A rapid synergistic cloud point extraction for nine alkylphenols in water using high performance liquid chromatography and fluorescence detection.

A rapid synergistic cloud point extraction for nine alkylphenols coupled with high performance liquid chromatography and fluorescence detection was developed. The non-ionic surfactant polyethylene glycol 6000 (PEG 6000) was selected as the extractant. Acetonitrile was used as a revulsant and synergistic reagent with Na2SO4 to lower the cloud point temperature of extractant to room temperature. These two reagents allowed a cloudy solution to form without heating. The affecting factors were optimized by multiple response optimization with a Box-Behnken design and the desirability function. The optimum conditions found were PEG 6000, 4% (m/v); acetonitrile, 1.5 mL; Na2SO4, 0.6 mol L-1; no pH adjustment or bathing and dilution; centrifugation for 3 min at 3500 rpm and less 8 min for the throughout sample pretreatment procedure. The extraction efficiencies of the nine alkylphenols ranged from 91.4% to 99.5%. These values varied by less than 2.78% from those predicted by the multiple response optimization model. Good linearity (r > 0.994) was obtained in the ranges of 0.6-200 µg L-1 for eight alkylphenols and 1.8-600 µg L-1 for nonylphenol. Simultaneously, the method showed low limit of detection (0.17-0.39 µg L-1) and excellent repeatability at 50 µg L-1 for eight alkylphenols and 150 µg L-1 for nonylphenol (Intraday and Interday of RSD <4.98%, n = 6). The proposed method was successfully applied to determination of the nine alkylphenols in environmental water samples with good recoveries (95.2-106%) and precision values (RSD <5.51%, spiked two levels of 10 and 100 µL of mixed standard, respectively).

Determination of total selenium in food samples by d-CPE and HG-AFS.

A dual-cloud point extraction (d-CPE) procedure was developed for the simultaneous preconcentration and determination of trace level Se in food samples by hydride generation-atomic fluorescence spectrometry (HG-AFS). The Se(IV) was complexed with ammonium pyrrolidinedithiocarbamate (APDC) in a Triton X-114 surfactant-rich phase, which was then treated with a mixture of 16% (v/v) HCl and 20% (v/v) H2O2. This converted the Se(IV)-APDC into free Se(IV), which was back extracted into an aqueous phase at the second cloud point extraction stage. This aqueous phase was analyzed directly by HG-AFS. Optimization of the experimental conditions gave a limit of detection of 0.023µgL-1 with an enhancement factor of 11.8 when 50mL of sample solution was preconcentrated to 3mL. The relative standard deviation was 4.04% (c=6.0µgL-1, n=10). The proposed method was applied to determine the Se contents in twelve food samples with satisfactory recoveries of 95.6-105.2%.