Sustainable and Rapid Determination of Two Halogenated Pesticides in a Commercial Formulation by Solid Phase Microextraction and Liquid Phase Chemical Ionization Mass Spectrometry

Abstract

This work presents a sustainable and rapid method for halogenated pesticide analysis without chromatographic separation. The system is composed of a microfluidic open interface (MOI) for solid-phase microextraction (SPME) liquid phase desorption, connected to a liquid electron ionization mass spectrometry interface (LEI-MS). Either a triple quadrupole mass spectrometer (QQQ-MS/MS, (low-resolution) or a quadrupole-time-of-flight tandem MS (QTOF-MS/MS, high-resolution) were employed, each operating in negative chemical ionization (NCI) conditions. The flow rate used (100 µL/min) to rapidly empty the MOI chamber (approximately 2.5 µL) is reduced to the working flow rate of the LEI interface (500 nL/min) by a passive flow splitter (PFS). NCI is an appropriate ionization technique for electrophilic compounds, increasing specificity and reducing background noise. Two halogenated pesticides, dicamba and tefluthrin, were extracted simultaneously from a commercial formulation matrix (CF) using a C18 fiber by direct immersion (3 min under vortex agitation). Analyte desorption occurred in static conditions inside MOI filled with acidified acetonitrile (ACN) (0.2% phosphoric acid, PA). Extraction and desorption steps were optimized to increase efficiency and accelerate the process. No chromatographic separation was involved; therefore, the system fully exploited MS/MS selectivity and HRMS accuracy demonstrating good linearity, repeatability and limits of detection (LODs) and limits of quantification (LOQs) in the pg/mL range (50 and 500 pg/mL, respectively). Low-resolution experiments showed that matrix effects (ME) did not affect the results. The fast workflow (5 min) makes the system suitable for high-throughput analysis observing the principles of green analytical chemistry (GAC).

Exploring Negative Chemical Ionization of Per- and Polyfluoroalkyl Substances via a Liquid Electron Ionization LC-MS Interface

“…Due to the vast experience of this research group with the LEI interface and the awareness concerning how it works properly in terms of flow rate and type of solvent, − the idea was not to see the trends but to focus on two values to observe how combining these parameters affects the NCI mechanisms and the sensitivity of PFAS.…”

“…LEI has been amply demonstrated to allow the proper vaporization of LC-amenable compounds before reaching an under-vacuum ionization source, such as EI or CI. Several articles have provided a detailed description of the LEI setup. − In summary, a tee-connector is used to direct the reduced LC eluate as a liquid flow inside the inlet capillary. On the opposite end, the inlet capillary releases the liquid flow into the hot zone/vaporization microchannel (VMC), a coaxial capillary heated by the transfer line heater where it is inserted.…”

“…Cappiello and co-workers successfully determined two pesticides, dicamba and tefluthrin, in a single analysis, present at ultratrace levels in a commercial formulation using LC-LEI-MS/MS in NCI mode. , …”