Porous separation membrane

A porous separation membrane that has an asymmetric structure with a dense layer located near a first surface and a coarse layer located near a second opposite surface, and that supports a biocompatible polymer, wherein a proportion of carbon atoms (atom count percentage) derived from an ester group by measurement by an X-ray photoelectron spectrometer (XPS) is larger near the second opposite surface than the first surface, and the porous separation membrane meets requirements (1) and (2) given below in a surface analysis of a cross section containing the dense layer and the coarse layer performed by TOF-SIMS:

• (1) a minimum value of normalized intensity of the ion signal attributed to the biocompatible polymer in the coarse layer is 0.15 times or more of a maximum value thereof and
• (2) a normalized average intensity of the ion signal attributed to the biocompatible polymer in the dense layer is 2.0 times or more of a normalized average intensity of the ion signal attributed to the biocompatible polymer in the coarse layer;
• wherein the biocompatible polymer is a polymer containing a monocarboxylic acid vinyl ester unit;
• wherein the polymer containing a monocarboxylic acid vinyl ester is a copolymer including a hydrophobic unit and a hydrophilic unit;
• wherein the hydrophobic unit comprises a monocarboxylic acid vinyl ester unit;
• and
• wherein the hydrophilic unit is a vinylpyrrolidone unit.