摘要:

482 Analyst, May, 1978, Vol. 103, p p . 482-491 Pyrolysis = Mass Spectrometry of Textile Fibres J. C. Hughes, B. B. Wheals and M. J. Mrhitehouse Metropolitan Police Forensic Science Laboratory, 109 Lirmbeth Road, London, SE 1 7LP A procedure for pyrolysis - mass spectrometry is described and the spectra (mass pyrograms) of various textile fibres are presented. The method is compared with infrared spectroscopy for the forensic characterisation of synthetic fibres. Samples of less than 5 pg can be analysed. Keywords : Textile fibre characterisation ; j~yrolysis - mass spectrometry ; in frayed spectroscopy The forensic analysis of synthetic fibres usually involves the characterisation and comparison of two or more samples and in this laboratory techniques such as microscopy, infrared spectroscopy and thin-layer chromatography combined with ultraviolet spectroscopy of extracted dyes are the methods in current use.In practice the amount of material available may be as little as a single fibre and in such circumstances the infrared method in particular is unable to provide the same amount of information as might be obtainable from a larger sample. Pyrolysis - mass spectrometry (Py - M:S)lp2 is an analytical technique capable of providing useful data on very small polymeric samples and this paper reports on its use for fibre characterisation and compares the method with infrared spectroscopy. Experimental Fibre Pyrolysis Single fibres 0.5-10mm in length were heated in a helium stream using a Curie-point (Pye) or filament pyrolyser (Chemical Data !Systems Pyroprobe, Model 190).On the Pyroprobe samples were generally pyrolysed isothermally for 20 s at a selected temperature (normally 600 or 800 "C), but some of the fibres were sequentially pyrolysed at increasing temperatures in the range 400-900 "C. For the Curie-point method a 15-s pyrolysis time was used. Fibres were mounted for analysis by crimping into a flattened wire for the Curie-point method or by insertion into a quartz tube mounted in the filament coil of the Pyroprobe. Either pyrolyser was connected to an empty glass column, 45 cm x 6.3 mm 0.d. x 2 mm id., heated at 200 "C in the oven of a Varian 2700 gas chromatograph. The pyrolyser was mounted outside the oven and was flushed with helium at 15mlmin-l in order to sweep the pyrolysate into the empty column.The e:mpty column provided a simple means of broadening the pyrolysate band before it entered the mass spectrometer.3 Mass Spectrometry A VG Micromass 12F mass spectrometer was used under standard electron-impact conditions: electron energy 70 eV, emission current 100 PA, accelerating voltage 4 kV and source temperature 240 "C. The pyrolysate emerging from the empty glass column passed into the mass spectrometer via a length of glass-lined stainless-steel tubing and a glass jet separator. A mass range of 25-250 a.m.u. was scanned at I s per decade with a magnet re-set time of 1 s. After pyrolysis 35 scans were collected, with data acquisition and storage achieved with a VG 2040 data system. The 25 most intense spectra of each series were integrated using standard software and a specially written Fortran IV program to produce a composite mass spectrum (i.e., a mass pyrogram).The ions of m / e 28, 32, 40 and 44 were not included in the integration procedure as they are associated with air in the system and only those ions with intensities greater than 0.1% of that of the base peak were included in the processed data. An FIT program was written in Fortran IV to allow the data-processing equipment to compare two sets of data. The FIT equation was defined asHUGHES, WHEALS AND WHITEHOUSE 483 m = 200 1 FIT = 1000 I- I m = 25 m = 200 I m = 25 -I where a and b are the intensities of the same ion of mass m in the spectra of samples A and B. The individual ion intensities were expressed as a fraction of the total ion current ( i e ., they were normalised) in order to compensate for variations in sample size and efficiency of pyrolysis. The FIT factor ranges between 1 000 (for perfectly matched mass pyrograms) and 0 (for completely dissimilar pyrograms). A comparison of the pyrolysers was made by the replicate analysis of ten samples of the same nylon 6 fibre and FIT factors were deter- mined for the resulting 45 pairs of pyrograms for each series. Infrared Spectroscopy Single fibres 1 cm long (mass 3-5 pg) were sealed into glass capillary tubes 2.5 cm x 1 mm i.d., together with 2-3 p1 of solvent, and were heated in an oven at 80-100 "C to effect solution. The solvent selected was dependent upon the type of fibre, e.g., dimethylformamide (acrylics) , m-cresol (nylons and polyesters), acetone (cellulose acetate) and chloroform (cellulose triacetates).The contents of the tubes were poured on to a silicone-coated Petri dish to form a film, which was washed with ethanol, dried and pressed in a 1-mm lead microdisc between layers of potassium bromide. The microdisc was then analysed by using a suitable infrared spectrophotometer with beam condensing facilities. Results and Discussion Fibres examined under the experimental conditions described gave results that were sufficiently reproducible to be used for characterisation. This finding is in agreement with previous studies using the same instrumentation.2J With the exception of Nornex [Fig. l(g)] and Kevlar [Fig. 1 ( h ) ] , which did not pyrolyse efficiently at 600 "C and were pyrolysed a t 800 "C, all of the samples were pyrolysed at 600 "C.This temperature was found experi- mentally to provide the highest yields of characteristic pyrolysis products with both pyro- lysers. The mass pyrograms shown in Figs. 1-9 are reproduced directly from the computer output. They were all obtained by using the Pyroprobe 190, which was operated at 600 "C unless another temperature is stated. In discussing the data an attempt has been made to assign probable identities to significant ions, but it must be noted that these have not been established experimentally but were deduced from the chemical composition of the fibre and experience gained in the pyrolysis - gas chromatography of such materials. Comparison of Pyrolysers The average FIT factors calculated for the 45 comparisons between the ten samples of nylon 6 were as follows: Curie-point pyrolyser, 975.9 (coefficient of variation 1.6%); and filament pyrolyser (Pyroprobe), 994.9 (coefficient of variation 0.3%).The reproducibility of the Pyroprobe was found to be slightly better than that of the Curie-point pyrolyser and fibre handling was easier. Although both pyrolysers produced characteristic mass pyrograms when operated at optimum temperatures, the form of the pyrogram was influenced by the pyrolyser and for comparative analysis it is essential to use the same equipment. Sensitivity with very small samples (ke., less than 1 mm in length). experienced in the analysis of 2-mm lengths of single fibres (mass 0.5-1 pg). The sensitivity of the method was limited principally by the handling difficulties associated No instrumental difficulties were484 HUGHES, WHEALS AND WHITEHOUSE: PYROLYSIS - Analyst, VOZ.103 Comparison of Polymers Nylons features that permit classification are shown in Table I. Typical mass pyrograms for different types of nylons are shown in Fig. 1 and the major J 1'7 I 'II; Y L I I Fig. 1. Mass pyrograms of nylon fibres pyrolysed a t 600 "C. (a), Nylon 4, Tajmir, Alrac Co.; (b), nylon 6, Firestone Synthetic Fiber Co.; (c), nylon 6.10, Grayni, Slack Brothers; ( d ) , nylon 11, Rilsan, Rhodiaceta (Lyon); (e), nylon 6.6, Columbian Rope Co.; (f), nylon, Qiana, Du Pont UK Ltd.; (g), nylon, Nomex, Du Pont Co. (Burlington Industries), pyrolysed a t 800 "C; and ( h ) , nylon, Kevlar, sample provided by the Shirley Institute, pyrolysed at 800 "C.The mass pyrograms of nylon 4 [Fig. l ( a ) ] and nylon 6 [Fig. l ( b ) ] are consistent with these materials pyrolysing to produce large amounts of their respective monomers, vix., butyrolactam and caprolactam.May, 1978 MASS SPECTROMETRY OF TEXTILE FIBRES 485 TABLE I FEATURES PERMITTING THE CLASSIFICATION OF NYLONS BY PYROLYSIS - MASS SPECTROMETRY Nylon type Structural unit 4 . . -[NH(CH,),CO-] ,, 6 . . -[NH(CHJ,CO-] ,, 6.10 . . -[NH(CH,),NHCO(CH,)*CO-] ,, 11 . . -[NH(CH2),,CO-] ,, 6.6 . . -[NH(CH,),NHCO(CH,),CO-] mle I -l Base peak Other prominent peaks 85 30, 41, 42, 84 30 30 or 41 30 or 41 41, 55, 84, 85, 113 Discriminated by minor peaks Discriminated by minor peaks 30 41, 55, 84 Nomex - [ H ~ N H c o ~ c o ] n Kevlar - * [ ~ C O N H ~ C O N H - ] n Discriminated by pyrolysis at 600 "C 103 Nylon 6.10 [Fig.l ( c ) J and nylon 11 [Fig. l ( d ) ] gave results that varied in having either m/e 30 or 41 as the base peak but with m/e 55 as the third most abundant ion. Despite the variability of the base peak, other spectral features in the region of m/e 60-150 are sufficiently characteristic to allow unambiguous classification. Nylon 6.6 [Fig. l ( e ) ] produced pyrograms similar to that of nylon 6, but the weakness or absence of m/e 113 in the spectra from the former material was a characteristic feature. The prominent ion m/e 84 in the nylon 6.6 pyrogram was consistent with the presence of c y clopen t anone. Qiana gave very characteristic pyrograms but it has not been possible to assign identities to the major ions [Fig.l(f)]. Nomex and Kevlar are chemically very similar and it was not found possible to discrimi- nate between these two fibres by Py - MS [Fig. I(g) and (h)]. A base peak of m/e 103 attributable to C,H,CN+ or C,H,NC+ was the dominant feature of both pyrograms. The close similarity of the pyrolysates of these materials is not immediately obvious from the data illustrated in Fig. 1, which reflects the quantitative variability of pyrolysates from these materials. The reason for this variability is not understood but it is far greater than that displayed by other polyamides and may be related to the thermal stability of these fibres or to pyrolysate interactions before entering the mass spectrometer. During experi- ments with the sample of Nomex fibre in our collection it was noticed that heating of this fibre at 400-600 "C using the Pyroprobe gave rise to a product with a mass spectrum matching that of NN-dimethylacetamide.It was assumed that this compound was introduced during the fibre processing and although it is not necessarily distinctive to Nomex such information could be of value in a forensic context. Cellulose acetate and triacetate Fibres of this type differ in the extent to which the fully acetylated product has been hydrolysed and the pyrograms of both [Fig. 2(a) and ( b ) ] show major peaks at m/e 43, 45 and 60, probably indicative of the acetic acid formed on pyrolysis. Variations in the intensities of major and minor peaks were not sufficiently reproducible to allow the discrimi- nation of acetates from triacetates, although the pyrograms were unlike those of any other fibre class investigated.486 HUGHES, WHEALS AND W:HITEHOUSE : PYROLYSIS - Analyst, VoZ.103 Fig. 2. Mass pyrograms of cellulose acetate and triacetate fibres pyrolysed at 600 "C. (a), Cellulose acetate, Silene, SNIA Viscosa; and ( b ) , cellulose triacetate, Tricel, British Celanese Ltd. Polyesters Four types of polyester were studied. The sample of A-Tell was readily distinguishable from other polyesters in giving a pyrogram [Fig. 3(a)] with a base peak of m/e 94 (C,H,O+). The other three materials gave similar mass pyrograms [Fig. 3(b)-(d)] with a base peak of m/e 105 (C,H,CO+) and major peaks at :m/e 77 (c6H5+), 122 (C,H&OOH+) and 149 (OCC,H,COOH+). The relative intensity of the last ion showed great variability between replicate runs of all three fibres, but was always significantly lower in Kodel. This, together with a higher ratio of m/e 43 to 51, appears to allow Kodel to be discriminated from Terylene or Dacron.The method was unable to distinguish between the latter fibres, which differ chemically only in the end grouping of the po1:ymer chains. $1) * c PI 1 Y c 2 n Y 51 > c J Y L I I"! u 5 1 (a 1 'I'l U f E Fig. 3. Mass pyrograms of polyester fibres pyrolysed at 600 "C. ( a ) , Polyester [poly(ethylene oxybenzoate)], A-Tell, Nippon Rayon Co. ; (b) , polyester (cyclohexanedimethanol - dimethyl terephthalate copolymer), Kodel IV, Cane Mills; (c), polyester [poly(ethylene terephthalate)], Dacron, Colurnbian Rope Co.; and ( d ) , polyester [poly(ethylene terephthalate)], Trevira (g-l), Farbwerke Hoechst AG. Acrylic jibres This class of fibres is defined as having a t least 85% of acrylonitrile in the final polymer and as would be expected the incorporation of a comonomer makes only a minor difference to the resulting mass pyrogram. A lOOyo acrylic fibre, Crylor, produced a characteristic pyrogram [Fig. 4(a)] with a base peak of m/e 66 (NCCH,CH=CH+) and major ions at m/eMay, 1978 MASS SPECTROMETRY OF TEXTILE FIBRES 487 105 and 119 (C,H,N+). Zefran (an acrylonitrile - vinylpyrrolidone copolymer) gave an identical pyrogram. Acrilan (an acrylonitrile - vinyl acetate copolymer) was found to give a slightly different result [Fig. 4(b)] with an enhanced peak at m / e 43 (CH,CO+).The other common acrylic fibre, Courtelle (a terpolymer containing acrylonitrile and methyl acrylate), also gave a modified pyrogram with significantly enhanced peaks a t m/e 41 and 54 [Fig. w 58 > n b- U J W LL li: 91 181 U t E Fig. 4. Mass pyrograms of acrylic fibres pyrolysed a t 600 "C. (a), Polyacrylonitrile, Crylor, Rhodiaceta (Lyon) ; ( b ) , polyacrylonitrile - poly(viny1 acetate) copolymer, Acrilan, Israel Chemical Fibres Ltd. ; and (c), terpolymer containing acrylonitrile and methyl acrylate, Courtelle , Courtaulds UK Ltd. iModi$ed acrylics (modacrylics) Modacrylics, i.e., materials containing between 35 and 85% of acrylonitrile, surprisingly gave rise to pyrograms [Fig. 5(a)-(e)] that showed little resemblance to those of acrylic fibres.In each instance a base peak of m / e 41 and intense peaks a t m / e 39 and 27 were the principal features of the spectra. The reproducibility of replicate runs with modacrylics was poorer than for any other class of fibre. This irreproducibility complicates the task of fibre discrimination. The variation in the relative intensity of the minor peaks may provide a basis for discrimination. Polyolefins grams [Fig. 6(a) and ( b ) ] . e g . , m / e 43 (C,H,+), 55 (C,H,+), 57 (C,H,+), 69 (C,H,+) and 83 (C,H,,+). grams can be distinguished from those of the other fibre classes analysed. Both polyethylene and polypropylene fibres break down to give distinctive mass pyro- The major ions are attributable to aliphatic hydrocarbons, The mass pyro- Poly (vinylidene chloride) and poly (vinyl chloride) The mass pyrogram of Saran [poly(vinylidene chloride)] [Fig. 7(a)] is very similar to that obtained in other s t ~ d i e s .~ The major ions are m/e 36, 38 (both associated with HCl+), with smaller contributions from m / e 61, 63 (CH,=C+-Cl), 96, 98 (CH,=C+-Cl,), 146 and 148 In contrast, poly(viny1 chloride) fibres gave a pyrogram notable for the absence of ions due to HCl+ [Fig. 7 ( b ) ] . This difference can possibly be explained by the adsorption of acid on active sites before entry into the mass spectrometer and could be reconciled with the detection of HC1+ in the instance of Saran due to a much higher yield of acid. Whatever the explanation, the mass pyrogram of poly(viny1 chloride) contains many features attributable (C,H,CL+) -488 HUGHES, WHEALS AND WH:ITEHOUSE: PYROLYSIS - Analyst, Vol.103 illl I t l / E 1 1 111 w 51 n > I- -I w Y I 1 6 1 n l E n l E i"l I Fig. 5. Mass pyrograms of modacrylic fibres pyrolysed at 600 "C. (a), Teklan, Courtaulds UK Ltd.; ( b ) , Verel, Type HB, Eastman Chemical International; (c), Verel, Type F, Eastman Chemical International; ( d ) , Dynel, Type 180, Union Carbide Corporation; and (e), Kanekalon (high bulk), Kanegafushi Chemical Industrial Co. to aromatic hydrocarbons, presumably formed by free-radical recombination after pyrolysis. Thus the major ions are m/e 78 (C,H,+), 91 (C,H,+), 104 (C8H8+), 115 (C,H,+) and 128 Two modified PVC fibres, Vinyon (a copolymer with vinyl acetate) and Bristrand (a copolymer with styrene), gave significantly different pyrograms to that of PVC [Fig.7(c) and (41. With Vinyon, ions at m/e 43, 45 and 60 are indicative of the presence of acetic acid in the pyrolysate. The Bristrand fibre produced a pyrogram displaying features that (c10H8+)m )o E HlE Fig. 6. Mass pyrograms of polyolefins. (a), Polyethylene, Suddeutsche CFAG, pyrolysed at 800 "C; and ( b ) , polypropylene, Magyar Viscosa, pyrolysed a t 600 "C.May, 1978 MASS SPECTROMETRY OF TEXTILE FIBRES 489 1 r n v( Y * W I sa n f I / I VI W + U W 58 > U c -I W 8 MlE 188, ‘ I H I E M l E Fig. 7. Mass pyrograms of poly(viny1idene chloride) and poly(viny1 chloride) fil res pyrolysed a t 600 “C. (a), Poly(viny1idene chloride), Saran, Thiokol l‘ibres Canada Ltd. ; ( b ) , poly(viny1 cl Joride), Rhovyl, Rhovyl SA, France ; (c), poly(viny1 chloride) - poly(viny ’ acetate) copolymer, Vinyon, F.M.( ,.Corporation (American Viscose Division) ; and ( d ) , poly(viny1 chloride) - polystyrene copolymer, Bristrand Polymers Incorporated. closely resembled those of polystyrene (Fik-. €9, but it could be differer tiated from the latter by the intensity of the m/e 91 peak. Polystyrene The mass pyrogram of a polystyrene fibr :, Kilmarn (Fig. 8), is distinctive and closely resembles the published mass spectra of styr :ne. The principal ior s are m/e 104 (C,H,+), 103 (C,H,+) and 78 (C6H6+). The intensity of the m/e 91 ion is high6 r in the mass pyrogram than in the normal electron-impact mass spetstrum of styrene ant this difference can be attributed to the formation of toluene during pjyrolysis.Fig. 8. Mass pyrogram of polyst Irene fibre pyrolysed a t 600 “C, Kilmarn, Polymer: Incorpc ‘r- ated. Natural $fibres A selection of natural fibres together with viscose rayoi gave characteristic mass pyro- grams [Fig. 9(a)-(e)], but the complexity of these materials rt-akes it difficult to interpret the data although their value as “fingerprints” is obvious. I! iterestingly, the pyrogram of viscose [Fig. 9(e)] is different to that of natural cellulose [Fig. O(d)] with respect to variation in the ratio of m/e 29 to 43.490 HUGHES, WHEALS AND WHITEHOUSE : PYROLYSIS - Analyst, VoZ. 103 "'1 I c 2 w 5 1 a w W L i i r i z i iii z Y 5 1 a H c w L I ii s i P I Fig. 9. Mass pyrograms of natural fibres and viscose rayon pyrolysed a t 600 "C.(a), Japanese raw silk (Bombyx mori); ( b ) , natural sheep wool; (c), Caucasian head hair, dark brown; (d), cotton (Gossy+m sp.), Brazil; and (e), viscose (bright), Courtaulds (Canada) Ltd. Comparison of Pyrolysis - Mass Spectrometry with Infrared Spectroscopy All of the samples analysed in this study had been previously examined by infrared spectroscopy. When a sufficient amount of material is available the latter technique is superior to Py - MS for discriminating fibres, particularly with those samples in which copolymerisation significantly modifies the infrared spectrum of the parent polymer, e.g., the modacrylics. Nevertheless, in a blind trial conducted with 12 fibres (each 1 cm in length, mainly nylons) Py - MS was used to identify every fibre correctly, whereas infrared spectroscopy led to only two correct assignments.Certainly for the nylons, and probably also for most other fibres, Py - MS has the following advantages over infrared spectroscopy: (1) much smaller samples can be examined; (2) fibres containing appreciable amounts of filler can be assigned with greater confidence than with infrared spectroscopy; (3) the analysis time is shorter, typically 20-30 min, depending on the computer handling facilities and peripherals available. However, it should be pointed out that batch handling of fibres for infrared analysis does significantly reduce this time advantage. Limitations of Pyrolysis - Mass Spectrometry The major factor limiting our approach to Py - MS at present is the poor reproducibility for certain types of polymer.It is not clear how this irreproducibility arises but if it could be overcome then it is likely that far greater discrimination could be achieved by attentionMay, 1978 MASS SPECTROMETRY OF TEXTILE FIBRES 491 to the fine structure of mass pyrograms. Obviously we are constrained by the need to work with equipment normally utilised for gas chromatography - mass spe~trometry,~ rather than a custom-built instrument1 and reaction in the empty glass column used to spread out the pyrolysate band may be contributing to the variability of some of the results. A further disadvantage of the Py - MS procedure described, in comparison with infrared spectroscopy, becomes apparent when the pyrogram is used for interpretation rather than as a fingerprint.The ions contributing to the mass pyrogram result from two vigorous decomposition processes, ie., a thermal and an electron-impact fragmentation, and not surprisingly, it is often difficult to relate the final ions to the starting polymer. The use of chemical ionisation to reduce fragmentation within the mass spectrometer could yield results more amenable to qualitative interpretation,6 and pyrolysis - gas chromatography followed by mass spectrometry is an obvious method of providing information on the significance of particular ions in a mass pyrogram. Conclusions This study indicates that Py - MS provides a rapid and sensitive method for the charac- terisation of synthetic fibres, which could have a wider range of application than infrared spectroscopy for forensic fibre examination. The equipment required for the technique is expensive but those laboratories currently using a mass spectrometer and data system could adapt their instruments at low cost. Provided that the reproducibility of Py - MS can be improved it should become a powerful method for the microanalysis of a wide range of natural and synthetic polymers. The infrared spectroscopic method described in this paper has been in use for some years in this laboratory. The development of this procedure was the work of R. Cook and co-workers at the Metropolitan Police Forensic Science Laboratory. References 1. 2. 3. 4. 5. 6 . Meuzelaar, H. L. C., and Kistemaker, P. G., Alzalyt. Chem., 1973, 45, 587. Hughes, J. C., Wheals, B. B., and Whitehouse, M. J., Forensic Sci., 1977, 10, 217. Hughes, J. C., Wheals, B. B., and Whitehouse, M. J., Analyst, 1977, 102, 143. Senoo, H., Tsuge, S., and Takeuchi, T., J , Chrornat. Sci., 1971, 9, 315. Zeman, A., in Wiedmann, H. J.. Editor, “Thermal Analysis,” Volume 3, Proceedings of the 3rd Saferstein, R., and Manura, J. J., J . Forensic Sci., 1977, 22, 748. International Conference on Thermal Analysis, Rirkauser Verlag, Basle, 1972, pp. 219-227. Received September 22nd, 1977 Accepted November 24th, 1977

ISSN:0003-2654    

DOI:10.1039/AN9780300482

出版商:RSC    

年代:1978

数据来源: RSC

摘要:

492 Analyst, May, 1978, Vol. 103, p p . 492-496 Determination of Probenecid in Serum by H ig h-performance Liquid Chromatography R. K. Harle and T. Cowen International Development Laboratories, E. R. Squibb wad Sons Limited, Moreton, Merseyside, L46 1Q W The determination of probenecid in serum samples by using high-performance liquid chromatography is described. The method gives satisfactory results over the normal therapeutic range, namely up to 150 pg ml-1 of probenecid in serum, and is not affected by metabolites of the drug. The method does not require derivatisation of the drug, as in gas - liquid chromatographic procedures, and is less subject to interferences than spectrophotometric procedures. It has been used in analysis of several hundred serum samples and has given a satisfactory performance in respect of precision and accuracy.Keywords : Probenecid determination ; serum ; high-performance liquid chromatography Probenecid [4-(dipropylamino)sulphonylbenzoic acid] is a uricosuric agent that has recently been used in conjunction with penicillin derivatives in the treatment of various diseases. Probenecid reduces the excretion of penicillins by the kidneys and thus enables therapeutic levels of the penicillins to be achieved with a lower initial dose. The normal dose of pro- benecid used to obtain this effect is 1 g daily. Several methods have been described for the determination of probenecid in body fluids,l-b mainly employing spectrophotometric or gas - liquid chromatographic methods for the final quantification step.The disadvantages of these methods are that the spectrophotometric methods are not specific and the gas - liquid chiromatographic methods require derivatisation of the sample before the injection on to the column. High-performance liquid chromatography was investigated as an alternative method. The extraction of probenecid from serum , followed by injection of the non-derivatised extract into the chromatographic column, should give advantages of specificity and time compared with the other methods. Experimental Reagents All reagents were of analytical-reagent grade unless otherwise stated. Potassium chloride. Citric acid. Disodium hyd~ogen orthophosphate. Sodium hydroxide. Potassium dihydrogen orthophosfihnte. Diethyl etlzcr. Acetonitrile. Reagent grade. Bufler, pH 4.0.Dissolve 35.5 g of disodium ;hydrogen orthophosphate in 250 ml of water, adjust the pH to 4.0 with approximately 40 g of citric acid, then dilute to 500 ml with water. Bufer, PH 6.0. Dissolve 27.2 g of potassium dihydrogen orthophosphate in 500 ml of water, adjust the pH to 6.0 with sodium hydroxide solution and dilute to 1 1 with water. Mobile phase. Dilute 50 ml of pH 6.0 buffer to 700 ml with water, add 300 ml of aceto- nitrile, mix and de-gas by applying a vacuum immediately before use. Apparatus The high-performance liquid chromatograph. was assembled using the following corn- poneii ts : a constant-volume , syringe type, high-pressure pump (Metering Pumps Ltd., London ; 3 000 lb in-2), a high-pressure septurn injector head (Perkin-Elmer, Part No.0087-3015) and a suitable Bourdon-type pressure gauge. The column used, 25 cm x 4 mm i.d., was made of stainless steel, and was fitted with a stainless-steel sinter at the outlet and a 2 mm thick PTFE sinter at the inlet. InjectionsHARLE AND COWEN 493 were made into this sinter. The packing material was Partisil, particle diameter 10pm, modified by treatment with octadecyltrichlorosilane to give a reversed-phase type of chromatography. The detector used was a variable-wavelength monitor (Model 212, Cecil Instruments Ltd., Cambridge) equipped with an 8-p1 flow-through cell. The detector was operated at 252.5 nm and the signal was recorded on a flat-bed recorder (W & W, Model 1100). Injections were made using a 10-pl high-pressure syringe (SGE, Type 10BLR).The operating conditions for this system were as follows: flow-rate, 1 ml min-l (about 50 bar) ; detector range, 0.05 A full-scale deflection (f.s.d.) ; and recorder range, 10 mV f.s.d. The apparatus used in the extraction procedure was normal laboratory glassware, together with a centrifuge and a vortex mixer Procedure Preparation of standard Weigh accurately about 30 mg of probenecid, dissolve it in methanol and make the volume up to 100.0ml. This is the stock solution. Dilute a 5.0-ml aliquot of stock solution to 50.0 ml with methanol to give a 30 pg ml-l working standard solution. Pipette an appropriate volume (usually 2.0 ml) of working standard solution into a 12-ml stoppered centrifuge tube and remove the methanol by blowing with air. Add 1.0ml of distilled water to the residue and swirl in a vortex mixer to dissolve the residue.Process this standard solution as for the serum samples. The concentration of this solution will be 60 pg ml-l when 2.0 ml of working standard solution are used in its preparation. Pre$aration qf samples Pipette a 1.0-ml aliquot of serum sample into a 12-ml stoppered centrifuge tube and to it add 1.0 ml of pH 4.0 buffer and approximately 1 g of potassium chloride. Stopper the tube and vortex mix for about 15 s, then add 8.0 ml of diethyl ether from a dispensing pipette. Stopper the tube, vortex mix thoroughly for 1 min and centrifuge a t 4000 rev min-1 for 5 min. Transfer a 5.0-ml portion of the ether layer into a second tube, add an anti-bumping granule and remove the ether by evaporation on a water-bath at 40-50 “C.Final traces of ether should be removed by gentle purging of the tube with a stream of air or nitrogen. Add 1.0ml of chromatographic mobile phase to the residue and mix briefly on a vortex mixer. Chromatogra$hic fvocedztre Inject 8-pl portions of the standard solution extract until reproducible peak heights are obtained, then inject 8-p1 portions of sample extract. Inject a further portion of the standard extract after every six sample injections. Rinse the syringe at least five times with each solution prior to injection of that sample. This ensures a negligible carry-over of solutions between injections. Establish a stable solvent flow and base-line conditions. Calculation Measure the probenecid peak heights of the standard extract and of the satiple extract.Take a mean value of the peak heights for the two standard injections on eitl er side of a sample. Then, sample peak height x standard concentration standard peak height Probenecid (pg ml-l) = A typical chromatogram is shown in Fig. 1. Investigation of Experimental Variables Extraction fyom serum When extracting probenecid from serum it was found that coagulated blood proteins formed a semi-solid “plug” a t the aqueous surface. The solvent used in the extraction should494 HARLE AND COWEN : DETERMINATION OF PROBENECID IN Analyst, VoZ. 103 Fig. 1. Chromatograms of serum containing probenecid. (l), Serum blank; (2), a 4-h serum sample containing 75 pg ml-1 of probenecid; and (3), a 12-h :serum sample containing 28 p g ml-l of probenecid.The probenecid peaks are marked P. therefore, for convenience of recovery, have a density lower than that of the aqueous phase, be readily removable by evaporation and be immiscible with water. Solvents evaluated included ethyl acetate, butyl acetate and a 2: 1 mixture of l-chlorobutane with chloroform. It was found that some of these solvents did not extract probenecid completely and others were difficult to evaporate or were too miscible with the aqueous phase. Diethyl ether was finally chosen, but it was found that the reduction in volume of the solvent due to loss into the aqueous phase (diethyl ether has a so1ubi:lity in water of 6.9% at 20 "C) resulted in a bias leading to high recoveries of 103-107% when assayed against external standards. The adoption of a standard that was passed through the extraction procedure obviated the errors arising from this effect.Linearity of response Linearity of the response was established by injection of standard solutions containing from 10 to 100 pg ml-l of probenecid. The mean peak heights of three injections of each of these solutions were plotted against the concentration of the solution injected. The linear response graph was found to pass through the origin, with a slope of 2.5 mm per pg ml-1. The level of 100 pg ml-l here corresponded to 160 pg ml-l in serum because only a 5-ml volume of the 8 ml of diethyl ether extract was removed. The sensitivity of the procedure, taken as being that of a peak of height equal: to twice the base-line noise, was generally 1 pg ml-1, depending on the instrumental conditions.In order to ensure a constant absorptivity for probenecid at the detector, it was necessary to buffer the mobile phase to pH 6, thus ensuring that the same ionic form of probenecid was measured in each determina- tion. Possible interferences Pro benecid metabolites. The chromatographic behaviour of probenecid metabolites was investigated, and the results are shown in Table I. The probenecid peak was well separated from all of the metabolite peaks and hence no interference could occur. The co-administrattion of probenecid and penicillins is now relatively common so that the method should ideally be unaffected by large doses (about Co-administered epicillin.May, 1978 SERUM BY HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY 495 TABLE I RETENTION DATA FOR PROBENECID METABOLITES Column and mobile phase as in text.Flow-rate, 1 ml min-1. Metabolite* Retention timelmin 1.67 /pr R-N ‘CH,CH,COOH R-NH, 2.00 2.20 /pr R-N ‘CH2CH,CH,0H 2.25 R-NH-‘ ?r 2.30 R-NPr, (probenecid) 3.50 * R = -SO,-Ph-COOH; Ph = C,H,; Pr = n-C,H,. 4 g) of penicillins. This was :ested in vivo by obtaining serum samples from a subject who had taken 4 g of epicillin (cc-: .mino-3,6-dihydrobenzylyenicillin). Samples were taken a t 0, 0.5, 1, 2, 3, 4, 5, 6, 9, 12, 24 and 30 h after the epicillin had been administered, extracted by using the above method and the chromatograms were examined for possible interferences. No peaks other than those d1.e to the solvent were found in samples taken up to 2 h after administration.In the 3-30-2 samples a small peak was eluted at 3.2 min (probenecid was eluted at 3.4 min). The maximum height of this peak was 2.5 mm, which occurred a t the 4-h sample, this height being aoproximately the same as that of a peak representing 1 pg ml-l of probenecid. This small pe;k was of short duration and in all instances was completely eluted by the start of the prcbenecid peak. No positive interference could thus occur. This smal peak does not correspnd to epicillin, which is not extracted from serum by this method, kut may be due to a met.1.bolite of epicillin. Some other drugs that might be found with probenecid in serum were examined by using the chromatogr; phic system described. The retention times for these drugs are given in Table 11. Other d~ugs. TABLE I1 RETENTION TIMES FOR SOME SELECTED DRUGS Column and mobile phase as in text.Flow-rate, 1.2 ml min-1. Compound Aspirin .. .. Ampicillin . . .. Epicillin . . .. Potassium penicillin G Probenecid . . .. Phenazone . . .. Niflumic acid .. Flufenamic acid . . .. .. .. . . .. .. .. .. .. .. .. .. .. .. .. .. Retention timelmin 1.6 1.95 2.00 2.05 2.9 4.0 5.8-8 (tailing) 10.5-1 5 (tailing) Results and Discussion This assly method was originally developed in order to give comparative data in clinical496 HARLE AND COWEN trial studies in which probenecid was administered in different dosage forms, alone and in conjunction with epicillin. Recovery experiments were therefore carried out at probenecid concentrations that approximated to the levels expected over the initial, clinically signifi- cant, part of the trial, i e ., from 0 to 12 h. 'The recovery and precision results are given in Table 111. TAB:LE I11 RECOVERY AND PRECISION RESULTS FOR PROBENECID I N WATER AND I N SERUM Probenecid Mean Coefficient added/ recovery, of variation, Number of Matrix pg ml-l % % determinations Water . . .. 30 97.8, 98.7 * 2 60 96.8, 98.2 * 2 90 99.3, 101.1 2 * Serum . . .. 5 96.2 3.6 12 30 95.3 1 .o 8 60 97.7 1.1 6 100 100..4 0.9 10 * Both values determined are given. The coefficients of variation of probenecid peak heights from standard injections over 3-6-h periods were 1.8% (6 values), 2.4% (6 values), 2.0% (5 values) and 2.4% (11 values) on four separate days. These results indica.te that the chromatographic conditions are relatively stable, as these values represent the cumulative error due to contributions from syringe inaccuracies and to variation in inject ion technique, eluent flow-rate, detector lamp stability and peak measurement. Between 35 and 50 samples can be assayed in an 8-h period. Over 400 samples, from several subjects in a clinical trial, have been assayed for probenecid. Samples of probenecid metabolites were kindly donated by Dr. W. D. Conway of the State University of New York at Buffalo, N.Y., USA. References 1. 2. 3. 4. 5. Tillson, E. K., Pusey, N. W., and Beyer, K. H., J . Pharmac. Exp. They., 1954, 112, 252. Sabih, K., Klaassen, C. D., and Sabih, K., J. Pharm. Sci., 1971, 60, 745. Dayton, P. G., and Perel, J. M., Ann. N.Y. A w d . Sci., 1971, 179, 399. Zacchei, A. G., and Weidner, L., J . Pharm. Sci., 1973, 62, 1972. Conway, W. D., and Melethil, S., J . Chronzat., 1975, 115, 222. Received A p i l 12th, 1976 Amended January 31st, 1977 Accepted December 6th, 1977

ISSN:0003-2654    

DOI:10.1039/AN9780300492

出版商:RSC    

年代:1978

数据来源: RSC

摘要:

Analyst, May, 1978, Vol. 103, $9. 497-508 497 Polarographic Method for the Identification of 1,4- Benzodiazepines W. Franklin Smyth, M. R. Smyth," J. A. Grovest and S. B. Tan Department of Chemistvy, Chelsea College, University of London, Manresa Road, London, S W3 6LX The polarographic behaviour of 12 therapeutically important 1,4-benzo- diazepines in Britton - Robinson universal buffers, pH 4.0 and pH 12.0, has been investigated. Differences in the polarographic peak potentials of these compounds in these media are explained. The rates of hydrolysis of certain benzodiazepines in acidic solution were investigated. Bromazepam and flunitrazepam, both of which possess a strongly electron-withdrawing substituent on the 5-o-phenyl group, were found to undergo rapid acid hydrolysis. On the basis of these findings, and taking into account the extraction profile of some of the compounds over a pH range, a scheme is devised for the identification of any one or more of 12 1,4-benzodiazepines.It is suggested that this procedure would be applicable to the analysis of unknown formulations or body fluids in forensic cases where the parent compound exists in relatively high concentrations compared with its meta- bolites. Keywords : 1,4-Benzodiazepine identification ; polarography The lJ4-benzodiazepines are one of the most frequently prescribed group of drugs in the UK and, with the ever increasing number of compounds in this series that are used for thera- peutic purposes, there is a need for the development of rapid methods of identification, particularly for use in forensic situations, e g ., identification of a particular 1,4-benzo- diazepine in unknown formulations or body fluids. The most commonly employed method of identification is thin-layer chromatography of the intact compounds or of their acid hydrolysis products, i.e., benz0phenones.l In the examination of body fluids, a separation step such as adsorption-column chromatography2 or solvent extraction3p4 is usually employed prior to thin-layer chromatography. Identification is usually effected by comparison of R, values, the colours produced by chromogenic spraying and spot patterns produced by the drug and its metabolite^.^^^^^ Gas - liquid chromatography using the nickel-63 electron- capture detector appears to be the method of choice for the determination of the 1,4- benzodia~epines.~-~ Smyth and co-workers10-l6 have investigated the acid - base properties and polarographic behaviour of many of the members of this group of drugs.Groves17 has made a detailed study of the mechanism of hydrolysis of 5-fluorophenyl-l,4-benzodiazepinesl7 and com- pared the rates of hydrolysis of other non-fluorinated 1,4-benzodia~epines.~s This paper shows how a knowledge of these physico-chemical properties can be used to devise a scheme for the identification of 12 lJ4-benzodiazepines : medazepam (I) , chlordiazepoxide (11) , potassium chlorazepate (111), bromazepam (IV), diazepam (V, X = C1, Y = CH,, 2 = H, W = H), oxazepam (V, X = Cl, Y = H, 2 = OH, W = H), prazepam (V, X = C1, Y = cyclopropyl, 2 = H, W = H), lorazepam (V, X = C1, Y = H, 2 = OH, W = Cl), nitrazepam (V, X = NO,, Y = H, 2 = H, W = H), clonazepam (V, X = NO,, Y = H, 2 = H, W = Cl), flunitrazepam (V, X = NO,, Y = CH,, 2 = H, W = F) and flurazepam (V, X = C1, Y = (CH,), NEt,, 2 = H, W = F).This scheme involves the combination of simple solvent-extraction procedures and polarographic examination of these extracts, in some instances following acid hydrolysis. It is not intended to be an absolute method of identifi- cation but it is suggested that it can be used as a rapid method for obtaining information complementary to that obtained by other identification techniques. The study has been confined to parent compounds so that it would be directly applicable to the identification of unknown fonnulations and in overdose cases where a relatively high concentration of the free parent drug still remained in the particular body fluid.* Present address : Chemistry Department, State University of Colorado, Fort Collins, Colo. 80523, USA. t Present address : Beecham Products, Block F2-F, Brentford, Middlesex.498 SMYTH et al. : POLAROGRAPHIC METHOD FOR Analyst, Vol. 103 1 I l l Br C=N I V v Experiment a1 Apparatus Instrumentation A PAR Model 174A Polarographic Analyser produced by Princeton Applied Research Corporation, N. J., USA, was used in conjunction with a Servoscribe 15 recorder throughout this study. A three-electrode operation was employed using a platinum counter electrode. The dropping-mercury electrode (D.M.E.) used had an outflow velocity of 2.571 mg s-1 and a drop time of 3.46 s at the potential of the calomel electrode and at a mercury pressure of 55 cm in 1 M potassium chloride solution.Polarographic cells For investigations on the polarographic behaviour in different buffer solutions, the cell shown in Fig. 1 was used. This was based on a 25-ml Quickfit flask and was suitable for volumes of solution from 2 to 20 ml, the optimum volume being about 5 ml. The platinum- wire counter electrode was sealed into the glass of the vessel, as were the inlet tubes for passing gas into and over the sample solution. A Radiometer-type saturated calomel electrode (S.C.E.) was used as the reference electrode. As it was intended to carry out and monitor the hydrolysis in the polarographic cell, a Socket( B 10) S.C.E. (25 ml) Solution Platinum counter electrode Fig. 1, Polarographic cell.May, 1978 THE IDENTIFICATION OF 1,4-BENZODIAZEPINES 499 vessel was required that could be maintained at constant temperature.The cell shown in Fig. 2 was designed and constructed specifically for this purpose. It is based on a 25-mI three-necked, pear-shaped flask that is enclosed in an outer glass jacket. Water at the required temperature could be pumped between the inner and outer vessels. A tap provided at the bottom of the cell allowed for emptying and cleaning purposes. Narrow-bore glass tubes were sealed into the apparatus to pass nitrogen through or over the solution. The cell functioned satisfactorily with solution volumes from 2 to 15 ml, but in practice 5-10 rnl was ideal. The reference electrode was again a Radiometer-type saturated calomel electrode.A platinum wire sealed into a glass tube served as the counter electrode. Water was circulated through the jacketed cell from a thermostatically controlled water-bath. A 10-ml volume of aqueous solution in the cell could be brought from room temperature to any temperature in the range 2545 "C in 10 min and maintained at that temperature within k0.05 "C. Throughout this study, the hydrolyses were performed at 25 "C. The passage of nitrogen saturated with water vapour either through or over the solution did not alter the temperature. Platinum counter. electrode Nitrogen Water jacket Water in __I.F_ out Fig. 2. Polarographic cell with water jacket used for hydrolysis studies. Reagents Sug5porting electrolyte A modified Britton - Robinson universal buffer was used to provide buffer solutions of pH 4.0 and 12.0.The stock solution of this buffer (pH 1.8) contained 0.04~ acetic acid, orthophosphoric acid and boric acid. The stock solution was adjusted to the required pH by adding 0.2 M sodium hydroxide solution until the desired pH had been reached, as monitored by using a pH meter. All reagents and solvents used were of analytical-reagent grade. Stock solutions of the benxodiazepines Stock solutions of concentration 1 X 1 0 - 3 ~ were freshly prepared in AnalaR methanol. The addition of 0.1 ml of solution to 9.9 ml of the buffer solution would produce a working concentration of 1 x M. Experimental Techniques Polarographic behaviour in p H 4.0 and 12.0 Britton - Robinson bufers For each run, 0.1 ml of the stock solution of the benzodiazepine was pipetted into a 10-ml calibrated flask and then diluted to the mark with the appropriate buffer solution.After thorough mixing, the solution was placed in the polarographic cell shown in Fig. 1, with the S.C.E. and the D.M.E. positioned in the cell, and nitrogen was passed through the solution for 10 min in order to remove oxygen from the solution. After de-gassing, nitrogen was500 SMYTH et al. : POLAROGRAPHIC METHOD FOR Analyst, Vol. 103 passed over the solution and the polarogram was recorded using the following polarographic conditions : mode, differential-pulse polarography (DPP) ; initial potential, 0.0 V veYsZts S.C.E. ; scan rate, 5 mV s-l; chart speed, 3 c;m min-l; modulation amplitude, 100 mV; low pass filter, 0.3 s; potential scan range, 3.0 V; scan direction, negative; current range, 2 or 5 PA; drop time, 1 s.Hydrolysis The addition of 0.1 ml of the stock solution to 9.9 ml of acid in the thermostatically controlled cell would produce a working concentration of 1 x l O A 5 ~ . The concentration of methanol in the solution was therefore only 1%. The hydrolysis of each compound included in this study was carried out in 0.1 M hydrochloric acid, which was prepared from a Volucon ampoule. The latter solution exhibited an acceptable polarographic background at the current ranges employed. A 9.9-ml volume of 0.1 M hydrochloric acid was pipetted into the thermostatically controlled cell and the oxygen removed by passing nitrogen through the solution for 10 min.During this time, the contents of the cell attained the required temperature. After de-gassing, nitrogen was passed over the solution and the S.C.E., platinum counter electrode and D.M.E. positioned in the cell. The polarogram of the acid alone was recorded using the polaro- graphic conditions described above for the buffer solution. Subsequently, 0.1 ml of the methanolic stock solution of the benzodiazepine was introduced into the cell by means of an automatic zero pipette. This addition was achieved by partially removing the platinum counter electrode and inserting the pipette through the neck into the cell. Timing was begun when approximately half of the 0.1-ml aliquot had been added. The solutions were thoroughly mixed by passing a stream of nitrogen through the cell for about 1 min.The polarogram of the solution was recorded after a convenient time. Preliminary experiments indicated that the method of recording the entire polarogram would be suitable for the present investigation. The use of a concentration of electroactive species of 1 x 1 0 - 5 ~ precluded the use of d.c. polarography as the polarograms at this concentration exhibit a certain degree of slope that makes measurement of the limiting current difficult. Also, the half-wave reduction potentials of some of the reactants and products are close (with a difference of less than 100mV) and so would not be resolved as individual waves when using d.c. polarography. The cathode-ray polarograph could have been employed but again, accurate measurement of the limiting current of two waves close to each other would be difficult.As a result of these considerations, differential-pulse polarography (DPP) was chosen as the means by which to record the polarograms. This technique has the required sensitivity and would allow a compromise between speed of recording and resolution of the polarographic waves. The shape of the peaks, without serrations, also allows for a more convenient way of measuring concentration, Results and Discussion Polarographic Behaviour The peak reduction potentials, E,, for each of the compounds were measured from consideration of the potential scan rate and the chart speed. Table I shows the E, values (volts veysus S.C.E.) obtained in the buffer solutions of pH 4.0 and 12.0.In pH 4.0 buffer, chlordiazepoxide shows three peaks, at -0.37, -0.73 and -1.17 V, corresponding to the reduction of the =N+Oi, C=N and N=C moieties, respectively.15 In pH 2.0 buffer it gives one peak at -1.24V. In pH 4.0 buffer, bromazepam shows two peaks, at -0.40 and -1.12 V (see Fig. 3). 'The electronegative influence of the 5-pyridyl moiety shifts the reduction of the azomethine C=N group from -0.7-O.80VJ as observed in other benzodiazepines, to -0.40 V. The wave at -1.12 V for bromazepam corresponds to a reduction process involving the 5-pyridyl group.ll In pH 12.0 buffer a well defined peak was observed at -0.99 V. At low concentrations, the waves at -1.17 and -1.12 V for chlordiazepoxide and bromazepam, respectively, (in pH 4.0 buffer) can be masked by the reduction of the supporting electrolyte or other impurities co-extracted from a body fluid. When in a mixture bromazepam and dhlordiazepoxide are best differentiated polaro-May, 1978 THE IDENTIFICATION OF 1,4-BENZODIAZEPINES 501 TABLE I E, VALUES OF SOME BENZODIAZEPINES IN pH 4.0 AND pH 12.0 BRITTON - ROBINSON BUFFERS E,/V ueYsus S.C.E.r I A 1 ,QBenzodiazepine pH 4.0 buffer pH 12.0 buffer Chlordiazepoxide . . .. -0.37, -0.73, -1.17 - 1.24 Nitrazepam .. . . -0.16, -0.78 -0.61, -1.23 Clonazepam . . . . -0.15, -0.73 -0.60, -1.22 Flunitrazepam . . . . -0.16, -0.73 -0.61, -1.20 Oxazepam . . . . . . -0.76 - 1.50 Lorazepam . . .. -0.74 - 1.45 Diazepam . . .. . . -0.74 -1.15 Bromazepam . . . . -0.40, -1.12 -0.99 Prazepam . . * . .. -0.73 -1.22 Flurazepam .... - 0.72 -1.10 Potassium chlorazepate . . -0.73 -1.15 Medazepam .. .. -0.82 - 1.23 graphically by the peaks observed in pH 12.0 buffer (Pig. 4). The peak a t -0.73 V at pH 4.0 for chlordiazepoxide is not used as it is also observed in other benzodiazepines, e.g., see Fig. 5, which shows the differential-pulse polarograms of a mixture of bromazepam, chlordiazepoxide and flunitrazepam in pH 4.0 and 12.0 buffers. Flunitrazepam is included in Figs. 3-5 as an example of a 1,4-benzodiazepine giving a typical C=N reduction in pH 4.0 and 12.0 buffers. Nitrazepam, clonazepam and flunitrazepam can be differentiated from all other 1,4- benzodiazepines included in this study by the peak observed at -0.16 V in pH 4.0 buffer, corresponding to the reduction of their NO, group.At pH 12.0 this reduction is observed at -0.60 to -0.61 V and this peak could also be used for identification. Figs. 6 and 7 show the differential-pulse polarograms of some other 1,4-benzodiazepines which have only one reducible group, i.e. , the 4,5-azomethine group. Oxazepam, lorazepam, diazepam, prazepam and medazepam give well defined peaks in pH 4.0 buffer, but the peak potentials do not differ significantly except for medazepam, which is reduced at a potential of the order of 75 The peak heights for the first two are approximately twice the size of the other peaks as they are reduced 15 mV more negative than the remainder. -0.2 -0.4 -0.6 -0.8 -1.0 -1.2 - 1 . 4 Potential/V Fig. 3. Diff erential-pulse polarograms of : A, flunitrazepam ; B. chlordiazepoxide ; and C , brom- azepam, as 1 x M solutions in pH 4.0 buffer solution.3.0 2.0 Q f? 3 1.0 -0.4 -0.6 -0.8 - 1.0 - 1.2 - 1.4 - 1.6 - 1.8 Potential/V Fig. 4. Differential-pulse polarograms of: A, flunitrazepam ; B, bromazepam ; and C, chlordiaz- epoxide, as 1 X M solutions in pH 12.0 buffer solution.502 SMYTH et al. : POLARCIGRAPHIC METHOD FOR Analyst, Vol. 103 3.0 --. % +.’ c 2.0 L a 1 .o 0 -0.2 -0.4 -0.6 -0.8 -1.0 -1.2 -1.4 PotentialN Fig. 5. Differential-pulse polarograms of a mixture of bromazepam, chlordiazepoxi de and flunitrazepam as 1 x M solutions in: A, pH 4.0 buffer solution; and B. pH 12.0 buffer solution. in four-electron processes that involve reductive dehydroxylation of the C-3 position.14 Oxazepam and lorazepam show different polarographic behaviour in pH 12.0 buffer in that they give rise to relatively small broad peaks at substantially more negative potentials than diazepam, prazepam and medazepam.This effect is a polarographic manifestation of the acid - base equilibrium in which species VI is reduced at a more negative potential than the neutral molecule, and is also due to repulsion of the anion (VI) from the negatively NH-CO H \ / L 7 CI C=N OH C1 C=N 0- VI charged mercury surface. This behaviour can be used to differentiate oxazepam and lorazepam from diazepam, prazepam and medazepam and also to a certain extent from each other. Diazepam can be differentiated fr,om prazepam and medazepam in this buffer as their E, values differ by 70 mV. Flurazeparn and potassium chlorazepate give reduction potentials of -0.72 and -0.73 V in pH 4.0 buffer and -1.10 and -1.15 V in pH 12.0 buffer, but these can be separated prior to polarographic analysis by using their unique acid - base properties, as discussed below under Analytical Applications.Hydrolysis Studies The aim of these investigations was to differentiate between members of groups of 1,4- benzodiazepines which it was not possible to resolve by polarography and/or solvent extrac- tion. In 0.1 M hydrochloric acid at 25 “C, flunitrazepam was found to hydrolyse much faster than either clonazepam or nitrazepam, and has a half-life of about 50 min. Fig. S(a) shows the differential-pulse polarograms obtained for flunitrazepam at 1 x M in 0.1 M hydro- chloric acid at 25 “C. The times indicated are those that elapsed between the start of the The three nitro-containing substances are an example of such a group.May, 1978 THE IDENTIFICATION O F 1,4-BENZODIAZEPINES 503 0 - 0.50 PotentiaVV - 1.0 Fig.6. Differential-pulse polarograms of: A, lorazepam; B, oxazepam; C, medazepam; D, diazepam; and E, prazepam, as 1 x M solutions in pH 4.0 buffer solution. reaction and the start of the recording. Fig. 8(b) and (c) shows the polarograms obtained for the acid hydrolyses of clonazepam and nitrazepam, respectively. The decrease in the polarographic peak currents caused by the disappearance of the reactants in 0.1 M hydro- chloric acid, and the corresponding increase in the reaction products of these three compounds are shown in Fig. 9. These results indicate that flunitrazepam can be differentiated from the other two nitro- containing benzodiazepines on the basis of its rate of hydrolysis in 0.1 M hydrochloric acid.Clonazepam hydrolysed at a slightly faster rate than nitrazepam (Fig. 9) but this could not be used to differentiate between these two compounds. Provided that no other benzo- diazepines were present in the unknown sample, they could be differentiated by their peak potentials in pH 4.0 buffer (Table I). Groves18 has studied the mechanism of hydrolysis of 1,4-benzodiazepines in dilute acidic solutions (pH 0-2) and found that such reactions occur relatively rapidly when there is an electron-attracting group in the 5-phenyl ring, e.g., 5-o-fluorophenyl-l,4-benzodiazepines. In addition, these reactions are most rapid in the region of the pKa value corresponding to the azomethine group and fall off at pH < pK, and pH > pK,.This suggests that the mechanism involves acid catalysis of the non-protonated benzodiazepine and benzophenones of type VII are generally formed. In strong acids (pH < 0 ) , benzophenones of type VIII are formed and it is these species that are used in identification procedures involving thin- layer chromatography .504 SMYTH et al. : POLAROGRAPHIC METHOD FOR Analyst, Vol. 103 R R I VI I Vlll The half-lives (tJ of these reactions and the corresponding changes in potential are given in Table I1 for flunitrazepam, clonazepam and nitrazepam. The slower rate observed for clonazepam presumably occurs as a result of i:he interference of the large chlorine atom in the hydrolytic reactions that involve the azoniethine group.This interference could come TABLE I1 HALF-LIVES OF HYDROLYSIS REACTIONS AN;D CORRESPONDING CHANGES IN POTENTIAL E, values in volts veysus S.C.E. OF FLUNITRAZEPAM, CLONAZEPAM AND NITRAZEPAM Medium f A > 1 .O M hydrochloric acid 0.1 M hydrochloric acid f n 7 f A \ E P E P E P E P Compound td/s (product) (reactant) t t / s (product) (reactant) E,(NO,) Flunitrazepam . . 237 -0.547 - 0.675 25 -0.584 -0.723 -0.069 Clonazepam . . .. 1069 -0.520 -0.654 285 -0.562 -0.701 -0.069 Nitrazepam . . .. 672 -0.552 -0.665 652 -0.589 -0.755 -0.069 2.0 a -3 E 5 1.0 + C 1 I I I I I I I I I I rl - 0.6 - 0.8 - 1.0 - 1.2 - 1.4 - 1.6 - 1.8 PotentiaVV Fig. 7. Differential-pulse polarograms of: A, diazepam; B, prazepam; C, medazepam; D, oxazepam; and E, lorezapam as 1 X M solutions in pH 12.0 ;buffer solution.May, 1978 THE IDENTIFICATION OF lJ4-BENZODIAZEPINES 505 - 0.ov 10.5 35 65 Time/min - 0.ov I 1 I 1 20 40 60 Time/min - 0.ov ‘ I I J 35 65 85 Timehin Fig.8. Diff erential-pulse polarograms of : (u), flunitrazepam ; ( b ) , clonazepam ; and (c), nitrazepam, as 1 x 10-5 M solutions in 0.1 M hydrochloric acid a t 25 “C. about by direct shielding of the group by chlorine and/or twisting the phenyl ring a t position 5 out of plane with the azomethine group, causing a reduction in conjugative interaction. These results seem to indicate that the presence of a relatively positively charged nitrogen atom in the azomethine group results in a relatively rapid hydrolysis in dilute acid solutions. Bromazepam, which contains a 5-pyridyl substituent, was found to react about ten times faster than flunitrazepam in 0.1 M hydrochloric acid with a t, of 5 min. Its rate of reaction increases with decreasing pH at pH values less than the pK, value of the azomethine group and Smyth et aZ.have proposed an alternative hydrolytic mechanism in these dilute acid solutions .11 Analytical Applications The results of the polarographic studies on the l,4-benzodiazepines show that it is possible to identify bromazepam and chlordiazepoxide in an unknown sample if a peak is found in pH 4.0 buffer in the potential range -0.37 to -0.40V. These two compounds can be differentiated by polarography in pH 12.0 buffer, determination of the rate of acid hydrolysis in 0.1 M hydrochloric acid in which chlordiazepoxide is stable or formation of the copper - bromazepam complex, as described elsewhere.If a peak occurs at approximately -0.16 V, a nitro-containing 1,4-benzodiazepine is suspected. Rapid acid hydrolysis in 0.1 M hydro- chloric acid will confirm the presence of flunitrazepam (“rapid” being defined as a marked decrease in the peak current corresponding to the azomethine group occurring within 15 min). Nitrazepam and clonazepam can be differentiated by the peak potentials corresponding to their azomethine reductions (-0.78 and -0.73 V, respectively) in pH 4.0 buffer provided that no other benzodiazepines are present. In such a sample, the azomethine reduction peak (plus the hydroxylammonium reduction peak) will appear abnormally low in relation to the nitro reduction peak (in theory, they should be identical in pH 4.0 buffer, but in practice, the differential-pulse peak corresponding to the nitro reduction is higher than the506 SMYTH et al.: POLAROGRAPHIC METHOD 1.3 1.2 1 .I 1 .o 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 r: 3 0 \ c F -.--- 10 20 30 40 50 60 70 80 ! Tiimdmin FOR Analyst, Vol. 103 Fig. 9. Hydrolyijis of clonazepam, nitrazepam and flunitrazepam as 1 x M solution:; in 0.1 M hydro- chloric acid at 25 "C. A, Clonazepam; B, nitrazepam; C, flunitrazepam; D, reaction product of flunitranepam; E, reaction product of clonazepam; and I;, reaction product of nitrazepam. sum of the other two reduction peaks). This effect occurs because differential-pulse polaro- graphy is not particularly responsive to the reduction of aromatic hydroxylamines.If only one peak is obtained and it occurs between --0.70 and -0.76 V, the presence of a benzo- diazepine with only the electroreducible azomethine group present is suggested. Oxazepam and lorazepam can be differentiated from diazepam, medazepam and prazepam by polaro- graphy in pH 12.0 buffer. The same buffer can be used to differentiate oxazepam and lorazepam as their peak potentials differ by 50 mV but, because of the broad nature of these peaks, this difference is of limited value. Diazepam can be differentiated from medazepam and prazepam in pH 12.0 buffer as it is reduced 70 mV earlier. Xledazepam is reduced 90 mV more negatively than prazepam in pH 4.0 buffer. The acid - base equilibria that exist in aqueous solutions of f l u r a ~ e p a m l ~ ~ ~ ~ and potassium chlorazepate12 have been the subject of previous publications.Briefly, flurazepam is extractable at neutral and alkaline pH but inextractable at acid pH (of the order of 3.0) owing to the formation of an extractable ion pair (IX) in the former pH region. The other CH3COO-- HO OH \ / X IX7-7 I Sample I L-----T----i I Adjust pH to 9.0 Aqueous phase contains potassium chlorazepate I 1 Adjust pH to 4.0 and extract with ethyl acetate Evaporate and tak up extract in pH 4.0 buffer mono protonate Solution pH 4.0 Record differential- pulse polarogram pulse polarogram pulse polarogram Peak a t - 0.73-0.74 V corresponds Peak a t - 0.16 V indicates n.itro- containing benzo- 1 diazepine Re-extract drug with ethyl acetate, evaporate, dissolve in 0.1 M hydrochloric acid, hydrolyse Rapid hydrolysis indicates flunitrazepam indicates chlordiazepoxide or bromazepam Ch lordiazepoxide stable in 0.1 M hydrochloric acid Bromazepam rapidly hydro- lysed, confirm by wave a t I - 0.99 V a t 1 pH 12.0 1 Only one peak a t - 0.70 to - 0.76 V indicates an azomethine )C = N group and suggests the presence I of one or more of oxazepam, 1 lorazepam, diazepam and prazepam; identify these by their polarographic I waves in pH 4.0 and 12.0 buffers concentration greater than 10 pg mi- I.This is confirmed by a peak a t - 0.82 V a t Fig. 10. Scheme for identification of a 1,4-b enzodiazepine in an unknown sample.508 SMYTH, SMYTH, GROVES AND TAN 11 1,4-benzodiazepines are extracted at pH 3.0 with a high efficiency.Potassium chlor- azepate is the only 1,4-benzodiazepine of the 12 under study that possesses a carboxylic acid group. Because of the formation of an inextractable species (X) in solutions of neutral and alkaline pH this is the only 1,4-benzodiazepine of this group that is not extractable a t pH 9. The scheme shown in Fig. 10 is therefore suggested for the identification of any one of the above-mentioned 1,4-benzodiazepines in an unknown formulation or in body fluids in forensic cases where the parent compound exists in relatively high concentrations compared with its metabolites. It should be possible to identify the drugs at concentrations of 10-5-10-7 M. Reproducibility of results can be achieved only by strict control of the polarographic con- ditions given in the section on Experimental 'Techniques.It would be expected that polarograms of all 12 benzodiazepines included here would be recorded under appropriate conditions before an identification is attempted. This procedure would allow for the inevitable differences in peak potentials that occur from one laboratory to the next. However, the relative positions of these peaks would not be affected. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 1s. References Lafargue, P., Meunier, J., and Lemontey, Y., J . Chromat., 1971, 63, 423. Hetland, L. B., Knowlton, D. A., and Couri, I)., Clinica Chim. Acta, 1972, 36, 473. Berry, D. J., and Grove, J., J . Chvomat., 1973, 80, 205. Sine, H. E., McKenna, M. J., Law, M. R., and Murray, M. H., J. Chromat. Sci., 1972, 10, 297. Schultz, C., Post, D., Schewe, G., and Schultz, H., 2. Analyt. Chem., 1972, 262, 282. Zingales, I. A., J . Chromat., 1971, 61, 237. Knowles, J. A., and Ruelius, H. W., Arzneimiltel-Forsch., 1972, 22, 687. Marcucci, F., Mussini, E., Airoldi, L., Guaitani, A,, and Garattini, S., J . Pharm. Pharmac., 1972, De Silva, J. A. F., Puglisi, C. V., and Munno, .N., J . Pharm. Sci., 1974, 63, 520. Barrett, J., Smyth, W. F., and Davidson, I. E., J . Pharna. Pharmac., 1973, 25, 387. Smyth, M. R., Beng, T. S., and Smyth, W. F., Analytica Chim. Acta, 1977, 92, 129. Smyth, W. F., and Leo, B., Analytica Chim. Acta, 1975, 76, 289. Clifford, J. M., Smyth, M. R., and Smyth, W. F., 2. Analyt. Chem., 1974, 272, 198. Goldsmith, J. A., Jenkins, H. A., Grant, J., and Smyth, W. F., Analytica Chim. Acta, 1973, 66, 427. Barrett, J., Smyth, W. F., and Hart, J. P., J . Pharm. Pharmac., 1974, 26, 9, Clifford, J. M., and Smyth, W. F., 2. Analyt. Chem., 1973, 264, 149. Groves, J. A., PhD Thesis, University of London, 1976. Groves, J. A., and Smyth, W. F., to be published. 24, 63. Received September 23rd, 1977 Accepted October 19th, 1977

ISSN:0003-2654    

DOI:10.1039/AN9780300497

出版商:RSC    

年代:1978

数据来源: RSC

摘要:

Analyst, May, 1978, Vol. 103, $9. 509-512 509 Ana lytica I Met hods Corn m i ttee REPORT PREPARED BY THE MEDICINAL ADDITIVES IN ANIMAL FEEDS SUB- COMMITTEE "A" Spectrophotometric Determination of Ronidazole in Animal Feeds Keywords : Ronidazole determination ; animal feeds ; spectrophotometry The Analytical Methods Committee has received and approved for publication the following Report from its Medicinal Additives in Animal Feeds Sub-committee "A." Report The constitution of the Sub-committee responsible for the preparation of this Report was : Mr. J. Markland (Chairman), Mr. R. J. Anderson, Mr. A. G. Croft, Mr. C. E. Dodd, Mr. R. Fawcett, Dr. K. Field, Mr. R. S. Hatfull, Mr. G. E. Kitson, Mr. D. H. Mitchell and Mr. J. A. Stubbles, with Mr. P. W. Shallis as Secretary. Introduction Ronidazole [ (l-methyl-5-nitroimidazol-2-yl)methyl carbamate] is used in poultry feeds for the control and treatment of blackhead; it is also used in pig feeds for the treatment and control of dysentery and as a growth-promoting agent.The normal level of inclusion of the drug in a feed is between 60 and 120 mg k g l . Experimental and Results The most promising method available when the Sub-committee began its work was that proposed by Szalkowski and Kan0ra.l In this method, the nitro group of the drug is split off by alkaline hydrolysis, which is followed by diazotisation of 4-aminobenzoic acid by the liberated nitrite ion and then coupling with N-2-aminoethyl-1-naphthylamine to form a coloured complex. The absorption of the coloured complex is measured at 550nm in a 10-mm cell.Preliminary work on the method by some members of the Sub-committee indicated that it was not specific for ronidazole as other drugs that contain a nitro group, such as dimetrid- azole and nitrofurazone, interfered. There was also some evidence to suggest that interference was encountered when grass meal or fish meal was present in the sample. It was realised that a gas - liquid chromatographic method might prove to be the best for the determination of ronidazole. However, in the absence of any suitable method a t that time, the Sub-committee decided to standardise the conditions of the spectrophotometric method. Subsequently, a gas - liquid chromatographic method based on the formation of a volatile silyl derivative of ronidazole in which no interference from the presence of grass meal, fish meal or other drugs in the feed was observed has been proposed by Harris et aZ.2 The conditions of the method proposed by Szalkowski and Kanoral were examined in detail by members of the Sub-committee.It was found that in common with most other methods of this type, the batch and grade of aluminium oxide used appeared to have a profound effect on the recovery of the drug and in this instance the type and grade of floridin earth used also had an effect. Acceptable batches and types of both materials are available and it is suggested that the suitability for the purpose of the aluminium oxide and the floridin earth should first be checked by taking a standard through the procedure; a recovery of at least 90% should be obtained. In their preliminary work, some members had found that recoveries of ronidazole added to animal feeds were good, despite variable and sometimes large feed blank values.The method makes use of liberated nitrite ion to diazotise 4-aminobenzoic acid and therefore any adventitious contamination with nitrite after cleavage of the molecule will give rise to an apparent ronidazole content. As a result of the exploratory work carried out by510 ANALYTICAL METHODS COMMITTEE : SPECTROPHOTOMETRIC Analyst, Vd. 103 members, a few modifications were incorporated into the published method. A collaborative test was then carried out by applying the modified method to the determination of ronidazole added within each laboratory to a circulated sample of feedingstuff at a level of 60 mg kg-1; the results are shown in Table I.TABLE I DETERMINATION OF RONIDAZOLE IN AN ANIMAL FEED BY THE RECOMMElNDED METHOD Ronidazole added/ Laboratory mg kg-l A 60 60 60 B 60 60 C 60 60 60 D 60 60 60 E 60 60 F 60 60 G 64.8 64.8 H 60 60 60 60 60 Ronidazole found/ mg kg-l 63.6, 64.2 52.8, 54.0 58.8, 57.6 56.3 55.1 51.5 51.6 51.0 60.5 55.8 67.6 63.0 55.0 69.0 69.0 67.3 75.7 61.0 68.0 60.0 59.0 57.0 Recovery, 106.0, 107.0 88.0, 90.0 98.0, 96.0 % 93.8 91.8 85.8 86.0 85.0 loo.s 93.0 96.0 105.0 91.7 115.0 115.0 103.9 116.8 101.7 113.3 100.0 98.3 95.0 Feed blank/ mg kg-l 7.9 7.9 5.2 2.5 2.5 4.4 6.4 3.6 4.5 4.5 7.0 7.0 Corrected recovery, % 80.7 78.7 77.2 81.8 80.8 93.5 82.3 90.0 107.5 107.5 83.1 106.0 Recommendation The Sub-committee recommends that the rnethod given in the Appendix should be used for the determination of ronidazole in animal feeds known to be free from grass meal, fish meal and interfering nitro compounds. APPENDIX Recommended Method for the Determination of Ronidazole in Feeds Scope and Field of Application meal, fish meal and other drugs containing a nitro group that will interfere.The method is for the determination of ronidazole in animal feeds in the absence of grass Principle Ronidazole is extracted from the feed with hot methanol and the extract is cleaned up on a column of aluminium oxide and floridin earth. The extracted drug is hydrolysed with alkali in the presence of copper and the nitrite formed is used to diazotise 4-aminobenzoic acid, which is then coupled with N-2-aminoeth;yl-l-naphthylamine to form a purple complex.The absorbance of the complex is measured at 550 nm. Reagents Methanol.M a y , 1978 DETERMINATION OF RONIDAZOLE I N ANIMAL FEEDS 511 Butan- 1-01. Sodium chloride. Aluminium oxide. Floridin earth. See Note 1. Copper(11) sul@hate solution. Alkaline co$@er solution. For chromatography (see Note 1). Dissolve 2.5 g of anhydrous copper(I1) sulphate in sufficient Add 1.0 ml of the copper(I1) sulphate solution to 100 ml of a Prepare this solution Dissolve 400 mg of 4-aminobenzoic acid in 250 ml of water, Dilute to 500ml with water and Dissolve 50 mg of N-2-aminoethyl-l- Dissolve 30.0 mg of pure ronidazole in sufficient methanol This solution is stable for 1 month if stored in a tightly water to produce 100 ml of solution.5% m/V aqueous solution of sodium hydroxide and mix thoroughly. freshly before use. add 100ml of hydrochloric acid (sp. gr. 1.18) and mix. mix thoroughly. N-2-aminoethyl-1-naphthylamine reagent solution. naphthylamine hydrochloride in 50 ml of water. Ronidaxole stock solutions. to produce 100ml of solution. stoppered container and protected from light, 4-Aminobenxoic acid solution. Cool the solution in an ice - water bath before use. Prepare this solution freshly each day. (A). 1 ml of solution = 300 pg of ronidazole. (E). Transfer 4.00 ml of solution A into a 100-ml calibrated flask, dilute to the mark with This solution is stable for 1 week if stored in a tightly stoppered water and mix thoroughly. container and protected from light. 1 ml of solution zz 12 pg of ronidazole.Ronidaxole working standard solution. Transfer 10.0 ml of solution B into a 100-ml Prepare this solution calibrated flask, dilute to the mark with water and mix thoroughly. freshly each day. Preparation of Chromatographic Column Into the bottom of a glass tube about 400 mm long and 11 mm i.d., constricted at its bottom end to a diameter of 4-5mm, place a small plug of Pyrex glass-wool. Place 3 . 0 g of aluminium oxide into the column and assist settling by gently tamping it with a glass rod. On top of the aluminium oxide place 2.0g of the floridin earth and also tamp this lightly with a glass rod. Procedure Weigh accurately sufficient of the finely divided sample to contain about 600 pg of ronidazole and transfer it into a 250-ml flat-bottomed flask.Add 100.0ml of methanol, place a magnetic stirrer bar in the flask and attach the flask to a reflux condenser. Heat, with stirring, on a magnetic-stirrer hot-plate to maintain a gentle reflux for 30min and then immerse the flask with the condenser still attached in cold water until it reaches room temperature. Transfer 5.0 ml of the clear extract to the top of the chromatographic column and allow it to drain through under gravity. Wash the column with three 5-ml portions of methanol and collect the washings in the same tube. Add 0.1 ml of glacial acetic acid, place the tube in a water-bath a t 50 "C and evaporate to dryness by passing over the surface of the liquid a stream of compressed air carefully controlled to avoid splashing (see Note 2).Dissolve the residue in 10.0 ml of chloroform, add 25.0ml of water, stopper the tube, shake it for 5 min on a mechanical shaker and then centrifuge for about 5 min. Transfer two 10.0-ml portions of the aqueous (top) layer into separate 50-ml centrifuge tubes (A, and A,). To further separate 50-ml centrifuge tubes transfer two 10.0-ml portions of ronidazole working standard solution (B, and B,) and two 10.0-ml portions of water (C, and To the tubes A,, B, and C , add 5.0ml of water and mix. To the tubes A,, B, and C, Transfer the mixture to centrifuge tubes and centrifuge for about 5 min. Collect the eluate in a 50-ml centrifuge tube. C2) -51 2 ANALYTICAL ME.THODS COMMITTEE add 5.0 ml of alkaline copper solution arid mix thoroughly. Place all tubes (without stoppers) into a stirred water bath at 80 "C, allow 1-2 min for the tubes and their contents to become warm and then insert the stoppers tightly.After 1 h, remove the tubes from the water-bath, momentarily loosen and replace the stoppers and then immerse the tubes in an ice - water bath until the temperature has been reduced to 3-5 "C (about 5 min). Remove the tubes from the ice - water bath, add 5.0 ml of cold 4-aminobenzoic acid solution to the contents of each tube and set them aside for 2 min. Then add 1.0 ml of N-Z-amino- ethyl-l-naphthylamine reagent solution to the contents of each tube, mix and set them aside at room temperature for 20 min. Finally, add 5.0 g of sodium chloride and 5.0 ml of butan-1-01 to the contents of each tube, insert the stoppers and shake each tube vigorously for 2-3 min.Allow the layers to separate and with a pipette carefully transfer the butanol layer to a small (about 15-ml) centrifuge tube. Spin the tubes in a centrifuge at about 2 000 rev min-l for 3 min. Measure the absorbances of the clarified butanol solutions from each of the tubes in 10-mm cells against butan-1-01. Calculation of Results Calculate the concentration of ronidazole in the feed sample from the expression 2 x 100 x x 2 x W x Y Ronidazole/mg kg-l = where X = corrected absorbance of sample, ie., (A, - A,) - (C, - C,). Y = corrected absorbance of standard, Le., (B, - B,) - (C, - C2). 2 = mass of ronidazole (micrograms) in ithe standard (usually 12 pg). W = mass of feed (grams) taken for analysis. NOTES- Various makes and grades of aluminium oxide, both neutral and basic, and of floridin earth have been found to be satisfactory. Before use a standard should be put through the column, which can be considered to be satisfactory for use if a recovery of at least 90% is obtained. It is essential to remove impurities from the compressed air supply used at the evaporation stage. For this purpose, pass the air through a train of three gas-washing bottles, the first containing a saturated solution of potassium hydroxide, the second conctmtrated sulphuric acid saturated with chromium(II1) oxide and the third Pyrex glass-wool. 1. 2. References 1. 2. Szalkowski, C. R., and Kanora, J., J . Ass. 08. Analyt. Chem., 1969, 52, 101. Harris, J. R., Baker, P. G., and Alliston, G., A4naZyst, 1977, 102, 580.

ISSN:0003-2654    

DOI:10.1039/AN9780300509

出版商:RSC    

年代:1978

数据来源: RSC

摘要:

Analyst, May, 1978, Vol. 103, $9. 513-520 513 Analytical Met hods Committee REPORT PREPARED BY THE MEDICINAL ADDITIVES IN ANIMAL FEEDS SUB-COMMITTEE ”B” Identification of Prophylactic and Growth-promoting Drugs in Animal Feedingstuffs Keywords : Prophylactic drugs ; growth-9romoting drugs ; feedingstu#s analysis ; thin-layer chromatography The Analytical Methods Committee has received and approved for publication the following Report from its Medicinal Additives in Animal Feeds Sub-committee “B.” Report The constitution of the Sub-committee responsible for the preparation of this Report was : Dr. D. R. Williams (Chairman), Mr. A. G. Croft, Mr. G. Drewery, Mr. R. Fawcett, Dr. K. Field, Mr. R. S. Hatfull, Dr. R. McEwan and Mr. G. H. Smith, with Mr. P. W. Shallis as Secretary. Introduction As part of its programme of work, the Sub-committee is required to recommend methods that can be used to confirm the presence of a declared prophylactic or growth-promoting drug in an animal feedingstuff.Although individual chemical tests for many of the permitted drugs are known, they are not necessarily specific for any one drug. The Sub- committee decided that, although the primary object of the work was to provide individual tests that could be used to confirm the presence of a declared drug in a feedingstuff, it would be advantageous if all the individual tests could be integrated into a composite scheme. Such a scheme had already been proposed by Hammond and Westonl and it was decided to attempt to apply this published scheme to the Sub-Committee’s requirements.Not all of the drugs of interest to the Sub-committee were covered in the published scheme and some preliminary work was carried out to extend the scheme to cover these drugs. As a result of the collaborative work carried out by the Sub-committee, it is recommended that the individual tests given in the Appendix should be used, as appropriate, to confirm the presence of a declared drug in a medicated feedingstuff. A procedure for the identifica- tion of ethopabate is included but, owing to the very low level at which this drug is incorporated in animal feeds, the procedure can seldom be successfully applied. It is given here only for guidance and will be replaced when a more successful procedure has been developed. In each individual test an indication of the chromatographic fraction in which the drug will be found is given.The named fraction is the one in which it is most likely to appear but experience has shown that on occasions it will appear in fractions other than the expected one. APPENDIX Identification of Prophylactic and Growth-promoting Drugs in Animal Feedingstuffs Scope and Field of Application drugs in animal feedingstuffs. The method is for confirming the presence of declared prophylactic and growth-promoting514 ANALYTICAL METHODS COMMITTEE IDENTIFICATION OF Analyst, VOl. 103 Principle The feed samples are extracted with methanol or with a mixture of acetonitrile and chloroform. The extract is passed through a column of aluminium oxide and the eluate is collected. Further elutions from the column with different solvents are carried out and the eluted fractions are concentrated and subjected to thin-layer chromatography on silica- gel plates.The drugs are identified from their positions on the plate, their reactions to different spray reagents and by examination of the plate in daylight and in ultraviolet light. A standard is included on every plate for comparison. Reagents Aluminium oxide. Silica gel G. C hloro f o m . Methanol. Acetonitrile - chloroform (4 + 1). give 100 ml. Acetonitrile - chloroform (1 + 1). Methanol - ammonia sol.ution. Mix 80 ml of methanol with 20 ml of ammonia solution (density 0.88 g ml-l). Development solvent A . Development solvent B. Development solvent C. Development solvent D. 1,2-Diaminoethane, anhydrous.Dragendor$’ s reagent. Stock solution. For chromatography, neutral, 100-250 mesh, Brockinan activity 1, For thin-layer chromatography. Mix SO ml of acetonitrile with sufficient chloroform t o Mix 20 ml of acetonitrile with 20 ml of chloroform. Mix 90 ml of chloroform with 10 ml of methanol. Mix 50 ml of ethanol with 50 ml of 1 M hydrochloric acid. Mix SO ml of ethanol with 20 ml of ammonia solution (density Mix 10 ml of dimethylformamide with 90 ml of chloroform. 0.88 g ml-l) . (i) Add 2.6 g of bismuth triiodide and 7.0 g of sodium iodide to 25 ml of glacial acetic acid and boil for a few minutes. Remove the precipitated sodium acetate on a sintered-glass funnel, add 8 ml of ethyl acetate to 20 ml of the filtrate and store in a dark glass bottle. Mix 10 ml of the stock solution with 25 ml of glacial acetic acid and 60 ml of ethyl acetate.(The detection se:nsitivity of this reagent is increased by spraying the plate finally with 0.1 N sulphuric acid.) Ehrlich’s reagent. Dissolve 1 g of 4-dimethylaminobenzaldehyde in 30 ml of hydro- chloric acid (density 1.18 g ml-l) and add 180 ml of butan-1-01. Picryl chloride reagent. Phenylhydraxine reagent solution. Dissolve 0.25 g of phenylhydrazine in 25 ml of water Silver nitrate spray reagent. Add 50 mg of silver nitrate to 45 ml of acetone and then add (ii) Spray solution. Dissolve 1 g of picryl chloride in 100 ml of ethanol. and add 25 ml of hydrochloric acid (density 1.18 g ml-1). distilled water dropwise until the solid dissolves. Apparatus Chromatographic column. Length 300 mm, internal diameter 10 mm, fitted with a poly- tetrafluoroethylene stopcock.Centrifuge. Mechanical shaker (or magnetic stirrer). Thin-layer chromatographic equipment. Ultraviolet lamp. With 254- and 350-nm tubes. Procedure Preparation of column Insert a small plug of cotton-wool in the blottom of the column and then slowly add 5 g of aluminium oxide, tapping the column gently during the addition. Immediately before use, wash the aluminium oxide with 50ml of water and allow it to drain. Then wash it with 50 ml of methanol and allow it to drain. Apply gentle suction to the lower end of the column for about 20 min to ensure the complete removal of methanol.May, 1978 PROPHYLACTIC AND GROWTH-PROMOTING DRUGS IN ANIMAL FEEDINGSTUFFS 515 Preparation of plates Use this slurry to coat six 200 x 200 mm plates with a layer 0.25-mm thick; commercially available pre-coated plates can also be used.Shake 30g of silica gel G with 60ml of water for 1-2min. Activate all plates before use by heating a t 100 "C for 1 h. Prefiaratioa of chromatographic tank development solvent (A-D) . Line the tank with filter-paper and equilibrate before use with 100 ml of the appropriate Extraction aT$d column chromatography Two different procedures are given below; the one to be used for any given drug will be specified appropriately. Method A . To 10.0 g of the prepared feedingstuff add 40 ml of acetonitrile - chloroform (4 + 1) and shake or stir for 1 h. Pour the slurry as completely as possible into a 50-ml centrifuge tube and centrifuge at about 2 500 rev min-l for 3 min.Decant the supernatant liquid on to the aluminium oxide column and collect the eluate (fraction 1) in a 50-ml beaker at a rate of about 2 drops per second. Then pass the following through the column successively, for each collecting the eluate in a separate beaker: 5 ml of chloroform (fraction 2), 40 ml of chloroform (fraction 3) and finally I 0 ml of methanol (fraction 4). Evaporate fraction 1 to dryness on a steam-bath under a stream of air, avoiding excessive heating, and dissolve the residue in 1 ml of acetonitrile - chloroform (1 + 1). By using a stream of air, reduce the volumes of both fractions 3 and 4 to 1 ml (examination of fraction 2 is unnecessary). To 1O.Og of the prepared feedingstuff add 40ml of methanol, stir or shake for 15 min and then centrifuge at about 3 500 rev min-l for 3 min.Decant the supernatant liquid on to the aluminium oxide column and elute with 25 in1 of methanol. Collect the eluate in a 100-ml beaker and evaporate it to a volume of about 1 mi on a steam-bath under a stream of air. Method B. Thin-layer chromatograj5hy Spot on to a prepared thin-layer plate (i) 2 0 4 of the appropriate sample extract, (ii) 10 pl of the sample extract, overspotted with 10 pl of standard drug solution, and (iii) 20 pl of the standard drug solution. (Note that these volumes are reduced when the presence of nifursol is being investigated.) Develop the plate and render the spots visible as described for the particular drug under investigation. Interpretation of resdts The chromatogram of the sample extract (spot i) will, if the drug under investigation is present, have a spot at the same R, value as, and be similar in colour to, the spot obtained for the standard solution (spot iii).The spot obtained for the sample extract overspotted with the standard (spot ii) must show no evidence of separation into two components. Identification of Acinitrazole Standard solution concentration to that expected in the sample Prepare a solution of acinitrazole in methanol containing 1.5 mg ml-l, or of similar Extraction and column chromatography Carry out by method A. The acinitrazole is expected to be present in fraction 4. Thin-layer chromatography Remove the plate from the tank, allow to dry in air, examine it in ultraviolet light (254nm) and note the response.Interpret the results as described above. Develop the plate with solvent A until the solvent front has moved 150mm. Spray the plate with 1,2-diaminoethane and note the response.516 ANALYTICAL METHODS COMMITTEE : IDENTIFICATION OF Analyst, VoZ. 103 Identification of Amprolium Standard solution centration to that expected from the sample. Prepare a solution of amprolium in methanol containing 0.6 mg ml-l, or of similar con- Extraction and column chromatography Carry out by method B. Thin-layer chromatography Remove the plate from the tank, allow it to dry in ah-, examine it in ultraviolet light (254 nm) and note the response. Spray the plate with Dragendorff’s reagent and note the response. Interpret the results as described on p. 515. Develop the plate with solvent B until the solvent front has moved 150mm.Identification of Buquinolate Standard solution concentration to that expected from the sample. Prepare a solution of buquinolate in chloroform containing 1.0 mg ml-1, or of similar Extraction and column chromatography Carry out by method A. The buquinolate is expected to be in fraction 3. Thin-layer chromatography Remove the plate from the tank, allow it to dry in air, examine it in ultraviolet light (254 nm) and note the response. Spray the plate with Dragendorff’s reagent followed by 0.1 N sulphuric acid and note the response. Develop the plate with solvent A until the solvent front has moved 150mm. Interpret the results as described on p. 515. Identification of Clopidol Standard solution tion to that expected from the sample.Prepare a solution of clopidol in methanol containing 1.25 mg ml-l, or of similar concentra- Extraction and column chromatography Carry out by method A. The clopidol is expected to be in fraction 4. Thin-layer chromatography Remove the plate from the tank, allow it to dry in air, examine it in ultraviolet light (254 nm) and note the response. Spray the plate with picryl chloride, expose the plate to ammonia vapour and note the response. The red spot formed, which fades after 2-3min, indicates the presence of clopidol. Develop the plate with solvent A until the solvent front has moved 150mm. Interpret the results as described on p. 515. Identification of Dinitolmide Standard solution mg ml-1, or of similar concentration to that expected from the sample. Extraction and column chromatography Prepare a solution of dinitolmide in acetonitrile - chloroform (1 + 1) containing 1.0 Carry out by method A.The dinitolmide i:s expected to be in fraction 1.May, 1978 PROPHYLACTIC AND GROWTH-PROMOTING DRUGS IN ANIMAL FEEDINGSTUFFS 517 Thin-layer chromatography Remove the plate from the tank, allow it to dry in air, examine it in ultraviolet light (254 nm) and note the response. Spray the plate with 1,2-diaminoethane and note the response. Interpret the results as described on p. 515. Develop the plate with solvent A until the solvent front has moved 150 mm. Identification of Ethopabate Standard solution concentration to that expected from the sample. Prepare a solution of ethopabate in methanol containing 0.04mgml-l, or of similar Extraction and column chromatography Carry out by method A.The ethopabate is expected to be in fraction 4. Thin-layer chromatography Remove the plate from the tank, allow it to dry in air, examine it in ultraviolet light (254nm) and note the response. Spray the plate with Ehrlich's reagent, heat the plate to 100 "C for 5 min and note the response. Develop the plate with solvent A until the solvent front has moved 150mm. Interpret the results as described on p. 515. Identification of Furazolidone Standard solution concentration to that expected from the sample. Prepare a solution of furazolidone in methanol containing 0.6 mg ml-1, or of similar Extraction and column chromatography Carry out by method A. The furazolidone is expected to be in fraction 1.Thin-layer chromatography Remove the plate from the tank, allow it to dry in air, examine it in ultraviolet light (254 nm) and note the response. Spray the plate with lJ2-diarninoethane or with Dragendorff's reagent and note the response. Interpret the results as described on p. 515. (Note that occasionally interference from co-extracted materials hampers the positive identification of furazolidone. If this occurs, it is necessary to repeat the test, but using solvent C to develop the plate.) Develop the plate with solvent A until the solvent front has moved 150mm. Identification of Halquinol Standard solution in the sample. Prepare a solution of halquinol in chloroform at a similar concentration to that expected Extraction and column chromatography Then elute the halquinol from the column with 15 ml of 1 M sulphuric acid, collecting the eluate in a separating funnel.Add 15 ml of chloroform, shake the funnel, allow the phases to separate and run off the lower (chloroform) layer. Reduce the volume of the chloroform extract to about 1 ml under a stream of air. Carry out by method A and collect all four fractions. Spot this solution on to the prepared thin-layer chromatographic plate. Thin-1 ayer chromatograp hy Remove the plate from the tank, allow it to dry in air, examine it in ultraviolet light (350 nm) and note the response. Spray the plate with silver nitrate spray reagent and note the response. Interpret the results as described on p. 515. Develop the plate with solvent A until the solvent front has moved 150mm.518 ANALYTICAL METHODS COMMITTEE : IDENTIFICATION OF Analyst, Vol.103 Identification of Nicarbazin Nicarbazin is an equimolecular mixture of 1,3-bis(4-nitrophenyl)urea (component 1) and 2-hydroxy-4,6-dimethylpyrimicIine (component 2). Standard solution to that expected in the sample. Prepare a standard solution of nicarbazin in methanol containing a similar concentration Extmctio;lz and column chrowatogvaphy Carry out by method B. Thin -1 ay er clz r o mat ogmp hy Remove the plate from the tank, allow it to dry in air, examine it in uitraviolet light (25-4 nm) and note the response. Component 1 will give it positive reaction with both 1,2-diarninoethane and Dragendorff's reagent. Component 2 will give a positive reaction with Dragendorff's reagent, the colour developing only after several hours provided that the plate is not sprayed with 0.1 N sulphuric acid, and with Ehrlich's reagent, for which a colour will develop on heating the plate at 100-105 "C for 10-15 min.Interpret the results as described on p. 515. Develop the plate with solvent A until the solvent front has moved 150 mm. Identification of Nifursol Standard solution in the sample. Prepare a solution of nifursol in acetone containing a similar concentration to that expected Extraction and column chromatography Then elute the nifursol from the column with 25 ml of methanol - ammonia solution, collecting the eluate in a 50-ml beaker. Evaporate the eluate just to dryness on a steam-bath and dissolve the residue in 1 ml of acetone. Carry out by method A and collect all four fractions.Thin-layer chromatography Spot on to the prepared thin-layer chromatographic plate (i) 10 p1 of the sample extract, (ii) 5 p1 of the sample extract, overspotted with 5 pl of standard nifursol solution, and (iii) lop1 of standard nifursol solution. Develop the plate with solvent D until the solvent front has moved 150 mm. Remove the plate from the tank, allow it to dry in air, examine it in ultraviolet light (254 nm) and note the response. Spray the plate with phenylhydrazine reagent solution, heat the plate at 100 "C for 5 min and note the response. Interpret the results as described on p. 515. (In daylight, nifursol gives a yellow spot that appears only just above the base line.) Identification of Nitrofurazone Standard solution concentration to that expected from the sample.Prepare a solution of nitrofurazone in methanol containing 0.6 mg ml-l, or of similar Extraction and column chromatogra$hy Carry out by method A. The nitrofurazorie is expected to be in fraction 4. Thin-lnysr chromatography Remove the plate from the tank, allow it to dry in air, examine it in ultraviolet light (254nm) and note the response. Interpret the results as described on p. 515. Develop the plate with solvent A until th.e solvent front has moved 150mm. Spray the plate with lJ2-diaminoethane and note the response.May, 1978 PROPHYLACTIC AND GROWTH-PROMOTING DRUGS I N ANIMAL FEEDINGSTUFFS 519 Identification of Nitrovin Standard solutioiz tion to that expected from the sample. Prepare a solution of nitrovin in methanol containing 0.1 mg rnl-l, or of similar concentra- E..itmction and colwnn claromatogrnphy Carry out by method A.The nitrovin is expected to be in fraction 4. Thin-layer chromatography Remove the plate from the tank, allow it to dry in air, examine it in ultraviolet light (254 nm) and note the response. Interpret the results as described on p. 515. Develop the plate with solvent A until the solvent front has moved 150mm. Spray the plate with 1 ,%diaminoethane and note the response. Identification of Sulphaquinoxaline Standard solution concentration to that expected from the sample. Prepare a solution of sulphaquinoxaline in methanol containing 1.0 mg m1-l’ or of similar Extraction and column chronzatography Carry out by method A. The sulphaquinoxaline is expected to be in fraction 1.Thin-layer chromat ograp hy Remove the plate from the tank, allow it to dry in air, examine it in ultraviolet light (254nm) and note the response. Interpret the results as described on p. 515. Develop the plate with solvent A until the solvent front has moved 150mm. Spray the plate with Ehrlich’s reagent and note the response. Identification of Decoquinate Standard solution concentration to that expected from the sample. Prepare a solution of decoquinate in chloroform containing 0.4 mg ml-l, or of similar Extraction and column chromatography Carry out by method A. The decoquinate is expected to be in fraction 3. Thin-layer chromatography Remove the plate from the tank, allow it to dry in air, examine it in ultraviolet light (254 nm) and note the response.Spray the plate with Dragendorff’s reagent followed by 0.1 N sulphuric acid and note the response. Develop the plate with solvent A until the solvent front has moved 150mm. Interpret the results as described on p. 515. Identification of Dimetridazole Standard sold ion concentration to that expected from the sample. Prepare a solution of dimetridazole in chloroform containing 1 .O mg ml-l, or of similar Extraction and column chromatograplzy Carry out by method A. The dimetridazole is expected to be in fraction 1.520 ANALYTICAL METHODS COMMITTEE : IDENTIFICATION OF ATZU,!pt, VOl. 103 Thin-layer chromatography Remove the plate from the tank, allow it to dry in air, examine it in ultraviolet light (254 nm) and note the response.Spray the plate with either Ehrlich’s reagent or Dragendorff’s reagent and note the response. Develop the plate with solvent A until the solvent front has moved 150 mm. Interpret the results as (described on p. 515. Identification of Methyl Benzoquate Standard solution 0.1 mg ml-l, or of similar concentration to that expected from the sample. Prepare a solution of methyl benzoquate in acetonitrile - chloroform (1 + 1) containing Extraction and column chromatography Carry out by method A. The methyl benzoquate is expected to be in fraction 1. Thin-layer chromatography Remove the plate from the tank, allow it to dry in air, examine it in ultraviolet light (254 nm) and note the response. Spray the plate with Dragendorff’s reagent followed by 0.1 N sulphuric acid and note the response. Develop the plate with solvent A until t:he solvent front has moved 150mm. Interpret the results as described on p. 515. Identification of Pyrimethamine Standard solution concentration to that expected from the sample. Prepare a solution of pyrimethamine in chloroform containing 0.05 mg ml-l, or of similar Extraction and column chromatography Carry out by method A. The pyrimethannine is expected to be in fraction 3. T hin-lay er chromatography Remove the plate from the tank, allow it to dry in air, examine it in ultraviolet light (254 nm) and note the response. Spray the plate with Dragendorff’s reagent followed by 0.1 N sulphuric acid, and note the response. Develop the plate with solvent A until the solvent front has moved 150mm. Interpret the results as described on p. 515. Identification of Robenidine Standard solution or of similar concentration to that expected from the sample. Prepare a solution of robenidine in acetonitrile - chloroform (1 + 1) containing 0.3 mg ml-1, Extraction and column chromatography Carry out by method A. The robenidine is expected to be in fraction 1. Thin-layer chromatography Remove the plate from the tank, allow it to dry in air, examine it in ultraviolet light (254nm) and note the response. Interpret the results as described on p. 515. Develop the plate with solvent A until the solvent front has moved 150mm. Spray the plate with 1,2-diaminoethane and note the response. Reference 1. Hammond, P. W., and Weston, R. E., Analyd, 1969, 94, 921.

ISSN:0003-2654    

DOI:10.1039/AN9780300513

出版商:RSC    

年代:1978

数据来源: RSC

摘要:

Analyst, May, 1978, Vol. 103, pp. 521-524 52 1 Analytical Met hods Com mittee REPORT PREPARED BY THE IRON SUB-COMMITTEE General Method for the Determination of Iron with 4,7-Diphenyl-l,lO-phenanthroline (Bathophenanthroline) Keywords Iron determination ; 4,7-diphenyl-l, 10-phenanthroline ; batho- phenanthroline ; spectrophotovnetry The Analytical Methods Committee has received and approved for publication the following Report from its Iron Sub-committee. Report The constitution of the Sub-committee responsible for the preparation of this Report was : Mr. A. G. Hill (Chairman), Professor E. Bishop, Dr. L. E. Coles, Dr. E. J. McLauchlan, Mr. D. W. Meddle, Mr. M. J. Pater, Mr. C. A. Watson and Mr. C. Whalley, with Mr. P. W. Shallis as Secretary. Introduction The Iron Sub-committee of the Analytical Methods Committee has earlier recommended a general method for the determination of iron with 1,lO-phenanthro1ine.l The work was carried out at the request of the British Standards Institution, acting on behalf of the International Standards Organisation (ISO), who needed a general method that could be used in all specifications that require the determination of iron content.After considering the available reagents and methods, the Sub-committee concluded that the use of 1,lO- phenanthroline, a reagent already widely used in IS0 specifications for the determination of iron, offered adequate sensitivity for the purpose. A standardised version of this method was evaluated and was recommended to IS0 for use as a general method. The Sub-committee then proceeded to the second phase of its programme, which was to carry out investigations that would lead to the recommendation of the best general method for determining iron.Several reagents are available that will form coloured complexes with iron that can be extracted into an organic solvent, and of these perhaps the best known and most widely used is 4,7-diphenyl-l , 10-phenanthroline (bathophenanthroline) . This reagent was recommended for the determination of iron by Smith et aL2 and, since its intro- duction, has been proposed by many different workers for determining iron in a variety of sample materials. The bright red complex of bathophenanthroline with iron(II), which is formed in the pH range 2-9, has a molar absorptivity of about 22 000, which is approximately twice that of the 1,lO-phenanthroline - iron(I1) complex in aqueous solution. Moreover, as the iron(I1) - bathophenanthroline complex can be extracted into an organic solvent and concentrated, it offers considerable advantages in terms of sensitivity over the use of 1 , 10-phenanthroline.Interferences in the method are few and the major problems that can be encountered have been summarised previ~usly.~ The Sub-committee therefore decided to investigate the bathophenanthroline method as it was so widely used and recommended. It was realised that other reagents, such as the disodium salt of 4,7-diphenyl-l,1O-phenanthrolinedisulphonic acid, FerroZine and 1,3,5- triazine, had been recommended for the determination of iron, but that these were, a t best, unlikely to be appreciably better than bathophenanthroline and were in any event much less widely available.Atomic-absorption spectrophotometry is another technique that it was considered could possibly provide a general method for determining iron, and some work done by the Sub- committee is the subject of a separate r e p ~ r t . ~522 ANALYTICAL METHODS COMMITTEE : DETERMINATION OF IRON Analyst, VoZ. 103 Experimental The bathophenanthroline method as recommended by Cluley and Newman3 was selected by the Sub-committee for investigation, except that ascorbic acid was to be used as the reducing agent as it can be obtained with a lower iron content that can hydroxylammonium chloride. It was suggested to the Sub-committee that propylene carbonate was a satisfactory alternative solvent to chloroform for the iron(I1) - bathophenanthroline complex, and it was decided to investigate this at the same time.A collaborative test was arranged in which the nine solutions already distributed to the collaborators for use in the work on the 1,lO-phenanthroline methodl were to be used. Each laboratory was asked to carry out at least two determinations of the iron contents of the nine solutions by the method given in Appendix I and also by virtually the same method but with propylene carbonate as the extraction solvent instead of chloroform. As the use of chloroform is now restricted in some laboratories, two of the collaborators also carried out some work by the method given in Appendix I but with l,l,l-trichloroethane as the extraction solvent.Results arid Discussion The results of the determination of iron at three different levels in each of the three sample materials are shown in Table I and indicaie that extraction of the iron(I1) - bathophen- anthroline complex into chloroform provides a good general method for the determination of iron. Only one set of results is given in Table I for the work in which the iron(I1) - bathophenanthroline complex was to have been extracted into propylene carbonate, as nearly all members found this to be unsatisfactory under the conditions employed. Of the two laboratories that carried out some work in which the coloured complex was extracted into l,l,l-trichloroethane, one prepared only a calibration graph covering the range 5-60 pg of iron, which was satisfactory and from which it was concluded that the sensitivity when using l,l, 1-trichloroethane was very similar to that when using chloroform.The other TABLE I DETERMINATIONS OF IRON IN SOLUTIONS OF TECHNICAL MATERIALS BY THE RECOMMENDED METHOD USING BATHOPHENANTHROLINE AND EXTRACTION INTO CHLOROFORM Sample Aluminium sulphate Ammonium sulphate Laboratory 2 3 4 5 6 7 72 Intra-laboratory Inter-laboratory11 , 1 Value A B C Mean*/vg mi-' 2.185 3.802 6.708 R.S.D.,? yo 1.80 1.80 0.35 hleanlyg ml-l 2.247 4.008 7.036 R.S.D., % 1.56 1.50 0.68 Mean/vg ml-1 2.121 3.854 7.004 R.S.D., yo 5.17 3.16 4.25 Mean/vg ml-1 2.168 3.790 6.667 R.S.D., % 0.73 0.33 0.45 hlean/yg ml-I 2.104 3.825 6.712 R.S.D., yo 0.41 0.81 0.30 Mean/vg ml-l 2.045 3.834 6.834 R.S.D., yo 0.177 2.83 0.53 Mean/vg ml-1 2.258 8 4.052 5 7,183 5 R.S.D., yo 0.127 0.216 0.373 Mean/wg ml-I 2.247 4 4.069 2 7.205 0 R.S.D., Yo 0.251 0.094 0.132 Mean R.S.D.,§ % 1.48 1.34 0.88 Mean/vg ml-1 2.172 3.904 6.919 R.S.D., yo 3.58 3.01 3.14 , 1 A B C 1.505 3.984 5.418 2.50 0.89 0.57 1.500 4.102 5.595 0.94 0.40 0.99 1.487 3.992 5.456 3.57 3.29 4.60 1.496 3.907 5.356 2.27 0.09 0.33 1.553 3.956 5.502 0.74 0.24 0.73 1.547 3.939 5.602 1.90 0.92 1.12 1.554 1 4.138 7 5.590 5 0.237 0.062 0.177 1.572 4 4.174 7 5.665 9 0.081 0.527 0.113 1.53 0.80 1.08 1.524 4.024 5.511 2.07 2.49 1.69 Sodium tetraborate ---- A B C 1.301 2.742 5.678 0.48 2.33 1.20 1.172 2.925 5.914 0.54 0.43 0.92 1.148 2.583 5.712 3.70 6.80 3.40 1.112 2.745 5.686 1.70 0.65 0.16 1.169 2.806 5.698 1.50 0.26 0.65 1.258 2.769 5.623 0.0 0.26 0.65 1.197 3 2.788 2 5.907 7 0.188 0.082 0.064 1.220 0 2.835 3 5.996 3 0.131 0.111 0.296 1.03 1.39 0.87 1.197 2.774 5.777 5.10 3.50 2.41 Instru- ment H700 SP 1800 SP 500 SP 1750 SP 500 DRGT Cary 16 Cary 16 * Mean of three separate complete experiments.3 Extraction into propylene carbonate carried out in parallel with the chloroform method and a t the same time. The high photometric accuracy, wide scale, logarithmic amplification and close thermostatting (0.02 "C) of the Cary 16 instrument warrant the additional significant figure for laboratory 7. f The average of the relative standard deviations within individual laboratories. 11 The unweighted mean of all 24 results for each sample, with the over-all R.S.D. as dehed in the second footnote.No results have been rejected. Relative standard deviation expressed as a percentage = 100 x standard deviationlmean.May, 1978 WITH 4,7-DIPHENYL-1 ,lO-PHENANTHROLINE (BATHOPHENANTHROLINE) 523 laboratory applied the method with extraction of the coloured complex into 1,1, l-trichloro- ethane to the determination of iron in the nine circulated solutions; the results are given in Table 11. TABLE I1 DETERMINATION OF IRON IN SOLUTIONS OF TECHNICAL MATERIALS BY THE RECOMMENDED METHOD WITH EXTRACTION INTO 1 ,l , 1-TRICHLOROETHANE The figures in parentheses are the means from Table I. Iron found/pg ml-I , I Aluminium sulphate Ammonium sulphate Sodium tetraborate - I 7 A B C A B C A B 2.29 3.90 7.01 1.66 3.98 5.71 1.16 2.84 2.12 2.25 (2.17) (3.90) (6.92) (1.52) (4.02) (5.61) (1.20) (2.77) C 5.82 (5.78) Recommendation The Sub-committee recommends that the method given in Appendix I should be used for the determination of iron when the highest sensitivity is required.It is also recommended that if necessary chloroform can be replaced with confidence by l,l,l-trichloroethane as the extraction solvent. APPENDIX Recommended General Method for the Determination of Iron with Bathophenanthroline Object diphenyl-1 ,lo-phenanthroline (bathophenanthroline) is described. A general spectrophotometric method for determining iron involving the use of 4,7- Principle Iron(I1) forms a bright red complex with bathophenanthroline within the pH range 2-9. Any iron(II1) present is reduced to iron(I1) with ascorbic acid. The coloured complex is extracted into chloroform (or 1,1, l-trichloroethane) and its absorbance is measured at the maximum at about 533 nm.Reagents Ascorbic acid solution, 100 g 1-1. Acetate bufer solution, 1 M in acetate (see Note 1). Prepare freshly each week. Dissolve 68 g of sodium acetate tri- hydrate and 28.6 ml of glacial acetic acid in 800 ml of water, adjust the pH to 4.6, if necessary, with sodium hydroxide solution or acetic acid, add 1 ml of ascorbic acid solution and dilute to 1 1 with water. Transfer the solution into a separating funnel, add 10 ml of batho- phenanthroline solution, mix and set aside for 15 min. Extract by shaking vigorously with 10-ml portions of chloroform successively until the solution is colourless. Discard the extracts, extract with two further 10-ml portions of chloroform and also discard the extracts.Store the solution in an iron-free glass or polyethylene container. Dissolve 0.332 g of 4,7-diphenyl- 1,lO-phenanthroline in 1 1 of absolute industrial methylated spirit. Store the solution in an iron-free glass bottle. Bathophenanthroline solution, approximately 0.001 M. Ethanol. Chloroform (or 1 ,1, l-trichloroethane) . Perchloric acid, 60% m/m. Ammonia solution, 5 M. Standard iron solution, 1 mg ml-l. Industrial methylated spirit, 74 0.p. Analytical-reagent grade. Dissolve 8.65 g of ammonium iron(II1) sulphate in 50 ml of concentrated nitric acid and dilute to 1 1 with water.524 ANALYTICAL METHODS COMMITTEE Dilute standard iron solution, 10 pg ml-l. Dilute 10.0 ml of the standard iron solution to 1 1 with water; this solution must be freshly prepared.Procedure Transfer 10ml of the sample solution containing between 0.25 and 1OOpg of iron (see Note 2) into a 100-ml Squibb’s-type separating funnel, add 1 ml of 60% m/m perchloric acid and 5ml of ascorbic acid solution, mix and add 10ml of bathophenanthroline solution. Set aside for 5 min, then add 2 ml of 5 M ammonia solution and 10 ml of buffer solution, mix and set aside for a further 10 min. Add 10 ml of chloroform (see Note 3), shake the funnel vigorously for 30 s, allow the layers to separate and run the chloroform layer into a 25-ml calibrated flask containing 1 ml of ethanol. Extract similarly with two further 5-ml portions of chloroform, run the extracts into the same 25-ml calibrated flask and dilute to the mark with ethanol.Measure the absorbance of this solution in a 10-mm cell at 533 nm against the reagent blank. Preparation of Calibration Graph Transfer appropriate portions of the dilute standard iron solution covering the range 0-100 pg of iron into separate Squibb’s-type separating funnels. Dilute the contents of each funnel to 10 ml with water and proceed with each as described for the sample, beginning a t “. . . add 1 ml of 60% m/m perchloric acid . . .” Construct a graph of iron content, in micrograms, against absorbance. NOTES- When necessary, the acetate buffer solution can be replaced by a citrate or tartrate buffer solution without further modification to the method. By altering the final volume and also the path length of the spectrophotometer cell used, the method can be applied to other ranges of iron contents, as indicated in Table 111. In each instance the figure in line (a) is the amount of iron, in micrograms, that will give an absorbance reading of about 0.004 and that in line (b) is the amount of iron, in micrograms, that will give an absorbance reading of about 1.6. 1. 2. TABLE I11 APPLICATION OF METHOD TO DIF:FERENT RANGES OF IRON CONTENTS Final volume/ml 5 10 25 50 100 5 (a) 0.1 0.2 0.5 1 .o 2.0 10 (a) 0.05 0.1 0.25 0.5 1 .o 7- A 3 Cell path length/mm (b) 40 $10 200 400 800 (b) 20 4,O 100 200 400 20 (a) 0.025 0.05 0.13 0.25 0.5 (b) 10 20 50 100 200 (b) 5 10 25 50 100 40 (a) 0.013 0.025 0.06 0.13 0.26 3. In all instances where chloroform is referred to in the method, it can be replaced if desired by 1,1,1-trichloroethane. References 1. 2. 3. 4. Analytical Methods Committee, Analyst, 1978, 103, 391. Smith, G. F., McCurdy, W. H., jun., and Diehl, H., Analyst, 1952, 77, 418. Cluley, H. J., and Newman, E. J., Analyst, 1963, 88, 3. Analytical Methods Committee, Analyst, 1978, 103, in the press.

ISSN:0003-2654    

DOI:10.1039/AN9780300521

出版商:RSC    

年代:1978

数据来源: RSC

摘要:

AnaJyst, May, 1978 Book Reviews 525 LIQUID CHROMATOGRAPHY DETECTORS. By Pi. P. W. SCOTT. Journal of Chromatogvaphy Library, Volume 11. Pp. x + 248. Amsterdam, Oxford and New York: Elsevier. Distributed by Elsevier North-Holland in USA and Canada. The text of this volume is divided into four parts, covering the general characteristics of liquid- chromatographic detectors, descriptions of bulk and solute property detectors, and their selection and use. The means of detection covered include those of ultraviolet, fluorimetric, polarographic, heat of adsorption, spray impact, radioactivity, electron-capture, transport, dielectric constant, refractive index , electrical and thermal conductivity, density, interferometer, vapour pressure and gas density bridge. In addition, a complete chapter is devoted to spectroscopic detectors and includes descriptions of liquid chromatography - ultraviolet and liquid chromatography - mass spectrometry systems.The author discusses the properties of the detectors, their effect on the quality of the chromato- graphic separations and the precision of the analytical results obtained, descriptions being given for the measurement of these properties. One of the chapters deals solely with practical hints on their operation, while another covers the special techniques of the differential and integral modes of detection and the technique of “vacancy chromatography.” Over the last decade, there have been numerous publications on liquid chromatography in its various forms and at present there seems little lessening of this output.This particular volume has been written by an acknowledged expert in the field and, while some of the content has been covered adequately elsewhere, the book has something extra to offer. For example, there is an interesting description of the spray electrification effect employed as a detector, mainly for use with reversed-phase liquid chromatography, and the use of a rotating gauze disc carrier in a transport system. The total number of references given is about 120; the index is short but the contents pages are very helpful. Very few specific practical applications are included but the book nevertheless is likely to find its way into many industrial and college libraries. D. SIMPSON 1977. Price $34.50; Dfl84. The text is clear and easy to follow and understand.APPLICATIONS OF ION-SELECTIVE MEMBRANE ELECTRODES IN ORGANIC ANALYSIS. By GEORGE E. BAILESCU and VASILE V. COSOFRET. Pp. xii + 235. Chichester: Ellis Honvood. Distri- buted by John Wiley in Australia, New Zealand, South-East Asia, Canada, Europe and Africa and by Halsted Press in North and South America and the rest of the world. 1977. Price k16: $30.40. This is a readable and well organised monograph, consisting of a first part devoted to the main classes and principles of ion-selective electrodes as a base for the main part, over three-quarters of the text being devoted to the complete process of analysis of organic materials, from pre- treatment designed to render the sought species in a detectable form to the actual determination by ion-selective electrodes. It is devoted, as its title implies, to organic analysis per se and is not in any way concerned with determining inorganic ions such as calcium and potassium in body fluids.I t is very much con- cerned with determinations of substances such as glucose, urea, choline and its esters. Ways and means of rendering these in a form detectable by ion-selective electrodes are therefore an important part of the discussion. Thus, taking glucose as an example, attention is given to the enzyme-liberation process of hydrogen peroxide, which can then be determined by the depletion of iodide following its reaction with the peroxide, which is catalysed by molybdate ions. Along- side is discussed the alternative determination of the enzyme-liberated hydrogen peroxide by direct amperometry with a catalytic platinum electrode.The determination of bound halogens is accompanied by discussions of oxygen flask and com- bustion train techniques as a means of conversion into ionic forms. More routine determinations are frequently accompanied by discussions of automated methods employing ion-selective electrodes. There is a genuine attempt by the authors to be critical in approach but, of course, in this they are frequently bedevilled by the scantiness of detail of some literature presentations, especially with less common determinations such as that of tetraphenylarsonium ions. There are some deficiencies in the first part, for example, the range of electrodes depicted on526 BOOK. REVIEWS Analyst, Vol. 103 p. 4 is deceivingly restricted, but otherwise this serves as a good introduction to the newcomer to ion-selective electrode methods.The second part is easily accessible according to different readers' interests. The main chapter headings themselves provide adequate guide-lines but further subdivisions such as heterocyclic aromatic compounds into penicillins, uric acid and vitamins, and hydroxy compounds into alcohols, vicinal glycols and epoxy resins, make for real ease of reference to any part of the text. All in all, the book invites browsing and its good index and copious references (664 in all) make for further delving, but must the price be so high? J. D. R. THOMAS ENVIRONMENTAL N-NITROSO COMPOUNDS-ANALYSIS AND FORMATION. PROCEEDINGS OF THE FOURTH WORKING CONFERENCE HELD [N TALLINN, ESTONIAN SSR, 1-3 OCTOBER 1975.Edited by E. A. WALKER, P. BOGOVSI~I and L. GRICIUTE. IARC Scientijk Publications, Number 14. Pp. xviii + 512. Lyon: International Agency for Research on Cancer. Distributed by the World Health Organization. Available in the UK through HM Stationery Office. 1976. Price Swfr110; $45. The International Agency for Research on Cancer conducts a programme of research concentra- ting particularly on the epidemiology of cancer and the study of potential carcinogens in the human environment. This publication is a record of the papers presented a t the fourth biennial conference in 1975, organised by IARC, on the analysis and formation of N-nitroso compounds. It describes the advances that had been made at: that time in their identification and determination and reports on their formation and occurrence.Studies of this type demand reliable analytical techniques and several papers discuss the use of gas chromatography coupled with chemical ionisation - mass spectroscopy to identify and determine the very low levels of nitrosamines that may be significant. Non-volatile compounds pose another problem and various detection methods coupled with high-performance liquid chromatography have been investigated. Of particular interest to those concerned with the safety of food is an investigation into methods suitable for monitoring food supplies. This demands the cse of techniques available in the ordinary routine laboratory. It was concluded that a gas-chromatographic technique using a nitrogen oxide selective detector warranted further investigation, particularly into the catalytic cleavage of nitrosamines.Much detailed work is reported on the occurrence and formation in vivo and in vitro of nitrosamines. Of particular interest are invest gations undertaken in areas where an abnormally high incidence of oesophageal cancer is recorded. Detailed investigations of the nitrosamine contents of the food intake of typical families in the area were compared with controls. At the time of reporting, no significant differences had been discovered. This book is a fascinating account of the state of knowledge and the advances that had been made a t the time of the meeting a t which the papers were presented. Although it records many successes, the list of recommendations prepared by three sub-committees set up a t the conference indicates the vast amount of work that is still required in this field in order to establish the forma- tion and the role of these compounds in the study of cancer.This collection of papers is to be recommended not only to the reader intimately concerned with the subject, but also to those who are more generally concerned with the presence of minor impurities in foodstuffs. P. S. HALL BIOMEDICAL APPLICATIONS OF IMMOBILIZED E'NZYMES AND PROTEINS. Volume 2. Edited by THOMAS MING SWI CHANG. Pp. xx + 359. New York and London: Plenum. 1977. $47.40. This volume contains, as its first 14 chapters, the applications of immobilised enzymes in the biomedical fields of diagnostics and public health.While some are now well established (e.g., their use in automated and semi-automated analysis and in enzyme linked imniunosorbent assay), their application in the diagnosis of bacterial infections, parasitic diseases and in the field of virology are still fascinating and exciting. The future world of the enzyme-based sensor is foretold with chapters on enzyme electrodes (now commercially available) and the thermal enzyme probe. Using column antibody immobilisation technology, a strategy to exploit this to simplify and auto- mate radioimmunoassay is outlined that eliminates pipetting and centrifuging. This first part of the book is completed by suggestions of p0s:;ible applications of the volatile enzyme product method.May, 1978 BOOK REVIEWS 527 The last eight chapters, under the heading of “Perspectives,” are spectacularly novel and exciting with viewpoints from the physiologist, physicist, biochemist and chemist of future appli- cations of immobilized enzyme technology.I found intriguing the concept of mechanosensitive and sound-sensitive enzyme systems as chemical amplifiers of weak signals. The development of multi-step enzyme systems and recycling coenzyme-dependent immobilised enzyme systems is already feasible. Already the first nylon-tube enzyme supports reviewed in one of the chapters are on sale under the trade- name CATALINKS and can last for 4 000 analyses with negligible activity loss whiIe giving a useful life of 7 000 analyses. The potential of soluble cross-linked enzyme polymers for enzyme therapy mentioned in the book has yet to be fulfilled.However, this book should be read by clinical chemists, biochemists and physiologists and serves notice to instrument manufacturers that immobilised enzymes are no longer research toys but are, and will be, integral parts of modern instruments. Congratulations on an excellent book and one I highly recommend. Artificial organs and cells are realistic targets of the technology. S. A. BARKER NUCLEAR MICROANALYSIS. By VLADO VALKOVI~. Garland Reference Library of Science and Technology, Volume 10. Pp. xii + 415. New York and London: Garland Publishing. 1977. Price $27. This book consists of five chapters, as follows: Fundamentals of Radioactivity (107 pp.) ; Nuclear Reactions (43 pp.) ; Charged Particle Activation Analysis (70 pp.) ; Neutron-activation Analysis (50 pp.) ; and Charged Particle Induced X-ray Emission Spectrometry (100 pp.).Theoretical aspects of the above topics are well described in a readable style. Practical matters are less evenly covered, except in the last chapter. Some applications are included, notably the determination of the elemental composition of fossil fuels. Chemical methods are scarcely mentioned, even in the section on neutron activation. In summary, this book will be useful for teachers wishing to up-date their knowledge of applied nuclear physics, and for research students interested in non-destructive analytical techniques. Chapter 5 on charged particle induced X-ray emission contains material not readily available elsewhere. H. J. M. BOWEN NOSH MANUAL OF ANALYTICAL METHODS.Second Edition. Volume 1. Part I. NIOSH MONITORING METHODS. Volumes 2 and 3. Part 11. STANDARDS COMPLETION PROGRAM VALIDATED METHODS. Volume 1, pp. xii + Methods P & CAM 102-262. Volume 2, pp. vi + Methods S1-134. Volume 3, pp. vi + Methods S135-391. Cincinatti, Ohio : U.S. Department of Health, Education and Welfare, Public Health Service, Center for Disease Control, National Institute for Occupational Safety and Health. 1977. By DAVID G. TAYLOR. Price $8.75, $9.75, $9 ($11, $12, $11.25 outside USA), respectively. DOCUMENTATION OF THE NIOSH VALIDATION TESTS. By DAVID G. TAYLOR, RICHARD E. KUPEL and JOHN M. BRYANT. Cincinatti, Ohio: U.S. Department of Health, Education and Welfare, Public Health Service, Center for Disease Control, National Institute for Occupational Safety and Health, Division of Physical Sciences and Engineering. 1977.Price $15.50 ($19.50 outside USA). In 1971, when occupational safety and health standards for some 400 chemical substances were adopted by the US Department of Labor, there were few analytical procedures for accurately monitoring the exposure of workers to such substances. Three years later the National Institute for Occupational Safety and Health (NIOSH) published a manual containing 39 analytical methods covering 130 of the toxic substances, and a 3-year programme was undertaken jointly by NIOSH and OSHA to produce properly evaluated methods for the remainder. The result is the current Second Edition of the manual, which now contains full details of 337 sampling and analytical methods for use in industrial hygiene environmental monitoring, covering various elements from aluminium to zirconium, inorganic compounds from arsine to zinc oxide, and organic compounds from acetic anhydride to xylidine.Some of the procedures are useful for measuring toxic constituents in blood, urine or body tissues, but most are intended for use in air exposure moni- toring. Part I (Volume 1) contains 110 methods developed by NIOSH or its contractors, each classified according to its reliability on a five-point scale (recommended, accepted, tentative, operational, Pp. xxx + Methods S1-385.528 BOOK REVIEWS Analyst, Vol. 103 proposed). A box form at the beginning of each gives the basic data in a standard manner, e.g., analyte, matrix, range, precision, classification, date issued , date revised.The method format is also standardised and perhaps best illustrated simply by listing the main headings as they are used: 1, Principle of the Method; 2, Range and Sensitivity; 3, Interferences; 4, Precision and Accuracy; 5, Advantages and Disadvantages of the Method; 6, Apparatus; 7, Reagents; 8, Procedure ; 9, Calibration and Standards; 10, Calculations ; 11 , References. A new section has been included in the Second Edition: Part I1 (Volumes 2 and 3) includes 227 methods that were evaluated and validated for accuracy and precision in the joint NIOSH/OSHA Standards Completion Programme during 197‘4-76. These are class B (accepted methods), but have not been field tested. Last b u t by no means least is a fourth and even more massive tome entitled “Documentation of the NOSH Validation Tests.” This presents an introduction to the programme and the statistical protocol used but, more important :For the practising analyst, the data reports.These form the main bulk of the volume and give full detailed technical information to support the validation of 216 of the sampling and analytical methods. Taken as a whole, the prospect of dealing with 7 kg of printed paper seems daunting, but good indexing and a sensible format make it easy to lind one’s way through the mass of detailed informa- tion. It is certain that no analyst with a serious interest in the determination of contaminants in the working atmosphere would want to be without this compilation. The total price of about L25 is far outweighed by the benefits of having not only 337 assessed methods b u t also the back-up data on which the assessments of many of them were made.My one very minor criticism is that the volumes are in paperback, probably to keep the costs within bounds, and the quality of the binding does not augur well for the survival intact of what are likely to be well thumbed books. They follow the same standardised format as those in Part I. G. E. PENKETH THE DETERMINATION OF VINYL CHLORIDE. .A PLANT MANUAL. 3rd Edition. Edited by W. THAIN. Pp. vi + 156. London: Chemical Industries Association Limited. 1977. Price L20 (CIA members, j515). This book presents the considered views of a specialist committee of the Chemical Industries Association on the best analytical methods for the control of vinyl chloride concentrations in and around vinyl chloride monomer and poly(vin:yl chloride) manufacturing plants. The methods cover the analysis of spot samples, area monitoring and personal monitoring and a brief account is given of the philosophy of monitoring adopted by UK manufacturers. Each method is complete in itself and contains information that will enable the user to choose the most appropriate method for his application. A loose-leaf format has been used to facilitate updating, but this will only be of value if information is given as to the procedure for notifying and issuing of new or revised methods. In addition to the methods, the book contains a series of analytical notes containing information on various instruments that have been used in vinyl chloride measurement, useful calibration and sampling techniques and a list of vinyl chloride monomer monitoring services available in the UK. A considerable amount of effort was expended on method development for monitoring vinyl chloride and the Chemical Industries Association is to be congratulated on bringing together all this information in such a digestable form. The co-operation between various companies to solve common problems is a worthwhile exercise an.d it is to be hoped that it will continue in the production of manuals for other toxic compounds. J. CHARLTON

ISSN:0003-2654    

DOI:10.1039/AN9780300525

出版商:RSC    

年代:1978

数据来源: RSC

摘要:

528 BOOK REVIEWS Analyst, Vol. 103 Errata JANUARY (1978) ISSUE, p. 105. Table I: heading of first column should read “Arsenic, parts per 109.’’ Reference 5: the authors should be Van Loon, J. C., Knechtel, J. R., and Pitts, A. E.

ISSN:0003-2654    

DOI:10.1039/AN9780300528

出版商:RSC    

年代:1978

数据来源: RSC