Sorption of As (III) and Se (IV) from aqueous solutions for subsequent determination by total reflection X-ray fluorescence

An approach to the simultaneous isolation of As (III) and Se (IV) from solutions on a new S,N-containing sorbent followed by determination of the analyte in the sorbent phase using total reflection X-ray fluorescence (TXRF) has been proposed. To match the goal, a sorbent with a branched structure was synthesized on the base of polyacrylamide modified with formaldehyde and hydrogen sulfide. This is a heteroatomic copolymer containing sulfide bridges in the chain and crosslinking by a tertiary amine. Conditions for the quantitative co-extraction of As (III) and Se (IV), i.e., sorption in solutions of 1 M HNO3 with calcium ions present, heating to 60°C and phase contact time of 1 h were determined. The mechanism of sorption interaction of the analytes under specified conditions is discussed. It is shown that a 100-fold excess of iron, zinc and copper does not interfere with the extraction of analytes, thus providing the possibility of As (III) and Se (IV) isolation from different types of raw materials and processed products using the synthesized sorbent. A method for the direct XRF quantification of arsenic and selenium with sr 0.09 and 0.08, respectively, in the sorbent phase has been developed. The correctness of the results was confirmed by the ICP-MS method in analysis of aqueous reference solution after dissolution of the sorbate in HNO3 (1:1).

Sorption of Se (IV) from aqueous solutions with subsequent determination by X-ray fluorescence analysis

An approach to sorptive separation of Se (IV) from solutions on a novel S,N-containing sorbent with subsequent determination of the analyte in the sorbent phase by micro-x-ray fluorescence method is presented. The sorbent copolymethylenesulfide-N-alkyl-methylenamine (CMA) was synthesized using «snake in the cage» procedure and proven to be stable in acid solutions. Conditions for quantitative extraction of Se (IV) were determined: sorption in 5 M HCl or 0.05 M HNO3 solutions when heated to 60°C, phase contact time being 1 h. The residual selenium content in the solution was determined by inductively coupled plasma mass spectrometry (ICP-MS) using 82Se isotope. The absence of selenium losses is proved and the mechanism of sorption interaction under specified conditions is proposed. The method of micro-x-ray fluorescence analysis (micro-RFA) with mapping revealed a uniform distribution of selenium on the sorbent surface. The possibility of determining selenium in the sorbent phase by micro-RFA is shown. When comparing the obtained results with the results of calculations by the method of fundamental parameters, it is shown the necessity of using standard samples of sorbates to obtain correct results of RFA determination of selenium in the sorbent phase.

Evaluation of Polyvinyl Alcohol/Pectin-Based Hydrogel Disks as Extraction Phase for Determination of Steroidal Hormones in Aqueous Samples by GC-MS/MS

A new extraction phase based on hydrogel disks of polyvinyl alcohol (PVOH) and pectin was proposed, characterized and evaluated for the extraction of six steroidal hormones (estriol, estrone, 17β-estradiol, 17α-ethinylestradiol, progesterone, and testosterone) in aqueous samples with subsequent determination by gas chromatography-tandem mass spectrometry (GC-MS/MS) after the derivatization procedure. The developed extraction procedure was based on the solid phase extraction (SPE) technique, but employed hydrogel as the sorbent phase. The effects of several parameters, including the amount and composition of the sorbent phase, pH, sample volume, flow rate, and gel swelling over the extraction efficiency, were evaluated. Gels with lower swelling indexes and larger amounts of sorbent ensured higher extraction yields of analytes. The main benefits of using the PVOH/pectin-based hydrogel as the extraction phase are the ease of synthesis, low-cost preparation, and the possibility of reusing the extraction disks. Limits of quantification of 0.5 μg L−1 for estrone and 17β-estradiol, and 1 μg L−1 for testosterone, 17α-ethinylestradiol, progesterone, and estriol were obtained. Accuracy values ranged from 80% to 110%, while the inter-assay precision ranged from 0.23% to 22.2% and the intra-assay from 0.55% to 12.3%. Since the sorbent phase has an amphiphilic character, the use of hydrogels is promising for the extraction of medium-to-high polarity compounds.