Echelle-spectrograph as a tool for studies of structured background in flame atomic absorption spectrometry

An echelle-spectrograph with solid-state image detector and active wavelength stabilization was developed. It is used as a tool for investigations of structured background in flame atomic absorption spectrometry (flame-AAS). The simultaneously recordable spectral range of the spectrograph extends from 200 to 465 nm. Its pixel-based bandwidth is λ/80 000. The wavelength stabilization was developed for suppressing spurious structures in the calculated ratios of sample and blank spectra. Such structures arise in case of wavelength shifting during recording of the spectra. The stabilization compensates for spectrum displacements with respect to the pixel matrix of the detector by correction of both position and dispersion of the spectrum. The achievable precision is 1% of the pixel width. By averaging a multitude of measurements, transmittance spectra with high signal-to-noise ratios are obtained. Using an air-acetylene flame, alternate measurement of 50 spectra of both sample and blank results in a transmittance spectrum with a noise level of less than 5×10−4 (rms). The spectra of highly concentrated samples of H3PO4, Fe, and Cu exemplary show the appearance of broad range, narrow structure background phenomena.