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1.
J Chromatogr A ; 1626: 461308, 2020 Aug 30.
Artigo em Inglês | MEDLINE | ID: mdl-32797813

RESUMO

The Wayne State University (WSU) experimental descriptor database is utilized to bench mark the current capability of the solvation parameter model for use as a quantitative structure-retention relationship tool for estimating retention in gas and reversed-phase liquid chromatography. The prediction error for the retention factors of varied compounds on six open-tubular columns for gas chromatography (Rtx-5 SIL MS, DB-35 ms, RtxCLPesticides, HP-88, HP-INNOWAX and SLB-IL76) and three packed columns for reversed-phase liquid chromatography (SunFire C18, XBridge Shield RP18, and XBridge Phenyl) is used to establish expectations related to current practices. Each column data set was divided into a training set for calibration and a test set for validation employing a roughly 1 to 2 split, such that each test set contained about 40 to 80 varied compounds. The average absolute error for the prediction of retention factors by gas chromatography varied from about 0.1 to 0.4 on the retention factor scale with the larger error typical of stationary phases ranked as the most polar (or cohesive). For reversed-phase liquid chromatography the average error for the prediction of retention factors was 0.3 to 0.5 and generally larger than for gas chromatography. Statistical filters where utilized to identify a group of polycyclic aromatic compounds without hydrogen-bonding functional groups with a larger prediction error on the SunFire C18 column than for other compounds of smaller size, flexible structure or containing hydrogen-bonding functional groups. The heterogeneity of the retention mechanism is speculated to be the main contribution to the prediction error for both gas and liquid chromatography using the solvation parameter model.


Assuntos
Cromatografia Gasosa/métodos , Cromatografia de Fase Reversa/métodos , Ligação de Hidrogênio , Cinética , Solventes/química
2.
J Chromatogr A ; 1626: 461365, 2020 Aug 30.
Artigo em Inglês | MEDLINE | ID: mdl-32797844

RESUMO

Sequential injection chromatography (SIC) is an alternative for fast chromatographic separations with low consumption of organic solvents. However, its separation capacity is restricted by the use of short chromatographic columns and the limitations for gradient elution. The present work aimed to expand the analytical capacity of SIC by exploiting a multidimensional approach with two chromatographic columns, different in their separation mechanisms, which increased the selectivity and peak resolution. The viability of the proposal was demonstrated by separation of aromatic biogenic amines (histamine, tyramine, phenylethylamine, and tryptamine), whose unidimensional separation was not achieved either by using cyanopropyl or C18 chromatographic columns. In the two-dimensional approach, the fraction of the eluate unresolved in the first dimension (containing tyramine and phenylethylamine) was collected in a sampling loop and, subsequently, inserted in the second chromatographic dimension (heart-cutting mode). Under the optimized conditions, the first chromatographic dimension was based on a cyanopropyl monolithic column and an aqueous mobile phase composed of phosphoric acid solution, pH 2.5, while the second dimension employed a C18 superficially porous particle column and a mobile phase composed of acetonitrile and phosphoric acid aqueous solution, pH 2.5 (7:93, v/v). The total analysis time was 8 min, and a resolution of 1.72 was achieved between the nearest peaks (tyramine and phenylethylamine). Linear responses were obtained within 10 and 50 mg L-1 (r > 0.997), with detection limits estimated at 2.7, 7.7, 1.9, and 0.3 mg L-1, for histamine, tyramine, phenylethylamine, and tryptamine, respectively, and a coefficient of variation of 3.0% (n = 12).


Assuntos
Cromatografia/métodos , Acetonitrilos/química , Aminas Biogênicas/isolamento & purificação , Ácidos Fosfóricos/química , Solventes/química
3.
J Chromatogr A ; 1627: 461395, 2020 Sep 13.
Artigo em Inglês | MEDLINE | ID: mdl-32823100

RESUMO

Nowadays, enantioseparation of racemic pharmaceuticals in preparations is a prime concern by drug authorities across the globe. In the present work, it was attempted to develop novel enantioselective extraction method for five clinically used drugs (atenolol, propranolol, metoprolol, racecadotril, and raceanisodamine in their tablets) as racemates. The enantioselective solid-liquid extraction of these racemic drugs was carried out successfully by the use of chiral ionic liquid (CIL) in combination with a metal organic framework (MOF) for the first time. The composite CIL@MOF was synthesized from tropine based chiral ionic liquids with L-proline anion ([CnTr][L-Pro], n=3-6) and HKUST-1 type MOF, which was comprehensively characterized before being used as sorbent for enantioselective dispersive solid-liquid extraction. Preliminary selection of appropriate CIL was carried out on thin layer chromatography (TLC); under the joint participation of copper ion in the developing reagent, [C3Tr][L-Pro] ionic liquid showed better resolution performance with ΔRf value of 0.35 between the enantiomers was obtained for racemic atenolol. Moreover, the effect of copper salt dosage, amount of CIL, soli-liquid ratio and extraction time were investigated. The optimal conditions were obtained after thorough investigations; i.e. sample solution: ethanol, elution solvent: methanol, solid-liquid ratio: 12.5 mg:50 mL, amount of copper salt: 8 mg L-1, amount of impregnated CIL: 30% and extraction time of 30 min. As a result, enantiomeric excess values are 90.4%, 95%, 92%, 81.6% and 83.2% for atenolol, propranolol, metoprolol, racecadotril and raceanisodamine, respectively. The developed enantioselective method was validated following ICH guidelines and it was proved to be simple, effective and enantioselective way for separation of racemic pharmaceuticals with similar behaviors.


Assuntos
Líquidos Iônicos/química , Estruturas Metalorgânicas/química , Preparações Farmacêuticas/isolamento & purificação , Extração em Fase Sólida/métodos , Antagonistas Adrenérgicos beta/análise , Antagonistas Adrenérgicos beta/isolamento & purificação , Atenolol/análise , Atenolol/isolamento & purificação , Cromatografia Líquida de Alta Pressão/métodos , Cobre/química , Metoprolol/análise , Metoprolol/isolamento & purificação , Preparações Farmacêuticas/análise , Propranolol/análise , Propranolol/isolamento & purificação , Solventes/química , Estereoisomerismo
4.
J Chromatogr A ; 1627: 461398, 2020 Sep 13.
Artigo em Inglês | MEDLINE | ID: mdl-32823103

RESUMO

A new mode of dispersive solid phase extraction based on in situ formation of adsorbent in aqueous phase has been introduced as an efficient method for the extraction of some pesticide residues in fruit juice samples. In this method, polycarbonate which is an inexpensive polymer is used as an adsorbent for the first time. The method is followed by dispersive liquid-liquid microextraction for more enrichment of the analytes. In the present study, a proper amount of the polymer is dissolved in N,N-dimethyl formamide and the obtained solution is injected into an aqueous phase containing the analytes. After injection, polycarbonate particles are formed and adsorbed the analytes. Then, the adsorbent is separated from the aqueous solution and eluted by acetone. The obtained acetone phase is mixed with 1,1,1-trichloroethane and the mixture is dispersed into deionized water and a cloudy solution is formed. Ultimately, after centrifugation, the obtained sedimented phase containing the extracted analytes is injected into gas chromatography-flame ionization detection. In the proposed method, the adsorbent synthesis step, which often is a time-consuming, expensive, and laborious step in most adsorbent-based sample preparation methods, has been removed. Moreover, there is no need for sonication or vortex agitation. Under the optimized experimental conditions, the relative standard deviation was equal or less than 7% for intra- (n = 6) and inter-day (n = 5) precisions at a concentration of 50 µg L-1 of each pesticide. The limits of detection and quantification were in the ranges of 0.34-1.2 and 1.1-4.0 µg L-1, respectively. In addition, extraction recoveries and enrichment factors varied in the ranges of 44-89% and 220-443, respectively.


Assuntos
Sucos de Frutas e Vegetais/análise , Cromatografia Gasosa-Espectrometria de Massas/métodos , Resíduos de Praguicidas/análise , Centrifugação , Limite de Detecção , Microextração em Fase Líquida/métodos , Resíduos de Praguicidas/isolamento & purificação , Extração em Fase Sólida , Solventes/química , Triazinas/análise , Triazinas/isolamento & purificação , Água/química
5.
J Chromatogr A ; 1627: 461400, 2020 Sep 13.
Artigo em Inglês | MEDLINE | ID: mdl-32823105

RESUMO

In this work, a single cross-linking functional monomer, 2,5-divinylterephthalaldehyde, was designed and synthesized to simplify the preparation of molecularly imprinted polymers (MIPs). In the presence of estradiol as a template, MIPs were successfully prepared using 2,5-divinylterephthalaldehyde along with a solvent and initiator. This method reduced most of the complex variables encountered in the traditional synthesis. Characterization of the morphology and structure of the MIPs was performed by scanning electron microscopy, Fourier transform infrared spectroscopy, and Brunauer-Emmett-Teller analysis. Compared with non-imprinted polymers, the MIPs had higher adsorption capacities for five estrogens with imprinting factors above 2.9. The MIPs had high extraction efficiencies, good functional properties, long lifetimes, and good reproducibility, which made them suitable for solid-phase microextraction (SPME). Coupled with ultra-high performance liquid chromatography tandem mass spectrometry, the MIP-based fibers were applied to SPME for the analysis of five estrogens in milk samples. Under the best conditions, the established method had a wide linear range (0.5-10000 ng kg-1), low limits of detection (0.08-0.26 ng kg-1) and quantification (0.26-0.87 ng kg-1), good precision (3.2-8.1%, n = 6), and fiber-to-fiber reproducibility (4.3%-8.8%, n = 3). The MIPs-based fibers can be reused at least 60 times without apparent loss of extraction efficiency. Finally, this method was applied to the determination of target estrogens in milk samples with satisfactory relative recoveries (84.3%-105%, relative standard deviation ≤ 7.8%).


Assuntos
Estrogênios/isolamento & purificação , Leite/química , Impressão Molecular , Polímeros/química , Microextração em Fase Sólida/métodos , Adsorção , Animais , Cromatografia Líquida de Alta Pressão , Estradiol/análise , Estrogênios/análise , Limite de Detecção , Reprodutibilidade dos Testes , Solventes/química , Espectrometria de Massas em Tandem
6.
J Chromatogr A ; 1628: 461439, 2020 Sep 27.
Artigo em Inglês | MEDLINE | ID: mdl-32822979

RESUMO

Numerous structurally different amides and imides including succinimide derivatives exhibit diverse bioactive potential. The development of new compounds requires rationalization in the design in order to provide structural changes that guarantee favorable physico-chemical properties, pharmacological activity and safety. In the present research, a comprehensive study with comparison of the chromatographic lipophilicity and other physico-chemical properties of five groups of 1-arylsuccinimide derivatives was conducted. The chemometric analysis of their physico-chemical properties was carried out by using unsupervised (hierarchical cluster analysis and principal component analysis) and supervised pattern recognition methods (linear discriminant analysis), while the correlations between the in silico molecular features and chromatographic lipophilicity were examined applying linear and non-linear Quantitative Structure-Retention Relationship (QSRR) approaches. The main aim of the conducted research was to determine similarities and dissimilarities among the studied 1-arylsuccinimides, to point out the molecular features which have significant influence on their lipophilicity, as well as to establish high-quality QSRR models which can be used in prediction of chromatographic lipophilicity of structurally similar 1-arylsuccinimides. This study is a continuation of analysis and determination of the physico-chemical properties of 1-arylsuccinimides which could be important guidelines in further in vitro and eventually in vivo studies of their biological potential.


Assuntos
Técnicas de Química Analítica/métodos , Cromatografia em Camada Delgada , Relação Quantitativa Estrutura-Atividade , Solventes/química , Succinimidas/química , Análise por Conglomerados , Simulação por Computador , Análise de Componente Principal
7.
PLoS One ; 15(8): e0237881, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32817641

RESUMO

At present, the identification of honeysuckle aroma depends on experienced tasters, which results in inconsistencies due to human error. The key odorants have the potential to distinguish the different species and evaluate the quality of honeysuckle. Hence, in this study, a more scientific approach was applied to distinguish various honeysuckles. The volatile compounds of different species and parts of honeysuckle were separately extracted by headspace-solid phase microextraction (HS-SPME) and solvent assisted flavor evaporation (SAFE). Compounds with greater volatility such as aldehydes, limonene, γ-terpinene, and terpinolene were preferentially extracted by HS-SPME. As a complementary extraction method to HS-SPME, SAFE was found to recover comparatively more polar compounds such as eugenol, decanoic acid, and vanillin. Subsequently, key odorants with the highest flavour dilution (FD) factors were detected by aroma extract dilution analysis (AEDA). These were benzaldehyde, 4-ethylphenol, decanoic acid, vanillin, 3-methyl-2-butenal, and ß-ionone in honeysuckle flowers and γ-octalactone, 4-ethyl phenol, and vanillin in honeysuckle stem. Finally, principal component analysis (PCA) was conducted to analyze not only the key odorants of species and parts of honeysuckle but also their different origins. The results of PCA suggested that the species of honeysuckle contributed much more to variations in aroma rather than their origins. In conclusion, the application of the key odorants combined with PCA was demonstrated as a valid approach to differentiate species, origins, and parts of honeysuckle.


Assuntos
Lonicera/química , Odorantes/análise , Olfatometria/métodos , Microextração em Fase Sólida/métodos , Cromatografia Gasosa-Espectrometria de Massas/métodos , Lonicera/classificação , Lonicera/metabolismo , Solventes/química
8.
J Chromatogr A ; 1627: 461387, 2020 Sep 13.
Artigo em Inglês | MEDLINE | ID: mdl-32823095

RESUMO

A simple and efficient magnetic solid-phase extraction (MSPE) method was established with magnetic covalent organic framework (COF) as adsorbent to enrich organophosphorus pesticides from fatty milk samples, followed by the sensitive determination via LC-MS/MS. The key parameters influencing the MSPE efficiency were comprehensively investigated to afford an optimized procedure. All the target analytes could be captured directly by magnetic COF from milk without protein precipitation, making the pretreatment rapid and convenient. Systematic method validation demonstrated its satisfactory linearity, recoveries (80.0-105 %), and precision (RSDs <12.3 %). The method limits of quantification were 0.2-0.5 µg L-1. A comparison experiment to the reported solid-phase extraction fully verified the present MSPE more rapid, accurate, and environment-friendly. Furthermore, FT-IR and XPS analysis were performed to reveal the adsorption mechanisms of magnetic COF to organophosphorus pesticides, which could offer guidance on the rational design of COF adsorbent for various target analytes.


Assuntos
Fenômenos Magnéticos , Estruturas Metalorgânicas/química , Leite/química , Compostos Organofosforados/análise , Praguicidas/análise , Extração em Fase Sólida/métodos , Acetonitrilos/análise , Adsorção , Animais , Limite de Detecção , Espectroscopia Fotoeletrônica , Padrões de Referência , Reprodutibilidade dos Testes , Solventes/química , Espectroscopia de Infravermelho com Transformada de Fourier
9.
J Chromatogr A ; 1627: 461390, 2020 Sep 13.
Artigo em Inglês | MEDLINE | ID: mdl-32823096

RESUMO

A dispersive solid phase extraction method was combined with deep eutectic solvent-based solidification of floating organic drop-dispersive liquid-liquid microextraction and used for the extraction/preconcentration of some organophosphorus pesticides residues from edible oil samples. The extracted analytes were quantified with gas chromatography-nitrogen phosphorous detector. In this procedure, the sample lipids are saponified with a sodium hydroxide solution and then the analytes are adsorbed onto a primary secondary amine sorbent. After that the analytes are desorbed with acetone as an elution/dispersive solvent and mixed with choline chloride: 3,3-dimethyl butyric acid deep eutectic solvent and the mixture is rapidly dispersed into deionized water. Then, the obtained cloudy solution is centrifuged and placed into an ice bath. The extraction solvent is solidified on the top of the solution. Finally, it is removed and dissolved in acetonitrile, and 1 µL of the solution is injected into the separation system. Validation of the method showed that limits of detection and quantification were in the ranges of 0.06-0.24 and 0.20-0.56 ng mL-1, respectively. Enrichment factors and extraction recoveries of the analytes ranged from 170-192 and 68-77%, respectively. The method had an acceptable precision with relative standard deviations less than ≤9.2% for intra- (n=6) and inter-day (n=6) precisions at four concentrations (3, 10, 50, and 250 ng mL-1, each analyte). Finally the method was used for determination of the analytes in five edible oil samples.


Assuntos
Microextração em Fase Líquida/métodos , Compostos Organofosforados/análise , Praguicidas/análise , Óleos Vegetais/química , Extração em Fase Sólida/métodos , Solventes/química , Acetonitrilos/química , Reprodutibilidade dos Testes , Hidróxido de Sódio/química , Soluções , Sonicação , Fatores de Tempo
10.
J Chromatogr A ; 1626: 461345, 2020 Aug 30.
Artigo em Inglês | MEDLINE | ID: mdl-32797825

RESUMO

Modern liquid-liquid chromatography mainly refers to the following two kinds of chromatographic apparatuses: countercurrent chromatography based on hydrodynamic equilibrium systems and centrifugal partition chromatography based on hydrostatic equilibrium systems. In this paper, the recent advancements in enantioseparations by liquid-liquid chromatography, including the separation mechanism, chiral selector, two-phase solvent system, methods to improve the peak resolution and recent applications, are reviewed. The future outlook for liquid-liquid chromatography in enantioseparations is also proposed.


Assuntos
Cromatografia Líquida/métodos , Algoritmos , Distribuição Contracorrente , Concentração de Íons de Hidrogênio , Ligantes , Solventes/química , Estereoisomerismo
11.
J Chromatogr A ; 1626: 461348, 2020 Aug 30.
Artigo em Inglês | MEDLINE | ID: mdl-32797828

RESUMO

Solid-phase extraction (SPE) is a widely-used and very well-established sample preparation technique for liquid samples. An area of on-going focus for innovation in this field concerns the development of new and improved SPE sorbents that can enhance the sensitivity and/or the selectivity of SPE processes. In this context, mixed-mode ion-exchange sorbents have been developed and commercialised, thereby allowing enhanced capacity and selectivity to be offered by one single material. The ion-selectivity of these materials is such that either anion-exchange or cation-exchange is possible, however one limitation to their use is that more than one sorbent type is required to capture both anions and cations. In this paper, we disclose the design, synthesis and exploitation of a novel SPE sorbent based on microporous polymer microspheres with amphoteric character. We show that it is possible to switch the ion-exchange retention mechanism of the sorbent simply by changing the pH of the loading solution; anion-exchange dominates at low pH, cation-exchange dominates at high pH, and both mechanisms can contribute to retention when the polymer-bound amphoteric species, which are based on the α-amino acid sarcosine (N-methylglycine), are in a zwitterionic state. This is an interesting and useful feature, since it allows distinctly different groups of analytes (acids and bases) to be fractionated using one single amphoteric sorbent with dual-functionality. The sarcosine-based sorbent was applied to the SPE of acidic, basic and amphoteric analytes from ultrapure water, river water and effluent wastewater samples. Under optimised conditions (loading 100 mL of sample at pH 6, washing with 1 mL of MeOH and eluting with an acidic or basic additive in MeOH) the recoveries for most of the compounds were from 57% to 87% for river water and from 61% to 88% for effluent wastewater. We anticipate that these results will lay the basis for the development of a new family of multifunctional sorbents, where two or more separation mechanisms can be embedded within one single, bespoke material optimised for application to challenging chemical separations to give significant selectivity advantages over essentially all other state-of-the-art SPE sorbents.


Assuntos
Ácidos/química , Microesferas , Polímeros/química , Extração em Fase Sólida/métodos , Adsorção , Cátions , Concentração de Íons de Hidrogênio , Troca Iônica , Porosidade , Rios/química , Solventes/química , Águas Residuárias/química , Poluentes Químicos da Água/análise
12.
J Chromatogr A ; 1626: 461351, 2020 Aug 30.
Artigo em Inglês | MEDLINE | ID: mdl-32797831

RESUMO

Traditional polymer-separation methods, such as size-exclusion chromatography and (gradient) liquid adsorption chromatography, cannot provide separations exclusively based on the number of deprotonated carboxylic-acid groups along the backbone chain of polymers. A novel separation method, based on non-aqueous ion-exchange chromatography (NAIEX), was developed, which allows such a separation of acid-functional polymers that are soluble in organic solvents. The polar, aprotic N-methyl-2-pyrrolidone was found to be a suitable solvent. It features a high relative permittivity (favouring dissociation of ion pairs into free ions) and it is a good solvent for polymers and organic salts, such as triethyl-ammonium formate. A negative charge is established on these polymers by deprotonation of the carboxylic-acid groups in the presence of an organic superbase (tetramethyl guanidine). Traditional potent organic bases, such as triethylamine, do not possess the base strength to compensate for the increase in pKa of polymeric carboxylic acid groups in non-aqueous conditions. Triethyl-ammonium formate is proposed as an alternative to traditional salts used for elution in aqueous ion-exchange chromatography. Separation was performed on an industry-standard strong-anion-exchange column and (near-)universal detection of the polymers was performed by high-temperature evaporative-light-scattering detection. The NAIEX method yielded a separation based on the acid-functionality distribution of the polymer. NAIEX was compared with traditional normal- and reversed-phase liquid-chromatography approaches for the separation of acid-functional copolymers.


Assuntos
Cromatografia por Troca Iônica/métodos , Cromatografia Líquida de Alta Pressão , Cromatografia de Fase Reversa , Polímeros/química , Espectroscopia de Prótons por Ressonância Magnética , Sais/química , Solventes/química
13.
J Chromatogr A ; 1626: 461358, 2020 Aug 30.
Artigo em Inglês | MEDLINE | ID: mdl-32797837

RESUMO

In this study, the in-situ conversion of the synthesized Co-Al layered double hydroxide (Co-Al LDH) nanosheets to three dimensional hierarchical zeolitic imidazolate framework-67 (3D HZIF-67) was presented as a cost-effective, highly efficient, flexible and robust sorbent to carry out the microextraction process. In the first stage, the anodized aluminum foil was prepared electrochemically. Then, the Co-Al LDH precursor was constructed on the surface of the previously-prepared anodized Al foil applying in-situ formation approach. The procedure is followed by the conversion of the prepared Co-Al LDH film to 3D HZIF-67 film via a facile solvothermal method without adding cobalt salt. The in-situ prepared 3D HZIF-67-anodized Al was used for the thin film microextraction (TFME) of caffeine. The effective factors in TFME procedure were investigated and optimized through applying Central Composite Design (CCD). In the obtained optimal condition, the calibration curves for TFME-HPLC-UV of caffeine were linear in the range of 1-200 µg L-1 with the coefficient of determination (r2) higher than 0.9915. The limits of detection were 0.33 and 0.38 µg L-1, in water and urine matrices, respectively. Moreover, the enrichment factors (EFs) and absolute recoveries (%AR) were also calculated as 173-198 and 57.1%-65.3%, respectively. The inter-day relative standard deviations (RSDs) were evaluated as the method precision for 20 and 200 µg L-1 of spiked sample and were between 4.9-6.1%. The repeatability of the preparation step was investigated as batch-to-batch reproducibility and it was found to be 4.9%; as a result, the reproducibility of the presented film was approved. Finally, the proposed method was utilized to determine caffeine (as the model analyte) from different types of real samples including urine, coffee, beverage (Pepsi) and shampoo. The obtained recoveries (higher than 88%) confirmed the capability of the method for real sample analysis.


Assuntos
Alumínio/química , Cafeína/isolamento & purificação , Cromatografia Líquida de Alta Pressão/métodos , Cobalto/química , Hidróxidos/química , Imidazóis/química , Raios Ultravioleta , Zeolitas/química , Adsorção , Eletrodos , Limite de Detecção , Microscopia de Força Atômica , Porosidade , Reprodutibilidade dos Testes , Solventes/química , Propriedades de Superfície
14.
J Chromatogr A ; 1626: 461427, 2020 Aug 30.
Artigo em Inglês | MEDLINE | ID: mdl-32739066

RESUMO

The physicochemical properties of small molecules that can be determined by retention measurements in reversed-phase liquid chromatography include solvent-based properties inferred from equilibrium processes occurring predominantly in the mobile phase and sorption properties for materials which can be used as stationary phases inferred from solute-stationary phase interactions. In addition, physicochemical properties can be estimated from correlation models based on surrogate chromatographic systems with a similar capability for intermolecular interactions to the chemical or biological system. Examples of properties determined by direct methods include molecular descriptors (solvation parameter model), acid dissociation constants, formation constants, and surface properties of solids determined by inverse liquid chromatography. Examples of properties estimated by indirect methods include hydrophobicity, lipophilicity, n-octanol-water partition constant, soil-water sorption constant, non-specific toxicity to fish and microorganisms, and permeation coefficients for the blood-brain and skin-water barriers. Since all approaches depend on an accurate measurement of chromatographic retention parameters typical operational and mechanistic problems are discussed from the perspective of data quality. Fundamentally the accuracy of direct methods is limited by stationary phase heterogeneity and indirect methods by the limited number of suitable surrogate chromatographic models.


Assuntos
Cromatografia Líquida de Alta Pressão/métodos , Cromatografia de Fase Reversa , Interações Hidrofóbicas e Hidrofílicas , Membranas Artificiais , Octanóis/química , Solo/química , Solventes/química , Água/química
15.
J Chromatogr A ; 1626: 461370, 2020 Aug 30.
Artigo em Inglês | MEDLINE | ID: mdl-32797849

RESUMO

Betacyanins, natural plant pigments, from Iresine herbstii Hook. ex Lindl. leaf extract were separated for the first time by high-speed countercurrent chromatography (HSCCC) in a highly polar solvent system composed of PrOH-ACN-(NH4)2SO4satd.soln-H2O (1.0:0.5:1.2:1.0; v/v/v/v) in the tail-to-head mode. The flow rate of the mobile phase was 2.0 ml/min and the column rotation speed was 860 rpm. The retention of the stationary phase was 81.0%. For the identification of separated betacyanins in the crude extract and in the HSCCC fractions, as well as for the molecular formulas and multi-step fragmentation pattern elucidation, liquid chromatography with tandem mass spectrometry and high-resolution ion-trap time-of-flight mass spectrometry were performed. The innovative application of the HSCCC system for fractionation of the betacyanins present in I. herbstii leaves enabled effective separation as well as preconcentration of the pigments for further low- and high-resolution LC-MS/MS analysis. HSCCC separation enabled identification of 22 betacyanins, of which 18 had not been detected previously in the leaves of I. herbstii, and four of these betacyanins (sinapoyl-gomphrenin and coumaroyl-gomphrenin as well as their epimers) were identified for the first time in the Iresine genus.


Assuntos
Amaranthaceae/química , Betacianinas/análise , Distribuição Contracorrente/métodos , Solventes/química , Amaranthaceae/metabolismo , Betacianinas/isolamento & purificação , Betacianinas/normas , Cromatografia Líquida de Alta Pressão/normas , Extratos Vegetais/química , Folhas de Planta/química , Folhas de Planta/metabolismo , Padrões de Referência , Espectrometria de Massas em Tandem/normas
16.
J Chromatogr A ; 1626: 461373, 2020 Aug 30.
Artigo em Inglês | MEDLINE | ID: mdl-32797851

RESUMO

Simulation software for liquid chromatography can accelerate method development capabilities. In two-dimensional chromatography this is particularly attractive because there are more method variables to consider, provided simulations can account for the effects of injecting effluent from the first dimension separation into the second dimension column. In this paper we describe the adaptation of a previously described model (the Forssén model) to enable prediction of the profile of an injection pulse as it exits an Active Solvent Modulation (ASM) valve and enters the second dimension column under a variety of flow rate and sample loop size conditions (a global model). Experimentally measured injection profiles were used to train empirical models capable of generating injection profiles as a function of sample loop volume and flow rate. The resulting parameters were then used to generate an injection profile for a loop volume not used in the training set. The resulting profile agreed well with the experimentally obtained profile for this sample loop. Finally, chromatograms were simulated using previously developed simulation software incorporating the injection profile models developed in this work. Chromatographic peaks were simulated for valerophenone on an Agilent Zorbax Stablebond C18 stationary phase with an acetonitrile/water mobile phase gradient. Results of simulations based on experimental injection profiles, profiles predicted using the Forssén or global models, and rectangular injection profiles were compared. Comparison of the resulting chromatographic peaks revealed good agreement between those produced using experimental profiles or the Forssén or global models, with less than ± 0.3% deviations for retention times and less than ± 10% deviations for the peak widths (expressed as σ).


Assuntos
Cromatografia Líquida/métodos , Solventes/química , Acetonitrilos/química , Água/química
17.
J Chromatogr A ; 1626: 461377, 2020 Aug 30.
Artigo em Inglês | MEDLINE | ID: mdl-32797853

RESUMO

This study reports the use ofa natural deep eutectic solvent (NADES) with hollow fiber-microporous membrane liquid-liquid microextraction (HF-MMLLE) for the multiclass determination of 11 compounds classified as emerging contaminantsin water. Different deep eutectic solvents were synthetized and Thymol: Camphor (1:1 molar fraction) wasused as extraction solvent. The Thymol:Camphor was impregnated into the polypropylene membrane porous for 10 min, replacing commonly used solvents (ex. hexane and octanol). The optimized parameters were obtained by multi and univariate models. Extractions were carried out for 50 min using 1.5 mL of water sample at pH 6 and without addition of salt while desorption was made in a mixture of acetone: methanol (3:1, v/v) for 15 min. Separation/quantification was conducted by HPLC with a diode array detection (DAD)and calibration curves were obtained for each analyte. Determination coefficients higher than 0.9906 and limits of detection ranged from 0.3 to 6.1 µg L-1. Intraday precision (n = 3) ranged from 1.6 to 18.4% and inter day from 5.0 to 21.3%. Relative recoveries were performed in tap and stream water and ranged from 64 to 123%.


Assuntos
Cromatografia Líquida de Alta Pressão/métodos , Microextração em Fase Líquida/métodos , Solventes/química , Poluentes Químicos da Água/análise , Calibragem , Cromatografia Líquida de Alta Pressão/normas , Interações Hidrofóbicas e Hidrofílicas , Membranas Artificiais , Polipropilenos/química , Porosidade , Espectrofotometria , Poluentes Químicos da Água/isolamento & purificação , Poluentes Químicos da Água/normas
18.
J Chromatogr A ; 1627: 461414, 2020 Sep 13.
Artigo em Inglês | MEDLINE | ID: mdl-32823112

RESUMO

Various techniques have been evaluated for the extraction and cleanup of pesticides from environmental samples. In this work, a Selective Pressurized Liquid Extraction (SPLE) method for pesticides was developed using a Thermo Fisher Scientific Accelerated Solvent Extraction (ASE) system. This instrument was compared to the newly introduced (2017) extraction instrument, the Energized Dispersive Guided Extraction (EDGE) system, which combines Pressurized Liquid Extraction (PLE) and dispersive Solid Phase Extraction (dSPE). We first optimized the SPLE method using the ASE instrument for pesticide extraction from alfalfa leaves using layers of Florisil and graphitized carbon black (GCB) downstream of the leaf homogenate in the extraction cell (Layered ASE method). We then compared results obtained for alfalfa and citrus leaves with the Layered ASE method to those from a method in which the leaf homogenate and sorbents were mixed (Mixed ASE method) and to similar methods modified for use with EDGE (Layered EDGE and Mixed EDGE methods). The ASE and EDGE methods led to clear, colorless extracts with low residual lipid weight. No significant differences in residual lipid masses were observed between the methods. The UV-Vis spectra showed that Florisil removed a significant quantity of the light-absorbing chemicals, but that GCB was required to produce colorless extracts. Recoveries of spiked analytes into leaf homogenates were generally similar among methods, but in several cases, significantly higher recoveries were observed in ASE extracts. Nonetheless, no significant differences were observed among pesticide concentrations in field samples when calculated with the isotope dilution method in which labelled surrogates were added to samples before extraction. The extraction time with the ASE methods was ~45 minutes, which was ~4.5 times longer than with the EDGE methods. The EDGE methods used ~10 mL more solvent than the ASE methods. Based on these results, the EDGE is an acceptable extraction instrument and, for most compounds, the EDGE had a similar extraction efficiency to the ASE methods.


Assuntos
Técnicas de Química Analítica/métodos , Praguicidas/análise , Folhas de Planta/química , Solventes/química , Lipídeos/química , Medicago sativa/química , Resíduos de Praguicidas/análise , Extratos Vegetais/química , Espectrofotometria Ultravioleta
19.
J Chromatogr A ; 1627: 461416, 2020 Sep 13.
Artigo em Inglês | MEDLINE | ID: mdl-32823114

RESUMO

Animal feeds are often reported to be contaminated with chemical residues, and when present above the maximum legal limit, these compounds can cause harmful effects to consumers of animal produce. Thus, animal feed safety is an important regulatory concern. The aim of this study was to optimise a multiresidue method for the simultaneous analysis of multi-class pesticides and a number of frequently used veterinary drugs using LC-MS/MS and GC-MS/MS. The method was validated in a range of feed matrices, including maize feed, poultry feed and mixed feed concentrate. The optimised sample preparation workflow involved extraction of feeds (5 g) with ethyl acetate (10 mL), followed by a freezing step (at -20°C) used for eliminating the matrix co-extractives. The extract was further cleaned by dispersive solid phase extraction with a combination of primary secondary amine, C18 and florisil sorbents. From the cleaned-extract, an aliquot was analysed by GC-MS/MS, while another portion of it was solvent-exchanged to acetonitrile:water (50:50) and then analysed by LC-MS/MS. This method effectively minimised the matrix interferences. A total of 192 pesticides was analysed by GC-MS/MS within a runtime of 22 min. The LC-MS/MS method was validated for 187 compounds including 17 veterinary drugs. For most of the compounds, the limit of quantification (LOQ) was 0.01 mg/kg. The recoveries at LOQ and higher levels ranged between 70% and 120%, with precision-RSDs of < 20%. The method provided a precise analysis in a wide range of market-feed samples. As shown, the method is suitable for regulatory and commercial testing purposes.


Assuntos
Ração Animal/análise , Cromatografia Líquida/métodos , Praguicidas/análise , Espectrometria de Massas em Tandem/métodos , Drogas Veterinárias/análise , Animais , Congelamento , Cromatografia Gasosa-Espectrometria de Massas , Limite de Detecção , Resíduos de Praguicidas/análise , Reprodutibilidade dos Testes , Solventes/química , Água/química
20.
J Chromatogr A ; 1627: 461421, 2020 Sep 13.
Artigo em Inglês | MEDLINE | ID: mdl-32823116

RESUMO

Herein we present an efficient, column-switching method that relies on a custom-made T-union passive diffusion micromixer to assist water dilution and promote trap solute focusing of a high sample volume dissolved in pure organic solvent using a 0.075 mm i.d. nano-LC column. This method allows injecting 20 µL (or higher) of sample volume, speeding up the analysis time, with a 400-fold increase of the limits of quantitation for selected compounds. Five pesticides in different media were used as model compounds, and the analyses were carried out with a triple quadrupole mass spectrometer equipped with a Liquid Electron Ionization (LEI) LC-MS interface working in multiple reaction monitoring (MRM) mode. The system microfluidics were investigated using COMSOL modeling software. Robustness of the entire system was evaluated using a post-extraction addition soil extracts with limits of detection values spanning from 0.10 to 0.45 µg/L. Reproducible results in terms of peak area, peak shape, and retention times were achieved in soil matrix. Repeatability test on peak area variations were lower than 10%.


Assuntos
Cromatografia de Fase Reversa/métodos , Elétrons , Microfluídica/métodos , Nanopartículas/química , Espectrometria de Massas em Tandem/métodos , Água/química , Acetonitrilos/química , Difusão , Limite de Detecção , Praguicidas/análise , Reprodutibilidade dos Testes , Solventes/química
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