High pH mobile phase effects on silica-based reversed-phase high-performance liquid chromatographic columns

Fast, sensitive LC-MS resolution of α -hydroxy acid biomarkers via SPP-teicoplanin and an alternative UV detection approach

Enantioseparation of α -hydroxy acids is essential since specific enantiomers of these compounds can be used as disease biomarkers for diagnosis and prognosis of cancer, brain diseases, kidney diseases, diabetes, etc., as well as in the food industry to ensure quality. HPLC methods were developed for the enantioselective separation of 11 α -hydroxy acids using a superficially porous particle-based teicoplanin (TeicoShell) chiral stationary phase. The retention behaviors observed for the hydroxy acids were HILIC, reversed phase, and ion-exclusion. While both mass spectrometry and UV spectroscopy detection methods could be used, specific mobile phases containing ammonium formate and potassium dihydrogen phosphate, respectively, were necessary with each approach. The LC-MS mode was approximately two orders of magnitude more sensitive than UV detection. Mobile phase acidity and ionic strength significantly affected enantioresolution and enantioselectivity. Interestingly, higher ionic strength resulted in increased retention and enantioresolution. It was noticed that for formate-containing mobile phases, using acetonitrile as the organic modifier usually resulted in greater enantioresolution compared to methanol. However, sometimes using acetonitrile with high ammonium formate concentrations led to lengthy retention times which could be avoided by using methanol as the organic modifier. Additionally, the enantiomeric purities of single enantiomer standards were determined and it was shown that almost all standards contained some levels of enantiomeric impurities.

Box-Behnken Design-Aided Validation and Optimization of a Stability-Indicating Reverse Phase-HPLC Method for the Estimation of Tamoxifen Citrate in Lipidic Nano-Vesicles

Stability indicating a reverse-phase HPLC analytical method for the quantification of tamoxifen citrate (TMX) in the bulk and lipidic nano-vesicles (LNVs) was developed. The optimized method was validated according to the ICH Q2 (R1) guidelines by following a three-factor interaction Box-Behnken design using Design-Expert® software. The responses measured at 236 nm were retention time (Rt), peak area, tailing factor (TF) and the number of theoretical plates. TMX was eluted best using the Luna® C18 LC Column along with a mobile phase of methanol (MeOH) and ammonium acetate buffer (AAB pH 4.5) 80:20 v/v mixture at 25 ± 2°C temperature. The currently developed method was linear in 100-5,000 ng/mL range with a detection limit of 4.55 ng/mL and a quantification limit of 13.78 ng/mL. The optimized method was utilized to evaluate the stability of TMX in different stress conditions by performing forced degradation studies. The results from the degradation study stipulated that on exposure to various stressors namely acid, alkali, oxidative, thermal and UV light, the TMX did not show considerable degradation except for UV light exposure. Further, the method was successfully used for the quantification of TMX in LNVs.

Further Evaluation of the Base Stability of Hydrophilic Interaction Chromatography Columns Packed with Silica or Ethylene-Bridged Hybrid Particles

One of the fundamental attributes of a liquid chromatography column is its stability when exposed to acidic and basic mobile phases. However, there have been relatively few reports to date on the stability of hydrophilic interaction chromatography (HILIC) columns. Here, we report the results of stability evaluations carried out for HILIC columns packed with ethylene-bridged hybrid or silica particles using accelerated conditions, employing a 100% aqueous pH 11.3 ammonium bicarbonate mobile phase at 70 °C. Under these conditions, the primary mode of column failure was a loss of efficiency due to the formation of voids resulting from the hydrolysis of the particles. We investigated the dependence of stability on the surface area of both unbonded and sulfobetaine-bonded ethylene-bridged hybrid stationary phases. The results show a clear trend of stability increasing as the surface area decreases. Several commercially available HILIC columns that are recommended for use with high-pH mobile phases were also evaluated. The results show times to 50% loss of the initial efficiency ranging from 0.3 to 9.9 h. Columns containing unbonded, sulfobetaine-bonded or diol-bonded ethylene-bridged hybrid stationary phases had longer lifetimes than amino-bonded silica or sulfobetaine-bonded, hybrid-coated, superficially porous silica columns.

Optimizing linear ion trap data independent acquisition towards single cell proteomics

A linear ion trap (LIT) is an affordable, robust mass spectrometer that proves fast scanning speed and high sensitivity, where its primary disadvantage is inferior mass accuracy compared to more commonly used time-of-flight (TOF) or orbitrap (OT) mass analyzers. Previous efforts to utilize the LIT for low-input proteomics analysis still rely on either built-in OTs for collecting precursor data or OT-based library generation. Here, we demonstrate the potential versatility of the LIT for low-input proteomics as a stand-alone mass analyzer for all mass spectrometry measurements, including library generation. To test this approach, we first optimized LIT data acquisition methods and performed library-free searches with and without entrapment peptides to evaluate both the detection and quantification accuracy. We then generated matrix-matched calibration curves to estimate the lower limit of quantification using only 10 ng of starting material. While LIT-MS1 measurements provided poor quantitative accuracy, LIT-MS2 measurements were quantitatively accurate down to 0.5 ng on column. Finally, we optimized a suitable strategy for spectral library generation from low-input material, which we used to analyze single-cell samples by LIT-DIA using LIT-based libraries generated from as few as 40 cells.

Unified-Hydrophilic-Interaction/Anion-Exchange Liquid Chromatography Mass Spectrometry (Unified-HILIC/AEX/MS): A Single-Run Method for Comprehensive and Simultaneous Analysis of Polar Metabolome

One of the technical challenges in the field of metabolomics is the development of a single-run method to detect the full complement of polar metabolites in biological samples. However, an ideal method to meet this demand has not yet been developed. Herein, we proposed a simple methodology that enables the comprehensive and simultaneous analysis of polar metabolites using unified-hydrophilic-interaction/anion-exchange liquid chromatography mass spectrometry (unified-HILIC/AEX/MS) with a polymer-based mixed amines column composed of methacrylate-based polymer particles with primary, secondary, tertiary, and quaternary amines as functional groups. The optimized unified-HILIC/AEX/MS method is composed of two consecutive chromatographic separations, HILIC-dominant separation for cationic, uncharged, and zwitterionic polar metabolites [retention times (RTs) = 0-12.8 min] and AEX-dominant separation for polar anionic metabolites (RTs = 12.8-26.5 min), by varying the ratio of acetonitrile to 40 mM ammonium bicarbonate solution (pH 9.8). A total of 400 polar metabolites were analyzed simultaneously through a combination of highly efficient separation using unified-HILIC/AEX and remarkably sensitive detection using multiple reaction monitoring-based triple quadrupole mass spectrometry (unified-HILIC/AEX/MS/MS). A nontargeted metabolomic approach using unified-HILIC/AEX high-resolution mass spectrometry (unified-HILIC/AEX/HRMS) also provided more comprehensive information on polar metabolites (3242 metabolic features) in HeLa cell extracts than the conventional HILIC/HRMS method (2068 metabolic features). Our established unified-HILIC/AEX/MS/MS and unified-HILIC/AEX/HRMS methods have several advantages over conventional techniques, including polar metabolome coverage, throughput, and accurate quantitative performance, and represent potentially useful tools for in-depth studies on metabolism and biomarker discovery.

Evaluation of the Base Stability of Hydrophilic Interaction Chromatography Columns Packed with Silica or Ethylene-Bridged Hybrid Particles

Stability as a function of mobile phase pH is an important consideration when selecting a chromatographic column. While the pH stability of reversed-phase columns is widely studied, there are relatively few reports of the stability of hydrophilic interaction chromatography (HILIC) columns. We evaluated the stability of silica and ethylene-bridged hybrid HILIC columns when used with mobile phases containing basic buffers. The predominant mode of column degradation observed in our studies was a decrease in efficiency due to voiding, resulting from the hydrolysis of the silica particles. Associated with this were increases in tailing factors. Retention factor changes were also noted but were smaller than the efficiency losses. The dependence of the rate of efficiency decrease on the key variables of temperature, mobile phase pH and water content were studied for an unbonded silica column. The effect of the acetonitrile concentration on the pH of the mixed aqueous/acetonitrile mobile phases was also investigated. Using conditions found to cause a 50% decrease in efficiency after approximately five hours of exposure to the basic solution, we evaluated eight different commercially available HILIC columns containing silica or ethylene-bridged hybrid particles. The results show large differences between the stability of the silica and ethylene-bridged hybrid particle stationary phases, with the latter exhibiting greater stability.

Hydrophilic silicon nanoparticles as a turn-off and colorimetric fluorescent probe for curcuminoids detection in food samples and cell imaging

Hydrophilic fluorescent silicon nanoparticles (SiNPs) with good pH stability, salt-tolerance and anti-photobleaching were for the first time prepared from hydrophobic 3-glycidoxypropyltrimethoxysilane. Employing SiNPs as the fluorescence probe, selective quantification of curcuminoids based on the quenching effect was realized with a linearity of 0.046-7.4 μg/mL and a limit of detection of 17.6 ng/mL. Moreover, in light of fluorescence redshift of SiNPs corresponding to the elevated concentration of curcuminoids, a fluorescence colorimetric method was established based on only one extra probe, i.e. herein SiNPs. Thus, semi-quantification of curcuminoids (0-14.7 μg/mL) was visualized from blue to yellow color. Both the developed quantitative and semi-quantitative probe were successfully applied to determine curcuminoids in various actual food samples. Furthermore, SiNPs possessed low cytotoxicity and succeeded in intracellular curcuminoids imaging. The proposed SiNPs could be a promising fluorescence probe for multiple applications.

T. M, Boissel C. Electrospray ionization mass spectrometry ion suppression/enhancement caused by column bleed for three mixed-mode reversed-phase/anion-exchange high-performance liquid chromatography columns

RATIONALE

Mixed-mode reversed-phase/anion exchange liquid chromatography is useful for separations of mixtures containing anions (e.g. ionized acids). However, when using this form of liquid chromatography with mass spectrometry detection, the bleed of amine-containing hydrolysis products from the columns may cause ion suppression or enhancement.

METHODS

Using electrospray ionization tandem quadrupole mass spectrometry detection, we determined the ion suppression or enhancement caused by column bleed for three mixed-mode reversed-phase/weak anion-exchange columns containing stationary phases that differ in chemical structure. Two of the stationary phases are based on silica particles, while the third uses ethylene-bridged hybrid organic/inorganic particles, which have improved hydrolytic stability. Mixtures of acidic and basic analytes were combined with the chromatography flow postcolumn, both with and without a column, and their mass spectrometry ion signal responses (peak areas) were determined. The ratio of signal response with and without a column is the matrix factor. Positive ion electrospray measurements were carried out using 0.1% formic acid (pH ~ 2.7) as a mobile phase additive, and 10mM ammonium formate (pH ~ 6.4) was used for negative ion electrospray detection.

RESULTS

The matrix factors under both positive and negative ionization modes were closest to 1 (0.74-1.16) for the hybrid particle-based columns, showing minimal ion suppression or enhancement. In contrast, the silica-based columns gave matrix factors ranging from 0.04 to 1.86, indicating high levels of ion suppression or enhancement. These results may be explained by the differences in the structures of the stationary phases, which affect the relative amounts of hydrolysis products that elute from the columns.

CONCLUSIONS

The low levels of mass spectrometry ion suppression or enhancement caused by column bleed from the hybrid particle-based columns should allow for accurate quantitative mass spectrometric detection combined with mixed-mode reversed-phase/weak anion-exchange chromatography.

An analytical "quality by design" approach in RP-HPLC method development and validation for reliable and rapid estimation of irinotecan in an injectable formulation

The objective of the present study was to develop a robust, simple, economical and sensitive HPLC-UV method using the "quality-by-design" approach for the estimation of irinotecan (IRI) in marketed formulations. RP-HPLC method was developed by applying Box-Behnken design with Hyper-Clone (Phenomenex®) C18 column (250 × 4.6 mm id, particle size 5 µm, ODS 130 Å) as a stationary phase. Acetonitrile and 20 mmol L-1 potassium phosphate buffer (pH 2.5) containing 0.1 % triethylamine in a ratio of 45:55 % (V/V) was used as a mobile phase. The sample was injected in a volume of 20 µL into the HPLC system. UV detector at 254 nm was used to estimate and quantify IRI. Isocratic elution was opted while the flow rate was maintained at 0.75 mL min-1. The retention time of IRI was found to be 4.09 min. The responses were found to be linear for concentration range of 0.5 to 18.0 µg mL-1 and the coefficient of determination value was found to be 0.9993. Percent relative standard deviation for intra- and inter-day precisions was found in the range of 0.1 to 0.4 %. LOD and LOQ values were found to be 4.87 and 14.75 ng mL-1, resp. Robustness studies confirmed that the developed method is robust with RSD of a maximum 0.1 %. The method is simple, precise, sensitive, robust and economical making it applicable to the estimation of IRI in an injectable formulation.

LC Troubleshooting Odds and Ends from 2020

Sometimes our approach to troubleshooting specific problems has to change in response to changes in high performance liquid chromatography (HPLC) technology over time. In this installment, we discuss changes in technologies for mobile-phase degassing, silica-based stationary phases, and models for reversed-phase selectivity.

Waxberry-like hierarchically porous ethyl-bridged hybrid silica microsphere: A substrate for enzyme catalysis and high-performance liquid chromatography

In this study, the ethyl-bridged hybrid silica microsphere with hierarchically meso-macroporous structure was initially synthesized through a method combining dispersion polymerization with sol-gel transition and phase separation. The flow-through macropores rendered the microsphere a rough surface like a waxberry, and thus the material was named as waxberry-like ethyl-bridged hybrid silica sphere (WEHS). WEHS was characteristic of appropriate alkali-stability, which was highly difficult for the pure silica. Additionally, WEHS possessed hierarchical meso- and macropores, which added additional value for faster mass transfer than the conventional fully porous silica materials. Taking the advantages of WEHS, it was successfully applied as the substrate to immobilize lipase; the prepared immobilized lipase exhibited high catalytic activity and favorable reusability under alkaline conditions, which was significant in pitch control of neutral-alkaline papermaking industry. Moreover, as the high-performance liquid chromatographic stationary phase matrix, WEHS made the separation under alkaline mobile phase into a reality for the silica-based materials. Besides, an ultra-fast and efficient separation in minutes was achieved with lower consumption of solvents and saving analytical time, which is highly desired in modern analysis. In general, WEHS was a novel and promising candidate in the myriads of silica-based materials.

Chromatographic behavior of selected antibiotic drugs supported by quantitative structure-retention relationships

As antibiotic drugs have a wide variety of applications, there is a growing demand for their selective determination, a task for which chromatographic methods seem to be appropriate. With this end in view, chromatographic measurements were performed with the use of six different HPLC columns (ACE 5C₁₈, IAM.PC.DD.2, octadecyl, phenyl, alkylamide and cholesteryl-alkylamide) to determine the logk_w of selected antibiotic drugs (amoxicillin, cefatoxime, ciprofloxacin, fluconazole, gentamicin, clindamycin, linezolid and metronidazole). The retention behavior of the analytes was investigated as a function of different binary hydro-organic mobile phases containing 10-45% (v/v) acetonitrile. The studied compounds were separated under isocratic conditions. The best results of separation of the tested biologically active compounds were obtained on the commercially available C18 column. Special attention was dedicated to the study of interactions among the stationary phase, mobile phase and the analytes. Another goal was to selecting the best column for separation of the tested biologically active compounds. Finally, QSRR models together with stationary phase characterization provided reliable information on the properties and characteristics of studied columns.

Separation behavior of basic compounds on unbonded silicon oxynitride and silica high-performance liquid chromatography stationary phases with reversed-phase eluents

Unbonded silicon oxynitride and silica high-performance liquid chromatography stationary phases have been evaluated and compared for the separation of basic compounds of differing molecular weight, pK_a , and log D using aqueous/organic mobile phases. The influences of percentage of organic modifier, buffer pH, and concentration in the mobile phase on base retention were investigated on unbonded silicon oxynitride and silica phases. The results confirmed that unbonded silicon oxynitride and silica phases demonstrated excellent separation performance for model basic compounds and both the unbonded phases examined possessed a hydrophobic/adsorption and ion-exchange character. The silicon oxynitride stationary phase exhibited high hydrophilicity compared with silica with a reversed-phase mobile phase. An ion-exclusion-type mechanism becomes predominant for the separation of three aimed bases on the silicon oxynitride column at pH 2.8. Different from silicon oxynitride stationary phase, no obvious change for the retention time of three model bases on silica stationary phase at pH 2.8 can be observed.

Probing Heterogeneity and Bonding at Silica Surfaces through Single-Molecule Investigation of Base-Mediated Linkage Failure

The nature of silica surfaces is relevant to many chemical systems, including heterogeneous catalysis and chromatographies utilizing functionalized-silica stationary phases. Surface linkages must be robust to achieve wide and reliable applicability. However, silyl ether-silica support linkages are known to be susceptible to detachment when exposed to basic conditions. We use single-molecule spectroscopy to examine the rate of surface linkage failure upon exposure to base at a variety of deposition conditions. Kinetic analysis elucidates the role of thermal annealing and addition of blocking layers in increasing stability. Critically, it was found that successful surface modification strategies alter the rate at which base molecules approach the silica surface as opposed to reducing surface linkage reactivity. Our results also demonstrate that the innate structural diversity of the silica surface is likely the cause of observed heterogeneity in surface-linkage disruption kinetics.

Aniline-modified porous graphitic carbon for hydrophilic interaction and attenuated reverse phase liquid chromatography

Most stationary phases for hydrophilic interaction liquid chromatography (HILIC) and reversed phase liquid chromatography (RPLC) are based on silica. Porous graphitic carbon (PGC) is an attractive alternative to silica-based phases due to its chemical and thermal stability, and unique selectivity. However, native PGC is strongly hydrophobic and in some instances excessively retentive. PGC particles with covalently attached aniline groups (Dimethylaniline-PGC and Aniline-PGC) were synthesized to alter the surface polarity of PGC. First, the diazonium salt of N,N-dimethyl-p-phenylenediamine or 4-nitroaniline was adsorbed onto the PGC surface. The adsorbed salt was reduced with sodium borohydride and (Aniline-PGC only) the nitro group was further reduced with iron powder to the aniline. X-ray photoelectron spectroscopy confirmed the surface functionalities and that these moieties were introduced to the surface at concentrations of 0.9 and 2.1molecules/nm(2), respectively. These modified PGC phases (especially Aniline-PGC) were evaluated as HILIC and reversed phases. The Dimethylaniline-PGC phase displayed only weak HILIC retention of phenolic solutes. In contrast, the Aniline-PGC phase displayed up to nearly a 7-fold increase in HILIC retention vs. an aniline-silica phase and selectivity that differed from 10 other HILIC phases. Introduction of aniline groups to the PGC surface reduced the RPLC retentivity of PGC up to more than 5-fold and improved the separation efficiency up to 6-fold. The chromatographic performance of Aniline-PGC is demonstrated by separations of nucleotides, nucleosides, carboxylic acids, basic pharmaceuticals, and other compounds.

Chiral selectors in CE: recent developments and applications

This review article provides an overview of the recent advances in enantioanalysis by use of electrophoretic techniques. Due to the big number of publications in the subject mentioned above, this article is focused on chiral method developments and applications published from 2008 until 2011, and it demonstrates chiral selectors used in CE. Numerous chiral selectors have been used over the years, and these include the cyclic and the linear oligo- and polysaccharides, the branched polysaccharides, the polymeric and monomeric surfactants, the macrocyclic and other antibiotics, and the crown ethers. Different dual-selector systems are also presented in this article, and the results are compared with those obtained by use of a single chiral selector. Finally, several pharmaceutical and biomedical applications based on chiral recognition are summarized.

Minimization of side reactions during Lys Tag derivatization of C-terminal lysine peptides

Several issues need to be considered concerning chemical labeling strategies in proteomics. Some of these are labeling specificity, possible side reactions, completeness of reaction, recovery rate, conserving integrity of sample, hydrolysis of peptide bonds at high pH, and signal suppression in mass spectrometry (MS). We tested the effects of different reaction conditions for 2-methoxy-4,5-dihydro-1H-imidazole (Lys Tag) derivatization of the ε-amine group of lysine (K) residues. By using nanoflow LC-electrospray ionization-MS (LC-ESI-MS) and MS/MS in combination with MSight 2-D image analysis, we found that standard Lys Tag derivatization processes and conditions induce side reactions such as (i) Lys Tag labeling of the N-terminus, (ii) methylation of internal aspartic acid (D), glutamic acid (E) and C- and N-peptide termini and (iii) deamidation of asparagine (N) and glutamine (Q). We found temperature and pH to be the main variables to control side reactions. Lowering the reaction temperature from 55°C to room temperature reduced deamidation from 22.8±1.4% (SEM) to 7.7±5.5% (SEM) and almost totally blocked methylation (7.0±1.2% (SEM) to 0.4±0.4% (SEM) of the internal acidic amino acids (D and E) at high pH. We conclude that lowering the reaction temperature minimizes undesired side reactions during Lys Tag derivatization in solution.

Determination of free catecholamines in urine by tandem affinity/ion-pair chromatography and flow injection analysis

BACKGROUND

A system was developed for the simultaneous measurement in urine of free catecholamines (i.e., dopamine, norepinephrine, epinephrine) and creatinine (i.e., an indicator of urine output and volume). This method was based on the use of tandem affinity/ion-pair HPLC and flow injection analysis.

METHODS

The free catecholamines were extracted directly from urine by using an on-line phenylboronic acid affinity column. The extracted solutes were then separated and measured by ion-pair chromatography followed by amperometric detection. Creatinine was measured by an on-line flow injection analysis system based on the Jaffe reaction, which analyzed creatinine as it eluted non-retained from the phenylboronic acid column.

RESULTS

Various factors were considered in the design and optimization of the phenylboronic acid column, the tandem affinity/ion-pair HPLC columns and the flow injection analysis system. The total analysis time for the final combined system was approximately 16 min per injection at 1 ml/min. This method was found to have good agreement with the expected results for control urine samples. The limits of detection for 20 microl samples (S/N=3.0) were 1.8, 1.0 and 4.3 microg/l for norepinephrine, epinephrine and dopamine, respectively, while the limit of detection of creatinine was 5.0 mg/l. The linear response of this method extended over a 450 to 930-fold range in concentration for the catecholamines and covered the range of clinical interest. The within-day precision of this method was +/-2.0-2.7%.

CONCLUSIONS

The ability of this method to simultaneously monitor both creatinine and other analytes makes this HPLC/FIA system an attractive method for use in monitoring urinary compounds. With this approach it was possible to provide fast results for small volumes of random urine samples that were collected as part of a psychological study. The same method could also be utilized with 12 or 24 h urine specimens.

Magnesium oxide microspheres as a packing material for the separation of basic compounds in normal-phase liquid chromatography

Uniform monodisperse magnesium oxide microspheres with a high surface area have been prepared by a facile seed-induced precipitation. By characterizing these particles with scanning electron microscopy and N(2) physisorption techniques, the results demonstrate that these magnesium oxide microspheres have an average particle diameter of 9.5 microm, a specific surface area of 211.7 m(2)g(-1), a total pore volume of 0.76 mL g(-1), and an average pore diameter of 143 A. The chromatographic properties of these microspheres have been investigated in normal-phase mode for the separation of various basic compounds including aniline, quinoline, and pyridine derivatives. In contrast to conventional silica, the magnesium oxide particles exhibit unique selectivity and retention property for the separation of the tested basic compounds, and these microspheres are promising as an alternative new packing material for high-performance liquid chromatography.

Applications of silica supports in affinity chromatography

The combined use of silica-based chromatographic supports with immobilized affinity ligands can be used in many preparative and analytical applications. One example is the use of silica-based affinity columns in HPLC, giving rise to a method known as high-performance affinity chromatography (HPAC). This review discusses the role that silica has played in the development of affinity chromatography and HPAC and the applications of silica in these methods. This includes a discussion of the types of ligands that have been employed with silica and the methods by which these ligands have been immobilized. Various formats have also been presented for the use of silica in affinity chromatographic methods, including assays involving direct or indirect analyte detection, on-line or off-line affinity extraction, and chiral separations. The use of silica-based affinity columns in studies of biological systems based on zonal elution and frontal analysis methods will also be considered.

A study of the effects of column porosity on gradient separations of proteins

The type of the stationary phase for reversed-phase liquid chromatography significantly affects the sample elution. Hydrodynamic properties, efficiency and gradient elution of proteins were investigated on five commercial C18 columns with wide-pore totally porous particles, with superficially porous layer particles, non-porous particles and a silica-based monolithic bed. The efficiency in the terms of reduced plate height is higher for low-molecular ethylbenzene than for proteins, but depends on the character of the pores in the individual columns tested. The superficially porous Poroshell and the non-porous Micra columns provide the best efficiency for proteins at high mobile phase flow rates, probably because of similar pore architecture in the stationary phase. The Zorbax column with similar pore architecture as the Poroshell active layer, i.e. narrow pore distribution of wider pores shows better efficiency than the packed column with narrow pores and broad pore distribution. The monolithic column shows lower efficiency for proteins at high flow rates, but it performs better than the broad-pore distribution totally porous particulate columns. Different pore architecture affects also the retention and selectivity for proteins on the individual columns. The retention times on all columns can be predicted using the model for reversed-phase gradient elution developed originally for low-molecular compounds. Consideration of the limited pore volume accessible to the biopolymers has negligible effect on the prediction of retention on the columns packed with non-porous or superficially porous particles, but improves the accuracy of the predicted data for the totally porous columns with broad pore distribution.

Selective Analysis of Secondary Amino Acids in Gelatin Using Pulsed Electrochemical Detection

A method was developed for selective analysis of the secondary amino acids proline and 4-hydroxyproline from gelatin hydrolysates using anion-exchange high-performance liquid chromatography followed by integrated pulsed amperometric detection (HPLC-IPAD). An extraction scheme was implemented prior to HPLC-IPAD analysis to isolate the secondary amino acids by the removal of primary amino acids through derivatization with o-phthalaldehyde followed by solid-phase extraction with C18 packed columns. The use of the IPAD technique eliminated the need for a second derivatization step to detect secondary amino acids. The removal of interfering primary amino acids prior to chromatographic analysis allowed the use of isocratic mobile-phase conditions to achieve effective and efficient separation of the amino acids. This led to a more precise and accurate quantitation of their content in gelatin hydrolysates. Detection limits approach 10 parts per billion ( approximately 2 pmol/injection) with a chromatographic analysis time under 8 min. The ratios of secondary amino acids, in addition to their abundances, were used to distinguish gelatin manufactured from bovine, porcine, and fish raw material sources.