Chiang Mai Journal of Science

              Sequential injection analysis (SIA) with electrochemical detection was developed for antioxidant capacity test by 2,2´-azino-bis(3-ethybenzothiazoline-6-sulfonic acid) (ABTS assay) with collaboration of researchers from chemistry and computing departments.  Manifold and sequential steps of the SIA system were designed prior to the computer program was written in Processing Language along with fabrication of electronic circuit using Arduino board for semi-automatic controlling of the bi-directional Masterflex peristaltic pump (model 77521-40).  The attaining pump drive controller program provided the following advantages: 1) Connection with the Arduino board so that the voltage in pulse width modulation mode was given to the pump according to the flow rate and time required. 2) User command screens to define flow rate, number of step and time of each step in the SIA system. 3) Pump operation timer with the warning sound and message for change of port position and flow direction at the end of each step.  Precision of results and user convenience were improved more than those without using the pump drive controller program. Amperometric detection after chemical reaction was performed by laboratory made electrochemical flow-through cell with three electrode system.  The ABTS radical cation left after reaction with antioxidant gave the cathodic current on glassy carbon working electrode at the applied potential of   -0.10 V vs. Ag/AgCl. The standard antioxidant, gallic acid showed linear calibration curve in the concentration range of  0-70 ppm (R² = 0.9969).  Antioxidant capacity tests of various commercial ginger samples were reported in gallic acid equivalent unit with satisfactory results.  The sample throughput rate of the SIA system was 9 samples/h at the constant flow rate of 2.0 mL/min.