You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

Determination of α-keto acids in pork meat and Iberian ham via tandem mass spectrometry. An analytical method which offers accurate determination and identification of eight α-keto acids (α-ketoglutaric acid, pyruvic acid, 4-hydroxyphenylpyruvic acid, 3-methyl-2-oxobutyric acid, α-keto-γ-methylthiobutyric acid, 4-methyl-2-oxovaleric acid, 3-methyl-2-oxovaleric acid, and phenylpyruvic acid) in pork meat and Iberian ham samples is reported. The method utilises a highly selective and sensitive method of multiple reaction monitoring (MRM) by mass spectrometry. The analytical method is simple (although the chemical derivatisation of the α-keto acids with dansylhydrazine is required), precise (<18% RSD), accurate (90-110%), sensitive (0.01-0.34mg/kg of defatted and freeze-dried meat depending on the α-keto acid) and linear (R>0.99) over several orders of magnitude (until 0.01-146.1mg/kg of defatted and freeze-dried meat depending on the α-keto acid). Using this methodology, α-keto acids were found to be present in pork meat to a low extent, and their concentration increased when they were determined in Iberian ham. This is the first report of the presence of α-keto acids in both pork meats and Iberian hams.
{"Chemical": ["3-methyl-2-oxobutyric acid", "phenylpyruvic acid", "4-methyl-2-oxovaleric acid", "pyruvic acid", "3-methyl-2-oxovaleric acid", "4-hydroxyphenylpyruvic acid", "dansylhydrazine", "\u03b1-keto-\u03b3-methylthiobutyric acid", "\u03b1-ketoglutaric acid", "\u03b1-keto acids", "\u03b1-keto acid"]}