Laboratory evaluation of a mercury CEM using atomic absorption with a deuterium background correction system

A prototype mercury (Hg) analyzer based on atomic absorption (AA) with a broadband background correction system using a deuterium (D2) lamp was developed and tested in the laboratory. Initial tests were performed using a small commercially available AA Hg detector operated in series with an optical breadboard version of the D2 background correction system. Based on encouraging results obtained with that system while using streams of elemental Hg and SO2 (an interfering gas), a compact prototype Hg analyzer for use in a Hg continuous emission monitor (CEM) was built. In laboratorytests performed in the absence of interfering gases, the analyzer could detect 0.5 microg/m3 or less of elemental Hg. The noise in the D2 channel of the analyzer was a limiting factor with respect to instrument sensitivity when background-corrected absorbance values were used. Tests with gas streams containing 9-26 microg/m3 of elemental Hg and 0.02-0.44% SO2 indicated that the D2 background correction approach did a good job at subtracting the large interfering signal due to SO2. However, a correction factor had to be applied to the absorbance readings from the D2 channel of the analyzer in order to obtain acceptable accuracy for the background-subtracted Hg measurements.