Spectral interferences on arsenic and mercury prominent emission lines in vacuum inductively coupled plasma-atomic emission spectrometry and use of methanol vapor as optical filter for spectral order sorting

Wavelength profiles for eleven prevalent concomitant elements on arsenic and mercury emission lines at 189.04 and 184.95 nm in the third order, were obtained by simultaneously scanning the arsenic and mercury channels of a vacuum spectrometer with an argon inductively coupled plasma (ICP) as an excitation source. The displacement of the polychromator primary slit was used for scanning. Vacuum ultraviolet (VUV) lines as well as ultraviolet (UV) lines above 200 nm were observed because the interference filter located before the channels' photomultipliers had some residual transmission to radiation above 200 nm. The VUV emission lines were differentiated from the UV lines by purging the optical path between the plasma and the spectrometer, with methanol vapor. The vapor absorbed the VUV lines and allowed the UV lines above 200 nm to pass through, acting as a gas optical filter. The arsenic channel experienced spectral interferences from Ti(200 mgl^-1), Mn(200 mgl^-1), Cr(200 mgl^-1), and Fe(1000 mgl^-1) due to VUV lines and from V(200 mgl^-1), and Cr due to UV lines, while Mg(1000 mgl^-1), Al(1000 mgl^-1), Si(11000 mgl^-1), Ca(1000 mgl^-1) and Fe exhibited background enhancement. Ni(200 mgl^-1) and Cu(200 mgl^-1) did not interfere. The mercury channel experienced spectral interferences from Si and Ca due to VUV lines and from Mn, Cr and Fe due to UV lines, whereas Mg and Al exhibited background enhancement, V, Ti, Ni and Cu did not interfere.