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.
S. P. L. Sørensen
Søren Peder Lauritz Sørensen (9 January 1868 – 12 February 1939) was a Danish chemist, famous for the introduction of the concept of pH, a scale for measuring acidity and alkalinity.