m-dSPE using 30 mg poly(1-vinyl-3-butylimidazolium bromide)-PS m-NPs under vortex for 2.5 min, a magnet was used for decantation, and elution with 7 mL ACN by sonication
HPLC-DAD
0.017-0.047 μg/L
77.8-102.1% at 2 and 20 μg/L
One sample of each water were analyzed and residues of DEP were found at 25.8 and 15.5 μg/L in the carbonate and soda waters, respectively
ACN showed higher extraction efficiency than acetone, petroleum ether and MeOH as elution solvent
[82]
DMP, DEP, DAP, DIBP, and DBP
Tap and well waters (5 mL plus 15% w/v NaCl)
m-dSPE using 15 mg Fe3O4-MIL-101(Cr) MOF under agitation for 20 min, a magnet was used for decantation, and elution with 1 mL hexane/acetone (1:1 v/v) by vortex for 3 min
GC-MS
0.3–0.5 μg/L
90.1–106.7% at 5 and 50 μg/L
One sample of each water were analyzed and no residues were detected
The use of Fe3O4-MIL-101(Cr) MOF showed higher enrichment capacity than Fe3O4 and MIL-101(Cr) MOF separately. Hexane/acetone (1:1 v/v) showed higher extraction efficiency than ethyl acetate, hexane, acetone and hexane/ethyl acetate (1:1 v/v) as elution solvent. Human plasma was also analyzed
[86]
DMP, DEP, DBP, BBP, DEHP, and DNOP
Tap, drinking and mineral waters (10 mL)
m-dSPE using 15 mg Fe3O4-MIL-100 MOF and 15-mg Fe3O4-SiO2-polythiophene under sonication for 1 min and oscillation for 15 min, a magnet was used for decantation, and elution with 1 mL ACN by agitation for 10 min
GC-MS
1.1–2.9 μg/L
76.9–109.1% at 1, 10 and 50 μg/L
One sample of each water were analyzed and no residues were quantified
A combination of 15-mg Fe3O4-MIL-100 MOF and 15-mg Fe3O4-SiO2-polythiophene gave better extraction efficiency than using 30-mg each separately. ACN showed higher extraction efficiency than acetone, ethyl acetate and hexane as elution solvent
[88]
DMP, DBP, BBP, DCHP, and DEHP
Tap and lake waters (100 mL adjusted at pH 6)
m-dSPE using 30 mg poly(1-vinylimidazole)-carboxy-latocalix[4] arene m-NPs under sonication for 15 min, a magnet was used for decantation, and elution with 0.5 mL MeOH by sonication for 5 min
HPLC-UV
0.05–0.11 μg/L
89.9–110.0% at 0.5, 1, and 5 μg/L
One sample of each water were analyzed and contained at least 1 PAE at levels from 0.4 to 8.9 μg/L
Methanol showed higher extraction efficiency than ACN and chloroform as elution solvent. The use of poly(1 -vinylimidazole)-carboxy-latocalix[4] arene m-NPs showed higher enrichment capacity than Fe3O4 and poly(1-vinylimidazole) separately. m-dSPE using poly(1-vinylimidazole)-carboxy-latocalix[4] arene m-NPs showed better results compared with SPE with C18 and Cleanert SCX cartridges. Drinks, tonic lotions, and human serum were also analyzed
[83]
DBP, DMP, DCHP, BBP, and DEP
River water (10 mL)
m-dSPE using 30 mg 3D N-Co-C/HCF MOF under agitation for 20 min, a magnet was used for decantation, and elution with 6 mL ACN by sonication for 10 min
HPLC-UV
0.077–0.377 μg/L
92.4–104.2% at 1, 10, and 50 μg/L
One sample was analyzed and contained DMP and DEP at 0.075 and 0.081 μg/L, respectively
Green tea, sports beverage and white spirit were also analyzed. ACN showed higher extraction efficiency than acetone, MeOH, and ethanol as elution solvent
m-dSPE using 120 mg Fe3O4-PDA under agitation for 1 min, a magnet was used for decantation, and elution with 1 mL dichloromethane by agitation for 30 s
GC-MS
0.0018–0.319 μg/L
79–116% at 0.4, 1, and 1.6 μg/L
Ten samples were analyzed and no residues were quantified
Figure 1.5 Scheme of a similar extraction procedure carried out by Chen et al. [75] using the same (β-CD-PNIPAM temperature-sensitive polymer as extractant for the determination of phenolic compounds in river water samples. Reprinted from [75] with permission of Elsevier. Peak identification: phenol (BP), 2,4-dichlorophenol (2,4-DCP), (β-naphthol ((β-NP), and bisphenol A (BPA).
Despite the simplicity of the dSPE, the whole procedure can be even improved and simplified if the sorbent particles can be manipulated with a magnet. Such dSPE mode is called m-dSPE and is based on the use of magnetic NPs (m-NPs), which can be applied as synthesized (though in very few cases), although they are generally functionalized or coated with other chemical species or materials, resulting in many cases a “coreshell” structure, in order to improve their selectivity, or even embedded them in the extraction sorbent to provide it with magnetic properties [50]. Despite the extraction step is performed in a similar way as in dSPE, in this case, the magnetic sorbent containing the analytes is retained in the extraction recipient using an external magnet while the sample matrix is easily discarded without the need of an additional centrifugation step or the retention of the sorbent in an empty column. Finally, the analytes are desorbed from the magnetic sorbent using a suitable solvent and, once more, the sorbent is retained with the magnet to separate the solvent containing the analytes by decantation for their determination with a suitable technique.
Although a wide variety of metals, metal oxides and alloys can be used to provide magnetic properties to the sorbent, Fe3O4
