LiangJun Xu

Speciation analysis of arsenic in Mya arenaria Linnaeus and Shrimp with capillary electrophoresis-inductively coupled plasma mass spectrometry.

An improved sheath-flow interface used to couple capillary electrophoresis (CE) with inductively coupled plasma mass spectrometry (ICP-MS) and a microwave-assisted extraction used to extract each arsenic species in seafood were developed in this work. The improved sheath-flow interface completely avoids laminar flow in CE capillary caused by the suction from ICP-MS, makes electric supply more stable in CE, and transports analyte solution to ICP-MS easily and more efficiently. CE-ICP-MS coupled with our interface have two quantitative analysis modes: continuous sample-introduction mode and collective sample-introduction mode. The collective sample-introduction technique greatly reduced the dead volume of interface to approximately zero, obviously avoided the excessive dilution of analyte, and eventually led to a much lower detection limit and a much better electrophoretic resolution. This was demonstrated by the better symmetry and narrow peak widths (10-12s) and much lower detection limits (0.030-0.042 microg/L) of four species of arsenic determined with collective sample-introduction mode. With the help of this improved sheath-flow interface and the microwave-assisted extraction, we have successfully separated and determined four arsenic species, As(III), As(V), monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) in dried Mya arenaria Linnaeus and Shrimp samples using CE-ICP-MS within 10 min with a relative standard deviation of 2-4% (peak areas, n=6) and a recovery of 96-105%.

Simultaneous separation of basic and acidic proteins using 1‐butyl‐3‐methylimidazolium‐based ion liquid as dynamic coating and background electrolyte in capillary electrophoresis

1‐Butyl‐3‐methylimidazolium tetrafluoroborate ionic liquids (1B‐3MI‐TFB ILs) were employed as a coating material and BGE in CE for simultaneous separation of basic and acidic proteins such as lysozyme, cytochrome C, ribonuclease A, albumin, and α‐lactalbumin. 1B‐3MI‐TFB ILs effectively reversed the surface charges on the capillary inner surface, preventing the adsorption of postively charged proteins onto the silica surface, as well as associated with proteins, thus benefiting the separation efficiencies and reproducibility. Consequently, simultaneous baseline separation of five proteins was achieved within 14 min by using 10 mM of 1B‐3MI‐TFB ILs as dynamic coating and the only running electrolyte at the voltage of +20 kV. The proposed coating technique is simple, less time‐consuming, reproducible, and also stable enough for proteins separation without the need of additives. Symmetrical peaks with efficiencies up to 670 000 plates/m were obtained. Recoveries of proteins with RSD (for migration times) of 0.23–0.42% (run‐to‐run) and 2.5–3.8% (day‐to‐day) were achieved, respectively. The applicability of the proposed method in proteins separation was evaluated by the separation of egg white samples.

Study on the simultaneous determination of seven benzoylurea pesticides in Oolong tea and their leaching characteristics during infusing process by HPLC–MS/MS

A method for the simultaneous determination of 7 benzoylurea pesticides (chlorfluazuron, diflubenzuron, fluazuron, flufenoxuron, hexaflumuron, teflubenzuron and triflumuron) in the manufactured Oolong tea leaves and its infusion was described. The method has a LOD of 0.03-1.00ng/mL, a recovery of 90.4-103% for made tea and 90.3-102% for tea-infused liquid, respectively. By using the proposed method, the leaching characteristics of above 7 pesticides during infusing process were investigated. The experimental results revealed that: (1) diflubenzuron can be most easily extracted out during infusing process, followed by triflumuron, teflubenzuron, hexaflumuron, chlorfluazuron, flufenoxuron and fluazuron. (2) The leaching of flufenoxuron and chlorfluazuron during infusing process seems to be controlled by only their solubility, whereas, the leaching of other 5 benzoylurea insecticides was primarily controlled by their partitioning coefficient between made tea and hot water. The results of this study are helpful for the accurate evaluation of the safety of Oolong tea.

Improved simultaneous enantioseparation of β-agonists in CE using β-CD and ionic liquids

In this study, approaches to improve chiral resolutions in simultaneous enantioseparation of β‐agonists by CE via a CD inclusion complexation modified with ionic liquids (ILs) are described. Different types of ILs, including tetraalkylammonium‐based ILs, alkylimidazolium‐based ILs and alkylpyridinium‐based ILs, were examined and compared for controlling the EOF in order to improve resolutions of β‐agonists enantiomers. In this regard, tetraalkylammonium‐based ILs were more effective because they could be used at much higher concentrations than other types of ILs. N‐octylpyridinium hexafluorophosphate gave poor resolutions of β‐agonists enantiomers. In addition, when different ILs were mixed to use, they would present particular properties of their own. Moreover, the presence of ILs was essential in the chiral separations of (±) salbutamol, (±) cimaterol and (±) formoterol, which were reportedly not enantioseparated by using the buffer electrolytes containing only β‐CD as a chiral selector.

Field enhancement sample stacking for analysis of organic acids in traditional Chinese medicine by capillary electrophoresis

A technique known as field enhancement sample stacking (FESS) and capillary electrophoresis (CE) separation has been developed to analyze and detect organic acids in the three traditional Chinese medicines (such as Portulaca oleracea L., Crataegus pinnatifida and Aloe vera L.). In FESS, a reverse electrode polarity-stacking mode (REPSM) was applied as on-line preconcentration strategy. Under the optimized condition, the baseline separation of eight organic acids (linolenic acid, lauric acid, p-coumaric acid, ascorbic acid, benzoic acid, caffeic acid, succinic acid and fumaric acid) could be achieved within 20 min. Validation parameters of this method (such as detection limits, linearity and precision) were also evaluated. The detection limits ranged from 0.4 to 60 ng/mL. The results indicated that the proposed method was effective for the separation of mixtures of organic acids. Satisfactory recoveries were also obtained in the analysis of these organic acids in the above traditional Chinese medicine samples.

Determination of organophosphorus pesticides by capillary electrophoresis-inductively coupled plasma mass spectrometry with collective sample-introduction technique.

A new method for the determination of organophosphorus pesticides using CE‐ICP‐MS with collective sample‐introduction technique has been developed in this study. The method has been successfully used to separate and determine dimethoate, trichlorfon and glyphosate with an RSD of <5% for migration times (n=6) and <4% for peak areas (n=6). The experimental results showed that the collective sample‐introduction considerably reduced the makeup volume and the dilution of analyte, and eventually resulted in a much lower detection limit and a much better electrophoretic resolution. The peak widths and the detection limits of dimethoate, trichlorfon and glyphosate obtained with this method are 15–17 s and 0.05–0.07 μg/mL (as compound), respectively. Using this method, we have successfully separated and determined dimethoate, trichlorfon and glyphosate in vegetable sample with a recovery of 90–96%.

Study on the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-methyl-4-chloro-phenoxyacetic sodium (MCPA sodium) in natural agriculture-soils of Fuzhou, China using capillary electrophoresis.

A new method of analyzing trace 2,4-Dichlorophenoxyacetic acid (2,4-D) and 2-methy-4-chloro-lphenoxyacetic sodium (MCPA sodium) in soils by capillary electrophoresis (CE) has been developed in this study. The optimum analytical conditions including chemical component and concentration of buffer solution, pH, separation voltage and sample injection time were studied in detail. Under the optimum conditions, 2,4-D and MCPA sodium in soils can be speedy separated and determined within 20 min with detection limits of 0.15 microg/g (2,4-D) and 0.25 microg/g (MCPA sodium) , a RSD (n=6)<5% and a recovery>89%. With the help of analytical method developed in this study, the degradations of 2,4-D and MCPA sodium in natural agriculture-soils of Fuzhou were studied. The experimental results indicated that the degradations of 2,4-D and MCPA sodium follow first-order kinetics with degradation constants of 0.1509 day(-1) (2,4-D) and 0.2722 day(-1) (MCPA sodium) respectively. The degradation half-life were calculated to be 4.6 days (2,4-D) and 2.6 days (MCPA sodium) at 27 degrees C, implied that 2,4-D and MCPA sodium can be speedy degraded in natural agriculture-soils of Fuzhou, China.

A new interface used to couple capillary electrophoresis with an inductively coupled plasma mass spectrometry for speciation analysis.

In this work, a novel and high‐efficiency interface has been developed in coupling CE with inductively coupled plasma MS (ICPMS). The interface completely avoids laminar flow in CE capillary caused by the suction of nebulizer, and can be easily and stably operated at room temperature with high analyte transport efficiency to ICPMS. The new interface has a liquid dead volume smaller than 5 nL, which was much smaller than those (65–2500 µL) reported previously for other interfaces. All above features led to a higher sensitivity and a better electrophoretic resolution for CE‐ICPMS coupled with this new interface. With the help of this new interface, we have successfully separated and determined five species of arsenic, As(III), As(V), monomethylarsonic acid, dimethylarsinic acid and p‐aminophenylarsonic acid using CE‐ICPMS within 11 min with a detection limit of 0.046–0.075 ng/mL and an RSD of 2–6% (n = 6).

Rolling circle amplification combined with gold nanoparticles-tag for ultra sensitive and specific quantification of DNA by inductively coupled plasma mass spectrometry

A novel method for the ultra specific and sensitive detection of DNA in biological samples was described in this paper based on magnetic beads (MBs)-based rolling circle amplification combined with gold nano-particles (AuNPs)-aptamer labeling technique and inductively coupled plasma mass spectrometry (ICP-MS) detection. The proposed assay has an ultra-high sensitivity and stability, excellent specificity and more robust resistibility to the complex matrix due to the utilization of MBs-based rolling circle amplification, AuNPs-aptamer labeling technique and ICP-MS detection. It can be used to determine DNA or single nucleotide polymorphisms (SNP) with an extremely low detection limit of 0.1fM (1.0×10(-16)M) and a discrimination factor for single-base mismatch of 27. The proposed assay has been successfully used to detect DNA in serum sample with a recovery of 91-106% and a relative standard deviation (RSD) <6% (n=6), suggesting that our method is sensitive and reliable. The ultra-high sensitivity and specificity, easiness of fabrication, operational convenience, short analysis time, better stability and robust resistibility to the complex matrix, make the assay a promising alternative for the detection of various DNA sequence in the clinical diagnosis.

Analysis of ultratrace triorganotin compounds in aquatic organisms by using capillary electrophoresis―inductively coupled plasma mass spectrometry

A microwave-assisted extraction used to extract trace triorganotin from aquatic organisms and a sensitive analytical method for the determination of ultratrace triorganotin (namely trimethyltin, triethyltin, tripropyltin and tributyltin) with capillary electrophoresis-inductively coupled plasma mass spectrometry were firstly described in this study. The extraction method is simple, effective and can be used to extract trace triorganotin in aquatic organisms within several min. The analytical method has a much lower detection limit of 0.2-0.7 ng Sn/mL for triorganotin compounds, and can be used to determine trace triorganotin in aquatic organisms directly without any derivatization and preconcentration. Using above methods, we have successfully determined trimethyltin, triethyltin, tripropyltin and tributyltin in dried Mya arenaria Linnaeus and Corbicula fluminea within 17 min with a recovery of 93-104% and a RSD (relative standard deviation, n=6) of 2-5%. Our results showed that dried M. arenaria Linnaeus contained an extremely high tributyltin of 5.1 microg Sn/g dried weight, indicating that it may be a good biomarker for the organotin pollution in ocean.