Isoelectric buffers, part 3: Determination of pK_a and pI values of diamino sulfate carrier ampholytes by indirect UV‐detection capillary electrophoresis

Abstract

Ampholytes with close pK(a) values (i.e., good carrier ampholytes (CAs)) are needed as buffers in pH-biased isoelectric trapping (IET) separations. The syntheses of two families of such good CAs were reported recently. Members of the family of diamino sulfate ampholytes (first series) had pI values in the 5.7 < pI < 9.0 range. Members of the family of quaternary ammonium dicarboxylic acid ampholytes (second series) had pI values in the pI < 4.3 range. To further characterize the diamino sulfate ampholytes, their effective mobilities were measured by indirect UV-absorbance detection capillary electrophoresis in a series of background electrolytes (BGEs) with different pH values. The pK(a) and limiting ionic mobility values of the CAs were obtained by fitting these mobility values, as a function of the pH and the ionic strength of the BGEs, to the theoretical mobility expression. These diamino sulfates complete the list of CAs suitable for IET separations.

A systematic study in CIEF: Defining and optimizing experimental parameters critical to method reproducibility and robustness

“…The results of intermediate precision studies performed with three mAbs having isoforms in the basic range demonstrate the excellent performance of the method: low %CV values were observed for both the estimated pI values and isoform group percent compositions. The approach used here can be readily adapted to other CA pI ranges as well by selecting sacrificial ampholytes from a list of isoelectric buffers [23] that best match the pI range of the CA mixture.…”

pH transients during salt removal in isoelectric trapping separations: A curse revisited

“…All chemicals, including methanesulfonic acid, glutamic acid (GLU, approximate pI value 3.2), arginine (ARG, approximate pI value 10.6) and NaOH used as anolytes and catholytes, boric acid and LiOH used as BGE constituents, m-aminobenzoic acid (MABA, approximate pI value 3.9), histidine (HIS, approximate pI value 7.6) and tyramine (TYRA, approximate pI value 10 [13]) used as ampholytic components, and benzenesulfonic acid, p-toluenesulfonic acid and benzyltrimethylammonium hydroxide used as strong electrolyte components were purchased from Aldrich Chemical Company (Milwaukee, WI, USA). The UV absorbing monovalent strong electrolyte salts, benzyltrimethylammonium benzenesulfonate (BzTMA…”

Physicochemical Properties of Buffers Used in Simulated Biological Fluids with Potential Application for In Vitro Dissolution Testing: A Mini-review

“…An analysis of these data shows that ionic strength for each buffer varies over the useful buffer pH range of pH = pKa ± 1, the greatest buffer-related contribution to ionic strength is by the phosphate buffer where the ionic strength at pH = pKa is greater than the total molar concentration of the buffer by a factor of two Svensson (62) discussed a classification of buffers known as isoelectric buffers, with histidyl-glycine being an example. These buffers have negligible ionic strength at their isoionic point, pI, while having finite buffer capacity if they meet the criterion that (pI -pK a1 ) < 1.5 (63).…”