L.E. Smythe

The progress of analytical chemistry 1910–1970

The progress of analytical chemistry during the period 1910-1970 is reviewed. Topics considered are: the volume of the relevant literature, the countries in which the work was done, the language in which the papers were written, the literature of analytical chemistry, broad trends in the subject, methods used, and the analytical chemistry of individual elements. Some tentative conclusions are made about future short-term trends.

A critical evaluation of fluorometric methods for determination of selenium in plant materials with 2,3-diaminonaphthalene

The published methods for fluorometric determination of Se in plants are reviewed, with particular attention to those using 2,3-diaminonaphthalene as the fluorometric reagent. Two steps in the analysis are shown to be critical: the final stages of the digestion and the complete conversion of the Se to Se(IV). A modified experimental procedure is given.

Spectrophotometric and fluorometric determination of traces of molybdenum in soils and plants

The reaction of the molybdenum oxypentathiocyanate ion with the dyestuff Rhodamine B (RhB) produces the ternary complex. MoO(SCN)(5)(RhB)(2) The formation of this complex is accompanied by a colour change and by extinction of the fluorescence of RhB. A spectrophotometric and fluorometric method for the determination of Mo has been developed from these observations. The method is free from interferences and has detection limits of 0.1 mug and 0.05 mug of Mo for absorption and fluorescence measurements, respectively. The spectrophotometric method is applicable to the determination of Mo in soils and the fluorometric method is suited to the determination of Mo in plants.

Fundamental studies on improvement of precision and accuracy in flameless atomic-absorption spectroscopy using the graphite-tube atomizer Lead in whole blood.

Some fundamental aspects concerning the formation of ash on a pyrolytic graphite surface and the resulting effects on precision and accuracy in flameless AAS, have been examined for the determination of lead in whole blood. The nature and composition of the ash from whole blood and the state of the pyrolytic graphite surface have been observed with the aid of a scanning electron microscope and non-dispersive X-ray microprobe analyser. The use of nitric acid to separate the analytical peak from the matrix peak, an examination of high-temperature clearing of the matrix, and removal of ash remnants between each analysis are reported. A procedure to improve precision and accuracy in flameless AAS using the graphite-tube atomizer is reported.

Determination of traces of Mo in soils and geological materials by solvent extraction of the molybdenum—thiocyanate complex and atomic absorption

Comprehensive studies of the extraction of the molybdenum-thiocyanate complex with methyl isobutyl ketone have resulted in an improved method for the determination of traces of molybdenum in soils and geological materials by atomic-absorption spectroscopy. The method is applicable in the range 1-500 ppm Mo, with 1-g samples, giving relative standard deviations not exceeding about 8% at a level of 1 ppm. The limit of detection is 0.1 ppm. There are few interferences, and large quantities of iron are without effect.

Spectrophotometric and fluorometric determination of cobalt.

The reaction of Co(II), pyridine-2-aldehyde-2-pyridyl hydrazone (PAPHY) and eosin at pH 5.6 produces the ternary complex Co(L)(HL)E(2) (where HL represents the protonated form of the ligand and E represents the eosinate anion). This complex is extracted by a chloroform-acetone mixture to give a strongly coloured and highly fluorescent extract. Spectrophotometric and fluorometric methods for the determination of Co have been developed with detection limits of 0.017 and 0.008 ppm respectively. Cu(II), Ni, Fe(II), Pd(II) and Hg(II) interfere. The Spectrophotometric method has been successfully applied to the analysis of steels, following ion-exchange separation of Co.

Rapid destruction of plant material with concentrated nitric acid vapour (vapour phase oxidation)

Concentrated nitric acid vapour is used in a simple rapid method for the destruction of organic matter in plant tissue before analysis for trace elements. About 90% of the organic matter is destroyed by the nitric acid vapour within 5-6 min and destruction is then completed by the addition of perchloric acid. The method gives zero or low blank values and has comparable precision and accuracy to conventional acid digestion methods.

Use of long-chain alkylamines for preconcentration and determination of traces of molybdenum, tungsten and rhenium by atomic-absorption spectroscopy-II: molybdenum in soils, sediments and natural waters.

Molybdenum is extracted as the thiocyanate complex with the quaternary long-chain aliphatic amine Aliquat 336 in chloroform, followed by evaporation of the solvent, dissolution in MIBK, and atomic-absorption spectroscopy. The method is simple, rapid and sensitive, with few interference problems for the determination of the Mo content of soils and sediments in the range 0.1-1.0 ppm with a relative standard deviation better than 5% when 1-g samples are used. Quantitative extraction from large volumes of aqueous solution has also been confirmed, allowing the determination of Mo in natural waters in the ppM range.

The use of long-chain alkylamines for preconcentration of traces of molybdenum, tungsten and rhenium in their determination by atomic-absorption spectroscopy—I: General studies

Long-chain alkylamines are used for the preconcentration of traces of molybdenum, tungsten and rhenium as thiocyanate complexes, in their determination by atomic-absorption spectroscopy. General studies of factors, influencing the extraction show that the thiocyanate complexes can be extracted into chloroform containing a low concentration of Amberlite LA1. Detection limits are 0.02 ppm Mo, 0.75 ppm W and 0.34 ppm Re in the final MIBK solution and are improved by a factor of 5-10 over those obtained by using current extraction methods. Serious interelement effects are eliminated and a range of other cations and anions are shown to have little effect on the absorption.

Synergistic influence of Zn(II) in the extraction—atomic-absorption determination of trace cadmium in waters

A very simple and rapid procedure is described in which the addition of a large amount of Zn(II) to a water sample before extraction by 2-mercaptobenzothiazole into n-butyl acetate brings about almost total extraction of Cd and allows determination of concentrations down to at least 0.02 ng/ml. High precision is achieved, and the interference of cyanide is also overcome.