Use of a pH-sensitive polymer in a microextraction and preconcentration method directly combined with high-performance liquid chromatography
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A pH-sensitive polymer based on the poly(styrene- alt -maleic anhydride) co-polymer serves as basis to develop a microextraction method (pH-HGME) in direct combination with high-performance liquid chromatography (HPLC) and fluorescence detection (FD) for the determination of seven organic com- pounds, including three polycyclic aromatic hydrocarbons (PAHs), three monohydroxylated PAHs and one alkylphenol, in urine. The method bases on the structural modification of the pH-sensitive polymer in the aqueous sample at a high pH value, followed by the formation and insolubilization of a hydrogel contain- ing the preconcentrated analytes by decreasing the pH, and the direct injection of the hydrogel-rich phase in the HPLC-FD system. The optimization of the main variables permitted the selection of low amounts of aqueous sample (10 mL), which was mixed with 10 mg of co-polymer also present in a low volume (150 μL) of concentrated NaOH. The method further requires the addition of 200 μL of concentrated HCl, 3 min of stirring, and 15 min of centrifugation. This pH-HGME-HPLC-FD method presented low limits of detection, ranging from 0.001 μg L −1 to 0.09 μg L −1 in ultrapure water, average relative recoveries of 96.9% for the concentration level of 0.60 μg L −1 , and enrichment factors between 1.50 and 17.7. The pro- posed method also exhibited high precision, with intermediate relative standard deviations lower than 16% for a concentration level of 0.60 μg L −1 . The developed pH-HGME-HPLC-FD method performed ade- quately when analyzing two human urine samples provided by a non-smoker male and a smoker female, respectively. One of the target analytes (2-hydroxynaphthalene) was quantified in both samples using the standard addition method, with a predicted concentration of 7.3 ±0.4 μg L −1 in the non-smoker male urine and 19.3 ±0.6 μg L −1 in the smoker female urine.