Xueju Lv

Preconcentration Procedures for Phthalate Esters Combined with Chromatographic Analysis

Phthalate esters are endocrine disrupters or mutagens. They are widely used as plasticizers and can be usually found in environmental samples, such as food, soil and polluted air. However, it is difficult to directly determine phthalate esters owing to their relatively low concentration and complex matrices. Therefore, preconcentration and separation have become increasingly important. In recent years, many preconcentration methods have been successfully developed and widely used, such as liquid-liquid extraction, dispersive liquid-liquid microextraction and solid-phase extraction. These preconcentration methods for phthalate esters can be applied to various real samples, water, soil, air, food and cosmetics. The aim of this paper is to review recent literature studies (primarily from the last five years) about preconcentration techniques for phthalate esters coupled with chromatographic analysis. The following text describes several preconcentration approaches, including liquid-liquid extraction, dispersive liquid-liquid microextraction, cloud point extraction, solid-phase extraction, solid-phase microextraction and stir bar sorptive extraction. Their advantages and disadvantages are also summarized.

Rapid HPLC-DAD quantitation of sulfonamides in honey using poly(methacrylic acid-ethylene dimethacrylate) monolith modified with 3-(trimethoxysilyl)propyl methacrylate-grafted sodium titanate nanotubes

3-(Trimethoxysilyl)propyl methacrylate-grafted sodium titanate nanotubes were synthesized and used as monomers to functionalize a poly(methacrylic acid-ethylene dimethacrylate) monolithic column. Various techniques, including scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, and thermal gravimetric analysis were employed to characterize the synthesized monolith. The modified polymer monolithic column was further applied to the determination of sulfonamides in honey samples coupled with high performance liquid chromatography-diode array detection. Several experimental parameters affecting the extraction efficiency were investigated by single-factor experiments, such as the sample pH, sample flow rate, sample volume, eluent flow rate, and eluent type. The first four factors were then further evaluated by means of the Taguchis L9(34) orthogonal array experimental design. Under the optimized conditions, good linearities were obtained for all targets with squared regression coefficient values greater than 0.9937. The limits of detection (S/N = 3) and limits of quantitation (S/N = 10) were in the range of 0.68–1.42 and 2.28–4.72 μg kg−1, respectively. The intra-day and inter-day relative standard deviations were determined to be from 1.9% to 6.9%. The recoveries of targets at different spiked levels ranged from 80.3% to 109.9% with relative standard deviations less than 9.5%, suggesting a promising prospect of the developed method in the application of real samples.

Preparation of an allyloxy-cucurbit[6]uril-modified polymer monolithic column for microextraction of estrogens in cosmetics

In the present study, a poly(butyl methacrylate-co-ethylene dimethacrylate) (poly(BMA–EDMA)) monolithic column modified with allyloxy-cucurbit[6]uril (ACB[6]) was prepared with an in situ polymerization process. A polymer monolith microextraction method was developed with the modified monolithic column for the preconcentration of estrogen combined with high performance liquid chromatography. The various experimental parameters affecting the extraction capacity were investigated and optimized with an orthogonal experiment design, L16(45). Under the optimum conditions, we obtained acceptable linearities, low limits of detection, and good intra-day/inter-day relative standard deviations. Hydrophobic interactions, π–π stacking, and hydrogen bonding interactions contributed to the extraction efficiency of the ACB[6]@poly(BMA–EDMA) monolithic column. The present method was employed to determine estrogens in cosmetic samples and the accuracy was assessed through recovery experiments. The obtained recovery values were in the range of 80.1–109.4% with relative standard deviations less than 9.9%.

Polymer monolith microextraction coupled to microwave plasma torch-atomic emission spectrometry for the determination of Nd, Eu and Yb in tea samples

A reliable and rapid method based on polymer monolith microextraction (PMME) combined with microwave plasma torch-atomic emission spectrometry (MPT-AES) was established for the determination of trace rare earth elements (REEs), Nd (light), Eu (medium) and Yb (heavy). Several parameters affecting extraction efficiency, including sample pH, sample flow rate, sample volume, eluent concentration, eluent flow rate and eluent volume, were investigated and optimized in detail. Under the optimum conditions, the limits of detection (n = 7) and limits of quantification (n = 7) for Nd, Eu and Yb (based on a 0.8 mL sample volume) were determined to be 1.07, 0.83 and 1.47 μg L−1, and 3.57, 2.78 and 4.90 μg L−1, respectively. The enrichment factors for Nd, Eu and Yb (5 μg mL−1) were determined to be 15.1, 12.8 and 12.5, respectively, with relative standard deviations (n = 7) of 5.10%, 5.43% and 7.84%. The proposed method has been successfully applied to the analysis of Nd, Eu and Yb in tea samples with a recovery range of 81.2–109.2%.

A magnetic hydrazine-functionalized dendrimer embedded with TiO 2 as a novel affinity probe for the selective enrichment of low-abundance phosphopeptides from biological samples

Dendrimers exhibit tunable terminal functionality and bio-friendly nature, making them of being promising materials for applications in the field of separation and enrichment. In this work, we prepared magnetic hydrazide-functionalized poly-amidoamine (PAMAM) dendrimer embedded with TiO2 for the enrichment of phosphopeptides. The novel affinity probe possessed superparamagnetism, realizing its rapid separation from sample solution. Electrostatic attraction and hydrogen bonding existed between PAMAM and phosphopeptides while Lewis acid-base interaction was originated between TiO2 and the targets. The combined synergistic strength of multiple binding interactions contributed to the highly selective enrichment of phosphopeptides. The specificity for the capture of phosphopeptides was reflected in quantities as low as 1:1000 mass ratio of phosphopeptides to non-phosphopeptides. The detection limit of β-casein digests was low to 0.4 fmol, indicating the high sensitivity of the developed method. Fifteen and four phosphopeptides could be selectively captured from non-fat milk digests and human serum samples, which further confirmed the great potential of the affinity probe in the extraction of low-abundance phosphopeptides from real complex biological samples.

Preparation of carboxylatocalix[4]arene functionalized magnetic polyionic liquid hybrid material for the pre-concentration of phthalate esters

In this work, we designed a novel hybrid material based on the polymerization of an ionic liquid on a magnetic core and further functionalized with carboxylatocalix[4]arene. Scanning electron microscope, transmission electron microscope, Fourier transform infrared spectroscopy, thermal gravimetric-derivative thermogravimetric analysis, energy dispersive X-ray spectroscopy, X-ray diffractometer, and vibrating sample magnetometer were utilized to examine the physicochemical properties of the hybrid material obtained. The material was used as the adsorbent for magnetic solid-phase extraction of phthalate esters. To obtain the maximum pre-concentration efficiency, a series of parameters influencing the extraction efficiency, including sample pH, adsorbent amount, adsorption time, eluent type as well as salt addition, was examined systematically. Under the optimum conditions, a fast and feasible pre-concentration protocol for phthalate esters was established with satisfactory enrichment factors between 158.7 and 191.3. The limits of detection from high-performance liquid chromatographic analysis for the target analytes were in the range of 0.02-0.31 ng mL-1. The wide linear ranges varying from 0.1 to 100 ng mL-1 were achieved with correlation coefficients greater than 0.9977. To evaluate the feasibility of this method, it was successfully applied to analyse phthalate esters in multiple kinds of real samples including tap water, lake water, drinks, tonic lotions, and human serum samples. The results obtained demonstrated that the synthesized magnetic material had potential as a candidate in the pre-concentration field for phthalate esters due to the special properties stemming from its structure and components.

Extraction of bismuth with mixing systems of sec-octylphenoxy acetic acid and 1,10-phenanthroline

ABSTRACT sec-Octylphenoxy acetic acid and 1,10-phenanthroline were employed for the extraction of bismuth from chloride medium, showing evident synergistic effects on bismuth extraction. Stoichiometry of the synergistic extraction was determined, giving a logarithm value of equilibrium constant of 6.75, which was much higher than those obtained by single sec-octylphenoxy acetic acid or 1,10-phenanthroline. Thermodynamic studies indicated that the synergistic extraction was an endothermic and spontaneous process. Moreover, antagonistic effects were found when the mixture was employed for lead extraction, demonstrating its potential to be applied to the separation of bismuth and lead at low mole fractions of sec-octylphenoxy acetic acid.