Permanent iridium modifier for electrothermal atomic absorption spectrometry

The suitability for chemical modification of a pure metal layer, deposited on the inner surface of a graphite tube by cathodic sputtering of Ir in a low pressure Ar discharge, was investigated. The characteristics of the deposited layer were studied using scanning electron microscopy and compared with those of Ir deposited from solution. The analytical performance of the modifier was assessed in the determination of Cd, Mn, Pb, Se and V. When sufficient Ir was deposited by sputtering, a homogeneous layer covering the entire tube surface was formed which changed only slightly during the entire lifetime of the graphite tube. Thus integrated absorbance remained essentially constant for more than 700 atomizations. The volatile elements Cd, Pb and Se were thermally stabilized in the absence of a matrix to 800,1200 and 1400 °C, respectively. The rate of atomization for Mn and V was, however, unfavourably delayed in the Ir-coated tubes.