To improve point-of-care quantification using microchip capillary electrophoresis (MCE), the chip-to-chip variabilities inherent in disposable, single-use devices must be addressed. This work proposes to integrate an internal standard (ISTD) into the microchip by adding it to the background electrolyte (BGE) instead of the sample-thus eliminating the need for additional sample manipulation, microchip redesigns, and/or system expansions required for traditional ISTD usage. Cs and Li ions were added as integrated ISTDs to the BGE, and their effects on the reproducibility of Na quantification were explored. Results were then compared to the conclusions of our previous publication which used Cs and Li as traditional ISTDs. The in-house fabricated microchips, electrophoretic protocols, and solution matrixes were kept constant, allowing the proposed method to be reliably compared to the traditional method. Using the integrated ISTDs, both Cs and Li improved the Na peak area reproducibility approximately 2-fold, to final RSD values of 2.2-4.7% (n = 900). In contrast (to previous work), Cs as a traditional ISTD resulted in final RSDs of 2.5-8.8%, while the traditional Li ISTD performed poorly with RSDs of 6.3-14.2%. These findings suggest integrated ISTDs are a viable method to improve the precision of disposable MCE devices-giving matched or superior results to the traditional method in this study while neither increasing system cost nor complexity.

Department of Physical and Macromolecular Chemistry Faculty of Science Charles University Hlavova 8 128 43 Prague 2 Czech Republic

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