Windows Xc 2011 V2 3 Isomers

The trans isomers of 5,8,11,14,17-eicosapentaenoic acid (EPA) and 4,7,10,13,16,19-docosahexaenoic acid (DHA) methyl esters were prepared by isomerisation with paratoluenesulfinic acid (PTSA) in dioxane. The isomers were fractionated by silver ion liquid chromatography with baseline resolution between the isomers with different number of trans double bonds. The fractions were analysed by GC-MS and the gas chromatographic properties of the EPA and DHA isomers with one and two trans double bonds were investigated on BPX-70 and SP-2560 cyanopropyl stationary phases. Different temperature and pressure programs were applied to introduce variations in retention indices of the isomers. The retention indices of all the trans isomers showed a strong linear correlation to the retention indices of the equivalent all-cis isomer, but the slopes for corresponding linear regression lines varied with the number of trans double bonds in the molecule. The regression lines were used to predict optimal conditions for the separation of trans isomers from the corresponding all-cis isomers. For DHA on BPX-70, and for EPA on both columns, it was possible to find windows where isomers with one trans double bond can be resolved from the corresponding all-cis isomers with R(s) > 1.0. In general, BPX-70 seems to have a more suitable selectivity for the analysis of these isomers than SP-2560. Two-dimensional fatty acid retention indices (2D-FARI) were found to be suitable for identification of trans geometry in polyunsaturated fatty acids (PUFA). Although there were substantial overlaps in the range of retention times between the all-cis isomers and isomers with one and two trans double bonds, 2D-FARI separated the isomers into distinct groups according to the number of trans double bonds.

Number of particles detected in the plastic detector vs time in the cycle for the combined measurement of the decays of Zr102 and Nb102m. The first part of the spectrum corresponds to no implantation, useful to check the level of background previous to the measurement. Two different sorting time windows are shown as an example.

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Comparison of the DTAS -gated spectra for the measurement of Zr102+Nb102m sorted with different time windows set within the total length of the cycle (11.6 s). The lengths of the time windows presented are 0.25, 0.5, 1, 2, 3, 4, 5, 6 s, and full cycle.

Spectrum of the decay of Tc103 extracted with different time windows from the measurement of the decay of Mo103 (black dots with errors). The spectrum is compared with a direct measurement of the decay of Tc103 (blue).

Spectrum of the decay of Zr100 extracted with different time windows (dots with error bars) as explained in the text. The spectrum is compared with MC simulations of the decay of Zr100 assuming different -intensity distributions as input for the DECAYGEN event generator [50] (see the text).

Spectrum of the decay of Zr102 extracted with different time windows (dots with error bars) as explained in the text. The spectrum is compared with MC simulations of the decay of Zr102 assuming different -intensity distributions as input for the DECAYGEN event generator [50] (see the text).

The study of metabolites and gangliosides is increasingly important in drug discovery (1) and immunology (2). Accurate analysis of biologically relevant isomers is important because their structure affects their molecular properties. Typically, the isomers are separated using chromatography prior to mass spectrometry (MS) analysis. However, specialized chromatographic methods that distinguish isomers frequently require a complex setup and long runs. Techniques that allow accurate results to be acquired quickly and efficiently would be beneficial.

High performance ion mobility spectrometry (HPIMS) deploys atmospheric pressure short drift tube technology, enabling it to be coupled as a practical front-end to an MS device without breaking vacuum. High pressure is used to increase the number of ion collisions in a smaller space, boosting performance in a smaller footprint device. It offers a high degree of flexibility for separating isomers and other compounds (14).

Changing to a more polar drift gas is expected to affect the drift separation of molecules that could be polarized (15). Because this may impact the mobility of two molecules differently, the net separation can be increased or decreased (or remain unchanged) when introducing a more polar drift gas, which is shown for corticosterone and 21-deoxycortisol in figure 5. Comparing the spectra in 100% air and in a 45:55 mixture of air and CO2, the CO2-rich drift gas shows longer drift times. More importantly, the minor separation of the two isomers in 100% air increased significantly in the gas mixture, most notably for the protonated species, but the effect is also visible for the sodiated species, which reflects a relatively stronger influence of CO2 on the mobility of one isomer over the other.

The same approach was taken for the remaining isomer pairs. Prednisolone and cortisone increased in separation to 10% in the protonated species and 20% in the sodiated species for 25% CO2. Dexamethasone and betamethasone could be separated 15% in their polymer state ([2M + Na]+, 807.403 m/z) with the optimum found at 50% CO2. Although these pairs benefited from a mix with CO2 100% CO2 yielded almost no benefit compared to air. The increased separation of the epimeric isomers by observing the sodiated dimer (as compared to protonated or sodiated monomer) has been shown for many biologically relevant pairs with a variety of drift gases, but until now has not been explored for gas mixtures.

Drift gas variation also has potential in the analysis of other biomolecules, for example saccharide isomers. Combined with drift gas temperature variation and the addition of liquid modifiers, HPIMS on the orbital trap MS instrument offers a powerful addition to the toolbox in the investigation of a wide variety of samples (liquid, thermal desorption, or headspace [21]) and applications, including molecular characterization, isomer identification, analysis of protein conformation states, and characterization of complex mixtures like polymers and petrochemical samples (22).

As an alternative technology to energy intensive distillations, adsorptive separation by porous solids offers lower energy cost and higher efficiency. Herein we report a topology-directed design and synthesis of a series of Zr-based metal-organic frameworks with optimized pore structure for efficient separation of C6 alkane isomers, a critical step in the petroleum refining process to produce gasoline with high octane rating. Zr6O4(OH)4(bptc)3 adsorbs a large amount of n-hexane but excluding branched isomers. The n-hexane uptake is ~70% higher than that of a benchmark adsorbent, zeolite-5A. A derivative structure, Zr6O4(OH)8(H2O)4(abtc)2, is capable of discriminating all three C6 isomers and yielding a high separation factor for 3-methylpentane over 2,3-dimethylbutane. This property is critical for producing gasoline with further improved quality. Multicomponent breakthrough experiments provide a quantitative measure of the capability of these materials for separation of C6 alkane isomers. A detailed structural analysis reveals the unique topology, connectivity and relationship of these compounds.

Adsorption-based separation of hydrocarbons by porous solids can be divided into two categories according to the separation mechanism: kinetically controlled and thermodynamically controlled process6,7. The former is based on the difference in diffusion rate, or in an ideal scenario, on selective molecular exclusion (or sieving), which usually results in high selectivity, as illustrated by two well-known examples: zeolite 5A for the separation of linear and branched alkane isomers and chabazite zeolite (CHA) for the separation of propane and propylene8. In contrast, thermodynamically controlled separation is governed by the difference in affinity between distinct, freely diffused adsorbates and the framework. While it is usually less selective than kinetically controlled separation, thermodynamically controlled processes can be advantageous when adsorbates are very similar in size which would be difficult to discriminate by kinetic separation9.

Structural isomers of an alkane will have the same molecular formula but different structural arrangement. Alkanes are characterized by single bonds between carbon atoms, so structures with double bonds are not isomers of an alkane. Isomers can be identified by the different attachments of CH3 (methyl) groups to the carbon skeleton.

Structural isomers are molecules that have the same molecular formula but different structural arrangement. The given molecule is an alkane, and its isomers will have similar chain-like structures, but the carbon atoms will be connected differently. Note, the examples provided which have double bonds (=) do not represent isomers of this alkane, as these molecules are alkenes, and not alkanes.

According to the question, there is no specific model of an alkane given, therefore, it's hard to pick isomers accurately without knowing the precise structure of the alkane. However, a general rule to consider when looking for alkane isomers is to search for different attachments of CH3 (methyl) groups to the carbon skeleton.

Profiling cellular protein glycosylation is challenging due to the presence of highly similar glycan structures that play diverse roles in cellular physiology. As the anomericity and the exact linkage type of a single glycosidic bond can influence glycan function, there is a demand for improved and automated methods to confirm detailed structural features and to discriminate between structurally similar isomers, overcoming a significant bottleneck in the analysis of data generated by glycomics experiments. We used porous graphitized carbon-LC-ESI-MS/MS to separate and detect released N- and O-glycan isomers from mammalian model glycoproteins using negative mode resonance activation CID-MS/MS. By interrogating similar fragment spectra from closely related glycan isomers that differ only in arm position and sialyl linkage, product fragment ions for discrimination between these features were discovered. Using the Skyline software, at least two diagnostic fragment ions of high specificity were validated for automated discrimination of sialylation and arm position in N-glycan structures, and sialylation in O-glycan structures, complementing existing structural diagnostic ions. These diagnostic ions were shown to be useful for isomer discrimination using both linear and 3D ion trap mass spectrometers when analyzing complex glycan mixtures from cell lysates. Skyline was found to serve as a useful tool for automated assessment of glycan isomer discrimination. This platform-independent workflow can potentially be extended to automate the characterization and quantitation of other challenging glycan isomers. be457b7860