employed for extract clean-up from matrices interfering components. These include,
for example, SPEs in the reverse phase (HLB, C8, C18, etc.), normal phase SPEs
(alumina, diol, Florisil, silica, etc.), and the ion exchange mode SAX (strong anion
exchange) or MCX (mixed-mode cation exchange). The various sorbents mentioned
are used in the form of discs, columns, dispersive phase or cartridges. However, the
latest format is the most widely used. In this section, we will discuss the commonly
used sorbents for soil and crop extract clean-up, as well as the newly introduced
sorbents.
6.1 Commonly Used Sorbents
Solid-phase extraction (SPE) in cartridge format is one of the most clean-up techniques used over the last years. The great selectivity of SPE in retaining the targeted
compounds and simultaneously eluting the matrix interferences, or vice versa, has
made this technique gain wide popularity. Moreover, they allow for a large volume
of extract to be purified and concentrated at the same time. As previously mentioned,
a large diversity of sorbents is today available; however, for soil and crop extracts,
SPEs using hydrophilic and lipophilic balance (HLB) sorbent cartridges solely
[72, 82] or in combination with the strong anion exchange sorbent (SAX) [70, 75],
which is more expensive, are the purification techniques predominantly employed.
HLB cartridges are able to bind non-polar and polar pharmaceuticals at the same
time if they are in their neutral form in the extract, whereas, when HLB is employed
in tandem with SAX on top of it, SAX cartridges are able to retain matrix interferences such as the negatively charged humic and fulvic acids present in soil extract or
the waxes, fatty acids, chlorophyll, and pigments present in plant extracts, while
pharmaceuticals are retained on HLB cartridges, resulting in further purified
extracts [58].
Those two dominant SPE sorbents are in general used packed in cartridges, and
they are mostly employed after a main extraction with ASE, MAE, and USE.
However, Malvar and coworkers [69] have recently employed an in-cell clean-up
with PLE (or ASE), also known as selective PLE (SPLE), where they added C18 and
PSA to the extraction cell with the sample in dispersive form, which allowed to avoid
the need of further treatment of sample extract. To our knowledge, this is the only
study in which SPLE was employed.
Besides SPE cartridges, dispersive SPE (d-SPE) is nowadays very popular. The
concept of d-SPE was first introduced by the fathers of QuEChERS [19], and from
that time, it was always employed for cleaning up the extracts of diverse kinds of
matrices obtained from QuEChERS extraction. SPE cartridges and d-SPE have
similar purpose; the main difference between them remains on the usage mode.
For the SPE cartridges, sample extract is loaded into the cartridges, whereas for the
d-SPE, sorbents are in powder form (sorbent salts) and are added on the extract,
where they absorb matrix interferences resulting in a free analyte extract (Fig. 2). By
comparing both SPE techniques, d-SPE is easier to use and saves time.
Development of Methods for the Determination of PhACs in Soil/Earthworm/Crop. . .
467
for example, SPEs in the reverse phase (HLB, C8, C18, etc.), normal phase SPEs
(alumina, diol, Florisil, silica, etc.), and the ion exchange mode SAX (strong anion
exchange) or MCX (mixed-mode cation exchange). The various sorbents mentioned
are used in the form of discs, columns, dispersive phase or cartridges. However, the
latest format is the most widely used. In this section, we will discuss the commonly
used sorbents for soil and crop extract clean-up, as well as the newly introduced
sorbents.
6.1 Commonly Used Sorbents
Solid-phase extraction (SPE) in cartridge format is one of the most clean-up techniques used over the last years. The great selectivity of SPE in retaining the targeted
compounds and simultaneously eluting the matrix interferences, or vice versa, has
made this technique gain wide popularity. Moreover, they allow for a large volume
of extract to be purified and concentrated at the same time. As previously mentioned,
a large diversity of sorbents is today available; however, for soil and crop extracts,
SPEs using hydrophilic and lipophilic balance (HLB) sorbent cartridges solely
[72, 82] or in combination with the strong anion exchange sorbent (SAX) [70, 75],
which is more expensive, are the purification techniques predominantly employed.
HLB cartridges are able to bind non-polar and polar pharmaceuticals at the same
time if they are in their neutral form in the extract, whereas, when HLB is employed
in tandem with SAX on top of it, SAX cartridges are able to retain matrix interferences such as the negatively charged humic and fulvic acids present in soil extract or
the waxes, fatty acids, chlorophyll, and pigments present in plant extracts, while
pharmaceuticals are retained on HLB cartridges, resulting in further purified
extracts [58].
Those two dominant SPE sorbents are in general used packed in cartridges, and
they are mostly employed after a main extraction with ASE, MAE, and USE.
However, Malvar and coworkers [69] have recently employed an in-cell clean-up
with PLE (or ASE), also known as selective PLE (SPLE), where they added C18 and
PSA to the extraction cell with the sample in dispersive form, which allowed to avoid
the need of further treatment of sample extract. To our knowledge, this is the only
study in which SPLE was employed.
Besides SPE cartridges, dispersive SPE (d-SPE) is nowadays very popular. The
concept of d-SPE was first introduced by the fathers of QuEChERS [19], and from
that time, it was always employed for cleaning up the extracts of diverse kinds of
matrices obtained from QuEChERS extraction. SPE cartridges and d-SPE have
similar purpose; the main difference between them remains on the usage mode.
For the SPE cartridges, sample extract is loaded into the cartridges, whereas for the
d-SPE, sorbents are in powder form (sorbent salts) and are added on the extract,
where they absorb matrix interferences resulting in a free analyte extract (Fig. 2). By
comparing both SPE techniques, d-SPE is easier to use and saves time.
Development of Methods for the Determination of PhACs in Soil/Earthworm/Crop. . .
467