Electronic micropipettor: A versatile fluid propulsion and injection device for micro-flow analysis

The shortage of ready to use small sized liquid propulsion and switching devices for microfluidic cells (μ-cell) is a bottleneck in the dissemination of micro-flow analysis (μ-FA), now that microfluidic electrochemical cells can be designed and assembled in any laboratory by thermal transfer of laser printed masks and CD-Rs. Microprocessor-controlled electronic pipettors, commercially available with minimum capacity of 10 μL, represent a compromise solution between oversized peristaltic pumps and tiny “on a chip” micropumps and valves. The versatility of the electronic pipette coupled with the μ-cell (13-μm deep longitudinal channel) was demonstrated in three operation modes: SIA like, FIA like and direct injection analysis (DIA). Injections of 100 nL K4Fe(CN)6 (0.1 mol L−1 KCl) define a linear analytical curve (r = 0.999) in the range of 5 × 10−7 to 1.0 × 10−3 mol L−1 for flow amperometry at a gold electrode potentiostated at 0.4 V versus Ag/AgCl. Methods for the amperometric μ-flow determination of promethazine (FIA like), dipyrone (SIA like) and chlorpromazine (DIA) in pharmaceutical formulations were developed and applied to real samples. Excellent linearity of analytical curves and high repeatability (R.S.D. < 3.0%) at the low picomole range was obtained and all results for real samples were in agreement with reference methods. The results reflect the stability and the reliability of the setups envisioned for the electronic pipette coupled with amperometric μ-cell and the validity of the μ-FA methods.