Optimization of the flow rate in high pressure liquid chromatography of explosives

The height of a theoretical plate of 7 nitroaromatic substances and 2 aliphatic explosives was determined in dependence on the flow rate. The optimal flow rate for the maximum of the number of theoretical plates is in the area of 0.4 to 0.6 ml/min. For difficult separations this should be considered, since most HPLC instruments are used in the area of 0.7 to 1.0 ml/min. The amount of theoretical plates was calculated and presented in dependence of the flow rate. The height of a theoretical plate was plotted against the retention time and the capacity factor. The optimal area for the separation of the substances was at a capacity factor of 2 to 10. The van Deemter equation and the Knox equation were adjusted using 2,4-dinitrotoluene. The data were fitted iteratively and the constants were determined. The equation for the conversion of the flow rate for other column diameters was shown, and using an example, the dependence of the flow rate on the column inner diameter and the flow rate was presented graphically.