Analysis of pharmaceuticals in environmental water samples by capillary elctrophoresis
Creators: name: Dawod, MDZ
Publisher: name: University Of Tasmania
Year: 2023

description: Capillary electrophoresis (CE) has been used for decades for the determination of different classes of pharmaceuticals in different sample matrices because of its advantageous high separation efficiency and fast analysis time. However, the major disadvantage of CE is its poor detection sensitivity. In the current work, the improvement in detection sensitivity of CE has been extensively studied and applied for the determination of two classes of pharmaceutical compounds. Electrokinetic supercharging (EKS), a powerful preconcentration technique in CE, has been studied for the analysis of seven non-steroidal anti-inflammatory drugs (NSAIDs). The separation selectivity was optimised via adjustment of the concentration of the separation buffer (disodium tetraborate pH 9.20) and the amount of methanol as an organic modifier. Different EKS parameters, including injection voltage, injection time, and amounts of leading and terminating electrolytes were studied. The optimised conditions allowed detection sensitivity to be improved by 2,400-fold when compared to field-amplified sample stacking (FASS) and the limits of detection (LODs) were down to 50 ng/L. A valuable modification to the EKS system, namely counter-flow EKS (CF-EKS), has been developed in order to decrease the amount of the interfering sample matrix involved in the system, hence, larger amount of analytes could be concentrated. Computer simulation studies were undertaken in order to understand the trends in sensitivity enhancement from EKS to CF-EKS. After assigning the optimal counter pressure and injection voltage in CF-EKS, an artificial neural network (ANN) was developed for optimising the injection time and the amount of terminating electrolyte. Upon comparison with FASS, the optimal conditions of CF-EKS allowed the sensitivity to be enhanced by 11,800-fold and the LODs were decreased to 10.70 ng/L for the studied NSAIDs. The on-line hyphenation of EKS-CE with the highly precise electrospray ionisation mass spectrometry (ESI-MS) was for the first time investigated, and then applied for the determination of five acidic hypolipidaemic drugs. The separation was performed in a co-electroosmotic flow (co-EOF) mode using the EOF reversal agent hexadimethrine bromide (HDMB) in ammonium bicarbonate buffer pH 9.00. An ANN was developed for the optimisation of the separation selectivity, and the EKS-ESI-MS system provided enhancement in detection sensitivity of 1,000-fold when compared to FASS. The LODs for the studied hypolipidaemic drugs were decreased to 180 ng/L. Simultaneous separation of charged and neutral hypolipidaemic drugs was made possible by the application of micellar electrokinetic chromatography (MEKC). Ammonium bicarbonate pH 8.50 was used as a separation electrolyte and sodium dodecyl sulfate (SDS) was used as a micelle-forming agent. In order to enhance the detection sensitivity in MEKC, three on-line preconcentration strategies, namely sweeping, analyte focusing by micelle collapse (AFMC) and simultaneous FASS-sweeping were investigated and applied for the determination of eight hypolipidaemic drugs. When compared with a hydrodynamic injection (5 s at 50 mbar, 0.51% of capillary volume to detection window) of drug mixture prepared in the separation background electrolyte (BGE), improvements in detection sensitivity were 60, 83, and 80-fold for sweeping, AFMC, and FASS, respectively. Finally, all the developed on-line preconcentration techniques were successfully tested for quantitative repeatability, and then applied for the determination of target analytes in wastewater as well as drinking water samples from Hobart city - Australia.