Buffers in pharmaceutical and biological system

it is about buffers that we use in pharmaceutical solutions and buffer system present in our body

1. NAME : BASIT MANZOOR ROLL NO: 13 B PHARMA 3 rd YEAR TOPIC: BUFFERS IN PHARMACEUTICAL AND BIOLOGICAL SYSTEM

2. Buffer Solution :-The resistance of change in hydrogen ion concentration upon the addition of small amounts of acids and bases is termed as buffer action ; a solution which posses such properties is known buffer solution .

3. BUFFER SYSTEMS IN THE BODY The buffer systems in the human body are extremely efficient, and different systems work at different rates. It takes only seconds for the chemical buffers in the blood to make adjustments to pH. The respiratory tract can adjust the blood pH upward in minutes by exhaling CO 2  from the body. The renal system can also adjust blood pH through the excretion of hydrogen ions (H + ) and the conservation of bicarbonate, but this process takes hours to days to have an effect. The buffer systems functioning in blood plasma include plasma proteins, phosphate, and bicarbonate and carbonic acid buffers. The kidneys help control acid-base balance by excreting hydrogen ions and generating bicarbonate that helps maintain blood plasma pH within a normal range. Protein buffer systems work predominantly inside cells.

4. BICARBONATE-CARBONIC ACID BUFFER The bicarbonate-carbonic acid buffer works in a fashion similar to phosphate buffers. The bicarbonate is regulated in the blood by sodium, as are the phosphate ions. When sodium bicarbonate (NaHCO 3 ), comes into contact with a strong acid, such as HCl, carbonic acid (H 2 CO 3 ), which is a weak acid, and NaCl are formed. When carbonic acid comes into contact with a strong base, such as NaOH, bicarbonate and water are formed. NaHCO 3  + HCl →  H 2 CO 3 +NaCl (sodium bicarbonate) + (strong acid) → (weak acid) + (salt) H 2 CO 3  + NaOH→HCO 3-  + H 2 O (weak acid) + (strong base)→(bicarbonate) + (water)

5. PHOSPHATE BUFFER Phosphates are found in the blood in two forms: sodium dihydrogen phosphate (Na 2 H 2 PO 4 − ), which is a weak acid, and sodium monohydrogen phosphate (Na 2 HPO42-), which is a weak base. When Na 2 HPO42- comes into contact with a strong acid, such as HCl, the base picks up a second hydrogen ion to form the weak acid Na 2 H 2 PO 4 −  and sodium chloride, NaCl. When Na 2 HPO42− (the weak acid) comes into contact with a strong base, such as sodium hydroxide (NaOH), the weak acid reverts back to the weak base and produces water. Acids and bases are still present, but they hold onto the ions. HCl + Na 2 HPO 4 →NaH 2 PO 4  + NaCl (strong acid) + (weak base) → (weak acid) + (salt) NaOH + NaH 2 PO 4 →Na 2 HPO 4  + H 2 O (strong base) + (weak acid) → (weak base) + (water)

6. HEMOGLOBIN AS A BUFFER Hemoglobin is the principal protein inside of red blood cells and accounts for one-third of the mass of the cell. During the conversion of CO 2  into bicarbonate, hydrogen ions liberated in the reaction are buffered by hemoglobin, which is reduced by the dissociation of oxygen. This buffering helps maintain normal pH. The process is reversed in the pulmonary capillaries to re-form CO 2 , which then can diffuse into the air sacs to be exhaled into the atmosphere.

7. PROTEIN BUFFERS IN BLOOD PLASMA AND CELLS Nearly all proteins can function as buffers. Proteins are made up of amino acids, which contain positively charged amino groups and negatively charged carboxyl groups. The charged regions of these molecules can bind hydrogen and hydroxyl ions, and thus function as buffers. Buffering by proteins accounts for two-thirds of the buffering power of the blood and most of the buffering within cells .

8. Pharmaceutical Buffers :- Buffer solutions are used frequently in pharmaceutical practice, particularly in the formulation of ophthalmic solutions .

9. General Procedures for Preparing Pharmaceutical Buffer Solutions:- The following steps should be helpful in the development of a new buffer. A - Select a weak acid having a pKa approximately equal to the pH at which the buffer is to be used . B - from the buffer equation, calculate the ratio of salt and weak acid required to obtain the desired pH. The buffer equation is satisfactory for approximate calculations within the pH range of 4 to 10 . C - Consider the individual concentrations of the buffer salt and acid needed to obtain a suitable buffer capacity.

10. A concentration of 0.05 to 0.5 M is usually sufficient, and a buffer capacity of 0.01 to 0.1 is generally adequate . D - Other factors of some importance in the choice of a pharmaceutical buffer include availability of chemicals, sterility of the final solution, stability of the drug and buffer on aging, cost of materials, and freedom from toxicity. For example, a borate buffer, because of its toxic effects, certainly cannot be used to stabilize a solution to be administered orally or parenterally. E - Finally, determine the pH and buffer capacity of the completed buffered solution using a reliable pH meter. In some cases, sufficient accuracy is obtained by the use of pH papers. Particularly when the electrolyte concentration is high, it may be found that the pH calculated by use of the buffer equation is somewhat different from the experimental value. This is to be expected when activity coefficients are not taken into account, and it emphasizes the necessity for carrying out the actual determination.