Phasor transform to extract glucose and ascorbic acid data in an amperometric sensor

A method for separating the signals from glucose and ascorbic acid on a sin gle recognition surface using an ac immittance technique is presented. It i s proposed that each oxidation process can be represented by a unique vecto r based on psi and Y-O, and that the concentration of each analyte can be d etermined by monitoring the change in the admittance magnitude in the direc tion of the characteristic angle for that particular species. The total Far adaic admittance ((Y) over right arrow (F,total)) for all electroactive spe cies present is given by a linear combination of the independent vectors fr om the different species. In the system tested, the analytes are glucose an d ascorbic acid, the former being estimated via the measurand, hydrogen per oxide. Thus, one of the electroactive species (hydrogen peroxide) is not a bulk solution species, but is 'generated' in the enzyme matrix. The admitta nce measurements from ascorbic acid and the enzyme-generated hydrogen perox ide showed the characteristic phase angles of each oxidation signal, allowi ng for good spatial resolution. The behaviour of each of these analytes is presented and calibration curves tested. Based on the calibration curves an d the basis vectors, samples containing both glucose and ascorbic acid were measured by transforming the measured total admittance from the complex Ca rtesian space into 'analyte space', where the X-Y axes are given by the bas is vectors (y) over cap (EGHP,GOD) and (y) over cap (AA,GOD), respectively.