Complexation effect of antimony compounds with citric acid and its application to the speciation of antimony(III) and antimony(V) using HPLC-ICP-MS

In this work, a complexation effect of Sb compounds with citric acid was observed using electrospray mass spectrometry (ES-MS). It was found that both Sb(III) and Sb(V) could form complexes readily with citric acid in an aqueous solution at room temperature. These complexes were found to be very stable in various matrices (moat water and aqueous extracts of airborne particulate matter), therefore, a novel HPLC-ICP-MS analytical method for the speciation of Sb(III) and Sb(V) in environmental samples was developed by using the observed complexation effect. Sb(III)and Sb(V)-citrate complexes were separated on a PRP-X100 anion-exchange column with 10 mmol l EDTA–1 mmol l phthalic acid (pH 4.5) as a mobile phase. All complexes were retained on the separation column, and none of them eluted in the solvent front. Low detection limits of 0.05 mg l and 0.07 mg l were achieved for Sb(III) and Sb(V), respectively. The calibration curves were linear over the range of 1.0–250 mg l for the investigated Sb species. The precisions, evaluated by using the relative standard deviation (%RSD) with a 2 mg l standard solution, were 1.8% and 3.3% for Sb(III) and Sb(V), respectively. Several advantages of the developed method, such as improving chromatographic separation, stabilizing Sb compounds in a water sample, and preventing Sb(III) from oxidizing to Sb(V) during the ultrasonic-assisted and microwaveassisted extraction of an airborne particulate matter (APM) sample using 26 mmol l citric acid as an extraction solvent, and alleviating the adsorption of Sb compounds on the sample surface, were observed. The developed method enabled us to detect the most toxic Sb specie, Sb(III), in an APM sample for the first time.