Characteristic Point Method Research Articles

The Competitive Adsorption of Water and Methanol on a Hybrid Silica Stationary Phase in Supercritical Fluid Chromatography

This study investigates the adsorption of methanol, water, and their mixture in a hybrid silica stationary phase with supercritical carbon dioxide as a mobile phase in supercritical fluid chromatography (SFC). The adsorption isotherms of methanol and water were determined by two dynamic methods: the elution by characteristic point (ECP) method and the inverse method (IM). Both the single-component and competitive bi-Langmuir models were pre-selected for the inverse method. The initial parameters of the single-component isotherm for both methanol and water were estimated with the ECP method by fitting the experimental data to the bi-Langmuir isotherm model. Then, using the inverse method, we refined the single-component isotherm parameter values, which were then further used for determining the competitive isotherm of the methanol–water mixture. The elution profile of the (methanol–water) mixture sample was calculated by the equilibrium-dispersive (ED) model. The results indicated that there is a good agreement between the experimental band profile and the calculated band profile, which was obtained from the parameters of the competitive bi-Langmuir isotherm model, revealing a competition between methanol and water to reach the adsorption sites. Furthermore, the saturation capacity of the adsorption sites in the stationary phase decreased in the case of the mixture sample compared to those for the single-component sample.

Seismic design of hybrid unbonded post-tensioned precast concrete joints based on bearing capacity and energy dissipation capacity

This paper provides a practical design method for hybrid unbonded post-tensioned precast concrete joints. Such joints featured with self-centering capacities have been widely favored in recent years. However, the absence of design methods hinders their further promotion. To solve the issue, two methods for calculating mechanical behavior of the joints were first studied: characteristic points method and iterative method. The effectiveness of the methods was verified by the existing test results. On this basis, a joint design method considering both yield bearing capacity and energy dissipation capacity was proposed. Moreover, to facilitate design, some factors affecting the bearing capacity were discussed. A five-story frame structure was designed by the proposed design method, and the influence of two design factors on structural response was analyzed by utilizing nonlinear time-history method. The analysis results show that: with the increase of energy dissipation factor αs, the post-earthquake residual deformation of the structure tends to increase linearly, while the accumulated damage of the structure will decrease continuously; both overdesign and underdesign of bearing capacity of the joint are unfavorable; and near-field earthquake may cause irreparable damage to structural columns, making the residual deformation of structures contrary to the self-centering capacity of joints, which shall be considered during engineering design.

Adsorption Equilibria of Rutin and Kaempferol-3-O-Rutinoside on CN-Bonded Silica from Supercritical Carbon Dioxide/Methanol

Rutin and K3R (kaempferol-3-O-rutinoside) in tartary buckwheat are flavonol glycosides with high medical value. It is necessary to separate them from tartary buckwheat before utilization because of their different medical functions. However, they have very similar molecular structures, causing troubles in thorough separation. The adsorption equilibrium of rutin and K3R from supercritical CO2/methanol was investigated. The adsorption capacities were measured by the elution at characteristic point method at 308.15, 313.15, and 318.15 K with 0.450–0.693 g/cm3 CO2/methanol on CN-bonded silica. The adsorption capacity of rutin and K3R showed a decreasing trend with the increasing mobile phase density and temperature. The capacity of rutin is larger than that of K3R under the same conditions, indicating that rutin was an easily adsorbed component. The data obtained from adsorption equilibria were fitted by both Freundlich and Langmuir isotherm models, which showed that the latter one performed better. This single-component model can extend to binary component and describe the competitive behavior well. Data and models obtained can be used to simulate adsorptive separation processes so as to design and optimize the separation process of rutin and K3R with supercritical fluid chromatography.

Adsorption equilibria of paeoniflorin and albiflorin on cyano-silica column from supercritical carbon dioxide/ethanol

Abstract Adsorption equilibria of paeoniflorin and albiflorin on a cyano-silica column (CN column) from the solution of supercritical carbon dioxide (scCO2) modified with ethanol were studied. The adsorption capacity at 308.15 K, 313.15 K, 318.15 K and 323.15 K under pressures corresponding to carbon dioxide/ethanol densities from 0.347 g·cm− 3 to 0.662 g·cm− 3 were determined using the elution by characteristic point method (ECP). The effects of temperature and pressure on the solute loading were investigated. The results showed that the lower the temperature, the higher the adsorption capacity. With the decrease of density of scCO2, the adsorption capacity strengthens. The maximum adsorption capacity of paeoniflorin (albiflorin) on the CN column was 15.24 mg·ml− 1 (31.14 mg·ml− 1) in the range of 0–1.84 mg·ml− 1 (0–1.67 mg·ml− 1) of paeoniflorin (albiflorin) standard solution. The adsorption capacity of albiflorin was twice as much as that of paeoniflorin under the same conditions. Adsorption data of paeoniflorin and albiflorin could be well described by the Langmuir model and Freundlich model. Compared with the two model fitting results, the adsorption of paeoniflorin and albiflorin belonged to the monolayer adsorption under conditions of 308.15–323.15 K and 10–17 MPa.

Extended Elution by Characteristic Point Method for Characterization of Protein Ion‐Exchange Adsorption

AbstractAn adequate characterization of adsorption isotherms is mandatory for chromatographic process development. Here, the elution by characteristic point (ECP) is a suitable method with low consumption of material and time. However, the ECP method requires a highly ideal behavior of the measured system. An innovative extended ECP approach is presented to characterize a non‐ideal system by the example of protein ion‐exchange adsorption. A marker, here bovine hemoglobin, is used to quantify all non‐idealities, e.g., convection, dispersion, or low number of theoretical plates. The system signal of the marker is used to compensate the system signal of the interesting solute, here bovine serum albumin. The resulting isotherm agrees well with the control results of a validated static approach.

Modeling adsorption on energetically heterogeneous surfaces with an extended SAFT-VR approach

Adsorption equilibria of methanol/carbon dioxide mixtures on plain silica particles at 308K and pressures of 10.1MPa, 12.7MPa, 15.1MPa and 20.1MPa were measured with the frontal analysis by characteristic points (FACP) method using supercritical fluid chromatography. The data show a bimodal adsorption energy distribution and cannot be sufficiently modeled with a two-dimensional SAFT-VR approach. Therefore, an extension of SAFT-VR is proposed to model adsorption on heterogeneous surfaces and applied to the presented data. It can be described by the extended model with very low ARDs between 1.0% and 2.4%.

A Comprehensive Database of Flood Events in the Contiguous United States from 2002 to 2013

Abstract Notwithstanding the rich record of hydrometric observations compiled by the U.S. Geological Survey (USGS) across the contiguous United States (CONUS), flood event catalogs are sparse and incomplete. Available databases or inventories are mostly survey- or report-based, impact oriented, or limited to flash floods. These data do not represent the full range of flood events occurring in CONUS in terms of geographical locations, severity, triggering weather, or basin morphometry. This study describes a comprehensive dataset consisting of more than half a million flood events extracted from 6,301 USGS flow records and radar-rainfall fields from 2002 to 2013, using the characteristic point method. The database features event duration; first- (mass center) and second- (spreading) order moments of both precipitation and flow, flow peak and percentile, event runoff coefficient, base flow, and information on the basin geomorphology. It can support flood modeling, geomorphological and geophysical impact studies, and instantaneous unit hydrograph and risk analyses, among other investigations. Preliminary data analysis conducted in this study shows that the spatial pattern of flood events affected by snowmelt correlates well with the mean annual snowfall accumulation pattern across CONUS, the basin morphometry affects the number of flood events and peak flows, and the concentration time and spreadness of the flood events can be related to the precipitation first- and second-order moments.

Using the local adsorption equilibrium distribution based on a Langmuir type adsorption model to investigate liquid phase adsorption of sugars on zeolite BEA

Adsorption isotherms generated by the Elution by Characteristic Point Method were used to determine the local adsorption equilibrium distribution (AEqD) on commercial zeolite BEA 150 extrudate pellets at room temperature. The linear sugar alcohol sorbitol and the circular sugar fructose were used as sensor molecules since both showed a rather strong adsorption with a typical type I isotherm. The expectation maximization method was transferred into a MATLAB code to calculate the most probable AEqD explaining the experimental data. The resulting distribution favors a bi-site Langmuir model that is in good agreement with the pore sizes of this zeolite, the critical diameters of the adsorptive molecules and gas phase experiments conducted previously. In summary, both molecules are too big to enter the zigzag channels of the zeolite. Instead they occupy two different binding sites in the straight channels and at the intersections between the straight and the zigzag channels. Therefore, sugars and sugar alcohol can be a good sensor to investigate the interaction between a zeolite crystal and adsorptive molecules in the liquid phase.

Zastosowanie skanerów 3D w technice wojskowej

In the article is presented a method to identify geometry of military objects based on 3D scanning technology and photogrammetric processes. During the scanning process different types of markers and calibrated patterns of length, placed on the object are used. Results of measurements using three different methods: base points measurementare method, 3D scanning method and 3D scanning in conjunction with the measurement geometry characteristic points method.

Adsorption equilibrium for Z-ligustilide on C18-bonded silica from supercritical carbon dioxide

Adsorption equilibrium is of great importance for the preparative supercritical fluid chromatography (pre-SFC) in defining supercritical adsorption behavior and the industrial amplification. This paper presents adsorption isotherms of Z-ligustilide from supercritical carbon dioxide (SC-CO2) on C18-bonded silica. Adsorption behavior was studied at 305.15K, 313.15K and 323.15K with SC-CO2 density varying from 0.687g·cm−3 to 0.863g·cm−3 with the elution by characteristic points (ECP) method. The adsorption amount of Z-ligustilide from SC-CO2 on C18-bonded silica decreased with the increasing density of the mobile phase as well as the increasing temperature. Adsorption equilibrium data were fitted by Langmuir and Freundlich isotherm models, and the Langmuir isotherm model performed better for describing the whole adsorption process on the column. The monolayer saturation adsorption capacity of Z-ligustilide is in the range of 3.0×10−4mg·cm−3 to 5.5×10−4mg·cm−3 with an average value of 4.0×10−4mg·cm−3.

Expanding the elution by characteristic point method to columns with a finite number of theoretical plates

The elution by characteristic point (ECP) method provides a rapid approach to determine whole isotherm data with small material usage. It is especially desired wherever the adsorbent or the adsorbate is expensive, toxic or only available in small amounts. However, the ECP method is limited to adsorbents that are well optimized for chromatographic use and therefore provide a high number of theoretical plates when packed into columns (2000 or more for Langmuir type isotherms are suggested). Here we present a novel approach that uses a new profile correction to apply the ECP method to poorly optimized adsorbents with less than 200 theoretical plates. Non-ideality effects are determined using a dead volume marker injection and the resulting marker profile is used to compensate the named effects considering their dependency from the actual concentration instead of assuming rectangular profiles. Experimental and literature data are used to compare the new ECP approach with batch method results.

Adsorption equilibrium of citric acid from supercritical carbon dioxide/ethanol on cyano column

Supercritical adsorption equilibrium has a significant role in defining supercritical adsorption behavior. In this paper, the adsorption equilibrium of citric acid from supercritical CO2/ethanol on a cyano column was systematically investigated with the elution by characteristic point method. Equilibrium loading was obtained at 313.15K and 321.15K with supercritical CO2/ethanol densities varying from 0.7068g·cm−3 to 0.8019g·cm−3. The experimental results showed that the adsorption capacity of citric acid decreased with increasing temperature and increasing density of the supercritical CO2/ethanol mobile phase. The adsorption equilibrium data were fitted well by the Quadratic Hill isotherm model and the isotherms showed anti-Langmuir behavior. The monolayer saturation adsorption capacity of citric acid is in the range of 44.54mg·cm−3 to 64.66mg·cm−3 with an average value of 56.86mg·cm−3.

Model Identification of Traveling Wave Ultrasonic Motor Using Step Response

Ultrasonic motor’s model adapting to control application is the foundation of the motor’s high performance control. Ultrasonic motor’s frequency-speed control model gives a signification to improve speed control performance. This paper shows the design of stepping response experiments, and also explains the model identification of USM by the way of characteristic point method. Considering its time-varying characteristic, model parameters can be fitted using functions with the independent variable is frequency or speed. Consequently, non-linearity can reflect in speed control model appropriately.

Mechanical behavior and failure criterion of the gangue-based haydite concrete under triaxial loading

Triaxial loading tests were carried out on the gangue-based haydite concrete cube specimens (100 × 100 × 100 mm3) and plate specimens (100 × 100 × 50 mm3) to investigate the mechanical behavior of this kind of lightweight aggregate concrete (LWAC) under multi-axial stress state, and accordingly to develop the failure criterion for the finite element analysis of LWAC structures. Experimental results revealed that, under triaxial compression loading, most of the haydites within the specimen were crushed when the stress ratios σ 1/ σ 3 ≥ 0.3 and σ 2/ σ 3 ≥ 0.5. The gangue haydite concrete exhibited “plastic flow plateau” at this stage, which was conservatively regarded as the ultimate strength of the LWAC under triaxial compressive stress state. As a result, the tensile and compressive meridians on failure envelope surface are intersected with hydrostatic axial at two points, completely different from the characteristics of normal weight concrete for which the failure surface is unclosed and open-ended under compression. In terms of the test data, a four-parameter triaxial failure criterion for LWAC was developed. The strength envelope in the deviatoric plane adopted elliptic curve similar to that of Willam–Warnke model, and the tensile and compressive meridians were represented by quadratic functions with four parameters. Two alternative methods, i.e. the characteristic strength points method and the least square regression method, were used to determine the model parameters. After compared with the failure criterion recommended by fib Model Code 2010, methods proposed in this study are preferred especially when the plastic flow property is taken into account.

Expanding the elution by characteristic point method for determination of various types of adsorption isotherms

Important improvements have recently been made on the elution by characteristic point (ECP) method to increase the accuracy of the determined adsorption isotherms. However, the method has so far been limited/used for only type I adsorption isotherms ( e.g. Langmuir, Tóth, bi-Langmuir). In this study, general strategies are developed to expand the ECP method for the determination of more complex adsorption isotherms including such containing inflection points. We will exemplify the methodology with type II, type III and type V isotherms. Guidelines are given for how to determine such isotherms using the ECP method and for the experimental considerations that must be taken into account or that may be eliminated in the particular case.

Determination of chromatographic separation parameters of tryptophan enantiomers on a Chirosil-SCA chiral stationary phase by using the inverse method based on the initial guesses estimated from elution by characteristic point method

An effective chiral stationary phase (CSP) for enantioseparation of amino acids was established previously by bonding (18-crown-6)-2, 3, 11, 12-tetracarboxylic acid to silica gel. This CSP has recently been commercialized under the name of Chirosil-SCA. As a first step for developing a Chirosil-SCA simulated moving bed chromatographic process for separation of tryptophan enantiomers, the adsorption isotherm and mass-transfer parameters of each tryptophan enantiomer on the Chirosil-SCA CSP were determined in this study while using only water as a mobile phase. For this task, inverse method (IM) was applied on the basis of the initial guesses estimated from elution by characteristic point (ECP) method, which was found to be more advantageous in the aspects of both accuracy and computational efficiency than the case of utilizing individually only IM or ECP method. The results revealed that the adsorption behavior of each tryptophan enantiomer on the Chirosil-SCA could be well described by the Langmuir–Freundlich isotherm. The model predictions based on the determined parameter values were in close agreement with the experimental chromatograms from a series of single-component or mixture pulse tests that were performed under various feed concentrations and flow rates. It was also found that the Langmuir–Freundlich isotherm parameters of each enantiomer were largely affected by temperature. Such a marked dependence of the parameters on temperature was investigated quantitatively. The results of such an investigation indicated that as the temperature decreases, the adsorption affinities of both enantiomers become higher and the heterogeneity of the Chirosil-SCA becomes more pronounced.

Improvement in the generation of adsorption isotherm data in the elution by characteristic points method—The ECP-slope approach

The elution by characteristic points (ECP) method is a very rapid and precise method for determination of the phase system equilibrium of phase systems in broad solute concentration ranges. Thus, the method is especially suitable for rapid characterization of high efficient separation systems. One important source of error, the effects by the post-loop dispersion, was eliminated in a recent investigation. In this study, the systematic error caused by the selection of the integration starting point at concentration equal to 0 is eliminated. This is done by developing and validating a new procedure for isotherm data generation; the ECP-slope method. The method generates raw slope data of the adsorption isotherm instead of raw adsorption data by integrations as the classical ECP does. Both numerical and experimental data were used for the comparison of the classical ECP approach with the slope-ECP method.

Enantioseparation of racemic paroxol on an amylose‐based chiral stationary phase by supercritical fluid chromatography

The separation of racemic paroxol, a key precursor of trans-(-)-paroxetine, on Chiralpak AD-H, an amylose-based chiral stationary phase, by supercritical fluid chromatography was studied. Pulse experiments were investigated using supercritical carbon dioxide modified with methanol (MeOH), ethanol and 2-propanol at 35°C and 15 MPa. Retention and separation factors were determined under analytical conditions for different mobile phase compositions. Among the modifiers used, MeOH was shown to be the best additive, and 5% v/v of MeOH was the preferable concentration at which selectivity of 1.14 and resolution of 3.0 was obtained. In order to evaluate the potential with respect to preparative separations, the adsorption isotherms of individual enantiomers of paroxol were estimated using the elution by characteristic point method. Isotherm parameters were determined from the overloaded elution profiles that were collected at pressure ranging from 15 to 24 MPa. The isotherms obtained were further validated by comparing experimentally recorded elution profiles with the predictions based on the equilibrium-dispersive model. The results are important to the process design and optimization of preparative supercritical fluid chromatography application.

Investigation of the adsorption behavior of glycine peptides on 12% cross-linked agarose gel media

The highly cross-linked 12% agarose gel Superose 12 10/300 GL causes retardation of glycine peptides when mobile phases containing varying concentrations of acetonitrile in water are used. An investigation has been made into the retention mechanism behind this retardation using the glycine dipeptide (GG) and tripeptide (GGG) as models. The dependence of retention times of analytical-size peaks under different experimental conditions was interpreted such that the adsorption most probably was caused by the formation of hydrogen bonds but that electrostatic interactions cannot be ruled out. Thereafter, a nonlinear adsorption study was undertaken at different acetonitrile content in the eluent, using the elution by characteristic points (ECPs) method on strongly overloaded GG and GGG peaks. With a new evaluation tool, the adsorption energy distribution (AED) could be calculated prior to the model selection. These calculations revealed that when the acetonitrile content in the eluent was varied from 0% to 20% the interactions turned from (i) being homogenous (GG) or mildly heterogeneous (GGG), (ii) via a more or less stronger degree of heterogeneity around one site to (iii) finally a typical bimodal energy interaction comprising of two sites (GG at 20% and GGG at 10% and 20%). The Langmuir, Tóth and bi-Langmuir models described these interesting adsorption trends excellently. Thus, the retardation observed for these glycine peptides is interpreted as being of mixed-mode character composed of electrostatic bonds and hydrogen bonds.

Injection Technique for Generating Accurate Adsorption Isotherm Data Using the Elution by Characteristic Points Method

With the use of the elution by characteristic points (ECP) method, the adsorption isotherms are rapidly determined from the diffusive part of an overloaded elution profile. However, very large injection volumes are required, which lead to extremely tailed rears of the injection profiles. The ECP method is based on a theory assuming rectangular injection profiles and can therefore not account for such profiles. Consequently, the use of the ECP method in the traditional way, with classical full-loop injections, results in serious errors on the determined adsorption isotherm parameters which has not been demonstrated until this study. Therefore, we developed and validated a new experimental injection method, here denoted the "cut-injection" technique where instead nearly rectangular injection profiles are generated. The result convincingly shows that adsorption isotherms acquired by using the new cut-injection technique nearly totally coincide with adsorption isotherms determined using the accurate reference methods.