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:

Laboratory performance on analysis of mandatory nutrients and preparation of nutrition labelling. This study assessed the performance of 17 laboratories in Thailand in analysing mandatory nutrients in salted, fried broad bean and in using data to prepare nutrition labels. Nutrient levels in the test material, as robust mean (x(∗)) and robust standard deviation (s(∗)), were assigned in line with ISO 13528. Data obtained from the laboratories were statistically evaluated against these values. Laboratories with satisfactory, questionable and unsatisfactory results for each nutrient were identified based on robust z-score. Laboratories achieving satisfactory analytical results (z-score⩽2) were for lipid, 82%; protein, 85%; Na, 82%; Ca, 62%; Fe, 81%; ash, 70%; and moisture, 62%. Reference values for some nutrients in broad bean powder were developed using data from satisfactorily performing laboratories. Less than 20% of the laboratories demonstrated good performance in preparing nutrition labels. Common mistakes were the nutrition information format, estimation of serving size and serving(s) per package.
{"Chemical": ["Ca", "Fe", "Na"]}