3. Results and discussion
3.1. Effect of NaBH4 concentration
The effect of NaBH4 concentration on cold vapor generation from
microwave digested samples can be seen in Fig. 1. The integrated
absorbance increases with an increase in the concentration of NaBH4
for total mercury in DOLT-3 and BCR 186 solutions up to 1.0% m/v,
decreasing for higher concentrations of the reducing agent. For the
mercury standard solution, the integrated absorbance increases with
the concentration of NaBH4, up to 1.0% m/v, reaching a plateau for
NaBH4 concentrations from 1.0 to 3.0% m/v. The decreasing on the
mercury signal from the sample for higher concentrations of NaBH4
can be related to the high production of vapors during the chemical
vapor generation reaction, which may dilute the mercury vapor and
decrease the residence time of the mercury atoms in the absorption
cell, and hence, the absorbance signal. Nevertheless, the NaBH4 concentration
was selected as 1.0% m/v in 0.5% m/v of NaOH for total Hg
determination. The selected NaBH4 concentration of 3.0% m/v in 1.0%
m/v of NaOH for inorganic mercury determination in samples treated
with TMAH was optimized in a previous work [14], in which the same
system and reagent were used.