commonly used mobile phases are acetonitrile [8, 45, 65, 86, 91, 92, 96, 102, 104,
109, 111] and methanol [8, 91, 102, 111]. pH adjustment is achieved with formic
acid [86, 91], trifluoroacetic acid [91], H 3 PO 4 [96], K 2 H 2 PO 4 [8, 45, 104], acetic
acid [65, 83, 109], or phosphate buffer [92]. The measurement is performed at
wavelengths ranging from 200 to 300 nm [8, 65, 86, 91, 92, 96, 109, 111].
By attaching the HPLC-DAD system to an HPLC-DAD-MS mass spectrometer,
detection limits of the order of ngL
À1 [42, 70] can be achieved. These detection
limits are also reached by coupling microextraction systems with HPLC-UV
(SPME-HPLC-UV) in a single module while achieving greater selectivity [55, 89,
95].
Capillary Electrophoresis Although less used than GC and HPLC, capillary
electrophoresis (CE) has also proven to be a powerful analytical tool for the
determination of NSAIDs in water samples. It is based on the different migration
speeds under the influence of an electric field, and can separate analytes previously
distributed between the mobile and the stationary phase within a capillary column,
depending on their different charge/mass relationships and affinity with the selected
buffer solution.
The most commonly used variants of CE for the detection of NSAIDs in aqueous
samples are capillary zone electrophoresis (CZE) [100, 125, 127, 129], capillary
electrokinetic microemulsion chromatography (MEEKC) [3, 125, 130, 131], capillary electrochormatography (CEC) [125, 128, 129], and chromatography micellar
electrokinetics (MEKC) [125, 132].
In the CE, the extraction and preconcentration stages are crucial [3]; hence, this
technique gained importance as on-line equipment were developed to perform the
extraction and concentration phase [127]. Although the method is less sensitive than
GC and HPLC, there are different strategies for improving its sensitivity, which
allow reaching limits of detection of the order of ng L
À1 , particularly when coupled
with SPME or LPME systems [100, 126].
For CE, columns of fused silica 30–80-cm-long [3, 126–131] with internal
diameters of 50–100 m [3, 100, 126–131] (usually 75 μm) covered with polyamide
with a window that allows the passage of UV light for detection are used. Buffer
solutions are nontoxic phosphate solutions [3, 125, 130–132], borates [3, 100, 125,
127, 130], citrates [125], and acetates [100, 125, 126, 129, 130], over a pH range of
7–9. Reference [125] gives a list of the most used columns for the determination of
NSAIDs. As background electrolytes (BGE), organic molecules such as methanol
[126–128], n-octane [130, 131], n-heptane [130, 131], acetonitrile [3, 128], and
mixtures thereof [125, 126] are used. In the case of MEEKC and MEKC, surfactant
solutions are also added to the BGE [3, 125, 130–132]. The sample is injected in
hydrodynamic form [3, 100, 126, 128–132] or electrokinetic [3, 127, 130]. The
analytes are separated inside the capillary by applying an electric field for which
10–30 kV sources are used. The most commonly used detectors are UV with and
without diode array [3, 100, 125, 127–130] although electrochemical detectors
(ECD) [125] and MS detectors [125, 128] have also been used. For degassing of
98
K. Isaac-Olivé et al.
109, 111] and methanol [8, 91, 102, 111]. pH adjustment is achieved with formic
acid [86, 91], trifluoroacetic acid [91], H 3 PO 4 [96], K 2 H 2 PO 4 [8, 45, 104], acetic
acid [65, 83, 109], or phosphate buffer [92]. The measurement is performed at
wavelengths ranging from 200 to 300 nm [8, 65, 86, 91, 92, 96, 109, 111].
By attaching the HPLC-DAD system to an HPLC-DAD-MS mass spectrometer,
detection limits of the order of ngL
À1 [42, 70] can be achieved. These detection
limits are also reached by coupling microextraction systems with HPLC-UV
(SPME-HPLC-UV) in a single module while achieving greater selectivity [55, 89,
95].
Capillary Electrophoresis Although less used than GC and HPLC, capillary
electrophoresis (CE) has also proven to be a powerful analytical tool for the
determination of NSAIDs in water samples. It is based on the different migration
speeds under the influence of an electric field, and can separate analytes previously
distributed between the mobile and the stationary phase within a capillary column,
depending on their different charge/mass relationships and affinity with the selected
buffer solution.
The most commonly used variants of CE for the detection of NSAIDs in aqueous
samples are capillary zone electrophoresis (CZE) [100, 125, 127, 129], capillary
electrokinetic microemulsion chromatography (MEEKC) [3, 125, 130, 131], capillary electrochormatography (CEC) [125, 128, 129], and chromatography micellar
electrokinetics (MEKC) [125, 132].
In the CE, the extraction and preconcentration stages are crucial [3]; hence, this
technique gained importance as on-line equipment were developed to perform the
extraction and concentration phase [127]. Although the method is less sensitive than
GC and HPLC, there are different strategies for improving its sensitivity, which
allow reaching limits of detection of the order of ng L
À1 , particularly when coupled
with SPME or LPME systems [100, 126].
For CE, columns of fused silica 30–80-cm-long [3, 126–131] with internal
diameters of 50–100 m [3, 100, 126–131] (usually 75 μm) covered with polyamide
with a window that allows the passage of UV light for detection are used. Buffer
solutions are nontoxic phosphate solutions [3, 125, 130–132], borates [3, 100, 125,
127, 130], citrates [125], and acetates [100, 125, 126, 129, 130], over a pH range of
7–9. Reference [125] gives a list of the most used columns for the determination of
NSAIDs. As background electrolytes (BGE), organic molecules such as methanol
[126–128], n-octane [130, 131], n-heptane [130, 131], acetonitrile [3, 128], and
mixtures thereof [125, 126] are used. In the case of MEEKC and MEKC, surfactant
solutions are also added to the BGE [3, 125, 130–132]. The sample is injected in
hydrodynamic form [3, 100, 126, 128–132] or electrokinetic [3, 127, 130]. The
analytes are separated inside the capillary by applying an electric field for which
10–30 kV sources are used. The most commonly used detectors are UV with and
without diode array [3, 100, 125, 127–130] although electrochemical detectors
(ECD) [125] and MS detectors [125, 128] have also been used. For degassing of
98
K. Isaac-Olivé et al.