摘要:

June, 19661 EMMOTT AXD LAW 383 A Flame -photometric Method for of Calcium in Lithium Determining Chloride Traces BY P. EMMOTT* AND G. LAW (M.G.O. Inspectorates, Chemical Inspectorate, Headquarters Building, Royal Arsenal, Woolwich, S.E. 18) The determination of calcium in solutions of lithium chloride (1-5 per cent. w/v) containing up to 2 p g per ml of calcium, and up to 1 p g per ml of aluminium has been investigated. The use of different organic solvents has been studied, and the sensitivity of the determination has been increased 3-fold by the use of an aqueous methanol - butanol mixture. It has been shown that the only serious interference effect, that arising from the presence of the aluminium content, can be prevented by the addition of trans-1,2- diaminocyclohexane-NNN’N’-tetra-acetic acid (CDTA) .Rccovcrics from synthetic samples showed no appreciable bias, and replicate results indicated a satisfactory precision, and a sensitivity o f about 0.02 p g per ml. THE use of alcohols and ketones to increase the sensitivity of flame-photometric methods is discussed by Dean,l who indicates that for calcium a 2-fold or 3-fold enhancement of the emission is possible. The organic solvents most commonly used2 93 9 4 include acetone, ethyl methyl ketone, methanol, ethanol, propanol, butanol and acetic acid. In view of the low concentrations of calcium expected to be found in the lithium chloride (between 0.001 and 0.012 per cent.) it was decided to investigate the use of organic solvents in increasing the calcium emission. The samples of lithium chloride, as received, may contain up to 0.006 per cent.of alu- minium (determined spectrographically), as well as small amounts of phosphorus, sulphur and iron, all of which are known1 to interfere with the calcium emission. It was, therefore, proposed to investigate the influence of aluminium and other possible sources of interference, and also methods of eliminating these effects. These include the use of releasing agent^,^,^ e.g., lanthanum and Group I1 elements, as well as complexing agents such as 8-hydroxy- quinoline and EDTA.8 I t was also proposed to consider the use of trans-1 ,2-diaminocyclo- hexane-WXN’X’-tetra-acetic acid (CDTA) for eliminating interference effects. This reagent is reportedg to form more stable complexes with cations than does EDTA. Other methods, e.g., prior removal of the source of interference, or addition of excess of the interfering element were not considered, as the former would considerably complicate the analysis and the latter would result in some loss of sensitil-ity.Ex I ~ E KI ME s TAL REAGEXTS- De-ionised water was used in a11 experiments. Lithium chloride-Further purify analytical-reagent grade quality by passing a 19 per cent. aqueous solution of lithium chloride through an ion-exchange column containing Dowex A1 ion-exchange resin. The resin had previously been converted to the lithium salt by using 2 N lithium hydroxide solution. Dilute the solution obtained as required, or evaporate to dryness for the experimental work. i%fethanoZ-Refine to meet the British Standard Specification 506 : 1958 and re-distil.Calcium-Prepare a standard solution (1000 pg per ml) from analytical-reagent grade Dilute the solution ALuminium-Prepare a standard solution (1000 pg per ml) from analytical-reagent grade All other reagents used were of analytical-reagent grade quality. calcium carbonate neutralised with re-distilled 6 N hydrochloric acid. according to requirements. aluminium dissolved in re-distilled hydrochloric acid. * Present address: Ministry of Defence, R.A.R.D.E., Royal Arsenal, Woolwich, London, S.E. It).384 [Analyst, Vol. 91 APPARATUS- Unicam SP900 $ame spectrophotometer-The instrument was modified slightly so that a Beckman oxy-hydrogen burner can be used in place of the normal burner, and fitted with a concave mirror behind the flame.This mirror effectively doubled the response to the calcium emission. Beckman oxy-hydrogen burner-Care was taken never to allow the burner to run without a liquid feed. Bristol Dynamaster Recorder, (0 to 10 mV). Agla 0.5-ml syringe pipette. Polythene laboratory ware, e.g., bottles, beakers, measuring cylinders. The operating conditions used during the experiment were as follows- EMMOTT AND LAW: A FLAME-PHOTOMETRIC METHOD FOR OPERATING CONDITIONS- Hydrogen pressure 3-2 p.s.i., flow-rate 3.0 litres per minute. Oxygen pressure 14 p.s.i., flow-rate 1.8 litres per minute. Flame position : burner position adjusted to give maximum response to calcium emission. Instrument Gain 3. Slit width 0-1 mm. Any greater slit width resulted in interference from the adjacent lithium peak.Spectrum scanned from 415 nip t o 428 mp, the peak height being measured a t 422 m p by taking the mean distance from the peak maximum to the trough on either side. WASHING PROCEDURE- each series of analyses. for 5 minutes at the conclusion of a series. never allow it to run dry. procedure could result in decreased reproducibility. THE USE OF ORGANIC SOLVENTS- Experiments were carried out with 1.5 per cent. solutions of lithium chloride containing calcium, and with different amounts of each of the following solvents relative to the aqueous solution ; acetone, ethyl methyl ketone, methanol, ethanol, propanol, butanol and acetic acid. The most effective of these solvents in enhancing the calcium emission appeared to be methanol and butanol.The relationship between the percentage enhancement of the intensity of the calcium line and the percentage of methanol and butanol in the solution is shown in Fig. 1. Light the burner and allow it to run for 5 minutes with water passing through it before Pass water through the burner for 1 minute between each sample and Do not switch off the burner at any time, and Preliminary experiments indicated that deviations from this u- Y 50 20 40 Percentage of methanol in water Percentage of butanol in water Percentage of butanol in 80 per cent. methanol Fig. 1 . Effects of the solvent on the calcium cmission The lithium chloride and the calcium content were kept constant. The relationship between the enhancement of the calcium emission and the butanol content of a solution containing 80 per cent.of methanol and 20 per cent. of water is also shown in Fig. 1. From these results it was decided to use as solvent in all subsequent work a mixture of 80 per cent. of methanol, 6 per cent. of butanol and 14 per cent. of water. This solvent increased the calcium emission %fold as compared with the calcium emission from a purely aqueous solution. It was con- sidered advisable to restrict the methanol content to 80 per cent. to avoid solubility and solvent-preparation difficulties. The lithium chloride content of the solutions was restricted to 1.5 per cent., as the use of more concentrated solutions tended to result in blockage of the burner. INTERFERENCE EFFECTS- (1-5 per cent.) of the solutions was found to be 10 per cent. factor, as the lithium chloride content was to be fixed at 1.5 per cent.Lithium chloride-The depression of the calcium emission by the lithium chloride content This was regarded as a constantJune, 19661 DETERMINING TRACES O F CALCIUM I N LITHIUM CHLORIDE 385 Sodium-No significant effect was found on the calcium emission in amounts up to 12-5 ,ug per ml (the highest anticipated sodium content). Phosphorus (as sodium phosphate)-No effect was found on the calcium emission in amounts up to 0-25 pg per ml. Sulphur (as sodium sulphate)-No effect was found on the calcium emission in amounts up to 0.25 pg per ml. Iron (as i r o a ( ~ ~ ~ ) chloride)-No effect was found on the calcium emission in amounts up to 10 pg per ml. A Zmzinium-The percentage depression of the calcium emission caused by varying amounts of aluminium in the 1.5 per cent.lithium chloride solutions containing 0.25 pg per ml of calcium is shown in Table I. At the highest expected aluminium level (1.0 pg per ml) a 32 per cent. depression was observed. TABLE I DEPRESSION OF THE CALCIUM PEAK HEIGHT IN THE PRESENCE OF ALUMINIUM Aluminium content, 0.05 0.125 0.25 1.0 1.25 2.5 PLg Per ml Depression of the calcium peak height, per cent. 0 0 - 15 - 32 - 40 - 60 ELIMINATION OF THE ALUMINIUM INTERFERENCE EFFECT- The use of several reagents suggested in the literature for the elimination of the alu- minium-interference effect on the determination of calcium was investigated. Table I1 shows the depression of the calcium emission of 0.5 pg per ml of calcium in the presence of 1 pg per ml of aluminium and the recommended amount of the particular reagent used.TABLE I1 EFFECT OF VARIOUS REAGENTS ON THE ALUMINIUM SUPPRESSION OF THE CALCIUM EMISSION Depression, Reagent per cent. Comments Lanthanum . . .. . * - 16 Strontium . . .. .. - 22 8-Hydroxyquinoline . . . . -6 High background contribution EDTA .. .. . . - Insoluble Magnesium . . , . . . -21 None . . . . . . - 32 The releasing agents, lanthanum, magnesium and strontium, did not appear to be completely successful in eliminating the interference effect of aluminium. The effect of 8-hydroxyquinoline had not been corrected for its calcium content, and the depression recorded could, therefore, be unrealistic. Also, there was a high background contribution from the reagent, and the 422-mp calcium line appeared on the steep slope of the background and was difficult to measure.The use of CDTA was prevented because of the insolubility of the reagent and its salts in the solvent used for the flame-photometric determination. As an effective anti-suppression agent had not been suggested by the results of these experiments, it was decided to investigate the use of CDTA. This reagent is reported to form more stable complexes than EDTA and its salts were found to be more soluble in organic solvents than those of EDTA. USE OF CDTA- Solutions were made up containing 0-1 M CDTA (as the lithium salt) and 1-5 per cent. of lithium chloride in methanol (80 per cent.), butanol (6 per cent.) and water (14 per cent.). These were made up in the following way. A solution, A , was made up containing 17.4 g of lithium chloride dissolved in a mixture of 930 ml of methanol and 70 ml of butanol.A further solution, B, was prepared, containing386 EMMOTT AND LAW: A FLAME-PHOTOMETRIC METHOD FOR [Analyst, Vol. 91 247 g of CDTA and 68-6 g of lithium hydroxide and made up to 1 litre with water. A 21-5-ml volume of solution A was combined with 3.5 ml of solution B. Calcium and aluminium were added to each 25 ml of these solutions so that each con- tained 1 pg per ml of calcium and varying amounts of aluminium (0 to 2.5 pg per ml). \Vhen measuring the intensity of the calcium line at 422 mp it was necessary to allow for the contribution of the calcium impurity content of the 0.1 M lithium CDTA. This was determined in a separate experiment by a normal standard-addition procedure, and was found to be 0.60 pg per ml. Each calcium peak height (of solutions containing 1.0 pg per ml of calcium and 0.1 M CDTA) was, therefore, multiplied by a factor 14/1.6 to give the cor- rected calcium content of the solution.These experiments were repeated for solutions con- taining 0.05 and 0.01 M CDTA as the lithium salt. In each experiment the calcium emission (corrected) was compared with the calcium emission of a similar solution containing 1.0 pg per ml of calcium but no aluminium or CDTA, and the percentage depression caused by the aluminium was calculated. The relationship between the percentage depression of the calcium emission (corrected for the calcium content of the lithium salt of the CDTA) and the amount of aluminium present is shown in Fig.2 for solutions containing 0.1, 0.05 and 0.01 M CDTA and no CDTA. I t can be seen that a 0.05 hi CDTA solution is effective in eliminating the interference of up to 1.0 pg per ml of aluminium, the depression of 3 per cent. being tolerable. The depression, found by using a 0.1 M solution of CTITA, was less than that found with a 0.05 CDTA solution, but the improvement was not good enough to compensate for the disadarantage of the doubled calcium-impurity content. !! 7 0 - u 80- a 5 sol- I ; L 100; 0 0 5 I 0 I 5 2 0 2 5 c? Fig. 8. Aluminium content, yg per ml Effect of CDTL\ on the depres- sion of t h e calcium emission: curve A, a 0.1 &I solution of CL)T=\; curvc B, a 0-05 R'I solution of CDTX; curve C, a 0.01 M solution of CDTA4; curvc I), a solution containing no CDT-4 I I 0 100 - '0 ' 0'5 ' 1'0 ' 1'5 ' 2 0 Calcium content, pg per ml Fig.3. Calibration graph for calcium in the presence o f CI)TA4 A calibration graph was prepared (Fig. 3) with solutions containing 0-05 M CDTA (as the lithium salt) and 1.6 per cent. of lithium chloride in the methanol (80 per cent.), butanol (6 per cent.) and water (14 pcr cent.) solvent. Each solution contained known amounts of calcium (up to 2 pg per ml) and no aluminium. This calibration graph was a straight line and was used in the analysis of synthetic sample solutions containing varying known amounts of aluminium, but which were otherwise similar to the solutions used in the preparation of the calibration graph. The contribution of the calcium-impurity content of the 0.05 M CDTA solution is the same for both the sample solutions and the solutions used for calibration, and therefore was ignored.Replicate results were obtained at the 0-125 pg per ml level and the 1-875 pg per ml level. The standard deviations were 0-012 ,ug per ml (10 determinations) and 0-115 pg per ml (10 determinations), respectively. The limit of detection (based on the 2a value) was approxi- mately 0.02 pg per ml. The recoveries obtained are recorded in Table 111.June, 1966j DETERMINING TRACES O F CALCIUM I N LITHIUM CHLORIDE TABLE I11 CALCIUM RECOVERIES FROM SOLUTIONS CONTAINING ALUMINIUM AND CDTA 387 Aluminium content, CLg Per ml 0 0.25 0.50 1.0 1.0 1.0 0.25 1.0 Known calcium content, pg per ml 0.126 0.375 0.625 0.875 1.125 1.625 1.875 2.135 Calcium recovered, Percentage Pg Per ml recovery 0.12 96 0.39 104 0.64 102 0.84 96 1.06 94 1.60 98 1.90 102 2.068 97 Mcan recovery 99 per cent.CON c LU s ION s Traces of calcium can be determined flame photometrically by using a Unicam SP900 and a Beckman oxy-hydrogen burner in solutions of lithium chloride (1.5 per cent.) containing aluminium (up to 1 pg per ml). The sensitivity of the determination can be increased 3-fold by using a mixed methanol - butanol- water solvent, and the interference of aluminium can be prevented by the use of diaminocyclohexane tetra-acetic acid. At the 2-pg per ml level the standard deviation is 0.115 pg per ml and at the 0.125 level the standard deviation is 0412 pg per ml, indicating a limit of detection (20) of 0.02 pg per ml. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. Dean, J. A., “Flame Photometry,” McGraw Hill, 1960. Fink, X., iWikrochim. Acta, 1955, 314. Kingsley, G. R., and Schaffcrt, R. R., Analyt. Chem., 1953, 25, 1738. Siebert, H., and Raporport, S., 2. analyt. Chern., 1956, 150, 81. Williams, C. H., Analytica Chirn. Acta, 1960, 22, 163. Dinnin, J. I., Analyt. Chem., 1960, 32, 1475. Debras-Gucdon, J., and Voinovitch, h1. Igor, C. R. Hebd. Se’anc. Acad. Sca., Paris, 1959,240, 3421. West, X. C., and Cook, W. D., Analyt. Chern., 1960, 32, 1471. Schwarzenbach, G., “Die Komplexometrische Titration,” Ferdinand Enlre, Stuttgart, 1955. Received September 28th, 1965

ISSN:0003-2654    

DOI:10.1039/AN9669100383

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

388 NERY : COLORIMETRIC DETERMINATION OF HYDROXAMIC ACIDS [Analyst, Vol. 91 The Colorimetric Determination of Hydroxamic Acids BY R. NERY (Chester Beatty Research Institute, Institute of Cancer Research, Royal Cancer Hospital, Fztlham Road, London, S. W.3) N-Hydroxycarbamates, mono-hydroxyureas and di-hydroxyureas in tissue extracts have been determined by diazotising sulphanilamide with the nitrite produced on oxidation and coupling with M-l-naphthylethylene- diamine. Mixtures of hydroxylamine and hydroxamic acids were determined (a), by selective oxidation a t pH 3.5 and pH 8.0, and ( b ) , after separation of the components by thin-layer chromatography. SOME hydroxamic acids, including the N-hydroxycarbamates, mono-hydroxyureas and di- hydroxyureas have carcinogenic,l anti-tumour,2 anti-viral3 and anti-bacterial4 properties.They also induce chromosomal aberration^,^ y 6 and inhibit thymidine incorporation into DNA of HeLa mono layer^.^ Hydroxamic acids of the type A-COKHOH, where A is aryl, alkyl or aralkyl, are commonly determined as ferric hydroxamates. The method is of limited sensitivity,* 9 9 and is unsuitable for the determination of N-hydroxycarbamateslO and hydroxy- ureall because of the instability and low optical densities of the ferric complexes. Benzo- hydroxamic and acetohydroxamic acids have been determined by diazotisation and coupling after oxidation to nitrite by iodine in acetic acid.g Hydroxamic acids,12 after acid hydrolysis to give hydroxylamine and hydr~xylaminel~ itself, have been similarly determined.These methods have a lower limit of sensitivity of about 0-5 pg of hydroxamic acid per ml of final solution, and hydroxylamine interferes.8 A less sensitive method,1° that can be applied in the presence of hydroxylamine makes use of the pen tacyanoferroate complexes of hydroxamic acids, but arylhydroxylamines and nitroso-aryls interfere.14 In the present method, hydrox- amic acids are determined at final concentrations of to 2 x M in water or tissue fluids, even in the presence of hydroxylamine. METHOD S$ectrophotometer-Optical densities were measured on a Unicam SP500 instrument, Potassium chloride - hydrochloric acid b u f e r , 0.1 M-A mixture of 0.1 M aqueous solutions Potassium hydrogen phthalate b u f e r , 0.1 M-A mixture of 0.1 M aqueous solutions of Acetate b u f e r , 0-1 M-A mixture of 0.1 M aqueous solutions of sodium acetate and acetic Phosphate b u f e r , 0.1 M-A mixture of 0.1 31 aqueous solutions of sodium dihydrogen Borate bulfjer, 0.1 ?ti --,4 mixture of 0.1 M aqueous solutions of boric acid and sodium Iodine--A 0.1 N aqueous solution.Sodium thzosulphate-A 0.1 N aqueous solution. Szd#haniZamide-A solution of 1 g sulphanilamide in 100 ml of 2 N hydrochloric acid. ~7-1-1L'a~hthyZethyZenedzamine hydrochloride-A solution of 0.05 g of the hydrochloride in Trichloroacetic acid-An aqueous solution of 36 g of the acid in 100 ml of solution. APPARATC'S- REAGENTS- of potassium chloride and hydrochloric acid. potassium hydrogen phthalate and hydrochloric acid. acid. orthophosphate and disodium hydrogen orthophosphate.hydroxide. 100 ml of water. THIN-LAYER CHROMATOGRAPHY- Glass plates were coated with films of silica gel G of 0.30-mm thickness, and the chromato- grams were developed in ( a ) , a mixture of 3 volumes of acetone and 7 volumes of light petroleum (b.p. 40" to 60" C), or ( b ) , a mixture of 3 volumes of ethanol and 7 volumes of propanol. Hydroxylamine was detected on chromatograms with (i), ammoniacal aqueousJune, 1966; NERY: COLORIMETRIC DETERMINATION OF HYDROXAMIC ACIDS 389 2 per cent. silver nitrate. Hydroxamic acids were detected with (i), (ii), 1 per cent. aqueous w/v sodium amminoprusside containing 0.1 per cent. w/v of magnesium chloride hexahydrate, (iii), 1 per cent. w/v ferric chloride in aqueous 50 per cent. ethanol, or (iv), 0.01 N iodine in phosphate buffer, pH 8-0, followed by sulphanilamide and N-1-naphthylethylenediamine hydrochloride, in the order given.All the compounds reduced reagent (i) and gave mauve spots with reagent (iu); the hydroxamic acids gave red to purple spots with reagent (ii) and purple-to-blue spots with reagent (iii). The R, values of the following compounds in solvents (a) and ( b ) , respectively, are given in parentheses : hydroxylamine hydrochloride (0, 0.21), methyl X-hydroxycarbamate (0.18, 0.65), ethyl N-hydroxycarbamate (hydroxyurethane) (0.23, 0.79), n-propyl N-hydroxycarbamate (0.37, 0-Sl), n-butyl N-hydroxycarbamate (0.41, 0-86), benzohydroxamic acid (0-22, 0.86), hydroxyurea (0, 0.59), dihydroxyurea (0, 0.71) and N-phenyl-X'-hydroxyurea (0.28, 0.87). MATERIALS- carbamateslO and other hydroxamic acids1* were prepared as described.aminelg was prepared by reducing nitromethane with zinc dust and ammonium chloride. Phenylhydr~xylamine,~~ hydroxyurea,16 N,N'-dihydroxyurea,17 the alkyl N-hydroxy- A'-Methylhydroxyl- PROCEDURES- Determination in water-The hydroxamic acid was dissolved in 0.5 ml of water (in triplicates); the solutions were treated with the following reagents in the order given and mixed after each addition: 0.5 ml of phosphate buffer (pH 8-0), 0-1 ml of iodine, 0.1 ml of sodium thiosulphate, 1-9 ml of sulphanilamide and 1.9 ml of N-1-naphthylethylenediamine hydrochloride. After 30 minutes, the optical density of the solution was measured in a 1-cm cell at 540mp against a reagent blank. The optical density was unchanged after 6 hours at 23" C.Hydroxylamine and dihydroxyurea were also determined by substituting 0.5 ml of acetate buffer (pH 3-5 and 4-5, respectively), for the phosphate buffer in the above procedure. Determination in an aqueous suspension of rat liver microsomes or in whole rat liver homogenate-The suspension of microsomes was prepared as described.20 The homogenate was prepared by homogenising 40 g of fresh rat liver in pH 7.4 phosphate buffer in a Potter & Elvehjem (1936)-type homogeniser with a Teflon pestle, and diluting to 200 ml with the same buffer. The hydroxamic acid was dissolved in 1 ml of water (in triplicates), mixed with 3 ml of the suspension of microsomes or homogenate, treated with 1 ml of trichloroacetic acid 1. 2. Molarity x 10-6 Fig.1. The optical density of hydroxylamine and some of its derivatives at varying concentrations, as deter- mined by procedure 1 : graph =, hydroxylamine (oxidised at pH 3.5); graph n, N,N'-dihydroxyurea; graph A, hydroxylamine ; graph A, hydroxyurea ; graph 0, N-hy- droxyurethanc ; graph 0, benzohydroxamic acid. Graphs 0 t o 0, compounds oxidised at pH 8.0390 NERY : COLORIMETRIC DETERMINATION OF HYDROXAMIC ACIDS [Analyst, Vol. 91 (reagent lo), mixed, and spun by centrifuge to give a clear supernatant liquid. A 0.5-ml portion of this liquid was treated with 0.3 ml of 0.5 N aqueous sodium hydroxide a t 0" C. I t was then treated with the following reagents in the order given, and mixed after each addition: 0.5 ml of pH 8-0 phosphate buffer, 0.1 ml of iodine, 0-1 ml of sodium thiosulphate, 2 ml of sulphanilamide and 1.5 ml of N-1-naphthylethylenediamine hydrochloride.The optical density was measured, as in procedure 1, against a blank made up similarly from 1 ml of water and 3 ml of the suspension of microsomes or homogenate. 3 (a). Determination in the presence of hydroxylamine : aqueous solutions of hydroxamic acid containing approximately the same or lower molar concentrations of hydroxylanzine-A 0-5 ml portion of the solution (in triplicates) was treated with 0.5 ml of pH 3.5 acetate buffer; the following reagents were added in the order given and mixed after each addition: iodine, sodium thiosulphate, sulphanilamide and N-1-naphthylethylenediamine as in procedure 1. The optical density was measured, as in procedure 1, against a reagent blank, and the con- centration ( x x 10P M) of hydroxylamine in the final solution determined by reference to a standard calibration curve (see Fig.1) obtained in a similar way for varying concentrations of hydroxylamine. Another 0.6-ml portion of the solution (in triplicates) was determined as in procedure 1. The contribution, A , of the hydroxamic acid to this optical density, B, was equal to B - C, in which B is the optical density measured at pH 8.0 and C the optical density of a x lop6 M hydroxylamine as determined by reference to the standard optical density - concentration curve for hydroxylamine at pH 8.0 (see Fig. 1). The concentration of hydroxamic acid was determined by reference of A to the standard optical density - concen- tration curve for the hydroxamic acid a t pH 8.0.This method was inapplicable to the determination of a mixture of dihydroxyurea and hydroxylamine, as the former, when oxidised at pH 3.5, gave about 75 per cent. of the colour given by the same solution oxidised at pH 8.0 (see Fig. 2). For this mixture, procedure 3 ( h ) , below, was applied. 1 I I I I I I 0 I I 3 5 6 7 8 9 PH Fig. 2. Effect of the variation of the pH of the oxidation medium on the optical density of the final solution during the determination of hydroxylamine and some of its derivatives by procedure 1: curve 0, N - hydroxyurethane; curve o, hydroxylamine ; curve a, hydroxyurea; curve 0, N,N'-dihydroxyurea 3 (h) . Determination in the presence of hydroxylamine aqueous solutions of hydroxarnic acid containing a higher molar concentration of hydroxylamine or a mixture of dihydroxyurea and hydroxylamine-Because the accuracy of the determinations by procedure 3 (a) was found toJune, 19661 NERY : COLORIMETRIC DETERMINATION OF HYDROXAMIC ACIDS 391 decrease as the value of the ratio A / B decreased, the components of the mixture in a measured volume were separated as described in the Section thin-layer chromatography.Samples of the known components were also run alongside the mixture and detected as described, to aid in the location of the components on the developed chromatograms. Each component was scraped off the chromatogram, eluted with water and the concentration determined as in procedure 1. RESULTS EFFECT OF pH ON THE OXIDATION OF HYDROXYLAMINE AND HYDROXAMIC ACIDS WITH IODIYE- The pH values were maintained during the oxidation stage with the following buffer solutions: potassium chloride - hydrochloric acid for pH 1.5 to pH 2.0; potassium hydrogen phthalate for pH 2.5 to pH 3.0; acetate buffer for pH 3.5 to pH 5.0; phosphate buffer for pH 5-5 to pH 8.0 and borate buffer for pH 8.5 to pH 10.0.The following compounds were oxidised : methyl and ethyl N-hydroxycarbamates, hydroxyurea, dihydroxyurea and hydroxyl- amine. M aqueous solution of the test compound (in triplicates) was treated with 1 ml of a 0.01 N solution of iodine in the appropriate buffer, mixed, treated with 0-1 ml of sodium thiosulphate, 2 ml of sulphanilamide and 1.4 ml of N-l-naphthyl- ethylenediamine, and mixed immediately after each addition. This was found to be especially important after the addition of sodium thiosulphate, otherwise cloudy solutions were obtained.The optical density was measured as in procedure 1. The results obtained are plotted in Fig. 2, except those for methyl N-hydroxycarbamate which gave a curve identical with that shown for the ethyl homologue; they show that whereas there were only small differences in the oxidation by iodine of hydroxylamine and the hydroxamic acids studied at pH's above 7 , significant differences occurred at lower pH values. At pH 3.5, hydroxylamine and di- hydroxyurea were oxidised whereas hydroxycarbamates and hydroxyurea were unaffected. EFFECT OF VARIATION OF TIME OF OXIDATION- M aqueous solution of hydroxyurea, N-hydroxyurethane or benzohydroxamic acid was treated with phosphate buffer and iodine reagents as in procedure 1, mixed, and allowed to stand for varying time intervals before the remainder of procedure 1 was followed.The results (see Fig. 3) indicated that the optical densities of the final solutions remained unchanged when the compounds were oxidised for 1 to 20 minutes. A 0.5-ml sample of a 2 x A 0-5-ml sample of a 2 x I 1 I I 1 4 8 I2 16 20 Time. minutes Fig. 3. Effect of the variation of the time of oxidation on the optical density of the final solution during the determination of hydroxy- urea (curve o), N-hydroxyurethane (curve 0) and benzohydroxamic acid (curve A) DETERMINATION I N WATER OR IN SUSPENSIONS OF RAT-LIVER MICROSOMES OR IN RAT-LIVER HOMOGE NATE- Hydroxylammonium chloride or the hydroxamic acid was dissolved in U.5 ml 01 water and determined as in procedure 1.The results (see Fig. 1) show that Beer's law was obeyed within the concentration range of Solutions of hydroxylamine, N-hydroxyurethane, hydroxyurea and benzohydroxamic acid in 1 ml of water were treated with 3 ml of an aqueous suspension of rat-liver microsomes, or rat-liver M to 2 x M in the final solutions.392 [:Analyst, Vol. 91 homogenate, and determined as in procedure 2. The results (molar extinction coefficients are given in Table 11) showed small deviations from those obtained in the determination of the same compounds in water. Standard deviations in triplicate determinations varied between &0-02 and ,t0-08. DETERMINATION IN THE PRESENCE OF HYDROXYLAMINE- M aqueous solution of hydroxylammonium chloride were mixed, and a 0.1-ml sample applied as a streak along the origin of a glass plate coated with silica gel G; this was then air-dried and developed in solvent ( a ) .Areas corresponding to each component were scraped off the chromatograms, eluted with 2 ml of water, and the component in 0 6 m l samples of the eluate determined as in procedure 3 ( b ) . A mixture of equal volumes of a 4 x M aqueous solution of hydroxyurea and a 6 x M aqueous solution of hydroxylammoniom chloride, or of 4 x M aqueous solutions of dihydroxyurea and hydroxylammonium chloride, was similarly examined after the chromatograms were developed in solvent system ( b ) . Mixtures of equal volumes of a 2 x M aqueous solution of hydroxylammonium chloride, or similar mixtures of hydroxylammon- ium chloride and hydroxyurea, were determined according to procedure 3 (a).The results (see Table I) show that the components of mixtures of each of the three hydroxamic acids with hydroxylammonium chloride were separately determined by the procedures described. Standard deviations in triplicate determinations in these experiments varied between & 0.05 and k0.11. TABLE I NERY : COLORIMETRIC DETERMINATION OF HYDROXAMIC ACIDS Equal volumes of a 4 x M aqueous solution of N-hydroxyurethane and a 6 x M aqueous solution of AT-hydroxyurethane and a 2 x DETERMINATION OF HYDROXYLAMINE - HYDROXAMIC ACID MIXTURES I N WATER Optical density x 100 a t A Percentage recovery ‘-7 Hydroxyl- Hydr- 7 pH 3.5 pH 8.0 r-----------J- Mixture (final concentration) Theoretical Found? Theoretical, 5 oundt amine oxamic acid A.N-hydroxyurethane (10-5 M) plus 10--5~)s . . . . 60 57 36 36 95 97 (ii) Hydroxylamine M ) / / 40 37 74 70 92 57 (2) Hydroxylamine (1.5 x (iii) Hydroxylamine (5 X M ) [ / . . 20 19 55 55 95 103 B. Hydroxyurea M) plus (i) Hydroxylamine (1-5 x 1 0 - 5 ~ ) $ . . 60 61 38 35 101 92 (ii) Hydroxylamine (lW5 M ) \ / 40 39 76 75 98 100 (iii) Hydroxylamine (5 x 10-6 M)II . . 20 21 57 53 105 87 C. S,S’-dihydroxyurea (10-5 M) plus hydroxylamine (lW5 11)s 40 4 0 39 34 100 87 * Determined by reference to concentration - optical density curve for Iiydroxylamine a t pH 3.5 (see t Mean of three determinations. Fig. 1. r\ (i), B (2) and C were determined by reference to the concentration - optical density ciirve for the hj-droxamic acid a t pH 8.0; others were determined by summation of the two appropriate values by reference to the concentration - optical density curves for hydroxylamine and the 11)-droxamic acid a t pH 8.0 (see Fig.1). 4 Iletermincd according to procedure 3 ( b ) . / / Determined according to procedure 3 (a). INTERFERING SUBSTANCES AND THE GENERAL APPLICABILITY OF PROCEDUI~ES 1 AND 2 TO THE M aqueous solutions of each of the compounds listed in Table I1 was determined according to procedure 1 so that the final concentration of each compound was 2 x 10-5 M. Sodium nitrite was determined similarly, except that the reagents iodine and sodium thiosulphate were replaced with 0.2 ml of water. Hydroxylamine, N-hydroxyurethane, hydroxyurea and benzohydroxamic acid were also determined according to procedure 2.The results indicate that only those compounds capable of yielding nitrite under the oxidative conditions used, gave a positive reaction. DETERMINATION OF HYDROXAMIC ACIDS- A 0.5-ml sample (in triplicates) of 2 xJune, 19661 NERY : COLORIMETRIC DETERMINATION OF HYDROXAMIC ACIDS TABLE I1 MOLAR EXTINCTION COEFFICIENTS ( E ) OF HYDROXYLAMINE AND RELATED COMPOUNDS DETERMINED ACCORDING TO PROCEDURES 1 AND 2 393 Molar extinction coefficient x lo-, in Formula of compound determined NH,OH . . . . . . . . CH,O.CONHOH . . . . . . C,H,O.CONHOH . . . . . . C,H,O.CONHOH . . . . . . C,H,O.CONHOH . . . . . . H,N.CONHOH . . . . . . C,H,.NH.CONHOH . . . . C,H,CONHOH . . . . . . CO(NHOH), . . . .. . (-CONHOH), . . . . . . [-C( = NH) NHOH 1 , . . . . CH,CO.N (C,H,) OH . . .. C,H,,NO,II . . . . . . . . CH,NHOH . . . . . . .. H,NOCH, .. . . .. .. C,H,NHOH . . . . . . . . C,H,OCO.NHOCO,C,H, . . . . NaNO, . . . . . . .. H.CONHOI3 . . .. . . Water* 38, 40: 35 36 38 37 38 34 32 34 39, 38s 35 55 0 0 0 0 0 0 50 Liver microsomest 36 35 - - Liver homogenate f 35 35 - - - 36 - - 33 - * Determined according t o procedure 1 a t pH 8.0 unless otherwise indicated. 7 Determined according to procedure 2. : Determined according to procedure 1 a t pH 3.5. 5 Determined according to procedure 1 a t pH 4.5. 11 yannose oxime. - h o t determined. DISCUSSION Many hydroxamic acids show important biological effects1 t o '; they form precipitates or coloured complexes with a variety of inorganic cations, and some are used as analytical reagents.21 y22 The iron, copper, cobalt and nickel chelates are coloured.22 Hydroxamic acids are formed, i n vivo, as biological intermediates in the metabolism of some amino-aryls or a ~ e t a m i d o - a r y l s , ~ ~ ~ ~ and some have been isolated from microbial fermentations.25 The oxidation of hydroxamic acids by several oxidising agents in aqueous and non-aqueous media yielded a variety of products, apparently by a free-radical mechanism.l* Compounds of the type A.CONHOH, where A was aryl, alkyl, aralkyl, amino or alkoxy, have been oxidised by iodine in aqueous bicarbonate solutions to yield condensation products mainly of the type A.CONHO.CO.A.ls 2 A.CO.NHOH + rO] + A.CO.NH0.CO.A + ONO- + other products where LO] was the oxidising agent.I t is unlikelv that hydroxylamine was produced at any stage of the reaction as hydroxamic acids, except N,N'-dihydroxyurea, were not osidised under some acidic conditions (see Fig. 2) under which hydroxylamine was rapidly osidised. Since 1 mole of hydroxamic acid produced between 68 and 70 per cent. of the colour produced by 1 mole of nitrite under the same conditions (see Table 11), the above relationship is qualit at ive. Hydroxylamine was rapidly oxidised by iodine in acid and alkali, while the hydroxamic acids were more readily oxidised in alkali. This marked influence of the pH of the reaction medium may be related to the difference in the oxidation potentials of the neutral, cationic and anionic species, e.g., -CO.NHOH, -CO.NH,OH and -CO.NHO, and to the energy requirements for the removal of a hydrogen atom to give free radicals of the type observed by electron spin resonance studies.26 These pH effects have been utilised to develop a method (procedure 3 (a)) for the determination of hydroxamic acids in the presence of small amounts of hydroxylamine.The procedures described were applicable to the determination of those compounds that gave a nitrite when oxidised by iodine. Substituted hydroxylamines in which the nitrogen The present work shows that the nitrite wits also formed, i.e., -t394 NERY : COLORIMETRIC DETERMINATION OF HYDROXAMIC ACIDS [Analyst, VOl. 91 or oxygen atom was attached to a saturated carbon atom, or to an aromatic ring, e.g., the N-aryl, O-aryl or alkylhydroxylamines, failed to give the reaction (see Table 11).N-Aryl- hydroxamic acids, on oxidation with lead tetra-acetate, gave the corresponding nitr~so-aryls.~~ Procedure 3 (b) indicated that a mixture of hydroxamic acids may be determined after separation of the components by the chromatographic procedures described. The author thanks Professor E. Boyland for his interest in this work. This investigation has been supported by grants to the Chester Beatty Research Institute (Institute of Cancer Research: Royal Cancer Hospital) from the Medical Research Council and the British Empire Cancer Campaign for Research, and by the Public Health Service Grant No. CA-03188-08 from the National Cancer Institute, U.S. Public Health Service. 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. 26. 27. REFERENCES Bercnblum, I., Ben-lshai, D., Haran-Ghera, N., Lapidot, A., Simon, E., and Trainin, N., Biochem. Stearns, B., Losee, K. A., and Bernstein, J., J . Med. Chem., 1963, 6, 201. De Sousa, C. P., Boyland, E., and Nery, R., Nature, 1965, 206, 688. Abe, Y., Osaka Shiritsu Daigaku Igaku Zasshi [ J . Osaka City Med. Centre], 1960, 9, 4029; Chem. Oppenheim, J . J., and Fishbein, W. N., Cancer Res., 1965, 25, 980. Boyland, E., Nery, R., Peggie, K. S., and Williams, K., Biochem. J . , 1963, 89, 113P. Young, C. W., and Hodas, S., Biochem. Pharmac., 1965, 14, 205. Seifter, S., Gallop, P. M., Michaels, S., and Mcilman, E., J . Biol. Chem., 1960, 235, 2613. Bergmann, F., and Segal, R., Biochem. J., 1956,62, 542. Boyland, E., and Nery, K., Analyst, 1964, 89, 520. Fishbein, W. N., and Carbone, P. P., Science, 1963, 142, 1069. Mirvish, S. S., Analyst, 1965, 90, 244. Feigl, F., and Demant, V., Mikrochem. Acta, 1937, 1, 132. Boyland, E., and Nery, R., Analyst, 1964, 89, 95. Kamm, O., in “Organic Syntheses,” Collective Volume I, J. Wiley & Sons Inc., New York and Dresler, W. F. C., and Stein, R., Justus Liebigs ,4nnln Chem., 1869, 150, 242. Boyland, E., and Nery, R., Nature, 1964, 203, 1379. _ _ _ _ _ , J . Chem. SOC., ( C ) , 1966, 354. Becimann, E., Justus Liebigs Annln Chem., 1909, 365, 204. Booth, J., and Boyland, E., Biochem. J . , 1964, 91, 362. Chamblin, V. C., Diss. Abstr., 1963, 24, 2243. Yale, H. L., Chem. Rev., 1943, 33, 209. Cramer, J. W., Miller, J . A., and Miller, E. C., J . Biol. Chem., 1960, 235, 885. Nelson, N., and Troll, W., Fedn Proc. Fedn Amer. SOCS Exp. Biol., 1961, 20, 41. Kaczka, E. A., Gitterman, C. O., Dulaney, E. L., and Folkers, K., Biochemistry, 1962, 1, 340. Gutch, C. J. W., and Waters, W. A., J . Chem. SOC., 1965, 751. Baumgarten, H. E., Staklis, A., and Miller, E. M., J . Org. Chem., 1965, 30, 1203. Pharmac., 1959, 2, 169. Abs, 1964, 61, 9977. London, 1941, p. 445. Received January 14th, 1966

ISSN:0003-2654    

DOI:10.1039/AN9669100388

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

June, 19661 SHORT PAPERS 395 Plant Mineral SHORT PAPERS Analysis by X-ray Fluorescence Spectrometry BY R. JENKINS, P. W. HURLEY (M.E.L. Equipment Co. Ltd., London) AND V. M. SHORROCKS ( H i l l Farming Research Organisation, Edinburgh) THE speed and versatility of X-ray fluorescence spectrometry is well established,' and many papers have been published describing the application of this technique to the elemental analysis of a wide range of materials2 As a result of improvements effected in instrument performance over the last few years, considerable attention has been directed to the analysis of trace quantities of metals in media of low average atomic number, The use of this method in plant analysis is therefore a natural development, as mineral elements in plants are normally present in trace quantities.Several workers3 to l3 have described the use of the method in the quantitative analysis of plant materials for a limited number of elements. The purpose of this paper is to report on a recent programme of work in which the analysis of plant materials by X-ray fluorescence spectrometry has been extended beyond that so far reported, for both number and concentration levels of the elements. Mention is also made of the preparation of synthetic standards by using impregnated cellulose as a carrier. EXPERIMENTAL APPARATUS-- The work was carried out on a standard Philips PW1540 X-ray spectrometer utilising a 1-kilowatt constant-potential generator. The equipment was modified by fitting an ultra-thin window to the gas-flow proportional counter. One of the limiting factors in the X-ray analysis of longer wavelengths is that counter efficiency is low owing to absorption of a large part of the relatively low-energy radiation by the counter window.This window normally consists of a 6-p sheet of poly(ethy1ene terephthalate) coated with a thin layer of aluminium. The purpose of the aluminium is to establish a homogeneous field around the anode of the counter; this, in turn, ensures the degree of energy resolution required for the successful application of pulse height selection. Recent successful attempts to extend the range of X-ray spectrometry into the soft X-ray and vacuum ultraviolet region14 have resulted in the development of ultra-thin flow counter windows, and in this work two such windows were used, one consisting of a 4-p poly(ethy1cne terephthalate) sheet and the other of a 1-p polypropylene sheet.With neither was a conductive coating used, as the disadvantage of a slight loss (about 15 per cent.) of the counter resolution was far outweighed by the increase in window transmission. The polypropylene window was used only for sodium as its long-term stability had not been established, although this particular window was, in fact, used for several days without showing signs of rupture. PROCEDURE- A range of plant materials consisting mainly of grasses was dried and milled to pass through a 0-5-mm sieve. The samples were then made into pellets at a pressure of 5 2 0.5 tons per sq. inch with sufficient sample to give a disc about 30 mm in diameter and 5 mm thick.I t is important that the thickness of the sample be in excess of the critical depth with respect to the shortest wavelength to be measured, which in this work was zinc K,, 1.437 A. On the assumption that the sample pellet density was unity, the critical depth was calculated as 2.9 rnm, after allowing for the 35" take-off angle of the spectrometer. Equipment conditions were established to give the largest value of (peak counting rate of analysis wave1cngth)l - (background counting rate)*, which is the optimum requirement for X-ray spectroscopic procedures.15 A list of the selected operating conditions is given in Table I.396 Element Sodium . . .. Magnesium . . Aluminium, phosphorus, potassium . . Calcium, titanium Manganese, iron . . Nickel, copper, zinc SHORT PAPERS TABLE I OPERATING COKDITIONS [Analyst, Vol.91 X-ray tube Crystal Detector Chromium Gypsum Flow proportional* plus pulse height Chromium Ammonium Flow proportional plus pulse height selection dihydrogen selection phosphate Chromium Penta-erythritol Flow proportional plus pulse height Chromium Lithium fluoride Flow proportional Gold Lithium fluoride Flow proportional Gold Lithium fluoride Scintillation selection * Flow proportional counter fitted with 1-p polypropylene window. All measurements were made under total vacuum conditions. Intensity measurements mere made on a range of elements between sodium and zinc, by a ratio technique. In general, a sufficient number of counts was taken to give a coefficient of variation within 1 per cent.entailing analysis times of between 4 and 200 seconds. Calibration curves were constructed by plotting count rates against element concentration. The slope, m, of such a calibration curve is a useful parameter as it represents the sensitivity for a particular element expressed in terms of counts per second per cent. The lower limit of detection was taken as the concentration giving a count rate equal to three times the standard deviation, u, of the background count rate.16 Since total counts, N , equals counting rate, R, multiplied by time, T , and a = .W; 30 of Rb = 3(~Vb)'/Tb, where Tb is the analysis time. Hence the lower limit of detection of counts due to the analytical wavelength is 3(Rb/Tb)', or expressed in terms of con- centration lower limit of detection = 3(Rb/Tb)4/m.TABLE I1 COUNTING RATES AND DETECTION LIMITS? Element Sodium . . .. Magnesium . . Aluminium . . Phosphorus . . Potassium . . Calcium . . Titanium . . Manganese . . Iron . . . . Nickel . . .. Zinc . . .. Copper . . . . m, counts per second for 1 per cent. concentration .. .. 16-5 . . .. 36 .. . . 480 .. . . 520 . . . . 5400 . . . . 35,000 . . . . 57,000 .. . . 20,000 . . . . 43,000 . . . . 138,000 . . . . 60,000 .. . . 100,000 R b counts per second 17 10 3 6 50 100 90 90 90 800 900 900 Tb seconds 200 100 100 20 4 4 10 20 20 10 10 10 Detection limit, per cent. 0.053 0.026 0.001 1 0.003 1 0*0020 0.0004 0.0002 0.0002 0*0001 0.0002 0*0005 0.0003 t T,imit of detection taken as 3(h'h/Tb).t/nz, where m equals counts per second for 1 per cent. concentration, Rh the background counting rate and T h the counting time of the background.RESULTS AND DISCUSSION In addition to the twelve elements listed, significant responses werc obtained from silicon, chlorine and titanium, b u t lack of analytical results prevented an assessment of detection limits being made. However, fairly accurate predictions can be made by interpolation of the results obtained for elements of similar atomic number, as the correlation between detection limits and atomic number follows a smooth curve with predictable adjustments for variations in the absorption coefficient of the matrix.17 The correlation found between measured intensity and concentration of an element was usually linear, as would be predicted for such a low average atomic number matrix.When the concentration of an element reached a relatively high level (e.g., potassium a t 1 per ccnt.), the corre- lation followed a smooth curve in which the slope decreased with increase of concentration of the Table I1 lists the counting rates and the calculated detection limits.June, 19661 SHORT PAPERS 397 measured element. This self-absorption effect is fairly common in X-ray spectroscopy, and is always found when the mass-absorption coefficient of the measured element for its own radiation is significantly greater than that of the matrix. It was also found necessary to correct the calcium curve for potassium concentration, and this was achieved with a simple linear correction factor. In addition, the slope factor for magnesium showed variations of up to 20 per cent.depending upon the absorption coefficient of the matrix. It is to be hoped that the second of these matrix effects can be cornpensated for, by use of an incoherently scattered tube line. PREPARATION OF SYNTHETIC STANDARDS- Finall\-, an assessment was made of the feasibility of preparing synthetic standards by adding “doped” cellulose to plant material. Preliminary measurements indicated that (1 + 1) dilution of a typical plant sample with cellulose made no significant difference to the slope factors of ele- ments between calcium (atomic number 20) and zinc (atomic number 30). A range of chromium standards was prepared by mixing equal weights of plant material with cellulose that had been impregnated with known amounts of chromium. Impregnation was carried out by adding known volumes of a standard solution of chromic chloride to weighed samples of cellulose, and drying overnight a t 110” C.A calibration graph was constructed covering the range 0 to 0.1 per cent. chromium, and was found to be linear with a slope factor of 21,600 counts per second for 1 per cent. concentration of the element. This figure compares very favourably with the predicted value from neighbouring atomic numbers (e.g., manganese gives 18,000 counts per second for 1 per cent. concentration of the element under identical conditions). The technique can also be applied to elements of lower atomic number than calcium, provided that the sample-to-cellulose ratio is increased. This is necessary as, owing to the shorter path length of these radiations, addition of large amounts of diluent significantly lowers the slope factors.We have found, however, that by increasing the sample-to-cellulose ratio to 10 to 1, the reduction in the slope factor for magnesium is only of the order of 1 per cent. 1. 2. 3. 4. 5. 6. I . 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. RE FE I< E N c E s Liebhafsky, H. A., Pfeiffer, H. G., Winslow, E. H., and Zemany, P. D., “X-Ray Absorption and Emission in Analytical Chemistry,” John Wiley & Sons Inc., New York and London, 1960. Buwalda, J., Edztor, “Review of Literature-X-Ray Spectrometry, ” Philips : Eindhoven, 1965. Brandt, C. A, and Lazar, V. -A,, J . .4gric. Fd Chem., 1958, 6, 306. Lazar, V. -A., and Beeson, K. C., J , Ass. Off. Agric. Chem., Washington, 1958, 41, 416. Handley, R., Analyf. Chem., 1960, 32, 1719. lvhittig, I,. D., Buchanan, J . K., and Brown, A . T.., J . Agric. Fd Chern., 1960, 8, 419. Lytle, F. IV., Dye, \\‘. B., and Seim, H. J . , “-4dvances in X-Ray analysis,” Volume 5, Plcnum: Sew York, 1961, p. 433. Sature Conservancy, Rep. Nat. Consevv., 1961, 50. Vose, P. B., Lab. Pract., 1961, 10, 30. Ball, D. F., and Pcrkins, D. F., Nntuve, 1962, 194, 1163. Chaussidon, J., “Proc. Colloque de Madrid,” Philips: Eindhoven, Volume 2, 1962. Chesnin, L., and Beavers, .\. H., Agron. J . , 1962, 54, 487. Norrish, I<., J . Sczenf. Instrum., 1962, 39, 659. Fischer, L). IY., and Baun, \V. l,., U.S. Technical Document, Report ,Yo. RTD-TDR- 63-4232, 1964. Mack, )I., and Spielberg, N., Spectvochim. ‘4cfa, 1958, 12, 169. Spielberg, N., and Bradenstein, )I., A p p l . Spectvosc., 1963, 17, 6. Jenkins, li., “Proceedings of the Exeter Conference on Limitations of Detection in Spectrochemical Received LVozlenabev 4/11, 1965 Xnalysis,” Hilger and M’atts Ltd., London, 1964,

ISSN:0003-2654    

DOI:10.1039/AN9669100395

出版商:RSC    

年代:1966

数据来源: RSC

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June, 19661 SHORT PAPERS 397 The Determination of Total Available Oxygen in Di-tertiary Butyl Peroxide BY D. B. ADAMS (Laporte Chemicals L t d . , Luton, Redfordshive) THE procedure described by Vaughan and Rust1 for the analysis of di-t-butyl peroxide, based on the reaction with hydriodic acid in glacial acetic acid solution a t 60" C, is not entirely satisfactory, as the calculation of results depends upon the use of an empirical factor. Mair and Graupner2 have recently published details of a method that involves boiling the sample with a mixture of hydro- chloric acid, acetic acid and sodium iodide under reflux. This is somewhat cunibersome in non- routine use and suffers from a relatively high blank.398 SHORT PAPERS [Analyst, Vol. 91 To achieve complete reaction of di-t-butyl peroxide with iodide it is necessary to maintain a high reaction temperature, a high hydrogen ion concentration and a high iodide concentration. The latter requirement serves not only to increase the rate of reaction but also to maintain the equilibrium of the reaction- as far to the right as possible, and thus to minimise any possible loss of iodine from the system.The high hydrogen ion concentration is necessary as the reaction is almost certainly catalysed by the presence of acid. A free-radical mechanism is discounted because the thermal decomposition of di-t-butyl peroxide in a solvent is slow even a t 110" C3 The presence of a mineral acid is necessary to obtain a sufficiently high hydrogen ion concentration. As Mair and Graupner2 have observed, conditions must also be maintained as anhydrous as possible.A relatively simple method was devised to satisfy these requirements and also to avoid errors arising from the loss of the volatile sample before iodine liberation could take place. The latter was achieved by weighing the sample into a gelatin capsule before analysis. I, + I- + 1.7 hl E TH o D APPARATVS- Gelatin capsules-Size KO. 3 gelatin capsules, as supplied by Parke, Davis & Co. Reaction jlasks-50-ml calibrated flasks fitted with ground-glass stoppers held in place by Water-bath-A water-bath thermostatically controlled a t 80" f_ 1" C. springs. R E A G E N T - All reagents should be of recognised analytical-reagent grade. Acetic acid (glacial), nitrogen saturated-Hcat acetic acid (glacial) under reflux for 30 minutes.Sodium iodide. l i ~ ~ d r o c l ~ l o ~ i c acid, concentrated, sp.gr. 1 . 1 8. Sodium thiosulphate solution, 0.1 N . Starch solution, 0.5 per cent. w / v , freshly prepared. Ile-inineralzsed water saturated with nitvogen-Boil de-niineralised water for 10 minutes. Cool the acid while bubbling nitrogen through the solution for 15 minutes. Cool the liquid while bubbling nitrogen through the water for 15 minutes. PROCEDURE- Introduce into the flask 3.0 g of sodium iodide, 20.0 nil of acetic acid arid 2.0 nil of hydrochloric acid as rapidly as possible, replacing the stopper between additions. Flush the flask again with nitrogen for 30 seconds and stopper firmly. L'l'eigh about 0.2 g of sample into a gelatin capsule. Place the capsule in the flask and fix the stopper in position with small springs.Place the flask in the water- bath a t 80" C for 15 minutes, swirling i t frequently. ,Ifter 15 minutes cool the flask and wash the contcnts into ;L BiK-nil beaker with about 150 nil of de-riiineralised water, saturated ivith nitrogen. Titrate the solution with 0.1 N sodium thiosulphatc solution, adding starch as the indicator \\.hen the end-point is approached. (This should not exceed 0.4 nil of the 0.1 s sodium thiosulphate solution. If this value is escecclctl it is probable that the sodium iodide used is impure.) Flush a reaction flask with nitrogen for 30 seconds. Fit the self-sealing cap tightlJ-. I'repare a reagent blank in exactly the same way. DISCUSSIOK The method described above can be used to determine the total a\-ailable oxygen content.The di-t-butyl peroxide content may be calculated after subtracting the available oxygen content arising from other impurities. These impurities are thought to be mainly hydroperoxide in character, although not necessarily t-butyl hydroperoxide. Their total may be determined by a suitable room-temperature available-oxygen procedure. *An iron (111)-catalysed method in \I hich saturated sodium iodide and glacial acetic acid4 are used has been found to be reliable for this purpose. Some samples analysed by the method described were also examined by gas - liquid chromato- graphy, and a determination made of the total impurity content. A I-metre, &inch external diameter, stainless-steel column, packed with 20 per cent.w/w di-isodecyl phthalate on firebrick, was used a t 75" C on a Perliin - Elmer Fractometer 451 with a flame-ionisation detector. A GasJune, 19661 SHORT PAPERS 399 Chromatography Ltd. integrator IE 165 was also used. The total inipurity content was deter- mined by using the relationship of the integrated peak areas to that obtained from a known con- centration of t-butyl hydroperoxide. This is an empirical approach, but is felt to be justified a t the low levels concerned. RESULTS The results given in Table I indicate that an essentially 100 per cent. reaction of the di-t-butyl The standard deviation of the deter- peroxide is occurring under the conditions of the method. mination of total available oxygen content was 0.03. TABLE I A4T\;ALYSES O F DI-T-BUTYL PEROXIDE SAMPLES Sample number 1 3 4 5 6 7 0 1 Total available oxygen, per cent. w/w 10.79 10.81 11-01 10.89 11.09 11.11 10.91 -Available oxygen content due to hydro-peroxide, per cent. w/w 0.0 1 0.06 0.11 0.12 0.44 0.42 0.41 Total impurity content, Di-t-butyl per cent. w/w, per oxide determined by content, gas - liquid per cent. w/:w chromatography 98.5 1-3 98.2 1.2 99.5 1-6 98.4 1-3 97.3 3.0 97.6 2.6 96.0 2.4 The author thanks Mr. I. M. Muten for the gas chromatography results, Messrs. N. J . Chalkley and 1%’. H. Redmayne for assistance and guidance and the Laporte Industries Limited, General Chemicals Division for permission to publish this paper. R E FE R E PI; c E s 1 . 2. 3. 4. Yaughan, W. E., and Kust, F. F., U.S. Patent 2,403,771 (September 7th, 1946). hlair, 1C. U., and Graupner, A. J . , AnaZ11t. Chew., 1964, 36, 194. Bell, E. R., Rust, F. F., and Yaughan, 12’. E., ,I. Amev. Chern. SOC., 1950, 72, 337. “Organic Peroxy (’onipounds,” Technical Leaflet, Laporte Chemicals Ltd., Luton, Redfordshire. R#.ceived Jaizuavj~ loth, 1966

ISSN:0003-2654    

DOI:10.1039/AN9669100397

出版商:RSC    

年代:1966

数据来源: RSC

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June, 19661 SHORT PAPERS 399 Modification of a Simple and Rapid Titrimetric Method for Determining Carbon in Iron and Steel BY R. F. JONES, P. GALE, P. HOPKINS AIW I>. N. POTVELL (The Steel Campany of R'ales Limited, A bbey TVnrks, Povt Talbot, Glapnorgan) SIXCE publishing our paper in the October issue of The Analyst, in which we described a method for determining carbon in iron and steel by the non-aqueous titration of the carbon dioxide e\-olvecl during the combustion of the saniple in oxygen, MT havc modified the design of the apparatus and certain o f the analytical conditions. This has resulted in a consiclerable inipro\-enlent with regard to the speed of analysis and the flexibility of the Iiiethocl. TJnder thew nclv conditions it is possible to determine carbon in the range of 0 to 0.2 per cent.in less than 2 minutes, and up to 0.63 per cent. of carbon can be determined before it is neccssarp to replenish the absorption solution. T\I 0 11 I FI C AT I 0 IK T 0 X P PA K A T US- The distancc between the combustion furnace and the absorption cell has been kept as short as possible. The magnesium perchlorate used to remove moisture from the combustion gases has been omitted, thereby making i t possible for a smaller prolong to be substituted to contain the manganese dioxide used for removing the sulphur gases. Whenever possible, flexible polythene tubing has been replaced with glass tubing, connections either being made with polythene or PTFE-lined neoprene sleeves. The issuing waste gases are passed through activated carbon to remove any toxic fumes that may be present.MODIFICATION OF ANALYSIS CONDITIONS- Increasing the temperature and flow-rate, together with an increase in the amount of mono- ethanolamine and indicator in the absorbent solution, has resulted in a marked improvement in the400 B.C.S. 264 237/1 270 270 295 29 1 159/2 293 SHORT PAPERS [Analyst, Vol. 91 TABLE I COMPARISON OF ANALYSIS TIMES Time 1 minute 36 seconds 2 minutes 5 seconds 1 minute 48 seconds 1 minute 40 seconds 2 minutes 20 seconds 3 minutes 15 seconds 3 minutes 5 seconds 3 minutes 10 seconds Percentage of carbon, Certificate value Found 0.037 0.038 0.105 0.105 0.22 0.2 16 0.22 0.216 0.265 0.269 0.47 0-47 0.54 0.54 0.63 0.635 speed of analysis. It can be seen that the analysis time is dependent upon the level of carbon in the sample.This is a consequence of the time taken to empty, and if necessary re-fill, the 10-nil micro burette during the course of the titration. Addition of the extra mono-ethanolaniine has improved the absorption capacity of the fornidiniethylamide solution, and it i s now possible to absorb the equivalent of 0.63 per cent. of carbon in a standard 20-1111 aliquot of this solution without any danger of losing carbon dioxide. It is apparent from this work that the dilution effect referred to in our original paper apper- tained to the niono-ethanolaniine constituent and not the formdiniethylarnide as originally thought. With these modified conditions, we no longer find it necessary to titrate the solution as the carbon dioxide is being evolved, and we have confirmed that quantitative yields can be obtained, even with the oxygen flowing for periods up to 5 minutes after all the carbon dioxide has been evolved. This feature makes the technique more flexible as the operator can, if necessary, perform other functions as the analysis proceeds.I t is, however, essential to titrate the carbon dioxide as the combustion gases are evolved to obtain rapid results, such as those quoted in Table I. Comparative times are shown in Table I. MODIFIED ANALYTICAL CONDITIONS Furnace temperature = 1300" C Saniple weight = l g Flux = Lead strip (7 cni x 4 cm) Oxygen flow-rate Titrant = 0.02 s tetra-n-butyl ammonium hydroxide TTolunie of absorption solution = 20 nil Composition of absorption solution = Formdimethylamide, mono-ethanolamine and thymol- Input = 2 litres per minute Throughput = 450 nil per minute phthalein indicator (150 to 5 to 2) REFERENCE 1 . Jones, K. F., Gale, P., Hopkins, P., and Powcll, L. N., Analyst, 1965, 90, 623. Rcceived Decemhev 13th, 1965

ISSN:0003-2654    

DOI:10.1039/AN9669100399

出版商:RSC    

年代:1966

数据来源: RSC

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400 SHORT PAPERS [Analyst, Vol. 91 A Simple Method of Preserving Thin-layer Chromatograms BY H. A. FONER (Ceramics Department, The Houldsworth School of Applied Science, The Universitjr, Leeds 2) THIN-LAYER chromatogranis may be preserved by fixing them directly on the glass plates. This method is both cumbersome and expensive and, therefore, several methods of removing and preserving the adsorbent films have been described. Barrollierl coated the adsorbent layer with a solution of collodion containing plasticiser, and peeled off the plastic film formed. Unfortunately, however, collodion films are tacky and tend to curl. -4 more widcly used technique is to spray the chromatogram with an aqueous dispersion of poly(viny1 chloride) or poly(viny1 propionate) .z The plastic impregnated layer is floated off in water, and subsequently strengthened by spraying more plastic on to the reverse side.An aqueous dispersion of poly(viny1 propionate) (Neatan) is available commercially.June, 19661 SHORT PAPERS 401 The method proposed in this paper makes use of a commercially available aerosol spray.* This material consists of poly(viny1 chloride) polymers and a plasticiser dissolved in organic solvents, with a fluorinated hydrocarbon propellent. The transparent plastic film produced by this spray is tough, pliable and does not yellow with age. The aerosol form of the package makes the spray convenient to use, and the resulting film is both stronger and dries more rapidly than the water- based dispersions. The material is particularly suited for preserving cellulose chromatograms, giving a strong pliable film when sprayed from one side of the thin layer only.The method may be used on 20 x 20-cm plates. In addition to the usual method of spraying thc finished chromatogram, it is sometimes possible to pre-coat the chromatographic plate with poly(viny1 chloride) to give an even stronger film that is more easily rcmoved. METHOD NORMAL CHROMATOGRAPHIC PLATES- Outline with plastic adhesive tape, or with a pencil, the portion of the chromatograni that it is required to preserve. Spray three separate times with the vinyl spray, allowing the solvent to evaporate between each application. The plastic should be applied each time until the film appears just saturated. It is good practice to turn the plate through 90" before each application and to let the solvent evaporate with the plate in a horizontal position.Cut through the outline on the plate with a sharp blade and scrape off the unwanted portion of the film. Immerse the chromatogram in cold water to which a wetting agent has been added. After a few minutes peel off the plastic film containing the adsorbent; this process may be facilitated by easing the film off the plate with a flexible blunt blade. If necessary, after drying, spray the reverse side of the film to give it added strcngth. POLY(VINYL CHLORIDE) COATED CHROMATOGRAPHIC PLATES- This modification is suitable if the developing solvents and the chromogenic reagents do not react with the plastic film and if the plate is not heated above 110" to 120" C. A strong, easily removable film is formed. RF values and development times do not appear to be affected by the presence of the poly(viny1 chloride) film. Spray a clean glass plate with 3 separate thin layers of poly(viny1 chloride), allowing the plate to dry in a horizontal position bctween applications. Turn the plate through 90" before each spraying. Coat the plate with adsorbent and carry out the chromatographic analysis as usual. Coat the chromatogram with poly(viny1 chloride) and strip it from its glass plate as described previously. REFERENCES 1. Barrollier, J . , Naturwissenschaften, 1961, 48, 404. 2. Lichtenberger, W., 2. analvt. Chenz., 1962, 185, 111. Received November 29th, 1965 * Clear vinyl aerosol spray available from Fisons Scientific Apparatus Ltd., Bishops Meadow Road, Loughborough, England.

ISSN:0003-2654    

DOI:10.1039/AN9669100400

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

June, 19661 SHORT PAPERS 401 The Detection of Cashew-nut Shell Liquid by Thin-layer Chromatography BY T. W. HAMRIONDS (Tropical Products Institztte, Gray's I n n Road, London, W.C. 1) COMPARISOX of mechanical and hand decortication procedures requires the detection of cashew-nut shell liquid on the surface of cashew kernels as a measure of efficiency. Paper chromatography of kernel extracts using methanol as the mobile phase, and detecting separated components by irradi- ation with ultraviolet light, is relatively insensitive (S. C. Bevan and S. Thorburn, private coin- munication). Pereira et al.' have detected cashew-nut shell liquid in ethereal kernel extracts using both diazotised p-nitraniline and sulphanilic acid, although a t low levels glyceride contamina- tion of the extract results in a significant decrease in sensitivity.Using a modification of the solvent system described by Bakshi et aZ.,2 thin-layer chromato- graphy of kernel extracts prepared with an acetone - water mixture (85 + 15), which minimises glyceride contamination, facilitates the detection of sub-microgram amounts of cashew-nut shell402 SHORT PAPERS [Analyst, Vol. 91 EXPERIMENTAL Shaking 20 g of cashew kernels with 50 ml of the acetone - water mixture (85 + 15) for 5 minutes results in the extraction of cashew-nut shell liquid residues without dissolving a significant amount of fat. Removal of the cashew-nut shell liquid from this aqueous extract was effected by adding a further 10 ml of water and partitioning with petroleum spirit (b.p. 40" to 60" C). The resulting extract was dried with anhydrous sodium sulphate and the solvent removed in vacuo.The residue was dissolved in cyclohexane, and suitable amounts were loaded on to 300-p chroniatoplates of silica gel and developed over a 10-cm solvent path length with an ethyl acetate - toluene (10 + 90) solvent system. The components were made visible by spraying first with a solution of diazotised p-nitraniline, and then with 20 per cent. w/v aqueous sodiutn arbo on ate.^ By this procedure the separation of the major component, anacardic acid (yellow spot R, 0.13) and the minor components cardol (yellow spot R, 042) and anacardol (orange spot R, 0.55), was achieved, leaving polymerised material a t the base-line. Semi-quantitative determination by diluting the cyclohexane solution obtained until the spot due to anacardic acid just disappears is possible. Assuming the anacardic acid concentration in undecarboxylated cashew-nut shell liquid is 90 per cent.,4 under these conditions approximately 0.07 pg of anacardic acid is just detectable, and may be used as the basis for the calculation of the approximate cashew-nut shell liquid content of a given sample. PROCEDURE- (a) Extvaction of cashew-nut shell lzquid-Shake 20 g of cashew kernels with 50 ml of an acetone - water mixture (85 + 15) for 5 minutes in a 250-ml extraction flask. Filter the extract through a Whatman No. 41 filter-paper, into a 250-ml separating funnel, washing the flask with portions of solvent and adding to the filtrate. Add 10 ml of water and 25 ml of petroleum spirit (b.p.40" to 60" C) and shake them together. Separate the aqueous phase and repeat the extraction with a further two 10-nil volumes of petroleum spirit (b.p. 40" to 60" C). Combine the petroleum extracts and filter through anhydrous sodium sulphate, washing the filter-paper and sodium sulphate with two 10-ml volumes of petroleum. Combine the extracts in a flask and remove the petroleum in uucuo in a 25-ml round-bottomed flask. (b) Preparation of thin-layer chromatoplates-Dissolve the residue from (a) in 1.0 nil of cyclo- hexane and load suitable volumes ( e g . , 5, 10 and 20 pl) on to a line 1.5 cm from the edge of a 10 x 20-cm chromatoplate, previously coated with a 300-p layer of Kieselgel G Merck dried for 1 hour a t 100" C. (c) Thin-layer clivornatogvaplzv of the extract-Develop the chromatoplate over a 1 O-cm solvent path length with an ethyl acetate - toluene (10 + 90) solvent system.Dry the developed chrom- atoplate under an infrared lamp for 1 minute. (d) Location of sepuvated components on the cJiroi?zntoplates-Spray first with diazotised p - nitraniline reagent (prepared by mixing 26 nil of 0.3 per cent. p-nitraniline in hydrochloric acid (80 per cent. w/v) with 1.5 nil of 5 per cent. w/v aqueous sodium nitrite) and then with 20 per cent. w/\- aqueous sodium carbonate, and observe thc presence or absence o f anacardic acid (yellow Add a fen- sodium chloride crystals if emulsification occurs. spot RF 0.13). I sc u s s I o N iVith this method, from 2 to 4 p.p.m. of cashew-nut shell liquid have been detected on commercial cashew kernels, and on cashew kernels produced by various experimental processes, 10 to 30 p.p.ni. cashew-nut shell liquid were found. Although the surface washing procedure described does not result in total recovery of cashew-nut shell liquid owing to its fat-solubility and a consequent tendency to penetrate into the kernel, the method is a useful guide for the comparative determination of cashew-nut shell liquid on cashew kernels. REFERENCES 1. 2. 3. 4. Pereira, A . , jun., Da Silveira Godinho, and Estorinho Marcal, M. E., Estudos Agron., 1960, 1, 29. Bakshi, S. H., and Krishnaswamy, N., J. Chromat., 1962, 9, 395. Block, R. J., Durrum, E. L., and Zweig, G., "A Manual of Paper Chromatography and Paper Jacqmain, D., OIPagineux, 1959, 14, 527. Electrophoresis," Academic Press lnc., New York, 1958, p. 305. Received October 1 l t h , 1965

ISSN:0003-2654    

DOI:10.1039/AN9669100401

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

June, 19661 BOOK REVIEWS 403 Book Reviews ELECTROCHEMICAL ANALYSIS : STUDIES O F ACIDS, BASES AND SALTS BY E.M.F., CONDUCTANCE, OPTICAL AND KIKETIC METHODS. Edited by ROGER G. BATES. Pp. xiv + 100. Washington D.C.: T7.S. Government Printing Ofice. 1965. Price 60 cents. This is the first of a series of annual summaries or progress reports that the N.B.S. proposes to issue in the form of the Technical Note. It is proposed to issue such summaries for a11 the Sections of the Analytical Chemistry Division, and the present issue deals with the Electrochemical Analysis Section headed by Dr. Bates. At present the Section is organised into seven groups, each of which contributes to the Report. 7’0 quote from the Preface, “It is the purpose of this report not only to review the individual projects of the Section but to convey as well, an impression of the inter- relationships of the separate activities as they fuse into a single Section programme.The first goal could be achieved in a most satisfactory way by collecting together the published-or soon to be published-work of the staff as listed a t the end of this document. The second aim, however, is more elusive. It can only be met by an integrated summary of the total Section effort, where accomplishment can be viewed against the backdrop of the mission, facilities, and personnel of the organisational unit.” The second aim is well and succinctly fulfilled, and such information about a laboratory of such importance and influence is both welcome and valuable. In addition to the account of facilities, equipment and personnel, there are reviews of the design of automated instrumentation for e.m.f.measurements, measurement of acidity, indicators as reference bases for acid - base studies in inert solvents, solvent effects on acid - base processes of analytical interest, aqueous solutions of mixed salts, bchaviour of sodiuni-responsive glass electrodes, conductometric determination of traces of water, reference materials for dielectric measurements and kinetic niethods of analysis. This document will be of interest to all those engaged in work of a similar nature and to those who make use of the results and end-products of this laboratory. July 1964 to June 1965. E. BISHOP NUCLEAR TECHNIQUES I N ANALYTICAL CHEMISTRY. By ALFRED J. bIOSES. Pp. viii + 142.Oxford, London, Edinburgh, New York, Paris and Frankfurt: Perganion Press. 1964. Price 45s. The first two chapters (37 pages) of this monograph are essentially introductory and deal with safe handling of radioactivity and with nuclear instrumentation, including radiation sources. Four further chapters (52 pages) cover measurement of natural radioactivity and activation analysis, including activation by positive ions and y-radiation, as well as neutron activation; this section, probably the most useful part of the book, contains by way of illustration experi- mental details of some 30 analytical methods, drawn from published work of other authors. The final four brief chapters (21 pages) cover radiation scattering, isotope dilution and tracer tech- niques, radiometric measurements and exchange reactions, and miscellaneous techniques including radiochernical-dating methods.Appendices, which include thermal neutron and fast-neu tron activation data, and an index complete the book. The declared purpose of this monograph is “to acquaint the analytical chemist with nuclear techniques.” If an analyst wishes to gain a superficial appreciation of what can be done with nuclear techniques, this book may fulfil his requirements. On the other hand, if he is seeking a practical manual with detailed experimental information to guide his first faltering footsteps into the strange world of radiochemistrv, this is not the book for him. It would seem that “acquaint” is the operativc word. H. J . CLULEY WAVE MECHAPL’ICS FOR CHEMISTS.By C. \ir. X. CUMPER, M.A4., Ph.D., F.R.I.C. Pp. x + 382. The analytical chemist must, of necessity, be, if not master of all disciplines, a t least master of the fundamental principles of all disciplines so far as he possibly can. lhere can be little of more general fundamental importance than the behaviour of electrons in atoms and molecules. The analytical chemist desirous of possessing himself of the very powerful weapon of understanding afforded by the wave-mechanical approach will find in this book a competent and readable treat- nient without too much coniplex mathematics. E. BISHOP London : Heineniann Educational Books Ltd. 1966. Price 50s.404 BOOK RFVIFWS [A?zazyst, I T O l . 91 OFFICIAL METHODS OF ANALYSIS OF THE ASSOCIATION OF OFFICIAL AGRICULTURAL CHEMISTS.Edited by WILLIAM HORWITZ. Tenth Edition. Pp. xx + 957. Washington D.C.: The Association of Official Analytical Chemists. 1965. Price $22.50 in the U.S.,4. ; $23.00 elsewhere. This collection of standard methods is well known to analysts connected with food, drugs and agriculture. Others may not be aware that its scope is far wider than the title suggests, because in the U.S.A. the work of the official agricultural chemists covers about the same field as the public analysts and the official agricultural analysts in Great Britain. Hence this volume deals with fertilisers ; herbicides ; pesticides ; mineral constituents of plants ; beverages of all kinds ; food ; animal feeding stuffs ; metals, other elements, preservatives and “residues,” i.e., of insecticides, in foods; oils, fats and waxes; drugs, including antibiotics and vitamins; cosmetics, and some minor commodities. All the A.O.A.C. methods are the product of collaborative trials and modification in members’ laboratories. After satisfying a specialised panel, they are published as “official-first action,” and only after 5 years of satisfactory use are they raised to the status of “official-final action.” Therefore, there will always be enough results for a proper statistical examination. This is often published in the Journal (of the Association) and can include an assessment of the standard devia- tion of a result, but regrettably the book never gives any indication of accuracy or precision. “Select bibliographies” are often included in the methods, usually to papers in the Journal, and this is far more than most standardising bodies condescend to do, so the required statistic could be found, but why can it not be stated a t the end of each method? No organisation can give equal attention to all fields of work, and the Preface stated that “the fastest growing area of interest is in pesticides, in formulations and in foods, and drugs in feeds.” The only “multiple detection method” for pesticides is by paper chromatography.It is stated that “the paper-chromatographic method is technically obsolete, but the preparative portions are sound and form the basis for gas and thin-layer chromatographic methods which have not been studied collaboratively by the A.O.A.C. in time for this edition.” These quotations sum up the difficulty of all comprehensive standardising organisations ; it is impossible for all the sections to be up to date.The A.O.A.C. methods for trace elements, certain additives to feeding stuff:, and fertilisers are more comprehensive, but not better, than the British equivalents, and few British agronomists would agree with the concept and determination of “available” nitrogen in certain fertiliser materials. Many sections reflect the great progress in chemical analysis in recent years ; one may cite the uses of ultraviolet and infrared spectrophotometry in pesticide analysis, the great and increasing uses of all kinds of chromatography, thin-layer chromatography for the examination of mixed flavouring additives to foods, gas chromatography for fatty acids and sterols, a radio- active-tracer method for y hexachlorocyclohexane ( y benzene hexachloride) to mention but a few.On the other hand, many traditional methods have been retained ; some, for example the methods for methanol and fuse1 oils in alcoholic drinks, look almost quaint and should be replaced by gas chromatography. The pyknometer used in this section is more cumbersome and no more accurate than Lipkin’s or Hennion’s, both well established in the petroleum industry. (Perhaps no citizen of a country in which Syke’s hydrometer and “proof spirit” are still legally the last word should comment adversely on any other country’s methods of dealing with alcoholic liquors.) B u t quite apart from exaniples like this, there are some inexplicable gaps. Perhaps the strangest is that no use a t all is made of the polarograph, yet with apparatus of moderate sensitivity and medium cost, the difficulties of determining numerous trace metals, e.g., tin, lead, zinc, thallium, cadmium, would be greatly diminished.The polarograph has also important applications to organic analysis, for example in determining certain chlorinated insecticides. Hardly any use is made of spectrography. There is, in this edition, a brief section on spectrographic methods, but it is too short to bc of much use. The same may be said of thc chapter on microchemical methods. Ten pages will not teach even the elements of the technique, and a microchemist will learn nothing from them. However, when all the adverse comments have been made (and every individualistic analyst can find a few more), it must still be said that this compilation is virtually essential to analysts working in the fields that it covers, and a wonderful testimony to the zeal and hard work of the members of the Association of Official Agricultural Chemists. It ends with 103 pages of numerical tables. The chapter on standard solutions is not worthy of the rest of the book. H. h-. M’ILSON

ISSN:0003-2654    

DOI:10.1039/AN9669100403

出版商:RSC    

年代:1966

数据来源: RSC