Emission Intensities Of Atomic Lines Research Articles

Comparative study on the emission spectrometric determination of manganese using nitrogen-oxygen Okamoto-cavity microwave induced plasma and argon radio-frequency inductively-coupled plasma

Microwave-induced plasma optical emission spectrometry (MIP-OES) using Okamoto-cavity was investigated in the determination of manganese, in comparison with argon radio-frequency inductively-coupled plasma (ICP)-OES. An important point of this study is that, in the Okamoto-cavity MIP, the emission intensity of particular atomic emission lines is much elevated by adding oxygen of ca. 10% to the nitrogen matrix plasma gas. Intensity variations in emission lines of manganese atom as well as the ion and in a band head of nitrogen molecule were observed, when oxygen was added to the nitrogen plasma, indicating that the emission intensity of the atomic lines was drastically elevated while the intensities of the ionic lines and the nitrogen band head decreased in a similar manner. This observation can be explained by the fact that the nitrogen excited species, contributing to the transition of the band head, are consumed through collisions with oxygen molecules to cause their dissociation, and eventually manganese atoms in the nitrogen–oxygen plasma would be less ionized than in the pure nitrogen plasma, because the ionization of manganese is also caused by collisions with the nitrogen excited species. Optimization of the measuring parameters in the Okamoto-cavity MIP-OES was conducted for the determination of manganese; as a result, the Mn I 403.076-nm line was recommended as the analytical line in the nitrogen-oxygen mixed gas MIP, while the most intense ionic line, Mn II 257.065nm, should be employed in the argon ICP. Their detection limits were of the same order, implying that the Okamoto-cavity MIP had as good analytical performance as the conventional ICP.

Carbon-related matrix effects in inductively coupled plasma atomic emission spectrometry

In Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES), it has been observed that the emission intensity of some atomic lines is enhanced or depressed by the presence of carbon in the matrix. The goal of this work was to investigate the origin and magnitude of the carbon-related matrix effects in ICP-AES. To this end, the influence of the carbon concentration and source (i.e. glycerol, citric acid and potassium hydrogen phthalate), the experimental conditions and sample introduction system on the aerosol characteristics and transport, plasma excitation conditions and the emission intensity of several atomic and ionic lines of a total of 15 elements has been studied. Results indicate that carbon related matrix effects do not depend on the carbon source and they become more severe when the amount of carbon loaded into the plasma increases, i.e., when using: (i) carbon concentrations higher than 5 g L − 1 ; (ii) high sample uptake rates; and (iii) efficient sample introduction systems. Thus, when introducing carbon into the plasma, the emission intensity of atomic lines with excitation energies below 6 eV is depressed (up to 15%) whereas the emission intensity of atomic lines of higher excitation energies (i.e. As and Se) are enhanced (up to 30%). The emission intensity of the ionic lines is not affected by the presence of carbon. The origin of the carbon-related interferences on the emission intensity of atomic lines is related to changes in the line excitation mechanism since the carbon containing solutions show the same aerosol characteristics and transport efficiencies as the corresponding aqueous solutions. Based on the previous findings, a calibration approach for the accurate determination of Se in a Se-enriched yeast certified material (SELM-1) has been proposed.

Atomic Emission Characteristics of Laser-Induced Plasmas in an Argon Atmosphere at Reduced Pressure

The emission characteristics of laser-induced plasma, with the use of a Q-switched ruby laser of 1.5 J, were studied in argon atmosphere at reduced pressure. The time- and spatially resolved emission profiles were measured. In argon atmosphere at reduced pressure, the emission period of plasma is elongated to over a hundred microseconds, and the emissive region expands to more than a few tens of millimeters above the sample surface. The emission intensities of atomic lines increase severalfold in an argon atmosphere, in comparison with those obtained in air at the same pressure. Moderate confinement of plasmas and a resultant increase of emission intensities are achieved at 50 Torr. These results are explained by the chemical inertness and the thermal characteristics of the argon atmosphere and the decrease in absorption of the laser pulse by the plasma plume. The re-excitation of emissive species by collisions with metastable argon atoms seems to be less important.