Determination of the acid values of edible oils via FTIR spectroscopy based on the OH stretching band.

A new method for determining the acid values (AVs) of edible oils based on the OH stretching band was developed. The oil sample was diluted with carbon tetrachloride and was placed in a quartz cuvette with a thickness of 1cm to record the FTIR spectrum. The peak at 3535cm(-1), which corresponds to the OH stretch of the carboxyl group in free fatty acids, together with the peak valley at 3508cm(-1) and the spectral data in the range of 3340-3390cm(-1) were used to determine the AV of the edible oil. The excellent linear relationship between the AVs measured in this work and those measured using a titration method, with a correlation coefficient (R) of 0.9929, indicates that the present procedure can be applied as an alternative to the classic method for determining the AVs of edible oils.

Poly(ionic liquid) immobilized magnetic nanoparticles as new adsorbent for extraction and enrichment of organophosphorus pesticides from tea drinks.

New poly(ionic liquid) immobilized magnetic nanoparticles (PIL-MNPs) were synthesized via co-polymerization of 1-vinyl-3-hexylimidazolium-based ionic liquid and vinyl-modified magnetic particles and were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, and magnetic measurements. The PIL-MNPs were utilized as adsorbent phases in magnetic solid-phase extraction (MSPE). The extraction and enrichment efficiency were evaluated by using four organophosphorus pesticides (parathion, fenthion, phoxim and temephos) as test analytes. Various parameters, such as amount of adsorbent, adsorption time, desorption solvent and time, and ionic strength were investigated. The proposed method showed good linearity for the analytes in the concentration range of 1-200µgL(-1) with a correlation coefficient (R)>0.9963. Low limit of detection of 0.01µgL(-1) and high enrichment factors ranging from 84 to 161 were achieved. The proposed method has been successfully used to determine organophosphorus pesticides from three tea drink samples with satisfactory recovery of 81.4-112.6% and RSDs of 4.5-11.3%. The PIL-MNP adsorbent can be reused for 20 times without a noticeable decrease in extraction efficiency.

Determination of trace copper in food samples by flame atomic absorption spectrometry after solid phase extraction on modified soybean hull.

Soybean hull was chemically modified with citric acid and used as a solid phase extraction adsorbent for the determination of trace amounts of Cu(2+) in food samples by flame absorption spectrometry (FAAS). The effect of pH, sample flow rate and volume, elution flow rate and volume and co-existing ions on the recovery of the analyte were investigated. The results showed that Cu(2+) could be adsorbed on the modified soybean hull at pH 8.0 and eluted by 2.0 mL of 1.0 mol L(-1) HCl. Under the optimized conditions, the adsorption capacity of modified soybean hull was found to be 18.0 mg g(-1) for Cu(2+). The detection limit of the proposed method was 0.8 ng mL(-1) for Cu(2+) with an enrichment factor of 18. The analytical result for the certified reference tea sample (GBW07605) was in a good agreement with the certified value. The proposed method has also been successfully applied to the determination of trace Cu(2+) in dried sweet potato, lake water and milk powder, the recovery of Cu(2+) for spiked samples was between 91% and 109.6%.