Analysis of I in groundwater samples: Direct and quantitative results below the drinking water standard

This paper highlights an analytical method based on mass measurement that can be used to directly quantify ¹²⁹I in groundwater samples at concentrations below the maximum contaminant level (MCL) without the need for sample pre-concentration or extraction. Samples were analyzed on a Perkin Elmer ELAN DRC II ICP-MS after minimal dilution using O₂ as the reaction gas. Analysis of continuing calibration verification standards indicated that the dynamic reaction cell (DRC) mode could be used for quantitative analysis of ¹²⁹I in samples below the MCL (0.0057 ng/mL or 1 pCi/L). The low analytical detection limit of ¹²⁹I analysis in the DRC mode coupled with minimal sample dilution (1.02x) resulted in a final estimated quantification limit of 0.0051 ng/mL. Subsequent analysis of three groundwater samples containing ¹²⁹I resulted in fully quantitative results in the DRC mode, and spike recovery analyses performed on all three samples confirmed that the groundwater matrix did not adversely impact the analysis of ¹²⁹I in the DRC mode. This analytical approach has been proven to be a cost-effective, high-throughput technique for the direct, quantitative analysis of ¹²⁹I in groundwater samples at environmentally relevant concentrations that reach below the current MCL.