Reversed-phase Liquid Chromatographic Separation Research Articles

Evaluation of Urinary Proteome Library Generation Methods on Data-Independent Acquisition MS Analysis and its Application in Normal Urinary Proteome Analysis.

As an important part of the data-independent acquisition-mass spectrometry (DIA-MS) analysis approach, spectral library generation is closely related to the final protein identification and quantitation. In this study, an attempt is made to evaluate the influence of different sample separation methods (reversed-phase liquid chromatography (RPLC) linear gradient elution and spin column step gradient fractionation) and data acquisition modes (data-dependent acquisition (DDA) and DIA) on library generation of the human urine proteome. The RPLC separation method provides more proteins for generating the library than the spin column; however, the spin column library leads to identification of more proteins when used for the urine proteome analysis. The DDA mode can provide a larger spectral library than the DIA mode and the DDA-library leads to more protein identifications in the study. Use of a combined urinary protein library provides the most complete protein and peptide information, and the DIA approach can provide accurate protein quantitative information even for low-abundance proteins. When the combined library is used to analyze the normal individual urine proteome (18 males and 18 females), gender-related and age-related proteins are discovered and functionally analyzed. This strategy may benefit urine proteome DIA analysis.

Peak distortion in reversed-phase liquid chromatography separation of active carbonyl-containing compounds: Mechanism and solution for this overlooked phenomenon

Peak distortion is frequently encountered for compounds containing active carbonyl groups during reversed-phase (RP) LC separation. However, as being commonly overlooked or misdiagnosed, this problem is rarely reported in the literature and lacks an effective solution. In the present study, six pharmaceutical-related compounds containing keto or aldehyde groups, that exhibited severe peak distortion in early method development, were selected as the model compounds for further investigation. Systematic pH-screening experiments and a series of LC quadrupole-time of flight (Q-TOF) MS and NMR experiments were conducted on each model compound. The underlying chemical behavior of this type of compound during RP-LC separation was explicitly revealed. The formation of gem-diol/hemiketal/hemiacetal species via nucleophilic addition with H2O/MeOH will occur in a low pH eluent, but will be completely suppressed when the pH is higher than an analyte-specific value. As further validated by twelve other pharmaceutical-related compounds belonging to this type, we confirmed that increasing the eluent pH using buffers without nucleophilicity is a simple and effective method to solve this peak distortion problem.

Reversed-phase liquid chromatography separation and mass spectrometry fragmentation analysis of mitiglinide and three isomers

The separation of mitiglinide and its three isomer impurities was achieved by reversed-phase ultra-performance liquid chromatography-high resolution mass spectrometry. An ACQUITY UPLC HSS T3 column (100 mm×2.1 mm, 1.8 μm) was used as the stationary phase and water-acetonitrile-n-pentanol (75:25:1, v/v/v; formic acid was added to adjust pH to 1.8) was used as the mobile phase with a flow rate of 0.4 mL/min. According to the exact mass and high resolution mass spectrometry fragmentation (Q Exactive), significant differences were observed in the fragment ion abundance in the secondary mass spectra of mitiglinide and its three isomer impurities. Two of these isomer impurities were newly discovered. The possible fragmentation mechanisms of mitiglinide and its three isomer impurities were also deduced. The limit of detection of the developed method was 1 μg/L. The linearity of the developed method was good from the limit of quantitation (2 μg/L) to 10000 μg/L with a correlation coefficient of 0.9999. The relative standard deviation of the peak area was 2.0%. On the basis of these results, the sources of the mitiglinide isomer impurities were discussed. Isomer impurity 1 was degraded at high temperature, while isomer impurities 2 and 3 were determined to be synthetic impurities. In addition, samples of mitiglinide calcium raw materials were analyzed.

Hydrophilic interaction chromatography for the analysis of biopharmaceutical drugs and therapeutic peptides: A review based on the separation characteristics of the hydrophilic interaction chromatography phases.

Applications of hydrophilic interaction chromatography for the analysis of biopharmaceutical drugs, i.e., glycosylated proteins represented by monoclonal antibodies are discussed in the manner of glycoproteomics. They can be analyzed using hydrophilic interaction chromatography in five different stages as (1) their intact forms, (2) their subunits, (3) N- and O-glycopeptides digested by proteases, (4) N- and O-glycans released from the glycoproteins or glycopeptides, and (5) monosaccharides. Hydrophilic interaction chromatography is a more useful tool in the order of (1) to (5). At the stages (4) and (5), quantitation of glycans and saccharides are also reported. Hydrophilic interaction chromatography is employed not only for analytical uses, but also pretreatment items as solid phase extraction, followed by reversed-phase liquid chromatography separations. Comprehensive search results of these application of hydrophilic interaction chromatography are summarized in tables to show what kind of hydrophilic interaction chromatography columns are suitable for each step of analysis.Relationship of favored and less favored hydrophilic interaction chromatography columns and their separation characteristics such as hydrophilicity, and selectivity for structural difference, is also discussed. Analysis of the therapeutic peptides (not glycosylated) using hydrophilic interaction chromatography is summarized, too.

A Peptidomic Analysis of the Potential Comorbidity Biomarkers for Type 2 Diabetes Mellitus and Alzheimer’s Disease

Objective: To investigate the potential comorbidity biomarkers for Type 2 Diabetes Mellitus (T2DM) and Alzheimer’s disease (AD). Methods: This is a randomized case-control study. There are three groups: 1) normal control group included 32 healthy elderly people in the hospital physical examination; 2) 30 patients with T2DM group; and 3) AD group has 28 cases. On-line reversed-phase liquid chromatography separation, tandem mass spectrometry analysis and iTRAQ quantification were used for identification of peptidomic analysis, then detection of three comorbidity biomarkers might be associated with T2DM and AD by ELISA. Results: The Peptidomic Analysis of the potential comorbidity biomarkers for T2DM and the AD group includes Osteopontin (OPN), Isoform 2 of Histone H2Btype 2-F and Histone H4. These potential comorbidity biomarkers for T2DM and the AD group are significantly increased than normal control group. OPN concentrations are 1.67 (0.13 - 2.63) mmol/L in the normal control group, 3.15 (1.51 - 5.35) mmol/L in the T2DM group, and 7.66 (3.55 - 15.38) mmol/L in the AD group. Histone H4 concentrations in three groups respectively are 0.21 ± 0.036 mmol/L (normal control), 0.21 ± 0.046 mmol/L (T2DM) and 0.21 ± 0.034 mmol/L(AD). Isoforms 2 of Histone H2Btype 2-F are 1.73 (0.12 - 2.60) mmol/L, 4.71 (1.26 - 6.84) mmol/L and 9.30 (0 - 20.8) mmol/Lin three groups respectively. Conclusion: The inflammatory mechanism may lead to an increase of histone content in the urine of AD and T2DM patients. Clinical test of these potential comorbidity biomarkers Histones and Osteopontin would be the diagnosis of comorbidity AD and T2DM.

Amino acid and ionic liquid modified polyhedral oligomeric silsesquioxane-based hybrid monolithic column for high-efficiency capillary liquid chromatography

In this study, a novel amino acid and ionic liquid dual organically functionalized reagents modified polyhedral oligomeric silsesquioxane methacryl substituted (POSS-MA) based hybrid monolithic column (POSS-VBI-Cys) was designed and reported. With amino acid L-cysteine and ionic liquid 1-vinyl-3-butylimidazolium bromide as dual monomers, POSS-MA as the crosslinker, the new POSS-VBI-Cys hybrid monolithic column could be facilely fabricated via the “one-pot” free radical copolymerization and thiol-ene click reaction. Because of the introduction of polar amino acid L-cysteine, the new POSS-VBI-Cys column exhibited attenuated hydrophobicity in reversed-phase liquid chromatography separation. Polar amides, nucleosides and nucleic acid bases displayed strong retention on the POSS-VBI-Cys column and could be successfully separated. Furthermore, the new POSS-VBI-Cys column displayed good separation selectivity for model glycoproteins and non-glycoproteins mixture and it was also successfully used for the purification and separation of TARG1 protein from its originally expressed sample. In the future research, we will further exploit its performances for separation of intact proteins and in-depth proteome applications.

Urine analysis of 28 designer benzodiazepines by liquid chromatography–high-resolution mass spectrometry

Hundreds of new psychoactive substances (NPS) covering most drugs-of-abuse classes have been introduced to the recreational drug market in recent years. One class of NPS drugs that has become more common recently is “designer” benzodiazepines. Due to a close structural resemblance with prescription benzodiazepines, some of these substances may elicit a positive response (i.e. cross react) in immunoassay screening. Consequently, it is increasingly important to include NPS benzodiazepines during method confirmation to ensure accurate identification of closely-related compounds as well as detection of the benzodiazepines themselves.Here, we present our efforts to develop a screening and confirmation method for detection of 28 NPS benzodiazepines in urine using reversed-phase liquid chromatographic separation in combination with high-resolution mass spectrometry (LC–HRMS). MS was performed in positive electrospray mode on a Thermo Fischer Scientific Q Exactive Orbitrap instrument using either full scan (for screening) or parallel reaction monitoring (for confirmation).We found the lower quantification limit of the method to range from 5 to 50 ng/mL. Analytical precision and accuracy were ≤15% for both screening and confirmation for all except one analyte. The method was used to analyze patient urine samples from routine drug testing and samples from acute intoxication cases presenting in emergency wards. Altogether, 16 of the 28 benzodiazepines (i.e., clobazam, clonazolam, deschloroetizolam, diclazepam, estazolam, etizolam, flubromazepam, flubromazolam, flunitrazolam, 3-hydroxyflubromazepam, 3-hydroxyphenazepam, ketazolam, meclonazepam, metizolam, nifoxipam, and pyrazolam) were detected in the urine samples.The results from patient sample analysis indicate a high prevalence of NPS benzodiazepine use, emphasizing the importance of including novel drugs of abuse in drug testing menus.

Predictive kinetic optimisation of hydrophilic interaction chromatography × reversed phase liquid chromatography separations: Experimental verification and application to phenolic analysis

Method development and optimisation for comprehensive two-dimensional liquid chromatography (LC × LC) is complex, since this involves the intricate relationships between a large number of experimental parameters with the aim of achieving three conflicting goals: maximising separation performance (peak capacity), minimising analysis time and minimising dilution. This is especially true for the on-line combination of hydrophilic interaction chromatography (HILIC) and reversed phase LC (RP-LC) due to the relative elution strengths of the mobile phases used in these modes, which has severe implications for the modulation process and dilution.In this study we report a predictive kinetic optimisation tool for on-line HILIC × RP-LC which is based on theoretical relationships between the optimisation goals, the target analyte properties and chromatographic parameters (column dimensions, flow rates, mobile phases, injection volumes, etc.), allowing all chromatographic parameters to vary simultaneously within defined ranges. Experimental restrictions, such as pressure limits, flow rates, etc., are enforced to ensure all results are practically achievable on a given instrumental configuration. A Pareto-optimality approach is then used to obtain optimal sets of experimental conditions, from which the one(s) best satisfying the requirements in terms of time, dilution and/or peak capacity can be chosen. To overcome the challenges associated with mobile phase incompatibility in the coupling of HILIC and RP-LC, splitting of the first dimension HILIC flow, dilution with an aqueous make-up, or a combination of both, were investigated to establish the best approach to minimise total dilution and maximise performance. The validity of the methodology is demonstrated by deriving optimal conditions for the HILIC × RP-LC separation of procyanidins on selected columns and subsequent experimental verification of the performance for the separation of a cocoa extract.

Analysis of hydrophobically modified ethylene oxide urethane rheology modifiers by comprehensive two dimensional liquid chromatography

Hydrophobically modified ethylene oxide urethane (HEUR) rheology modifiers are polymers used widely in waterborne coatings and other consumer products. The incorporation of hydrophobic end-groups significantly affects the thickening performance of HEURs. Therefore, understanding the degree of incorporation of hydrophobic end-groups on the polymer chain can help gain important insights on the structure/property relationship for HEUR rheology modifiers.A comprehensive two-dimensional liquid chromatography (2D-LC) method was developed for separating polymeric HEUR rheology modifiers based on the number of hydrophobic end-groups incorporated on the polymer chain. Our 2D-LC method uses a size exclusion chromatography (SEC) separation in the first dimension (1D) using an ultra-high performance Advance Polymer Chromatography (APC) column and a gradient reversed-phase liquid chromatography (RPLC) separation in the second dimension (2D). A low flow rate was used in the first dimension SEC separation to minimize the strong organic eluent transferred to the second dimension LC column. A small inner diameter (ID) LC column was used for the second dimension to reduce the total solvent consumption for routine analysis of process samples. The 1D flow rate, 2D transfer volume and gradient profile were all optimized to avoid polymer breakthrough and to achieve optimal separation of the polymer chains based on end-groups. Three types of polymer chains with 0, 1, and 2 terminal hydrophobes were successfully separated using this method. The total run time was further reduced by implementing flow programing in the first dimension separation. The 2D-LC method was applied to study how the polymerization process recipes affected hydrophobe incorporation and how the hydrophobe incorporation correlated with thickening efficiency. The method was also used to separate HEUR rheology modifier with branched polymer architecture.

Determination of 4-Nonylphenol in Surface Waters of the Guandu River Basin by High Performance Liquid Chromatography with Ultraviolet Detection

4-Nonylphenol, a degradation product of ethoxylated alkylphenols, due to its harmful effects on the environment, has been banned in European Union countries, alongside their precursors. The guide on quality of drinking water from the United States Environmental Protection Agency (US EPA) recommends a maximum concentration of 28 µg L-1 for fresh water. In Brazil, there is no clear legislation containing values of maximum concentration of 4-nonylphenol. Due to this lack of regulation, a continuous monitoring is necessary for this pollutant in environmental samples. The occurrence of 4-nonylphenol (4-NP) in the surface waters of Guandu River in the state of Rio de Janeiro, Brazil, was studied by using solid-phase extraction and reversed phase liquid chromatography separation with UV detection. The analytical method satisfies these requirements, being able to detect and quantify 4-NP in a desired concentration range. Of the 19 samples analyzed, 4-nonylphenol was detected in 12, quantified in 2, showing concentration levels of 1.73 and 2.32 µg L-1 in Santa Cruz and Paracambi, respectively. This is the main hydrographic basin in the state of Rio de Janeiro, where water is collected for treatment and later distributed to most cities in the metropolitan region, including Rio de Janeiro City, and these results are therefore alarming.

Determination of Phenolic Acids in Sugarcane Vinasse by HPLC with Pulse Amperometry.

A reversed-phase liquid chromatographic separation with pulsed amperometric detection of phenolic acids at a glassy carbon electrode is described. Chromatographic separation was carried out in isocratic conditions using 0.20 mol·L−1 acetic acid (pH 5.0)/water (80 : 20, v/v) as mobile phase under constant working potential mode of 0.80 V. Chromatographic peaks presented high resolution and separation. Calibration curves exhibited excellent correlation coefficients, above 0.995. Linear ranges of the analytes, in mg L−1, were of 0.018–18 (gallic acid), 0.146–19 (vanillic acid), 0.13–17 (caffeic acid), 0.016–16 (ferulic acid), and 0.008–17 (p-coumaric acid), respectively. Limits of detection ranged from 1.6 to 97 μg·L−1 and precision varied in 1.73–3.78% interval. Concentrations of 19 ± 0.51 mg·L−1 and 7.8 ± 2.5 mg·L−1 were found for vanillic and caffeic acids, respectively, in a sugarcane vinasse sample. Gallic, ferulic, and p-coumaric acids were not detected. Recovery results demonstrated that the proposed method is accurate, and it can be used to detect and quantify phenolic acids in sugarcane vinasse without any influence of interferents.

Forensic Identification of Dyes in Ballpoint Pen Inks Using LC–ESI–MS

The aim of this work was to develop a new technique using flow injection analysis combined with LC–ESI–MS which allows identification of dyes in ballpoint pen inks. A sample preparation procedure for the extraction of dyes from ballpoint pen strokes has been developed. The characteristic group of ions for each sample of 21 studied ballpoint pen inks corresponding to the present dyes has been determined using flow injection method. LC separation conditions for identified dyes have been optimized on reversed-phase sorbent based on silica gel. The best composition of the mobile phase for the dyes mixture LC separation was 0.1% aqueous formic acid and acetonitrile. Detection of dyes was carried out using mass spectrometry with electrospray ionization in positive and negative modes after reversed-phase liquid chromatography separation. Dye composition of ink was additionally confirmed comparing the data obtained from the literature. Flow injection analysis allows obtaining intensive ions of unknown strokes. It is difficult to get this information using only chromatographic methods, because dyes peak intensity can be low and noise of basic line high. Flow injection method allows distinguishing the analyzed 21 ballpoint pens by determining a characteristic set of dyes. The developed flow injection technique is very simple and quick. As a result, a novel approach for the identification of dyes in the ballpoint pen inks by flow injection analysis with LC–ESI–MS and UV detection without using standard dye samples has been established. It can be an effective alternative to the existing LC–DAD–MS and IR spectroscopy methods.

Determination of Melatonin in Cow’s Milk by Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS)

The aim of the present study is the development of a rapid and accurate analytical method to determine melatonin in milk. In this method, melatonin extracted from milk with ethyl acetate, after application of reversed phase liquid chromatographic separation melatonin, was detected and quantified with tandem mass spectrometry. Performance of method was tested by conducting method validation study wherein limit of detection, limit of quantification, linearity recovery, and precision parameters were determined. Limit of detection and limit of quantification were calculated as 0.016 and 0.054 μg/kg, respectively. Recovery of the method was checked at two different concentration namely 0.5 and 2.5 μg/kg and determined as 106 and 100%, respectively. Precision of the method was determined as interday and intraday precision. Intraday precision calculated as 3.92 and 2.15% for 0.5 and 2.5 μg/kg spike levels. In this study, we describe an analytical method for determination of melatonin in milk with LC-MS/MS. This method offers an efficient, rapid, and easy sample preparation procedure with high selectivity and good sensitivity for the determination of melatonin in milk.

Development of an on-line mixed-mode gel liquid chromatography × reversed phase liquid chromatography method for separation of water extract from Flos Carthami

A novel on-line comprehensive two-dimensional liquid chromatography (2D-LC) method by coupling mixed-mode gel liquid chromatography (MMG-LC) with reversed phase liquid chromatography (RPLC) was developed. A mixture of 17 reference compounds was used to study the separation mechanism. A crude water extract of Flos Carthami was applied to evaluate the performance of the novel 2D-LC system. In the first dimension, the extract was eluted with a gradient of water/methanol over a cross-linked dextran gel Sephadex LH-20 column. Meanwhile, the advantages of size exclusion, reversed phase partition and adsorption separation mechanism were exploited before further on-line reversed phase purification on the second dimension. This novel on-line mixed-mode Sephadex LH-20×RPLC method provided higher peak resolution, sample processing ability (2.5mg) and better orthogonality (72.9%) versus RPLC×RPLC and hydrophilic interaction liquid chromatography (HILIC)×RPLC. To the best of our knowledge, this is the first report of a mixed-mode Sephadex LH-20×RPLC separation method with successful applications in on-line mode, which might be beneficial for harvesting targets from complicated medicinal plants.

Deep-Dive Targeted Quantification for Ultrasensitive Analysis of Proteins in Nondepleted Human Blood Plasma/Serum and Tissues.

Mass spectrometry-based targeted proteomics (e.g., selected reaction monitoring, SRM) is emerging as an attractive alternative to immunoassays for protein quantification. Recently we have made significant progress in SRM sensitivity for enabling quantification of low nanograms per milliliter to sub-naograms per milliliter level proteins in nondepleted human blood plasma/serum without affinity enrichment. However, precise quantification of extremely low abundance proteins (e.g., ≤ 100 pg/mL in blood plasma/serum) using targeted proteomics approaches still remains challenging, especially for these samples without available antibodies for enrichment. To address this need, we have developed an antibody-independent deep-dive SRM (DD-SRM) approach that capitalizes on multidimensional high-resolution reversed-phase liquid chromatography (LC) separation for target peptide separation and enrichment combined with precise selection of target peptide fractions of interest, significantly improving SRM sensitivity by ∼5 orders of magnitude when compared to conventional LC-SRM. Application of DD-SRM to human serum and tissue provides precise quantification of endogenous proteins at the ∼10 pg/mL level in nondepleted serum and at <10 copies per cell level in tissue. Thus, DD-SRM holds great promise for precisely measuring extremely low abundance proteins or protein modifications, especially when high-quality antibodies are not available.

Revisiting shape selectivity in liquid chromatography for polycyclic aromatic hydrocarbons (PAHs) – six-ring and seven-ring Cata-condensed PAH isomers of molecular mass 328 Da and 378 Da

The relationship of reversed-phase liquid chromatography (RPLC) retention on a polymeric C18 stationary phase and the shape of polycyclic aromatic hydrocarbons (PAHs) was investigated for three-ring to seven-ring cata-condensed isomers. We report the first RPLC separation for six-ring and seven-ring cata-condensed PAH isomers. Correlations of LC retention and shape parameters (length-to-breath ratio, L/B and thickness, T) were investigated for 2 three-ring isomers (molecular mass 178Da), 5 four-ring isomers (molecular mass 228Da), 11 five-ring isomers (molecular mass 278Da), 17 six-ring isomers (molecular mass 328Da), and 20 seven-ring isomers (molecular mass 378Da). Significant linear correlations were found for all isomer groups (r=0.71 to 0.94). Nonplanarity of the PAH isomers was found to influence retention (i.e., nonplanar isomers eluting earlier than expected based on L/B) and linear correlations of retention vs. T for isomer groups containing nonplanar isomers were significant (r=0.71 to 0.86). Graphical abstract.

Behavior of macroporous vinyl silica and silica monolithic columns in high pressure gas chromatography

80% vinyltrimethoxysilane-based hybrid silica monoliths (80-VTMS), which have been initially developed for separation in reversed-phase liquid chromatography, have been investigated in high pressure gas chromatography separations (carrier gas pressure up to 60bar) and compared to silica monolithic columns. The behavior of both silica and 80-VTMS monolithic columns was investigated using helium, nitrogen and carbon dioxide as carrier gas. The efficiency of 80-VTMS monolithic columns was shown to vary differently than silica monolithic columns according to the temperature and the carrier gas used. Carrier gas nature was a significant parameter on the retention for both silica and vinyl columns in relation to its adsorption onto the stationary phase in such high pressure conditions. The comparison of retention and selectivity between 80-VTMS monoliths and silica was performed under helium using the logarithm of the retention factor according to the number of carbon atoms combined to Kovats indexes. The very good performances of these columns were demonstrated, allowing the separation of 8 compounds in less than 1min.

Graphene Oxide Nanoparticles and Their Influence on Chromatographic Separation Using Polymeric High Internal Phase Emulsions

This work presents the first instance of reversed-phase liquid chromatographic separation of small molecules using graphene oxide nanoparticle-modified polystyrene-divinylbenzene polymeric high internal phase emulsion (GONP PS-co-DVB polyHIPE) materials housed within a 200-µm internal diameter (i.d.) fused silica capillary. The graphene oxide nanoparticle (GONP)-modified materials were produced as a potential strategy to increase both the surface area limitations and the reproducibility issues observed in monolithic stationary phase materials. GONP PS-co-DVB polyHIPEs were found to have a surface area up to 40% lower than unmodified polymeric high internal phase emulsion (polyHIPE) stationary phases. However, despite having a surface area significantly lower than that of the unmodified material, the GONP-modified polyHIPEs demonstrated superior analyte adsorption properties. Reducing the GONP material did not have any significant impact on elution order or retention factor of the analytes, which was most likely due to low GONP loading attributed to the 250-nm GONPs utilised. The lower surface area of GONP-modified polyHIPEs provided similar separation efficiency and increased repeatability from injection to injection resulting in % relative standard deviations (%RSDs) of less than 0.6%, indicating the potential offered by graphene oxide (GO)-modified polyHIPES in flow through applications such as adsorption or separation processes.

Fast non-aqueous reversed-phase liquid chromatography separation of triacylglycerol regioisomers with isocratic mobile phase. Application to different oils and fats.

The distribution of fatty acid species at the sn-1/3 position or the sn-2 position of triacylglycerols (TAGs) in natural fats and oils affects their physical and nutritional properties. In fats and oils, determining the presence of one or two regioisomers and the identification of structure, where they do have one, as well as their separation, became a problem of fundamental importance to solve. A variety of instrumental technics has been proposed, such as MS, chromatography-MS or pure chromatography. A number of studies deal with the optimization of the separation, but very often, they are expensive in time. In the present study, in order to decrease the analysis time while maintaining good chromatographic separation, we tested different monomeric and polymeric stationary phases and different chromatographic conditions (mobile phase composition and analysis temperature) using Non-Aqueous Reversed Phase Liquid Chromatography (NARP-LC). It was demonstrated that mixed polymeric stationary bonded silica with accessible terminal hydroxyl groups leads to very good separation for the pairs of TAGs regioisomers constituted by two saturated and one unsaturated fatty acid (with double bond number: from 1 to 6). A Nucleodur C18 ISIS percolated by isocratic mobile phase (acetonitrile/2-propanol) at 18°C leads to their separations in less than 15min. The difference of retention times between two regioisomers XYX and XXY are large enough to confirm, as application, the presence of POP, SOP, SOS and PLP and no PPO, SPO, SSO and PPL in Theobroma cacao butter. In the same way, this study respectively shows the presence of SOS, SOP and no SSO, PSO in Butyrospermum parkii butter, POP, SOP, SOS and no PPO, PSO and SSO in Carapa oil and finally POP and no PPO in Pistacia Lentiscus oil.

Biosynthetic approach to combine early steps of cardenolide biosynthesis in Saccharomyces cerevisiae

A novel on-line comprehensive two-dimensional liquid chromatography (2D-LC) method by coupling mixed-mode gel liquid chromatography (MMG-LC) with reversed phase liquid chromatography (RPLC) was developed. A mixture of 17 reference compounds was used to study the separation mechanism. A crude water extract of Flos Carthami was applied to evaluate the performance of the novel 2D-LC system. In the first dimension, the extract was eluted with a gradient of water/methanol over a cross-linked dextran gel Sephadex LH-20 column. Meanwhile, the advantages of size exclusion, reversed phase partition and adsorption separation mechanism were exploited before further on-line reversed phase purification on the second dimension. This novel on-line mixed-mode Sephadex LH-20 × RPLC method provided higher peak resolution, sample processing ability (2.5 mg) and better orthogonality (72.9%) versus RPLC × RPLC and hydrophilic interaction liquid chromatography (HILIC) × RPLC. To the best of our knowledge, this is the first report of a mixed-mode Sephadex LH-20 × RPLC separation method with successful applications in on-line mode, which might be beneficial for harvesting targets from complicated medicinal plants.