Protein separations with induced pH gradients using cation-exchange chromatographic columns containing weak acid...

Area of Science:

• Biochemistry
• Analytical Chemistry
• Chemical Engineering

Background:

• Chromatographic separations are crucial for protein analysis and purification.
• Developing efficient and scalable protein separation techniques is an ongoing challenge.
• Internally generated pH gradients offer a novel approach to enhance chromatographic resolution.

Purpose of the Study:

• To investigate protein separation using internally generated pH gradients in cation-exchange chromatography.
• To develop a model for predicting pH transitions based on resin properties.
• To optimize separation conditions for preparative-scale protein purification.

Main Methods:

• Utilized mixed-bed cation-exchange resins with weak and strong ion-exchange groups.
• Developed a local equilibrium model to predict pH gradients using non-adsorbed buffers.
• Employed acetate and phosphate buffer mixtures to generate gradients between pH 5 and 7.
• Separated protein mixtures (ovalbumin, albumin, transferrin) under preparative conditions.

Main Results:

• Achieved near baseline resolution for protein mixtures at high protein loads (10 mg/mL) and flow velocities (460 cm/h).
• Observed significantly sharper protein peaks compared to isocratic or externally generated gradients due to peak compression.
• Demonstrated effective separation at very low ionic strengths (2-3 mS/cm).
• Systematically investigated the impact of flow velocity, mobile phase composition, injection time, and protein load on separation outcomes.

Conclusions:

• Internally generated pH gradients are effective for high-resolution, preparative protein separations.
• The developed model accurately predicts pH transitions, enabling gradient optimization.
• This approach offers advantages in peak sharpness, efficiency, and reduced ionic strength requirements for protein purification.