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See detailIs supercritical fluid chromatography hyphenated to massspectrometry suitable for the quality control of vitamin D3 oilyformulations?
Andri, Bertyl ULiege; Dispas, Amandine ULiege; Klinkenberg, Régis et al

in Journal of Chromatography. A (2017), 1515

Nowadays, many efforts are devoted to improve analytical methods regarding efficiency, analysis timeand greenness. In this context, Supercritical Fluid Chromatography (SFC) is often regarded as a ... [more ▼]

Nowadays, many efforts are devoted to improve analytical methods regarding efficiency, analysis timeand greenness. In this context, Supercritical Fluid Chromatography (SFC) is often regarded as a goodalternative over Normal Phase Liquid Chromatography (NPLC). Indeed, modern SFC separations arefast, efficient with suitable quantitative performances. Moreover, the hyphenation of SFC to mass spec-trometry (MS) provides additional gains in specificity and sensitivity. The present work aims at thedetermination of vitamin D3 by SFC-MS for routine Quality Control (QC) of medicines specifically. Basedon the chromatographic parameters previously defined in SFC-UV by Design of Experiments (DoE) andDesign Space methodology, the method was adapted to work under isopycnic conditions ensuring a base-line separation of the compounds. Afterwards, the response provided by the MS detector was optimizedby means of DoE methodology associated to desirability functions. Using these optimal MS parameters,quantitative performances of the SFC-MS method were challenged by means of total error approachmethod validation. The resulting accuracy profile demonstrated the full validity of the SFC-MS method. It was indeed possible to meet the specification established by the European Medicines Agency (EMA) (i.e. 95.0 − 105.0% of the API content) for a dosing range corresponding to at least 70.0-130.0% of theAPI content. These results highlight the possibility to use SFC-MS for the QC of medicine and obviouslysupport the switch to greener analytical methods. [less ▲]

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See detailAdvanced method optimization for volatile aroma profiling of beer using two-dimensional gas chromatography time-of-flight mass spectrometry
Stefanuto, Pierre-Hugues ULiege; Perrault, Katelynn ULiege; Dubois, Lena ULiege et al

in Journal of Chromatography. A (2017)

The complex mixture of volatile organic compounds (VOCs) present in the headspace of Trappist and craft beers was studied to illustrate the efficiency of thermal desorption (TD) comprehensive two ... [more ▼]

The complex mixture of volatile organic compounds (VOCs) present in the headspace of Trappist and craft beers was studied to illustrate the efficiency of thermal desorption (TD) comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC × GC-TOFMS) for highlighting subtle differences between highly complex mixtures of VOCs. Headspace solid-phase microextraction (HS-SPME), multiple (and classical) stir bar sorptive extraction (mSBSE), static headspace (SHS), and dynamic headspace (DHS) were compared for the extraction of a set of 21 representative flavor compounds of beer aroma. A Box-Behnken surface response methodology experimental design optimization (DOE) was used for convex hull calculation (Delaunay’s triangulation algorithms) of peak dispersion in the chromatographic space. The predicted value of 0.5 for the ratio between the convex hull and the available space was 10% higher than the experimental value, demonstrating the usefulness of the approach to improve optimization of the GC × GC separation. Chemical variations amongst aligned chromatograms were studied by means of Fisher Ratio (FR) determination and F‐distribution threshold filtration at different significance levels (α = 0.05 and 0.01) and based on z‐score normalized area for data reduction. Statistically significant compounds were highlighted following principal component analysis (PCA) and hierarchical cluster analysis (HCA). The dendrogram structure not only provided clear visual information about similarities between products but also permitted direct identification of the chemicals and their relative weight in clustering. The effective coupling of DHS-TD-GC × GC-TOFMS with PCA and HCA was able to highlight the differences and common typical VOC patterns among 24 samples of different Trappist and selected Canadian craft beers. [less ▲]

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See detailSampling only ten microliters of whole blood for the quantification of poorly soluble drugs: Itraconazole as case study
Thiry, Justine ULiege; Evrard, Brigitte ULiege; Nys, Gwenaël ULiege et al

in Journal of Chromatography. A (2017), 1479

Nowadays in animal studies, it is important to comply with the so-called Three Rs rule by replacing or reducing the number of tested animals. Volumetric absorptive microsampling (VAMS) can be used to ... [more ▼]

Nowadays in animal studies, it is important to comply with the so-called Three Rs rule by replacing or reducing the number of tested animals. Volumetric absorptive microsampling (VAMS) can be used to collect small quantities (10 or 20 µL) of whole blood, thereby limiting the amount of animals needed. In this study, a quantitative method was developed and subsequently validated for the poorly soluble drug itraconazole (ITZ) using VAMS and ultra-high performance liquid chromatography (UHPLC) coupled to tandem mass spectrometry (MS). A proof of concept study showed that the optimized method is applicable to test the bioavailability of drug formulations containing ITZ. Using VAMS, smaller blood volumes can be taken per sampling point (10-20 µL instead of the conventional 0.2-0.5 mL) avoiding the sacrifice of animals. Moreover, the same rats can be used to compare different drug formulations which strengthens the validity of the results. In long-term bioavailability studies, it is necessary to guarantee the stability of the tested drugs supported on VAMS devices. In this study, we show that ITZ was only stable for 24 hours after collection with VAMS, but for at least two weeks by the storage of extracted samples at -80°C. [less ▲]

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See detail(+) or (-)-1-(9-fluorenyl)ethyl chloroformate as chiral derivatizing agent: A review.
Moldovan, Radu-Cristian ULiege; Bodoki, Ede; Servais, Anne-Catherine ULiege et al

in Journal of Chromatography. A (2017), 1513

Over the last 30years, (+/-)-1-(9-fluorenyl)ethyl chloroformate ((+/-)-FLEC) was used as a chiral derivatizing agent in various analytical applications involving a wide range of endogenous, pharmaceutical ... [more ▼]

Over the last 30years, (+/-)-1-(9-fluorenyl)ethyl chloroformate ((+/-)-FLEC) was used as a chiral derivatizing agent in various analytical applications involving a wide range of endogenous, pharmaceutical and environmentally relevant molecules. This comprehensive review aims to present all the significant aspects related to the state of the art in FLEC labeling and subsequent chiral separation of the resulting diastereomers using LC, SFC and CE techniques. [less ▲]

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See detailTowards a chromatographic similarity index to establish localised Quantitative Structure-Retention Relationships for retention prediction. II Use of Tanimoto similarity index in ion chromatography
Park, S. H.; Talebi, M.; Amos, R. I. J. et al

in Journal of Chromatography. A (2017)

Quantitative Structure-Retention Relationships (QSRR) are used to predict retention times of compounds based only on their chemical structures encoded by molecular descriptors. The main concern in QSRR ... [more ▼]

Quantitative Structure-Retention Relationships (QSRR) are used to predict retention times of compounds based only on their chemical structures encoded by molecular descriptors. The main concern in QSRR modelling is to build models with high predictive power, allowing reliable retention prediction for the unknown compounds across the chromatographic space. With the aim of enhancing the prediction power of the models, in this work, our previously proposed QSRR modelling approach called "federation of local models" is extended in ion chromatography to predict retention times of unknown ions, where a local model for each target ion (unknown) is created using only structurally similar ions from the dataset. A Tanimoto similarity (TS) score was utilised as a measure of structural similarity and training sets were developed by including ions that were similar to the target ion, as defined by a threshold value. The prediction of retention parameters (a- and b-values) in the linear solvent strength (LSS) model in ion chromatography, log k = a - blog[eluent], allows the prediction of retention times under all eluent concentrations. The QSRR models for a- and b-values were developed by a genetic algorithm-partial least squares method using the retention data of inorganic and small organic anions and larger organic cations (molecular mass up to 507) on four Thermo Fisher Scientific columns (AS20, AS19, AS11HC and CS17). The corresponding predicted retention times were calculated by fitting the predicted a- and b-values of the models into the LSS model equation. The predicted retention times were also plotted against the experimental values to evaluate the goodness of fit and the predictive power of the models. The application of a TS threshold of 0.6 was found to successfully produce predictive and reliable QSRR models (Qext(F2) 2 >. 0.8 and Mean Absolute Error. <. 0.1), and hence accurate retention time predictions with an average Mean Absolute Error of 0.2. min. © 2017. [less ▲]

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See detailTowards a chromatographic similarity index to establish localized quantitative structure-retention models for retention prediction: Use of retention factor ratio
Tyteca, Eva ULiege; Talebi, M.; Amos, R. et al

in Journal of Chromatography. A (2017), 1486

Quantitative Structure-Retention Relationships (QSRR) have the potential to speed up the screening phase of chromatographic method development as the initial exploratory experiments are replaced by ... [more ▼]

Quantitative Structure-Retention Relationships (QSRR) have the potential to speed up the screening phase of chromatographic method development as the initial exploratory experiments are replaced by prediction of analyte retention based solely on the structure of the molecule. The present study offers further proof-of-concept of localized QSRR modelling, in which the retention of any given compound is predicted using only the most chromatographically similar compounds in the available dataset. To this end, each compound in the dataset was sequentially removed from the database and individually utilized as a test analyte. In this study, we propose the retention factor k as the most relevant chromatographic similarity measure and compare it with the Tanimoto index, the most popular similarity measure based on chemical structure. Prediction error was reduced by up to 8 fold when QSRR was based only on chromatographically similar compounds rather than using the entire dataset. The study therefore shows that the design of a practically useful structural similarity index should select the same compounds in the dataset as does the k-similarity filter in order to establish accurate predictive localized QSRR models. While low average prediction errors (Mean Absolute Error (MAE) < 0.5 min) and slopes of the regression lines through the origin close to 1.00 were obtained using k-similarity searching, the use of the structural Tanimoto similarity index, considered as the gold standard in Quantitative Structure-Activity Relationships (QSAR) studies, generally resulted in much higher prediction errors (MAE > 1 min) and significant deviations from the reference slope of 1.0. The Tanomoto similarity index therefore appears to have limited general utility in QSRR studies. Future studies therefore aim at designing a more appropriate chromatographic similarity index that can then be applied for unknown compounds (that is, compounds which have not been tested previously on the chromatographic system used, but for which the chemical structures are known). © 2016 [less ▲]

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See detailRetention prediction of low molecular weight anions in ion chromatography based on quantitative structure-retention relationships applied to the linear solvent strength model
Park, S. H.; Haddad, P. R.; Talebi, M. et al

in Journal of Chromatography. A (2017), 1486

Quantitative Structure-Retention Relationships (QSRRs) represent a popular technique to predict the retention times of analytes, based on molecular descriptors encoding the chemical structures of the ... [more ▼]

Quantitative Structure-Retention Relationships (QSRRs) represent a popular technique to predict the retention times of analytes, based on molecular descriptors encoding the chemical structures of the analytes. The linear solvent strength (LSS) model relating the retention factor, k to the eluent concentration (log k = a − blog [eluent]), is a well-known and accurate retention model in ion chromatography (IC). In this work, QSRRs for inorganic and small organic anions were used to predict the regression parameters a and b in the LSS model (and hence retention times) for these analytes under a wide range of eluent conditions, based solely on their chemical structures. This approach was performed on retention data of inorganic and small organic anions from the “Virtual Column” software (Thermo Fisher Scientific). These retention data were recalibrated via a “porting” methodology on three columns (AS20, AS19, and AS11HC), prior to the QSRR modeling. This provided retention data more applicable on recently produced columns which may exhibit changes of column behavior due to batch-to-batch variability. Molecular descriptors for the analytes were calculated with Dragon software using the geometry-optimized molecular structures, employing the AM1 semi-empirical method. An optimal subset of molecular descriptors was then selected using an evolutionary algorithm (EA). Finally, the QSRR models were generated by multiple linear regression (MLR). As a result, six QSRR models with good predictive performance were successfully derived for a- and b-values on three columns (R2 > 0.98 and RMSE < 0.11). External validation showed the possibility of using the developed QSRR models as predictive tools in IC (Qext(F3) 2 > 0.7 and RMSEP < 0.4). Moreover, it was demonstrated that the obtained QSRR models for the a- and b-values can predict the retention times for new analytes with good accuracy and predictability (R2 of 0.98, RMSE of 0.89 min, Qext(F3) 2 of 0.96 and RMSEP of 1.18 min). © 2016 Elsevier B.V. [less ▲]

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See detailCombination of Partial Least Squares regression and Design of Experiments to model the retention of pharmaceuticals in Supercritical Fluid Chromatography
Andri, Bertyl ULiege; Dispas, Amandine ULiege; Marini Djang'Eing'A, Roland ULiege et al

in Journal of Chromatography. A (2017)

This work presents a first attempt to establish a model of the retention behaviour for pharmaceutical compounds in gradient mode SFC. For this purpose, multivariate statistics were applied on the basis of ... [more ▼]

This work presents a first attempt to establish a model of the retention behaviour for pharmaceutical compounds in gradient mode SFC. For this purpose, multivariate statistics were applied on the basis of data gathered with the Design of Experiment (DoE) methodology. It permitted to build optimally the experiments needed, and served as a basis for providing relevant physicochemical interpretation of the effects observed. Data gathered over a broad experimental domain enabled the establishment of well-fit linear models of the retention of the individual compounds in presence of methanol as co-solvent. These models also allowed the appreciation of the impact of each experimental parameter and their factorial combinations. This approach was carried out with two organic modifiers (i.e. methanol and ethanol) and provided comparable results. Therefore, it demonstrates the feasibility to model retention in gradient mode SFC for individual compounds as a function of the experimental conditions. This approach also permitted to highlight the predominant effect of some parameters (e.g. gradient slope and pressure) on the retention of compounds. Because building of individual models of retention was possible, the next step considered the estab- lishment of a global model of the retention to predict the behaviour of given compounds on the basis of, on the one side, the physicochemical descriptors of the compounds (e.g. Linear Solvation Energy Relationship (LSER) descriptors) and, on the other side, of the experimental conditions. This global model was established by means of partial least squares regression for the selected compounds, in an experimental domain defined by the Design of Experiment (DoE) methodology. Assessment of the model’s predic- tive capabilities revealed satisfactory agreement between predicted and actual retention (i.e. R2 = 0.942, slope = 1.004) of the assessed compounds, which is unprecedented in the field. [less ▲]

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See detailOptimization and validation of a fast Supercritical Fluid Chromatography method for the quantitative determination of vitamin D3 and its related impurities.
Andri, Bertyl ULiege; Lebrun, Pierre ULiege; Dispas, Amandine ULiege et al

in Journal of Chromatography. A (2017)

In the uprising context of green analytical chemistry, Supercritical Fluid Chromatography (SFC) is often suggested as an alternative to Normal Phase Liquid Chromatography. Indeed, SFC provides fast ... [more ▼]

In the uprising context of green analytical chemistry, Supercritical Fluid Chromatography (SFC) is often suggested as an alternative to Normal Phase Liquid Chromatography. Indeed, SFC provides fast, efficient and green separations. In this report, the quantitative performances of SFC were challenged on a real-life case study: the Quality Control (QC) of vitamin D3. A rapid and green SFC method was optimized thanks to the Design of Experiments–Design Space (DoE–DS) methodology. It provided robust and high quality separation of the compounds within a 2 min timeframe, using a gradient of ethanol as co-solvent of the carbon dioxide. The analytical method was fully validated according to the total error approach, demon- strating the compliance of the method to the specifications of U.S. Pharmacopeia (USP: 97.0–103.0%) and European Pharmacopeia (EP: 97.0–102.0%) for an interval of [50–150%] of the target concentration. In order to allow quantification of impurities using vitamin D3 as an external standard in SFC-UV, correction factors were determined and verified during method validation. Thus, accurate quantification of impu- rities was demonstrated at the specified levels (0.1 and 1.0% of the main compound) for a 70.0–130.0% dosing range. This work demonstrates the validity of an SFC method for the QC of vitamin D3 raw material and its application to real samples. Therefore, it supports the switch to a greener and faster separative technique as an alternative to NPLC in the pharmaceutical industry. [less ▲]

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See detailThe performance of atmospheric pressure gas chromatography–tandem mass spectrometry compared to gas chromatography–high resolution mass spectrometry for the analysis of polychlorinated dioxins and PCBs in food and feed samples
ten Dam, Guillaume; Pussente, Igor; Scholl, Georges ULiege et al

in Journal of Chromatography. A (2016), 1477

Recently, gas chromatography tandem mass spectrometry (GC–MS/MS) has been added in EuropeanUnion (EU) legislation as an alternative to magnetic sector high resolution mass spectrometry (HRMS) for the ... [more ▼]

Recently, gas chromatography tandem mass spectrometry (GC–MS/MS) has been added in EuropeanUnion (EU) legislation as an alternative to magnetic sector high resolution mass spectrometry (HRMS) for the analysis of dioxins and dioxin like polychlorinated biphenyls (dl-PCB) in food and feed. In this study the performance of APGC–MS/MS compared to GC–HRMS is investigated and compared with EU legislation. The study includes the legislative parameters, relative intermediate precision standard devia-tion (SRw,rel), trueness, sensitivity, linear range and ion ratio tolerance. In addition, over 200 real samplesof large variety and spanning several orders of magnitude in concentration were analyzed by both techniques and the selectivity was evaluated by comparing chromatograms. The SRw,rel and trueness were evaluated using (in-house) reference samples and fulfill to EU legislation, though the SRw,rel was better with GC–HRMS. The sensitivity was considerably better than of GC–HRMS while the linear range was similar. Ion ratios were mostly within the tolerable range of ±15%. A (temporary unresolved) systematic deviation in ion ratio was observed for several congeners, yet this did not lead to exceeding of the maxi-mum ion ratio limits. The APGC–MS/MS results for the non-dioxin-like-PCBs (ndl-PCBs) were negatively biased, particularly for PCB138 and 153 in contaminated samples. The selectivity of APGC–MS/MS was lower for several matrices. Particularly for contaminated samples, interfering peaks were observed in the APGC chromatograms of the native compounds (dioxins) and labeled internal standards (PCBs). These can lead to biased results and ultimately to false positive samples. It was concluded that the determination of dioxins and PCBs using APGC–MS/MS meets the requirements set by the European Commission. However, due to generally better selectivity and SRw,rel, GC–HRMS is the preferred method for monitoring purposes. [less ▲]

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See detailLiquid chromatography separation of the chiral prodrug eslicarbazepine acetate and its main metabolites in polar organic mode. Application to their analysis after in vitro metabolism.
Servais, Anne-Catherine ULiege; Janicot, Bertrand; Takam, Arnold et al

in Journal of Chromatography. A (2016), 1467

A LC method using a chiral stationary phase (CSP) with cellulose tris(3-chloro-4-methylphenylcarbamate) as chiral selector in polar organic mode (POM) was developed for the separation of the ... [more ▼]

A LC method using a chiral stationary phase (CSP) with cellulose tris(3-chloro-4-methylphenylcarbamate) as chiral selector in polar organic mode (POM) was developed for the separation of the biopharmaceutic classification system (BCS) class II chiral prodrug eslicarbazepine acetate (ESL) and its main metabolites, namely eslicarbazepine, its optical antipode, (R)-licarbazepine, and the achiral oxcarbazepine (OXC). The percentage of methanol (MeOH) in the mobile phase containing acetonitrile (ACN) as the main solvent was found to significantly influence analyte retention and resolution. A reversal of elution order of OXC and (R)-licarbazepine was observed, depending on the MeOH percentage in the mobile phase. The optimized mobile phase consisted of ACN/MeOH/acetic acid/diethylamine (95/5/0.2/0.07; v/v/v/v). The potential of this chemo- and enantioselective LC method combined with solid-phase extraction (SPE) was then evaluated for in vitro metabolism studies using ESL as a model case. Only eslicarbazepine could be detected after incubation of ESL in human liver microsome systems. [less ▲]

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See detailImpact of injection solvent composition on protein identification incolumn-switching chip-liquid chromatography/mass spectrometry
Houbart, Virginie ULiege; COBRAIVILLE, Gaël ULiege; Nys, Gwenaël ULiege et al

in Journal of Chromatography. A (2016), 1445

In shotgun proteomics, the gold standard technique is reversed-phase liquid chromatography coupledto mass spectrometry. Many researches have been carried out to study the effects on identification per ... [more ▼]

In shotgun proteomics, the gold standard technique is reversed-phase liquid chromatography coupledto mass spectrometry. Many researches have been carried out to study the effects on identification per-formances of chromatographic parameters such as the stationary phase and column dimensions, mobilephase composition and flow rate, as well as the gradient slope and length. However, little attention isusually paid to the injection solvent composition.In this study, we investigated the effect of the injection solvent on protein identification parameters(number of distinct peptides, amino acid coverage and MS/MS search score) as well as sensitivity. Trypticpeptides from six different proteins, covering a wide range of physicochemical properties, were employedas training set. Design of experiments was employed as a tool to highlight the factors related to thecomposition of the injection solvent that significantly influenced the obtained results. Optimal resultsfor the training set were applied to analysis of more complex samples. The experiments pointed outoptimising the composition of the injection solvent had a strong beneficial effect on all the consideredresponses. On the basis of these results, an approach to determine optimal conditions was proposed tomaximise the protein identification performances and detection sensitivity. [less ▲]

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See detailTravelling-wave ion mobility time-of-flight mass spectrometry as an alternative strategy for screening of multi-class pesticides in fruits and vegetables
Goscinny, Séverine ULiege; Joly, Laure; De Pauw, Edwin ULiege et al

in Journal of Chromatography. A (2015), 1405

This paper reports a novel approach to screening multi-class pesticides by ion mobility timeof- flight mass spectrometry detection. Nitrogen was selected as mobility gas. After optimization of the ... [more ▼]

This paper reports a novel approach to screening multi-class pesticides by ion mobility timeof- flight mass spectrometry detection. Nitrogen was selected as mobility gas. After optimization of the different ion mobility parameters, determination of matrix effect on the drift times was conducted using different matrix extracts. The results showed that drift time values are not influenced by the matrix and also are independent of the concentration within the working range for 100 pesticides tested, making drift time a powerful additional identification tool. Based on statistics, 2% variation criteria provides a good fit for all the pesticides targeted, and could be considered as a maximum acceptable criteria associated with the drift time parameter for identification purpose. This 2% value is in agreement with already reported criteria, for instance, for GC or LC retention time in European documents. Finally, the well-known feature of mobility to separate complex mixtures was also tested to obtain purified extracted mass spectra of pesticides in fruit extract. [less ▲]

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See detailOn the inherent data fitting problems encountered in modelingretention behavior of analytes with dual retention mechanism
Tyteca, Eva ULiege; Desmet, G.

in Journal of Chromatography. A (2015), 1403

Some valuable insights have been obtained in the inherent fitting problems when trying to predict theretention time of complex, multi-modal retention modes such as encountered in HILIC and SFC. In ... [more ▼]

Some valuable insights have been obtained in the inherent fitting problems when trying to predict theretention time of complex, multi-modal retention modes such as encountered in HILIC and SFC. In thisstudy, we used mathematical models with known input parameters to generate different sets of numericaltest curves representative for systems exhibiting a complex, non-LSS dual retention behavior. Subse-quently, we tried to fit these data sets using some popular (non-linear) literature models. Even in caseswhere a physical fitting model exists (e.g., the mixed model in case of pure additive adsorptive andpartitioning retention), the fitting quality can only be expected to be relatively good (prediction errorsexpressed in terms of a normalized resolution error εRs) when carefully selecting the scouting runs andthe appropriate starting values for the fitting algorithm. The latter can best be done using a comprehen-sive grid search scanning a wide range of different starting values. This becomes even more importantwhen no good physical model is available and one has to use a non-physical fitting model, such as theempirical Neue-model. The use of higher-order models is found to be quasi indispensable to keep theprediction errors on the order of some ΔRs= 0.05. Also, the choice of the scouting runs becomes evenmore important using these higher-order models. For highly retained compounds we recommend usingscouting runs with long tG/t0-values or to include a run with a higher fraction of eluting solvent at thestart of the gradient. When trying to predict gradient retention, errors with which the isocratic retentionbehavior is fitted are much less important for high retention factors k than errors made in the range of knear the one at the point of elution. The results obtained with a so-called segmented Neue-model (con-taining 7 parameters) were less good and thus practically not interesting (because of the high number ofinitial runs). © 2015 Elsevier B.V. [less ▲]

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See detailPossibilities of retention modeling and computer assisted method development in supercritical fluid chromatography
Tyteca, Eva ULiege; Desfontaine, V.; Desmet, G. et al

in Journal of Chromatography. A (2015), 1381

The multi-modal retention mechanism in supercritical fluid chromatography (SFC) results in a non-linear dependency of log(k) on the fraction of organic solvent ϕ and log(ϕ). In the present study, the ... [more ▼]

The multi-modal retention mechanism in supercritical fluid chromatography (SFC) results in a non-linear dependency of log(k) on the fraction of organic solvent ϕ and log(ϕ). In the present study, the possibility of retention modeling for method development purposes in SFC was investigated, considering several non-linear isocratic relationships. Therefore, both isocratic and gradient runs were performed, involving different column chemistries and analytes possessing diverse physico-chemical properties. The isocratic retention data of these compounds could be described accurately using the non-linear retention models typically used in HILIC and reversed-phase LC. The interconversion between isocratic and gradient retention data was found to be less straightforward than in RPLC and HILIC because of pressure effects. The possibility of gradient predictions using gradient scouting runs to estimate the retention parameters was investigated as well, showing that predictions for other gradients with the same starting conditions were acceptable (always below 5%), whereas prediction errors for gradients with a different starting condition were found to be highly dependent on the compound. The second part of the study consisted of the gradient optimization of two pharmaceutical mixtures (one involving atorvastatin and four related impurities, and one involving a 16 components mixture including eight drugs and their main phase I metabolites). This could be done via individual retention modeling based on gradient scouting runs. The best linear gradient was found via a grid search and the best multi-segment gradient via the previously published one-segment-per-component search. The latter improved the resolution between the critical pairs for both mixtures, while still giving accurate prediction errors (using the same starting concentrations as the gradient scouting runs used to build the model). The optimized separations were found in less than 3. h and 8. h of analysis time (including equilibration times), respectively. © 2015 Elsevier B.V. [less ▲]

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See detailComputer-assisted multi-segment gradient optimization in ion chromatography
Tyteca, Eva ULiege; Park, S. H.; Shellie, R. A. et al

in Journal of Chromatography. A (2015), 1381

This study reports simulation and optimization of ion chromatography separations using multi-segment gradient elution. First, an analytical expression for the gradient retention factor under these complex ... [more ▼]

This study reports simulation and optimization of ion chromatography separations using multi-segment gradient elution. First, an analytical expression for the gradient retention factor under these complex elution profiles was derived. This allows a rapid retention time prediction calculations under different gradient conditions, during computer-assisted method development. Next, these analytical expressions were implemented in an in-house written Matlab® routine that searches for the optimal (multi-segment) gradient conditions, either via a four-segment grid search or via the recently proposed one-segment-per-component search, in which the slope is adjusted after the elution of each individual component. Evaluation of the retention time simulation and optimization approaches was performed on a mixture of 18 inorganic anions and different subsets with varying number of compounds. The two considered multi-segment gradient optimization searches resulted in similar proposed gradient profiles, and corresponding chromatograms. Moreover, the resultant chromatograms were clearly superior to the chromatograms obtained from the best simple linear gradient profiles, found via a fine grid search. The proposed approach is useful for automated method development in ion chromatography in which complex elution profiles are often used to increase the separation power. © 2015 Elsevier B.V. [less ▲]

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See detailEffect of gradient steepness on the kinetic performance limits and peak compression for reversed-phase gradient separations of small molecules
Vaňková, N.; De Vos, J.; Tyteca, Eva ULiege et al

in Journal of Chromatography. A (2015), 1409

The effect of gradient steepness on the kinetic performance limits and peak compression effects has been assessed in gradient mode for the separation of phenol derivatives using columns packed with 2.6μm ... [more ▼]

The effect of gradient steepness on the kinetic performance limits and peak compression effects has been assessed in gradient mode for the separation of phenol derivatives using columns packed with 2.6μm core-shell particles. The effect of mobile-phase velocity on peak capacity was measured on a column with fixed length while maintaining the retention factor at the moment of elution and the peak-compression factor constant. Next, the performance limits were determined at the maximum system pressure of 100MPa while varying the gradient steepness. For the separation of small molecules applying a linear gradient with a broad span, the best performance limits in terms of peak capacity and analysis time were obtained applying a gradient-time-to-column-dead-time (t<inf>G</inf>/t<inf>0</inf>) ratio of 12. The magnitude of the peak-compression factor was assessed by comparing the isocratic performance with that in gradient mode applying different gradient times. Therefore, the retention factors for different analytes were determined in gradient mode and the mobile-phase composition in isocratic mode was tuned such that the difference in retention factor was smaller than 2%. Peak-compression factors were quantitatively determined between 0.95 and 0.65 depending on gradient steepness and the gradient retention factor. © 2015 Elsevier B.V. [less ▲]

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