Principal component analysis in liquid chromatography proton nuclear magnetic resonance: differentiation of three regio-isomers

H-1 LC-NMR is recorded of a 1:2:1 mixture of 2,6-, 1,3- and 2,3-dihydroxyna phthalene isomers which closely elute and have several resonances in common . The data is analysed using Fourier transformation techniques and baseline correction. All protons resonate in the aromatic region in which all furth er data analysis was performed. PCA is applied using various different type s of scaling, namely: (1) none; (2) standardising the variables prior to PC A; and (3) normalising the scores and loadings after PCA keeping only the m ost significant PCs both on the full dataset and the dataset after selectin g the most significant variables. A variety of graphs are presented, both o f pure scores and loadings plots, and loadings plots with an added chemical shift axis. The merits of each type of display are explored. (C) 2001 Else vier Science B.V. All rights reserved.