Jiří Starý

Isotopic dilution analysis by solvent extraction—I: Principle and theory of the method

Abstract The proposed method serves for the selective determination of trace amounts of metals. The analytical procedure consists of a single extraction of the metal to be determined, in the form of a complex with an organic reagent, and measuring the radioactivity of the extract obtained. The amount of the organic reagent employed must always be less than would correspond to the stoichiometric ratio. A theoretical evaluation of the extraction is given for these conditions, from which the conclusion may be drawn that a number of metals may thus be determined with greater selectivity than in a conventional extraction with a stoichiometric excess of organic reagent. On the basis of the relation obtained, conditions have been predicted for the determination of many elements. The possibilities of the selective determination of metals in the presence of interfering metals are also discussed.

A new principle of activation analysis separations—I: Theory of substoichiometric determinations

Abstract Separation procedures in the activation analysis of elements mainly consist of many steps which are usually derived from classical analysis schemes. In all cases an excess of reagent (precipitating, complexing, etc. ) is used for separation of the element to be determined. In the present paper separations by means of a smaller amount of reagent than corresponds to the stoichiometric ratio of element to be determined are discussed. The use of an insufficient amount of the reagent has two advantages : greater selectivity (possibility of eliminating many steps) and elimination of the necessity for determining the chemical yield of the element in question. As a result the analysis is more rapid.

Metal chelate exchange in the organic phase-II Extraction and exchange constants of dithizonates and diethyldithiocarbamates.

Dithizonates and diethyldithiocarbamates of Ag, Tl(I), Cu(II), Zn, Cd, Hg(II), Pb, Fe(II), Co(II), Ni, Pd(II), In(III), As(III), Sb(III), Bi, Se(IV) and Te(IV) have been prepared and their reactions in carbon tetrachloride have been studied spectrophotometrically. From the exchange constants determined, the extraction constants of metal diethyldithiocarbamates have been calculated. Where formation of mixed chelates has been observed, corresponding exchange constants have been determined. Finally, the influence of organic solvents (CCl(4), CHCl(3), C(6)H(6) and C(6)H(5)Cl) on the exchange reaction of zinc diethyldithiocarbamate with dithizone has been investigated.

Substoichiometric determination of traces of metals

Abstract The possibilities of substoichiometric determination of traces of metals by activation analysis and isotope-dilution analysis are critically discussed and optimum conditions given for the determination of 24 metals.

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.

Isotopic dilution analysis by ion-exchange—I: Determination of traces of iron

Abstract Isotopic dilution analysis with the use of ion-exchangers serves for the determination of trace amounts of metals. A theoretical evaluation of this method is given, from which the conditions for the determination of a number of metals can be predicted. The selectivity of the method may be further increased by the use of masking and precipitating agents. The proposed method has been verified by the determination of iron using EDTA and Dowex 50 cation-exchanger. The average precision of mean values for amounts of 10−7 g of Fe/5 ml was 1.2%, for amounts of 10−8 g of Fe/5 ml, 4.0% and for amounts of 10−9 g of Fe/5 ml, 4.1%. Even a large excess of many metals does not interfere in the analysis. The method has been applied to the analysis of NaI(Tl) crystals. The procedure which has been developed is very simple, and is far more sensitive than colorimetry, activation analysis or other methods used up to now for determining traces of iron.

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.

Isotopic-dilution analysis by solvent extraction-IV : Selective determination of traces of copper with dithizone

Abstract Copper is determined by a single extraction in the form of a complex with dithizone in amounts of 10−7 to 10−10 g ml . Even a large excess of metals which form extractable complexes with dithizone do not interfere in the analysis. The method is very simple and rapid, consisting of a single extraction of the solution to be analysed, and measurement of the activity of the extract. The procedure is more sensitive than other methods of determining copper.

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.