Tube in flame atomisation: a way of enhancing detection limits in flame atomic absorption spectrometry

Abstract

The use of a graphite tube introduced by means of a graphite rod handle in an air–acetylene flame is described for the atomisation of lead. Tubes of different sizes and made of different types of graphite were compared regarding detection limit, reproducibility and useful lifetime. Using this system, the extended residence time of the atoms in the absorption volume allows lead to be determined with an absolute detection limit about fifty times lower than that obtained using conventional flame atomisation. Reproducibility of the measurements, expressed as percentage relative standard deviation, at the 5 ng Pb level is 3.9%. HGA-type pyrolytically coated graphite tubes were found to be the most appropriate atom cells among the tubes tested. Lifetime of the tubes wasca. 350 twenty-second heating periods. The determination of lead in the NIST Standard Reference Material 2704, Buffalo River Sediment, demonstrates the accuracy of the tube in flame approach, giving an average result of 168±3 µg g^–1 of Pb, in close agreement with the 161±17 µg g^–1 certified value.