Determination of trace fluoroquinolones in honey and milk based on cyclodextrin modified magnetic metal-organic frameworks solid phase extraction coupled with ultra-high performance liquid chromatography.

Long-term intake of animal-derived foods with excessive fluoroquinolones (FQs) will cause damage to human health, so it is critical to establish a feasible approach for sensitive and rapid monitoring of FQs residues. In this study, a new cyclodextrin modified magnetic metal-organic frameworks (Fe3O4@UiO-66-CD) was successfully synthesized by amidation reaction and applied to magnetic solid phase extraction (MSPE) for FQs analysis. The adsorption behavior of Fe3O4@UiO-66-CD was consistent with the pseudo-second-order kinetics and Freundlich isothermal adsorption model, which indicated that the designed material had various interactions on FQs, such as host-guest interaction and π-π interaction. The parameters of MSPE were optimized and the determination method of norfloxacin, enrofloxacin, lomefloxacin and gatifloxacin was established by using MSPE combined with ultra-high performance liquid chromatography (UHPLC) and fluorescence detector (FLD). The method validation results displayed that the detection limits were 0.02-0.09 ng/mL, and the RSDs of intra-day and inter-day precision were less than 4.1 and 6.4 %, respectively. In the target FQs analysis of real honey and milk samples, the recoveries at different fortified concentrations were in the ranges of 88.4 % to 108.6 % with RSD ≤ 5.7 %. The results showed that the proposed method was sensitive, accurate and reliable for the determination of trace FQs in animal-derived foods.

A magnetic solid phase extraction microfluidic chip coupled with gas chromatography-mass spectrometry for the determination of polycyclic aromatic hydrocarbons in aqueous samples.

In this paper, we designed and manufactured a reliable magnetic solid phase extraction (MSPE) microfluidic chip for determination of polycyclic aromatic hydrocarbons (PAHs) in water combined with gas chromatography-mass spectrometry. Sample loading, washing and elution are implemented with microinjection pump and integrated on a single chip, which reduced manual operation. Magnets were used to fix octadecyl/phenyl bifunctional Fe3O4@SiO2 extractant to avoid the design of weir structure in extraction chamber. The whole microfluidic chip was simple and low cost. Based on the microfluidic chip extraction platform, the on-chip MSPE method for the determination of PAHs was optimized and established. The results showed that this method required only 2 mL of sample, 2 mg of extractant, and 50 µL of elution organic solvent for whole on-chip MSPE process, which was environmentally friendly and consistent with green chemistry. Method verification results were displayed which the linear range of five PAHs was between 1-100 ng/mL with good linearity (R2≥ 0.9985), and the detection limits (S/N = 3) were 0.08-0.26 ng/mL. The RSDs of intra-day precision (n=6) and inter-day precision (n=9) for PAHs were less than 6.1 % and 7.2 %, respectively. Enrichment factors were determined to be 31.3-37.7. The recoveries of river water, tap water, bottle water, waste water and urine at three spiked levels were in the range of 89.9% to 113.7% and the matrix effect values were between 83.8% to 109.6%. The extraction platform has the advantages of accurate analysis, simple design and cost-effective, which is conducive to the widespread use of microfluidic chips.

A pre-column derivatization high-performance liquid chromatography method for simultaneous determination of short-chain and medium-chain fatty acids in a fecal sample.

Short-chain and medium-chain fatty acids have plentiful biological functions, which play a crucial role in the diagnosis and therapy of many diseases. Herein, a new method for simultaneous quantifying 17 short-chain and medium-chain fatty acids with high-performance liquid chromatography coupled with an ultraviolet detector was developed and the pre-column derivatization by indole-3-acetic acid hydrazide was performed to improve the separation and detection. The conditions of the derivatization reaction were systematically investigated. Subsequently, the method was validated and the results showed a satisfactory linearity (linear regression coefficients > 0.9969), the limit of detection (4.0×10-3 -1.9×10-2 µmol/L), precision (0.9%-7.3% for intra-day and 2.0%-9.8% for inter-day), recovery (90.0%-109.1% with relative standard deviation <7.7%) and stability (0.1%-3.3% for standard solution and 0.2%-3.9% for fecal sample). Finally, the established method was successfully applied to quantify short-chain and medium-chain fatty acids in the feces of healthy control and diabetic rats. Eleven kinds of short-chain and medium-chain fatty acids were detected and six of them showed a significant difference between the control group and the model group.

A colorimetric aptasensor based on a hemin/EpCAM aptamer DNAzyme for sensitive exosome detection.

Exosomes are considered as potential biomarkers that can reflect information from their parent cell-associated cancer microenvironment. Recently, aptasensors have been widely used for cancer and tumor exosome detection. Aptamers related to exosome surface proteins are usually used to introduce a sequence; the aptamer is used for exosome recognition, and the introduced sequence is used to form G-quadruplexes and for signal amplification. In this paper, we found that the EpCAM aptamer is rich in guanine and unimolecular G-quadruplex with a two-layer G-tetrad under acidic conditions, and we investigated its topology, thermal stability and dissociation constant with hemin. Based on this, our proposed colorimetric aptamer sensor combines the unmodified EpCAM aptamer with hemin to construct a hemin/G-quadruplex DNAzyme and catalyze the TMB-H2O2 system to generate a strong colorimetric signal. Therefore, colorimetric signal changes were negatively correlated with the exosome concentration. The linear range of the 1 h assay was 106-108 particles per mL, and the detection limit was 3.94 × 105 particles per mL. In addition, this method can detect exosomes in complex fetal bovine serum samples with good specificity and high sensitivity toward exosomes from breast, liver, and lung cancers with abnormal EpCAM protein expression.

Application of ß-Cyclodextrin metal-organic framework/titanium dioxide hybrid nanocomposite as dispersive solid-phase extraction adsorbent to organochlorine pesticide residues in honey samples.

A simple and efficient dispersive solid-phase extraction (D-SPE) method combined with gas chromatography tandem mass spectrometry (GC-MS/MS) was developed to determine organochlorine pesticides (OCP) in honey. Firstly, a type of hybrid nanocomposite (CD-MOF/TiO2) was prepared by grafting a metal-organic framework material synthesized with cyclodextrin as an organic ligand onto titanium dioxide. Then, the CD-MOF/TiO2 was used as a D-SPE adsorbent to extract the OCP, and the effects of the amount of adsorbent, ultrasonic time, vortex time, pH, and salinity on the extraction were investigated using Plackett-Burman design and Box-Behnken Design. Under the optimized adsorption and desorption conditions, an analysis method that combined D-SPE with GC-MS/MS was established. The linear ranges of 14 OCP are 1-500 µg kg-1 and the correlation coefficients are between 0.9991 and 1.000. The limits of detection and quantification vary from 0.01 to 0.04 µg kg-1 and 0.04 to 0.12 µg kg-1, respectively. The intra-day and inter-day precision of this method are suitable (RSDs% less than 11.3%). The established CD-MOF/TiO2 / D-SPE method was used for the extraction of OCP in honey samples with recovery in the range of 76.4 to 114.3%. The results demonstrate that the CD-MOF/TiO2 has a good selective enrichment ability for OCP and is suitable for the D-SPE pretreat of honey sample analysis.

Rapid determination of folic acid and riboflavin in urine by polypyrrole magnetic solid-phase extractant combined ultra-performance liquid chromatography.

Determination of folic acid and riboflavin in biological samples is difficult due to their high polarity, low concentration, chemical instability, and complex matrix. In this study, the polypyrrole-coated magnetic nanocomposite (Fe3O4@PPy) was synthesized innovatively with the assistance of hexadecyltrimethylammonium bromide. To evaluate the adsorption mechanism and the feasibility of synthesized Fe3O4@PPy as an adsorbent, the adsorption capacities, kinetics and thermodynamics of folic acid and riboflavin were investigated systemically. Furthermore, in light of the chemical instability of folic acid and riboflavin a method for rapid extraction and detection of them from human urine within 10 min was developed successfully by combining magnetic solid phase extraction with ultra-performance liquid chromatography (MSPE/UPLC). The adsorption parameters including sorbent amount, pH value, extraction time, desorption solvent and desorption time were studied. Under optimum conditions, the performance of the established determination method was validated with the linearly dependent coefficients (>0.9995), the limits of detection (0.02-0.05 µg/mL), the limits of quantification (0.07-0.18 µg/mL), and the recoveries (92.2-105.1%, with relative standard deviation < 3.3%). The rapid extraction and detection of folic acid and riboflavin from real urine samples were achieved subsequently. The present study suggests that the developed method exhibits a promising application in the analysis of free folic acid and riboflavin in human urine samples, which can provide a reference for the clinical drug monitoring and treatment.

Refining androstenedione and bisnorcholenaldehyde from mother liquor of phytosterol fermentation using macroporous resin column chromatography followed by crystallization.

Androstenedione is an androgen and intermediate in the biosynthesis of most adrenocortical, anabolic, sex and synthetic steroids, such as canrenone, eplerenone, norethindrone and spironolactone. Bisnorcholenaldehyde is an important intermediate in the synthesis of progesterone. This study established an androstenedione and bisnorcholenaldehyde separation method that used a macroporous adsorption resin and an ethanol-water mixture as eluent. The adsorption properties of 12 non-polar or weakly polar macroporous adsorption resins were compared, and three resins exhibited a high adsorption capacity and high desorption rate for both androstenedione and bisnorcholenaldehyde. The three resins were then compared using column chromatography, and one resin was selected and parameters (flow rate, resin size, ethanol concentration and volume) of chromatography were optimized to obtain high purity and recovery. Chromatography eluate was concentrated, dissolved in suitable solvent and crystallized at an optimal temperature to obtain a high purity of both androstenedione and bisnorcholenaldehyde from the same starting material. The levels of androstenedione and bisnorcholenaldehyde in the raw material were 39.78% and 19.15%, respectively. After preparative separation and enrichment by resin column chromatography and crystallization, the purity of androstenedione and bisnorcholenaldehyde was 94.3% and 98.6%, respectively, with their recovery yields of 66.8% and 57.9%, respectively. In addition, the resin maintained over 90% separation efficiency for 5 cycles of adsorption. These results indicated that the combination of macroporous resin chromatography followed by crystallization provide a simple, effective, environmentally friendly and low-cost method for the simultaneous purification of androstenedione and bisnorcholenaldehyde.

[Optimization of preparation of poly ( glycidyl methacrylate-divinylbenzene) monolithic column with orthogonal experiments for separation of small molecules].

A monolithic column of macro porous poly (glycidyl methacrylate-divinylbenzene) (poly(GMA-DVB)) has been prepared by free radical polymerization within the confines of a chromatographic stainless steel tube (50 mm x 4.6 mm). For the best separation and low back pressure, orthogonal experiments were carried out with V (cyclohexanol): V (dodecanol), V (GMA): V (DVB) and BPO dosage as the three main factors. The characteristic feature of the column, including specific surface area, pore volume as well as pore diameter distribution, was studied by scanning electron microscopy (SEM), mercury intrusion porosimetry analysis and BET analysis. The obtained optimum preparation conditions were that the volume ratio of GMA, DVB, cyclohexanol and dodecanol was 0.825: 0.825: 1.32: 2.03 and the BPO dosage was 0.7% (mass percentage), then it was heated at 70 degrees C for 24 h. Using this monolithic column, benzene and ethylbenzene and a drug of oxiracetam can be well separated on a high performance liquid chromatographic (HPLC) system equipped with a ultraviolet (UV) detector at 254 nm. A solution of acetonitrile-water (50 : 50, v/v) for the separation of benzene and ethylbenzene, and acetonitrile-water (80 : 20, v/v) for the separation of oxiracetam were used as mobile phases at a flow rate of 1 mL/min. The theoretical plate number was 37 000 plates/m and the resolution of peak width at half height (R1/2) was 7.14. The separation time was less than 10 min. The monolithic column prepared by this method is reproducible and has high column efficiency. It is an economical method to prepare monolithic column, which can be applied to separate small molecules.