Use of Principal Component Analysis for the Study of the Influence of Physicochemical Parameters on the Retention of Barbiturates on Porous Graphitized Carbon Column

Abstract

Porous graphitized carbon (PGC) has proved to be an excellent tool for the separation of positional-and stereoisomers of steroids, cephalosporin antibiotics and cresols. 1 The retention mechanism of PGC has been extensively discussed. Under non-polar conditions, PGC acted as an electron-pair acceptor of solutes. 2 Another study indicated the importance of dipoleinduced dipole interactions in the retention mechanism. 3 The influence of physicochemical parameters of some ring-substituted aniline derivatives on their retention on the PGC column has been studied in aqueous eluent systems. It has been established that the retention on the PGC column of ring-substituted aniline derivatives is mainly governed by the sterical parameters of the substituents. 4,5 Multivariate mathematical-statistical methods such as canonical correlation 6 and cluster analysis (CA) 7 , stepwise regression analysis (SRA) 8 , and principal component analysis (PCA) 9 have been frequently used to extract maximum information from retention data matrices of considerable dimensions.The objective of our investigations was to study the retention behavior of some barbituric acid derivatives on a PGC column using ethanol-water mixtures as eluents, to assess the relationship between the physicochemical characteristics and retention parameters of barbituric acid derivatives by means of PCA combined with CA and SRA, and to elucidate the similarities and dissimilarities in the information content of the various calculation methods. The study was motivated by the fact that, to the best of our knowledge the combination of PCA, CA and SRA has not been used so far in the study of molecular structure-retention behavior relationships. ExperimentalThe HPLC system was identical to that described in ref. 5. The flow rate was 1.0 ml min -1 and the detection wavelength was set to 240 nm. Mixtures of ethanolwater were used as eluents; ethanol concentration ranged from 70 to 90%v/v (in steps of 5%v/v). The eluents were not buffered. In agreement with the results of refs. 10 and 11, we found that the column temperature exerts a considerable effect on the retention. The column was thermostated at 22.5±0.5˚C in order to reduce the influence of temperature oscillation. The chemical structure of barbituric acid derivatives is depicted in Table 1. They were dissolved in the eluents in 0.05 mg ml -1 concentration. The retention time of each compound in each eluent was determined with three consecutive determinations. The logarithm of the capacity factor, k′ was linearly correlated to the ethanol concentration, V (vol%): log k′=log k′ 0 +bC (1) where log k′ 0 and b are constants to be determined by the least square method. For the determination of the molecular parameters significantly influencing the retention, the intercept and slope values of Eq. (1) were correlated with the physicochemical characteristics of barbituric acid derivatives, using PCA followed by CA and two-dimensional nonlinear mapping. The physicochemical parameters included in the calculation were: π=Ha...

Solvent Strength and Selectivity on a Porous Graphitized Carbon Column Separated by a Spectral Mapping Technique Using Barbiturates as Solutes

“…The b values and their standard deviations determined in the presence of methanol, 19 ethanol, 20 acetonitrile, 21 tetrahydrofuran 5 and dioxane 22 were included in the calculation. SPM was carried out twice:…”

“…The physicochemical parameters of barbiturates were taken from Ref. 20; those of organic modifiers were calculated by the additivity rule.…”

Porous graphitic carbon sorbents in biomedical and environmental applications

“…They found a linear decrease in the logarithm of the retention factor with the concentration of the organic modifier. and Forgacs and coworkers studied the effect of the concentration of the organic modifier on retention for different classes of compounds (Cserhati and Forgacs 1993;Forgacs and Cserhati 1995, 1997, 1998a, 1998b, 1998cNemeth-Kiss et al 1997;Balcan et al 1997) such as aniline derivatives ) phenol derivatives ) phenoxy acetic acid derivatives (Cserhati and Forgacs 1993) and steroids (Forgacs and Cserhati 1998a, 1998b, 1998c. They also found a linear relationship between log k and the concentration of the organic modifier for all those chemical classes.…”

“…The PGC with an alkaline eluent consisting of tetrahydrofuran-water (7:3 v/v) with 1% ammonia gives excellent separation. Forgacs and co-worker determined the retention behavior of 45 barbituric acid derivatives in various unbuffered eluent systems: methanol-water, ethanol-water (Forgacs and Cserhati 1998a, 1998b, 1998c, dioxane-water (Forgacs and Cserhati 1998a) and acetonitrile-water . Linear correlations were calculated between the logarithm of the capacity factor and the concentration of organic modifier in the eluents.…”

Spectrofluorometric Resolution of Closely Overlapping Drug Mixtures Using Chemometrics Methods

“…All of these methods are based on improving the selectivity of the coexisting components. Chemometric methods, such as factor analysis, [6][7][8][9][10] have become even more popular in solving problems that are difficult to handle using conventional techniques, without having to resort to expensive or time-consuming procedures. Especially, three-way resolution and calibration methods [11][12][13] play important roles in solving the problem of closely overlapping fluorescence spectra.…”