Column peak shape

Question

Hello team, 
 We have an issue of peak shape deterioration during the analysis(Column details: Zorbax Eclipse plus C18 4.6 x 100 x 3.5&micro;m) Pressure was constant throughout the sequence. 
 Tried with other eclipse plus column with same dimensions, but we got the same peak deterioration after every 3 or 4 sequences. 
 We use dedicated columns for each product. 
 Mobile phase details: Potassium Dihydrogen phosphate buffer at pH 8.5(Mobile phase-A and acetonitrile(Mobile phase-B) 
 Column temperature: 40 &deg;C. Filtered the Mobile phase with 0.45&micro;m PVDF membrane filter. 
 Column washing post sequence with 80:20 Methanol and water. 
 Kindly suggest recommendations to improve the peak shape and column.

Dr. Know · Accepted Answer

Hi sravan, 
 you use a buffer at pH 8.5 which is only defined in 100% water. Your eluent is 80% methanol, i. e. your pH increases 1-2 units and is therefore above pH 9. 
 This is, unfortunately, a very common mistake. But to answer your question directly pH 8.5 does not affect the column, but you are way higher. 
 Knowing more about your analyte structures, we might be able to give you better advice. 
 Regards, 
 Norbert

Column peak shape

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