decrease of theoretical plates

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lakshminarayana's picture
decrease of theoretical plates

hai this is lakshminarayana ,i am using symmetry c18(waters)column . using buffer is ammonium acetate .injection to injection what i absorbed is theoretical plates is decreasing . is there any problem by using this to calculate theoretical plates .how to fix the limits.

Dr. Analytical
Dr. Analytical's picture
Theoretical plates are

Theoretical plates are calculated from the retention time and peak width:

N = 16 (tr/W)2.  tr is retention time and W is width at base.

Ammonium acetate is a common buffer for LC systems, so it should not cause any problems.  However, buffers can decrease the performance of a column, but this usually requires a long time (months).  Also, the buffers can be mildly corrosive to the LC equipment.  So, always remove the buffer if the system is not being used.

Please give us more information about your separation system.  When the theoretical plates decrease, how does the peak shape change?  Are the peaks broader, or tailed?