Determination of Inorganic Arsenic Using Non-Aqueous Hydride Generation–Atomic Fluorescence Spectrometry Coupled with Deep Eutectic Solvent-Based Liquid Phase Microextraction

The analysis of arsenic content and its speciation in environmental media such as water and biological samples is of great significance to the early warning of geological disaster and ecological safety assessment. Traditional hydride generation atomic fluorescence spectrometry (HG-AFS) suffers from severe interference from transition metal ions and instability of the reductant solution. For the analysis of arsenic valence states, ion chromatography columns and coupled instruments are usually required, which limits its wide application and development. Here, ammonium pyrrolidine dithiocarbamate (APDC) was used to selectively extract As(Ⅲ), and the formed APDC-As(Ⅲ) complex was extracted into the prepared hydrophobic deep eutectic solvent with the assistance of ultrasound. Enrichment of the analyte was achieved while potential interference from transition metal ions was eliminated. Furthermore, solid potassium borohydride powder was directly used to reduce the extracted As(Ⅲ), establishing a new and highly sensitive method for arsenic determination. Firstly, using thymol, menthol and choline chloride as hydrogen bond acceptors (HBAs), and n-octanoic acid, decanoic acid and lauric acid as hydrogen bond donors (HBDs), deep eutectic solvents with good hydrophobicity and stability were prepared and screened for the extraction of inorganic arsenic. The parameters affecting the microextraction and hydride generation process were further optimized. Under the selected experimental conditions, the detection limit of this method for arsenic was as low as 0.02ng/mL, with an enhancement factor of 72. After reducing As(Ⅴ) in the sample with 1% L-ascorbic acid and thiourea, the total inorganic arsenic was determined, and the content of As(Ⅴ) was calculated by the difference, thereby achieving the speciation analysis of inorganic arsenic. The accuracy of the method was verified by certified reference materials, and the measured values were in good agreement with the certified values. Meanwhile, the inorganic arsenic in actual samples such as Wumu spring water (Sichuan), bottled water, tap water and white vinegar was determined, with recoveries of 96.0%–104.0%. This method has potential application prospects in the determination of inorganic arsenic in environmental water samples and biological samples.