Chromatography Forum

dear friends...

[quote]The Surveyor PDA Plus Detector is a photodiode array detector that is capable of scanning the UV/Vis range from 190 to 800 nm. In addition to collecting scan data, the detector is capable of simultaneously collecting up to three discrete channels. You can use this capability to set the bandwidth and data rate parameters for the discrete channels separately from those of the scan data.[/quote]

Question: why do we need to set 3 discrete channels? if the PDA scans from 190 to 800, why do we set (discrete) wavelengths like 254? 260?

Thank you.

Question: why do we need to set 3 discrete channels?

Answer:

You can use this capability to set the bandwidth and data rate parameters for the discrete channels separately from those of the scan data.

Admittedly, not something that most people would want or need.

Yes, but as I understood, the software needs at least one channel to show us the spectra, chromatogram etc, like this one below (with 3 channels). The software allows us to set 3 different channels.
click to see picture

What if I dont set any channel, how will the software give me any collected data?

Thank you.

is it because such channels might get us the best results?

thank you.

I don't have any "hands-on" experience with that detector. As a general comment, many instruments (and software, for that matter) have "features" that very few people actually use.

"is it because such channels might get us the best results?" - ask the PDA producer/provider or check on your own samples and methods

Thank you very much.

In many cases a PDA is purchased for use to determine the concentration of a few components. In this case it is usually easier to set up channels on a PDA and use it as a multiple wavelength UV detector.

Tom's answer (as usual) was correct.

The point is that you can use the discrete wavelength channels to produce data at a very fast rate so you get many measured points across a chromatographic peak, at the wavelengths you intend to use for quantification. Many points across peak means accurate quantification.

Meanwhile you can use a much slower rate of collecting spectra, and the spectra can be used to confirm that you have the expected UV spectrum for the expected product. Collecting full spectra as fast as you collect individual wavelength measurements would be too much data for some elderly systems to handle.

In our less-than-cutting-edge LC-MS system, if we collect MS data and UV spectral data as fast as we would like, we encounter the occasional inexplicable system crash, so I do indeed use this feature of the Surveyor detector from time to time.