Determination of thallium and lead in nickel-based alloys by direct solid sampling with graphite furnace laser-excited atomic fluorescence

Abstract

The direct analysis of solid nickel-based alloys was investigated using laser-excited atomic fluorescence spectrometry with an electrothermal atomiser (ETA-LEAFS) and a Perkin-Elmer cup solid sampling accessory. Advantages of direct solid sampling include high sensitivity and reduced risk of sample contamination as no dissolution step is used. Using the front-surface illumination approach for ETA-LEAFS, it has proved possible to apply modern graphite furnace solid sampling technology directly to LEAFS. The advantages of ETA-LEAFS include a long linear dynamic range (5–7 orders of magnitude) and limits of detection that can be 1–4 orders of magnitude better than electrothermal atomic absorption spectrometry (ETAAS). High temperature nickel-based alloy standard reference materials were accurately analysed for low and sub-µg g–1 concentrations of the trace metals thallium and lead, using aqueous calibration. These analyses were carried out on single alloy chips weighing between 0.5 and 2 mg with typical analytical relative standard deviations of 7–20%. The use of an internal gas flow, during atomisation, has been reported in the solid sampling ETAAS literature as a means of reducing the sensitivity of the ETAAS method, a necessity due to the short linear dynamic range of ETAAS. The long linear dynamic range of LEAFS allowed the elimination of the use of an internal gas flow through the furnace for the determination of lead. The analyte backgrounds for thallium and lead in nickel-based alloy solid samples using ETA-LEAFS and ETAAS were compared. The analyte backgrounds for solid sampling by ETA-LEAFS were significantly lower than those for solid sampling by ETAAS.