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Abstract
The interferences of phosphate, sodium sulfate and chloride, aluminum nitrate, potassium chloride and selenous acid (singly and in combination) with the determination of arsenic by graphite furnace atomic absorption spectrometry were investigated. The arsenic signals were not only dependent on the phosphate concentration but also on the phosphate/arsenic ratio. Ashing curves (As signals as a function of ashing temperature) showed that arsenite and arsenate in salt-free solutions with 400mg/L Ni (as nitrate, sulfate or chloride) can be determined at ashing temperatures > 1100°. In the absence of Ni the signals are less intense and the ashing temperature should not be higher than 900°. Ni addition to solutions of methylarsonic acid, dimethylarsinic acid, arsenocholine and arsenobetaine enhanced the signal intensity but did not change the range of usable ashing temperatures. When salts are present at levels commonly found in freshwater, even addition of Ni does not produce acceptable results at ashing temperatures < 900°. The determination of an ashing curve is recommended before a water sample is analyzed for arsenic. A procedure for the determination of arsenic was developed and successfully applied to a synthetic and natural freshwater samples.