Difference Between VWD & Dual wavelength

[Chromatocrat]

Hi Experts,

Is there a defference between Agilent Programmable Variable Wavelength Detector & Waters Dual Wavelength UV/VIS detector in connection with pharma analysis & Pharmacopia?

regards,

[DR]

Both are good detectors, capable of putting out 2 different wavelength channels or analog signals at once.

Which would be better for you is probably a function of your data system.

[Dan]

A minor correction, the Agilent VWD has only one wavelength output. It is the Agilent MWD (multiple wavelength detector) that has 2 (or more) output channels. At least that is if my memory serves me correctly, I haven't worked with the Agilents in a while.

Regards,
Dan

[unmgvar]

a VWD is a Variable Wavelenght Detector, meaning you can change wavelenght, especially within your run.
a MWD is a Multi Wavelenght Detector meaning you can see several wavelenght in parallel in parallel channels.
in the past MWD were only detectors that had PDA optics.

today a VWD can be a MWD but not necessarely and a MWD is always also a VWD. the most important question is what are the optics?

is it a PDA optic or a monochromat optic.
a monochromat detector will have a slower speed when working as a MWD. how fast depends upon the distance between the wavelenghts and the number of channels that you wish to see. generally less then 5 Hz.

a PDA detector has the advantage of working at top speed if you need but the noise levels are such that you will loose sensitivity. by how much depends upon the application in it self. at very low level of detections a PDA detector is generally 6-7 less sensitive then a monochromat.

in your case both detectors have monochromat optics. for standard analitical work both will do the work.

it is possible that the waters rep will tell you about the possibility of doing applications with 2 channels, from my experience all the applications that i had like this were some of the more annoying ones and they were like this due to poor R&D and they could almost always be changed to be used in a normal VWD. the worst ones were those where you needed to use information from one channel to do calcualtion in the second channel. always needed to do those by excel (millenium could not do it, mabe today?)

[Chromatocrat]

Hello,

Thanks for the clarification.
That means both the detectors can acquire two signals. But acquiring two signals simultaneously will have to compromise on data rate and it may contributte some noise too?


regards,

[unmgvar]

well not exactely.

let's go by examples:

for the agilent detector you probably speak of the low end VWD. this detector can see only one channel- meaning you get 1 chromatogram.

for the Waters detector it is probably the 2489, dual wavelenght. this detector can see 2 channels in parallel. meaning that you get in one run 2 chromatograms. this function when used will affect the data sampling rate down. for standard analitycal work it will not matter, only for fast LC analyses.

both optics are monochromats so the noise rate for both will be very small.
i do not think that the dual channel specification makes a difference here if you have the possibility to switch the wavelenght within the run, which is more convenient.