K. P. Ang

Electrochemical detection for liquid chromatography using the wall-jet cell/ultramicroelectrode detector

Abstract A carbon fibre array and a platinum thin ring ultramicroelectrode were constructed and used in conjunction with a large volume wall-jet cell as an amperometric detector in liquid chromatography. Electrode characterization studies were performed in 5.00 m M K 3 Fe(CN) 6 + 1 M KCl aqueous solution. It was found that the wall-jet cell/ultramicroelectrode combination has much reduced flow rate dependence compared to the wall-jet cell/conventional electrode system. LC application in the absence of supporting electrolyte was found to be possible and have good sensitivity using the ultramicroelectrode. Detection limits were 100 pg and 10 ng for the platinum thin ring and the carbon fibre array electrodes respectively.

Electrochemical detection of polynuclear aromatic hydrocarbons following reversed-phase gradient high-performance liquid chromatography using a large-volume wall-jet detector

Abstract Electrochemical detection is rarely used in conjunction with gradient high-performance liquid chromatography. The problem is the changing eluent composition and electrolyte concentration during a gradient run which greatly affects the performance of electrochemical detectors. However, by the use of a large-volume wall-jet detector a means of obviating the problem is afforded. This paper reports on an application to the analysis of polynuclear aromatic hydrocarbons.

The electrolytic efficiency of amperometric detection in normal-phase high-performance liquid chromatography

Abstract The electrolytic efficiency of the wall-jet detector in normal-phase high-performance liquid chromatography (between 0.1 and 5%) is significantly less than its efficiency in reversed-phase separations. A large-volume wall-jet cel with a Ag/Ag+ reference serves as the detector system in evaluating the effects of various chromatographic conditions on efficiency. Anthraquinone, phenanthrenaquinone (both at 10-3–10-4 M) and three estrogen gen steroids (at 10-2–10-3 M) are used as samples with ethanol/ hexane eluents. The effect of pH depends on the sample; increased ethanol concentrations and lower flow rates improve the efficiency.

Development of an in-line blood-glucose monitor

Abstract The development of a practical electrochemical system for in-line blood-glucose monitoring requires the combination of several modifications to achieve reliability. The prototype monitor described includes stopped-flow dialysis, a carbon-fibre pre-electrolysis cell, an immobilized glucose-oxidase reactor and a membrane-coated electrode used with square-wave amperometry. Under microprocessor control, the system is well suited for routine monitoring applications with minimal user interaction. Good precision (RSD of 3–4% ) is achieved over extended use. The linear response range for blood glucose is 1–20 mM.

The distribution of polynuclear aromatic hydrocarbons in ambient air particulates in Singapore.

Ambient air particulates were collected using high volume samplers at seven locations throughout Singapore. The particulates were analyzed for eleven polynuclear aromatic hydrocarbons (PAH) using high performance liquid chromatography (HPLC) with fluorescence detection. Several sample preparation techniques were used to determine which method would yield the most PAHs from the bulk sample matrix. PAH profiles (standardised against the concentration of benzo(a)pyrene) were obtained to characterise the different sampling sites chosen.

Determination of oestriol in pregnancy urine by normal-phase high-performance liquid chromatography with electrochemical detection

A method for the determination of oestriol in pregnancy urine by normal-phase high-performance liquid chromatography with electrochemical detection is described. A large-volume wall-jet cell with an Ag-Ag+ reference electrode was used as the detector system. The limit of detection obtained is comparable to that of electrochemical detection following reversed-phase liquid chromatography. One of the advantages of electrochemical detection with normal-phase systems is that adsorption problems are minimized.

The determination of heavy metal content in the coastal sea waters of Singapore

The levels of cadmium, copper, lead and zinc in coastal sea water samples were determined by an automated anodic stripping voltammetry (ASV) with flow injection system. The ASV analysis was performed in the differential pulse mode at a glassy carbon based mercury film electrode. The results represent a first attempt to establish baseline concentrations of cadmium, copper, lead and zinc in the coastal sea waters of Singapore.

The determination of cadmium, copper and lead in ambient air particulates in Singapore

Between October 1986 and September 1987, 540 samples were collected at seven locations throughout Singapore for a study of heavy metal composition in ambient air particulates. The samples were analysed for cadmium, copper and lead using an automated anodic stripping voltammetry (ASV) technique with flow injection system. The reliabililty and suitability of the automated ASV technique is evaluated and compared with established atomic absorption spectrometry (AAS) procedures. The findings serve as a useful reference for future study of the Singapore atmospheric environment.

Polycyclic aromatic hydrocarbons in diesel exhaust emissions

Samples of diesel exhaust emissions were analysed for eleven polycyclic aromatic hydrocarbons (PAHs) by high performance liquid chromatography (HPLC) with flourescence detection. The PAHs present in the diesel extracts were then represented by a PAH profile with reference to the concentration of benzo(a)pyrene.

The occurrence of some PAHs in ambient air in Singapore

Singapores uniformly tropical weather and dense urban and industrial environment makes it prone to air pollution. Up to now no significant study of air pollution has been carried out. This paper seeks to evaluate the occurrence of PAHs in ambient air particulates. PAHs are extracted with cyclohexane and determined by gradient HPLC and fluorescence detection.