Analytical challenges in the confirmative identification of dipyrone as an adulterant in illicit drug samples

- Dipyrone undergoes thermal and/or hydrolytic decomposition during GC and GC-MS analysis.
- There are two possible decomposition products: aminopyrine and 4-methylaminoantipyrine.
- NMR spectroscopy and ESI mass spectrometry can be used to confirm the presence of dipyrone.
- NMR spectroscopy can be used to confirm or refute the presence of dipyrone, aminopyrine and 4-methylaminoantipyrine.

Dipyrone is an analgesic and antipyretic drug that is sometimes encountered as an adulterant in illicit drug samples, particularly illicit fentanyl containing samples. It undergoes thermal decomposition to aminopyrine and 4-methylaminoantipyrine during analysis via gas chromatography (GC-FID) and gas chromatography-mass spectrometry (GC-MS). During analysis via high pressure liquid chromatography (HPLC) and high pressure liquid chromatography-mass spectrometry (HPLC-MS), it undergoes hydrolytic decomposition solely to 4-methylaminoantipyrine. Given that mass spectrometry is a widely used confirmatory analytical technique, these instabilities present challenges for the forensic chemist seeking to confirm the presence of dipyrone. Studies were conducted to determine rigorous confirmative protocols for the identification of dipyrone in multicomponent illicit drug samples.