Theoretical Plate count

[Narendra]

Dear All viewer / Replier / Reader

Can Injection Volume & Concentration of sample affect theorectical plate count ?

Thanks in Advanced

[tom jupille]

Depends on the circumstances.

Injection volume first.

If the sample is dissolved in the mobile phase (or a diluent of approximately the same strength) then injection volume is a part of "extra column volume". As a rough approximation, if the injection volume is more than about 15% of the volume of the narrowest peak of interest, then the effect will be noticeable.

If the sample diluent is significantly weaker than the mobile phase, then injection volume usually has no effect (unless it is really huge).

If the sample diluent is stronger than the mobile phase, then the injection can be a major contribution to band broadening (i.e., decrease the plate number).

Now sample concentration. If you are within the linear range of the method, then plate count should be independent of sample concentration. If the plate count decreases for higher concentration samples, this is evidence of overloading.