Preparation of buffer solution and measurement of pH
Citation: Chaudhari, M. (2022). Preparation of buffer solution. Pharmacy Infoline. https://doi.org/10.5281/zenodo.10826597
buffer solution ph measurement can be performed as
Aim:
To prepare carbonate buffer and its measurement of PH by using PH meter
Material/Requirement:
- Sodium bicarbonate
- Sodium carbonate
- Distilled water
- 100ml volumetric flask
- Beaker
- Stirrer
Procedure:
To 93 ml of 0.1M sodium bicarbonate in volumetric flask and 0.1M sodium bicarbonate was added to make up the volume up to 100ml. The PH was measured by the pH meter
Preparation of 0.1M sodium bicarbonate
8.4gm of sodium bicarbonate in 1000ml of water
Preparation of 0.1M sodium carbonate
28.6 g of sodium carbonate in 1000ml of water.
Report:
Carbonate buffer was prepared and the pH was found to be ——–
Preparation of Buffer Solutions: A Standard Procedural Guide
Buffer solutions are fundamental components in various scientific disciplines, particularly biochemistry, molecular biology, and analytical chemistry. They maintain a stable pH environment, crucial for many biological processes and chemical reactions. This article outlines the standard procedure for preparing buffer solutions.
Materials:
- Analytical balance
- Graduated cylinders
- Volumetric flasks
- Pipettes
- Magnetic stirrer with stir bar
- pH meter (calibrated)
- Deionized (DI) water
- Acid (weak)
- Base (conjugate of the weak acid) or vice versa
Procedure:
- Selection of Buffer System: Choose a suitable buffer system based on the desired pH range. Common buffer systems include:
- Acetate buffer (pH 3.6 – 5.5): Acetic acid (CH3COOH) and sodium acetate (CH3COONa)
- Phosphate buffer (pH 5.8 – 8.0): Phosphoric acid (H3PO4) and sodium phosphate (Na2HPO4 or Na3PO4)
- Tris-HCl buffer (pH 7.0 – 9.2): Tris(hydroxymethyl)aminomethane (Tris) and hydrochloric acid (HCl)
- Preparation of Stock Solutions: Prepare 0.1 M solutions of the chosen weak acid and its conjugate base (or vice versa) in separate volumetric flasks using DI water. Accurately weigh the required amount of the acid/base using the analytical balance and dissolve it in a portion of DI water. Dilute to the final volume with DI water and mix thoroughly using a magnetic stirrer.
- Calculation of Buffer Ratio: Utilize the Henderson-Hasselbalch equation to determine the appropriate ratio of acid to conjugate base for achieving the desired pH:
pH = pKa + log ([Base] / [Acid])
where:
- pH is the desired final pH
- pKa is the acid dissociation constant of the weak acid
- [Base] is the concentration of the conjugate base
- [Acid] is the concentration of the weak acid
Resources providing pre-calculated ratios for various buffer systems at specific pH values are available online or in reference books.
- Buffer Preparation: Using pre-calculated ratios or the Henderson-Hasselbalch equation, determine the volume of each stock solution needed. Pipette the calculated volumes of the acid and base stock solutions into a clean volumetric flask. Add a small amount (around 60%) of DI water and mix thoroughly.
- pH Measurement and Adjustment: Measure the pH of the prepared solution using a calibrated pH meter. If the pH deviates from the desired value, carefully add small aliquots of the more concentrated acid or base solution (depending on whether the measured pH is higher or lower than desired) while continuously monitoring the pH with stirring.
6. Dilution and Storage: Once the desired pH is achieved, dilute the solution to the final volume with DI water and mix thoroughly. Store the prepared buffer solution in a clean, labeled bottle at the appropriate temperature (usually 4°C).
Safety Precautions:
- Wear personal protective equipment (PPE) such as gloves, safety glasses, and lab coat while handling chemicals.
- Handle concentrated acids and bases with caution.
- Dispose of waste solutions according to recommended protocols.
Additional Notes:
- This is a general guideline, and specific protocols may vary depending on the chosen buffer system and application.
- For high-precision applications, consider using commercially prepared buffer solutions.
- Buffer capacity refers to the ability of a buffer to resist changes in pH upon addition of small amounts of acid or base. You can adjust the total concentration of the buffer solution (acid + conjugate base) to achieve the desired buffer capacity.
By following these steps and considering the additional notes, you can effectively prepare buffer solutions for your scientific experiments.
Frequently Asked Questions (FAQs)
A buffer solution is prepared to maintain a stable pH in a solution, even when small amounts of an acid or base are added. This stability is crucial in various chemical, biological, and pharmaceutical processes where pH fluctuations can affect the outcome or behavior of the substances involved.
A carbonate buffer consists of a mixture of weak acid (sodium bicarbonate) and its conjugate base (sodium carbonate). It is commonly used in laboratory settings to stabilize the pH around 9-10, which is ideal for various biochemical reactions, enzyme activities, and cell culture applications.
To prepare a 0.1 M sodium bicarbonate solution, dissolve 8.4 grams of sodium bicarbonate in 1000 mL of distilled water. Ensure the solute is fully dissolved by stirring the solution, and then transfer it to a volumetric flask to make up to the final volume accurately. This concentration provides an effective buffer capacity for maintaining a stable pH in slightly alkaline conditions.
A pH meter measures the hydrogen ion concentration in a solution to determine its pH. To measure, first calibrate the pH meter using standard buffer solutions of known pH (typically 4.0, 7.0, and 10.0). After calibration, rinse the electrode with distilled water, immerse it in the test solution, and wait for the reading to stabilize, which indicates the pH level.
Buffer solutions are critical in pharmaceutical sciences for formulating stable drug solutions, ensuring the correct pH for drug activity, and maintaining the stability and efficacy of active pharmaceutical ingredients (APIs). They also help in mimicking physiological conditions in research and testing.
Besides the carbonate buffer, common examples include acetate buffers, phosphate buffers, and tris buffers, each serving different pH ranges and specific applications such as protein purification, nucleic acid isolation, and cell culture.
Always wear appropriate personal protective equipment (PPE), such as gloves, goggles, and lab coats. Handle chemicals with care, especially when working with concentrated acids or bases. Ensure proper ventilation in the workspace and dispose of chemical waste following safety guidelines.