Evaluation of Different Substrates for Electrodeposition of Riboflavin Films for Determination of Boric Acid in Eye Drops

Interactions between riboflavin (of known and reversible electrochemical behavior) and boric acid (electrochemically inactive) were explored to expand the applicability of voltammetric techniques allied to composite sensors aiming at minimum sample consumption. The electrochemical cell used in this research consists of three electrodes: a working electrode which is a graphite composite electrode modified by riboflavin film electrodeposition, an Ag|AgCl|KCl \({}_\textrm{sat}\) reference electrode, and a steel needle counter electrode surgical. Graphite composite electrodes were evaluated, whose insulating phases were EPOXY, PLA, and ABS resin, using AFM, SEM, and contact angle. The limits of detection (LOD) and quantification (LOQ) were 1.4 and 4.5 mmol \(\mathrm {L^{-1}}\) , respectively, under optimized conditions using the square wave voltammetry technique. The developed method was applied to four samples of eye drops and one boric water sample as a model of chemical warfare agent transported in small vials, with use in microvolumes, the sensor being a proof of concept for the present proposal. The voltammetric method was compared to the UV–Vis spectrophotometric method with azomethine-H using the t-student test (95%). There was no statistically significant difference between the results obtained by both methods of analysis to four of the five analyzed samples, and also when comparing with the label values.