Factors other than the column may affect performance of a chromatographic system. While usually less important than the column, mobile phase and sample, these extracolumn effects may become important under certain circumstances.
Extracolumn elements in the chromatographic system:
(1) injector
(2) tubing
(3) fittings
(4) detector
Extracolumn effects may be an issue if:
(1) the observed plate number (N) is < 80% of the expected plate number under working conditions (not ideal manufacturer conditions), AND
(2) there is a need to improve resolution
Extracolumn effects tend to negatively affect peaks that have shorter retention times more than those with longer retention times.
Screening for an extracolumn effect consists of examining the number of plates for peaks at the beginning, middle and end of the run.
Normally the early peaks should be narrower (higher N) than later peaks.
If the plate number progressively increases (N number late > middle > early, peak broadening early > middle > late) then an extracolumn effect should be looked for.
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