Waldemar Tomaszewski

Limits of detection of explosives as determined with IMS and field asymmetric IMS vapour detectors

Performance of two handheld trace explosives detectors types: SABRE 4000 and MO-2M was compared in terms of the limits of detection determined for: trinitrotoluene, hexahydro-1,3,5-trinitro-1,3,5-triazine, pentaerythritol tetranitrate and nitroglycerin in the particle detection mode. SABRE 4000 detector is a conventional detector based on the ion mobility spectrometry (IMS) and radioactive nickel as the ionization source, whereas in the MO-2M type detector a variant of this technique, viz. the field asymmetric ion mobility spectrometry (FAIMS), and a different β emitter, tritium, as an ionization source are employed. In determining limits of detection the sampling technique was suggested which resorts to binomial distribution for the determination of the indispensable number of positive measurements required to regard a given amount of explosives detected as reliable. Lower limits of detection were achieved in the study for trinitrotoluene and hexahydro-1,3,5-trinitro-1,3,5-triazine with the MO-2M detector (10- and 100-fold, respectively) than with the SABRE detector, whereas for the remaining two substances limits of detection were identical for either detector. The results obtained were discussed in the aspect of the effect of the detector design, ionization mechanism and volatility of substance as the factors that determine the limits of detection values.

High-density polystyrene-grafted silver nanoparticles and their use in the preparation of nanocomposites with antibacterial properties

The achievement of uniform nanoparticles distribution in polymer matrix is still a major challenge in the design and fabrication of polymer nanocomposites with desired properties. In this paper we propose a novel approach for the preparation of homogeneous polystyrene/silver nanocomposites utilizing Nitroxide Mediated Radical Polymerization (NMRP). In the first step of the developed procedure, the polystyrene grafted silver nanoparticles (Ag@PS) with well-defined core-shell structure and exceptionally high grafting density (from 2 chains/nm2 to 5.9 chains/nm2) have been synthesized through late injection of nitroxide-coated silver nanoparticles (N-AgNPs) into a TEMPOL mediated styrene polymerization system. Afterwards, the synthesized Ag@PS have been used for the preparation of nanocomposites (PS/Ag@PS) by mixing them with narrow-dispersity polystyrenes and thermoforming at 140°C. Due to the high flexibility of polymer chains attached to silver surface through nitroxide linker, free volume effect enables interpenetration of polystyrene molecules that provides excellent mutual miscibility of Ag@PS with polymer matrix. The synthesized nanohybrids (Ag@PS) and their nanocomposites (PS/Ag@PS) exhibit effective antibacterial activity with respect to pathogenic bacteria: Pseudomonas aeruginosa (Gram-negative representative) and Staphylococcus aureus (Gram-positive representative).

A smart synthesis of gold/polystyrene core-shell nanohybrids using TEMPO coated nanoparticles†

This paper describes a novel route to the synthesis of core–shell nanostructures utilizing Nitroxide Mediated Radical Polymerization (NMRP). The hybrid nanostructures with nanogold cores and precisely designed polystyrene shells (PDI < 1.3) have been synthesized through late injection of TEMPO coated gold nanoparticles into a TEMPOL (4-hydroxy-TEMPO) mediated styrene polymerization system. Thermal analyses have shown that the thus obtained polystyrene modified gold nanoparticles are significantly more stable to the thermal treatment than only thiol-stabilized gold nanoparticles (aggregation has not been observed even at 300 °C). The obtained materials exhibit intensive surface plasmon resonance (SPR) observed near 520 nm that provides an opportunity to apply them as high-temperature optical sensors. The proposed procedure allows for precise synthesis of tailor-made nanohybrids via macroradical coupling.

Evaluation of adsorption and desorption steps in the solid‐phase extraction of explosives using carbon/silica gel nanocomposites

New series of carbon/silica gel nanocomposites, carbosils, prepared by the carbonization of starch bound to silica gel, and carbosils additionally silylated with octadecyldimethylchlorosilane were synthesized. These materials were applied as adsorbents in the solid-phase extraction of explosive nitrate esters and nitroaromatics from aqueous solutions. The adsorption and desorption steps were evaluated separately. It was found that both the molecular properties of explosives (dipole moments, orbital energies, solvation effects) and textural properties influenced by carbon deposits or octadecyl moieties have a large impact on the recovery rates. It was shown that the composites with moderate content of carbon deposits or with the highest amounts of carbon deposits and additionally silylated can be used as materials tailored for extraction of explosives from the aqueous solutions.

Effect of the surface properties of resorcinol–formaldehyde resin/carbon nanocomposites and their carbonization products on the solid-phase extraction of explosives

Two polymer–nanocarbon composites, containing carbon nanotubes or exfoliated graphite, were prepared using resorcinol–formaldehyde resin. By carbonization of the composites, two additional carbon-based nanomaterials were obtained. The resulting materials were investigated with respect to their textural and morphological characteristics. The prepared composites were employed as sorbents for the separation of explosives (nitramines, nitrate esters and nitroaromatics) from aqueous samples by solid-phase extraction (SPE). The SPE results, i.e., the adsorption and desorption rates, are separately discussed. Both polymeric and carbonized composites (with nanotubes as a filler) gave high recovery rates, which reached 90%, and proved to be very effective for the extraction of explosives. The observed differences in the SPE performance of the carbonized composites were explained in terms of their porous structure, which depended on the route followed in the carbonization process. It was suggested that this process was predominantly influenced by the properties of the nanofillers employed, e.g., their high thermal conductivity, tendency to agglomerate and interactions with resin components.

Interfacial behavior of water bound to nitrocellulose containing residual nitric and sulfuric acids

To prepare nitrocellulose (NC), microcrystalline cellulose was treated in a mixture of nitric and sulfuric acids. Prepared NC containing a small amount of acids was studied at a different hydration degree (h = 10–1000 mg g−1) in different dispersion media (chloroform-d, acetone-d6 or their mixtures) using low-temperature 1H NMR spectroscopy. The hydration degree and the presence of residual acids affected the temperature dependence of the chemical shifts of proton resonance of water bound to NC. The Gibbs free energy of bound water became less negative with increasing hydration rate. The chloroform and acetone media affect the behavior of bound-to-NC water unfrozen at T<273 K differently. Quantum chemical calculations were performed using ab initio (HF/6-31G(d,p)), DFT (B3LYP/6-31G(d,p)) and semiempirical PM7 methods to analyze the interfacial behavior of water interacting with NC containing residual amounts of nitric and sulfuric acids.

Solid-phase extraction of explosive nitramines on macroreticular polymers modified by freezing with water or acetone.

A novel approach is proposed to modify the porous structure and surface properties of the polymers used in solid-phase extraction. The approach involves soaking in water or acetone, followed by freezing in liquid nitrogen (77.4 K) and was employed for two polymeric materials: Amberlite XAD-7 and Amberlite XAD-16. Variations in the surface properties of the adsorbents were justified by the action of acetone and water as solvents affecting the textural and other characteristic of the materials. The initial and treated adsorbents were used in extraction of explosive nitramines from aqueous samples. The performed modifications of the polymer texture allow us to increase the recovery rate as compared with the initial adsorbents. The results were justified by the swelling of fragments of the polymers and by the additional process of sorption of nitramines. The results indicate that polymeric adsorbents can be easily modified by the soaking/freezing process and the materials can be achieved that prove usefulness for the effective separation of explosive nitramines from aqueous samples.

Application of Carbon Adsorbents for Extraction of MDMA Impurities in TLC Drug Profiling

Abstract The efficiency of carbon adsorbents in the extraction of impurities from 1‐phenylethylamine (a model substance) and MDMA (3,4‐methylenedioxymethamphetamine), the main psychoactive component of ‘ecstasy’ tablets, was investigated. MDMA was synthesized according to two different ways in which piperonal and isosafrole were used as precursors. Three types of carbon absorbents were tested: Envicarb (surf. area 98 m2/g, Supelco), Carboprep (surf. area 400 m2/g, Restek Corporation), and Hypercarb (surf. area 94 m2/g, Thermo Electron Corporation UK). The efficiency of extraction was studied by thin layer chromatography (TLC) with UV detection (254 and 366 nm). The separation of impurities was carried out on silica gel plates with fluorescent indicator F254 and the mixture of chloroform:methanol:acetonitrile (5∶2∶3 v/v/v) was used as TLC eluent. The elaborated profiling procedure enables distinction between samples of MDMA obtained according to different synthesis methods.

Interaction of methoxy- and methylenedioxyamphetamines with carbon and polymeric adsorbents in polar liquids

AbstractSolid phase extraction (SPE) of methoxy- and methylenedioxyamphetamines from diluted aqueous solutions was investigated on carbon and polymeric adsorbents of different textures and chemical compositions. Those adsorbents were applied cartridges packed with three chemically modified carbons prepared from plum stones (initial A2PS, oxidized A2PS-O, and reduced A2PS-H) and commercially available adsorbents (polymeric LiChrolut EN, graphitized Hypercarb and Carboprep). Several factors influence the recovery rates of amphetamine derivatives such as the polarity of adsorbates (free energy of salvation), the specific surface area and surface composition of adsorbents, and the solvent characteristics. Different combinations of these factors affect the recovery rate (R1) for high- and low-surface area adsorbents. The minimal R1 values are observed for an amphetamine derivative at a maximal solvation effect and for a set of amphetamines adsorbed on graphitized carbons.