Large tailing

<p>Hello,</p><p></p><p>I am developing a method to analyze several water soluble vitamins simultaneously.  For the most part, they all work out fine except for Thiamine.  Thiamine is the first to come off but has extremely bad tailing and I believe this is the cause for inconsistancy between replicate injections.  My gradient program is basically 100% A to 100% B to 100% A over 9 minutes.  A is 0.1% Formic acid + 10mM Ammonium formate in H2O.  B is 0.1% Formic acid + 10mM Ammonium formate in methanol.  The diluent for thiamine is water but I have tried a few other things including mobile phase A, and the tailing remains.  Attached is a picture of thiamine's chromatogram at 0.08023 mg/mL 1uL injection (10uL loop).  The base line is exagerated to show the tailing.  Any suggestions would be most welcome!  Thanks!</p>