Yb. Wang et Jw. Carnahan, BINARY MOBILE PHASES FOR SUPERCRITICAL-FLUID CHROMATOGRAPHY WITH HELIUM MICROWAVE-INDUCED PLASMA DETECTION, Analytical chemistry, 65(22), 1993, pp. 3290-3294
Microwave-induced plasma atomic emission detection is examined for sup
ercritical fluid chromatography detection with binary methanol/carbon
dioxide mobile phases. Spectra are obtained and compared with pure hel
ium plasmas, plasmas with added carbon dioxide, and added binary mobil
e phases. Trends of molecular emission intensities and species were ex
amined as functions of methanol/carbon dioxide composition ratios and
supercritical fluid pressures. Adding carbon dioxide to the pure heliu
m plasma reduced and/or eliminated molecular bands from OH and N2+ whi
le producing intense bands of CN, C2, NH, and N2. The addition of meth
anol to the carbon dioxide ''doped'' plasma produced intense OH emissi
on while depressing the intensities of the other aforementioned molecu
lar bands. Emission from OH increased significantly with additional me
thanol. As the pressure of the methanol/carbon dioxide mobile phase wa
s increased, the general trend was that molecular band intensities ten
ded to decrease. The effect was attributed to plasma cooling. The plas
ma easily tolerated the mixed mobile phases despite the added spectral
complications of these molecular emissions. The advantages of the bin
ary mobile phases for chromatography are illustrated with separations
of moderately high molecular weight chlorinated organic compounds. Ret
ention times are reduced and detectabilities are in the range of 1.4-1
.9 ng/s for p-chlorobiphenyl, 2,4'-dichlorobenzophenone and hexachloro
benzene.