Direct measurement of lithium in whole blood using a glass chip with integrated conductivity detection for capillary electrophoresis

Introduction: At the present state of micro fluidic chip technology, it is now possible to combine sample treatment steps with separation methods on a single device. However, still few examples have been presented, which fully exploit combining multiple functionalities. We demonstrate here that the measurement of alkali metals in a drop of whole blood can be performed on a capillary electrophoresis (CE) chip with defined sample loading applying the principles of column coupling. Using this approach specifically the analysis of lithium in whole blood was examined. Methods: Whole blood collected from a finger prick was mixed with anticoagulant and transferred directly onto the chip without diluting, extracting or removal of components. The electrokinetic transport of red blood cells inside the channels was studied to find sample loading conditions suitable for analysis of lithium, but that did not inject cells into the separation channel. Both bare glass chips and CE chips coated with polyacrylamide were used showing the behaviour of the cells under different electroosmotic flow conditions. Results: Lithium could be determined in whole blood diluted only with anticoagulant and spiked with lithium. In a matrix of 150 mmol/L sodium the detection limit for lithium is with 0.4 mmol/L on the high side as a quantitation limit of 0.2 mmol/L is desirable for clinical use. Chips with untreated surfaces quickly fouled with proteins, but devices with coating gave reproducible electropherograms. In addition potassium and sodium can also be detected in the same separation run. Conclusion: The presented experiments demonstrate that it is possible to measure alkali metals in a sample as complex as whole blood with a micro fluidic glass chip.