Investigations of reactions involved in flameless atomic absorption procedures : Part II. An experimental study of the rôle of hydrogen in eliminating the interference from chlorine in the determination of lead in steel

The rôle of hydrogen in eliminating the interference from chlorine in the flameless a.a.s. method for lead in steel has been experimentally studied with the Perkin-Elmer HGA 72 and Varian-Techtron CRA 63 graphite furnaces. Hydrogen is generated at high temperatures in both systems by the reaction of graphite with water left in the tube after the drying step. The amount of hydrogen formed during the ashing procedure in the Perkin-Elmer tube is about five times larger than that in the Varian tube. The removal of chlorine from graphite tubes containing dissolved steel samples has been determined as a function of temperature for (i) the CRA 63 without hydrogen added, (ii) the CRA 63 with hydrogen added, and (iii) the HGA 72 without hydrogen added. At 950 K, a significant amount of chlorine is left only in case (i); thus the amount of hydrogen formed in the HGA 72 is large enough to remove all of the chlorine through the reaction FeCl₂(g) + H₂(g) → Fe(s) + 2 HCl(g). If a sample is ashed at 950 K, losses of lead as lead chlorides only occur for the case (i) which is in accordance with theoretical prediction. The theoretically predicted optimum ashing temperature range of 900–1000 K is shown to be in good agreement with the experimental results.