High Performance Liquid Chromatographic Study of the Retention and Sorption of Sulfas on Porous Copolymers

Buffered superheated water as an eluent for reversed-phase high performance liquid chromatography

“…As this ionization is not reflected in the correlation equation (1) the retention at pH = 3.0 was omitted from the analysis. From the regression equation the calculated pKa, 2 for sulfacetamide at 90 ~ was 5.2, which is very similar to that reported pKa,2 = 5.4 at room temperature [ 16], which also agreed closely with the equivalent experiment on the XAD-2 column [ 11 ]. A similar close relationship was found between the experimental value for the pKa,2 = 10.71 for sulfanilamide at 60 ~ and the literature value of 10.4 [16].…”

“…Only sulfaguanidine, which has a high pKa,2 = 11.3, remained unchanged. Similar effects were found for the XAD-2 column at pH 11.7, when all the sulfonamides had retention factors of less than one [11]. Because of the instability of ODS silica stationary phases at high pH no comparable results can be obtained for these columns.…”

“…For example, using an acetonitrile-buffer pH 3.1 eluent on a PRP-1 column, Lee [12] found the elution order: sulfanilic acid, sulfaguanidine, sulfanilamide, sulfathiazole, sulfamerazine, and sulfamethazine. An earlier study on a PS-DVB (XAD-2) column with an acetonitrile-pH 2.8 buffer eluent reported the same order although the efficiency was much poorer [ 11 ].…”

“…As the pH of the eluent was successively reduced, the retention factor of sulfacetamide rose to a maximum at pH 4.0 and then decreased from pH 3.5 to pH 3.0. This effect was assumed to represent the protonation of the amino-group (pKa,~ = 1.78) and reflects similar results on the XAD-2 column [11]. As this ionization is not reflected in the correlation equation (1) the retention at pH = 3.0 was omitted from the analysis.…”

“…Changes in the retention of a series of sulfonamides on a polystyrene-divinylbenzene (PS-DVB) column with the pH of the eluent are compared with separations in conventional eluents. These drugs have been of considerable analytical interest over many years and a large number of methods have been reported for their determination, including reversed-phase liquid chromatography with buffered eluents on both ODS silica [6][7][8][9][10] and PS-DVB columns [11][12][13] and more recently capillary electrophoresis [14][15][16]. Changes in retention over a limited pH range are used to determine if the apparent pKa of the analytes is changed significantly by the elevated temperature.…”