Developments in Gas Chromatography - Forensic Applications of Gas Chromatography - page 69

7

Developments in Gas
Chromatography

7.1 Introduction

This chapter considers progress in GC from the point of view of develop-
ments in

• Sample preparation
• Column technology
• Instrumentation

7.2 Developments in Sample Preparation Techniques

7.2.1 Sample Derivatisation to Aid Volatility for GC
For analysis of samples by GC, the analytes of interest should be volatile,
be thermally stable at the operating temperatures of the injection port and
column oven, and give good peak shape. However, it is possible to analyse
analytes that do not meet these criteria by carrying out an additional step
of sample (and hence compound) pretreatment known as derivatisation.
Derivatisation is carried out in order to modify the functionality of an ana-
lyte to facilitate separation by GC and is generally used with analytes of low
volatility and those that are thermally labile, that is, compounds that could
often be analysed by high performance liquid chromatography (HPLC)
( Note: For topics on HPLC, see Further Reading at the end of the chapter.)
Derivatisation is therefore normally done for the following reasons:

• To improve the resolution (see Section 3.2.4) and reduce peak tail-
ing (see Section 3.2.3) of polar compounds; by definition polar com-
pounds contain the following functional groups: -OH, -COOH,
=NH, -NH 2 and -SH.
• To improve column eiciency (see Section 3.2.2).
• To analyse relatively nonvolatile compounds (e.g., those compounds
with higher molecular weight).
• To increase detector sensitivity (in some cases) (see Sections 2.6.2,
2.6.3 and 2.6.4).
• To improve the thermal stability of some compounds.