DETECTION OF TRACE AMOUNTS OF CR BY 2 LASER-BASED SPECTROSCOPIC TECHNIQUES - LASER-ENHANCED IONIZATION IN FLAMES AND LASER-INDUCED FLUORESCENCE IN GRAPHITE-FURNACE

The detectability of Cr in water solutions by two-step laser-enhanced ionization (LEI) in flames and two-step excitation laser-induced fluorescence in graphite furnace (LIF-GF) with nonresonant detection is investigated for what is, to our knowledge, the first time. A thorough investigation of possible excitation and detection routes for Cr for both techniques is given. The detection limit of Cr in water by the LEI technique was found to be 2 ng/mL, while the LIF-GF technique showed a detection limit of 1.4 pg (which corresponds to 0.3 ng/mL, with a 5-muL sample volume), both of which are limited by contamination (from the burner head-nebulizer unit in the flame and from the graphite material in the furnace). A more sensitive two-step LEI excitation scheme than that used here is also proposed. A new technique for reducing fluctuations from blackbody radiation by using sequential detection of the blackbody radiation from one photomultiplier by two boxcar integrators is presented. A possible means of increasing the nonresonant signal in two-step excitation LIF-GF by adding small amounts of quenching enhancing N2 to the Ar atmosphere gives no positive results. The influence of large-amounts of Na on the detectability of Cr by LEI is investigated.