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author

articleHeike Gleisner, Alf Liebmann

Analytik Jena AGKonrad-Zuse-Strasse 1

07745 Jena, Germany

Tel.: +49/3641/7770

Fax: +49/3641/779279

info@analytik-jena.com

Thomas Furche

H.C. Starck Hermsdorf GmbHRobert-Friese-Strasse 4

07629 Hermsdorf

Germany

Tel.: +49/36601/922101

Fax: +49/36601/922111

Measurement of Tungsten in Molybdenum using High-Resolution Continuum Source

Atomic Absorption Spectrometry (HR-CS AAS)

Introduction based on classical line source AAS (LS AAS) however has its Results and discussion

30Analytical Instrumentation

Looking back over the last few years at the development of AAS, there appear to have been no outstanding technical and analytical innovationsin this field. Changes have primarily involved accessories and software and serve to enhance automation and improve device handling. Firstly,

the optimisation of software improves user-friendliness, and secondly, the steady growth in quality control and data security standards are

addressed. Nevertheless, by virtue of its simple operability, rapid readiness for measurement, low operating costs and high degree of interference

immunity, AAS is still well established in inorganic analytics today. The commercial introduction of HR-CS AAS technology marks a developmental

leap opening up a whole new generation of atomic spectroscopy devices to the user.

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31Analytical Instrumentation

Bibliography:

[1] B. Welz, H. Becker-Ross, S. Florek, U. Heitmann,

High-Resolution Continuum Source AAS The

better Way to do Atomic Absorption Spectrometry,

ISBN 3-527-30736-2, Wiley-VCH, Weinheim, 2005

[2] H. Gleisner, K. Eichardt, G. Schlemmer, U. Heitmann:

Die AAS wird neu definiert, LABO 4/ 2004, S.64-67

[3] U. Heitmann, H. Becker-Ro: Atomabsorptions-

Spektrometrie mit einem Kontinuumstrahler

(CS AAS), GIT 7/2001, S.728-731

[4] H. Gleisner: Applikationsberichte Analytik Jena,

CSAA_FL_01_04_d | 11 / 2004

Summary

The W content values measured for molybdenum samples lie in the anticipated range and show good correspondence with the

internal reference values. The performance of the method is simplified, because, as a result of the possibility of measuring the

spectral vicinity of the analysis line simultaneously, significantly more information is available on the sample under investigation.

Fluctuations in the radiant intensity of the lamp, in the detector sensitivity and in the permeability of the flame and therefore all

continuous background absorption are measured simultaneously and are automatically corrected at selected reference pixels.

Through the use of a high-resolution double monochromator, discontinuous spectral disturbances, e.g. through absorption lines

from the Mo matrix, are not identified by the pixels used for analysis and are thereby eliminated. There is therefore no necessity for

background correction as exists for LS AAS. The detection limit in HR-CS AAS is fundamentally improved, as no second lamp noise

source is present in the optical system. The use of an extremely low noise CCD array detector in the contrAA 300 is also superior

to the photomultipliers common in LS AAS and the use of a high-energy Xe short arc lamp with very high radiation intensity further

improves the signal-to-noise ratio significantly. The detection limit for tungsten was consequently improved by a factor of 5.

Finally, it can be seen that the measurement of tungsten in molybdenum using the contrAA 300 with HR-CS AAS can be

performed easily, correctly and without laborious sample preparation. The minimisation of investment and operating costs produces

in a significant increase in laboratory effectiveness and flexibility together with a noticeably higher sample throughput.

only the main resonance line is taken for analytical evaluation in

this example. The second absorption line can be used if the

concentration is exceeded in order to expand the dynamic working

range for calibration. As a comparison, an energy scan over 1.0 nm

around the analysis wavelength of the W-HCL used was performedin the classical LS AAS (Fig. 3). The two W lines can hardly be

distinguished given the significantly lower resolution of LS AAS. It

was also apparent that not every HCL can be deployed, as not all

lamp manufacturers use UV transparent quartz windows for their

W-HCLs., in which case one has to turn to the longer wavelength

and somewhat less sensitive W absorption line at 294.4 nm. In the

Mo sample spectrum (Fig. 4) there are three additional W

absorption lines in the spectral vicinity of the 255.135 nm analysis

line, which could be assigned to the molybdenum matrix. The

255.086 nm Mo line lies directly in the spectral transmission band

of the slit in the LS AAS instrument with deuterium background

correction and consequently further attenuates the D2 broadband

source. This attenuation distorts the background measurement onthe analysis line leading to over-correction of the background and

hence to a lower analysis result (Table 2). For this reason, the Mo

Fig. 4: Absorption spectrum of the W sample Mo-HZ, spectral

observation width 0.43 nm (W main resonance line 255.135 nm, W

secondary line 255,039 nm, Mo lines: 255.017 nm; 255.086 nm;

255.287 nm)

matrix must be separated using special sample preparation prior to

measurement of W with LS AAS. The high-resolution double

monochromator in the contrAA?300 separates the Mo absorption

lines significantly from the W absorption line. As HR-CS AAS

always identifies the background and the analysis line

simultaneously and measures selected correction pixels, the

measurement of tungsten using this method is not affected by the

molybdenum absorption line.

Table 2: Results of W measurement with HR-CS AAS and LS AAS