- •1.1 Introduction
- •1.2 Sample preparation and clean-up procedures
- •1.2.1 Liquid-liquid extraction
- •1.2.2 Solid phase extraction
- •1.2.3 Purge and trap
- •1.2.5 Derivatization
- •1.2.6 Clean-up procedures
- •1.3 Instrumentation
- •1.3.1 Gas chromatography
- •1.3.1.1 Capillary columns
- •1.3.1.2 Sample introduction systems
- •1.3.2 High performance liquid chromatography
- •1.3.2.1 Hplc columns
- •1.3.2.2 Hplc detectors
- •Volatile organic compounds
- •2.1 Introduction
- •2.2 Compounds
- •2.3 General Procedure
- •2.4 Sensitivity
- •3.1 Introduction
- •3.2 Compounds
- •3.3 General Procedure
- •3.4 Sensitivity
- •3.5.1 Procedure 1: Solid phase extraction/cgc/ms
- •4.1 Introduction
- •4.2 Compounds
- •4.3 General Procedure
- •4.4 Sensitivity
- •4.5 Detailed Procedures
- •4.5.1 Procedure 1: pah analysis using hplc (epa 550.0)
- •5.1 Introduction
- •5.2 Compounds
- •5.3 General Procedure
- •5.4 Sensitivity
- •6.1 Introduction
- •7.1 Introduction
- •7.2 Compounds
- •7.3 General Procedure
- •9.1 Introduction
- •9.3 General Procedure
- •9.4 Sensitivity
- •9.5 Detailed Procedures
- •9.5.1 Procedure 1: Tropolone extraction/cgc/aed or cgc/ms
- •10.1 Introduction
- •10.2 Compounds
- •10.3 General Procedure
- •10.4 Sensitivity
- •10.5 Detailed Procedures
- •11.1 Introduction
- •12.1 Introduction
- •12.2 Compounds
- •13.1 Introduction
- •100-90-80-70-60 50 40 30 20-10-0-
- •20 30 40
- •Iceland
- •Ireland
1.2.5 Derivatization
Derivatization constitutes an additional cleaning of a complex sample where interferences may hinder the analysis of the components of interest. In gas chromatography, when highly polar compounds are to be analysed, they are best transformed to volatile apolar solutes, for example methylation of phenoxy acids. Ideal derivatization agents are selective and non-toxic, sustain good reaction kinetics with fast reaction times and high yields and do not interfere with the analysis. Generally, the derivatized product is thermally more stable, more volatile and is easier to detect. As examples, the derivatization of chloro-phenols into their pentafluorobenzoyl derivatives provides better sensitivity and selectivity for capillary GC/ECD analysis and the two step post-column reaction-derivatization of methylcarbamates yields better sensitivity for HPLC/FLD detection. The latest trend is to fully automate derivatization both in GC and HPLC, reducing the risk of artefacts and enhancing the reproducibility and repeatability of analyses.
1.2.6 Clean-up procedures
When direct GC or HPLC analysis of samples obtained by liquid-liquid extraction leads to deterioration of chromatographic performance or undesired interferences in the chromatographic profile, further clean-up is required. The most widely used method is adsorption column chromatography on alumina, florisil and/or silica used for example in pesticide or PAH fractionation. In general, adsorption is useful for separating analytes with well defined and narrow polarity ranges from extraneous, interfering solutes of different polarity. Some disadvantages of adsorption clean-up include the variability in activity of the adsorbents and the need for large volumes of high purity solvents which afterwards must be removed in order to enrich the analytes of interest.
Still rarely used in environmental laboratories, size exclusion chromatography (SEC) is a very elegant way to fractionate pollutants on the basis of their molecular shape. The main reasons this method has not proved more popular is the need for a complete HPLC system, preferably with refractive index detection and the relatively high cost of size exclusion columns. The possibilities of SEC are illustrated in Figure 1.5. showing the fractionation of polychlorobiphenyls (Arochlor 1260) and polyaromatic hydrocarbons (the 16 on the priority pollutants list) from triglycerides.
The different classes are very close in polarity and adsorption chromatography would not be able to achieve this separation. Another advantage of the HPLC/ SEC approach is that the PCB and PAH containing fractions have a volume of only a few millilitres, avoiding time-consuming evaporation of the solvent.
Acid-base partitioning is a very effective clean-up for fractionating acidic or basic pollutants from each other and/or from neutral pollutants. The method is intensively used in the analyses of chlorophenols and phenoxy acids.
Elementary sulphur, sometimes present in industrial waste waters, causes chromatographic interference with analytes such as pesticides and PCBs in CGC/ECD and CGC/MS analyses. A sulphur clean-up is performed by mixing the sample with either copper, mercury or tetrabutylammonium sulphite, the latter giving the best results for pesticides. SEC offers another alternative to remove sulphur.