Page 225 - Tandem Techniques

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The sample was extracted with toluene and then derivatized in the manner described by Lee et al. [30].
A Varian 6000 gas chromatograph was employed in conjunction with a Finnigan ITD (model 800 cl)
mass spectrometer. A DB-5 column was used, 30 m long, 312 µm I.D., with a film thickness of 1 µm. A
example of the results of the analysis of an air sample is shown in figure 5.28. The peak for the
herbicide is reported to be equivalent to 9 pg of derivatized material. The limit of detection was
reported to be about 0.72 ng /m of air.
3

Derivatization Techniques

Derivatization procedures are employed in GC/MS tandem analyses mainly for two reasons. First, to
render the sample components volatile, so that they can be separated by development in a gaseous
mobile phase, and second, so that they can be used with a simple direct-inlet MS interface. Involatility
can arise from two causes. The sample may be strongly polar, e.g. aliphatic acids, carbohydrates or the
higher molecular weight alcohols. Alternatively, the sample can have a very high molecular weight, e.g.
waxes, synthetic polymers, biopolymers, etc. Substances that are involatile as a result of strong polarity
can often be successfully derivatized and made relatively volatile. Unfortunately, substances that are
involatile as a result of their high molecular weight can rarely be rendered volatile merely by
derivatization. It follows that whereas it is easy to produce a volatile derivative of a low molecular
weight aliphatic acid, it is virtually impossible to make a volatile derivative of a biopolymer. Such
substances are usually analyzed on the complementary LC/MS tandem systems, using special interfaces
which will be discussed later in this book.

GC derivatizing agents are classified on the basis of the chemical nature of the materials they render
volatile. Different reagents are used to make volatile derivatives of diverse materials, for example,
acids, alcohols, amino acids, etc.

Esterification

Esterification is a procedure commonly used to form volatile derivatives of organic acids. The most
popular and useful method is esterification