Identification of new interferences leached from plastic microcentrifuge tubes in electrospray ionization mass spectrometry

Abstract

Rationale: The incredible sensitivity of the modern mass spectrometry instrument enables scientists to detect a large number of molecules ranging from small organic compounds to biological macromolecules. However, the same sensitivity often throws up challenges with respect to background interferences and contaminants. The identification and source of these contaminants is very important for reducing background contamination and ensuring the accuracy of the analysis results. Methods: The interfering compounds were analyzed by high-performance liquid chromatography coupled with a hybrid quadrupole-orbitrap mass spectrometer. The structural analysis was conducted by obtaining the accurate masses of precursors and their fragment ions. The retention time and MS/MS spectrum of one of the interfering compounds (N-lauryldiethanolamine) were compared with an authentic standard to reach an unequivocal structural assignment. Results: The interferences (m/z 274 and 318 in positive mode) were observed during the analysis of herbicides in tea samples by electrospray ionization mass spectrometry (ESI-MS). Their structures were identified to be N-lauryldiethanolamine and N-(2-hydroxyethyl)-N-(2-(2-hydroxyethoxy)ethyl)dodecylamine by fragmentation interpretation and further confirmed by a standard compound. These interferences were found to be leached from the plastic microcentrifuge tubes used during sample pretreatment. The plastic tubes from two of the five suppliers tested were found to contain these two interferences. Conclusions: In this work, we presented an example about the observation, identification and source of interferences in ESI-MS. The N-lauryldiethanolamine and other ethoxylated aliphatic alkylamines are common plastic antistatic agents. They possess high proton affinity so that they show a strong response in ESI positive mode. In order to avoid their interference during mass spectrometric analysis we need to choose plastic tubes (or other plastic materials) that do not contain such antistatic agents.