Yes. What you do is to run an initial "scouting" gradient. Choose the conditions to give a reasonable k* value (somewhere around 5 is a good choice). You can estimate the gradient time from the equations you mentioned at the beginning:

**tG = k* x S x Vm x ΔΦ / F** where ΔΦ is the gradient range expressed as a decimal fraction (e.g. 5% - 95% would make ΔΦ = 0.9). I usually use S = 5 as a convenient value (this is only an approximation in any case). Vm is the column internal volume (for reversed phase columns you can estimate this as

**0.5 x L x dc^2** where L is length and dc is column internal diameter) and F is the flow rate.

As Peter said, if you get a reasonably shaped peak somewhere in the gradient, then your compound was retained.

You can take things a step further: by looking at the difference in retention time between the first peak of interest and the last peak, you can make an informed choice about whether or not you need a gradient. If you need a gradient, you can make another informed choice about the range (initial and final %B). If you can do it isocratically, you can make a reasonable guess as to a %B to start with for method development. This is all stuff that we cover in our

Advanced HPLC Method Development course (shameless plug here!

).

We've actually put together a spreadsheet that does all the calculations. I just set up an auto-reply e-mail address for the download link, so if anyone is interested, send an e-mail to:

gradient-screening-request@lcresources.comYou can put anything you want in the subject or the body. You will get an automated reply with the download link. Obviously, please make sure that your spam filter is set to "whitelist" e-mail from lcresources.com so that it gets through. The "quid pro quo" here is that you will be added to our mail list to receive announcements about upcoming courses (you can unsubscribe from the list at any time).