Chemstation and VWD timetable

[lcrandall]

Hello,
I have the latest Chemstation B0302 and am trying to do a wavelength timetable.

Pretty much, I want to change the wavelength by one step every 30 sec. I programed the timetable, but am not sure that it actually ran as set up.

I can't figure out how to even look at this data (if it ran correctly) in Data Analysis. This is a non-3d version of Chemstation, but that shouldn't matter, right?

Thanks,
Lisa

[unmgvar]

depending on your actual application, generally the detector needs to perform an autozero command.
depending on the instrument and other parameters it can take several seconds or more.
maybe 30 seconds is to short a time. you switch before the detector is actually ready on to see anything so you might be getting nothing.

maybe try a longer step time of maybe 2-3 minutes to see if the detector does it correclty

[lcrandall]

Thanks unmgvar
I'm not sure if it ran correctly because I don't know how to view this kind of data in Chemstation.
I just ran some Agilent diagnostics on the detector and it failed wavelength calibration. I'm really not sure what to do from here.

[HPLCCONSULT]

This is pretty straightforward though a few basic things should be kept in mind.

You asked about "how to view" this in ChemStation. Simply load the signal file you used for the analysis in the the data analysis screen. Keep in mind that it will be labeled as a single wavelength in the file info, but in fact you changed the wavelength during the run so it will look rather "odd" (sharp transitions from the baseline being offset).

If you change the wavelength during a run (with solvent flowing) you will throw off the zero (you can re-zero on the fly, but it may fail due to the moving liquid). As noted, the process takes time and is not meant to replace a DAD. The real purpose of the feature is to use a VWD to perform a scan (like a DAD) with the flow stopped during the run. This feature was available in all the HP VWD systems and can be useful when you do not have access to a DAD (Simply park the peak in the flow cell and set the scan range. The result is similar to a DAD spectra).

BTW: You have a 2D HPLC system so you can really only monitor one wavelength at a time for an analysis (practically speaking). As I mentioned, there are tricks such as stopped flow analysis and using the timetable to change the wavelength during a run which can net you more info. These features work best if the baseline is stable, quiet and the detector balanced at the start.

[lcrandall]

Great, thanks.
I believe that my problem of not being able to see the change in abs due to the wavelength change is that the lamp was kaput. I ran a bunch of diagnostics through Chemstation and they failed. I will try again with a new lamp, and hopefully will be able to see it.
I had the pump flow=0 and balanced at the start. So, I think it's coming down to the failed lamp.
Thanks!
Lisa