Rj. Dijkstra et al., On-line coupling of column liquid chromatography and raman spectroscopy using a liquid core waveguide, ANALYT CHEM, 71(20), 1999, pp. 4575-4579
The on-line coupling of Raman spectroscopy and conventional-size liquid chr
omatography (LC) by using a plastic liquid core waveguide (LCW) was explore
d. The LCW considered (length 30 cm, internal diameter 280 mu m, internal v
olume 18 mu L) is suitable for light guiding through aqueous LC eluents sin
ce the refractive index of the plastic perfluorinated material (denoted as
Tenon AF2400) is 1.29, i.e., smaller than that of water (1.333) or methanol
(1.329). Three-dimensional chromatograms showing on-the-fly Raman spectra
are shown for a test mixture of 4-nitroaniline, 4-nitrophenol, 2,4-dinitrop
henol, and nitrobenzene, compounds with slightly different NO2 vibrations.
A limit of detection of 10 mu g/mL for 4-nitroaniline, the most favorable o
f the test compounds, was achieved; the linearity ranged from 0.05 to 3.0 m
g/ mt (six data points in duplicate, r(2) = 0.997). The improved detectabil
ity is due to the increased optical path length provided by the LCW and to
the use of a large-volume-injection procedure (500-mu L injections which ef
fected a 35-fold improvement compared to standard, 10 mu L, injections). Th
e results of this preliminary study indicate that LC-Raman has potential.