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Y S Fung

Publications and source records attributed to Y S Fung.

18 recordsLinked to original sources
PubMed2006

Separation and determination of cations in beverage products by capillary zone electrophoresis.

Cation determination is important for quality control of beverage products. To determine a large group simultaneously, a capillary electrophoresis procedure is developed with indirect UV at 214 nm in a three-complex buffer system (10 mM N,N-dimethylbenzylamine (DBA), 8 mM lactic acid and 2 mM 18-crown-6) with good mobility matching with desired cations. Under optimized conditions with pH adjusted to 4.65, a baseline separation is achieved for 14 cations (Rb(+), NH(4)(+), K(+), Ca(2+), Na(+), Mg(2+), Mn(2+), Co(2+), Fe(2+), Cd(2+), Cr(3+), Ni(2+), Zn(2+) and Cu(2+)) within 7 min using an uncoated silica column. To cover ng/l to mug/l range, both hydrostatic and electrokinetic sampling are studied, showing working ranges within (0.05-50)/(0.005-2) microg/l and detection limits (13-78)/(1.4-10) ng/l, respectively with satisfactory repeatability (RSD 0.31-0.47% for migration time, and 3.0-4.0% for peak height measurement). Agreeable results with established inductively coupled plasma-atomic emission spectrometry method have been obtained for orange juice and tea samples.

Beverages↗
PubMed2002

Immunosensor for the differentiation and detection of Salmonella species based on a quartz crystal microbalance.

Immunosensors based on the microgravimetric quartz crystal microbalance (QCM) technique have been developed for the detection of Salmonella species from serogroups A, B and D. Salmonella serogroup-specific murine monoclonal antibodies, respectively, raised against these serogroups were immobilized onto the silver electrodes of piezoelectric (PZ) crystals by cross-linkage via glutaraldehyde (GA) to the electrode surfaces pre-coated with thin polyethyleneimine (PEI) layer. The specific immunosensors developed gave responses in linear ranges from 10(5) to 5x10(8) cells per ml with no significant interference from other strains of Salmonella and Escherichia coli up to 10(8) cells per ml. They showed good repeatability and excellent linear range, achieving detection limits down to 10(4) cells per ml with ability to distinguish different strains of Salmonella. These biosensors exhibited an exquisite specificity evidenced by their ability to discriminate antigens, the structures of which differ only by the isomeric form of di-deoxyhexose. The antibody-modified crystals showed no loss in activity over 4 days under storage at 4 degrees C.

Animals↗
PubMed2001

Self-assembled monolayers as the coating in a quartz piezoelectric crystal immunosensor to detect Salmonella in aqueous solution.

A new procedure based on the self-assembled monolayers (SAM) of alkanethiols was developed to immobilize antibodies onto gold electrodes of a quartz crystal microbalance (QCM) for detecting Salmonella paratyphi A. The procedure includes (1) chemisorption of 3-mercaptopropionic acid (MPA) at electrode surfaces to produce a carboxylic acid terminated monolayer, (2) activation by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydrosuccinimide (NHS) to generate a stable acyl amino ester intermediate, and (3) condensation of antibodies after aminolysis of the NHS adduct. Activation by two coupling agents (EDC and NHS) was shown to enhance the stability of the coating and facilitate the formation of a suitable intermediate to condense antibodies reproducibly and densely at the SAM, leading to high sensitivity and good precision of the developed immunosensor. With 50 min incubation under continuous monitoring, working ranges from 10(2) to 10(5) cells/mL with repeatability < 10% RSD were obtained. On the basis of S/N = 3, the detection limit was 1.7 x 10(2) cells/mL The MO2 piezoimmunosensor developed was specific to differentiate S. paratyphi A against Escherichia coli and other serogroups of Salmonella that are commonly present together.

Antibodies, Bacterial↗
PubMed2001

Determination of phenols in soil by supercritical fluid extraction-capillary electrochromatography.

A new analytical procedure is developed to couple supercritical fluid extraction with capillary electrochromatography (SFE-CEC) to extract and determine phenols in soil. Ten phenols consisting of phenol, methylphenols (p-cresol and o-cresol), dimethylphenols (3,5-xylenol, 3,4-xylenol and 2,6-xylenol), trimethylphenol, ethylphenols (p-ethylphenol and o-ethylphenol), and o-isopropylphenol are investigated. The use of supercritical CO2 with 10% methanol as the organic modifier was found to give satisfactory extraction of alkylphenols from soil at 1200 p.s.i. and 50 degrees C for 45 min under a total extractant flow-rate of 0.2 ml/min (1 p.s.i.=6894.76 Pa). Baseline resolution was achieved for the 10 selected phenols under optimised CEC conditions at 20 kV in a mobile phase of acetonitrile-4 mM Tris, pH 7.0 (35:65) in a 45 cm (25 cm packed with 3 microm ODS) x 75 microm I.D. fused-silica capillary column. Using SFE with a 10-fold preconcentration factor, all alkyl-substituted phenols in soil can be determined with detection limits ranging from 0.0032 to 0.014 mg/kg and working range from 0.019 to 2.72 mg/kg. The SFE-CEC procedure developed has been applied successfully to determine phenols extracted from real soil sample contaminated with medical disinfectant. It will provide a rapid method for the direct determination of phenol and alkyl-substituted phenol in soils, with capability for confirmation of unknown peaks.

Chromatography, Micellar Electrokinetic Capillary↗
PubMed2001

Electrophoretic migration behavior of DNA fragments in polymer solution.

A newly developed polymer coil shrinking theory is described and compared with the existing entangled solution theory to explain electrophoretic migration behaviour of DNA in hydroxypropylmethylcellulose (HPMC) polymer solution in buffer containing 100 mM tris(hydroxymethyl)aminomethane 100 mM boric acid, 2 mM ethylenediaminetetraacetic acid at pH 8.3. The polymer coil shrinking theory gave a better model to explain the results obtained. The polymer coil shrinking concentration, Cs, was found to be 0.305% and the uniform entangled concentration, C+, 0.806%. The existence of three regions (the dilute, semidilute, and concentrated solution) at different polymer concentrations enables a better understanding of the system to guide the selection of the best conditions to separate DNA fragments. For separating large fragments (700/ 800 bp), dilute solutions (HPMC < 0.3%) should be used to achieve a short migration time (10 min). For small fragments (200/300 bp), concentrated solutions are preferred to obtain constant resolution and uniform separation. The best resolution is 0.6% HPMC due to a combined interaction of the polymer coils and the entangled structure. The possibility of DNA separation in semidilute solution is often neglected and the present results indicate that this region has a promising potential for analytical separation of DNA fragments.

Buffers↗
PubMed2001

Application of capillary electrophoresis for organic acid analysis in herbal studies.

A capillary electrophoresis (CE) procedure has been developed for the separation of 25 inorganic and organic acid anions using a buffer system consisting of 15 mM tris(hydroxymethyl)aminomethane, 3 mM 1,2,4-benzenetricarboxylic acid, 1.5 mM tetraethylenepentaamine (TEPA) and 20% methanol with pH adjusted to 8.4. A good separation of organic acids extracted from a mixture of Chinese traditional medicine (TCM) containing three herbs, Flos chrysthemi, Spica prunellae, and Folium mori was obtained using the procedure developed with satisfactory working range (0.20-77 mg/g), low detection limit (90-190 microg/g), and good repeatability (relative standard deviation 4.47-6.99%, n = 4). A satisfactory extraction of organic acids was achieved within 20 min using 0.1 M NaOH. The addition of TEPA to provide a reduced electroosmotic flow (EOF) environment was shown to remove interfering organic compounds extracted from TCM. The applicability of using organic acids as markers for determining the mixing ratio of constituent herbs for a TCM mixture was investigated using a three-component mixture with a 1:1:1 mixing ratio. A satisfactory mixing ratio of 1.04:1.09:0.98 was obtained using the methodology developed based on organic acids as markers. The application of our method for determining more complicated TCM mixtures has been discussed.

Buffers↗
PubMed2001

Determination of oxoanions in river water by capillary electrophoresis.

A new capillary electrophoresis (CE) procedure was developed for simultaneous determination of ten oxoanions (CrO4(2-), SeO4(2-), MoO4(2-), WO4(2-), VO4(3-), SeO3(2-), As04(3-), TeO3(2-), TeO4(2-), and AsO3(3-)) which were baseline-separated from each other and from the interfering UV absorbing anions (NO3- and NO2-) commonly found in environmental water samples. The new background electrolyte system developed contained 5 mM potassium phosphate and 0.007 mM octadecyltrimethylammonium hydroxide, pH 11.2. The optimized working conditions were electrokinetic sampling at -5 kV for 10 s, running voltage at -15 kV with 5 microA current, and detection wavelength at 205 nm. No interference was observed for non-UV-absorbing anions and UV-absorbing anions up to 20 and 10 times higher concentrations respectively. The speed of analysis was fast, with a complete CE run within 6 min. Wide linear ranges (1-2,000 microg/L), good repeatability in migration time (relative standard deviation RSD 0.55-2.8%), satisfactory precision in peak area (RSD 3.8-5.6%) and peak height (RSD 3.9-5.3%) measurement, and detection limits (1-25 microg/L) sufficiently sensitive to detect oxoanions found in environmental water samples were obtained. The reliability of the CE procedure developed had been established by recovery test and parallel method determination using atomic absoprtion spectrophotometry for real river water sample.

Anions↗
PubMed2001

Determination of pesticides in drinking water by micellar electrokinetic capillary chromatography.

A new analytical procedure using a two-step sample preconcentration (solid-phase extraction (SPE) and field-amplified sample stacking) prior to separation by micellar electrokinetic capillary chromatography was developed for the determination of 14 pesticides such as aldicarb, carbofuran, isoproturon, chlorotoluron, metolachlor, mecoprop, dichlorprop, MCPA, 2,4-D, methoxychlor, TDE, DDT, dieldrin, and DDE in drinking water. Good recoveries of pesticides were obtained using SPE with sample pH adjusted to 2-3. Field-amplified sample stacking was found to give enrichment factors up to 30-fold preconcentration of various pesticides under reversed polarity at -2 kV for 50 s. The optimized background electrolyte (BGE) consisted of 50 mM sodium dodecyl sulfate (SDS), 10 mM borate buffer, 15 mM beta-cyclodextrin (beta-CD), and 22% acetonitrile at pH 9.6, running was under 25 kV and detection at 202 nm. Good linearity was obtained for all pesticides with detection limits down to 0.04-0.46 ng/mL and a working range of 0.1-40 ng/mL. The repeatabilities of migration time and peak area were satisfactory with relative standard deviations (RSDs) between 0.66 and 13.6% and 4.1 and 28%, respectively. All pesticides except dieldrin were found to be detected at concentrations at least tenfold lower than the World Health Organization (WHO) guideline values. The analytical procedure developed offers an economic method for fast screening of multiple pesticide residues in drinking water for health protection. It had been applied to determine carbofuran and MCPA in agricultural run-off water samples, giving satisfactory repeatabilities of 10 and 12%, respectively, with n=5 for the determination of pesticides in contaminated water samples.

Electrophoresis, Capillary↗
PubMed2001

Determination of carbonyl compounds in air by electrochromatography.

A new analytical procedure based on electrochromatography was developed for the separation and quantitation of 14 aldehydes and ketones (formaldehyde, acetaldehyde, acetone, acrolein, propionaldehyde, butanone, crotonaldehyde, isobutyraldehyde/butyraldehyde, 2-pentenaldehyde, isovaleraldehyde, valeraldehyde, benzaldehyde and hexanaldehyde) in ambient air currently to be regulated by the Hong Kong Environmental Protection Department. A volatile mobile phase using ammonium acetate compatible with mass spectrometry detection was developed and optimized as follows. Methanol: acetonitrile: aqueous buffer (4 mM ammonium acetate) = 65:5:30% v/v. With electrokinetic injection at 5 kV for 2 s, aqueous buffer pH adjusted to 8, applied voltage controlled at 25 kV, and detection at 360 nm in a fused-silica column packed with 3 microm ODS, a satisfactory separation was obtained for the 14 carbonyl compounds investigated. The working ranges in acetonitrile solution were found to vary from 0.25 to 79 mg/L with a correlation coefficient greater than 0.99, detection limits from 0.10 to 0.63 mg/L, and precision (relative standard deviation, n = 3) from 2.3 to 9.2%. Under an air flow rate of 0.3 L/min for a sampling time of 1 h, the working ranges varied from 0.030 to 11,000 microg/m3 and detection limits from 0.011 to 0.084 microg/ m3. The method has been successfully applied to monitor three carbonyl compounds in four urban and rural sites in Hong Kong and gave hourly readings of three carbonyl compounds for all the sites investigated with a separation time less than 25 min.

Air Pollutants↗
PubMed2001

A collision model for DNA separation by capillary electrophoresis in dilute polymer solution.

A theoretical description, based on chemical kinetics and electrochemistry, is given of DNA separation in dilute polymer solution by capillary electrophoresis. A self-consistent model was developed leading to predictions of the DNA electrophoretic velocity as a function of the experimental conditions--polymer concentration, temperature, and electric field strength. The effect of selected experimental variables is discussed. The phenomena discussed are illustrated for the example of 100 bp DNA ladder separation in dilute HPMC solution by capillary electrophoresis. This model is the first single model that can fully explain the dependence of DNA electrophoretic velocity on electrophoretic conditions.

DNA↗
PubMed2001

Capillary electrophoresis for the determination of albumin binding capacity and free bilirubin in jaundiced neonates.

This study develops a capillary electrophoresis/frontal analysis (CE/FA) method to separate free bilirubin from its albumin bound complex, with only small-sized samples. Under our optimized conditions, CE/FA is proven to be a simple and accurate method in assaying the concentration of free bilirubin in the jaundiced serum. Upon saturation of albumin-binding, the amount of bilirubin added to the serum bears a linear relationship with the absorbance at OD44OnM (R = .9987, P < .00001). Application of this method to study jaundiced neonates has yielded precise data on the residual binding capacity, which may be of significant therapeutic implications. The CE/FA method we have developed appears to be promising and applicable for clinical use as it is highly reproducible and it only requires a small sample size for tests. Our method should be an invaluable adjunct to the neonatal management of hyperbilirubinaemia.

Aspirin↗
PubMed2000

Capillary electrophoresis for determination of free and albumin-bound bilirubin and the investigation of drug interaction with bilirubin-bound albumin.

Capillary electrophoresis (CE) is a promising technique for assessment of free bilirubin and its interaction with albumin, as it requires only a small sample volume and provides a rapid and efficient separation of free bilirubin from its albumin-bound complex in a one-phase system. In order to maintain the equilibrium without dissociation of bilirubin from the albumin/bilirubin complex as in real clinical conditions, the coupling of CE with frontal analysis (FA) was investigated. A very large sample plug was introduced hydrodynamically into the capillary (36 cm length, 50 microm inner diameter) at 15 psi x s to develop the frontal conditions during CE separation. The working conditions for CE/FA separation of bilirubin and albumin were optimized as follows: +20 kV; running buffer, 10 mmol/L phosphate and 1 mmol/L ethylenediaminetetraacetic acid (EDTA), pH 7.4. The working range for bilirubin was found to vary from 5 to 206 micromol/L; precision with relative standard deviation (RSD) <2.0% for n = 3 and detection limit (signal to noise, S/N = 2) was 2 micromol/L. The residual binding capacity of a simulated cord blood serum for bilirubin was 26 mg/100 mL at pH 7.4. Bilirubin was shown to be displaced from albumin when aspirin was added. The free bilirubin concentration was found to increase to clinical significant concentrations from 11.9 to 21.1% when increasing aspirin was added in the range of 5-50 mg/100 mL, respectively. Thus, the investigation of aspirin displacement of bilirubin from albumin is clinically important and the CE/ FA method is a suitable procedure for this purpose.

Bilirubin↗
PubMed1999

Capillary electrophoresis for trace metal ion analysis in environmental studies.

A new buffer system consisting of 30 mM hydroxylamine hydrochloride, 0.1 mM 1,10-phenanthroline, 1% methanol and pH 3.7 was optimized for simultaneous determination of water and acid leachable metals from respirable, fine and coarse air particulate matters. A reducing environment was used to resolve metal ions with variable oxidation states. A suitable counteranion was employed to enable acidic pH to be used and methanol was added to improve the resolution of the electropherograms and to achieve simultaneous determination of several metal ions. Compared to existing capillary electrophoresis (CE) buffers, the buffer developed, based on direct UV detection of ion-pair with weak interaction, gives improved resolution and sharper, more stable and well-resolved peaks. It detects total irons and solves interfering problems due to the variable oxidation states of iron in environmental samples. Compared to existing mostly alkaline CE buffers for metal analysis, the acidic nature of the buffer system developed makes the pretreatment step simpler and reduces the risk of reagent contamination. Satisfactory working ranges (15-5500 ppb) and detection limits (0.5-3 ppb) were obtained for leachable Zn, Cu, Co, Fe and Cd. The NIST 1648 urban particulate matters were found to leach out 2.53-42.8% water-extractable and 2.76-71.7% acid-extractable Zn, Cu, Fe and Cd. High iron contents, and lower copper and zinc concentrations were found in respirable suspended particulates (RSP) sampled in Hong Kong.

Air Pollutants↗
PubMed1993

Neural networks for molecular sequence classification.

A neural network classification method has been developed as an alternative approach to the search/organization problem of large molecular databases. Two artificial neural systems have been implemented on a Cray supercomputer for rapid protein/nucleic acid sequence classifications. The neural networks used are three-layered, feed-forward networks that employ back-propagation learning algorithm. The molecular sequences are encoded into neural input vectors by applying an n-gram hashing method or a SVD (singular value decomposition) method. Once trained with known sequences in the molecular databases, the neural system becomes an associative memory capable of classifying unknown sequences based on the class information embedded in its neural interconnections. The protein system, which classifies proteins into PIR (Protein Identification Resource) superfamilies, showed a 82% to a close to 100% sensitivity at a speed that is about an order of magnitude faster than other search methods. The pilot nucleic acid system, which classifies ribosomal RNA sequences according to phylogenetic groups, has achieved a 100% classification accuracy. The system could be used to reduce the database search time and help organize the molecular sequence databases. The tool is generally applicable to any databases that are organized according to family relationships.

Base Sequence↗
PubMed1990

Polarographic determination of sorbic acid in fruit juices and soft drinks.

A simple differential-pulse polarographic method using a laboratory-built hanging mercury drop electrode as the working electrode was developed for the determination of sorbic acid in fruit juices and soft drinks. Sorbic acid was extracted from the samples with diethyl ether. After reduction of the ethereal solution to a small volume by direct evaporation, the residual ether was dissolved in the supporting electrolyte (25 ml of acetonitrile + 1 ml of 0.06 M acetic acid + 0.8 g of tetraethylammonium bromide). Peak current was measured at -1.7 V. The working range of the method, without dilution or pre-concentration of the samples, was from 4 to 229 p.p.m. for the original juice and drink samples. The validity of the method was confirmed by parallel determinations using the method of the Association of Official Analytical Chemists and by recovery tests on a large variety of juice samples. Satisfactory recoveries and agreement in results from the two methods were obtained. The recovery and precision (relative standard deviation) of the method were 97 +/- 4 and 100 +/- 3%, respectively, for blackcurrant juice for five determinations.

Beverages↗