A MINIATURE GLOW-DISCHARGE FOR LASER-EXCITED ATOMIC FLUORESCENCE DETECTION OF LEAD

A miniature glow discharge atom reservoir has been designed for laser excited atomic fluorescence spectrometric measurements of nanoliter-si zed solution residues. A copper vapor laser pumped dye laser was used to measure the fluorescence of Ph atoms sputtered from the Ni cathode of the discharge. Excitation of Pb occurred at 283.3 nm, and fluoresce nce was monitored at 405.8 nm. The optimal discharge operating pressur e and current were 5.5 Torr and 20 mA with continuous fill gas introdu ction. No improvement was found in S/N with stop flow versus flowing o peration; however, considerable improvement in the S/N was achieved wh en gated peak integration, in contrast to peak detection, was employed . The temporal profiles indicated that the Pb atoms were rapidly sputt ered from the surface of the cathode and that a high percentage of the se atoms diffused back toward the cathode. The redeposition of the Pb atoms led to peak tailing with signals lasting more than 60 s. In effe ct, atoms were sputtered, atomized, and excited several times during a measurement. The limit of detection for Pb was 0.6 pg based on peak d etection and 0.03 pg based on peak area measurements. These detection limits were several orders of magnitude higher than the theoretical, i ntrinsic detection Limit due to the interfering background emission of molecular impurities, such as N-2 and H2O, present in the discharge. (C) 1995 Academic Press, Inc.