I apologize for the untimeliness of this reply, but I have just started to participate in this forum. Our new controlled pH gradient technology gives very significantly improved results for MAb separation on both cationic and anionic stationary phases when compared with salt. We have published a detailed theoretical and experimental description of the method, Journal of Chromatography A, 1200 (2008) 166–182, and some MAb data in a paper last October in American Biotechnology Laboratory,Application of Well-Controlled pH Gradients at Variable Isocratic Salt Concentrations to IEX Chromatography. A short paper exclusively about MAb separation will appear shortly in the January, 2009 issue of American Biotechnology Laboratory. The classic "wisdom" about pH gradients is that they are confined to short ranges and, because the proteins are thought to elute from the columns very near their pI, aggregation problems are a common difficulty. The truth is much more interesting and encouraging than this picture. In fact, if you can run wide range pH gradients on both cationic and anionic stationary phases then you find that on anionic columns at typical gradient slopes, e.g. 0.1 pH units/column volume, the proteins almost always come out at least 0.5 to 1.0 pH units below their electrophoretic pI, and conversely, on cationic resins they usually emerge at least 0.5 to 1.0 pH units above their pI. As the gradient is steepened the difference between the elution pH and the “trueâ€
