Combination of hollow fiber-based liquid-phase microextraction with sweeping techniques in micellar electrokinetic chromatography for the determination of Strychnos alkaloids in human urine

A new method for the enrichment of Strychnos alkaloids in biological samples via liquid-phase microextxaodon （LPME） based on porous polypropylene hollow fibers in combination with on-line sweeping in micellar electrokinodc chromatography was developed. The calibration curve was linear over the range of 20-200 ng mL^-1 for both strychnine and brucine in human urine sample. The detection limits （S/N = 3：1） for strychnine and brucine were 1 ng mL^-1 and 2 ng mL^-1, respectively. The LPME-sweeping method has been successfully applied to the analysis of strychnine and brucine in real urine samples.

Trace Determination of Tamoxifen in Biological Fluids Using Hollow Fiber Liquid-Phase Microextraction Followed by High-Performance Liquid Chromatography-Ultraviolet Detection

The applicability of hollow fiber liquid-phase microextraction (HF-LPME) combined with high-performance liquid chromatography-ultraviolet detection (HPLC-UV) was evaluated for the extraction and determination of tamoxifen (TAM) in biological fluids including human urine and plasma. The drug was extracted from a 15 mL aqueous sample (source phase;SP) into an organic phase impregnated in the pores of the hollow fiber (membrane phase;MP) followed by the back-extraction into a second aqueous solution (receiving phase;RP) located in the lumen of the hollow fiber. The effects of several factors such as the nature of organic solvent, compositions of SP and RP solutions, extraction time, ionic strength and stirring rate on the extraction efficiency were examined and optimized. An enrichment factor of 360 along with substantial sample clean up was obtained under the optimized conditions. The calibration curve showed linearity in the range of 1 - 500 ng?mL–1 and the limit of detection was found to be 0.5 ng?mL–1 in aqueous medium. A reasonable relative recovery (≥89%) and satisfactory intra-assay (3.7% - 4.2%, n = 3) and inter-assay (7.5% - 7.8%, n = 3) precision illustrated good performance of the analytical procedure in spiked human urine and plasma samples.

Combination of dynamic hollow fiber liquid-phase microextraction with HPLC analysis for the determination of UV filters in cosmetic products

A simple method based on hollow fiber liquid-phase microextraction (HF-LPME) followed by high performance liquid chro-matography (HPLC) analysis was successfully developed for the determination of UV filters in cosmetic products. A canular extractor was assembled by mounting a hollow fiber inside an external tube with a tee-connector. The organic solvent was immobilized into the fiber to form a liquid membrane as the acceptor phase. The sample was continuously injected into the extractor and the UV filters were extracted from the aqueous sample into organic acceptor phase. The main parameters affecting HF-LPME including extraction solvent, sample volume, sample flow rate, pH values and ionic strength were investigated. Toluene has been verified to be suitable as the acceptor phase. Under the optimized HF-LPME conditions, the enrichment factors of five UV filters varying from 24 to 57 were achieved. The limits of detection for the five UV filters were in the range of 1-100 μg L-1 .The relative standard deviations (RSDs) of HF-LPME and HPLC analysis were lower than 5.2%. The proposed method has been successfully applied to the analysis of the varied cosmetic products.

Combination of ionic liquid dispersive liquid-phase microextraction and high performance liquid chromatography for the determination of triazine herbicides in water samples

A temperature-controlled ionic liquid dispersive liquid-phase microextraction in combination with high performance liquid chromatography was developed for the enrichment and determination of triazine herbicides such as cyanazine,simazine,and atrazine in water samples.1-Octyl-3-methylimidazolium hexafluorophosphate（[C8MIM][PF6]） was selected as the extraction solvent.Several experimental parameters were optimized.Under the optimal conditions,the linear range for cyanazine was in the concentration range of 0.5–80 mg/L and the linear range for simazine and atrazine was in the range of1.0–100 mg/L.The limit of detection（LOD,S/N = 3） was in the ranges of 0.05–0.06 mg/L,and the intra day and inter day precision（RSDs,n = 6） was in the ranges of 3.2%–6.6% and 4.8%–8.9%,respectively.Four real water samples were analyzed with the developed method,and the experimental results showed that the spiked recoveries were satisfactory.All these exhibited that the developed method was a valuable tool for monitoring such pollutants.

A New Approach for the Determination of Metronidazole Using Switchable Solvent Coupled with Au-MWCNTs-Modified Electrochemical Sensor

In this work,a new liquid-phase microextraction method coupled with an electrochemical technique using a switchable solvent was proposed for the determination of metronidazole.The extraction solvent used was dipropylamine(DPA),which exhibited switchable hydrophilicity.This means that it can become miscible or immiscible when in contact with carboxylic acids in the aqueous sample.The metronidazole was then measured using a glassy carbon electrode that was modified with Au-multiwalled carbon nanotubes(MWCNTs).The eff ect of diff erent parameters such as the type and amount of trigger,the addition of salt,and the volume of extraction solvent on the e fficiency of switchable hydrophilic solvent-based liquid-phase microextraction(SHS-LPME)was investigated using the one-factor-at-a-time method.After optimizing the conditions,the linear calibration curve was obtained in the concentration range of 0.005–250μmol/L.Accordingly,the limit of quantification(LOQ)of 0.005μmol/L and the limit of detection(LOD)of 0.0015μmol/L were obtained,respectively.

Capillary electrophoresis with laser-induced fluorescence detection of main polyamines and precursor amino acids in saliva

A hollow-fiber liquid-phase microextraction （HF-LPME） method has been developed for the purification and preconcentration of biogenic polyamines and their precursor amino acids in human saliva. Putrescine （Put）, cadaverine （Cad）, spermidine （Spe）, ornithine （Orn）, lysine （Lys）, and arginine （Arg） were determined by the CE-LIF detection after microextraction. Several factors that affect extraction efficiency, separation, and detection were investigated. Under the optimum conditions, six analytes could achieve baseline separation within 30 min, exhibiting a linear calibration at three orders of magnitude （r2 〉 0.998）; the obtained enrichment factors of HF-LPME were between 19 （for Orn） and 2] 8 （for Cad）, and the LODs were in the range of 0.0072-0.26 nmol/L. The proposed HF-LPME/CE-LIF method has been successfully applied for the sensitive analyses of the real-world saliva samples collected from healthy volunteers and different patients with oral diseases, providing a potential method for primary non-invasive diagnosis of some oral diseases.

QSRR Study of GC Retention Indices of Volatile Compounds Emitted from Mosla chinensis Maxim by Multiple Linear Regression

The volatile compounds emitted from Mosla chinensis Maxim were analyzed by headspace solid-phase micro- extraction （HS-SPME） and headspace liquid-phase microextraction （HS-LPME） combined with gas chromatography-mass spectrometry （GC-MS）. The main volatiles from Mosla chinensis Maxim were studied in this paper. It can be seen that 61 compounds were separated and identified. Forty-nine volatile compounds were identified by SPME method, mainly including myrcene, a-terpinene, p-cymene, （E）-ocimene, thymol, thymol acetate and （E）-fl-farnesene. Forty-five major volatile compounds were identified by LPME method, including a-thujene, a-pinene, camphene, butanoic acid, 2-methylpropyl ester, myrcene, butanoic acid, butyl ester, a-terpinene, p-cymene, （E）-ocimene, butane, 1,1-dibutoxy-, thymol, thymol acetate and （E）-fl-farnesene. After analyzing the volatile compounds, multiple linear regression （MLR） method was used for building the regression model. Then the quantitative structure-retention relationship （QSRR） model was validated by predictive-ability test. The prediction results were in good agreement with the experimental values. The results demonstrated that headspace SPME-GC-MS and LPME-GC-MS are the simple, rapid and easy sample enrichment technique suitable for analysis of volatile compounds. This investigation provided an effective method for predicting the retention indices of new compounds even in the absence of the standard candidates.

Application of LPME/GC-ECD for determination of PCP in water

Liquid-phase microextraction (LPME) followed by gas chromatography (GC) coupled with an electron capture detector (ECD) was applied for the analysis of pentachlorophenol (PCP) in aqueous samples. After alkalization with Na2CO3 solution, PCP was acetylated with acetic anhydride. The pentachlorophenyl acetate derivative was then extracted with n-hexane by LPME. 1.5 μL organic drop exposed to the aqueous sample solution at 15℃ for 5 min, stirring rate at 100 r/min was chosen as the optimum extraction condition. Under this condition, LPME provided a very simple, fast and solvent-less procedure to collect PCP from aqueous sample for GC determination. The linearity of LPME/GC-ECD for PCP in distilled water was investigated at the range of 2-200 μg/L with a coefficient of correlation 0.998. The repeatability of this method was determined at the level of 50 μg/L with the average of relative standard deviations (RSDs) 7%. Detection limit was obtained at less than 0.5 μg/L levels. When LPME/GC-ECD was applied to the determination of PCP in municipal sewage, the average of relative recoveries and RSDs were 70% and 6.5%, respectively.