3312
In very heterogeneous samples with NMR nuclei at low abundance , such as soils , sediments , and air particulates , it can take days to acquire a conventional ( 13 ) C spectrum .
 ( 13 ) C
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 ( 13 ) C