Validation of the accuracy of the perturbation peak method for determination of single and binary adsorption isotherm parameters in LC

An analytical validation of the precision and accuracy of the perturbation peak (PP) method for determination of single and competitive thermodynamic isotherm parameters was performed using frontal analysis as a reference. The isotherm parameters of 11alpha-hydroxyprogesterone were determined in an achiral system and the isotherm parameters of (+)-methyl L-mandelate and (-)-methyl D-mandelate were determined in a chiral system, both for the single components and for the competitive binary mixture. The experimental errors in the PP method using different injection techniques were investigated, and we devised a new injection technique for the determination of competitive isotherm parameters that considerably reduced the experimental errors and also made both perturbation peaks detectable. We showed that the PP method with the new injection technique can be used to determine isotherm parameters directly from a racemic mixture. These parameters agreed well with those determined using several enantiomer ratios. Elution-band profiles simulated using the isotherm parameters showed excellent agreement with experimental profiles.     

Second-order peak detection for multicomponent high-resolution LC/MS data

The first step when analyzing multicomponent LC/MS data from complex samples such as biofluid metabolic profiles is to separate the data into information and noise via, for example, peak detection. Due to the complex nature of this type of data, with problems such as alternating backgrounds and differing peak shapes, this can be a very complex task. This paper presents and evaluates a two-dimensional peak detection algorithm based on raw vector-represented LC/MS data. The algorithm exploits the fact that in high-resolution centroid data chromatographic peaks emerge flanked with data voids in the corresponding mass axis. According to the proposed method, only 4 per thousand of the total amount of data from a urine sample is defined as chromatographic peaks; however, 94% of the raw data variance is captured within these peaks. Compared to bucketed data, results show that essentially the same features that an experienced analyst would define as peaks can automatically be extracted with a minimum of noise and background. The method is simple and requires a priori knowledge of only the minimum chromatographic peak width-a system-dependent parameter that is easily assessed. Additional meta parameters are estimated from the data themselves. The result is well-defined chromatographic peaks that are consistently arranged in a matrix at their corresponding m/z values. In the context of automated analysis, the method thus provides an alternative to the traditional approach of bucketing the data followed by denoising and/or one-dimensional peak detection. The software implementation of the proposed algorithm is available at http://www.anchem.su.se/peakd as compiled code for Matlab.     

Characterization of structural parameters of porous materials by a new adsorption isotherm

A new adsorption isotherm equation, log logP=C+n logv, has been developed which characterizes many properties of the structure of porous materials, such as monolayer capacity of isotherms of Types I, II and IV, limiting micropore volume at extremely low pressure, degree and dispersion of micropores, mesopore surface area, mean pore size, etc. The equation has been successfully extended to binary and ternary mixtures, data for which have been obtained from the individual isotherms. It is also shown that a linear plot of the new isotherm implies that the distribution of adsorption volume with adsorption potential is Gaussian. Various other well know isotherm equations have been deduced from this new equation. The equation is direct and involves fewer mathematical calculations for solving the structural parameters of porous materials.     

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.     

Empirical determination of adsorption isotherm for nitrogen on glass for various conditions of vacuum and near-ambient temperature

We have measured the adsorption isotherm of nitrogen on glass in the ranges 10^?2–10^?3 torr and ?78–0°C and compared it with Hobson's theory.     

Validation of the tracer-pulse method for multicomponent liquid chromatography, a classical paradox revisited

The tracer-pulse method was extended and validated for the determination of multicomponent adsorption isotherms in liquid chromatography. Competitive adsorption isotherms can be determined for any number of solutes, up to the column resolution limit. The basic principle is to equilibrate the column with an eluent containing a mixture of the solutes and then measure the migration velocity of each of them through the column. It is easy to calculate the stationary phase concentrations from these velocities, given the eluent composition. As in frontal analysis, real competitive isotherm data are measured using this method, unlike other methods, which only produce parametric estimates. The method was used to measure the binary isotherms of beta-blockers on a Kromasil C8 column. The data were fitted to competitive bi-Langmuir adsorption isotherm functions and was found to agree well with the results of frontal analysis and the perturbation method. Computer simulations based on the isotherm parameters were performed and displayed very good agreement with the experimental chromatograms. An intriguing and seemingly paradoxical property is visualized and discussed: the fact that the injected molecules are not found in the detected peaks.     

A LC/MS method for the determination of cyanobacteria toxins in water

The cyanobacteria toxins anatoxin-a, microcystin-LR, microcystin-RR, microcystin-YR, and nodularin were separated in less than 30 min on several 1 mm x 15 cm reversed-phase liquid chromatography (LC) columns, and their electrospray mass spectra were measured using injections of 50 ng or less with a benchtop time-of-flight (TOF) mass spectrometer. New data from this work include the following: (a) the impact of acetic acid concentrations in the methanol-water mobile phase on measured ion abundances; (b) the performance of the electrospray-TOF mass spectrometer as an LC detector; (c) the accuracy and precision of exact m/z measurements after LC separation with a routinely used mass spectrometer resolving power of 5000; and (d) recoveries of the five toxins from reagent water, river waters, and sewage treatment plant effluent samples extracted with C-18 silica particles enmeshed in thin Teflon membrane filter disks. This technique has the potential of providing a relatively simple and reasonable-cost sample preparation and LC/MS method that provides the sensitivity, selectivity, reliability, and information content needed for source and drinking water occurrence and human exposure studies.     

Characterisation of structural parameters of finely divided and porous materials by a new adsorption isotherm

An adsorption isotherm log log p = C+nlog v was developed and applied earlier. The isotherm has been used to determine the structural parameters of adsorbents. The application of the isotherm has been extended to determine separation factor of mixture of gases, surface area of adsorbed monolayer from energy consideration, categorisation of micropores etc. It is shown that equation of Lewis et al. for partial adsorption and equation of Langmuir can be deduced from isotherm equation of John. Advantages of John's isotherm are enumerated.     

Comparison of linear and non-linear method in estimating the sorption isotherm parameters for safranin onto activated carbon

Comparison analysis of linear least square method and non-linear method for estimating the isotherm parameters was made using the experimental equilibrium data of safranin onto activated carbon at two different solution temperatures 305 and 313 K. Equilibrium data were fitted to Freundlich, Langmuir and Redlich-Peterson isotherm equations. All the three isotherm equations showed a better fit to the experimental equilibrium data. The results showed that non-linear method could be a better way to obtain the isotherm parameters. Redlich-Peterson isotherm is a special case of Langmuir isotherm when the Redlich-Peterson isotherm constant g was unity.     

Model-independent method for the determination of guiding thin-film optical parameters

A method for the determination of the optical constants of thin films based on the combination of a waveguide measurement procedure with the spectroscopic measurements made from the UV to the IR is presented. As a test material AlN thin film on sapphire substrates is investigated.     

LC/MS/MS method for quantitative determination of long-chain fatty acyl-CoAs

Long-chain acyl-CoA esters (LCACoAs) are activated lipid species that represent key substrates in lipid metabolism. The relationship between lipid metabolism disorders and type 2 diabetes has attracted much attention to this class of metabolites. This paper presents a highly sensitive and robust on-line LC/MS(2) procedure for quantitative determination of LCACoAs from rat liver. A fast SPE method has been developed without the need for time-consuming evaporation steps for sample preparation. LCACoAs were separated with high resolution using a C18 reversed-phase column at high pH (10.5) with an ammonium hydroxide and acetonitrile gradient. Five LCACoAs (C16:0, C16:1, C18:0 C18:1, C18:2) were quantified by selective multireaction monitoring using a triple quadrupole mass spectrometer in positive electrospray ionization mode. It is possible to perform a neutral loss scan of 507 for lipid profiling of complex LCACoA mixtures in tissue extracts. The method presented was validated according to ICH guidelines for quantitative determination of five LCACoAs for physiological concentrations in 100-200 mg of tissue with accuracies ranging from 94.8 to 110.8%, interrun precisions between 2.6 and 12.2%, and intrarun precisions between 1.2 and 4.4%. Due to the high sensitivity of the developed method, the amount of tissue biopsied for reliable quantification can be reduced. This may be advantageous in the quantification of LCACoAs in humans.     

A method for determination of parameters of wet solids in the drying process

The possibility of determining the moisture and temperature gradients in real wet solids of irregular shape, inhomogeneous composition, etc. by simplified engineering methods is described.Institute of Nuclear Sciences Vina, Laboratory of Thermal Engineering and Power, Mechanical Engineering Faculty, Belgrade University, Yugoslavia. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 66, No. 1, pp. 87–92, January, 1994.     

Comparative analysis of linear and non-linear method of estimating the sorption isotherm parameters for malachite green onto activated carbon

The experimental equilibrium data of malachite green onto activated carbon were fitted to the Freundlich, Langmuir and Redlich-Peterson isotherms by linear and non-linear method. A comparison between linear and non-linear of estimating the isotherm parameters was discussed. The four different linearized form of Langmuir isotherm were also discussed. The results confirmed that the non-linear method as a better way to obtain isotherm parameters. The best fitting isotherm was Langmuir and Redlich-Peterson isotherm. Redlich-Peterson is a special case of Langmuir when the Redlich-Peterson isotherm constant g was unity.     

Fuzzy interval perturbation method for uncertain heat conduction problem with interval and fuzzy parameters

This paper proposes a fuzzy interval perturbation method (FIPM) and a modified fuzzy interval perturbation method (MFIPM) for the hybrid uncertain temperature field prediction involving both interval and fuzzy parameters in material properties and boundary conditions. Interval variables are used to quantify the non‐probabilistic uncertainty with limited information, whereas fuzzy variables are used to represent the uncertainty associated with the expert opinions. The level‐cut method is introduced to decompose the fuzzy parameters into interval variables. FIPM approximates the interval matrix inverse by the first‐order Neumann series, while MFIPM improves the accuracy by considering higher‐order terms of the Neumann series. The membership functions of the interval temperature field are eventually derived using the fuzzy decomposition theorem. Three numerical examples are provided to demonstrate the feasibility and effectiveness of the proposed methods for solving heat conduction problems with hybrid uncertain parameters, pure interval parameters, and pure fuzzy parameters, respectively. Copyright © 2015 John Wiley & Sons, Ltd.     

小麦PFC模型细观参数标定方法的验证与分析

为了验证PFC模型细观参数标定方法的可行性,以小麦试样为例,根据PFC软件提供的模型细观参数标定方法的要求,在实验室进行了三轴压缩试验,并利用PFC软件对实验室三轴压缩试验进行了数值模拟。结果表明:通过反复调整PFC模型细观参数能够使数值模拟结果与试验结果基本一致,但很难使二者完全吻合。同等条件下,数值模型的颗粒摩擦系数对偏应力峰值的影响显著,颗粒法向刚度控制偏应力-应变关系曲线的初始斜率,颗粒孔隙率影响偏应力-应变关系曲线达到峰值后的平缓趋势。     

A method for the determination of the parameters of the hysteresismodel of magnetic materials

Many methods have been proposed for the determination of the hysteresis loops of magnetic materials, and many mathematical approaches have been proposed to find a good model for the hysteresis phenomenon. However, very few attempts have been made to determine the parameters of the hysteresis model experimentally. This paper shows how, starting from a digital method for the experimental determination of the hysteresis loop under different maximum induction values, the parameters of a hysteresis model can be automatically estimated with good accuracy. Due to its good behavior in terms of accuracy and to the comparative ease in determining its parameters, the Preisach model for rate-independent hysteresis phenomena was chosen. Experimental determination of the model and consequent hysteresis loop computation were carried out. An accuracy below 1% was attained over the peak induction range from 0.49 T to 1.68 T and the frequency range from 50 Hz to 100 Hz     

Equilibrium data, isotherm parameters and process design for partial and complete isotherm of methylene blue onto activated carbon

Equilibrium data for the adsorption of methylene blue onto activated carbon was reported. The equilibrium data were splitted to different data sets to have an idea on the partial and complete isotherm. The equilibrium data were analyzed using Freundlich, Langmuir and Redlich-Peterson isotherm. The influence of partial isotherm and complete isotherm on the equilibrium parameters in isotherm expression were estimated. Equilibrium data covering the complete isotherm is the best way to obtain the parameters in isotherm expressions. Present investigation showed that for successful batch sorber design, equilibrium data with partial isotherm is not sufficient, instead equilibrium data that covers complete isotherm is required. Redlich-Peterson and Langmuir isotherm well represent the adsorption of methylene blue onto activated carbon. Redlich-Peterson isotherm is a special case of Langmuir when the constant 'g' equals unity.