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11. |
Modification of dithiol tests for the field determination of molybdenum |
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Analyst,
Volume 93,
Issue 1102,
1968,
Page 59-60
M. F. Stubbs,
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摘要:
Analyst, January, 1968, Vol. 93, jbjb. 59-60 59 Modification of Dithiol Tests for the Field Determination of Molybdenum BY M. F. STUBBS (Department of Chemistry, Texas Technological College, Lubbock, Texas 79409, U.S.A .) Modifications of currently used dithiol tests for the field determination of molybdenum have been developed. Molybdenum is oxidised and ex- tracted quickly and selectively with sodium hypochlorite at room temperature. The disadvantages of using an alkaline fusion or oxidation with potassium chlorate and hot hydrochloric acid are avoided. SEVERAL methods have been reported for the determination of molybdenum in the field, primarily for use in geochemical prospecting. We have found the most satisfactory of these methods to be that of North,l as modified by the Applied Geochemistry Research Group, Royal School of Mines., However, in this method fusion with an alkaline flux is required, and there may be inconsistent decomposition of samples containing large amounts of silica or silicates. Also, silicic acid gels sometimes form when the sodium carbonate extract is added to the hydroxylamine hydrochloride solution.Furthermore, care is required at this point to prevent too rapid evolution of carbon dioxide. Clark and Tamale-ssali3 have reported a quick, preliminary field test for molybdenum that involves heating a small amount of 30 to 40-mesh sample with hydrochloric acid and potassium chlorate. The supernatant liquid is then treated with a small amount of solid zinc dithiol. No results are given to indicate the sensitivity of the test.Because of the disadvantages of using an alkaline fusion, or oxidation with potassium chlorate in hot concentrated hydrochloric acid, a reagent was sought that would extract molybdenum quickly and selectively at room temperature. Cox and Schellinger4 have suggested the use of sodium hypochlorite, ordinary household bleach , for leaching molybdenite, MoS,, and its alteration products. Bhappu, Reynolds and Stahmann5 have studied the hypochlorite leaching of molybdenite in detail and have found that the over-all reaction may be represented by the equation- 9 OC1- + MoS, + 6 OH- + MOO,,- + 2SO,,- + 9C1- + 3H,O. An excess of about 3 per cent. sodium hypochlorite was found to extract the molybdenum quantitatively from about 100-mesh molybdenite concentrate at room temperature in 70 minutes.We have confirmed this result and have modified the two field tests cited by using about 5 per cent. sodium hypochlorite, ordinary household bleach, for the oxidation and extraction. MODIFIED PROCEDURE FOR TEST OF THE APPLIED GEOCHEMISTRY RESEARCH GROUP- Add 2 ml of the household bleach to a 0.25-g sieved sample in a 15-ml porcelain crucible or 10-ml beaker. Allow to stand for 1 hour, with occasional swirling, or, if preferred, overnight. TABLE I COMPARISON OF AVERAGE TYPICAL RESULTS Expressed as molybdenum, p.p.m. Applied Geochemistry Sodium hypochlorite Sample Research Group extraction Moly No. 1 . . .. 400 400 Moly No. 4 . . .. 200 300 Moly No. 6 . . .. 1800 2000 Moly No. 10 . . .. 2000 2400 100 100 FAG Tails No. 1 .. .. 80 (gel) FAG Tails No. 2 . . .. 100 FAG Tails No. 3 . . .. 100 (gel) 140 RO Tails No. 2 , . .. 140 (gel) 200 Chino copper . . .. 80 (gel) 160 10 6 Soil No. 7 . . .. .. 8 (gel) Soil No. 10 . . .. 4 (gel) 0 SAC and the authors.60 STUBBS Transfer the solution to a calibrated test-tube and adjust to 5 ml with water washings. Use a 0-1 to 2-ml aliquot for carrying out operation instructions 7, 9, 10 and 11, as given in Technical Communication No. 15.2 The values given in Table I show that, in general, the two methods give comparable values. However, the modified procedure gives somewhat better results when gel formation occurs. Furthermore, sodium hypochlorite extraction and oxidation is much simpler and quicker, no heat is required and carbon dioxide evolution is avoided.MODIFIED PROCEDURE FOR PRELIMINARY FIELD TEST OF CLARK AND TL~&~LE-SSALI~- Place about 0005g of 100-mesh sample in a small test-tube. Add 5 drops of about 5 per cent. sodium hypochlorite solution and shake the tube for about 1 minute. Allow the undissolved part of the sample to settle. Remove 1 drop of supernatant liquid to a spot plate. Add 1 drop of concentrated hydrochloric acid, then 2 drops of mineral-free water. Now add a trace of solid zinc dithiol. Stir with a glass rod. A bright green precipitate forms in a short time if molybdenum is present. Copper ores containing molybdenum give a black precipitate when oxidised with hydrochloric acid - potassium chlorate, thus making it impossible to test for molybdenum in the presence of copper by the method of Clark and Tamale-ssali. Copper does not interfere when alkaline sodium hypochlorite solution is used.SENSITIVITY OF THE MODIFIED TEST- A standard solution containing 500 p.p.m. of molybdenum was prepared by-dissolving 0.0834 g of 99.8 per cent. molybdenite in 12 ml of the 5 per cent. sodium hypochlorite solution and diluting to 100 ml. Standards were prepared down to 5 p.p.m. of molybdenum and the test described above was found to be sensitive down to 10 p.p.m., with about 1 minute required for the appearance of the green precipitate at this concentration. TABLE I1 COMPARISON OF AVERAGE TYPICAL RESULTS Molybdenum, Sample per cent. Moly No. 1 . . .. 0.04 Moly No. 3 . . .. 0.30 Moly No. 4 . . . . 0.03 lMoly No. 10 . . .. 0.24 Moly No. 13 . . ..0.14 RO Tail No. 1 . . .. 0.0 1 FAG Tail No. 1 . . .. 0.0 1 Copper No. 1 . . .. 0-08 Moly No. 2 . . .. 0.90 Approximate time required for formation of green precipitates f A Clark and Tamale-ssali procedure Proposed procedure grey - green, 2 minutes 2 minutes 5 minutes 5 minutes 1 minute 2 minutes grey - green, 5 minutes grey, 2 minutes grey - black, 30 seconds 30 seconds 15 seconds 30 seconds 30 seconds 30 seconds 30 seconds 2 minutes 5 minutes 2 minutes Only Moly No. 2 gave a green precipitate when hydrochloric acid alone was used for extraction. Both the method of Clark and Tamale-ssali and the modified procedure usually give a bright green precipitate in about 15 seconds with samples containing above 1 per cent. of molybdenite. The results given in Table I1 show that the modified method is much more sensitive for low concentrations of molybdenum, can be used in the presence of copper and requires no heat. The author thanks the New Mexico State Bureau of Mines and Mineral Resources for supplying samples. REFERENCES 1. 2. 3. 4. 5. North, A. A., Analyst, 1956, 81, 660. Applied Geochemical Research Group, Technical Communication No. 15, Revised 1965, Royal Clark, R. E. D., and Tamale-ssali, C. E., Analyst, 1959, 84, 16. Cox, H., and Schellinger, A. K., Engng Min. J., 1958, 159, 101. Bhappu, R. B., Reynolds, D. H., and Stahmann, W. S., Circular 66, New Mexico State Bureau of Mines and Mineral Resources, Socorro, New Mexico, 1963. Received June 9th, 1967 School of Mines, Imperial College of Science and Technology, London, S.W.7.
ISSN:0003-2654
DOI:10.1039/AN9689300059
出版商:RSC
年代:1968
数据来源: RSC
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12. |
Book reviews |
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Analyst,
Volume 93,
Issue 1102,
1968,
Page 61-64
W. T. Elwell,
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摘要:
Analyst, January, 1968, Vol. 93, $p. 61-64 61 Book Reviews ORGANIC CHEMISTRY. VOLUME 1: THE FUNDAMENTAL PRINCIPLES. By I. L. FINAR, B.Sc., Ph.D.(Lond.), A.R.I.C. Fifth Edition. Pp. xiv + 906. London: Longmans, Green and Co. Ltd. 1967. Price 60s. Since 1951, when this book made its first appearance, the title “Organic Chemistry” and the name Finar have become almost synonymous. The previous edition of Volume I (Volume I1 deals with “Stereochemistry and the Chemistry of Natural Products”) was only published in 1963, and this new edition demonstrates the desire by all concerned to retain this publication in the forefront of text-books on the subject. Text-books on organic chemistry usually aim at a comprehensive survey of the fundamentals on which a study of the science is based, whereas similar books that deal with inorganic chemistry tend to cover a more restricted field.This comparison emphasises the problem of presenting a text-book on organic chemistry in the best way, especially in the first edition, and of maintaining the standard by appropriate deletions and additions, and not merely corrections, in subsequent editions. There is no doubt that this book has established and maintained these objectives throughout its lifetime, and the fifth edition is no exception. In writing this book, the author does not claim to have any particular educational course in mind, but the standard is, at least, that of the general honours degree in chemistry, Part I of the special honours degree in chemistry, and Part I of the graduate membership of the Royal Institute of Chemistry.Subjects, and their arrangement, follow, broadly, the usual pattern for introducing and developing a study of organic compounds and their reactions, but in this edition, to cite one example, the author has endeavoured to remove the idea that organic chemistry is a science in which it is essential for students to memorise a large number of apparently unrelated methods and reactions. This has been approached by introducing the electronic theories of organic chemistry at a very early stage, so as to impart a more meaningful coherence to a systematic study of the subject , Throughout the book, descriptions of reactions are usually followed by discussions of the mechanisms involved, and these are followed by an account of the evidence on which currently accepted reaction mechanisms are based.Much of the theoretical discourse in previous editions has been expanded, and more has been included in this edition. The theory of acids and bases is now discussed, and more has been included on partial-rate factors. Accounts of the selectivity relationship and the Hammett equation have been included, and thermodynamics has been applied to some problems. Other added, or expanded, sections deal with ylids, free radicals, carbene chemistry, con- formational analysis, aromaticity, aromatic substitution and heterocyclic compounds. Where a more detailed study of some of the subjects is required, a selected list of references is available at the end of each chapter, and a brief account of the literature on organic chemistry is given in an appendix.Because of the increasing use of newer physical methods for solving structural problems, the reader is given a useful insight into some of the methods currently used. For example, brief explanations of ultraviolet and nuclear magnetic resonance spectroscopy appear early in the book, and, thereafter, appropriate references are made to each of these techniques. Infrared spectroscopy is dealt with in much the same way, but in more detail. The interpretation of complex infrared spectra is the province of the expert, but a basic understanding of relatively simple spectra, particularly for solving problems relating to functional groups, should readily be gained from the author’s presentation of the subject. In this way the uninitiated should soon learn, not only how to make use of infrared spectroscopy as an analytical tool, but to appreciate the problems that confront the expert in the field.This latest edition of Finar’s “Organic Chemistry’’ is welcomed, because it ensures its con- tinued pride of place on the bookshelves of the student and the expert, or, indeed, anyone with an occasional need for information on basic organic chemistry. It is interspersed with typical examination questions. W. T. ELWELL62 BOOK REVIEWS [Analyst, VOl. 93 SUBSTITUENT EFFECTS IN ORGANIC POLAROGRAPHY. By PETR ZUMAN. Pp. xvi + 384. New The title of this work does not quite encompass its real aim, which is no less than the prediction of half-wave potentials, Et, of organic compounds from the precepts of physical organic chemistry (predominantly, from linear free-energy relationships).The relationship between the Hammett - Taft a,p substituent-reaction constants and E+ values is amply demonstrated in correlations for numerous substrate series throughout the book. The author’s achievements might well be enumerated. Firstly, it is eminently satisfactory that topics as diverse as polarographic reductions, and kinetics and equilibria in homogeneous phases, can be shown to have a common basis of treatment. Secondly, as this is the case, polaro- graphy now provides a useful adjunct to the physical organic chemist’s armoury. Thirdly, from the purely utilitarian point of view, analyses are benefited in a general way by the availability of an extensive semi-theoretical background, and, in particular, by the possibility of approximate E+ predictions for hitherto uninvestigated substrates; only one or a few polarograms are required for a whole series (possibly 30 to 50) of derivatives.On the other hand, linear free-energy relation- ships in polarography have limitations at least equal to those for homogeneous systems, in that reasons for failure are rarely self-evident, the effect of temperature is obscure, and the parameters themselves can usually be only qualitatively related to fundamental molecular properties. The scatter in the polarographic correlation graphs is generally rather greater than in their homo- geneous-phase analogues. This is to be expected : longer series are accessible to polarographic study; hence more stringent tests are being made.In addition, however, as the author points out, in irreversible reductions, a large fraction of those studied, the polarographic relationships require either constancy, or a monotonous variation through the series under study, of an extra parameter, viz., the transfer coefficient a ; similarly they require a constancy of electron-transfer mechanism. It is unfortunate that in several plots, lines are rather summarily drawn where linearity might well be doubted, and the author’s designations of sundry points as “deviating,” as opposed to the remainder, presumably “fitting,” are often arbitrary. Here, what is in any case a good argument is being pushed, unnecessarily, far beyond its limits. The first chapter comprises a brief introduction to substituent effects and some useful pages on polarographic technique.Chapter 2 outlines the relationship between E+ and the equilibrium or rate constants of the electrochemical processes (the rate-constant - E) relationship being taken on trust) ; also there is given a brief outline of polar and steric effects of substituents on activation parameters, which are then expressed algebraically following Hammett and Taft as dependences of Ea on o and p. Two comments are called for here: the exposition would be clearer (to the reviewer a t least) with stronger distinction between the original and the new polarographically relevant expressions. Also, the neophyte will need considerably more discussion than is given of the physical organic background, which requires study of the original references or of later authors such as Leffler and Grunwald.The third and longest chapter, on benzene derivatives, includes the useful section on the predictive use of the op parameters. Further chapters on heterocyclics, compounds with particular electro-active sites, polycyclic hydrocarbons and quinonoid and alicyclic compounds complete the story. A long gestation, from a foetal 1955 review article, preceded publication of the book, of which the first half is said to be polarographically up to date to 1963 and the second half to 1965. The physical theory is 1961 to 1962 vintage, which perhaps accounts for such statements as, on page 26, “Polar interaction can be propagated along single bonds . . . or directly through space (field effect) .” (Whence the “space” ?) The book is well produced, with tables (61) and diagrams (109) of pleasing appearance, and 511 references are cited.Few mistakes were noted, but equation (5) on page 24, intended to embody the transition-state theory for rate constant K, is given as RTln K = AF+, which lacks a minus sign, has (as elsewhere) an unusual superscript in place of Eyring’s double cross, and is, in other respects, either unsettlingly mistaken or an unusual definition of free energy of activation. Page 34 has an erroneous, or at least extremely obscure, statement in brackets, and, similarly, brackets on page 122 are either misprinted or curiously disposed. Despite the reservations above, the book is a tour de foyce, providing an excellent collation of data, and commendable to organic analysts, physical organic chemists and electrochemists generally.D. R. ROSEINSKY York: Plenum Press. 1967. Price $17.50.January, 19681 BOOK REVIEWS 63 THE GAS LIQUID CHROMATOGRAPHY OF STEROIDS. (Memoirs of the Society for Endocrinology No. 16.) Proceedings of a Symposium held at the University of Glasgow on 4 to 6 April, 1966. Edited by J. K. GRANT. Pp. viii + 294. Cambridge: University Press. 1967. Price 70s. The application of gas-chromatographic methods to the determination of steroids in biological materials is rapidly becoming recognised as one of the most important advances in analytical biochemistry. To obtain maximum information from such techniques and to appreciate their potentialities and limitations it is necessary for the biochemist to be aware of current trends in steroid analysis.A Symposium arranged by the Society for Endocrinology was held in Glasgow with the objects of (a) assessing the present state of gas chromatography as applied to steroid determinations, and (b) considering other techniques, such as isotope counting and mass spectro- metry, in conjunction with gas chromatography. “The Gas Liquid Chromatography of Steroids” contains the Proceedings of this Symposium at which eighteen papers were presented. Seven of these, including two papers not reported, dealt with basic gas-chromatographic techniques, handling of sub-microgram amounts of sample, radiochemical detection of gas - liquid chromatographic effluents and combined gas chromato- graphy - mass spectrometry. The remaining papers dealt with the general conditions necessary for the gas chromatography of steroids, systematic analysis of steroids in biological material , detection and determination of ultra-micro quantities of steroids by using electron capture detectors, determination of cortico- steroids and their metabolites and the analysis of plant sterols.In many of the methods outlined, additional techniques such as solvent extraction, thin-layer chromatography and derivative formation were used to improve specificity and sensitivity of the final gas-chromatographic step. From the many different aspects of steroid analysis that were discussed a t the Symposium it was difficult to detect a clear pattern of current trends. However, the overriding problem appeared not to be lack of sensitivity but one of identification, and in this respect mass spectrometry went a long way to solving such difficulties.The book is recommended as a valuable addition to the bookshelf of every worker in the field of steroid analysis. D. A. ELVIDGE POLAROGRAPHIE MIT BESONDERER BER~CKSICHTIGUNG DER KLASSISCHEN METHODEN. By DR. J. PROSZT, DR. V. CIELESZKY and DR. K. GYdRBfR6. Pp. 587. Budapest: Akadkmiai Kiad6. 1967. Price L7. This book is an unrevised translation of the original Hungarian edition, first published in 1964, and is divided into three parts. The first part deals with the theoretical background and experimental principles. The limited survey of apparatus is confined to two electrode systems and mainly to equipment of East European origin.The types of polarographic limiting current are classified, adsorption phenomena and polarographic maxima are also fully covered. The importance of polarography in physical chemistry research is stressed, particularly in the field of reaction kinetics. Several related electroanalytical techniques that are of practical analytical importance, i.e., controlled potential electrolysis, microcoulometry and the use of the dropping- mercury electrode in a flowing stream, are competently covered. There are also useful sections on amperometric titration and oscillopolarography, but the section dealing with the more recent pulse techniques is rather dated and too brief to be of any real value. They consist of a collection of tested methods for the determination of inorganic and organic substances. Methods for the individual cations, based on the Periodic classification, are given in the second section.Electroactive anions and inorganic molecules are also covered, and the section concludes with several examples of analyses of industrial importance. In the third section, the broad field of organic polarographic analysis is surveyed. Although there has been considerably development in this field since the date of the last reference quoted (1961), the general treatment is of a high standard. The influence of structure on polarographic behaviour is treated wherever possible. The book is well produced and the figures are extremely clear. It provides a useful manual of the polarographic methods of analysis published prior to 1961.The two remaining sections are of most value to analytical chemists. B. FLEET64 BOOK REVIEWS [Analyst, Vol. 93 QUALITY CONTROL IN THE FOOD INDUSTRY. Edited by S. M. HERSCHDOERFER. Pp. xiv + 385. London and New York: Academic Press Inc. 1967. Price 90s. In spite of the tremendous advances that have been made in recent years, and the symposia that have been held in order to discuss the control of quality in food production, no authoritative book has previously appeared to cover the subject as a whole. Dr. Herschdoerfer has persuaded a team of experts to act as contributors to his first volume and the authors of the two following volumes are equally authoritative. The first impression one gains of the book is that of readability, a quality generally lacking in scientific and technical literature, and, if one does not take it too seriously, it makes an ideal bedside book. It is, however, a work to be taken seriously and is, therefore, unsuitable for that purpose.The volume is divided into the following sections : “The organisation of quality control,’’ by Prof. J. Hawthorn; “Health problems in quality control, chemical aspects,” by Prof. A. C. Frazer; and “Microbiological aspects,” by Dr. Betty Hobbs; “Statistical methods,” by Dr. E. H. Steiner; “Sensory assessment,’’ by Dr. N. T. Gridgeman; and “Food standards,” by Dr. F. Towns- hend. Prof. Hawthorn illustrates his procedure by describing the production of canned “okebits” and does it extremely well, even pointing out details such as the necessity to choose one’s control stafI by their regular attendance at work.Unfortunately, he appears to have overlooked the fact that his okebits are not canned acorns, but are canned processed acorns. Prof. Frazer and Dr. Hobbs are, as would be expected, completely at home with their subjects, and many analysts who have no microbiological department will be grateful to Dr. Hobbs for the working details of methods for sorting out pathogenic bacteria in food products. One cannot help feeling, however, that this introductory volume should have included a chapter on general hygiene and microbiological deterioration of foods. Many foods, wines, beers, pickles, sauces and yoghourt, to name a few, are produced by microbiological methods, and most foods can be spoiled in manufacture by faulty microbiological techniques.In the reviewer’s laboratory, from two to six complaints are received every day from members of the public through public health departments. Many of these are due to faulty hygiene in the factory and in subsequent handling, and it is interesting to note that in the City of Westminster 14 tons of prepared and 217 tons of raw and frozen foods were condemned in 1966. In these cases there is seldom any suggestion of pathogenic organisms being responsible. Dr. Steiner tries to simplify statistics, and makes one realise the advisability of a good elementary education in mathematics. Dr. Gridgeman writes an excellent section on sensory assessment and attempts to deal with the delicate subject of the effect of coloiirs on taste and odour, but one hesitates to agree with him that the know-how of sensory testing is as recent as he believes. There are extant fifteenth century German wood-cuts showing the method of wine-tasting, and one has only to think of the tasting of the good wine at the wedding feast at Cana, the wine degustateurs or vignoliers of France, whosc history goes back for centuries, and the garblers and ale-conners of our own country to realise that, while nothing was put into print as such, our ancestors had to rely on sensory tests, where we are able to employ chemical and physical determinations. Finally, Dr. Townshend’s section on food standards will be a help to any food manufacturer seeking to make foods for export. Dr. Townshend is an international lawyer and writes from this aspect; he does not deal with the laws of any specific country, although he admires Canadian regulations and hopes for international standards. Most of the contributors provide excellent lists of references, Dr. Gridgeman gives a good glossary of terms, and the index is adequate. Volume 1. THOMAS MCLACHLAN
ISSN:0003-2654
DOI:10.1039/AN9689300061
出版商:RSC
年代:1968
数据来源: RSC
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