Effect of elevated gas pressure on atomization in graphite furnace continuum source atomic absorption spectrometry with linear photodiode array detection

Abstract

Absorbances for Al, Cd, Cr, Mn and Pb, integrated with respect to wavelength and time, were determined at pressures as high as 6 atmospheres (1 atm = 101.325 Pa) in a standard integrated contact cuvette (ICC)(tube ends open) and an end-capped ICC (tube ends restricted) and with the injection port open and plugged. In a standard ICC, the maximum increase in signal was limited to a factor of 3 at 6 atmospheres owing to a strong convection component. Plugging the injection port reduced, but did not eliminate, the convection component for Cd and Pb. Use of an end-capped ICC increased the sensitivity by an average factor of 3.2, but did not reduce the convection component. Plugging the injection port of the end-capped ICC gave sensitivity increases proportional to the pressure increase, suggesting that convection had been eliminated. Factors of 4–6 improvement in sensitivity were obtained for atomization at 6 atmospheres. Reasonable agreement was found between the experimental data and a simple model that incorporated diffusion and convection as loss mechanisms. The rate of analyte loss by convection in an ICC at 1 atm is approximately 1/8 that by diffusion. In 3% NaCl, Pb showed improved recoveries at higher pressure with the injection port open or plugged. Good recoveries for Cr were obtained only with the injection port plugged; pressure had no effect. With an end-capped ICC, the injection port plugged, and 6 atmospheres of pressure, detection limits of 50, 100, 30 and 90 fg were obtained for Cd, Cr, Mn and Pb, respectively.