Chromatographic Stationary Phases Research Articles

Ground Organic Particles of ca. 3 μm Size as Chromatographic Separation Media in High Performance Liquid Chromatography

A new chromatographic stationary phase was prepared by making a soft organic monolith based on thermal polymerization of methyl methacrylate and ethylene glycol di-methacrylate with an aid of gas evolution via decomposition of urea, and by crushing the monolith into particles. The original purpose of urea incorporation was formation of monolith particles with affluent mesopores, but the actual effect was reduction of the particle size to a proper range (mostly in the range of 1–5 μm with an average of ca. 3 μm), which was very crucial for improvement of separation efficiency. A series of washing processes (including common washing and reflux washing) were carried out to remove un-reacted materials and free oligomers. The columns were made by packing the organic monolith particles in glass-lined stainless-steel tubing and evaluated for their performance with the mixture of six aromatic compounds (3-phenyl-1-propanol, acetophenone, methyl benzoate, 2-nitroaniline, ethylbenzene, cumene). The overall number of theoretical plates (N) over 6 analytes based on 6 columns was 32,000 plates/column (107,000 plates/m, 9.4 µm plate height).

A HILIC stationary phase fuctionalized with glutathione by thiol-ene chemistry on monodisperse-porous polymer microparticles

Monodisperse-porous microparticles functionalized a with a zwitterionic ligand were synthesized as a new stationary phase for hydrophilic interaction chromatography. Monodisperse-porous poly(3-trimethoxysilylpropyl methacrylate-co-ethylene dimethacrylate), poly(TMSPM-co-EDMA) microspheres (6 μm in size) were obtained with different seed latex/monomer ratios and diluent compositions by multistage microsuspension copolymerization. The zwitterionic chromatographic ligand containing thiol moiety (i.e. glutathione) were covalently attached onto the TMSPM attached-poly(TMSPM-co-EDMA) microparticles. The selected starting material allowed the direct attachment of zwitterionic ligand onto the support material using thiol-ene chemistry. The derivatized microparticles were slurry packed into the microbore columns with 2 mm i.d. and used as stationary phase for the separation of nucleosides in hydrophilic interaction chromatography with the plate numbers up to 54.000 plates/m. The results showed the usability of tailored poly (TMSPM-co-EDMA) microparticles as a stationary phase and thiol-ene chemistry in the manufacture of a chromatographic stationary phase with high efficiency in hydrophilic liquid chromatography applications.

Metal-Organic Framework Stationary Phases for One- and Two-Dimensional Micro-Gas Chromatographic Separations of Light Alkanes and Polar Toxic Industrial Chemicals.

Despite promising advances with metal-organic frameworks (MOFs) as stationary phases for chromatography, the application of MOFs for one- and two-dimensional micro-gas chromatography (μGC and μGC×μGC) applications has yet to be shown. We demonstrate for the first time, μGC columns coated with two different MOFs, HKUST-1 and ZIF-8, for the rapid separation of high volatility light alkane hydrocarbons (natural gas) and determined the partition coefficients for toxic industrial chemicals, using μGC and μGC×μGC systems. Complete separation of natural gas components, methane through pentane, was completed within 1 min, with sufficient resolution to discriminate n-butane from i-butane. Layer-by-layer controlled deposition cycles of the MOFs were accomplished to establish the optimal film thickness, which was validated using GC (sorption thermodynamics), quartz-crystal microbalance gravimetric analysis and scanning electron microscopy. Complete surface coverage was not observed until after ~17 deposition cycles. Propane retention factors with HKUST-1-coated μGC and a state-of-the-art polar, porous-layer open-tubular (PLOT) stationary phase were approximately the same at ~7.5. However, with polar methanol, retention factors with these two stationary phases were 748 and 59, respectively, yielding methanol-to-propane selectivity factors of ~100 and ~8, respectively, a 13-fold increase in polarity with HKUST-1. These studies advance the applications of MOFs as μGC stationary phase.

Preparation and chromatographic properties of mixed-mode chromatographic stationary phases modified by imidazole side-group functionalized poly(ionic liquids)

A novel mixed-mode chromatographic stationary phase was prepared via surface initiated atom transfer radical polymerization using an imidazole side-group functionalized ionic liquid monomer, 1-(4-vinylbenzyl)-3-cyanomethyl bromide. The structure of the stationary phase was characterized by infrared spectroscopy, elemental analysis, and thermogravimetric analysis. The stationary phase showed good separation ability. The retention mechanism of reversed-phase/ion exchange toward solutes on the stationary phase was verified by determining the effect of mobile phase pH on the retention of substances. Compared with octadecylsilyl-bonded silica stationary phase, it is confirmed that the poly(ionic liquid)-modified stationary phase provides π-π interaction toward the retention of the solutes. The results show that the functionalization of imidazole side groups is a feasible method for preparing new ionic liquid stationary phases.

Preparation of reversed-phase/hydrophilic chromatographic stationary phase based on dialdehyde microcrystalline cellulose-functionalized C18

A novel reversed/hydrophilic chromatographic stationary phase based on dialdehyde microcrystalline cellulose (DMCC)-functionalized C18 was prepared by covalent bonding between the amino groups of octadecylamine with the aldehyde groups of DMCC, which was used in reversed-phase liquid chromatography (RPLC) and hydrophilic interaction liquid chromatography (HILIC) modes. The prepared DMCC-functionalized C18 modified silica (C18-DMCC/SiO2) stationary phase exhibited good hydrophobic selectivity and aromatic selectivity by separating alkylbenzenes and polycyclic aromatic hydrocarbons (PAHs) in the RPLC mode. Polar compounds, including anilines, phenols, and glycosides were chosen as analytes to evaluate the polar selectivity of this column in the RPLC mode, and the evaluation results were satisfactory compared with the commercial C18 column. Nucleobases were used for evaluating the hydrophilic interaction liquid chromatography performance of the C18-DMCC/SiO2 column. By investigating the impact of organic solvent content on the retention, it could be found that this new stationary phase had the typical characteristics of reversed-phase/hydrophilic chromatography.

Separation of New Coumarin Glycosides from Toddalia asiatica Using Offline Two-Dimensional High-Performance Liquid Chromatography.

Coumarins and flavonoids are the major constituents of Toddalia asiatica. The separation and purification of ingredients from T. asiatica is an important procedure to acquire high-purity compounds for subsequent pharmacological investigation to discover leading compounds. In the present work, an offline two-dimensional high-performance liquid chromatography (HPLC) method was successfully established for the separation of high-purity glycosides from T. asiatica. Based on the separation results obtained with two different chromatographic stationary phases, a phenyl-bonded silica-based reversed-phase column was employed as the first HPLC preparation, and three fractions were obtained from the sample. Then, the fractions were isolated and purified on an octadecyl-bonded silica-based reversed-phase column to obtain high-purity compounds in the second HPLC separation. As a result, three coumarin glycosides, including two undescribed and one known, along with one known flavonoid glycoside with more than 98% purity were isolated from the sample. The structures of the isolated compounds were elucidated on the basis of extensive spectroscopic evidence derived from optical rotation, mass spectrometry, and nuclear magnetic resonance experiments. Two-dimensional HPLC with different stationary phases has the potential to be an efficient method for the separation of high-purity compounds from T. asiatica.

Preparation and application of polyvinyl alcohol-decorated cell membrane chromatography for screening anti-osteoporosis components from Liuwei Dihuang decoction-containing serum.

Cell membrane chromatography is a powerful tool for screening active components from complex matrices. New cell membrane carriers need to be developed to increase the coverage of cell membranes on the surface of stationary phases, thereby improving cell membrane chromatographic retention. In this work, we prepared polyvinyl alcohol-poly dimethyl diallyl ammonium chloride modified silica gel as a cell membrane carrier. Osteoblast cell was used as cell membrane source, which was widely used to evaluate the osteogenic activity of drugs. The new cell membrane chromatographic stationary phase was used to screen anti-osteoporosis components in Liuwei Dihuang decoction-containing serum. The chemical structures of the new modified materials were characterized by scanning electronic microscopy, Fourier transform infrared spectroscopy, and elemental analysis characterization. Compared with the common cell membrane column, the cell membrane coverage of this modified material was increased by 30%, and thus provided a stronger retention effect in positive drugs. Nineteen metabolites in rat serum samples were retained on the cell membrane chromatography and identified by ultra-high-performance liquid chromatography/time-of-flight mass spectrometry. Among those, four components (morroniside, catalpol, loganin, and acteoside) were selected for in vitro pharmacodynamics validation. They significantly increased the osteoblast proliferation. The new modified material was successfully applied to screen anti-osteoporosis components from Liuwei Dihuang Decoction-containing serum.

Fabrication and Characterization of Polypyrrole Nanoparticles for Supercapacitor Electrode Materials

In the present work Polypyrrole nanoparticles are synthesized by oxidative polymerization method in the presence of aqueous nitric acid(HNO3) as solventandferric chloride (FeCl3) as oxidizing agent. During polymerization process the solvent and oxidizing agents played a crucial role in modifying the nanostructures of polypyrrole (PPy). Scanning electron microscopy (SEM) revealed theuniform globule morphology and narrow size distribution of produced PPy particles in acid medium. Combined effect of solvent and oxidant are advantageous for the production of PPy nanoparticles (PPyNPs) with a yield of 90%.Four point probe method and strong UV-Visible band confirmhigh electrical conductivity of PPy due to a large Π-conjugation in the polymer structure. The nature and composition of PPyNPs were confirmed by X-ray diffraction (XRD) spectrometer and Fourier transform infrared spectroscopy (FTIR). Electrochemical properties were confirmed by cyclic voltammetry (CV) and galavanostatic charge discharge (GCD) spectrum.CV and GCD spectra illustrate the excellent electrochemical properties of PPyNPs which show higher specific capacitance of 398F g−1 at 100mAg−1 current density.It has wide applications in electronic and electrochromic devices, sensors, membrane separation,corrosion protection, chromatographic stationary phase, rechargeable batteries, drug delivery,supercapacitors,light-weight batteries and microwave shielding etc.

Facile preparation of polymer-brush reverse-phase/hydrophilic interaction/ion-exchange tri-mode chromatographic stationary phases by controlled polymerization of three functional monomers

Stationary phases with multiple-mode mechanism are beneficial to meet the needs of complex samples, but there are few multiple-mode stationary phases which can adjust the relative strength among multiple-forces imposed on the solutes. This work presents a facile preparation method of reverse-phase/hydrophilic interaction/ion-exchange tri-mode stationary phase, in which three functional monomers, lauryl methacrylate (LMA), hydroxyethyl methylacrylate (HEMA) and dimethylaminoethyl methacrylate (DMAEMA) as co-monomers underwent surface initiated-atom transfer radical polymerization (SI-ATRP) on the surface of silica. The structure of stationary phases was characterized and their chromatographic properties were investigated using various solutes. By comparison with classical single-mode columns, it is found that the newly designed columns can offer multiple interactions including hydrophobic, hydrophilic and electrostatic interactions and show good separation abilities to the tested solutes. Besides, changing the ratios of LMA, HEMA and DMAEMA in SI-ATRP system can easily adjust the relative strength of three interactions imposed on the solutes, inducing adjustable separation selectivity of the columns. The improved separation of multivitamin sample and the successful use of the columns in Per aqueous liquid chromatography indicate the potential of the tri-mode stationary phases.

Are we approaching a post‐monolithic era?

Thirty years after the introduction, monolithic stationary phases are an important member of chromatographic phases. When compared to conventional particulate materials, the continuous internal structure of both inorganic-based silica and organic polymer-based monoliths allows some hydrodynamic and analytical possibilities that are not provided by conventional particulate stationary phases. Polymer-based monolithic stationary phases offer simple preparation and straightforward surface modification which makes them very versatile materials that are applicable, for example, as chromatographic stationary phases, sample enrichment units, enzymatic reactors, and external trigger-responding materials. On the other hand, current polymer monoliths cannot compete with efficiency provided by superficially porous and sub 2 μm particles. In this highlight article, I take advantage of the thirtieth anniversary of their introduction to discuss several concerns related to polymer-based monolithic stationary phases. Particularly, I focus on preparation repeatability, porous properties, swelling of the polymers in organic solvents, column efficiency for small molecules, and heterogeneity of dominant flow-through pores. In the end, I offer three possible approaches on how to overcome drawbacks related to stationary phases heterogeneity to further increase the applicability of polymer-based monolithic stationary phases. This article is protected by copyright. All rights reserved.

Call for papers on special issue “Recent developments of molecularly imprinted materials”

Aim & Scope: Molecularly imprinted materials are a family of highly specific synthetic materials. Their specificity is comparable to that found in nature (enzyme/substrate, antibody/antigen interactions). Their high specificity is at the origin of their use as preconcentration phase in Solid Phase Extraction (SPE), Solid Phase Microextraction (SPME) and Stir Bar Sorptive Extraction (SBSE,) as stationary phase in chromatography and electro-chromatography, as recognition element or sensitive materials in sensors, as drug delivery system or as enzyme mimics. This special issue deals with the above applications of molecular imprinting. Molecularly imprinted materials could be synthesized using sol-gel chemistry or using acrylate bases monomers and radical polymerization. We kindly invite you to submit a manuscript(s) for this Special Issue. Full papers, communications, and reviews are all welcome.

Imidazolium ionic liquid-enhanced poly(quinine)-modified silica as a new multi-mode chromatographic stationary phase for separation of achiral and chiral compounds

In this work, a novel imidazolium ionic liquid-functionalized poly(quinine)-modified silica stationary phase (Sil-PQn-MIm) was successfully synthesized via surface radical chain transfer and nucleophilic substitution reaction. The modified silica was confirmed by series of characterizations including Fourier transform infrared spectroscopy (FT-IR), elemental analysis (EA), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). The multi-mode chromatographic performances of the Sil-PQn-MIm column were investigated by anion-exchange mode for separation of aromatic acid samples, hydrophilic interaction mode for separation of nucleosides/nucleobases and sulfanilamides, and reversed-phase mode for separation of alkylbenzenes, benzene and polycyclic aromatic hydrocarbons (PAHs), and the Tanaka test mixtures, respectively. As expected, compared to the Sil-PQn column only with quinine as functional group, the Sil-PQn-MIm column further modified by imidazolium ionic liquid possessed higher separation performance, especially for the separation of nucleosides/nucleobases. The effects including buffer concentration, pH, organic solvent content and column temperature on chromatographic performance were studied, which proved that multiple interactions including electrostatic, hydrophobic and hydrophilic interactions can be simultaneously existed between the stationary phase and the analytes. In addition, reproducibility and efficiency of the Sil-PQn-MIm column were also investigated, the results illustrated that the stationary phase have good enough reproducibility (RSDs 0.15%–0.72%, n = 7) and high efficiency (plates per meter, ~90000 plates/m). In conclusion, the prepared stationary phase with multiple-mode retention capabilities could realize separation for various types of samples by optimizing chromatographic conditions, even for some chiral compounds.

A new strategy for the preparation of mixed-mode chromatographic stationary phases based on modified dialdehyde cellulose

A new strategy for the preparation of mixed-mode chromatographic stationary phases based on modified dialdehyde cellulose was proposed. Two novel mixed-mode chromatographic stationary phases, dicarboxyl cellulose-modified silica (DCC/SiO2) and (S)-α-phenylethylamine-bonded DCC/SiO2 ((S)-α-PEA/DCC/SiO2), were prepared by utilizing the easy functionalization characteristics of dialdehyde cellulose. The chromatographic evaluation showed that DCC/SiO2 column could be used in hydrophilic interaction liquid chromatography (HILIC) and ion exchange chromatography (IEC) modes, (S)-α-PEA/DCC/SiO2 column could be used in HILIC, IEC and chiral separation modes. The DCC/SiO2 column and (S)-α-PEA/DCC/SiO2 column exhibited excellent chromatographic performance by separating strongly polar compounds, phenylamines and chiral compounds in the above separation modes. The preparation method of modified dialdehyde cellulose-based mixed-mode chromatographic stationary phases was simple, and also provided a new idea for the development of the subsequent novel mixed-mode chromatographic stationary phases.

Synthesis of a poly(sulfobetaine-co-polyhedral oligomeric silsesquioxane) hybrid monolith via an in-situ ring opening quaternization for use in hydrophilic interaction capillary liquid chromatography.

An in-situ approach is described for synthesis of poly(sulfobetaine-co-polyhedral oligomeric silsesquioxane) [poly(sulfobetaine-co-POSS)] that can be used in a hybrid monolithic column as a hydrophilic liquid chromatography (HILIC) stationary phase. Synthesis involves (a) radical polymerization of octa(propyl methacrylate)-polyhedral oligomeric silsesquioxane (MA-POSS) and organic monomers such as dimethylaminopropyl methacrylate or vinyl imidazole, and (b) in-situ ring-opening quaternization between 1,4-butane sultone and the organic monomers. The sulfobetaine groups are generated in-situ monolith. This obviates the need for synthesis of sulfobetaine monomer previously. The pore size and permeability of the material can be tuned by using a binary porogenic system (polyethyleneglycol 600 and acetonitrile) and via the composition of the polymerization mixture. The optimized hybrid monolith owns its merits to the presence of POSS and sulfobetaine groups with good mechanical stability, the lack of residual silanol groups, and adequate hydrophilicity. The column filled with the monoliths was evaluated as a stationary phase for HILIC. Several kinds of polar compounds (including nucleosides, bases, phenols, aromatic acids and amides) were separated by using mobile phases with high organic solvent fractions in capillary liquid chromatography. Graphical abstractAn in-situ approach is described for synthesis of poly(sulfobetaine-co-polyhedral oligomeric silsesquioxane) hybrid monolithic column for use in hydrophilic liquid chromatography. The optimized monolith owns good mechanical stability, the lack of residual silanol groups and adequate hydrophilicity. Baseline separation of several kinds of polar compounds is achieved on the column. MA-POSS: octa(propyl-methacrylate) polyhedral oligomeric silsesquioxane; DMAEMA: dimethylaminoethyl methacrylate; AIBN: azodiisobutyronitrile. Poly(DMABS-co-POSS): poly(N-(4-sulfobutyl)-N-methacryloxypropyl- N,N-dimethylammonium-betaine-co-polyhedral oligomeric silsesquioxane).

Preparation and evaluation of a molybdenum disulfide quantum dots embedded C18 mixed-mode chromatographic stationary phase.

Molybdenum disulfide quantum dots (MoS2 QDs) were chosen as a functional two-dimensional material to improve the separation performance of a traditional C18 column. In this work, MoS2 QDs were synthesized by the combination of sonication and solvothermal treatment of bulk MoS2. The prepared MoS2 QDs were characterized by transmission electron microscope (TEM), Zeta potential measurement, UV-visible absorption and fluorescence spectroscopy. Then, a novel MoS2 QDs embedded C18 (Sil-MoS2-C18) stationary phase was prepared for performing mixed-mode liquid chromatography. The results of elemental analysis (EA), thermogravimetric analysis (TGA), Fourier transform infrared spectrometry (FT-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and Brunauer-Emmett-Teller (BET) measurements indicated the stationary phase was prepared successfully. Five types of compounds including alkylbenzenes, polycyclic aromatic hydrocarbons (PAHs), nucleosides and nucleobases, anilines and flavonoids were utilized to evaluate reversed phase, weak cation exchange and hydrophilic interaction of the new column. To a certain extent, the column could achieve separation for different properties of samples on one column, with less organic solvent and shorter time than conventional alkyl and amino columns. Furthermore, the mechanism for separation was studied by investigating effects of mobile phase composition and pH on retentions. In summary, the Sil-MoS2-C18 stationary phase was deemed able to serve the performance of various types of phases, which revealed the prepared mixed-mode column could be potentially applied for the analysis of complex samples. Graphical abstract.

Potential of topological descriptors to model the retention of polychlorinated biphenyls in different gas chromatography stationary phases, including ionic liquid-based columns

The aim of this study was to develop a statistical model based on a set of intuitive topological descriptors that will help to determine the influence of the polychlorinated biphenyls (PCBs) structural features on the chromatographic behavior of these analytes in a variety of gas chromatographic stationary phases, including the highly polar ionic liquid (IL)-based SLB-IL76 and SLB-IL60 columns. The model was developed using the stepwise multiple linear regression method, and constructed through several levels of increasing complexity to make evident the relative influence of the selected descriptors.The proposed model was easy to implement and provided similar satisfactory results irrespective of the dependent variables used (i.e., retention index or retention time) or the chromatographic conditions applied (i.e., pseudo-isotherm and programmed temperature) for IL-based phases. The model also allowed the correct prediction of the elution order of selected PCBs in these and other less polar phases evaluated (i.e., SW-10, DB-17, ZB-5 and HT-8). To our knowledge, this is the first models based on topological descriptors described in the literature that provided a satisfactory fitting of the PCB behavior in IL-based phases. Our results indicated that the mechanism governing the chromatographic separation of PCBs in these highly polar columns showed significant differences compared with those observed in other less polar stationary phases.

Experience with the application of gas chromatography-mass spectrometry in combination with solid-phase microextraction for the study of the composition of volatile organic compounds in matrices with the high fat content

Current article presents a methodological approach for a comparative study of the composition of volatile organic compounds ( VOCs ) in a natural product and a nature-identical flavoring substance. The identification of VOCs was performed by gas chromatography-mass spectrometry without reference compounds. The identification was made based on coincidence of the experimental and reference mass spectra and linear retention indices. During the first step, the closest match factor substance was selected based on the library search. During the second step, the result was verified by the means of experimental and reference retention indices data proximity. The reference retention indices were selected considering the identity of the experimental conditions (chromatographic stationary phase, temperature programming mode). The impossibility of identification of aroma components in acetonitrile extract of fragrance was shown due to the overlapping of their peaks with peaks of di- and tri- glycerides of fatty acids. The extraction and concentration of VOCs from vapor were carried out using the head space solid-phase microextraction. The fragrance content investigation revealed 39 volatile organic compounds including propylene glycol and triacetin as the markers of synthetic fragrances. In natural cocoa butter, also 39 volatile organic compounds were identified. All of them were common for the fermented cocoa beans. Pyrazines derivatives, characteristic of cocoa aroma, were presented with the following 7 components: 2,3-dimethylpyrazine; 2,5-dimethylpyrazine; ethylpyrazine; 2-methyl-6-ethylpyrazine; 2,3,5-trimethylpyrazine, 2,5-dimethyl-3-ethylpyrazine; tetramethylpyrazine. In quantitative terms, the isomeric 2,3-butandiols predominate in the head space of natural cocoa butter accounting for 37 percent of total VOC content. The analytical technique used allows investigation of multicomponent objects including the heterogeneous ones. Key words: gas chromatography-mass spectrometry, head space solid-phase microextraction, mass spectra, retention indices, fragrance DOI: http://dx.doi.org/10.15826/analitika.2020.24.1.003 E. Savelieva E. Kessenikh and L. Gustyleva Research Institute of Hygiene, Occupational Pathology and Human Ecology, g/p Kiz’molovskii, Vsevolozhskii raion, Leningradskaia oblast’, 188663, Russian Federation

An alternative approach for the preparation of a core-shell bimetallic central metal-organic framework as a hydrophilic interaction liquid chromatography stationary phase.

A new type of core-shell composite material was prepared and applied as a hydrophilic interaction liquid chromatography (HILIC) stationary phase. In this work, silica spheres were first modified with a bimetallic central metal-organic framework (ZnCoMOF) by a new strategy of static self-assembled in situ growth. This strategy was beneficial for increasing the electrostatic interaction between the MOF ligand and silica via introducing a sodium dodecylbenzenesulfonate (SDBS) group. The ZnCoMOF@silica stationary phase was characterized and evaluated in comparison with amino-modified and bare silica columns in terms of various polar analytes including eight nucleosides and nucleobases, seven carbohydrates, and multiple sulfonamides and antibiotics. The effects of organic solvent concentration, water content, the concentration of the salt and the pH of the buffer solution on the retention time were studied, which demonstrated the typical retention behavior of HILIC on the ZnCoMOF@silica column. Compared with most reported MOF-based stationary phases, the new composite material showed excellent hydrophilic properties and separation efficiency for various polar analytes. Moreover, the obtained stationary phase showed good reproducibility and stability. The relative standard deviation (RSD) of the retention time for repeatability was found to range from 0.1% to 0.6%, and the RSD of the retention time for stability was found to range from 0.3% to 0.7%. Furthermore, the column batch-to-batch reproducibility showed excellent preparation reproducibility, which few reported in most previous MOF@silica composite materials. This specific preparation method offers an easy and novel way to manipulate the amount of MOF particles on silica, which extends a universal way to produce various MOF@silica stationary phases by the method of static self-assembled in situ growth.

A brief review on: Separation techniques chromatography

Chromatography is an important biophysical process, allowing the components of a mixture to be isolated, classified and extracted for qualitative and quantitative analysis. Proteins can be purified based on features such as size and shape, total charge, surface hydrophobic groups and stationary phaset binding ability. Four separation strategies based on molecular characteristics and form of interaction Four separation techniques based on molecular characteristics and form of interaction use ion exchange mechanisms, surface adsorption, partition, and exclusion of the size. Column chromatography is one of the most common methods of protein purification Chromatography is based on the theory of separation of fluid stationary phase (stable phase) when traveling with the support of a mobile phase. The variables that are involved in this separation process include adsorption (liquid-solid), partition (liquid-solid), and affinity or variations between their molecular weights. Due of these variations, certain components of the mixture stay in the stationary phase longer, and travel gradually in the chromatography system, while others move rapidly through the mobile phase, leaving the system faster. Based on this method, three components form the basis of the chromatography technique. Stationary phase: is a phase consisting of a phase or a surface adsorbed Mobile phase: is a phase consisting of a or a part. Separate molecules which form the interaction between stationary phase, mobile phase and substances contained in the mixture are the basic component that is successful in separating molecules from the partition-based chromatography methods are very effective in separating small molecules and distinguishing them as amino acids, carbohydrates and fatty acids. In the separation of macromolecules as nucleic acids and proteins, however, affinity chromatography’s (i.e. ion-exchange chromatography) are more efficient. Paper chromatography is used in protein separation and protein synthesis studies; gas-liquid chromatography is used to isolate alcohol, ethanol, lipid, and amino groups, and to analyze enzymatic interactions, while molecular-sieve chromatography is used in particular to evaluate molecular protein weights. Agarose gel chromatography is used to purify RNA, DNA particles, and viruses. The chromatography stationary phase is a solid phase or liquid phase that is sprayed on a solid phase surface. A gaseous or liquid phase is a mobile phase which flows through the stationary phase. If the mobile phase is liquid, it is called liquid chromatography, and if it is gas, it is called gas chromatography. of gases and mixtures of volatile liquids, and solid material, gas chromatography is used. Liquid chromatography is used in particular for thermal unstable and non-volatile materials. The purpose of applying chromatography, which is used as a quantitative analysis tool apart from its separation, is to record a sufficient separation within an acceptable time interval. Various chromatography methods have been developed to that end. Some of these have chromatography on columns, thin layer chromatography (TLC), paper chromatography, gas chromatography, ion exchange chromatography, gel permeation chromatography, liquid high pressure chromatography, and affinity chromatography.

Ionic liquids as gas chromatographic stationary phases: how can they change food and natural product analyses?

The volatile fraction of natural products often consists of complex mixtures of isomeric and/or homologous components with similar structural and physical characteristics (e.g. mono- and sesquiterpenoids) that are not easy to separate simultaneously with conventional GC stationary phases, even when used with multidimensional systems. The introduction of ionic liquids (ILs) as stationary phases has opened up new perspectives in this field as their unique solvation properties result in uncommon selectivity, which is completely different to that of classic polydimethylsiloxane (PDMS)- and polyethyleneglycol (PEG)-based columns. Because of their peculiar selectivity and high inertness, IL-based columns have already found several applications in the natural product field in mono- and multidimensional GC and preparative GC, leading to the exhaustive analysis of complex samples (including aqueous solutions), and the separation of challenging pair(s) of compounds. This article provides an overview of how IL-based columns can be exploited in the fields of food and natural products, explores the wide range of applications that have already been developed and highlights the main features of these promising stationary phases, which are expected to be further extended in the near future, in particular, for routine use. Graphical abstract.