2 Affinity-Based Methods for the Analysis of Emerging …
55
analytes were metopropol and two of its metabolites: deaminated metoprolol and αhydroxy metoprolol (Barclay et al. 2012). These compounds were first extracted by
SPE. The chiral separation of these compounds was then investigated by LC-MS/MS
using CSPs based on AGP, a cellulose derivative, vancomycin, and cellobiohydrolase
I (CBH I) (Barclay et al. 2012). Complete separation of the enantiomers for metopropol and its metabolites was seen with the AGP and CBH I columns, allowing
analysis in the pM to nM range for several of the analytes (Barclay et al. 2012)
CBH I, as used in the previous example (Barclay et al. 2012), is an enzyme that can
also act as a CSP. CBH I has a molecular weight of 52.2 kDa and takes part in fungal
cellulose degradation (Patel et al. 2006). This enzyme is composed of loops and a
concave β-sandwich that forms a 40 Å-long tunnel in which the active site is located
(Henriksson et al. 1996). CBH I can be covalently coupled to silica for use as a CSP
(Patel et al. 2006). A CBH I column has been used with MS to separate and measure
56 drugs in wastewater after extraction by SPE (Camacho-Muñoz and KasprzykHordern 2017). These drugs included amphetamine, cocaine, heroin, opioid analgesics, anesthetics, stimulants, sedatives, and some designer drugs. A good separation
was obtained for each pair of 18 enantiomers, and detection limits were acquired in
the parts-per-trillion range (Camacho-Muñoz and Kasprzyk-Hordern 2017). Multiresidue analysis of chiral β-blockers, antidepressants, and amphetamines in wastewater has also been conducted by utilizing CBH I and vancomycin as CSPs with
LC-MS/MS detection (Evans et al. 2015).
2.5 Potential Areas for Future Work
Besides the tools and applications that have already been mentioned, there are many
other binding agents and formats for affinity chromatography and extraction that
might be used in the future for the analysis of emerging contaminants in wastewater
and related samples. One class of such binding agents is the aptamers. Aptamers
are typically made up of single-stranded oligonucleotides with 20–100 base pairs
and that can undergo relatively strong and specific interactions with target molecules
(Musheev and Krylov 2006; Li et al. 2019). It is possible to generate aptamers against
a given target by using a method known as the systematic evolution of ligands by
exponential enrichment (or SELEX) (Musheev and Krylov 2006; Li et al. 2019). The
specificity exhibited by aptamers toward their targets is due to the complex threedimensional shapes that form in these binding agents, which may be composed of
loops, stems, bulges, triplexes, hairpins, quadraplexes, and pseudoknots (Pichon et al.
2015). Aptamers have been harnessed in a number of applications, and especially
in biosensors (Li et al. 2019). In aptamer-based extractions, these binding agents
are usually immobilized to a solid support and packed in a column (Pichon et al.
2015). Aptamers have been used as absorbents for the extraction of arsenites from
groundwater as well as to bind cocaine and diclofenac in drinking water (Kim et al.
2009; Hu et al. 2011). Optical aptamer-based sensors have been employed for the
detection of 17β-estradiol and bisphenol A in wastewater (Yildirim et al. 2012, 2014).
55
analytes were metopropol and two of its metabolites: deaminated metoprolol and αhydroxy metoprolol (Barclay et al. 2012). These compounds were first extracted by
SPE. The chiral separation of these compounds was then investigated by LC-MS/MS
using CSPs based on AGP, a cellulose derivative, vancomycin, and cellobiohydrolase
I (CBH I) (Barclay et al. 2012). Complete separation of the enantiomers for metopropol and its metabolites was seen with the AGP and CBH I columns, allowing
analysis in the pM to nM range for several of the analytes (Barclay et al. 2012)
CBH I, as used in the previous example (Barclay et al. 2012), is an enzyme that can
also act as a CSP. CBH I has a molecular weight of 52.2 kDa and takes part in fungal
cellulose degradation (Patel et al. 2006). This enzyme is composed of loops and a
concave β-sandwich that forms a 40 Å-long tunnel in which the active site is located
(Henriksson et al. 1996). CBH I can be covalently coupled to silica for use as a CSP
(Patel et al. 2006). A CBH I column has been used with MS to separate and measure
56 drugs in wastewater after extraction by SPE (Camacho-Muñoz and KasprzykHordern 2017). These drugs included amphetamine, cocaine, heroin, opioid analgesics, anesthetics, stimulants, sedatives, and some designer drugs. A good separation
was obtained for each pair of 18 enantiomers, and detection limits were acquired in
the parts-per-trillion range (Camacho-Muñoz and Kasprzyk-Hordern 2017). Multiresidue analysis of chiral β-blockers, antidepressants, and amphetamines in wastewater has also been conducted by utilizing CBH I and vancomycin as CSPs with
LC-MS/MS detection (Evans et al. 2015).
2.5 Potential Areas for Future Work
Besides the tools and applications that have already been mentioned, there are many
other binding agents and formats for affinity chromatography and extraction that
might be used in the future for the analysis of emerging contaminants in wastewater
and related samples. One class of such binding agents is the aptamers. Aptamers
are typically made up of single-stranded oligonucleotides with 20–100 base pairs
and that can undergo relatively strong and specific interactions with target molecules
(Musheev and Krylov 2006; Li et al. 2019). It is possible to generate aptamers against
a given target by using a method known as the systematic evolution of ligands by
exponential enrichment (or SELEX) (Musheev and Krylov 2006; Li et al. 2019). The
specificity exhibited by aptamers toward their targets is due to the complex threedimensional shapes that form in these binding agents, which may be composed of
loops, stems, bulges, triplexes, hairpins, quadraplexes, and pseudoknots (Pichon et al.
2015). Aptamers have been harnessed in a number of applications, and especially
in biosensors (Li et al. 2019). In aptamer-based extractions, these binding agents
are usually immobilized to a solid support and packed in a column (Pichon et al.
2015). Aptamers have been used as absorbents for the extraction of arsenites from
groundwater as well as to bind cocaine and diclofenac in drinking water (Kim et al.
2009; Hu et al. 2011). Optical aptamer-based sensors have been employed for the
detection of 17β-estradiol and bisphenol A in wastewater (Yildirim et al. 2012, 2014).