Enabling Field Asymmetric Ion Mobility Spectrometry Separation of Fentanyl-Related Compounds Using Controlled Humidity

Advances in Heavy Metal Sensing: Utilizing Immobilized Chromogenic Reagents, Nanomaterials Perovskite and Nanonzymes

Heavy metal pollution is a major environmental and health problem due to the toxicity and persistence of metals such as lead, mercury, cadmium, and arsenic in water, soil, and air. Advances in sensor technology have significantly improved the detection and quantification of heavy metals, providing real-time monitoring and mitigation tools. This review explores recent developments in heavy metal detection, focusing on innovative uses of immobilized chromogenic reagents, nanomaterials, perovskites, and nanozymes. Immobilized chromogenic reagents, with their high specificity and visual detection capabilities, provide cost effective solutions for heavy metal detection. Techniques to improve their stability and sensitivity, including surface modifications and hybrid materials, are discussed. Nanomaterials, including quantum dots, metal-organic frameworks, and carbon-based nanostructures, have emerged as versatile platforms due to their unique physicochemical properties. These materials enable highly sensitive and selective sensing mechanisms, such as fluorescence quenching and electrochemical sensing. Perovskites, a class of materials known for their tunable optoelectronic properties, have shown great promise in the optical and electrochemical detection of heavy metals. Despite challenges related to stability and environmental safety, their potential for low-cost and scalable applications is remarkable. Nanozymes, synthetic enzyme mimics, offer robust and catalytic sensing capabilities, particularly in colorimetric and electrochemical analyses. Their superior stability and reusability compared to natural enzymes make them ideal candidates for environmental monitoring. This review provides a comparative analysis of these techniques, highlighting their strengths, limitations, and real-world applicability. Emerging trends include hybrid systems that combine the benefits of multiple approaches. The discussion concludes by addressing current challenges and providing perspectives on future directions for advancing heavy metal detection technologies to improve environmental health and safety. Integrating chromogenic reagents with perovskite materials represents a promising direction for developing robust, sensitive, and easy-to-use sensors for health and environmental safety monitoring.

Dependency of fentanyl analogue protomer ratios on solvent conditions as measured by ion mobility-mass spectrometry

Recently, our group has shown that fentanyl and many of its analogues form prototropic isomers ("protomers") during electrospray ionization. These different protomers can be resolved using ion mobility spectrometry and annotated using mobility-aligned tandem mass spectrometry fragmentation. However, their formation and the extent to which experimental variables contribute to their relative ratio remain poorly understood. In the present study, we systematically investigated the effects of mixtures of common chromatographic solvents (water, methanol, and acetonitrile) and pH on the ratio of previously observed protomers for 23 fentanyl analogues. Interestingly, these ratios (N-piperidine protonation vs. secondary amine/O = protonation) decreased significantly for many analogues (e.g., despropionyl ortho-, meta-, and para-methyl fentanyl), increased significantly for others (e.g., cis-isofentanyl), and remained relatively constant for the others as solvent conditions changed from 100% organic solvent (methanol or acetonitrile) to 100% water. Interestingly, pH also had significant effects on this ratio, causing the change in ratio to switch in many cases. Lastly, increasing conditions to pH ≥ 4.0 also prompted the appearance of new mobility peaks for ortho- and para-methyl acetyl fentanyl, where all previous studies had only showed one single distribution. Because these ratios have promise to be used qualitatively for identification of these (and emerging) fentanyl analogues, understanding how various conditions (i.e., mobile phase selection and/or chromatographic gradient) affect their ratios is critically important to the development of advanced ion mobility and mass spectrometry methodologies to identify fentanyl analogues.

Protonation-Induced Chirality Drives Separation by Differential Ion Mobility Spectrometry

Upon development of a workflow to analyze (±)-Verapamil and its metabolites using differential mobility spectrometry (DMS), we noticed that the ionogram of protonated Verapamil consisted of two peaks. This was inconsistent with its metabolites, as each exhibited only a single peak in the respective ionograms. The unique behaviour of Verapamil was attributed to protonation at its tertiary amino moiety, which generated a stereogenic quaternary amine. The introduction of additional chirality upon N-protonation of Verapamil renders four possible stereochemical configurations for the protonated ion: ( R,R ), ( S,S ), ( R,S ), or ( S,R ). The ( R,R )/( S,S ) and ( R,S )/( S,R ) enantiomeric pairs are diastereomeric and thus exhibit unique conformations that are resolvable by linear and differential ion mobility techniques.  Protonation-induced chirality appears to be a general phenomenon, as N -protonation of 12 additional chiral amines generated diastereomers that were readily resolved by DMS.