Interfacing HPLC-flame AAS Using a Thermospray Nebulizer Speciation Studies of Calcium and Magnesium.

A new sample introduction device for flame AAS was developed based on the use of a thermospray nebulizer. The thermospray nebulizer produced a relatively uniform aerosol droplet size which underwent desolvation before entering the flame. As a result, signal dependence on different solvents as seen in common pneumatic nebulizers was not observed with the thermospray nebulizer. By placing the nebulizer below the flame burner head, the analyte transportation efficiency was significantly improved up to 60%. Sensitivity improvement over commercial pneumatic nebulizers was 5 to 10 fold depending on the metal studied. Detection limits of pg level were achieved with the thermospray nebulizer. When interfaced to LC, chromatographic resolution was maintained. The system was compatible with most solvents, buffer solution or mixtures of solvents produced in gradient elution. The thermospray nebulizer was also used in conjunction with the circular flame atomizer system developed for mercury detection. The system yielded a sensitivity (1% absorption) of 0.20 ppm and detection limits of 10 ppb at 1.0 mL/min solvent flow rate using 253.7 nm mercury line. This compares with a sensitivity of 7.5 ppm for a conventional burner. The developed HPLC-thermospray nebulizer interfaced flame AAS has been applied for metal speciation studies. The HPLC-Flame AAS system was used to study the effect of heavy metals on the chlorophyll in duckweed. Studies indicated that the heavy metals were involved in the destruction of chlorophylls. The mode of destructions appeared to be the promotion of degradation by heavy metals. It appeared that heavy metals did not replace the central Mg in chlorophyll. The subsequent detection limit of chlorophyll was about 10 ng. This system was also used to initiate study of calcium compounds in body fluids, i.e. urine and perspiration, in order to understand their relationships with blood plasma. The chromatographic conditions were developed to improve the chromatographic resolutions of urinary calcium. Studies indicated that different individuals excreted similar but slightly different calcium compounds through urine, which appeared different from those of perspiration based on the chromatographic retention time. Further attempts to characterize the peaks using mass spectroscopy and infrared spectroscopy were not successful