Nanoconfined Ionic Liquids
2.5 Analytical Applications of Ionic Liquids Confined in a Solid Matrix
2.5.1 Solid‐Phase Extraction
Solid‐phase extraction (SPE) plays a very important role in sample pretreatment, replac- ing classical liquid–liquid extraction (LLE) in the preparation of biological, food, and environmental samples. SPE is recognized as a useful alternative to LLE. It eliminates many drawbacks of LLE [187] providing low solvent consumption, low costs of the whole process, and reduction in time. Moreover, there is also a possibility to automate the process [188]. The classic sorbents used in SPE are [189] silica modified with C18, C8, −phenyl, –CH, –CN, or –NH2 groups; carbon‐based sorbents, including graphitized carbon black (GCB) and porous graphitic carbon (PGC); and porous polymeric
0 100 200 300 400 500 600
Number of papers
Year
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017
Figure 2.9 Number of articles presenting application of ionic liquids in analytical chemistry.
Analyte(s) Evaluated ILs Precursor Analytical
technique Sample type Recovery (%) Enrichment
factor ( EF ) LOD ( μ g l −1 ) LDR ( μ g l −1 ) Reference Pharmaceuticals [C 1 IM]
[CF 3 COO] TEOS HPLC‐UV River water and
wastewater 72–101 [168]
Lactic acid [IM][Cl] [C 1 IM]
[Cl] [C 2 C 1 IM]
[Cl]
CPTS HPLC‐UV Fermentation
broth 91.9 0.002
25 2.0
35.0 [169]
Organic acids, amines, and aldehydes
[RC 1 IM] TEOS LC‐MS and
GC‐MS Atmospheric
aerosol 87–105
3.8–23
[170]
Fe(III) ions [C 6 Py][PF 6 ] TEOS FAAS Bottled mineral, tap and underground water
97.8–105.4 200 0.70 2.5–50 [171]
Organochlorine
pesticides [{(C 2 O) 3 SiC 3 }
C 3 NH 2 IM] [Br] TEOS GC/GC‐MS Environmental
and food 65.65–129.61 [172]
La(III) [ N ‐PhenacylPyr]
[NTf 2 ] Activated
silica glass ICP‐OES Drinking, lake,
sea, and tap water 95.57–98.39 [173]
Cadmium [C 4 MIM][PF 6 ] Silica powder AAS Lake and tap water 95–103 75 0.60 1.0–800 [174]
Lead [C 4 MIM][Br] Silica powder AAS River water 98–100 185 0.70 [168]
LOD – limits of detection; LDR – linear dynamic range.
Table 2.5 Applications of ionogel‐based sorption materials in solid‐phase microextraction methodologies.
Analyte(s) Evaluated ILs Precursor Analytical technique Sample type Recovery (%) LOD ( μ g l −1 ) a LDR ( μ g l −1 ) a Reference Polar phenolic
environmental estrogens and aromatic amines
[Allyl‐C 1 IM][PF 6 ] and [allyl‐C 1 IM]
[NTf 2 ]
MPTS GC‐FID Lake water and sewage
drainage outlet water 83.1–104.1;
89.1–97.1 0.0030–0.1248 0.1–1000 [175]
Alcohols, phthalate esters, phenolic environmental estrogens, fatty acids and aromatic amines
[Allyl(benzo 15 C 5 ) C 6 IM][PF 6 ] and [allyl‐C 1 IM][PF 6 ]
TEOS GC‐FID Water — — — [176]
Aromatic amines, alcohols, fatty acids, and PAEs
[TESPMIM][PF 6 ] [TESPMIM][BF 4 ], [TESPMIM][NTf 2 ]
TEOS and
OH‐TSO GC‐FID Water — — — [177]
Triazines [Vinyl‐C 4 IM] [NTf 2 ] (PMHS)
TEOS GC‐FID Cherry tomato,
strawberry, cucumber, garlic sprout, cole, cabbage, and tomato
73.7–95.1 3.3–13.0 μ g kg −1 25–5000 [178]
Organophosphate
esters [C 16 C 1 IM][NTf 2 ] MTMS,
TEOS GC‐FPD River and tap water,
municipal sewage 64.8–125.4 0.04–0.95 0.5–10.0 [179]
Benzene, toluene, ethylbenzene and o ‐xylene
[C 4 C 1 IM][PF 6 ] MTMS and PDMS
GC‐FID River, tap, well water 91.2–103.3 1–500 pg l −1 4–200 000 pg ml −1 [180]
Volatile chlorinated
organic compounds [C 4 C 1 IM][NTf 2 ] MTMS GC‐PDD Bottled mineral, tap
and ground water 88.7–113.9 0.03–1.27 — [181]
(Continued )
Analyte(s) Evaluated ILs Precursor Analytical technique Sample type Recovery (%) LOD ( μ g l −1 ) a LDR ( μ g l −1 ) a Reference Volatile chlorinated
organic compounds [C 4 C 1 Py][NTf 2 ], [C 4 C 1 Pyrr][NTf 2 ], [C 4 C 1 Pip][NTf 2 ]
MTMS GC‐PDD Tap and river water 95–106 0.011–0.151 — [182]
Organophosphate
esters [Allyl‐C 1 IM][BF 4 ] TEOS GC‐FPD Lake water,
wastewater, sewage treatment plant effluent, and tap water
75.2–101.8 70–12 000 0.005–50 [183]
Phthalate esters [Allyl‐C 1 IM][NTf 2 ] TEOS and
PMHS UA‐SPME‐GC‐FID Agricultural plastic
films 90.2–111.4 0.003–0.063 0.003–0.063 [184]
Pesticides [C 4 C 1 IM][OH] TEOS HF‐ HPLC–DAD Human hair and water 86.2–98.8 0.004–0.095 0.01–25 000 [185]
Organophosphorus
pesticides (PYBS) 3 PW 12 O 40 , TEOS HPLC–PDA Human hair 86–95.2 0.0074–1.300
μ g g −1 0.02–50 000 μ g g −1 [186]
a LOD – limits of detection; LDR ‐ linear dynamic range.
Nanoconfined Ionic Liquids 49
sorbents, e.g. the macroporous polystyrene‐divinylbenzene (PS‐DVB). To improve the selectivity, molecularly‐imprinted materials (MIPs) were designed to overcome the limitation of the traditional restricted‐access materials (RAMs) and immunosorbents (ISs) [190]. Over last 20 years scientists have widely modified classical materials used in SPE. However, only a few papers have been published with the results of studies on combining silica with ILs or on the polymerization of materials with ILs, successfully used as sorbent materials. ILs have been mainly used in SPE in order to covalently attach the imidazole group to the silica surface [168–170, 191]. In case of polymers, imidazole [171, 172] or pyridine [173] groups have been most often applied in the polymerization process.
In a pioneering work, Fontanals et al. [174] proposed the slightly cross‐linked polymer‐supported imidazolium trifluoroacetate salt (IL‐CF3COO−) that favorably combines the properties of ionic liquids and the advantages of a solid support. The IL‐
confined material was evaluated as a solid‐phase extraction (SPE) sorbent in studies on the selective and quantitative extraction of pharmaceuticals (salicylic acid, 4‐nitrophe- nol, carbamazepine, nalidixic acid, flumequine, naproxen, fenoprofen, diclofenac sodium, ibuprofen, and gemfibrozil) from aqueous samples. The authors have proved that the obtained novel sorption material, under strong cation exchange conditions, was capable of selective and quantitative extraction of a group of acidic compounds from aqueous samples in the presence of washing basic analytes. The developed SPE method utilizing the obtained material was applied in the analysis of samples of ultrapure water, tap water, and water from the river. The results for prepared SPE sorb- ent were satisfactory and comparable to those obtained with the use of commercially available Oasis MAX, though slightly lower in case of ibuprofen and gemfibrozil (∼75%
for IL‐CF3COO− compared to ∼100% for Oasis MAX) and salicylic acid (∼55% for IL‐CF3COO− compared to ∼100% for Oasis MAX).
In another study [168], three different anion‐exchange silica‐based ILs, i.e. Silpr[IM]
[Cl], Silpr[C1IM][Cl], and Silpr[C2C1IM][Cl], were synthesized and applied to solid‐
phase extraction of lactic acid from fermentation broth. In this case, the fermentation broth was washed with 4 ml of different solvents (e.g. water, methanol, acetonitrile, n‐hexane, and dichloromethane), which allowed interferences to be removed, while lactic acid remained retained through strong anion exchange interactions between the analyte and the sorbent. Lactic acid was successfully separated from the matrix with a recovery of 91.9%.
Vidal et al. [192] proposed an ionic liquid‐functionalized silica material for SPE application based on the imidazolium cation (N‐methylimidazolium and 1‐alkyl‐3‐
(propyl‐3‐sulfonate)imidazolium). The obtained sorbent was used to isolate analytes (organic acids, amines, and aldehydes) from atmospheric aerosol particles. The analytes were separated and identified by liquid chromatography–mass spectrometry (LC‐MS) and by gas chromatography–mass spectrometry (GC‐MS) as a comparative technique.
Lower extraction efficiencies for amines and aldehydes confirmed that anionic exchange was the predominant interaction. The authors compared the results with those obtained with commercial SPE materials. This comparison showed that the IL‐functionalized materials offer different selectivity and better extraction efficiency than SAX for aro- matic compounds. Extraction efficiencies for organic acids ranged from 87% to 110%, except for cis‐pinonic acid (19–29%). The new materials give satisfactory results in extraction from atmospheric aerosol sample.
1‐Hexylpyridinium hexafluorophosphate [C6Py][PF6] ionic liquid was for the first time confined in silica material by the acid‐catalyzed sol–gel processing. The obtained pyridinium IL‐modified silica was applied as a SPE sorbent for removal of trace levels of Fe(III) ions from aqueous samples. Under optimal experimental conditions, the limit of detection and limit of quantification were 0.7 and 2.5 μg l−1, respectively [193]. The developed method was validated by the analysis of certified reference material and applied successfully to the isolation and determination of iron in several water samples.
In other research, a novel dummy molecularly imprinted polymer (DMIP) was prepared through a sol–gel process using bisphenol A as the dummy template and synthesized 1‐(triethoxysilyl)propyl‐3‐aminopropylimidazole bromide [{(C2O)3SiC3} C3NH2IM][Br] as a functional monomer. This novel DMIP was applied as a SPE mate- rial to develop a method for the simultaneous determination of nine organochlorine pesticides (OCPs) in environmental and food samples. The developed method was applied to the analysis of water, rice, and tea leaf samples spiked with nine OCPs. The OCPs were simultaneously determined with satisfactory recoveries from 65.65% to 129.61% and a good relative standard deviation (n = 3) of 0.91–11.47%, indicating acceptable accuracy and precision of the developed method [194].
In another study, a new solid‐phase extractant (SG‐[N‐phenacylPyr][NTf2]) was pro- posed by Marwani et al. [195]. The material was based on a hybrid combination of the hydrophobic character of newly synthesized ionic liquid with silica gel (SG) properties, without the need for partial treatment by chelating compounds. The selectivity of SG‐[N‐phenacylPyr][NTf2] towards different metal ions, including Co(II), Fe(II), Fe(III), La(III), and Ni(II), was investigated. The adsorption isotherm fit well with the Langmuir adsorption model. A kinetic study also demonstrated that the adsorption of La(III) on the SG‐[N‐phenacylPyr][NTf2] phase was in accordance with the pseudo second‐order kinetic model. The proposed method was applied to real water samples with satisfac- tory results.
In some studies [196, 197], the performance of the IL‐supported sorbents turned out to be favorable in terms of preconcentration factors and limits of detection achieved for other ionic materials and processes of metals extraction. For example, a [C4C1IM][PF6]‐
modified silica sorbent was used to preconcentrate Cd2+ after the addition of the chelat- ing agent dithizone. Recoveries for 150 ml of lake water and tap water were greater than 95% and at least 20 extractions could be made with the same sorbent without a decrease in the recovery of Cd2+.