This is the third part of a three‐part series of papers. In Part I, we presented a method for determining the actual effective geometry of a reference column as well as the thermodynamic‐based parameters of a set of probe compounds in an in‐house mixture. Part II introduced an approach for estimating the actual effective geometry of a target column by collecting retention data of the same mixture of probe compounds on the target column and using their thermodynamic parameters, acquired on the reference column, as a bridge between both systems. Part III, presented here, demonstrates the retention time transfer and prediction from the reference column to the target column using experimental data for a separate mixture of compounds. To predict the retention time of a new compound, we first estimate its thermodynamic‐based parameters on the reference column (using geometric parameters determined previously). The compound's retention time on a second column (of previously determined geometry) is then predicted. The models and the associated optimization algorithms were tested using simulated and experimental data. The accuracy of predicted retention times shows that the proposed approach is simple, fast, and accurate for retention time transfer and prediction between gas chromatography columns. 相似文献
The transfer of thermodynamic parameters governing retention of a molecule in gas chromatography from a reference column to a target column is a difficult problem. Successful transfer demands a mechanism whereby the column geometries of both columns can be determined with high accuracy. This is the second part in a series of three papers. In Part I of this work we introduced a new approach to determine the actual effective geometry of a reference column and thermodynamic‐based parameters of a suite of compounds on the column. Part II, presented here, illustrates the rapid estimation of the effective inner diameter (or length) and the effective phase ratio of a target column. The estimation model based on the principle of least squares; a fast Quasi‐Newton optimization algorithm was developed to provide adequate computational speed. The model and optimization algorithm were tested and validated using simulated and experimental data. This study, together with the work in Parts I and III, demonstrates a method that improves the transferability of thermodynamic models of gas chromatography retention between gas chromatography columns. 相似文献
Thermodynamics‐based models have been demonstrated to be useful for predicting retention time and peak widths in gas chromatography and two‐dimensional gas chromatography separations. However, the collection of data to train the models can be time consuming, which lessens the practical utility of the method. In this contribution, a method for obtaining thermodynamic‐based data to predict peak widths in temperature‐programmed gas chromatography is presented. Experimental work to collect data for peak width prediction is identical to that required to collect data for retention time prediction using approaches that we have presented previously. Using this combined approach, chromatograms including retention times and peak widths are predicted with very high accuracy. Typical errors in retention time are < 0.5%, while errors in peak width are typically < 5% as demonstrated using polycycic aromatic hydrocarbons and a mixture containing compounds with aldehyde, ketone, alkene, alkane, alcohol, and ester functionalities. 相似文献
We present an algorithm for reducing the computational work involved in coupled‐cluster (CC) calculations by sparsifying the amplitude correction within a CC amplitude update procedure. We provide a theoretical justification for this approach, which is based on the convergence theory of inexact Newton iterations. We demonstrate by numerical examples that, in the simplest case of the CCD equations, we can sparsify the amplitude correction by setting, on average, roughly 90% nonzero elements to zeros without a major effect on the convergence of the inexact Newton iterations. 相似文献
Recent applications of retention modelling in liquid chromatography (2015–2020) are comprehensively reviewed. The fundamentals of the field, which date back much longer, are summarized. Retention modeling is used in retention‐mechanism studies, for determining physical parameters, such as lipophilicity, and for various more‐practical purposes, including method development and optimization, method transfer, and stationary‐phase characterization and comparison. The review focusses on the effects of mobile‐phase composition on retention, but other variables and novel models to describe their effects are also considered. The five most‐common models are addressed in detail, i.e. the log‐linear (linear‐solvent‐strength) model, the quadratic model, the log–log (adsorption) model, the mixed‐mode model, and the Neue–Kuss model. Isocratic and gradient‐elution methods are considered for determining model parameters and the evaluation and validation of fitted models is discussed. Strategies in which retention models are applied for developing and optimizing one‐ and two‐dimensional liquid chromatographic separations are discussed. The review culminates in some overall conclusions and several concrete recommendations. 相似文献
In this paper, by combination of the statistical thermodynamic method with the Freundlich isotherm, the retention equations to describe the effects of the mobile phase composition, concentration of the ion-pair reagent and the ionic strength on the amount of adsorbed ion-pair reagent and the retention value of the ionic solute have been reported by simultaneously considering the electrostatic and molecular interaction between solutes, ion-pair reagent and molecule or ion in each phase in the reversed-phase ion-pair chromatography. The validity of these retention equations has been confirmed by calculation of capacity factor of the different phenylamine and naphthylamine sulphonic acids during systematic change of concentration of the strong solvent, the ion-pair reagent and the ionic strength in the mobile phase.Symbols
a, b, c, d, d1,e, f, h, g anda, b, c, d, e, f', g, h
parameters related to chromatographic system
-
A
solute
-
B
constant
-
Bi
solventi
-
Cb andCp
concentration of strong solvent and ion-pair reagent
-
CPa
amount of adsorbed ion-pair reagent
-
D
dielectric constant
-
EAP,
andEpp
molecular interaction of adjacent pair of solute-ion-pair reagent, solute-solventBi, ion-pair reagent-solventBi and ion-pair reagent-ion-pair reagent
-
Epa
andEea
non-electrostatic and electrostatic adsorption energy of ion-pair reagent
-
F
Faraday constant
-
h
Planck constant
-
I
ionic strength
-
jA,
andjp
internal partition function of solute, solventBi and ion-pair reagent
-
k
Boltzmann constant
-
k
capacity factor
-
kp,np andk1,n1
parameters of Freundlich isotherm of ion-pair reagent and solventB1
-
KAP,
and
constants related with the molecular size of solute, ion-pair reagent and solventBi
-
mA,mP and
molecular weight of solute, ion-pair reagent and solventBi
-
NA,NP and
numbers of solute, ion-pair reagent and solventBi in solution
-
NAa
,NPa
and
numbers of solute, ion-pair reagent and solventBi adsorbed on the surface
-
Ns
number of adsorbed sites on the surface
-
P
ion-pair reagent
-
R
gas constant
-
T
absolute temperature
-
V0
volume of solution
-
Vp and
volume of ion-pair reagent and solventB
-
X
potential function
-
XP1
andXPl
potential function of ion-pair reagent on the surface and in the solution
-
XAa
andXAl
potential function of solute on the surface and in the solution
-
ZA,ZP andZi
charge numbers of soluteA, ion-pair reagent and inorganic ioni
-
ZAP and
numbers of ion-pair reagentP and solventBi surrounding the soluteA
-
0
permittivity in a vacuum
-
electrostatic potential of the surface
Dedicated to Professor J. F. K. Huber on the occasion of his 65th birthday 相似文献
A prediction model of the peptide retention time was developed on the basis of 358 non-phosphorylated peptides, which had various amino acid residues in the C-terminal from the casein pancreatic hydrolysates. This model was applied to predict the retention times (RT) of another 43 peptides on C4 reversed phase columns with trifluoroacetic acid (TFA) as the ion-pairing reagent, with a relatively high R2 value (0.969). Furthermore, the experimental RTs of 32 phosphopeptides were compared with the predictive RTs of their non-phosphorylated cognates. Mono- and poly-phosphopeptides seemed to elute after or before the non-phosphorylated predictive cognates, respectively. The positive charges of peptides were partly masked by the ion-pairing reagent TFA. Single and multiple phosphorylation might generally lead to an increase or reduction in the overall hydrophobicity of peptides, respectively. 相似文献
Summary The work described in Part I has been extended to show that the basic equation derived therein can be reduced to allow a direct
analytical solution. For convenience, solution by this technique is termed DAMAT-X (Direct Approach Minimising Analysis time
based on X) to distinguish it from solutions obtained by the technique in Part I, named here simply DAMAT. An additional advantage
of the reduced equation is that some solutions are readily available by inspection and this feature is illustrated diagrammatically.
Finally it is indicated how DAMAT-X can be used as the basis for assessing the accuracy of other techniques based on the (h/ū)
group, but which require less data for approximating to minimising conditions. 相似文献
Protein phosphorylation is a type of posttranslational modification which plays an important role in cell regulation and signal transduction. Because of its biological relevance, a considerable amount of interest has been paid to the development of efficient techniques for phosphopeptide analysis. Although advances in MS control have enabled the high-throughput discovery of proteins from limited amounts of sample, automated selection of MS/MS precursor ions based on intensity alone can significantly hamper the detection of low-abundance phosphopeptides. On the basis of the observation that the introduction of a phosphate moiety does not dramatically change peptide retention time in reverse-phase chromatography, phosphopeptide specific MS/MS fragmentation attempts based on LC retention time and m/z were evaluated using a standard protein mixture, then using in vitro phosphorylated myelin basic protein. Results indicated that the majority (98%) of phosphopeptides identified eluted within a +/- 4-min window of the predicted LC elution time. While studies presented here are primarily proof of concept in nature, data suggest that the use of LC retention time prediction could be a valuable constraint for the identification of phosphopeptides within a set of off-line LC deposited sample spots. It is expected that the development of these methods will not only permit the targeted identification of protein phosphorylation sites but also allow the in-depth analysis of the dynamic events linked to the posttranslational modification. 相似文献
A model for prediding retention time of solutes undeir linear gradient elulioa conditions has been established. In this model,the theorelkal expressions under different eluflon modes were derived and tested with the retention behaviors of p-hydroxy-benzaldehyde, vanilUn, biphenyl, phenanthrene in gradient elution. With halting into account the dwell time of the instrumeatal system, the theoretically predicted retention times agreewell with those experimentally determined. 相似文献
Chromatographic modeling software packages are valuable tools during method optimization steps. These are well established for reversed-phase applications utilizing retention time (RT) prediction to optimize separations and receive robust methods, which is of high interest for the analysis of pharmaceuticals. In contrast to liquid chromatography, the knowledge of RT prediction in supercritical fluid chromatography is limited to a manageable number of studies. 相似文献
Using factor analysis and stepwise linear regression methods, two parameters – CMR and ECCR – were selected from eight solute‐related structure parameters as the most retention‐influencing parameters. The relationships between the retention data (k ´) and the two structure parameters were established for 13 O‐aryl,O‐(1‐methylthioethylideneamino)phosphate compounds under a wide range of experimental conditions. The retention data (k ´) of another seven compounds with similar structures were predicted using these QSRR equations. Good agreement was obtained between the experimental k ´ values and predicted ones. 相似文献
A coarse‐grained model of heteropolymer (polypeptide) chains in a slit was designed in order to study the folding process in confinement. The idealized chains represented heteropolymers consisted of hydrophobic and hydrophilic united atoms, which were restricted to vertices of a (310) lattice. The force field consisted of the excluded volume, the long‐distance potential between pairs of segments and the local helical potential. Monte Carlo simulations were performed using the algorithm with micromodifications of the chain's conformation and employing the Replica Exchange technique. The influence of the size of the slit, the temperature and the force field on the dimension and the structure of chains were studied. It was shown that a moderate confinement stabilizes folded chains while a strong confinement does not.
Metabolite identification is a crucial step in nontargeted metabolomics, but also represents one of its current bottlenecks. Accurate identifications are required for correct biological interpretation. To date, annotation and identification are usually based on the use of accurate mass search or tandem mass spectrometry analysis, but neglect orthogonal information such as retention times obtained by chromatographic separation. While several tools are available for the analysis and prediction of tandem mass spectrometry data, prediction of retention times for metabolite identification are not widespread. Here, we review the current state of retention time prediction in liquid chromatography–mass spectrometry‐based metabolomics, with a focus on publications published after 2010. 相似文献
The harmful health effects caused by phthalic acid esters have been supported from the increasing scientific evidence, developing the efficient methodologies to monitor the levels of phthalic acid esters in various foods become especially important from the aspects of human exposure assessment and their migration mechanistic understanding. In this study, quantitative structure‐retention relationship studies on both the gas and liquid chromatographic retention times of 23 phthalic acid esters were performed by genetic function approximation, and the optimal quantitative structure‐retention relationship models (r2 > 0.980, r2CV > 0.960, and r2pred > 0.865) passed the statistical tests of cross‐validation, randomization, external prediction, Roy′ rm2 metrics, Golbraikh‐Tropsha′ criteria and applicability domain. The established predictive models elucidate the structural requirements for the retention of phthalic acid esters over different chromatographic columns, which were finally used to predict the retention times of 11 new phthalic acid esters. Hopefully, this work could provide useful guidelines for better understanding and accurate prediction of the retention behavior of undetermined phthalic acid esters when lacking standard samples or under poor experimental conditions, and make the simultaneous identification and quantification of numerous phthalic acid esters possible. 相似文献
