摘要:

290 SHORT PAPERS [Analyst, VOl. 91 Interference from Silica in Phosphate Analysis BY A. HENRIKSEN (The Norwegian Institute for Water Research, Oslo 3, Norway) IN a recent publication,l automatic methods for determining orthophosphates and acid-hydrolysable phosphates on the AutoAnalyzer were described. These automatic methods were based on generally accepted methods2 with some slight modifications. It was shown, however, that when samples were analysed by both the manual and the automatic methods, statistically identical results were obtained. By using these methods in surveys of polluted and unpolluted lakes, fjords and rivers in Norway, it was found that unexpectedly high values of acid-hydrolysable phosphates were observed, particularly in unpolluted waters. The method was therefore believed to be subjected to inter- ference from a substances normally present in natural waters.Although the manual method is claimed to be free from interference,2 it was thought that the high values were caused by the interference of silica; this element is determined by a basically identical procedure, except for the lower acidity required for its determination. The main difference between the orthophosphate and acid-hydrolysable phosphate methods is that the sulphuric acid is added to the sample before the molybdate in the acid-hydrolysable phosphate method, while in the orthophosphate method a mixture of the two reagents is added to the sample, the final reagent concentrations being the same in both methods. When heating of the sample was omitted in the acid-hydrolysable phosphate method, the same degree of inter- ference was obtained.This indicated that the interference could be due solely to the different ways of adding reagents in the two methods. When the molybdate concentration of the reagent in the acid-hydrolysable phosphate method was reduced from 10 to 5 per cent., the interference from silica was only 3 pg of phosphate phos- phorus per litre per mg of silicate per litre. With further reduction below 5 per cent. in molybdate concentration, the sensitivity of the method was considerably decreased. Thus, although the molybdate concentration could be reduced to 5 per cent. without any reduction in sensitivity occurring, there was still under these conditions a significant interference from silica.The sulphuric acid solution used for hydrolysis was then made 7 N, and the molybdate solution was made 2 N with respect to sulphuric acid and 5 per cent. with respect to molybdate, the final concentration of sulphuric acid being as before. This modified procedure resulted in no inter- ference from silicic acid up to 10 mg of silicate per litre.April, 19661 SHORT PAPERS 291 Therefore, in order to eliminate the interference from silica in the method for determining acid- hydrolysable phosphates described previously, the following modifications in the reagents described therein (page 31) should be made- (a) substitute 7 N sulphuric acid for 9 N sulphuric acid used for hydrolysis; (b) substitute a 5 per cent. ammonium molybdate in 2 N sulphuric acid solution for the solution of 10 per cent.ammonium molybdate. The molybdate concentration could be reduced from 10 to 5 per cent. in the orthophosphate method without any reduction in sensitivity, so making this procedure a little cheaper. The previous and the modified procedures were used to analyse 80 sea-water samples and 15 fresh-water samples for acid-hydrolysable phosphates. They were also analysed for silica. The difference in values obtained from the two phosphate methods should be due to the interference of silica in the original procedure. These values and the silica values have been subjected to correlation analysis. The correlation coefficients of the results (see Table I) for the interference values and the silica values are highly significant (P = less than 0-1 per cent.), thus indicating that silica is the interfering substance in the previous method. TABLE I CORRELATION BETWEEN INTERFERENCE VALUES AND SILICA VALUES IN THE ACID-HYDROLYSABLE PHOSPHATE METHOD Sea-water Fresh water Number of samples . . .. . . .. . . . . . . 80 15 Mean values -+ Previous method . . . . . . pg of phosphorus per litre 50.95 55.0 Modified method . . . . . . pg of phosphorus per litre 42.30 20.5 Difference . . . . . . . . pg of phosphorus per litre 8-65 34.5 SiO, . . . . . . . . mg of silicate per litre 0.98 3.9 Si0,as P . . . . . . . . pg of phosphorus per litre 8.82 35.1 Correlation coefficient . . . . . . . . . . . . . . 0.8993 0.8500 1 mg of silicate per litre = 9 pg of phosphorus per litre. REFERENCES 1. Henriksen, A., Analyst, 1965, 90, 29. 2. hssociation of the American Soap and Glycerine Producers Inc., Sub-committee on Phosphates, Receil-ed March 19th, 1965 J . Amer. Wat. Wks Assoc., 1958, 50, 1563.

ISSN:0003-2654    

DOI:10.1039/AN9669100290

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

April, 19661 SHORT PAPERS 291 The Collection of Fractions Separated by Gas - Liquid Chromatography BY M. D. D. HO’CVLE1’T AND D. WELT1 ( Unilever Research Laboratory, Colworth House, Sharnbrook, Bedford) MANY methods have been reported for trapping gas - liquid chromatography fractions for further infrared spectroscopic examination. Some methods are too crude to trap efficiently fractions containing less than 1 mg of component, others are too specific in their applications. We would like to draw attention to a method of trapping that combines two techniques not generally used together. The two techniques are (a), the trapping of the fraction in a tube containing normal gas - liquid chromatography column packing, and ( b ) , Swoboda’s total-trapping technique. The use of a stationary phase on the support reduces the vapour pressure of the sample component more than Shearer’s method2 of using support material on its own.The sample com- ponents can also be stored more easily when the stationary phase is present. The combination of these techniques is suitable for trapping the more volatile components, liquids, or components soluble in common infrared solvents. For less volatile compounds or solids,292 SHORT PAPERS [Analyst, VOl. 91 and particularly those which are insoluble in the common infrared solvents, we used a third method which is a variation on Leggon's method3 for trapping fractions in potassium bromide powder. This was suggested by the success of Philpotts and his colleagues4 in handling 1 to 100 microgram samples from liquid - solid chromatographs.GAS - LIQUID CHROMATOGRAPHY COLUMN PACKING, TOTAL-TRAPPING TECHNIQUE A 9-cm long, 3-mm i.d. tube packed with 7 per cent. Apiezon "L" on 60 to 80 mesh celite or firebrick, which has been previously stripped, is fitted on to the exit port of the detector by-pass system. Any sensitivity of the detector t o the increase in back-pressure caused by fitting the tube is eliminated by building a suitable restriction into the by-pass. The tube is cooled with crushed solid carbon dioxide, and a calcium chloride drying-tube is fitted to the other end. After collecting the fraction, the tube is sealed with caps and stored a t a low temperature until required. It is then inserted into a small copper tube, 7.5 cm long, 1 cm i.d., electrically heated to 220" C.One end of the collecting tube is connected to a miniature conventional cold-trap (Fig. l), and the other end is connected to the argon supply via a rotameter and needle valve. Back flow Dry argon A = Calcium chloride drying tube B = Glass column containing gas - liquid C = Heating coil D = Liquid nitrogen chromatographic packing Fig. 1. Apparatus for thc column packing, total-trapping technique The miniature cold-trap consists of a test-tube, 10 cm long, 1.2 cm i.d., made from a standard Quickfit I310 socket with a tapered bottom, and fitted with a side arm placed 0.5cm from the neck. ,4 centre tube is prepared from a Quickfit MF 15/0 joint, 3.5 mm i.d. with a stern 6-5 cm long. The other end is fitted with a B5 cone that is attached to the short column via two glass sockets as shown in Fig.1. When the collecting tube has been heated for 60 seconds the trap is immersed in liquid nitrogen, and argon (60 ml per minute) is passed through the system for up to 5 minutes. The condensing argon traps the sample completely,l and as the vapour pressure of liquid argon at -196" C is about 200 mm of mercury it causes a back-flow of 140 ml per minute of air, which is dried in a calcium chloride drying-tube fitted to the outlet of the trap. In 5 minutes, 0.9 ml of condensed gas is collected. No side effects with oxygen sensitive compounds have been observed. When any doubt has arisen, the air inlet has been placed directly above the liquid nitrogen. The collecting tube is removed from the trap and a bubble flow-meter is attached in its place. The Dewar flask is slowly lowered down the trap so that the argon boils at a rate of less than 6 ml per minute, When all the argon has been removed, the trap is sealed at both ends with Quickfit caps.Liquids with a high vapour pressure are cold-distilled into the tip of the trap by immersing The side arm is fitted with a B5 cone on which a drying tube is placed.April, 19661 SHORT PAPERS 293 the tip in liquid n i t r ~ g e n . ~ Higher-boiling components are centrifuged into the tip without loss. The fractions can be examined as liquids or solutions by normal infrared methods with either microcells or a beam condenser. The times for eluting various components from the collecting tubes, which were measured by attaching a flame-ionisation detector to the tube in place of the cold trap, were: ethyl acetate, 50 seconds; isobutyl acetate, 120 seconds; octanol, 150 seconds; eugenol, 300 seconds.High- boiling polar materials “tail” badly on elution from the collection tubes. Examination of both the “total-trapping” step and the whole sequence of operations gave recoveries of greater than 90 per cent. for 2 mg of ethyl acetate (as determined by the absorbance of the infrared carbonyl stretching band measured in 50 plitres of carbon tetrachloride). By inference, the efficiency of the collecting tube must be close to 100 per cent. Similarly, 0.1 mg of ethyl caproate gave recoveries of greater than 85 per cent. Spectra of 0.05-mg samples can be obtained that show all the dominant bands without beam condensation or scale expansion.Beam condensation tends to evaporate volatile samples, but scale expansion will increase the sensitivity to below 0.01 mg. The storage efficiency of the collecting tubes was also determined by infrared methods. The percentage recoveries of ethyl acetate and isobutyl acetate were- Percentage recovery after- r -7 0 hours a t 5 hours a t 24 hours a t A - 7- Ethyl acetate.. . . 100 100 75 52 82 48 40 Isobutyl acetate . . 100 100 95 98 102 98 91 17°C -78°C -10°C 17°C -78” -10°C 17OC No appreciable amounts of water were detected after 24 hours’ storage. A single component can be processed in 45 minutes, but six Components can be processed This method has been used successfully in practice for 18 months on complex mixtures. in parallel and their spectra determined in less than 3 hours.THE TRAPPING OF LESS VOLATILE COMPOIJNDS IN POTASSIUM BROMIDE POWDER- The fractions are collected directly into a short tube, 10cm long and 2.5mm i.d., fitted with B5 cones a t each end, and containing a plug (approximately 50 mg) of dry, powdered potas- sium bromide. A constriction in the tube wedges the powder close to the chromatograph outlet. The tube is cooled with solid carbon dioxide, and a drying tube is attached to the outlet. The tube can be capped a t both ends and stored in a refrigerator. The disc is prepared in a normal disc holder (23 mm in diameter, slot-size, 1 mm x 5 mm). The potassium bromide plug from the tube is placed on top of a small amount of dry powder a t the bottom of the slot. The slot is “topped up” with more dry powder.The disc holder is placed in a die loaded with a pressure of 200 lb per sq. inch for 90 seconds. Where the components are sufficiently involatile the die is also evacuated. The disc can be examined spectroscopically with or without a beam condenser. Good spectra were obtained even with 0.025 mg of the marginally volatile liquid 2,4-xylenol, using a beam condenser. The compressibility of liquids during pressing will reduce the efficiency of the process. For instance, 0.1 mg of 2,4-xylenol gave a recovery efficiency of 37 per cent. ; 0.05 mg, 52 per cent. ; but 0.025 mg, 96 per cent. The trapping efficiency has been examined with a flame-ionisation detector attached to the outlet of the trap. No losses occur if the trap is cooled in solid carbon dioxide. At room tenipera- ture, 70 per cent. of 2,4-xylenol was lost before the peak was complete. Interference from water is negligible, provided that the potassium bromide powder is continually protected from water vapour. REFERENCES This method can be used routinely for samples sizes down to 0.05 to 0.1 mg. With a good tcchnique, sample sizes of less than 0.01 mg could be examined. 1. Swoboda, P. A. T., Nature, 1963, 199, 31. 2. 3. 4. 5. Shearer, D. A,, Stone, B. C., and McGugan, W. A., Analyst, 1963, 88, 147. Leggon, H. TV., Analyt. Chew., 1961, 33, 1295. Philpotts, A. R., in Lippincott, E. R., and Margoshes, M., Editors, “Proceedings, Xth Colloquium Haslam, J., Jeffs, A. K., and Willis, H. A., Analyst, 1961, 86, 44. Spectroscopicum Internationale,” Spartan Books, Washington, 1962, p. 577. Received April 7th, 1965

ISSN:0003-2654    

DOI:10.1039/AN9669100291

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

294 BOOK REVIEWS [Analyst, VOl. 91 Book Reviews VITAMIN ASSAY; TESTED METHODS. By ROLF STROHECKER AND HEINZ M. HENKING. Translated by D. D. Libman. Weinheim: Verlag Chemie, GmbH. Pp. 360. 1965. Price DM 48; $12.00. The German edition of this book was published in 1963 and was reviewed by me in The Analyst, 1964, 89, 375. The translation has been carried out by D. D. Libman, and this has now made available, to a much wider reading sphere, an excellent compilation of methods of vitamin assay. In the previous review, I mentioned the comprehensive nature of the work and its scope. For those interested in all phases of vitamin assay this is an ideal volume of reference, and I am quite sure that, with the appearance of this English edition, it will find its place in many laboratories in which this work is carried out.For those dealing purely with chemical mcthods, there are plenty of methods to suit the taste: good choice is given of ultraviolet absorption, photonietric, polarographic and chromatographic techniques, all of which are made available to the reader. Those more interested in microbiological methods will also find this a useful reference book, and although the detail of the technique might appear to be a little on the scanty side it is well referenced, and the reader may readily fill in the gaps by going to the original work on the subject. I can say no more in tribute to this volume except that since I reviewed it in 1964 it has found regular use and is probably the most widely used of all vitamin books in my laboratory.K. F. MILTON DOUBLE LAYER AND ELECTRODE KINETICS. By PAUL DELAHAY. Pp. xii + 321. New York, London and Sydney: Interscience Publishers, a division of John Wiley & Sons Inc. 1965. Price 110s. An extended review and critical appraisal of this field has been needed for some time. None is better qualified than Professor Delahay to write on this topic, and he does so with his usual competence. This, of course, means that the result is strong meat. At times progression is leisurely and assimilation is effortless; a t other times one is led into fascinating but concentrated detail so that connecting links get submerged and the over-all picture dislimns. A good deal of concentration is needed in certain places, but is well rewarded. The first deals with the double layer and can be read independently of the second, but to make full use of the second part on kinetics an intimate knowledge of double layer phenomena is necessary.The valuable and extensive docu- mentation extends through 1964, and is used in part to extend the coverage of the text to more specialised studies. After an excellent brief historical introduction, Part I on the double layer follows and is divided into 5 chapters covering first, the thermodynamics of the ideal polarised electrode and second, the structure of the diffuse double layer without specific adsorption. Then follow 2 chapters dealing with adsorption : third, the structure of the double layer with specific adsorption and fourth, adsorption a t an ideal polarised electrode. The final chapter in this part deals briefly with electrode systems other than the mercury - aqueous solution interface. I t is in respect to solid electrodes that the subject is least well developed, indeed, is still in the qualitative stage, as Ilelahay emphasises in a very good summary of the problems involved.Part IT, on electrode kinetics, is again divided into 5 chapters dealing with: first, the kinetics of simple electrode processes without specific adsorption ; second, with processes involving more than one step; third, with the correlation between electrode kinetics and double layer structure in the absence of specific adsorption ; fourth, with kinetics of electrode processes with chemisorption of reactants or products, and last with potential-dependent adsorption of reactants and products.Good indexes are provided. Results are critically compared and interpreted with judgment and the author does not hesitate to express his own views. An outstanding feature of the book is the extensive collection of diagrams reproduced from the original literature which facilitate the comparison of theory with experiment. This monograph will undoubtedly assume the r61e of the authoritative source on this subject for both analytical and electrochemical research and development for some time to come. The book is divided into two almost equal parts. This is no impersonal review. E. BISHOPApril, 19661 BOOK REVIEWS 295 STEROID-SPEKTRENATLAS : ATLAS OF STEROID SPECTRA. By Dr.-Ing. WALTER NEUDERT and Dr.-Ing. HORST KOPKA. Translated by Dr. JOHN B.LEANE. Pp. viii + 471 + scale. Berlin, Heidelberg and New York : Springer-Verlag. The only other atlas of steroid spectra is that by Dobriner and colleagues (Volume 1, 1953; Volume 2, 1958) and this deals exclusively with the infrared spectra of 656 steroids. In this new work, information is presented on the infrared, ultraviolet and nuclear magnetic resonance spectra of 900 steroids. In addition, optical rotation and dipole-moment data are given. Because, in the Dobriner atlas, emphasis lay on the identification of a particular steroid, the spectra there were recorded in general for the ranges 1800 to 1600 and 1500 to 700 cni-l. Six hundred of the spectra refer to solutions, the remaining 56 are for potassium bromide dispersions. In the Neudert - Ropke atlas, infrared spectra are given for all the 900 compounds, which, apart from the three liquids, are all for potassium bromide dispersions.In addition, 64 of the compounds are examined in nujol suspension and three in chloroform solution. The range covered is from 2.5 to 1 5 . 0 , ~ . The size of the graphs is somewhat small (147 x 60 mm), but they are printed clearly. Ultraviolet spectra are given uniformly for methanol solutions, and all the 900 compounds are referred to 41 actual spectra. Full practical details are given for the procedures used to obtain all the absorption spectra. The last third of the book is concerned with a discussion of absorption spectroscopy leading up to the assignment of bands to the particular groups in the compounds studied. Reference to the previous graphs is easy.There is a valuable section on dipole moments and one on punched- card systems which includes, of course, the coding system adopted in the atlas. The selection of compounds in this work is directed, in large measure, by the steroid research work of the Schering A.G. However, the main types of steroid compounds are included, though there are some omissions, e.g., equilenin. Literature sources for the compounds themselves are unfortunately, not given. Although it might have been a formidable task it would have been worth the effort. There is a wealth of information here which is inherently valuable, both to the general chemist and to the steroid specialist. The work is especially valuable for the amount of material that has been collected into one volume, and bearing this in mind the price is reasonable.HANDBOOK OF ULTRAVIOLET METHODS. By ROBERT G. WHITE. Pp. viii + 365. New York: This book is an extended card index catalogue of 1600 analytical methods for pharmaceuticals, fine chemicals, foods, soaps, cosmetics, etc., classified in alphabetical order of principal author, with a chemical-compound subject index. Sometimes the abstract gives adequate information for direct analysis without reference to the original literature. The abstracts were drawn from about 260, mainly English, journals during the period 1940 to 1964. There is every indication that adequate coverage of the pertinent techniques has been achieved. The contents will be particularly useful to the newer, small laboratory and should prove a blessing to the inexperienced analyst confronted with inadequate facilities for literature search.Ideally, frequent new editions will be required to keep the contents up-to-date, but the volume can prove a solid foundation for building a comprehensive card index system. 1 hope this book proves the forerunner of many similar publications in techniques other than ultraviolet spectro- scopy. W. L. SHEPPARD 1965. Price DM 144. This is an important work. The compounds are numbered making cross reference easy. (A transparent scale is provided for reading the corresponding cm-l values.) Nuclear magnetic resonance spectra are provided for 95 compounds. It is impossible in so short a space to do justice to a work of this nature. J. S. WHITEHURST Plenum Press.1965. Price $17.50. LABORATORY METHODS IN INFRARED SPECTROSCOPY. Edited by R. G. J. MILLER. Pp. 164. The analyst using infrared spectroscopy is faced with the separate problems of first obtaining a satisfactory spectrum and then getting his information from it. The second of these has been well documented for some time, but systematic information on the practical side has appeared comparatively recently, and then usually only as part of a complete treatment. For those who wish to buy a separate book on laboratory methods, this is by far the best value for money. The first few chapters cover the general ground of using a spectrometer, handling samples, recording the spectrum and coping with optical materials. The others give detailed information on obtaining spectra a t extreme temperatures, dealing with polymeric materials of various kinds, using aqueous solutions and dispersions, and studying crystals with polarised radiation.The London: Heyden & Son Ltd. Price 45s.; $6.50.296 BOOK REVIEWS [Analyst, Vol. 91 identification of chromatography fractions is probably the most important application of infrared spectroscopy, so the excellent account presented here is most welcome. The tracking down of spurious bands is treated with humour, and the short notes on this topic lead off with a practical enthusiasm that lasts the book through. The editor has done a good job in choosing the material, and any disagreement on emphasis is largely a matter of personal preference. The chapter on spectrometers might well have included a comparison of the performances of commercial instruments.The description of grinding and polishing optical materials seems too long; cells are usually made commercially nowadays. It is a pity that the original plan to cover quantitative analysis was changed although, to be fair, most of the principles and problems are discussed under other headings and this is, alas, a dying art. The separate chapters are written by different specialists who have avoided the pitfall of repetition with some success. Indeed, where two authors do include the same topic, something of further interest often arises. For instance, there is healthy disagreement between chapters about the importance of the attenuated total reflection method for aqueous solutions, and some very important limitations of the bromide disc technique arc mentioned under chromatography but not under sample handling.The alcohol inhibitor had not been removed from the sample of chloroform that was used to record the spectrum given among the solvents, in spite of good advice from the tracker down of spurious bands, who should find further scope for his activities in the spectra of cyclohesane and tetrahydrofuran. This book is well arranged in cross-referenced chapters with sections and sub-sections but would still benefit from an index. The diagrams are excellent and the text is clear except for the presentation of a few equations and a number of trivial misprints. TRANSITIONAL ELEMENTS. By EUWIN M. LAKSEN. Pp. xii + 183. New York and Amsterdam: The avowed intent of this text is to introduce the chemistry of the transitional elements to university chemists. As a result of the development in the analytical chemistry of the transitional elements in recent years, it is more than ever desirable that the practising analyst should have a good working knowledge of the specialist chemistry of these metals.Such a knowledge is neatly suniniarised in this little book. The five chapters are headed: The Properties of the Transitional Elements; The Metals and their Compounds; The Structures of the Metals and their Compounds; Solution Chemistry ; and Co-ordination Chemistry. In addition, there are useful appendices entitled : U7riting Net Equations ; Writing Equilibrium Constants ; Conventions for Standard Electrode Potentials ; h-onienclature of Complex Compounds ; Tables of Data and Reference Texts.The reviewer would, however, query the quaint choice of certain reference texts in the last appendix, The book is lucidly written and contains many of the quite excellent figures and diagrams that one has come t o associate with Benjamin books. ,4s a means of obtaining an abbreviated, but broad, introduction to the transitional elements, this book makes a valuable contribution, and also scrves as an excellent introduction to further A. R. PHILPOTTS W. ,4. Benjamin Inc. 1965. Price (cloth) $4.95; (paper) $2.45. reading in this field. EDWARD ABEL PHOTOSYNTHETIC BACTERIA. By E. N. KONDRAT’EVA. Pp. vi + 243. Jerusalem : Israel Program Distributed in Great Britain and the Commonwealth, South The photosynthetic bacteria form an ill-defined group, and probably represent the simplest of living organisms.Some are responsible for an appreciable fraction of the sulphur deposits in nature-by oxidation of the hydrogcn sulphide previously produced by sulphate-reducing bacteria. They have not, however, so far achieved the economic importance of the latter group. Their interest lies largely in the fact that they afford an opportunity for studying photosynthesis un- complicated by respiration or by liberation of free oxygen. It was the study of this process that first led to the view that the oxygen released by higher plants is derived from water and not from carbon dioxide, as was previously thought. The present volume contains no new work, but gives a well translated and admirably arranged summary of the literature to date. Some 1200 references are given, of which 234 are in the Russian language. Biochemical aspects receive special attention, notably the physiology of the group, the mechanism of photosynthesis, and the analysis and composition of the carotenoids and the photosynthetic pigments- bacteriochlorophyll in the purple, bacterioviridine in the green sulphur bacteria. The publication of this book should do much to stimulate research on this difficult and interesting group of bacteria. for Scientific Translations. Africa, Eire and Europe by the Oldbourne Press, London. 1965. Price 72s. L. D. GALLOWAY

ISSN:0003-2654    

DOI:10.1039/AN9669100294

出版商:RSC    

年代:1966

数据来源: RSC