There was a case in which the theoretical plate was reduced and a peak tailing occurred (see chromatogram A) after a conventional column (150 X 4.6mm I.D.) had been replaced with a short column (75 X 4.6mm I.D.) to reduce the analysis time. Although this problem was corrected by replacing the injector, the cause remained unclear. The primary difference between before and after the replacement of the injector was the amount of sample dispersion. The shorter the retention time, the more a peak shape becomes adversely affected by extracolumn dispersion.
As a result, extracolumn dispersion had greater influence on the peak shape with the short column than on that with conventional columns, and caused the peak shape deterioration. Although it is often thought that such problems are due to an insufficient number of theoretical plates and poor peak shapes are caused by a defective column, some cases are caused by hardware problems such as dead volumes of the system. The impact of extracolumn dispersion indeed is often overlooked when using a short column. Even with the short column, a tubing system, an injector and suchlike should lead to minimal extracolumn dispersion.