Omission of the ashing stage in the determination of aluminium and lead in waters by graphite furnace atomic absorption spectrometry

Abstract

Omission of the ashing stage in the determination of aluminium and lead in waters by graphite furnace atomic absorption spectrometry on uncoated tubes initially led to lower sensitivity and poor accuracy. Sensitivity could be restored by increasing the drying time to about 40 s or by increasing the drying temperature. The original effect is thought to be due to interference from water vapour; the time was insufficient to remove water vapour before atomisation occurred. Higher drying temperatures (180–260 °C), leading to rapid expulsion of the water vapour, gave results with no loss in precision. A temperature of 250 °C held for 12 s was chosen for drying. With these revised programmes having no ashing stage, satisfactory recovery was demonstrated for aluminium (98 ± 6%, n= 10) and lead (101 ± 2%, n= 8) in domestic water samples. Cycle times were 54 and 55 s for aluminium and lead, respectively. The method for lead involved the use of a mixture of lanthanum and nitric acid as a modifier, but omission of the ashing stage did not affect the accuracy. In a separate experiment, it was shown that the suppression of sulphate interference by the lanthanum modifier was the same with and without an ashing stage.