Environmental Engineering Reference
In-Depth Information
C
4
H
9
H
3
C
S
H
3
C
N
N
NH
C
4
H
9
O
O
O
O
OH
O
O
O
CH
3
CH
3
CH
3
Oxidation
in vivo
Hydrolysis
CH
3
CH
3
CH
3
Carbosulfan
Carbofuran
Hydroxybenzofuran
Figure 1.10
Degradation of carbosulfan to carbofuran, via oxidation, then hydrolysis of carbofuran
to hydroxybenzofuran
1.5 Analytical methods used to detect carbofuran
The types of samples that are collected for carbofuran residue analysis are further discussed in
Chapter 2, and throughout this topic. In general terms, an ideal analytical detection method should
have a high rate of recovery, a low limit of detection, high selectivity and sensitivity, and good repro-
ducibility (Fodor-Csorba 1998). A number of spectrophotometric and/or chromatographic methods
are available for identifying and quantifying the presence of carbofuran in environmental samples.
Selecting an appropriate analytical technique depends upon the chemical and physical properties of
the compound(s) of interest within a sample, referred to as the analyte(s). In addition, the analytical
method is selected on the basis of whether or not the compounds are known targets, or whether a
preliminary non-specifi c screening is required (Maurer 1999). Here, we briefl y review the analytical
methods that are typically used to assess the presence of carbofuran residues in wildlife samples.
Throughout this topic, they are referred to as: high performance (or pressure) liquid chromatog-
raphy (HPLC, Figure 1.11), gas chromatography with mass spectrometry (GC/MS, Figure 1.12),
liquid chromatography with mass spectrometry (LC/MS (Figure 1.13, or also LC-MS/MS) and thin
layer chromatography (TLC). We also mention a bioassay method, and introduce the concept of
cholinesterase inactivation, which is explored further in Chapter 2.
1.5.1 Principles of chromatography
In general, samples to be analysed using chromatographic techniques fi rst undergo a preparation
stage, which can include homogenisation, centrifugation, fi ltration, liquid-liquid extraction, Soxhlet
extraction, solid-phase extraction (SPE) and column 'cleanup' before the sample even reaches the
instrumental analysis stage (GC/MS or LC/MS for example). All chromatographic techniques are
based on the principle that the components (or compounds) within a complex mixture as either a gas
or a liquid can be separated and analysed individually using a variety of detectors, by mass or UV/
visible spectrometry, for example. Compounds in a mixture are separated as they pass in a mobile
phase/state over/through a stationary phase (a liquid or solid). The stationary phase is mounted on
a chromatography column-generally, in the simplest terms, a small tube containing the stationary
phase. The sample containing the mixture of compounds is washed through the column and the
compounds elute from (or leave) the column after a set time (t) which is highly repeatable, and
determined by the specifi c affi nity each compound has for the stationary phase. This in turn affects
how quickly it will move through the column.
Search WWH ::
Custom Search