Microchip Internal Standards: improving quantitative point-of-care capillary electrophoresis

To realise portable microchip capillary electrophoresis systems for routine use in point-of- care (POC) settings, measurements must be robust across many single-use chips. While it is well-known that internal standards (ISTDs) improve run-to-run reproducibility in conventional analytical chemistry methods, this thesis explores ISTDs in two novel ways. First, two ISTDs are used in a systematic investigation to determine the significance of chip-to-chip imprecision. Six basic, in-house fabricated microchips were used to determine the reproducibility of NaCl quantification with two ISTDs: CsCl and LiCl. Chip-to-chip imprecision was significantly larger than intrachip. We attributed this to a significant variation in microchannel surface properties, while microchip dimension and detector variations were small in comparison. Cs and Li ISTDs both corrected the chip-to-chip precision; however, Cs was clearly superior, suggesting that the ISTD must be carefully chosen as in conventional methods. In a second investigation, the same experiments were performed again – except with the ISTDs added to the background electrolyte (BGE) instead of the sample, resulting in the formation of two system peaks. While this phenomena is well-known, intentionally adding a system peak for use as a quantitative reference standard has yet to be reported – perhaps due to the availability of traditional ISTDs in conventional laboratories. When CsCl and LiCl were added to the BGE, the chip-to-chip precision of Na quantification improved without using the reference peak, and was further reduced when Cs or Li was used as a correction factor. Furthermore, both Cs and Li performed comparably well, suggesting that the method was more robust and less selective than a traditional ISTD under these simple experimental conditions. Finally, the method was further investigated using a more-complex and less-varying sample matrix, with cation concentrations similar to human blood. The BGE-added "Cs" system peak improved the measurement of clinically relevant K concentrations and resulted in linear calibration curves. While further investigation is necessary, the novel method proposed in this thesis gave promising results and is attractive for use in POC settings due to its simplicity: no additional sample manipulation, microchip changes, or system expansions are required for implementation.