15.2.3 Solid-Phase Extraction
Solid-phase extraction is based on the principle of liquid–solid chromatography. The
solid adsorbent is used to adsorb the target compounds or impurities in the liquid
sample. After elution of the impurities with an adequate solvent, the target compounds are then eluted with a specific solvent from the solid adsorbent, and the
eluted solvent is used for analysis. This technique can be divided into online solidphase extraction and offline solid-phase extraction. The former connects the extraction cartridge with the chromatographic system to achieve simultaneous extraction
and analysis. Compared with the liquid–liquid extraction, solid-phase extraction has
the advantages of simple operation and solvent-saving and is conducive to the
realization of automation. However, most of the commercialized solid-phase extraction cartridges use plastic columns, which are easy to bring high phthalate background. The reproducibility of lab-made glass cartridges is poor, and also, they are
rather expensive.
According to the physicochemical characteristics of the packing material, solidphase extraction can roughly be divided into three modes, i.e. normal phase, reverse
phase, and ion exchange. The mode used in the extraction of phthalates in water is
usually reverse phase.
The packing materials of the reverse phase cartridges used for phthalates extraction are generally non-polar or weak polar materials, such as octadecylsilane (Salazar-Beltrán et al. 2017), magnetic graphene (Ye et al. 2014), ionic liquid-mixed
hemimicelles (Li et al. 2008), poly(2,6-diphenyl-1,4-phenylene ether) (Liu et al.
2008), and molecularly imprinted polymers (Yang et al. 2016; Guo et al. 2019a).
Chao et al. (2016) used octadecylsilane glass as solid-phase extraction cartridge to
extract 16 phthalates in water samples. They used dichloromethane as eluent, and the
eluent was separated and detected by gas chromatography–mass spectrometry. The
average recovery rates of the method were 72.0–112%. Ma et al. (2009) compared
the extraction efficiencies of different cartridges, i.e. Supelclean LC-18, Supelclean
ENVI-Carb, and Cleanert ODS-SPE, for phthalates in water samples. Supelclean
LC-18 was considered superior, so it was applied to the extraction of dimethyl
phthalate, di(2-ethylhexyl) phthalate, and dioctyl phthalate in tap water samples
and then eluted with methanol, and finally, the phthalates were analyzed by highperformance liquid chromatography. The recoveries of the method were between
83.6% and 110.2%. Cai et al. (2003) used multi-walled carbon nanotubes packed
cartridges to extract four phthalates in tap, river, and sea water samples using
acetonitrile as eluent. The eluent was separated and detected by high-performance
liquid chromatography, and the recoveries of 80.3–104.5% were obtained.
Solid-Phase Microextraction
Solid-phase microextraction, developed by Pawliszyn and coworkers (PiriMoghadam et al. 2016) in 1989, uses adsorbent-coated fibers (extraction head) to
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C. Sun et al.
Solid-phase extraction is based on the principle of liquid–solid chromatography. The
solid adsorbent is used to adsorb the target compounds or impurities in the liquid
sample. After elution of the impurities with an adequate solvent, the target compounds are then eluted with a specific solvent from the solid adsorbent, and the
eluted solvent is used for analysis. This technique can be divided into online solidphase extraction and offline solid-phase extraction. The former connects the extraction cartridge with the chromatographic system to achieve simultaneous extraction
and analysis. Compared with the liquid–liquid extraction, solid-phase extraction has
the advantages of simple operation and solvent-saving and is conducive to the
realization of automation. However, most of the commercialized solid-phase extraction cartridges use plastic columns, which are easy to bring high phthalate background. The reproducibility of lab-made glass cartridges is poor, and also, they are
rather expensive.
According to the physicochemical characteristics of the packing material, solidphase extraction can roughly be divided into three modes, i.e. normal phase, reverse
phase, and ion exchange. The mode used in the extraction of phthalates in water is
usually reverse phase.
The packing materials of the reverse phase cartridges used for phthalates extraction are generally non-polar or weak polar materials, such as octadecylsilane (Salazar-Beltrán et al. 2017), magnetic graphene (Ye et al. 2014), ionic liquid-mixed
hemimicelles (Li et al. 2008), poly(2,6-diphenyl-1,4-phenylene ether) (Liu et al.
2008), and molecularly imprinted polymers (Yang et al. 2016; Guo et al. 2019a).
Chao et al. (2016) used octadecylsilane glass as solid-phase extraction cartridge to
extract 16 phthalates in water samples. They used dichloromethane as eluent, and the
eluent was separated and detected by gas chromatography–mass spectrometry. The
average recovery rates of the method were 72.0–112%. Ma et al. (2009) compared
the extraction efficiencies of different cartridges, i.e. Supelclean LC-18, Supelclean
ENVI-Carb, and Cleanert ODS-SPE, for phthalates in water samples. Supelclean
LC-18 was considered superior, so it was applied to the extraction of dimethyl
phthalate, di(2-ethylhexyl) phthalate, and dioctyl phthalate in tap water samples
and then eluted with methanol, and finally, the phthalates were analyzed by highperformance liquid chromatography. The recoveries of the method were between
83.6% and 110.2%. Cai et al. (2003) used multi-walled carbon nanotubes packed
cartridges to extract four phthalates in tap, river, and sea water samples using
acetonitrile as eluent. The eluent was separated and detected by high-performance
liquid chromatography, and the recoveries of 80.3–104.5% were obtained.
Solid-Phase Microextraction
Solid-phase microextraction, developed by Pawliszyn and coworkers (PiriMoghadam et al. 2016) in 1989, uses adsorbent-coated fibers (extraction head) to
552
C. Sun et al.