Speciation of inorganic selenium in wastewater using liquid electrode plasma-optical emission spectrometry combined with supramolecule-equipped solid-phase extraction system

A new approach for the rapid analysis of inorganic Se (i-Se: Se-IV and Se-VI) in an aqueous acidic matrix is proposed. A supramolecule-equipped solid-phase extraction (SPE) system is used for the ion-selective retention and pre-concentration of i-Se as Se-IV, followed by analysis using a portable liquid electrode plasma-optical emission spectrometer (LEP-OES). The Se-IV in the matrix is analyzed in the preliminary step. The total i-Se (i-Se-Tot) is transformed to Se-IV via an acid-induced reduction treatment in a concurrent step, and the value from the initial step is subtracted from the latter for the quantification of Se-VI. Eight different SPE systems, containing diverse supramolecules, were evaluated in terms of selectivity towards SeIV or Se-VI, in addition to retention intensity and capacity. Superior performance was observed with AnaLig As-01. AnaLig As-01 was optimized considering implementation at different solution pHs, sample-loading flow rate, eluent-type or eluent-volume, and the influence of competing ions in the matrix. The intrusive factors of LEP-OES sensitivity, such as interfering component ions or low i-Se content in the matrix, were minimized by SPE-assisted pretreatment. The LEP-OES operating variables, e.g., applied voltage, on-time, off-time, and pulse count for the applied voltage, were optimized to obtain a distinct peak in the spectrum for i-Se at lambda(max), 196.026 nm. The limit of detection (3s) for iSe determination using the proposed process was 2.15 mu g mL(-1). The method was applied to the analysis of i-Se in a certified reference material of wastewater (SPS-WW1). The recoveries (%) by the standard addition method were <= 100 for Se-IV and <= 83 for Se-VI. The datasets from the LEP-OES analysis and inductively coupled plasma optical emission spectrometric measurements were also comparable for the same matrix (coefficient of variation: Se-IV, 0.9%; Se-VI, 3.6%).