Large Volume Injection in Fast Gas Chromatography with On‐Column Injector

In this work a fast gas chromatography set‐up with on‐column injection was optimized and evaluated with a model mixture of C₈–C₂₈ n‐alkanes. Usual injection volumes when using narrow‐bore (e. g., 0.1 mm i.d.) analytical columns are ca. 0.1 μL. The presented configuration allows introduction of 10–30‐fold larger sample volumes without any distortion of peak shapes. In the set‐up a normal‐bore retention gap (1 m×0.32 mm i. d.) was coupled to a narrow‐bore (4.8 m×0.1 mm i. d.×0.4 μm film thickness) analytical column using a low dead volume column connector. The effects of the experimental conditions such as inlet pressure, sample volume, initial injection temperature, and oven temperature on a peak focusing are discussed. H‐u curves for helium and hydrogen are used to compare their suitability for high speed gas chromatography and to show the dependence of separation efficiency on the carrier gas velocity at high inlet pressures. In the fast gas chromatography system a baseline separation of C₁₀–C₂₈ n‐alkanes was achieved in less than 3 minutes.     

Incarceration of Higher‐Order Fullerenes within Cyclotriveratrylene‐Based Hemicarcerands Allows Selective Isolation of C76, C78, and C84 from a Commercial Fullerene Mixture

Size‐complementary cyclotriveratrylene (CTV)‐based hosts can incarcerate C₇₆, C₇₈, and C₈₄, thus allowing the selective isolation of these higher‐order fullerenes from a commercially available mixture of fullerenes. The hemicarceplexes, formed after the encapsulation of the size‐complementary fullerenes within the hosts, are isolated by column chromatography and released at elevated temperature, thereby leading to the isolation of C₇₆/C₇₈ and C₈₄ in good purities (up to 95 and 88 %, respectively).     

C18‐bound porous silica monolith particles as a low‐cost high‐performance liquid chromatography stationary phase with an excellent chromatographic performance

Ground porous silica monolith particles with an average particle size of 2.34 μm and large pores (363 Å) exhibiting excellent chromatographic performance have been synthesized on a relatively large scale by a sophisticated sol–gel procedure. The particle size distribution was rather broad, and the d(0.1)/d(0.9) ratio was 0.14. The resultant silica monolith particles were chemically modified with chlorodimethyloctadecylsilane and end‐capped with a mixture of hexamethyldisilazane and chlorotrimethylsilane. Very good separation efficiency (185 000/m) and chromatographic resolution were achieved when the C₁₈‐bound phase was evaluated for a test mixture of five benzene derivatives after packing in a stainless‐steel column (1.0 mm × 150 mm). The optimized elution conditions were found to be 70:30 v/v acetonitrile/water with 0.1% trifluoroacetic acid at a flow rate of 25 μL/min. The column was also evaluated for fast analysis at a flow rate of 100 μL/min, and all the five analytes were eluted within 3.5 min with reasonable efficiency (ca. 60 000/m) and resolution. The strategy of using particles with reduced particle size and large pores (363 Å) combined with C₁₈ modification in addition to partial‐monolithic architecture has resulted in a useful stationary phase (C₁₈‐bound silica monolith particles) of low production cost showing excellent chromatographic performance.     

Dimerization of C60: Symmetry Considerations

Orbital‐symmetry analysis (OCAMS) of the dimerization of C₆₀ via [2+2] cycloaddition indicates that the reactant monomers should approach one another along a pathway in which C_2h symmetry is conserved. Point‐by‐point computations (AM1/UHF) confirm this prediction: a low‐energy pathway leads to a single‐bonded dimer 2 with C_2h symmetry. Closure to the stable D_2h dimer 1 is effected by relatively facile rotation about the single bond. A similar symmetry analysis was performed on a second isomer 3 with D_2h symmetry, the moieties of which are linked by two two‐atom chains. It raises the possibility that 3 , the so‐called `window' isomer, may be interconvertible with 1 along a pathway that retains C_i (S₂) symmetry. Although the computational results indicate that C₆₀ is in thermal equilibrium with its stable dimer 1 at moderate temperatures, the latter is not observed in the gas phase for thermodynamic reasons. According to THERMO computations (AM1/RHF), the equilibrium is shifted strongly towards the monomer pair at temperatures where vaporization of the solid C₆₀ is observed (>400°).     

Gas‐Phase Synthesis of the Elusive Cyclooctatetraenyl Radical (C8H7) via Triplet Aromatic Cyclooctatetraene (C8H8) and Non‐Aromatic Cyclooctatriene (C8H8) Intermediates

The 1,2,4,7‐cyclooctatetraenyl radical (C₈H₇) has been synthesized for the very first time via the bimolecular gas‐phase reaction of ground‐state carbon atoms with 1,3,5‐cycloheptatriene (C₇H₈) on the triplet surface under single‐collision conditions. The barrier‐less route to the cyclic 1,2,4,7‐cyclooctatetraenyl radical accesses exotic reaction intermediates on the triplet surface, which cannot be synthesized via classical organic chemistry methods: the triplet non‐aromatic 2,4,6‐cyclooctatriene (C₈H₈) and the triplet aromatic 1,3,5,7‐cyclooctatetraene (C₈H₈). Our approach provides a clean gas‐phase synthesis of this hitherto elusive cyclic radical species 1,2,4,7‐cyclooctatetraenyl via a single‐collision event and opens up a versatile, unconventional path to access this previously largely obscure class of cyclooctatetraenyl radicals, which have been impossible to access through classical synthetic methods.     

From Solar Energy to Fuels: Recent Advances in Light‐Driven C1 Chemistry

Catalytic C₁ chemistry based on the activation/conversion of synthesis gas (CO+H₂), methane, carbon dioxide, and methanol offers great potential for the sustainable development of hydrocarbon fuels to replace oil, coal, and natural gas. Traditional thermal catalytic processes used for C₁ transformations require high temperatures and pressures, thereby carrying a significant carbon footprint. In comparison, solar‐driven C₁ catalysis offers a greener and more sustainable pathway for manufacturing fuels and other commodity chemicals, although conversion efficiencies are currently too low to justify industry investment. In this Review, we highlight recent advances and milestones in light‐driven C₁ chemistry, including solar Fischer–Tropsch synthesis, the water‐gas‐shift reaction, CO₂ hydrogenation, as well as methane and methanol conversion reactions. Particular emphasis is placed on the rational design of catalysts, structure–reactivity relationships, as well as reaction mechanisms. Strategies for scaling up solar‐driven C₁ processes are also discussed.     

Position‐specific 13C/12C analysis of amino acid carboxyl groups – automated flow‐injection analysis based on reaction with ninhydrin

Rationale

The fundamental level of stable isotopic knowledge lies at specific atomic positions within molecules but existing methods of analysis require lengthy off‐line preparation to reveal this information. An automated position‐specific isotope analysis (PSIA) method is presented to determine the stable carbon isotopic compositions of the carboxyl groups of amino acids (δ¹³C_CARBOXYL values). This automation makes PSIA measurements easier and routine.

Methods

An existing high‐performance liquid chromatography (HPLC) gas handling interface/stable isotope ratio mass spectrometry system was modified by the addition of a post‐column derivatisation unit between the HPLC system and the interface. The post‐column reaction was optimised to yield CO₂ from the carboxyl groups of amino acids by reaction with ninhydrin.

Results

The methodology described produced δ¹³C_CARBOXYL values with typical standard deviations below ±0.1 ‰ and consistent differences (Δ¹³C_CARBOXYL values) between amino acids over a 1‐year period. First estimates are presented for the δ¹³C_CARBOXYL values of a number of internationally available amino acid reference materials.

Conclusions

The PSIA methodology described provides a further dimension to the stable isotopic characterisation of amino acids at a more detailed level than the bulk or averaged whole‐molecule level. When combined with on‐line chromatographic separation or off‐line fraction collection of protein hydrolysates the technique will offer an automated and routine way to study position‐specific carboxyl carbon isotope information for amino acids, enabling more refined isotopic studies of carbon uptake and metabolism.

     

Analysis of light hydrocarbons C1–C5 with Porous Layer Open Tubular fused silica columns of aluminum oxide. Part 1: The column

A method is described for the preparation of a Porous Layer Open Tubular (PLOT) fused silica column coated with submicron particles of aluminum oxide for the analysis of light hydrocarbons. The column is thermally stable and provides reproducible analytical data over a long period of time. The column can be operated at temperatures easily controlled by commercially available gas chromatographic apparatus. 1,3-Butadiene is retarded much more than its principal impurities: thus the polarity of aluminum oxide is extremely useful for butadiene analysis because none of the contaminants is obscured by the butadiene peak. The analysis of the 16 most common C₁–C₄ hydrocarbons is achieved within 5 min at 60°C with helium as the carrier gas. Conditioning of the carrier gas with water vapor from CuSO₄.5H₂O to decrease the activity of the aluminum oxide is described. Some applications of a 30 m × 0.32 mm aluminum oxide PLOT column are given.     

Application of vapour phase chromatography in the gas-analytical field

Of the various, types of gas chromatography developed in the past few years gas-liquid partition chromatography has been found to be the best method for the analysis of hydrocarbon gases.By a suitable choice of the liquid phase and the other conditions it is possible to separate each individual hydrocarbon in the C₁–C₅ range from the other components. The influence of size of column nature of carrier material, concentration of liquid phase on carrier, and gas velocity, has been discussed.For the quantitative determination of the components two methods were used, viz.: (a) Continuous measurement of the thermal conductivity of the gas mixture leaving the column. This method is preferred for the analysis of gas mixtures consisting of a limited number of components and for the determination of a single component in a complex mixture. (b) Measurement of the pressure increments obtained by collecting the components in an evacuated vessel after the CO₂ stripper gas has been removed by absorption in a caustic solution. This method is particularly suitable for the analysis of gas mixtures consisting of many components with widely different boiling points.     

Crystal structure and photoreactivity of a halogen‐bonded cocrystal based upon 1,2‐diiodoperchlorobenzene and 1,2‐bis(pyridin‐4‐yl)ethylene

The formation of a photoreactive cocrystal based upon 1,2‐diiodoperchlorobenzene ( 1,2‐C₆I₂Cl₄ ) and trans‐1,2‐bis(pyridin‐4‐yl)ethylene ( BPE ) has been achieved. The resulting cocrystal, 2( 1,2‐C₆I₂Cl₄ )·( BPE ) or C₆Cl₄I₂·0.5C₁₂H₁₀N₂, comprises planar sheets of the components held together by the combination of I…N halogen bonds and halogen–halogen contacts. Notably, the 1,2‐C₆I₂Cl₄ molecules π‐stack in a homogeneous and face‐to‐face orientation that results in an infinite column of the halogen‐bond donor. As a consequence of this stacking arrangement and I…N halogen bonds, molecules of BPE also stack in this type of pattern. In particular, neighbouring ethylene groups in BPE are found to be parallel and within the accepted distance for a photoreaction. Upon exposure to ultraviolet light, the cocrystal undergoes a solid‐state [2 + 2] cycloaddition reaction that produces rctt‐tetrakis(pyridin‐4‐yl)cyclobutane ( TPCB ) with an overall yield of 89%. A solvent‐free approach utilizing dry vortex grinding of the components also resulted in a photoreactive material with a similar yield.     

Factors influencing chromatographic data in fast gas chromatography with on‐column injection

The use of larger volume injection with on‐column injection and fast GC commercial instrumentation was evaluated with the model mixture of n‐alkanes of a broad range of volatility (C₁₀–C₂₈). The presented configuration allows introduction of 40–80‐fold larger sample volumes without any distortion of peak shapes compared to “usual” fast GC set‐ups using narrow‐bore columns. A normal‐bore retention gap (1–5 m×0.32 mm ID) was coupled to a narrow‐bore (5 m×0.1 mm ID×0.4 μm film thickness) analytical column using a standard press‐fit connector. The connection was tight and reliable, and hence suitable for hydrogen as carrier gas. The effect of pre‐column and analytical column connector, injection volume, pre‐column length, column inlet pressure, and analyte volatility on peak shape, peak broadening, and focusing are discussed. The precision of chromatographic data measurements and peak capacity under optimised temperature programmed conditions for fast separations with large volume injection were found to be very good. The presented fast GC set‐up with on‐column injection extends the applicability of the technique to trace analysis.     

Catalytic Oxidation of Methane to C2‐C4 Hydrocarbons over CeO2 Promoted W‐Mn/SiO2 Catalysts at Higher Pressure

CeO₂‐promoted Na‐Mn‐W/SiO₂ catalyst has been studied for catalytic oxidation of methane in a micro‐stainless‐steel reactor at elevated pressure. The effect of operating conditions, such as GHSV, pressure and CH₄/O₂ ratio, has been investigated. 22.0% CH₄ conversion with 73.8% C₂‐C₄ selectivity (C₂/C₃/C₄ = 3.8/1.0/3.6) was obtained at 1003 K, 1.5 × 10⁵ h^?;1 GHSV and 1.0 MPa. The results show: Elevated pressure disadvantages the catalytic oxidation of methane to C₂‐C₄ hydrocarbons. Large amounts of C₃ and C₄ hydrocarbons are observed. The unfavorable effects of elevated pressure can be overcome by increasing GHSV; the reaction is strongly dependent on the operating conditions at elevated pressure, particularly dependent on GHSV and ratio of CH₄/O₂. Analyses by means of XRD, XPS and CO₂‐TPD show that CO₂ produced from the reaction makes a weakly poisoning capacity of the catalyst; information of changeful valence on Ce and Mn was detected over the near‐surface of the Ce‐Na‐W‐Mn/SiO₂ catalyst; the existence of Ce³⁺/Ce⁴⁺ and Mn²⁺/Mn³⁺ ion couple supported that the reaction over the catalyst followed the Redeal‐Redox mechanism. Oxidative re‐coupling of C₂H₆ and CH₄ in gas phase or over surface of catalyst produces C₃ or C₄ hydrocarbons.     

Use of a recently developed thermal modulator within the context of comprehensive two‐dimensional gas chromatography combined with time‐of‐flight mass spectrometry: Gas flow optimization aspects

The present research is based on the use of a recently developed comprehensive two‐dimensional gas chromatography thermal modulator, which is defined as solid‐state modulator. The transfer device was installed on top of a single gas chromatography oven, while benchtop low‐resolution time‐of‐flight mass spectrometry was used to monitor the compounds exiting the second analytical column. The solid‐state modulator was first described by Luong et al. in 2016, and it is a moving modulator that does not require heating and cooling gases to generate comprehensive two‐dimensional gas chromatography data. The accumulation and remobilization steps occur on a trapping capillary, this being subjected to thermoelectric cooling and micathermic heating. In this study, the effects of the gas linear velocity on the modulation performance were evaluated by using two different uncoated trapping capillaries, viz., 0.8 m × 0.25 mm id and 0.8 m × 0.20 mm id. Solid‐state modulator applications were carried out on a standard solution containing n‐alkanes (C_9, C_10, C₁₂), and on a sample of diesel fuel. The results indicated that the type of trapping capillary and gas velocity have a profound effect on modulation efficiency.     

Borohydrides from Organic Hydrides: Reactions of Hantzsch’s Esters with B(C6F5)3

We report herein that the reaction between a series of Hantzsch’s ester analogues 1 a – d with the Lewis acidic species B(C₆F₅)₃ results in facile transfer of hydride to boron. The main products of this reaction are pyridinium borohydride salts 2 a – d , which are obtained in high to moderate yields. The N‐substituted substrates (N‐Me, N‐Ph) reacted in high yield 90–98 % and the connectivity of the products were confirmed by an X‐ray crystallographic analysis of the N‐Me borohydride salt 2 a . Unsubstituted Hanztsch’s ester 1 a reacted less effectively generating only 60 % of the corresponding borohydride salt, with the balance of the material sequestered as the ester‐bound Lewis acid–base adduct 3 a . Formation of the Lewis acid–base adduct could be minimized by increasing the steric bulk about the ester groups as in 1 d . The connectivity of the carbonyl‐bound adduct was confirmed by an X‐ray crystallographic analysis of 3 e the product of the reaction of methyl ketone 1 e with B(C₆F₅)₃. We also explored the generation of these pyridinium salts by employing frustrated Lewis pair methodology. However, the reaction of mixtures of the corresponding pyridine and B(C₆F₅)₃ with hydrogen gas only resulted in formation of trace amounts of the pyridinium borohydride, along with the Lewis acid–base adduct of the starting material and B(C₆F₅)₃. The 1,2‐dihydropyridine adduct was the final product of this reaction. This was ascribed to the low basicity of the pyridine nitrogen and the complicating formation of an ester bound Lewis acid–base adduct.     

The Chemical Bond in C2

Quantum chemical calculations using the complete active space of the valence orbitals have been carried out for H_nCCH_n (n=0–3) and N₂. The quadratic force constants and the stretching potentials of H_nCCH_n have been calculated at the CASSCF/cc‐pVTZ level. The bond dissociation energies of the C?C bonds of C₂ and HC≡CH were computed using explicitly correlated CASPT2‐F12/cc‐pVTZ‐F12 wave functions. The bond dissociation energies and the force constants suggest that C₂ has a weaker C?C bond than acetylene. The analysis of the CASSCF wavefunctions in conjunction with the effective bond orders of the multiple bonds shows that there are four bonding components in C₂, while there are only three in acetylene and in N₂. The bonding components in C₂ consist of two weakly bonding σ bonds and two electron‐sharing π bonds. The bonding situation in C₂ can be described with the σ bonds in Be₂ that are enforced by two π bonds. There is no single Lewis structure that adequately depicts the bonding situation in C₂. The assignment of quadruple bonding in C₂ is misleading, because the bond is weaker than the triple bond in HC≡CH.     

Capillary gas chromatography of lower aliphatic C2?C5 aldehydes in the free form as a group of pungent odorants in air

The capillary gas chromatography of the C₂-C₅ lower aliphatic aldehydes (e.g.,acetaldehyde, propionaldehyde, n- and i-butyraldehydes, n- and i-valeraldehydes) which, in the free form in air, have unpleasant odors and low threshold odor values, has been studied using cold-trap preconcentration with liquid oxygen. The capillary column outlet was connected to enable simultaneous detection by FID, ECD, FPD AND FTD (SID).     

Comparison of different mass spectrometry techniques in the measurement of L‐[ring‐13C6]phenylalanine incorporation into mixed muscle proteins

Precise measurement of low enrichment of stable isotope labeled amino‐acid tracers in tissue samples is a prerequisite in measuring tissue protein synthesis rates. The challenge of this analysis is augmented when small sample size is a critical factor. Muscle samples from human participants following an 8 h intravenous infusion of L‐[ring‐¹³C₆]phenylalanine and a bolus dose of L‐[ring‐¹³C₆]phenylalanine in a mouse were utilized. Liquid chromatography tandem mass spectrometry (LC/MS/MS), gas chromatography (GC) MS/MS and GC/MS were compared to the GC‐combustion‐isotope ratio MS (GC/C/IRMS), to measure mixed muscle protein enrichment of [ring‐¹³C₆]phenylalanine enrichment. The sample isotope enrichment ranged from 0.0091 to 0.1312 molar percent excess. As compared with GC/C/IRMS, LC/MS/MS, GC/MS/MS and GC/MS showed coefficients of determination of R² = 0.9962 and R² = 0.9942, and 0.9217 respectively. However, the precision of measurements (coefficients of variation) for intra‐assay are 13.0%, 1.7%, 6.3% and 13.5% and for inter‐assay are 9.2%, 3.2%, 10.2% and 25% for GC/C/IRMS, LC/MS/MS, GC/MS/MS and GC/MS, respectively. The muscle sample sizes required to obtain these results were 8 µg, 0.8 µg, 3 µg and 3 µg for GC/C/IRMS, LC/MS/MS, GC/MS/MS and GC/MS, respectively. We conclude that LC/MS/MS is optimally suited for precise measurements of L‐[ring‐¹³C₆]phenylalanine tracer enrichment in low abundance and in small quantity samples. Copyright © 2013 John Wiley & Sons, Ltd.     

Dynamic Entangled Porous Framework for Hydrocarbon (C2–C3) Storage,CO2 Capture,and Separation

Storage and separation of small (C1–C3) hydrocarbons are of great significance as these are alternative energy resources and also can be used as raw materials for many industrially important materials. Selective capture of greenhouse gas, CO₂ from CH₄ is important to improve the quality of natural gas. Among the available porous materials, MOFs with permanent porosity are the most suitable to serve these purposes. Herein, a two‐fold entangled dynamic framework {[Zn₂(bdc)₂(bpNDI)]?4DMF}_n with pore surface carved with polar functional groups and aromatic π clouds is exploited for selective capture of CO₂, C2, and C3 hydrocarbons at ambient condition. The framework shows stepwise CO₂ and C₂H₂ uptake at 195 K but type I profiles are observed at 298 K. The IAST selectivity of CO₂ over CH₄ is the highest (598 at 298 K) among the MOFs without open metal sites reported till date. It also shows high selectivity for C₂H₂, C₂H₄, C₂H₆, and C₃H₈ over CH₄ at 298 K. DFT calculations reveal that aromatic π surface and the polar imide (RNC=O) functional groups are the primary adsorption sites for adsorption. Furthermore, breakthrough column experiments showed CO₂/CH₄ C₂H₆/CH₄ and CO₂/N₂ separation capability at ambient condition.     

Towards perfunctionalized dodecahedranes--en route to C20 fullerene

“One‐pot” substitution of the twenty hydrogen atoms in pentagonal dodecahedrane (C₂₀H₂₀) by OH, F, Cl, and Br atoms is explored. Electrophilic insertion of oxygen atoms with DMDO and TFMDO as oxidizing reagents ended, far off the desired C₂₀(OH)₂₀, in complex polyol mixtures (up to C₂₀H₁₀(OH)₁₀ decols, a trace of C₂₀H(OH)₁₉?). Perfluorination was successful in a NaF matrix but (nearly pure) C₂₀F₂₀ could be secured only in very low yield. “Brute‐force” photochlorination (heat, light, pressure, time) provided a mixture of hydrogen‐free, barely soluble C₂₀Cl₁₆ dienes in high yield and C₂₀Cl₂₀ as a trace component. Upon electron‐impact ionization of the C₂₀Cl₁₆ material sequential loss of the chlorine atoms was the major fragmentation pathway furnishing, however, only minor amounts of chlorine‐free C₂₀⁺ ions. “Brute‐force” photobrominations delivered an extremely complex mixture of polybromides with C₂₀HBr₁₃ trienes as the highest masses. The MS spectra exhibited exclusive loss of the Br substituents ending in rather intense singly, doubly, and triply charged C₂₀H_4–0^+(2+)(3+) ions. The insoluble ～C₂₀HBr₁₃ fraction (C₂₀Br₁₄ trienes as highest masses) obtained along a modified bromination protocol, ultimately allowed the neat mass selection of C₂₀^? ions. The C₂₀Cl₁₆ dienes and C₂₀H_0–3Br_14–12 tri‐/tetraenes, in spite of their very high olefinic pyramidalization, proved resistant to oxygen and dimerization (polymerization) but added CH₂N₂ smoothly. Dehalogenation of the respective cycloaddition products through electron‐impact ionization resulted in C_22–24H_4–8⁺⁽²⁺⁾ ions possibly constituting bis‐/tris‐/tetrakis‐methano‐C₂₀ fullerenes or partly hydrogenated C₂₂, C₂₃, and C₂₄ cages.