High through-put groundwater arsenic speciation analysis using an automated flow analyzer

The occurrence of geogenic arsenic (As) in groundwater is a global public health concern. However, there remain large gaps in groundwater As data, making it difficult to identify non-compliant domestic wells, partly due to lack of low-cost methods capable of rapid As analysis. Therefore, the development of high through-put and reliable on-site determination methods for inorganic As is essential. Herein, a portable automated analyzer was developed for the determination of arsenite (As(III)), arsenate (As(V)) and phosphate in As contaminated groundwater based on a previously adapted method for molybdenum blue spectrophotometry. After the optimization of the chemical reactions and flow manifold, the system demonstrated a high sample through-put (4.8/hr for As(III), As(V) and phosphate analysis), allowing this system to screen 125 samples in 24 hr. Other advantages include low operational costs (0.3 CNY¥ per sample), appropriate sensitivity for contaminated groundwater (detection limits of 4.7 µg/L, 8.3 µg/L and 5.4 µg/L for As(III), As(V) and phosphate, respectively), good linearity (R² > 0.9996 at As concentrations up to 1600 µg/L) and high precision (relative standard deviations of 3.5% and 2.8% for As(III) and As(V), respectively). The portable system was successfully used for As speciation analysis in 5 groundwater samples collected from multi-level wells at Yinchuan Plain, northwestern China, with total As concentrations ranging from 75.7 to 295.0 µg/L, independently assessing As speciation, providing a promising novel method for the rapid on-site screening of As in tens of millions of domestic wells worldwide.