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The use of matrix-specific calibrations for oxygen in analytical glow discharge spectrometry.

Gonzalez-Gago C, Smid P, Hofmann T, Venzago C, Hoffmann V, Gruner W - Anal Bioanal Chem (2014)

Bottom Line: The importance of a "blue shifted" line of oxygen at 130.22 nm (first reported by Köster) for quantitative analyses by GD-OES is confirmed.Matrix-specific calibrations for oxygen in GD-MS are presented.Additional experiments using Ar-He mixtures or μs pulsed GD are carried out in ELEMENT GD aiming to improve the oxygen sensitivity.

View Article: PubMed Central - PubMed

Affiliation: Leibniz Institute for Solid State and Materials Research (IFW) Dresden, P.O. Box 270116, 01171, Dresden, Germany.

ABSTRACT
The performance of glow discharge optical emission spectroscopy and mass spectrometry for oxygen determination is investigated using a set of new conductive samples containing oxygen in the percent range in three different matrices (Al, Mg, and Cu) prepared by a sintering process. The sputtering rate corrected calibrations obtained at standard conditions for the 4 mm anode (700 V, 20 mA) in GD-OES are matrix independent for Mg and Al but not for Cu. The importance of a "blue shifted" line of oxygen at 130.22 nm (first reported by Köster) for quantitative analyses by GD-OES is confirmed. Matrix-specific calibrations for oxygen in GD-MS are presented. Two source concepts-fast flow (ELEMENT GD) and low gas flow (VG9000)-are evaluated obtaining higher sensitivity with the static flow source. Additional experiments using Ar-He mixtures or μs pulsed GD are carried out in ELEMENT GD aiming to improve the oxygen sensitivity.

No MeSH data available.


Oxygen 130.22 nm line profile at different voltages (500, 700, and 900 V) for the sample with 6 g Mg and 2 g MgO sputtered in Ar
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Fig5: Oxygen 130.22 nm line profile at different voltages (500, 700, and 900 V) for the sample with 6 g Mg and 2 g MgO sputtered in Ar

Mentions: Figure 4 shows the oxygen 130.22 nm line profile of the three samples containing oxygen with sputtering rate of about 0.08 μg/s (red curve for 10 g Cu + 0.5 g CuO, blue for 6 g Mg + 1 g MgO and black for 6 g Al + 2 g Al2O3). Clearly, there is a second line at lower wavelength, which interferes with the O I 130.22 nm line. This contribution is smallest for the Cu sample. After interference correction, the emission yield (defined as the ratio of intensity and the product of the concentration and the sputtering rate) of the different matrices are very close together. However, the accurate correction of such interferences is difficult due to the high noise of the signals. Considering the integrated area of the complete wavelength range at both emission lines did not show any improvement in terms of matrix independent calibration. One possible explanation for this additional emission line is the blue shift of the O I 130.22 nm line. This effect in GD-OES has been reported by Michael Köster [24]. Unfortunately, the origin of this effect is not fully understood and nothing was published about it yet. Nevertheless, our present investigations confirm this effect and demonstrate the importance for quantitative analyses by GD-OES. We found that the line shifts to the blue side proportionately to the square root of the applied voltage (see Fig. 5), which points to the Doppler Effect as suggested by Michael Köster. However, we could not find this effect with a similar size at the three lines at 777 nm. Furthermore, a low pressure causes a higher ratio of the shifted to the non-shifted line, which can be related to an extended cathode dark space. Therefore, the effect becomes more and more essential at materials with high secondary electron emission yield as Al and Mg, where the plasma show the same voltage and current but at a lower pressure. The Ar pressure in the GD-OES experiments decreased from about 12.5 hPa at Cu over about 10.7 hPa at Al and finally to 8.7 hPa at Mg. Higher oxygen concentration also enhances the secondary electron emission of the Cu and Mg samples. Therefore, the pressure of the experiments with the samples with highest oxygen concentration was about 0.5 hPa lower than when measuring the bulk sample. For Al, the pressure was nearly independent of the oxygen concentration.Fig. 4


The use of matrix-specific calibrations for oxygen in analytical glow discharge spectrometry.

Gonzalez-Gago C, Smid P, Hofmann T, Venzago C, Hoffmann V, Gruner W - Anal Bioanal Chem (2014)

Oxygen 130.22 nm line profile at different voltages (500, 700, and 900 V) for the sample with 6 g Mg and 2 g MgO sputtered in Ar
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4225055&req=5

Fig5: Oxygen 130.22 nm line profile at different voltages (500, 700, and 900 V) for the sample with 6 g Mg and 2 g MgO sputtered in Ar
Mentions: Figure 4 shows the oxygen 130.22 nm line profile of the three samples containing oxygen with sputtering rate of about 0.08 μg/s (red curve for 10 g Cu + 0.5 g CuO, blue for 6 g Mg + 1 g MgO and black for 6 g Al + 2 g Al2O3). Clearly, there is a second line at lower wavelength, which interferes with the O I 130.22 nm line. This contribution is smallest for the Cu sample. After interference correction, the emission yield (defined as the ratio of intensity and the product of the concentration and the sputtering rate) of the different matrices are very close together. However, the accurate correction of such interferences is difficult due to the high noise of the signals. Considering the integrated area of the complete wavelength range at both emission lines did not show any improvement in terms of matrix independent calibration. One possible explanation for this additional emission line is the blue shift of the O I 130.22 nm line. This effect in GD-OES has been reported by Michael Köster [24]. Unfortunately, the origin of this effect is not fully understood and nothing was published about it yet. Nevertheless, our present investigations confirm this effect and demonstrate the importance for quantitative analyses by GD-OES. We found that the line shifts to the blue side proportionately to the square root of the applied voltage (see Fig. 5), which points to the Doppler Effect as suggested by Michael Köster. However, we could not find this effect with a similar size at the three lines at 777 nm. Furthermore, a low pressure causes a higher ratio of the shifted to the non-shifted line, which can be related to an extended cathode dark space. Therefore, the effect becomes more and more essential at materials with high secondary electron emission yield as Al and Mg, where the plasma show the same voltage and current but at a lower pressure. The Ar pressure in the GD-OES experiments decreased from about 12.5 hPa at Cu over about 10.7 hPa at Al and finally to 8.7 hPa at Mg. Higher oxygen concentration also enhances the secondary electron emission of the Cu and Mg samples. Therefore, the pressure of the experiments with the samples with highest oxygen concentration was about 0.5 hPa lower than when measuring the bulk sample. For Al, the pressure was nearly independent of the oxygen concentration.Fig. 4

Bottom Line: The importance of a "blue shifted" line of oxygen at 130.22 nm (first reported by Köster) for quantitative analyses by GD-OES is confirmed.Matrix-specific calibrations for oxygen in GD-MS are presented.Additional experiments using Ar-He mixtures or μs pulsed GD are carried out in ELEMENT GD aiming to improve the oxygen sensitivity.

View Article: PubMed Central - PubMed

Affiliation: Leibniz Institute for Solid State and Materials Research (IFW) Dresden, P.O. Box 270116, 01171, Dresden, Germany.

ABSTRACT
The performance of glow discharge optical emission spectroscopy and mass spectrometry for oxygen determination is investigated using a set of new conductive samples containing oxygen in the percent range in three different matrices (Al, Mg, and Cu) prepared by a sintering process. The sputtering rate corrected calibrations obtained at standard conditions for the 4 mm anode (700 V, 20 mA) in GD-OES are matrix independent for Mg and Al but not for Cu. The importance of a "blue shifted" line of oxygen at 130.22 nm (first reported by Köster) for quantitative analyses by GD-OES is confirmed. Matrix-specific calibrations for oxygen in GD-MS are presented. Two source concepts-fast flow (ELEMENT GD) and low gas flow (VG9000)-are evaluated obtaining higher sensitivity with the static flow source. Additional experiments using Ar-He mixtures or μs pulsed GD are carried out in ELEMENT GD aiming to improve the oxygen sensitivity.

No MeSH data available.