Peak compression induced by large volume injection of hidrophobic alcohols in reversed-phase liquid chromatography

Injections of high volumes of samples containing hydrophobic diluents are possible in reversed-phase liquid chromatography, and in some cases an effect of peak compression can be observed. Three classes of organic compounds were studied as target compounds for peak compression: pharmaceuticals (pentoxifylline; salicylic acid; caffeine, ethylparaben); pollutants (simazine, atrazine), and natural compounds from tabacoo provenience nicotine). Five aliphatic alcohols from butanol to octanol as hydrophobic solvents were used as sample diluent in the view of influencing the peak efficiency for the studied analytes. Among them, only pentanol, hexanol and heptanol were observed to produce peak compression resulting in a very high chromatographic efficiency for the studied compounds, while butanol and octanol allowed large volume injection with gradual decrease of the retention time of the dissolved analytes, but without their peak compression. Pentoxifylline, salicilic acid, simasine, are some examples of analytes that are characterized by sharp chromatographic peaks (high chromatographic efficiency, with over 10,000 plates/column), when high volumes of pentanol or hexanol (50 – 100 μL) solutions are injected. Chromatogram monitoring was performed by UV-spectrometry detection or refractive index detection.