A second-order advantage achieved with the aid of gold nanoparticle catalytic activity. Determination of nitrophenol isomers in binary mixtures
A novel, simple and rapid spectrophotometric method for the determination of nitrophenol (NP) isomer mixtures based on the catalytic activity of gold nanoparticles is described. Gold nanoparticle (∼13 nm) solution was used to catalyze the reduction of NP isomers to aminophenols with an excess amount of NaBH4. The second-order data were obtained by spectrophotometrically monitoring the reduction process of NP isomers. So, multivariate curve resolution optimized by alternative least squares (MCR-ALS) was used to analyze such data. MCR-ALS, an appropriate second-order method, can exploit the so-called ‘second order advantage’ (the ability to determine in the presence of uncalibrated interference). With the use of this multivariate curve resolution method, we applied a single calibration sample, instead of a large number of calibration samples. The results obtained by MCR-ALS analysis were in good agreement with the true concentration of NP isomers. Furthermore, the ranges of all possible concentrations of NP isomers were obtained by calculating all feasible solutions. These concentrations are all amounts which may be achieved by applying different initial estimates in MCR-ALS. The proposed procedure was further applied to determine the NP isomers spiked in dam water samples, and it showed good promise for quantitative detection of NP isomers.