Determination of inorganic cations in biological fluids using a hybrid capillary electrophoresis device coupled with contactless conductivity detection.

We describe the assembly of a hybrid electrophoresis device that contains fused silica capillaries interconnected to a microfabricated interface in a cross format for the determination of inorganic cations in biological samples. The sample transport in the proposed hybrid device was performed under gated injection mode and the separations were monitored with a capacitively coupled contactless conductivity detector. The capillary extremities were inserted into polypropylene tubes to create solution reservoirs. Sensing electrodes were produced using stainless-steel hypodermic needles previously cut with 2.0 mm length. The running composition and injection time were optimized and the best results were found using 50 mmol/L lactic acid, 20 mmol/L histidine and 3 mmol/L 18-crown-6 ether, and an electrokinetic injection time of 15 s. The separation of six inorganic cations was achieved with baseline resolution, and efficiencies were between 9.1 × 103 and 5.4 × 104 plates/m. The proposed hybrid device was explored for determining the concentration levels of inorganic cations in urine, saliva, and tear samples, employing Li+ as an internal standard. The achieved results were in good agreement with the data reported in the literature. The reliability of the proposed method ranged from 93 to 98%, thus suggesting satisfactory accuracy for bioanalytical applications.