[QFIPGUTIESA]

Hello.

I just started to use a PDA detector and I have found the 3D graph, but I don't what to see, I mean I know it works to get purity of the compounds but I don't know what parameters I must look for or how can I know if my signal on single wavelenght is affected by other compound.

Thanks

[Arkcon]

Umm ... OK.  That question is kinda all over the place -- seems to be made up of about half of three unconnected questions.  I'm going to guess you're looking at the 3-D output of an HPLC run using a PDA as a detector.  You're possibly looking at the 3-D false solid projection.  Maybe you'd like to try looking at the 2-D contour plot -- that will have time vs wavelength plotted, and you will see intensity as concentric contours.  That is the same as a terrain contour map, which you may have seen before if you've seen a map like that.  Or maybe not.  TMMV.

Presumably you know what wavelength your product has.  If you do, you should be able to see the different wavelengths as the sources of  possible impurities, but we will need to more about the sample and analysis conditions.

[QFIPGUTIESA]

Hello Arkcon and thanks for answering.

Mobile phase is Methanol:water (98:2) and the compound is retinyl palmitate, the max wavelength is 325 nm.

On the contour plot I can´t see any other significant  signal at the same wavelength, I suppose that´s good because I have no other compound added to my interest compound or am I wrong?

[Arkcon]

Yes.  But if you're interested in the purity of your peak using a PDA detector, you might be able to find the software's peak purity function.  It will compare the spectra across multiple slices of the peak, and give a threshold of probability that the peak is pure, based on subtle spectral changes -- not necessarily another wavelength peak in the extracted spectrum, but also any change in the spectrum that might be caused by another wavelength hidden underneath.  This is a more powerful function of the PDA detector.  You will determine what threshold is significant, using the limit of detection you require for you analysis --  because the very edge of a n HPLC peak will always give a shitty purity test.  And logically, towards the end (or or beginning) of an HPLC peak is when a chemically distinct peak is likely to occur.

[QFIPGUTIESA]

OK.

I'll look for that funtion on the software and try it.

Thanks a lot for your help.

If I have any other question I'll post it.