As a basic metric of separation for comparing isothermal and temperature-programmed GC (gas chromatography), we used the separation measure. S (defined elsewhere). We used this metric as both a measure of separation of any two peaks, and a measure of separation capacity of arbitrary intervals where peaks can potentially exist. We derived several formulae for calculation of S for any pair of peaks regardless of their shape and the distance from each other in isothermal and temperature-programmed GC. The formulae for isothermal GC can be viewed as generalizations of previously known expressions while, in the case of temperature-programmed GC, no equivalents for the new formulae were previously known from the literature. In all formulae for S. we identified similar key component-metrics (solute separability, intrinsic efficiency of separation, specific separation measure, separation power) that helped us to identify and better understand the key factors affecting the separation process. These metrics also facilitated the quantitative comparison of separation capacities and analysis times in isothermal and temperature-programmed GC. Some of these metrics can be useful beyond GC. In the case of GC, we have shown that, if the same complex mixture was analyzed by the same column, and the same separation requirements were used then isothermal analysis can separate more peaks than its temperature-programmed counterpart can. Unfortunately, this advantage comes at the cost of prohibitively longer isothermal analysis time. The latter is a well know fact. Here, however, we provided a quantitative comparison. In a specific example, we have shown that a single-ramp temperature program with a typical heating rate yields about 25% fewer peaks than the number of peaks available from isothermal analysis of the same mixture using the same column. However, that isothermal analysis would last 1000 times longer than its temperature-programmed counterpart. Using twice as longer column in the case of a temperature-programmed analysis, allows one to recover the 25% disadvantage in the number of separated peaks, while still retaining a 500-fold advantage in the speed of analysis. 相似文献
Flow modulation of methane-doped carrier gas is used to visualize the second dimension hold-up time in GC × GC continuously throughout the run. This provides an internal reference of hold-up time and presents a straightforward means of examining retention in each dimension of GC × GC. Retention factors on similar and dissimilar column pairs are examined. Stationary phase bleed is shown to be retained by the second dimension column. 相似文献
Novel water‐insoluble, and reduction‐responsive nonwoven scaffolds were fabricated from γ‐PGA and tested in cell culture. An electrospinning method was developed to produce scaffolds of fibers with diameters of 0.05–0.5 µm. Crosslinking of the fibers with cystamine in the presence of EDC resulted in water‐insoluble γ‐PGA nonwovens with disulfide crosslinkages. These crosslinked fibers were easily decomposed under physiological conditions using L ‐cysteine, a biocompatible reductant. In vitro experiments with mouse L929 fibroblasts showed good adhesion onto γ‐PGA‐SS fiber matrices and excellent cell proliferation. These γ‐PGA‐SS nonwovens can be used as novel biocompatible and biodegradable scaffolds with reduction‐responsiveness for biomedical or tissue engineering applications.
Hyperbranched epoxide‐amine adducts were synthesized by a one‐pot microwave (MW) assisted reaction. 4‐(2,3‐epoxypropyl‐1‐oxy)benzonitrile was hydrogenated using Pd/C under microwave conditions, forming the AB2 monomer 1‐aminomethyl‐4‐(2,3‐epoxypropyl‐1‐oxy)benzene. Depending on the reaction temperature this monomer immediately reacts to give hyperbranched epoxide‐amine adducts. Mass spectrometric investigations proved the formation of a homologous series of oligomers containing up to six repeating units. Due to the complexing properties of the poly(amino alcohol) moieties in the presence of Cu2+ ions, large aggregates were formed.
Summary: The hydrogel poly(vinyl alcohol)-graft-poly[(rac-lactide)-co-glycolide)] [PVA-g-P(LGA)], containing nine ester groups in the polyester grafts (lactide:glycolide ratio 50:50) grafted onto PVA to an extent of 13%, and crosslinked via terminal acrylate groups was subjected to degradation experiments in phosphate buffer solution (pH 7.4) at room temperature and at 37 °C during 8 weeks. In the course of degradation, the properties of the hydrogel change as a result of the decrease of the polyester content. The increased temperature has a significant influence on the degradation rate but its amount varies with the methods applied. Thus, a large drop of the elastic modulus takes place in samples degraded at 37 °C with time and relative to RT. Thermal and IR analysis show changes while the initial difference between two sets of samples in contact angle is reduced with time. 相似文献
Chemical modification of recombinant hirudin (r‐hirudin) is necessary whenever surface‐confinement to a biomaterial or biotinylation for subsequent conjugation with carriers is intended. Here, we report a modification strategy that permits chemical discrimination between r‐hirudin's amino groups and preserves its thrombin inhibitor activity. By reaction with Msc‐ONSu, protective groups were successively introduced in r‐hirudin yielding four derivatives (Msc)x‐hirudin (1 ≤ x ≤ 4) and pure fractions were isolated by ion exchange chromatography. Structure–function relationships were studied for all derivatives and revealed a decrease in activity of more than 90% as compared to unprotected r‐hirudin. MALDI‐TOF MS was used to determine the locations of the Msc groups. Furthermore, evidence was provided that r‐hirudin's N‐terminal amino group is highly important for its anti‐thrombin activity. Selective modification of the lysine residues which maintained the free N‐terminal amino group preserved the anti‐thrombin activity of r‐hirudin even after biotinylation and subsequent linkage to streptavidin or confinement to a polymer surface. 相似文献
This paper is concerned with the various inner and outer radii of a convex bodyC in ad-dimensional normed space. The innerj-radiusrj(C) is the radius of a largestj-ball contained inC, and the outerj-radiusRj(C) measures how wellC can be approximated, in a minimax sense, by a (d —j)-flat. In particular,rd(C) andRd(C) are the usual inradius and circumradius ofC, while 2r1(C) and 2R1(C) areC's diameter and width.Motivation for the computation of polytope radii has arisen from problems in computer science and mathematical programming. The radii of polytopes are studied in [GK1] and [GK2] from the viewpoint of the theory of computational complexity. This present paper establishes the basic geometric and algebraic properties of radii that are needed in that study.Much of this paper was written when both authors were visiting the Institute for Mathematics and Its Applications, 206 Church Street S.E., Minneapolis, MN 55455, USA. The research of P. Gritzmann was supported in part by the Alexander-von-Humboldt Stiftung and the Deutsche Forschungsgemeinschaft. V. Klee's research was supported in part by the National Science Foundation. 相似文献
Cylindrical rock salt single crystals have been plastically deformed by compression in the [001]-direction at room temperature to shear stresser τE of 200 N/cm2 and 350 N/cm2, respectively. Isochronal annealing experiments reveal, that workhardening recovers at >300° C. The characteristic annealing temperature was found between 400° C and 450° C. At 600° C the residual workhardening still amounts to 15–20%. The isochronal reduction of screw dislocation density between 400 and 600° C shows qualitatively the same behaviour as recovery of workhardening. From the isothermal annealing curves of the samples deformed to 200 N/cm2 the activation energy for recovery of workhardening was found to be about 1 eV. Assuming that the kinetics of recovery can be explained by processes distributed in activation energy, an approximate spectrum of activation energies (with a maximum arising at ～1 eV) has been evaluated. The results show that recovery of workhardening after low deformation (stage I of the stress strain curve) is mainly due to the dislocations. 相似文献
