Assessing the hyphenation of ion chromatography with optical emission spectrometry for trace analysis of oxyhalide bromine and chlorine species

Abstract

Background

The increased application of oxidative water treatment is associated with the presence of halogenated disinfection by-products (DBPs) in aqueous systems. Due to their hazard potential, permanent measurements of selected analytes are required to monitor their compliance with regulatory limits and guidelines. However, the simultaneous acquisition of alarming inorganic oxyhalide species by conventional ion chromatography (IC) is often impeded by co-elution of interfering analyte or matrix components, especially when DBPs of multiple halogens are present in solution. This necessitates a complementary, orthogonal detection setup that allows for an element-specific analysis.

Results

The present work evaluates the hyphenation of IC with optical emission spectrometry (ICP-OES) for the simultaneous quantification of five prominent bromine and chlorine species, namely ${\text{Br}}^{–}$, ${{\text{BrO}}_3}^{–}$, ${\text{Cl}}^{–}$, ${{\text{ClO}}_2}^{–}$ and ${{\text{ClO}}_3}^{–}$, at trace concentrations ranging from 2.5 to 100 μmol L⁻¹ for Br species and 5–100 μmol L⁻¹ for Cl species. It is shown that ICP-OES detection in the vacuum UV region below 170 nm leads to higher sensitivity for Br species, with ${{\text{BrO}}_3}^{–}$ showing a significantly ($p=5·{10}^{‐9}$) stronger signal response than ${\text{Br}}^{–}$. The developed method enables the selective quantification of co-eluting (oxy-)halides and shows excellent linearity (R² $\ge$ 0.999) and coefficients of variation of the procedure V_x0 < 5 % for all analytes. Limits of detection below 100 μg L⁻¹ were achieved, in conjunction with mean recovery rates of 98 $\pm$ 4 % in challenging matrices.

Significance

For the first time, Br and Cl speciation was successfully achieved by using IC-ICP-OES hyphenation. The results highlight the robustness and applicability of the developed method exemplarily for oxyhalide speciation, clearly differentiating species-specific behavior of halogens in an emission spectrometer. This hyphenation technique generally enables solving complex separation problems by simultaneously evaluating different spectral properties, hence demonstrating to be a valid alternative to ICP-MS, especially for pool and spa water quality monitoring.