摘要:

Analyst October 1983 Vol. 108 PP. 1235-1239 1235 Rapid Colorimetric Procedure for the Determination of Acid Volatile Sulphide in Sediments William Davison and Jean P. Lishman Freshwater Biological Association The Ferry House Ambleside Cumbria L A 22 OLP A method is described for the determination of acid volatile sulphide in sediments. Sulphide is released using 5.93 M hydrochloric acid and the resultant solution is separated from the sediment by filtration in a sealed system of syringes. The concentration in solution is determined spectro-photometrically as ethylene blue. The procedure which has been used successfully for several years uses simple equipment and is more rapid than the alternative distillation method. The limit of detection is 0.3 pmol 1-1 in solution 2 pg g-l expressed as mass of sulphide in dry mass of sediment.The relative standard deviation for standards was 1-3% in the concentration range of 15-28 pmol 1-1 and 2-7% in the range 4-15 pmol l-l. For a sediment sample containing 118 p g 8-l it was 5%. Keywords A cid volatile sulphide ; spectrophotometry ; ethylene blue ; sediments Iron sulphides are ubiquitous in marine and freshwater sediments. They are usually present either as pyrite or as monosulphides which can be liberated by hydrochloric acid. These acid volatile sulphides (AVS) give rise to an intense black colour that is characteristic of anoxic sediments. They play an important role in recent diagenetic processes in sediment9 and the ratio of pyrite to AVS has been used as an historical indicator to determine whether sediments were formed in marine or freshwater conditions.2 They can be present over a wide range of concentrations.Oxic muds do not have any free sulphide whereas anoxic muds may contain as much as 10 mg g-1. The traditional method of analysis3 is based on the method of Kolthoff and Sandell,4 in which 1 M hydrochloric acid is added to a sediment sample and the mixture is boiled. Hydrogen sulphide is trapped as zinc sulphide and the final analysis is performed by iodide titration after re-acidification of the metal sulphide. Gilboa-Garber5 improved the final analysis step by using a colorimetric procedure based on methylene blue. However the inherent disadvantage of the method including the lengthy distillation step and extensive handling of an oxygen-sensitive sample remained.A procedure has been devised based on the colorimetric determination as ethylene blue,6 which used syringes to simplify sample handling and remove the necessity for a distillation step. Experimental Apparatus The absorbance of solutions was measured at 670 nm using various spectrophotometers fitted with 1-cm flow-through cells. All glassware including the syringes was borosilicate. It was cleaned with 6 M hydrochloric acid and then washed thoroughly with distilled water. Disposable plastic three-way taps (Pharmaseal) with Luer fittings did not introduce any sulphide contamination. Filtration was performed using 25-mm Swin-Lok (Nucleopore) filter holders containing 5-pm cellulose acetate membrane filters (Millipore). Reagents Unless stated otherwise all reagents were of AnalaR grade.Water. Singly distilled. Hydrochloric acid 5.93 & 0.07 M. Dilute 500 ml of hydrochloric acid (sp. gr. 1.18) to Zinc acetate solution. Dissolve 5 g of zinc acetate and 1.25 g of sodium acetate in 1000 ml of Reagent A NN-diethyl-p-phenylenediamine sulphate. Dissolve 2 g of the salt in 100 ml of 1000 ml. distilled water. 50% V/V sulphuric acid. Dilute to 200 ml with water 1236 DAVISON AND LISHMAN RAPID COLORIMETRY Analyst Vol. 108 Dissolve 18 g of NH4Fe(S04),.12H,0 in water and dilute to 200 ml. Wash and dry a selected crystal (0.5-0.7 g) of Na2S.9H,O with tissue. Accurately weigh and transfer it into a flask containing 200 ml of water that has been deoxygenated by bubbling with argon. This solution was checked by titration with iodine.' We found in agreement with the observations of Wilson et a1.,* that the weighed crystal gave a more precise determination of the concentration than the iodine titration.Procedure Introduce a sample (20-100 mg) of wet sediment and re-weigh the syringe to determine the exact amount of wet sediment. Re-place the piston connect a three-way tap to the Luer fitting and close off. Using a l-ml syringe introduce 0.5 ml of 5.93 M hydrochloric acid via the three-way tap. Place the sealed syringe in an oven at 60 "C for 30 min. After cooling add via the three-way tap deoxygen-ated zinc acetate solution to a volume of 20 If necessary store at 4 "C and then within 24 h attach in series with the three-way tap a filter unit and then another graduated 20-ml glass syringe (Fig.1). Separate the solution from the sediment by transferring it in this sealed system through the filter into the previously empty syringe. Verify from the syringe calibration that there is 19-20 ml of solution such that any volume error is less than 0.3%. Introduce using a l-ml syringe and a three-way tap 0.5 ml of reagent A seal and mix and, after 2 min add 0.5 ml of reagent B and seal and mix. After 15 min and within 2 h read the absorbance at 670 nm. Calibration was performed by starting with zinc acetate solution containing 0.5 ml of 5.93 M hydrochloric acid to which was added an appropriate volume of sodium sulphide solution. All other procedural steps were the same. Blanks were performed in the same way omitting the sodium sulphide solution.If the final volume after filtration is less than 19 ml the volume can be read from the syringe graduation to a precision of 0.2 ml and the appropriate correction factor applied to the reagent volumes. Reagent B ammoniwn iron(III) sdphate. Sodifim sulphide solution. Weigh the barrel of a graduated 20-ml glass syringe. 0.2 ml. Graduated syringe Filter unit Graduated syringe 1 Sulphide solution Fig. 1. Schematic diagram of syringe assembly as the solution is separated from the sediment by filtration. Selection of Measuring Conditions The objectives of the method were two-fold to achieve efficient release of sulphide from the sediment and then to retain the sulphide until the analysis step. This method differs from traditional techniques by using filtration rather than distillation to separate the liberated sulphide from the solid material.Preliminary tests showed that colour formation was impeded if solid sediment was present and that filtration could completely remove this inter-ference. A 0.5-ml volume of 5.93 M hydrochloric acid was found to be optimal for ensuring efficient liberation of sulphide without interfering with the colour development step by drastic modification of the final pH. The temperature of 60 "C was chosen as the maximum value permissible to avoid any decomposition of the plastic taps. No further release of sulphide occurred when the incubation time exceeded 30 min. In the preliminary work zinc acetate was not used and tests with standards showed that considerable loss of sulphide could occur prior to the final analysis.This loss was attributed to volatilisation because although the system was sealed the possibility of loss around the syringe barrels and during passage through the filter could not be completely discounted. The zinc acetate solution contains sufficient zinc (0.023 M) to accommodate adequately the maximum concentration of all the sulpliide species (3 x M). However at this low pH of approximately 1 the equilibriu October 1983 FOR ACID VOLATILE SULPHIDE IN SEDIMENTS 1237 concentration of S2- is sufficiently low that the solubility product of zinc sulphide (pK = 24.37)9 is not reached. Thus there appears to be sufficient complexation to stabilise the solu-tion species and prevent volatilisation without inducing precipitation of zinc sulphide which could be removed by filtration.Results and Discussion Standards Fig. 2 is a typical calibration graph that shows that the response is linear to about 30 pmol l-l. It contains two data sets one from standards that have undergone the complete procedure and the other from standards analysed in a single syringe with the heating and filtration steps omitted. The two sets of measurements are indistinguishable indicating that loss of sulphide during these procedures is negligible. An absorbance of 1.000 corresponds to 17.5 pmol l-l, which is in good agreement with the value of Rees et aL6 of 16.6 pmol l-l especially considering that our solutions were initially acidified with 0.5 ml of 5.93 M hydrochloric acid. 0 25 50 Concentration of sulphide/pmol I-' Fig.2. Graph of absorbance against concentration of sulphide for 0 standards undergoing the complete procedure; and 0, standards for which the heating and filtration steps were omitted. The precision of the measurements can be assessed from Table I which gives the mean and standard deviation of the difference between duplicate determinations performed over two concentration ranges. Increasing the concentration does not appreciably increase the dis-parity between duplicates. Therefore the percentage error is largest for the lowest concentra-tions. Results for determinations omitting the heating and filtration step also indicate a constant error of 0.3 pmol 1-1 irrespective of concentration and further show that these pro-cedures do not substantially contribute to precision errors.The mean of seven blanks performed on different days was 0.0139 units of absorbance with a TABLE I MEAN AND STANDARD DEVIATION OF THE DIFFERENCE BETWEEN DUPLICATE STANDARDS FOR A GIVEN RANGE OF CONCENTRATION Concentration range/ Mean of differences/ S.D. (n)*/ PM PM p~ Error yo 4-15t 0.28 0.28 (6) 2-7 8-26 0.32 0.26 (7) 1-4 15-28t 0.40 0.46 (6) 1-3 * S.D. is the standard deviation; n is the number of replicates. t Standards underwent complete procedure. The analyses were performed in a single syringe omitting the heating and filtration steps 1238 DAVISON AND LISHMAN RAPID COLORIMETRY Analyst Vol. 108 standard deviation of 0,0013. The latter can be used to assess the limit of detection of the method at a given confidence level as 22/2t(S.D.),1° where t is Student’s t and S.D.is the standard deviation of the blank. The resultant value for the 95% confidence level is 0.15 pmol l-l but implicit in this determination is the assumption that the precision error of the method will be proportional to the concentration at values near the limit of detection. Table I does not support this supposition and so the true limit of detection might approach the mean error of 0.3 pmol 1-1 found for duplicates. Sediment Samples The method has been used regularly for more than 2 years to measure acid volatile sulphide in the sediment of lakes. Fig. 3 shows values obtained for a sediment core taken from Blelham Tarn in the English Lake District. It was collected on 30 July 1980 using a Mackerethll l-m corer from the site labelled WD781 by Haworth.12 The core was sampled by inserting syringes fitted with 75-cm 21 G stainless-steel needles into pre-drilled 3 mm diameter holes in the core liner.They were at 1.3 cm depth intervals and were sealed with polythene tape. This technique enabled a sub-sample to be removed from the core without exposure to oxygen. All measurements were performed in duplicate within 2 d of the core being collected. If the absorbance exceeded 1.6 the solution was diluted to return it to scale and then appropriate volume corrections were applied. Tests showed that this procedure did not introduce any appreciable errors. n 0 20 40 60 Depth in sedimenvcm Fig. 3. Bar graph of acid volatile sulphide in a sediment core collected from Blelham Tarn on 30 July 1980.0 Rowlatt’s mean data for the sediments of this lake.13 Rowlattl3 has determined AVS on cores from Blelham Tarn. He used a distillation pro-cedure and either titration with iodine or colorimetric determination as methylene blue for the final measurement. He found differences in AVS between summer and winter but all our values lie within the range of his determinations. His mean values (Fig. 3) agree with our data indicating that the methods are compatible. It is difficult to obtain a good determination of the precision of the method as applied to sediment samples because of the contribution from other errors associated with sampling an unstable and heterogeneous material. The water content of the sediment which can be in excess of 90% is determined on a separate sub-sample and so the heterogeneity between sub-samples can introduce errors in the final assessment of sulphide in terms of unit mass of dry sediment.To obtain a realistic determination of the precision a discrete section of sediment was removed exposed to air and then replicate determinations were performed on this mor October 1983 FOR ACID VOLATILE SULPHIDE IN SEDIMENTS 1239 stable sample. Table I1 shows that the standard deviation for six replicates is less than 5% of the measured value. Table I1 also shows that errors can be introduced if the zinc acetate solution is not introduced immediately after the samples have been heated in the oven. TABLE I1 PRECISION OF MEASUREMENTS ON AN OXIDISED SAMPLE OF SEDIMENT Dry mass of sediment/ mg 33.9 24.8 37.3 40.8 40.1 94.5 33.7 39.0 Concentration of sulphidel Absorbance ie K’ 0.348 121.1 0.249 118.4 0.340 107.5 0.410 118.5 0.401 117.9 0.979 122.1 Mean 117.6 Standard deviation 5.2 0.286 0.169 100.0* 46.9* * Samples stored prior to addition of acetate solution.Conclusions The substitution of filtration for a distillation step in the determination of acid volatile sulphide can result in problems owing to the loss of sulphide during the handling steps. The use of a sealed system overcomes these difficulties and the resultant method is easy to use, requires simple equipment and can be used to analyse a complete sediment profile in a day. As naturally occurring acid volatile sulphides are often unstable this consideration of time can be an important factor in their successful determination.The method has been in regular use for more than 2 years and has consistently produced reproducible results with no problems other than those common to all methods associated with sub-sampling heterogeneous sedi-ment. This work received financial support from the Natural Environment Research Council. We thank Peter Allen and Colin Woof for collecting the sediment core and Mrs. J. Hawksford for typing the manuscript. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. References Howarth R. W. and Teal J. M. Lirnnol. Oceanogr. 1979 24 999. Berner R. A. Baldwin T. and Holdren G. R. J. Sed. Petrol. 1979 49 1345. Berner R. A. Mar. Geol. 1964 117. Kolthoff I. M. and Sandell E. B. “Textbook of Quantitative Inorganic Analysis,” Macmillan, Gilboa-Garber N. Anal. Biocheun. 1971 43 129. Rees T. D. Gyllenspetz A. B. and Docherty A. C. Analyst 1971 96 201. Mackereth J. H. Heron J. and Talling J. F. “Water Analysis,” Scientific Publication No. 36, Wilson B. L. Schwarzer R. R. and Chukwuenye C. O. Mzcrochem. J. 1982 27 558. Inczedy J . “Analytical Applications of Complex Equilibria,” Ellis Horwood Chichester 1976. Cheeseman R. V. and Wilson A. L. “Manual on Analytical Quality Control for the Water Industry,” TR66 Water Research Centre Medmenham 1978. Mackereth F. J. H. Limnol. Oceanogr. 1969 14 145. Haworth E. Y. in Haworth E. Y. and Lund J . W. G. Editors “Lake Sediments and Environ-Rowlatt S. M. PhD Thesis “Geochemical Studies of Recent Sediments from Cumbria England,” Received hfarch 23rd 1983 Accepted May 6th 1983 New York 1952. Freshwater Biological Association Ambleside 1978. mental History,” Leicester University Press Leicester 1983 Chapter 7. University of Liverpool 1980

ISSN:0003-2654    

DOI:10.1039/AN9830801235

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

1240 Analyst October 1983 Vol. 108 $9. 1240-1246 Selective Spectrophotometric Determination of Iron in River Waters Using 44 4-Methyl-2 -t hiazolylazo)resorci no1 Kazumasa Ueda Osamu Yoshimura and Yoshikazu Yamamoto Japan De9artment of Industrial Chemistry Faculty of Technology Kanazawa University Kodatsuno Kanazawa 920, Thiazolylazophenols react sensitively with iron(I1) to form brown complexes, which show a characteristic absorption in the near-infrared region. These compounds possess a hydroxyl group in the o-position next to the azo group. Amongst them the iron(I1) - 4-(4-methyl-2-thiazolylazo)resorcinol complex has an absorption maximum a t 735 nm. The absorbance is constant a t pH 8.9-11.6 and Beer's law is obeyed for up to 2 p.p.m. of iron with a molar absorptivity of 2.49 x lo4 1 mol-l cm-l.Many ionic species can be tolerated, especially transition metal ions of the 3d series. The method has been applied successfully to the analysis of river waters coffee green tea and synthetic mixtures containing transition metal ions. Keywords ; Iron determination ; spectrophotometry ; 4- (4-methyl-2-thiazolylazo) -resorcinol ; river waters Highly sensitive methods are being increasingly demanded for colorimetric analysis coupled with the wider use of sensitive instrumental analysis.lS2 However because of their poor spectrally selective nature applications of these methods to practical samples are often limited. For this reason the development of sensitive colorimetric reagents which enable a given metal ion to be distinguished spectrally from other co-existing ions is required Such a reagent can be applied not only to the colorimetric method but also to many automated analysers e.g.flow injection and various methods of chromatography. Many spectrophotometric methods have been proposed for the determination of i r ~ n ~ ~ * and of these thiocyanate 1 ,lo-phenanthroline and 4,7-diphenyl-l 10-phenanthroline methods have been commonly used. However these methods have many drawbacks e.g. low sensitiv-ity variation of colour intensity necessity for some separation processes and lack of selectivity owing to the formation of coloured products. Other methods using azo dyes,5 nitrosophenols6 and triphenylmethane derivatives' are highly sensitive but serious interferences arising from the coloration of transition metal ions are sometimes unavoidable.We found that iron(I1) complexes of thiazolylazophenol and naphthol derivatives showed characteristic absorptions in the near-infrared region and these compounds possessed a hydroxyl group in the o-position next to the azo group.8~~ In this paper a new reagent 4-(4-methyl-2-thiazolylazo)resorcinol (MeTAR) prepared from 2-amino-4-methylthiazole and resorcinol is proposed as a spectrophotometric reagent for iron determination. MeTAR reacts sensitively with iron(I1) to form a brown water-soluble com-plex which has a selective absorption band at 735 nm. By utilising this absorption a con-venient method has been developed for the routine determination of trace amounts of iron in river waters. The method does not require any separation processes and can determine iron directly by a simple procedure.It is applicable to all complex materials because most ions do not interfere spectrally. The additional advantages of this method over commonly used methods are that the coloration of the complex is stable for many hours and the accuracy for iron determination is favourable because the absorbance of the reagent blank is negligible. In addition we examined complexing properties of thiazolylazophenols with iron( 11) in order to elucidate these peculiar absorption features and obtain information about the substituent effect of the chelate ligand and the nature of the iron(I1) complex. Experimental Apparatus Absorption spectra and absorbances were measured with a Shimazu UV-BOOS recording spectrophotometer and a Hitachi Perkin-Elmer 139 spectrophotometer using a quartz cell o UEDA YOSHIMURA AND YAMAMOTO 1241 A Hitachi-Horiba Model M-5 pH meter equipped with a combined 10mm path length.glass electrode was used for the pH measurements. Reagents Preparation of thiazolylazophenols Thiazolylazophenols were synthesised by the diazotisation of 2-aminothiazole (or 2-amino-4-methylthiazole) with nitrous acid and subsequent coupling with phenols at 0 O C . 1 0 The phenols used were resorcinol hydroquinone $-chlorophenol $-methoxyphenol and pyro-catechol. The products were purified by repeated crystallisation with ethanol or re-precipita-tion with dilute hydrochloric acid and were identified by elemental analyses. 4-(2-Thiazolylazo)-resorcinol (TAR) 2-(2-thiazolylazo)-4-methylphenol (TAC) and 2-(2-thiazolylazo)-5-dimethylaminophenol (TAM) were commercially available and were used without further purification.A o.0570 MeTAR solution was prepared by dissolving 50 mg of reagent in 5 ml of 1 N sodium hydroxide solution and diluting to 100 ml with water. Standard iron(l1) solution. The iron(I1) solution was prepared by dissolving ammonium iron(I1) sulphate in water. The solution was acidified to pH 1 with sulphuric acid and standardised by titration with permanganate. Ascorbic acid solution. A 0.1% solution was freshly prepared every 3 d. Bufer solzdion. An ammonia buffer solution of pH 9.5 was prepared by mixing 3 M ammonia solution and 3 M ammonium chloride solution. Procedure Transfer the sample solution containing up to 100 pg of iron into a 50-ml calibrated flask.Add 5 ml of 0.1% ascorbic acid and 5 ml of o.06y0 MeTAR solution and adjust the pH to 9.5 with 5 ml of 3 M ammonia buffer solution. Dilute to volume with water and measure the absorbance of the solution at 735 nm against the reagent blank. Results and Discussion Complexing Properties of Thiazolylazophenols with Iron( 11) Table I shows the complexing properties of thiazolylazophenols with iron (11). Thiazolyl-azophenols react with iron(I1) to form brown complexes in the weakly acidic to the alkaline region which are soluble in water or chloroform owing to the differences in the substituent group and the composition of the iron complex. The dyes with a phenolic hydroxyl group in the o-position (A) next to the azo group give characteristic absorption naxima beyond 700 nm and 4-(2-thiazolylazo)pyrocatechol (TAPC) possessing this group in the m- (B) and $-positions TABLE I COMPLEXING PROPERTIES OF THIAZOLYLAZOPHENOLS WITH IRON( 11) Molar absorptivity/ No.* Compound A B C D E F hmax./nm lmol-lcm-l PH Solvent 1 TARu OH H OH H H H 730 2.90 x lop 8.9-10.3 Water 2.49 x lop 8.9-11.6 Water 3 TAH OH H H OH H 1.02 x 104 8.0 Water 1.36 x lo4 5.8-8.5 Chloroform 2 MeTAR OH H OH 4 TACl OH H H C1 H H 757 5 TAC OH H H CH H H 762 1.37 x lo4 4.8-10.0 Chloroform cHH 7736: 6 TAMP OH H H OCH H H 784 1.54 x lo4 5.0-9.3 Chloroform 7 TAM* OH H NgHHS) :' H 760 2.70 x lo4 8.2-10.0 Chloroform 8 TAPC H OH H 590 3.43 x 104 6.5 Water 1 4-(2-Thiazolylazo)resorcinol~ 2 4-(4-methyl-2-thiazolylazo)resorcinol; 3 2-(2-thiazolylazo)hydroquinone; 4 2-(2-thiazolylazo)-4-chlorophenol; 5 2-(2-thiazolylazo)~4-&ethylphenol; 6 2-(2-thiazolylazo)-4-methoxyphenol; 7 2-(2-thiazolylazo)-5-dimethylaminopheno1; and 8 4-(2-thiazolylazo)pyrocatechol 1242 UEDA et al.SELECTIVE SPECTROPHOTOMETRY Analyst VoE. 108 (C) shows different absorption features. The bathochromic shift of absorption maxima is promoted by the resonance effect of the m-(D) substituent group and the molar absorptivity is influenced by the resonance and inductive effects of the substituent in the m- and $-positions. The dyes with a 9-substituent e.g. TAR MeTAR and TAM show higher molar absorptivities than those which possess a substituent in the m-position. The difference would be attributable to the fact that the resonance effect of the 9-substituent group is small compared with that of the m-substituent but the inductive effect of the 9-substituent contributes greatly to the chelate system.It is not easy to clarify the peculiar absorption of the iron(I1) complex but we assigned this absorption band to the t,g +T* transition of 3d electrons of iron because many iron(I1) complexes show the charge transfer band of metal -f ligand type in the lower wavelength region.1l The effect of a substituent group in the thiazole ring is not so noticeable, but the absorption maximum shifts slightly to longer wavelength. Acid Dissociation Constant of MeTAR in a 5% Dioxane - Water Solution The acid dissociation behaviour of MeTAR is considered to be similar to that of TAR,12 but the dissociation constants are still unknown.The constant was calculated from the equation PKa = pH + log(A -A)!(A-Al) where A, A and A are the absorbances of the acid form, the base form and the mixed solution respectively. Fig. 1 shows the plots of pH versus log(A - A)/(A - A,) ; they are straight lines of slope -1. The constants were calculated to be pK, = 1.51 & 0.08 pK, = 6.17 & 0.03 and pKa = 9.91 & 0.06. The values are to some extent larger than those of TAR. The hyperconjugation effect of the methyl group in the thiazole ring may contribute to the higher basicity of MeTAR. 0 2 4 6 8 1 0 1 2 PH Fig. 1. Graphs of pH vs. log(A - A ) / ( A - A,) for MeTAR. Conditions as follows: MeTAR 3.0 x M ; ionic strength 0.1 (KC1); and measured wavelength (1) 510, (2) 500 and (3) 540 nm.Spectral Characteristics Fig. 2 shows absorption spectra of metal - MeTAR complexes of the 3d type and a reagent blank at pH 9.5. The iron(I1) complex has two absorption maxima at 550 and 735 nm while the other complexes have only one maximum each near 560 nm copper (562 nm) nickel (560 nm) cobalt (571 nm) and zinc (555 nm). We could not find any other metal - MeTAR complex that showed an absorption maximum over 700 nm. Hence the maximum at 735 nm is thought to be a characteristic absorption for iron(I1). The maximum shifts a little to a longer wavelength by the introduction of a methyl group into the thiazole ring of TAR compared with that of the iron(I1) - TAR complex.8 As the MeTAR blank shows no absorption above 640 nm we might expect enhancement of the accuracy for the determination of iron.Effect of pH The effect of pH on the absorbance of the complex was examined at 735 nm as shown in Fig. 3. A constant absorbance was obtained over the pH range from 8.9 to 11.6 which is more extensive than that of the TAR method October 1983 0.6 0.4 C (D 2 s 2 0.2 0 FOR IRON IN RIVER WATERS USING MeTAR 1243 \ 550 600 650 700 750 800 Wavelengthlnm Fig. 2. Absorption spectra of MeTAR complexes with 1 Fe; 2 Cu; 3, Conditions as follows metal 50 pg; pH Ni; 4 Co; and 5 reagent blank. 9.5; 0.05% MeTAR 5 ml; and 0.1% ascorbic acid 5 ml. Effect of MeTAR Concentration The maximum absorbance was obtained by adding from 2 to 20ml of 0.05% MeTAR solution for 50 pg of iron.Although 5 ml of MeTAR solution was used in practice the amount corresponds to 11.9 times the molar excess of iron. Whenever the consumption of MeTAR is noticeable owing to the presence of large amounts of other metal ions further addition of MeTAR may be allowed because the absorbance of the reagent blank is negligible. Choice of Buffering Agent The iron complex is stable even in higher concentrations of ammonia solutions and the absorbance remained constant on adding from 0.1 to 20 ml of 3 M ammonia buffer solution. The use of disodium tetraborate(II1) and diethylbarbiturate buffer also gave the same absorb-ance. Considering the masking effect of the other metal ions 5 ml of 3 M ammonia buffer solution were used. Effect of Reducing Agent Because the iron(II1) - MeTAR complex shows a weak colour it is necessary to maintain the iron as iron(I1).The effect of addition of ascorbic acid and hydroxylammonium chloride was examined but no significant difference was seen. In this work ascorbic acid was used and a constant absorbance was obtained by adding from 1 to 10 ml of 0.1% ascorbic acid solution. Beer’s Law Sensitivity and Precision of the Method The optimum range for accurate determinations as evaluated from a Ringbom plot,ls is 0.4-1.8 p.p.m. of iron. The molar absorptivity coefficient and Sandell’s sensitivity index for logIo/I = 0.001 are 2.49 x lo4 1 mol-l cm-1 and 2.24 x pg cm-2 respectively which is more sensitive than for most common reagents,4 such as 1,lO-phenanthroline 4,7-diphenyl-l 10-phenanthroline, 2,2’-bipyridyl 8-hydroxyquinoline and 1-(2-pyridylazo)naphth-2-01.The coefficient of variation of the absorbance for 0.98 p.p.m. of iron is 0.71% which was determined by 18 measurements and the reproducibility for iron determination is satisfactory. The colour system obeys Beer’s law over the range 0-2.0p.p.m. of iron 1244 UEDA et al. SELECTIVE SPECTROPHOTOMETRY Analyst Vol. 108 I 1 I I 7 8 9 10 11 12 PH Fig. 3. Effect of pH. Conditions as follows: Fe 50pg; 0.05% MeTAR 5ml; and 0.1% ascorbic acid 5 ml. 0 0.2 0.4 0.6 0.8 1.0 [Fel/([Fel+ [MeTAR]) Fig. 4. Continuous variation graphs. Con-ditions as follows [Fe] + [MeTAR] 7.039 x M ; pH 9.5; and measured wavelength (1) 735 (2) 720 and (3) 700 nm. Composition of the Complex The result obtained by the continuous variation method is shown in Fig.4; it is confirmed that iron(I1) forms a 1:2 complex with MeTAR. The complex will be an inner complex of the six-co-ordinate octahedral type because thiazolylazo compounds usually act as tridentate ligands . l4 Effect of Diverse Ions The effect of diverse ions on the determination of iron was examined. The results are summarised in Table I1 for cations and in Table 111 for anions where the tolerance limit is set to 6 5% for iron recovery. As the proposed method utilises a characteristic absorption the selectivity is significantly increased. Iron can be determined in the presence of greater than 10 p.p.m. of each of 37 metal ions, where metal ions generally present in natural waters such as alkali and alkaline earth metals, aluminium and zinc are tolerable even in large amounts.Metal ions of the 3d series form coloured complexes but copper can be effectively masked by thiosemicarbazide. As the concentrations of these ions in most natural waters are generally low compared with iron their interferences are almost negligible. Amongst the anions examined tartrate glycine and citrate can also serve as masking agents. TABLE I1 EFFECT OF CATIONS Tolerance Cations added* limit p.p.m. Na(I) K(I) Mg(II) Ca(II) Sr(II) Ba(II) Sb(III) Mo(VI) Tl(III) B(II1) Al(III) Cd(II) As(III) W(VI) Se(IV) V(V) U(VI) Cu(1I)t 100 Ru(III) Sn(II) Zr(IV) Hf(IV) Co(II),$ Ni(I1) . . 20 Mn(II) In(III) Rh(III) Cr(V1) 10 Cu(II) Co(II) Ni(I1) . . 5 200 Zn(II) Pb(II) Hg(II) Pd(II) Bi(III) Ga(III) Th(IV) Au(III) AgiI), * Iron taken 1 p.p.m.t Thiosemicarbazide 50 mg. $ Thiosemicarbazide 50 mg ; dimethylglyoxime 10 mg October 1983 FOR IRON I N RIVER WATERS USING MeTAR 1245 TABLE I11 EFFECT OF ANIONS Tolerance Anions added* limit p.p.m. C1- Br- I- NO,- SO,*- S,O,*- ClO,- tartrate glycine . . . . 20000 PO,,- . . . . * . 10000 CO,*- citrate oxalate . . . . 2000 F- thiosemicarbazide . . . . 1000 Dimethylglyoxime . . * . 200 SCN- * . 100 * Iron taken 1 p.p.m. Applications The proposed method does not require the separation of iron as hydroxide and the extraction of iron with isoamyl alcohol whereas 1,lO-phenanthroline and 4,7-diphenyl-1 10-phenanthro-line methods It is applicable to the direct analysis of various materials by a simple procedure.TABLE IV DETERMINATION OF IRON IN SYNTHETIC MIXTURES 7 Fe(I1) 50.0 100.0 60.0 60.0 50.0 60.0 Ion added/pg Co(I1) Ni(I1) Cu(I1) 50.0 60.0 50.0 50.0 50.0 50.0 - 200.0 50.0 - - 200.0 50.0 A 200.0 50.0 -- -- Fefound/ 50.0 50.1 60.0 100.0 - 60.3 - 50.2 50.0 49.9 200.0 50.0 Zn(I1) Pg Determination of iron in synthetic mixtzcres The determination of iron in mixtures containing metal ions of the 3d series is comparatively difficult without some separation procedures but it could be determined easily using the pro-posed method as shown in Table IV. Determination of iron in river waters co$ee and green tea The river water was filtered through a filter-paper immediately after sampling and acidified with 8 ml 1-1 of concentrated hydrochloric acid.An aliquot of the solution was pre-concen-TABLE V DETERMINATION OF IRON IN RIVER WATERS COFFEE AND GREEN TEA Iron found? Sample* Uchikawa . . Okuwa Outfall . . Shimoda Tokiwa . . Matudera . . Coffee . . . . Green tea . . Sai river: Asano river: A I I Amount taken MeTAR method AAS method 100 ml 0.064 p.p.m. 0.060 p.p.m. 100 ml 0.076 p.p.m. 0.078 p.p.m. 50 ml 0.439 p.p.m. 0.438 p.p.m. 100 ml 0.079 p.p.m. 0.082 p.p.m. 100 ml 0.125 p.p.m. 0.121 p.p.m. 100 ml 0.154 p.p.m. 0.161 p.p.m. 1.1155 g 170.4 pg g-l 171.2 pg g-1 1.2065 g 266.7 pg g-1 268.3 pg g-l * The Sai and Asano rivers are the two largest rivers in Kanazawa City. t Average of 5 separate determinations.$ Atomic-absorption spectrophotometry. The waters were sampled on July 8th 1982 1246 UEDA YOSHIMURA AND YAMAMOTO trated to about 20 ml on a water-bath and the iron was determined according to the recom-mended procedure. Coffee and green tea were treated by the dry ashing method in an electric furnace at 550 “C. The ash was dissolved in 10 ml of 6 N hydrochloric acid and evaporated to dryness on a sand-bath. The solid residue was redissolved in 4 ml of 6 N hydrochloric acid and submitted to the recommended procedure. The results agreed well with those obtained by atomic-absorption spectrometry as shown in Table V. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. References Shibata S . and Furukawa M.Bunseki Kagaku 1974 23 1412. Motomizu S. Iwachido T. and Tbei K. Bunseki 1980 234. Sandell E. B. “Colorimetric Determination of Traces of Metals,” Third Edition Interscience New Hirano S. Editor “Muki Oy6hishokubunseki No. 2,” Kyoritsu Shuppan Tokyo 1974 p. 324. Takeuchi T. and Shijo Y. Bunseki Kagaku 1965 14 930. TBei K. Motomizu S. and Korenaga T. Analyst 1975 100 629. Shijo Y. and Takeuchi T. Bunseki Kagaku 1968 17 1519. Ueda K. and Yamamoto Y. Nippon Kagaku Kaishi 1980 1713. Ueda K. Kiyota Y. and Yamamoto Y. Bull. Chem. SOC. Jpn. 1981 54 3763. Hovind H. R. Analyst 1975 100 769. Yamazaki K. and Yamadera H. “Mukikagaku Zensho Bekkan Sakutai (Ja),” Maruzen Tokyo, Kojima I. Anal. Chim. Acta 1971 57 460. Ayres G. H. Anal. Chem. 1949 21 652. Kurahashi M. and Kawase A. Bull. Chem. SOG. Jpn. 1976 49 1419. Japanese Industrial Standard K 0102 1974. York 1959 p. 525. 1977 p. 117. Received November 16th 1982 Accepted May 4th 198

ISSN:0003-2654    

DOI:10.1039/AN9830801240

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

Analyst, October, 1983, Vol. 108, pp. 1247-1251 1247 Rapid Spectrophotometric Determination of Chromium(V1) using Cyclohexane-1,3-dione Bisthiosemicarbazone Monohydrochloride K. Hussain Reddy and D. Venkata Reddy Department of Chemistry, Sri Krishnadevaraya University, Anantapur 515 003, India Cyclohexane- 1,S-dione bisthiosemicarbazone monohydrochloride produces coloured solutions with the chromium(V1) ion in a sodium acetate - hydro- chloric acid medium. The yellow species obtained (molar absorptivity 1.2 x lo4 1 mol-l cm-l a t 370 nm) has been used for the spectrophotometric deter- mination of micro-amounts of chromium(V1). An important advantage of the method is that the tolerance limit for associated ions is very high. Hence this method can be used for the determination of chromium in alloy steels.Keywords : Chromium( V I ) determination ; cyclohexane- 1,3-dione bisthio- semicarbazone monohydrochloride ; spectrophotometry ; sodium acetate - hydrochloric acid buffer solution The most frequently employed and recently developed photometric methods for the deter- ination of chromium are reviewed in the 1iterature.l Most of the methodss4 involve heating the reaction mixture. However, heating at a specific temperature5-* and for a long times-' is laborious and time consuming. Also, some methods require extraction pro~edures~~~s~-ll and in some the tolerance limit for associated foreign ions is 10w.293J2-14 In this method the interference of associated foreign ions is low, extraction is not essential and the colour reaction between metal ion and the reagent is instantaneous and the absorbance of the colour is con- stant for over 24 h.Experimental Apparatus ELICO, Model LI-120, pH meter, were used. An ECIL, Model GS 865A, spectrophotometer, equipped with 1.0-cm quartz cells and an Solutions All reagents used were of AnalaR grade unless stated otherwise. Cyclohexane-l,3-dione bisthiosemicarbazone monohydrochloride (CHDT.HC1) was prepared according to the literature15 and the reagent solution (2 x M) was prepared in distilled, de-ionised water. The standard chromium(V1) solution (1 x 1 0 - 2 ~ ) was prepared using analytical-reagent grade potassium dichromate (previously dried at 140 "C) . Solutions of lower concentration were diluted as required. Buffer solutions of 1 M hydrochloric acid - 1 M sodium acetate (pH 0.5-3.5) and 0.2 M sodium acetate - 0.2 M acetic acid (pH 4-6) were used.Procedure Samples were prepared in 25-ml calibrated flasks by taking 12 ml of sodium acetate - hydrochloric acid (pH 3.0) buffer solution, 0.4-3.7 p.p.m. of chromium(VI), 2.5 ml of dimethyl- formamide and 5 ml of 1 x 10-2 M CHDT.HC1 solution. Solutions were diluted to volume (25 ml) and the absorbance was measured against a reagent blank at 370 nm. A calibration graph was prepared similarly. Results and Discussion Thiosemicarbazones are oxidised easily, but this property is infrequently utilised for the However, phthalimide dithiosemicarbazone has been used for the determination of oxidants.1248 REDDY AND REDDY: RAPID SPECTROPHOTOMETRIC Analyst, VoZ. 108 spectrophotometric determination of osmium(VIII)ls and the oxidation of CHDT.HC1 was also used for the spectrophotometric determination of chlorateJ17 bromatela and iodate.19 Chromium(V1) reacts with CHDT.HC1 instantaneously over the pH range 1-5 to give a yellow species.Maximum absorbance was observed at 370 nm, hence all the studies were carried out at this wavelength. The absorption spectrum of chromium(V1) with CHDT.HC1 is shown in Fig. 1. 0.8 f 0.6 Q e 5: 2 0.4 0.2 0 370 390 410 430 450 Wavelengthlnm Fig. 1. Absorption spectra of (A) reagent us. water blank and (B) coloured species us. reagent blank. Conditions as follows: [Cr(VI)] = 4 x 1 0 - 5 ~ ; [I,$-CHDT.HC11 = 5.0 x l o - 3 ~ ; and pH = 3.0. Reaction with Chromium(V1) Efect of fiH studies were carried out at this pH.A maximum and constant absorbance was observed in the pH range 1.5-4.0 and all further Efect of dimethy@wnamide (DMF) In aqueous media the yellow species formed between chromium(V1) and reagent was precipitated. This was avoided by the addition of 2.5 ml of DMF in a 25-ml calibrated flask as the yellow species was found to be stable for 1 d in 10% aqueous DMF solution. Injhence of the reagent concentration The effect of the reagent on the absorbance was studied by keeping the metal ion concentra- tion constant and varying the molar ratio of the reagent to chromium(V1). It was found that a 50-fold excess of the reagent was required for constant and maximum absorbance. S$ectrofdwtometric characteristics The system obeys Beer's law over the concentration range 0.4-3.7 p.p.m.; the optimum range for the determination of chromium(V1) from a Ringbom plot was found to be 0.8- 3.3 p.p.m.; the molar absorptivity and Sandell's sensitivity of the method were 1.2 x lo4 1 mol-l cm-l and 0.0043 pg cm-2 of chromium(VI), respectively. The standard deviation for ten determinations of 2.0 p.p.m. of chromium(V1) was 0.003 p.p.m. Natwe of the oxidation reactioB Job's method and the molar ratio method gave the composition of the yellow species as 2 : 3 (metal: ligand). According to Ramakrishna and Irvingm the redox reaction may be written as 2Cr(VI) + 3(reduced reagent) + 2Cr(III) + 3(oxidised reagent)October, 1983 DETERMINATION OF CHROMIUM(VI) 1249 Two electrons are involved for each reagent molecule and the oxidation of :C=S gives :c-s-s-c:.Direct mixing of chromium(II1) and reagent solution did not produce the yellow colour. Complexation may, therefore, be taking place between chromium( 111) ions formed in situ and the oxidised product of the reagent. The important physico-chemical data for the solid complex [CrC12L.(H20)2] (where L is CHDT) are presented in Table I. + + TABLE I PRYSICO-CHEMICAL DATA OF THE SOLID COMPLEX Property Effective magnetic moment (pert) . . .. .. Thermogravimetric analysis .. .. .. Assignment . . .. * . .. .. .. Ligand . . .. .. .. . . .. Complex . . .. .. . . . . .. Conductivity .. .. .. .. .. Infrared spectral bandslcm-l- Elemental analysis- Sulphur, yo: Chromium, yo : Chlorine, yo : Found .. .. . . 15.60 Calculated .. . . 15.48 Found .. .. . . 12.50 Calculated ... . 12.53 Found . . .. . . 16.60 Calculated .. . . 16.80 Value ca. 4.0 Loss of water molecules is two, residue obtained is Cr20, NH and NH, GN21 G S Cr-Claa 3 420-2 920 1630 840 - 3 420-2 920 1600 1510 - 300 Complex does not conduct in benzene The effective magnetic moment (peff) (ca. 4.0) suggests a high-spin octahedral structure23 for the complex. Infrared data for C=N suggest the participation of the azomethine nitrogen atom in ~omplexation.~4 Conductivity data suggests an inner sphere complex. From the above observations the structure of the complex may be represented as where X = water or chlorine. Efect of foreign ions Various ions were examined for their effect on the determination of 2.0 p.p.m. of chromium- (VI). The tolerance limit was taken as the amount of foreign ion required to cause a &2% error in the absorbance.Of the 40 ions studied only platinum(IV), palladium(I1) and copper- (11) were found to interfere because of their colour reaction with the reagent, which occurs under the chosen experimental conditions; the colour reaction of palladium was utilised for its determinati0n.~5 The tolerance limits for associated ions are given in Table 11. Larger amounts of iron(II1) (a 300-fold excess) can be masked with 2 ml of 1.0 M sodium fluoride solution. Molybdenum(V1) and cerium(1V) (in a 12-fold excess) were masked with the sari amount of fluoride. 40 p.p.m. of oxalate. The main advantages of the proposed method are that the reaction between metal i q reagent is instantaneous, the effect of pH is not critical over the pH range 1.5-4 and the ference from foreign ions is low (Table 11).A 2-fold excess of vanadium(V) was tolerated in the presence . 11250 REDDY AND REDDY : RAPID SPECTROPHOTOMETRIC TABLE I1 INTERFERENCES OF FOREIGN IONS IN THE DETERMINATION OF 50 pg OF CHROMIUM(VI) Analyst, Vol. 108 Ion added Tolerance limitlpg Br-, I-, SO4!+, citrate, tartrate, thiourea .. .. . . . . .. .. 30 000 Zn(II), W(VI), Fe(III),* Mn(II), Fe(I1) . . .. .. 14000 475 T1, Sn(I1) . . .. .. .. .. .. . . . . .. . . .. 225 Ce(1V) .. . . .. .. .. .. .. .. .. .. 70 Cu(II), Bi(II1)' .. .. .. .. .. .. .. .. .. 25 F-, PO,+, NO,-, ClO,-, C1-, tetraborate .. .. .. .. .. .. 19 000 Ti(IV), Ni(II), Ce(IV),* Mo(VI),* IO,-, S,O,-, carbonate, hydrogen carbonate Mo(VI), V(V)t .. ,. .. .. .. .. .. .. .. . . 100 Al(III), Cd(II), Co(II), Cr(III), EDTA, SCN-, B;O,-, oxalate. * . . . . .. 1000 . . V(V), Pd(II), Pt(1Vj ' . . .. . . .. .. . . .. .. .. 10 * In the presence of 15000 pg of sodium fluoride. t In the presence of 1000 pg of oxalate. Applications Alloy steel sample solutions were prepared by following the procedure given in the literature.26 A sample containing 0.5 g of steel was dissolved in 40 ml of 1 + 4 sulphuric acid. A 5-ml volume of nitric acid was added to remove the carbonaceous residue, the solution was boiled to remove the excess of nitric acid, cooled and diluted to 80 ml. A 2-ml volume of a 1.7% silver nitrate solution and 2 g of potassium persulphate were added and the solution was swirled for dissolution to occur and heated at 80 "C for 10 min.The purple colour of manganese was destroyed by the addition of hydrochloric acid (1 + 1). The solution was cooled and diluted in order to obtain the required concentration of chromium in the stock solution. The chromium concentrations in stock solutions of BCS 409, 406, 406/1 and 405/1 were 2.93 x 2.038 x 2.08 x and 2.0 x M, respectively. To 12 ml of buffer solution of pH 3.0,2 ml of 1.0 M sodium fluoride, steel sample solution (in the optimum concentration range), 2.5 ml of DMF and 5 ml of 1 x M reagent were added. The solution was diluted to volume (25 ml) and the absorbance was measured at 370 nm against a reagent blank. The results are presented in Table 111. The interference of vanad- ium was suppressed with 1000 pg of oxalate in the analysis of a BCS 405/1 sample.The molar absorptivity value obtained for the system [chromium(VI) + buffer + DMF + reagent] and the molar absorptivity for [oxidised product of chromium(II1) + buffer + DMF + reagent] were found to be the same, indicating that chromium(II1) is oxidised quantitatively to chromium(V1). TABLE I11 ANALYSIS OF STANDARD STEEL SAMPLES Volume/ Chromium Error, BCS 409t . . .. .. 1.5 1.254 +2.78 3.0 1.228 +0.65 Steel sample ml found,* % % 4.5 1.203 - 1.4 BCS 406: . . .. .. 1.9 2.173 +2.5 3.8 2.120 f O . 0 5.7 2.100 - 0.98 BCS 406/1$ . . . . . . 2.0 2.074 - 1.24 4.0 2.125 + 1.20 6.0 2.074 - 1.24 BCS 405/7 . . . . .. 2.0 0.154 +2.90 4.0 0.148 - 1.30 6.0 0.147 - 2.00 * Average of ten determinations. t 0.48% Mn, 1.22% Cr, 0.77% Mo, 3.14% Ni, 0.23% Cu and 0.028% V.30.55% Mn, 2.12% Cr, 1.037% Mo, 1.69% Ni, 0.32% Cu and 0.020~0 V. §0.61% Mn, 2.10% Cr, l . O O ~ o Mo, 1.52% Ni, 0.28% Cu and 0.01770 V. 71.28% Mn, 0.15% Cr, 0.002% Mo, 0.22% Ni, 0.013% Cu and 0.28% V. Standard deviation, yo 0.002 8 0.003 2 0.0035 0.0024 0.002 8 0.003 0 0.003 4 0.002 8 0.003 3 0.002 5 0.0024 0.003 0October, 1983 DETERMINATION OF CHROMIUM(VI) 1251 One of the authors (K.H.R.) is grateful to the Council of Scientific and Industrial Research for awarding a Junior Research Fellowship. The authors also thank Prof. G. Aravamudan and Prof. T. V. Ramakrishna, Indian Institute of Technology, Madras, for their interest in this work. 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.References Snell, F. D., “Photometric and Fluorimetric Methods of Analysis, Part I,” Wiley-Interscience, New Yamamoto, Y., Murata, T., and Veda, M., Bunseki Kagaku, 1976, 25, 851. De Angelis, G., and Chiacchierini, E., Ric. Sci. Parte 1, 1966, 36, 53. Hushmi, M. H., Rashid, A., Ahmed, H., Ayaz, A. A., and Azam, F., Anal. Chem., 1965, 37, 1027. Subramanyan, B., and Eswar, M. C., Microchim. Acta, 1976, 579. Yamamoto, K., Ametani, K., and Anagai, K., Buaseki Kagaku, 1967, 16, 229. Johnston, J. R., and Holland, W. T., Mikrochim. Acta, 1972, 321. Tonasaki, K., Otomo, M., and Tauka, K., Bunseki Kagaku, 1960, 15, 683. Vartanyan, S. V., and Tarayan, V. M., Arm. Khim. Zh., 1976, 29, 303. Komatsu, S., and Takahashi, K., Nippon Kagaku Zasshi, 1962, 83, 879. McKaveney, J. P., and Freiser, H., Anal. Chem., 1958, 30, 1965. Buscarons, F., and Artigas, J., Anal. Chim. Acta, 1957, 16, 452. Yostsuyanigi, T., Takeda, Y., Yamashita, R., and Aronura, K., Anal. Chim. Ada, 1973, 67, 297. Snell, F. D., “Photometric and Fluorimetric Methods of Analysis, Part I,” Wiley-Interscience, New Berzas Nevado, J. J., Muiioz Leyva, J. A., and Roman Ceba, M., Talanta, 1976, 23, 257. Guzman, M., Perez Bendito, D., and Pino, F., Anal. Chim. Acta, 1976, 83, 259. Roman Ceba, M., Muiioz Leyva, J. A., and Berzas Nevado, J. J., Analyst, 1978, 183, 963. Roman Ceba, M., Muiioz Leyva, J. A., and Berzas Nevado, J. J., Anal. Quim., 1978, 74, 620. Roman Ceba, M., Muiioz Levya, J. A., and Berzas Nevado, J. J., Anal. Quim., 1978, 74, 1075. Ramakrishna, R. S., and Irving, H. M. N. H., Anal. Chim. Acta, 1969, 48, 251. Dutt, N. K., and Chakder, N. C., J . Inorg. Nucl. Chem., 1970, 32, 2303. Clark, R. J. H., Spectrochim. Acta, 1965, 21, 955. Levis, J., and Earshaw, A., Nature (London), 1958, 181, 1261. Wiles, D. M., and Suprunchuk, T., Can. J . Chem., 1969, 47, 1087. Reddy, K. H., and Reddy, D. V., Indian J . Chem., in the press. Alden, B. H., and Dean, J. A., Anal. Chem., 1957, 29, 1298. York, 1978, pp. 703-744. York, 1978, p. 715. Received March 8th, 1983 Accepted May 17th, 1983

ISSN:0003-2654    

DOI:10.1039/AN9830801247

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

1262 Analjst, October, 1983, Vol. 108, PP. 1252-1256 Analytical Met hods Corn m i ttee REPORT PREPARED BY THE MEDICINAL ACTIVITIES IN ANIMAL FEEDS SUB-COMMITTEE (B) Determination of Halofuginone Hydrobromide in Medicated Animal Feeds Keywords ; Halofuginone hydrobromide determination ; medicinal additives ; animal feeds ; high-performance liquid chromatography The Analytical Methods Committee has received and approved for publication the following report from its Medicinal Additives in Animal Feeds Sub-committee (B). Report The Constitution of the Sub-committee responsible for the preparation of this report was Mr. G. H. Smith (Chairman until March 1980), Mr. P. Sanderson (Chairman from March 1980), Mr. A. Anderson, Mrs. C. Billingshurst (from July 1980), Mr. C. G. Clifford (from October 1980), Mr.K. T. Chisnell (from November 198l), Mr. A. G. Croft, Dr. N. T. Crosby (from July 1981), Mr. G. Drewery, Mr. R. Fawcett (until February 1979), Dr. K. Field (until February 1979), Dr. M. J. Gliddon, Mr. E. Goodall (from December 1979), Mr. N. G. Hall (from December 1979 until November 1981), Mr. J. R. Harris (from February 1978 until July 1981), Mr. R. S. Hatfull, Dr. J. R. Salmon and Dr. R. Woodhouse, with (the late) Dr. N. W. Hanson (until August 1979) and Mr. J. J. Wilson (from September 1979) as Secretaries. Introduction Halofuginone hydrobromide, ( -J ) -trans-7-bromo-6-chloro-3- [3- (3-h ydroxy-2-piperidyl) - acetonyl]-4(3H)-quinazolinone hydrobromide, is an anti-coccidial drug added to poultry feeds at an inclusion concentration of 3 mg kg-l.H I “&;--CH2 - C O - C H z T .HBr Br HO The Sub-committee was provided with a method1 developed by the Huntingdon Research Centre. In this method halofuginone, in the form of the free base, was extracted into ethyl acetate, partitioned as the chloride into aqueous hydrochloric acid and concentrated using a macroreticular resin column. High-performance liquid chromatography (HPLC) , using an ultraviolet detector, was used to determine the final concentration of halofuginone. Experimental In the first series of tests, a number of different poultry feeds were taken and fortified with halofuginone hydrobromide by aqueous addition to each to produce spiked feeds containing 3.14 mg kg-l of halofuginone hydrobromide. The halofuginone hydrobromide content of these samples was determined and recoveries of 58-88% were obtained.The HPLC procedure was modified by the originating laboratory. A pBondapak C-18 analytical column replaced the Partisill0 ODS column and the mobile phase was altered from methanol - 0.25 M ammonium acetate buffer solution, pH 4.3 (7 + 3) to methanol - 0.125 M ammonium acetate buffer solution, pH 4.3 (6 + 4). The flow-rate was increased from 1.0 to 1.5ml min-l. Under these conditions recoveries of 93-95.7% were obtained from a feed fortified immediately prior to extraction and 73-92% from a feed fortified 30 min prior to extraction (the fortificaton level was 3 mg kg-l in both instances).ANALYTICAL METHODS COMMITTEE 1253 Further experiments gave mean recoveries of 94.3% from samples analysed immediately after fortification and 82.8% from samples analysed 30 min after fortification. The method was further modified by raising the flow-rate to 2 ml min-l and using acetoni- trile - 0.5 M ammonium acetate buffer solution (1 + 3) as the mobile phase.Recoveries of 93.&97.4y0 were obtained. Another laboratory, using substantially this method ,but with a 25-cm Partisil 10 column, obtained recoveries of 83-88y0. Some other laboratories, which had used the original method, reported recoveries of 80 and 91%. The originating laboratory made some further modifications to the method producing the procedure as given in the Appendix and carried out 60 determinations using three analysts. The mean procedural recovery value obtained was 93.4% with a coefficient of variation of 4.6%. Typical chromatograms are shown in Figs.1 and 2. 1. + + Ha lof ug inone/pg m 1- ' Fig. 2. Typical calibration chromato- grams for halofuginone. The arrows indicate the retention time of halofuginone. Fig. 1. Typical analytical chromatograms for halofuginone in poultry feed. (a) Fortified feed (3 mg k g ' ) ; and (b) control feed. The arrows denote the retention time of halofuginone. One laboratory medicated five feeds at approximately 3 mg kg-l and, using this method, obtained the results given in Table I. Further laboratories carried out analyses on samples spiked at approximately 3 mg kg-1 using this method and obtained the results given in Table TT II. TABLE I RECOVERY OF HALOFUGINONE HYDROBROMIDE FROM MEDIC14TED FEEDS Six determinations were made on each sample. Amount found/mg kg-l Recovery, yo Amount added to Sample feed/mg kg-1 S.D.*/mg kg-l A .... .. 2.97 2.91 2.52 2.73 0.14 98.0 86.0 B .. . . . . 3.00 2.62 2.26 2.40 0.12 87.3 76.3 c . . .. .. 3.00 2.85 2.66 2.75 0.09 95.0 88.6 D . . .. .. 3.01 2.70 2.53 2.60 0.06 89.7 84.1 E . . . . .. 3.03 2.81 2.56 2.66 0.09 92.8 84.3 * S.D. = standard deviation.1254 ANALYTICAL METHODS COMMITTEE : DETERMINATION OF Analyst, Yol. 108 TABLE I1 RECOVERY OF HALOFUGINONE HYDROBROMIDE FROM SAMPLES SPIKED AT THE 3 mg kg-1 LEVEL Recovery, yo No. of 7- Laboratory determinations Mean Range A .. .. .. .. 3 85.5 79.9-93.3 B .. .. .. .. 6 81.3 73.0-87.3 D .. .. .. .. 6 87.8 84.3-92.8 c .. .. .. .. 2 80.5 78-83 A collaborative exercise was arranged by the EEC Expert Working Group on the Determina- tion of Coccidiostats and, by permission of the Chairman, Dr.S. Dormal-van den Bruel, the results obtained by other members of this group are included with those of the Sub-committee. Three samples were circulated; these consisted of a blank feed (described as a broiler starter meal) (A), the same feed medicated with 3.27 mg kg-l of halofuginone hydrobromide (B) and a further amount of this medicated feed which had been formed into pellets (C). Partici- pants were asked to analyse these samples immediately on receipt and after storage for two months, under ordinary laboratory conditions (Table 111). TABLE I11 HALOFUGINONE HYDROBROMIDE CONTENT OF MEDICATED FEEDS Halofuginone hydrobromide contentlmg kg-I Sample B -7 Sample A After 2 Laboratory on receipt On receipt months A .... N.d.* 2.89 2.45 B .. .. 0.1 2.80 2.25 c .. .. 0 2.40 2.50 Dt . . .. N.d. 2.99 2.58 Et . . .. N.d. 3.16 3.07 Ft .. .. 0 3.29 2.81 G .. .. 0 1.90 1.80 H .. .. N.d. 3.00 1.90 Mean . . .. 2.80 2.42 S.D. .. .. 0.45 0.43 * N.d., not detected. t Laboratories D, E and F are members of the Sub-committee. Sample C On receipt 2.62 2.65 2.55 3.01 3.32 3.56 2.40 3.00 2.89 0.40 After 2 ’ months 2.20 2.35 2.62 2.63 3.26 2.59 2.05 1.95 2.45 0.42 The Sub-committee recommends the use of the method given in the Appendix for the determination of halofuginone hydrobromide in medicated poultry feeds. APPENDIX Determination of Halofuginone Hydrobromide in Animal Feeds Principle as the hydrochloride into aqueous acid solution.by the use of a macroreticular resin. phase column and a variable-wavelength ultraviolet detector. Halofuginone is extracted as the free base into ethyl acetate and subsequently partitioned Concentration of halofuginone is accomplished Final analysis is achieved by HPLC using a reversed- Reagents Water. Glass distilled. Halofuginone hydrobromide (standard mbstance) . Ethyl acetate. HPLC grade. Acetonitrile. HPLC grade. Supplied by Roussel Uclaf, Paris.October, 1983 HALOFUGINONE HYDROBROMIDE IN MEDICATED ANIMAL FEEDS 1255 Methanol. HPLC grade (used for analysis) and standard laboratory-reagent grade (used only for the purification of XAD-2 resin). Sodium chloride. Laboratory-reagent grade. Sodium carbonate. Analytical-reagent grade. Sodium carbonate solution, 10% m/V.Salt-saturated sodium carbonate solution, 5% m/V. Hydrochloric acid, sp. gr. 1.16. Hydrochloric acid solution, approximately, 0.1 M. Acetic acid, glacial. Analytical-reagent grade. Ammonium acetate. Analytical-reagent grade. Ammonium acetate bufer solution, 0.25 M. Dissolve 38.54 g of ammonium acetate and 60 ml of acetic acid in water and dilute to 2 1 in a calibrated flask. Amberlite XAD-2 resin. Wash 500 g of fresh resin with water until free from chloride ions (silver nitrate test) and, in a Soxhlet apparatus, extract with methanol (standard laboratory- reagent grade, approximately 2 1) overnight. Store under methanol (HPLC grade) in a stoppered glass bottle until use. Using methanol (HPLC grade) transfer 10 g of Amberlite XAD-2 resin into a glass chromatographic column.Add a small plug of glass-wool to the top of the resin bed. Drain the methanol from the column and wash the resin with 100ml of water, stopping the flow as the liquid level reaches the top of the resin bed. Allow the column to equilibrate for 10 min before use. Halofuginone stock standard solution. Dissolve an accurately weighed amount of halo- fuginone hydrobromide (approximately 50 mg) in ammonium acetate buffer solution and dilute to volume in a 250-ml calibrated flask with the buffer solution (this solution is stable for 3 weeks at 5 "C). Dissolve 100 g of sodium carbonate in water and dilute to 1 1 in a calibrated flask. Dissolve 50 g of sodium carbonate in water and dilute to 1 1 in a calibrated flask, add sodium chloride until the solution is saturated.Analytical-reagent grade. Dilute 10 ml of hydrochloric acid (sp. gr. 1.16) with water to 1 1 in a calibrated flask (actual acid concentration>O.l M). Preparation of XAD-2 column. Apparatus Liquid chromatograph with a variable-wavelength ultraviolet detector and a loop injector. Liquid chromatographic column, pBondapak C-18, 30 cm x 3.9 mm i.d. Glass chromatographic column, 30 cm x 1 cm i.d., jtted with a sintered-glass jlter. Rotary film evaporator. Typical Liquid Chromatograph Operating Conditions The following conditions were used: mobile phase, acetonitrile - 0.25 M acetate buffer solu- tion -water (5 + 3 + 12), adjusted to pH 4.3 with acetic acid after mixing; flow-rate, 2 ml min-l; detector sensitivity, 0-0.04 a.u.f .s. ; detector wavelength, 243 nm; injection volume, 40 p1; temperature, ambient (23&3 "C) ; and chart speed, 0.5 cm min-l.Under these conditions, the retention time for halofuginone is approximately 7 min and the number of theoretical plates, relative to halofuginone, is more than 2000. Procedure Transfer a 10-g sample of the finely divided feed into a centrifuge bottle. Add 1 O m l of sodium carbonate solution and 100 ml of ethyl acetate and macerate for 3 min. Centrifuge for 2 min and decant the ethyl acetate phase into a 500-ml separating funnel. Add a further 100 ml of ethyl acetate to the solid residue and macerate for 3 min. Centrifuge for 2 min and, by decanting, remove the ethyl acetate and add it to the solution in the separating funnel. Wash the combined extracts, for 1 min, with 50 rnl of salt-saturated sodium carbonate solution and discard the aqueous layer.NOTE-During the above operations, halofuginone (as the free base) should not remain in the ethyl Extract the organic layer for 1 min with 50 ml of 0.1 M hydrochloric acid. Remove the Re-extract the ethyl acetate, for 1.5 min, acetate for more than 30 min. lower acid layer into a 250-ml separating funnel.1256 ANALYTICAL METHODS COMMITTEE with a further 50 ml of 0.1 M hydrochloric acid and combine with the first extract . Wash the combined acid extracts, by swirling for approximately 10 s, with 10 ml of ethyl acetate. Quantitatively transfer the aqueous layer into a 250-ml round-bottomed flask and discard the organic phase. Evaporate all of the remaining ethyl acetate from the acid solution using a rotary film evaporator.Under a vacuum of 20 Torr all of the residual ethyl acetate will be removed within 5 min at 38 "C. Transfer the aqueous acid to the top of the prepared Amberlite XAD-2 column and elute, discarding the eluate. The rate of elution should not exceed 20 ml min-l. Rinse the round- bottomed flask with 20 ml of 0.1 M hydrochloric acid and use this to wash the resin column. Blow through any remaining acid solution with a stream of air. Discard the washings. Add 100 ml of methanol to the column and allow 5-10 ml to elute, collecting the eluate in a 250-ml round-bottomed flask. Leave the remaining methanol for 10 min to equilibrate with the resin and continue the elution at a rate not exceeding 20 ml min-l, collecting the eluate in the same round-bottomed flask.Evaporate the methanol to residual moisture on the rotary film evaporator, the temperature of the water-bath should not exceed 40 O C , and quantitatively transfer the residue into a 10-ml calibrated flask using the mobile phase. Dilute to volume with mobile phase. The temperature of the water-bath should not exceed 40 "C. Procedural Recoveries Transfer by pipette 5 ml of the stock standard solution of halofuginone hydrobromide into a 100-ml calibrated flask and dilute to volume with water (this solution contains approximately 10 pg ml-l of halofuginone). Transfer by pipette 3 ml (equivalent to 30 pg of halofuginone) of this solution on to 1Og of unmedicated (control) feed and proceed immediately with the analysis.Instrument Calibration Dilute the stock standard solution of halofuginone hydrobromide with HPLC mobile phase to provide calibration solutions in the range 0-6 pg of halofuginone hydrobromide per milli- litre. Inject 40-pl portions of these solutions on to the liquid chromatograph. Calculation of Results Construct a calibration graph of chromatographic peak height in millimetres veYsws con- centration of halofuginone hydrobromide at injection in micrograms per millilitre. For each of the sample extracts, measure the chromatographic peak height at the characteristic reten- tion time for halofuginone hydrobromide. Determine, by interpolation from the calibration graph, the concentration of halofuginone hydrobromide in the sample extract (at analysis) and hence in the original sample as shown below: (A-a) C Concentration of halofuginone hydrobromide/mg kg-l = - B where A is the peak height in millimetres; a, the intercept at x = 0 of the calibration graph, in millimetres; B, the gradient of the calibration graph; C, the total volume of sample extract (at analysis) in millilitres; and D, the mass of diet extracted in grams. Correct, as necessary, according to procedural recovery data : where a, A , B, and C are as above and E is the amount of halofuginone hydrobromide in micrograms added to the control feed. Reference 1. Anderson, A., Christopher, D. H., and Woodhouse, R. N., J. Ckromatogr., 1979, 168, 471.

ISSN:0003-2654    

DOI:10.1039/AN9830801252

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

Analyst, October, 1983 SHORT PAPERS 1257 Simultaneous Determination of Lead and Tin in Fruit Juices and Soft Drinks by Potentiornetric Stripping Analysis Saverio Mannino Istituto d i Chimica Agraria, University of Milan, Via Celoria 2, 20133 Milan, Italy Keywords : Tin determination ; lead determination ; potentiometric stripping analysis; fruit juices; soft drinks Potentiometric stripping analysis (PSA), recently reviewed by Jagner,l has been shown to be a technique well suited to the determination of some trace metals of nutritional and toxicological interest. The technique has recently been described for the determination of lead in fruit juices and soft drinks and the extent of the interference between lead and tin has also been reported.2 This paper describes a method for the simultaneous and direct determination of lead and tin based on potentiometric stripping analysis, using methanol as a supporting electrolyte.In this medium, at pH 1, lead and tin signals do not overlap and both elements can be determined simultaneously . Experimental Reagents and Instrumentation reported previously.2 Unless otherwise specified, all reagents and solutions employed were identical with those Methanol. Analytical-reagent grade (Koch-Light) . Tin standard solutions, 1.0 g dm-3. Aristar grade (BDH Chemicals Ltd.). Potentiometric measurements were carried out with an ISS820 Ion Scanning system (Radiometer) as described previously.2 Atomic-absorption measurements were performed with a Pye Unicam SF9 single-beam instrument using a dinitrogen oxide - acetylene burner head for the determination of tin and an ESA, Model 3010A, anodic stripping voltammeter for the determination of lead.Procedure Sample preparation necessary. previously2 except that 20 g of sample were used. Soft drinks were acidified to a pH of 1 with 37% hydrochloric acid and de-gassed when Fruit juices required treatment with dilute hydrochloric acid at 40 "C as described Electrode ere-t reatment This was previously reported.2 Analytical procedwe Pipette 2 cm3 of acidified sample into the electrochemical cell and add 18 cm3 of previously de-aerated methanol. Add 0.2 cm3 of the mercury(I1) stock solution, start stirring and remove oxygen by bubbling with nitrogen for 5 min. Select the following working parameters: electrolysis potential, -1.1 V versus S.C.E., and electrolysis time, 2 min.After de-aeration allow nitrogen to pass above the sample surface and perform two plating - stripping cycles of analyses. Add appropriate aliquots of the standard solutions of the two elements and evaluate the concentration from the standard additions graphs. Two standard additions were made and each time two plating - stripping cycIes of analyses were performed.1258 SHORT PAPERS AIzalyst, Vol. 108 Results and Discussion In preliminary experiments, using PSA, the behaviour of lead and tin was investigated in a variety of supporting electrolytes including acetate, tartrate and ammonium acetate buffer solutions. Although ammonium acetate solution, at pH 4.6, was the most sensitive and effective medium for tin - lead separation, it could not be used because of the presence, in the samples under study, of citric acid, which shows a great masking effect on the tin signal.This can be attributed to the formation of a tin-citric acid complex with a high conditional stability constant. The concentrations of lead and tin were determined in bottled and canned products by the proposed method and the results were compared with those obtained by an anodic stripping voltammetric method3 for lead and by an atomic-absorption method for tin.* The average results of triplicate analyses are reported in Table I. Close agreement between the different methods for the determination of both elements was encountered for all samples that varied appreciably in tin and lead concentrations.TABLE I DETERMINATION OF TIN AND LEAD IN FRUIT JUICES AND SOFT DRINKS Sample Bottled orange juice . . .. Canned orange juice . . .. Canned orange juice . . .. Canned grapefruit juice . . Bottled pear juice . . .. Canned tomato juice . . .. Canned orangeade: . . .. Canned lemonade: . . .. Canned soda: . . . . .. . I Tin concentration*/pg g-l P PSAt AASt 38 40 120 125 62 55 230 225 25 28 so 50 0.150 0.140 5 6 0.120 0.130 Lead concentration*/pg g-1 P PSAt ASVt 0.280 0.270 0.160 0.180 0.400 0.380 0.255 0.250 0.350 0.340 0.400 0.430 0.095 0.100 0.155 0.160 0.060 0.060 * Values based on three replicate determinations. PSA, potentiometric stripping analysis ; AAS, atomic-absorption spectrometry; ASV, anodic Aluminium cans. stripping voltammetry. A typical stripping potentiogram of a synthetic solution showing a good separation of lead, tin, copper and cadmium signals in methanol medium (pH 1.0) is presented in Fig.1. The stripping potentials for cadmium, tin, lead and copper are -0.75, -0.61, -0.53 and -0.36 V (all verszts S.C.E.), respectively. By increasing the water content, the tin signal is shifted towards less negative potentials and an overlap of the tin and lead signals occurs when the water content in methanol is about 40% V/V. To ensure an adequate separation it is therefore recommended not to exceed a 20% water content in methanol. The stripping potential depends, however, on the water to methanol ratio. -0.9 -0.7 -0.5 -0.3 PotentialN vs. S.C.E. Fig. 1. Potentiometric stripping curve of a standard solution showing good separation of tin (50 p.p.b.), lead (75 p.p.b.), cadmium (75 p.p.b.) and copper (10 p.p.b.) in methanol medium at pH 1.0.October, 1983 SHORT PAPERS 1259 As tin is usually present in the type of food examined at concentrations higher than those of lead, the influence of adding an excess of tin was also investigated.It was found that lead and tin can be simultaneously determined even in a concentration ratio of 1 : 1000, by operating at anodic potentials of -1.1 V veisus S.C.E. As can be seen from Fig. 2, the tin signal is highly dependent on the plating potential, whereas the lead signal is virtually constant. It is consequently possible to increase or decrease the tin signal response by modifying the plating potential and tin and lead can be simultaneously determined even when present in an unfavour- able ratio.Fig. 3 shows two stripping graphs obtained by operating at -0.8 V v e i s m S.C.E. in tomato and grapefruit samples, which contained amounts of lead and tin in the ratio of about 1 : 100 and 1 : 1000, respectively. However, con- sidering that this element was found in a negligible amount in the samples under study and that some samples were diluted prior to analysis, no significant interference was noted. As already reported,2 copper also shows a masking effect on the tin signal. v) (0 S tn v) \ - .- I I 1 I 1 I -0.7 -0.8 -0.9 -1.0 -1.1 -1.2 PotentialN vs. S.C.E. - Sn Jsn Fig. 2. Influence of the electrolysis potential on the a, tin and .. lead signals. -0.6 -0.4 -0.2 PotentialN vs. S.C.E. Fig. 3. Stripping potentiograms of A, tomato and B, grapefruit samples. Con- ditions : electrolysis voltage - 0.8 V zlers'sus S.C.E.; electrolysis time 4 min; and chart speed (A) 0.5 cm s-l and (B) 0.2 cm s-l. Recovery To determine the recovery of lead and tin, appropriate volumes of lead and tin standard solutions were added to all samples examined, Both spiked and unspiked samples were analysed in triplicate by the proposed method. The results obtained show recoveries ranging from 93 to 105% for lead and from 92 to 107% for tin. Detection Limit In potentiometric stripping analysis the detection limit depends mainly on the plating time. If 16 min is regarded as the maximum practical electrolysis time and a stripping plateau of 0.1 cm is considered to be the minimum measurable signal, the detection limit for tin and lead is of the order of 1 p.p.b.(1 part in lo9) at an electrolysis potential of -1.1 V veisysus S.C.E. and a chart speed of 1 cm s-l. Repeatability The repeatability of the proposed method was assessed by means of ten replicate analyses of two food samples containing different concentrations of lead and tin and requiring different pre-treatments. At such concentration levels the relative standard deviations for lead and tin were 3.5 and 4.6% for tomato juice and 3.2 and 5.2% for orangeade, respectively.1260 SHORT PAPERS Analyst, Vol. 108 Conclusions A simple, rapid method has been developed for the simultaneous determination of lead and tin in fruit juices and soft drinks. The use of methanol as a supporting electrolyte permits the determination of both elements with little or no sample pre-treatment. Good agreement between potentiometric stripping and atomic-absorption data confirms the efficiency of the proposed method and the applica- bility of potentiometric stripping analysis to food samples with a minimum of sample manipu- lation. References 1. 2. 3. 4. Jagner, D., Analyst, 1982, 107, 593. Mannino, S., Analyst, 1982, 107, 1466. Horwitz, W., Editov, “Official Methods of Analysis of the Association of Official Analytical Chemists,” Thirteenth Edition, Association of Official Analytical Chemists, Washington, DC, 1980, pp. 399. Dabeka, R. W., and McKenzie, A. D., J. Assoc. OH. Anal. Chem., 1981, 64, 1297. Received February 25tk, 1983 Accepted May 9th, 1983

ISSN:0003-2654    

DOI:10.1039/AN9830801257

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

1260 Differential Electrolytic Potentiometry with Periodic Po I a risa tio n Part XXVIII.* Polarisation in Oxidation Titrimetry with Lead(lV) Acetate in Anhydrous Acetic Acid Direct and Mark-space Biased Periodic E. Bishop and Abdalla M. S. Abdennabit University of Exeter, Chemistry Defiartment, Stocker Road, Exeter, EX4 4QD Keywords ; DiBerential electrolytic potentiometry ; non-aqueous oxidation titration; lead(I V ) acetate ; periodic polarisation ; anhydrous acetic acid solvent Lead(1V) acetate is an extensively used oxidant,l often employed in glacial acetic acid solution, in which the water accelerates many of the reactions. Conditional potentials in various media have been reported,2J which indicate strong oxidising powers if hydrolysis is avoided. Anhyd- rous media do not appear to have been examined.Potentiometric titration has been ~ s e d , ~ ~ but polarised electrodes have not. Direct current (d.c.) and mark-space biased square wave periodic (m.s.b.) differential electrolytic potentiometry (DEP) are compared with zero-current potentiometry for a selection of titrations with lead(1V) acetate in anhydrous acetic acid. Experimental The apparatus, general procedure and the preparation of anhydrous acetic acid and of solutions have been d e ~ c r i b e d . ~ ~ ~ The supporting electrolyte was 0.05 mol 1-1 lithium per- chlorate in anhydrous acetic acid. Lead(1V) acetate solzction, approximately 0.04 moll-l. The approximate mass of lead( IV) acetate (BDH Chemicals Ltd.), drained of its accompanying glacial acetic acid, was rinsed with anhydrous acetic acid and dissolved in the approximate volume of anhydrous solvent.The solution was standardised by the addition of an excess of iodide and titrated with standardised thiosulphate using starch as the indicator. The result was checked by electro- metric titration of 0.1 mol 1-1 AnalaR quinol. The solution is stable,l provided that no excess of acetic anhydride is used. * For Part XXVII of this series see reference list, p. 1262. t Present address : University of Petroleum and Minerals, P.O. Box 144, Dhahran International Airport, Dhahran, Saudi Arabia.October, 1983 SHORT PAPERS 1261 Results and Discussion Several were too slow for direct titration, despite the high potential of the reagent system: resorcinol, arsenic( 111) chloride (surprisingly1), bis(pentane-2,4-dionato)oxovanadium( IV), lithium chlor- ide and sulphur dioxide.Examples of successful determinations are given in Figs. 1 and 2. Most of the differential curves are peaks of type 1, showing degrees of charge transfer over- potential originating as shown by the anodic and cathodic curves, and indicating moderately fast electrode processes. The products and molar reacting ratios are, as expected, quinol: 1,4- benzoquinone, 1 : 1 ; catechol : 1,2-benzoquinone, 1 : 1 ; a-toluenethiol : disulphide, 2 : 1 ; ascorbic acid : dehydroascorbic acid, 1 : 1 ; lithium bromide : bromine, 2 : 1 ; and lithium iodide : iodine 2: 1. Generally, the m.s.b. potentials equilibrate quickly, showing enhanced symmetry and lower charge transfer overpotential in the curves, the d.c.potentials follow and the zero-current potentials equilibrate considerably more slowly ; the m.s. b. electrodes retain unimpaired activ- ity for long periods, while adsorption fouling is evident in the other electrodes, particularly the zero-current electrode. The 1 ,kdihydroxybenzene reaction is fast and the titration is highly satisfactory, whereas the 1,2-dihydroxybenzene reaction is slow, equilibration near equivalence taking 30 min, and the quality of this titration and that of a-toluenethiol are decidedly worse, although acceptable. The titration of ascorbic acid is excellent, but the zero-current electrode suffers from adsorption of the inactive dehydro compound. The titration curves for bromide are curious, characteristic of type 2(A), with the rising-Z shape of an extremely electrodically slow titrant.This behaviour can be ascribed to the strong adsorption of bromide, perhaps as lead(I1) bromide, on all electrodes. The titration of iodide is eminently satisfactory, but the determination is useless, because on dissolution of lithium iodide in anhydrous acetic acid iodine is immediately liberated to the Generally, reactions appear to be slower in anhydrous than in glacial acetic acid. 960 880 800 4 3 E iu' 640 y 720 > ~ ~ 0.0 0.2 ml 1 560 - 480 - 2 / 3 4 A Z C 5 400 I Volume of 0.038 mol I-' lead(N) acetate/mt Fig. 1. Titration curves of 1, 2.00 ml of 0.05 moll-' quinot; 2, 10.00 mol of 0.01 moll-' 1,2-dihydroxy- benzene; 3, 2.00 ml of 0.1 moll-l a-toIuenethio1; 4, 10.00 ml of 0.01 moll-' L-ascorbic acid; 5, 10.00 ml of 0.01 rnoll-l lithium bromide; and 6, 10.00 ml of 0.01 moll-' lithium iodide with 0.038 mol 1-1 lead(IV) acetate in anhydrous acetic acid.A, Anode - S.C.E. potential; C, cathode - S.C.E. potential; 2, zero- current electrode - S.C.E. potential. A cm-*, rn.s.b. bias 23%, frequency 60 Hz. D.c. current density, 3 x1262 SHORTPAPERS Analyst, Vol. 108 extent, under present circumstances, of about 20%. This is not due to dissolved oxygen in the solvent, careful deoxygenation afforded no improvement. The covalency of lithium halides dictated their choice as analytes on the grounds of their solubility in the ion-pairing solvent. This, and the peculiar properties of completely water-free acetic acid, lead to the establishment of an equilibrium between iodine and iodide.300 > 5 200 .ll 100 1 2 3 4 5 6 Volume of 0.038 mol I-’ lead(1V) acetate/ml Fig. 2. Differential curves corresponding to titration curves in Fig. 1. Solid lines, d.c. DEP; broken lines, m.s.b. DEP. Analytical Validity The d.c. and m.s.b. DEP end-points coincided in all instances with the acknowledged2s3 zero-current end-points and were much more easily located. A series of titrations of quinol gave a standard deviation of 0.018 ml for x = 26.32 ml for n = 6, which is on the limit of the experimental error of careful volumetric titrimetry. Conclusions The applicability of lead(1V) acetate as an oxidative titrant is more restricted in anhydrous than in glacial acetic acid on account of a slower reaction. Both d.c. and m.s.b.DEP offer improvement over classical potentiometry in the ease of location of the end-point, and m.s.b. DEP has the additional attraction of accelerated equilibration of potentials and enhanced active duration of the electrodes. References 1. 2. 3. 4. 5. Berka, A., Vulterin, J., and Zfka, J., “Newer Redox Titrants,” Pergamon Press, Oxford, 1965, p. 76. TomiEek, O., and Valcha, J., Chem. Listy, 1950, 44, 283. Berka, A., Dvoiak, V., N6mec, I., and Zfka, J., J . Electroanal. Chem.. 1962, 4, 150. Abdennabi, A. M. S., and Bishop, E., Analyst, 1982, 107, 1032. Abdennabi, A. M. S., and Bishop, E., Analyst, 1983, 108, 1227. NOTE-References 4 and 5 are to Parts XXV and XXVII of this series, respectively. Received March 25th, 1983 Accepted May 9th, 1983

ISSN:0003-2654    

DOI:10.1039/AN9830801260

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

October, 1983 SHORT PAPERS 1263 Spectrophotometric Determination of Palladium in Alloys and Minerals with 4-Amino-5-Nitrosopyrimidine=2,6-diol Ajai Kumar Singh, Bani Roy" and Rajendra Pal Singh" Department of Chemistry, Indian Institute of Technology, New Delhi-110 016, India Keywords : Palladium determination ; 4-amino-5-nitrosopyraimidine-2,6-diol ; spectrophotometry ; alloys ; minerals Nitrosopyrimidinols act as better spectrophotometric reagents for Fe(II), Co(II), Ru(II1) and Rh( 111) than nitrosopyridinols, naphthols and phenols.lS2 However, the pyrimidine nucleus with the -C(NO)=C(OH)- grouping has been little investigated for its complexation reaction with palladium. This paper describes the use of 4-amin0-5-nitrosopyrirnidine-2~6-diol (4-ANP) (Fig. 1) for the spectrophotometric determination of this metal.Fig. 1. Structure of 4-ANP, which has the following Amax. (nm) and Emax, (1 mol-l cm-l): 260, 3.1 x lo3; 312, 8.8 x loa; and 610, 6.1 x lo1, respectively. Experiment a1 Reagents and Apparatus Stock solutions of palladium(I1) and other salts were prepared from analytical-reagent grade compounds and standardised. The stock solutions were appropriately diluted to the desired concentrations when necessary. 4-ANP was procured from K and L Laboratories (USA) and a 0.01 M solution was prepared in doubly distilled water. A Perkin-Elmer, Model 554, (ultraviolet - visible) spectrophotometer, with matched cells of 10-mm path length, was used for absorbance measurements. A Beckman Expandomatic SS-2 pH meter with glass and calomel electrodes was used for pH measurements.Procedure for the Determination of Palladium acid and 2 ml of 0.006 M 4-ANP solution. 400 nm against a water blank. To a suitable aliquot (palladium content between 18 and 50 pg) add 2 ml of 10 N' hydrochloric Dilute to 10 ml and measure the absorbance at Calculate the palladium content from the calibration graph. Results and Discussion Characteristics of Palladium( 11) - 4-ANP Complex Addition of aqueous 4-ANP to palladium(I1) solution results instantaneously in the forma- tion of a brown precipitate that dissolves when the acidity is brought to 0.4 N. The absorbance of the resulting brown - yellow complex [Amax. = 400 nm, molar absorptivity(€) = 1.88 x lo4 1 mol-l cm-l] attains a maximum in the presence of 1.5-2.5 N' hydrochloric acid and re- mains constgnt for 14 h.For full colour development, a 30-fold excess of the ligand over palladium is needed. Because the ligand solution becomes colourless at acidity >1 N and does not absorb at 400 nm, the water blank, in this instance, is suitable for the absorbance measurements. The composition of the complex has been found to be 1:2 (palladium to ligand) by Job's method; Beer's law is followed up to 10 p.p.m.; the range for an accurate determination, found from a Ringbom plot, is 1.8-5.0 p.p.m. ; Sandell's sensitivity of the * Present address: University of Delhi, New Delhi-110 007, India.1264 SHORT PAPERS Analyst, Vol. 108 reaction is 0.005 pg cm-2 and the coefficient of variation for six determinations a t 2.7 p.p.m. of palladium is calculated to be 0.33%.Effect of Diverse Ions The effect of diverse ions in the determination of 2.7 p.p.m. of palladium has been studied. An error of & 2% in the absorbance reading was considered tolerable. Tolerance limits (in p.p.m.) are given in parentheses along with those of the masking agent, if required: F-, Br-, CH,COO-, C2042-, tartrate (8000) ; I- (2000) ; S2032-, EDTA (1 500) ; Sod2-, citrate, (1 000) ; NO3-, BO:-, (500); NO2-, SCN- (50); CN- (15); Ca(II), Sr(II), Ba(I1) (200); Ni(II), Cu(II), Fe(II), (150, EDTA) ; Mg(II), Al(II1) (100) ; Ir(III), Pt(1V) (60) ; Zn(II), Cd(II), Ru(III), Os(VII1) (50) ; Fe(II1) (25, F-) ; Sn(II), Pb(II), Mn(II), V(V) (20) ; Hg(I1) (20, I-) and Ag(1) (40). Cobalt(II), Au(II1) and Rh(II1) do not form complexes with 4-ANP if the solution is made acidic before ligand additi0n.l Using this modification in the procedure, 80 p.p.m.of each of these metals can be tolerated; however, thiourea interferes seriously. Comparison with Other Reagents On comparing 4-ANP with other reagents having the -C(NO)=C(OH)- grouping on a benzene, naphthalene or pyridine ring, it is found that this compound is far superior in sensitivityss4 (Sandell’s sensitivity for nitrosonaphthols, phenols and pyridinols is ca. 0.01 pg cm-2). The method for palladium determination is very selective as all the platinum and transition metals are tolerated in large amounts. Its commercial availability, complexation in an aqueous medium, simplicity, rapidity and high precision are other distinct advantages that make the use of this reagent for the determination of trace amounts of palladium attractive.TABLE I DETERMINATION OF PALLADIUM IN ALLOYS, MINERALS AND CATALYSTS I Alloy/mineral/catalyst Jewellery alloy (95% Pd - 4.5% Ru) . . Stibiopalladinite .. .. Porperzite mineral . . .. .. .. Pd - asbestos catalyst . . .. .. . . Pd - A1,0, catalyst . . . . .. .. Pd - CaSO, catalyst . . .. .. .. Pd - BaSO, catalyst . . .. .. .. Pd - charcoal catalyst . . .. .. .. Au - Pt - Pd (dental) alloy . . . . .. Au - Pd (dental) alloy . . .. .. .. . . Jewellery alloy (50% Pd - 5OO/b‘Au) . . . . * Average of six determinations. Palladium content, yo Reported 95 75 50 6.7 4.34 4.14 5.91 10.02 9.01 0.16 2.26 Found* 94.93 75.03 50.06 6.68 4.33 4.16 5.89 10.06 9.00 0.162 2.25 Relative standard deviation, yo 2.60 2.40 1.96 1.42 0.84 0.76 0.80 0.82 0.75 1 .oo 0.65 Determination of Palladium in Alloys, Catalysts and Minerals The samples were brought into solution by the procedures reported in the literature5ss and the palladium contents of these solutions were determined by the recommended procedure. The results are recorded in Table I. References 1. 2. 3. 4. 5. 6. Singh, A. K., Mukherjee, B., Singh, R. P., and Katyal, M., Tulunta, 1982, 29, 95. Katyal, M., McBryde, W. A. E., and Singh, A. K., “Pyrimidines: Analytical Aspects,” South Asian Snell, F. D., “Photometric and Fluorimetric Method of Analysis, Parts I and 11,” John Wiley, New Sandell, E. B., and Onishi, H., “Photometric Determination of Traces of Metals,” John Wiley, New Beamish, F. E., “The Analytical Chemistry of Noble Metals,” Pergamon Press, Oxford, 1966. Salvin, W., “Atomic Absorption Spectroscopy,” Interscience, New York, 1968. Publishers, New Delhi, 1981. York, 1978. York, 1978. Received February 22nd, 1983 Accepted May loth, 1983

ISSN:0003-2654    

DOI:10.1039/AN9830801263

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

October, 1983 SHORT PAPERS 1265 Separation of Dichlorophenol Isomers by Gas = Liquid Chromatography Aoi Ono Defiartment of Chemistry, Faculty of Education, Niigata University, Niigata 950-2 1, Japan Keywords : Gas - liquid chromatography ; dichlorophenol isomer separation ; dibenzo-l8-crown-6 The gas-chromatographic analysis of dichlorophenol isomers as the free phenol have been previously described.l-' Despite the difficulty of the analysis of these isomers as the free phenol, excellent resolutions using a modified Bentone-34 liquid stationary phase with mannit018 have been reported. Recently, an effective liquid stationary phase, dibenzo-18- crown-6, was found and important results concerning its application to the separation of dichlorophenol isomers have been obtained. Experimental Stationary Phases The following chemicals were all of Pure grade, unless stated otherwise, and used without further purification.The crown ethers dibenzo-18-crown-6, dicyclohexyl-18-crown-6 and 18-crown-6, were obtained from Nippon Soda Co. Ltd (Tokyo, Japan) ; silicones KF-54, KF-53, KF-56, KF-50 (phenylmethylpolysiloxane), KF-965 (methylpolysiloxane) and FL-100 (trifluoropropylmethylpolysiloxane) were obtained from Shinetsu Chemical Co. (Tokyo, Japan) ; silicone SH-7 10 (50% phenylmethylpolysiloxane) , was obtained from Torey Silicone Co. Ltd. (Tokyo, Japan) ; and dioctyl phthalate (DOP) and terephthalic acid of guaranteed grade were obtained from Nakarai Chemical Co. (Kyoto, Japan). Terephthalic acid was further purified by recrystallisation.Samples purified prior to use. Dichlorophenol isomers of Guaranteed grade from Tokyo Kasei Co. (Tokyo, Japan) were Apparatus was used. A Shimadzu, Model GC-5A, gas chromatograph equipped with a flame-ionisation detector Chromatographic Procedure The separation column was a 2.25 m x 3 mm i d . stainless-steel U-tube packed with acid- washed firebrick C,, (60-80 mesh) support (Johns-Manville, Denver, CO, USA) coated with 20% m/m of the stationary phase, The column and injector temperatures were 140 and 270 "C, respectively. Nitrogen was used as the carrier gas at a flow-rate of 25 cm3 min-l. Results and Discussion As previously discussed: it is very tlificult to analyse dichlorophenol isomers as the free phenol by gas - liquid chromatography. Harry and Normans reported this difficulty and separated the isomers as their methyl ethers.Modified Bentone-34, with sorbitol or mannitol, was the most effective, and Bentone-34 with rnannitol provided an excellent separation and base-line resolution.8 Adenosine, inosine, 2,4,7-trinitroAuoren-9-one and polyethylene glycol 1540, etc.,lo--12 which gave effective resolutions of xylenol isomers, did not provide an effective separation of di- chlorophenol isomers. In contrast, dioctyl phthalate,13Ja efiective for the separation of cresols and xylenols, was examined and appreciable resolutions were obtained8 for which the data are given in Table I. Subsequently, terephthalic acid was examined as a possible separation medium because a1266 SHORT PAPERS Analyst, Vol. 108 TABLE I RELATIVE RETENTION' OF DICHLOROPHENOL ISOMERS Relative retention* I 2,6-Dichloro- 2,5-Dichloro- 2,4-Dichloro- 2,J-Dichloro- 3,5-Dichloro- 3,4-Dichloro- , 2,6-dichlorophenol/ Retention time of A Stationary phase phenol phenol phenol phenol phenol phenol min Terephthalic acid .. . . 1.25 1.00 1.00 1.06 2.97 3.67 Silicone KF-50 .. . . 1.14 1.00 1.00 1.00 2.64 3.07 Silicone KF-53 . . .. 1.20 1.00 1.00 1.08 2.68 3.33 Silicone KF-54 . . . . 1.26 1.00 1.00 1.10 2.79 3,55 Silicone KF-56 . . .. 1.18 1.00 1.00 1.07 2.77 3.23 Silicone KF-965 . . . . 1.16 1.00 1.00 1.00 2.67 3.00 Silicone FL-100 . . . . 1.30 1.00 1.00 1.00 2.25 3.05 Silicone SH-710t . . . . 1.28 1.00 1.00 1.12 2.48 3.13 Dibenzo-18-crown-6 . . . . 1.00 1.08 1.23 1.42 8.50 12.50 Dicyclohexyl-18-crown-6 . . 1.00 1.10 1.10 1.16 8.32 11.24 18-Crown-6 .. . . 1.00 1.00 1.00 1 .oo 4.76 7.12 Dioctyl phthaiite . . . . 1.00 1.04 1.04 1.11 5.10 - * Relative to retention time of 2,6- or 2,5-dichlorophenol (Le., to the shortest retention time). t At 170 "C. 8.60 8.40 10.80 14.20 8.90 5.90 2.65 9.40 2.40 5.00 1.70 14.30 strong hydrogen bonding interaction would be expected (Table I). Although the 2,4- and 2,5-dichlorophenol isomers could not be separated using terephthalic acid, it provided some appreciable resolutions. Likewise, the crown ethers dibenzo-18-crown-6, dicyclohexyl-18- crown-6 and 18-crown-6 were examined ; dicyclohexyl-18-crown-6 did not resolve the 2,4- and 2,5-isomers, 18-crown-6 separated only the 2,3-, 33- and 3,4-isomers but dibenzo-18-crown-6 resolved all the isomers and provided appreciable resolutions. As a result, it was postulated that the oxygen atoms arranged in the six-membered ring in hexaoxacyclooctadecane (cyclic oxygens) is effective in the separation ; further, it was per- ceived that phenyl groups play an important role in their analysis.Fig. 1 shows effective separations of dichlorophenols on dibenzo-18-crown-6. Silicones KF-54, KF-53, KF-56 and KF-50 are phenylsilicones and their phenyl contents are as follows : KF-54, ca. 25%; KF-53, ca. 20%; KF-56, ca. 18%; and KF-50, ca. 5%. Silicones KF-50, KF-965 and FL-100 could not resolve 2,4-, 2,5- and 2,3-isomers. Silicones KF-54, KF-53 and SH-7 10 gave appreciably effective resolutions. 0 10 20 Retention timehin 30 Fig. 1. Separation of dichlorophenol isomers by a column coated with 20% dibenzo-18-crown-6 on C,, 60-80 mesh at 140 "C.Peaks: 1, solvent; 2, 2,6- dichlorophenol ; 3, 2,5-dichlorophenol; 4, 2,4-dichlorophenol; 5, 2,3-dichloro- phenol ; 6, 3,5-dichlorophenol; and 7, 3,4-dichlorophenol.October, 1983 SHORT PAPERS 1267 As shown in Table I, for the separation on polysiloxanes, the greater the phenyl content, the better is the separation and it is therefore concluded that the phenyl group plays an important role in the separation of dichlorophenol isomers on polysiloxanes. The elution order on silicones KF-54, KF-53, KF-56, KF-50, KF-965, SH-710 and FL-100 is the same as the order of increase in boiling-point (2,5-, 2,4-, 2,3-, 2,6-, 3,5- and 3,4-dichlorophenol) and that on dioctyl phthalate, a Bentone-34 modified with sorbitol or mannitol and crown ethers, is 2,6-, 2,5-, 2,4-, 2,3-, 33-, and 3,4-isomers, which is different from the former elution order.Conclusion Although it is difficult to analyse dichlorophenol isomers as the free phenol by gas - liquid For the resolution It is con- chromatography, their isomers were resolved well on dibenzo-18-crown-6. on polysiloxanes, the elution order followed the order of increase in boiling-point. cluded that phenyl groups present in liquid stationary phases play an important role. The author thanks Nippon Soda Co. Ltd., Shinetsu Chemical Co. and Torey Silicone Co. Ltd. for kindly supplying the crown ethers, polysiloxanes and silicone SH-7 10, respectively. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. References Barry, J. A., Vasishth, R. C., and Shelton, F. J., Anal. Chem., 1962, 34, 67. Kolloff, R. H., Breuklander, L. J., and Barkley, L. B., Anal. Chem., 1963, 35, 1651. Sugi, A., Dan, M., and Fujihara, M., Nippon Daigaku Yakugaku Kenkyu Hokoku, 1963, 5-6, 13. German, I. A., and Ciot, N., Rev. Chim. (Bucharest), 1966, 17, 177; Chem. Abs.fr., 1966, 65:61216. Andrzei, N., Aleksy, P., and Stanislaw, W., Chem. Anal. (Warsaw), 1969, 14, 1115. Ress, J., and Higginbotham, G. P., J . Chromatogr., 1970, 47, 474. Hudzik, M., and Sokolowska, J., Chem. Anal. (Warsaw), 1971, 16, 183. Ono, A., Takase, T., and Komagata, H., Fresenius 2. Anal. Chem., 1982, 313, 533. Harry, D. R., and Norman, R. 0. C., J . Chern. SOG., 1961, 3604. Ono, A. J., Chrornatogr., 1980, 193, 300. Ono, A., Chromatographia, 1980, 13, 574. Ono, A., Chromatographia, 1980, 13, 752. Sassenberg, W,, and Wrabetz, K., Fresenius 2. Anal. Chem., 1961, 179, 333. Sassenberg, W., and Wrabetz, K., Fresenius 2. Anal. Chem., 1961, 184, 423. Received January 7th, 1983 Accepted May 17th. 1983

ISSN:0003-2654    

DOI:10.1039/AN9830801265

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

1267 Initial Deactivation of Florisil Adsorbent for Column Chromatographic Separation of Lipids Toru Todoroki" and Kazuhiro lmai Faculty of Pharmaceutical Sciences, University of Tokyo, 7-3-1 Hongo, Bukyo-ku, Tokyo, 113, Japan Kojiro Matsumoto and Shojiro Kano Keio University, 35 Shinanomachi, Shinjuku-ku, Tokyo, 160, Japan Keywords : Florisil column chromatography ; lipid separation Florisil column chromatography has been used extensively for the separation of lipids,l but its high adsorptive activity often resulted in low recoveries of lipids and low reproducibility. Therefore, to lower the activity and keep its activity constant, pre-conditioning of Florisil with 50% V/V methanol solution was performed, and better resolution and recoveries for all classes of lipids were obtained, as described in this paper.* To whom correspondence should be addressed. Present address : School of Medicine, Keio University, 35 Shinanomachi, Shinjuku-ku, Tokyo, 160, Japan.1268 SHORT PAPERS Analyst, VoE. 108 Experimental Reagents Special-grade organic solvents were obtained from Kanto Kagaku (Tokyo, Japan). Florisil was purchased from Iwai Kagaku (Tokyo, Japan). Lipid standards for Florisil column chromatography were obtained from Sigma (St. Louis, MO, USA), BDH Chemicals (Poole, Dorset, England) and Nakarai Chemicals (Kyoto, Japan). Serum samples were obtained from out-patients without hyperlipoproteinaemia at Keio University Hospital. Procedure Florisil, pre-treated by washing with 5 volumes of dichloromethane and 5 volumes of methanol, heating for 2 h at 140 "C and suspension in hexane, successively, was packed into a 15 x 1 cm column.The column was pre-conditioned before use by washing with 50 ml of dichloromethane, 50 ml of methanol, 50 ml of methanol - water (1 + l), 50 mI of methanol, 50 ml of dichloromethane and 50 ml of hexane at a rate of 1.7 ml min-l. The lipid class separation was examined on a pre-conditioned Florisil column using hexane, dichloromethane, methanol and a chloroform - methanol - pyridine - acetic acid mixture. Authentic lipid samples in hexane contained 10 mg each of Cholesterol oleate as a representa- tive cholesterol ester, trilionolein as a triglyceride, distearin as a diglyceride, monopalmitin as a monoglyceride, palmitoleic acid as a free fatty acid and phosphatidylcholine dimyristate as a phospholipid.Serum was extracted by the method of Folch et d2 and the extracted lipids were dissolved in 1 ml of hexane. These lipid samples were loaded on to the column and eluted by stepwise elution with the above eluent from lower to higher polarity at a flow- rate of 1.7 mI min-I. Each fraction (50 ml) obtained from Florisil column chromatography, to which 10 mg of tridecanoic acid were added as an internal standard, was evaporated to dryness and subjected to methanolysis and gas-chromatographic analysis. Methanolysis to prepare fatty acid methyl esters from lipids was conducted by a modified Morrison and Smith's method with boron trifluoride as catalyst.a Gas-chromatographic analysis of the fatty acid methyl esters thus obtained was carried out with a Shimadzu GC-7A gas chromatograph equipped with a 30 m x 0.3 mm i d .SCOT-type glass capillary column coated with ethylene glycol succinate. Quantitation was effected by the peak-area ratio method against the internal standard. D/H-M/D- CMPA Eluent composition, ?h Fig. 1. Elution profile of each class of lipid by pre- conditioned Florid column chromatography. Stepwise elution was carried out at a ffow-rate of 2.0 ml mitr-l. 1, Cholesterol ester; 2, triglyceride ; 3, diglyceride ; 4, mano- ; 5, free fatty acid; and 6, phospholipid. €3, gYefid: exam , D, dichloromethane ; M, methanol ; CMPA, chloro- f a n - methanol - pyridine - acetic wid (3 + 2 + 1 f 3).October, 1983 SHORT PAPERS 1269 Results and Discussion Firstly, the composition of the eluent using 10 mg of each class of lipids as the samples on the pre-conditioned Florisil column was examined individually.The elution order was cholesterol ester, triglyceride, diglyceride, monoglyceride, free fatty acid and phospholipid. In order to find suitable eluents for the separation of lipids, the column was eluted with different eluents (50 ml of each). Fig. 1 summarises the elution profile for each class of lipids. Cholesterol ester was found to be eluted by 15% V/V dichloromethane in hexane (15% D/H), triglyceride by Soy0 V/V dichloromethane in hexane (50% D/H), diglyceride by 75% V/V dichloromethane in hexane (75% D/H), monoglyceride by 20y0 V/V methanol in dichloromethane (20% M/D), free fatty acid by 100% methanol (1OOyo M) and phospholipid by chloroform - methanol - pyridine - acetic acid (3 + 2 + 1 + 3).Based on these results, the eluent composition was fixed as follows: 15% D/H for cholesterol ester, 20% M/D for tri-, di- and monoglycerides, 100% M for free fatty acid and chloroform - methanol- pyridine - acetic acid (3 + 2 + 1 + 3) for phospholipid. An authentic sample of the lipid mixture was then loaded on to the column and eluted with the above eluents. As shown in Table I, 98% of the cholesterol oleate in the 15% D/H fraction, 93% trilinolein, 95% distearin and 90% monopalmitin in the 20% M/D fraction, 92% palmitoleic acid in the 100~o M fraction and 98% phosphatidylcholine dimyristate in the chloroform - methanol - pyridine - acetic acid (3 + 2 + 1 + 3) fraction were recovered. The coefficients of variation were within 5% for each of these recoveries (n = 5 ) .On loading the column with a serum sample, recoveries determined with respect to the total amount of each fatty acid in the original serum sample were in the range 92-109y0 (n = 5), indicating that high recoveries of each class of lipids are obtained in biological samples. TABLE I RECOVERY OF LIPIDS FROM FLORISIL COLUMN USING DIFFERENT ELUENTS Eluent composition Lipid Cholesterol oleate Trilinolein . . Distearin .. Monopalmitin . . Palmitoleic acid Phosphatidylcholine dimyristate . . 15% D/H Recovery, % c v , t % . . 98 4 .. 0 0 .. 0 0 .. 0 0 .. 0 0 .. 0 0 20% M/D r 1 Recovery, % cv,t % 2 3 93 6 95 3 90 4 0 0 0 0 100% M 7- Recovery, % cv,t % 0 0 7 5 5 4 3 92 lo 4 0 0 CMPA* f 1 Recovery, % CVIt % 0 0 0 0 0 0 0 0 0 0 98 6 * CMPA = chloroform - methanol - pyridine - acetic acid (3 + 2 + 1 + 3). t CV = coefficient of variation. It is considered that these high recoveries and better precision obtained using Florisil column chromatography are due to the initial deactivation of the Florisil adsorbent by pre-conditioning with 50% V/V methanol solution. This deactivated Florisil might be useful for the chro- matographic class separation of lipids. References 1. 2. 3. Carrol, K. K., J . Lipid Ras., 1961, 2, 135. Folch, J., Lees, M., and Sistamley, G. H., J . Bzol. Chem., 1957, 226, 497. Morrison, W. R., and Smith, L. M., J . Lipid Res., 1964, 5 , 600. Received January llth, 1983 Accepted Afiril 8th, 1983

ISSN:0003-2654    

DOI:10.1039/AN9830801267

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

1270 Book Reviews Analyst, October, 1983 ESSENTIAL OILS ANALYSIS BY CAPILLARY GAS CHROMATOGRAPHY AND CARBON- 13 NMR SPECTRO- SCOPY. By V. FORMACEK AND K.-H. KUBECZKA. Pp. xiv + 373. Wiley-Heyden. 1982. Price k53.50. ISBN 0 471 26218 8. Essential oils are associated with a charismatic character that extends even to their scientific analyses, and this is understandable in view of their complex and variable compositions. Almost all classes of organic compounds can be found in the appropriate essential oil and because of their generally volatile character it is not surprising that they are particularly amenable to examination by gas chromatography. In recent years the improvements in capillary chromatography have been applied as much to essential oil analyses as to other areas and several compendia of selected chromatograms have been published.In this work under review, the authors have combined the publication of capillary chromato- grams with the newly emerging technique of carbon-13 NMR spectroscopy. The chromatogranis and spectra for a range of 35 essential oils are given in a well presented and easy to read form, and this information makes up the larger part of the book. In addition there are carbon-13 NMR spectra for 134 reference compounds likely to be found in essential oils and an Appendix of carbon-13 NMR data listing the reference compounds in decreasing parts per million values. The chromatogram and spectrum for each essential oil are presented alphabetically and in seven instances oils of different origins are compared.The quantitation of the components of the oils has been done by peak normalisatim without the application of response factors and these figures are tabulated below the chromatograms. In those instances where oils of different origins have been compared these tabulated lists are repeated under each chromatogram with the comparison tables overprinted in shade. The identity of each component is indicated by easy to read codes, which are likewise self-evident. The conditions of the analyses are given in a preface and the chromatography has been carried out using nitrogen carrier gas and a proprietary stationary phase whose character is not revealed by its coded nomenclature. However, the reproducibility of the retention times is remarkably good. The authors are at pains to point out that the oils were mostly obtained through commercial sources and that their authenticity cannot be guaranteed.This detracts somewhat from the value of the book as an absolute reference work and although each oil is accompanied by a short descriptive monograph there is no indication given of the likely provenance and quality of the oil; in the case of the oil of lavender, the presence of camphor is a clear indication of its adulteration. Having given an outline of the chromatographic part of the book, it is difficult to say much about the potential for the application of carbon-13 NMR analyses. This is still an emerging technique and its ultimate value is difficult to predict. The authors themselves have little to say on the matter, perhaps hoping that the results will speak for themselves.This is not explained in the text but becomes self-evident. A. M. HUMPHREY TOPICS IN ENZYME AND FERMENTATION BIOTECHNOLOGY, VOLUME 7. Edited by ALAN WISEMAN. Pp. 314. Ellis Horwood. 1983. Price k32.50. ISBN 0 85312 465 5 (Ellis Horwood); 0 470 27366 6 (Halstead Press) ; ISSN 0140 0835. “Topics in Enzyme and Fermentation Biotechnology’ ’ has become a well established series, containing a wide variety of review articles covering the whole of this very topical area. The present volume continues in this vein. The chapter on immobilised plant and animal cells (Rosevear and Lamb) will be of interest to analytical chemists, because such systems are finding applications in analytical flow reactors and in bacterial electrodes.“Monoclonal antibodies : production, pro- perties and applications,” (Hubbard) is another timely report, of especial importance in clinical analysis. Their implications for immunoassays, as well as numerous other applications, are des- cribed in detail. A brief article by the Editor on the potential use of immobilised enzymes for waterBOOK REVIEWS 1271 and air purification presents some interesting ideas for removal, for example, of pesticides or detergents from water samples. The other chapters, less relevant to analytical chemists, describe microbial enzymes involved in biodegradation of sulphated surfactants, disordering macromolecular structure to facilitate enzyme attack, methanotrophs, thermophilic, anaerobic and cellulolytic bacteria and fermentation processes for utilisation of food wastes.As usual, the over-all presenta- tion is clear and the contents are indexed. ALAN TOWNSHEND CHROMATOGRAPHY. FUNDAMENTALS AND APPLICATIONS OF CHROMATOGRAPHIC AND ELECTRO- PHORETIC METHODS. PART A : FUNDAMENTALS AND TECHNIQUES ; PART B : APPLICATIONS. Edited by E. HEFTMANN. Journal of Chromatography Library, Volumes 22A and 22B. Pp. xxii + 338 (Volume 22A); xviii + 564 (Volume 22B). Elsevier. 1983. Price $83 (USA & Canada), Dfl195 (Rest of World) (Volume 22A); $138 (USA & Canada), Dfl325 (Rest of World) (Volume 22B). ISBN 0 444 42043 6 (Volume 22A) ; 0 444 42044 4 (Volume 22B) ; 0 444 42045 2 (two-volume set). This is the Fourth Edition of Heftmann’s book, but substantially revised and enlarged. Its two parts are, respectively, Volumes 22A and 22B in the Journal of Chromatography Library.Part A surveys the subject and covers the history and theory of chromatography, with separate chapters on column, planar (mainly thin-layer), gas, ion-exchange and gel chromatography and a final chapter about electrophoresis. Part B covers applications, in the following groups : amino acids, lipids, proteins, steroids, terpenoids, carbohydrates, pharmaceuticals, antibiotics, nucleic acids, porphyrins, phenolics, pesticides, hydrocarbons, non-hydrocarbon gases and inorganic compounds. The chapters in each volume are contributed by authors each of whom is either very well known or a leading protagonist in his field. The chapters have individual lists of contents and references and each volume contains a subject index covering the two parts.Part A is designed for undergraduates in analytical chemistry and, as it is mainly theoretical in character, contains little in the way of practical methodology. It provides good explanations of the terms used for the different techniques and, in the gas chromatography chapter, an adequate description of the various types of detectors. There is not a great deal on the latter elsewhere, although this may be deliberate with a view to avoiding the possibility of repetition in some instances. Part B is stated to be useful especially for advanced students and specialists who are seeking solutions to particular problems. Here, the different detectors are discussed under various head- ings ; for example in the chapter about amino acids and oligopeptides, ultraviolet, fluorimetric, electrochemical and mass spectrometric detectors are compared.However, on seeking in the index for detectors and detection methods it was found that reference was made only to Part A and a classification by type was not provided. (As the subject index comprised already 20 pages it may have been considered that to do this would have made the index too bulky.) Part A contained more than 1000 references, ranging from the 28 given following the gas- chromatography chapter to 412 under gel chromatography. As would be expected, the review part, B, contained in total almost 5000. As one would anticipate from a glance through the list of authors in Part A, all topics are dealt with very competently; the reviews in Part B are in some instances more critical than others, but all topics are dealt with more than adequately.It may seem a little strange that these subjects are being covered at this stage in the development of the Journal of Chromatography Library and of course they have been anticipated to some degree in earlier volumes and explored extensively elsewhere. Possibly, it may be the intention of the publisher to expand the series eventually into a systematic review of the whole subject, and of course the examples given in these volumes are often more recent than may be so elsewhere. The volume may be recommended to libraries as a work of reference. Part A should be useful to an undergraduate who has had some practical analytical experience and Part B to those inindustry and academic or research establishments specialising in particular fields.The two parts are priced separately and it may perhaps be that they can be purchased individually if this is desired. In Sterling terms the cost would appear to be over ten pence per page and the personal purchaser may see this as rather expensive. In summary, however, it is clear that much thought and effort has been employed in the preparation of this edition and the Editor in particular is to be congratulated once again. D. SIMPSON1272 BOOK REVIEWS Analyst, Vol. 108 VACUUM TECHNOLOGY. AN INTRODUCTION. Second Edition. L. G. CARPENTER. Pp. x + 118. Adam Hilger. 1983. Price k13.95. ISBN 0 85274 481 1. This slim volume is the Second Edition of a most readable and understandable account of the basics of vacuum technology.The first ten pages cover briefly and simply the important aspects of conductance and pump speed, after which the book gets down to more extensive, practical dis- cussion of the various types of pump, methods of measuring pressure, materials of construction and design of apparatus. There is a brief discussion of ultra-high vacuum and a final ten pages on applications of vacuum technology, a chapter so brief that perhaps it should either be expanded or omitted altogether. Overall, the value of the book lies in the practical information that it contains and it is certainly recommended reading for anyone who is contemplating the use of vacuum technology in their laboratory. G. E. PENKETH HPLC IN FOOD ANALYSIS. Edited by R.MACRAE. Food Science and Technology; A Series of Monographs. Pp. xii + 340. Academic Press. 1982. Price f128; $50. ISBN 0 12 464780 4; CCN 82 83666. HPLC was very rapidly applied within the pharmaceutical industry where many aspects of the analytical work are ideally suited to the technique. Application of HPLC to food analysis has, however, been retarded by the complexity of the sample substrate. This has necessitated the develop- ment of suitable clean-up procedures; in addition, the component of interest is often present at inconveniently low levels. “HPLC in Food Analysis” now demonstrates, however, that HPLC is firmly established as one of the most important techniques available to the food analyst. The book is divided into chapters on theory, instrumentation, separation modes and data hand- ling and automation, followed by a further seven chapter on specific areas of application, ranging from natural components (carbohydrates, lipid, amino acids, vitamins, etc.) through food additives and colourants to contaminants (mycotoxins).This group of chapters is preceded by a short introduction on the application of HPLC to food analysis and concluded with a discussion on future developments. Each of the application chapters are presented by analysts working in the parti- cular field and are both authoritative and current. This in many ways represents the strength of the book as each area is discussed critically. Sample preparation, work-up procedures, limitations and current developments are an integral part of each chapter, avoiding the failing of similar books that lack depth and revert to listing literature references. The breadth of application of HPLC to food analysis precludes a fully comprehensive review in only one volume. However, it is a little disappointing not to find a separate chapter devoted to peptides and proteins although peptides are briefly discussed in the chapter covering amino acids. Protein is of course a prime food source and is a t present the subject of one of the fastest growth areas for the application of HPLC. Despite this omission, the book should find considerable use within the food analysis laboratory as a valuable reference text providing both specific information and (more importantly) insight into the problems and possible approaches to the analysis of a wide range of food constituents, additives and contaminants. A. D. JONES

ISSN:0003-2654    

DOI:10.1039/AN9830801270

出版商:RSC    

年代:1983

数据来源: RSC