HF-LPME is simple, fast, and inexpensive allowing for the extraction and concentration of the analytes in a single step [99]. It allows for use of different configurations depending on the particular analysis that is chosen.
The DLLME consists of a very small acceptor organic phase, almost microscopic
droplets, on the surface of the donor aqueous phase in order to achieve a large
exchange surface. To achieve this, the organic phase is dispersed with a second
solvent so that two organic solvents are used concurrently, one immiscible in the
aqueous phase (acceptor) and the other miscible in the aqueous phase (dispersant).
When the dispersant-acceptor mixture comes into contact with the aqueous phase,
and the emulsion is formed, the analyte is then transferred from the sample to the
extraction phase. It is then centrifuged in order to separate the two phases. The
microvolume of the organic phase contains the extracted analytes, and the aqueous
phase contains the impurities and the dispersing agent. The extraction is carried out
quickly with high enrichment values [61, 103, 119]. As dispersing solvents, methanol [61, 103], acetone [61, 119], or acetonitrile [61, 103] are used. Instead of a third
solvent, ultrasound is used to achieve dispersion; the technique is called ultrasoundassisted emulsification microextraction (USAEME) [54, 103].
3.2.3 Stage 3: Separation, Identification, and Quantification
The complexity of the water samples and the low concentrations of NSAIDs in them
require that identification and quantification be carried out using very sensitive
separation and detection methods, which allow multiple quantifications of analytes.
The most commonly used for this purpose are chromatographic techniques, especially GC and HPLC. To a lesser extent, capillary electrophoresis (CE) [3, 100, 125–
132], supercritical fluid chromatography (SFC) [111], and other techniques that are
characterized by their speed and selectivity have been used, such as determination
using biosensors [116]. For the final quantification of the products, different types of
detectors are used.
Gas Chromatography Despite the advantages of GC for the determination of
analytes in complex samples, the data provided is not sufficient for an unequivocal
identification of the sample components. For its part, mass spectrometry
(MS) identifies pure substances almost unequivocally but not the individual components of a mixture that have not been previously separated. The association of both
techniques constitutes a powerful tool for the analysis of water samples. Both are
compatible because they work in the gas phase and require a very small amount of
sample. GC provides the successive elution of the analytes isolated from the mixture,
which are then identified in the mass spectrometer (MS) based on their spectra. In
this way, the MS acts as a chromatographic detector.
GC-MS It was the first technique used successfully for the determination of
NSAIDs in water samples [123] and is still widely used [16, 30, 32, 44–49, 53,
54, 56, 58, 59, 62, 64, 66, 67, 70, 75, 76, 79, 85, 87, 88, 90, 98, 106, 113, 114,
123]. It detects concentrations in the order of μgL
À1 to ngL
À1 and less. It is fast,
Quantification of Non-steroidal Anti-inflammatory Drug in Water
95
The DLLME consists of a very small acceptor organic phase, almost microscopic
droplets, on the surface of the donor aqueous phase in order to achieve a large
exchange surface. To achieve this, the organic phase is dispersed with a second
solvent so that two organic solvents are used concurrently, one immiscible in the
aqueous phase (acceptor) and the other miscible in the aqueous phase (dispersant).
When the dispersant-acceptor mixture comes into contact with the aqueous phase,
and the emulsion is formed, the analyte is then transferred from the sample to the
extraction phase. It is then centrifuged in order to separate the two phases. The
microvolume of the organic phase contains the extracted analytes, and the aqueous
phase contains the impurities and the dispersing agent. The extraction is carried out
quickly with high enrichment values [61, 103, 119]. As dispersing solvents, methanol [61, 103], acetone [61, 119], or acetonitrile [61, 103] are used. Instead of a third
solvent, ultrasound is used to achieve dispersion; the technique is called ultrasoundassisted emulsification microextraction (USAEME) [54, 103].
3.2.3 Stage 3: Separation, Identification, and Quantification
The complexity of the water samples and the low concentrations of NSAIDs in them
require that identification and quantification be carried out using very sensitive
separation and detection methods, which allow multiple quantifications of analytes.
The most commonly used for this purpose are chromatographic techniques, especially GC and HPLC. To a lesser extent, capillary electrophoresis (CE) [3, 100, 125–
132], supercritical fluid chromatography (SFC) [111], and other techniques that are
characterized by their speed and selectivity have been used, such as determination
using biosensors [116]. For the final quantification of the products, different types of
detectors are used.
Gas Chromatography Despite the advantages of GC for the determination of
analytes in complex samples, the data provided is not sufficient for an unequivocal
identification of the sample components. For its part, mass spectrometry
(MS) identifies pure substances almost unequivocally but not the individual components of a mixture that have not been previously separated. The association of both
techniques constitutes a powerful tool for the analysis of water samples. Both are
compatible because they work in the gas phase and require a very small amount of
sample. GC provides the successive elution of the analytes isolated from the mixture,
which are then identified in the mass spectrometer (MS) based on their spectra. In
this way, the MS acts as a chromatographic detector.
GC-MS It was the first technique used successfully for the determination of
NSAIDs in water samples [123] and is still widely used [16, 30, 32, 44–49, 53,
54, 56, 58, 59, 62, 64, 66, 67, 70, 75, 76, 79, 85, 87, 88, 90, 98, 106, 113, 114,
123]. It detects concentrations in the order of μgL
À1 to ngL
À1 and less. It is fast,
Quantification of Non-steroidal Anti-inflammatory Drug in Water
95