Chemicals and reagents

Reagent water, LC-MS Ultra CHROMASOLV (Honeywell, Charlotte, NC), was used to prepare the standards and for the sample dilutions. Cr (VI) standards were prepared using K₂CrO₄ (Sigma-Aldrich, St. Louis, MO). As (V) and Se (VI) standards were prepared using Na₂HAsO₄ • 7H₂O (J.T. Baker, Phillipsburg, NJ) and Na₂SeO₄ (ACROS Organics, Geel, Belgium). ClO4− standards (Metrohm; cat. no. REAIC1023) and mixed anion standard (Metrohm; cat. no. REAIC1035) were used to generate the calibration curves for ClO4−, F^–, Cl^–, NO2−, NO3−, and SO42−.

The eluent and the MSM suppressor solutions were prepared using deionized and purified water using a PURELAB Ultra (ELGA LabWater, United Kingdom) with a specific resistance ≥18.2 MΏ-cm. The eluent (mobile phase) contained 10.8 mM Na₂CO₃ (3% [v/v] of Metrohm's A Supp 7 eluent 100 × concentrate) and 35% (v/v) gradient grade acetonitrile (Sigma-Aldrich) in deionized water. The pH of the eluent as prepared was 11.9 ± 0.02. The MSM suppressor solution contained 500 mM H₂SO₄ in deionized water.

The 10% (v/v) H₂SO₄ and 10% (v/v) H₃PO₄ solutions for colorimetric determination of Cr (VI) were prepared from concentrated H₂SO₄ (95–98% solution; VWR, Randor, PA) and concentrated H₃PO₄ (85% solution; Alfa Aesar, Haverhill, MA), respectively. The complexing reagent contained 5 g/L of 1,5-diphenylcarbazide (Sigma-Aldrich) in acetone.