During MS/MS analysis of unknown compounds there are fragment ions that form via the loss of a neutral fragment, which can either be a neutral molecule or a neutral radical. We are using the term “dark matter,” somewhat tongue in cheek, to describe this classic neutral loss. Similar in concept to the physics term for dark matter, the neutral loss is not directly observed. Rather it is determined as the accurate mass difference between two ions. Typically, it is the major loss between the protonated molecule and its major fragment ion. It can also be the neutral loss between various fragment ions within a molecule. In this talk, we will show the use of an acquisition mode called “All Ions” to fragment all possible precursors in a wastewater sample followed by searching for all neutral losses of the dimethylamine fragment with an accurate mass loss of 45.0578 mass units. The dimethylamine fragment has been shown to give rise to NDMA in the presence of monochloramine (a drinking water chlorination reagent). The dimethylamine gives a neutral loss of 45.0578 mass units which can only result from the structure of dimethylamine in the precursor molecule. A hidden assumption is that there is a link between the bond strength required to cleave the dimethylamine-carbon bond by monochloramine and the MS/MS fragmentation pattern. Using the neutral loss of 45.0578, we found several possible NDMA precursors in wastewater samples, including metabolites of a cough suppressant (dextromethorphan) and methadone (a drug used to treat heroin addiction). Methadone was then shown to have a high NDMA potential (60% conversion), while the dextromethorphan had a low potential. Both examples are related to the MS/MS fragmentation pattern but in different ways, which will be related to MS/MS intensity. This “dark matter” neutral loss tool could be used to find other nitrosoamines, such as ethyl and methyl combinations and this will be demonstrated using the same accurate mass data set.

Using dark matter accurate mass to discover NDMA precursors in wastewater

253rd National Meeting (2017)

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