Chien-Hou Wu

Capillary electrophoretic determination of organic acids with indirect detection

Abstract Methods for the determination of several organic acids commonly found in foods and beverages, including oxalic, citric, acetic, tartaric, malic, succinic, lactic, carbonic, aspartic, glutamic, ascorbic and gluconic acids, by capillary electrophoresis (CE) with indirect absorbance detection were developed. Several absorbance providers, including chromate, p-hydroxybenzoate, phthalate, terephthalate, trimellitate and pyromellitate, were investigated for their suitability as background electrolytes (BGEs). CE was performed in the negative voltage (reverse polarity, detector towards anode) mode. The effects of pH and various additives on CE separations were evaluated. The BGE and pH each played a major role in affecting the selectivity and resolution of CE. All analytes except malate and succinate could be baseline resolved in one run by performing CE with 5 mM trimellitate (as the BGE)-1 mM tetradecyltrimethylammonium bromide at pH 9.0 in less than 10 min. On the other hand, the CE separation of the tri- and dicarboxylic acids and hydroxydicarboxylic acids (the first five) could best be obtained at pH 5.5 in 5 min. The precision of the method for most monoprotic analytes is typically less than 1% for the migration time and 1–4% for the peak area (n = 6). The detection limit for most analytes is of the order of 2.0·10−6 M. The new methods developed are rapid, sensitive and quantitative and can be readily applied to real food samples for quantitative analysis.

Measurement of toxic volatile organic compounds in indoor air of semiconductor foundries using multisorbent adsorption/thermal desorption coupled with gas chromatography-mass spectrometry.

A method for the qualitative and quantitative analysis of volatile organic compounds (VOCs) in the air of class-100 clean rooms at semiconductor fabrication facilities was developed. Air samples from two semiconductor factories were collected each hour on multisorbent tubes (including Carbopack B, Carbopack C, and Carbosieve SIII) with a 24-h automatic active sampling system and analyzed using adsorption/thermal desorption coupled with gas chromatography-mass spectrometry. Experimental parameters, including thermal desorption temperature, desorption time, and cryofocusing temperature, were optimized. The average recoveries and the method detection limits for the target compounds were in the range 94-101% and 0.31-0.89 ppb, respectively, under the conditions of a 1 L sampling volume and 80% relative humidity. VOCs such as acetone, isopropyl alcohol, 2-heptanone, and toluene, which are commonly used in the semiconductor and electronics industries, were detected and accurately quantified with the established method. Temporal variations of the analyte concentrations observed were attributed to the improper use of organic solvents during operation.

Vortex-assisted liquid-liquid microextraction coupled with derivatization for the fluorometric determination of aliphatic amines.

A new one-step derivatization and microextraction technique was developed for the fluorometric determination of C(1)-C(8) linear aliphatic primary amines in complex sample solutions containing high levels of amino acids. In this method, amines were derivatized with o-phthalaldehyde (OPA) and 2-mercaptoethanol (2-ME) in aqueous solution and extracted simultaneously by vortex-assisted liquid-liquid microextraction (VALLME). Parameters affecting the extraction efficiency were investigated in detail. The optimum conditions were as follows: 50 μL of isooctane as the extractant phase; 2.0 mL aqueous donor samples with 12 mM OPA, 24 mM 2-ME, and 0.1 M borate buffer at pH 10; 1 min vortex extraction time; centrifugation for 4 min at 6000 rpm. After centrifugation, the enriched analytes in the floated extractant phase were determined by HPLC-FL in less than 14 min. Under the optimum conditions, the limits of detection were of the order of 0.09-0.31 nM. The calibration curves showed good linearity over the investigated concentration range between 0.4 and 40 nM. The proposed method has been applied to the determination of aliphatic amines in acidophilus milk, beer, and Cu(II)/amino acid solution.

Evaluation of Effects of Selected Wax Inhibitors on Paraffin Deposition

Abstract Deposition from decane solutions of model paraffins such as n-C24H50 (C24), and n-C36H74 (C36), as well as a mixture of n-alkanes (C21 to C44) was examined with and without chemical wax deposition inhibitors. The device used to produce the deposits investigated was a “Cold Disk” Wax Deposition Apparatus (CoDWaD) capable of producing field like deposits with relatively small volumes of oil in minutes. It was found that most of commercial wax inhibitors tested could decrease the deposition of low molecular weight paraffins (C34 and below), while having little effect on the wax deposition for high molecular weight paraffins (C35–C44). In many cases, although the total amount of wax formed on the cold plate was reduced, the absolute amount of deposition for high molecular wax was actually increased. Therefore, the net effect of many commercial inhibitors is to make even harder wax under the tests conditions studied here. One intriguing result was that the addition of an oleic imidazoline c rrosion inhibitor improved the performance of two wax inhibitors tested. It was also observed that there are subtle differences in inhibitor performance depending on whether the test solutions are binary mixtures, synthetic wax mixtures, or crude oil.

Purge-and-trap ion chromatography for the determination of trace ammonium ion in high-salinity water samples.

It has always been assumed that purge-and-trap (P&T) method is only used for the analysis of volatile organic compounds (VOCs) in aqueous samples. In this paper, a novel P&T preconcentrator has been developed for the determination of trace amounts of ammonium ion in high-salinity water samples by ion chromatography (IC). Method performance is evaluated as a function of concentration of assistant purging material, purging time, and flow rate. Under the optimum P&T conditions with the purified nitrogen gas at flow rate 40 mL/min for 15.0 min at 40 degrees C, the overall collection efficiency is independent of the concentration of ammonium over the range 1.2-5.9 microM. The enrichment factor (EF) of ammonium correlates the ratio of the sample volume to the acceptor solution volume in the trap vessel, providing potentially unlimited increase of the ammonium signal. Our results indicate that environmental samples with low levels of ammonium in matrices with high concentrations of sodium can be easily analyzed and the detection limit down to 75 nM (1.35 ppb) level, corresponding to picomole of ammonia in the injected sample. Calibration graph was constructed with ammonium standards ranging from 0.05 to 6.0 microM and the linearity of the present method was good as suggested by the square of correlation coefficients being better than 0.997. Thus, we have demonstrated that the P&T-IC method allows the routine determination of ammonium ion in seawater samples without cation interferences.

Capillary electrophoretic analysis of the derivatives and isomers of benzoate and phthalate

A capillary electrophoretic method for the analysis of 12 commonly found derivatives and isomers of benzoate and phthalate, including p-toluic acid, p-acetamido and p-hydroxy derivatives of benzoic acid, salicylic acid and its acetyl ester, 2- and 4-isomers of carboxybenzaldehyde, meta-, para-, and ortho-isomers of phthalic acid, and monomethyl terephthalic acid was developed. Capillary electrophoresis (CE) was performed in the free zone electrophoresis mode. Performing CE in 10 mM phosphate buffer, pH 7.0 could separate most of the benzoic acid derivatives except the structural or positional isomers. The positional isomers of phthalic acids could be completely separated with co-addition of alpha- and beta-cyclodextrins. Addition of poly(ethylene glycol) 600 (4%) could further resolve some structural isomers. The CE method developed here is rapid, i.e. complete separation could be achieved in less than 8 min for the nine monoanionic benzoate derivatives and in less than 14 min for the three dianionic phthalate isomers. The new method has good precision and linearity and can be readily applied to real samples for quantitative analysis. It is sensitive and can detect sub-ppm (w/w) level of impurity in real terephthalic samples.

Influence of silver and titanium dioxide nanoparticles on in vitro blood-brain barrier permeability

An in vitro blood-brain barrier (BBB) model being composed of co-culture with endothelial (bEnd.3) and astrocyte-like (ALT) cells was established to evaluate the toxicity and permeability of Ag nanoparticles (AgNPs; 8nm) and TiO2 nanoparticles (TiO2NPs; 6nm and 35nm) in normal and inflammatory central nervous system. Lipopolysaccharide (LPS) was pre-treated to simulate the inflammatory responses. Both AgNPs and Ag ions can decrease transendothelial electrical resistance (TEER) value, and cause discontinuous tight junction proteins (claudin-5 and zonula occludens-1) of BBB. However, only the Ag ions induced inflammatory cytokines to release, and had less cell-to-cell permeability than AgNPs, which indicated that the toxicity of AgNPs was distinct from Ag ions. LPS itself disrupted BBB, while co-treatment with AgNPs and LPS dramatically enhanced the disruption and permeability coefficient. On the other hand, TiO2NPs exposure increased BBB penetration by size, and disrupted tight junction proteins without size dependence, and many of TiO2NPs accumulated in the endothelial cells were observed. This study provided the new insight of toxic potency of AgNPs and TiO2NPs in BBB.

Analysis of volatile organic compounds in wastewater during various stages of treatment for high-tech industries

SummaryA protocol combining purge-and-trap (P&T) and solid-phase microextraction (SPME) was established for the analysis of volatile organic compounds (VOCs) in the wastewater plant of high-tech industries. Over 60 VOCs could be analyzed by P&T coupled to gas chromatography/mass spectrometry (P&T-GC-MS). Four polar VOCs commonly used in the high-tech industries were determined by SPME coupled to gas chromatography/flame ionization detection (SPME-GC-FID). The limits of detection for the analytes were less than 1.1 μg L−1 with P&T-GC-MS, and between 1.5 and 12.5 μg L−1 with SPME-GC-FID. Satisfactory recoveries (83% to 130%) were obtained. Real samples were analyzed from a wastewater treatment plant during various stages of treatment. The major pollutant in the wastewater influent was found to be acetone (>4 ppm).

Markedly Enhanced Surface Hydroxyl Groups of TiO2 Nanoparticles with Superior Water-Dispersibility for Photocatalysis

The benefits of increasing the number of surface hydroxyls on TiO2 nanoparticles (NPs) are known for environmental and energy applications; however, the roles of the hydroxyl groups have not been characterized and distinguished. Herein, TiO2 NPs with abundant surface hydroxyl groups were prepared using commercial titanium dioxide (ST-01) powder pretreated with alkaline hydrogen peroxide. Through this simple treatment, the pure anatase phase was retained with an average crystallite size of 5 nm and the surface hydroxyl group density was enhanced to 12.0 OH/nm2, estimated by thermogravimetric analysis, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Especially, this treatment increased the amounts of terminal hydroxyls five- to six-fold, which could raise the isoelectric point and the positive charges on the TiO2 surface in water. The photocatalytic efficiency of the obtained TiO2 NPs was investigated by the photodegradation of sulforhodamine B under visible light irradiation as a function of TiO2 content, pH of solution, and initial dye concentration. The high surface hydroxyl group density of TiO2 NPs can not only enhance water-dispersibility but also promote dye sensitization by generating more hydroxyl radicals.

Evaluation of Effects of Selected Wax Inhibitors on Wax Appearance and Disappearance Temperatures

Abstract In this investigation, a light transmittance method was used to evaluate the wax appearance temperatures (WAT) and wax disappearance temperatures (WDT) of model paraffin compounds (n-C24H50 (C24) and n-C36H74 (C36)) in n-decane (C10) solutions both with and without wax inhibitors. The change in WAT at different paraffin concentrations in the presence of an inhibitor behaves as though there is a constant amount of paraffin removed by the inhibitor. However, the amount of apparent paraffin reduction by an inhibitor (e.g. 160 g of C24 by one gram of an inhibitor) indicates that the inhibition mechanism cannot easily be explained by a simple “sequestering” effect. Wax inhibitors that decrease the WAT tend to also increase the WDT. Most of the wax inhibitors tested at a dosage of 100 ppm did suppress the WAT of lower molecular weight paraffin (C24) solutions, but had little or no effect for higher molecular weight paraffin (C36) solutions. Side-chain length of polymethacrylate wax inhibitors is an important performance parameter. Of the three polymethacrylate wax inhibitors tested, the one with the longest alkyl side-chain (C18) had the most effect on suppressing the WAT and increasing the WDT of the binary mixtures (n-C10–n-C24 solutions).