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Applications of Ionic Liquids in Gas Chromatography

By Umaima Gazal

Submitted: August 20th 2020Reviewed: February 18th 2021Published: March 29th 2021

DOI: 10.5772/intechopen.96702

Downloaded: 27

Abstract

The environment offers an enormous innovative panorama of prospects intended for the research of novel biodegradable diluents. Regular composites have been lately recycled to formulate the anionic and cationic fraction of RTIL. Numerous applications of ionic liquids have been explored in segregation discipline. Attributable to the extraordinary polarization as well as exceptional current steadiness, IL-centered immobile segments have been applied to resolution of varied series of critically stimulating complexes frequently extremely polar composites using great boiling points plus physical resemblances comprising elongated sequence fatty acids, essential oils, polycyclic aromatic sulfur heterocycles (PASHs) and PCBs. IL-centered immobile segments facilitated the gas chromatography study for effective as well as precise amount of liquid in the industrialized yields for example pharmaceutical as well as petrochemicals complexes.

Keywords

  • ionic liquids
  • gas chromatography
  • static stages
  • Zwitterionic liquids
  • polymeric ionic liquids

1. Introduction

Ionic liquids are the utmost promising liquid green solvents with wide applications in separation science. The effect of the IL organic configuration as well as the stimulus of tributary factors, for example the IL temperature, pH, concentration, analysis time and voltage, are compatibly rationally talked concerning the accomplished parting enlargements. Gas chromatography is unique and extreme proficient, dependable, as well as stout methods for the study of unstable plus semi-volatile composites. Effective along with rapid gas chromatographic investigation of objective analytes is mostly reliant on the enactment of the gas chromatography column. Though here have be present main active developments, there quiet a solid claim of extremely choosy, indolent, polar also thermally constant gas chromatography pillars intended for critically stimulating composites for example polychlorinated biphenyls, unrestricted fatty acids and unstable amines [1]. Furthermore, the physicochemical characteristics for instance surface tension, viscosity and melting point are too acute to yield extremely proficient gas chromatography columns. The viscosities of furthermost ionic liquids are frequently 1–3 remits of scale greater than outmoded biological diluents [2]. In demand for an ionic liquid to be measured as a immobile stage, the solid must have great viscosity that rests fixed above a comprehensive high temperature choice. Van der Waals as well as Hydrogen bonding kind interfaces amongst the anion plus cation of Ionic liquids rule the viscosity-properties. Furthermore, it is imperative to ruminate the surface tension of the Ionic liquids. Its values extending as of 30 to 50 dyne/cm usually display bigger wettability on the barrier of unprocessed tube pillars [2]. Ionic liquids establish an assembly of biological salts which are fluid lower than 100 °C, moreover, the ionic liquids that are fluid at room temperature are generally recognized as room temperature ionic liquids [3]. Ionic liquids are easy to manufacture, thermally steady, flameproof, chemically inactive, retain small vapor density, polar, and their discernment can be simply regulated by means of fluctuating the component anion or cation; and from now they have been extensively recycled as static stages in conservative gas chromatography (Figure 1) [4, 5, 6, 7, 8, 9, 10].

Figure 1.

Applications of ionic liquids in various fields.

Ionic liquids can also be recycled as diluents for the suspension of various resources for example fiber [11], chitin [12], etc. The outstanding solubility of biological/inert composites in ionic liquids as well as a extensive variety of it as the fluid state brand them noble diluents for several responses. Furthermore, they displayed modest produces when related with conservative biological diluents [13, 14]. Thermodynamic factors of these ionic liquids were studied through chromatographic methods. ILs are centered on the numerous method, in company with the utmost extensively considered are N-alkylpyridinium, alkylammonium, N’N-dialkylimidazolium, and alkylphosphonium.

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2. Stationary phase in gas chromatography using ILs

Owing to the ever-developing mandate for the great determination, high sympathy, as well as statistics amusing investigation of composite models for instance aromas, smells, petrochemicals, plus pharmacological uncooked supplies, continuous expansions of gas chromatography supports through exclusive discrimination, squat bleed, high dullness, and in addition varied high temperature operational series are desirable. Because of the high polarization then exceptional thermal constancy, IL-centered stationary stages have been employed to decide an extensive series of methodically stimulating complexes typically precise polar complexes with high steaming facts also fundamental resemblances comprising lengthy sequence oily acids, vital oils and polycyclic aromatic sulfur heterocycles [15, 16]. ILs are characteristically organized with a phosphorous- or nitrogen-comprising biological cation as well as an inorganic or else organic anion. Meanwhile the chief outline of IL-centered GC supports in 1999, ILs have been effectively engaged as stationary stages because of their trivial high polarity, tunable selectivity, high thermal stability and vapor pressure [17]. The ILs can be altered through diverse efficient collections to endure countless solvation interfaces in addition to display exclusive chromatographic discernment such as GC immobile phases. ILs have been exposed to have exclusive solvation competences plus discernment’s on the distinctive solvent/solute interfaces [18]. Imidazolium-centered ILs be able to as per contrived to discrete equally non-polar and polar analytes [17]. As, by means of varying the anionic lot of the imidazolium IL since chloride [Cl]- to hexafluorophosphate [PF6]-, a substantial variance in discernment was perceived for polar analytes equaled to the non-polar complexes (Figure 2).

Figure 2.

Common cations and anions.

Additional examination of dissimilar modules of ILs, containing monocationic imidazolium, pyridinium, as well as pyrrolidinium exposed that the hydrogen contributor capability of the IL immobile phases was subjugated through IL cation. In contrast, the anionic lot was create to adopt the part of hydrogen acceptor anion as of proton giver analytes for example carboxylic acids plus alcohols [2]. Consequently, dicationic [19], tricationic [20], as well as phosphonium-centered cations [21] were oppressed to expand great thermal constancy plus fluid variety of ILs equated to customary monocationic static levels. Lately, in an effort to extend the applicability of IL static phases, task-specific ionic liquids (TSILs) were familiarized by functionalizing the IL cation with numerous agents [22]. For instance, the integration of aromatic segments in the IL cation improved the discernment for scented complexes, for example polycyclic aromatic hydrocarbons (PAHs). This is owing to enriched π-π sort communications amongst analytes as well as the aromatic clusters of the IL cation [4]. Overview of polar efficient clusters, for example hydroxyl segments, can effect in enlarged discernment for hydrogen compliant analytes [23]. Consequently, tweaking the IL-centered GC static phase configuration might augment choosiness essential for parting of precise compound model elements with comparable polarizations.

One of the important physical property of static stage is melting point as it basically commands the least effective high temperature of the ensued GC column. ILs with short melting points are extremely required as well as are usually acquired via integrating proportion-flouting sections also alkyl sideways chains with diverse dimensions [24, 25, 26]. Analytes naturally intermingle using IL-centered stationary segments over moreover partition- or adsorption-kind contrivance [6, 27, 28]. Better parting efficacies existed usually providing through the partition-kind retaining contrivance. Once the furnace temperature is lesser than the melting point of the IL-centered static stage, the molecular interface amongst the analytes as well as static stage is to be expected to be controlled by means of adsorption. Variance perusing calorimetry is usually operated to define the melting point of IL-centered stationary stages [25].

3. Incorporation of ionic liquids in multidimensional gas chromatography

Multidimensional gas chromatography is an influential method to accomplish progressive parting of impulsive as well as quasi-impulsive composites in compound environments [29, 30, 31]. By means of Multidimensional gas chromatography method, two or else extra gas chromatographic partings are engaged in a consecutive manner [29]. The paramount requirement to effectively enhance peak capacity in the composite system is to employ a combination of GC stationary phases possessing different selectivities. It was presented to the chromatographic state compromises advanced ultimate ability than conservative one-dimensional gas chromatography, permitting on behalf of the determination of model elements by means of comparable polarizations otherwise instabilities [32]. In this method, analytes are evaporated then exposed to a sequence of gas chromatography supports by means of chemically diverse static stages attached over an edge. In multidimensional gas chromatography analyte parting is preserved on both column, prominent to an upsurge in the parting control associated to the one [33]. Two types of multidimensional gas chromatography are usually engaged, specifically, core-wounding also inclusive. In core-wounding multidimensional gas chromatography, merely a choice rare portions of overflow after the first support are transported to the second support for extra parting [34].

Diverse support selectivity, which can be characterized using a liberated parting procedure, is the significant requisite to acquire advanced top capability in multidimensional gas chromatography methods [35]. Several customary non-ionic gas chromatography static segments are categorized as both non-polar and polar segments. These supports display a deficiency of variety in positions of solvation abilities, which can bound their capacity to decide composite models through gas chromatography× gas chromatography. Because of this hitch, ionic liquids centered supports have appeared as alternate gas chromatography × gas chromatography static stages. Utilizing ionic liquids centered stakes can permit exclusive solvation abilities in addition selectivities, moreover to advance thermal constancies comparative to customary segments. Ionic liquids have been applied as existing segments combined with customary non-ionic segments in numerous gas chromatography× gas chromatography partings [36]. Meanwhile maximum gas chromatography × gas chromatography partings can be controlled constructed on analyte instability in the first measurement monitored through involvement of dissimilar relations in the second measurement, it is collective to practice ionic liquids supports as the second measurement to estimate their enactment in relations of retaining contrivances. Presently, a huge amount of profitably accessible ionic liquids supports, for example the Supelco Low Bleed community, comprise numerous phosphonium and imidazolium grounded di cations which are typically combined with frequently tri fluoromethanesulfonate and bis[(trifluoromethyl)sulfonyl]imide anions [2, 20]. Economical ionic liquids static stages have been engaged in the parting of total of analytes for instance savor plus fragrance amalgams [36], aromatic hydrocarbons [37], alkyl halides [38], alkyl phosphonates [39], fatty acid methyl esters [40], as well as additional polar analytes (nitrogen, sulfur as well as oxygen-comprising composites). These analysis specify that ionic liquids supports establish considerable advanced selectivity plus retaining in the direction of commonly polar analytes associated to non-polar analytes owing to hydrogen-bonding interaction, electrostatic interactions and dipole–dipole relations, amongst ions [41].

4. Polymeric ionic liquids centered static stages in gas chromatography

Polymeric ionic liquids are stimulating family of composites that can be recycled as sorbent coverings in solid phase micro extraction. Polymeric ionic liquids are artificial polymers manufactured after ionic liquids monomers. Furthermore, Polymeric ionic liquids can be basically modified to display greater sensitivity and selectivity nearby diverse section of analytes. Polymeric ionic liquids are characteristically manufactured through functionalizing a polymerizable practical cluster on the cationic component of the ionic liquid by free radical polymerization in the attendance of a thermal originator. Polymeric ionic liquids reveal greater thermal constancy in addition to a confrontation to viscosity decrease at greater temperatures. These valuable structures can develop fiber lifespan, toughness plus eligibility of Polymeric ionic liquids while retentive the discrimination relics the intrinsic to ionic liquids. Polymeric ionic liquids have been displayed to extant extraordinary possessions as well as exhibitions [42, 43, 44, 45, 46, 47, 48], assisting novel plus stimulating parting procedures [49, 50, 51]. Ionic liquids have drawn abundant consideration in latest centuries as constituents for static stages in gas chromatography, because of stuffs similar their capability to create concurrent nonpolar as well as polar interfaces with the analytes, their extraordinary thermal constancy, before their insignificant air compressions then extensive fluid series [52, 53, 54, 55, 56]. Also, it is price revealing that these things can be effortlessly well-adjusted over minor fluctuations in the assembly of either the anion or cation, which, also, can intensely modify the choosiness or else the parting capability for the analyte of concern [36, 57, 58, 59]. The concern in ionic liquid-covered gas chromatography supports has enlarged afterward their marketable outline in 2008, also today, numerous ionic liquids glazed supports with dissimilar features are viably accessible. Though, one main task for the growth of static stages built on ionic liquids is the research of extremely standardized coverings, which would service decent ultimate regularities as well as extremely active complex partings, also concurrently, deliver extraordinary thermal constancies for the subsequent gas chromatography supports [60, 61, 62]. At extraordinary temperatures, identical ionic liquid-glazed silica supports can practice flick commotion prominent to a diminution in the analyte retaining periods as well as efficacy. In this respect, polymerized ionic liquids can offer the compulsory replies, preserving the outstanding thermal constancy of the supports, in addition to uniting the chief structures of an ionic liquid as well as the distinctive polymer characteristics for example better automated constancy plus development capability [62, 63, 64, 65].

5. Preference of Zwitterionic liquids in gas chromatography

Zwitterions, consequent after ionic liquids have inimitable characteristics for example reasonably small crystal conversion temperature, slight ion conductivity as well as exclusive stage conduct afterward partying with water. Moreover, the combination of convinced zwitterions plus negligible quantity of water can be observed as an exceptional liquid ideal of cell tissues. Zwitterionic liquids can be chemically precise like to predictable aprotic ionic liquids, excluding that the negative as well as positive charges exist in on the similar particle. Zwitterionic complexes are elements that have an entire clear charge of zero as well as are therefore electrically impartial. They transmit proper electrical charges of reverse symbol contained on diverse particles as well as formerly can be measured as internal salts. The utmost collective zwitterionic-kind ionic liquids are nitrogene heterocycles with sulfonate component. These Zwitter ionic Liquids have been competently considered as designable electrolyte constituents for fuel cells [66] as well as lithium batteries [67]. Not as much of discovered Zwitter ionic Liquids are configurations founded on imidazoliums with carboxylate occupations. They have been cast-off as forde sulfurization of fuels [68], Bronsted acidic catalytic agent [69], as liquid crystals [70] or for metallic oxides solubilization [71]. Therefore amino acids be existent typically as per zwitterions in a definite variety of pH then the pH at which the regular charge is zero is known as the particle’s isoelectric fact (Figure 3).

Figure 3.

Zwitter ionic liquids.

Through zwitterionic composites, anions as well as cations are roped covalently. Imidazolium sulfonate is one of the example of zwitterionic liquids. The production of room temperature zwitterionic liquids in which both sulfonate anion as well as imidazolium cation elements attribute to the parental particle was conveyed in literature (Figure 4) [72, 73].

Figure 4.

Imidazolium sulfonate Zwitterionic liquids.

Motivated via means of the proclamation that these composites can be organized as fluids at room temperature, three zwitterionic liquids integrating alkyl side chain and oligoether substituents were intended then inspected as gas chromatography static stages. The fundamentally-regulated zwitterionic liquids -centered static stages offer distinctive choosiness, robust retaining, exceptional top regularity, also a reasonably widespread employed series appropriate for the study of volatile carboxylic acids. This comprising volatile fatty acids for instance lactic acid as well as butyric acid are significant for the construction of cosmetics, pharmaceuticals and fuels [74, 75, 76]. Gas chromatography is furthermost usually recycled for the quantification as well as parting of specific acids in acylated lipids. Derivatization of volatile carboxylic acids by means of numerous approaches for example alkylation plus acylation is characteristically accomplished to upsurge the explosive nature of these composites in addition to mark their investigation viable through gas chromatography (Table 1).

S. NoEmbattled CompositesIonic liquidsUsesReference
1.Methyl esters / Fatty acids1,9-di(3-vinyl-imidazolium)nonane
bis(trifluoromethyl)sulfonylimidate
Gas chromatography stage[77]
2.Aromatic
Composites /Alcohols
[BMIM][NTf2], [BMIM]ClGas chromatography stage[78]

Table 1.

Use of ionic liquids as superficial-integrated static segments.

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6. Green aspects of ionic liquids

The adjustable physicochemical properties of ionic liquids have prolonged their usage addicted to a wide variety of diverse uses. Ionic liquids have an abundant prospective in biological amalgamation, electrochemistry, mass spectrometry, green chemistry as well as partings [79, 80]. In the field of analytical chemistry, ionic liquids have been recycled as static segments as well as diluents for headspace gas chromatography [80], movable segment extracts plus external-attached static segments in liquid chromatography [79, 81] for liquid–liquid abstractions as well as solid-phase micro abstraction [79, 80, 82]. Several “green-engrossed” manufacturing have originate that ionic liquids are outstanding applicants for their uses because of their precise small vapor compression [83, 84]. The overview of ionic liquids such as static segments has released up and around novel outlooks in this arena by means of their exclusive solvation features outcome in unusual discernment, which is entirely dissimilar to that of typical polyethylene glycol as well as poly dimethyl siloxane centered supports. Since of their atypical discernment plus extraordinary unresponsiveness, ionic liquids centered supports have previously establish numerous solicitations in the normal item for consumption ground in and multidimensional as well as mono gas chromatography in addition to preparative gas chromatography, prominent to the comprehensive investigation of composite sections (containing aqueous resolutions), plus the parting of stimulating sets of complexes. The speedily growing usage of Ionic liquids equally in educational plus manufacturing arenas have created an increasing apprehension approximately their effect on the environs. Meanwhile Ionic liquids are extremely solvable in liquid however are not continuously ecofriendly, a discharge of ionic liquids into the atmosphere might clue to substantial water contamination complications. Furthermore, Ionic liquids could develop insistent contaminants in discarded water seepage because of their great constancy in water. Intended for this purpose, research inspecting Ionic liquids biodegradability are of inordinate significance. The rising character of Ionic liquids in production as well as study plus the growing alarm nearby their green influence have advised a requisite for the progress of profligate, dependable as well as reproducible techniques for the classification plus investigation of Ionic liquids [85].

7. Conclusion

Ionic liquids have solicitations in various areas in chemistry. The applications of ionic liquids as extracts in chromatography displays abundant rewards equated to further extracts. Ionic liquids have been realistic in diverse extents of parting, for instance ionic liquid sustained tissues, as moveable segment extracts as well as external-joined static stages in chromatography partings also as the abstraction diluent in model provisions, since they can be collected from numerous anions in addition to cations that alter the things as well as stage conduct of fluids. The inflammable, non- explosive environment of ionic liquids marks them an outstanding optimal for the expansion of nontoxic methods. A substantial benefit of ionic liquids-centered stationary segments is their capability to have adequate to high updraft solidity though similarly unveiling a comprehensive host of solvation proficiencies, specific of their inimitable selectivities. In spite of their attainment, viable Ionic liquids-centered immobile segments dearth the solving authority for non-polar analytes, predominantly unsaturated as well as saturated hydrocarbons, cycloalkanes. This nonexistence of discernment has diminished fervor amongst certain parting experts who might modulate the feature of fundamental fine-tuning (in relations of anion/cation combining in addition to operational structures of every constituent) while emerging ionic liquids to display great discernment also robust solving influence. Ionic liquids have strained substantial consideration as gas chromatography immobile segments as of their tunable chemical plus physical properties. Conversely, profitable Ionic liquids-centered gas chromatography supports have not reconnoitered entirely of the solvation characteristics that can be obtainable through ionic liquids.

Moreover, their polarization, viscosity, hydrophobicity plus further physical and chemical properties can be designated by means of selecting the anionic and cationic component. Ionic liquids are considered as “exclusive diluents” as of this adjustable environment, which rises their prospective solicitations. The consumption of ionic liquids is maiden innovative prospects in diverse regions of parting discipline, with novel countless solicitations. Additional uses in partings are linked to the ecological, pharmacological, biomedical as well as various manufacturing trades. Ionic liquids have been discovered in partings for abstraction, reinforced fluid membranes, as extracts then as static segments in chromatography.

Acknowledgments

The author received no financial support for writing this article. I want to acknowledge my mother Mrs. Nargis Sultanaand husband Mr. Safdar Hussainfor his encouragement and support for writing this article.

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Umaima Gazal (March 29th 2021). Applications of Ionic Liquids in Gas Chromatography [Online First], IntechOpen, DOI: 10.5772/intechopen.96702. Available from:

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