Chromatography Forum

By Meifi on Wednesday, July 28, 2004 - 05:54 pm:

Hello...
I need suggestion of chromatgraphy system for risendronate determination. We have used ion pairing chromatography with 0.005 M Tetrabutyl amoniumhydrogen sulfate, but the peak is fat.
Anyhelp will be appreciated.

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By Chris Pohl on Friday, July 30, 2004 - 01:10 am:

Your problem is most likely due to the fact that this compound is a decent chelating agent and metal contamination of your sample, column and/or eluent is responsible for the tailing due to partial separation of the complexed and "naked" forms of the chelator (along with on column interconversion of the two forms). See my comments in another recent thread "Mobile Phase Additive for Chelating Agent" for suggested corrective actions.

Hello,everyone: I have same difficult in this issue, the tailing is disappeared when I add EDTA to the mobilephase, but a "ghost peak" is occoured at about 7min(major peak is about 10min) in sample solution(which is not occoured in blank), and the LC/MS/MS confirmed that the "ghost peak" is EDTA, why?

zhengmin,

If I understand you correctly, you are interested in understanding why you see a "ghost peak" for EDTA even though your sample didn't contain any EDTA. It is common to see a ghost peak when you add an eluent component which is visible to your detector. Whether it is negative or positive depends on the relative affinity of your analyte and your eluent additive. In the most common case, the presence of an observable peak in the chromatogram when working with an eluent system containing a detectable eluent component is caused by your sample disturbing the equilibrium between the stationary phase and the mobile phase with regard to this component. If the analyte has a higher affinity for the stationary phase than the eluent additive, this will displace at least some of the eluent additive into the mobile phase. This disturbance in equilibrium between the mobile phase and the stationary phase will be translated through the column as if you had injected the eluent component. In this case, since risendronate has a longer retention time than EDTA, it can be expected to operate in the manner described above. If you are interested in changing the location of the ghost peak, switch to a different chelating agent as your eluent additive. For example, NTA will undoubtedly elute significantly earlier than EDTA whereas DTPA can be expected to elute significantly after risendronate.