Gradient curves- can you explain?

[EmpowersBane]

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?

[Hollow]

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

[lmh]

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.

[EmpowersBane]

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