A high-efficiency photooxidation reactor for speciation of organic arsenicals by liquid chromatography - Hydride generation - ICPMS

A novel postcolumn photooxidation reactor with remarkably high efficiency was developed. It was installed into a system of liquid chromatography (LC) combined with inductively coupled plasma mass spectrometry (ICPMS) using a hydride generation (HG) technique to enable sensitive speciation of organic arsenicals. An LC eluent was passed into a reaction tube that runs through a low-pressure mercury lamp of a high-efficiency photooxidation (HEPO) reactor. It provided efficient irradiation with vacuum ultraviolet light at 185 nn, which induced oxidative decomposition of persistent organic arsenicals, for example, arsenobetaine, to the final product, arsenate, for an extremely short time, 3.5 s, without using any oxidizing agents. That arsenate was subsequently detectable by HG-ICPMS. In contrast, conventional photooxidation reactors require more than 100 s for completion, even when using a peroxodisulfate solution as an oxidizing agent. Because of the absence of broadening and dilution of the LC-separated peaks caused by mixing with the oxidant solution, the detection limits for 10 arsenic species including the persistent organic arsenicals by the proposed LC-HEPO-HG-ICPMS ranged from 2.3 to 18 ng of As/L, which were about one-tenth as low as those by LC-ICPMS. The proposed method revealed for the first time the occurrence of 20 arsenic species, including the unknown trace species, which were undetectable by LC-ICPMS and LC-HG-ICPMS, in human urine.