Adolf Zeman

A new principle of activation-analysis separations—VII: Substoichiometric determination of traces of arsenic

Abstract The radiochemical procedure is based on the solvent extraction of arsenicIII diethyldithiocarbamate into chloroform from 2–3M hydrochloric acid, and eliminates the necessity of determining the chemical yield. Moreover, using a substoichiometric amount of reagent (zinc diethyldithiocarbamate in chloroform), the separation of arsenic becomes very selective. When the dissolved irradiated sample is first extracted with diethylammonium diethyldithiocarbamate (arsenic present in quinquevalent form), only antimony and tin subsequently interfere. This interference can be completely eliminated by a cupferron extraction performed after reduction of both arsenic and antimony to the tervalent state. The procedure developed is far more simple and rapid than previously described radiochemical separations for arsenic. It has been used for the determination of arsenic in pure silicon semi-conductor material (down to 10−6 %) and can undoubtedly be used with little adaptation for the determination of arsenic in various other materials.

A new principle of activation analysis separations-II: Substo chiometric determination of traces of zinc and copper in germanium dioxide

Abstract A substoichiometric determination of zinc and copper in germanium dioxide is based on dissolution of the irradiated sample in sodium hydroxide followed by addition of known amounts of carriers for the metals to be determined, then adjustment to suitable conditions for extraction. An irradiated standard sample is treated simultaneously in exactly the same way. The solutions thus prepared are extracted with substoichiometric amounts of dithizone in carbon tetrachloride and the amounts of zinc and copper in the germanium dioxide calculated from the activities of the extracts obtained. The present procedure is far more simple and rapid than previously published methods. It eliminates not only distillation but also many separation steps commonly used, thus shortening the time of analysis to 20 min.

Substoichiometric separation using ion-association extraction systems

Abstract A theory of ion-association extraction using tetraphenyl-arsonium, triphenylsulphonium and tetraphenylphosphonium ions is given, from which these reagents are shown to be suitable for selective substoichiometric separations. From these considerations it follows that the substoichiometric determination of manganese, rhenium and iodine by activation analysis should be possible; however, the use of these reagents for isotope dilution seems to be doubtful.

A NEW PRINCIPLE OF ACTIVATION-ANALYSIS SEPARATIONS. IV. SUBSTOICHIOMETRIC DETERMINATION OF TRACES OF SILVER

Abstract A substoichiometric determination of traces of silver in germanium dioxide and in metallic lead has been developed. It consists of simultaneous irradiation of a standard and test sample in a nuclear reactor followed by dissolution and addition of silver carrier. After adjusting the pH, the samples are extracted with the same substoichiometric amount of dithizone in carbon tetrachloride and the activities of the organic extracts measured. This single-step separation procedure is fully satisfactory because of its high selectivity. Moreover, substoichiometry avoids the necessity of determining the chemical yield. The procedure developed could be adapted without difficulty for the determination of traces of silver in other materials.

A NEW PRINCIPLE OF ACTIVATION-ANALYSIS SEPARATIONS. VIII. SUBSTOICHIOMETRIC DETERMINATION OF TRACES OF ANTIMONY

A highly selective, very simple substoichiometric separation of antimony from an irradiated test sample has been developed. After irradiation, isotopic carrier for antimony is added and the test sample dissolved under oxidising conditions. To the acid solution (2M sulphuric acid) cupferron is added in excess and the resulting cupferrates, except for those of antimonyV and arsenicV extracted with chloroform. After reduction of antimonyV (and arsenicV) to the tervalent state, it is precipitated using a substoichiometric amount of cupferron at pH 2–3 and selectively extracted with chloroform. A simultaneously irradiated standard sample of antimony is treated in exactly the same way. As in other substoichiometric determinations the necessity of determining the chemical yield is avoided. The utility of the method has been verified by the determination of antimony (down to 10−8%) in pure silicon semi-conductor material. Because of its high selectivity, the method may also prove useful for determining traces of antimony in various other materials.

A new principle of activation-analysis separations—v: Substoichiometric determination of traces of indium

A rapid method for the substoichiometric determination of gallium by neutron-activation analysis has been developed. After irradiation and dissolution of the test sample, gallium carrier is added and two preliminary separation steps are performed: the extraction into chloroform of cupferrates from 7N sulphuric acid and of diethyldithiocarbamates from 2-3N sulphuric acid. The pH of the remaining aqueous phase is then adjusted to 5.5, the solution extracted with a substoichiometric amount of 8-hydroxyquinoline in chloroform and the activity of the gallium hydroxyquinolate extract measured. A simultaneously irradiated gallium standard is treated in exactly the same way. From the activities of these two substoichiometric extracts the amount of gallium originally present in the test sample can be calculated. The method has been applied to the determination of 10(-6) to 10(-3)% of gallium in metallic aluminium and transistor-grade silicon.

Chelating radiometric titrations by ion exchange for determination of traces of metals

Abstract A new type of radiometric titration has been developed. Using EDTA solutions, the negatively charged or neutral metal chelates are formed, and these can easily be separated from the excess of unreacted metal ions using a cation exchanger. Titration curves are constructed from the activities of the eluates. The method has been used for the determination of microgram amounts of indium using 114mIn as an isotopic tracer, and for the determination of submicrogram traces of cobalt using the same indicator as a non-isotopic tracer.

SUBSTOICHIOMETRIC DETERMINATION OF MANGANESE BY NEUTRON-ACTIVATION ANALYSIS

A simple and rapid method for the substoichiometric determination of traces of manganese in various materials by neutron-activation analysis has been developed. After dissolution of the irradiated test sample, manganese(II) carrier is added and subsequently oxidised by peroxodisulphate to the heptavalent state. The permanganate thus formed is finally extracted into chloroform as tetraphenylarsonium permanganate using a substoichiometric amount of tetraphenylarsonium chloride. This single separation step isolates radiochemically pure manganese-56 in the analysis of a relatively simple material in which interfering elements (gold, rhenium, etc.) are absent. When this is not true, a preliminary separation of manganese from the irradiated sample, based on the extraction of manganese diethyldithio-carbamate into chloroform and followed by stripping of the manganese with dilute sulphuric acid, must be used. A simultaneously irradiated standard containing manganese must be treated in exactly the same way as a test sample. In the materials analysed by the new method 10(-5) to 10(-3)% of manganese has been determined.

A new principle of activation-analysis separations—IX: Substoichiometric determination of traces of bismuth

Abstract A simple radiochemical separation of bismuth has been developed, based on two dithizone extraction steps, the second of which is a substoichiometric extraction. When copper, gold, mercury, palladium, platinum and silver are not present in interfering amounts, only the substoichiometric dithizone extraction is necessary. The method has been applied to the determination of bismuth by activation analysis in granite and in silicon.

Selective extraction and separation of cadmium using tri-n-octylamine

The extraction of cadmium by tri-n-octylamine in benzene and cyclohexane from a mixture of sulphuric acid and potassium bromide has been investigated in detail. The optimum conditions for the extraction and back-extraction of cadmium have been found. The procedure for the concentration of cadmium is described and the separation of cadmium in the presence of more than 30 metals including fission products is presented.