Environmental Engineering Reference
In-Depth Information
table 14.2
applications of fuls in as adsorbent
detection
limit (ng/ml)
Analyte
sample
Technique
a
R.s.d.(%)
Comments
Pb
Waters
FAAs
5
2.1
study of adsorption isotherms
Cd
biological
FAAs
0.3-2.0
1.9-2.3
Comparison of APdC and 8-hydroxyquinoline
as chelating reagents
Cu
Waters
FAAs
0.3-3.0
1.7-3.1
Comparison of C
60
and C
70
fullerene. sorption
of neutral chelates and ion pairs
Cd
Waters
ETAAs
0.002
Tungsten coil atomizer
Pb
0.023
Ni
0.075
Co
Wheat
flour
ETAAs
0.008
4.0
Comparative study of C
60
fullerene and RP-C
18
.
Autosampler as interface
lead species
Waters
FAAs
0.5-4
3.5
Precipitation of inorganic lead. selectivity
related to column conditioning
organic and
organometallic
compounds
Waters
GC/FId,
FAAs
5-15
2.4-3.0
systematic study of retention of organic and
organometallic compounds on C
60
fullerene
Alkyl lead species
Waters
FAAs,
GC/Ms
0.5
6.0
screening by FAAs and speciation by GC.
derivatization with Grignard reagent
0.001-0.004
Alkyl lead species
Waters
GC/Ms
0.004-0.012
4.5
In situ derivatization with NabPr
4
dithiocarbamates of
Zn, Mn, and Fe
Grain
FAAs
1-5
2.5
Group speciation according to the metal
present in the fungicide
Reproduced with permission from Ref. [4]. © science direct Elsevier.
FAAs, flame atomic absorption spectrometry; ETAAs, electrothermal atomic absorption spectrometry; GC/FId, gas chromatography with flame ionization
detector; GC/Ms, gas chromatography/mass spectrometry; R.s.d., relative standard deviation,
n
= 11.
14.4.1.1 CNTs as SPE Material
CNTs have been extensively studied as sorbent material for conventional sPE. In-depth
detailed reviews have been published in the literature where CNTs as sPE sorbent have been successfully used for diverse
organic and inorganic analytes from water, seawater, food, and pharmaceutical samples [3, 14-17].
As already mentioned, in general, CNTs tend to demonstrate higher capacity than conventional carbon-based adsorbents.
CNTs have been used in conventional sPE preconcentration of a variety of polar and nonpolar analytes including endocrine dis-
rupters such as phenolic compounds, highly polar sulfonylurea herbicides, and molecules of pharmaceutical origin. They have
been compared to other conventional sorbents such as C18 and XAd. They demonstrated advantages such as superior break-
through volumes, better retention of polar species, better efficiency with seawater, and higher extraction efficiencies [3, 17].
Covalent functionalization that usually incorporates hydroxyl, carboxyl, or carbonyl groups onto side walls of CNTs can
selectively alter their selectivity. CNTs are also covalently immobilized onto solid supports such as steel or silica, and thus
changes in the geometry of the sPE device can take place. Alternatively, noncovalent side-wall functionalization of CNTs also
provides a change in selectivity. This type of functionalization includes ionic interactions (e.g., dipole-dipole), π-π stacking,
hydrogen bonds, electrostatic forces, van der Waals forces, dative bonds, and hydrophobic interactions. The combination of two
or more similar or different interactions increases the stability and the selectivity of the system. Nonpolar organic analytes gen-
erally show high capacity sorption with unfunctionalized CNTs as hexagonal arrays of carbon atoms in graphene sheets interact
strongly with aromatic rings, due to van der Waals interactions, whereas functionalized CNTs showed higher retention of polar
organic analytes. sPE using CNTs has been carried out in cartridges and disks. The disk format provides a larger surface area
leading to good mass transfer and fast flow rates. MWNTs are assembled into a disk by means of a filtration process, firmly
fixed on a piece of polytetrafluoroethylene (PTFE) membrane filter, and then used as a preconcentrator. Enrichment factors as
high as 4000 with recoveries in the range of 87-110% have been reported [3, 7, 16].
14.4.1.2 FULs as SPE Materials
A limited number of applications of FUls for sPE have been reported. ballesteros et al.
studied the adsorption behavior of FUls C60 using organic compounds and organometallic compounds as model analytes. The
adsorption capacity of FUls was found to be significantly higher for organometallic compounds. Extraction of benzene, tol-
uene, ethylbenzene, and xylenes (bTEX) from water samples on a home-made C60-packed minicolumn was also reported,
where FUls were found to be better than conventional C18 and Tenax TA in terms of sensitivity and precision. Adsorption of
