Determination of arsenic in soil and plant materials by atomic-absorption spectrophotometry with electrothermal atomisation

Mechanism of volatile hydride formation and their atomization in hydride generation atomic absorption spectrometry

The mechanism of volatile hydride generation (HG) and the formation of analyte atoms in the quartz cell atomizer used in the determination of hydride-forming elements (As, Bi, Ge, Pb, Sb, Sn, Te etc.) by atomic absorption spectrometry (AAS), have been critically reviewed. The nascent hydrogen mechanism failed to explain hydride generation under different experimental conditions when tetrahydroborate (THB), amineboreanes (AB) and cyanotrihydroborate (CBH) were used as reductants. Various experimental evidence suggested a non-nascent hydrogen mechanism, in which the transfer of hydrogen directly bonded to boron to an analyte takes place. In electrochemical hydride generation (EcHG), the reduction of the analyte species and subsequent hydrogenation was proposed. The mechanism of analyte atom formation in a quartz tube atomizer has been explained by the following hypotheses: thermal decomposition, oxidation by 02 and collisions by hydrogen free radicals. The free-radical mechanism satisfactorily explains most of the analytical implications. The significant variation in the experimental conditions required to generate different analyte hydrides makes it difficult to arrive at a generalized mechanism of hydride formation.

The determination of trace levels of arsenic in human biological materials

The authors have reviewed the techniques developed for measuring the concentration of total arsenic and that of some specific arsenic species (As V, As III, aromatic and aliphatic arsenic derivatives) in biological materials mainly in urine. Whether the relative concentrations of these arsenical species found in human urine represent their true distribution in the urine secreted by the kidney (possible change in valence state in the bladder mainly at alkaline pH, breakdown of arsenical derivatives during urine pretreatment) remains to be investigated further. No technique is yet available for measuring specifically the organoarsenic derivative(s) excreted after ingestion of marine animals. No available system has been found that will digest tissues without changing the original valence states of arsenic. Therefore only total arsenic can be measured with accuracy in tissue.