No abstract

This paper addresses the solution of peak overlapping, as a fundamental problem in TLC, by multivariate analysis of the images recorded by a digital camera. We report the results of our study on the application of multivariate image analysis (MIA) for simultaneous determination of several species on thin layer chromatography (TLC) sheet for the first time. An imaging system, composed of a dark cabinet, a digital camera and a multivariate image analysis program, was prepared for recording the images of TLC plates after development of a multi-component solution. The written program was able to produce 2- and 3-dimensional chromatograms of the solutions, which were subsequently used as inputs of partial least squares, as an efficient multivariate calibration method. The ability of the proposed MIA-TLC method for simultaneous determination of the co-eluting components was validated by analysis of ternary synthetic mixtures of indicators of highly overlapped chromatograms (i.e., methyl yellow, bromocresol green and creseol red) and a real mixture of nifedipine and its photo-degradation product. By application of different strategies like principal component analysis and variable selection, models were obtained that could estimate the concentration of indicators in the external prediction set with relative errors of lower than 10% and in most cases lower than 5%.

The solvent polarity E T (30) scale has found wide-spread applications in studying chemical processes in solvents. This parameter is usually measured by vis spectrophotometric measurements of the longwavelength intramolecular charge-transfer (CT) absorption band of Reichardt's pyridinium-N-phenolate betaine dye, e.g. the E T (30) dye, dissolved in the solvent or solvent mixture of interest. Recent advances in colorimetric measurements based on digital photo-capturing devices suggest these methods as a simple, cheap and fast alternative to spectrophotometric measurements in some analytical applications.In this work, we studied the feasibility of colorimetric measurements coupled with multivariate data analysis to determine the empirical solvent polarity parameter E T (30). The picture of the E T (30) dye dissolved in different solvents was captured by a digital camera and then color values in the RGB space were analyzed by the principal component analysis (PCA) method. PCA scores of the unfolded image were then used as input of multiple linear regression and an artificial neural network model to predict the E T (30) parameter. The ANN models were optimized to gain a model of lower prediction ability utilizing a cross-validation test. Then, this was used to predict E T (30) values for an external solvent test set. The generated model could explain and predict 99% of the variances in the polarity data and can predict E T (30) values with a root mean square error of 2.25 kcal mol À1 (in the E T (30) scale). The results suggest colorimetric measurements as a useful and practical alternative to the vis spectrophotometric measurements for determination of solvent polarity parameters derived from solvatochromic betaine dyes.

Fluorescent gold nanoclusters (AuNCs) have found widespread applications for designing of novel sensing elements for diagnostics and in vivo and in vitro imaging. Herein, we investigated the effect of ultraviolet (UV) irradiation on the fluorescence characteristics of bovineserum-albumin-capped AuNCs. When the aqueous solution of these nanoclusters was exposed to UV irradiation, a rapid decrease in the emission intensity at about 620 nm accompanied by an increase in emission at about 420 nm was observed. After turning off the UV light and keeping the solution in the dark, a gradual recovery of the quenched fluorescence was observed such that after about 400 min it reached its original emission value. The mechanism of these fluorescence changes was investigated by transmission electron microscopy, X-ray photoelectron spectroscopy, and monitoring of the effect of pH. The observed on−off fluorescence characteristics can be used as the basis for development of novel sensors. In this work, we used this system for an assay of antioxidant activity. The antioxidant inhibited the photobleaching and thus could turn on the photoquenched fluorescence of the BSA-AuNCs.

A simple pH-independent optical method for the sensing of heparin, as a biomedically important polyionic drug, based on aggregation of gold nanoparticles (AuNPs) is described. The polyanionic heparin induces the aggregation of positively charged ionic liquid stabilized AuNPs, which results in a shift in the surface plasmon band and a consequent color change of the AuNPs from red to blue. The color change was monitored using UV-vis spectrophotometry and image analysis methods. The aggregation was confirmed by transmission electron microscopic measurements. The degree of aggregation was found to be proportional to the concentration of the added heparin, allowing its quantitative detection. The change in the absorbance and color-value has been used to monitor the concentration of heparin. This optical method can quantify heparin as low as 0.010 μg mL(-1) and the calibration is linear for a wide range of concentration.