Li-Qing Peng

Determination of Tetracycline Antibiotic Residues in Honey and Milk by Miniaturized Solid Phase Extraction Using Chitosan-Modified Graphitized Multiwalled Carbon Nanotubes

A rapid, simple, and strongly selective miniaturized solid phase extraction (SPE) technique, requiring only small amounts of sorbent (24 mg) and elution solvent (600 μL), coupled with ultrahigh-performance liquid chromatography and quadrupole time-of-flight mass spectrometry was developed for detecting tetracycline antibiotics. These analytes were extracted from honey and milk using chitosan-modified graphitized multiwalled carbon nanotubes (G-MWNTs) as the solid sorbent and acetonitrile/acetic acid (8:2, v/v) as the eluent in miniaturized SPE. Under the optimum experimental conditions, a satisfactory linearity (r(2) > 0.992) was obtained, and the limits of detection were in the range of 0.61-10.34 μg/kg for the analytes. The mean recoveries of the five tetracycline antibiotic residues in the real samples were between 81.5 and 101.4%. The results demonstrated that chitosan-modified G-MWNTs comprise a promising material for the enrichment of tetracycline antibiotics from complex food matrices.

Application of ionic liquids for elution of bioactive flavonoid glycosides from lime fruit by miniaturized matrix solid-phase dispersion

In this work, two flavonoid glycosides (neohesperidin and naringin) in lime fruit were effectively extracted by miniaturized matrix solid phase dispersion (MSPD), followed by ultra-performance liquid chromatography-ultraviolet detection. The best results were obtained using Florisil (150mg) as the sorbent and 1-butyl-3-methylimidazolium tetrafluoroborate (0.4mL, 250mM) as the elution solvent. This work represents the first attempt of using ionic liquids as a green eluent for extraction of the investigated compounds in miniaturized MSPD. Compared with the conventional methods, the proposed method is advantageous due to improved enrichment factor and reduced reagent consumption. A good linearity was observed with r(2) values (>0.998). Meanwhile, the method gave acceptable recoveries (90.16-96.47%) for the determination of flavonoids in plant samples. The limits of detection of the two analytes ranged between 4.08 and 5.04μg/g. The results showed that the optimized method has a great potential for sample preparation in routine analysis of complex plant samples.

Quantitative analysis of flavanones from citrus fruits by using mesoporous molecular sieve-based miniaturized solid phase extraction coupled to ultrahigh-performance liquid chromatography and quadrupole time-of-flight mass spectrometry

An analytical procedure based on miniaturized solid phase extraction (SPE) and ultrahigh-performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry was developed and validated for determination of six flavanones in Citrus fruits. The mesoporous molecular sieve SBA-15 as a solid sorbent was characterised by Fourier transform-infrared spectroscopy and scanning electron microscopy. Additionally, compared with reported extraction techniques, the mesoporous SBA-15 based SPE method possessed the advantages of shorter analysis time and higher sensitivity. Furthermore, considering the different nature of the tested compounds, all of the parameters, including the SBA-15 amount, solution pH, elution solvent, and the sorbent type, were investigated in detail. Under the optimum condition, the instrumental detection and quantitation limits calculated were less than 4.26 and 14.29ngmL(-1), respectively. The recoveries obtained for all the analytes were ranging from 89.22% to 103.46%. The experimental results suggested that SBA-15 was a promising material for the purification and enrichment of target flavanones from complex citrus fruit samples.

Screening of thrombin inhibitors from phenolic acids using enzyme-immobilized magnetic beads through direct covalent binding by ultrahigh-performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry

Thrombin was immobilized on dynabeads®M-270 epoxy by direct covalent binding method for the first time. The enzyme coated magnetic beads were combined with ultrahigh-performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry technique to establish a simple, rapid and reliable approach for screening thrombin inhibitors from Danshen preparation. The conjugation of thrombin to the magnetic beads was characterized using scanning electron microscope, transmission electron microscope and infrared spectroscopy, and the enzyme activity was determined by the analysis of enzyme-bead ratio and peak areas of target compounds. Several factors including amount of magnetic beads, type of elution solvent, incubation temperature and time were optimized. Additionally, two thrombin-bound compounds (protocatechuic aldehyde and salvianolic acid C) in Danshen injection were validated by conventional inhibitory assay and the IC50 values were 286.11 and 66.09μg/mL, respectively. Our findings suggested that the proposed method was efficient in screening active compounds from medicinal plants.

Determination of natural phenols in olive fruits by chitosan assisted matrix solid-phase dispersion microextraction and ultrahigh performance liquid chromatography with quadrupole time-of-flight tandem mass spectrometry.

A simple, efficient and low-cost method based on matrix solid-phase dispersion (MSPD) microextraction and ultrahigh-performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry (UHPLC-Q-TOF/MS) was developed for the determination of seven main natural phenols (gallic acid, hydroxytyrosol, methyl gallate, luteolin 7-O-β-d-glucoside, rutin, ellagic acid and oleuropein) and other eleven compounds in olive fruits. The experimental conditions for the MSPD extraction, including the type of adsorbent, the amount of dispersing sorbent, the grinding time, and the type of elution solvent were investigated and optimized. The optimized parameters were determined to be that middle-molecular-weight chitosan was used as adsorbent, the amount of middle-molecular-weight chitosan was selected to be 25mg, the grinding time was chosen to be 60s, and methanol: water (6:4, v:v) was used as elution solvent. Compared with reported methods, the proposed method was more simple, rapid, and efficient. Moreover, this method required less extraction time and less amount of sample and solvent. The method showed good linearity (r(2)≥0.9909) for the seven analytes, with the limits of detection in the range of 69.6-358.4ng/g. And recoveries were above 80.06%. The methodology was successfully applied to the extraction and determination of seven phenolic compounds in olive fruits（Canarii fructus）.

Simultaneous microextraction of inorganic iodine and iodinated amino acids by miniaturized matrix solid-phase dispersion with molecular sieves and ionic liquids

This study presents an effective method of using miniaturized matrix solid phase dispersion (MSPD) for the microextraction of inorganic iodine and iodinated amino acids from seaweed samples. Quantification of the target analytes was performed by ultrahigh performance liquid chromatography with UV detection. Molecular sieve (SBA-15) was chosen as the dispersing adsorbent with an ionic liquid (1-dodecyl-3-methylimidazolium bromide) as the elution solvent. The experimental conditions for the MSPD, such as the type of sorbent, ratio of sorbent to sample, type and concentration of the elution solvent, and grinding time were evaluated and optimized. Under the final working conditions, good recoveries were obtained in the range of 86.5-95.4%, with relative standard deviation values below 6.0% in all cases. The limits of detection and limits of quantitation were in the ranges of 3.7-16.7ng/mL and 12.4ng/mL, respectively. Compared with common ultrasound assisted extraction, the advantages of this green approach are low consumption of the sorbent and solvent, short extraction time and good selectivity, even in complicated matrices. The proposed SBA-15-based MSPD method was successfully applied to the microextraction of potassium iodide, 3-iodo-l-tyrosine, and 3,5-diiodo-l-tyrosine from kelp, nori and undaria pinnatifida, respectively.

Characterization and determination of isomers in plants using trace matrix solid phase dispersion via ultrahigh performance liquid chromatography coupled with an ultraviolet detector and quadrupole time-of-flight tandem mass spectrometry.

Here, a novel β-cyclodextrin (β-CD) based trace matrix solid-phase dispersion (MSPD) method was developed to extract isomers from different honeysuckle samples using ultrahigh performance liquid chromatography. The structures of the analytes were characterized and determined via quadrupole time-of-flight tandem mass spectrometry and nuclear magnetic resonance. Under optimum conditions, 25mg of sample was dispersed with 75mg of β-CD, and 0.5mL of methanol was used as the elution solvent. The proposed method produced a good linearity (r(2)>0.99) for the isomers, with limits of detection ranging from 1.62 to 3.33ng/mL. The average recovery values that were obtained from analyzing the spiked samples were calculated to be in the range of 87.04-105.20%. Moreover, the trace MSPD method required less reagents and a shorter extraction time in comparison with the traditional pharmacopoeia method and other reported approaches. The developed method was successfully applied for the determination of three real honeysuckle samples that were collected from different cultivated areas.

Trace amounts of poly‐β‐cyclodextrin wrapped carbon nanotubes for the microextraction of flavonoids in honey samples by capillary electrophoresis with light‐emitting diode induced fluorescence detection

A novel dispersive micro‐SPE method with trace poly‐β‐CD wrapped multiwalled carbon nanotubes as sorbents was applied to extract flavonoids in honey samples. The analytes were then determined by CE with LED‐induced fluorescence detection. The influencing parameters, such as the sorbent concentration, extraction time, and eluent type, were properly optimized. The established method had the advantages of simplicity, low consumption of sorbent amount (0.009 mg) and organic solvent (100 μL), and high sensitivity, meeting the principle of green chemistry. Under the optimum conditions, the sorbents allowed the extraction and preconcentration of the flavonoids with enrichment factors in the range from 78 to 166. The recovery study performed at two different fortification levels provided an average recovery >91%. LODs for all the compounds ranged from 0.07 to 17.99 ng/mL. These results demonstrated that the proposed method could be used as a convenient and efficient extraction technique for analysis of flavonoids in different honey matrices.

Effervescence and graphitized multi-walled carbon nanotubes assisted microextraction for natural antioxidants by ultra high performance liquid chromatography with electrochemical detection and quadrupole time-of-flight tandem mass spectrometry.

In this article, effervescence and graphitized multi-walled carbon nanotubes assisted microextraction was first developed for the extraction of antioxidants in hawthorn samples. The use of an effervescent tablet composed of sodium dihydrogen phosphate, sodium carbonate and micro-scale carboxyl graphitized multi-walled carbon nanotubes (extraction sorbent) was the core of the method. In this study, ultra high performance liquid chromatography coupled with electrochemical detection and quadrupole time-of-flight tandem mass spectrometry was performed for qualitative and quantitative analyses of target analytes in hawthorn foodstuffs. Several experimental factors, such as amount of effervescent salts, the sorbent, elution time and elution solvent, were systematically assessed. Under the optimized conditions, a good linearity with R values better than 0.9980 was obtained. The detection limits estimated at a signal-to-noise ratio of 3:1 were ranging from 0.01 to 0.18ng/mL. These results suggested that the proposed method could be an alternative and promising sample preparation tool in future food analysis.

Application of a highly sensitive magnetic solid phase extraction for phytochemical compounds in medicinal plant and biological fluids by ultra-high performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry

A highly sensitive method using reduced graphene oxide with iron oxide (rGO/Fe3O4) as the sorbent in magnetic SPE has been developed for the purification of five anthraquinones (emodin, rhein, aloeemodin, physcion, and chrysophanol) in rhubarb and rat urine by ultra‐HPLC coupled with quadrupole TOF/MS. The extraction was accomplished by adding trace amount rGO/Fe3O4 suspension to 200 mL of aqueous mixture, and the excellent adsorption capacity of the nanoparticles was fully demonstrated in this procedure. Under the optimized conditions, the calibration curves were linear in the concentration range of 0.05–27.77 ng/mL with correlation coefficients varying from 0.9902 to 0.9978. The LODs ranged from 0.28 to 58.99 pg/mL. The experimental results indicated that the proposed method was feasible for the analysis of anthraquinones in rhubarb and urine samples.