Comparison of several methods for the determination of arsenic compounds in water and in urine

Summary Several arsenic species (inorganic tri- or pentavalent arsenic, mono-and dimethylated arsonic acids) can be determined in water samples by electrothermal atomic absorption spectrometry after appropriate acidification procedures (concentrated HCl or a mixture HCl/HClO₄/HBr) and extraction by toluene in the presence or absence of KI; the determination of aromatic derivatives and of arsenic thiol complexes needs a wet or dry ashing step. The procedures for water analysis are not directly applicable to urine samples; in the best conditions, total inorganic plus 85% on the average of the methylated arsenicals present in urine are measured after acidification with concentrated HCl and extraction by toluene in the presence of KI. Total arsenic content (including arsenic from marine origin) is measured only after a drastic mineralization step like MgO treatment at 600°C. The results obtained by the electrothermal atomic absorption technique and those obtained by neutron activation analysis are in excellent agreement.When the presence of arsenic of marine origin is suspected in urine, the analysis of inorganic arsenic and its metabolites is preferably performed by an arsine generation technique. The sum of inorganic arsenic and of its mono and dimethylated derivatives determined by such a technique is identical with the results obtained by electrothermal atomic absorption spectrometry after complete mineralization of the samples as long as no arsenic from marine origin is present.After oral ingestion of As₂O₃ by man, the urinary excretion of inorganic arsenic and its metabolites is important and rapid (approximately 60% are eliminated by the oral route with a half life of 30 h).While the excretion occurs in the form of inorganic species during the first hours following the ingestion, a methylating process is rapidly triggered and leads to a preponderant excretion of dimethylarsinic acid 1 day after ingestion. In the case of ingestion of seafood containing arsenic, the urinary excretion occurs at a higher rate (half life 18 h) apparently without transformation.The absence of interference of arsenic from marine origin and the capacity of measuring separately inorganic arsenic and its main urinary metabolites makes the arsine generation technique the best suited for the monitoring of workers exposed to inorganic arsenic. However, since the technique may sometimes be too elaborate and time-consuming for routine work, the biological monitoring of workers can be performed by determining total arsenic concentration in urine after mineralization with MgO. Samples with high arsenic content are then re-analyzed to distinguish between occupational exposure and ingestion of the organic arsenic present in marine organisms. This is carried out either by the arsine generation method or, if this technique is not available, by a direct extraction procedure in the presence of KI of a sample acidified with HCI. With the latter procedure, 85% of the methylated arsenic is measured on average without interference of arsenic from marine origin.