I am trying to develop a method and no can reduce tailing. Tailing = 1.93 I have tried many
columns, TEA, buffers, pH and temperatures. Some a little better but all bad. Drug pKa = 9.36

I no understand many numbers. Stastical moments m0=2569, m1=2.645, m2=0.002329, m3=0.000105, m4=0.000023, skew=0.938, excess=1.286, symmetry=0.432

Sorry for my English, no have used for 10 years.

Thank you,

Sinjo

Would you please give some mobile phase conditions you have tried and, if possible, the compound you are analyzing.

And the column? It sounds like interaction of a base with acidic silanols.

Statisitcal moments are used to describe asymmetric peaks:
M0 is the peak area; M1 is the retention time at the center of mass of the peak. Imagine cutting out your peak then balancing the cutout on a needle, the retention time of the balance point is M1. M2 is the peak variance and measures the degree of lateral spread. M3 is skew or symmetry with respect to the vertical axis. M4 is excess which is a measure of how much a peak is stretched or compressed along the vertical axis relative toa gaussian peak of the same area.

The difference in numbers between your M3 and skew is because one number is dimensionless and one is not. I think your M3 and M4 are retaining your data systems dimensional units and skew and excess are unitless and normalized to 1 for a gausian peak.

Symmetry is a ratio of the width of the front half of the peak to the back half of the peak relative to tangents to the inflection points. Different data systems calculate this differently.

Your peak has an area of 2569 and a retention time of about 2.645 min. Assumin a 4.6x150mm column with a t0 of 1.5 min your compound is not very strongly retained k'0.02) something other than tailing is going on.

Your symmetry value is very messed up with the back half of your peak more than twice as wide as the front half. If your data system uses a tangent method to calculate this then I think your peak is overloaded not tailing.

Blow up your peak until it is very large if it looks like a right triangle it is overloaded not tailing. There is another thread here somewhere where the early overload of basic compounds was discussed.

What is the logP of your compound? Hydrophilic bases tend to overload at very low column loadings. The general solution to this class of problems that I use is a base stable column Waters Xterra/Zorbax Extend/Develosil at a pH sufficiently high to partially deprotonate the base (pH 7-8 for amines).

Sorry, I think I rambled too much and the middle of my post got chopped.

That should have been your k' is less than 2. Take a careful look at M1 relative to peak retention time even with tailing peaks these should be very close (+/- 0.005) if the difference is large (>0.02) something other than tailing is going on.

Good Luck

I try ph 7.5 and much better tailing 1.13. I don't think column overloaded, not much injected. I don't understand why tailing better at ph 7.5 than pH 2. I was instructed low ph would protonate silanols and reduce tailing of bases. What is theory of less tailing at higher ph. Thank you for help.

How did your retention time (or better, k) change in going from pH 2 to 7.5? It may be that you have an unfavorable equilibrium toward a strongly retained substance. Or alltogether different: maybe your substance decomposes at pH 2?

I think you were seeing overload not tailing. If it was just tailing you would expect it to be worse at pH 7.5 not better. Hydrophilic basic compounds can overload a column at very low on column amounts.

As far a theory goes, Snyder et al explained the overload of basic compounds as mixed mode retention and an overload of the silanol sites. There are much fewer silanol sites at pH 2.0 than at 7.0

I've looked into this a little and think more along the lines of charged basic compounds poorly partitioning into the adsorbed organic layer.

Good Luck.

HAVE A LOOK AT THIS ARTICLES AND GOOD LUCK:
REVERSE-PHASE HPLC OF BASIC SAMPLES.LC-GC EUROPE OCTOBER 1999.David V.McCalley

THE SILANOL GROUP AND ITīS ROLE IN LIQUID CHROMATOGRAPHY.Journal of chromatography A, 779(1997)29-71.Review.Jacek Nawrocki

JOURNAL OF CHROMATOGRAPHY A, 844(1999)23-38DAVID v.McCALLEY

I could really use some help. Im running an aliphatic hydrocarbon standard(straight alkane chain C9-C36) on my GC FID 5890. I have a new RTx-5 column which all of a sudden is displaying peak tailing on the early eluting hydrocarbons. The later eluting peaks C30- C36 are crisp and tight. My email is jeffo@eailabs.com. Can anyone email me with some tips on how to eliminate peak tailing?
thanks