Reduction of background absorption in the measurement of cadmium, lead and selenium in whole blood using iridium-sputtered graphite tubes in electrothermal atomic absorption spectrometry

The thermal behaviour during pyrolysis and of the vapour phase during atomization for Cd, Pb and Se in acid-digested whole blood using Ir-sputtered tubes is described. The performance of Ir as a permanent modifier was affected unfavourably by the complex matrix compared with conventional modifiers. Background absorption was measured using an atomic absorption spectrometer in addition to a diode-array spectrometer and compared with the background obtained in pyrolytic graphite-coated graphite tubes. Both methods of measurement indicated that the background was much reduced in the Ir-sputtered tubes. The decrease in background absorption improves conditions for the measurement of these elements. Background molecular absorption was also measured as a function of time. Molecular species such as NO were detected in the vapour phase using pyrolytic graphite-coated tubes, whereas CS and CO were detected using Ir-sputtered tubes.