improve the chromatographic behaviour and detection properties, not the extraction
efficiency (Pawliszyn 2002; Kudlejova et al. 2012). The fact that extraction and
derivatization can be performed simultaneously is illustrated for example in the
study on in-matrix derivatization of amphetamine-like molecules, where Mohamed
(2017) presents a simple method in which both procedures can be carried out in
one step.
Sample preparation is a critical step and the main source of uncertainties in the
analysis of environmental samples (Ribeiro et al. 2014); it adds complexity to the
analytical process, but on the other hand it is a potential source of bias, variance,
contamination and mechanical loss. Therefore, sample preparation should be
planned carefully and adequately documented to provide a complete record of the
sample history (Keith et al. 1983). Especially derivatization should be performed
only when necessary, since the derivatizing agents can interfere and introduce errors
in the system (Kudlejova et al. 2012).
After pretreatment, samples are finally prepared to be measured by highly
selective and sensitive instrumental analytical methods, such as molecular spectroscopic methods (UV-vis, fluorescence, infrared (IR) and Raman spectroscopy),
atomic spectroscopic methods (atomic absorption flame and non-flame spectrometry, atomic fluorescence flame and non-flame spectrometry and atomic emission
spectrometry (including inductively coupled plasma (ICP) and microwave
plasma (MP)), chromatographic methods (gas chromatography (GC), liquid chromatography (LC), high-performance liquid chromatography (HPLC) and thin-layer
chromatography (TLC)), mass spectrometric methods, electrochemical methods,
thermal methods and radiological methods.
5.3
The Types of Extraction Techniques
Extraction is considered a crucial step in most chemical analyses; it entails removing
the target analyte from the sample matrix and passing it into the phase required for
identification and quantification performed mostly by spectroscopic and chromatographic techniques. The analyte might be one specific compound or a group
of compounds of similar nature. Solubilization and separation of the analyte of
interest from other material is done with an appropriate solvent, chosen with regard
to the solubility of the target analyte and on the balance of cost, safety and environmental concerns. In order to perform an extraction, the analyte must have a higher
solubility in the latter phase than in the starting phase (JoVE 2019). The starting
phase might be the original sample matrix or a solution in which the sample has been
dissolved or digested (Tissue 2013). Two most common types of laboratory extraction are liquid-liquid and solid-liquid extraction; their principles, the types and
amounts of solvents used and some current trends that favour effective analyte
extractions from environmental matrices are discussed in the next section. The
most widely used liquid-liquid and solid-liquid extraction procedures with their
advantages, drawbacks and suitability for the extraction of different compounds
are presented in Table 5.1.
134
L. Nemček and I. Hagarová
efficiency (Pawliszyn 2002; Kudlejova et al. 2012). The fact that extraction and
derivatization can be performed simultaneously is illustrated for example in the
study on in-matrix derivatization of amphetamine-like molecules, where Mohamed
(2017) presents a simple method in which both procedures can be carried out in
one step.
Sample preparation is a critical step and the main source of uncertainties in the
analysis of environmental samples (Ribeiro et al. 2014); it adds complexity to the
analytical process, but on the other hand it is a potential source of bias, variance,
contamination and mechanical loss. Therefore, sample preparation should be
planned carefully and adequately documented to provide a complete record of the
sample history (Keith et al. 1983). Especially derivatization should be performed
only when necessary, since the derivatizing agents can interfere and introduce errors
in the system (Kudlejova et al. 2012).
After pretreatment, samples are finally prepared to be measured by highly
selective and sensitive instrumental analytical methods, such as molecular spectroscopic methods (UV-vis, fluorescence, infrared (IR) and Raman spectroscopy),
atomic spectroscopic methods (atomic absorption flame and non-flame spectrometry, atomic fluorescence flame and non-flame spectrometry and atomic emission
spectrometry (including inductively coupled plasma (ICP) and microwave
plasma (MP)), chromatographic methods (gas chromatography (GC), liquid chromatography (LC), high-performance liquid chromatography (HPLC) and thin-layer
chromatography (TLC)), mass spectrometric methods, electrochemical methods,
thermal methods and radiological methods.
5.3
The Types of Extraction Techniques
Extraction is considered a crucial step in most chemical analyses; it entails removing
the target analyte from the sample matrix and passing it into the phase required for
identification and quantification performed mostly by spectroscopic and chromatographic techniques. The analyte might be one specific compound or a group
of compounds of similar nature. Solubilization and separation of the analyte of
interest from other material is done with an appropriate solvent, chosen with regard
to the solubility of the target analyte and on the balance of cost, safety and environmental concerns. In order to perform an extraction, the analyte must have a higher
solubility in the latter phase than in the starting phase (JoVE 2019). The starting
phase might be the original sample matrix or a solution in which the sample has been
dissolved or digested (Tissue 2013). Two most common types of laboratory extraction are liquid-liquid and solid-liquid extraction; their principles, the types and
amounts of solvents used and some current trends that favour effective analyte
extractions from environmental matrices are discussed in the next section. The
most widely used liquid-liquid and solid-liquid extraction procedures with their
advantages, drawbacks and suitability for the extraction of different compounds
are presented in Table 5.1.
134
L. Nemček and I. Hagarová