A sensitive and selective method for the determination of selected pesticides in fruit by gas chromatography/mass spectrometry with negative chemical ionization

Multispectroscopic studies of binding interaction of phosmet with bovine hemoglobin

Phosmet is a phthalimide derived broad spectrum organophosphate pesticide which is vastly used across the globe to protect several ornamental or horticulture crops. The toxicity of phosmet is of utmost concern because of its direct effect on the nervous system of the victim after exposure. The mechanism of phosmet toxicity was explored by the interaction with the model blood protein which is hemoglobin. Bovine Hemoglobin (BHb) is a major protein of red blood cells (RBCs) that plays an important role in the exchange of gases for respiration and ensures adequate oxygen supply to tissues for oxygenation. In the current study, the interaction of BHb with phosmet was revealed using various spectroscopic techniques. Circular dichroism (CD) and Fourier transform infrared spectroscopy (FTIR) studies of BHb in the presence of phosmet showed secondary structural changes in the protein post binding, Fluorescence study shows the involvement of the dynamic quenching predominantly, Van't Hoffs thermodynamic study showed negative enthalpy value and free energy change and negative entropy change that revealed the involvement of hydrogen bonding and van der Waal forces predominantly further revealing spontaneous nature of binding interaction. The shift in Ultraviolet-visible spectra also revealed the nature of the interaction. In-silico study finally deduced the involvement of hydrogen bonding and polar interaction. The study inferred the moderate interaction of BHb with phosmet.

Liquid Chromatography-Electron Capture Negative Ionization-Tandem Mass Spectrometry Detection of Pesticides in a Commercial Formulation

Negative chemical ionization (NCI) and electron-capture negative ionization (ECNI) are gas chromatography-mass spectrometry (GC-MS) techniques that generate negative ions in the gas phase for compounds containing electronegative atoms or functional groups. In ECNI, gas-phase thermal electrons can be transferred to electrophilic substances to produce M^-• ions and scarce fragmentation. As a result of the electrophilicity requirements, ECNI is characterized by high-specificity and low background noise, generally lower than EI, offering lower detection limits. The aim of this work is to explore the possibility of extending typical advantages of ECNI to liquid chromatography-mass spectrometry (LC-MS). The LC is combined with the novel liquid-EI (LEI) LC-EIMS interface, the eluent is vaporized and transferred inside a CI source, where it is mixed with methane as a buffer gas. As proof of concept, dicamba and tefluthrin, agrochemicals with herbicidal and insecticidal activity, respectively, were chosen as model compounds and detected together in a commercial formulation. The pesticides have different chemical properties, but both are suitable analytes for ECNI due to the presence of electronegative atoms in the molecules. The influence of the mobile phase and other LC- and MS-operative parameters were methodically evaluated. Part-per-trillion (ppt) detection limits were obtained. Ion abundances were found to be stable with quantitative linear detection, reliable, and reproducible, with no influence from coeluting interfering compounds from the sample matrix.

Development of a flexible, sweat-based neuropeptide Y detection platform

Neuropeptide Y (NPY) biomarker levels have a close association with the diagnosis of Major Depression Disorder (MDD) and anxiety disorders. Quantifying NPY in correlation to self-reported symptoms will be an important measure to ensure a relatively uniform diagnosis and help with disease prognosis of these disorders. The work presented is a novel, passive eccrine sweat based, electrochemical detection platform for quantification of NPY biomarker levels. The paper offers a comparison between non-porous and porous sensor platforms using various electrochemical detection techniques. This work uses a novel strategy towards designing an optimal nanobioelectronic interface to measure NPY. The portability aspect of this detection platform is discussed by the demonstration a novel, portable EmStat Pico based electronic platform. The detection limit of the sensor is 10 pg mL⁻¹ and its range is 20–500 pg mL⁻¹. The NPY detection platform is envisioned to be a wearable point-of need monitoring system for management of chronic anxiety disorders and MDD.

Novel wearable NPY biomarker tracking system, envisioned to be a chronic anxiety and MDD management platform via self-monitoring.

Genomic Survey, Transcriptome, and Metabolome Analysis of Apocynum venetum and Apocynum hendersonii to Reveal Major Flavonoid Biosynthesis Pathways

Apocynum plants, especially A. venetum and A. hendersonii, are rich in flavonoids. In the present study, a whole genome survey of the two species was initially carried out to optimize the flavonoid biosynthesis-correlated gene mining. Then, the metabolome and transcriptome analyses were combined to elucidate the flavonoid biosynthesis pathways. Both species have small genome sizes of 232.80 Mb (A. venetum) and 233.74 Mb (A. hendersonii) and showed similar metabolite profiles with flavonols being the main differentiated flavonoids between the two specie. Positive correlation of gene expression levels (flavonone-3 hydroxylase, anthocyanidin reductase, and flavonoid 3-O-glucosyltransferase) and total flavonoid content were observed. The contents of quercitrin, hyperoside, and total anthocyanin in A. venetum were found to be much higher than in A. hendersonii, and such was thought to be the reason for the morphological difference in color of A. venetum and A. hendersonii. This study provides valuable genomic and metabolome information for understanding of A. venetum and A. hendersonii, and lays a foundation for elucidating Apocynum genus plant flavonoid biosynthesis.

Ultra-sensitive biosensor based on genetically engineered acetylcholinesterase immobilized in poly (vinyl alcohol)/Fe-Ni alloy nanocomposite for phosmet detection in olive oil

An ultra-sensitive screen-printed biosensor was successfully developed for phosmet detection in olive oil, based on a genetically-engineered acetylcholinesterase (AChE) immobilized in a azide-unit water-pendant polyvinyl alcohol (PVA-AWP)/Fe-Ni alloy nanocomposite. Fe-Ni not only allowed amplifying the response current but also lowering the applied potential from 80 mV to 30 mV vs Ag/AgCl. The biosensor showed a very good analytical performance for phosmet detection, with a detection limit of 0.1 nM. This detection limit is lower than the allowable concentrations set by international regulations. In addition to the good reproducibility, operational and storage stability, the developed biosensor was successfully used for the determination of phosmet in olive oil samples without any laborious pre-treatment. The phosmet recovery rate was about 96% after a simple liquid-liquid extraction.

Analysis of Trace Quaternary Ammonium Compounds (QACs) in Vegetables Using Ultrasonic-Assisted Extraction and Gas Chromatography-Mass Spectrometry

A reliable, sensitive, and cost-effective method was developed for determining three quaternary ammonium compounds (QACs) including dodecyltrimethylammonium chloride, cetyltrimethylammonium chloride, and didodecyldimethylammonium chloride in various vegetables using ultrasonic-assisted extraction and gas chromatography-mass spectrometry. The variety and acidity of extraction solvents, extraction times, and cleanup efficiency of sorbents were estimated to obtain an optimized procedure for extraction of the QACs in nine vegetable matrices. Excellent linearities (R(2) > 0.992) were obtained for the analytes in the nine matrices. The limits of detection and quantitation were 0.7-6.0 and 2.3-20.0 μg/kg (dry weight, dw) in various matrices, respectively. The recoveries in the nine matrices ranged from 70.5% to 108.0% with relative standard deviations below 18.0%. The developed method was applied to determine the QACs in 27 vegetable samples collected from Guangzhou in southern China, showing very high detection frequency with a concentration of 23-180 μg/kg (dw).

Negative chemical ionization gas chromatography coupled to hybrid quadrupole time-of-flight mass spectrometry and automated accurate mass data processing for determination of pesticides in fruit and vegetables

Gas chromatography coupled to high resolution hybrid quadrupole time-of-flight mass spectrometry (GC-QTOF MS), operating in negative chemical ionization (NCI) mode and combining full scan with MSMS experiments using accurate mass analysis, has been explored for the automated determination of pesticide residues in fruit and vegetables. Seventy compounds were included in this approach where 50 % of them are not approved by the EU legislation. A global 76 % of the analytes could be identified at 1 μg kg(-1). Recovery studies were developed at three concentration levels (1, 5, and 10 μg kg(-1)). Seventy-seven percent of the detected pesticides at the lowest level yielded recoveries within the 70 %-120 % range, whereas 94 % could be quantified at 5 μg kg(-1), and the 100 % were determined at 10 μg kg(-1). Good repeatability, expressed as relative standard deviation (RSD <20 %), was obtained for all compounds. The main drawback of the method was the limited dynamic range that was observed for some analytes that can be overcome either diluting the sample or lowering the injection volume. A home-made database was developed and applied to an automatic accurate mass data processing. Measured mass accuracies of the generated ions were mainly less than 5 ppm for at least one diagnostic ion. When only one ion was obtained in the single-stage NCI-MS, a representative product ion from MSMS experiments was used as identification criterion. A total of 30 real samples were analyzed and 67 % of the samples were positive for 12 different pesticides in the range 1.0-1321.3 μg kg(-1).

Screening and quantification of pesticide residues in fruits and vegetables making use of gas chromatography-quadrupole time-of-flight mass spectrometry with atmospheric pressure chemical ionization

An atmospheric pressure chemical ionization source has been used to enhance the potential of gas chromatography coupled with quadrupole time-of-flight (QTOF) mass spectrometry (MS) for screening and quantification purposes in pesticide residue analysis. A screening method developed in our laboratory for around 130 pesticides has been applied to fruit and vegetable samples, including strawberries, oranges, apples, carrots, lettuces, courgettes, red peppers, and tomatoes. Samples were analyzed together with quality control samples (at 0.05 mg/kg) for each matrix and for matrix-matched calibration standards. The screening strategy consisted in first rapid searching and detection, and then a refined identification step using the QTOF capabilities (MS(E) and accurate mass). Identification was based on the presence of one characteristic m/z ion (Q) obtained with the low collision energy function and at least one fragment ion (q) obtained with the high collision energy function, both with mass errors of less than 5 ppm, and an ion intensity ratio (q/Q) within the tolerances permitted. Following this strategy, 15 of 130 pesticides were identified in the samples. Afterwards, the quantitation capabilities were tested by performing a quantitative validation for those pesticides detected in the samples. To this aim, five matrices were selected (orange, apple, tomato, lettuce, and carrot) and spiked at two concentrations (0.01 and 0.1 mg/kg), and quantification was done using matrix-matched calibration standards (relative responses versus triphenyl phosphate used as an internal standard). Acceptable average recoveries and relative standard deviations were obtained for many but not all pesticide-matrix combinations. These figures allowed us to perform a retrospective quantification of positives found in the screening without the need for additional analysis. Taking advantage of the accurate-mass full-spectrum data provided by QTOF MS, we searched for a higher number of compounds (up to 416 pesticides) in a second stage by performing extra data processing without any new sample injection. Several more pesticides were detected, confirmed, and/or tentatively identified when the reference standard was unavailable, illustrating in this way the potential of gas chromatography-QTOF MS to detect pesticides in addition to the ones targeted in quantitative analysis of pesticides in food matrices.