Biomedical subjects

C L Ng

Publications and source records attributed to C L Ng.

10 recordsLinked to original sources

PubMed1994

Determination of pharmaceuticals and related impurities by capillary electrophoresis.

In the first part of this work, the use of capillary electrophoresis (CE) for the separation of two groups of pharmaceuticals, namely a metabolite of tamoxifen and a basic drug substance, DS1 was investigated. The effects of pH and types of modifiers, e.g. surfactant, bile salt, gamma-cyclodextrin and hydroxypropyl-beta-cyclodextrin on selectivity, separation and peak shape were studied. Besides achieving complete separation of the compounds, the CE system was capable of providing separation with significant improvements in overall peak shape of the compounds compared with HPLC. In the case of the basic drug substance DS1, validation of the CE system developed in terms of linearity, selectivity, sensitivity and reproducibility was satisfactorily performed. At the same time, a study of the sample solvent matrix effects on the separation of this group of compounds was examined. The system was successfully applied to the analysis of laboratory-synthesized samples. Good correlation was observed between CE and HPLC, although higher efficiency and faster speed of separation were obtained using the CE system developed. For the tamoxifen metabolite, special emphasis was placed on the use of CE for the separation of the pair of isomers. This was readily achieved through the introduction of gamma-cyclodextrin in the electrolyte. Resolution of at least 1.5 was obtained for the isomers using the CE method.

2-Hydroxypropyl-beta-cyclodextrin↗

PubMed1994

The use of mixed surfactants in micellar electrokinetic chromatography.

The use of mixed surfactants for the separation of nine phenylthiohydantoin amino acids (PTH amino acids) by micellar electrokinetic chromatography (MEKC) was examined. The potential of a mixed surfactant system, consisting of cationic and anionic surfactants, for enhancing the selectivity of MEKC separations was explored. Both sodium dodecyl sulfate (SDS) and cetyltrime-thylammonium bromide (CTAB) in the electrophoretic medium were found to improve the separation of the PTH-amino acids compared to the use of CTAB or SDS alone. Complete separation of the PTH amino acids was achieved using a buffer containing 2.5 mM CTAB and 40 mM SDS. The analysis was performed without the need to reverse the polarity of the electrodes, typically required if oppositely charged micelles are used. The migration behavior of the nine PTH amino acids using the mixed surfactant system was compared with MEKC in presence of SDS alone.

Amino Acids↗

PubMed1993

A biometric study of ocular changes during accommodation.

We performed a biometric study that used A-mode ultrasonography on 106 subjects during ocular accommodation. The subjects were divided into two groups; group 1 included 76 subjects and group 2 included 30 subjects. In group 1, we measured the anterior chamber depth, lens thickness, and axial length in the right eye while the left eye, wearing corrective spectacles, focused at distances of 6 m, 33 cm, and 33 cm with an additional correction of +3.0 diopters to offset any accommodative effect. In group 2, we measured the anterior chamber depth, lens thickness, and axial length in the right eye while the left eye focused at distances of 6 m, 33 cm, and 12.5 cm. Similar to the left eyes in group 1, the left eyes in group 2 wore corrective spectacles during all procedures. During accommodation, decreased anterior chamber depth and thickening of the lens were noted in all cases. In group 1, axial length significantly increased an average of 0.06 +/- 0.01 mm (P < .0005) while the left eye focused at a distance of 33 cm. There were no significant changes with the additional +3.0 diopters (P < .05). In group 2, axial length significantly increased an average of 0.05 +/- 0.01 mm (P < .0005) when the left eye focused at a distance of 33 cm, and there was further significant elongation of 0.05 +/- 0.01 mm when the left eye focused at a distance of 12.5 cm. Collectively, these results suggest that axial length increases along with changes in the lens and anterior chamber depth during ocular accommodation.

Accommodation, Ocular↗

PubMed1992

Analysis of food additives by ion-pairing electrokinetic chromatography.

A mixture of food additives is separated using ion-pairing electrokinetic chromatography with on-column ultraviolet detection at 190 nm. Tetrabutyl ammonium hydrogen sulfate (TBA) is used as modifier. The effect of the concentration of TBA on the migration behavior of the solutes is investigated. This method is used for the determination of the amount of additives in food samples. The percent relative standard deviation (%RSD) for the migration time is found to be less than 0.9% and that of the peak area is less than 2.5%.

Benzoates↗

PubMed1991

Determination of antihistamines in pharmaceuticals by capillary electrophoresis.

Capillary electrophoresis with on-column UV detection at 214 nm was used to separate a group of nine antihistamines. All these compounds were satisfactorily separated within ca. 6 min using a mixed carrier system containing sodium dodecyl sulphate with beta-cyclodextrin and tetrabutylammonium hydrogensulphate as modifiers. The application of the method to the determination of the amount of antihistamines present in commercial pharmaceutical samples was demonstrated. In addition, the migration behaviour of the antihistamines in the mixed carrier system was examined.

Capillary Action↗

PubMed1990

Retention of eleven priority phenols using micellar electrokinetic chromatography.

The use of micellar electrokinetic chromatography (MECC) for the separation of eleven substituted phenols listed by the United States Environmental Protection Agency as priority pollutants was investigated. Solutions of potassium and sodium dodecyl sulphate in phosphate-borate buffer of pH 6.6, 7.0 and 7.5 were used as the electrophoretic media. Satisfactory separation of the eleven phenols was obtained using a 180-microns capillary at 10 kV and pH 6.6 with a solution containing both sodium and potassium dodecyl sulphate. Observations on the retention behaviour of the phenols in MECC were related to their physico-chemical properties.

Chromatography↗

PubMed1990

Calcium ion activation of the anion-conducting channel in the rat liver mitochondrial inner membrane.

Stimulation of the rat liver mitochondrial inner-membrane anion-conducting channel by aeration is dependent on the concentration of Ca2+ ions in the assay medium. Ca2+ activates anion conduction in both aerated and non-energised mitochondria but acts over a wider concentration range and produces a greater increase in anion-conductivity in aerated mitochondria. EGTA reverses Ca2+ stimulation but takes several seconds to act, indicating slow release of Ca2+ from the activation site possibly on the matrix side of the inner mitochondrial membrane. It is suggested that this channel may respond to hormone-induced changes in cytosolic Ca2+ concentration.

Aerobiosis↗

PubMed1983

Pressure garments in the prevention and treatment of keloids.

Hypertrophic scarring and keloids are frequent sequelae following trauma. Continuous and controlled pressure through the use of pressure garments can yield a high degree of non-surgical control of both hypertrophic scar formation and scar contracture resulting in soft, pliable scars with relief from itch and pain. This paper is a study of 280 patients, carried out in the Department of Plastic Surgery, Singapore General Hospital, over a period of 3 years. Not only are the results highly encouraging but the garments themselves are readily and simply constructed from locally available materials, using basic sewing skills.

Burns↗

PubMedDate not supplied

IgA binding lectins isolated from distinct Artocarpus species demonstrate differential specificity.

The discovery of jacalin, a group of lectins from jackfruit seeds (Artocarpus heterophyllus), has attracted considerable attention due to its numerous interesting immunological properties as well as its usefulness in the isolation of various serum proteins. We have further identified a similar lectin from the seeds of Champedak (Artocarpus integer) which we refer to as lectin-C and performed comparative studies with two types of jacalin isolated from different batches of the Malaysian jackfruit seeds (jacalin-M1 and jacalin-M2). The three purified lectins demonstrated equivalent apparent Mr of about 52,500, each of which comprised of a combination of two types of non-covalently-linked subunits with apparent Mr of approximately 13,300 and 16,000. The lectins demonstrated equal haemagglutinating activity against human erythrocytes of blood groups A, B, AB and O. Our data also demonstrated that lectin-C, jacalin-M1 and jacalin-M2 are similar by selectively precipitating human serum IgA1 and colostral sIgA but not IgA2, IgD, IgG and IgM. When immunoelectrophoresis was performed on normal human sera and reacted with the lectins, single precipitin arcs corresponding to IgA immunoprecipitates were detected with lectin-C and jacalin-MI. Jacalin-M2, however, exhibited two closely associated precipitin arcs. The binding of these lectins with IgA was pronouncedly inhibited in the presence of p-nitrophenyl-beta-D-galactopyranoside, 1-o-methyl-alpha-D-galactopyranoside, D-melibiose, N-acetyl-D-galactosamine and D-galactose. The data therefore provide evidence on the differential specificity of IgA binding lectins isolated from seeds of similar as well as distinct Artocarpus species.

Binding, Competitive↗

PubMedDate not supplied

The Moberg pickup test: results of testing with a standard protocol.

The purpose of this study was to propose a standard protocol for administering the Moberg pickup test. One hundred subjects (53 male and 47 female subjects, aged 11 to 77 years) volunteered. A wide variety of occupations were represented. No subjects had a history of upper extremity dysfunction. The materials and the testing procedures were clearly described to the subjects. Both hand dominance and gender difference were found to have significant effects on test performance. Norms were established for dominant/nondominant hands and for male/female subjects. Standard scores were calculated and used for comparison. The inter-rater reliability of the test was also determined. Administered with a standard protocol, the Moberg pickup test is a valuable test of functional sensibility. It is simple and quick to administer, easy to replicate, and inexpensive to acquire.

Activities of Daily Living↗