Introduction
Potassium phosphate buffer is commonly used as a biological buffer in various biochemical and molecular biology applications. It is used mainly to maintain pH and stabilize the solution. The buffer solution is prepared by mixing the potassium dihydrogen phosphate and disodium hydrogen phosphate in specific proportions to achieve the desired pH. In this article, we will discuss the preparation calculation of potassium phosphate buffer in detail.
Types of Potassium Phosphate Buffer
There are two types of potassium phosphate buffer: monobasic and dibasic. Monobasic potassium phosphate is also known as potassium dihydrogen phosphate and has a chemical formula KH2PO4. Dibasic potassium phosphate is also known as disodium hydrogen phosphate and has a chemical formula Na2HPO4. These two salts are combined in different proportions to prepare different pH ranges of the buffer solution.
Preparation Calculation
The preparation calculation of potassium phosphate buffer involves the calculation of the required amount of monobasic and dibasic potassium phosphate salts to achieve the desired pH. The pH of the buffer solution depends on the ratio of the two salts. The pH can be calculated using the Henderson-Hasselbalch equation:
pH = pKa + log([A-]/[HA])
where pH is the desired pH, pKa is the dissociation constant of the buffer, and [A-]/[HA] is the ratio of the conjugate base to the acid of the buffer.
The required amount of monobasic and dibasic potassium phosphate salts can be calculated using the formula:
Amount of salt (g) = (Molarity x Volume x Molecular weight) / 1000
where Molarity is the desired molarity of the buffer solution, Volume is the volume of the buffer solution required, and Molecular weight is the molecular weight of the respective salt.
Example Calculation
Suppose we want to prepare a 1 liter of 0.1 M potassium phosphate buffer at pH 7.4. The pKa of the buffer is 7.2. The required amount of monobasic and dibasic potassium phosphate salts can be calculated as follows:
Amount of KH2PO4 (g) = (0.1 x 1000 x 136.09) / 1000 = 13.609 g
Amount of Na2HPO4 (g) = (0.1 x 1000 x 142.04) / 1000 = 14.204 g
So, we need to weigh 13.609 g of KH2PO4 and 14.204 g of Na2HPO4 and dissolve them in distilled water to make 1 liter of 0.1 M potassium phosphate buffer at pH 7.4.
Conclusion
Potassium phosphate buffer is an essential buffer solution used in various biochemical and molecular biology experiments. The preparation calculation of the buffer involves the calculation of the required amount of monobasic and dibasic potassium phosphate salts to achieve the desired pH. The ratio of the two salts determines the pH of the buffer solution. The calculation can be done using the Henderson-Hasselbalch equation and the formula for the amount of salt required. By following the correct procedure, one can prepare a highly stable and reliable potassium phosphate buffer solution.