Elemental Determination of Microsamples by Liquid Film Dielectric Barrier Discharge Atomic Emission Spectrometry

In this study, a new liquid-film dielectric barrier discharge (LFDBD) atomic emission source was developed for microsample elemental determination. It consists of a copper electrode, a tungsten wire electrode, and a piece of glass slide between them, which serves as the dielectric barrier as well as the sample plate. The sample solution with 1 mol L-1 nitric acid, when deposited onto the surface of the glass slide, forms a thin liquid film. The plasma is generated between the tip of the tungsten wire electrode and the liquid film surface when alternating-current (ac) high voltage (peak voltage similar to 3.7 kV, frequency similar to 30 kHz) is applied on the electrodes. Qualitative and quantitative determinations of metal ions in the sample solution were achieved by atomic emission measurements in the plasma and were demonstrated in this study with elements Na, K, Cu, Zn, and Cd. Detection limits were in the range from 0.6 ng (7 mu g L-1) for Na to 6 ng (79 mu g L-1) for Zn. Repeatability, expressed as relative standard deviation from seven repetitive analyses of samples with analyte concentrations at 1 mg L-1, varied from 2.1% to 4.4%. Compared with other liquid discharge systems that operate at atmospheric pressure, the current system offers several advantages: First, it eliminates the use of a sample flow system (e.g., syringe or peristaltic pump); instead, a small aliquot of sample is directly pipetted onto the glass slide for analysis. Second, it is a microanalysis system and requires sample volume <= 80 mu L, a benefit when a limited amount of sample is available. Third, because the sample is applied in aliquot there is no washout time, and the analysis can be easily extended to sample array for high throughput analysis. The proposed LFDBD is promising for in-field elemental determination because of its simplicity, cost effectiveness, low power supply, and no inert gas requirement.