SI-50 application and Shodex catalog

Record: 870

Category: Column Problem
Product: SI-90 4E
Sample:

Question
I was also looking at the response from your colleague in Japan, he suggests dissolving 1.008g of sodium bicarbonate into 1.0L of solution. This would make a 0.012 M solution or 12 mM solution, am I missing something here?

Answer
I see some significant digit discrepancy. I think the Japanese rational for the math goes like this: The 1.0 L is two significant figures, so when the calculation gives 0.011999 M; rounded to two significant figures it is 0.01 M or 10 mM. I’m not saying it is accurate; I’m just explaining the rational. I will make our tech support aware of the discrepancy.

Personally, for a 10 mM solution I would use 0.840 g NaHCO3 in 1.00 L. I’m not sure a 2 mM difference will change the retentions times significantly.

So the pressure of your column has decreased from 900 psi to 700 psi after the cleaning procedure. But your retentions times are still longer than what is shown on the application? You mention that the fluorine is eluting at 18 min rather than 5 min from the application, has the retention time improved since washing the column?

At this point, I do not think changing the eluent conditions are going to improve the retention times. Perhaps the problem is the contaminant exists as benzoate with the ionic interaction with the packing material making it difficult to remove. Either the use of organic solvent did not remove the benzoic acid or it still exists on the column. You could try running more acetonitrile through the column or use the washing procedure that uses 10x concentrated eluent to see if the retention times improve as a last resort.

I would consider getting a new column is the washing procedures do not work. However, you will need to find a way to remove the organic acids before injecting them onto the column or you will run into the same problem again.

I will forward this and your delayed retention times to our tech support in Japan and see if they have further recommendations.

 
 
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