Determination of ultra-trace rare earth elements in urine samples by photo-Fenton-coprecipitation-plasma mass spectrometry.

The monitoring of trace elements in urine has emerged as an important tool for health risk assessments. However, direct detecting urine samples by ICP-MS is a great challenge as the complex organic content of urine (e.g., uric acid and other organic acids, urea, creatinine) and mineral components present in urine. A separation and preconcentration procedure, using photo-Fenton process and iron hydroxide coprecipitation, was developed for analysis of rare earth elements (REEs) in urine samples. The organic components in urine samples were mineralized by photo-Fenton process, avoiding their inhibitory effects on subsequent coprecipitation. The coprecipitation provides quantitative collection of trace target metal ions and effective separation them from alkaline salts present in urine matrices. The Fe2+ plays a dual role in our experiment: firstly, it is catalyst in the photo-Fenton process; then, it serves as the precipitant in the subsequent coprecipitation. Experimental parameters affecting the photo-Fenton reaction and coprecipitation, were optimized and discussed. The method has good linearity (R2 > 0.9985), excellent sensitivity (LOD as low as 0.02 ng L-1 for Tb and Tm) and satisfactory precision (RSD <3 % for most elements). The method was validated by analysis of urine samples spiked with REEs, the recoveries of REEs were in the range from 85.88 % to 102.01 %. The proposed method offers excellent sensitivity and robust anti-interference capability, which is suitable for the analysis of trace heavy metals in biological samples with high concentration of salts and organic matters, such as urine, serum, whole blood, saliva, etc.