Re: what is tris buffered salt solution?

Hi Suzi,

TRIS is the short name commonly used for tris-(hydroxymethyl)aminomethane, a compound that is commonly used as a pH buffer in molecular biology/ biochemistry laboratory techniques. I'll discuss buffers briefly in this answer, but we already have some answers in our archives that discuss buffers. You can find those here, here, and here, and you can also use our Search Engine to look for more answers about pH buffers.

In general, a pH buffer is used to maintain a solution within a narrow pH range when strong acids or bases are introduced to that solution. For example, most (if not all) enzymes have an optimal pH in which they will function, and it is important to make sure that they remain in this pH range while they are working. Perhaps the products of the enzyme activity are strong acids or bases; we don't want these products to kill the activity of the enzyme.

In general, pH buffers are weak acids and bases that are present in a solution at high coincentrations. For biochemistry and molecular biology labwork, we tend to use what are called conjugate acid-base pairs to buffer our solutions. These are weak acids and bases that are forms of the same basic compound. When a strong acid or base is added to the solution, the weak base or acid of the buffer effectively neutralizes the strong acid or base, maintaining the pH. This system will work as long as the buffer exists in the solution in great excess over the volume of strong acid or base added to the solution.

The chemical formula of TRIS is (HOCH2)3CNH2. From the perspective of a pH buffer, the important part is the -NH2 group on the end. This group acts as a weak base. The conjugate acid (also called the salt) of TRIS is TRIS hydrochloride (aka TRIS HCl), which has the formula (HOCH2)3CNH3+ Cl-. Here, the important part is the -NH3+ group. TRIS HCl is a weak acid.

So, a TRIS HCl buffered solution is important to maintain a specific pH range for your DNA extraction. You didn't specify the pH of the solution in your question, so you should check your protocol to make sure you are using the proper conditions for your extraction.

You can find more information about TRIS in the Merck Index (which should be available in your local public or college library if it isn't in your lab), and (in addition to our archives) you should be able to find information about buffer systems in any college-level biochemistry textbook. I recommend "Biochemistry" by L. Stryer.

Good luck with your labwork, and keep asking questions!