1. Introduction
Citric acid (2-hydroxy-propane-1,2,3-tricarboxylic
acid) derives its name from the Latin word citrus, the
citrus tree, the fruit of which resembles a lemon. The acid
was first isolated from lemon juice in 1784 by Carl
Scheele, a Swedish chemist (1742–1786). Citric acid is a
tricarboxylic acid with a molecular weight of 210.14 Da.
In view of its three carboxylic acid functional groups, it
has three pKa values at pH 3.1, 4.7, and 6.4. Citric acid is a
nearly universal intermediate product of metabolism and
its traces are found in virtually all plants and animals.