We report the synthesis of a series of manganese-containing oxychalcogenides with general formula A 2 O 2 Mn 2 OSe 2 (A = La, Ce, Pr) as well several new A 2 O 2 Fe 2 OSe 2 materials (A = La-Sm). We report the structural, magnetic, and conduction properties of the manganesecontaining materials: La 2 O 2 Mn 2 OSe 2 , Ce 2 O 2 Mn 2 OSe 2 , and Pr 2 O 2 Mn 2 OSe 2 . These materials are isostructural with La 2 O 2 Fe 2 OSe 2 , and are shown to undergo a phase transition on cooling, apparently related to displacement of oxide ions from the [Mn 2 O] 2þ plane. Peak splitting has been observed in the Pr 3þ containing material at low temperatures, consistent with a reduction to orthorhombic symmetry. All of the manganese containing materials order antiferromagnetically on cooling with k = (0, 0, 0), T N = 164-184 K, and have a 12 K Mn 2þ moment of around 4 μ B . The magnetic structure of La 2 O 2 Co 2 OSe 2 is also reported. Conductivity studies have shown that La 2 O 2 Mn 2 OSe 2 and La 2 O 2 Co 2 OSe 2 are both semiconducting, with activation energies of ∼0.24 and 0.35 eV.

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A key issue with any analytical system based on mass spectrometry with no initial separation of compounds is to have a high level of confidence in chemical assignment. This is particularly true for areas of security, such as airports, and recent terrorist attacks have highlighted the need for reliable analytical instrumentation. Proton transfer reaction mass spectrometry is a useful technology for these purposes because the chances of false positives are small owing to the use of a mass spectrometric analysis. However, the detection of an ion at a given m/z for an explosive does not guarantee that that explosive is present. There is still some ambiguity associated with any chemical assignment owing to the presence of isobaric compounds and, depending on mass resolution, ions with the same nominal m/z. In this article we describe how for the first time the use of a radio frequency ion-funnel (RFIF) in the reaction region (drift tube) of a proton transfer reaction-time-of-flight-mass spectrometer (PTR-ToF-MS) can be used to enhance specificity by manipulating the ion-molecule chemistry through collisional induced processes. Results for trinitrotoluene, dinitrotoluenes, and nitrotoluenes are presented to demonstrate the advantages of this new RFIF-PTR-ToF-MS for analytical chemical purposes.

The high sensitivity of proton transfer reaction-mass spectrometry (PTR-MS) makes it a suitable analytical tool for detecting trace compounds. Its specificity is primarily determined by the accuracy of identifying the m/ z of the product ions specific to a particular compound. However, specificity can be enhanced by changing the product ions (concentrations and types) through modifying the reduced electric field. For current PTR-MS systems, this is not possible for trace compounds that would only be present in the reaction chamber of a PTR-MS for a short time (seconds). For such circumstances, it is necessary to change the reduce electric field swiftly if specificity enhancements are to be achieved. In this paper we demonstrate such a novel approach, which permits any compound that may only be present in the drift tube for seconds to be thoroughly investigated. Specifically, we have developed hardware and software which permits the reaction region's voltages to be rapidly switched at a frequency of 0.1-5 Hz. We show how this technique can be used to provide a higher confidence in the identification of compounds than is possible by keeping to one reduced electric field value through illustrating the detection of explosives. Although demonstrated for homeland security applications, this new technique has applications in other analytical areas and disciplines where rapid changes in a compound's concentration can occur, for example, in the Earth's atmosphere, plant emissions and in breath. Importantly, this adaptation provides a method for improved selectivity without expensive instrumental changes or the need for high mass resolution instruments.

This paper describes the application of the receptor density algorithm, an artificial immune system, as used to detect chemicals from data provided by various spectrometers. The system creates chemical signatures which are matched to a library of known chemicals, allowing the positive identification of hazardous substances. The performance of the system is tested against a publicly available mass-spectrometry dataset, against which it has previously been demonstrated as an effective anomaly detection algorithm. An autonomous chemical-detection device is then discussed, in which the algorithm is running on hardware embedded in a Pioneer robot carrying a portable chemical agent monitor.Peer reviewe