Chromatographic behaviour of aminoalcohols

CORRAL, C.; SUBIRATS, X.; GOTTA, J.; GAGLIARDI, L. G; CASTELLS, C. B.; C. RÀFOLS; M. ROSÉS; BOSCH, E.

Budapest

Simposio; 36th. Internacional Symposium on HPLC and Related Techniques (HPLC2011); 2011

HPLC Symposium

The chromatographic retention for some drugs containing amino and -OH groups in adjacent carbons (β-blockers and alkaloids) shows different values when the mobile phases of the same pH (= 8.5) and organic modifier contents were buffered by Tris(hydroxymethyl)aminomethane (Tris) or by phosphate. Retention times of these analytes in presence of Tris buffer are significantly increased in relation to those obtained with dihydrogenphosphate buffer. Thus, in this work the origin of this extra retention in presence of Tris has been investigated.   Several β-blockers, alkaloids and even the difenhydramine, which contains an amino group but not an ?OH group, have been chromatographed using mobile phases buffered at different pH values in the whole pH range allowed by the buffering agent. Studied buffers have been Tris, ethanolamine, phosphate and carbonate which allow overlapped measurement pH ranges. These measurements allow us to compare the extra retention time observed in amino-buffers (Tris and ethanolamine) with the expected chromatographic behaviour achieved with inorganic-buffers (phosphate and carbonate).   The analysis of the retention measurements leads us to attribute the extra retention to the formation of a complex between the protonated form of the analyte and the basic form of the amino-buffer. A new chromatographic model which involves the formation of the mentioned complex has been proposed and successfully tested for the selected analytes.     Literature   L.G. Gagliardi, C.B. Castells, C. Ràfols, M. Rosés, E. Bosch, J. Sep. Sci. 31, (2008), 969-980