Optimizing separations in on-line comprehensive two-dimensional liquid chromatography

Online comprehensive two-dimensional liquid chromatography (LC × LC) has become an attractive option for the analysis of complex non-volatile samples found in various fields (e.g. environmental studies, food, life, and polymer sciences). LC × LC complements the highly popular hyphenated systems that combine liquid chromatography with mass spectrometry. LC × LC is also applied to the analysis of samples that are not compatible with mass spectrometry (e.g. high-molecular-weight polymers), providing important information on the distribution of the sample components along chemical dimensions (molecular weight, charge, lipophilicity, stereochemistry, etc.). Also, in comparison with conventional one-dimensional liquid chromatography, LC × LC provides a greater separation power (peak capacity). Because of the additional selectivity and higher peak capacity, the combination of LC × LC with mass spectrometry allows for simpler mixtures of compounds to be introduced in the ion source at any given time, improving quantitative analysis by reducing matrix effects. In this review, we summarize the rationale and principles of LC × LC experiments, describe advantages and disadvantages of combining different selectivities and discuss strategies to improve the quality of LC × LC separations.
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Abstract

Online comprehensive two-dimensional liquid chromatography (LC × LC) has become an attractive option for the analysis of complex non-volatile samples found in various fields (e.g. environmental studies, food, life, and polymer sciences). LC × LC complements the highly popular hyphenated systems that combine liquid chromatography with mass spectrometry. LC × LC is also applied to the analysis of samples that are not compatible with mass spectrometry (e.g. high-molecular-weight polymers), providing important information on the distribution of the sample components along chemical dimensions (molecular weight, charge, lipophilicity, stereochemistry, etc.). Also, in comparison with conventional one-dimensional liquid chromatography, LC × LC provides a greater separation power (peak capacity). Because of the additional selectivity and higher peak capacity, the combination of LC × LC with mass spectrometry allows for simpler mixtures of compounds to be introduced in the ion source at any given time, improving quantitative analysis by reducing matrix effects. In this review, we summarize the rationale and principles of LC × LC experiments, describe advantages and disadvantages of combining different selectivities and discuss strategies to improve the quality of LC × LC separations.

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Magnetic molecularly imprinted polymers for recognition and enrichment of polysaccharides from seaweed

New magnetic molecularly imprinted polymers with two templates were fabricated for recognition of polysaccharides (fucoidan and alginic acid) from seaweed by magnetic solid-phase extraction, and the materials were modified by seven types of deep eutectic solvents. It was found that the deep eutectic solvents magnetic molecularly imprinted polymers showed stronger recognition and higher recoveries for fucoidan and alginic acid than magnetic molecularly imprinted polymers, and the deep eutectic solvents-4-magnetic molecularly imprinted polymers had the best effects. The practical recovery of the two polysaccharides (fucoidan and alginic acid) purified with deep eutectic solvents-4-magnetic molecular imprinted polymers in seaweed under the optimal conditions were 89.87, and 92.0%, respectively, and the actual amounts extracted were 20.6 and 18.7 μg·g−1, respectively. To sum up, the developed method proved to be a novel and promising method for the recognition of complex polysaccharide samples from seaweed.
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Abstract

New magnetic molecularly imprinted polymers with two templates were fabricated for recognition of polysaccharides (fucoidan and alginic acid) from seaweed by magnetic solid-phase extraction, and the materials were modified by seven types of deep eutectic solvents. It was found that the deep eutectic solvents magnetic molecularly imprinted polymers showed stronger recognition and higher recoveries for fucoidan and alginic acid than magnetic molecularly imprinted polymers, and the deep eutectic solvents-4-magnetic molecularly imprinted polymers had the best effects. The practical recovery of the two polysaccharides (fucoidan and alginic acid) purified with deep eutectic solvents-4-magnetic molecular imprinted polymers in seaweed under the optimal conditions were 89.87, and 92.0%, respectively, and the actual amounts extracted were 20.6 and 18.7 μg·g−1, respectively. To sum up, the developed method proved to be a novel and promising method for the recognition of complex polysaccharide samples from seaweed.

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Deep eutectic solvent based magnetic nanofluid in the development of stir bar sorptive dispersive microextraction: An efficient hyphenated sample preparation for ultra-trace nitroaromatic explosives extraction in wastewater

A deep eutectic solvent based magnetic nanofluid was coupled with stir bar sorptive dispersive microextraction as a hyphenated sample preparation technique. The neodymium core magnetic stir bar was coated physically with nanofluid of magnetic carbon nanotube nanocomposites and deep eutectic solvents. The prepared nanofluid has magnetic and strong sorbing properties and is compatible with gas chromatography. In this nanofluid, the deep eutectic solvent acts simultaneously as both carrier and stabilizer for magnetic nanotubes. The predominant experimental variables affecting the extraction efficiency of nitroaromatic compounds were evaluated. Under the optimized conditions, the limit of detection and enrichment factor were in the range of 0.2–4.9 ng L−1 and 852–1480, respectively. The relative standard deviations were between 5.6 and 10.2% (n = 6). Method validation was performed by both spiking–recovery method and comparison of results with other methods. Finally, the proposed method was successfully applied for the extraction and preconcentration of nitroaromatic explosives in water samples, followed by determination by gas chromatography with micro-electron capture detection.
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Abstract

A deep eutectic solvent based magnetic nanofluid was coupled with stir bar sorptive dispersive microextraction as a hyphenated sample preparation technique. The neodymium core magnetic stir bar was coated physically with nanofluid of magnetic carbon nanotube nanocomposites and deep eutectic solvents. The prepared nanofluid has magnetic and strong sorbing properties and is compatible with gas chromatography. In this nanofluid, the deep eutectic solvent acts simultaneously as both carrier and stabilizer for magnetic nanotubes. The predominant experimental variables affecting the extraction efficiency of nitroaromatic compounds were evaluated. Under the optimized conditions, the limit of detection and enrichment factor were in the range of 0.2–4.9 ng L−1 and 852–1480, respectively. The relative standard deviations were between 5.6 and 10.2% (= 6). Method validation was performed by both spiking–recovery method and comparison of results with other methods. Finally, the proposed method was successfully applied for the extraction and preconcentration of nitroaromatic explosives in water samples, followed by determination by gas chromatography with micro-electron capture detection.

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Core–shell microspheres with porous nanostructured shells for liquid chromatography

The development of new stationary phase has been the key aspect for fast and efficient high-performance liquid chromatography separation with relatively low backpressure. Core–shell particles, with a solid core and porous shell, have been extensively investigated and commercially manufactured in the last decade. The excellent performance of core–shell particles columns has been recorded for a wide range of analytes, covering small and large molecules, neutral and ionic (acidic and basic), biomolecules, and metabolites. In this review, we firstly introduce the advance and advantages of core–shell particles (or more widely known as superficially porous particles) against non-porous particles and fully porous particles. This is followed by the detailed description of various methods used to fabricate core–shell particles. We then discuss the applications of common silica core–shell particles (mostly commercially manufactured), spheres-on-sphere particles, and core–shell particles with a non-silica shell. This review concludes with a summary and perspective on the development of stationary phase materials for high-performance liquid chromatography applications.
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Abstract

The development of new stationary phase has been the key aspect for fast and efficient high-performance liquid chromatography separation with relatively low backpressure. Core–shell particles, with a solid core and porous shell, have been extensively investigated and commercially manufactured in the last decade. The excellent performance of core–shell particles columns has been recorded for a wide range of analytes, covering small and large molecules, neutral and ionic (acidic and basic), biomolecules, and metabolites. In this review, we firstly introduce the advance and advantages of core–shell particles (or more widely known as superficially porous particles) against non-porous particles and fully porous particles. This is followed by the detailed description of various methods used to fabricate core–shell particles. We then discuss the applications of common silica core–shell particles (mostly commercially manufactured), spheres-on-sphere particles, and core–shell particles with a non-silica shell. This review concludes with a summary and perspective on the development of stationary phase materials for high-performance liquid chromatography applications.

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Direct preparation of a graphene oxide modified monolith in a glass syringe as a solid-phase extraction cartridge for the extraction of quaternary ammonium alkaloids from Chinese patent medicine

Packed cartridges have been widely used in solid-phase extraction. However, there are still some drawbacks, such as they are blocked easily and the method is time-consuming. In view of the advantages of monoliths, a monolithic extraction material has been directly synthesized in a glass syringe without any gap between the monolith and syringe inner wall. The monolithic syringe was modified with graphene oxide by loading graphene oxide dispersion onto it. The content of graphene oxide and the surface topography of the monolith have been evaluated by elemental analysis and scanning electron microscopy, respectively, which confirmed the successful modification. This prepared graphene oxide-modified monolithic syringe was directly used as a traditional solid-phase extraction cartridge. As expected, it shows good permeability and excellent capability for the extraction of quaternary ammonium alkaloids. The sample loading velocity (1–6 mL/min) does not affect the recovery. Under the optimal conditions, good linearities (R = 0.9992–0.9998) were obtained for five quaternary ammonium alkaloids, and the limits of detection and quantification were 0.5-1 and 1–2 μg/L, respectively. The proposed method was successfully applied for the analysis of quaternary ammonium alkaloids in Chinese patent medicine.

Abstract

Packed cartridges have been widely used in solid-phase extraction. However, there are still some drawbacks, such as they are blocked easily and the method is time-consuming. In view of the advantages of monoliths, a monolithic extraction material has been directly synthesized in a glass syringe without any gap between the monolith and syringe inner wall. The monolithic syringe was modified with graphene oxide by loading graphene oxide dispersion onto it. The content of graphene oxide and the surface topography of the monolith have been evaluated by elemental analysis and scanning electron microscopy, respectively, which confirmed the successful modification. This prepared graphene oxide-modified monolithic syringe was directly used as a traditional solid-phase extraction cartridge. As expected, it shows good permeability and excellent capability for the extraction of quaternary ammonium alkaloids. The sample loading velocity (1–6 mL/min) does not affect the recovery. Under the optimal conditions, good linearities (= 0.9992–0.9998) were obtained for five quaternary ammonium alkaloids, and the limits of detection and quantification were 0.5-1 and 1–2 μg/L, respectively. The proposed method was successfully applied for the analysis of quaternary ammonium alkaloids in Chinese patent medicine.

Recent advances in methods for the analysis of protein o-glycosylation at proteome level

O-Glycosylation, which refers to the glycosylation of the hydroxyl group of side chains of Serine/Threonine/Tyrosine residues, is one of the most common post-translational modifications. Compared with N-linked glycosylation, O-glycosylation is less explored because of its complex structure and relatively low abundance. Recently, O-glycosylation has drawn more and more attention for its various functions in many sophisticated biological processes. To obtain a deep understanding of O-glycosylation, many efforts have been devoted to develop effective strategies to analyze the two most abundant types of O-glycosylation, i.e. O-N-acetylgalactosamine and O-N-acetylglucosamine glycosylation. In this review, we summarize the proteomics workflows to analyze these two types of O-glycosylation. For the large-scale analysis of mucin-type glycosylation, the glycan simplification strategies including the ‘SimpleCell’ technology was introduced. A variety of enrichment methods including lectin affinity chromatography, hydrophilic interaction chromatography, hydrazide chemistry, and chemoenzymatic method were introduced for the proteomics analysis of O-N-acetylgalactosamine and O-N-acetylglucosamine glycosylation.
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Abstract

O-Glycosylation, which refers to the glycosylation of the hydroxyl group of side chains of Serine/Threonine/Tyrosine residues, is one of the most common post-translational modifications. Compared with N-linked glycosylation, O-glycosylation is less explored because of its complex structure and relatively low abundance. Recently, O-glycosylation has drawn more and more attention for its various functions in many sophisticated biological processes. To obtain a deep understanding of O-glycosylation, many efforts have been devoted to develop effective strategies to analyze the two most abundant types of O-glycosylation, i.e. O-N-acetylgalactosamine and O-N-acetylglucosamine glycosylation. In this review, we summarize the proteomics workflows to analyze these two types of O-glycosylation. For the large-scale analysis of mucin-type glycosylation, the glycan simplification strategies including the ‘SimpleCell’ technology was introduced. A variety of enrichment methods including lectin affinity chromatography, hydrophilic interaction chromatography, hydrazide chemistry, and chemoenzymatic method were introduced for the proteomics analysis of O-N-acetylgalactosamine and O-N-acetylglucosamine glycosylation.

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Poly(norepinephrine)-coated open tubular column for the separation of proteins and recombination human erythropoietin by capillary electrochromatography

Recombinant human erythropoietin is an important therapeutic protein with high economic interest due to the benefits provided by its clinical use for the treatment of anemias associated with chronic renal failure and chemotherapy. In this work, a poly(norepinephrine)-coated open tubular column was successfully prepared based on the self-polymerization of norepinephrine under mild alkaline condition, the favorable film forming and easy adhesive properties of poly(norepinephrine). The poly(norepinephrine) coating was characterized by scanning electron microscopy and measurement of the electro-osmotic flow. The thickness of the coating was about 431 nm. The electrochromatographic performance of the poly(norepinephrine)-coated open tubular column was evaluated by separation of proteins. Some basic and acidic proteins including two variants of bovine serum albumin and two variants of β-lactoglobulin achieved separation in the poly(norepinephrine)-coated open tubular column. More importantly, the column demonstrated separation ability for the glycoforms of recombinant human erythropoietin. In addition, the column demonstrated good repeatability with the run-to-run, day-to-day and column-to-column relative standard deviations of migration times of proteins less than 3.40%.
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Abstract

Recombinant human erythropoietin is an important therapeutic protein with high economic interest due to the benefits provided by its clinical use for the treatment of anemias associated with chronic renal failure and chemotherapy. In this work, a poly(norepinephrine)-coated open tubular column was successfully prepared based on the self-polymerization of norepinephrine under mild alkaline condition, the favorable film forming and easy adhesive properties of poly(norepinephrine). The poly(norepinephrine) coating was characterized by scanning electron microscopy and measurement of the electro-osmotic flow. The thickness of the coating was about 431 nm. The electrochromatographic performance of the poly(norepinephrine)-coated open tubular column was evaluated by separation of proteins. Some basic and acidic proteins including two variants of bovine serum albumin and two variants of β-lactoglobulin achieved separation in the poly(norepinephrine)-coated open tubular column. More importantly, the column demonstrated separation ability for the glycoforms of recombinant human erythropoietin. In addition, the column demonstrated good repeatability with the run-to-run, day-to-day and column-to-column relative standard deviations of migration times of proteins less than 3.40%.

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A review of methods for the chemical characterization of cannabis natural products

Cannabis has garnered a great deal of new attention in the past couple of years in the United States due to the increasing instances of its legalization for recreational use and indications for medicinal benefit. Despite a growing number of laboratories focused on cannabis analysis, the separation science literature pertaining to the determination of cannabis natural products is still in its infancy despite the plant having been utilized by humans for nearly 30 000 years and it being now the most widely used drug world-wide. This is largely attributable to the restrictions associated with cannabis as it is characterized as a Schedule 1 drug in the United States. Presented here are reviewed analytical methods for the determination of cannabinoids (primarily) and terpenes (secondarily), the primary natural products of interest in cannabis plants. Focus is placed foremost on analyses from plant extracts and the various instrumentation and techniques that are used, but some coverage is also given to analysis of cannabinoid metabolites found in biological fluids. The goal of this work is to provide a collection of relevant separation science information, upon which the field of cannabis analysis can continue to grow.
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Abstract

Cannabis has garnered a great deal of new attention in the past couple of years in the United States due to the increasing instances of its legalization for recreational use and indications for medicinal benefit. Despite a growing number of laboratories focused on cannabis analysis, the separation science literature pertaining to the determination of cannabis natural products is still in its infancy despite the plant having been utilized by humans for nearly 30 000 years and it being now the most widely used drug world-wide. This is largely attributable to the restrictions associated with cannabis as it is characterized as a Schedule 1 drug in the United States. Presented here are reviewed analytical methods for the determination of cannabinoids (primarily) and terpenes (secondarily), the primary natural products of interest in cannabis plants. Focus is placed foremost on analyses from plant extracts and the various instrumentation and techniques that are used, but some coverage is also given to analysis of cannabinoid metabolites found in biological fluids. The goal of this work is to provide a collection of relevant separation science information, upon which the field of cannabis analysis can continue to grow.

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Critical comparison of the on-line and off-line molecularly imprinted solid-phase extraction of patulin coupled with liquid chromatography

Reaching trace amounts of mycotoxin contamination requires sensitive and selective analytical tools for their determination. Improving the selectivity of sample pre-treatment steps covering new and modern extraction techniques is one way to achieve it. Molecularly imprinted polymers as selective sorbent for extraction undoubtedly meet these criteria. The presented work is focused on the hyphenation of on-line molecularly imprinted solid-phase extraction with a chromatography system using a column-switching approach. Making a critical comparison with a simultaneously developed off-line extraction procedure, evaluation of pros and cons of each method, and determining the reliability of both methods on a real sample analysis were carried out. Both high-performance liquid chromatography methods, the one using off-line extraction on molecularly imprinted polymer and the on-line column-switching approach, were validated, and the validation results were compared against each other. Although automation leads to significant time savings, fewer human errors and no required handling of toxic solvents, it reached worse detection limits (15 vs. 6 μg/L), worse recovery values (68.3–123.5 vs. 81.2–109.9%) and worse efficiency throughout the entire clean-up process in comparison with the off-line extraction method. The difficulties encountered, the compromises made during the optimization of on-line coupling and their critical evaluation are presented in detail.
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Abstract

Reaching trace amounts of mycotoxin contamination requires sensitive and selective analytical tools for their determination. Improving the selectivity of sample pre-treatment steps covering new and modern extraction techniques is one way to achieve it. Molecularly imprinted polymers as selective sorbent for extraction undoubtedly meet these criteria. The presented work is focused on the hyphenation of on-line molecularly imprinted solid-phase extraction with a chromatography system using a column-switching approach. Making a critical comparison with a simultaneously developed off-line extraction procedure, evaluation of pros and cons of each method, and determining the reliability of both methods on a real sample analysis were carried out. Both high-performance liquid chromatography methods, the one using off-line extraction on molecularly imprinted polymer and the on-line column-switching approach, were validated, and the validation results were compared against each other. Although automation leads to significant time savings, fewer human errors and no required handling of toxic solvents, it reached worse detection limits (15 vs. 6 μg/L), worse recovery values (68.3–123.5 vs. 81.2–109.9%) and worse efficiency throughout the entire clean-up process in comparison with the off-line extraction method. The difficulties encountered, the compromises made during the optimization of on-line coupling and their critical evaluation are presented in detail.

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Solvent-vapor-assisted liquid–liquid microextraction: A novel method for the determination of phthalate esters in aqueous samples using GC–MS

A novel liquid–liquid microextraction method, namely, solvent-vapor-assisted liquid–liquid microextraction for the determination of dimethyl phthalate, diethyl phthalate, dibutyl phthalate and bis(2-ethylhexyl) phthalate in the aqueous samples using gas chromatography with mass spectrometry was developed. In the proposed method, extracting solvent was heated, and solvent vapor as the extracting phase was injected into the sample solution. As a result of the low temperature of the sample solution and higher density of the extracting phase than the aqueous medium, solvent vapor was condensed and an organic-phase drop formed in the bottom of sample tube. Because of the gas status of the extracting solvent, the surface area between the extracting solvent and the aqueous sample was remarkably high. Under the optimized conditions, tetrachloride carbon was used as an extracting solvent. The method shows high coefficient of determination (R2) values in the range of 0.5–200 and 1.0–200 ng/mL for the target analytes. Enrichment factors and limits of detection for the studied phthalates are obtained in the ranges of 2800–3000 and 0.15–0.3 ng/mL, respectively. Recoveries and relative standard deviations were in the range of 80.0–100.0 and 2.2–7.8%, respectively. The proposed method successfully used for analysis of several aqueous samples.

Abstract

A novel liquid–liquid microextraction method, namely, solvent-vapor-assisted liquid–liquid microextraction for the determination of dimethyl phthalate, diethyl phthalate, dibutyl phthalate and bis(2-ethylhexyl) phthalate in the aqueous samples using gas chromatography with mass spectrometry was developed. In the proposed method, extracting solvent was heated, and solvent vapor as the extracting phase was injected into the sample solution. As a result of the low temperature of the sample solution and higher density of the extracting phase than the aqueous medium, solvent vapor was condensed and an organic-phase drop formed in the bottom of sample tube. Because of the gas status of the extracting solvent, the surface area between the extracting solvent and the aqueous sample was remarkably high. Under the optimized conditions, tetrachloride carbon was used as an extracting solvent. The method shows high coefficient of determination (R2) values in the range of 0.5–200 and 1.0–200 ng/mL for the target analytes. Enrichment factors and limits of detection for the studied phthalates are obtained in the ranges of 2800–3000 and 0.15–0.3 ng/mL, respectively. Recoveries and relative standard deviations were in the range of 80.0–100.0 and 2.2–7.8%, respectively. The proposed method successfully used for analysis of several aqueous samples.

Analysis of six active components in Radix Tinosporae by nonaqueous capillary electrophoresis with mass spectrometry

Nonaqueous capillary electrophoresis with mass spectrometry has advantages for the analysis of active components in herbs. Here, a rapid nonaqueous capillary electrophoresis with mass spectrometry method was developed to separate, identify, and quanti…

Nonaqueous capillary electrophoresis with mass spectrometry has advantages for the analysis of active components in herbs. Here, a rapid nonaqueous capillary electrophoresis with mass spectrometry method was developed to separate, identify, and quantify palmatin, columbin, cepharanthine, menisperine, magnoflorine and 20-hydroxyecdysone in Radix Tinosporae. Electrospray ionization MS1-3 spectra of the six components were collected and possible cleavage pathways of main fragment ions were elucidated. The conditions which could affect separation like the composition of running buffer, applied voltage were studied and which could affect the mass spectrometry detection like the composition and flow rate of sheath liquid, the pressure of nitrogen gas, the temperature and flow rate of the dry gas were also optimized. Under the optimized conditions, the correlation coefficient was > 0.99. The relative standard deviations of migration time and peak areas were < 10%. The recoveries were calculated to be 99.31–107.80% in real samples. It has been demonstrated that the proposed method has good potential to be applied to determine the six bioactive components in Radix Tinosporae.

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A validated LC–MS/MS method for the simultaneous determination of 20-(S)-protopanaxatriol and its two active metabolites in rat plasma: Application to a pharmacokinetics study

We present a validated liquid chromatography with tandem mass spectrometry method for simultaneous determination of 20-(S)-protopanaxatriol and its two oxidative stereoisomeric metabolites (20S,24S)-epoxy-dammarane-3,6,12,25-tetraol (M1) and (20S,24R)…

We present a validated liquid chromatography with tandem mass spectrometry method for simultaneous determination of 20-(S)-protopanaxatriol and its two oxidative stereoisomeric metabolites (20S,24S)-epoxy-dammarane-3,6,12,25-tetraol (M1) and (20S,24R)-epoxy-dammarane-3,6,12,25-tetraol (M2) in rat plasma. 20-(S)-Protopanaxatriol, M1 and M2 were extracted with methanol and separated on an ACQUITY HSS T3 column. The mass spectrometry detection was accomplished in selected reaction monitoring mode with precursor-to-product ion transitions of m/z 493.4[RIGHTWARDS ARROW]143.1 for M1 and M2, m/z 475.4[RIGHTWARDS ARROW]391.3 for 20-(S)-protopanaxatriol, and m/z 459.4[RIGHTWARDS ARROW]375.3 for 20-(S)-protopanaxadiol (internal standard). The method showed good linearity over the concentration ranges of 1–1000 ng/mL for 20-(S)-protopanaxatriol and 0.5–200 ng/mL for M1 and M2, with correlation coefficients of more than 0.995. The lower limits of quantification for 20-(S)-protopanaxatriol, M1 and M2 were 1, 0.5, 0.5 ng/mL, respectively. The intra- and inter-day precisions (RSD, %) were less than 10.41% while the accuracy (relative error, %) ranged from –3.14 to 8.73%. Under the current conditions, M1 and M2 were completely separated within 3 min. The validated assay was successfully applied to evaluating pharmacokinetic profiles of 20-(S)-protopanaxatriol, M1 and M2 in rat.

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Electrochemical preparation of zinc oxide/polypyrrole nanocomposite coating for the highly effective solid-phase microextraction of phthalate esters

In this work, zinc oxide/polypyrrole nanocomposite coating was fabricated on stainless steel and evaluated as a novel headspace solid phase microextraction fiber coating for extraction of ultra-trace amounts of environmental pollutants, namely, phthal…

In this work, zinc oxide/polypyrrole nanocomposite coating was fabricated on stainless steel and evaluated as a novel headspace solid phase microextraction fiber coating for extraction of ultra-trace amounts of environmental pollutants, namely, phthalate esters, in water samples. The fiber nanocomposite were prepared by a two-step process including the electrochemical deposition of polypyrrole on the surface of stainless steel in the first step, and electrochemical deposition of zinc oxide nanosheets by in the second step. Porous structure together with zinc oxide nanosheets with the average diameter of 30 nm were observed on the surface by using scanning electron microscopy. The effective parameters on extraction of phthalate esters (i.e., extraction temperature, extraction time, desorption temperature, desorption time, salt concentration, and stirring rate) were investigated and optimized by one-variable-at-a-time method. Under optimized conditions (extraction temperature, 90°C; extraction time, 40 min; desorption temperature, 270°C; desorption time, 5 min; salt concentration, 25% w/v; and stirring rate, 1000 rpm), the limits of detection were in the range of 0.05–0.8 μg L−1, and the repeatability and fiber-to-fiber reproducibility were in the ranges of 6.1–7.3% and 8.7–10.2%, respectively.

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Modeling and predicting the solute polarity parameter in reversed-phase liquid chromatography using quantitative structure–property relationship approaches

A prediction of quantitative structure–property relationships is developed to model the polarity parameter of a set of 146 organic compounds in acetonitrile in reversed-phase liquid chromatography. Enhanced replacement method and support vector machine regressions were employed to build prediction models based on molecular descriptors calculated from the structure alone. The correlation coefficients between experimental and predicted values of polarity parameter for the test set by enhanced replacement method and support vector machine were 0.970 and 0.993, respectively. The obtained results demonstrated that the support vector machine model is more reliable and has a better prediction performance than the enhanced replacement method.

Abstract

A prediction of quantitative structure–property relationships is developed to model the polarity parameter of a set of 146 organic compounds in acetonitrile in reversed-phase liquid chromatography. Enhanced replacement method and support vector machine regressions were employed to build prediction models based on molecular descriptors calculated from the structure alone. The correlation coefficients between experimental and predicted values of polarity parameter for the test set by enhanced replacement method and support vector machine were 0.970 and 0.993, respectively. The obtained results demonstrated that the support vector machine model is more reliable and has a better prediction performance than the enhanced replacement method.

Development of a simple and valid method for the trace determination of phthalate esters in human plasma using dispersive liquid–liquid microextraction coupled with GC–MS

A new method was developed for the trace determination of phthalic acid esters in plasma using dispersive liquid–liquid microextraction and gas chromatography with mass spectrometry analysis. Plasma proteins were efficiently precipitated by trichlor…

A new method was developed for the trace determination of phthalic acid esters in plasma using dispersive liquid–liquid microextraction and gas chromatography with mass spectrometry analysis. Plasma proteins were efficiently precipitated by trichloroacetic acid and then a mixture of chlorobenzene (as extraction solvent) and acetonitrile (as dispersive solvent) rapidly injected to clear supernatant using a syringe. After the centrifuging, chlorobenzene were sedimented in the bottom of the test tube. 1 μL of this sedimented phase was injected into the gas chromatograph for phthalic acid esters analysis. Different factors affecting the extraction performance, such as the type of extraction and dispersive solvent, their volume, extraction time and the effects of salt addition were investigated and optimized. Under the optimum conditions, the enrichment factors and extraction recoveries were satisfactory and ranged between 820–1020 and 91–97%, respectively. The linear range was wide (50–1000 ng mL−1) and limit of detection was very low (1.5–2.5 ng mL−1 for all analytes). The relative standard deviations for analysis of 1 μg mL−1 of the analytes were between 3.2–6.1%. Salt addition showed no significant effect on extraction recovery. Finally, the proposed method was successfully utilized for the extraction and determination of the phthalic acid esters in human plasma samples and satisfactory results were obtained.

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