Division 2.4.5 Specific requirements for hydride generation atomic absorption spectrometry

Organic compounds containing elements such as arsenic, bismuth, germanium, lead, antimony, selenium, tin and tellurium can be very stable and require oxidative decomposition to obtain correct results for total element content. Therefore, microwave digestion or high-pressure ashing under strong oxidative conditions is recommended. The greatest care shall be devoted to the complete and reproducible conversion of the elements into their corresponding hydrides.

The formation of arsenic hydride in hydrochloric acid solution with NaBH₄ depends on the oxidation state of arsenic (As III: fast formation, As V: longer formation period). To avoid a loss of sensitivity for the determination of As V with flow injection technique, caused by the short reaction time in this system, As V has to be reduced to As III after the oxidative decomposition. Potassium iodide/ascorbic acid or cysteine are suitable for this purpose. Blanks, calibration solutions and sample solutions shall be treated in the same way. Working with a batch system allows determining both arsenic species without affecting accuracy. Due to the delayed formation of As V-hydride, calibration shall be performed by peak area integration. The instrument settings shall be optimised. The gas flow, which transfers the hydride to the atomisator, is especially important and shall be checked.