What is the fine-grained topic of the following text: Separation was carried out using a Discovery ZR-PBD analytical column (150 × 4.6 mm, 5 μm), and a mobile phase composed of a mixture of triethylammonium acetate buffer (pH 9; 50 mM) and methanol (22 : 78, v/v). Only return the topic.
Chemical Separation Process