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eluent was passed to the nebulizer and into the plasma. The sample volume was 200 µl of a solution
containing 10 µg/ml of each arsenic species. As a consequence, each peak represents the injection of 2
µg of the arsenic compound.

Employing the same chromatographic column, but with a mobile phase that consisted of 90% 5 mM
tetrabutylammonium phosphate in water and 10% methanol, the authors easily separated a selenite from
a selenate. The flow rate was again 0.75 ml/min, and about 15% of the eluent was passed to the
nebulizer. Each peak represented a mass of 0.6 µg and the wavelength monitored to detect the selenium
was 196.1 nm. The signal to noise ratio appeared from the chromatogram to be about 20 and so the
lower limit of detection for the different selenium species appeared to be about 60 ng.

It is interesting to note that Mürer et al. [25] produced a similar separation of the arsenic compounds
using an ion exchange procedure but monitored the eluents using a standard atomic absorption
spectrometer (PE FIAS 200). the separation obtained is shown in Figure 10.12.

Figure 10.12
The Speciation of Arsenic in Urine by LC/AAS (ref. 25)