The synthesis of iron and nickel carbonyl as calibration materials for spectroscopic systems

Iron pentacarbonyl, Fe(CO)5, was employed in a number of spectroscopic systems as the calibration source for Fe during the analysis of toxic and reactive gases such as anhydrous hydrogen chloride and chlorine. Although nickel tetracarbonyl, Ni(CO)4, has similar properties to Fe(CO)5, its use is limited owing to the unavailability of low ppm (v/v) standard gas mixtures. Gas mixtures of these two compounds were produced by synthesizing Fe(CO)5 and Ni(CO)4 and diluting them with Ar or N2 as required. Low ppm (v/v) gas mixtures of both metal carbonyls were stable for at least 20 days. The fluctuations in concentration were negligible. The %R.S.D.’s were 2.22 and 0.59 for Fe(CO)5 and Ni(CO)4, respectively. The other step in synthesizing these compounds as standard materials was to determine their concentrations. Concentrated nitric acid (70% v/v), was employed to absorb the carbonyls. The solutions were subsequently analyzed with a graphite furnace atomic absorption spectrometer (GFAAS). When compared against a reference gas mixture, the recovery for Fe(CO)5 was 98%.