Page 494 - Tandem Techniques

Page 479

basically off-line procedures. Serious consideration should be given to the alternative use of LC/MS or
LC/IR for an analysis before a TLC tandem system is chosen, and then perhaps it should be chosen only
as a last resort, under very special circumstances.

Matrix peaks occurred at masses ranging from 250 to 400 Da and thus interfered with the spectrum.
Consequently, a limit is set on the mass measurement of low molecular weight materials. The
sensitivity quoted was 40 pg but the size of the spot was not given. Nevertheless, very useful mass
spectra were obtained by directly scanning the thin layer plate and taking advantage of the unique
properties of the time of flight mass spectrometer. The spot dispersion was examined by the authors
using guineas green B and the three-dimensional image of the spot after processing is shown in Figure
12.16.

Figure 12.16
The Tree Dimensional Image of Guinea Green B
(20 ng) Separated on a Plastic Backed TLC Silica Gel Plate
Reprinted with permission from A. I. Gusev, O. J. Vasseur,
A. Proctor, A. G. Sharkey and D. M. Hercules, Anal. Chem.,
67(1995)4565, Copyright 1995 American Chemical Society.

Synopsis

True in-line TLC tandem systems are not actually possible, as the TLC separation must be developed
before the spots can be monitored. It follows