Fundamental noise studies in flame atomic magneto-optic rotation and atomic absorption spectrometry

A study of inherent noise sources present in a purpose built flame atomic m agneto-optic rotation (AMOR) spectrometer system was carried out with a vie w to identifying their sources. Two different optical configurations were e mployed, a crossed polariser and a 45 degrees offset polariser configuratio n. The offset polariser configuration was operated in both an AMOR and atom ic absorption (AA) mode for the noise measurements. Two main interference frequencies were found to occur in all the optical me asurement modes. An interference flame feature frequency (15.5 Hz -39.0 Hz) which arose from an "organ-pipe" effect in the gas flow through the flame cooling sheets. The second interference frequency (at 100 Hz) was thought t o arise due to modulation of the analytes magneto-optic properties due to r ipple on the electromagnet d.c. power supply. Photon noise and fluctuation noise were found to be present as background noise. The fluctuation noise w as dominant at higher analyte concentrations. The characteristics and origins of fluctuation noise are discussed and inve stigated for each measurement mode. The noise spectra of the conventional A A measurements were compared with those of the contemporary AMOR measuremen ts, to ascertain any differences in noise power spectra which may affect th e signal-to-noise ratio.