Integration of laminar flow extraction and capillary electrophoretic separation in one microfluidic chip for detection of plant alkaloids in blood samples

The design, construction and testing for integration of liquid-liquid extraction (EX) and capillary electrophoretic (CE) separation on one glass microchip was reported. In this EX-CE chip, a 1.5 cm-long and 200 μm-wide EX channel was used for extraction based on the two-phase laminar flow, followed by a single-cross CE unit for on-line analysis without any auxiliary devices. One side of the EX channel surface for the organic solvent phase was selectively modified to be hydrophobic while the surface of the other side for the aqueous phase remained hydrophilic, and the extraction product reservoir is also used as the sample reservoir for the subsequent chip separation in the CE channel. With the surface-directed liquid flow behavior and liquid level adjustment in various reservoirs of the EX-CE chip, no disturbance occurred between the extraction (EX) and capillary electrophoretic (CE) units. A small heating block was placed under the chip to accelerate solvent evaporation after liquid-liquid extraction. Sanguinarine (SAN), a plant alkaloid, was used as a model analyte to evaluate the performance of the EX-CE chip. The influences of organic solvent type and liquid flow speed on the extraction efficiency were investigated. Rhodamine 123 (Rh123) was used as an internal standard for quantification of Sanguinarine (SAN) in a physiological buffer (e.g. PBS) or blood samples. A good linearity in the concentration range of 0.05 μg mL⁻¹ to 0.1 mg mL⁻¹ for SAN in PBS was obtained, with the detection limit of 0.5 ng mL⁻¹. Good repeatibilities for migration times (RSD of SAN is 0.63%, Rh123 is 0.91%, n = 5) and peak area ratio of SAN to Rh123 (RSD is 1.3%, n = 5) were obtained. For blood sample analysis, only 20 μL of sample was needed, and the whole analysis was finished in 17 min. In addition to the advantages in fast analysis speed, minimum sample handling, potential automation, the reported method showed an on-line sample pre-concentration capability.