Baseline shifts in inverse Zeeman-effect graphite furnace atomic absorption spectrometry ascribed to the Zeeman effect of the CN molecule

The background-corrected Zeeman absorbance baseline shows shifts for lines of several hollow cathode lamps up to tenths of an absorbance unit with firings of an empty graphite furnace atomiser and clear differences in the sizes of the shifts according to whether the furnace is purged with nitrogen or argon. Baseline shifts are seen for hollow cathode lines close to listed rotation lines of the (0,0) and higher bands of the CN violet system. Such shifts, it is suggested, are caused by overlap of the hollow cathode lines with Zeeman-shifted CN lines and in support of this suggestion the known behaviour of CN lines in magnetic fields (spin doublet contraction) is cited. Evidence is presented for the existence of interfering CN lines near the main atomic absorption line of Cr (357.9 nm), as a spectral interference occurs in both the inverse Zeeman configuration (with lamps containing iron) and with continuum source correction.