Buffer solutions have the useful property of resisting changes in pH when hydrogen ions are added to or subtracted from the solution by chemical reactions or by other means. This is because a buffer solution contains both an acidic and a basic component. Buffer solutions are important because many reactions will work best within a cerain range of pH values. Aqueous buffer solutions can be prepared by several methods with the basic principle of all of them: the solution must contain the acid and the base of a conjugate in a reasonably similar and reasonably high concentration. In the direct method, the buffer is prepared by mixing the appropriate moles of “conjugate acid” with the appropriate number of moles of “conjugate base”. If the conjugate acid and base are not available, the buffer can be prepared by a indirect method, i.e. by partial conversion of the conjugate acid to conjugate base (and vice versa) using a strong acid or base as appropriate. In practice, biochemical buffers which cover a range of defined pH-values are prepared from stock solutions of the respective substances by mixing of appropriate amounts.