Electrochemical Determination of Synephrine by Hydrophilic Interaction Liquid Chromatography Using a Zwitterionic Monolith Column

A sensitive method for the electrochemical determination of synephrine (SYN) by hydrophilic interaction liquid chromatography (HILIC) has been developed. Optimal chromatographic separation and high sensitive determination by HILIC with electrochemical detection (HILIC‐ECD) was achieved using a sulfobetaine‐type zwitterionic monolith column (100×1.02 mm, i.d.), a mixture of 10 mM sodium phosphate (pH 4) and acetonitrile (20 : 80, v/v) as mobile phase, and a glassy carbon working electrode which was applied with a potential at +1.0 V vs. Ag/AgCl. The chromatographic peak height of SYN was proportional to the concentration from 5.0 µg/L to 1.0 mg/L (r=0.999). The detection limit of SYN (S/N=3) was 3.7 pg on the column. Moreover, the present HILIC‐ECD could be applied to the accurate and precise determination of SYN in Aurantii nobilis Pericarpium. In conclusion, we have demonstrated that an ECD is one of useful detection methods applicable to HILIC.     

Separation of nucleotides by hydrophilic interaction chromatography using the FRULIC-N column

A stationary phase composed of silica-bonded cyclofructan 6 (FRULIC-N) was evaluated for the separation of four cyclic nucleotides, six nucleoside monophosphates, four nucleoside diphosphates, and five nucleoside triphosphates via hydrophilic interaction chromatography (HILIC) in both isocratic and gradient conditions. The gradient conditions gave significantly better separations by narrowing peak widths. Sixteen out of nineteen nucleotides were baseline separated on the FRULIC-N column in one run. Unlike other known HILIC stationary phases, there can be dual-retention mechanisms unique to this media. Traditional hydrogen bonding/dipolar interactions can be supplemented by dynamic ion interaction effects for anionic analytes. This occurs because the FRULIC-N stationary phase is able to bind certain buffer cations. The extent of the ion interaction is tunable, in comparison to stationary phases with embedded charged groups, where the inherent ionic properties are fixed. The best mobile phase conditions were determined by varying the organic modifier (acetonitrile) content, as well as salt type/concentration and electrolyte pH. The thermodynamic characteristic of the FRULIC-N column was investigated by evaluating the column temperature effect on retention and utilizing van’t Hoff plots. This study shows that there is a greater entropic contribution for the retention of nucleotide di and triphosphates, whereas there is a greater enthalphic contribution for the cyclic nucleotides with the FRULIC-N column.     

Evaluation of BEH C18, BEH HILIC, and HSS T3 (C18) column chemistries for the UPLC-MS-MS analysis of glutathione, glutathione disulfide, and ophthalmic acid in mouse liver and human plasma

Glutathione (GSH), glutathione disulfide (GSSG), and ophthalmic acid (OA) are important biological oxidative stress biomarkers to be monitored in pathological and toxicological studies. With the advent of liquid chromatography tandem mass spectrometry (LC-MS-MS) technology, sensitive and selective analysis of these biomarkers in biological samples is now being performed routinely. Due to the hydrophilic and polar natures of GSH and its endogenous derivatives, achieving good retention, resolution, and peak shape is often a chromatographic challenge. In this study, three ultra-performance (UP) LC column chemistries (namely, BEH C18, BEH HILIC, and HSS T3 [C18]) are evaluated for the UPLC-MS-MS analysis of GSH, GSSG, and OA extracted from mouse liver and human plasma samples. The chromatographic parameters evaluated are retentivity, tailing factor, MS sensitivity, and resolution of the three analytes. Based on the optimized method for each column chemistry, our results indicate that the HSS T3 (C18) column chemistry affords the best retention and separation of these analytes when operated under the ultra high-pressure chromatographic conditions.     

A reversed-phase/hydrophilic interaction mixed-mode C18-Diol stationary phase for multiple applications

A mixed-mode chromatographic packing material, C18 and diol groups modified silica (C18-Diol), was prepared with controllable hydrophobicity and hydrophilicity. It demonstrated excellent aqueous compatibility and stability in aqueous mobile phase; compared to the traditional C18 column, improved peak shape of basic analytes was also obtained. Additionally, it exhibited both reversed-phase liquid chromatographic (RPLC) and hydrophilic interaction chromatographic (HILIC) performance; the analyte separation scope was thus enlarged, demonstrated by simultaneous separation of twenty acids, bases and neutrals. More interestingly, a novel on-line two-dimensional liquid chromatography on the single column (2D-LC-1C) was established by modifying the high performance liquid chromatographic instrument only with the addition of an extra six-port two-position valve. The early co-eluted components of the extract of Lonicera japonica on the 1st-dimension (RPLC) were collected for the online re-injection to the 2nd-dimension (HILIC) by conveniently varying the mobile phase components. Six more peaks were obtained. The established system was simple, easy operation and low cost, which had advantages in analyzing complicated samples.     

反相/亲水色谱法分析糖苷类化合物

根据皂苷、黄酮苷等糖苷类化合物的结构特点,采用亲水色谱模式分析该类化合物,以弥补反相色谱模式分离结构类似糖苷类化合物选择性的不足。首先选择14个糖苷类化合物,比较了反相色谱柱(XAqua C18)和亲水色谱柱(Click XIon)的分离效果,评价了反相/亲水色谱的正交性,并构建了反相/亲水二维体系用于西洋参样品的分离。结果表明,糖苷类化合物在反相及亲水色谱柱上均有很好的保留,但两者具有不同的分离选择性,14种物质在反相和亲水柱的出峰顺序有较大差异,在反相色谱中不易分离的人参皂苷Rg1和Re在亲水色谱柱可获得很好的分离,反相/亲水模式分离糖苷化合物具有很好的正交性。以构建的RPLC/HILIC二维色谱体系分离西洋参样品,有效地提高了分离能力及峰容量,有利于后续更多极性及微量化合物的制备、结构表征与活性研究,且该方法操作简便、流动相兼容性好,可作为糖苷分离分析、制备的有效手段,也可以为其他中药复杂体系的分析提供参考。     

Separation of phospholipid classes by hydrophilic interaction chromatography detected by electrospray ionization mass spectrometry

A new isocratic separation method was developed for separation of phospholipid (PL) classes based on a silica hydrophilic interaction liquid chromatography (HILIC) column with electrospray ionization (ESI) mass spectrometric detection. Although HILIC is typically used for polar compounds, also amphiphilic molecules like phospholipids can be separated very well. Compared to normal-phase (NP) chromatography, which is usually used for PL class separation, HILIC has the advantage to use on-line ESI-MS detection because its eluents are ESI compatible. Furthermore, this HILIC method is isocratic and hence less time consuming than most (gradient) NP HPLC methods. A chromatographic baseline separation of a standard mixture containing phosphatidylglycerol (PG), phosphatidylethanolamine (PE), phosphatidylcholine (PC), sphingomyelin (SM) and lysophosphatidylcholine (LPC) was achieved within a total run time of 17 min using a mobile phase consisting of acetonitrile, methanol and ammonium acetate 10 mM. The new method was subsequently tested on phospholipid fractions of a body fluid (human blood plasma) and a tissue extract (swine brain) whereby it achieved nearly the same baseline separation of the PL classes. The detected classes in both cases were PE, PC, SM and LPC.     

Chromatographic characterization of hydrophilic interaction liquid chromatography stationary phases: hydrophilicity, charge effects, structural selectivity, and separation efficiency

Fourteen commercially available particle-packed columns and a monolithic column for hydrophilic interaction liquid chromatography (HILIC) were characterized in terms of the degree of hydrophilicity, the selectivity for hydrophilic-hydrophobic substituents, the selectivity for the regio and configurational differences in hydrophilic substituents, the selectivity for molecular shapes, the evaluation of electrostatic interactions, and the evaluation of the acidic-basic nature of the stationary phases using nucleoside derivatives, phenyl glucoside derivatives, xanthine derivatives, sodium p-toluenesulfonate, and trimethylphenylammonium chloride as a set of samples. Principal component analysis based on the data of retention factors could separate three clusters of the HILIC phases. The column efficiency and the peak asymmetry factors were also discussed. These data on the selectivity for partial structural differences were summarized as radar-shaped diagrams. This method of column characterization is helpful to classify HILIC stationary phases on the basis of their chromatographic properties, and to choose better columns for targets to be separated. Judging from the retention factor for uridine, these HILIC columns could be separated into two groups: strongly retentive and weakly retentive stationary phases. Among the strongly retentive stationary phases, zwitterionic and amide functionalities were found to be the most selective on the basis of partial structural differences. The hydroxyethyl-type stationary phase showed the highest retention factor, but with low separation efficiency. Weakly retentive stationary phases generally showed lower selectivity for partial structural differences.     

Evaluation of mobile phase, ion pairing, and temperature influence on an HILIC-MS/MS method for L-arginine and its dimethylated derivatives detection

Asymmetric N(G),-N(G)-dimethylarginine (ADMA) increases in diseases such as renal failure, diabetes mellitus, and hypercholesterolemia. The feasibility and utility of a hydrophilic interaction chromatography (HILIC) method for the separation of free L-arginine (Arg), ADMA, and symmetric N(G),-N(G')-dimethylarginine (SDMA) on a typical silica column were explored and the impact of some experimental parameters on the chromatographic behavior of these analytes was investigated. The effect of water and TFA content in mobile phase and of column temperature was investigated during the development of a fast and simple HILIC-MS/MS method that might be suitable for the quantification of free Arg, ADMA, and SDMA in plasma for routine analysis. Our results show that a good compromise between efficiency and peak shape with acceptable retention and total chromatographic run time is achieved using an ACN/water (90:10) mobile phase with TFA% as additive ranging from 0.015 to 0.025% and column temperature ranging from 25 to 30 degrees C.     

Determination of isoascorbic acid in fish tissue by hydrophilic interaction liquid chromatography–ultraviolet detection

A new hydrophilic interaction liquid chromatographic (HILIC) method for the simultaneous determination of isoascorbic (IAA) and ascorbic acid (AA) was developed. The separation of IAA and AA was studied in various HILIC stationary phases and the influence of the composition of the mobile phase, the ionic strength and the column temperature to the chromatographic characteristics is presented. The final method used an aminopropyl column under isocratic elution with acetonitrile–100 mM ammonium acetate solution (90:10, v/v) at a flow rate of 0.4 mL/min and a detection wavelength of 240 nm. This method was validated and the calibration curves were found to be linear in the range of 1.0–65 μg/mL for both IAA and AA. The method limit of detection for IAA determination in fish tissue was 2.3 μg/g. Inter-day precision (as %RSD_R) was ranged between 0.56% and 8.3% at three concentration levels, whereas the respected recoveries ranged between 82% and 98%. This method was applied to the determination of IAA (as additive E315) in frozen redfish samples. The hyphenation of the HILIC separation with a tandem mass spectrometer was also studied and the problems encountered with negative electrospray ionization under HILIC separation conditions are discussed.     

Dual Retention Mechanism in Two-Dimensional LC Separations of Barbiturates,Sulfonamides, Nucleic Bases and Nucleosides on Polymethacrylate Zwitterionic Monolithic Micro-Columns

In-house prepared zwitterionic polymethacrylate micro-columns using in situ polymerization of N,N-dimethyl-N-metacryloxyethyl-N-(3-sulfopropyl) ammonium betaine (MEDSA) functional monomer with bisphenol A glycerolate dimethacrylate (BIGDMA) cross-linker provided excellent stability and reproducibility of preparation and separation efficiency of 60,000–70,000 theoretical plates m⁻¹ for small molecules under isocratic conditions. The column showed a dual retention mechanism, reversed-phase (RP) in highly aqueous mobile phases and aqueous normal-phase (HILIC) in acetonitrile-rich mobile phases. This property can be used to obtain complementary separation and combined information on the sample from repeated injections of a sample on a single column, in different mobile phases characteristic for the HILIC and for the RP modes, which is in fact a form of offline two-dimensional chromatography on a single column. The dual retention mechanism has been observed with a variety of columns, however, often with impractically narrow retention range in one of the two modes. To take full advantage from the combined single-column RP–HILIC experiments, the column should provide a sufficiently broad mobile phase interval both in the RP and in the HILIC mode. The BIGDMA-MEDSA micro-columns proved suitable earlier for the combined RP–HILIC separations of some phenolic compounds and flavonoids. In the present work, we investigated the effects of the mobile phase composition on the retention of a variety of polar compounds over full retention range of buffered aqueous acetonitrile mobile phases, to find potentially useful HILIC and RP retention ranges for barbiturates, sulfonamides, nucleosides and nucleic bases. In the HILIC mode, proton donor–acceptor interactions show a major effect on retention and selectivity of separation, whereas the size of the non-polar hydrocarbon part of the sample molecule is the most important factor in the water-rich mobile phases. The sample structure strongly affects the composition of aqueous–organic mobile phases at which the transition between the two retention modes occurs. Of the investigated sample types, barbiturates show better separation under reversed-phase conditions, whereas nucleosides and nucleic bases in the HILIC mode. Aromatic carboxylic acids and sulfonamides can be separated either in the reversed phase or under HILIC conditions, the two separation modes showing complementary selectivity of separation.

     

Simultaneous determination of myocardial nucleotides, nucleosides, purine bases and creatine phosphate by ion-pair high-performance liquid chromatography.

An ion-pair reversed-phase high-performance liquid chromatographic method is described for the separation and quantification of myocardial nucleotides, nucleosides, their metabolites and creatine phosphate-related compounds in a single run. Separation of a standard mixture containing 21 compounds was achieved on a 5-microns Hypersil ODS column with a 5-min isocratic elution (buffer: 0.1 M NaH2PO4, pH 5.5, containing 5.9 mM tetrabutylammonium hydrogen-sulphate) followed by a slow linear gradient to 17% acetonitrile. The method was applied to extracts of freeze-clamped rat heart tissue samples as well as to extracts of neonatal rat heart cardiomyocytes, and it provided good resolution of high-energy phosphates, including creatine phosphate, as well as of their degradation products.     

Development of orthogonal two‐dimensional hydrophilic interaction chromatography systems with the introduction of novel stationary phases

Two different offline 2‐D hydrophilic interaction chromatography (2D‐HILIC/HILIC) systems have been developed. In the two systems, a click maltose column was used in the first dimension, an amide column or a click β‐CD column was used in the second dimension, respectively. Both of the systems were used for the analysis of very polar components in Carthamus tinctorius Linn., which is a traditional Chinese medicine. Excellent orthogonality and separation results were obtained in both 2D‐HILIC/HILIC systems, while the peak capacity of the system based on click maltose and amide column was higher for its adoption of stationary phase with smaller particle size in the second dimension.     

Fast HPLC method for the determination of glimepiride, glibenclamide, and related substances using monolithic column and flow program

This work presents a fast method for the simultaneous separation and determination of glimepiride, glibenclamide, and two related substances by RP LC. The separation was performed on a Chromolith Performance (RP-18e, 100 mm x 4.6 mm) column. As mobile phase, a mixture of phosphate buffer pH 3, 7.4 mM, and ACN (55:45 v/v) was used. Column oven temperature was set to 30 degrees C. The total chromatographic run time was 80 s. This was achieved using a flow program from 5 to 9.9 mL/min. Precisions of the interday and the intraday assay for both retention times and peak areas for the four analyzed compounds were less than 1.2%. The method showed good linearity and recovery. The short analysis time makes the method very valuable for quality control and stability testing of drugs and their pharmaceutical preparations.     

Hydrophilic interaction liquid chromatography in the separation of a moderately lipophilic drug from its highly polar metabolites--the cardioprotectant dexrazoxane as a model case

This paper presents a systematic study of the retention behavior of a model bisdioxopiperazine drug, dexrazoxane (DEX) and its three polar metabolites (two single open-ring intermediates-B and C and an EDTA-like active compound ADR-925) on different stationary phases intended for hydrophilic interaction liquid chromatography (HILIC). The main aim was to estimate advantages and limitations of HILIC in the simultaneous analysis of a moderately lipophilic parent drug and its highly polar metabolites, including positional isomers, under MS compatible conditions. The study involved two bare silica columns (Ascentic Express HILIC, Atlantis HILIC) and two stationary phases with distinct zwitterionic properties (Obelisc N and ZIC HILIC). The chromatographic conditions (mobile phase strength and pH, column temperature) were systematically modified to assess their impact on retention and separation of the studied compounds. It was found that the bare silica phases were unable to separate the positional isomers (intermediates B and C), whereas both columns with zwitterionic properties (Obelisc N and ZIC HILIC) were able to separate these structurally very similar compounds. However, only ZIC HILIC phase allowed appropriate separation of DEX and all its metabolites to a base line within a single run. A mobile phase composed of a mixture of ammonium formate (0.5 mM) and acetonitrile (25:75, v/v) was suggested as optimal for the simultaneous analysis of DEX and its metabolites on ZIC HILIC. Thereafter, HILIC-LC-MS analysis of DEX and all its metabolites was performed for the first time to obtain basic data about the applicability of the suggested chromatographic conditions. Hence, this study demonstrates that HILIC could be a viable solution for the challenging analysis of moderately polar parent drug along with its highly polar metabolites including the ability to separate structurally very similar compounds, such as positional isomers.     

Characterization of enhanced-fluidity liquid hydrophilic interaction chromatography for the separation of nucleosides and nucleotides

Hydrophilic interaction chromatography (HILIC) is a liquid chromatographic separation mechanism commonly used for polar biological molecules. The use of enhanced-fluidity liquid chromatography (EFLC) with mixtures of methanol/water/carbon dioxide is compared to acetonitrile/water mobile phases for the separation of nucleosides and nucleotides under HILIC conditions. Enhanced-fluidity liquid chromatography involves using common mobile phases with the addition of substantial proportions of a dissolved gas which provides greater mobile phase diffusivity and lower viscosity. The impact of varying several experimental parameters, including temperature, addition of base, salt, and CO₂ was studied to provide optimized HILIC separations. Each of these parameters plays a key role in the retention of the analytes, which demonstrates the complexity of the retention mechanism in HILIC. The tailing of phosphorylated compounds was overcome with the use of phosphate salts and the addition of a strong base; efficiency and peak asymmetry were compared with the addition of either triethylamine (TEA), 1,4-diazabicyclo [2.2.2] octane (DABCO) or 1,5-diazabicyclo [4.3.0] non-5-ene (DBN). DBN and DABCO both led to increased efficiency and lower peak asymmetry; DBN provided the best results. Sodium chloride and carbon dioxide were added to enhance the selectivity between the analytes, giving a successful isocratic separation of nucleosides and nucleotides within 8 min. The retention mechanism involved in EFL-HILIC was explored by varying the temperature and the mole fraction of CO₂. These studies showed that partitioning was the dominant mechanism. The thermodynamics study confirmed that the solvent strength is maintained in EFLC and that a change in entropy was mainly responsible for the improved selectivity. The selectivity using methanol/water/carbon dioxide varied greatly compared to that obtained with acetonitrile/water. Finally while this study highlights the optimization of EFL-HILIC for the separation of nucleosides and nucleotides under isocratic conditions, this is also an example of the broad range of polarities of compounds that EFL-HILIC can separate.     

Development of a comprehensive two-dimensional hydrophilic interaction chromatography/quadrupole time-of-flight mass spectrometry system and its application in separation and identification of saponins from Quillaja saponaria

Hydrophilic interaction chromatography (HILIC) was used in two dimensions in a comprehensive two-dimensional HILIC hyphenated with a quadrupole time-of-flight mass spectrometry (HILICxHILIC-Q-TOF-MS) system for the analysis of complex samples of hydrophilic compounds. A TSKgel Amide-80 column was employed as the first dimension, and a short PolyHydroxyethyl A column was as the second dimension. The column system showed moderate orthogonality at defined operational conditions. A high speed Q-TOF-MS detector as a third complementary dimension significantly improved the peak capacity. The separation capability of the developed HILICxHILIC-Q-TOF-MS system was tested by separating an extract from Quillaja saponaria. The major components, quillaja saponins, in the extract were well identified by means of [M-H](-) ions, characteristic product ions, and their two-dimensional retention behaviors. Several pairs of isomers, which were often co-eluted on conventional LC-MS methods and had similar fragmentation characteristics in MS/MS spectra, were well separated on the two-dimensional system based on their different hydrophilicity. The developed comprehensive two-dimensional HILIC system demonstrates unique selectivity for hydrophilic compounds and satisfactory peak capacity and resolution for analogues by making sufficient use of two-dimensional separation plane.     

Streamlined pentafluorophenylpropyl column liquid chromatography-tandem quadrupole mass spectrometry and global (13)C-labeled internal standards improve performance for quantitative metabolomics in bacteria

Streamlined quantitative metabolomics in central metabolism of bacteria would be greatly facilitated by a high-efficiency liquid chromatography (LC) method in conjunction with accurate quantitation. To achieve this goal, a methodology for LC-tandem quadrupole mass spectrometry (LC-MS/MS) involving a pentafluorophenylpropyl (PFPP) column and culture-derived global (13)C-labeled internal standards (I.Ss.) has been developed and compared to hydrophilic interaction liquid chromatography (HILIC)-MS/MS and published combined two-dimensional gas chromatography and LC methods. All 50 tested metabolite standards from 5 classes (amino acids, carboxylic acids, nucleotides, acyl-CoAs and sugar phosphates) displayed good chromatographic separation and sensitivity on the PFPP column. In addition, many important critical pairs such as isomers/isobars (e.g. isoleucine/leucine, methylsuccinic acid/ethylmalonic acid and malonyl-CoA/3-hydroxybutyryl-CoA) and metabolites of similar structure (e.g. malate/fumarate) were resolved better on the PFPP than on the HILIC column. Compared to only one (13)C-labeled I.S., the addition of global (13)C-labeled I.Ss. improved quantitative linearity and accuracy. PFPP-MS/MS with global (13)C-labeled I.Ss. allowed the absolute quantitation of 42 metabolite pool sizes in Methylobacterium extorquens AM1. A comparison of metabolite level changes published previously for ethylamine (C2) versus succinate (C4) cultures of M. extorquens AM1 indicated a good consistency with the data obtained by PFPP-MS/MS, suggesting this single approach has the capability of providing comprehensive metabolite profiling similar to the combination of methods. The more accurate quantification obtained by this method forms a fundamental basis for flux measurements and can be used for metabolism modeling in bacteria in future studies.     

Comparison of hydrophilic-interaction, reversed-phase and porous graphitic carbon chromatography for glycan analysis

Hydrophilic-interaction liquid chromatography (HILIC), reversed-phase chromatography (RPC) and porous graphitic carbon (PGC) chromatography are typically applied for liquid chromatographic separations of protein N-glycans. Hence the performances of these chromatography modes for the separation of fluorescently labeled standard glycan samples (monoclonal antibody, fetuin, ribonuclease-B) covering high-mannose and a broad range of complex type glycans were investigated. In RPC the retention of sialylated glycans was enhanced by adding an ion-pairing agent to the mobile phase, resulting in improved peak shapes for sialylated glycans compared to methods recently reported in literature. For ion pairing RPC (IP-RPC) and HILIC ultra-high performance stationary phases were utilized to maximize the peak capacity and thus the resolution. But due to the shallow gradient in RPC the peak capacity was lower than on PGC. Retention times in HILIC and IP-RPC could be correlated to the monosaccharide compositions of the glycans by multiple linear regression, whereas no adequate model was obtained for PGC chromatography, indicating the significance of the three-dimensional structure of the analytes for retention in this method. Generally low correlations were observed between the chromatography methods, indicating their orthogonality. The high selectivities, as well as the commercial availability of ultra-high performance stationary phases render HILIC the chromatography method of choice for the analysis of glycans. Even though for complete characterization of complex glycan samples a combination of chromatography methods may be necessary.     

Investigation of polar stationary phases for the separation of sympathomimetic drugs with nano-liquid chromatography in hydrophilic interaction liquid chromatography mode

In this study, the retention and selectivity of a mixture of basic polar drugs were investigated in hydrophilic interaction chromatographic conditions (HILIC) using nano-liquid chromatography (nano-LC). Six sympathomimetic drugs including ephedrine, norephedrine, synephrine, epinephrine, norepinephrine and norphenylephrine were separated by changing experimental parameters such as stationary phase, acetonitrile (ACN) content, buffer pH and concentration, column temperature. Four polar stationary phases (i.e. cyano-, diol-, aminopropyl-silica and Luna HILIC, a cross-linked diol phase) were selected and packed into fused silica capillary columns of 100 μm internal diameter (i.d.). Among the four stationary phases investigated a complete separation of the all studied compounds was achieved with aminopropyl silica and Luna HILIC stationary phases only. Best chromatographic results were obtained employing a mobile phase composed by ACN/water (92/8, v/v) containing 10 mM ammonium formate buffer pH 3. The influence of the capillary temperature on the resolution of the polar basic drugs was investigated in the range between 10 and 50 °C. Linear correlation of ln k vs. 1/T was observed for all the columns; ΔH° values were negative with Luna HILIC and positive with aminopropyl- and diol-silica stationary phases, demonstrating that different mechanisms were involved in the separation.To compare the chromatographic performance of the different columns, Van Deemter curves were also investigated.     

C18丙烯酰胺硅胶柱对肌肽分离能力的比较

建立了一种以牛肉中肌肽为代表,反相分离测定亲水性物质的方法.选用丙基酰胺键合硅胶亲水作用色谱柱,反相分析测定牛肉中亲水性成分-肌肽的含量,样品无需衍生处理.结合HPLC-MS联用技术确定了保留时间为10.276～10.609min的色谱峰就是肌肽峰.将该色谱柱与常规C18色谱柱进行对比后发现,该色谱柱对L-肌肽的保留能...