High-performance liquid chromatography of basic compounds - Problems, possible solutions and tests of reversed-phase columns

Column testing in unbuffered mobile phases is adequate for identifying very active impure silicas used in reversed-phase chromatography, but inadequate for evaluating new generation phases, which still show considerable differences in activity towards strong bases. Overloading can seriously confound test results; buffered acetonitrile and tetrahydrofuran (THF) produce results similar to those previously shown for methanol. Principal component analysis (PCA) of a large data set indicates that relative performance for a given modifier at high and low pH is different. At a given pH, relative performance with methanol and acetonitrile is fairly similar, but distinct with THF. PCA also allows selection of a range of compounds assessing overall column performance; the use of a single probe for evaluation of activity towards bases is clearly inadequate. The newest columns give considerably improved peak shape for bases; the low back pressure generated by some allows coupled columns at least 75 cm long to be used, generating efficiencies similar to capillary electrochromatography. (C) 1998 Elsevier Science B.V. All rights reserved.