PURPOSE: To prevent damage to a column due to thermal and oxidative deterioration even when the column is used at high temp. of 500°C or higher by coating the surface of an aluminum coated capillary column with a ceramic type oxidation preventing protective film.

CONSTITUTION: A ceramic type oxidation preventing protective film is formed by coating a column with a coating solution containing a metal oxide type polymer and drying the coated film at room temp. or heating the same at low temp. to form a ceramic film excellent in heat resistance. The thickness thereof is pref. 5 - 20 μm and, when said thickness is below 5 μm, desired heat resistance imparting effect is not obtained and, when the thickness exceeds 20 μm, flexibility becomes inferior. As the metal oxide type polymer, alkali metal or organopolymetal having a specific structure is used. A capillary column is prepared, for example, by a method wherein a quartz pipe 1 is heated and melted in a melting furnace 2 to be drawn out from the other end of the furnace 2 so as to form a fine pipe having an outer diameter of 500 μm or less and this fine pipe is coated with aluminum immediately after drawing-out and subsequently coated with ceramics using a die 5 and cured in a curing oven 6 to be taken up by a winder 7.