Carbon dioxide-based pump system for portable HPLC equipment

Sammanfattning: To make chemical analysis available both practically and economically, one approach is to miniaturise the equipment needed for the analysis. High-performance liquid chromatography (HPLC) is an example of a flow chemistry analysis system where active work is performed to achieve miniaturised systems. In this thesis, the focus is on creating a miniatyrised pump system constructed of pressurised CO2 (PCO) and a microfluidic chip with a restriction channel. The assignment of the PCO is to force a separate medium, which in this case is water, through the remaining system. The pump system will therefore be defined as pressure-driven, which has advantages as pulse-free flows. Utilising the latent energy from the PCO also reduces the need for electrical power, hence allowing a smaller battery. However, the pressure from the carbon dioxide source will gradually decrease as the content is consumed. To obtain continuous pressure, heaters have been integrated into the chip, and thus, the pressure drop can be controlled by changing the viscosity and density of the through-flowing fluid. A cooling table was also used to enable the cooling of the chip and thus further increase the pressure drop. PID control was implemented for the temperature to be adjusted to maintain a constant pressure downstream of the chip. By using this technology, runs of just over 80 minutes have been achieved with a pressure of 60 bar and a flow of 100 µl/min downstream, with a maximal error of around 0.03 bar. Then a chip adapted for water was used to control the water flow. Chips adapted for carbon dioxide placed right after the carbon dioxide source were also tested andruns of just over 10 minutes at 75 bar and 100 µl/min could be achieved with a maximal error closer to 1 bar. The pressure vessel used held a maximum of 100 ml of CO2 at 60 bar. The idea is that the pump system, in the end, will be applied for portable HPLC, and the PCO will then be stored in a cartridge, but in the experiments, a turned-off ISCO pump functioned as a carbon dioxide source.