INCREASING DATA PRECISION IN REVERSED-PHASE LIQUID-CHROMATOGRAPHY LEADS TO NEW INFORMATION LEVEL

Reversed-phase liquid chromatographic systems as commonly used yield retention time data at a precision and reproducibility level of 0.05 to, at best, 0.01 standard deviation units within a set of several (typically 5-10) runs. This corresponds to a time resolution of some hundredths to some tenths of a minute. Improving the apparatus can reduce the data standard deviation to 0.001. At this precision level, several effects usually hidden in the data scatter band become clearly visible. This is demonstrated for the column dead volume determination via the t(n + 1)/t(n) method using n-alkane solutes in a octadecylsilane-methanol system. Whereas standard precision data yield erratically scattering results, improved precision data show an apparently linear decrease in the effective dead volume with increasing solute size. This observation can be explained by steric exclusion effects, which seem to have a far greater influence on retention data than is commonly assumed.