In situ fabrication of microporous organic network coated capillary column for high resolution gas chromatographic separation of hydrocarbons

Microporous organic networks (MONs) are a new class of porous materials synthesized via Sonogashira coupling reactions between organic building blocks. Here we report an in situ synthesis approach to fabricate MONs coated capillary column for high resolution GC separation of hydrocarbons. The McReynolds constant evaluation reveals the MONs coated capillary is a non‐polar column. The MONs coated capillary column shows good resolution for GC separation of diverse important industrial hydrocarbons such as linear and branched alkanes, alkylbenzenes, pinene isomers, ethylbenzene and styrene, cyclohexane and benzene. The MONs coated capillary column gave a high column efficiency of 1542 plates per meter for hexane and good precision for replicate separations of the selected hydrocarbons with the RSDs of 0.2–0.3, 1.5–3.1, and 1.9–3.3% for retention time, peak height and peak area, respectively. The MONs coated capillary also offered better resolution than commercial Inert Cap‐1 and Inert Cap‐5 capillary columns for hexane and heptane isomers. These results reveal the potential of MONs as novel stationary phases in GC.     

Exploitation of a microporous organic polymer as a stationary phase for capillary gas chromatography

Microporous organic polymers (MOPs) have emerged as a new class of functional porous materials with unique characteristics and potential uses in diverse areas. However, the field of MOPs for gas chromatographic (GC) separations has not been well explored. Herein, a MOP namely KAPs-1 was dynamic coated onto a capillary column for the first time. The fabricated column exhibited a nonpolar nature and the column efficiency for n-dodecane was up to 7769 plates m⁻¹. The KAPs-1 coated column showed high GC separation performance for a series of volatile organic compounds (VOCs) including the challenging ethylbenzene and xylene isomers, which could not be resolved at baseline on the commercial 5% phenyl polysiloxane stationary phase. Moreover, the relative standard deviations for five replicate determinations of the studied analytes were 0.0–0.6%, 0.9–3.2%, 1.1–5.9%, 0.8–3.7% for retention time, peak area, peak height and peak width, respectively. To investigate the interaction between some analytes and the stationary phase, thermodynamic and kinetic parameters were also evaluated. The results of this study show it is very promising to utilize MOPs as stationary phases for capillary GC.     

A multiple-function stationary phase based on perhydro-26-membered hexaazamacrocycle for high-performance liquid chromatography

A perhydro-26-membered hexaazamacrocycle-based silica (L¹GlySil) stationary phase for high-performance liquid chromatography (HPLC) was prepared using 3-glycidoxypropyltrimethoxysilane as coupling reagent. The structure of new material was characterized by infrared spectroscopy, elemental analysis and thermogravimetric analysis. The chromatographic performance and retention mechanism of the new phase were evaluated in reversed-phase (RP) and normal-phase (NP) modes using different solute probes including aromatic compounds, organophosphorus pesticides, carbamate pesticides and phenols. The results showed that L¹GlySil was a sort of multimode-bonded stationary phase with excellent chromatographic properties. The new phase could provide various action sites for different solutes, such as hydrophobic, hydrogen bonding, π–π, dipole–dipole interactions and acid–base equilibrium. The presence of phenyl rings, secondary amino groups and alkyl linkers in the resulting material made it suitable for the separation of above-mentioned analytes by multimode retention mechanisms.     

Reversed-phase systems for the separation of pentapeptides by high-performance liquid chromatography

Summary Reversed-phase systems using octyl modified silica as such and as a support for dynamically coated ion-exchangers, were investigated for their ability to separate pentapeptides. Normal reversed-phase adsorption with C-8 bonded silica in combination with citrate bufferpropanol-1 mixtures were found useful for the separation of a number of pentapeptides. The separation of pentapeptides differing widely in retention can be speeded up by applying an organic modifier and/or sodium citrate gradient. A solvent generated cation-exchange system with sodium dodecylsulfate as surfactant showed a high selectivity for the pentapeptides under investigation and is better for analytical purposes than the normal reversed-phase adsorption systems investigated. With respect to the detection of pentapeptides with fluorescamine, the use of dry pyridine as a basic buffer and as diluent for the fluorescamine was also investigated. Compared to the commonly used diluent acetone, pyridine is better when using acidic eluents of moderate buffer strength. At pH>6 no significant differences in sensitivity between acetone and pyridine could be noticed.     

Cholesteric bonded stationary phases for high-performance liquid chromatography: a comparative study of the chromatographic behavior

The properties of four cholesteric bonded stationary phases differing in the nature of the spacer and the end-capping were assessed using simple chromatographic tests based on the retention of nonpolar compounds and of planar or nonplanar probe solutes. All cholesteric columns showed a hydrophobicity close to that of conventional octadecyldimethylsilyl (ODS) materials. Non-end-capped cholesteric bonded phases showed greater selectivity than ODS ones and both end-capped cholesteric bonded phases exhibit behavior intermediate between that of the non-end-capped original material and that of the ODS bonded phase.     

High-performance liquid chromatographic separation of polyolefin antioxidants and light-stabilisers

Summary A scheme was devised for the identification of 22 common antioxidants and light-stabilisers in polyolefins. The separation of these stabilisers was performed by isocratic reversed phase high-performance liquid chromatography on a RP-18 column. Three different separation conditions have been used: the mobile phase composition was 100% acetonitrile (MeCN), 90/10 meCN/H₂O and 80/20 MeCN/H₂O. The UV₂₅₄/UV₂₈₀ ratio and the elution time of each stabiliser were determined for these three mobile phase compositions. The values of UV₂₅₄/UV₂₈₀ ratios may be used together with the retention time values for the identification of unknown stabilisers in polyolefin samples.     

Versatile ligands for high-performance liquid chromatography: An overview of ionic liquid-functionalized stationary phases

Ionic liquids (ILs), a class of unique substances composed purely by cation and anions, are renowned for their fascinating physical and chemical properties, such as negligible volatility, high dissolution power, high thermal stability, tunable structure and miscibility. They are enjoying ever-growing applications in a great diversity of disciplines.     

Immobilized polysiloxanes as stationary phases for high-performance liquid chromatography and solid phase extraction

Polysiloxanes immobilized onto the surfaces of porous silica particles have proven to be good stationary phases for the separation of multiresidues of pesticides and their metabolic/degradation products by reversed-phase high-performance liquid chromatography (RP-HPLC). Similar materials have proven effective for pre-concentration and clean-up procedures using solid phase extraction. The present paper describes the preparation and some applications of several of these packing materials.     

Per(3-chloro-4-methyl)phenylcarbamate cyclodextrin clicked stationary phase for chiral separation in multiple modes high-performance liquid chromatography

In this work, a detail study has been performed on the enantioselectivity of per(3-chloro-4-methyl)phenylcarbamate-β-CD clicked chiral stationary phase (CSP) in high-performance liquid chromatography. Both normal phase and polar organic mobile phases have been explored for the enantioseparation of 39 model racemic pairs including aromatic alcohols, flavonoids, β-blockers and amino acids. Chiral resolution values over 10 were achieved for flavonoids. The comparison study with reference perphenylcarbamate-β-CD clicked CSP reveals the significance of 3-chloro-4-methyl functionality in improving the enantioselectivities. This study may provide insight on the multiple interactions between functionalized CD and analytes.     

Reversed-phase high-performance liquid chromatographic/mass spectrometric method for separation of 4-methylimidazole and 2-acetyl-4-(1,2,3,4-tetrahydroxybutyl)imidazole at pg levels

A high-performance liquid chromatographic/mass spectrometric method (HPLC/MS) has been developed to determine both 4-methylimidazole (4MeI) and 2-acetyl-4-(1,2,3,4-tetrahydroxybutyl)imidazole (THI) in one run. Among three sorbents tested, the best peak shape of 4MeI was achieved on a reversed-phase MetaChem Polaris C18-A at pH 9.5. The sensitivity and the range of UV detection at 215 and 290 nm for 4MeI and THI, respectively, were compared to the parameters achieved by the electrospray ionization mass spectrometric (ESI/MS) detection in the presence of 5 mmol l⁻¹ ammonium hydroxide using selected ion-monitoring (SIM) mode. The on-column limits of detection were 0.147 ng of 4MeI and 0.084 ng of THI using UV detection and 1 pg of 4MeI and 3 pg of THI using ESI/MS detection, respectively. The effect of both ammonium ion concentration and energy of fragmentation on 4MeI and THI ionization is discussed. The method could be applied for a fast and sensitive determination of 4MeI and THI in different biological materials as well as in Class III Caramels.     

Preparation of core-shell microporous organic polymer-coated silica microspheres for chromatographic separation and N-glycopeptides enrichment

Through a “one-pot” strategy, a layer of microporous organic polymer was coated onto the surface of monodisperse amino-functionalized silica microsphere via amino-aldehyde condensation reaction with core-shell structure. The change in chemical structure of material before and after modification was determined by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. Due to existence of a large number of amino and aldehyde groups in microporous organic polymer shell, the water contact angle decreased from 56.8° (silica microspheres) to 34.7° (microporous organic polymer-coated silica microspheres). Based on these properties, microporous organic polymer-coated silica microspheres were employed as the stationary phase for capillary liquid chromatography and successfully offered baseline separation of polar small molecules. Additionally, the material could also be served as the sorbent of hydrophilic interaction chromatography to enrich glycopeptides from human serum digest. A total of 470 unique N-glycopeptides and 342 N-glycosylation sites mapped to 112 N-glycosylated proteins were unambiguously identified from 2 μL of human serum, exhibiting a promising application prospect of microporous organic polymer-coated silica microspheres in the pretreatment of proteomics samples.     

Surface-bonded ionic liquid stationary phases in high-performance liquid chromatography—A review

Ionic liquids (ILs) are a class of ionic, nonmolecular solvents which remain in liquid state at temperatures below 100 °C. ILs possess a variety of properties including low to negligible vapor pressure, high thermal stability, miscibility with water or a variety of organic solvents, and variable viscosity. IL-modified silica as novel high-performance liquid chromatography (HPLC) stationary phases have attracted considerable attention for their differential behavior and low free-silanol activity. Indeed, around 21 surface-confined ionic liquids (SCIL) stationary phases have been developed in the last six years. Their chromatographic behavior has been studied, and, despite the presence of a positive charge on the stationary phase, they showed considerable promise for the separation of neutral solutes (not only basic analytes), when operated in reversed phase mode. This aspect points to the potential for truly multimodal stationary phases. This review attempts to summarize the state-of-the-art about SCIL phases including their preparation, chromatographic behavior, and analytical performance.     

The evaluation of “reversed phase” high-performance liquid chromatography packing materials

Summary For the evaluation of reversed phase packing materials a mixture of acetylacetone, I-nitronaphthalene and naphthalene is proposed. This will reveal the usual optimum kinetic chromatographic parameters (the naphthalene peak), the degree of activity or endcapping status of the column (the ratio of the I-nitronaphthalene and naphthalene retention times) and trace metal activity (the shape and intensity of the acetylacetone peak).     

Improved stochastic resonance algorithm for enhancement of signal-to-noise ratio of high-performance liquid chromatographic signal

Based on the theory of stochastic resonance, an improved stochastic resonance algorithm with a new criterion for optimizing system parameters to enhance signal-to-noise ratio (SNR) of HPLC/UV chromatographic signal for trace analysis was presented in this study. Compared with the conventional criterion in stochastic resonance, the proposed one can ensure satisfactory SNR as well as good peak shape of chromatographic peak in output signal. Application of the criterion to experimental weak signals of HPLC/UV was investigated and the results showed an excellent quantitative relationship between different concentrations and responses.     

Fully automated high-performance liquid chromatographic separation of DL-amino acids derivatized witho-phthaldialdehyde together withN-isobutyryl-cysteine. Application to food samples

Summary A method is presented that enables the fully automated precolumn derivatization of mixtures of DL-amino acids (DL-AA) witho-phthaldialdehyde together withN-isobutyryl-L(orD)-cysteine. HPLC on a 250 mm×4 mm i.d. column packed with Shandon Hypersil ODS, 5 μm, and a linear gradient formed from 23 mM sodium acetate (pH 6.0) and methanol/acetonitrile (600 ml+50 ml) separates completely an AA standard composed of 17 pairs of DL-AA (including Asn and Gln), Gly and the internal standard L-homo-Arg, within 75 min at a flow rate at 1 ml/min. Applications are shown of the determination of free D-AA isolated from an orange juice concentrate and from soy sauce, and the detection of D-AA in a gelatine total hydrolysate. In the case of these foodstuffs fluorescence detection (excitation at 230 nm, emission at 445 nm) allows the routine detection of 5–10 pmol per AA; and approx. 0.2–1% D-AA, in an excess of L-AA, are quantifiable. Presented in part at the “International Symposium on Separation of Peptides, Proteins and Polynucleotides”, October 29–31, 1990, Wiesbaden (abstract 620), ANAKON '91, April 22–24, Baden-Baden (abstract C 5), and at the “15th International Symposium on Column Liquid Chromatography”, June 3–7, 1991, Basel (abstract P26/2).     

Rapid high-performance liquid chromatographic analysis of adenovirus type 5 particles with a prototype anion-exchange analytical monolith column

To support effective process development there is a requirement for rapid analytical methods that can identify and quantitate adenoviral particles throughout the manufacturing process, from cellular lysate through to purified adenovirus. An anion-exchange high-performance liquid chromatography method for the analysis of adenovirus type 5 (Ad5) particles has been developed using a novel quaternary amine monolithic column (Bio-Monolith QA, Agilent). The developed method separates intact Ad5 from contaminating proteins and DNA, thus allowing analysis of non-purified samples during process development. Regeneration conditions were incorporated to extend the functional life of the column. Once developed, the method was qualified according to performance criteria of repeatability, intermediate precision and linearity. The linear working range of analysis was established between 7.5 × 10⁸ to at least 2.4 × 10¹⁰ viral particles (3 × 10¹⁰ to 9.6 × 10¹¹ viral particles/mL), with a correlation coefficient of 0.9992. Relative standard deviations (RSDs) for intra- and inter-day repeatability and precision for retention time and peak area were less than 1 and 2.5%, respectively.     

Adjustment of a GC automatic liquid sampler for high-performance liquid chromatography

Summary An automatic liquid sampler for high-performance liquid chromatography is described.The sampler is based on a GC-injection system from Hewlett-Packard. The HPLC sampler has a unique cleaning system, excellent reproducibility and a plug-in compatibility for sample identification and computer control for Hewlett-Packard integrators and Laboratory Data Systems.     

Role of the organic solvent modifier in the reversed phase high-performance liquid chromatography of polypeptides

Summary The retention behaviour of several polypeptide hormones on Bondapak C₁₈ columns has been examined using mobile phases of different acetonitrile percentage compositions containing 15 mM triethylammonium phosphate or 15 mM orthophosphoric acid buffers. Under these elution conditions, the capacity factors and the selectivity parameters of these polypeptide hormones show pronounced dependencies on the volume fraction of the organic solvent modifier. In the range 0–40% acetonitrile, the capacity factors were monotonously attenuated with increasing modifier percentages with the elution order essentially in accord with that hat anticipated for a reversed phase separation mode. At higher concentrations of acetonitrile, retention of the polypeptides to the octadecylsilica support progressively increased with elution order reversals indicative of a normal- or polarphase separation mode. These observations are discussed in terms of the interplay of hydrophobic and silanophilic interactions which occur between the ionised polypeptides and the stationary phase under these changing mobile phase conditions.High Performance Liquid Chromatography of Amino Acids, Peptides and Proteins, XXXII. For previous publication see ref. [1].     

Semi-preparative high-performance liquid chromatographic separation of trimedlure isomers

Summary Semi-preparative high-performance liquid chromatographic procedures on 5 m silica were developed for the isolation of gram quantities of eight trimedlure isomers (trans: A, B₁, B₂, and C;cis: V, W, X, and Y) for comparative biological evaluation and NMR studies. Isolations were made from an eight-component 21cis: trans-trimedlure mixture, a four-componentcis-trimedlure mixture, trimedlure-B₂:X and trimedlure-C:W epimerization merization mixtures, a trimedlure-B₁:Y:B₂ mixture, and a trimedlure-A concentrate.