title: Chromatographic studies of unusual on-column degradations of aniline compounds on XBridge Shield RP18 column in high pH aqueous mobile phase.
abstract: This paper reports unusual on-column degradations of aniline compounds on Waters XBridge Shield RP18 column when ammonium hydroxide in water and acetonitrile were used as mobile phases in liquid chromatography. The change of the level of on-column degradation of a model compound (Compound 1) with time was observed in the first fifteen injections when started at 60 °C. During a subsequent cooling program from 60 °C to 10 °C with a 10 °C interval, the levels of the degradation products of Compound 1 changed with the change of temperature and reached a maximum at 40 °C. The on-column degradation of Compound 1 was observed when started at 10 °C in the first injection, however, the magnitude of the change of the level of on-column degradation of Compound 1 with time in the first fifteen injections was much smaller than that at 60 °C. During a subsequent heating program from 10 to 60 °C with a 10 °C interval, the levels of the degradation products of Compound 1 increased with the increase in temperature but without a maximum. The change of the degradation product levels of this model compound in the heating process is not super-imposable with that in the cooling process, which demonstrates the degree of the degradation also depends on the heating or cooling process. Column history studies demonstrated that the on-column degradation of Compound 1 changed dramatically on the used columns at both starting temperatures while the dependency of heating and cooling processes on on-column degradation still existed. The unusual on-column degradation of Compound 1 on the used columns can be regenerated in a very similar fashion with an acetic acid column-wash procedure, but is not identical to that on the new column. Similar degradations of other commercially available aniline compounds were also observed with this high pH aqueous mobile phase system.
authors.affiliation: Department of Analytical Research and Development, Amgen Inc., Thousand Oaks, CA 91320, USA. fwang@amgen.com
authors.forename: Fang
authors.initials: F
authors.lastname: Wang
authors.forename: Xiao-Keng
authors.initials: XK
authors.lastname: Liu
authors.forename: Susanna
authors.initials: S
authors.lastname: Lai
authors.forename: Jan
authors.initials: J
authors.lastname: Fang
authors.forename: David
authors.initials: D
authors.lastname: Semin
mesh_terms: D064753:Ammonium Hydroxide; D000814:Aniline Compounds / Q000737:chemistry*; D002853:Chromatography, Liquid / Q000295:instrumentation* / Q000379:methods*; D006863:Hydrogen-Ion Concentration; D006878:Hydroxides / Q000737:chemistry; D013696:Temperature
chemical_list: D000814:Aniline Compounds; D006878:Hydroxides; D064753:Ammonium Hydroxide