Biomedical subjects

Jing-fu Liu

Publications and source records attributed to Jing-fu Liu.

7 recordsLinked to original sources

PubMed2006

Equilibrium sampling of freely dissolved alkylphenols into a thin film of 1-octanol supported on a hollow fiber membrane.

A new negligible depletion extraction procedure was proposed for equilibrium sampling of 4-tert-octylphenol (OP) and 4-nonylphenol (NP) into a thin film of 1-octanol supported on a hollow fiber membrane. This thin liquid film extraction technique was directed at the determination of (1) freely dissolved concentrations, (2) distribution coefficients to 1-octanol (D(ow)), and (3) binding to dissolved organic matter (DDOC). The sampling device was prepared by dipping pieces of polypropylene microporous hollow fiber membrane (10-mm length, 30-microm wall thickness, 240-microm inner diameter) into 1-octanol for a few seconds to impregnate the pores of the hollow fiber wall. After stirring in 100 mL of sample solution for 24 h, the sampling device was harvested and desorbed with 30 microL of methanol, of which 20 microL was injected for HPLC analysis. With the measured D(ow) of a chemical and its equilibrium concentration in the 1-octanol sampling phase (C(octanol)), the freely dissolved concentration (Cfree) was calibrated based on Cfree = C(octanol)/D(ow). Measured log Dow values of OP (4.32 +/- 0.06) and NP (4.79 +/- 0.02) were independent of the chemical concentration, only minimally affected by the environmentally relevant pH, buffering capacity, and salinity of samples, and agreed well with reported values. Log DDOC values of OP (4.89 +/- 0.43) and NP (5.14 +/- 0.37), determined in Aldrich humic acid solution, agreed with reported partition coefficients to organic carbon (log Koc) for particles in river water and effluent wastewater. Short equilibration times and high enrichment factors were obtained for both analytes due to the high surface to volume ratio of the new sampler. The technique was successfully applied to determine Cfree of OP and NP in real water samples and to study their association with humic acids and bovine albumin.

Journal Article↗

PubMed2006

Evaluating the impacts of some environmentally relevant factors on the availability of bisphenol A with negligible-depletion SPME.

The effect of some environmentally relevant factors including salinity, pH, and humic acids on the availability of bisphenol A (BPA) was evaluated by using the negligible-depletion solid-phase microextraction (nd-SPME) biomimetic method. With the variation of salinity (0-500 mM NaCl) and pH (5.0-8.5) of aqueous solutions, the partition coefficients of BPA between the nd-SPME fiber and the aqueous solution varied in the range of logD=3.55-3.86, which indicates that the salinity and pH can influence the availability of BPA. By using Acros humic acid as model dissolved organic matter (DOM), it was also demonstrated that the environmental factors such as salinity and pH could affect the partitioning of BPA between DOM and aqueous solutions. The determined partition coefficients of BPA between dissolved organic carbon (DOC) and aqueous solutions were in the range of logD(DOC)=4.03-5.60 for Acros humic acid solutions with 1-50 mg l(-1) DOC. The influence of salinity and pH on logD(DOC) was more significant at low concentration (0-5 mg l(-1)) of DOC.

Benzhydryl Compounds↗

PubMed2005

Equilibrium sampling through membranes of freely dissolved chlorophenols in water samples with hollow fiber supported liquid membrane.

The freely dissolved concentration (C(free)) of pollutants is generally believed to be bioavailable and thus responsible for toxic effects. The C(free) of organic weak acids and bases consists of a dissociated and a nondissociated fraction. By using chlorophenols as model compounds, a negligible-depletion extraction technique, equilibrium sampling through membranes (ESTM), was developed for the measurement of the nondissociated part of the C(free). Polypropylene hollow fiber membranes (280-microm i.d., 50-microm wall thickness, 0.1-microm pore size, 15-cm length) were impregnated with undecane in the pores in the fiber wall as liquid membrane and filled with buffer solution in the lumen as acceptor. Then, the hollow fiber membranes were placed into the sample (donor) for an equilibrium extraction after sealing the two ends. The chlorophenol concentrations in the acceptor were then determined by direct injection into a HPLC system. Finally, the C(free) of the nondissociated and the dissociated species of a chlorophenol were calculated based on its measured concentration in the acceptor, its pK(a) value, and the measured pH in sample and acceptor. Theoretically calculated distribution coefficients (D = 8-970) agree well with the experimental enrichment factors (E(e(max)) = 6-1124), and the equilibration time was observed to increase with increasing distribution coefficients (hours to days). The freely dissolved concentration of five chlorophenols, with a wide range of pK(a) (4.9-9.2) and log K(ow) (2.35-5.24), were successfully determined in model solutions of humic acids and at low-ppb levels in river and leachate water.

Buffers↗

PubMed2005

Ionic liquid for high temperature headspace liquid-phase microextraction of chlorinated anilines in environmental water samples.

Based on the non-volatility of room temperature ionic liquids (IL), 1-butyl-3-methylimidazolium hexafluorophosphate ([C4MIM][PF6]) IL was employed as an advantageous extraction solvent for high temperature headspace liquid-phase microextraction (LPME) of chloroanilines in environmental water samples. At high temperature of 90 degrees C, 4-chloroaniline, 2-chloroaniline, 3,4-dichloroaniline, and 2,4-dichloroaniline were extracted into a 10 microl drop of [C4MIM][PF6] suspended on the needle of a high-performance liquid chromatography (HPLC) microsyringe held at the headspace of the samples. Then, the IL was injected directly into the HPLC system for determination. Parameters related to LPME were optimized, and high selectivity and low detection limits of the four chlorinated anilines were obtained because the extraction was performed at high temperature in headspace mode and the very high affinity between IL and chlorinated anilines. The proposed procedure was applied for the analysis of the real samples including tap water, river water and wastewater samples from a petrochemical plant and a printworks, and only 3,4-dichloroaniline was detected in the printworks wastewater at 88.2 microg l(-1) level. The recoveries for the four chlorinated anilines in the four samples were all in the range of 81.9-99.6% at 25 microg l(-1) spiked level.

Aniline Compounds↗

PubMed2004

Ionic liquid-based liquid-phase microextraction, a new sample enrichment procedure for liquid chromatography.

Room temperature ionic liquids (RTILs) were used as extraction solvent in liquid-phase microextraction (LPME) coupled with liquid chromatography. Using 1-hexyl-3-methylimidazolium hexafluorophosphate ([C6MIM][PF6]) as extraction solvent, some parameters related to LPME of 4-nonylphenol (4-NP) and 4-tert-octylphenol (4-t-OP) were optimized. Although [C6MIM][PF6] can suspend a much larger volume of drop on the needle of the microsyringe than the conventional solvents such as 1-octanol and carbon tetrachloride, the method sensitivity was analyte dependent because of the different partition coefficients and the relatively large viscosity of [C6MIM][PF6]. The proposed procedure has a detection limit and enrichment factor of 0.3 microg l(-1) and 163 for 4-NP, and 0.7 microg l(-1) and 130 for 4-t-OP, respectively. Aqueous samples including tap water, river water, and effluent from sewage treatment plant were analyzed by the proposed method and the recoveries at 10 microg l(-1) spiked level were in the range of 90-113%.

Chromatography, High Pressure Liquid↗

PubMed2003

Use of ionic liquids for liquid-phase microextraction of polycyclic aromatic hydrocarbons.

This paper demonstrates, for the first time, that ionic liquids (IL) such as 1-octyl-3-methylimidazolium hexafluorophosphate ([C(8)MIM][PF(6)]) are excellent extraction solvents in liquid-phase microextraction (LPME). The unique properties of nonvolatility and adequate viscosity allow IL to be conveniently adopted as extraction solvents in both direct-immersion and headspace LPME. Model compounds, polycyclic aromatic hydrocarbons (PAHs), are conveniently and rapidly enriched in a 3-microL drop of [C(8)MIM][PF(6)] suspended on the tip of a microsyringe followed by liquid chromatographic determination. Compared to 1-octanol, a larger volume drop of [C(8)MIM][PF(6)] can be formed and survive for a longer extraction time; therefore, a much higher enrichment factor for PAHs can be reached. For low-volatility PAHs, direct-immersion LPME provides higher enrichment factors than that of headspace LPME. However, the enrichment factor obtained by headspace LPME was almost 3-fold of that by direct-immersion LPME in a 30-min extraction of the most volatile PAH, naphthalene. For 30-min direction-immersion LPME of EPA priority PAHs, the enrichment factor, correlation coefficient (R(2)), and reproducibility (RSD, n = 5) were in the range of 42-166, 0.9169-0.9976, and 2.8-12%, respectively. Considering that IL can be easily prepared from relatively inexpensive materials and tuned by combination of different anions and cations for task-specific extraction of analytes from various solvent media, this proposed method should have great potentiality in sample preparation. Furthermore, the nonvolatility of IL makes it potentially useful for headspace LPME of volatile analytes.

Journal Article↗

PubMed2003

Trace analysis of sulfonylurea herbicides in water by on-line continuous flow liquid membrane extraction--C18 precolumn liquid chromatography with ultraviolet absorbance detection.

An on-line system that consists of continuous-flow liquid membrane extraction (CFLME), C18 precolumn, and liquid chromatography with UV detection was applied to trace analysis of sulfonylurea herbicides in water. During preconcentration by CFLME, five target compounds, including metsulfuron methyl, bensulfuron methyl, tribenuron methyl, sulfometuron methyl, and ethametsulfuron, were enriched in 960 microl of 0.5 mol l(-1) Na2CO3-NaHCO3 (pH 10.8) buffer used as acceptor. This acceptor was on-line neutralized and transported to the C18 precolumn where the analytes were absorbed and focused. Then the focused analytes were injected onto a C18 analytical column for separation and detection at 240 nm. The proposed method was applied to determine sulfonylurea herbicides in water, river, and reservoir water with detection limits of 10-50 ng l(-1) when enriching a 120-ml sample. Throughput is typically one sample per hour.

Chromatography, Liquid↗