Zaifa Pan

Derivatization following hollow‐fiber microextraction with tetramethylammonium acetate as a dual‐function reagent for the determination of benzoic acid and sorbic acid by GC

Derivatization at the injection port following hollow-fiber-based liquid-liquid-liquid microextraction with tetramethylammonium acetate as a dual-function reagent, i.e. an acceptor and derivatization reagent, for the determination of benzoic acid (BA) and sorbic acid (SA) in real samples by GC was developed. BA and SA were extracted from aqueous samples to an organic phase impregnated into the pores of the hollow fiber wall, and then back-extracted to the acceptor solution located inside the lumen of the hollow fiber. Upon injection, the extracted analytes were quantitatively derivatized to their methyl esters with tetramethylammonium acetate in the GC injection port. Several parameters related to the derivatization and extraction efficiency were optimized. The linearity was satisfactory over a concentration range of 0.1-50 mg/L with r > 0.993 for both analytes. The LODs were 2.0 μg/L for SA and 20 μg/L for BA. The recoveries (83-116%) and precisions (RSDs of 1.2-11.4% (n = 3)) were examined by analyzing real spiked samples. The enrichment factors of BA and SA were 300 and 425. The results demonstrated that this is a simple, rapid, accurate, and sensitive method for the determination of BA and SA in various samples.

Characterization of Alkylphenol Components in Ginkgo biloba Sarcotesta by Thermochemolysis–Gas Chromatography/Mass Spectrometry in the Presence of Trimethylsulfonium Hydroxide

A method to determine alkylphenols in Ginkgo biloba sarcotesta, especially focusing on polyunsaturated ginkgolic acid components, was developed on the basis of thermochemolysis–gas chromatography/mass spectrometry with a DB-23 column in the presence of trimethylsulfonium hydroxide [(CH3)3SOH]. By using this technique, powder sample of Ginkgo biloba sarcotesta can be directly analyzed without any tedious and time-consuming pretreatment. On the resulting chromatograms, seven kinds of ginkgolic acids including polyunsaturated ginkgolic acid GA17:2 and two kinds of ginkgols were clearly observed as their methyl derivative. Based on the peak areas, the ginkgolic acid compositions are in good agreement with these obtained by a high-performance liquid chromatography method dedicated to analysis of ginkgolic acid.

Three‐phase hollow‐fiber microextraction combined with ion‐pair high‐performance liquid chromatography for the simultaneous determination of five components of compound α‐ketoacid tablets in human urine

The determination of α-ketoacid concentration is demanded to evaluate the absorption and metabolic behavior of compound α-ketoacid tablets taken by chronic kidney disease patients. To eliminate the interference of endogenous substance of urine and enrich the analytes, a three-phase hollow-fiber liquid-phase microextraction combined with ion-pair high-performance liquid chromatography method was established for the determination of d,l-α-hydroxymethionine calcium, d,l-α-ketoisoleucine calcium, α-ketovaline calcium, α-ketoleucine calcium, and α-ketophenylalanine calcium of compound α-ketoacid tablets in human urine samples. The extraction parameters, such as organic solvent, pH of donor phase and acceptor phase, stirring rate, and extraction time were optimized. Under the optimal conditions, the obtained enrichment factors were up to 11-, 110-, 198-, 202-, and 50-fold, respectively. The calibration curves for these analytes were linear over the range of 0.1-10 mg/L for α-ketovaline calcium, d,l-α-ketoisoleucine calcium, and α-ketoleucine calcium, 0.5-10 mg/L for d,l-α-hydroxymethionine calcium, and α-ketophenylalanine calcium with r > 0.99. The relative standard deviations (n = 5) were less than 6.27% and the LODs were 100.7, 10.0, 5.8, 7.8, and 8.6 μg/L (based on S/N = 3), respectively. Good recoveries from spiked urine samples (92-118%) were obtained. The proposed method demonstrated excellent sample clean-up and analytes enrichment to determine the five components in human urine.

Determination of anions and cations in biodiesel with on-line sample pretreatment column-switching ion chromatography.

An ion chromatographic approach with on-line sample pretreatment column-switching technique was proposed for the determination of anions and cations in biodiesel. By the employment of the column-switching technique combined with a polymer-based reversed-phase column (An IonPac NG1 guard column), organic residues in the aqueous extracts of biodiesel samples could be on-line removed automatically before flowing into analytical columns. An IonPac AG 11–HC guard column and IonPac AS 11–HC separation column were utilized for the anion separation, whereas an IonPac CG 12A guard column and IonPac CS12A was utilized for cations. Under the optimized separation conditions, a series of standard solutions consisting of nine anions of various concentrations from 0.05 to 40 mg/kg were analyzed with correlation coefficients r ≥ 0.9990, as well as six cations of various concentrations from 0.05 to 20 mg/kg. The limits of detection were in the range of 3.2 to 23.3 µg/kg for anions and 5.1 to 31.3 µg/kg for cations. Relative standard deviations of both anions and cations for retention time, peak area, and peak height were less than 2.98%. A spiking study was performed with satisfactory recoveries between 88.6 and 104.0% for all ions. The chromatographic system was successfully applied to the analysis of five biodiesel samples.

Analysis of trace inorganic anions in weak acid salts by single pump cycling‐column‐switching ion chromatography

The application of ion chromatography with the single pump cycling-column-switching technique was described for the analysis of trace inorganic anions in weak acid salts within a single run. Due to the hydrogen ions provided by an anion suppressor electrolyzing water, weak acid anions could be transformed into weak acids, existing as molecules, after passing through the suppressor. Therefore, an anion suppressor and ion-exclusion column were adopted to achieve on-line matrix elimination of weak acid anions with high concentration for the analysis of trace inorganic anions in weak acid salts. A series of standard solutions consisting of target anions of various concentrations from 0.005 to 10 mg/L were analyzed, with correlation coefficients r ≥ 0.9990. The limits of detection were in the range of 0.67 to 1.51 μg/L, based on the signal-to-noise ratio of 3 and a 25 μL injection volume. Relative standard deviations for retention time, peak area, and peak height were all less than 2.01%. A spiking study was performed with satisfactory recoveries between 90.3 and 104.4% for all anions. The chromatographic system was successfully applied to the analysis of trace inorganic anions in five weak acid salts.

Analysis of volatile organic compounds in pleural effusions by headspace solid‐phase microextraction coupled with cryotrap gas chromatography and mass spectrometry

Headspace solid-phase microextraction coupled with cryotrap gas chromatography and mass spectrometry was applied to the analysis of volatile organic compounds in pleural effusions. The highly volatile organic compounds were separated successfully with high sensitivity by the employment of a cryotrap device, with the construction of a cold column head by freezing a segment of metal capillary with liquid nitrogen. A total of 76 volatile organic compounds were identified in 50 pleural effusion samples (20 malignant effusions and 30 benign effusions). Among them, 34 more volatile organic compounds were detected with the retention time less than 8 min, by comparing with the normal headspace solid-phase microextraction coupled with gas chromatography and mass spectrometry method. Furthermore, 24 volatile organic compounds with high occurrence frequency in pleural effusion samples, 18 of which with the retention time less than 8 min, were selected for the comparative analysis. The results of average peak area comparison and box-plot analysis showed that except for cyclohexanone, 2-ethyl-1-hexanol, and tetramethylbenzene, which have been reported as potential cancer biomarkers, cyclohexanol, dichloromethane, ethyl acetate, n-heptane, ethylbenzene, and xylene also had differential expression between malignant and benign effusions. Therefore, the proposed approach was valuable for the comprehensive characterization of volatile organic compounds in pleural effusions.