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signal, the size of the sample that is placed onto the column will need to be increased, which, however,
may be unacceptable to the chromatographic system, particularly if small-bore columns are used.

As a result of these problems, prior to about 1975, LC/IR analyses were carried out off-line, the peaks
being collected and the solvent removed by appropriate procedures. The eluted solutes were then either
redissolved in a suitable IR solvent, or compressed into a potassium bromide disk, and the spectrum
obtained employing standard techniques.

The introduction of the Fourier transform IR spectrometer not only partly solved the problem of
sensitivity but, as the spectra are stored, the problem of solvent absorption could also be partly solved.
In theory, the background spectrum of the solvent can be subtracted from the spectrum obtained for the
solute, leaving the actual spectrum of the solute as a difference value. Unfortunately, this involves
subtracting two very large signals, and thus the signal to noise of the difference spectrum is rather low.
It follows that spectra obtained in this way would be very noisy, causing uncertainty both in spectra
interpretation and in the confirmation of substance identity. Nevertheless, in the early days of FTIR,
Kizer et al. [1] demonstrated that this technique would work but, as would be expected, the spectra
were, indeed, very noisy which resulted in very poor sensitivity.

LC/IR Transport Interface
The introduction of the concept of employing transport interfaces to conduct the sample from the
chromatograph to the spectrometer was introduced by Scott et al. [2] for liquid chromatography/mass
spectrometry tandem systems. In due course, the transport concept was also adopted for LC/IR
combinations. Probably the most practical LC/FTIR interface that is commercially available is based on
the solvent transport concept.

An Early LC/FTIR Interface

Some of the first to attempt to utilize a transport system for LC/IR operation were Kuehl and Griffiths
[3]. Initially they tried to employ