A detection scheme that makes use of the Hadamard transform has been employed with an atmospheric-pressure ion mobility spectrometer fitted with an electrospray ionization source. The Hadamard transform was implemented through the use of a linear-feedback shift register to produce a pseudorandom sequence of 1023 points. This pseudorandom sequence was applied to the ion gate of the spectrometer, and deconvolution of the ion signal was accomplished by the Hadamard transform to reconstruct the mobility spectrum. Ion mobility spectra were collected in both a conventional and Hadamard mode, with comparisons made between the two approaches. Initial results exhibited low spectral definition, so an oversampling technique was applied to increase the number of data points across each analyte spectral peak. The use of the Hadamard transform increases the duty cycle of the instrument to 50% and results in a roughly 5-fold enhancement of the signal-to-noise ratio with a negligible loss of instrument resolution. It is also shown that any potential multiplex disadvantage, which limits the attractiveness of some high-throughput techniques, is not a limiting factor in this new implementation.

This note describes the design of a simple, wire-array ion gate that is easy to create and machine. The gate consists of two separate wires that can be pulsed differentially to either neutralize ions or deflect the path of an ion beam. Unlike previous designs, the gate described herein consists of only a single piece: an insulator through which two wires are woven to create an interdigitated array. The wires are then terminated at both ends, where electrical connections to external voltage sources can be made. Once constructed, the gate has a 1 mm grid spacing and takes about 3–4 h to complete after the initial support is machined. A gate constructed with this design has been successfully installed in an ion-mobility spectrometer, and its performance compares favorably to that of a previously configured gate system.

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There is a general need for optical sensors that respond to multiple substances or physical parameters. Multiple-parameter sensing is not only more efficient, but also permits interacting or interdependent parameters to be individually determined. In this paper, we describe a novel approach to the fabrication of an optical sensor, sensitive to two separate atmospheric conditions, but made from a single fibre optic. The optical fibre is drawn from polycarbonate, with a temperature-sensitive phosphor (La2O2S:Eu3+) incorporated directly into the core. Thus, the light-guiding portion of the fibre is responsible for determining the first parameter of measurement, ambient temperature. A thin fibre cladding is subsequently added to the temperature-sensitive core and serves as a chemically sensitive component. This cladding is made from Nafion®, and is doped with rhodamine 800. Fluorescence at 750 nm from the rhodamine 800 is shown to be enhanced by the presence of atmospheric moisture, and is used in conjunction with a ratiometric means of measuring temperature provided by the phosphorescence from the fibre core. This scheme provides a simple and potentially inexpensive way to manufacture fibre-optic sensors capable of multicomponent determinations. In addition, the temperature-sensitive core material provides a built-in normalization factor for the temperature-dependent response of the chemically sensitive cladding. The developed dual sensor was evaluated over the temperature range from 20 to 95 °C and demonstrated better than 1% relative standard deviation (RSD). The humidity sensor component was evaluated over the range of relative humidity (RH) from 0 to 20% RH over temperatures up to 56 °C. The detection limits for the humidity sensor were 0.17 and 2.35% RH at 20 and 56 °C, respectively.

Sensitivity, selectivity, and speed are the most important analytical parameters in sensing chemical warfare agents (CWAs) and toxic industrial chemicals (TICs). For homeland security applications, where protection from chemical releases in public facilities such as at airports or subway stations is desired, selectivity becomes even more critical since false alarms can cause costly societal disruptions and trigger public panic. Currently, ion mobility spectrometry (IMS) has been widely deployed in the battlefield for CWA detection because of its excellent sensitivity and speed. However, IMS alone has suffered from low selectivity, especially for lower molecular weight TICs, which results in false alarms. This article describes an emerging technology that combines differential mobility spectrometry (DMS) and IMS in one package. In this configuration, the DMS serves as an ion filter for the IMS, prescreening targets from background with a separation mechanism that is complementary to the IMS. The tandem analyzer consists of a microfabricated DMS and two miniaturized IMS detectors arranged in an orthogonal configuration, enabling the detection of positive and negative ions simultaneously. The combination of these two technologies can significantly reduce false alarm rates. The tandem DMS–IMS provides a real‐time, powerful technology to counter terrorist threats in infrastructure protection scenarios.