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HPLC and Ion Chromatography Co-elution Primer

Looks can be Deceiving

Co-elution in HPLC and Ion Chromatography

What is it?

Co-elution is the occurrence of one single or almost single, eluted chromatographic peak, where the peak is actually the manifestation of the presence of more than one analyte.

This is often visualised as peak tailing, apparent peak splitting, a seemingly single peak which is actually an extraneous peak/s from a previous analytical run or a seemingly single peak which is actually the elution of more than one analyte.

Why does it occur?

Co-elution is due to the unresolved chromatographic peaks of more than one analyte and/or carry-over from previous injections.

How can we check for Co-elution?

A scientist must be certain that each chromatographic peak seen, represents a

single analyte from the current chromatographic run.

In order to clarify which peaks are the products of co-elution, the nature of each chromatographic peak should be checked.

For the purpose of co-elution detection, there are some detectors which lend

themselves very well to scanning chromatographic peaks as they elute,

providing that each analyte has its own discernible profile/spectrum.  

These detectors include mass spectrometers, ultra-fast

scanning UV/Visible HPLC detectors, diode array, some

scanning fluorescence, and scanning voltammetry detectors.

These detectors may help to elucidate the Peak Purity of a

chromatographic peak.

There are limitations, to the above detection methods,

particularly if one or more analytes are very closely related, if the spectra are similar, or if the analytes do not have

discernible spectra/profiles.

During method development another analytical confirmatory

technique, such as a mass spectroscopy, X-ray fluorescence, X-ray

diffraction and nuclear magnetic resonance etc., may be used to check the identity of each eluted peak.

Tips for better separation of Analytes within the Co-eluted peak

Cecil Instruments Limited  

Milton Technical Centre, Cambridge  United Kingdom      telephone  +44 (0)1223 420 821