Three methods for quantitative determination of the ligand in Phenyl-Sepharose CL-4B

¹³C SPE MAS measurement of ligand concentration in compressible chromatographic beads

A method for measuring the ligand concentration in heterogeneous materials like chromatography media is described. In this method, (13)C single pulse excitation magic angle spinning NMR experiment with broadband (1)H decoupling is used to determine the peak integrals for a butyl ligand in the spectrum of a dried chromatography medium. Within a carefully controlled protocol, those integrals compared with that of the internal reference compound dimethyl sulfone provide the required volume concentration with an accuracy of ca 2%. The effects of temperature, degree of hydration, and other experimental parameters are discussed.

Quantitative determination of the ligand content in Benzamidine Sepharose 4 Fast Flow media with ion-pair chromatography

A quantitative hydrochloric acid hydrolysis-HPLC method was developed for the analysis of the ligand content of Benzamidine Sepharose 4 Fast Flow media. The method requires about 100 mg of dried sample and simple reaction vials can be utilised. Release of the ligand (p-aminobenzamidine) from the base matrix (Sepharose 4 Fast Flow) was obtained after hydrolysis for 180min at 70 degrees C in concentrated hydrochloric acid. When Benzamidine Sepharose 4 Fast Flow media were treated this way p-aminobenzoic acid and p-aminobenzamidine were the only products released from the ligand. A chromatographic system based on ion-pair reversed phase separation was used to quantify these ligand products. The mobile phase was made acidic enough to make p-aminobenzoic acid and p-aminobenzamidine positively charged in order to make ion-pair formation with hexanesulfonic acid possible. The relative standard deviation of th e method was below 2% and no systematic errors could be detected when the results were compared to an independent method based on elemental analysis (nitrogen). The new HPLC method was used to analyse ligand densities in the range of 2-20 micromol/ml medium.

Superporous agarose beads as a hydrophobic interaction chromatography support

Superporous agarose beads were used as a support for hydrophobic interaction chromatography. These beads have large connecting flow pores in addition to their normal diffusion pores. The flow pores, which are approximately one fifth of the overall diameter of the superporous agarose beads, were earlier shown to give the beads improved mass transfer properties relative to homogeneous agarose beads (Gustavsson and Larsson, J. Chromatogr. A, 734 (1996) 231-240). Superporous agarose beads and homogeneous agarose beads of the same particle size range (106-180 microns) were derivatized with phenyl groups. The properties of the superporous beads were then compared with the homogeneous beads in the separation of a mixture of three model proteins (ribonuclease A, lysozyme and bovine serum albumin) at various superficial flow velocities from 30 to 600 cm/h. The superporous beads gave satisfactory separation at flow velocities five times higher than was possible for homogeneous beads. The performance of the two types of beads was also compared in the purification of lactate dehydrogenase from a beef heart extract at a superficial flow velocity of 150 cm/h. The superporous beads performed considerably better, leading to twice the purification factor and twice the concentration of the desired product. The results were interpreted using the theoretical treatment given by Carta and Rodrigues (Carta and Rodrigues, Chem. Eng. Sci., 48 (1993) 3927).

Design of novel affinity adsorbents for the purification of trypsin-like proteases

A number of ligands for the selective purification by affinity chromatography of the trypsin-like protease, porcine pancreatic kallikrein, were designed de novo by computer-aided molecular design. The ligands were designed to mimic the side-chains of a number of arginyl dipeptides and included a benzamidine moiety substituted on a triazine ring. The ligands displayed inhibitory activities against pancreatic kallikrein which mirrored the specificity constants of the dipeptides they were designed to mimic. The ligand with the highest affinity for the enzyme, an analogue of a Phe-Arg dipeptide, when immobilized to Sepharose CL-4B via a hexamethylene spacer arm, purified pancreatic kallikrein 110-fold in one step from a crude pancreatic acetone extract.

Determination of the leakage from Phenyl-Sepharose Cl-4B, Phenyl-Sepharose FF and Phenyl-Superose in bulk and column experiments

The release of ligands from Phenyl-Sepharose CL-4B, Phenyl-Sepharose FF and Phenyl-Superose has been studied in bulk and column experiments. The leakage products have been identified and quantified by liquid chromatography, fluorescence spectroscopy and proton NMR spectroscopy. It is demonstrated that the leakage occurs primarily through hydrolysis of the agarose support. However, leakage via ether cleavage of the spacer arm-ligand moiety is also observed especially for Phenyl-Superose. The release of ligands at acidic pH is in agreement with a first-order reaction and correspondingly the rate constants have been estimated for all three gels at pH 1 and 2. These show that 50% of the ligands are intact after 15 years of incubation at pH 2. Phenyl-Superose is the most stable gel at acidic pH, whereas Phenyl-Sepharose CL-4B and Phenyl-Sepharose FF are the most stable at neutral and basic pH.