/3,14,16-triol), light yellow ; strophanthidin (3/3,5p,14-triol and CHO group at C,,), yellow, which intensified to about 0.5 C on standing. Conessine-This has twenty-four carbon atoms and is described on p. 857 of steroid^"^; it has the A5 configuration, but a N-dimethyl group at position 3. A sample from source No. 4 gave a negative result. Bile acids-These have twenty-four carbon atoms and are described on p. 422 of steroid^."^ The positions of the substituent hydroxyl groups in the parent cholanic acid are given after each trivial name and are followed by the source number; the colours are those formed after 30 minutes.Lithocholic (3a; No. IS), none; hyodeoxycholic (3a, 6,; No. 1 1), none ; chenodeoxycholic (3a, 7a ; No. 1 1), red-yellow, intensity about 10 ; deoxycholic (3a, 12a; No. ll), yellow-green, intensity about 10; hyocholic (3a, 6a, 7a; No. S), none; acid IT (a-muricholic; 3a, 6P, 7a; No. S), none; acid I (P-muricholic; 3a, Sp, 7p; No. €9, none; acid IV (a-muricholic; 3cc, 6a, 7/3; No. €9, none; cholic (3a, 7a, 12a; No. 16), red-yeilow. Sapogenins (spimfans)-These have twenty-seven carbon atoms and are described on p. 831 of steroid^."^ The main substituents, sources and colours after 30 minutes of the compounds tested were: tigogenin (5a, 3/3-hydroxy ; No. lo), pale yellow; hecogenin (5a, 3/3-hydroxy, 12-0x0; No.lo), pale yellow; 9(11)-dehydrohecogenin (as for hecogenin, but with Ag(11); No. 4), pale yellow; diosgenin, (A5, 3p-hydroxy; No. lo), pale yellow-green; kryptogenin is included in Table I (sample No. 53). CHOLESTERYL ESTERS- The cholesteryl acetate tested was from source No. 6; the others were from source No. 27 (preparation and properties described by Swell and Treadwell12). All the compounds were tested in chloroform; the esters of fatty acids up to C1, were also tested in acetic acid, those with longer chains being insoluble. These tests were carried out by Mr. A. El Sheltawy. Cholesterol in chloroform gives an intensity of 120, compared with 100 in acetic acid. The results are expressed as comparative to the standard in a particular solvent and are given as the cholesterol equivalent in the compound (calculated from the molecular weight).Acetate and propionate, respectively, 60 and 90 (chloroform), 70 and 160 (acetic acid). Dimethylacetate, isobutyrate, n-valerate, isovderate, DL-ethylmethylacetate, isohexanoate, octanoate and decanoate, about 130 (chloroform) and about 90 (acetic acid). Dodecanoate (laurat e) , te tradecanoate (myrist ate), hexadecanoate (palmit ate), oct adecanoate (st earat e) and octadecenoate (oleate) were insoluble in acetic acid and each gave an intensity of about COOK : REACTIONS OF STEROIDS WITH ACETIC ANHYDRIDEJune, 19611 AND SULPHURIC ACID (THE LIEBERMANN - BURCHARD TEST) 379 130 in chloroform. A “fast” reaction, i.e., development of colour after 1-5 minutes, was obtained with most of the esters in chloroform, and the intensity did not decrease greatly after 35 minutes.The benzoate behaved similarly. DISCUSSION OF RESULTS The production of chromogens, some of which are fluorescent, from steroids by relatively large amounts of the so-called Lewis acids, i.e., electron acceptors (including with the con- ventional strong acids such compounds as antimony tri- and pentachlorides) , is a commonly used qualitative and quantitative pr0~edure.l~ The mechanism of the reaction or reactions is obscure,14 and it was not our primary intention to study this, but to obtain information on the value and limitations of the Liebermann - Burchard test. The blue-green colour developed in this test by certain sterols and their derivatives is remarkable for the small amount of sulphuric acid needed, but only slight green-yellow colours are given by androgens, corticoids, bile acids , cardenolides and sapogenins.Oestrogens give, inconsistently, a red- green fluorescence, presumably owing to the phenolic nature of ring A. Trimethyl sterols (lanostane derivatives) give a yellow-green fluorescence. Five broad divisions of colour development and intensity for sterols and their derivatives can be made. These divisions are set out below, the sample numbers referring to Table I. Compounds producing a colour of slight or zero intensity-This class includes 5a- cholestan-3P-01 (sample No. 2) and the corresponding mono- and dimethylstanols (samples Nos. 5 and 6), most oxosteroids (samples Nos. 43, 44, 45 and 46), ‘I-0x0- cholesterol (sample No.52) , 5a-chole~tane-3j3~7P-diol (sample No. 9) and dicholesteryl ether (sample No. 59). The methyl ether (sample No. 58), however, is reactive, possibly because of the relative ease of hydrolysis. Compounds producing a colour intensity half that developed by cholesterol-This class includes coprostanol (sample No. 4) and 24-dehydrocholesterol (sample No. 35). Compounds Producing a colow intensity about the same as that developed by cholesterol- This class has two subdivisions, “fast-acting” and “slow-acting” compounds. The former subdivision includes stenols (samples Nos. 15 and 17) and zymosterol (sample No. 37). The latter subdivision includes all stenols having one double bond in position 5; the substitution of a hydroxy, methyl or ethyl group in the side-chain did not affect the intensity developed (compare results for samples Nos.23, 24, 25, 30, 31 and 32), but the introduction of a double bond other than ethylidene into the side-chain appeared to cause lower intensities (compare samples Nos. 34, 35, 36 and 39, for which the intensities were 70, 50, 70 and 85, respectively). Cholesterol hydrate consistently gave an intensity 10 per cent. greater than that developed by cholesterol. Compo.unds producing a colour intensity about twice that developed by cholesterol- This class has the same subdivisions as Class 3. The “fast-acting” compounds include 4-mOnO- and 4,4-dimethylstenols having double bonds in positions 6, 8, 8(14) or 14 (samples Nos, 19, 20, 21 and 22) and the cholestanediols (samples Nos.7 and 8). The “slow-acting” compounds include epicholesterol (sample No. 12) and thiocholesterol (sample No. 57). Compounds producing a colozlr intensity five to six times that developed by cholesterol- Members of this class are “fast acting,” but the intensities developed decrease after 35 minutes. The compounds all have a double bond in position 7, either alone (samples Nos. 16, 18 and 42) or conjugated with a double bond in position 5 (samples Nos. 33 and 40); others are capable of conversion by dehydration to a conjugated diene (samples Nos. 26, 28 and 29). This “stenadiene” group will form a colour with acetic anyhydride and zinc chloride as dehydrating agent,15 a reaction not given by 7-en stenols; the intensity developed is similar to that de- veloped by cholesterol, and the colour is stable.(This test is useful for differentiating between 7-en and 5,7-dien stenols.) Although oxosteroids are not generally reactive , A7-cholestenone (sample No. 47) is “fast acting” (see also sample No. 50). A few generalisations may be made, namely, that a blue-green colour is obtained only when the steroid has the complete nineteen carbon atoms of the steroid skeleton (for other examples, see paper by Pesez7) and a side-chain of at least eight carbon atoms. The nature380 COOK: REACTIONS OF STEROIDS WITH ACETIC ANHYDRIDE [Vol. 86 and conformation of the substituents at positions 3 and 7 are important. At position 3, the group may be a free or esterified hydroxyl group or a thiol group, and the axial con- formation is apparently more reactive.0x0 sublstituents at position 3 are unreactive, except when there is a double bond at position 7. Cholesteryl esters are of interest in that they are apparently more reactive than the free sterol when in chloroform solution; this established fact16 is still without explanation. At position 7, the presence of a double bond, or the possi- bility of dehydration to form one, confers increased reactivity; the presence of an 0x0 group decreases reactivity . Much of the experimental work was done by Miss D. Young, Miss Marian Greig, Mr. D. I. Cargill, Mr. A. D. Tait and Mr. A. El Sheltawy, to whom I am grateful. Dr. P. Bladon has kindly helped with timely and constructive advice. Part of the expenses was met by a grant from the Scottish Hospital Endowments Research Trust.I thank the persons named in the Appendix for donating the steroids tested. Appendix The steroids tested were obtained from the sources listed below; unless otherwise stated, samples were kindly donated. SOURCES 1. D. H. R. Barton, London. 2. C. A. Baumann, Madison, Wisconsin, 1J.S.A. 3. The late W. Bergmann, Yale University, New Haven, Connecticut, U.S.A. 4. P. Bladon, Royal College of Science and Technology, Glasgow. 5. Burroughs Wellcome & Co. Ltd., London, by courtesy of R. 0. Thomson. 6. This laboratory; most of the compounds were recrystallised or prepared by A. D. Tait. 7. J. W. Cornforth, London. 8. E. A. Doisy, St. Louis University, St. Louis, Missouri, U.S.A. 9. L. F. Fieser, Harvard University, Cambridge, Massachusetts, U.S.A.10. Glaxo Laboratories Ltd., London, by courtesy of T. F. Macrae. 11. G. A. D. Haslewood, London. 12. H. B. Henbest, Queen’s University, Belfast, Northern Ireland. 13. R. N. Jones, Ottawa, Canada. 14. A. A. Kandutsch, Bar Harbor, Maine, U.S.A. 15. W. Klyne, London (Steroid Reference Collection). 16. L. Light & Co. Ltd., Colnbrook, Bucks., by purchase. 17. Merck & Co. Inc., Rahway, New Jersey, U.S.A., by courtesy of M. Tishler. 18. E. Mossetig, Bethesda, Maryland, U.S.A. 19. L. N. Owen, London. 20. Peboc Ltd., London, by purchase. 21. V. Prelog, Zurich, Switzerland. 22. The late 0. Rosenheim, London. 23. Sandoz, Basle, Switzerland, by courtesy of R. A. Ellis. 24. Schering Corporation, Bloomfield, New Jersey, U.S.A., by courtesy of A. Ryer. 25. G. D. Searle & Co., Chicago, Illinois, IJ.S.A., by courtesy of V. A. Drill. 26. R. Stevenson, Brandeis University, Waltham, Massachusetts, U.S.A. 27. C. R. Treadwell, Washington, D.C., U.S.A. 28. W. W. Wells, Pittsburgh, Pennsylvania, U.S.A. 29. U.C.L.A.F., Paris, by courtesy of P. Poirier. REFERENCES 1. 2. 3. 4. 6. 6. 7. Pesez, M., Bull. SOC. Chim. France, 1958, 369. 8. 9. Dam, H., in Cook, R. P., Editor, “Cholesterol,” Academic Press Inc., New York, 1958, p. 5. Moore, P. R., and Baumann, C. A., J . Bid. Chem., 1952, 615, Fieser, L. F., and Fieser, M., “Steroids,” Reinhold Publishing Corporation, New York, 1959. “Handbook for Chemical Society Authors, Reiss, 0. K., Fed. Proc., 1955, 14, 268. Idler, D. R., and Baumann, C. A., J . Bid. Chem., 1953, 203, 389. Neiderheiser, D. H., and Wells, W. W., Arch. Biochem. Bioflhys., 1959, 81, 300. Kandutsch, A. A., and Russell, A. E., J . Biol. Chem., 1960, 235, 2253. Special Publication. No. 14, The Chemical Society, London, p. 132.June, 19611 AND SULPHURIC ACID (THE LIEBERMANN - BURCHARD TEST) 381 Frantz, I. D., jun., Mobberley, M. L., and Schroepfer, G. J., jun., Progress Cardiovascular Diseases, Bladon, P., Cornforth, J . W., and Jaeger, R. H., J . Chem. SOC., 1958, 863. Swell, L., and Treadwell, C. R., J . Biol. Chem., 1955, 212, 141. Kalant, H., Biochem. J., 1958, 69, 79. Bladon, P., iiz Cook, R. P., Editor, 09. cit., p. 84. Meesemaecker, R., and Griffon, H., J . Pharm. Chim., 1930, 11, 572. Kenny, A. P., Biochem. J . , 1952, 52, 611. 10. 11. 12. 13. 14. 15. 16. 1960, 2, 511. Received February 3rd, 1961

ISSN:0003-2654    

DOI:10.1039/AN9618600373

出版商:RSC    

年代:1961

数据来源: RSC

摘要:

June, 19611 AND SULPHURIC ACID (THE LIEBERMANN - BURCHARD TEST) 381 The Iodimetric Determination of Acetaldehyde Bisulphite BY L. F. BURROUGHS AND A. H. SPARKS (Research Station, Long A shton, Bristol) Methods for the iodimetric titration of acetaldehyde bisulphite in the presence of borate buffer solution give low results. This is shown to be caused by oxidation of sulphite by dissolved oxygen and can be overcome by a simple modification to the usual procedure. THE determination of acetaldehyde is of considerable importance in the study of wine and cider, and the methods generally used are based on iodimetric titration of acetaldehyde bisulphite in slightly alkaline solution. This procedure has been attributed1 to Tomoda,2 although the same principle was previously used by Clausen3 in 1922 and was adopted by Friedmann, Cotonio and Schaffefl for determining lactate in blood after oxidation to acetaldehyde.Tomoda allowed the acetaldehyde to react in aqueous solution with a slight excess of sodium bisulphite and, after 15 minutes, destroyed the excess of bisulphite by adding iodine, with starch as indicator, until a pale-blue end-point was reached. The acetaldehyde - bi- sulphite compound was then caused to dissociate by saturating the solution with sodium hydrogen carbonate. This increased the pH to about 8, and, although the complex was only dissociated to the extent of a few per cent., the rate of dissociation was such that the liberated bisulphite could be titrated with iodine. Jaulmes and Espezell modified this method in order to determine smaller amounts of acetaldehyde in distillates from wine.They showed that the rate of combination of acetalde- hyde with sodium bisulphite was dependent on pH and was maximal at pH 7 ; they therefore carried out the addition reaction at this pH. Their other modification was to replace sodium hydrogen carbonate by an alkaline borate solution, which they said produced a sharper end-point in the titration with iodine. Jaulmes and Espezel's method has become widely accepted5 for determining acetaldehyde in wines, both in its original form6$' and with minor modificati~ns.~~~~~O Joslyn and Comar' found that recovery of acetaldehyde was only about 90 per cent., both from pure solution and after distillation from wine. Ribereau-Gayon and Peynaud8 claimed that the error by their method was less than 1 per cent., but did not give results for the recovery of added acetalde- hyde.They emphasised that the final titration with iodine should be carried out immediately after the alkaline borate solution had been added, otherwise sulphur dioxide was lost by oxidation. Paulg mentioned difficulty with the iodimetric end-point when sodium hydrogen carbonate was used and devised a sodium carbonate - sodium tetraborate buffer ; he claimed that his results for standard solutions of acetaldehyde agreed well with the amounts known to be present, but did not report actual figures. DukhovnyilO used a method similar to that described by Ribereau-Gayon and Peynaud and reported an error of less than 3 per cent. in the recovery of acetaldehyde added to wine; however, the presence of ethanol in the dis- tillates may have protected the sulphur dioxide from oxidation.382 BURROUGHS AND SPARKS : THE IODIMETRIC (Vol.86 Our investigation was initiated because Ribereau-Gayon and Peynaud’s method was found to give low recoveries (about 90 per cent.) of acetaldehyde from standard solutions. This and other methods were therefore examined in an attempt to find the source of this error and a means to remove it. EXPERIMENTAL The four methods examined are essentially the same in principle, and the various stages (i) The acetaldehyde solution is allowed to react for 20 minutes with a large excess of sodium bisulphite solution in phosphate buffer (pH 7) at room temperature. (ii) The solution is acidified (pH 1 to 2), and the excess of sodium bisulphite is removed by adding 0-1 N iodine to a pale-blue end-point (starch as indicator).The rate of dissociation of the acetaldehyde - bisulphite compound is extremely slow at this pH. (iii) The pH is then increased to about 8 by adding alkaline borate solution (or solid sodium hydrogen carbonate in Tomoda’s method2). At this pH, the rate of dis- sociation of the acetaldehyde - bisulphite compound is greatly increased. (iv) The liberated sulphite is immediately titrated with a dilute standard solution of iodine. The methods differed mainly in the volume and composition of the alkaline borate solution used in stage (iii), and this affects the pH at which the final titration is carried out. The volumes of the various solutions used in this investigation are shown in Table I.are outlined below. TABLE I AMOUNTS OF REAGENTS USED The volume of sample solution used throughout was 25 ml Volume of reagent used in- A I -7 Reagent method A,* method B,t method C,S method D,$ Stage (i)- ml ml ml ml Buffer solution, pH 7 . . .. .. * . 50 25 25 25 Sodium bisulphite solution, 2 per cent. w/v . . 10 5 5 5 Stage (ii)- Hydrochloric acid, 25 per cent. v/v .. 10 5 2.5 5 Stage (iii)- Alkaline borate solution . . .. .. 100 X 62-5 NaHCO, (solid) * Jaulmes and Espezel’s rneth0d.l t Ribereau-Gayon and Peynaud’s method.* Water (75ml) was also added a t stage (i). In stage (iii), the solution was titrated with the alkaline Paul’s r n e t h ~ d . ~ For comparison with the oth.er methods, the volumes used were 2.5 times greater ij Tomoda’s method.2 In the original procedure, buffer solution was not used in stage (i) ; it was added borate solution to a phenolphthalein end-point; the value of x was approximately 20 ml.than those originally recommended. here to ensure completeness of reaction and for the sake of uniformity. REAGENTS- With the exception of sodium metabisulphite, all materials used were of analytical-reagent grade. Phosphate h f e r solution, P H 7-Prepare a solution containing 15 g of disodium hydrogen orthophosphate, Na2HP0,.12H,O, and 3.35 g of anhydrous potassium dihydrogen ortho- phosphate per litre. Sodium bisulphite solution, 2 per cent. w/v-Freshly prepare this reagent from sodium metabisulphite having a purity of 93 per cent. Hydyochloric acid solution, 25 per cent.v / v . Alkaline borate solution foy use in method A-Dissolve 16 g of sodium hydroxide and 8.75 g Alkaline borate solution for use in method B-Dissolve 40g of sodium hydroxide and Alkaline borate solution JOY use in method C-Dissolve 114 g of sodium carbonate deca- of boric acid in water, and dilute to 1 litre. 30 g of boric acid in water, and dilute to 1 litre. hydrate and 8-75 g of boric acid in water, and dilute to l litre.June, 19611 DETERMINATION OF ACETALDEHYDE BISULPHITE 383 Sodium hydrogen carbonate. Iodine solutions, 0.1, 0.02 and 0.01 N. Starch indicator-Freshly prepare a 0.5 per cent. w/v solution of soluble starch. Standard acetaldehyde solation-Prepare acetaldehyde from paraldehyde by slow dis- tillation in the presence of 1 per cent.v/v of concentrated sulphuric acid. Collect the distillate in an ice-cooled flask, store it in a refrigerator, and re-distil small portions immediately before use. Prepare standard solutions by dissolving 1.5 g of sodium metabisulphite in 20 ml of water in a 25-ml calibrated flask, accurately weigh the flask and its contents, add 0.8 ml of re-distilled acetaldehyde, by pipette, and again weigh. Dilute the solution to the mark, and use suitable dilutions of this solution for analysis. (The incorporation of sodium bisulphite in slight excess over the amount required to react with the acetaldehyde was designed to prevent loss of acetaldehyde by volatilisation.) RESULTS AND DISCUSSION OF THE METHOD A solution containing 0-4814 g of acetaldehyde per litre was analysed by the four methods.Recoveries of acetaldehyde from 25-ml aliquots, each containing 12.04 mg of acetaldehyde, are shown in Table 11, together with the pH values at different stages. TABLE I1 RECOVERIES OF ACETALDEHYDE BY THE FOUR METHODS Each sample (25 ml) contained 12.04 mg of acetaldehyde pH at pH after pH after Acetaldehyde found, Recovery, Method stage (i) acidification titration mg % A 6-68 1.34 8.30 11.35, 11-23, 11-16 (mean 11.25) 93.4 B 6-64 1.06 8.48 10.90, 11.20, 11.05 (mean 11-05) 91.7 C 6.64 1-46 9.30 9.88, 9.55, 9.86 (mean 9.76) 81-1 D 6.64 1.06 7.48 12.08, 12-12, 12.07 (mean 12.09) 100-4 Recovery was inversely related to the pH of the solution after titration with iodine. The low recoveries when methods A, B and C were used were not due to incomplete dissociation of the acetaldehyde - bisulphite compound, as the rate at which the iodine was decolorised during these titrations was almost instantaneous and much faster than in method D.The losses were attributed to oxidation of sulphite, presumably by oxygen already dissolved in the solution, since all titrations were carried out immediately after the alkaline borate solution had been added. INHIBITION OF SULPHITE OXIDATION BY ISOPROPYL ALCOHOL- Oxidation of sulphite by dissolved oxygen is a chain reaction and can be inhibited by the use of isopropyl alcohol.ll The protective action of isopropyl alcohol on the iodimetric titration of sulphite at pH 8.5 was studied as follows. Each of a series of 10-ml portions of 0.01 N sodium bisulphite $.us 5 ml of 25 per cent.v/v hydrochloric acid and a known volume of isopropyl alcohol was titrated with the alkaline borate solution used in method B to a phenolphthalein end-point, and the sulphite was then immediately titrated with 0.01 N iodine. The results were- Isopropyl alcohol present before titration with iodine solution, yo v/v 0.0 0-3 1.6 3.1 13.7 Recovery of sulphite, yo . . .. . . . . .. . . 56 92 96 96 98 from which it can be seen that even 0.3 per cent. of isopropyl alcohol markedly inhibits the oxidation of sulphite at this pH. A solution containing 0.4920 g of acetaldehyde per litre was then analysed in the presence of sufficient isopropyl alcohol (added before the alkaline borate solution) to give a concen- tration of 10 per cent. v/v in the solution to be titrated with iodine.The recoveries of acetaldehyde by methods B and C were 97.7 and 98.9 per cent., respectively, thereby con- firming that the losses shown in Table I1 were caused by oxidation of sulphite by dissolved oxygen. EFFECT OF pH ON RATE OF OXIDATION O F SODIUM BISULPHITE SOLUTION- The results in Table I1 suggest that the oxidation of sulphite is critically influenced This reaction has been studied in detail by Abel,12 who found by the pH of the solution.384 BURROUGHS AND SPARKS : THE IODIMETRIC [Vol. 86 that the rate of oxidation was proportional to the concentration of sulphite and inversely proportional to the square root of the concentration of hydrogen ions. The influence of these two factors under conditions similar to those of the determination of acetaldehyde was examined as described below.Approximately 45 ml of a buffer solution (containing 25 ml of the pH 7 buffer, 5 ml of the 25 per cent. hydrochloric acid and sufficient alkaline borate solution to give the required pH) were added to 20 ml of 0.01 N sodium bisulphite. After it had been set aside for a measured time, the mixture was poured into 25 ml of 0.01 N iodine acidified with 5 ml of N hydrochloric acid, and the residual iodine w'as titrated with 0.01 N sodium thiosulphate. In the control titration, representing contact with the buffer solution for zero time, 45 ml of water were used instead of the buffer. The results of this experiment are shown in Table 111. EFFECT Time of contact with buffer solution 10 seconds . . . .30 seconds . . . . 1 minute . . . . 2 minutes . . . . 6 minutes . . . . At pH 7 and above, most TABLE I11 OF pH ON OXIDATION OF SULPHITE Loss of sulphite with buffer solution of- . . 8.7 22-4 29.0 37-0 . . 13.7 33.8 37.4 40-2 . . 21.6 37.5 39.8 44.0 . . 31.4 39.3 41.8 43.4 . . 34.2 41.0 46.0 48.6 of the oxidation occurred within 30 seconds and was pre- sumably caused by oxygen already in solution. The slower oxidation occurring when-the solution was set aside may be attributed in part to the further absorption of atmospheric oxygen and also to the progressively decreasing concentration of sulphite ions. The effect of concentration of sulphite was demonstrated by repeating the experiment with 5 ml of 0.01 N sodium bisulphite instead of 20ml. At pH 7 , only 15 per cent.of the sulphite was oxidised in 10 seconds and 26 per cent. in 5 minutes. The effect of concentration of sulphite on the rate of oxidation would also account for the fact that the oxidative loss of sulphite in the form of sodium bisulphite (see Table 111) is much greater than that observed in the determination of acetaldehyde (see Table II), in which only a small fraction, dependent on the pH, of the total sulphite is ionised. An experiment similar to that giving the results in Table I11 was carried out with 20-ml aliquots of 0.01 N acetaldehyde - sodium bisulphite; after contact for 1 minute with buffers of pH 7 , 8 and 9, the losses of sulphite were 4.8, 7.0 and 7.8 per cent., respectively. ~ODIFICATION TO PROCEDURE- The factors responsible for low results in the iodimetric titration of the acetaldehyde - (i) When the pH is increased by adding alkaline borate solution, the sulphite liberated becomes susceptible to oxidation by dissolved oxygen. (ii) This is a chain reaction, the rate of which (a) increases with increasing pH, (b) is proportional to the concentration of sulphite ions and (c) is inhibited by the presence of isopropyl alcohol.Oxidative loss of sulphite can be largely overcome by adding isopropyl alcohol before the alkaline borate solution, but some slight loss may still occur, depending on how long the solution is set aside before titration with iodine. However, this oxidative loss can be completely prevented by adding 90 to 95 per cent. of the iodine required in the titration before the alkaline borate solution is added.In this way, the sulphite, as it is progressively liberated by increasing the pH, reacts immediately with the iodine and is not subject to oxidation by dissolved oxygen. A preliminary determination by the normal procedure is necessary to find the approximate amount of iodine needed in the titration. Huff13 used a similar procedure to avoid loss of sulphite in the determination of hydroxyacetone. It is not clear, however, whether or not the loss of sulphite was caused by oxidation, since he used sodium hydrogen carbonate to liberate the bound sulphite, and, further, this modification was apparently not necessary with other carbonyl compounds. bisulphite compoupd can be summarised as follows.June, 19611 DETERMINATION OF ACETALDEHYDE BISULPHITE 385 The same standard acetaldehyde solution used for the experiments reported in Table II was analysed by methods A, B and C, with this modification.Recoveries were 100.2, 100.2 and 100-7 per cent., respectively, with close agreement between triplicate titrations. It is noteworthy that method D, in which sodium hydrogen carbonate is used, also gives complete recovery of acetaldehyde, although the final pH of 7.5 is such that some oxidative loss of sulphite would be expected. That this does not occur is probably due in part to the fact that titration with iodine is usually begun before all the sodium hydrogen carbonate has dissolved, so that, effectively, the sulphite reacts with the iodine as soon as it is liberated. In this way, method D approximates to the modified procedures involving use of alkaline borate solution.Another factor minimising oxidative loss of sulphite is that the dissolved oxygen may be largely removed from solution by the vigorous evolution of carbon dioxide. It is unfortunate that this method has the disadvanatages of slow liberation of sulphite and a less distinct end-point, as it is otherwise reliable and accurate. Since all three methods in which alkaline borate solution is used give complete recovery of acetaldehyde the choice becomes a matter of convenience, Method B can be simplified by using a fixed volume (about 23 ml) of alkaline borate solution without recourse to titration with phenolphthalein as indicator. This slight excess of alkaline borate solution does not affect the modified procedure.The possibility was considered that some of the iodine might react with the acetaldehyde liberated concomitantly with the sulphite. Solutions of acetaldehyde (2.5 mg) in 20 ml of buffer solution (pH 8) were set aside in contact with 10 ml of 0.01 N iodine, acidified and then titrated with sodium thiosulphate solution. After contact for 2 minutes, the loss of iodine was barely detectable and after 15 minutes it was only 0.5 ml of 0.01 N iodine. The oxidation of acetaldehyde by iodine is therefore negligible under the conditions of these deter- minat io ns. Finally, a standard solution of acetaldehyde was analysed, ten replicate determinations at each of two concentrations (11.8 and 2.36 mg per 25 ml) being made by the modified procedure of method B. The mean recoveries were 100.0 and 100.3 per cent. and coefficients of variation were 0.112 and 0.211 per cent., respectively. 1. 2. 3. 4. 5. 6 . 7. 8. 9. 10. 11. 12. 13. REFERENCES Jaulmes, P., and Espezel, P., Ann. Falsif., 1935, 28, 325. Tomoda, Y., J . SOC. Chem. I n d . , 1929, 48, 761.. Clausen, S. W., J . Biol. Chem., 1922, 52, 263. Friedmann, T. E., Cotonio, M., and Schaffer, P. A., Ibid., 1927, 73, 335. hmerine, M. *4., Adv. Food Res., 1954, 5, 382. Amerine, M. A, and Joslyn, M. A., “Table Wines,” University of California Press, Berkeley and Joslyn, M. A., and Comar, C. L., I n d . Eng. Chem., Anal. Ed., 1938, 10, 364. Kibereau-Gayon, J., and Peynaud, E., Ann. Inst. Pasteur, 1947, 73, 777. Paul, F., Mitt. Wein u.-Obstbazt, Wien, A , 1954, 4, 225; Anal. Abstr., 1954, 1, 3118. Dukhovnyi, A. I., Sadovodstvo, Vinogradarstvo i Vinodelie Moldavii, 1957, 12, 46; Clzem. Abstr., Alyea, H. N., and Backstrom, H. L. J., J . Amer. Chem. SOL, 1929, 51, 90. Abel, E., Monatsh., 1951, 82, 815; Chem. Abstr., 1962, 46, 3442~. Huff, E., Ana2. Chem., 1959, 31, 1626. Los Angeles, 1951. 1957, 51, 18,4611. Received February 8th, 1961

ISSN:0003-2654    

DOI:10.1039/AN9618600381

出版商:RSC    

年代:1961

数据来源: RSC

摘要:

386 BILEFIELD AND VINCENT : DE.TERMINATION OF CADMIUM (Vol. 86 Determination of Cadmium in Rocks by Neutron- activation Analysis BY L. I. BILEFIELD AND E. A. VINCENT (Department of Geology and Mineralogy, University Museum, Oxford) A neutron-activation method has been developed for determining 0.1 to 1 p.p.m. of cadmium in rocks. It depends on the separation of l15Cd (half-life 55 hours) with added cadmium carrier from a solution of the irradiated pow- dered rock by successive precipitations with trimethylphenylammonium iodide, 5,6-benzoquinoline and brucine. The precipitates are re-dissolved in a mixture of sulphuric and perchloric acids, and the cadmium is finally mounted for beta-counting as its brucinium salt. Standards are prepared by irradiating microgram amounts of cadmium acetate, The method has been applied to a suite of rocks from the Skaergaard Intrusion, Greenland, and also to the international standard rock samples G-1 and W-1.BECAUSE of the lack of sufficiently sensitive analytical methods, little is known of the occurrence of cadmium in igneous rocks other thian those rich in sulphide minerals. A colori- metric method1 has yielded most of the results hitherto available, but it is not claimed to be highly accurate. Cadmium has also been determined by ~pectrography~~~~~ and polaro- graphy5.6~7; the excitation of cadmium in flames has recently been reviewed.8 Neutron-activation analysis has been applied to the determination of cadmium in vinylite resins,g which were found to contain 100 to 400 p.p.m. of the element, and DeVoe and Meinkel0 have studied the radiochemical separation of cadmium from about twenty ele- ments.The results obtained when the method described here was applied to rocks and minerals of the Skaergaard Intrusion have already been discussedll from a geochemical standpoint. NUCLEAR CHEMISTRY From a consideration of the isotopic composition of natural cadmium and the half-lives of the expected (.n,y) products, it can be concluded that the only active nuclides present in significant amount in a sample of cadmium after irradiation for 1 week in a flux of thermal neutrons and then decay for 24 hours should be l15Cd (half-life 55 hours) and its metastable form 1lbCd (half-life 43 days). Since the cross-section for formation is eight times greater for 115Cd than for llbCd and since the shorter-lived nuclide attains 87 per cent.of its saturation yield in 1 week (against 9 per cent. for llhCd), it follows that the observed activity of a sample of cadmium treated as indicated above should be mainly due to l15Cd. This conclusion is substantiated by the behaviour of the cadmium activity separated from rock samples and standards, and, since a half-life of 2.3 days allows ample time for chemical treatment, the determination of traces of cadmium by neutron activation seems feasible. The decay scheme of 115Cd involves a radioactive daughter isotope, l151n (half-life 4.5 hours), so that the total activity of a freshly prepared sample of 115Cd increases during the first few hours. In general, for the scheme- A, AB A (active) -+ B (active) -+ C(stab1e) where AA and AB are the respective disintegration constants, if AA is less than AB maximum total activity occurs at a time after separation of pure A given by the equation12- In this instance, tmax.is 12.9 hours. After maximum activity has been reached, transient equilibrium is established between parent and daughter isotopes, and the total activity decays smoothly with the parent's half-life. In a method based on l15Cd, therefore, it is necessary to wait about 24 hours after separation before the sources are counted.June, 19611 IN ROCKS BY NEUTRON-ACTIVATION ANALYSIS 387 Consideration must be given to the possible occurrence of nuclear reactions yielding llTd in samples of rock, but not in standards, thereby invalidating comparison between the two; three such reactions are- (i) l161n (n,p) l16Cd (ii) ll*Sn (%,a) l15Cd (iii) 236U (n, fission) l15Cd 49 60 The types of reaction involved in (i) and (ii) rarely occur by the action of therrnal neutrons on elements of atomic number greater than about 40,13 and reaction (iii) is unlikely to be significant, since cadmium lies in the trough of the uranium fission yield curve.Experiments with indium, tin and uranium monitors showed that the maximum error that could be caused by the presence in a sample of rock of all three of these elements in concentrations similar to that of cadmium was about 0.5 per cent.; this was negligible for our purpose. Other potential sources of error are self-shielding and self-absorption. Self-shielding during irradiation is likely to be exceptionally severe for cadmium, owing to its high capture cross-section for thermal neutrons, and so the amount of a pure cadmium compound that can be used as an irradiation standard is expected to be correspondingly low.If self-shielding occurs, a large sample exhibits a lower specific activity than does a small one. Two separate irradiations of cadmium acetate dissolved in de-mineralised water, showed that only little self-shielding occurred in the range 0.01 to 1.0 pg of cadmium; the results were- Irradiation No. . . . . .. .. 1 2 Cadmium irradiated, p g .. . . 0.926 0-672 0.107 0.0115 0.908 0.474 0.095 0.0093 A A f \ I \ Activity per pg, counts per minute . . 3594 3466 3883 3899 3835 3973 4007 4103 If self-shielding occurs in the samples of rock, the lower specific activity of a large sample of a particular rock will lead to an under-estimate of its cadmium content when compared with the result from a smaller sample irradiated at the same time.The results in Table I do not show this effect. TABLE I REPLICATE RESULTS FOR SAMPLES OF ROCKS Sample No. Type of rock Weight of sample, Cadmium found, mg p.p.m. E.G.5321 . . .. . . Gabbro 92-6 0.32 208.6 0-34 E.G. 4507 . . .. . . Gabbro 105-5 0.125 216.1 0-131 w-1 . . .. . . Diabase 101.3 0.34 116.2 0.30 227.3 0-33 144.5” 0-34 * Separate irradiation. Self-absorption is severest when low-energy beta-particles are counted. The results below show that the apparent activity of a source of cadmium “brucinate” having constant surface area slowly decreases as its thickness (proportional to the amount of cadmium present) increases.To minimise this cause of error, it was desirable to restrict the thickness of these sources to the equivalent of 5mg of cadmium or less. Cadmium present, mg . . .. .. 15 12 9 6 3 Activity, counts per minute . . .. 235 242 247 273 267 ANALYTICAL CHEMISTRY In developing a method for isolating radiochemically pure cadmium from the complex mixture of isotopes produced in a rock by irradiation with neutrons, a survey was made of the organic precipitants available. The most popular gravimetric reagents for cadmium have been14 anthranilic acid, quinaldinic acid and oxine, but these were insufficiently specific for our purpose. 2-(o-Hydroxyphenyl) benzoxazole is said to be highly specific for cadmium,16 but this has been questionedlOsl6; further, the necessary careful adjustment of pH is tedious.388 BILEFIELD AND VINCENT : DETERMINATION OF CADMIUM [Vol.86 In the presence of potassium halide, brucine sulphate forms a white precipitate with cad- miuml7; this brucinium salt contains only 9.2 per cent. of cadmium and so is a convenient means of handling a small amount of the element. Cobalt, nickel, copper, iron, chromium and zinc form similar precipitates. 5,6-Benzoquinoline and trimethylphenylammonium iodide behave alike as precipitants for cadmium1* and are not subject to interference from nearly all the elements just mentioned. There is interference from copper, lead, zinc and bismuth, however, but these elements can be displaced by the addition of elemental iron.Hexamine allylo-iodide has been recommended for use with cadmium,19 but the results are not always satisfactory . 2o On the basis of this survey and experiments to ascertain the characteristics of the precipitates involved, 5,6-benzoquinoline, trimethylphenylammonium iodide and brucine were selected as precipitants, with the brucinium salt as the “plating-out” form. Aqua regia was found to be unsatisfactory for re-dissolving the precipitates, but a mixture of sul- phuric and perchloric acids (17 + 3) gave good results. I t was ascertained that the precipitated cadmium “brucinate” was of reproducible known composition. To assist in attaining radiochemical purity, scavenge steps with ferric hydroxide and silver iodide were included. Together with the iron solution were added manganese and magnesium carriers, which, when made alkaline, remove 56Mn and l14“In, respectively21 ; otherwise, indium closely follows cadmium.Holdback carriers were used to assist the puri- fication each time a cadmium compound was precipitated. PREPARATION OF STANDARDS AND SAMPLES FOR IRRADIATION- AnalaR cadmium acetate was chosen for preparing the irradiation standards in preference to the chloride, which gives rise to excessive extraneous activity, or the metal, which is not available in a pure condition and would suffer from self-shielding. About 0.2 ml of cadmium acetate solution, containing 0.01 to 1.Opg of cadmium, is introduced into a tared silica ampoule. After the ampoule has been re-weighed and its contents evaporated to dryness, it is sealed and sent for irradiation.As the concentration of the acetate solution is known, the exact amount of cadmium taken can be calculated. After return from irradiation, each ampoule is rinsed in a warm dilute solution of cadmium, dried and cut open. The portions are immersed in hot water for about 30 minutes, with thorough rinsing, and the solution is made up with washings to 50 ml. Samples of rock are ground to a fine powder in an agate mortar and sealed in lengths of silica or (more conveniently) polythene tubing marked with black Chinagraph pencil ; 100 to 300 mg of powder is a convenient amount. The tubes should be only two-thirds full, so that, after irradiation, the ends can be cut off and the powder removed by tapping without loss. Samples and standards were irradiated for 1 week in a flux of 10l2 neutrons per sq.cm per second. REAGENTS- Trimethyl~henylammonium iodide solution--Prepare an aqueous 3 per cent. solution of the reagent, and filter to remove dark insoluble matter. Trimethylphenylammoniu~ iodide wash solution-Dissolve 1 g each of the reagent and potassium iodide in 200 ml of water, and filter. Brucine sulphate so1utio.n-Dissolve 1 g of brucine in 100 ml of cold 20 per cent. sulphuric acid; alternatively, use an aqueous 1 per cent. solution of brucine sulphate. The yellow colour that develops when the solution is stored is not detrimental. Brucine wash solution-Mix 40 ml of the brucine sulphate solution, 15 ml of 20 per cent. potassium bromide solution and 100ml of water. 5,6-Benzoquinoline solution-Dissolve 2-5 g of the reagent in 100 ml of 0.2 N sulphuric acid.5,6-Benxoquinolinne wash solutiort-Mix 10 ml of the 5,6-benzoquinoline solution, 10 ml of 0-2 N potassium iodide and 150 ml of water, and add a few crystals of sodium sulphite. Holdback carrier solution A-Prepare to contain approximately 1 mg each of lead, copper, bismuth, mercury, arsenic and tin per ml, as nitrates or chlorides. Holdback carrier solution B-Prepare to contain approximately 1 mg each of cobalt, nickel, manganese, chromium, magnesium, zinc and sodium per ml, as nitrates or chlorides. METHODJune, 19611 IN ROCKS BY NEUTRON-ACTIVATION ANALYSIS 389 Holdback carrier soZution C-Prepare to contain 1 mg each of copper, magnesium, man- ganese, potassium and sodium per ml, as chlorides or sulphates, but not as nitrates.Perchloric - sulphuric acid mixtare-Add 3 ml of 60 per cent. perchloric acid to 17 ml of concentrated sulphuric acid, with stirring. Iron-scavenge solation-Prepare to contain 10 mg of ferric iron (as ammonium ferric sulphate), 5mg of manganese (as potassium permanganate) and 5 mg of magnesium (as sulphate) per ml. PROCEDURE FOR SAMPLES OF ROCK- Take norrnal precautions for handling moderate levels of radioactivity, and begin work as soon as the irradiation can is returned. Bring the powdered rock into solution in the presence of 15 mg of cadmium, usually by Rafter’s method22 (dissolve the cake resulting from the fusion with sodium peroxide in the minimum volume of water containing the cadmium carrier as sulphate). To the solution add 5ml of concentrated hydrochloric acid, and evaporate to incipient dryness; repeat this step, adding 1 ml of concentrated nitric acid if necessary, until only silica has not been dissolved.To the moist solid add 2 ml of holdback carrier solution A, 1 g of sodium sulphite, 10 ml of 20 per cent. sulphuric acid (7 N) and a few bright iron nails. Cover, and boil for about 20 minutes until the yellow or green of the solution is obscured by the dark colour of iron and the displaced metals. Decant the hot mixture into a centrifuge tube, spin, and decant the supernatant solution (or remove it by filtration). Wash the solids by centrifugation with hot water, and combine the solutions until 25 to 35 ml of mixture approximately 2 N in sulphuric acid are obtained.Add 1 g each of potassium iodide and sodium sulphite and 2 ml of holdback carrier solution B; then add, with vigorous stirring, excess of trimethylphenylammonium iodide solution. Set aside for a few minutes, spin in a centrifuge, reject the supernatant solution to active waste, and wash the precipitate once with trimethylphenylammonium iodide wash solution. At this stage, the activity is generally down to tracer level. Iodine is evolved, and then the solution slowly clears ; if necessary, add further small volumes of the acid mixture until a pale yellow or colourless solution results. Cool, dilute until no further heat is evolved, and cool again. Add 2ml of holdback carrier solution C, 8ml of 20 per cent. potassium bromide solution and 16ml of brucine sulphate solution.Stir vigorously to coagulate the precipitate, set aside for at least 10 minutes, spin in the centrifuge, and reject the supernatant solution. Wash the precipitate once with brucine wash solution, and boil it with small volumes of the acid mixture to obtain a pale solution. Cool, dilute a little, add 1 ml of iron-scavenge solution, and stand the tube in ice - water mixture. Cautiously add ammonia solution, sp.gr. 0.880, until an excess is present, boil, filter, and wash the residue with hot ammonia solution. Stir into the filtrate 0.1 g of potassium iodide, and add 1 ml of a silver nitrate solution containing 10 mg of silver per ml. Boil to coagulate the silver iodide, filter, and wash the precipitate with ammonia solution. Dissolve 1 g each of Rochelle salt and sodium sulphite in the filtrate, cool, and add concentrated sulphuric acid dropwise until the solution is yellow and acid.Add 2 g of potassium iodide and 2 ml of holdback carrier solu- tion B, and dilute to 30ml with water. Add 5ml of 5,6-benzoquinoline solution, with thorough stirring, and warm, if necessary, to initiate coagulation. Allow the precipitate to settle, add a surface layer of ethanol to repel the solid, and spin in the centrifuge. Discard the supernatant solution, and wash the precipitate once with 5,6-benzoquinoline wash solution ; stir well to dissolve any precipitated reagent, and add ethanol before centrifugation. Dissolve the residue in the minimum of acid mixture by boiling, and cool the clear solution. Dilute a little, and add 2 ml of holdback carrier solution C and some decolorising charcoal.Boil for 1 minute, allow to cool to about 50” C, add 5 ml of 20 per cent. potassium bromide solution, and filter. To the cooled filtrate, which should be nearly colourless, add 10ml of brucine sulphate solution, stir to initiate precipitation, and set aside for at least 20 minutes. Wash the white precipitate twice with brucine wash solution and then three times with a mixture of ethanol and diethyl ether (1 +- ti), breaking up the lumps of solid. Suspend the “brucinate” in a little pure diethyl ether, transfer to a tared aluminium counting tray, distribute the solid evenly, and dry under a heat lamp. Allow to cool, weigh, and count next day in a beta- counter. Boil the precipitate with 5 ml of perchloric - sulphuric acid mixture.Stir, spin in the centrifuge, and reject the supernatant solution.390 BILEFIELD AND VINCENT : DETERMINATION OF CADMIUM [Vol. 86 PROCEDURE FOR STANDARDS- Prepare 50-ml portions of standard solutions containing 0.01 to 1.Opg of cadmium as described under “Preparation of Standards and Samples for Irriadation.” Evaporate aliquots (containing 0.1 pg of cadmium) of the concentrated standards and the total volumes of the less concentrated ones to 5 ml. To each solution add 10 mg of cadmium carrier, as sulphate solution, and then 1 ml of iron-scavenge solution and excess of ammonia solution. Filter, wash the residue, add the washings to the filtrate, and stir in 0.1 g of potassium iodide. Add 1 ml of the silver nitrate solution, boil to ,coagulate the silver iodide, and filter or spin in the centrifuge. Dissolve in the filtrate 1 g each of Rochelle salt and sodium sulphite, cool, and acidify with concentrated sulphuric acid.Add 1 g of potassium iodide, 2 ml of holdback carrier solution B and excess of trimethylphenylammonium iodide solution, with vigorous stirring. Allow the precipitate to settle, spin in the centrifuge, discard the supernatant solution, and wash the precipitate once with trimethylphenylammonium iodide wash solution. Dis- solve it by boiling in the minimum amount of perchloric - sulphuric acid mixture, cool, dilute a little, and add 2 ml of holdback carrier solution C and 0.5 g of potassium chloride. Stir, filter, add 5 ml of 20 per cent. potassium bromide solution to the filtrate, thoroughly cool, and then add 10ml of brucine sulphate solution. Stir well, set aside, wash the precipitate, and mount it for counting as described for samples of rock.Wash the residue once with dilute ammonia solution. TESTS FOR RADIOCHEMICAL PURITY- The simplest way to check the radiochemical purity of the sources is to follow the decay of the activity from 24 hours after preparation for about a week. Since the sources prepared from an average rock give only 50 to 100 counts per minute at the outset, the activity usually merges into the background after this period. For the same reason, it is not usually convenient to obtain absorption curves, and hence the maximum beta-energy, with sources from rock samples. When sources prepared from standards, together with aluminium absorbers, are used, maximum beta-energy occurs at about 460 mg per sq.cm, which corresponds closely to the published value of 1.1 MeV for l15Cd. The observed half-life is usually 56 to 57 hours, slightly longer than the accepted value for 115Cd. The difference is ascribed to the presence of a small amount of l1wCd (half-life 43 days) ; since this is present in both samples and standards, which contain roughly the same weight of cadmium, it does not affect the validity of the comparison between the two. The small “tail” observed in the absorption measurements is attributed to the same cause (for 11hCd, maximum beta-energy is 1.6 MeV, equivalent to 740 mg per sq. cm of aluminium). RESULTS AND DISCUSSION OF THE METHOD The precision of the proposed method may be judged from the results in Table I1 for a series of rocks from the Skaergaard Intrusion, East Greenland.TABLE I1 CADMIUM CONTENTS FOUND IN SKAERGAARD ROCKS Sample No. Type of rock ’ * } Transgressive acid granophyre E.G. 5259 .. E.G. 4489 . . .. E.G. 4332 . . . . Basic hedenbergite granophyre E.G. 4328 . . . . Fayalite ferrogabbro, purple band E.G. 5196 . . . . Melanocratic ferrogabbro E.G. 5181 .. . . Average rock E.G. 5321 .. . . Plagioclase cumulite E.G. 5052 .. . . Middle gabbro (olivine-free) a } Lower olivine gabbro E.G. 5087 . . E.G. 5086 .. .. E.G. 4526 . . . . Gabbro picrite E.G. 4443 .. . . Border group E.G. 4507 . . . . Chilled marginal gabbro (initial magma) Cadmium content found, p.p.m. 0.57, 0-59, 0.54 (mean 0.57) 0.44, 0.44 (mean 0-44) 0-27, 0.28 (mean 0-28) 0.28, 0-27 (mean 0.28) 0.11, 0.12 (mean 0-12) 0.38, 0.43 (mean 0.40) 0.34, 0.32 (mean 0.33) 0.08, 0-09 (mean 0.09) 0-20, 0.19 (mean 0.20) 0.08, 0.09 (mean 0.09) 0.11 0.13, 0-11, 0.13, 0-13 (mean 0.13) { The accuracy of our results can only be a,ssessed for the standard rocks G-1 and W-1, The results in Table I11 show that agreement for which independent analyses are available.June, 19611 IN ROCKS BY NEUTRON-ACTIVATION ANALYSIS 391 with other methods is satisfactory for G-1, but not W-1, and, although we have endeavoured to eliminate potential sources of systematic error from our method, further independent determinations are clearly required.TABLE 111 CADMIUM FOUND IN STANDARD ROCKS BY VARIOUS METHODS Method Cadmium found in- Reference A \ No.* granite G-1, p.p,m.diabase W-1, p.p,m. Neutron activation (proposed procedure) - 0.054, 0.056, 0.066 0.30, 0.33, 0-34, 0.34 Anion-exchange enrichment and spectro- (mean 0-06) (mean 0-33) graphy . . .. .. .. .. 23 - 0.07, 0.09 (mean 0.08) Square-wave polarography . . . . 7 0.06, 0.08, 0.09, 0.10 0.24, 0.27, 0.33, 0.35 (mean 0.08) (mean 0.30) * See reference list below. The proposed procedure appears to be serviceable, but is probably capable of refinement. It may be possible with some samples to omit certain of the precipitation steps, so increasing the chemical yield (at present about 25 per cent.) and the sensitivity of the method. When carried out as described above, analysis of twelve samples of rock, with four standards, takes 4 days from the return of the irradiated material.I 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. We thank Mr. A. A. Smales, U.K. Atomic Energy Research Establishment, Harwell, for suggesting the determination of cadmium as a problem in radioactivation analysis and Professor L. R. Wager for making available the Skaergaard material and for his interest in the work. The necessary irradiations in the Harwell pile BEPO were arranged through the IsotoDe Division of the Atomic Energy Research Establishment. REFERENCES Sandell, E. B., and Goldich, S. S., J . Geol., 1943, 51, 99 and 167. Oftedal, I., Skr. Norske VidenskAkad., 1941, No. 8. Marks, G. W., and Jones, B. M., U.S. Bureau of Mines Report of Investigation No. 4363, Washing- Rusanov, A. K., and Alekseeva, V. M., Zavod. Lab., 1945, 11, 181. Miholic, S., J . Chem. Soc., 1950, 3402. Smythe, L. E., and Gatehouse, B. M., Anal. Chem., 1955, 27, 901. Carmichael, I., and McDonald, A., Geochim. Cosmochim, A d a , 1961, 22, 87. Gilbert, P. T., jun., Anal. Chem., 1959, 31, 110. Brooksbank, W. A., Leddicote, G. W., and Mahlman, H. A., J . Phys. Chem., 1953, 57, 815. DeVoe, J. R., and Meinke, W. W., Anal. Chem., 1959, 31, 1428. Vincent, E. A., and Bilefield, L. I., Geochim. Cosmochim. Acta, 1960, 19, 63. Cook, G. B., and Duncan, J. F., “Modern Radiochemical Practice,” The Clarendon Press, Oxford, -- , op. cit., p. 205. Weliher, F. J., “Organic Analytical Reagents,” D. Van Nostrand Co. Inc., New York, Volume Walter, J. L., and Frieser, H., Anal. Chem., 1952, 24, 1985. Smit, J . van R., D.Phi1. Thesis, University of Oxford, 1966. Nikitina, E. I., Zavod. Lab., 1938, 7, 409. Pass, A,, and Ward, A. M., Analyst, 1933, 58, 667. Evrard, V., Ann. Chim. Anal., 1929, 11, 322. Hurd, L. C., and Evans, R. W., Ind. Eng. Chem., Anal. E d . , 1933, 5, 16. Jacobi, E., Helu. Phys. Acta, 1949, 22, 66. Rafter, T. A., Analyst, 1950, 75, 485. Brooks, R. R., Ahrens, L. H., and Taylor, S. R., Geoclzim. Cosmochim. Acta, 1960, 18, 162. ton, 1948. 1952, p. 49. IV, 1948. Received February 15th, 1961

ISSN:0003-2654    

DOI:10.1039/AN9618600386

出版商:RSC    

年代:1961

数据来源: RSC

摘要:

392 SCHOLES: THE DETERMINATIOK OF TIN I N PURE IRON, MILD STEEL [VOl. 86 The Determination of Tin in Pure Iron, Mild Steel and Certain Low-alloy Steels by Cathode-ray Polarography BY P. H. SCHOLES (British Iron and Steel Research Association, Hoyle Street, Shefleld 3) A method is described in which a linear-sweep cathode-ray polarograph is used for determining tin in pure iron and mild steel. Tin is separated by co-precipitation with manganese dioxide and is determined in a base electrolyte containing peptone and ascorbic acid in 5 M hydrochloric acid. Molybdenum interferes, but, provided that the molybdenum content of the sample does not exceed 0-5 per cent., a correction can be made, so that the method may also be used for the analysis of low-alloy steels. The method is suitable for tin contents down to 0.001 per cent., and a standard deviation of 0.001 per cent.is claimed at the 0.02 per cent. level. A BRITISH Standard method for determining tin in iron and steel has been published.1 After isolation of the sulphide with molybdenum sulphide as carrier, tin is reduced with metallic aluminium in the presence of an antimony salt and is then titrated with potassium iodate solution. For irons, carbon steels and certain low-alloy steels, the sulphide separation is unnecessary and the filtered solution can be titrated immediately. This method has been shown2 to be suitable for tin contents in the range 0.01 to 0.25 per cent., and the reproducibility is stated to be within k0.003 per cent. when 0.05 per cent. of tin is present. A more precise method was required for the analysis of pure iron and mild steel containing 0.001 to 0-02 per cent.of tin, and it was considered that a polarographic approach might offer increased accuracy and sensitivity at these levels. Ferrett and Milner3 have described an attractive direct method for determining tin in steel by square-wave polarography and claim that it is suitable for tin contents as low as 0.0005 per cent.; chemical separations are unnecessary, and the valency state of the iron is unimportant. As base electrolyte, these workers used 5 M hydrochloric acid in preference to the 1 M hydrochloric acid - 4 M ammonium chloride mixture recommended by Li~~gane.~ Trials with this method in conjunction with a cathode-ray polarograph were disappointing; instrumental sensitivity for tin reductions did not approach that of the square-wave polaro- graph, and application of the method was limited to steels containing more than 0.01 per cent.of tin, with a probable standard deviation of 0.01 per cent. Some form of separation was therefore necessary for determining tin contents less than 0.01 per cent. As well as by precipitation as sulphide, tin can be separated from iron by precipitation as metastannic acid or distillation as chloride or bromide; all these techniques have been used as preliminaries to the polarographic determination of tin in steel. Allsopp and pamere115 described a method in which tin was co-precipitated with molybdenum sulphide and the reduction of stannic tin was recorded in Lingane’s base electrolyte.Mahr and Waff enschmidt6 distilled tin as tetrachloride by passing an azeotropic mixture of steam and hydrogen chloride through a solution of the sample in perchloric acid. An alternative separation procedure for alloy steel has been based on the method described by Kallmann, Liu and Oberthin,‘ in which a solution of the sample in sulphuric acid is distilled with a mixture of steam and hydrogen bromide; tin is co-precipitated from the distillate with aluminium hydroxide, and the wave for stannic tin is measured in 5 M hydrochloric acid. Co-precipitation of tin as metastannic acid with manganese dioxide from a solution of the sample in dilute nitric acid is a well established technique in non-ferrous analysis and has found particular application in the formulation of A.S.T.M.methods for analysing pig leads and special brasses and bron~es.~ As well as tin, arsenic and antimony are quantitatively precipitated, and iron, molybdenum, tungsten and bismuth are precipitated in part, GotG, Ikeda and WatanabelO first demonstrated the practical use of this separation combined with a polarographic finish for the analysis of steel. After separation, tin was reduced with metallic aluminium and was measured in Lingane’s base electrolyte ; antimonyJune, 1961 J AND CERTAIK LOW-ALLOY STEELS BY CATHODE-RAY POLAROGRAPHY 393 was also co-precipitated and was measured in a sulphuric acid base electrolyte. BrhGek later used powdered iron as reductant,ll and Rooney used the same technique for separating antimony from cast iron.12 Of the three separation procedures considered, co-precipitation with manganese dioxide is possibly the simplest and most suited to repetitive analyses.In this paper, a polarographic method is described for determining tin in pure iron, mild steel and certain low-alloy steels after preliminary separation of the tin by a co-precipitation method closely similar to that described by Rooney.12 EXPERIMENTAL SEPARATION OF TIN- Tests indicated that co-precipitation of tin with manganese dioxide was practically quantitative over a fairly wide range of concentrations of free acid. It seemed desirable, however, to adhere as closely as possible to conditions found by other workers to be suitable for the co-precipitation of antimony, so that, if necessary, this element could be determined at the same time.Babko and Shtokalo13 found that co-precipitation of antimony was complete in the pH range 1 to 7; this was confirmed by Rooney,12 who pointed out that, in order to obtain a pH in this range, the minimum amount of acid must be used to dissolve the sample and care must be taken to prevent loss of acid during solution so as to avoid hydrolysis of ferric iron. Trials with Got8, Ikeda and Watanabe’s procedurelo produced precipitates heavily contaminated with iron and difficult to filter. Rooney12 incorporated preliminary treatment with potassium permanganate to oxidise carbonaceous matter ; the eficess of permanganate was removed with hydrogen peroxide, and a controlled addition of permanganate was then made to precipitate manganese dioxide.This technique was more satisfactory, provided that the volume of solvent acid recommended was increased by 10 to 15 per cent. to prevent hydrolysis of iron salts. The degree to which iron was co- precipitated was largely dependent on the concentration of acid and the amount of perrnan- ganate used in the initial oxidation. Contamination by iron was considerably decreased when the volume of permanganate solution was kept to a minimum. The presence of man- ganese salts, as suggested by GotB, Ikeda and Watanabe,lo improved the coagulation of the precipitate, especially when it contained iron. Tests on samples of steel produced precipitates that could easily be separated on Whatman No. 541 filter-papers. Samples containing molybdenum produced precipitates that did not settle rapidly; for such samples it was necessary to pass the solution through the filter-paper two or three times to obtain a clear filtrate.POLAROGRAPHIC MEASUREMENT- Most previous workers reduced tin to the bivalent state after solution of the manganese dioxide precipitate in hydrochloric acid and hydrogen peroxide. It seemed more convenient, however, to determine tin in the stannic state, thereby avoiding the difficulties encountered in the reduction and in maintaining the element in the stannous state during polarography. The polarographic behaviour of tin in the presence of chloride has been investigated by Lingane.4314 Stannic tin produces an ill defined wave in 1 M hydrochloric acid at -0.47 volt, with a small pre-wave beginning at about -0.05 volt.As the concentration of chloride is increased, the waves are resolved into two well defined steps having half-wave potentials at -0.25 and -0.52 volt in a base electrolyte consisting of 4 M ammonium chloride and 1 M hydrochloric acid. The first wave involves a two-electron reduction of the hexachloro- stannate ion to tetrachlorostannate and is irreversible; the second wave is produced by the reduction of tetrachlorostannate to the metal. Ferrett and Milner3 reported inconsistent results for tin when Lingane’s base electrolyte was used; they used 5 M hydrochloric acid in order to obtain maximum definition. With use of a cathode-ray polarograph, I have confirmed this observation and found that peak heights are consistent for concentrations of hydrochloric acid in the range 3 to 6 M.Irreversible reductions produce characteristically rounded and rather drawn-out waves on a cathode-ray polarogram, and the second wave, which has a peak potential of -0.48 volt against the mercury-pool anode, was therefore chosen for quantitative measurement. The diffusion-current plateau of the first wave (peak potential at about -0.2 volt) provides a horizontal or nearly horizontal base line for measuring the height of the main wave for stannic tin. Antimony, if present, is reduced at a peak potential of -0.15 volt, and its wave is therefore superimposed on the first tin wave; it does not interfere with the second tin wave.394 SCHOLES: THE DETERMINATION OF TIN I N PURE IRON, MILD STEEL [VOl. 86 At first, waves were ill defined and had sloping base lines (see Fig.l), but the addition of 5 mg of peptone to the contents of the polarographic cell after de-oxygenation improved the definition considerably. The presence of a small unidentified wave at the foot of the tin wave still caused difficulties; however, when the solution was evaporated until fumes were evolved and fuming was maintained for a few minutes, this unidentified wave dis- appeared (see Fig. 2) and measurement of the peak height became much easier. Tests showed that, if fuming was continued for 5 minutes, there was some danger of loss of tin, presumably by volatilisation, and for this reason heating to fumes for 2 minutes is stipulated in the proposed procedure. Potential, volts Potential, volts Fig. 1. Typical polarogram for tin Fig. 2.Polarogram for tin in B.C.S. (0.02 per cent.) in B.C.S. No. 272 before No. 272 after heating t o fumes and inclusion of heating to fumes and addition of peptone The proposed method was tested by adding different amounts of a tin solution to 1-g samples of pure iron dissolved in 35 ml of dilute nitric acid (1 + 4) without heating. Some difficulty was experienced in preparing a standard tin solution in dilute nitric acid, but a satisfactory technique was established by dissolving AnalaR tin in dilute nitric acid (1 + 4) without heating. The tin dissolves completely in about 2 hours, and the solution is stable for several hours, provided that the room temperature does not exceed about 20" C. The percentage of tin recovered was determined by comparison with a calibration graph plotted from the results obtained with solutions of pure tin.The results are shown in Table I and indicate that the mean recovery is 97 per cent. in the range 0.01 to 0.10 per cent. of tin and between 90 and 110 per cent. for tin contents below 0.01 per cent. This is considered to be satisfactory for a method depending on co-precipitation ; it seems probable that complete recovery could be obtained by a second precipitation from the filtrate, but this would con- siderably increase the time required for a determination. In order that the method of calibration should be representative of the method of test, the calibration procedure in the pro- posed method is based on adding tin to a solution of pure iron. Similar tests were carried out on 5-g samples of pure iron dissolved in 135 ml of solvent acid, and the results are also shown in Table I.The mean recovery was 87 per cent., which can hardly be considered satisfactory for accurate determination of tin at the 0-01 per cent. level. On the other hand, use of the larger weight of sample permitted the extension of the method to a lower limit of 0.0002 per cent. of tin, and poor recovery may therefore be balanced by improved sensitivity in the range, say, 0.0002 to 0.002 per cent. of tin. METHOD REAGENTS- addition of peptone All reagents should be of the highest grade of purity obtainable. Standard tin solzttion-Transfer exactly 50 mg of AnalaR tin metal to a 500-ml calibrated flask, add 250ml of dilute nitric acid (1 + 4), and allow the metal to dissolve; maintain the temperature below 20" C.Dilute to the mark with dilute nitric acid (1 + 4), and use immediately. One millilitre of this solution is equivalent to 100 pg of tin (0.01 per cent. of tin in a 1-g sample or 0.002 per cent. in a 5-g sample).June, 19611 AND CERTAIN LOW-ALLOY STEELS BY CATHODE-RAY POLAROGRAPHY 395 PROCEDURE- Transfer 1 g of sample (see Note) to a 400-ml conical beaker, add 35 ml of dilute nitric acid (1 + 4), and allow to dissolve without heating. Add 150 ml of water and 10ml of a 10 per cent. w/v solution of manganese sulphate, insert a boiling rod, and heat to boiling- point on a hot-plate. Oxidise the solution with a 1 per cent. w/v solution of potassium per- manganate, added dropwise. When the solution has attained a deep-purple colour, add 5 drops of pennanganate solution in excess, and boil gently for 3 to 5 minutes.Reduce the solution by adding 20-volume hydrogen peroxide dropwise, and boil to remove excess of peroxide. Dilute the solution to 200 ml, if necessary, bring to the boil, and add 2 ml of the potassium permanganate solution. Boil gently for 15 minutes, remove from the hot-plate, allow the precipitate to settle, and filter the solution through a fluted Whatman No. 541 filter-paper into a clean beaker. (If the sample contains molybdenum, the precipitate settles slowly, and several filtrations may be necessary before a clear filtrate is obtained; set solutions from such samples aside for about 30 minutes before filtration.) The filtrate should be TABLE I RECOVERY OF TIN ADDED TO SOLUTIONS OF PURE IRON Tin recovered from- A r \ Tin added, l-g sample of iron, 5-g sample of iron, Yo % % 0-0005 0.001 0-002 0.004 0-005 0.01 0.02 0.10 - 0-0004, 0-0004 0.001, 0.001 0.0010, 0-0008 0.002, 0.002 - - 0.0034, 0-0036 0.0045, 0.0055 - 0.0095, 0.0095 0.0080, 0.0080 0.0095, 0.0105 - 0.0095, 0.0095 - 0.096, 0.098 - 0.095, 0-097 - 0.098, 0.099 - - 0-0168, 0.0170 perfectly clear; if it is not, re-filter it through the same filter-paper until a clear filtrate is obtained.Wash the precipitate thoroughly with hot water. Place the funnel containing the filter-paper in the neck of the original beaker, pierce a hole in the paper with a pointed glass rod, and wash the precipitate into the beaker with hot water and dropwise additions of diluted hydrochloric acid (1 + 1) and 20-volume hydrogen peroxide.To the solution add 5 ml of nitric acid and 10 ml of diluted sulphuric acid (1 + l), evaporate until fumes are evolved, and continue to fume for 2 minutes. Cool, add 10ml of diluted hydrochloric acid (1 + l), heat to boiling-point, and oxidise with 2 or 3 drops of a saturated solution of potassium chlorate. Concentrate the solution to about 10 ml, add 10 ml of water and 20 ml of hydro- chloric acid, sp.gr. 1.18, cool, and dilute to 50 ml in a calibrated flask. Add 1 g of ascorbic acid, and shake until solution is complete. Transfer 2 to 3ml of the solution to the cell of a cathode-ray polarograph (Southern Analytical Ltd.), remove oxygen by passing nitrogen for 5 to 10 minutes, add about 5 mg of peptone, and pass nitrogen until solution is complete.Measure the peak height of the second tin wave; use a start potential of -0.10 volt. (If the sample contains tungsten, a wave will be visible at about -0.6 volt, and it may be necessary to use the derivative circuit to resolve the tin wave; for such solutions, re-set the start potential at -0.30 volt.) If the sample contains molybdenum, a correction factor must be applied; multiply the apparent tin content of such a sample by the factor- 100 100 - (Molybdenum content, yo x 50) to give the true tin content. be multiplied by the factor- If the derivative circuit is used, the apparent tin content must 100 100 - (Molybdenum content, yo x 25) For other types of polarograph, the extent to which molybdenum interferes should be estab- lished as described under “Interfering Elements.”396 SCHOLES: THE DETERMINATION OF TIN IN PURE IRON, MILD STEEL [VOl.86 With each batch of samples, examine a reagent blank and a standard steel as a check The peak current of the reagent blank is normally 0.02 to 0.06 ph. NOTE-The sensitivity and lower limit of detection can be improved by using a 5-g sample dissolved Separation is then only about 87 per cent. complete, and on the calibration graph. in 135 ml of 20 per cent. v/v nitric acid. i t is therefore essential to plot a separate calibration graph based on a 5-g sample. CALIBRATION- Prepare solutions by dissolving l-g portions of pure iron having a low tin content in dilute nitric acid (1 + 4). To these solutions add amounts of standard tin solution suitable for the construction of two calibration graphs to cover the ranges 0.001 to 0.01 per cent.and 0.01 to 0.10 per cent. of tin. The volume of dilute acid used for dissolving the iron should be decreased by an amount equal to the volume of tin solution added, so that the total volume of final solution is always 35 ml. Treat these solutions as described under “Procedure.” INTERFERING ELEMENTS IRON- If the amount of co-precipitated iron exceeds a few milligrams, reduction of ferric iron at zero potential gives rise to a large standing current, which cannot be fully “backed-off.” This can be avoided by reducing the iron to the ferrous state with ascorbic acid, but even then, excessive amounts of ferrous iron tend to produce a sloping base line to the tin wave and may cause difficulties in polarographic measurement at high instrumental sensitivity. Potential, volts Potential.volts Fig. 3. Effect of molybdenum on tin Sample contained 0.01 per cent. Fig. 4. Effect of tungsten on tin wave. Sample (B.C.S. No. 277) contained 0.003 per cent. of tin and 0.12 per cent. of tungsten wave. of tin and 0.5 per cent. of molybdenum ARSENIC- There is no arsenic wave when the value selected for the start potential is more negative than -0.05 volt, but the presence of arsenic distorts the tin wave and causes high results; the extent of interference is dependent on the start potential. To prevent this interference, arsenic is oxidised to the quinquivalent state with potassium chlorate after the solution has been fumed; quinquivalent arsenic is not reduced a t the mercury electrode.MOLYBDENUM- In concentrated hydrochloric acid, molybdenum is reduced at about -0.25 volt, pro- ducing a small rounded wave ; its presence leads to base-line difficulties, which are particularly serious when the concentration of tin is low and the ratio of molybdenum to tin is high. Molybdenum distorts the shape of the first tin wave, which becomes more rounded and less well defined, and the slope of the base line of the second wave progressively increases with the concentration of molybdenum. This is indicated in Fig. 3, which shows the effect of 0.5 per cent. of molybdenum in a sample containing 0.01 per cent. of tin. To determine the effect of molybdenum on the peak height of the tin wave, various amounts of the element were added to solutions containing 1 g of pure iron and four different levels of tin.TheJune, 19611 AND CERTAIN LOW-ALLOY STEELS BY CATHODE-RAY POLAROGRAPHY 397 recoveries of the tin are shown in Table I1 and indicate that molybdenum exerts negative interference. At each level of tin, increasing amounts of molybdenum decrease the height of the tin wave by a value approximately proportional to the amount of molybdenum added, Le., for each 0.1 per cent. of molybdenum, the peak height is decreased by 5 per cent. A correction can therefore be applied to the apparent tin content to correct for interference from molybdenum, provided that the molybdenum content does not exceed 0.5 per cent. ; at higher contents of molybdenum interference is inconsistent and difficult to measure. A similar experiment, in which the derivative circuit was used, indicated that the peak height is decreased by approximately 2-5 per cent.for each 0.1 per cent. of molybdenum, but this decrease in interference is offset by a considerable reduction in sensitivity. TABLE I1 EFFECT OF MOLYBDENUM ON RECOVERY OF TIN ADDED TO 1-g SAMPLES OF PURE IRON % % % % Molybdenum added, Tin added, Tin found, Mean recovery, 0.019, 0.019 0.092, 0.094 0.0035, 0.004 0.009, 0.0085 0.018, 0.018 0.086, 0,088 0.003, 0.0035 0-0075, 0.008 0.0165, 0.017 0.080, 0.082 0-003, 0.003 0.008, 0.007 0.016, 0.016 0.076, 0.078 95 93 94 88 90 87 81 78 84 81 75 75 80 77 TUNGSTEN- Tungsten is reduced a t about -0-6 volt and produces a rather poorly defined wave, which tends to merge with the tin wave when the ratio of tungsten to tin approaches 10 to 1; Fig.4 shows the effect of tungsten when the ratio of tungsten to tin was 40 to 1. If the ratio of 10 to 1 is exceeded, the derivative circuit must be used to resolve the tin wave. With this circuit it has been found possible to determine 0.01 per cent. of tin in a sample known to contain 1 per cent. of tungsten. RESULTS The proposed method was applied to three British Chemical Standard samples of pure iron and one sample of B.I.S.R.A. vacuum-melted pure iron (AH iron). The results are shown in Table 111; at the level of 0.002 per cent. of tin, the standard deviation is 0.0005 per cent. The tin contents of three of these irons were also determined on 5-g samples; the results, expressed to the nearest 0.0002 per cent., were- Sample .. . . . . B.C.S. No. 149/1 B.C.S. No. 260/1 AH iron Tin content found, yo . . 0.0014, 0.0014 0.0018, 0.0018 0.0018, 0.0022 and the standard deviation was estimated to be about 0.0002 per cent. of tin. When it had been established that the method was suitable for analysing pure iron, a series of British Chemical Standard mild steels, containing alloying elements up to a maximum of 0.3 per cent., and two low-alloy steels containing molybdenum were analysed; the results are shown in Table IV. The peak heights for some of these samples were also measured by means of the derivative circuit. It is evident from Table IV that there is good agreement between results by the proposed and established procedures, with the possible exception of B.C.S.No. 276. It was not possible to measure the peak height for B.C.S. No. 277 with the direct circuit because of interference from tungsten, but resolution was perfect with the derivative circuit. The standard deviation is 0.001 per cent. at the 0.02 per cent. level and 0.005 per cent. a t the 0.10 per cent. level.398 SCHOLES: THE DETERMINATION OF TIN IN PURE IRON, MILD STEEL [Vol. 86 TABLE I11 TIN CONTENTS FOUND BY PROPOSED METHOD IN l-g SAMPLES OF IRON Each result is expressed to the nearest 0.0005 per cent. B.C.S. certificate Sample value for tin, Tin content found, % % B.C.S. No. 149 . . . . .. 0.0005, 0.001 < 0.002 { 0.0005, O*OOl} 0.0025, 0.002, 0.0015 B.C.S. No. 149/1 . . .. 0,002 { 0.002, 0.0025, 0.0015) 0.0015, 0.0015, 0.0015 { 0.002, 0.0025, 0-002 } < 0.002 B.C.S.No. 260/1 . . . . 0.001, 0.001, 0.001 (0.001, 0.002, 0.002 } - AH iron . . . . .. Mean, 0.001 % 0.002 0.002 0-0015 TABLE IV TIN CONTENTS FOUND BY PROPOSED METHOD I N 1-g SAMPLES OF MILD AND LOW-ALLOY STEELS Certificate values for tin in B.C.S. Nos. 271, 272, 273, 274, 275, 276 and 277 are quoted to the nearest 0.005 per cent. Results for tin in the range 0.02 to 0.10 per cent. are expressed to the nearest 0.001 per cent. and those below 0.02 per cent. to the nearest 0.0005 per cent. Tin content found- A r \ B.C.S. certificate value for- No. of Sample tin, moIybdenum, tungsten, determinations circuit), circuit), Yo % % % % B.C.S. No. 271 . . B.C.S. No. 272 . . B.C.S. No. 273 . . B.C.S. No. 274 . . B.C.S. No. 275 . . B.C.S. No. 276 .. B.C.S. No. 277 . . B.C.S. No. 239/1 . . B.C.S. No. 239/2 . . B.C.S. No. 218/2 . . B.C.S. No. 219/2 . . B.C.S. No. 256 . . 0.1 10 0.020 0.065 0.020 0.040 0.010 < <0.005 0.06 0.024 0.035 -0.025 -0.013 0.19 0.17 0-05 0.07 0.10 :0.01 0.02 0.03 0.03 0.03 0.43 0.54 0.02 0.01 0.28 0.04 0.05 0.20 0.12 - 6 0.110 - 3 0.020 0-019 3 0.068 - 3 0.025 0.023 3 0.044 - 6 0.017 0.018 3 - 0,003 3 0.049 - 3 0.022 0.020 3 0.033 - 3 0.026 0-023 0.012 6 0.012 CONCLUSIONS Separation of tin by co-precipitation on manganese dioxide is a suitable preliminary to the determination of this element by cathode-ray polarography. The method offers considerable improvement in sensitivity and accuracy over the British Standard volumetric procedure and was primarily designed for determining 0-001 to 0.02 per cent.of tin in pure iron and mild steel. Higher contents of tin can be determined in samples soluble in dilute nitric acid, provided that the molybdenum content does not exceed 0.5 per cent. Tungsten interferes with the measurement of the tin wave when the tungsten content is more than ten times the tin content. If this ratio is exceeded, it is possible to obtain reasonably accurate results by using the derivative circuit of the instrument to measure the tin wave. The sensitivity of the method may be further improved by using a larger weight of sample; the theoretical limit of detection is extended down to 0-0002 per cent. of tin in a 5-g sample. Poor recovery with large weights of sample is a disadvantage, but this is balanced by an improvement in sensitivity. Previous workerslO J1 $2 have shown that co-precipitation on manganese dioxide is also suitable for isolating antimony from iron and steel, and it should therefore be possible to determine this element in an aliquot from the solution after separation. Base electrolytes suitable for the polarographic determination of antimony have been described.lOJ1LYOl J AND CERTAIN LOW-ALLOY STEELS BY CATHODE-RAY POLAROGRAPHY 399 1. 2. 3. 4. 6. 6. 7. 8. 9. 10. 11. 12. 13. 14. REFERENCES “Determination of Tin in Iron and Steel,” British Standard 1121 : Part 20: 1951. B.I.S.R.A. Report No. MG/D/185/59. Ferrett, D. J., and Milner, G. W. C., Analyst, 1956, 81, 193. Lingane, J. J., J . Amer. Chem. SOC., 1945, 67, 919. Allsopp, W. E., and Damerell, V. R., Anal. Chevn., 1949, 21, 677. Mahr, C., and Waffenschmidt, K., Arch. Eisenhuttelzzer., 1960, 31, 221. Kallmann, S., Liu, R., and Oberthin, H., Anal. Chem., 1958, 30, 485. “A.S.T.M. Methods for Chemical Analysis of Metals,” American Society for Testing Materials, American Society for Testing Materials, op. cit., p. 339. GotB, H., Ikeda, S., and Watanabe, S., Japan Analyst, 1954, 3, 320. BrhGek, L., Hutn. Listy, 1957, 12, 140. Rooney, R. C., Analyst, 1957, 82, 619. Babko, A. K., and Shtokalo, M. I., Zavod. Lab., 1955, 21, 767. Lingane, J. J., I n d . Eng. Chem., Aizal. Ed., 1943, 15, 583. Philadelphia, 1956, p. 456. Received Decenzbev 6th, 1960

ISSN:0003-2654    

DOI:10.1039/AN9618600392

出版商:RSC    

年代:1961

数据来源: RSC