摘要:

296 Analyst, April, 1971, Vol. 96, pp. 296-305 The Separation and Determination of Pen tachlorophenol in Treated Softwoods and Preservative Solutions BY A. I. WILLIAMS (Department of the Environment, Forest Products Reseaych Laboratory. Princes Risborough, Bucks.) A method is described for the extraction, separation and determination of pentachlorophenol or its sodium salt in softwoods and preservative solutions. Pentachlorophenol is separated from lower chlorophenols and wood extrac- tives by adsorption on to Bio-Rad AG 2-x8 anion-exchange resin, eluted with glacial acetic acid, extracted into chloroform, and determined by spectro- photometric measurement of the blue 4-aminophenazone - pentachlorophenol complex. The effect of time and temperature on the oxidation - condensation reaction of 4-aminophenazone with pentachlorophenol has been investigated. The procedure is particularly useful for the study of the distribution of pentachlorophenol-containing preservatives in wood.PENTACHLOROPHENOL and its sodium salt have excellent fungicidal properties and are used extensively in wood preserving solutions. Some preservative solutions contain pentachloro- phenol alone, but in others the compound may be present together with y-benzene hexa- chloride, dieldrin, tri-n-butyltin oxide, or-monochloronaphthalene, zinc naphthenate, copper naphthenate or disodium octaborate. Often it is necessary to be able to determine penta- chlorophenol in preserved wood in the presence of lower chlorophenols, phenols and chlorinated hydrocarbons. The commercial product usually contains between 10 and 15 per cent.of lower chlorophenols, the principal impurity being 2,3,4,6-tetrachlorophenol. The lower chlorophenols interfere in the determination of pentachlorophenol when the existing stan- dard methods1 p2 are being used and chlorinated hydrocarbons will also cause interference in techniques that rely on the determination of the total chlorine content.2 Methods based on neutron-activation analysis? X-ray fluorescence spectrometry,4 com- bustion method^,^ s6 9 7 98 colorimetric techniquesg ,lo ,11 and titration procedures12s13J* have also been described for the determination of pentachlorophenol. However, none of these methods is entirely satisfactory, as they are either insensitive or not specific for pentachlorophenol, or require expensive instrumentation.Often they are slow, tedious and unsuitable for batch analysis, while some give inaccurate results. Methods based on gas - liquid chromato- graphyl5,lG 9 1 7 that are very sensitive and specific are available for pentachlorophenol, but gas - liquid chromatographs are not always accessible and wood extractives interfere in the determination of pentachlorophenol by this technique. In the present work it has been shown that pentachlorophenol can be readily determined by ion-exchange separation and colorimetric analysis with a relatively inexpensive spectrophotometer. Chemical analysis of pentachlorophenol is needed for the study of the loading, per- manence and distribution of preservatives ; because of the variable nature of wood, research projects often require a large number of determinations to ensure significant results.For these reasons, the developed analytical technique should require minimum operator time, permit batch analysis, and give results that are both accurate and relate specifically to penta- chlorophenol. The methodl usually employed at present for separating the pentachloro- phenol from wood involves leaching out the preservative by reflux distillation with sodium hydroxide solution followed by steam distillation of the solution after acidification. This procedure is slow, requires constant attention (which makes it unsuitable when large batches of samples need to be analysed), and does not separate pentachlorophenol from lower chloro- phenols or phenols that occur naturally in wood. Recent work in this laboratory has shown that preservation chemicals can be rapidly and quantitatively leached from thin sections of wood up to 0.3 mm in thicknes~l~9~~s~O or from sawdust.21 It has now been found that 0 SAC; Crown Copyright Reserved.WILLIAMS 297 pentachlorophenol or its sodium salt can be rapidly leached from thin sections of wood with acetic acid - methanol and separated from the lower chlorophenols, phenols and wood extractives by anion-exchange chromatography with AG 2-x8 resin in the acetate form, 200 to 400 mesh. The most sensitive reagent for the colorimetric determination of phenols is 4-amino- phenazone.This reagent reacts with pentachlorophenol in the presence of an oxidising agent between pH 7.0 and 7.5 to form a blue 4-aminophenazone - pentachlorophenol oxidation condensate that can be extracted into chloroform. 2,3,5,6-Tetrachlorophenol also reacts at pH 7.0 to 7.5 to form a chloroform-soluble complex, but this complex shows maximum absorbance at wavelength 480nm and would cause a small but significant interference in the measurement of the optical density of solutions containing the 4-aminophenazone - pentachlorophenol condensate, which shows a maximum absorbance at wavelength 585 nm.2,3,5,6-Tetrachlorophenol is separated from pentachlorophenol during the anion-exchange stage. Ammonium persulphate was used in the oxidation - condensation reaction, as Bencze22 observed that this reagent is much more stable than potassium ferricyanide. During work on the colour formation it was observed that the oxidation - condensation reaction depends on time and temperature.Gas - liquid chromatography was used to check the purity of the pentachlorophenol used for calibration purposes and to examine anion-exchange eluates. Wood extractives in leach solutions examined by gas - liquid chromatography seriously contaminated the column material. The proposed procedure has been successfully applied to the determination of pentachlorophenol in treated samples of Corsican pine, Douglas fir, Japanese larch, Norway spruce, Scots pine, Sitka spruce, Western hemlock and Western red cedar. EXPERIMENTAL COLOUR FORMATION- To bring about the oxidation - condensation of 4-aminophenazone with pentachlorophenol the pH of the solution must be in the range 7.0 to 7.5.A borax - boric acid buffer solution was used to achieve the pH range for the maximum colour intensity. To obtain the correct mixture, solutions of 045 M borax and 0.2 M boric acid were mixed together and added to 50-pg quantities of pentachlorophenol in 1 ml of methanol. Volumes of 0-5 ml of 0.3 per cent. w/v 4-aminophenazone and 0-5 ml of 8 per cent. w/v ammonium persulphate solution were added. After 3.5 minutes the blue complex was extracted into 5 ml of chloroform and its optical density was measured at wavelength 585 nm. The results below showed that the 0.60 0.40 0.20 0.80 I 1 - - - "i I I I I 1 2 4 6 8 10 01 Time/m i nutes Fig. 1. Change of colour intensity with time at 20 "C: A, solution containing 90 pg of pentachlorophenol plus ammonium persulphate ; B, solution containing 50pg of pentachlorophenol plus potassium ferricyanide ; and C , solution containing 40 pg of pentachlorophenol plus ammonium persulphate298 WILLIAMS : SEPARATION AND DETERMINATION OF PENTACHLOROPHENOL [ArtdySt, VOl.96 0.4 ~ 1 ; ; ; 0.2 X 1 2 3 4 5 6 1 2 3 4 5 Time/minutes i Fig. 2. Change of colour intensity with time a t various temperatures: (a), 18 OC; (b), 20 "C; (c), 22 "C; (4, 24 OC; and (e), 26 "C 'i 0 16 18 20 22 24 26 B Temperature/OC Fig. 3. Time and temperature relationship for development of maximum colour intensityApril, 19711 IN TREATED SOFTWOODS AND PRESERVATIVE SOLUTIONS 299 maximum colour intensity was produced in a mixture of 0.15 ml of 0.05 M borax solution and 9-85 ml of 0.2 M boric acid solution.A buffer solution of this composition was used in all subsequent work. Volume of 0.05 M borax solution/ml . . . . 0.05 0.10 0.15 0.20 0.25 Volume of 0.2 M boric acid solution/ml . . . . 9.95 9.90 9.85 9.80 9.75 Optical density. . . . . . . . . . . . 0-243 0.390 0.392 0.366 0.345 During the investigation of buffer solution mixtures it was found that the optical densities of the chloroform extracts were dependent on the length of time between adding the am- monium persulphate solution and extracting the blue complex into chloroform. Two series of solutions of 40 and 90 pg of pentachlorophenol in 1-ml volumes of methanol were diluted with 10 ml of buffer solution and 0.5 ml of 0.3 per cent. w/v 4-aminophenazone solution. Then 0.5 ml of 8 per cent. w/v ammonium persulphate solution was added to each solution and the reactions were allowed to proceed for timed periods (1 to 10 minutes) at 20 "C.Twenty seconds before the end of the period 5 ml of chloroform were added. At the end of the period the solution was shaken for 1.5 minutes, the phases were separated, and the optical density of the chloroform extract was measured at wavelength 585 nm. The optical densities were plotted against the timed reaction period. The curves plotted from the results are shown in Fig. 1, from which it is obvious that the colour-forming reaction depends on time. The experiment was repeated by using solutions containing 50 pg of pentachloro- phenol and with 2 per cent. w/v potassium ferricyanide solution instead of ammonium persulphate solution, but maximum colour intensity occurred much earlier (Fig.1) and the reaction was too quick to allow time for mixing and preparation for the next stage of the procedure. Theref ore, ammonium persulphate was retained as the more suitable oxidising reagent. It was observed that the time for development of maximum colour intensity also varied with different temperatures, so this effect was investigated. Curves similar to that for 40 pg of pentachlorophenol shown in Fig. 1 were plotted from the results of experiments carried out at constant temperatures of 18,20,22,24 and 26 "C in the time range from 1 to 6 minutes. The results (Fig. 2) show that the oxidation - condensation reaction depends on both time and temperature. To obtain a working relationship the time to reach maximum colour intensity was plotted against temperature.A linear relationship was obtained (Fig. 3). This time versus temperature relationship was used during subsequent work to select the 1200 A 0 50 Volume of acetic acid/ml Volume of acetic acid - methanol (1 +9)/rnl Fig. 4. Elution of wood extractives (A) and pentachlorophenol (B)300 WILLIAMS : SEPARATION AND DETERMINATION OF PENTACHLOROPHENOL [ L ~ % L Z I ! ~ S ~ , VOl. 96 period between adding ammonium persulphate and extracting the coloured complex into chloroform for the temperature concerned. SEPARATION OF PENTACHLOROPHENOL- S k e l l ~ ~ ~ has shown that pentachlorophenol and lower chlorophenols can be adsorbed on to anion-exchange resin and selectively eluted with acetic acid - methanol.This technique was adapted and applied to leach solutions containing commercial pentachlorophenol and wood extractives. It was found that pentachlorophenol or its sodium salt can be rapidly and quantitatively leached from thin sections of wood or sawdust with acetic acid - methanol (1 + 9 v/v) . Pentachlorophenol can then be separated from lower chlorophenols and wood extractives by passing the leach solutions through chromatographic columns containing anion-exchange resin Bio-Rad AG2-x8 in the acetate form, 200 to 400 mesh. To determine the volume of solution needed to elute wood extractives, 1 g of Scots pine heartwood was leached with acetic acid - methanol (1 + 9) and the leach solution was passed through the resin column. The eluate was collected in fractions and evaporated to dryness, and the residues were weighed.The weights of the residues were plotted against the volumes of the fractions of eluate and the results (Fig. 4, curve A) show that the bulk of the wood extractives does not remain adsorbed on the resin. Traces do remain on the resin, however, and contaminate the eluate containing pentachlorophenol to give a blank value equivalent to 13 pg of pentachlorophenol. Next, the elution of commercial pentachlorophenol was examined. A volume of 25 ml of acetic acid - methanol (1 + 9) containing 1 mg of penta- chlorophenol, as the sodium salt, was passed through the resin column. Elution was con- tinued with the same solvent, and the collected fractions were analysed for pentachlorophenol by the colorimetric procedure and by gas - liquid chromatography.The results are given in Fig. 5, curves A and B. Lower chlorophenols were detected in the early fractions (curve A) but not in the later fractions (curve B), which contained only pentachlorophenol. B 100 2c i 600 Volume of acetic acid - methanol(l+9)/ml Fig. 5 . Elution of lower phenols (A) and pentachlorophenol (B) It can be seen from Fig. 5 that a large volume of acetic acid - methanol (1 + 9) is needed to remove pentachlorophenol from the resin; hence, glacial acetic acid was used to speed up the elution of the compound. The rapid elution of 1 mg of pentachlorophenol with glacial acetic acid, after elution with 190 ml of acetic acid - methanol (1 + 9), is shown by Fig. 4, curve B. Pentachlorophenol in the acetic acid eluate was concentrated by extraction into 10ml of chloroform.The eluate was diluted with water and the pentachlorophenol was extracted, serially, with 3 volumes of chloroform. The pentachlorophenol was quantitatively transferred into the chloroform extracts together with small amounts of acetic acid. A portion or all, if necessary, of the chloroform extract was evaporated to dryness in a cylindrical separating funnel, held in the horizontal position, by gently sucking or blowing air over theApril, 19711 IN TREATED SOFTWOODS AND PRESERVATIVE SOLUTIONS 301 solution at room temperature. At temperatures up to 21 "C no pentachlorophenol was lost by volatilisation, but slight losses occurred above 21 "C. These losses were predictable and therefore, instead of maintaining the laboratory temperature at or below 21 "C, calibration graphs were constructed at the various temperatures encountered up to 28 "C.The residue from the evaporation stage was dissolved in methanol, then borax - boric acid buffer solution and 4-aminophenazone solution were added. Ammonium persulphate solution was added and the reaction was timed according to the atmospheric temperature by using the graph given in Fig. 3. A 5-ml volume of chloroform was added so that completion of the delivery coincided with the end of the timed reaction period. The blue complex was extracted into the chloroform and its optical density was measured at wavelength 585 nm. ELUTION RATE- Quickfit semimicro chromatographic columns fitted with reservoirs and Buchner flask receivers for use under vacuum were used.The elution rate was adjusted to approximately 1 drop per second by applying gentle suction to the eluate receiver. This allowed the deter- mination to be completed within 4 hours. When the suction technique is being used to assist elution, care must be taken not to reduce the pressure to such an extent that the resin bed is compacted. PREPARATION OF STANDARD SAMPLES- To examine techniques for determining pentachlorophenol in wood it was necessary to prepare standard samples of different species of wood containing a known amount of pre- servative. This was achieved by impregnating wood with aqueous solutions of sodium pentachlorophenate of known different concentrations and using the full-cell process24 and free~e-drying~~ to prevent redistribution of preservative.Weighed flat-sawn blocks of wood of known moisture content, with over-all dimensions of 3 x 2 x 1 cm, cross-section 2 x 1 cm, radial face 3 x 1 cm and tangential face 3 x 2 cm, were subjected to a vacuum of 71 cm of Hg for 3 hours to evacuate the air from the wood cells. While still under vacuum, sodium pentachlorophenate solution was run into the treating vessel until the wood was submerged, and the vacuum was released. A pressure of 10.5 kg cm-2 was applied for 1 hour to the solution containing the wood. The pressure was released and the specimens were removed from the solution and weighed after their surfaces had been superficially dried on filter-paper to remove excess of solution. The sample blocks were freeze-dried to a moisture content of about 6 per cent.From the observed weight of treating solution retained in the blocks the percentage of sodium pentachlorophenate, expressed as the pentachlorophenol equivalent and based on oven-dry wood, was found by calculation to range from 0.001 8 to 0.353 per cent. Owing to the anatomical structure of the wood the distribution of pentachlorophenol in the treated blocks will not be uniform. Concentration gradients of deposited sodium pentachlorophenate can occur across the annual rings; more will be found in the spring or early wood, as the void space is greater, than in the summer or late wood. Therefore, for development work on the procedure, it was decided to use radial sections, cut across the annual rings, because they are more representative of the bulk of the wood.The standard samples were sectioned on a microtome, thin sections being taken at intervals through the block and combined to make one sample. Adjacent thin sections were taken to make up another matched sample for the determination of moisture content of the wood. The weights of the samples taken for analysis were in the range of 0.1 to 1.0 g. EFFECT OF INSECTICIDES AND OTHER FUNGICIDES- Commercial formulations of pentachlorophenol wood-preservative solutions may also contain lindane (y-isomer of 1,2,3,4,5,6-hexachlorocyclohexane), dieldrin, tri-n-butyltin oxide, a-monochloronaphthalene, copper naphthenate or zinc naphthenate. Aqueous solutions of disodium octaborate, used for the diffusion treatment of timber, frequently include sodium pentachlorophenate.The effect of the presence of these compounds on the determination of pentachlorophenol was examined. Solutions containing 250 pg of pentachlorophenol and 10 mg each of lindane, dieldrin, tri-n-butyltin oxide and disodium octaborate were analysed by the proposed procedure. In each case no interference occurred and complete recovery of pentachlorophenol was attained.302 WILLIAMS : SEPARATION AND DETERMINATION OF PENTACHLOROPHENOL [ArtaZyyst, Vol. 96 Lindane, dieldrin, tri-n-butyltin oxide and disodium octaborate were recovered in the first 65 ml of acetic acid - methanol eluate. To investigate the effect of cc-monochloronaphthalene, copper naphthenate and zinc naphthenate on the determination of pentachlorophenol by the proposed procedure, com- mercial solutions containing these chemicals were examined. Samples of the solutions were dissolved in acetic acid - methanol (1 + 9) and put through the procedure.The results given below are in good agreement with those obtained by gas - liquid chromatographic analysis of the preservative solutions. No interference was caused by the organic solvent white spirit, solution A, or the presence of the anti-blooming agent di-n-butylphthalate, solution B. Solution C contained zinc naphthenate and solution D copper naphthenate and cc-mono- chloronaphthalene . Pentachlorophenol content, per cent. w/v Preservative I A \ A 3.17 3.11 B 4.67 4.7 1 C 1.47 1-54 D 3.54 3.45 solution by proposed procedure by gas - liquid chromatography RESULTS The procedure described was used to determine the loading of pentachlorophenol in standard samples of Corsican pine, Douglas fir, Japanese larch, Norway spruce, Scots pine, Sitka spruce, Western hemlock and Western red cedar.The results (Table I) were in good agreement with the calculated pentachlorophenol content. The standard deviation, based on six determinations at the 0-02 per cent. of pentachlorophenol level, was +_ 0.000 5 per cent. To demonstrate the usefulness of the proposed method, the distribution and depth of penetration of pentachlorophenol in Scots pine sapwood that hadbeen dip-treated for 3 minutes in a commercial wood-preservative solution were investigated. A specimen, surf ace dimen- sions 25 x 25 mm and depth 20 mm, was sawn from the bulk of the treated wood.Starting a t the surface, 10 thin sections, 0.1 mm in thickness, were cut on a microtome to form one TABLE I LOADING OF PENTACHLOROPHENOL IN STANDARD SAMPLES COMPARED WITH LOADING CALCULATED FROM SOLUTION RETENTIONS Species and sample number Corsican pine heartwood 1 2 2 . . . . Sitkaspruce 1 . . . . . . 2 . . . . . . Western hemlock 1 . . .. 2 . . . . Douglas fir heartwood 1 . . 2 .. Japanese larch heartwood 1 . . 2 .. 2 .. .. Western red cedar heartwood 1 2 Douglas fir heartwood 1 . . 2 .. 2 . . . . Western hemlock 1 . . .. 2 . . . . Western red cedar heartwood 1 2 . . Scots pine sapwood 1 . . . . Norway spruce 1 . . .. Scots pine sapwood 1 . . . . Calculated pentachlorophenol content based on oven-dry weight, per cent. 0.117 0.122 0-227 0-215 0.346 0.353 0-268 0.262 0.019 0.019 0-014 0.015 0.026 0-033 0.033 0.033 0-001 8 0.001 9 0.002 0 0.002 1 0.002 1 0.002 3 0.003 3 0.003 2 Pentachlorophenol found, per cent.0.113 0.124 0.227 0.222 0.342 0.347 0.276 0.268 0.019 0.019 0.0 14 0.016 0.026 0.034 0-035 0.034 0.001 8 0.001 9 0.002 1 0.002 2 0.002 0 0.002 3 0.003 3 0.003 2April, 19711 IN TREATED SOFTWOODS AND PRESERVATIVE SOLUTIONS 303 sample for analysis. The sampling process was repeated down to a depth of 10 mm from the surface of the specimen. The curve obtained by plotting the pentachlorophenol content of each of the ten samples against depth is shown in Fig. 6. It can be seen from Fig. 6 that it is possible to evaluate rapidly the distribution of penta- chlorophenol-containing preservatives over very small areas.If necessary, it is practicable to analyse each 0-1-mm section of wood separately to obtain a more close distribution pattern. This is not feasible by previously available methods of chemical analysis, I 1 Depth from surface/mm Fig. 6. Distribution of pentachlorophenol in dip-treated Scots pine sapwood. The pentachlorophenol content is based on oven-dry wood METHOD APPARATUS- taps. Reservoirs , 50-ml capacity. Buchner flask receivers, 100-ml capacity. Chromatographic column-Quickfit semimicro, 10-cm effective length, 1-cm bore, with Separating funnels-50-ml cylindrical, 250-ml pear-shaped. S$ectrophotometer-Unicam SP600. REAGENTS- Use analytical-grade reagents when possible. Acetic acid - methanol, (1 + 9 v/v)-Dilute 100 ml of glacial acetic acid to 1 litre with Bu#er solution-Dissolve 0.133 8 g of sodium borate, Na2B40,.10H20, and 6.113 2 g of 4-Aminophenaxone solution, 0.3 per cent.w/v-Dissolve 0.15 g of 4-aminophenazone in Ammonium persulphate soZution, 8 per cent. w/v-Dissolve 4 g of ammonium persulphate Anion-exchange resin-Bio-Rad AG 2-x8, 200 to 400 mesh, chloride form. methanol. boric acid in water and dilute to 500ml with water. water, dilute to 50 ml with water and mix. in water, dilute to 50 ml with water and mix, Prepare freshly each day and store at 0 "C. PREPARATION OF CHROMATOGRAPHIC COLUMN- Slurry sufficient resin into the chromatographic column to form a bed 8-cm deep when the solids settle down. Elute with 10 per cent. w/v sodium acetate solution until chloride cannot be detected in the eluate with silver nitrate solution acidified with nitric acid.Elute, sequentially, with 100m.l of water, Soak the anion-exchange resin in water for 24 hours.304 WILLIAMS : SEPARATION AND DETERMINATION OF PENTACHLOROPHENOL [Analyst, Vol. 96 50 ml of glacial acetic acid and 100 ml of methanol. The resin column is now ready for use. At no stage should the column be allowed to run dry; maintain the liquid level at approximately 0.5 cm above the top of the resin bed. To regenerate the resin after each run elute successively with 50 ml of glacial acetic acid and 50 ml of methanol. PROCEDURE- Weigh the sample and transfer to a 100-ml covered beaker. Add 25 ml of acetic acid - methanol and warm in a water-bath for 10 minutes at 55 "C. Remove the beaker from the water-bath, cool to room temperature, and decant the solution into the reservoir of the chromatographic column.Open the column tap and apply gentle suction to the Buchner flask receiver so that the eluate flows at the rate of approximately 1 drop per second. Wash the beaker wall and cover with 20 ml of acetic acid - methanol, warm the sample and washings at 55 "C for 10 minutes, cool to room temperature, and decant the solution into the column reservoir when the first leach solution has eluted. Repeat once more with another 20 ml of acetic acid - methanol. When this solution has run through the resin, elute with 125 ml of acetic acid - methanol. Discard the acetic acid - methanol eluates. Elute with 50 ml of glacial acetic acid. Transfer the acetic acid eluate to a 250-ml pear-shaped separating funnel, dilute to 230 ml with water, and mix.Extract the solution serially with 5, 4 and 3 ml of chloroform, run off the organic phases into a 10-ml calibrated flask, make up to the mark with chloroform, andmix again. Transfer a suitable aliquot of the chloroform solution to a50-ml cylindrical separating funnel. Carefully clamp the separating funnel in the horizontal position and evaporate the solution to dryness by sucking or blowing air over the solution. Dissolve the residue in 1 ml of methanol, add 10 ml of buffer solution, mix, add 0.5 ml of 0.3 per cent. w/v 4-aminophenazone solution, mix, add 0.5 ml of 8 per cent. w/v ammonium persulphate solution, and mix. Time the reaction period according to the atmospheric temperature by using the graph shown in Fig.3. Twenty seconds before the end of the timed period add 5 ml of chloroform. At the end of the timed period shake the solution for 1.5 minutes, allow the phases to separate, and run off the organic layer through a dry 7.0-cm Whatman No. 1 filter-paper into a 10-mm cell. Measure the optical density of the blue complex against chloroform at wavelength 585 nm. To obtain the pentachlorophenol content of the test solution compare the spectrophotometer reading with a calibration graph. Subtract the blank value obtained in a similar way to that of the test solution. PRESERVATIVE SOLUTIONS- Transfer 1 ml of preservative solution to a 100-ml calibrated flask, dilute to the mark with acetic acid - methanol, and mix. Dilute 1 ml of solution to 25 ml with acetic acid- methanol, transfer to the reservoir of the chromatographic column, and continue as described in the second paragraph of the Procedure. CALIBRATION- Preparation of standard solution A-Dissolve 0.100 0 g of pure pentachlorophenol in chloroform, transfer to a 100-ml calibrated flask, dilute to the mark with chloroform, and mix.Preparation of standard solzdioa B-Transfer, by pipette, with suitable precautions, 10 ml of standard solution A into a 100-ml calibrated flask, dilute to the mark with chloroform, and mix. 1 ml of standard solution A = 1 000 pg of pentachlorophenol. 1 ml of standard solution B = 100 pg of pentachlorophenol. Transfer 0.1, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2 and 1.4 ml of standard solution B into separate cylindrical separating funnels.The volumes taken contain 10, 20, 40, 60, 80, 100, 120 and 140 pg of pentachlorophenol, respectively. Evaporate the solutions to dryness as described under Procedure. Dissolve each residue in 1 ml of methanol and continue as described under Procedure, paragraph 2. Unless the laboratory temperature is controlled, prepare calibration graphs at the atmospheric temperatures normally encountered. This paper is published by permission of the Department of the Environment.April, 19711 IN TREATED SOFTWOODS AND PRESERVATIVE SOLUTIONS 305 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. REFERENCES British Wood Preserving Association, London, Standard 104, 10. British Wood Preserving Association, London, Standard 104, 12. Gheorge, M., Catrina, I., and Constantinescu, O., Drevar Vyskum, 1964, 3, 113. Wright, J. P., and Storks, K. H., American Wood-Preservers Association Annual Convention, Parr, S. W., J . Amer. Chem. Soc., 1943, 30, 764. Bonstein, T. E., Frauenfelder, L. J., and Lohr, L. J., Analyt. Chem., 1953, 25, 1115. Agazzi, E. J., Brooks, F. R., and Parks, T. D., Ibid., 1951, 23, 1011. Safford, H. W., and Stragand, G. L., Ibid., 1951, 23, 520. Wallin, G. R., Ibid., 1950, 22, 1208. Haskins, W. T., Ibid., 1951, 23, 1672. Erkama, J., and Loamanen, A.. Acta Chem. Fenn., 1956, 13, 37. Fritz, J. S., and Keen, R. T., Analyt. Chem., 1953, 25, 179. McKinney, R. W., and Reynolds, C. A., Talanta, 1958, 1, 46. Bruss, 14. B., and Harlow, G. A., Analyt. Chem., 1958, 30, 1836. Barthel, W. F., Curley, A., Thrasher, C. L., Sedlak, V. A., and Armstrong, R., J . Ass. Ofl. Agric. Bevenue, A., Emerson, M. L., Casarett. L. J., and Yauger, W. L., J . Chromat., 1968,38, 467. Argauer, P. J., Analyt. Chem., 1968, 40, 122. Williams, A. I., Analyst, 1968, 93, 111. - , Ibid., 1968, 93, 611. Chicago, 1957, p. 57. Chem., 1969, 52, 294. -, Ibid., 1969, 94, 30. -, Ibid., 1970, 95, 498. Bencze, K., Ibid., 1963, 88, 622. Skelly, N. E., Analyt. Chem., 1961, 33, 271. Cartwright, K. St. G., and Findlay, W. P. K., “Decay of Timber and its Prevention,” Second Edi- Smith, 14. N. R., and Cockcroft, R., Nature, 1961, 189, 163. Received October 29th, 1970 Accepted January 4th, 1971 tion, H.M. Stationery Office, London, 1958, p. 286.

ISSN:0003-2654    

DOI:10.1039/AN9719600296

出版商:RSC    

年代:1971

数据来源: RSC

摘要:

306 Analyst, April, 1971, Vol. 96, $9. 306-309 The Determination of Ethanol in Paints, Inks and Adhesives by Gas Chromatography BY J. R. HARRIS (Department of Trade and Industry, Laboratory of the Government Chemist, Cornwall House, Stamford Street, London, S.E. 1) A gas-chromatographic method for the determination of ethanol in paints, inks, adhesives and similar composite products has been developed by which the time required for the analysis of samples has been greatly reduced. The ethanol is distilled azeotropically from the sample in the presence of toluene, and the distillate is examined directly by gas chromato- graphy without any further treatment other than mixing with an internal standard. The problem of the longer retention time of toluene, compared with those of the lower aliphatic alcohols, has been overcome by the use of back-flushing. From the results obtained by the analysis in duplicate of a series of samples, including a number prepared in the laboratory containing known amounts of ethanol, the accuracy and precision of the method have been established.FOR many years, the most widely used method for the determination of ethanol in an extensive variety of products has been that of obtaining, by distillation, an aqueous mixture containing all of the ethanol, measuring its specific gravity, and finding out the ethanol content by reference to the appropriate Spirit Tab1es.l For essences, tinctures and toilet preparations, Methods I, I1 and I11 of the British Pharmacopoeia2 and Method IV of the British Pharma- ceutical Codex3 are generally used.Paints, inks and adhesives, however, often contain a variety of organic solvents such as alcohols, esters, hydrocarbons and ketones, and for this reason more elaborate and lengthy methods for the determination of ethanol are necessary. By means of an azeotropic distillation with toluene as the entraining agent, the ethanol, together with certain other low boiling- point solvents, can be separated. The distillate thus obtained can then be treated by one of the extraction procedures of the British Pharmacopoeia or of the British Pharmaceutical Codex and an aqueous distillate containing the ethanol ultimately results. In spite of the clean-up procedures used, the distillate may still contain substantial amounts of methanol, propan-2-01, low boiling-point ketones, etc.The determination of ethanol in these circum- stances is particularly time-consuming and relies to a large extent on the identification of the interfering substances and the selection of suitable procedures to effect their removal. If removal is not possible, the ethanol must be determined by a chemical method, the one most frequently used being that of Boorman: in which the ethanol is oxidised to acetic acid. Gas chromatography, having been successfully applied to the determination of ethanol in tinctures, etc.,5 appeared to offer an alternative method which could lead to a considerable reduction in the time required for analysis. Its use in the determination of the ethanol content of such composite products as paints has attracted less attention than in the case of toilet goods or tinctures.Jones, Ritchie and Newburger6 described a method for the analysis of the solvents used in nail lacquers, but were unable to separate ethanol and propan-2-01 ; Hoover' and Haken8 have both reviewed the application of gas chromatography in the analysis of coating materials. However, no method for the routine determination of ethanol in these products appears to have been published. By their nature paints, inks and similar products are not amenable to direct injection into a gas chromatograph, although Jones et al. and Hoover described proceduresin which this was done. Haken states that the solvents must be separated from the resins and pig- ments, and this principle was adhered to in devising the procedure described in this paper.Distillation offered the simplest method for the preliminary separation of the ethanol, but it was essential for the distillate to be homogeneous for subsequent examination by gas 0 SAC; Crown CopyrigFt Reserved.HARRIS 307 chromatography. For this reason the distillation was carried out in the presence of toluene, which is relatively non-toxic and forms an ethanol-rich azeotrope. As the final separation of the ethanol was by gas chromatography, the distillate needed no additional clean-up. Furthermore, it was not necessary to perform a controlled azeotropic distillation; a fairly rapid distillation, with minimal loss of ethanol, was all that was required and this was achieved by using a flask fitted with a still-head and Revenue condenser.The lower aliphatic alcohols were adequately resolved at 160 "C on a 2-m column filled with Chromosorb 102, mesh size 80 to 100; typical retention times were 4 minutes for ethanol and 8 minutes for propan-1-01. Toluene, however, was found to have a retention time of 50 to 60 minutes, so that injections of the toluene distillate could be made only at hourly intervals, thereby lessening the advantages of the rapid distillation and gas-chro- matographic determination of ethanol. To overcome this problem of long retention, the use of both back-flushing and temperature programming was investigated. The former technique was preferred. By reversing the gas flow through the first column after 2 to 3 minutes (from the time of injection) most of the unwanted components were removed from the system and injections could be made at intervals of approximately 15 minutes.As a result of using a two-column system the retention times of the ethanol and propan-1-01 were slightly in- creased, to 5-5 and 11.5 minutes, respectively. Temperature programming permitted injections to be made at intervals of approximately 30 minutes and gave highly satisfactory results, but it was not adopted in view of the superiority of back-flushing. METHOD APPARATUS- A Perkin-Elmer F11 gas chromatograph was used, equipped with a flame-ionisation detector. By the use of suitable pressure gauges and valves, the existing single-column arrangement was modified for back-flushing in accordance with the principles of Deans,9 whose system avoids the use of taps in the sample path.The columns used were both of stain- less steel, with internal diameter 2-2 mm and lengths 0.38 and 2.0 m. The layout was such that the sample passed through the shorter column first, and unwanted substances were back-flushed from this column by reversing the gas flow through it. Nitrogen was used as the carrier gas, and the applied gas pressures were chosen so that no change in pressure occurred at the junction of the two columns when the direction of the gas flow through the first column was reversed. A pressure gauge temporarily connected at this point facilitated the selection of the correct gas pressures. The carrier gas flow-rate was approximately 10 ml minute-l and that of the hydrogen 40 ml minute-l, the temperatures of the oven and injection block being 160 "C and approximately 200 "C, respectively.The flame-ionisation amplifier with the output set at 10 mV was connected to a potentiometric recorder and the peak areas were measured as integrator pulses by a Kent Chromalog 3 integrator set at 100-mV input and connected in parallel with the recorder. The amplifier attenuation was normally set at 20 x lo2 to give peaks of adequate size. PROCEDURE- Standard ethanol solutions-Prepare a series of ethanol - water mixtures covering the range from 0.2 to 20 per cent. v/v of ethanol. Determine the specific gravities of these mixtures and obtain the actual ethanol contents by reference to the Spirit Tab1es.l Prepare the standards for the gas chromatograph by adding 3.0 ml of propan-1-01 to 25.0 ml of each of the ethanol solutions.Distillation of the sample-Weigh out into a 30-ml specimen tube an amount of sample expected to contain not more than 3 ml of ethanol. Transfer the tube and its contents to a wide-necked distillation flask and add 30 ml of toluene, or 20 ml of toluene and 10 ml of benzyl alcohol if the sample contains nitrocellulose. Fit the flask with a still-head and Revenue condenser and distil the contents of the flask, collecting 20ml of distillate, pre- ferably in a 25-ml stoppered measuring cylinder into which 5 ml of toluene have first been placed. (CAUTION-Nitrocellulose, if present, may be precipitated by the toluene with the result- ing possibility of an explosion during the distillation. The benzyl alcohol, by keeping the nitrocellulose in solution, avoids this danger.)308 HARRIS: DETERMINATION OF ETHANOL IN PAINTS, [Analyst, Vol.96 Gas-chromatographic examination-Add 3.0 ml of propan-1-01 to the distillate and mix. If the solution is still cloudy following this addition because of the presence of a small amount of water, add sufficient propan-2-01 (usually 1 or 2 ml) to clear it. Inject a suitable volume into the gas chromatograph, which should conform to the description given under Apparatus. Operate the gas chromatograph, with the gas flow in the forward direction until the ethanol and propan-1-01 have both been eluted from the first column (this takes from 2 to 3 minutes) and then reverse the flow through this column. Calculate from the integrator counts the peak area ratio of ethanol to propan-1-01 for the sample.By using the value obtained, select two standard ethanol solutions whose concentrations are just above and just below that of the sample. Examine these on the gas chromatograph under the same operating conditions except that back-flushing need not be used. Calculation-From the peak area ratios, calculate the ethanol content of the distillate from the equation given in the National Formulary XII,l0 which is as follows- A (Y - 2) + B (2 - X) Ethanol, per cent. v/v, in distillate = Y - x where A and B are the volume percentages of ethanol in the lower and higher standards, respectively, and X, Y and 2 are the peak area ratios of the lower standard, higher standard and sample, respectively. The concentration of ethanol in the original sample is probably most conveniently expressed in terms of the volume of ethanol per unit weight.A suitable form is millilitres of ethanol per 100 g, which, in commercial terms, is identical with litres of ethanol per 100 kg. The concentration in these terms is obtained as follows- If the volume percentage of ethanol in the distillate is V , then V x 25 ml of ethanol per 100 g sample = - W where W is the weight of the sample. RESULTS AND DISCUSSION Before examining samples by this method, it was considered necessary to establish that the presence of toluene and other volatile solvents in the distillate would not adversely affect the precision of the determination of ethanol. A mixture containing methanol, ethanol, propan-2-01, propan-1-01 and toluene was examined on the gas chromatograph five times.The peak area ratios of ethanol to propan-1-01 were calculated and the following results were obtained: 0.746 7, 0-746 6, 0.741 9, 0.741 7 and 0.735 3. The mean of these results is 0.742 4, with a standard deviation of 0.004 6, indicating that adequate precision was obtained. The reliability of the method was further checked by distilling mixtures containing known amounts of ethanol in toluene, adding the internal standard to the distillate and determining the ethanol content with the gas chromatograph by using aqueous ethanol standards for the quantitation. The results in Table I show that satisfactory recovery of the ethanol was obtained. TABLE I ETHANOL CONTENTS OF TOLUENE DISTILLATES Ethanol, per cent. v/v As prepared By distillation Percentage recovery L -l 4.90 4.9 1 100.2 9.86 9.86 100.0 20.19 20.10 99.5 40.17 39.52 98.3 The method was applied to the analysis of a series of typical samples.The actual ethanol contents of some were unknown, but a number of samples prepared in the laboratory, incorporating known amounts of ethanol, were also examined. Each sample was analysed in duplicate and from the results obtained estimates of the precision and accuracy of the method were made. The results of these experiments are shown in Table 11; the ethanol contents of the samples prepared in the laboratory are given in the third column of the table.April, 19711 INKS AND ADHESIVES BY GAS CHROMATOGRAPHY TABLE I1 ETHANOL CONTENTS OF PAINTS AND OTHER COMPOSITE PRODUCTS 309 7 Number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Product 7 Description Actual A --l * * Floor coating . ... .. Nail lacquer . . . . .. Printing ink . . . . .. 13.07 Paint . . .. .. .. 7.03 Acrylate copolymer solution . . 26-15 Paint . . .. .. .. 14.09 Varnish . . .. .. .. Paint . . .. . . .. 9.42 Acrylate terpolymer solution . . * Lacquer . . , . . . . . * Printing ink . . . . . . * Lacquer . . .. .. .. Varnish . . .. .. .. 13-39 Metallised lacquer . . .. Edible ink . . .. .. Varnish . . . . .. .. 7.92 * * * * * Not known. Ethanol, ml per 100 g Found A > & Mean 11-45 11.64 11-55 4.76 4-63 4.70 13-06 12.76 12.91 6-79 7.10 6.95 25-96 24.3 1 25.14 13.84 13.94 13.89 13-63 13-52 13-58 9.16 9.3 1 9-24 3.65 3-81 3.73 29.20 29.26 29.13 33.26 33.26 33.26 11.06 10.68 10.87 13.05 13.17 13-11 5.53 5.24 5.39 31.64 32.55 32.10 7.81 7-80 7.81 From the duplicate results in Table 11, the standard deviation was calculated to be 0.355 ml of ethanol per 100 g of sample.As a number of samples contained known amounts of ethanol the precision of the method was also estimated by using the relationship- x ml of ethanol per 100 g (actual)] The values of the terms a and b were found to be 0.34 and 0.952, respectively, and the residual standard deviation was estimated as 0.366ml of ethanol per lOOg, which is of the same order as that for the variation between the results of replicate determinations. ml of ethanol per 100 g (found) = a + CONCLUSION The use of gas chromatography for the determination of ethanol has been successfully extended into the field of paints, inks and similar composite products. Compared with the existing methods, the procedure shows a great saving in time, and the examination of a sample can be completed within one hour. This paper is published by permission of the Government Chemist. 1. 2. 3. 4. 5. 6. 7. 8. 9. 20. REFERENCES Spirit Tables, H.M. Stationery Office, London, 1955. British Pharmacopoeia, The Pharmaceutical Press, London, 1968, p. 1278. British Pharmaceutical Codex, The Pharmaceutical Press, London, 1968, p. 1380. Boorman, E. J., Analyst, 1939, 64, 791. Harris, J. R., Ibid., 1970, 95, 158. Jones, J. H., Ritchie, C. D., and Newburger, S. H., J . Ass. 08. Agric. Chem., 1958, 41, 673. Hoover, W. S., Paint Varn. Prod., 1964, 54, [7], 69; [8], 41; and [9], 61. Haken, J. K., J . Oil Colour Chem. Ass., 1966, 49, 993. Deans, D. R., J . Chromat., 1965, 18, 477. National Formulary, 12th Edition, First Supplement, American Pharmaceutical Association, Received November 1 lth, 1970 Accepted November 30th, 1970 Washington, D.C., 1965, p. 20.

ISSN:0003-2654    

DOI:10.1039/AN9719600306

出版商:RSC    

年代:1971

数据来源: RSC

摘要:

310 Analyst, April, 1971, Vol. 96, $9. 310-313 The Determination of Residues of Dichlorvos and Malathion in Wheat Grain by Gas - Liquid Chromatography BY S. CRISP AND K. R. TARRANT (Department of Trade and Industry, Laboratory of the Government Chemist, Cornwall House, Stamford Street, London, S.E. 1) A procedure is described for the determination of malathion and di- chlorvos in grain. After extraction with methanol, and clean-up on a charcoal column, if required, the pesticide residues are determined by gas - liquid chromatography on Apiezon L and butane-1,4-diol succinate columns with a phosphorus-sensitive detector. Between the concentrations of 0.25 and 10 p.p.m. both pesticides were recovered from spiked samples with between 87 and 99 per cent. efficiency. MALATHION, added at a concentration of about 10 p.p.m., has been one of the chosen insecti- cides for the treatment of stored grain since about 1960.Its effectiveness at that level against granary pests, combined with its relatively low mammalian toxicity, is probably the main reason for its extensive use in countries, like Australia, where the climate favours the multi- plication of insects in stored grain. The United Kingdom imports from Australia grain that has been treated in this fashion and that may have been given further treatment at the dock- side. Hill and Thompson1y2 have shown that, after the long voyage to the United Kingdom, including passage through the tropics, the malathion content has fallen by degradation to between 2 and 5 p.p.m. (mean value about 4 p.p.m.). Grain treated in a similar manner is also imported from the Argentine and the same authors have shown it to contain about 2 p.p.rn.of malathion on arrival in the United Kingdom. Dichlorvos, which also has a relatively low mammalian toxicity, has also been shown to be very effective against granary pests at the level of 10 p.p.m. in the treatment of cereal products. It is therefore necessary when examining grain for pesticide residues to allow for the presence of both malathion and dichlorvos, which may have been added at separate stages of storage or transportation. The Food and Agriculture Organisation and the-World Health Organisation of the United Nations jointly have recommended tolerances of 8 p.p.m. of malathion and 2 p.p.m. of dichlorvos in cereals.3 Most procedures for the determination of malathion have been based on that of Norris, Vail and Averell: in which malathion is hydrolysed by alkali to sodium 00-dimethylphos- phorodithioate, which forms a yellow complex with copper(I1) ions at about pH 5 and is soluble in carbon tetrachloride.These methods have been applied to fruit and vegetable crops4 y5 and cereal^,^ 97 although interference from co-extracted materials has led to difficulties in some instances. Interference with the colorimetric finish from the presence of other organophosphorus insecticide residues has also been reported.8 A form of the method has been recommended by the Joint Malathion Panels for application to wheat grain, and was used for this purpose by Hill and Th0mpson.l y2 Weisenberg, Gertner and SchoenberglO have recommended another variant for wheat.Instability of the complex may cause fairly rapid fading of the yellow colour; Hillll has studied the stability of this complex and devised a means of reducing dissociation to less than 1 per cent. Jeffs, Lord and Tuppen12 used gas - liquid chromatography to determine carbophenothion and chlorfenvinphos on single wheat seeds by immersion in acetone - hexane (1 + 1) for several hours. Such a method has been shown in the present investigation to be unsuitable for dichlorvos. Elms,13 by using gas - liquid chromatography for the determination, extracted malathion from wheat, after grinding it, by Soxhlet extraction with hexane for 4 hours. This extraction procedure also has been shown in the present investigation to be inadequate for dichlorvos.A spectro- photometric method is available for determining dichlorvos in air.14 More recently, Ivey and Claborn15 developed methods for extracting dichlorvos from milk, egg, and cattle and chicken 0 SAC; Crown Copyright Reserved.CRISP AND TARRANT 311 tissues. The extraction solvent used for muscle, blood and egg was acetonitrile; chicken was extracted with hexane and acetonitrile; and milk was extracted with a mixture of dichloro- methane and hexane. Dichlorvos was determined by gas - liquid chromatography with a phosphorus-selective flame-spectrophotometric detector. St. Clair, Lamberton, Claeys and Gouldingle developed methods for determining dichlorvos vapour emitted from PVC Vapona strips and the residue left in the strip.Various columns used for gas - liquid chromatography were compared. When used in conjunction with the caesium bromide tipped themionic detector, gas - liquid chromatography provides the means of determining very small residues of dichlorvos and malathion. Other advantages are that no chemical treatment is required before the chromatography, thus ensuring specificity, and the method is relatively unaffected by the presence of co-extractives. The method now proposed has therefore been developed for the simultaneous extraction of residues of both of these compounds from wheat, with their determination by gas - liquid chromatography by using this type of detector. Malathion can be recovered from grain by most common solvents but dichlorvos is much more difficult to recover.Because of the volatility and high polarity of dichlorvos a more specific method is required. METHOD APPARATUS- High-speed cofee grinder. High-speed food mixer-For macerating grain with methanol. Centrifuge-This should be able to take 150 ml of solution and rotate a t 2 000 r.p.m. Evaporator-Kuderna-Danish, 500 ml. ChromatograPhic column-This was 30 cm long and of 1.5 cm o.d., fitted with tap and 100-ml reservoir. Conical $?ask-l50-ml capacity, with B24 neck and side-arm. Water-pump. Two 100-ml calibrated $asks. Pear shaped $flask-25-ml capacity, with B14 neck. Pipette, 0.1 mi. An accurate balance. REAGE~TS- Methanol, analytical-reagent grade. Cotton-wool. Celite 545 or 560-Available from Johns Manville Co. Charcoal, Nuchar C-190.Acetone, analytical-reagent grade. Dichlorvos and malathion-Technical grades of known purity. PREPARATION OF STANDARD SOLUTIONS- acetone (solution A). flask and dilute it to 100 ml with acetone (solution B). corresponding to 5 ng of pesticide on the gas - liquid chromatographic column. for each determination. malathion after 1 month. cent. purity for dichlorvos and of 96.3 per cent. purity for malathion. GAS - LIQUID CHROMATOGRAPHIC COLUMNS- These consisted of (a) Apiezon L (1.3 per cent.) and Epikote (0.1 per cent.) on 100 to 120-mesh acid-washed silanised Chromosorb G, and (b) butane-1,4-diol succinate (1.3 per cent.) and Epikote (0.1 per cent.) on the same solid support as (a). The columns were circular, glass, 1.5 m long and 3 mm i.d., fitted to a caesium bromide tipped thermionic detector a Weigh 0.1 g of pesticide into a 100-ml calibrated flask and dissolve it in 100 ml of With a pipette, introduce 0.1 ml of solution A into a 100-ml calibrated Use 5 pl of solution B to give a peak Prepare separate solutions of dichlorvos and malathion.Use a freshly prepared solution B Renew solution A for dichlorvos after 1 week and solution A for The pesticides used in this work were specified by the manufacturers to be of 95-1 per Keep solutions A in a refrigerator.312 CRISP AND TARRANT: DETERMINATION OF RESIDUES OF DICHLORVOS AND [A~zalyst, Vol. 96 the same temperature as the columns. Gas flow-rates were: carrier gas (nitrogen) 15 to 20 ml minute-l; hydrogen 8 to 10 ml minute-l; and air 150 to 200 ml minute-l. The columns were maintained at 220 "C for malathion and 190 "C for dichlorvos. PROCEDURE- Grind 20 g of grain in a high-speed coffee grinder and macerate with three 50-ml portions of methanol.Centrifuge the combined methanolic extracts for a few minutes a t 2 000 r.p.m. Evaporate the clear solution to a small volume in a Kuderna-Danish evaporator. For samples containing residues of less than 0-25 p.p.m., clean up the solution on a charcoal column prepared as follows: place a plug of cotton-wool in the chromatographic column, and cover with a 0-5 to l-O-cm layer of Celite 545 or 560; place 3 g of charcoal in a 150-ml conical flask with a side-arm and stopper, cover with acetone and de-gas by suction from a water-pump for about 1 minute; pour this slurry into the column, allow it to settle, and run off the excess of acetone.Add the methanolic concentrate to the column and elute with 1 O O m l of acetone. Adjust the final volume as required. If a final volume of a few millilitres is required, concentrate the solution in a Kuderna-Danish evaporator. Determine the pesticides in the final solution by gas - liquid chromatography with the columns as specified. Make injections of 5 pl of solution. Do not use a final volume of test solution of less than 5 ml, and for samples with residues in excess of 0-25 p.p.m. adjust the volume of the test solution to obtain a pesticide concentration of about 1 pg ml-l. DISCUSSION PREPARATION OF STANDARD- To attain a reasonable comparison with current commercial practice the untreated grain samples were spiked by covering the grain with a solution of pesticides in acetone and evaporating off the acetone with a gentle stream of air at room temperature.No significant difference was found between samples taken as a whole and as sub-samples. METHOD OF EXTRACTION- Three methods were compared: shaking by hand with a solvent for 1 minute; high-speed maceration with a solvent for 1 minute; and grinding followed by the same maceration procedure. In each instance three 50-ml portions of solvent were used and the grain was spiked with 0.25 p.p.m. of each pesticide. Typical recoveries are shown in Table I. TABLE I COMPARISON OF METHODS OF EXTRACTING THE PESTICIDES FROM GRAIN Method Percentage recovery Percentage recovery Solvent of dichlorvos of malathion Shaking . . . . .. Acetone Maceration . . . . . . Acetone Maceration . . .. . . Methanol Grinding and maceration . . Methanol 23 38 87 98 67 87 95 99 The figures for methanol suggest that some dichlorvos penetrates below the surface of the grain. The best of these methods is clearly grinding followed by maceration of the grain. EXTRACTION SOLVENT- Acetone and dichloromethane give good recoveries of malathion but hexane and aceto- nitrile were less effective; none of these solvents was efficient in extracting dichlorvos as Table I1 shows. Dichloromethane has to be removed completely after extraction, as small amounts of this solvent have a marked effect on the sensitivity of the thermionic detector. Evaporation to dryness is undesirable in view of the appreciable volatility of dichlorvos.Acetonitrile also must be removed so as not to interfere with the determination of dichlorvos, as the thermionic detector responds to nitrogen-containing compounds. Propan-2-01 was unsuitable for both dichlorvos and malathion. Methanol was found to be by far the best solvent for both pesticides.April, 19711 MALATHION IN WHEAT GRAIN BY GAS - LIQUID CHROMATOGRAPHY TABLE I1 COMPARISON OF SOLVENTS FOR EXTRACTING THE PESTICIDES FROM GRAIN Percentage recovery of dichlorvos Percentage recovery of malathion Acetone . . . . 38 87 Acetonitrile . . . . 43 58 Dichloromethane . . 33 100 Hexane . . . . 18 65 Methanol . . . . 87 96 Propan-2-01 . . . . 56 31 313 CLEAN-UP- The clean-up stage may be unnecessary, especially for samples with high residue levels. Some grades of methanol contain impurities that give rise to early peaks that mask the dichlorvos peak; these impurities are removed by the charcoal.On addition of the methanolic concentrate to acetone, a white material, which was shown by infrared spectroscopy to be mainly glucose-like in nature, was precipitated; it was found not to affect the method. RECOVERIES- Because of the high volatility of dichlorvos, a check was made by evaporating to dryness in a gentle stream of air at room temperature 5 ml of acetone solution containing 5 pg of dichlorvos and evaporating 5 p g of dichlorvos in 1OOml of acetone to 5ml in a modified Kuderna-Danish evaporator. The recoveries were 98 and 91 per cent., respectively. On eluting from a charcoal column with acetone 100 per cent.recovery for 5 p g of dichlorvos and 93 per cent. for 5 pg of malathion were achieved. Recovery on the over-all method was found to be 98, 93 and 87 per cent. (3 runs) for dichlorvos and 99 per cent. for malathion with grain samples spiked at 0.25 p.p.m. and 88 per cent. for dichlorvos and 95 per cent. for malathion with grain samples spiked at 10 p.p.m. SENSITIVITY- At normal working amplification, full-scale deflection was obtained with 5 ng of malathion and 1.0 ng of dichlorvos. With a 20-g sample and a final test solution of 5 ml, residues of the order of 0.025 p.p.m. of malathion and 0.005 p.p.m. of dichlorvos can be conveniently determined by the method. CONCLUSION The proposed method is a rapid and sensitive procedure for determining dichlorvos and Permission to publish this paper has been given by the Government Chemist, Department malathion in grain.of Trade and Industry. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. REFERENCES Hill, E. G., and Thompson, R. H., J . Sci. Fd Agric., 1968, 19, 119. Thompson, R. H., and Hill, E. G., Ibid., 1969, 20, 293. Report of the 1967 Joint Meeting of the FA0 Working Party of Experts and the WHO Expert Committee on Pesticide Residues, Food and Agriculture Organisation, Rome, and World Health Organisation, Geneva, 1968. Norris, M. V., Vail, W. A., and Averell, P. R., J . Agric. Fd Chem., 1954, 2, 570. Rowlands, D. G., Analyst, 1964, 89, 498. Bates, A. N., Rowlands, D. G., and Harris, A. H., Ibid., 1962, 87, 643. Bates, A. N., and Rowlands, D. G., Ibid., 1964, 89, 286 and 288. Conroy, H. W., J . Ass. Off. Agric. Chem., 1959, 42, 551. Joint Malathion Panel, Analyst, 1960, 85, 915. Weisenberg, E., Gertner, S., and Schoenberg, J., Ibid., 1968, 93, 443. Hill, A. C., J . Sci. Fd Agric., 1969, 20, 4. Jeffs, K. A., Lord, K. A., and Tuppen, R. J., Ibid., 1968, 19, 195. Elms, K. D., J . Stored Prod. Res., 1967, 3, 393. Hughes, J. T., Analyst, 1963, 88, 318. Ivey, M. C., and Claborn, H. V., J . Ass. Off. Analyt. Chem., 1969, 52, 1248. St. Clair, A. D., Lamberton, J. G., Claeys, R. R., and Goulding, R. L., Ibid., 1969, 52, 1010. Received J u l y 29th, 1970 Accepted November 18th, 1970

ISSN:0003-2654    

DOI:10.1039/AN9719600310

出版商:RSC    

年代:1971

数据来源: RSC

摘要:

314 Analyst, April, 1971, Vol. 96, pp. 314-318 The Microbiological Assay of the Vitamin 336 Complex (Pyridoxine, Byridoxal and Pyridoxamine) with Kloeckera Breois BY E. C. BARTON-WRIGHT (Gallowajr and Barton- Wright, Haldane Place, London, S. 14’. 18) A complete re-investigation of the microbiological assay of the vitamin B, complex (pyridoxine, pyridoxal and pyridoxamine) with the yeast Kloec- kera brevis has been made. The superiority of the proposed method over others e.g., those involving Saccharomyces carlsbergensis 4228 (ATCC 9028), the protozoan Tetrahymena pyriformis and the X-ray mutant Neurospora sitophila 299, is discussed and suitable methods of extraction are described, particularly for blood, liver, human and rat brain, and urine. Kloeckera brevis has also been found to be a more suitable organism for the cup-plate assay of the vitamin B, complex than S.carlsbergensis. The zones of exhibition are sharp and clear and background growth is reduced to a minimum, which is frequently not so with S. carlsbergensis. SERIOUS difficulties have been encountered in the author’s laboratory with the microbiological assay of the vitamin B, complex with the “bottom” yeast Sascharowzyces carlsbergensis 4228 (ATCC 9028) because of the frequent and inexplicable incidence of unrestricted growth in the blanks. This difficulty has apparently been encountered in other laboratories and Garel has suggested that S. carlsbergensis should be completely depleted of pyridoxine before an assay by growing it in a pyridoxine-free liquid medium and then using this medium directly as the inoculum.This modification of technique was tested and proved to be successful for a few weeks, but later the blanks again showed unrestricted growth, which became progressively worse with time. Baker and Frank2 have used the protozoan Tetrahymena pyri formis for the microbiological assay of pyridoxine, pyridoxal and pyridoxamine in blood, brain, muscle and urine. This method, however, has many and serious disadvantages : the composition of the basal medium is complex ; the assay as described occupies a great deal of incubator space ; and the organism, while responding equally well to pyridoxal and pyridoxamine, has only 50 to 80 per cent. activity towards pyridoxine. This last criticism also applies to S . carZsbergensis, which responds equally well to pyridoxine and pyridoxal, but has only about 80 to 84 per cent.activity towards pyridoxamine. The evidence for the behaviour of the X-ray mutant Neurospora sitophila towards the three forms of the vitamin B, complex is contradictory. In any event, the assay with this organism is time consuming, occupies much incubator space and is unsuitable for routine assay work. The yeast Kloeckera brevis has been used in this laboratory for some years for the assay of the vitamin B, complex and, although unacceptably high blanks were occasionally en- countered, nevertheless, most assays were successful. At no time was the massive growth encountered with S. carlsbergensis blanks found with K. brevis. The blanks, however, tended to be high, leading to an undesirable flattening of the standard curve.It was, therefore, decided to test Gare’s “depletion” technique with K. brevis, to ascertain if there was any improvement in the blanks. The attempt proved to be unsuccessful; the same massive growth occurred in the blanks as with S. carlsbergensis and unrestricted growth was even more marked when an inoculum was started up from a freeze-dried culture on a pyridoxine-free basal medium. It therefore occurred to the author that the same situation obtains in K. brevis as in Lactobacillus fermenti 36, which, when used for the microbiological assay of thiamine, has to be maintained on an agar stock medium containing free thiamine, and has to have the 0 SAC and the author.BARTON-WRIGHT 315 inoculum prepared by growing the organism in a liquid medium also containing free thiamine.This analogy was confirmed and no further difficulties were encountered with unacceptably high blanks. The pyridoxine-free basal medium has also been modified in several respects; notably, by substituting a 10 per cent. charcoal-treated malt extract solution for vitamin-free casein hydrolysate, which often proved difficult to free completely from pyridoxine. EXPERIMENTAL MAINTENANCE OF ORGANISM- malt agar slope. The liquid stock culture medium has the following composition: KZoeckera brevis is maintained in liquid stock culture instead of on the conventional Malt extract (10 per cent.) solution . . . . 100 ml Difco yeast extract . . . . . . . . 0.20 g Glucose . . . . . . . . . . . . 2.00 g Pyridoxine hydrochloride .. . . . . 1000 pg Dissolve 10 g of malt extract in approximately 150 ml of water, boil the solution gently until the volume has been reduced to less than 100 ml and allow it to cool. Make the volume up to 100 ml with water and filter under suction with filter aid. Re-adjust the volume of the solution, if necessary, add 0.2 g of Difco yeast extract, 2 g of glucose and 1 000 pg of pyridoxine hydrochloride, adjust the pH to between 4.8 and 5-0 by using bromocresol green as external indicator, and dispense the solution in 20-ml portions into 250-ml conical flasks plugged with cotton-wool; sterilise them by steaming for 30 minutes. Cool in the dark, since all three forms of the vitamin B, complex are photosensitive, especially in hot solution, and store at a temperature not exceeding 4 "C.Slope cultures of the organism should also be maintained as a safeguard against accidental contamination of a liquid stock culture. The slopes are prepared by adding 2 g of agar to the liquid medium described above. The medium is steamed to melt the agar and dispensed in 5-ml aliquots in 1-02 screw-capped bottles, sterilised at 10 p.s.i. for 10 minutes and sloped in the dark. Slope and liquid cultures are renewed at weekly intervals. A slope is prepared in the usual way and incubated overnight at any selected temperature between 25 and 30 "C, with the cap loose. After incubation, the cap is tightened and the culture kept in a refrigerator at a temperature not exceeding 4 "C. The liquid stock culture is prepared by transferring 1*0ml of a culture under strictly aseptic conditions to a fresh flask of medium and incubating for 24 hours on a shaker at any selected temperature between 25 and 30 "C.A fresh liquid stock culture is prepared by suspending the cells from a slope in 10 ml of sterile water and then transferring 1.0 ml of the suspension to a fresh flask of medium and incubating for 24 hours on a shaker at any selected temperature between 25 and 30 "C. BASAL MEDIUM- The pyridoxine-free basal medium (5 x strength) has the following composition : Charcoal-treated 10 per cent. malt . . extract solution (see below) L- Asparagine . . .. . . Ammonium sulphate . . .. Potassium dihydrogen orthophos- phate . . . . . . . . Tripotassium citrate . . . . Citric acid . . . . .. .. Potassium chloride . . .. .. Calcium chloride (anhydrous) . . L-Arginine hydrochloride . . . . L-Histidine hydrochloride . . . . 20.0 ml 1.0 g 1.0 g 0.6 g 5.0 g 0.5 g 1.0 g 0.2 g 20.0 mg 10.0 mg DL-Isoleucine . . . . .. L-Lysine hydrochloride . . .. DL-Methionine . . .. .. DL-Tryptophan . . .. .. DL-Valine . . . . .. .. Niacin (Nicotinic acid) . . .. Calcium d-pantothenate . . .. Thiamine hydrochloride . . .. Biotin .. .. .. .. Inositol . . . . . . .. Inorganic salt solution (see below) Water to . . . . . . . . 20.0 mg 20.0 mg 20-0 mg 20.0 mg 20.0 mg 5 000 pg 5 000 pg 5 000 pg 40.0 pg 30.0 mg 6.3 ml 100 ml After mixing, adjust the pH of the medium to between 4.8 and 5.0 with hydrochloric acid, using bromocresol green as external indicator, store a t a temperature not exceeding 4 "C and use within 7 days.Immediately before an assay, gently warm the solution, add 20g of glucose and make up to a total volume of 200 ml.316 BARTON-WRIGHT MICROBIOLOGICAL ASSAY OF THE VITAMIN Bg [AIzaZySt, VOl. 96 Malt extract solution (10 per certt.)-Dissolve 10 g of malt extract in approximately 150 ml of water and then proceed exactly as described under "Maintenance of organism." After making the volume of the solution up to 100 ml, adjust the pH to between 2.5 and 3.0 with concentrated hydrochloric acid, using bromocresol green as external indicator, add 5 g of a good quality activated charcoal and stir the solution mechanically for 30 minutes. Filter under suction. Repeat the operation twice more with 5-g portions of charcoal. Steam the solution for 30 minutes after final filtration, cool, store under sulphur-free toluene at a temperature not exceeding 4 "C and use within 14 days of preparation.Inorganic salt solution-This solution has the same composition as that devised by the author for microbiological assays with lactic organisms. Dissolve 10 g of magnesium sulphate (MgS0,.7H20), 0-5 g of manganese(I1) sulphate (MnS0,.4H20) and 0.1 g of anhydrous iron(II1) chloride in 250ml of water and add 5 drops of concentrated hydrochloric acid. This solution will maintain its activity indefinitely at room temperature. The recommended additions of trace amounts of boron, zinc, copper, molybdenum and iodate described in the literature have been found to be unnecessary (L. Gare, private com- munication). ASSAY PROCEDURE- A separate standard curve must be established for every assay.The amounts of pyri- doxine hydrochloride required to establish such a curve are: 0.000, 0.001, 0.002, 0.004, 0.006 and 0.008 pg. Prepare a solution of pyridoxine hydrochloride containing 0.002 pg ml-1 and add the following amounts to establish the range of standards: blank (4 ml of water); 0.5 ml of standard solution plus 3.5 ml of water; 1.0 ml of standard solution plus 3 ml of water; 2.0 ml of standard solution plus 2 ml of water; 3 ml of standard solution plus 1.0 ml of water; and 4.0ml of standard solution. Adjust the level of liquid in all of the tubes to 5ml by the addition of 1.0 ml of basal medium and place a glass bead in each tube. Set up the test preparation at three concentrations by taking 1, 2 and 4 ml of the test extract, making the volume up to 4 ml with water and adding 1 ml of basal medium.Add the water and basal medium to each tube with a 5-ml calibrated B-D Cornwall Luer-Lok syringe, and the standard and test solution with a 2-ml calibrated instrument. This will be found to be a more accurate and expeditious method than addition with a manual pipette. Set up all concentration levels of standard and test solutions in triplicate, cap the tubes with aluminium thimbles, with coloured thimbles for the blanks, sterilise by steaming for 20 minutes, cool in the dark and inoculate. PREPARATION OF INOCULUM- Place 10-ml portions of the liquid stock medium described above into 1-oz screw-capped bottles and sterilise them at 10 p.s.i.for 10 minutes, cool in the dark and store at a temperature not exceeding 4 "C and use within 1 month of preparation. The inoculum is prepared as follows: add 1 ml of a liquid stock culture, which should not be more than 48 hours old, under strictly aseptic conditions to a bottle of liquid medium, loosen the cap and incubate at between 25 and 30 "C for 24 hours. Centrifuge aseptically, wash the deposit twice on the centrifuge with sterile distilled water and suspend the deposit in 10 ml of sterile distilled water, and dilute the suspension 1 to 100 with sterile distilled water. Add 1 drop of this final suspension to each tube, but omit to inoculate one of the blanks, so that it can be used to set the colorimeter. Incubate the tubes at any selected temperature between 25 and 30 "C on a shaker in the dark for 24 hours.Whichever temperature is selected for incubation, it is essential that the temperature of the incubator remains constant to +1 "C, otherwise erratic results will be encountered among the replicates, especially among the lower levels of pyridoxine con- centration in the standard tubes. After incubation, add 5 ml of water to each tube, steam for 15 minutes and determine the response nephelometrically. PREPARATION OF SAMPLES FOR ASSAY- The vitamin B, complex occurs naturally not only as free pyridoxine, pyridoxal and pyridoxamine, but also as the phosphorylated derivatives of each form. To obtain an accurate estimate of the vitamin B, complex content of natural materials, it is necessaryApril, 19711 317 that dephosphorylation should first be carried out.The conventional method recommended in the literature is to hydrolyse the material with 0.055 N hydrochloric acid for 4 hours at 15 p.s.i. This method proved satisfactory in our hands for meat and meat products and most plant materials, except cereals, in which the presence of any unhydrolysed starch led to filtration difficulties. A modification of the technique recommended by Jones and Morris: in which takadiastase was used, was found to be more satisfactory with all products, with the exception of those described below. Weigh an appropriate amount of the sample (2 to 5 g) into a 250-ml conical flask and add 50 ml of 0.05 N hydrochloric acid. Autoclave for 1 hour at 15 p.s.i. and cool in the dark. Add 2ml of a 1 per cent.sodium acetate solution and adjust the pH to 4.5, using bromo- cresol green as external indicator, add 0-3 g of takadiastase and incubate overnight under a thin layer of sulphur-free toluene at .37 "C. Steam the flask for 30 minutes to inactivate the diastase, make up to 100ml or other suitable volume with water and filter. Further dilution may be necessary depending upon the pyridoxine content of the material. The final test solution should contain between 0.001 and 0.002 pg ml-l of pyridoxine. The following materials require special extraction treatment : blood, serum or plasma, liver, human and rat brain, and urine. The methods given in detail below are minor modifi- cations of those described by Baker and Frank2 and will be found to be satisfactory.Blood, semvz and @asma-Place 2-ml samples in three 30-ml Quickfit borosilicate glass centrifuge tubes and dilute each with 2 ml of a 0.02 M sodium monophosphate buffer solution (pH 4.5). The buffer is prepared by dissolving 2.76 g of sodium dihydrogen orthophosphate (NaH,PO,.H,O) in 1000 ml of distilled water. Set up at the same time an enzyme blank consisting of 2 ml of distilled water and 2 ml of buffer solution. Stopper the tubes and autoclave for 30 minutes at 15 p.s.i., cool in the dark and add 6 ml of enzyme solution. The recommended enzyme is Clarase, and is prepared by dissolving it to give a concentration of 5 mg ml-l in the buffer solution and filtering before use. Stir the mixture to distribute any coagulum and incubate overnight a t 37 "C under a thin layer of sulphur-free toluene.After incubation, autoclave the tubes for 30 minutes at 15 p.s.i., cool in the dark and centrifuge to remove any debris. Bulk the contents of the three tubes and set up the assay in triplicate by using 1, 2 and 4-ml portions in the tubes. Liver-Accurately weigh 10-mg portions of lyophilised liver powder into six 30-ml Quickfit centrifuge tubes and add 5ml of water to each. Incubate the suspension under a thin layer of sulphur-free toluene for 3 days at 37 "C. Autoclave for 30 minutes at 15 p.s.i., cool in the dark and centrifuge. The contents of the tubes are bulked and 1, 2 and 4 ml of the supernatant liquid are transferred to the assay tubes. Liver contains all enzymes for liberating vitamin B, from proteins during the incubation period.Human and rat brah-Accurately weigh 50-mg portions of lyophilised human or rat brain into two 30-ml Quickfit centrifuge tubes and add 1 ml of buffer solution to each. Set up at the same time an enzyme blank by placing 1-ml aliquots of buffer solution into two 30-ml centrifuge tubes. Stopper the tubes and autoclave for 30 minutes at 15 p s i , cool in the dark and add 4 ml of enzyme solution (Clarase dissolved in water to give a concen- tration of 4 mg ml-l and filtered before use). Stir the mixture to disperse the coagulum and incubate for 3 days under a thin layer of sulphur-free toluene at 37 "C. After incubation, autoclave the tubes for 30 minutes at 15 p s i , cool in the dark and add 20ml of distilled water to each tube. Centrifuge, bulk the contents of the tubes and add 1 , 2 and 4-ml portions of the supernatant liquid in triplicate to the tubes.Urine-With a pipette, introduce four 1-ml aliquots of a 24-hour sample of urine into four 30-ml Quickfit centrifuge tubes and dilute each with 1 ml of buffer solution, autoclave for 30 minutes at 15 p s i , cool in the dark and add 8ml of distilled water to each tube. Centrifuge if necessary. Bulk the contents of the tubes and, by pipette, place in triplicate 1, 2 and 4-ml portions of the supernatant liquid into assay tubes. Enzyme hydrolysis to release the loosely bound vitamin B, is unnecessary. COMPLEX (PYRIDOXINE, PYRIDOXAL AND PYRIDOXAMINE) WITH K. Brevis CUP-PLATE ASSAY- Add 20 g of glucose and 20 g of agar to the basal medium described above, make up to 1000 ml with distilled water, steam until the agar has dissolved, cool to 45 "C and add the inoculum.318 BARTON-WRIGHT The inoculum is prepared in exactly the same way as for the tube assay, but after centri- fuging and re-suspending the deposit in 10 ml of sterile distilled water, the suspension is diluted so that the opacity corresponds to tube No.9 or 10 of the Wellcome series of standard opacity tubes. One millilitre of this suspension is added for every 20ml of medium. Cool the dishes on a flat surface and, after the agar has set, leave in a refrigerator overnight. The rest of the assay conforms with normal cup-plate procedure. The range of pyridoxine concentrations to establish a standard curve is: 0.25, 0.50, 1.0 and 2.0 pgml-1 and the dilutions of the test extract are 1 + 1, 1 + 3, 1 + 7 and 1 + 15.The plates are incubated at between 25 and 30 “C for 20 to 22 hours. CALCULATION- The main responses in the standard series are plotted against the doses and the results of the test samples evaluated by direct reading. The results should not differ among them- selves by more than k10 per cent. The method has the advantage of rapidity and shows immediately whether an assay is valid or not. A regular upward or downward drift in the figures shows the presence of interfering substances in the test solution and makes the assay invalid. As the standard curves are invariably curvilinear by this method of assay, it is strongly advised that, after approximate values have been calculated by direct reading from the standard curve, exact values should be determined by the Wood4 “log-log” procedure. If fiducial limits are required, they should be calculated by computer. DISCUSSION After the addition of the inoculum, thoroughly mix and pour into Petri dishes. The microbiological assay of the vitamin B, complex with Kloeckera brevis has several advantages over previously recommended procedures with other microorganisms. Apart from the relatively simple composition of the basal medium and the straightforward assay technique, the great advantage of this method is that K . brevis shows virtually equal activity towards all three forms of the B, complex; there is, however, a slight but persistently higher activity (2 to 3 per cent.) towards pyridoxamine. This compares favourably with Saccharo- myces carlsbergensis, which shows only 80 per cent. activity towards pyridoxamine, and Tetrahymena pyri formis , which shows equal activity towards pyridoxal and pyridoxamine but only about 50 to 80 per cent. activity towards pyridoxine. REFERENCES 1. 2. 3. 4. Gare, L., Analyst, 1968, 93, 456. Baker, H., and Frank, C., “Clinical Vitaminology,” Interscience Publishers Inc., New York, 1968, Jones, A., and Morris, S., Analyst, 1950, 75, 608. Wood, E. C., Ibid., 1947, 72, 84. p. 66. Received October 5th, 1970 Accepted November 19th, 1970

ISSN:0003-2654    

DOI:10.1039/AN9719600314

出版商:RSC    

年代:1971

数据来源: RSC

摘要:

AnaZyst, April, 1971, Vol. 96, p . 319 319 Book Reviews TOPICS IN ORGANIC MASS SPECTROMETRY. Edited by A. L. BURLINGAME. Pp. xii + 471. New York, London, Sydney and Toronto : Wiley-Interscience, a division of John Wiley & Sons. 1970. Price A10.55. This book, one in the series “Advances in Analytical Chemistry and Instrumentation,” shows how the scope of organic mass Spectrometry has been enlarged in recent years. The book, which presents a wide range of topics in the field, is written by acknowledged experts in their particular areas. There are nine chapters in the book, with an introductory chapter by Beckey and Comes on techniques of molecular ionisation. This is followed by chapters on gas - liquid chromato- graphy - mass spectrometry combination by Stallberg-Stenhagen and Stenhagen, high resolution320 NOTICE TO AUTHORS [Analyst, Vol. 96 mass spectrometry by Biemann, mass spectrometry of complex natural products by Das and Lederer, and applications of mass spectrometry in flavour and aroma chemistry by McFadden and Buttery.There is a chapter on correlation of fragment ion structures with energy of formation by Harrison and another on mechanics of ion decomposition reactions by McLafferty. Another chapter, which is possibly out of harmony with the size of the book, covers the subject of mass discriminations caused by electron-multiplier detectors. Finally, there is a chapter on the application of mass spectrometry to organic geochemistry. The chapters are well written, the diagrams are clear, and the references will bring the reader very up-to-date in the topics covered. The book can be recommended because of its remarkable freedom from errors of any kind. The book will be in the main of interest to specialists in the field. N. R. DALY

ISSN:0003-2654    

DOI:10.1039/AN971960319b

出版商:RSC    

年代:1971

数据来源: RSC

摘要:

320 NOTICE TO AUTHORS [Analyst, Vol. 96 Notice to Authors FURTHER NOTES ON THE WRITING OF PAPERS FOR The Analyst THE Final Report of the Commission on Symbols, Terminology and Units of the International Union of Pure and Applied Chemistry’s Division of Physical Chemistry, as adopted by I.U.P.A.C. on July 7th, 1969, was published in Puve and Applied Chenzistvy, 1970, 21, 3-44. It is entitled “Manual of Symbols and Terminology for Physicochemical Quantities and Units, ’’ and reprints are available from Buttenvorths, London, price jtll. The Royal Society and the Chemical Society are supporting the use of the styles laid down in this Manual. These styles are to a large extent those already in use in papers in The Analyst. However, certain changes are now required to further the standardised presentation of terms and symbols.Numbers-The Manual recommends that the decimal sign should in general be a comma (,), except that in English-language texts it should be a full-stop (.). This will NOT at present be adopted by The Analyst, which will continue to use the centred decimal point (.). However, because of this recommendation, the use of a comma to divide the digits of long numbers into threes (e.g., 34,500) is no longer acceptable. The Analyst will in future use a small space (technically a “hair space”) instead (e.g., 34 500). Physical quantities, units and numerical values-The Manual lays down that a physical quantity equals the product of a numerical value and a unit. For example, a volume (e.g., of titrant) would be- V = 17ml. This statement is to be treated as a mathematical relationship, and may equally well be written as- V/ml = 17.This style will be used in headings to tables and in labels on the axes of graphs, where the numbers represent numerical values- Volume/ml 17 27 37 The diagonal line (“solidus”) will not be used to present “per.” such as grams per millilitre are already expressed in the form: g ml-l. this would appear as- Concentration of solution/g ml-1. It should be noted that the “combined” unit, gml-l, must not have any “intrusive” numbers. To express concentration in grams per 100 millilitres, the word “per” will still be required- Concentration/g per 100 ml (not g 100 ml-1). It may be preferable for an author to express concentrations in grams per litre (g 1-l) rather than grams per 100 ml, viz., instead of “3 per cent. w/v” being expressed as “3 g per 100 ml”, it could well appear as “30 g 1-l.” In accordance with S.I., units For a table (or graph),

ISSN:0003-2654    

DOI:10.1039/AN9719600320

出版商:RSC    

年代:1971

数据来源: RSC