Peak shape problem

[vahur]

Hello,
I´m doing sugar analysis(glycose, fructose, maltose, lactose..) on zorbax carbohydrate(250 mm 5um). I use isocratic 70:30 ACN:water eluation. For the last few analysises my peaks have been distorted and look something like this

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(this is standard solution so this is not from other peaks). I have had the problem before but it diminshed after I changed the precolumn but not this time. My coworker says he wants to put the column in reversed and wash it but it does not seem a good idea to me(the information with the column always suggests to use it with one flow direction). I on the other hand think it would be better to try to wash the column with tetrahydrofuran(maybe there is a contamination). Which one is better idea or should I try something else?
Thanks in advance.

[Gerhard Kratz]

It looks like you have a small void volume on the column inlet. First I would Open the column (manufacturers please stopp reading from now) and check if there is a void volume. Minimum I would than change the frit, close the column and flush the column in reversed mode at low flow rate with ACN, without connection to the detector!!!!
If there is a void volume I would take some material from the column end of an used column and fill it up carefully. But than only use it in reversed flow!!
Hope that helps.
But it is only a short help. Be ready to purchase a new column.

[samani]

try to rise temperature
and diminish polarity of your eluant
if nothing you have to improve physic parameters and wach the system with methanol for sometimes
regards

[tom jupille]

try to rise temperature
and diminish polarity of your eluant
if nothing you have to improve physic parameters and wach the system with methanol for sometimes

No, Gerhard called it correctly. When you see the same problem on multiple peaks in a chromatogram, that is almost certain evidence of an inlet flow profile anomaly; either a void at the column inlet or a partially-blocked frit.

[vahur]

It looks like you have a small void volume on the column inlet. First I would Open the column (manufacturers please stopp reading from now) and check if there is a void volume. Minimum I would than change the frit, close the column and flush the column in reversed mode at low flow rate with ACN, without connection to the detector!!!!
If there is a void volume I would take some material from the column end of an used column and fill it up carefully. But than only use it in reversed flow!!
Hope that helps.
But it is only a short help. Be ready to purchase a new column.

Thank you alot. As I have never opened a column i just washed it in reversed mode with ACN and the results were pretty astonishing to me. The problem was solved completely as you can see from the chromatograms


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(peak areas were the same even though they seem different)
Can anyone explain to me what could have been the problem and what happened? Was it probably some kind of blocking contamination in the inlet?
Thanks alot so far to everyone.

[Gerhard Kratz]

Congratulation!
If it was a slight void on top of the column and you reversed the column, the void is at the end of the 25cm long column! There the void has no significant impact on the peak form anymore. But: the optimum packing density of the packing material will go, after 1 day, maybe 2 or 3, maybe in 1 week. If you will get peak shoulders or split peaks again, than it's really time for a new column.
Good luck.