TEACl

Prepare a 5 M solution of TMACl or a 3 M solution of TEACl in H₂O. TMACl is used with probes that are 14-50 nucleotides in length, whereas TEACl is used with oligonucleotides that are 50-200 nucleotides in length. To the solution of TMACl or TEACl, add activated charcoal to a final concentration of approx. 10% and stir for 20-30 minutes. Allow the charcoal to settle, and then filter the solution of quaternary alkylammonium salts through a Whatman No. 1 paper. Sterilize the solution by passage through a nitrocellulose filter (0.45-μm pore size). Measure the refractive index of the solution, and calculate the precise concentration of the quaternary alkylammonium salts from the equation: C = (n - 1.331)/0.018, where C is the molar concentration of quaternary alkylammonium salts and n is the refractive index.

Store the filtered solution in dark bottles at room temperature.