Simulated intestinal fluid USP or Intestinal fluid, simulated, TS (Test Solution) is a simple buffer containing pancreatin used for dissolution testing. It is described in the Test Solution section of the United States Pharmacopeia. The term simulated intestinal fluid USP (without enzyme) refers to the commonly used solution without pancreatin (enzyme) and is often abbreviated to USP-SIF (sp), where "sp" stands for sine pancreatin. It was one of the first dissolution media to simulate the pH of the intestinal tract. However, it is significantly different from biorelevant intestinal media because it is just a buffer and does not contain the essential physiological surfactants present in human intestinal fluid.
USP-SIF (sp) – is a phosphate buffer containing a higher concentration of potassium ions compared to sodium.
The buffer has a pH of 6.8, with an osmolarity of approximately 110mOsmol/kg and buffer capacity around 18.5mEq/L/pH unit.