A good food source of magnesium contains a substantial amount of magnesium in relation to its calorie content and contributes at least 10 percent of the U.S. Recommended Dietary Allowance (U.S. RDA) for magnesium in a selected serving size. The U.S. RDA for magnesium is 400 milligrams per day. (The U.S. RDA given is for adults, except pregnant or lactating women, and children over 4 years of age.) Source USDA Citrates are compounds containing this group, either ionic compounds, the salts, or analogous covalent compounds, esters. An example of a salt is sodium citrate and an ester is trimethyl citrate. See category for a bigger list. Since citric acid is a multifunctional acid, intermediate ions exist, hydrogen citrate ion, HC6H5O72- and dihydrogen citrate ion, H2C6H5O7-. These may form salts as well, called acid salts. Salts of the hydrogen citrate ions are weakly acidic, while salts of the citrate ion itself (with an inert cation such as sodium ion) are neither acidic nor basic. Source from "http://en.wikipedia.org/wiki/Citrate"