please read and show for me

[vinhvinh1979g]

i am determining a mixed organic acids including formic, ACETIC, PROPIONIC, LACTIC
OXALIC, MALONIC, SUCCINIC, MALIC, TARTARIC, CITRIC. i set up with condition: buffer format ammonium(pH =3, 4, 5), flow rate = 0.5ml/min, ratio buffer/ACN = 90/10; WAVELENGHT 210nm, uv detector, column trinity p1 Acclaim Trinity P1( 3µm 3.0 x 50 mm). the first I determined each standard, but I have no peak of each substance. what am I wrong?

[tom jupille]

First of all, are you trying to follow a validated method, or are you developing the conditions on your own?

The Acclaim P1 is a mixed-mode column, and part of the retention mechanism is reversed-phase. If you are developing the conditions yourself, you need to experiment with the ratio of buffer to acetonitrile in the mobile phase.

[InfraredRoses]

I recommend you run a UV-Vis for each acid separately to see the wavelength of max. absorption. Then run a standardized curve to get the absorption coefficient at the respective wavelength(s). This should go a long way to getting you the towards the answers you seek. You must realize the dicaboxylic acids should absorb at a different "rate" than the monocarboxylic acids. You may find you can use one wavelength for all of them, but the coefficient will almost definitely be different.

[tom jupille]

If the OP is not seeing *any* peaks, the major problem is not detection wavelength. Almost any molecule with a double bond will have ar least some absorbance at 210 nm.

[Consumer Products Guy]

I've run most of those organic acids on a (surprise) organic acid column, from either Grace Alltech or Restek. I've used both low UV and conductivity to detect.

[InfraredRoses]

I agree they should have some absorption at 210nm. Maybe some of them are coelluting? Since you say you have run standards for each, what are the retention times? Are you getting good separation for each? When they are run all together in one sample this can change the efficiency of the column and cause some to coellute. If they are not getting held up in the column and you know there is enough response to see a peak through standards, you have yourself a bit of a problem.