On-line coupling of flow injection microcolumn separation and preconcentration to electrothermal atomic absorption spectrometry for determination of (ultra)trace selenite and selenate in water

A flow injection manifold with an ah-segmented and air-transported operatio nal sequence for on-line coupling of microcolumn separation and preconcentr ation to electrothermal atomic absorption spectrometry (ETAAS) was develope d for the determination of (ultra)trace selenite and selenate in water. The determination of selenite was achieved by selective reaction with pyrrolid ine dithiocarbamate (PDC), sorption of the resultant Se-PDC compound onto a conical microcolumn (10.2 mu L) packed with RP C18 sorbent, elution with e thanol, and detection by ETAAS, The concentration of selenate was obtained as the difference between the concentrations of selenite after and before p rereduction of selenate to selenite, With the developed manifold and operat ion sequence, the dispersion during elution and eluate transport and the el uent volume required for complete elution of the sorbed analyte were minimi zed. As a result, the sorbed analyte was quantitatively eluted from the col umn with only 26 mu L of ethanol, and all the eluate was automatically intr oduced into the graphite tube by an air flow without the need of preheating the graphite tube or precise timing. Pretreatment of the graphite tube wit h iridium as a long-term "permanent" modifier effectively prevented analyte loss arising from the high volatility of the Se-PDC compound and greatly i mproved the precision, sensitivity, and detection limit. One thermal pretre atment of the graphite tube with injection of 150 pg of iridium made possib le at least 200 repetitive atomization cycles, With a preconcentration time of 180 s and a sample flow rate of 1.4 mt min(-1), an enhancement factor o f 112 was achieved in comparison with direct injection of 30 mu L of aqueou s solution. The detection limit (3s) was 4.5 ng L-1 Se. The RSD (n = 7) was 3.8% at 20 ng L-1 Se. The concentrations of selenite and selenate determin ed in synthetic aqueous mixtures were in good agreement with the expected v alues. The recoveries for selenite from spiked seawater samples ranged from 98 to 102%, The concentrations of selenite in several seawater reference m aterials obtained with simple aqueous standard solutions for calibration ag reed well with the certified and information values, respectively, In addit ion, the developed method was successfully applied to the certification of selenite and selenate in water.