Potentiometric and surface topography studies of new carbon-paste sensors for determination of thiamine in Egyptian multivitamin ampoules

We report here for the first time two potentiometric carbon-paste sensors for determination of thiamine chloride hydrochloride in aqueous solutions. The proposed sensors use the ion-pair of thiamine with tetraphenylborate as an electro-active species and dibutyl phthalate (sensor I) or o-nitrophenyloctyl ether (sensor II) as solvent mediators. The effect of solvent mediator was studied using dibutyl phthalate, o-nitrophenyloctyl ether, ethylhexyl adipate, dioctyl phthalate, tricresyl phosphate and paraffin oil. The slopes of the calibration graphs are 29.49 ± 0.24 and 29.60 ± 0.15 mV/decade for sensors (I) and (II), respectively. The sensors are able to detect down to 5.25 × 10−6 and 3.57 × 10−6 for (I) and (II), respectively. Both sensors show reasonable thermal stability and fast response time. The selectivity coefficients obtained from the matched potential method indicate high selectivity of the proposed sensors toward thiamine over commonly interfering cations. Sensor (I) has a lifetime of only 1-2 days; however, sensor (II) remains usable for up to one month. Analytical applications to pure solutions and Egyptian multivitamin ampoules show excellent recovery values ranging from 97.92 to 103.72% and 97.21 to 102.19% for sensors (I) and (II), respectively. Moreover, the precision and reproducibility of the sensors are indicated from the low values of %RSD of five replicate measurements. In addition, the surface topography of the sensors was studied using scanning electron microscopy to investigate the effect of chemical modification on the surface structure.