Tungsten coil devices in atomic spectrometry: absorption, fluorescence, and emission.

In this work, tungsten coil (W-Coil) devices are used as atomizers for electrothermal atomization atomic absorption spectrometry (ETAAS), electrothermal atomization laser excited atomic fluorescence spectrometry (ETA-LEAFS), and electrothermal vaporization inductively coupled plasma atomic emission spectrometry (ETV-ICP-AES). For most cases in ETAAS and ETA-LEAFS, limits of detection (LODs) using the W-Coil are within a factor of ten of those observed with commercial graphite furnace systems. LOD for Cd by W-Coil AAS is 10 pg, while LODs for As, Se, Cr, Sb and Pb by W-Coil LEAFS are 950, 320, 1400, 330, and 160 fg, respectively. The compact W-Coil device makes it an ideal atomizer for portable atomic spectrometry instrumentation, especially when coupled with a miniature charge coupled device spectrometer. Alternatively, the atomizer can be used as an inexpensive, modular add-on to an existing commercial ICP-AES system; and the thermal separation of Pb with interference elements Al, Mn, and Fe is demonstrated.

Time-resolved emission studies of ArF-laser-produced microplasmas.

ArF-laser-produced microplasmas in CO, CO(2), methanol, and chloroform are studied by time-resolved emission measurements of the plasma decay. Electron densities are deduced from Stark broadening of the line profiles of atomic H, C, O, and Cl. Plasma ionization and excitation temperatures are determined from measurements of relative populations of ionic and neutral species produced in the plasmas. A discussion of the thermodynamic equilibrium status of ArF-laser microplasmas is presented. In general, the ArF-laser-produced microplasma environment is found to be similar in all the gases studied, in terms of both temperature (15,000-20,000 K) and electron density (10(17) cm(-3)-10(18) cm(-3)), despite the considerable differences observed in the breakdown thresholds and relative energies deposited in the various gases.

Development of an electrothermal atomization laser-excited atomic fluorescence spectrometry procedure for direct measurements of arsenic in diluted serum.

A procedure for the direct determination of arsenic in diluted serum by electrothermal atomization laser-excited atomic fluorescence spectrometry (ETA-LEAFS) is reported. Laser radiation needed to excite As at 193.696 and 197.197 nm is generated as the second anti-Stokes stimulated Raman scattering output of a frequency-doubled dye laser operating near 230.5 and 235.5 nm, respectively. Two different LEAFS schemes have been utilized and provide limits of detection of 200-300 fg for As in aqueous standards. When measurements of serum samples diluted 1:10 with deionized water are performed, a stable background signal is observed that can be accounted for by taking measurements with the laser tuned off-wavelength. No As is detected in any of the bovine or human serum samples analyzed. Measurements of 100 pg/mL standard additions of As to a diluted bovine serum sample utilizing either inorganic or organic As species demonstrate a linear relationship of the fluorescence signal to As spike concentration, but exhibit a sensitivity of approximately half that observed in pure aqueous standards. The limit of detection for As in 1:10 diluted serum samples is 65 pg/mL or 650 fg absolute mass, which corresponds to 0.65 ng/mL As in undiluted serum. To our knowledge, the ETA-LEAFS procedure is currently the only one capable of directly measuring As in diluted serum at these levels.

Laser-induced fluorescence of se, as, and sb in an electrothermal atomizer.

Trace detection of Se, As, and Sb atoms has been performed by electrothermal atomization laser-induced fluorescence (ETA-LIF) approaches. Production of far-UV radiation necessary for excitation of As atoms at 193.696 nm and Se atoms at 196.026 nm was accomplished by stimulated Raman shifting (SRS) of the output of a frequency-doubled dye laser operating near 230 nm. Both wavelengths were obtained as second-order anti-Stokes shifts of the dye laser radiation and provided up to 10 µJ/pulse, which was shown through power dependence studies to be sufficient for saturation in the ETA. An excited-state direct line fluorescence approach using excitation at 206.279 nm was also investigated for the LIF detection of Se. High-sensitivity LIF of Sb atoms was accomplished using 206.833-nm excitation and detection at 259.805 nm. The accuracy of the ETA-LIF approaches was demonstrated by determining the As and Se content of aqueous reference samples. The limits of detection (absolute mass) were 200 fg by ground-state LIF and 150 fg by excited-state direct line fluorescence for Se, 200 fg for As, and 10 fg for Sb; these LODs compare favorably with results reported previously in the literature for ETA-LIF, GFAAS, and ICP-MS methods.

Development of ultratrace laser spectrometry techniques for measurements of arsenic.

Several techniques based on laser induced fluorescence (LIF) spectrometry and laser enhanced ionization (LEI) spectrometry have been investigated for ultratrace measurements of arsenic. Studies by our group in this area that have been published previously are reviewed here, and are presented along with the results of recent studies that have not yet been published. The techniques presented include LIF detection in the inductively coupled plasma atomizer, the electrothermal atomizer, the tungsten coil atomizer, the flame atomizer and LEI detection in the flame atomizer, and include approaches that utilize hydride generation or laser ablation sample introduction. Recent efforts have been directed towards developing speciation approaches for arsenic that utilize LIF spectrometric detection. The capabilities of each technique are summarized including the sensitivity and limits of detection, which range from sub-pg ml(-1) to ng ml(-1) levels. Selected applications of the techniques are presented to demonstrate their utility for environmental and biological samples, and areas for future investigation and further development are discussed.