Enhanced LC-ESI-MS/MS Sensitivity by Cationic Derivatization of Organophosphorus Acids

Area of Science:

• Environmental Chemistry
• Analytical Chemistry
• Mass Spectrometry

Background:

• Organophosphorus (OP) acids are critical environmental degradants of OP nerve agents and pesticides.
• Accurate detection of these compounds is vital for environmental monitoring and safety.
• Existing analytical methods may lack sufficient sensitivity for trace-level OP acid detection.

Purpose of the Study:

• To develop and illustrate a chemical derivatization method to enhance signal intensity and signal-to-noise ratios for OP acids.
• To improve the limits of identification (LOIs) for OP acids using liquid chromatography tandem mass spectrometry (LC-ESI-MS/MS).
• To investigate the utility of this derivatization for screening and identifying target and unknown OP acids in various matrices.

Main Methods:

• Utilized N-(2-(bromomethyl)benzyl)-N,N-diethylethanaminium bromide (CAX-B) for derivatization.
• Analyzed a panel of eight OP acids, including alkyl methylphosphonic acids and dialkylphosphate analogs.
• Conducted derivatization in acetonitrile with potassium carbonate at 70 °C for 1 hour.
• Performed analysis using LC-Orbitrap-ESI-MS/MS and LC-MS(QqQ) in MRM mode.

Main Results:

• Derivatization with CAX-B increased LOIs by one to over two orders of magnitude (from 1-10 ng/mL to 0.02-0.2 ng/mL).
• Enhanced sensitivity was observed across various sample matrices, including hair, concrete, and plant extracts.
• ESI-MS/MS spectra of derivatized acids showed characteristic neutral losses and a core organophosphorus ion, aiding identification.

Conclusions:

• The CAX-B derivatization method provides a significant improvement in the detection sensitivity of OP acids.
• This approach is effective for the screening and identification of both known and unknown OP acids in complex environmental samples.
• The enhanced LOIs make this method valuable for trace analysis of OP acid contaminants.