Search Results (10)

Paper spray ionization mass spectrometry (PSI-MS) enables rapid analysis with minimal sample preparation, yet negative-ion mode performance has been limited by poor sensitivity and unstable signals, similar to conventional electrospray ionization. In this study, we optimized negative PSI tandem MS (MS/MS) for twelve endocrine-disrupting chemicals (EDCs) and related biomarkers—including bisphenols, phthalates, parabens, and substituted phenols—used as model analytes. A systematic solvent and additive screen identified 1 mM ammonium fluoride in methanol and 0.1% ammonium hydroxide in 9:1 MeOH/carbon tetrachloride as optimal conditions, providing enhanced deprotonated-ion intensities and improved stability. Calibration curves generated under these conditions showed excellent linearity, with limits of quantitation (LOQs) in the low-ppb range. Application to cosmetic formulations demonstrated reliable paraben quantitation. In fortified hand cream, LOQs below 1 mg/kg were achieved, with recoveries of 93–110% and intra- and inter-day precision below 10% RSD. Notably, PSI-MS/MS performance was comparable to LC–MS/MS, without a separation step. These results demonstrate the feasibility of optimized negative PSI-MS as a sensitive and robust tool for paraben determination in cosmetics and highlight its potential as a versatile platform for broader EDC quantification. Full article

This work reports on the development of an analyte sampling strategy on a plasmonic substrate to amplify the detection capability of a dual analytical system, paper spray ionization–mass spectrometry (PSI-MS) and surface-enhanced Raman spectroscopy (SERS). While simply applying only an analyte solution to the plasmonic paper results in a limited degree of SERS enhancement, the introduction of plasmonic gold nanoparticles (AuNPs) greatly improves the SERS signals without sacrificing PSI-MS sensitivity. It is initially revealed that the concentration of AuNPs and the type of analytes highly influence the SERS signals and their variations due to the “coffee ring effect” flow mechanism induced during sampling and the degree of the interfacial interactions (e.g., van der Waals, electrostatic, covalent) between the plasmonic substrate and analyte. Subsequent PSI treatment at high voltage conditions further impacts the overall SERS responses, where the signal sensitivity and homogeneity significantly increase throughout the entire substrate, suggesting the ready migration of adsorbed analytes regardless of their interfacial attractive forces. The PSI-induced notable SERS enhancements are presumably associated with creating unique conditions for local aggregation of the AuNPs to induce effective plasmonic couplings and hot spots (i.e., electromagnetic effect) and for repositioning analytes in close proximity to a plasmonic surface to increase polarizability (i.e., chemical effect). The optimized sampling and PSI conditions are also applicable to multi-analyte analysis by SERS and MS, with greatly enhanced detection capability and signal uniformity. Full article

Mass spectrometry (MS) is a highly selective and sensitive analytical tool with a myriad of applications, but such techniques are typically used in laboratory settings due to the handling and preparations that are necessary. The merging of two streams of robust research, portable MS systems and next-generation ambient ionization methods, now provides the ability to perform high-performance chemical screening in an on-site and on-demand manner, with natural applications in disciplines such as forensic science, where samples of interest are typically found in field environments (i.e., traffic stops, crime scenes, etc.). Correspondingly, investigations regarding the suitability and robustness of these methodologies when they are utilized for authentic forensic evidence processing are prudent. This work reports critical insights into the role that choice of spray solvent system plays regarding analytical performance of two spray-based ambient ionization sources, paper spray ionization (PSI) and filter cone spray ionization (FCSI), when employed for evidence types containing emerging synthetic cannabinoids. The systematic characterization studies reported herein show that the applied spray solvent can dramatically affect both spectral intensity and signal duration, and in some circumstances, yield deleterious false negative responses. Overall, acetonitrile-based systems are shown to strike a balance between analyte solubility concerns and spray ionization dynamics of the novel ion sources employed on portable MS systems. Full article

Sulfite, a widely used food additive, is subject to regulated labeling. The extraction of sulfite as the stable hydroxymethylsulfonate (HMS) form and its quantitative analysis by liquid chromatography-tandem mass spectrometry (LC-MS/MS) has been recognized for their good sensitivity, selectivity, and versatility across various food materials. This study aimed to develop a cost-effective and simpler method for sulfite quantitation, while maintaining the superior sensitivity and selectivity of mass spectrometry (MS). To achieve this, we introduced paper spray ionization (PSI), an ambient desorption ionization technique that could achieve the direct measurement of analytes without employing separation. We also employed a novel internal standard (IS) structurally similar to the analyte, replacing the more expensive isotopically labeled IS. Although the PSI-MS/MS method developed in this study exhibited slightly lower analytical performance compared to the conventional LC-MS/MS, it remained effective for sulfite analysis in dried fruits. Full article

Paper spray ionization mass spectrometry (PSI MS) has emerged as a notable method for the rapid analysis of biological samples. However, the typical cellulose-based paper tip is incompatible with protein detection due to the strong interaction between cellulose hydroxyl groups and proteins. In this study, we utilized a commercially available polyolefin-based synthetic paper, Teslin^®, as an alternative PSI substrate for simple protein analysis. We have named this method “droplet PSI” MS, as the aqueous protein solution droplet retains its shape on the Teslin^® paper tip. For droplet PSI, no further chemical pretreatment was necessary for the Teslin^® substrate; the only required preparation was shaping the Teslin^® paper into a triangular tip. In droplet PSI MS, protein ion signals were instantly detected from a protein solution droplet upon applying a spray solvent in situ along with high voltage (HV). When compared with conventional PSI MS, our method demonstrated superior sensitivity. The droplet PSI MS utilizing Teslin^® also showcased flexibility in real-time observation of protein alterations induced by an acid additive. Additionally, the effects of spray solvent composition and the application method were discussed. Full article

Rapid detection of harmful estrogens in cosmetics is essential in protecting public health. To reduce time-consuming pretreatment and analytical procedures, a novel reactive paper spray ionization mass spectrometry (RPSI-MS) methodology was developed. RPSI-MS is suitable for quantitatively analyzing estrogens in cosmetics by utilizing an online derivatization reaction between estrogens and 2-fluoro-1-methyl-pyridinium-p-toluene-sulfonate (FluMP). Using estradiol valerate as the internal standard (I.S.), three estrogens, estradiol, estriol, and ethinyloestradiol, in cosmetics were quantitatively characterized within minutes. Multiple parameters were optimized including FluMP concentration and volume, triethylamine amount as well as the drying time. The three estrogens displayed good linearity ranging from 0.002 to 1 μg/mL, with R² above 0.99. The recovery results of all the estrogens were within 80~111%. The limit of detection (LOD) was 0.001 μg/mL for the three estrogens. Compared to conventional paper spray ionization mass spectrometry (PSI-MS), extraction is not required and the detection sensitivity of RPSI-MS was improved by 34,000, 80,000, and 1400 times for estradiol, estriol, and ethinyloestradiol, respectively. The protocol established in this paper is sensitive, eco-friendly, and suitable for rapid testing of estrogens in cosmetics. Full article

Estrogens in personal care products are harmful to customers. Conventional methods such as HPLC and LC-MS require tedious sample pretreatment and long analytical time. Paper-spray ionization mass spectrometry (PSI-MS) is a powerful tool for the determination of compounds with little time and minimal pretreatment procedures. Since most estrogens show poor responses in PSI-MS, we developed a chemical derivatization and PSI-MS method to determinate three estrogens: estradiol, estriol and ethinyloestradiol with estradiol valerate as the internal standard (I.S.). After derivatization with 2-fluoro-1-methyl-pyridinium-p-toluene-sulfonate, the three estrogens could be quantified in seconds. This method showed good linearity in the range of 0.1~30 μg·mL⁻¹, with R² > 0.999. Their recovery results were all between 85%~115%. The limits of detection (LOD) were 0.04 μg·mL⁻¹, 0.02 μg·mL⁻¹ and 0.02 μg·mL⁻¹ for estradiol, estriol and ethinyloestradiol respectively, which improved around 200, 2000, and 900 times compared to non-derivative PSI-MS. The method could quantitatively determine estrogens in cosmetics. Full article

Paper spray ionization mass spectrometry (PSI-MS) is a direct MS analysis technique with several reported bacterial metabolomics applications. As with most MS-based bacterial studies, all currently reported PSI-MS bacterial analyses have focused on the chemical signatures of the cellular unit. One dimension of the bacterial metabolome that is often lost in such analyses is the exometabolome (extracellular metabolome), including secreted metabolites, lipids, and peptides. A key component of the bacterial exometabolome that is gaining increased attention in the microbiology and biomedical communities is extracellular vesicles (EVs). These excreted structures, produced by cells in all domains of life, contain a variety of biomolecules responsible for a wide array of cellular functions, thus representing a core component of the bacterial secreted metabolome. Although previously examined using other MS approaches, no reports currently exist for a PSI-MS analysis of bacterial EVs, nor EVs from any other organism (exosomes, ectosomes, etc.). PSI-MS holds unique analytical strengths over other commonly used MS platforms and could thus provide an advantageous approach to EV metabolomics. To address this, we report a novel application representing, to our knowledge, the first PSI-MS analysis of EVs from any organism (using the human gut resident Oxalobacter formigenes as the experimental model, a bacterium whose EVs were never previously investigated). In this report, we show how we isolated and purified EVs from bacterial culture supernatant by EV-specific affinity chromatography, confirmed and characterized these vesicles by nanoparticle tracking analysis, analyzed the EV isolate by PSI-MS, and identified a panel of EV-derived metabolites, lipids, and peptides. This work serves as a pioneering study in the field of MS-based EV analysis and provides a new, rapid, sensitive, and economical approach to EV metabolomics. Full article

Paper spray ionization (PSI) is an extractive ambient ionization technique for mass spectrometry (MS), whereby a triangular paper tip serves as the sampling base and the electrospray tip. During PSI, analytes are extracted and transported to the edge of the paper tip by the applied spraying solvent. Analytes can be purified from a sample matrix and separated from each other by this transportation process. In this study, we investigated and utilized the analyte transportation process of PSI for the in situ separation and analysis of lipid mixtures. We found that differential transport of phosphatidylcholine (PC) and triacylglycerol (TAG), the two most abundant lipid classes in animals, occurred during PSI. We also found that the order in which these lipids moved strongly depended on how the spraying solvent was applied to the paper base. The more polar PC moved faster than the less polar TAG during PSI, when a polar solvent was slowly fed into a paper tip, whereas TAG was transported faster than PC when excess solvent was applied to the tip at once. In addition, we achieved a complete separation and detection of PC and TAG by slowly supplying a nonpolar solvent to a PSI tip. Full article

Portable mass spectrometers (MS) are becoming more prevalent due to improved instrumentation, commercialization, and the robustness of new ionization methodologies. To increase utility towards diverse field-based applications, there is an inherent need for rugged ionization source platforms that are simple, yet robust towards analytical scenarios that may arise. Ambient ionization methodologies have evolved to target specific real-world problems and fulfill requirements of the analysis at hand. Ambient ionization techniques continue to advance towards higher performance, with specific sources showing variable proficiency depending on application area. To realize the full potential and applicability of ambient ionization methods, a selection of sources may be more prudent, showing a need for a low-cost, flexible ionization source platform. This manuscript describes a centralized system that was developed for portable MS systems that incorporates modular, rapidly-interchangeable ionization sources comprised of low-cost, commercially-available parts. Herein, design considerations are reported for a suite of ambient ionization sources that can be crafted with minimal machining or customization. Representative spectral data is included to demonstrate applicability towards field processing of forensic evidence. While this platform is demonstrated on portable instrumentation, retrofitting to lab-scale MS systems is anticipated. Full article