Acid effects on the measurement of mercury by cold vapor atomic absorption spectrometry

The influence of nitric, hydrochloric and sulfuric acids on the measurement of mercury by cold vapor atomic absorption spectrometry has been investigated. Small pre-reduction peaks associated with the instability of mercury were observed in solutions containing ≤ 12.5, < 2 and ≤ 12.5% v/v of each acid, respectively. Mercury was found to be most stable in ≥ 2% v/v hydrochloric acid and the measured absorbance was not greatly influenced by varying concentration of the acid. The mercury absorbance measurements were more sensitive in solutions containing ≤ 6.3% v/v hydrochloric acid than in similar concentrations of nitric and sulfuric acids. The use of the three acids as a digestion mixture result in serious interference from nitrogen oxides. The interferant was removed by use of expelling agents such as urea and sulfamic acid or overcome by use of excess stannous chloride, prior to the reduction of mercury(II) ions. The determination of mercury in NBS albacore tuna using both of these approaches to overcome the interference problem proved to be successful.