Buffer Solutions have a useful property of remaining at a stable pH when a strong acid or base is added to the system. Each Buffer Solution has a maximum amount of acid/base it can absorb which is called its Buffer Capacity. Buffer Solutions are made with an aqueous mixture of a weak acid and it congregate base or a weak base with it congregate acid.

For example, the human body uses a buffer solution of carbonic acid and bicarbonate. Carbon Dioxide forms Carbonic Acid (H2CO3) when in contact with water. This is in equilibrium with Bicarbonate (HCO3-). Another example is Acetate buffer solutions with Acetic Acid and Sodium Acetate. The salt, Sodium Acetate completely disassociates to Na+ and CH3COO-. Acetic Acid is in equilibrium shown as CH3COOH ↔ CH3COO- + H+. As an acid is introduced to the system, the H+ ions are converted to Acetic Acid while any base OH- ions react with H+ ions to form water. A new equilibrium is established with almost no changes to pH.

Proper mixing of the solution is critical in producing a good Buffer Solution. First, the salt form needs to be completely dissolved and disassociated for all of its ions to be available to the equilibrium system. Next, the weak acid or base needs to be homogeneous in the solution for the proper equilibrium to be achieved. The pH usually needs to be adjusted to the final system’s pH level to be effective so good mixing is important during this step to ensure the correct additions are made for the final preparation.

Buffer Preparation, or “buffer prep” is a very common application in biopharma. Portable mixtanks or larger scale blending vessels are used to make up a buffer solution used in downstream feed for bioreactors.

Potential WMProcess mixers that could be used:

• SANITARY TOP ENTRY MIXER – for open top tank a C Clamp Mount mixer is typical, or for closed sealed vessels a TC mount agitator is common – mixers can be used on sanitary stainless vessels or FDA/USP VI poly tanks
• HIGH SHEAR MIXER– for rapid dispersion and dissolving on salts, powders, and pellets
• BOTTOM ENTRY MAGMIXER – Low shear gear drive mixers, medium shear direct drive bottom mag mixers, and high shear mag drive agitators can be used for buffer make up. WMProcess can accommodate mag drive mixers on either stainless tanks or poly vessels.