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In the generation of an aerosol by pneumatic nebulization, concurrent with the production of a distribution of droplet sizes is a second distribution of net charge on the droplets. The influence that the droplets with net charge exert, spatially, on Ca(II) emission in the inductively coupled plasma (ICP) has been examined in the absence and presence of NaCl, an easily ionized element chemical matrix. Tertiary aerosol droplet size distributions were also measured. A mesh positioned in the spray chamber was used to establish an electric field between it and the grounded solution being nebulized. A 200 V dc potential applied to the mesh discriminated against the transport of droplets with net charge to the plasma. For samples that contained 100 mM NaCl, the full width at half-maximum of the Ca(II) emission profile viewed at 10 mm above the load coil was significantly reduced with 200 V applied to the mesh. The source of off-axis analyte emission enhancement low in the plasma in the presence of a NaCl matrix has been attributed to desolvation of the droplets with net charge beyond the coulomb fission limit, causing progeny droplets to be created within the aerosol. Droplets with net charge comprise ∼ 50% of the aerosols studied in this work, and these droplets do have a role in determining the analyte emission profiles in the inductively coupled plasma.

A new method that relies on tertiary aerosol laser light scatter signals to alleviate the NaCl chemical matrix effect in inductively coupled plasma atomic emission spectroscopy (ICP-AES) is introduced. The method involves monitoring the laser light scatter signal from the entire tertiary aerosol with a line-shaped laser beam and the plasma off. In this work, the tertiary aerosol laser scatter signal was measured to increase nonlinearly with NaCl concentration. The source of the increased scatter signal is described as originating from Coulomb fission events that droplets with net charge experience while inside the spray chamber. Each droplet in the secondary aerosol that undergoes Coulomb fission introduces ∼ 20 progeny droplets into the aerosol stream. The introduction of progeny droplets to the aerosol stream measured by increased laser light scatter signals coincides with an increase in analyte emission, off-axis, at low viewing heights in an inductively coupled plasma, a characteristic of the easily ionized element chemical matrix effect. It is shown that a direct-current potential applied to a mesh screen positioned inside the spray chamber can coarsely control the transport of droplets with net charge through the spray chamber, by effecting their removal from the aerosol stream. With an appropriate voltage applied to the mesh, the laser scatter signal from the tertiary aerosol from a solution containing 100 mM NaCl can be made similar to the scatter signal from a solution that does not contain NaCl. Under the same conditions, calcium-ion lateral emission signal intensity contour maps in a plasma for the same two solutions become similar within the normal analytical zone in the plasma (2 mm wide, from 13 to 19 mm above the load coil).

SummaryStructural studies on fulvic acids (FAs) are significantly important since they are believed to be involved in many environmentally important processes, such as adsorption and transportation of organic and inorganic pollutants. In this research, morphology characteristics of FAs were studied by atomic force microscopy (AFM). FAs that were isolated from three soil layers (A1, B and C) of the same vertical profile in a Korean pine forest were divided into four fractions (FA-1, FA-2, FA-3 and FA-4) by a sequence of successive elution processes. Most of FAs appeared as a platy particle in the AFM topographic and phase images. Among these platy particles, some have a regular shape, such as round flake and oblong flake; others have irregular structures, such as sand heaps. Particle morphologies of different FA fractions, including hydrophilic and hydrophobic FAs fractions, were similar. However, particle sizes and distributions of FA fractions from different soil layers at the same vertical profile did differ. Particle sizes of hydrophobic FAs were relevant with respect to the soil depth. They were increased with the increasing of the soil depth. FAs from C layers were more heterogeneous with respect to the A1 and B. Our results may foster a better understanding for the relevance between the morphology of FA particles with the soil layers and the soil depth.

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