**2. Extraction techniques**

The earliest sample preparation method is extraction, in which the analyte of interest is separated from a sample matrix with an optimum yield and selectivity. Two major kinds of extraction include solid-phase extraction (SPE) and liquidliquid extraction (LLE). In SPE, the analyte can be separated from a solid sample, and in LLE, it is extracted from sample solutions [7]. The solvents, in which the analyte is extracted, may be organic liquids, supercritical fluids, and superheated liquids [3]. Also, the extractor solvent may be bonded to a polymeric support, as in membrane extractions [4]. By optimizing the extraction conditions such as temperature, pressure, and pH of the solution and also appropriately using additives and reagents, the selectivity and yield of the extraction process will be improved.

The basic purpose of all extraction methods is to concentrate the analyte selectively in one phase. Each analyte is distributed between two phases according to the distribution constant, temperature, and relative volumes of the phases. In many of these methods, there is a conflict between the analytes of interest and the other soluble interferences to be quite extracted into the extractor phase. Exhaustive extraction techniques, like Soxhlet extractions, are often designed to provide thorough extractions regardless of the matrix. So, this kind of extraction can be applied to a range of samples such as different soil types but limits selectivity [3].

In order to enhance the selectivity of the extraction process, the supercritical fluid extraction (SFE) was introduced. In comparison with organic solvents, the carbon dioxide solvent is a weaker eluent and more selective extractor medium.

#### **2.1** *Solid-phase* **extraction (SPE)**

In general, SPE involves four steps:


**49**

SPME.

reached.

temperature.

*Sample Preparation Techniques for Gas Chromatography DOI: http://dx.doi.org/10.5772/intechopen.84259*

pesticides were determined by GC-MS.

**2.2 Solid-phase microextraction (SPME)**

covered on the surface of a fused silica core fiber.

time prior to achieving equilibrium.

The properties of extraction process, by SPME, are as follows [2]:

1.By SPME, samples are analyzed after equilibrium is reached or at a specified

2.Exhaustive extraction of analyte from the sample matrix is not achieved by

4.SPME is directly applicable for field applications in air and water sampling.

5.It does not require continuation of extraction by SPME until equilibrium is

6.A quantitative extraction may be obtained by careful control of time and

7.SPME is a solventless sample preparation procedure.

3.So, SPME operationally encompasses non-exhaustive, equilibrium and preequilibrium, batch, and flow-through microextraction techniques.

below.

Also, sorbent phases can be purchased, and typical column housings are manufactured of polypropylene or glass. In order to contain the column with the sorbent phase, porous frits made of polyethylene, stainless steel, or Teflon can be used [2]. There are some examples for applying SPE as sample preparation step before GC detection of different analytes in a variety of samples. Some of them are pointed

Lee et al. reported the determination of endocrine-disrupting phenols, acidic pharmaceuticals, and personal care products in sewage by solid-phase extraction and gas chromatography-mass spectrometry [8]. In this work, an anion exchanger was used as a solid-phase extractor, and a multiresidue method was developed and optimized for the extraction of 21 phenols and acids in sewage. The phenols and acids were then selectively eluted in separate fractions and were converted into

volatile derivatives, by suitable reagents, for GC-MS determination.

Stajnbaher et al. studied a multiresidue method for determination of 90 pesticides in fresh fruits and vegetables using solid-phase extraction and gas chromatography-mass spectrometry [9]. In this study, a SPE on a highly crosslinked "*poly(styrene-co-divinylbenzene)"* column was used for cleanup and preconcentration of the pesticides from the water-diluted acetone extracts, and then the

Miniaturization of analytical processes into microchip platforms designed for micro total analytical systems is a new and rapidly developing field. Solid-phase microextraction (SPME) is a modern technique that consists in direct extraction of the analytes with the use of a small-diameter fused silica fiber coated with an adequate polymeric stationary phase [10]. On the other hand, in two designs of SPME, a thin layer of sorbent is coated on the outer surface of fibers (fiber design), and the inner surface of a capillary tube (in-tube design) is covered. The fiber design can be used as an interface in both GC and HPLC, but in-tube design has been just applied as an easier approaching interface with HPLC. In fiber design, a thin film of liquid polymer or mixture of a solid sorbent with a liquid polymer has

SPE sorbents are commercially available in three formats:


*Gas Chromatography - Derivatization, Sample Preparation, Application*

**2. Extraction techniques**

**2.1** *Solid-phase* **extraction (SPE)**

and/or sorbent.

away.

1.Cartridge.

3.Disks.

In general, SPE involves four steps:

an appropriate eluting solvent.

2.Columns fashioned like syringe barrels.

SPE sorbents are commercially available in three formats:

1.Column preparation or prewash step.

On the other hand, different samples possess a variety of sample treatment methods. Therefore, in this chapter, by paying attention to the type of sample matrix, information required (quantitative or qualitative), and sensitivity required,

The earliest sample preparation method is extraction, in which the analyte of interest is separated from a sample matrix with an optimum yield and selectivity. Two major kinds of extraction include solid-phase extraction (SPE) and liquidliquid extraction (LLE). In SPE, the analyte can be separated from a solid sample, and in LLE, it is extracted from sample solutions [7]. The solvents, in which the analyte is extracted, may be organic liquids, supercritical fluids, and superheated liquids [3]. Also, the extractor solvent may be bonded to a polymeric support, as in membrane extractions [4]. By optimizing the extraction conditions such as temperature, pressure, and pH of the solution and also appropriately using additives and reagents, the selectivity and yield of the extraction process will be improved. The basic purpose of all extraction methods is to concentrate the analyte selectively in one phase. Each analyte is distributed between two phases according to the distribution constant, temperature, and relative volumes of the phases. In many of these methods, there is a conflict between the analytes of interest and the other soluble interferences to be quite extracted into the extractor phase. Exhaustive extraction techniques, like Soxhlet extractions, are often designed to provide thorough extractions regardless of the matrix. So, this kind of extraction can be applied

the sample preparation methods used before GC analyses are discussed.

to a range of samples such as different soil types but limits selectivity [3].

In order to enhance the selectivity of the extraction process, the supercritical fluid extraction (SFE) was introduced. In comparison with organic solvents, the carbon dioxide solvent is a weaker eluent and more selective extractor medium.

2.Sample loading or the retention of the analytes of interest on the cartridge

3.Column postwash to remove undesirable contaminants. In reality, the compounds of interest are retained on the sorbent, while interferences are washed

4.Analyte desorption from the cartridge. The adsorbed analytes are recovered by

**48**

Also, sorbent phases can be purchased, and typical column housings are manufactured of polypropylene or glass. In order to contain the column with the sorbent phase, porous frits made of polyethylene, stainless steel, or Teflon can be used [2].

There are some examples for applying SPE as sample preparation step before GC detection of different analytes in a variety of samples. Some of them are pointed below.

Lee et al. reported the determination of endocrine-disrupting phenols, acidic pharmaceuticals, and personal care products in sewage by solid-phase extraction and gas chromatography-mass spectrometry [8]. In this work, an anion exchanger was used as a solid-phase extractor, and a multiresidue method was developed and optimized for the extraction of 21 phenols and acids in sewage. The phenols and acids were then selectively eluted in separate fractions and were converted into volatile derivatives, by suitable reagents, for GC-MS determination.

Stajnbaher et al. studied a multiresidue method for determination of 90 pesticides in fresh fruits and vegetables using solid-phase extraction and gas chromatography-mass spectrometry [9]. In this study, a SPE on a highly crosslinked "*poly(styrene-co-divinylbenzene)"* column was used for cleanup and preconcentration of the pesticides from the water-diluted acetone extracts, and then the pesticides were determined by GC-MS.
