Flame photometric detection of some transition metals. I. Calibrations and spectra

Abstract

After gas-chromatographic separation as volatile organometallics, some transition elements were found to respond with analytically relevant sensitivities in the flame photometric detector. Their minimum detectable amounts, in mole of metal per second at an S/Np-t-p ratio of 2, were 1 × 10−14 for nickel and 6 × 10−13 for rhenium, as well as a less sensitive 2 × 10−12 for molybdenum and 3 × 10−12 for cobalt. (When divided by 3.7, these values yield the S/σ = 3 limit of detection as recommended by IUPAC.) Calibration curves were established for these elements in comparison with transition metals already known to respond in the flame photometric detector. Their chemiluminescent spectra, together with that of chromium, were measured in the detector at analytically (as opposed to spectroscopically) optimized conditions. Atomic lines, molecular bands, and continua were all present. Also, the spectra produced by several types of carbon compounds were recorded for a definition of potential spectral interferences from hydrocarbonaceous sample matrices. The atomic lines and the massive continua displayed by certain metals are discussed in some detail. Atomic lines appear up to a limiting energy level of 3.6 eV above ground state. It is suggested that continua could arise from small, perhaps catalytically active particles. Also discussed, in accordance with a reviewer's request, are the analytical performance of the FPD compared to ICP and MIP sources, and the definition and influence of noise on measured performance criteria.