2-STEP LASER-EXCITED ATOMIC FLUORESCENCE SPECTROMETRY DETERMINATION OF MERCURY

A novel method for the determination of mercury by laser excited atomi c fluorescence with electrothermal atomization (LEAFS-ETA) has been de veloped. The experimental set-up consisted of a dual dye-laser system pumped with a XeCl excimer laser operated at 10 Hz, and an electrother mal atomizer with platform atomization. The atomization program allowe d time for the injection of Pd (as a matrix modifier) and used a dryin g step at 110-degrees-C and an atomization step at 1200-degrees-C. The collection is made at 90-degrees using a pierced mirror, an achromat lens and a long-pass filter. The monochromator is fitted with a 1P28 P MT. The signal is processed by using a boxcar and an analog to digital interface. The excitation scheme is a two-step process, with lambda1 = 253.7 nm and lambda2 = 435.8 nm. Direct fluorescence is observed at 546.1 nm. The limit of detection (LOD) obtained is 90 fg (9 pptr with 10 mul injection). The linear dynamic range (LDR) is five orders of ma gnitude and is limited by the non-linearity of the co-operative proces ses occurring at higher concentrations. In order to extend the LDR to higher amounts of mercury, indirect fluorescence is collected with the less sensitive line at 407.8 nm, allowing concentrations of 1 ppm and up to be measured, extending the LDR of the technique to at least sev en orders of magnitude.