176 / 197
8.
The sensitivities reported in Table 4 are troubling. The sensitivity for As(III) is ~15% lower than
that of MMAs and As(V), and the sensitivity for DMAs is 10% higher than that of MMAs and
As(V). This strongly suggests that there are either impurities in standards (possible) or that the
integrations are not correct (more likely). The sensitivities for all species should be identical, and
this is an important QA measure to control. When this method was published on the FDA
website, there were some chromatogram posted as well, and they showed some As(III) tailing
into the DMAs, and the integration for DMAs was being biased, causing high-bias for DMA.
Based on the sensitivities listed in Table 4, this could be happening with this method.