Portable EDXRF Analysis of Eight Heavy Metals in Environmental Water Using Pre-concentration with Purolite S930 and Thin-layer Sample Technique

Analysis of environmental water samples is primarily conducted in the laboratory, which costs considerable time and money. Pre-concentration methods coupled with portable X-ray Fluorescence (XRF) have been developed for the determination of almost twenty kinds of heavy metals, but with a relatively high detection limit, complex operation, and less element types can be measured using one pre-concentration strategy. All of these problems restrict the development of the technique. To solve these issues an on-site-oriented rapid and convenient analysis method of heavy metal ions in aqueous solutions has been developed utilizing a bench-top type portable Energy-Dispersive X-ray Fluorescence (EDXRF). Based on pre-concentration with purolite S930 chelating resin and thin-layer sample preparation technique, the method could determine trace V⁵⁺, Mn²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺ and Pb²⁺ in environmental water samples. After the heavy metal ions have been absorbed by 20 mg of S-930 resin powder for about 30 min in the pH=4 solution, the resin powders are filtrated onto a 0.45 m filter to form a thin-layer sample which can be directly measured by EDXRF using a homemade double polypropylene film sample cup. With an amount of 100 mL of solution, the linear ranges were 10-1000 g/L and the correlation coefficients of the calibration curves were good (R²>0.997) for all the eight elements. The lower limit of detection was between 1.0 and 6.2 g/L. Precision tests carried out on multi-element mixed solutions showed that the relative standard deviations (RSD, n=12) were better than 5% except for those of Zn and Pb at the concentration level of 20 g/L. Most of the recoveries were 80%-120% with spikes of 20 g/L for each element. The analysis results of DW standard substances and simulation samples were consistent with reference values and the theoretical value respectively. This method skillfully uses a double polypropylene membrane preparation method to make a thin-layer film sample which solves the pollution problem and simplifies the pre-concentration steps. The resin film samples can be directly measured by XRF. A lower detection limit and better stability make the method suitable for a spot investigation, water quality monitoring, and assessment of Fe, Co, Ni, Cu, V, Zn, Mn and Pb in heavy metal polluted environmental water.