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By amin askari on Sunday, June 6, 2004 - 05:58 am:
a problem for sepration of sulfate and phosphate
with carbonate eluent .
when work ion chromatography how effect composition of carbonate and bicarbonate on resolution of ions .
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By Einar Pontén - SeQuant AB on Sunday, June 6, 2004 - 01:47 pm:
When you are using {hydrogen carbonate/carbonate} buffer SO4(2-) and PO4(2-) will be most affected by a change of the CO3(2-) concentration in your mobile phase.
Try this first.
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By Anonymous on Tuesday, June 8, 2004 - 07:27 am:
The ratio of NaHCO3/Na2CO3 will change the pH of the eluent. This can change the retention of Phosphate with respect to sulphate. (Altering the concentration will change them too, but I assume you are trying to increase separation of these two peaks).
Depending on the column, the order of PO4 and SO4 can be reversed. If the peaks co-eluete, I suggest you dilute your sample and / or use a higher capacity column.
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By Chris Pohl on Saturday, June 12, 2004 - 04:54 pm:
To expand upon the comments above, one can generalize the effects as follows: bicarbonate has only a minor effect on the retention time of sulfate as it is fully ionized even when using 100% bicarbonate eluent. Changing the amount bicarbonate will only have a tiny effect on the retention time of sulfate. However, phosphate as a divalent species will elute before sulfate and as a trivalent species will elute after sulfate. Since the second pKa of carbonic acid is 10.33 and the third pKa of phosphoric acid is 12.38, the ratio of carbonate to bicarbonate will determine whether or not there is a significant percentage of phosphate in the trivalent form. An equimolar mixture of bicarbonate and carbonate should have a pH value of 10.3. At this pH phosphate should be around 1% trivalent. Under these conditions phosphate will elute before sulfate on most columns. Further decreases in the bicarbonate concentration will tend to move phosphate backward in the chromatogram toward sulfate. Depending upon the column and the concentration of carbonate, 100% carbonate eluent will result in phosphate eluting just before sulfate, coeluting with sulfate or eluting just after sulfate. Addition of hydroxide to the eluent system will move phosphate after sulfate.
a problem for sepration of sulfate and phosphate
with carbonate eluent .
when work ion chromatography how effect composition of carbonate and bicarbonate on resolution of ions .
-------------------------------------------------------------------------------------------------------
By Einar Pontén - SeQuant AB on Sunday, June 6, 2004 - 01:47 pm:
When you are using {hydrogen carbonate/carbonate} buffer SO4(2-) and PO4(2-) will be most affected by a change of the CO3(2-) concentration in your mobile phase.
Try this first.
-------------------------------------------------------------------------------------------------------
By Anonymous on Tuesday, June 8, 2004 - 07:27 am:
The ratio of NaHCO3/Na2CO3 will change the pH of the eluent. This can change the retention of Phosphate with respect to sulphate. (Altering the concentration will change them too, but I assume you are trying to increase separation of these two peaks).
Depending on the column, the order of PO4 and SO4 can be reversed. If the peaks co-eluete, I suggest you dilute your sample and / or use a higher capacity column.
-------------------------------------------------------------------------------------------------------
By Chris Pohl on Saturday, June 12, 2004 - 04:54 pm:
To expand upon the comments above, one can generalize the effects as follows: bicarbonate has only a minor effect on the retention time of sulfate as it is fully ionized even when using 100% bicarbonate eluent. Changing the amount bicarbonate will only have a tiny effect on the retention time of sulfate. However, phosphate as a divalent species will elute before sulfate and as a trivalent species will elute after sulfate. Since the second pKa of carbonic acid is 10.33 and the third pKa of phosphoric acid is 12.38, the ratio of carbonate to bicarbonate will determine whether or not there is a significant percentage of phosphate in the trivalent form. An equimolar mixture of bicarbonate and carbonate should have a pH value of 10.3. At this pH phosphate should be around 1% trivalent. Under these conditions phosphate will elute before sulfate on most columns. Further decreases in the bicarbonate concentration will tend to move phosphate backward in the chromatogram toward sulfate. Depending upon the column and the concentration of carbonate, 100% carbonate eluent will result in phosphate eluting just before sulfate, coeluting with sulfate or eluting just after sulfate. Addition of hydroxide to the eluent system will move phosphate after sulfate.
