Odd Chromatography Problem... Help

[chemboy831]

Hi Everyone,

Got a perplexing problem. Working in a toxicology lab running a drugs of abuse/pharmaceuticals method detecting about 35 compounds on an Agilent 1290 LC. Mobile phase A is 0.1% formic acid. Mobile phase B is methanol. The gradient is 5%B - 85%B over 6 minutes, and I'm using a Zorbax Eclipse Plus 2.1x50x1.8 column. We run urine samples, prepared by solid phase extraction, on one instrument and oral fluid samples, again prepared by solid phase extraction, on a second instrument. All of the mobile phases and reagents are prepared in batches and shared on both systems. Been running samples this way for about 18 months, about 100 urines and 50 oral fluids a day. Now all of a sudden, in my oral fluid samples i'm getting poor peak shapes for very specific compounds, namely fentanyl, amitriptyline, nortriptyline, Imipramine, and buprenorphine. The peaks are very broad and in some instances are splitting. All of the other compounds look normal. Urine samples look great, no problems. Replaced the LC column and everything looked good again. But three days later the peak shape issues cropped up again. I've replaced all of my rotor seals/filters/capillary tubing, cleaned everything I could think of but still my LC columns are failing after only 3-4 days of use! Anyone have any suggestions or advice? I'm pulling my hair out over this one.

Thanks in Advance,

Chemboy831

[LCFan]

Dear Chemboy831,

it seems that you have problems with some bases that are prone to bad peak shape (e.g. amitriptylin).

Some months ago, I also had a problem with a very rapid loss of peakshape of bases; I used an ion-pairing method with acetic acid as pH adjusting agent. One day, I ordered acetic acid in Suprapur quality and used it for pH adjustement. Since then, the lifetime of my columns is substantially longer.

Due to the fact that I only need a small amount of acetic acid, "my heart" cannot really believe that the quality of acetic acid is the reason for good or bad peak shape. But up to now, it works.

Regards

Florian