Wavelength Rnge for PDA Peak Purity

[gbalock]

Typically when we perform a method validaton, we evaluate the peak purity from about 210nm to 300nm. Is this enough or is it too much. What wavelength range do you use, or do you use a range around the analysis wavelength?

[amitavaghosh]

we should use wavelength range 210 to 400nm

[juddc]

Your wavelength range for peak purity really depends upon two factors: The UV absorbance spectrum of your compound and the background absorbance of your mobile phase. If you are assaying a sunscreen with an absorbance maximum of 360 nm and you're using an acetate based mobile phase, 210-300nm won't do too well. You'd want to be between 230 - 450 nm. On the other hand, if you have an abs max at 234 with nothing beyond 250 nm and are using a phosphate-ACN MP, you might want to look at 205-270. It all depends on what you'relooking at and the conditions you're using.

[gbalock]

Juddc,
Thanks for the input. To rephrease the question how much is enough, 50nm on either side of yoiur analysis wavelength, 100nm?