Chromatography Forum

I always have one question. As detector become more sensitive, will peak become fatter? I always observe that MS peak is much fatter than UV peak. if this is the case, how can we calculate intrinsic plate number for column?

As detector become more sensitive, will peak become fatter?

So long as you are within the linear range of the detector, the answer is "No". It can look that way if a large part of the peak is off-scale, but peak width (measured as either baseline width or width-at-half-height) remains constant. If you go above the linear range of the detector, then width measurements will become unreliable.

Hi

Check your tubing and connections between the detector and the MS, you maybe getting some band broadening, hence the wider MS peaks in relation to the UV.

Thanks. this makes sense.
I was totally off when I posted this thread.

As detector become more sensitive, will peak become fatter?

So long as you are within the linear range of the detector, the answer is "No". It can look that way if a large part of the peak is off-scale, but peak width (measured as either baseline width or width-at-half-height) remains constant. If you go above the linear range of the detector, then width measurements will become unreliable.

I am going to assume the simplest interpretation of your question. That you are comparing sensitivity [really limit of detection] between UV and MS and the MS peaks are also broader. As LCBob suggested individual fittings with large void volumes are most frequently to blame. Another major culprit can be the UV detector cell especially if it is older generation. Next, the exit tubing from the UV detector may be of much large ID. A final area of broadening is frequently in the valved inlet of the MS itself.

If you suspect the UV cell, either remove it or perform a split prior to the UV detector as a test to see if peak width reduces for the MS. As a general rule keep all tubing < 0.010" id and if possible 0.007" id even up to the mass spec.

Exit tubing on a cell contributing to peak broadening?

Exit tubing on a cell contributing to peak broadening?

Peak broadening on the MS when it's connected after the UV - yes