Hello,everyone,I want to ask a question:should I get a same RRF from different UV detectors,(for example;waters 2487 and agilent1100 MWD).I test one of samples for RRF, get the value : RRF=1.5 from 1100MWD,and RRF=1 from 2487.What wrong with me?

is your Waters detector a diode array one?

The 2487 is a VWD, the 996 is a PDA.

we can obtain the same result at 2487 and 996.but differ from aglinet1100 MWD.

I'm sorry, but, I'm not sure:
MWD is for Multiwavelength Detector
VWD is for Variable wavelength detector
PDA ?
I'm asking that because the only reason I may imagine for such a difference is a different kind of detector (but still it seems to me quite high).

Briefly, a photodiode array detector generates a chromatogram by extracting a single wavelength, either one you specify or the local lambda max. You should recheck how you've set it up to see if your PDA is setup to the same wavelength as your other detectors. A different acquisition wavelength could cause a slight RRT shift.

Remember a PDA detector has to scan an entire range of wavelengths, and may be set to a slower acquisition rate in the method. This could also cause a slight retention time shift.

I've said slight twice, and I mean it. The large retention time shift you observe is probably caused by something else. Is the flow cell for one of your detectors a semi-prep flow cell with a wide bore? When you swap detectors, do you use the same connection tubing?

R.C:the flow cell is not semi_prep flow cell with a wide bore. and the connection tubing is not entirely same.

Dear Anon,
R u using different detector using different HPLC system?? the method u r using , is it gradient ? if yes, the difference in RRT has nothing to do with detector. It could be cos of difference in dead volumn and mixing chamber volumn in different HPLC system.every HPLC system differ in zero dead volumn on account of change in tubing, mixing chamber etc.it affect not only RRTs but gradient profile as well.

Din

i'm sorry (again!) but I understood RRF as Relative Response Factor, not Relative Retention Time.
Anyway, if we are discussing about RRF and PDA is Photo Diode Array, the difference of response factor can be due to the bandwidth that you are using around your analytical wavelength. If you are working at a WL which is close to the UV maximum of one of your spectra, maybe the bandwidth includes it, while the single WL, of course, doesn't. This can influence very much the absolute, and the relative, response. A similar problem was discussed in "Is all detector are same ? " a couple of weeks ago.

Oops, sorry everyone. I misread RRF as RRT. Please disregard my comments as pure random raving. Cheers all.

Depending on the substances you are detecting the rrf value can change dramatically due to very small changes in wavelength. Thus you should check the wavelength calibration of your detectors as due to prolongued operation there could be an offset.

Every detector is using a range of wavelength (bandwith) to meassure UV absorbance, not only a single wavelength.
If the bandwith differs with different detectors, there is a chance - when the spectra of a peak is stronly increasing for example at a lower uv - that one detector (with smaller bandwith) isn't meassuring this increase of absorbance. A second detector with wider bandwith is meassuring this increase of absorbance and so gaves a stronger signal than the first detector at the same wavelength.
If you have a pda detector, meassure the spectra of your peak. If the spectra shows a strong increase (or decrease) of absorbance near the wavelength you have choosen for detection, you have the explanation for your problem.

Extending labcat: Why so much worry about rrf? You should calibrate your system.

Sorry, can anybody explain me what are the advantages of the PDA? Why should I adquire one?? Is there anything better than that?
Thanks,
edgar

PDA is a very efficient tool to evaluate the best wave lenght your molecule is absorbing at.
You also can have an UV scan, that works as a "fingerprint" of your component (library).
Finally, you can detect coelution of some molecules.
The PDA is very usefull in R&D while developping analysis method.
But the response is less accurate than a single wave lenght detector.

Edgar, there is at least one spec scanning UV detector (used to be Linear, is something else now?). I bought this as it was more sensitive and had higher wavelength resolution as PDA at that time. It seems that modern PDA´s have cought up with it, at least regarding sensitivity, but I don´t know whether grating spectrometers have also improved.

A PDA detector is more of a research tool and it is very handy during the initial stages of method development to check for co-elution. The manner in which a PDA detector and a standard UV detector works are different therefore there will be a difference in the RRF factors obtained.
The modern PDA detectors are more sensitive but I would not use a PDA on a daily basis for LOD work.
I agree with an earlier comment that as long as your detectors are properly calibrated and maintained then the difference in RRF between them becomes irrelevant.
Hope this helps

Thank you guys so much!! I never thought this forum would be so helpful. My job is actually in quality assurance. We use a UV detector now and I think it workd fine. The idea is to improve accuracy and precission of results. If PDA is not the answer, then what can I do. And I am talking from the hardware stand point.Evidently there will method to work on but now we are trying to concentrate on equipment.
Thanks,
edgar

What is the difference between a uv detector and a photo diode array detector ?

I am a student can u help me anser these

1. What is the relationship between method development and a stability indicating assay .

2 . Could you send me to a website where i can find out the simlpiest way to understand some of the analytical tools used in method devlopment, uv, nmr, ir hplc , uv dta etc,,, and when to use what and the disadvanteg over one or the other .

Thanks
Stephanir