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:

Simultaneous determination by LC-MS/MS of 25-methoxydammarane-3β,12β,20-triol epimers and active metabolites in rat plasma after intravenous administration. Abstract 1. The pharmacokinetics of the 25-OCH3-PPD epimers and active metabolites in rat plasma after a single intravenous (i.v.) administration were studied by a rapid, selective and sensitive UPLC-MS/MS method. 2. Chromatographic separation was performed on an Acquity UPLC with Agela C18 column, and the solvents of 5 mM ammonium acetate (pH 7.8) - acetonitrile (65: 35, v/v) were used as mobile phase for elution. The quantification was performed with the transitions of m/z 493.5 → 475.5 for 20(R,S)-25-OCH3-PPD, m/z 479.5 → 461.5 for 20(R,S)-25-OH-PPD. The Lower Limit Of Quantitation (LLOQ) was 20.0 ng mL(-1) for 20(R,S)-25-OCH3-PPD, 2.0 ng mL(-1) for 20(R,S)-25-OH-PPD in the plasma samples assay. 3. The pharmacokinetic parameters of AUC, t1/2 and MRT had no difference between 20(R)- and (S)-25-OCH3-PPD, but S-epimer has a lower plasma clearance compared to the R-isomer. The active metabolite 20(S)-25-OH-PPD showed significantly higher AUC, MRT and a longer half-life than that of 20(R)-25-OH-PPD. These assay results are necessary for the evaluation of the pharmacokinetic behavior of 25-methoxydammarane-3β,12β,20-triol in vivo.
{"Chemical": ["25-methoxydammarane-3\u03b2,12\u03b2,20-triol", "25-OCH3-PPD", "20(R)- and (S)-25-OCH3-PPD", "20(R)-25-OH-PPD", "20(R,S)-25-OH-PPD", "20(S)-25-OH-PPD", "ammonium acetate", "20(R,S)-25-OCH3-PPD", "acetonitrile"]}