Chromatography Forum

I tried to determine gabapentin using USP30-NF25 method for gabapentin and got this result:

Assay conditions:
Column packings : Phenomenex Luna C18(2) 5U 100Ã… 150x4.6 mm
Buffer solutions : 0.005 M monobasic ammonium phosphate + 0.015 M sodium perchlorate, adjusted with perchloric acid to a pH of 1.8
Mobile phase : Buffer solutions : Acetonitrile (80:20)
Diluent : 0.02 M monobasic ammonium phosphate, adjusted with phosphoric acid to a pH of 2.0.
Standard solutions : 6000 ppm Gabapentin in diluent
Column temperature : 45 C
Flow rate : 1.0 mL/min.
Detection : UV-Vis 215 nm.
The problem is that the tailing factor of gabapentin is >2.0
I already tried different ranges of mobile phase pH (from pH of 2.0 to pH of 7.5) but it didn't improve the tailing factor.
I also tried raising the column temperature up to 45 Celcius degree (from 40 degree) and adjust the mixture of the mobile phase, but still haven't achieve the best result yet.
What do you think I should try next to improve the tailing factor of the gapapentin peak?
I prefer not to use the derivatisation method and try to stick to the USP method since it's quite simple.

Peak shape should be better on a cyano column. As this phase is more polar, acetonitrile content in the mobile phase must be lower (at 10 % for example). Perhaps methanol will be better than acetonitrile you can try it if you have time.

pH adjustment is difficult here because of 2 pKa at 3.7 for the acid function and 10.7 for amino function. Anionic form around pH 12 should avoid tailing but it will be a too high pH for the most columns. I would think that cationic form at pH 2 should give more tailing than zwiterrionic form at pH 6.

You could also try another buffer (KH2PO4 / K2HPO4 for example) with higher concentration (50 mM) to have lower tailing.

If possible I advise you to try a cyano column (Luna CN for example) first with 20 mM pH 6 buffer with 10 % acetonitrile. If it's not good you can secondly try to shift to stronger buffer, to methanol or to pH 2.

Best regards.

Tailing is greater than 2 so what? You have a good separation, if it is consistent there is nothing to worry about.

Two things:

1-The monograph does not list tailing factor as a suitability requirement, so it is what it is and as a previous poster pointed, so what.
2-The monograph tells you to use a L1 column (i.e. a C18 column), that only narrows it down to about a thousand different choices, try a different C18 column, maybe it works better.

Try a Waters XTerra RP 18 4.6 x 100 mm or an XBridge of the same dimensions. I don't have much other experience with other manufacturer's columns.

What is your matrix?

We analyze Gabapentin in postmortem blood, serum, plasma, tissue, gastric, and urine. We have transferred to Acquity UPLC/MS/MS with a simple acetonitrile crash/dilution.

What is your matrix?

It is gabapentin capsules

Thanks for any advice. I will try other C18 columns.

The monograph recommends a Symmetry C8 column.

C8? but the monograph for gabapentin in USP30 said:
The liquid chromatograph is equipped with a 215-nm detector and a 4.6-mm x 25-cm column that contains packing L1.

I used Gemini C18 from Phenomenex and got a good shape for a similar compound. I think your tailing comes from residual silanols, try to play with pH and see if you can improve peak shape.

Uwe is right , USP31 monograph of Gabapentin Capsule uses L7 column .
whereas Gabapentin API monograph uses C18.

You can use Hypersil BDS or Xterra RP18 in USP conditions after optimisation of flow rate and temp.

JM