Spatially and Temporally Resolved Detection of Arsenic in a Capillary Dielectric Barrier Discharge by Hydride Generation High-Resolved Optical Emission Spectrometry.

A new method for arsenic detection by optical emission spectrometry (OES) is presented. Arsine (AsH3) is generated from liquid solutions by means of hydride generation (HG) and introduced into a capillary dielectric barrier discharge (DBD) where it is atomized and excited. A great challenge in OES is the reduction of the recorded background signal, because it negatively affects the limit of detection (LOD). In conventional DBD/OES methods, the signal intensity of the line of interest, in this case arsenic, is integrated over a long time scale. However, due to the pulsed character of the plasma, the plasma on-time is only a small fraction of the integration time. Therefore, a high amount of noise is added to the actual signal in each discharge cycle. To circumvent this, in the present study the emitted light from the DBD is collected by a fast gated iCCD camera, which is mounted on a modified monochromator. The experimental arrangement enables the recording of the emission signal of arsenic in the form of a monochromatic 2D-resolved picture. The temporal resolution of the iCCD camera in the nanosecond range provides the information at which point in time and how long arsenic is excited in the discharge. With use of this knowledge, it is possible to integrate only the arsenic emission by temporally isolating the signal from the background. With the presented method, the LOD for arsenic could be determined to 93 pg mL-1 with a calibration curve linear over 4 orders of magnitude. As a consequence, the developed experimental approach has a potential for both mechanistic studies of arsine atomization and excitation in DBD plasmas as well as routine applications, in which arsenic determination at ultratrace levels is required.

Pulsed Blue Laser Diode Thermal Desorption Microplasma Imaging Mass Spectrometry.

An ambient air laser desorption, plasma ionization imaging method is developed and presented using a microsecond pulsed laser diode for desorption and a flexible microtube plasma for ionization of the neutral desorbate. Inherent parameters such as the laser repetition rate and pulse width are optimized to the imaging application. For the desorption substrate, copper spots on a copper-glass sandwich structure are used. This novel design enables imaging without ablating the metal into the mass spectrometer. On this substrate, fixed calibration markers are used to decrease the positioning error in the imaging process, featuring a 3D offset correction within the experiment. The image is both screened spot-by-spot and per line scanning at a constant speed, which allows direct comparison. In spot-by-spot scanning, a novel algorithm is presented to unfold and to reconstruct the imaging data. This approach significantly decreases the time required for the imaging process, which allows imaging even at decreased sampling rates and thus higher mass resolution. After the experiment, the raw data is automatically converted and interpreted by a second algorithm, which allows direct visualization of the image from the data, even on low-intensity signals. Mouse liver microtome cuts have been screened for dehydrated cholesterol, proving good agreement of the unfolded data with the morphology of the tissue. The method optically resolves 30 µm, with 30 µm diameter copper spots and a 10 µm gap. No conventional chemical matrices or vacuum conditions are required.

Review: Miniature dielectric barrier discharge (DBD) in analytical atomic spectrometry.

The development of miniature, sensitive, high throughput, and in-situ analytical instruments has been becoming developing field of modern analytical chemistry. Due to its unique advantages such as easy operation, simple configuration, ambient working temperature and pressure, low power consumption, and miniature dimension, dielectric barrier discharge (DBD) has always been a hot topic in analytical chemistry. This review gives an overview of miniature DBD application in analytical atomic spectrometry, starting with an introduction to its geometrical configuration and ionization mechanisms. Then, its applications such as excitation or atomization sources in atomic emission spectrometry (AES), atomic absorption spectrometry (AAS) and atomic fluorescence spectrometry (AFS) are reviewed. Also, its application as vapor generation system in atomic spectrometry is discussed.

Enhancement of emission from indium in flowing liquid anode atmospheric pressure glow discharge using organic media.

The effect of addition of low molecular weight organic compounds, i.e. acids, salts and alcohols, on the emission measured from In with flowing liquid anode atmospheric pressure glow discharge optical emission spectrometry (FLA-APGD-OES) was studied. It was revealed that a small addition of CH3OH or C2H5OH (0.5%, v/v) enhanced the intensity of In 451.1 nm atomic line over 30-times. The observed boosting of emission was caused both not only by promotion of the analyte transport efficiency from the liquid sample to the plasma phase (increased from 19% to 35%) but also due to some other factors, presumably the improvement of atomization/excitation conditions. The developed FLA-APGD-OES method offered a very low detection limit of In which was 0.21 µg L-1 (using a miniaturized spectrometer) or even 0.030 µg L-1 (using a high-resolution spectrometer). Furthermore, it was demonstrated that addition of alcohols significantly reduced the matrix effects from several interfering species, e.g. Ag, Cu, Pb and Zn, and only in case of Na, the anti-interference effect was observed. The intensity improvement which resulted from the addition of alcohols, was observed for In only and it did not occur for other elements such as Ag, Cd, Hg, Pb, Tl and Zn.