MadSci Network: Chemistry |
Hello, Ron. You are more astute than our standard titration methods! When titrating, the (basic) titrant only "recognizes" total acidity in the product being tested. In titrations where there is more than one acid present in the sample, calculations are based on the predominant acid. In vinegars - whether they are produced from cider, grapes, malt, sugars, etc. - the main acid is acetic acid. As you already know from your classes, each ml of 0.1N NaOH titrant is the equivalent of 0.006005 g of acetic acid. Standard vinegar is usually about 5% acetic acid. In food production plants, they use more concentrated vinegars, right up to glacial acetic acid, diluting it as needed. To determine the quantities of individual acids present in a sample, you would use chromatography. High Performance Liquid Chromatography (HPLC) is commonly used now for analyzing components of many types of samples, including those with organic acids (such as acetic acid). After a sample is prepared, it is run on the HPLC with RI/UV detection (Refractive Index/Ultraviolet). A graph printout then shows peaks of the various components; the components are identified - as acetic acid, tartaric acid, etc. - by the time at which the peaks "come off" and they are quantified by comparing the size of the peaks against a standard. So, Ron, to measure the concentration of acetic acid in vinegar more precisely than titration allows, you will have to look at using a chromatographic technique. Carol Crouse The Food Chain Ltd.
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