Biomedical subjects

E P Lai

Publications and source records attributed to E P Lai.

8 recordsLinked to original sources

PubMed2001

Determination of low-molecular-mass carboxylic acids in atmospheric aerosol and vehicle emission samples by capillary electrophoresis.

A method is developed for the determination of a large number of airborne and vehicle-emitted low-molecular-mass mono- and dicarboxylic acids using capillary electrophoresis with indirect UV detection. A background electrolyte (BGE) consisting of 2,6-naphthalenedicarboxylic acid and tetradecylmethylammonium bromide, adjusted to pH 6.2 with 2,2-bis(hydroxymethyl)-2,2',2"-nitrilotriethanol, is employed. Separations are robust using the buffered BGE, proper rinse steps, and constant current mode with migration time variations less than 3% RSD on a day-to-day basis, using different capillaries and performed by different analysts. Detection limits are at the tens of microg/l level using pressure injection. A comparison of the CE method with ion chromatography is also made.

Aerosols↗

PubMed2000

Surface plasmon resonance-based immunoassays.

Surface plasmon resonance (SPR) has been successfully incorporated into an immunosensor format for the simple, rapid, and nonlabeled assay of various biochemical analytes. Proteins, complex conjugates, toxins, allergens, drugs, and pesticides can be determined directly using either natural antibodies or synthetic receptors with high sensitivity and selectivity as the sensing element. Immunosensors are capable of real-time monitoring of the antigen-antibody reaction. A wide range of molecules can be detected with lower limits ranging between 10(-9) and 10(-13) mol/L. Several successful commercial developments of SPR immunosensors are available and their web pages are rich in technical information. This review highlights many recent developments in SPR-based immunoassay, functionalizations of the gold surface, novel receptors in molecular recognition, and advanced techniques for sensitivity enhancement. Furthermore, it describes the challenge of current problems and provides some insights toward the future technologies.

Antibodies↗

PubMed1999

Separation of carbonyl 2,4-dinitrophenylhydrazones by capillary electrochromatography with diode array detection.

The applicability of capillary electrochromatography (CEC) with photodiode array detection for the analysis of carbonyl hydrazones is presented. The CEC separation of thirteen hydrazones was optimized by a systematic variation of conditions using a commercially available CE system and a 3-micron porous C18-bonded silica capillary column. The separation profile obtained under optimal isocratic conditions (60% actonitrile-4% tetrahydrofuran-5 mM Tris, pH 8) is similar to those reported for gradient HPLC, with significant improvements in efficiency (to 150,000-250,000 theoretical plates/m) and analysis time (by a factor of 4). The retention time reproducibility is better than 0.2% (RSD) from run to run and 1% from day to day. The limits of detection for individual carbonyl hydrazones range between 0.1 and 0.5 microgram/ml. Applications to ambient air and automobile exhaust are shown.

Air↗

PubMed1999

Silver cationization of thia fatty acids and esters in laser desorption/ionization time-of-flight mass spectrometry.

A laser desorption/ionization (LDI) time-of-flight mass spectrometric (TOF-MS) technique was used for the molecular mass analysis of thia fatty acids and esters, samples without appreciable light absorption at the laser wavelength. After a sample overlayer is deposited by solvent evaporation on a thin silver film substrate, it is subjected to 355 or 532 nm Nd : YAG laser irradiation. Photoablation of the Ag film substrate occurs with sufficient laser fluence, producing silver cluster cations, which can react with the desorbed thia fatty acid or ester molecules in the gas phase. Silver cation attachment of thia fatty esters may produce a silver-cationized analyte and fragments of structural diagnostic value, whereas thia fatty acids would not. With oxygen(s) present on the sulfur in sulfoxy fatty acids and esters, a silver-cationized analyte and additional fragments are produced. Formation of these fragments is consistent with charge-remote mechanisms through simple cleavage and rearrangement pathways. The structural reactivity of these compounds with ablated silver cations is hence comprehensively analyzed.

Esters↗

PubMed1999

Separation of theophylline, caffeine and related drugs by normal-phase capillary electrochromatography.

A capillary electrochromatography (CEC) method has been developed for the separation of theophylline, caffeine and five related drugs on a normal-phase column with UV or photodiode array detection. Several binary, ternary and quaternary mobile phase compositions are evaluated for optimal resolution and elution of these drug analytes. The importance of selecting suitable organic solvents, buffer electrolyte, pH and applied voltage is demonstrated by a systematic study. Excellent separation is achieved for the eight drugs using a ternary mobile phase composition of isopropanol/hexane/1 mM Tris (52:40:8, pH 8), with an efficiency of 63000 theoretical plates per meter at room temperature. Detection limits are typically at the low microg/mL level. The developed method is simple to use and it gives acceptable day-to-day reproducibility.

Acetaminophen↗

PubMed1999

Rapid determination of theophylline in serum by selective extraction using a heated molecularly imprinted polymer micro-column with differential pulsed elution.

Molecular imprinting of theophylline in poly(methacrylic acid ethylene dimethacrylate) form binding sites with complementary size, shape and chemical functionalities to theophylline. This molecularly imprinted polymer (MIP) can be packed into a micro-column for selective solid phase extraction (SPE) of theophylline from 20 microl of sample solution. Its chemical inertness and thermal stability allow the use of various organic solvents and elevated column temperatures for effective binding of theophylline. Non-specific adsorption of interfering drugs on the MIP surface is eliminated by an intermediate wash with 20 microl of acetonitrile, prior to quantitative desorption of the bound theophylline by 20 microl of methanol for in-line UV spectrophotometric determination. In this differential pulsed elution (DPE) technique, both the column temperature and solvent flow rate can be optimized to enhance selectivity. Application of this micro-analytical method, molecularly imprinted solid phase extraction DPE (MISPE-DPE), is demonstrated for accurate determination of theophylline in human blood serum. The method is validated over a linear range from 2 microg/ml to at least 20 microg/ml.

Acetonitriles↗

PubMed1998

Immunoassay of fumonisins by a surface plasmon resonance biosensor.

A surface plasmon resonance (SPR) immunosensor is developed to determine concentrations of the mycotoxin, fumonisin B1 (FB1), in spiked samples. Polyclonal antibodies produced against FB1 are adsorbed onto a thin gold film substrate, which is coupled to a glass prism in the Kretschmann configuration. The output beam of a planar light-emitting diode is focused through the prism to excite SPR at the surface of the gold film. When a sample containing FB1 is added to a cell on the outside of the gold film, the angular profile of reflected light intensity shifts. This changes the resonance angle and the reflected beam intensity at a selected angle, both of which are proportional to the FB1 concentration. After optimization of the antibody overlayer, a detection limit of 50 ng/mL is obtained for the direct assay with an analysis time under 10 min. Multiple sample additions and large-volume sample circulation can be used with the high-affinity antibodies to achieve lower detection limits.

Biosensing Techniques↗

PubMedDate not supplied

Separation of polynuclear aromatic hydrocarbons by micellar electrokinetic capillary chromatography using sodium taurodeoxycholate modified with organic solvents.

The usefulness of a bile acid salt, sodium taurodeoxycholate (STDC), as a surfactant and organic solvents as organic modifiers for the separation of 16 polynuclear aromatic hydrocarbons (PAHs) on the U.S. EPA priority pollutant list by micellar electrokinetic capillary chromatography (MEKC) was investigated. The best resolution of analytes was obtained with a phosphate-borate buffer containing 50 mM STDC and 30% acetone. Short capillaries effected rapid (< 6 min) partial PAH separation, an approach that has potential use in screening studies. The capability of the developed separation system was demonstrated in the analysis of ambient air extracts.

Acetone↗