Rapid screening method for arsenic speciation by combining thin layer chromatography and laser ablation-inductively coupled plasma-dynamic reaction cell-mass spectrometry

Abstract

In this work, a rapid screening method for arsenic speciation, based on the use of polyethyleneimine (PEI) cellulose thin layer chromatographic (TLC) plates for separation and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) for the detection of the As species, has been implemented. The TLC plates were developed with a mixture consisting of acetone : acetic acid : water (2 : 1 : 1 v/v/v). The procedure proposed has been shown to be capable of the separation of picograms (an LOD of 3 pg has been calculated) to nanograms levels of arsenite [As(III)], arsenate [As(V)], monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA), while arsenobetaine (AsB) and arsenocholine (AsC) practically remained on the sample application point of the TLC plate, allowing their separation from the rest of the compounds but not enabling separating them from one another. The separation procedure only requires approximately 20 min (up to 8 samples can be simultaneously separated) while the LA-ICP-MS protocol only needs a couple of minutes per chromatographic lane. The use of the dynamic reaction cell pressurized with H₂ permits one to overcome the possible overlap of the signals of ⁷⁵As⁺ and ⁴⁰Ar³⁵Cl⁺, ensuring reliable monitoring of the analyte species. The different As species found in NIST SRM 1568a rice flour, after prior enzymatically-assisted extraction with an ultrasonic processor, could be satisfactorily detected, suggesting that the method may be of interest for the fast and qualitative monitoring of As species in biological samples.