High‐buffering capacity, hydrolytically stable, low‐pI isoelectric membranes for isoelectric trapping separations

Abstract

Hydrolytically stable, low-pI isoelectric membranes have been synthesized from low-pI ampholytic components, poly(vinyl alcohol), and a bifunctional cross-linker, glycerol-1,3-diglycidyl ether. The low-pI ampholytic components used contain one amino group and at least two weakly acidic functional groups. The acidic functional groups are selected such that the pI value of the ampholytic component is determined by the pK(a) values of the acidic functional groups. When the concentration of the ampholytic component incorporated into the membrane is higher than a required minimum value, the pI of the membrane becomes independent of variations in the actual incorporation rate of the ampholytic compound. The new, low-pI isoelectric membranes have been successfully used as anodic membranes in isoelectric trapping separations with pH < 1.5 anolytes and replaced the hydrolytically less stable polyacrylamide-based isoelectric membranes. The new low-pI isoelectric membranes have excellent mechanical stability, low electric resistance, good buffering capacity, and long life time, even when used with as much as 50 W power and current densities as high as 33 mA/cm(2) during the isoelectric trapping separations.

The Biflow: An instrument for transfer‐loop mediated, continuous, preparative‐scale isoelectric trapping separations

“…The Immobiline-based buffering membranes [21] were obtained from Gradipore (French's Forest, NSW, Australia). The poly(vinyl alcohol)-based buffering membranes were synthesized in our laboratory [29][30][31]. All solutions were freshly prepared using deionized water from a Milli-Q unit (Millipore, Milford, MA, USA) and were filtered, immediately prior to use, through 0.65 mm PVDF membrane filters (Millipore).…”

Hydrolytically stable, diaminocarboxylic acid‐based membranes buffering in the pH range from 6 to 8.5 for isoelectric trapping separations

“…All solutions were freshly prepared using deionized water from a Milli-Q unit (Millipore, Milford, MA, USA). The alkaline buffering membranes (QPVA, synthesized from glycidyltrimethylammonium chloride, GDGE, and PVA), as well as the acidic buffering membranes (IDAPVA, synthesized from IDA, GDGE, and PVA) were prepared in our laboratory as described in [41,42].…”

“…When the concentration of an immobilized, good carrier ampholyte molecule in the membrane is higher than a certain minimum value, the pH of the buffering membrane is practically constant, even when the incorporation rate changes slightly [42]. These anodic membranes had pH values in the 1.7 , pH , 3.4 range [42].…”

“…High incorporation rates were achieved when GDGE and PVA were reacted with the primary amino group of dicarboxylic acids to produce the PVA-based acidic buffering hydrogels [42]. Work on the synthesis of single-component, diaminosulfopropane carrier ampholytes indicated that many diaminocarboxylic acids (DACAs) had pI values in the 6 , pI , 10 range [43].…”

“…These membranes had pH values above 11.5 and were used as cathodic membranes [41] in the BF200IET unit. Encouraged by the stability of the PVA-based cathodic membranes, anodic membranes were also synthesized by incorporating iminodicarboxylic acids, such as iminodiacetic acid (IDA), or aminodicarboxylic acids, such as aspartic acid or glutamic acid, as the buffering species into the cross-linked PVA matrix [42]. When the concentration of an immobilized, good carrier ampholyte molecule in the membrane is higher than a certain minimum value, the pH of the buffering membrane is practically constant, even when the incorporation rate changes slightly [42].…”