Chromatography Forum

I am quite familiar with Empower and chromatograms etc but I have never been able to read a detailed description of what "curves" actually mean and when they are used or not used. There are curve options from 1 to 6 when programming instrument methods and gradients and up to now, the only detail I have been able to get was along the lines of "it controls the speed of your programmed action".

Can anyone here explain or link to the science behind curves?

Hi
Have a look at the help of Empower, there all the 11 gradient profiles are shown (use the "?" on the corresponding instrument method tab, or use search function in help)

Type 6 is linear change
Type 1 and 11 are step changes
All others are concave or convex changes

if you want to be able to reproduce your gradient on other systems forget about the concave/-vex types.
i've never used them and they can also be construced by several linear changes. Nowadays programming additional lines isn't a problem anymore

Yes, they're a not-very-useful feature probably dating back to the time when pumps couldn't be so easily programmed to do multi-step gradients. I never use them. There are similar things in other packages: Shimadzu can pump curves, but number their curves totally differently (0 = linear, with concave and convex being denoted by negative and positive numbers). I have no idea whether the shape of Shimadzu curves is the same as that of Waters curves. Agilent's more modern systems can emulate other manufacturers, and in Waters-emulation mode can emulate Waters' curves.

Thanks very much for the replies guys, I found some useful explanations on the Waters HELP tab.