Determination of non-metals via molecular absorption using high-resolution continuum source absorption spectrometry and graphite furnace atomization

This work describes investigations on the determination of the non-metals fluorine, chlorine, sulfur and phosphorus in a graphite furnace atomizer using high-resolution continuum source absorption spectrometry. With this technique, the general problem of limited accessibility to the non-metal resonance lines, all located in the vacuum ultraviolet wavelength region, could be avoided by evaluation of narrow-band molecular absorption in the ultraviolet spectral region. The absorption originates from diatomic molecules produced under certain conditions in the graphite atomizer in the presence of the element in question. In detail, an excess of the metals gallium and aluminium was used to convert fluorine and chlorine to their molecular forms GaF and AlCl, respectively. In a similar manner, sulfur could be converted to CS and phosphorus to PO molecules. For all species, narrow spectral structures, belonging to specific band heads or individual rotational lines, could be found at well-accessible wavelengths between 211 and 261 nm. Using these absorption structures, analytical parameters were evaluated for the determination of the four non-metals. The obtained values for the characteristic masses and the limits of detection are as follows: 13 pg and 9 pg for fluorine; 300 pg and 70 pg for chlorine; 12 ng and 2.3 ng for sulfur; 4.4 ng and 0.9 ng for phosphorus. All methods developed were confirmed by measurements on certified reference materials. In comparison to previous investigations with an air–acetylene flame system, an improvement of up to three orders of magnitude in the limits of detection was achieved.