Development of a reliable microwave plasma-atomic emission spectrometry (MP-AES) method for the determination of total arsenic in groundwater using l-cysteine as a reducing agent

Accurate determination of arsenic in groundwater is critically important due to the widespread occurrence of arsenic contamination worldwide. This study aimed to develop a reliable and affordable analytical method for the determination of total arsenic in groundwater. The method uses hydride generation microwave plasma atomic emission spectrometry (HG-MP-AES) coupled with a multimode sample introduction system (MSIS), with l-cysteine as the reducing agent. The results demonstrated that accurate determination of total arsenic, comprising both As(III) and As(V), requires the complete reduction of As(V) to As(III) prior to analysis. This was achieved by treating samples with 1% l-cysteine in a 1% hydrochloric acid (HCl) solution for 3 h. The effectiveness of the reduction process was verified by high-performance liquid chromatography coupled with inductively coupled plasma mass spectrometry (HPLC-ICP-MS) analysis. The developed method provides reliable and accurate determination of total arsenic in groundwater and offers a practical analytical approach for the routine monitoring of arsenic-contaminated water resources. The method achieved a limit of detection (LOD) of 0.49 ppb and a limit of quantification (LOQ) of 1.47 ppb. Spike recovery values for groundwater samples ranged from 98% to 107%, while the relative standard deviation (RSD) was below 5%, demonstrating excellent accuracy and precision. A total of 40 groundwater samples collected from two different regions of Bangladesh were analysed using the developed method. The results were in excellent agreement with those obtained by conventional inductively coupled plasma mass spectrometry (ICP-MS), demonstrating the method's suitability for accurate determination of total arsenic in groundwater.