Magnetic scavengers as carriers of analytes for flowing atmospheric pressure afterglow mass spectrometry (FAPA-MS)

Explosives removal and quantification using porous adsorbents based on poly(2-oxazoline)s with various degree of functionalization

Polymeric porous adsorbents are reported for removal of explosives, namely picric acid, 1,3,5-trinitro-1,3,5-triazinane (RDX), and pentaerythritol tetranitrate (PETN) and their subsequent quantification using direct analysis with ambient plasma mass spectrometry. The adsorbents are obtained by functionalization of short-chain poly(2-oxazoline)s with methyl ester side chains using 4-(aminomethyl)pyridine with a degree of functionalization equal to 0, 5, 10, and 20%. The subsequent step consist of cross-linking using a high internal phase emulsion procedure by further side-chain amidation with diethylenetriamine as crosslinker. Picric acid, RDX, and PETN were chosen as the model compounds as they belong to three different groups of explosives, in particular nitroaromatics, nitroamines, and nitrate esters, respectively. The adsorption isotherms, kinetics, as well as the influence of pH and temperature on the adsorption process was investigated. The porous adsorbents showed the highest maximum adsorption capacity towards picric acid, reaching 334 mg g-1, while PETN (80 mg g-1) and RDX (17.4 mg g-1) were less efficiently adsorbed. Subsequent quantification of the adsorbed explosives is performed by a specially designed ambient mass spectrometry setup equipped with a thermal heater. The obtained limits of detection were found to be 20-times improved compared to direct analysis of analyte solutions. The effectiveness of the proposed analytical setup is confirmed by successful quantification of the explosives in river water samples. The research clearly shows that functional porous adsorbents coupled directly with ambient mass spectrometry can be used for rapid quantification of explosives, which can be, e.g., used for tracking illegal manufacturing sites of these compounds.

The Electrospray (ESI) and Flowing Atmosphere-Pressure Afterglow (FAPA) Mass Spectrometry Studies of Nitrophenols (Plant Growth Stimulants) Removed Using Strong Base-Functionalized Materials

The functional silica-based materials functionalized with a strong nitrogen base TBD (SiO₂-TBD) deposited via a linker or with a basic poly(amidoamine) dendrimer containing multiple terminal amine groups -NH₂ (SiO₂-EDA) and functional polymers containing a strong phosphazene base (Polymer-Phosphazene) or another basic poly(amidoamine) dendrimer (PMVEAMA-PAMAM) were tested as sorbents dedicated to a mixture of nitrophenols (p-nitrophenol and 2-methoxy-5-nitrophenol), which are analogs of nitrophenols used in plant growth biostimulants. The adsorptive potential of the studied materials reached 0.102, 0.089, 0.140, and 0.074 g of the nitrophenols g⁻¹, for SiO₂-TBD, SiO₂-EDA, polymer-phosphazene, and PMVEAMA-PAMAM, respectively. The sorptive efficiency of the analytes, i.e., their adsorption on the functional materials, the desorption from the obtained [(sorbent)H⁺ − nitrophenolates^–] complexes, and interactions with the used soil, were monitored using mass spectrometry (MS) technique with electrospray (ESI) and flowing atmosphere-pressure afterglow (FAPA) ionizations, for the analysis of the aqueous solutions and the solids, respectively. The results showed that the adsorption/desorption progress is determined by the structures of the terminal basic domains anchored to the materials, which are connected with the strength of the proton exchange between the sorbents and nitrophenols. Moreover, the conducted comprehensive MS analyses, performed for both solid and aqueous samples, gave a broad insight into the interactions of the biostimulants and the presented functional materials.

Application of Molecularly Imprinted Polymers (MIP) and Magnetic Molecularly Imprinted Polymers (mag-MIP) to Selective Analysis of Quercetin in Flowing Atmospheric-Pressure Afterglow Mass Spectrometry (FAPA-MS) and in Electrospray Ionization Mass Spectrometry (ESI-MS)

Molecularly imprinted polymer (MIP) and magnetic molecularly imprinted polymer (mag-MIP) for solid extraction and pre-concentration of quercetin have been successfully prepared by thermal polymerization method using quercetin (Q) as a template, acrylamide (AA) as a functional monomer, and ethylene glycol dimethacrylate (EGDMA) as a cross-linking agent. The MIP and mag-MIP were successfully applied in analysis of quercetin by mass spectrometry (MS) methods. To perform ambient plasma ionization experiments, a setup consisting of the heated crucible, a flowing atmospheric-pressure afterglow (FAPA) plasma ion source, and amaZon SL ion trap (Bruker, Bremen, Germany) was used. The heated crucible with programmable temperature allowed desorption of the analytes from MIPs structure which resulted in their direct introduction into the ion stream. The results of Q-MIP/Q-mag-MIP and FAPA-MS measurements were compared with those of the analysis of quercetin by the ESI-MS method without extractions and pre-concentration of analytes on polymers. Limits of detection (LOD) for quercetin solutions in both positive and negative ESI-MS were established at 10⁻⁸ M and 10⁻⁷ M, respectively. The linearity (R² = 0.9999) of the proposed analytical procedure for quercetin determination in positive ions was provided in the range between 10⁻⁴ M and 10⁻⁷ M. Moreover, the same parameters were established for FAPA-MS in positive ions, reaching LOD at 0.005 mg/gMIP and the linearity of the method in the range of 0.015–0.075 mg/gMIP with the correlation coefficient value R² = 0.9850.

Molecularly imprinted polymers as selective adsorbents for ambient plasma mass spectrometry

The application of molecularly imprinted polymers (MIPs) as molecular scavengers for ambient plasma ionization mass spectrometry has been reported for the first time. MIPs were synthesized using methacrylic acid as functional monomer; nicotine, propyphenazone, or methylparaben as templates; ethylene glycol dimethacrylate as a cross-linker; and 2,2′-azobisisobutyronitrile as polymerization initiator. To perform ambient plasma ionization experiments, a setup consisting of the heated crucible, a flowing atmospheric-pressure afterglow (FAPA) plasma ion source, and a quadrupole ion trap mass spectrometer has been used. The heated crucible with programmable temperature allows for desorption of the analytes from MIPs structure which results in their direct introduction into the ion stream. Limits of detection, linearity of the proposed analytical procedure, and selectivities have been determined for three analytes: nicotine, propyphenazone, and methylparaben. The analytes used were chosen from various classes of organic compounds to show the feasibility of the analytical procedure. The limits of detections (LODs) were 10 nM, 10, and 0.5 μM for nicotine, propyphenazone, and methylparaben, respectively. In comparison with the measurements performed for the non-imprinted polymers, the values of LODs were improved for at least one order of magnitude due to preconcentration of the sample and reduction of background noise, contributing to signal suppression. The described procedure has shown linearity in a broad range of concentrations. The overall time of single analysis is short and requires ca. 5 min. The developed technique was applied for the determination of nicotine, propyphenazone, and methylparaben in spiked real-life samples, with recovery of 94.6–98.4%. The proposed method is rapid, sensitive, and accurate which provides a new option for the detection of small organic compounds in various samples.

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Flowing atmospheric pressure afterglow combined with laser ablation for direct analysis of compounds separated by thin-layer chromatography

A thin-layer chromatography-mass spectrometry (TLC-MS) setup for characterization of low molecular weight compounds separated on standard TLC plates has been constructed. This new approach successfully combines TLC separation, laser ablation, and ionization using flowing atmospheric pressure afterglow (FAPA) source. For the laser ablation, a low-priced 445-nm continuous-wave diode laser pointer, with a power of 1 W, was used. The combination of the simple, low-budget laser pointer and the FAPA ion source has made this experimental arrangement broadly available, also for small laboratories. The approach was successfully applied for the characterization of low molecular weight compounds separated on TLC plates, such as a mixture of pyrazole derivatives, alkaloids (nicotine and sparteine), and an extract from a drug tablet consisting of paracetamol, propyphenazone, and caffeine. The laser pointer used was capable of ablating organic compounds without the need of application of any additional substances (matrices, staining, etc.) on the TLC spots. The detection limit of the proposed method was estimated to be 35 ng/cm² of a pyrazole derivative.

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