Investigations of reactions involved in flameless atomic absorption procedures: Part III. A study of factors influencing the determination of lead in strong sodium chloride solutions

Abstract

The factors influencing the direct determination of lead in strong sodium chloride solutions with a Varian Techtron CRA 63 are discussed. The sodium chloride matrix affects the determinations in two ways: (i) non-specific absorbance causes poor precision (the standard deviation for 50 p.p.b. of lead in 4 % sodium chloride was 11 % and the detection limit 11 p.p.b.); (ii) the sensitivity is decreased by about 20 %. Addition of nitric acid to the sodium chloride solution does not improve the sensitivity but decreases the non-specific absorbance to a very low value. This sample treatment improved the standard deviation for 50 p.p.b. of lead in 4% sodium chloride to 4% and the detection limit to 4 p.p.b. After treatment of the sodium chloride solution with nitric acid, the matrix is mainly sodium nitrate; if this matrix is not ashed at a sufficiently high temperature, the sensitivity decreases. At low ashing temperatures, the partial pressure of oxygen, as a result of incomplete reaction between oxygen and graphite, exceeds 10 −5 atm during atomization so that, theoretically, the formation of gaseous lead oxide is significant and responsible for the decrease in sensitivity.