Detection of trace amounts of Cr by two 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-microL 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 N(2) to the Ar atmosphere gives no positive results. The influence of large amounts of Na on the detectability of Cr by LEI is investigated.

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