Is there any body who can enlighten me on peak purity interpretation using a PDA, I am interested in what a purity angle and purity threshold means.
Does concentration plays a vital role in determing peak purity.

I thank you all in anticipation

Peak purity analysis is designed to detect the presence of an impurity that is coeluting with the analyte peak.

Waters has produced a number of documents that explain what peak purity is, how to interperte the results of a peak purity analysis and much more.

To see these documents, first go to the Waters web site (www.waters.com) then go to the applications pull down menu and choose applications library. Once there, search using the term peak purity and you should see a list of references. Some are PDF files, some are journal references.

Have fun

As a rule if your peak angle is less than your peak threshold than you have a pure peak. The software takes the spectrum at the peak apex and measures that against every other spectrum from each data point across the peak, this is where your peak angle and threshold numbers come from. If the difference is too large between the apex spectrum and one of the other points, then the software detects it as a co-eluting peak. This process can be repeated and for the millenium 32 software you can theoretically detect up to five co-eluting peaks. Hope this helps

i am working in toxicology were we are sometimes iterested in very small peaks (~0,001 Au). i noticed on our systems peak-purity-angels and match-angles on this level is not as easy as discriped above. sometimes looking at the spectra and the matches teles me that the match is perfect(?) ore the peak is pure, but the angles compared to the treshhold says different. anybody seen this?

in response to the last anonymous, I have seen that also. The criteria for a library match is not the same as the criteria for a pure peak. So at low conc. it may not show up as a pure peak. The signal is just not strong enough to counteract baseline effects, although it may be a pure peak. At that concentration a siginificant part of the peak you integrate is baseline and this will give you varying spectra across the peak.

The match angle/threshold is only using the apex of your peak to match against your library of known spectra. A match in this case is not implying a pure peak, it is simply stating that your compound of interest is in your peak. As described before the peak purity is matching the apex spectra against all other spectra within the peak. Hope this helps explain the difference in peak angle/threshold vs. match angle/threshold

In response to the last two messages, concentration will play an important factor when matching to a library standard. As you all know, the concentration of analyte will affect the shape of the UV spectrum. When you are matching to a library standard, make sure that you have included a Standard in your library, at or near the same concentration as the sample. There is no way around this, you must do this to have a meaningful match.

Now, as far as the inconsistencies with peak Purity numbers. Concentration will play NO part in determining peak purity. What will play the biggest part is what you have selected as a noise interval. The noise interval you select must be free from any peaks at any wavelength. If the noise interval is not free from any peaks, the purity angle and threshold will not be meaniful.

I also suggest tracking down some information from Waters or other vendors. Spectral contrast theory is not easily explained in a brief message. I hope this helps.