Improved standardization in reversed-phase high-performance liquid chromatography using 1-nitroalkanes as a retention index scale.

A retention index scale based on 1-nitroalkanes was introduced for reversed-phase high-performance liquid chromatography. The retention behaviour of nitroalkanes was examined using two different ODS-silica columns. The nitroalkanes are stable compounds having high UV absorbances at 200-220 nm. The correlation between the logarithm of the capacity factor and the carbon number was linear from the second homologue. The compounds up to 1-nitrohexane are easily available commercially, and they cover the retention range for the majority of toxicologically relevant substances. The retention indices of several test compounds showed that the scale based on 1-nitroalkanes is comparable to that based on alkyl aryl ketones, and additionally may cover the early eluted compounds, for which reference compounds on the alkyl aryl ketone scale are not available.