Determination of trihalomethanes in drinking water by GC-ICP-MS using compound independent calibration with internal standard

Abstract

Compound independent calibration with an internal standard in combination with GC-ICP-MS allowed standardless determination of trihalomethanes (CHCl₃, CHBrCl₂, CHBr₂Cl and CHBr₃) in drinking waters following European Norm ISO 10301. It was demonstrated that the ratio of peak areas (analyte to internal standard) is linear with the ratio of concentrations with slope of 1 and intercept of 0, both for chlorine and bromine, when the concentrations of analyte and internal standard are expressed in terms of elemental concentrations. Then, the use of CBrCl₃ as internal standard allowed the simultaneous determination of all four compounds in one single injection by detecting chlorine at mass 35 and bromine at mass 79. For the determination of trihalomethanes (THMs) in drinking waters the method required only the addition of a known amount of internal standard to 100 mL of sample, the extraction of the THMs using 4 mL of n-pentane and the direct injection of the extract in the GC-ICP-MS system. No additional injections were required for quantitation. Extraction recoveries were between 80 and 98%, reproducibility was below 3% and method detection limits were below 0.01 ng mL⁻¹ for all compounds, meeting the requirements of international legislation for the routine determination of THMs in drinking waters.