Concentrated lemon juice is made by removing water from lemon juice. It is still sold in liquid form but is typically more sour than regular or freshly squeezed lemon juice, so you don't need to use very much to get a tart lemon taste. Pure lemon juice is used for cooking, baking and making salad dressings and marinades.
Like other citrus fruits, lemons are high in vitamin C; a cup of bottled lemon juice contains 60.5 milligrams of this vitamin. It also contains 37 international units of vitamin A, 27 milligrams of calcium, 249 milligrams of potassium and 51 milligrams of sodium. Additionally, the U.S. Department of Agriculture's Nutrient Database notes that lemon juice contains trace amounts of iron, zinc, vitamin E and other nutrients.