Look for the chemical in the MW database. Then use the MW Remove shell preset. If the chemical is not in the database and you can find the molar mass or molecular weight of the chemical, you may add it yourself with the Create Program tool. Let's say the molecular weight of substance X is 1234.56 g/mol. Then, put the letter M in front of the molecular weight as a frequency, i.e., M1234.56.
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