[Methodology improvement in background elimination in plant Cd measurement by graphite furnace atom absorption]

A problem of higher background value and lower measured Cd value exists when Cd is digested by conventional dry digestion method, measured by graphite furnace atomic absorption, and calculated with peak height numeration. This problem results in difficulty for evaluating samples with Cd contents in the neighborhood of critical values. In order to solve the problem, the present paper focused on background measurement with graphite furnace atomic absorption, modified the pre-preparation procedures of the traditional method, and screened the optimal concentration of the modifier. Results showed that addition of Mg (NO3)2 as a modifier into the samples before incineration was preferred. It could not only yield a clear solution but also reduce its background by ten times, considerably eliminating background interference. In addition, using 3% HNO3 in stead of 1 mol x L(-1) HCl as dilution for the incinerated sample could eliminate the background. The improved methods could acquire a zero concentration of measurement for the blank, re-correct the values measured by graphite furnace atomic absorption and obtain more reliable results.