Resolution of overlapping optical signals: Dual sensing vs chemometrics

Signal overlapping is a common issue that often prevents the full implementation of UV-Vis dip probes in on-site analysis, even in the case of relatively simple chemical systems. In this work, two strategies for the resolution of optical signals without the need of sample treatment are compared: (i) dual sensing based on the combination of optical and electrochemical signals; and (ii) data treatment of optical signal by means of chemometrics. For this purpose, two different systems were evaluated. The first one comprised pyrocatechol (CC) and isonicotinamide (INAM) as an example of a system containing only one electroactive species and the second one contained CC and isoniazide (INH) as an example of a chemical system with two electroactive compounds. Both strategies proved successful in the resolution of the optical overlapping in static conditions (i.e., non-stirred solutions), with slopes in the range of 0.88-1.08 and R² values higher than 0.989 for the representation of predicted vs expected concentration values for both chemical systems. Nevertheless, only chemometrics was able to resolve both systems in dynamic conditions (slopes in the range of 0.873-1.10 and R² values higher than 0.99), as the increased transport of INH significantly affected electrochemical measurements. Dual sensing was also successful in the resolution of CC and INAM (slopes in the range of 1.014-1.035 and R² values higher than 0.99), proving even better than chemometric analysis, particularly in the region of lower CC concentrations.