Hollow-Fiber-Based LPME as a Reliable Sampling Method for Gas-Chromatographic Determination of Pharmacokinetic Parameters of Valproic Acid in Rat Plasma

Progress in pretreatment and analysis of organic Acids: An update since 2010

Organic acids, as an important component of food, have great influence on the flavor, texture, freshness of food. By lowering the pH of food to bacteriostatic acidity, organic acids are also used as additives and preservatives. Because organic acids are crucial to predict and evaluate food maturity, production and quality control, the rapid and sensitive determination methods of organic acids are necessary. This review aims to summarize and update the progress of the determination of organic acids in food samples. Pretreatment methods include simple steps (e.g., "dilute and shoot," protein precipitation, filtration, and centrifugation) and advanced microextraction methods (e.g., hollow fiber liquid phase microextraction, stir bar sorptive extraction and dispersive micro-solid phase extraction). Advances in novel materials (nanomaterial), solvents (ionic liquids and supercritical fluids) and hybrid methods are clearly displayed in detail. Continuous progress which has been made in electrochemical method, two-dimensional chromatography, high resolution mass is thoroughly illustrated.

Development of Membrane Hollow Fiber for Determination of Maleic Anhydride in Ambient Air as a Field Sampler

This research develops a rapid method for sampling and analysis of maleic anhydride (MA) in air using a one-step hollow fiber (HF) membrane in the liquid phase followed by high-performance liquid chromatography. A sampling chamber was prepared for sampling of MA with HF-supported de-ionized water absorbency. Several important parameters, such as sampling flow rate, sampling time, and breakthrough volume (BTV), were optimized at different concentrations using a central composite design. The results showed that sampling could be performed at the maximum period of 4 h with a flow rate of 1 mL min-1 for different concentrations (in the range of 0.05-2 mg m-3). The BTV was 240 mL. The relative standard deviations for the repeatability of interday and intraday were 7-10%, 10%, respectively, and the pooled standard deviation was 0.088. The limit of detection and limit of quantitation values were 0.033 and 0.060 mg m-3, respectively. Moreover, our findings revealed that the samples could be stored in sealed HF flexible plastic tubes in a cover at refrigerator temperature (4°C) for up to 7 days. The HF method was compared with method number 3512 National Institute Occupational Safety and Health for determination of MA. There was a good correlation (R2 = 0.99) between the two methods at a concentration of 0.05 to 2 mg m-3 in the laboratory and the average concentration of MA for both methods was 0.11 mg m-3 in the ambient air at an adhesive manufacturer. Our findings indicated that the proposed HF can act as a reliable, rapid, and effective approach for sampling of MA in workplaces.

Hollow Fiber Supported Liquid Membrane Extraction Combined with HPLC-UV for Simultaneous Preconcentration and Determination of Urinary Hippuric Acid and Mandelic Acid

This work describes a new extraction method with hollow-fiber liquid-phase microextraction based on facilitated pH gradient transport for analyzing hippuric acid and mandelic acid in aqueous samples. The factors affecting the metabolites extraction were optimized as follows: the volume of sample solution was 10 mL with pH 2 containing 0.5 mol·L⁻¹ sodium chloride, liquid membrane containing 1-octanol with 20% (w/v) tributyl phosphate as the carrier, the time of extraction was 150 min, and stirring rate was 500 rpm. The organic phase immobilized in the pores of a hollow fiber was back-extracted into 24 µL of a solution containing sodium carbonate with pH 11, which was placed inside the lumen of the fiber. Under optimized conditions, the high enrichment factors of 172 and 195 folds, detection limit of 0.007 and 0.009 µg·mL⁻¹ were obtained. The relative standard deviation (RSD) (%) values for intra- and inter-day precisions were calculated at 2.5%–8.2% and 4.1%–10.7%, respectively. The proposed method was successfully applied to the analysis of these metabolites in real urine samples. The results indicated that hollow-fiber liquid-phase microextraction (HF-LPME) based on facilitated pH gradient transport can be used as a sensitive and effective method for the determination of mandelic acid and hippuric acid in urine specimens.

Ultrasound-assisted dispersive liquid–liquid microextraction followed by GC–MS/MS analysis for the determination of valproic acid in urine samples

Background: Valproic acid (VPA) is an anticonvulsant drug used for the treatment of epilepsy and bipolar disorder. A method based on simultaneous derivatization and dispersive liquid–liquid microextraction followed by GC–MS/MS analysis has been developed for the determination of VPA in urine samples. Results: This optimized and validated method shows good linearity with R2 value of 0.999. LOD and LOQ of VPA was found to be 0.4 ng ml-1 and 1.4 ng ml-1, respectively. Recovery of VPA was found to be in the range of 80 to 92%. Conclusion: The developed method can find its wide applicability for the routine analysis of VPA in toxicological and clinical laboratories.

Pharmacokinetics of geniposide by monoclonal antibody-based icELISA in mice after oral administration of Huanglian-Jiedu-Tang

Geniposide, Geniposide, the main active component in extracts of Gardenia jasminoides ELLIS., is one of the main components of Huanglian-Jiedu-Tang (HJT). This study aimed to validate an indirect competitive enzyme-linked immunosorbent assay (icELISA) based on monoclonal antibodies (mAb) against geniposide (anti-geniposide mAb), which was developed by our lab, and apply the assay to study the pharmacokinetics of geniposide in HJT in mice. Blood samples were drawn from mice at predetermined time points after oral administration of HJT in three dosages. A linear correlation was obtained for geniposide concentrations in the range from 1.17 to 37.50 µg/mL. The intra-day and inter-day precision values of the icELISA method were well within the recommended range (≤10%). The recovery rates ranged from 99.74 to 102.40%. Stability studies showed that geniposide sample solutions were intact for 12 h. The Tmax and mean residence time (MRT) of geniposide of the three groups were consistent with previous data. The results suggest that a reliable and effective method was established and could be applied to the study of the pharmacokinetics of geniposide in HJT.

Assessment of baicalin in mouse blood by monoclonal antibody-based icELISA

An indirect competitive enzyme-linked immunosorbent assay (icELISA) based on monoclonal antibaodies (MAb) was recently developed. This new method displays high sensitivity and accuracy, and is especially suitable for pharmacokinetic studies in small laboratory animals. This study aimed to develop an icELISA procedure for baicalin (BAL) quantitation in blood. We successfully developed the icELISA and applied in pharmacokinetic assays of Gegen Qinlian Decoction in mice. A linear correlation was obtained for BAL concentrations in the range from 34.69 to 2220.00 µg/L. The regression equation was y = 1.5557 - 0.4028log(C) with a correlation coefficient of 0.9936. Precision and accuracy of the icELISA method were evaluated by the variations between replicates from well to well (intra-assay) and plate to plate (inter-assay). The values obtained for these parameters were within the normal range (<15%). The recovery rates ranged from 98.93 to 126.78%, meeting the requirements for biological samples. Stability studies showed that BAL sample solutions were intact for 1 h, enough time for UV detection. However, long-term storage and especially freeze-thaw procedures were detrimental to BAL. The pharmacokinetic parameters derived from mouse experiments were as follows: area under the curves from time 0 to 48 h, 1876.15 ± 1108.14 mg h/L; mean maximum blood concentrations, 101.09 ± 31.53 mg/L; time of maximum concentration, 3.58 ± 2.88 h; mean residence time, 79.30 ± 61.21 h.