Achieving 100% Efficient Postcolumn Hydride Generation for As Speciation Analysis by Atomic Fluorescence Spectrometry
Abstract
An experimental setup consisting of a flow injection hydride generator coupled to an atomic fluorescence spectrometer was optimized in order to generate arsanes from tri- and pentavalent inorganic arsenic species (iAs(III), iAs(V)), monomethylarsonic acid (MAsV), and dimethylarsinic acid (DMAsV) with 100% efficiency with the use of only HCl and NaBH4 as the reagents. The optimal concentration of HCl was 2 mol L-1 the optimal concentration of NaBH4 was 2.5% (m/ v), and the volume of the reaction coil was 8.9 mL.
To prevent excessive signal noise due to fluctuations of hydride supply to an atomizer, a new design of a gas-liquid separator was implemented. The optimized experimental setup was subsequently interfaced to HPLC and employed for speciation analysis of arsenic.
Two chromatography columns were tested: (i) ion-pair chromatography and (ii) ion exchange chromatography. The latter offered much better results for human urine samples without a need for sample dilution.
Due to the equal hydride generation efficiency (and thus the sensitivities) of all As species, a single species standardization by DMAsV standard was feasible. The limits of detection for iAs(III), iAs(V), MAsV, and DMAsV were 40, 97,57, and 55 pg mL(-1), respectively.
Accuracy of the method was tested by the analysis of the standard reference material (human urine NIST 2669), and the method was also verified by the comparative analyses of human urine samples collected from five individuals with an independent reference method.