Hydrogen-Bond Acidic Materials in Acoustic Wave Sensors for Nerve Chemical Warfare Agents' Detection.

The latest trends in the field of the on-site detection of chemical warfare agents (CWAs) involve increasing the availability of point detectors to enhance the operational awareness of commanders and soldiers. Among the intensively developed concepts aimed at meeting these requirements, wearable detectors, gas analyzers as equipment for micro- and mini-class unmanned aerial vehicles (UAVs), and distributed sensor networks can be mentioned. One of the analytical techniques well suited for use in this field is surface acoustic wave sensors, which can be utilized to construct lightweight, inexpensive, and undemanding gas analyzers for detecting CWAs. This review focuses on the intensively researched and developed variant of this technique, utilizing absorptive sensor layers dedicated for nerve CWAs' detection. The paper describes the mechanism of the specific interaction occurring between the target analyte and the sensing layer, which serves as the foundation for their selective detection. The main section of this paper includes a chronological review of individual achievements in the field, largely based on the peer-reviewed scientific literature dating back to the mid-1980s to the present day. The final section presents conclusions regarding the prospects for the development of this analytical technique in the targeted application.

Surface Acoustic Wave Immunosensor for Detection of Botulinum Neurotoxin.

A Love-type acoustic wave sensor (AT-cut quartz substrate, SiO2 guiding layer) with a center frequency of approximately 120 MHz was used to detect a simulant of pathogenic botulinum neurotoxin type A-recombinant of BoNT-A light chain-in liquid samples. The sensor was prepared by immobilizing monoclonal antibodies specific for botulinum neurotoxin via a thiol monolayer deposited on a gold substrate. Studies have shown that the sensor enables selective analyte detection within a few minutes. In addition, the sensor can be used several times (regeneration of the sensor is possible using a low pH buffer). Nevertheless, the detectability of the analyte is relatively low compared to other analytical techniques that can be used for rapid detection of botulinum neurotoxin. The obtained results confirm the operation of the proposed sensor and give hope for further development of this label-free technique for detecting botulinum neurotoxin.

Semiconductor Gas Sensors for Detecting Chemical Warfare Agents and Their Simulants.

On-site detection of chemical warfare agents (CWAs) can be performed by various analytical techniques. Devices using well-established techniques such as ion mobility spectrometry, flame photometry, infrared and Raman spectroscopy or mass spectrometry (usually combined with gas chromatography) are quite complex and expensive to purchase and operate. For this reason, other solutions based on analytical techniques well suited to portable devices are still being sought. Analyzers based on simple semiconductor sensors may be a potential alternative to the currently used CWA field detectors. In sensors of this type, the conductivity of the semiconductor layer changes upon interaction with the analyte. Metal oxides (both in the form of polycrystalline powders and various nanostructures), organic semiconductors, carbon nanostructures, silicon and various composites that are a combination of these materials are used as a semiconductor material. The selectivity of a single oxide sensor can be adjusted to specific analytes within certain limits by using the appropriate semiconductor material and sensitizers. This review presents the current state of knowledge and achievements in the field of semiconductor sensors for CWA detection. The article describes the principles of operation of semiconductor sensors, discusses individual solutions used for CWA detection present in the scientific literature and makes a critical comparison of them. The prospects for the development and practical application of this analytical technique in CWA field analysis are also discussed.

Acoustic Wave Sensors for Detection of Blister Chemical Warfare Agents and Their Simulants.

On-site detection and initial identification of chemical warfare agents (CWAs) remain difficult despite the many available devices designed for this type of analysis. Devices using well-established analytical techniques such as ion mobility spectrometry, gas chromatography coupled with mass spectrometry, or flame photometry, in addition to unquestionable advantages, also have some limitations (complexity, high unit cost, lack of selectivity). One of the emerging techniques of CWA detection is based on acoustic wave sensors, among which surface acoustic wave (SAW) devices and quartz crystal microbalances (QCM) are of particular importance. These devices allow for the construction of undemanding and affordable gas sensors whose selectivity, sensitivity, and other metrological parameters can be tailored by application of particular coating material. This review article presents the current state of knowledge and achievements in the field of SAW and QCM-based gas sensors used for the detection of blister agents as well as simulants of these substances. The scope of the review covers the detection of blister agents and their simulants only, as in the available literature no similar paper was found, in contrast to the detection of nerve agents. The article includes description of the principles of operation of acoustic wave sensors, a critical review of individual studies and solutions, and discusses development prospects of this analytical technique in the field of blister agent detection.

Inverse gas chromatographic evaluation of polysiloxanes containing phenolic and fluorophenolic functional groups for use in gas sensors.

The paper presents the results of inverse gas chromatographic (IGC) research on two novel polysiloxanes: poly{dimethylsiloxane-co -[4-(2,3-difluoro-4-hydroxyphenoxy)butyl]methylsiloxane} and poly{dimethylsiloxane-co -[4-(4-hydroxyphenoxy)butyl]methylsiloxane}, dubbed PMFOS and PMOS respectively, designed for use as chemosensitive coatings for acoustoelectronic sensors. These materials contain phenolic functional substituents that differ by the presence of fluorine atoms. The materials' solvation properties were identified by IGC with application of an LSER solvation model at temperatures ranging from 40 to 120 °C. In the case of both polysiloxanes, the research revealed that the dominant type of intermolecular interaction was the formation of acidic hydrogen bonds. The material with fluorine-activated hydroxyl groups, PMFOS, is much more acidic and less basic than the other one and thus more interesting. According to LSER, PMFOS exhibits high affinity and selectivity to hydrogen bond bases. In addition, the material retains its properties even at a temperature of 120 °C.

Sensors to Detect Sarin Simulant.

This work presents a literature review concerning the construction, properties and application of different sensors used to detect dimethyl methylphonate (DMMP), which is the simulant of sarin. Sensors sensitive to mass are described, together with such sensors as: SAW, QCM, MEMS, also chemical capacitors, semiconductors, and field effect transistors.

Chromatographic determination of the free energy of adsorption and absorption characteristic of 4-(trans-4'-n-alkylcyclohexyl) benzoates.

The characterisation of the energetic properties of liquid crystals, i.e., esters with elongated molecules has been performed. The changes of the free energies of adsorption and absorption (dissolutions), ΔG, for liquid crystals have been estimated, based on the retention times of the centre of gravity of the elution peaks determined for the substances with defined physicochemical properties. The temperature-dependent van der Waals component of the free energy, [Formula: see text] , for a crystalline form of liquid crystal has been estimated by employing the Dorris-Gray approach. These approaches have been widened to mesophases, namely, the absorption(dissolution) of n-alkanes in the smectic B and nematic phases.

Novichoks - The A group of organophosphorus chemical warfare agents.

Novichok use has become symbol for the chemical substances use to carry out political assassinations. In the last century, poisonous warfare agents were used for the first time on the battlefields, almost all over the world. After the World War II, new types of organophosphorus chemical warfare agents were developed. Novichoks are only ones, but the most important part of them - the 4th generation of chemical warfare agents. Despite the Chemical Weapons Convention, entered into force in 1997, there is still real threat of use of chemical weapons. This weapon can be used by both states, and transnational terrorist organisations. Novichoks, A code-named substances, should be permanently introduced into a number of chemical substances contained in organophosphorus chemical warfare poisonous agents. This article presents a short fourth-generation nerve agents' description. Group A compounds together with G and V groups compounds are organophosphorus chemical warfare agents which are very dangerous ones. Our article is an attempt to provide answer for the question - what are Novichoks? And why they should be introduced into Chemical Weapons Convention.

Analysis of the Precursors, Simulants and Degradation Products of Chemical Warfare Agents.

Recent advances in analysis of precursors, simulants and degradation products of chemical warfare agents (CWA) are reviewed. Fast and reliable analysis of precursors, simulants and CWA degradation products is extremely important at a time, when more and more terrorist groups and radical non-state organizations use or plan to use chemical weapons to achieve their own psychological, political and military goals. The review covers the open source literature analysis after the time, when the chemical weapons convention had come into force (1997). The authors stated that during last 15 years increased number of laboratories are focused not only on trace analysis of CWA (mostly nerve and blister agents) in environmental and biological samples, but the growing number of research are devoted to instrumental analysis of precursors and degradation products of these substances. The identification of low-level concentration of CWA degradation products is often more important and difficult than the original CWA, because of lower level of concentration and a very large number of compounds present in environmental and biological samples. Many of them are hydrolysis products and are present in samples in the ionic form. For this reason, two or three instrumental methods are used to perform a reliable analysis of these substances.

Determination of Adsorption Equations for Chloro Derivatives of Aniline on Halloysite Adsorbents Using Inverse Liquid Chromatography.

Chloro derivatives of aniline are commonly used in the production of dyes, pharmaceuticals, and agricultural agents. They are toxic compounds with a large accumulation ability and low natural biodegradability. Halloysite is known as an efficient adsorbent of toxic compounds, such as phenols or herbicides, from wastewater. Inverse LC was applied to measure the adsorption of aniline and 2-chloroaniline (2-CA), 3-chloroaniline (3-CA), and 4-chloroaniline (4-CA) on halloysite adsorbents. A peak division (PD) method was used to determine a Langmuir equation in accordance with the adsorption measurement results. The values of adsorption equilibrium constants and enthalpy were determined and compared by breakthrough curve and PD methods. The physical sense of the calculated adsorption enthalpy values was checked by applying Boudart's entropy criteria. Of note, adsorption enthalpy values for halloysite adsorbents decreased in the following order: aniline > 4-CA > 2-CA > 3-CA.

Nitrogen oxides as dopants for the detection of aromatic compounds with ion mobility spectrometry.

Limits of detection (LODs) in ion mobility spectrometry (IMS) strictly depend on ionization of the analyte. Especially challenging is ionization of compounds with relatively low proton affinity (PA) such as aromatic compounds. To change the course of ion-molecule reactions and enhance the performance of the IMS spectrometer, substances called dopants are introduced into the carrier gas. In this work, we present the results of studies of detection using nitrogen oxides (NOx) dopants. Three aromatic compounds, benzene, toluene, toluene diisocyanate and, for comparison, two compounds with high PA, dimethyl methylphosphonate (DMMP) and triethyl phosphate (TEP), were selected as analytes. The influence of water vapour on these analyses was also studied. Experiments were carried out with a generator of gas mixtures that allowed for the simultaneous introduction of three substances into the carrier gas. The experiments showed that the use of NOx dopants significantly decreases LODs for aromatic compounds and does not affect the detection of compounds with high PA. The water vapour significantly disturbs the detection of aromatic compounds; however, doping with NOx allows to reduce the effect of humidity. Graphical Abstract Two possible ionization mechanisms of aromatic compounds in ion mobility spectrometry: proton transfer reaction and adduct formation.

Rate of dibutylsulfide decomposition by ozonation and the O3/H2O2 advanced oxidation process.

A process of dibutylsulfide (DBS) oxidation using advanced methods of oxidation with ozone and hydrogen peroxide was studied. It was demonstrated that depending on pH value there are two mechanisms of DBS oxidation present: ionic and radical. The ionic mechanism predominates in acidic environment and the radical mechanism predominates in alkaline environment. At high pH ozone stability decreases and hydrogen peroxide has a deciding effect on DBS oxidation rate. At pH 9, and at high concentration of hydrogen peroxide (ranging from 0.1 to 1 mol/L), a clear increase in DBS decomposition rate was observed. That was caused by production of hydroperoxide radicals in reaction of hydrogen peroxide and ozone. In solutions pH value of which is close to 2, the rate of DBS oxidation by ozone alone is slower than in a O(3)/H(2)O(2) system, regardless the H(2)O(2) concentration. For higher H(2)O(2) concentrations (ranging from 0.1 to 1 mol/L), regardless the pH value of the solution, oxidation in a O(3)/H(2)O(2) system is faster, compared to a situation in which ozone is a sole oxidizer. For H(2)O(2) concentrations below 0.1 mol/L and when pH>2DBS oxidation in O(3)/H(2)O(2) system is slower compared to the situation in which ozone was the only oxidizer.

Effect of temperature and initial dibutyl sulfide concentration in chloroform on its oxidation rate by ozone.

A scheme of dibutyl sulfide (DBS) oxidation with ozone and generation of transitional products was determined in this study. The main identified intermediate product was dibutyl sulfoxide (DBSO), and the main end product of DBS oxidation was dibutyl sulfone (DBSO2). It was determined that for three temperatures: 0, 10 and 20 degrees C there was certain initial DBS concentration for which half-times observed in experimental conditions were equal and independent from temperature. Generation of phosgene and water as by-products was confirmed for the reaction of DBS with ozone in chloroform. Results of the described study allowed to present generalized mechanism of sulfide oxidation with ozone.

Sulfur mustard destruction using ozone, UV, hydrogen peroxide and their combination.

Numerous methods are used for destruction of sulfur mustard. Oxidation is one of those methods. There have been only limited data concerning application of the advanced oxidation technologies (AOTs) for mustard destruction available before. In this study sulfur mustard oxidation rate depending on kind of the oxidative system and process parameters used was assessed using selected AOT. The following were selected for mustard oxidation: ozone (O(3)), UV light (UV), hydrogen peroxide (H(2)O(2)); double systems: UV/O(3), UV/H(2)O(2), and O(3)/H(2)O(2); a triple system: O(3)/H(2)O(2)/UV and Fenton reaction. Effectiveness of the selected AOT methods has been evaluated and the most suitable one for mustard destruction was chosen. Using ozone in various combinations with hydrogen peroxide and UV radiation mustard can be destroyed much quicker comparing to the classical oxidizers. Fast mustard oxidation (a few minutes) occurred in those systems where ozone alone was used, or in the following combinations: O(3)/H(2)O(2), O(3)/UV and O(3)/H(2)O(2)/UV. When those advanced oxidation technologies are used, mustard becomes destroyed mainly in course of the direct oxidation with ozone, and reactions of mustard with radicals formed due to ozone action play a secondary role. Rate of sulfur mustard oxidation in the above mentioned ozone-containing oxidative systems decreases with pH value increasing from 2 to 12. Only when pH value of reaction solutions is close to pH 5, mustard oxidation rate is minimal, probably due to "disappearance" of radicals participating in oxidation in this pH. Sulfur mustard can be most effectively destroyed using just ozone in pH 7. In that case mustard destruction rate is only slightly lower than the rate achieved in optimal conditions, and the system is the simplest.

The reactions of sulfur mustard with the active components of organic decontaminants.

Reactions of sulfur mustard with active components of decontaminants ORO and C9 (Polish abbreviations of organic decontaminating solutions) were studied and their products were identified by GC/AED. Quantitative determinations of individual products in the reaction mixtures allowed to evaluate the kinetic parameters of the mustard reactions. The major decontamination product was divinyl sulfide, the product of the elimination reaction. At certain proportions of mustard to the decontaminant's active component, substitution products were also formed.

The GC/AED studies on the reactions of sulfur mustard with oxidants.

A gas chromatograph coupled with an atomic emission detector was used to identify and to determine the products formed on oxidation of sulfur mustard. The oxidation rate and the resulting oxidates were studied in relation to oxidant type and reaction medium parameters. Hydrogen peroxide, sodium hypochlorite, sodium perborate, potassium monopercarbonate, ammonium peroxydisulfate, potassium peroxymonosulfate (oxone), and tert-butyl peroxide were used as oxidants. Oxidations were run in aqueous media or in solvents of varying polarities. The oxidation rate was found to be strongly related to oxidant type: potassium peroxymonosulfate (oxone) and sodium hypochlorite were fast-acting oxidants; sodium perborate, hydrogen peroxide, ammonium peroxydisulfate, and sodium monopercarbonate were moderate oxidants; tert-butyl peroxide was the slowest-acting oxidant. In non-aqueous solvents, the oxidation rate was strongly related to solvent polarity. The higher the solvent polarity, the faster the oxidation rate. In the acid and neutral media, the mustard oxidation rates were comparable. In the alkaline medium, oxidation was evidently slower. A suitable choice of the initial oxidant-to-mustard concentration ratio allowed to control the type of the resulting mustard oxidates. As the pH of the reaction medium was increased, the reaction of elimination of hydrogen chloride from mustard oxidates becomes more and more intensive.

Liquid-crystalline stationary phases for gas chromatography.

Physico-chemical properties of new liquid-crystalline stationary phases (LCSPs) for gas chromatography are reviewed. The mechanism of chromatographic separation on liquid-crystalline stationary phases is discussed and examples of analyses of complex mixtures of organic compounds using capillary and packed columns are given.

Changes in the order of elution of some organic compounds in high-resolution gas chromatography on polar columns depending on the injection method and water content in the sample.

During the GC analysis of apple aroma essence using a capillary column with polar stationary phases, i.e., bonded/crosslinked polyethylene glycol (HP-Innowax) and acid-modified polyethylene glycol (FFAP) the phenomenon of changing the elution order of some compounds was observed ("cross-over phenomenon"). The elution order within two pairs of closely eluting compounds: 2-methylbutyl acetate/pentan-3-ol (internal standard) and trans-2-hexen-1-al/2-methylbutan-1-ol differed between samples introduced onto the column with direct injection and with static headspace method. Experiments carried out on standard solutions of investigated compounds in water-acetone mixtures of gradually reduced water ratio (99:1 to 0:100) proved that changes of elution times leading first to co-elution and subsequently to reversion of elution order of compounds within both pairs depended on the amount of water in the injected sample. The same effect was observed while the amount of water was diminished by reducing the sample volume introduced into the column.

Determination of dependencies between the specific retention volumes and the parameters characterising adsorbent properties.

Propane adsorption isotherms have been chromatographically determined on active carbon for different amounts of the injected adsorbate on column. The dependencies between the specific retention volume corrected to the standard temperature (273.15 K), Vg(273), and the molar differential work of adsorption, A, have been calculated on the basis of the propane isotherms and using the retention times of the peak maxima. The obtained equations: ln Vg(273) = f1(A) and (dW/dA)T.F(C) = f2(ln Vg(273)) have been used to explain the dependency between the chromatographic peak profile and the distribution function of pore volumes filled with propane with respect to the molar differential work of adsorption at different column temperatures (303-318 K).