Peak Shapes

[wheeltops]

Here's a straightforward question. Peak shapes when using NPD detectors are notorious for tailing. Why? What is it about the NPD geometry or function that causes the peaks to tail?

Any thoughts?

Cheers

[dblux_]

Here's a straightforward question. Peak shapes when using NPD detectors are notorious for tailing. Why? What is it about the NPD geometry or function that causes the peaks to tail?

Any thoughts?

Cheers

low make-up flow ?

[chromatographer1]

Most NPD detectors sense analytes that have a great tendency to absorb in injectors, columns, and the bare metal parts of the detector. They contain nitrogen and phosphorus.

It is the nature of the beast, not the gun that shoots it.

best wishes,

Rod

[thohry]

Most NPD detectors sense analytes that have a great tendency to absorb in injectors, columns, and the bare metal parts of the detector. They contain nitrogen and phosphorus.

It is the nature of the beast, not the gun that shoots it.

best wishes,

Rod

I analyzed organophosphorus pesticides by both NPD and MSD and they all showed tailing.

[wheeltops]

Most NPD detectors sense analytes that have a great tendency to absorb in injectors, columns, and the bare metal parts of the detector. They contain nitrogen and phosphorus.

It is the nature of the beast, not the gun that shoots it.

best wishes,

Rod

While this is a good point, I don't believe it's the whole answer.
Thohry writes that peak tailing is evident on both his/her NPD and MS detection systems but, following severe peak tailing on my own NPD system I transferred the OPP method I was working on to an MS system which exhibited virtually no peak tailing at all.
To borrow your own analogy, I think the beast is rather more elusive than you suggest.

[chromatographer1]

Of course, you are right. Without a visual clue it is difficult to determine how bad the tailing is.

Misinstallation, poor trimming of columns, dirt and other problems can be issues. My experience with a NPD was a kind one. I never had MUCH tailing although the peaks were not often perfectly symmetrical.

USUALLY the problem is with the operator, not the equipment.

It is always good to complain to the GC vendor. They often have cures that help, especially training.

But any detector can make problems for the poor overworked chemist.

I hope wheeltops finds a solution.

best wishes,

Rod

[AICMM]

wheeltops,

While not an expert on NPD's, I would throw out a couple of comments for you to consider. First, their mechanism of operation is actually an interaction just above the surface of the bead so they have to come in contact (or close to it) to the surface of the active bead. Second, the bead is a heated ceramic material which is going to be somewhat porous and reactive by it's very nature. And, as noted by Rod, the compounds you are usually talking about with NPD are somewhat sticky anyway.

There are beads that are supposed to be better for tailing and I would recommend you get a hold of Paul Patterson at det-gc.com if you want to get more info on the different types of beads available for NPD detectors.

Best regards,

AICMM