Corrosion of transversely heated graphite tubes by mineral acids

Corrosive changes of transversely heated graphite atomizer (THGA)-tube and platform surfaces were studied by scanning electron microscopy in combinati on with tube lifetime measurements under recommended conditions for vanadiu m determination. This was done for the four mineral acid matrices HNO3, HF, HCl and HClO4. Rising corrosion and reduced tube lifetime are observed for these matrices in the sequence HNO3 < HF much less than HCI < HClO4. Morph ological changes related to the corrosive attack are different for each aci d matrix and so are the effects on the analytical behaviour of the tubes. T he results are compared to relevant data for vanadium and chromium measurem ents, which are applied for routine quality control of THGA- and LHGA-tubes by Perkin Elmer. The average mass loss of the investigated tubes per analy sis cycle is also determined and is a further essential parameter of tube c orrosion. Mass loss is mainly caused by carbon evaporation and particle emi ssion during atomization and tube scavenging steps. Changes in electrical r esistivity of the investigated tubes before and after the lifetime experime nts were found, however, they were within the specified range for the quali ty control of THGA-tubes. Hence, they do not affect the temperature setting by voltage control in the relevant spectrometer systems. (C) 1999 Elsevier Science B.V. All rights reserved.