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A new method for arsenic detection by optical emission spectrometry (OES) is presented. Arsine (AsH) 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 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.

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Dielectric barrier discharges (DBDs) are well-established and useful tools for scientific as well as industrial applications. They have been of high interest for analytical applications due to the fact that DBDs can produce small, low temperature/power, and atmospheric plasmas. These kind of plasmas can be applied for the detection and quantification of analytes in several ways: either, DBDs can be used for example as fragmentation and excitation sources to detect elements via optical emission spectrometry (OES), or as ionization sources of molecules for the detection via mass spectrometry (MS). ISAS has developed several of these discharges and studied the impact of the DBD itself on the subsequent application. This work summarizes the development from low pressure DBD implemented in diode laser atomic absorption spectrometry to atmospheric DBDs that can be used for different ambient applications such as the trace detection of arsenic species via OES or the soft ionization of molecular compounds via MS.

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