How to Make Sodium Citrate Buffer

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In six easy steps, learn how to make sodium citrate buffer. Sodium citrate or trisodium citrate can buffer solutions in the pH range of about 3 to 6.2. Citric acid can do the job as well.

Sodium citrate buffer is used for RNA isolation because it minimizes base hydrolysis of the RNA strands. This makes it an important step in the mRNA purification during genomic research or for studying transcription. Citrate-based buffers can also aid the detection of antigens in fixed tissue preparations because they break the cross-links formed between the antigens and the fixation media.

With the guide below, make a sodium citrate buffer of pH 6. The instructions are not only easy but quick to execute also. It should only take you about 10 minutes to complete these steps.

Two Options to Make the Buffer

There are two ways to go about making a sodium citrate buffer. First, determine whether you have both citric acid and the conjugate base, sodium citrate, to work with. If you only have citric acid, it's not a problem. You can still make the buffer.

On the other hand, if you have both the acid and base, create a stock solution of each. Mix 21 grams of citric acid in 1 liter of distilled water, and 29.4 grams of sodium citrate in 1 liter of distilled water.

If you only have citric acid, mix 2.1 grams in just under 1 liter of distilled water and proceed to the next step.

Mixing Citric Acid and Sodium Citrate Solutions

Now that you've created your stock solution (if you had both an acid and a base) or mixed your acid in distilled water (if you didn't), you can focus on your solutions.

Mix 82 milliliters of the citric acid solution with 18 milliliters of the sodium citrate solution. Then, make the total volume of the mixture up to just under 1 liter with distilled water. Leave enough volume to allow for the addition of sodium hydroxide (NaOH) in the next step.

Adjusting the pH

While gently stirring the solution using a magnetic stirrer, use 1M sodium hydroxide to adjust the pH of the mixture to 6.0. After that, make the final volume of the solution up to 1 liter with distilled water by using a volumetric flask.

What You Need to Make the Buffer

Not only won't it take you very long to make the sodium citrate buffer, you also won't need many materials for it either. With citric acid, 1M of sodium hydroxide, distilled water, and a calibrated pH probe, you'll be halfway there. Using sodium citrate is optional.

Making the buffer will also require a 1 liter graduated cylinder, a 1-liter volumetric flask, and three 1 liter media bottles. Lastly, you'll need a magnetic stir bar and a magnetic stirrer.

If you don't have all of these materials, consider using the lab at your school or work site, so you don't have to purchase them yourself. You can also easily purchase these materials online or visit a specialty goods store in your area.