Browsing by Author "Fong Yau Li, Sam"

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    Determination of cyanobacterial cyclic peptide hepatotoxins in drinking water using CE
    (Electrophoresis, 2009) Birungi, Grace; Fong Yau Li, Sam
    Four cyanobacteria hepatotoxins microcystin LR, microcystin RR, microcystin YR, and nodularin were simultaneously determined in drinking water using CZE and MEKC coupled with UV detection. The toxins were satisfactorily separated in both CZE and MEKC modes. Detection limits were in the range of 0.82–4.81 mg/mL, with R2 values of 0.994–0.999. The linearity range tested for the standards was 5–100 mg/mL and RSD percentages were in the range of 1.0–2.5% for retention time and 3.0–10.2% for peak area. When a known amount of standard was spiked into a known volume of water and extracted, recoveries were 90.3% (RR), 101.5% (nodularin), 90.6% (YR), and 88.2% (LR). The use of SPE enabled cleanup and pre-concentration of a real sample to achieve a 100- fold concentration factor. Detection limits after SPE of the real sample spiked with microcystins were 0.090 mg/L (RR), 0.076 mg/L (YR), and 0.110 mg/L (LR), with RSD percentage values of 9.9–11.7% for peak area and 2.2–3.3% for retention time. The technique developed provides an alternative method for determining microcystins at levels of concentration that will be able to meet WHO drinking water guidelines for microcystins.
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    Investigation of the effect of exposure to non cytotoxic amounts of microcystins
    (Metabolomics, 2011) Birungi, Grace; Fong Yau Li, Sam
    This paper describes a metabolomic approach for investigation of the potential effect of exposure of humans to low amounts of microcystins using HepG2 cell line. Microcystins are hepatotoxins produced by cyanobacteria (blue-green algae) which occur in water bodies with high eutrophication especially those with a slow flow rate or those that are stagnant in warm climates. Mammalian exposure to these compounds has been associated with deleterious effects and in high dosage cases, deaths of animals has been reported. The metabolic profile of HepG2 cells is closely related to that of hepatocytes and therefore serves as a good model due to their human origin. Proton nuclear magnetic resonance spectroscopy (1H NMR) and direct injection mass spectrometry (DIMS) were used to analyse media extracts from the cells and data obtained was reduced by chemometric methods. The use of principal component analysis (PCA) enabled achievement of a visual distinction between the metabolic profiles of samples exposed to microcystins, control samples (unexposed), and those which were exposed to acetaminophen (positive control). A profile of media components showed that some components in the samples exposed to microcystins increased compared to those in control samples. They included amino acids, organic acids, lipids, some purines and pyrimidines. In general exposure to low concentration of microcystin was found to interfere with amino acid metabolism, carbohydrate metabolism, lipid metabolism and nucleic acids metabolism. Furthermore, low concentration of microcystins did not result in significant cell death; rather the cells continued to proliferate.