摘要:

Analyst Aztgust 1983 Vol. 108 pp. 1013-1017 1013 Flow Injection Analysis System for Determining Soil pH Tony E. Edmonds" and Grace Coutts The Macaulay Institute for Soil Research Craigiebuckler Aberdeen Scotland A flow injection analysis system is described for the determination of soil pH in filtered 0.01 M calcium chloride solution extracts. The system is con-structed entirely from off -the-shelf components and is capable of analysing up to 90 samples in 1 h. The unbuffered nature of filtered soil extracts causes problems in terms of electrode response times and imposes restrictions on the composition of the carrier-stream buffer and reference standards. Keywords Flow injection analysis; soil fiH The single most significant chemical measurement that is made on soil is pH (the laboratories of this Institute make over 10000 of these measurements each year).Hitherto soil pH has been determined manually or complex automated systems have been designed.l These machines are difficult to build and maintain and in addition in many designs the pH electrode is continuously being moved in and out of the sample and wash solutions. Under these conditions the electrode potentiometric response may be strongly influenced by a wet and dry bulb thermometer effect in which solvent evaporation from the periodically exposed pH-sensitive tip causes cooling and subsequent loss of Nernstian response at the pre-selected temperature of the determination. Clearly the determination of soil pH is a technique that would greatly benefit from the application of flow injection analysis (FIA) methods.FIA has been used to determine the pH of such diverse samples as sea water and serum as well as providing a detectable end-point for urea assay. An FIA system is described which uses off-the-shelf components for the measurement of the pH of soil. The system is easily built and may be operated manually or automatically to give a sampling rate of 90 h-1. Experimental Apparatus A Watson-Marlow 501 peristaltic pump was used in conjunction with a 501M pump head. The 501M is a triple roller occlusion pump head arranged in two groups of five channels. It was simple to convert the module into a five-channel six-roller occlusion device. A Rheodyne Type 50 four-way PTFE rotary valve was used in conjunction with a 0.5-ml sample loop.The pH electrode was of the capillary flow-through type (Russell UTTFC/CAP). The reference electrode was silver - silver chloride (EIL). A Corning 113 pH meter was the principal pH measuring device although for development work the meter was connected to a y - t chart recorder. The FIA system is shown in Fig. 1. The indicated flow-rates were obtained by using appropriate lengths and diameters of silicone-rubber tubing; the remainder was of 0.8 mm i d . PTFE tubing. This large diameter was selected to reduce the possibility of blockage that could occur even with filtered soil extracts. To avoid sample dispersion a minimum length of tubing (5 cm) was used to connect the sample valve to the pH electrode. Noise in the system arose from three sources (a) pulsing of the peristaltic pump; (b) static, generated at the pump head by the occlusion action of the steel rollers on the silicone-rubber tubing; and (c) trapped air bubbles in the carrier stream.We reduced (a) by increasing the number of rollers from three to six. Short lengths (2 cm) of stainless-steel tubing incorporated into the silicone-rubber pump lines before and after the pump head acted as guard electrodes. When these were shorted and taken to ground (b) was eliminated. Source (c) proved most troublesome. De-gassing the carrier-stream reagent helped but the problem was best over-come by adopting the pH electrode - reference electrode configuration shown in Fig. 1. The Present address Department of Chemistry Uni-versity of Technology Loughborough Leicestershire LE11 3TU.* To whom correspondence should be addressed 1014 0.9 ml min-’ 3.3 rnt min-’ 0.9 ml min-’ C r w r W S-EDMONDS AND COUTTS FLOW INJECTION D Analyst Vol. 108 Fig. 1. Flow injection analysis system for pH measurement C, carrier steam; P pump; I injection valve; D pH electrode; R, reference electrode; W waste; and S sample. carrier stream left the capillary pH electrode and flowed through a 20-cm length of silicone-rubber tubing into a 100-ml beaker. The liquid level in the beaker was kept constant by differential pumping. The reference electrode simply dipped into the liquid in this beaker. Reagents and Techniques Three manual techniques and the FIA method were used to measure soil pH and are described as follows. In each instance 15 g of air-dried soil sieved to less than 2 mm were shaken for 1 h on a reciprocal shaker with 25 ml of the extractant.In methods I I1 and I11 the reagent was 0.01 M calcium chloride solution (AnalaR). In method IV it was carbon dioxide-free distilled water. At the end of the shaking the pH of the suspension was directly measured by a conventional pH electrode in methods I and IV. In methods I1 and I11 the suspension was filtered through Whatman No. 41 filter-paper and the pH of the filtrate measured by conventional pH electrode and FIA respectively. The key to successful pH measurement by FIA is the correct choice of carrier-stream buffer and standard reference buffers. Rfiiiiika and Hansen2 recommended the use of a carrier buffer with a buffer capacity of one tenth that of the sample.Such an option is not available for filtered soil extracts because their buffering capacity is extremely low. In a typical soil solution P0,S- and HCO are the most significant species for pH control. Table I shows the buffer capacity (p) for P043- and HCO at typical soil pH values; /3 values for water at the same pH are included for compari-son. Obviously the requirement mentioned earlier cannot be met and accordingly we have used a carrier stream of M sodium dihydrogen orthophosphate - disodium hydrogen ortho-phosphate (both AnalaR) in 0.01 M calcium chloride solution at a pH of 5.54. This solution TABLE I BUFFER CAPACITIES (18) FOR SOIL SOLUTION AND WATER B* r 1 Soil solutiont Water r PH Pod3-6.0 2.3 x 10-5 6.5 7.3 x 10-6 6.0 2.4 x 10-6 6.5 2.6 x 8.0 3.1 x 7.0 3.6 x 10-5 7.6 1.9 x 10-5 1 HC03-2.3 x 10-5 2.3 x 10-6 7.3 x 10-6 7.3 x 10-6 2.9 x 10-6 2.3 x 6.6 x 8.0 x 10-7 5.8 x 10-5 4.6 x 10-7 5.5 x 10-4 8.0 x 10-7 3.3 x 10-3 2.3 x fi values calculated according to Perrin and Dempsey.6 t Assuming concentrations of 1 x M and 2 x 10-3 M HC0,-AugNst 1983 ANALYSIS SYSTEM FOR DETERMINING SOIL PH 1015 simulates the principle features of soil extracts with respect to ionic strength and buffer capacity (/3 = 6.65 x 1W6).Firstly the electrode is functioning in a dynamic manner. Thus the sample plug flows through the electrode for a limited period of time and in this time the equilibrium response of the electrode is approached more or less closely. When soil solutions pass through this electrode long equilibrium times are needed because of their low buffering capacity.It would be advan-tageous to ensure a long residence time so that a complete equilibrium could be reached but this would severely limit the sampling rate of the FIA system. Accordingly we have selected compromise conditions for flow-rate sample size and residence time (see FIA Parameters). Because these conditions do not permit full equilibration between the sample and the electrode, the selected pH standards must reach equilibrium with the electrode at a similar rate for valid st andardisation. A second problem with standardisation buffers arises because of the nature of the carrier stream. When pH buffers with typical /3 values of 0.054.01 were injected into the FIA system the electrode response reached equilibrium very rapidly but took several minutes to regain its base-line pH because of the low /3 value of the carrier stream.Hence the selected pH standards must be diluted in order to overcome both of these problems. We used 5 x loA5 M potassium hydrogen phthalate (AnalaR) in 0.01 M calcium chloride solution for the low standard (pH 4.76 and 5 x 10-5 M sodium tetraborate(II1) (AnalaR) in 0.01 M calcium chloride solution (pH = 8.71 /3 = 4.34 x It was necessary to check these “secondary standards” regularly against conventional pH standards, for example at the beginning and end of a sample run. The pH electrode - pH meter system was calibrated with the secondary standard buffers in the flowing system the buffers replacing the sample solution for the standardisation.Standardising the pH electrode in the FIA system also gives rise to problems. 6.26 x for the high standard. FIA Parameters The response graphs for various sample volumes at two different flow-rates are shown in Fig. 2. The sample consisted of 0.01 M calcium chloride solution to simulate a soil extract. We have also plotted the response graph of a dilute 5 x l O - 4 ~ sodium tetraborate(II1) buffer (pH = 9.01 /3 = 1.14 x 10-3) in Fig. 2 using the same scale. This latter graph demonstrates that the FIA system’s maximum response is reached very quickly (within 5 s) and that the dispersion is minimal (pH determined by FIA 9.01 the same as measured by a conventional pH electrode). Clearly the peak responses observed for the simulated soil extract do not only reflect the FIA parameters but also include the electrode response.The time required for full equilibration between sample and electrode was 70 s; at a flow-rate of 0.9 ml min-l this would require a 1 100-pl sample. A smaller sample could be used if the flow-rate was decreased. Stopping the flow and allowing the sample to equilibrate was not a satisfactory procedure The pH of a low volume (< 5 pl) of unbuffered solution resident in the pH-sensitive capillary of the detector did not remain constant even after sufficient time (b) D C B A I I I I I 0 10 20 30 40 50 60 0 10 20 30 40 50 60 Time/s Fig. 2. pH v w w s time graphs for (A-D) simulated soil solutions and (E) 5 X lo-* M Sample volumes A 100 p1; B 500 p1; C 800 p1; D, Flow-rates (a) 0.9 ml min-l; and (b) 3.3 ml rnin-l.Time scale sodium tetraborate(II1) buffer. 1300 pl; and E 500 p1. for D in (a) only is 0-120 s 1016 EDMONDS AND COUTTS FLOW INJECTION Analyst Vol. 108 for equilibration had elapsed. We presumed that this was due to alteration of the number of protons in the sample volume as the solution equilibrated with the hydrated layer of pH-sensitive glass. This enabled us to maintain an acceptable rate of sample throughput (90 h-l) for a reasonable flow-rate (0.9 ml min-1). A judicious choice of pH standards overcame the problem of calibrating a system in which an equilibrium response was not attained (see Fig. 3). Ultimately a compromise sample volume of 500 pl was selected. I I I I 10 30 50 70 Time/s Fig.3. pH UeYsus time graphs for (A-E) soil solutions; (F) 5 x M potassium hydrogen phthalate in 0.01 M CaCl, pH 4.76; and (G) 6 x M sodium tetraborate(II1) in 0.01 M CaCl, pH 8.71. Results and Discussion Thirty-eight soils whose pH values (determined by Method IV) varied from 4.34 to 7.20 The pH of each soil was determined independently by each of the were selected for analysis. four methods and the following regression equations were obtained from the results : ~ 1 1 1 = 1.04~1 - 0.12 r2 = 0.95 . . * (1) * * (3) ym = 1.04X1 + 0.22 r2 = 0.92 . . TWO soils were each divided into 60 sub-samples. The pHs of 20 of these sub-samples were determined by Method 11 20 by Method I11 and 20 by Method IV. Relative standard deviations of 0.8,0.8 and 0.7% were obtained for Methods 11 I11 and IV respectively for the higher pH soil (ca.6.8). Relative standard deviations of 0.4,0.4 and 0.9% were obtained for Methods 11 I11 and IV respectively for the lower pH soil (ca 5.1). The coefficient of deter-mination r2 which is equivalent to the square of the correlation coefficient indicates how closely these results follow a linear pattern. In terms of precision there is little to choose between conventional pH measurement method (IV) and the FIA method (111). There is good correlation between the two methods in which the pH is measured in a filtrate [equation (l)]. However when the FIA method is compared with either method involving pH measurement in a suspension (Methods I and IV), the correlation is worse [equations (3) and (2)].The correlation coefficient of equation (1) precludes the possibility that the action of filtering introduces an extra source of error into th August 1983 ANALYSIS SYSTEM FOR DETERMINING SOIL PH 101 7 determinations thus increasing the scatter of points when FIA is compared with suspension measurements. Indeed it is more likely that the measurements in the suspension are the sources of the scatter. The “suspension effect3” in potentiometric measurements is well known. It arises from abnormal reference electrode junction potentials that occur in colloidal systems. This generally results in a decrease in pH for negatively charged colloids such as soil clays when measured in suspension compared with the pH of the supernatant. This is most clearly seen in equation (3) where there is a positive intercept on they axis (k.the pH measured by FIA in filtered 0.01 M calcium chloride solution extracts is greater than the pH measured by a glass electrode in unfiltered 0.01 M calcium chloride extracts). [The effect is masked for equation (2) because the pH of a soil measured in a 0.01 M calcium chloride extract is lower than one measured in a carbon dioxide-free extract.] This effect can be variable from soil to soil depending on the amount and charge of colloidal material present in the sample, although with careful sub-sampling and preparation the pH value of a single soil may be determined repetitively with a high degree of precision. Conclusions The FIA system described provides a simple convenient and rapid method for measuring soil pH.The system may be progressively automated by the addition of a sample changer and/or the introduction of microprocessor control and data processing. The resultant pH measurements although precise are not necessarily accurate. The effective pH of a slurry has been described* as “the pH value corresponding to that for the localised part of the solution between the charged particles of the slurry.” Unfortunately it is only this value that is most susceptible to uncertainties in measurements because of the suspension effect. In other words conventional pH measurements on soil suspensions also give precise results which are not necessarily accurate. High precision in soil pH measurements may not however be worth attaining in view of the uncertainty surrounding the thermodynamic meaning of soil pHe6 In spite of this soil advisers have made effective lime recommendations based on these measured pH values for many years. There is no reason to suspect that this success will not be repeated when FIA pH values are used instead. References 1. 2. 3. 4. 5. 6. Goodman D. Analyst 1976 101 943. RfiiiCka J. and Hansen E. H. “Flow Injection Analysis,” John Wiley New York 1981. Bates R. G. “Determination of pH,” John Wiley New York 1964. LaMer V. K. J. Phys. Chern. 1962 66 973. Bache B. W. “Soil Reaction,” in Fairbridge R. W. and Finkl C. W. Editors “Encyclopedia of Perrin D. D. and Dempsey B. “Buffers for pH and Metal Ion Control,” Chapman and Hall London, Received December 29th 1982 Accepted February 26th 1983 Soil Science Part 1,” Dowden Hutchison and Ross Strondsberg PA 1979 p. 487. 1974 p. 12

ISSN:0003-2654    

DOI:10.1039/AN9830801013

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

1018 SHORT PAPERS Analyst August 1983 Rapid Spectrophotometric Determination of Nitrate with Phenol Noel Velghe and Albert Claeys Laboratory of Analytical Chemistry University of Ghent B-9000 Ghent Belgium Keywords Nitrate determination ; spectrophotometry ; phenol; nitrite Various spectrophotometric methods can be used for the determination of nitrate.lJ A standard procedure is reduction to nitrite followed by reaction with a suitable organic reagent. Hydra~ine,~ zinc4 and cadmi~m59~ are used as reductants; the most applied colour reaction consists of the diazotisation of an aromatic amine and subsequent coupling to form an azo dye. Recently Nakamura' proposed the use of chloride in sulphuric acid media as reductant and a solution of 4,5-dihydroxycoumarin in benzene as the colour reagent.This work is a modifica-tion of this method whereby the 4,5-dihydroxycoumarin is replaced by an aqueous solution of phenol. The advantages of this method over the one proposed by Nakamura are that it is simpler to perform because of the use of a single-phase system and a shorter time is required for each analysis. A simple procedure is described to minimise the interference of nitrite and sulphide . Experimental Apparatus absorption spectra. A Beckman Acta V spectrophotometer was used for the determination and recording of Reagents reagent grade. sulphuric acid to 50 ml of water. solution. With the exception of P-nitrosophenol (Aldrich-Europe) all chemicals were of analytical-Szclphwic acid solution 33.5 N. This was prepared by adding 500 ml of concentrated Phenol aqueozcs solutions.p-Nitrosophenol solution 30 mg 1-l. Prepared by dissolution in 0.02 N sodium hydroxide Procedure Transfer 2 ml of the sample solution or 2 ml of water (blank) into a 25-ml conical flask. Add 100 p1 of 12 N hydrochloric acid and 50 p1 of 2% phenol and mix. Without shaking add 2.4 ml of 33.5 N sulphuric acid and stopper the flask. Gently shake for 2 s and allow to stand for 6 min. Then shake again in order to mix with the condensate on the walls of the flask. Measure the absorbance at 388 nm. For samples containing iron(II1) (concentration <25 mg 1-l) the blank is prepared by the addition of 100 p1 of hydrochloric acid 50 pl of water and 2.4 ml of sulphuric acid to 2 ml of sample. Reaction Mechanism In chloride-containing sulphuric acid media nitrate is reduced to nitrite and converted to volatile nitrosyl chloride; optimum concentrations of sulphuric acid used are 14-15 N' and 20 N.* In this work a concentration of 18-19 N gave the best results SHORT PAPERS 1019 By consecutive reaction with phenol p-nitrosophenol is formed in equilibrium with the yellow-coloured p-benzoquinone mon~xime.~-~~ The reaction mechanism is as follows : c1-NO3- .-> NO2-H2SO4 NO2- + C1- + 2 H+ + NOCl + H,O Fig.1 shows an absorption spectrum obtained for nitrate (A) which conforms to the pro-posed reaction mechanism ; the graph is similar to the spectrum of P-nitrosophenol (C) . Nitrite gives an analogous spectrum (B). The peaks with maxima at 388 and 302 nm corre-spond to p-benzoquinone monoxime and P-nitrosophenol respectively.0.8 0.6 Q) S 0 n $ 0.4 2 0.2 300 350 400 450 Wavelengthhm Fig. 1. Absorption spectra obtained for (A) nitrate; (B) nitrite; and (C) p-nitrosophenol. Prep-aration of samples as under Procedure. Concentra-tion of nitrate and nitrite nitrogen 2.2 mg 1-l and p-nitrosophenol 30 mg 1-1. Results and Discussion Effect of Acid Concentration We preferred the use of 33.5 N sulphuric acid over concentrated acid because of better reproducibility. In Fig. 2(a) the influence of change in sulphuric acid volume is shown. From 1.8 to 2 ml of sulphuric acid (16-17 N) the absorbance increases sharply from 2.2 to 2.4 ml (18-19 N) optimum absorbance is obtained and above 2.4 ml the absorbance slowly decreases.This is partly explained by the equilibrium shift from p-nitrosophenol (A 302 nm) to P-benzoquinone monoxime (Amax 388 nm) with increasing concentration of sulphuric acid. This shift is illustrated by the spectra in Fig. 3; between 14.5 and 28.5 N its effect on absorbance at 388 nm becomes less pronounced with increasing concentration. In this way above 2.4 ml [Fig. 2(a)] the increase of absorbance by equilibrium shift becomes smaller than the decrease by dilution which results in a net decline in absorbance 1020 0.4 0) C m e 2 9 0.3 SHORT PAPERS Analyst Vol. 108 2.0 2.5 3.0 Volume of H2S04/mI 2 4 6 8 3 6 9 1 2 Concentration of pheno1,Concentration of chloride/ Y O M Fig. 2. Effect of (a) sulphuric acid; (b) phenol; and (G) chloride on absorbance.Concentration of nitrate-nitrogen 1 mg ml-l. The optimum concentration found by Nakamura' was smaller (14-15 N) ; however this value is related to the reduction step only while in this work the whole process of determination is involved. Effect of Phenol and Chloride Concentration The influence of phenol and chloride concentration is shown in Fig. 2(b) and (c). The use of 50 p1 of phenol with a concentration above 4% or 100 pl of hydrochloric acid with a concentra-tion below 3 M causes a marked decrease in absorbance. These effects are explained by the occurrence of a direct reaction between nitrate and phenol (nitration) which is favoured by decreasing the concentration ratio between chloride and phenol. Maximum absorbance is obtained using 50 p1 of 2% phenol (2.3 x 10-2%) and 100 pl of 12 M hydrochloric acid (2.8 x 10-1 M).In the method described by Nakamura' nitration reactions do not occur by the use of preliminary reduction of nitrate before addition of 4,5-dihydroxycoumarin ; this probably explains the much smaller chloride concentration (4 x 1 0 - 3 ~ ) required in that study. In some of our preliminary experiments we also added the organic reagent (phenol) only after the completion of the reduction to nitrite. The average absorbance was equal to the value obtained using reduction in the presence of phenol; however we abandoned this pro-cedure because of its unsatisfactory reproducibility. 0.8 8 0.6 C rn 2 a 2 0.4 0.2 300 350 400 450 Wavelengthhm Fig. 3. Absorption spectra obtained for nitrate a t sulphuric acid concentrations of (A) 6 N (B) 14.5 N; (C) 17.5 N; and (D) 28.5 N.Concentration of nitrate nitrogen in reaction mixture 0.8 mg 1-l A%& 1983 SHORT PAPERS 1021 Effect of Reaction Time within 1 h while a 6% decrease was observed after 3 h. The reaction was complete after about 5 min. No change of absorbance was measured Effect of Shaking Time in order to avoid the loss of volatile nitrosyl chloride. The shaking time of the solution after the addition of sulphuric acid should be less than 6 s, Calibration A linear calibration graph passing through the origin was obtained for concentrations of up to 3 mg 1-1 of nitrate-nitrogen. The relative standard deviation calculated by a 12-fold determination of a 0.2 and a 1 mg 1-1 sample was 2.5 and 0.7% respectively.Interferences The effect of various inorganic ions was investigated on a sample containing 1 mgl-l of nitrate-nitrogen. At the 100 mg 1-1 level only nitrite sulphide iodide and iron(II1) interfered (Table I A). TABLE I INTERFERENCE OF DIVERSE IONS Ion Fluoride bromide phosphate carbonate sulphite Ammonium calcium magnesium mercury(II), manganese(II) lead zinc copper . . . . . . Nitrite . . . . . . . . . . . . . . Sulphide . . . . . . . . . . . . Iodide . . . . . . . . . . . . . . Iron(II1) . . . . . . . . . . . . Concentration/ mg 1-1 100 100 1 6 10 0.6 1 10 1 10 100 10 26 60 100 Interference % 5?-77 <3 <3 94 0 2 4 -9 0 - 16 -1 - 90 -6 -3 -6 -1 - 78 -2 0 1 -9 2 - 16 0 * Results obtained after removing nitrite and sulphide by volatilisation or precipitation.The effect of nitrite and sulphide was minimised by using the following procedure. A 100-pl volume of 12 N hydrochloric acid was added to 2 ml of sample solution. Nitrogen was blown over this solution for 5 min and nitrite and sulphide were removed by volatilisation as nitrosyl chloride and hydrogen sulphide. A volume of water equal to the amount evaporated during this step was then added. Analysis was continued by the addition of phenol and sulphuric acid (see Procedure). The effect of iron(II1) and iodide was eliminated by precipitation and filtration; ammonia solution and mercury(I1) chloride followed by ammonia solution were used as reagents, respectively. Warming of the solution was required for the quantitative precipitation of iron(II1).Results obtained after the application of these different pre-treatments are given in Table 1,B. 1. Thomas L. C. and Chamberlin G. J. “Colorimetric Chemical Analytical Methods,” John Wiley, 2. Williams W. J. “Handbook of Anion Determination,” Buttemorths London 1979 p. 119. 3. Mullin J. B. and Riley J. P. Anal. Cltim. Acta 1956 12 464. 4. Matsunaga K. and Hishimura M. And. Cbim. Ada 1969 45 360. 6. Davison W. and Woof C. Analyst 1978 103 403. References New York 1974 p. 264 1022 SHORT PAPERS Analyst Vol. 108 6. 7 . 8. 9. 10. 1 1 . 12. Willis R. B. Anal. Chem. 1980 52 1376. Nakamura M. Analyst 1981 106 483. Afghan B. K. Leung R. Kolkarni A. V. and Ryan Y. F. Anal. Chem. 1975 47 556. Coffey S. “Rodd’s Chemistry of Carbon Compounds,” Elsevier Amsterdam 1971 Volume 111, Coffey S. “Rodd’s Chemistry of Carbon Compounds,” Elsevier Amsterdam 1974 Volume 111, Havinga E. and Schors A. Red. Trav. Chim. Pays-Bas 1950 69 457. Hays J. T. De Butts E. H. and Young H. L. J . Org. Chem. 1967 32 153. Part A p. 346. Part B p. 203. Received December 30th 1982 Accepted March 15th 198

ISSN:0003-2654    

DOI:10.1039/AN9830801018

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

1022 SHORT PAPERS Analyst Vol. 108 lodimetric Micro-determination of Aliphatic Acids by a Potentiometric Titration Method and Comparison with Acid - Base Potentiometry Anjou Wadhwa and Raj Mohan Verma Defiartment of Post-Graduate Studies and Research in Chemistry University of Jabalpur Jabalpur 482001 (M.P.) India Keywords A liphatic acid micro-determination ; potentiometry ; iodate iodide and sodium hydroxide reagents The largest group of organic acids the carboxylic acids are usually weakly dissociated. The carboxyl function can be determined by titration with 0.1 N alkali using phenolphthalein as indicator. However the micro-determination of carboxylic acids suffers from the following difficulties. The inflection on the pH - neutralisation graph is small and progressively shortens as the concentration of the acid sample and the titrant solution decreases.This makes it difficult to recognise the end-point which is further increased by the fact that the phenol-phthalein colour fades rapidly at the end-point when 0.01 N or more dilute solution of alkali is used as the titrant. Moreover carbon dioxide in the atmosphere interferes with the deter-rninati0n.l According to Steyermark,2 an organic acid sample containing 0.05 mequiv. of the substance upon titration with 0.01 N alkali using phenolphthalein indicator can give an error as large as 2%. The alkalimetry of weak organic acids in protophilic solvents has also been attempted. However with micro-samples the detection of the end-point may not be easy; further reagents such as triphenylmethylsodium and lithium aluminium hydride are too unstable to be used as 0.01 N standards1 Weak organic acids can be potentiometrically titrated with alkali using a glass - calomel electrode combination but owing to the formation of a b ~ f f e r ~ the potential jump near the equivalence point is small and decreases progressively with increasing dilution of the titrant.When the concentration of the titrant sodium hydroxide solution is less than 0.003 N the end-point cannot be located. Acids can also be determined iodimetrically by treating the sample with an excess of neutral iodide and iodate solution followed by titration of the liberated iodine. The method gives excellent results with dilute solutions of strong acids but fails when applied to weak acids even at the macro level.* The reaction mixture cannot be heated to speed up the reaction owing to the volatility of iodine.Bruhn~’~ modified procedure is applicable only to certain hydroxy acids at the 0.1 N level provided that 30 min are allowed for the reaction. Another modifica-tion (based on the Le Chatelier and Braun principle) due to Kolthoff6 consists of adding a measured excess of thiosulphate to the acidic sample containing an excess of iodide and iodate solution and subsequently titrating the surplus thiosulphate with iodine. The time required for the completion of the reaction is 15-30 min with 0.1 N acids and could be much larger with more dilute solutions. Long reaction periods or heating the reaction mixture to accelerate the reaction can give rise to errors because thiosulphate may then react with hydrogen ions.August 1983 SHORT PAPERS 1023 rapid direct iodimetric determination' of certain weak acids by using suitable amounts of solid iodide and iodate has been described. An indirect procedures based on the measurement of iodate consumed has also been suggested. These procedures are satisfactory with samples containing as little as 0.03 mequiv. of acids. At greater dilutions the starch end-point is not sharp. This paper describes an iodimetric micro-procedure for the potentiometric determination of some aliphatic carboxy acids. The sample solution is treated with an excess of potassium iodate and iodide followed by the potentiometric titration of the liberated iodine with thio-sulphate employing platinum - calomel electrodes.The end-points (pH 7.03) are sharp even with 0.001 N thiosulphate solution in contrast to the acid - base titration using glass -calomel electrodes. The reactions involved are as follows : HA + A- + H+ @03- + :I- + H+ -+ &I2 + gH20 $I2 + S203" -+ QS,O6" + I-1 ml of 0.001 N thiosulphate = 0.045 mg of carboxyl group Experimental Reagents The following solutions were prepared using analytical-reagent grade chemicals and con-ductivity water. Potassiwn iodate solution 0.0166 M (= 0.1 N). Prepared by transfering 3.5667 g of the dried salt into a 1000-ml calibrated flask dissolving it in about 400 ml of water and then diluting to the mark with water. A 5% m/V solution of potassium iodate was also prepared. Sodium thiosulphate solution 0.1 N.Prepared by standardisation with potassium i ~ d a t e . ~ Solutions of 0.01 0.005 0.001 6 and 0.001 N were prepared by dilution. Starch solution 1% m/V. A fresh solution was always used. Oxalic acid solution 0.1 N. Prepared and suitably diluted to obtain 0.01 0.005 0.0016 and 0.001 N solutions. Sodium hydroxide solution 0.1 N. Prepared by titration with standard oxalic acid solution and then diluted to obtain 0.01 0.005 0.001 6 and 0.001 N solutions. Phenolphthalein solution 1% m/V in 1 1 ethanol - water. Carboxylic acid solutions. Acid solutions of 0.1 N were prepared by titration with standard alkali. The 0.1 N solutions of formic acetic propionic butyric isobutyric valeric and iso-valeric acid so prepared were then suitably diluted to obtain test solutions.For caproic acid, the solubility in water is comparatively small so a 0.025 N solution was prepared and then diluted. Apparatus A digital pH meter with a glass - calomel electrode combination and a titration potentio-meter with platinum - calomel electrodes were used for performing the potentiometric titra-tions. Procedure A 5-10 ml volume of a sample solution containing 0.01-0.1 mequiv. of the acid is taken in a 100-ml beaker 1 g of potassium iodide and 4 ml of 5% potassium iodate solution are added and the mixture is stirred with a magnetic stirrer. A platinum and a calomel electrode are dipped into the solution and are connected to a potentiometer. Thiosulphate solution (0.001-0.01 N) is gradually added through a micro-burette. After each addition the solution is stirred and the potentiometer reading is recorded.Later the end-point is located by plotting a graph between the volume of the titrant added and AEIAV; a sharp peak in the graph gives the end-point (AE is the change in potential resulting from the addition of AV a definite volume of the titrant). The thiosulphate solution is standardised potentiometrically with a standard oxalic acid solution by the procedure described above for titrating the sample solution. The concentra-tion of oxalic acid solution used for standardising the thiosulphate should be comparable to that of the acid present in the sample solution 1024 SHORT PAPERS Analyst Vol. 108 Results and Discussion The results for the potentiometric titration of some aliphatic carboxylic acids at four con-centration levels are given in Table I.The average error calculated from six determinations was 0.1-0.5~0 and the relative standard deviation was 0.2-0.3%. The procedure has been found to be applicable to the determination of carboxylic acids having pKa values as high as 4.88. The amino functional group and those substances reacting with iodine would interfere in the procedure. Phenols cannot be determined by this method. Acid Formic . . Acetic . . Propionic Butyric . . Isobu tyric Valeric . . Isovaleric Caproic . . I . TABLE I RESULTS FOR MICRO-DETERMINATION OF ALIPHATIC ACIDS BY Acid taken/ mg 4.603 2.302 0.767 1 0.460 3 6.005 3.003 1.001 0.6005 7.408 3.704 1.235 0.7408 8.810 4.405 1.468 0.881 0 8.810 4.405 1.468 0.881 0 10.213 5.107 1.702 1.021 0 10.213 5.107 1.702 1.0210 11.616 5.808 1.936 1.162 * Average of six determinations.POTENTIOMETRIC METHODS Iodimetry f A \ Found*/ mg 4.599 2.305 0.7690 0.461 4 6.010 3.005 1.003 0.602 5 7.402 3.701 1.239 0.743 2 8.803 4.412 1.472 0.883 9 8.817 4.412 1.471 0.883 9 10.221 5.115 1.705 1.023 10.221 5.115 1.708 1.026 1 11.625 5.813 1.942 1.167 8 Error, % 0.09 0.13 0.25 0.24 0.08 0.08 0.20 0.33 0.08 0.08 0.32 0.32 0.08 0.16 0.27 0.33 0.08 0.16 0.20 0.33 0.08 0.17 0.18 0.20 0.08 0.17 0.35 0.50 0.08 0.09 0.31 0.50 Relative standard deviation, 0.20 0.25 0.27 0.27 0.20 0.21 0.26 0.26 0.20 0.20 0.26 0.26 0.20 0.26 0.27 0.26 0.20 0.26 0.26 0.26 0.20 0.26 0.26 0.27 0.20 0.26 0.26 0.32 0.20 0.20 0.26 0.32 % Alkalimetry A f \ Found*/ Error, * g 4.610 2.308 --6.015 3.012 --7.421 3.723 --8.825 4.434 --8.825 4.420 --10.230 5.132 --10.230 5.124 --11.654 5.832 --% 0.15 0.30 --0.17 0.30 --0.18 0.51 I -0.17 0.66 --0.17 0.34 --0.17 0.50 --0.17 0.33 --0.33 0.41 --Relative.standard deviation, 0.41 0.52 % --0.40 0.51 --0.40 0.54 --0.26 0.52 --0.41 0.52 --0.41 0.54 --0.41 0.52 --0.52 0.50 --The proposed iodimetric method was developed after studying the effect of the variation in the amount of potassium iodate and iodide and in the reaction period on the completeness of the reaction of the acids tested with potassium iodate and iodide.It was observed that the addition of 4 ml of 5% potassium iodate solution and 1 g of potassium iodide to sample solu-tions containing 0.01-0.1 mequiv. of the acids examined was sufficient for the quantitative liberation of iodine. The potentiometric titration required about 15 min which is sufficient for the completion of the reaction; hence it is not necessary to allow time before starting the titration. The thiosulphate solution used as the titrant in these potentiometric titrations can be standardised either with oxalic acid or with iodate in the presence of an excess of acid and potassium iodide.The concentration of oxalic acid or potassium iodate used for the standard-isation should be near the acid concentration in the sample solution August 1983 SHORT PAPERS 1025 In these potentiometric titrations the potential jump at the end-point was observed to be 60-100 mV per 0.1 ml of the titrant solution when the concentration of the thiosulphate used was 0.001-0.01 N. In the acid - base titration using glass - calomel electrodes the change in the potential near the end-point was 2040 mV per 0.1 ml of the titrant when the concentration of sodium hydroxide solution used was 0.005-0.01 N. With a 0.003 N or more dilute solution of the alkali as the titrant the potential jump near the end-point became much smaller and a series of almost equal changes in the potential were observed so that location of the end-point was not possible.Fig. 1 shows the potentiometric titration graphs obtained by titrating 10 ml of 0.001 N propionic acid with 0.001 N sodium hydroxide solution and iodimetric titration with 0.001 N thiosulphate. For the acid - base titration the detection of the end-point is not possible whereas a sharp peak is obtained in the proposed iodimetric titration. Further the iodimetric procedure is to be preferred for determining the acid content of substances that contain a component capable of reacting with alkali. For example for determining the carboxylic acids in lac the alkalimetric method cannot yield accurate results because the lac resin is readily saponified by alkali.1° 600 500 400 b 3 300 200 100 a 8.0 9.0 10.0 11.0 NaOH/Na2S203 (0.001 N ) / d Fig.1 . Potentiometric titration of 10 ml of 0.001 N propionic acid. I Obtained by the pro-posed iodimetric method and 11 by acid - base titration. Thanks are due to the Council of Scientific and Industrial Research New Delhi for the award of a Fellowship to one of the authors (A.W.). 1 . 2. 3. 4. 5. 6. 7 . 8. 9. 10. References Cheronis N. D. and Ma T. S. “Organic Functional Group Analysis,’’ John Wiley New York 1964, pp. 396 402 and 485. Steyermark A. “Quantitative Organic Microanalysis,’’ Second Edition Academic Press New York, 1961 p. 412. Kosonen P. Finn. Chem. Lett. 1975 5 124. Kolthoff I. M. Belcher R. Stenger V. A. and Matsuyama G. “Volumetric Analysis,” Volume 3, Interscience New York 1967 p. 276. Bruhns G. 2. Anal. Chem. 1916 55 45. Kolthoff I. M. Chem. Weekbl. 1926 23 260. Nema S. N. and Verma R. M. Analyst 1979 104 691. Saxena R. Pateria M. G. Soni G. P. and Verma R. M. Microchenz. J. 1981 26 334. Vogel I. “Quantitative Inorganic Analysis,’’ Second Edition Longmans London 1960 p. 334. Kamath N. R. and Mainker V. B. Anal. Chem. 1960 22 724. Received August 4th 1982 Accepted February 8th 198

ISSN:0003-2654    

DOI:10.1039/AN9830801022

出版商:RSC    

年代:1983

数据来源: RSC

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1026 SHORT PAPERS Analyst Vol. 108 Determination of Nitrate in Lake Water by the Adaptation of the Hydrazine = Copper Reduction Method for Use on a Discrete Analyser: Performance Statistics and an Instrument-induced Difference from Segmented Flow Conditions John Hilton" and Eric Rigg Freshwater Biological Association Windermere Laboratory The Ferry House Far Sawrey Ambleside, Cumbria LA22 OLP Keywords Nitrate determination ; hydrazine - copper reduction ; lake water ; discrete analyser ; pow injection analysis After the purchase of a discrete analyser system a method was required for the measurement of nitrate in lake waters which could contain relatively high concentrations of dissolved organic compounds. The autoanalyser method of Downes,l based on the procedure of Kamphake et aZ.,2 uses an excess of zinc ions to protect the copper catalyst from chelation by organic matter which fitted our requirements.However direct adaptation to the discrete analyser met with little success owing to a non-zero intercept of approximately 50 pg 1-1 on the concentration axis although nitrate and nitrite standards of the same concentration gave the same absorbance. The conditions obtained after re-optimisation are presented and the reason for the difference is discussed. Experimental The final method for use on the discrete analyser is given below. Apparatus A Pye Unicam AURA system (AC1) automatic chemistry unit with an SP6-550 ultraviolet -visible spectrophotometer and a Hewlett Packard 9815A calculator was used. The instru-ment settings were as given in Table I.TABLE I INSTRUMENT SETTINGS FOR THE PYE UNICAM AURA DISCRETE ANALYSER Cycle time 15 s; temperature 33 "C; path length 10 mm; and wavelength 640 nm. Dispenser Reaction Syringe Syringe Stroke/ Reagent colour Position timelmin size/pl volume/pl mm Sample . . 47 460 400 32.0 Sodium hydroxide solution . . Blue 47 1.6 2 000 800 13.8 Reductant solution . . . . Orange 41* 7 1000 260 14.0 Diazotisation reagent . . . . Green 13* 3.26 1000 400 22.6 * Stirrer. Reagents de-ionised water. AnalaR-grade reagents should be used where possible and solutions made up in distilled or CoPper(I1) sulphate sohtion 2.28 g 1-1 CuS04.5H,0. Zinc(II) sulphate sohtion 51.0 g 1-1 ZnS04.7H20. Sodium hydroxide solation 0.2 M (8 g 1-1 sodium hydroxide).* To whom correspondence should be addressed August 1983 SHORT PAPERS 1027 Dissolve 0.218 g of hydrazine sulphate in 400 ml of de-ionised water. Add 5 ml of copper(I1) sulphate solution and 5 ml of zinc(I1) sulphate solution. Make up to 500 ml. Diazotisation reagent. Dissolve 2.5 g of sulphanilamide in 400 ml of de-ionised water. Add 25 ml of concentrated phosphoric acid. (Check each new bottle of concentrated phosphoric acid for low nitrite content prior to use.) Dissolve 0.125 g of N-1-naphthylethylenediamine dihydrochloride (NED) in the resulting solution and dilute to 500 ml. Store in a refrigerator. Reductant solution. Prepare freshly as required. Results and Discussion The non-zero intercept on the concentration axis could have been caused by allowing insufficient time for the colour to develop after the addition of the diazotisation reagent (although loss of sensitivity would be a more likely result).Varying this time showed no differences in either the sensitivity or concentration axis intercept as long as the time was greater than 3 min after the addition of the last reagent. Addition of the colour reagent as a single solution produced exactly the same results. The latter form of reagent addition was retained in the final method reducing the total analysis time to below 13 min. This allowed a cycle time setting of 15 s to be used which increased the throughput to 240 samples per hour. A second possible cause of the concentration axis intercept was the presence of an excess of hydrazine reducing nitrate to nitrite prior to diazotisation.The concentration of hydrazine had been set at 190 mg 1-I in the reduction step as recommended by Downec,l which agreed with other published procedures for optimised hydrazine - copper reductions e.g. Kamphake et d2 The temperature time of reduction and copper and zinc concentrations were fixed as in Downes methodl and the hydrazine concentration was varied. The absorbances from standard nitrite and nitrate solutions were measured and the peak of the nitrate - hydrazine concentration plot was found. The resulting hydrazine concentration of 75 mg 1-1 in the reduction stage was then used in the optimisation of the other parameters. These were found to peak at the original settings. The calibration using the re-optimised concentration for the reduction step was now found to pass through zero.The resulting method is linear up to 600 pg 1-1 of nitrate as N with a sensitivity of 0.051 absorbance unit per 100 pg 1-l. Interpretation of the performance statistics given in Table I1 shows a limit of detection as defined by Cheeseman and Wilson,3 of 14 pg 1-1 (9576 confidence levels). A plot of the concentration of total oxidised nitrogen determined in a variety of natural waters versus the concentration measured for the same samples using the manual cadmium reduction method,4 gave a good straight line (r = 0.967; n = 107) passing through the origin. However it was decided to re-optimise this parameter. TABLE I1 PRECISION MEASUREMENTS OF NITRATE IN STANDARD SOLUTIONS Solution concentration/ Mean Pg I-' absorbance 0 0.005 200 0.101 400 0.202 600 0.299 800 0.395 1000 0.474 Standard deviation*/pg 1-1 * The degrees of freedom for the within- (sw) and the between-batch (sb) standard deviations are given in parentheses; st is the total standard deviation.The optimum hydrazine concentration is 40% of the concentration required to produce an equivalent reduction in the autoanalyser system. It is worth noting that this concentration (75 mg 1-l) is much closer to the 56 mg 1-1 found to be the optimum by Mullin and Riley5 for the manual method than the 190 mg 1-1 concentration which was found to be optimum by th 1028 SHORT PAPERS segmented flow analysis users requiring high sensitivities (e.g. references 1 and 2). Mullin and Riley5 noted that low concentrations of hydrazine were oxidised on standing by dissolved oxygen in the water.In the segmented flow autoanalyser system air is introduced between sequential aliquots of liquid. The mass transfer coefficient across this air - liquid interface is very high owing to the turbulence introduced by friction on the tube wall and the presence of mixing coils. This would increase both the total amount of hydrazine reduced and the rate compared with the batch method where oxygen exchange across the quiescent gas - liquid interface will be small at low stirrer speeds and short stirring times. In the manual method of Mullin and Riley5 there is only sufficient oxygen in solution to oxidise half the total hydrazine (56 mg 1-l) present. However in the autoanalyser method there is sufficient oxygen to oxidise twice the total amount of hydrazine present (190mg1-l) using the sample to air ratio of D0wnes.l This explanation is consistent with the fact that early unoptimised autoanalyser methods which used Mullin and Riley’s reagent5 concentrations without optimisation gave considerably lower sensitivities than the manual method typically 1/27thB6 It is also con-sistent with the results of Hale,* who showed that increases in discrete analyser stirrer speeds, above a given value at which vortexing occurred gave reduced recoveries of nitrate which could be corrected by increasing the hydrazine concentration.It is probable therefore that application of this nitrate method to flow injection systems where no segmentation is used, will require the reduced hydrazine concentrations to produce reliable results.Conclusion The hydrazine - copper reduction method for the determination of the total oxidised nitrogen in water has been optimised for use on a discrete analyser and its performance statistics have been reported. Differences between the hydrazine concentration required for discrete analysis compared with the requirement for segmented flow analysis have been rationalised on the basis of rapid oxidation in the latter. This is likely to affect the adaptation of this method to flow injection technology. References 1. 2. 3. Cheeseman R. V. and Wilson A. L. “Manual on Analytical Quality Control for the Water Industry,” Water Research Centre Technical Report TR66 Water Research Centre Medmenham, 1978. Downes M. T. Water Res. 1978 12 673. Kamphake L. J. Hannah S. A. and Cohen J. M. Water Res. 1967 1 205. 4. 5. 6. 7. Davison W. and Woof C. Analyst 1978 103 403. Mullin J. B. and Riley J . P. Anal. Chim. Acla 1955 12 464. Terrey D. R. Anal. Chim. Acta 1966 34 41. Hale D. R. Int. Lab. 1980 Jan./Feb. 79. Received December 15th 1982 Accepted March 15th 198

ISSN:0003-2654    

DOI:10.1039/AN9830801026

出版商:RSC    

年代:1983

数据来源: RSC

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Analyst A ugust 1983 Book Reviews 1029 ATOMIC AND NUCLEAR METHODS IN FOSSIL ENERGY RESEARCH. Edited by ROYSTON H. FILBY. Pp. xiv + 506. Plenum. 1982. Price $59.50. ISBN 0 306 40899 6. As the proceedings of the American Nuclear Society conference on Atomic and Nuclear Methods in Fossil Fuel Energy Research held in Puerto Rico in December 1980 this volume is a collection of 33 invited and contributed papers reproduced directly from typescript. The papers are presented in three sections methods of elemental analysis; investigations of mechanisms and structures ; and characterisation of species predominantly with reference to coal but including oil oil shale and tar sands and describe the application of a wide range of methods to investigations of inorganic and organic species in these fuels their processing and the environmental conse-quences of their use.Plenary state of the art review papers are mentioned in the preface but are not emphasised in the text. The section on methods of elemental analysis includes nine contributions on neutron-activation analysis and one on fission track analysis the remainder describing multi-technique investigations. Atomic methods such as AAS and ICP are not highlighted in separate contributions although they are considered in the multi-technique approaches. The section on mechanisms and structures includes details of the use of D and 14C tracers (in studies of coal chemistry) isotope excited XRF electron probe microanalysis and NMR together with a description of geological factors that control the mineral content of coal.The section on characterisation of species includes contributions on GC GC - MS MS Moss-bauer spectrometry and or-spectrometry (for radioactivity in emissions from coal-powered stations). Most of the papers are application oriented and refer to American situations but the results are a useful indication of which techniques can be used to solve similar problems elsewhere. Intro-ductions provide useful background information about areas of activity that proponents of other analytical methods may wish to enter. The methods that are described do not consider principles or detailed methodology but these can be found in relevant text-books. Details of sample selection and preparation will be useful for those working with fossil fuels. As a conference proceedings this volume provides a good indication of procedures used in fossil fuel research albeit with some emphasis on nuclear methods and all workers in this field can expect to find something of relevance in its contents although some parts may be of limited interest.At approximately 7 pence per page it is not expensive at current-day prices. J. E. WHITLEY L’ATOMISATION ELECTROTHERMIQUE EN SPECTROMETRIE D’ABSORPTION ATOMIQUE ET SON APPLICATION DANS LES ETUDES DE L’ENVIRONMENT. By MICHEL HOENIG STEPHANE DUPIRE and ROLLAND WOOLAST. Pp. vi + 218. Technique et Documentation. 1982. Price FF 180; BF 1260. ISBN 2 85206 115 5. (In French.) This paperback is intended as a practical guide to the application of atomic-absorption spectro-metry with electrothermal atomisation to the analysis of environmental materials such as bio-logical fluids and tissues water samples atmospheric particulates foodstuffs soils and vegetables.The most useful part of the book and constituting more than half of the total number of pages, is a detailed discussion of methods for 14 elements (Sb Ag As Be Cd Cr Co Cu Mn Ni Pb Se, V and Zn). No procedures are given which is a disadvantage in such a practical guide but a relatively up-to-date and comprehensive bibliography will allow methods to be found rapidly from the literature. The methods section takes up the second half of the book the earlier chapters being concerned with the principles of electrothermal atomisation kinetic and thermodynamic aspects of the atomisation process interferences and methods of overcoming them and practical problems involved in using electrothermal atomisers such as control of contamination and the analysis of solids.Some interesting information is given on the effects of carrying out atomisation under higher pressures and a useful chapter on sample preparation of environmental materials is included 1030 BOOK REVIEWS Analyst Vol. 108 Finally a short chapter is used to describe instruments which are or have been commercially available unfortunately without pictures or diagrams. Many fairly recent innovations have been included for example the coating of tubes with tantalum carbide and the use of matrix modifiers to overcome some chemical interferences. The use of platform atomisation does not appear, however which is an indication of the rate of progress in this field a t the present time.Although published in French the text is easy to assimilate and the extensive bibliography will be useful to anyone not already up-to-date in this field. J. ALVARADO and J. M. OTTAWAY METHODS FOR THE EXAMINATION OF WATERS AND ASSOCIATED MATERIALS. BY THE STANDING COMMITTEE OF ANALYSTS (TO REVIEW STANDARD METHODS FOR QUALITY CONTROL OF THE Stationery Office. WATER CYCLE) ; DEPARTMENT OF THE ENVIRONMENT NATIONAL WATER COUNCIL. HM Cobalt in Potable Waters (Tentative Methods) 1981. Pp. 22. 1982. Price L2.40. ISBN 0 11 761603 1. Ammonia in Waters 1981. Pp. 47. 1982. Price i3.80. ISBN 0 11 751613 9. Cadmium Chromium Copper Lead Nickel and Zinc in Sewage Sludges by Nitric AcidlAAS 1981. Pp. 12.1982. Price L1.85. ISBN 0 11 751615 5. Phenols in Waters and Efluents by Gas - Liquid Chromatography 4-Aminoantipyrine or 3-Methyl-2-benzothiazolinone Hydrazone 1981. Pp. 39. 1982. Price i3.40. ISBN 0 11 751617 1. Chloride in Waters Sewage and Efluents 1981. Pp. 46. 1982. Price L3.80. ISBN 0 11 751626 0. Quantitative Samplers for Benthic Macroinvertebrates in Shallow Flowing Waters 1980. Pp. 15. 1982. Price L2.25. ISBN 0 11 751627 9. Pyrethrins and Permethrin in Potable Waters by Electron-Capture Gas Chromatography 1981. Pp. 15. 1982. Price f12.25. ISBN 0 11 751628 7. Reviews of earlier booklets in this series appeared in the Analyst in 1982 107 464 and 1099, and 1983 108 126 and the appearance of a further seven methods sheets clearly indicates that progress in publication is proceeding rapidly through HM Stationery Office.The methods which succeed those given in the Department of Environment “green book,” “Analysis of Raw Potable and Waste Waters” (HMSO 1972) are of extremely high quality and will be essential to all working water analysis laboratories. It is hard if not impossible to fault the format designed by the Committee in the presentation of these booklets. Each step of each analytical procedure (most booklets contain more than one method) is described clearly and concisely with notes explaining the principles involved. The detailed specification of each method is particularly welcome and will allow an analyst to decide rapidly whether a method will be suitable for a particular problem or not. This information includes detection limits precision sensitivity interferences and the time for analysis and this careful attention to detail will do much to improve the quality of analysis in this field.The booklet on cobalt contains two atomic-absorption procedures for roughly 1-100 pg 1-1 of cobalt. Both methods involve pre-concentra-tion the first by extraction of the pyrrolidine dithiocarbamate cobalt complex into 4-methyl-pentan-2-one and the other by evaporation in the presence of nitric acid. Both procedures ensure dissolution of suspended and colloidal material and use measurements with an air - acetylene flame the former involving direct aspiration of the 4-methylpentan-2-one extract. A useful scheme by which the analyst can establish the accuracy of his analysis is included as an Appendix to the booklet.Six different procedures are given for ammonia; a titrimetric method and a potentiometric method involving a gas sensing membrane electrode being included together with four spectrophotometric methods based on two different chemistries. The familiar indophenol blue method is modified by the inclusion of sodium dichloroisocyanurate instead of hypochlorite and for non-saline waters sodium salicylate is preferred to phenol. For sea water samples the method based on phenol is still preferred to avoid partial precipitation of magnesium a t the high pH needed in the salicylate method. Both phenol and salicylate methods are given in manual Specifically the methods included are as follows August 1983 BOOK REVIEWS 1031 and continuous flow automatic procedures.A careful comparison of all six methods is given in order that the analyst can easily select the method required for a particular application. The method for the determination of the six metals in sewage sludges was designed for rapid routine analysis and involves digestion of 0.5-g samples of dried sludge or 10 ml of wet sludge with 6 ml of nitric acid for 15 min. The residue is diluted to 50 ml and the soluble fraction of the metals is determined by flame atomic absorption by direct aspiration into an air - acetylene flame after allowing the residue to settle. As indicated by the title the phenol booklet contains three different methods and includes the colorimetric 4-aminoantipyrine procedure which is given in three different versions depending on the relative concentrations of monohydric phenol present in the sample and whether chloro-substituted phenols are indicated.The gas-chromatographic method is based on extraction of phenols into 4-methylpentan-2-one and conversion into their trimethylsilyl ethers before GLC analysis. Three stationary phases are recommended and sample chromatograms allow the analyst to decide which is most suitable for his particular application. The four methods given for chloride appear to be well established procedures e.g. silver nitrate titration mercury(I1) nitrate titration both with indicators a potentiometric titration with silver nitrate and the continuous flow automatic method involving mercury(I1) thiocyanate and iron(II1) nitrate. Notes are also given on the use of ion chromatography coulometry with electrogeneration of silver and the use of a chloride ion-selective electrode.The recovery of silver and mercury from the wastes and residues from many of these procedures is also described. The use of two types of sampler are detailed in the methods for benthic macroinvertebrates. Both the Surber and cylinder samplers are intended for use in shallow waters i.e. less than an arm’s length. The pyrethrin insecticides used in potable waters are determined by extraction into hexane and analysis by gas chromatography using an electron-capture detector. A useful list of retention times for two different chromatographic columns is included. As indicated previously all these booklets are informative and comprehensive and will be essential to all routine water laboratories involved in the relevant determinations.J. M. OTTAWAY WILSON AND WILSON’S COMPREHENSIVE ANALYTICAL CHEMISTRY. VOLUME XVI. Chemical Microscopy. Thermovnicroscopy of Organic Compounds. Edited by G. SVEHLA. Pp. xii + 513. Elsevier. 1982. Price $151; Dfl325. ISBN 0 444 41950 0 (Volume 16); 0 444 41735 4 (Series). Chemical Microscopy by H.-H. Emons K. Keune and H.H. Seyfarth In their foreword the authors say that their aim has been to give chemists an initial survey of the present state of microscopical applications in the field of chemistry. They have produced a “manual of instruction a work of reference and a source of inspiration to the practical worker.” Interestingly the book begins with a glossary of technical terms mostly admirably and clearlyexplained.It would have been helpful had more terms such as optic axis been included. The introduction includes a review of light microscopical capabilities on static and “kinematic” (melting reacting) specimens and goes on to give a statement of the advantages and disadvantages of microscopy. There follows a concise perhaps too concise review of crystal optics i.e. the study and representation of passage of light through crystalline solids. The chapter on microscopical equipment skates briskly over bright field (normal viewing) on its way to consideration of phrase contrast and interference systems. The latter are confined to the Zeiss Jena Interphako system. It is very helpful that charts and tables are given for presenting adjustment schemes and fields of application.There are descriptions of universal (tilting) and spindle stages and of heating and cooling stages. The tables of capabilities and applications of light microscope systems on their own and in combination with other analytical tools are particularly valuable. There is a chapter on strategies and tactics of sampling and specimen preparation; again presentation of methods in the form of charts and tables eases the problem of “yes but where do I start with m y material?’’ The short chapter on image recording reviews still- and cine-photomicrography with a para-graph on videorecording and gives a brief account of image analysis systems. Few authors have committed their thoughts on these last two topics to paper 1032 BOOK REVIEWS Analyst Vol.108 The meat of the book lies in a chapter on measurement of physical properties of specimens and an account of some applications. The former deals with measurements of refractive indices by various methods and states the accuracies attainable with each before dealing more briefly with other optical property determinations. There is consideration too of morphological observations, of thermal methods and of chemical tests under the microscope. The choice of applications to be included must have been most difficult and the authors have settled for a range that includes phase analysis solid solutions polymorphic inversions some polymer microstructures solid state reactions and orientation studies. The final chapter reviews future trends which is more than many of us would care to do.The book is well produced though sadly the micrographs are lumped together at the end. I t goes a long way towards satisfying the authors’ stated aims though in its thoroughness it may deter all but the stouthearted beginner. There is plenty to interest established practitioners and this forms a valuable reference work. There are omissions liquid crystals for one and few of the copious lists of references date from the 1970s or 1980s but in all this is a substantial contribution to microscopical literature intended for chemists. Thermomicroscopy of Organic Compounds by M. Kuhnert-Brandstatter The second part of Volume XVI of Wilson and Wilson’s Comprehensive Analytical Chemistry (pp. 329-498) is devoted to the observation of the microscopical behaviour of organic compounds on heating and cooling.Maria Kuhnert-Brandstatter’s objective is aimed particularly at the analytical chemist who has a modicum of practical microscopy. She gives numerous experi-mental descriptions mainly exemplified by pharmaceutical compounds to illustrate a number of fundamental principles. The latter including polymorphism nucleation crystal growth and phase behaviour in two component systems are not restrictive and can be applied to other classes and new organic compounds. The work deals very briefly with equipment and mainly concerns the determination of melting-points eutectic temperatures phase investigations in primary and binary systems polymorphism, contact preparations in relation to phase diagrams and refractive indices of melts.Less emphasis is placed on micro-chemical reactions and the characterisation of liquids and liquid crystals. The temptation to proliferate with photomicrographs has been resisted throughout. It might how-ever have been advantageous to have included the observed appearances of the more common textures of liquid crystals in view of their commercial significance. To limit their investigative descriptions to only two pages is a failing. The writer states more than once that although hot-stage microscopy can serve as a basic tool, the best results can be achieved in combination with other methods such as differential thermal analysis. Correlating thermochemical microscopic observation with thermograms obtained by differential scanning calorimetry can accomplish results unattainable by either when used indepen-dently. One problem associated with transcribed texts is that references are usually to papers in the original language. The present volume is no exception the majority of references being to German sources. Such a comment would not have been necessary if the teaching of German for scientists had been generally supported in English-speaking universities. In spite of such criticisms this section of the book is eminently readable and the reviewer found it difficult to put down; the printing quality on a gloss substantial paper is good and there are few if any printing errors. I t is strongly recommended for microscopists especially if their interests lie in polymorph identification not only in pharmaceuticals but in any other application of organic compounds. F. JONES P. C. ROBINSON This correlation might well have been described and illustrated

ISSN:0003-2654    

DOI:10.1039/AN9830801029

出版商:RSC    

年代:1983

数据来源: RSC