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304 Multidimensional Chromatography

12.2 GENERAL

Multidimensional techniques have been applied for the analysis of polymer additives
and polymer samples employed in polymer chemistry. Such additives, which include
antioxidants (mainly sterically hindered phenols), are present in order to enhance the
performance of the polymers and to ensure processing and long-term stability.
Antioxidants, such as 2,6-di-tert-butyl-p-cresol and butylated hydroxytoluene
(BHT), are added since many polymers are often subject to thermal and oxidative
degradation. However, the additives themselves are also subject to oxidation, espe-
cially during processing or UV irradiation. The analysis of these additives and their
transformation products has become very important for routine quality control, espe-
cially in the medical plastic and food packaging industries, where the identity and
levels of potentially toxic substances must be accurately controlled and known (1).
The use of multidimensional chromatography for the analysis of polymer additives
in food products, including edible oils, are described in this contribution.
The usual means of identifying and quantifying the level of these additives in
polymer samples is performed by dissolution of the polymer in a solvent, followed
by precipitation of the material. The additives in turn remain in the supernatant liq-
uid. The different solubilites of the additives, high reactivity, low stability, low con-
centrations and possible co-precipitation with the polymer may pose problems and
lead to inconclusive results. Another sample pretreatment method is the use of
Soxhlet extraction and reconcentration before analysis, although this method is very
time consuming, and is still limited by solubility dependence. Other approaches
include the use of supercritical fluids to extract the additives from the polymer and
subsequent analysis of the extracts by microcolumn LC (2).
Multidimensional chromatography has also been applied for the analysis of
industrial chemicals and related samples. Industrial samples which have been ana-
lyzed by multidimensional chromatography include coal tar, antiknock additives in
gasoline (3), light hydrocarbons (4, 5), trihaloalkanes and trihaloalkenes in industrial
solvents (6–8), soot and particulate extracts, and various industrial chemicals that
might be present in gasoline and oil samples.
In this present chapter, the applications of multidimensional chromatography
using various types of coupled techniques for the analysis of industrial and polymer
samples, and polymer additives, are described in detail. The specific applications are
organized by technique and a limited amount of detail is given for the various instru-
mental setups, since these are described elsewhere in other chapters of this volume.

12.3 LC–GC

High performance liquid chromatography (HPLC) is an excellent technique for sam-
ple preseparation prior to GC injection since the separation efficiency is high, analy-
sis time is short, and method development is easy. An LC–GC system could be fully
automated and the selectivity characteristics of both the mobile and stationary