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:

A new method for preparing pentacyclic triterpene rich Centella asiatica extracts. This study evaluated microwave-assisted extraction (MAE) for four pentacyclic triterpenes as well as developed a method for preparing a pentacyclic triterpenene rich extract from Centella asiatica. MAE was capable of increasing the yield of the pentacyclic triterpenes up to twice that produced by the heat reflux method, and it was also much less time consuming. The optimal conditions of MAE employed were extraction with absolute ethanol as solvent, an irradiation power of 600 W, at 75°C, four irradiation cycles and four extraction times. Here, we provide a simple method for the preparation of the pentacyclic triterpene rich C. asiatica extracts, which contained not less than 65% w/w total pentacyclic triterpenes. The method involved a macroporous resin (Diaion® HP-20) column eluted with ethanol and a decolourisation step with activated charcoal.
{"Chemical": ["pentacyclic triterpenes", "pentacyclic triterpenene", "pentacyclic triterpene", "ethanol"]}