An FDA chemist uses gas chromatography to measure levels of melamine in food samples. In March 2007, FDA learned that some pet foods were making cats and dogs sick; in fact, many died. An investigation led FDA to discover contaminants that were imported into the United States and used as ingredients in pet food. Ultimately, investigators linked the melamine contamination to other products. Gas chromatography (GC), is a common type of chromatography used in analytical chemistry for separating and analyzing compounds that can be vaporized without decomposition. Typical uses of GC include testing the purity of a particular substance, or separating the different components of a mixture.