Chromatography Forum

Hi,

I am using a USP method for lidocaine. This uses acetic acid as buffer at pH 3.4 with 20% acetonitrile and 80% buffer.

The standard is 1.7 mg/mL.

I'm trying to avoid changing the method so I don't have to validate. Any advice on what to try?

I changed the column from Zorbax SB-C18 to XDB-C18 to Eclipse Plus C18.

Thanks,

As stated in a previous post - USP methods are challenging.............
Take the hydrophobicity tables from different sources and look for a column which is far away from the area of the columns you already used.
Acetic acid has not the best buffer capacity. At what temperature do you operate?
Slight changes in column temperature will change pH of your buffer.
Depending on the dimension of your L1 column maybe it is recommended to have the buffer solution also on the same temperature as the column to avoid a temperature gradient on your column.
Good luck.

Looks like a "bad" molecule"... Tertiary amines are not easy to get good peak shapes of.

Since you cannot change the method, you will need a C18 column with as little silanols as possible. Waters XBridge?

I just consulted http://www.uspchromcolumns.com, where it is stated that for lidocaine in the USP monograph a MicroBondapak C18 column shall be used.

Yes I saw that too. It seems that the microbondapak column can do things that imitators can not. My chromatogram with the Zorbax SB C18 looks exactly like a perfect example of mass overload. When I inject 5% of the original injection tailing is 1.4 (it was 3.0 with the USP condition).

Why would microbondapak be better at handling more mass. I'm assuming tailing is better than 3.0 for the microbondapak.

Another time that I miss the late Uwe Neue to give some insight information about column chemistry. What a loss for the chromatographic community and this forum...

Hey MestizoJoe,

Do you happen to have something with medium ligand density such as Waters Atlantis to try? You'll be very happy at the lack of tailing with bases even with acidic eluents.

Otherwise, I'm getting good results for a similar analyte with a Waters BEH C8...the hybrid silica-organic phases seem to be pretty nice for tailing.

Overall...you may need a stationary phase that is more polar, like the old-school uicroBondapak or LiChrosphere, but with good endcapping. Atlantis is ideal for this on both counts...there are other phases like Atlantis, don't know that polar-embedded or polar-endcapped phases still jibe with L1 categorization.

don't know that polar-embedded or polar-endcapped phases still jibe with L1 categorization.

They don't.

Poor peak shape comes from overloading of silanols. less silanols you have better peak shape you have. You can suppress ionization of silanols at lower pH, but unfortunately you cannot change mobile phase composition (using TFA instead of acetc acid). End-capped columns and columns with higher ligand density usually show better peak shape, but since you are talking about electrostatic interaction it does not address problem completely. Mixed-mode addresses this issue, since acidic groups on the surface have 5-50 times higher capacity than silanols...but you cannot change the column

µBondapak was one of the first stationary phases available commercially with a high reproducibility column to column and batch to batch. It seams that millions of methods were validated with this column!
Irregulare particles and no endcapping! Base silica was/is produced in a different way as modern silicas. That means µBondapak has a different hydrophobicity, different pH of the silica, with a high bonding density but still give access to the rest silanol groups.
Many years ago, during my "NEW Hire" training at Waters I mentioned that µBondapak is an old fashioned column material. I had to learn that this is not the case and it has a unique surface chemistry.
To switch a methode, developed on a µBondapak column, to a "new" generation column, and this is also my experiance during my lab time, is in most cases not possible. It was a pleasure and honour at these days to talk with Uwe Neue also about such things.
My recommendation is to go with the µBondapak column. That will save you time and money!

Good luck.

Hello Again,

As Gerhard notes high above this post; "Take the hydrophobicity tables from different sources and look for a column which is far away from the area of the columns you already used." Here is an excellent web site to employ in this work:

http://www.hplccolumns.org/database/compare.php

Just locate your column(s) that aren't working out for lidocaine, and go to the opposite Fs factor.

An off-the-cuff idea, Spherisorb is created in a Vaguely Similiar way to uBondapak (the phase USP recommends), why not give that a whirl--it still comes in a non-endcapped version? I still like Atlantis (medium ligand density and endcapped), if for no other reason than Atlantis, which is L1 material, works in a similar fashion to polar-embedded phases such as Supelco RP-Amide or Agilent Bonus-RP, which are L60 material, and recent articles published in Elseveir journals seem to use polar-embedded phases for lidocaine and similar compounds, including their metabolites (my thanks to Tom Jupille...I've been away from Pharma for a while, but things are coming back to me, albeit slowly).

Thanks for the replies.

What worked for me was just trying all the different C18s that were in house. The one that gave the best tailing and proper retention was Harmony C18 from ES.