Aluminas used for column chromatography or thin-layer chromatography are treated with acid or base to adjust the pH of the 10% slurry (weight/volume in water) to acidic, basic or neutral. These are designated A, B, and N, respectively. Acidic alumina has a pH of about pH 4.5, basic alumina has a pH of about pH 10. After preparation (precipitation), alumina contains an alkaline extract (up to pH 11), from which neutral alumina is obtained by washing with distilled water. If acidic alumina is required, the adsorbent is adjusted with an acid in suspension until the pH of the extract is 4-6.