Gastric acid
The highest concentration that gastric acid reaches in the stomach is 160 mM in the canaliculi. This is about 3 million times that of arterial blood, but almost exactly isotonic with other bodily fluids. The lowest pH of the secreted acid is 0.8, but the acid is diluted in the stomach lumen to a pH between 1 and 3.
Enceladus
A model suggests that Enceladus's salty ocean (-Na, -Cl, -CO) has an alkaline pH of 11 to 12. The high pH is interpreted to be a consequence of serpentinization of chondritic rock that leads to the generation of H, a geochemical source of energy that can support both abiotic and biological synthesis of organic molecules such as those that have been detected in Enceladus's plumes.