Reversed-phase high-performance liquid chromatography of proteins and peptides on a pellicular support based on hydrophilic resin

Chemometric-assisted method development in hydrophilic interaction liquid chromatography: A review

With an enormous growth in the application of hydrophilic interaction liquid chromatography (HILIC), there has also been significant progress in HILIC method development. HILIC is a chromatographic method that utilises hydro-organic mobile phases with a high organic content, and a hydrophilic stationary phase. It has been applied predominantly in the determination of small polar compounds. Theoretical studies in computer-aided modelling tools, most importantly the predictive, quantitative structure retention relationship (QSRR) modelling methods, have attracted the attention of researchers and these approaches greatly assist the method development process. This review focuses on the application of computer-aided modelling tools in understanding the retention mechanism, the classification of HILIC stationary phases, prediction of retention times in HILIC systems, optimisation of chromatographic conditions, and description of the interaction effects of the chromatographic factors in HILIC separations. Additionally, what has been achieved in the potential application of QSRR methodology in combination with experimental design philosophy in the optimisation of chromatographic separation conditions in the HILIC method development process is communicated. Developing robust predictive QSRR models will undoubtedly facilitate more application of this chromatographic mode in a broader variety of research areas, significantly minimising cost and time of the experimental work.

Protein- versus peptide fractionation in the first dimension of two-dimensional high-performance liquid chromatography-matrix-assisted laser desorption/ionization tandem mass spectrometry for qualitative proteome analysis of tissue samples

The availability of robust and highly efficient separation methods represents a major requirement for proteome analysis. This study investigated the characteristics of two different gel-free proteomic approaches to the fractionation of proteolytic peptides and intact proteins, respectively, in a first separation dimension. Separation and mass spectrometric detection by matrix-assisted laser desorption/ionization tandem mass spectrometry (MALDI-MS/MS) were performed at the peptide level in both methods. Bottom-up analysis (BU) was carried out employing well established peptide fractionation in the first separation dimension by strong cation-exchange chromatography (SCX), followed by ion-pair reversed-phase chromatography (IP-RPC) in the second dimension. In the semi-top-down approach (STD), which involved intact protein fractionation in the first dimension, the separation mode in both dimensions was IP-RPC utilizing monolithic columns. Application of the two approaches to the proteome analysis of proteins extracted from a tumor tissue revealed that the BU method identified more proteins (1245 in BU versus 920 in STD) while STD analysis offered higher sequence coverage (14.8% in BU versus 17.5% in STD on average). The identification of more basic and larger proteins was slightly favored in the BU approach, most probably due to higher losses of these proteins during intact protein handling and separation in the STD method. A significant degree of complementarity was revealed by an approximately 33% overlap between one BU and STD replicate, while 33% each of the protein identifications were unique to both methods. In the STD method, peptides obtained upon digestion of the proteins contained in fractions of the first separation dimension covered a broad elution window in the second-dimension separation, which demonstrates a high degree of "pseudo-orthogonality" of protein and peptide separation by IP-RPC in both separation dimensions.

Effect of chromatographic conditions on resolution in high-performance ion-exchange chromatography of proteins on nonporous support

We explored chromatographic conditions to obtain high resolution in protein separations by ion-exchange chromatography (IEC) on a nonporous anion-exchange resin of 2.5 microm in particle diameter. We studied the effects of gradient time (steepness of salt concentration gradient), flow-rate and column length on resolution in much wider ranges than had been studied before. It was found that two distinct conditions exist that provide high resolution. The first is a condition which has widely been employed in current high-performance IEC, namely, a combination of short gradient time, high flow-rate and comparatively short column. Separation times are usually 5-30 min, and even more rapid (1-2 min) separations are possible. The second is the condition which has rarely been employed in high-performance IEC. It is a combination of long gradient time, low flow-rate and long column. Although it takes several hours for one separation, very high resolution is attainable.

Evaluation of 1.5 microM reversed phase nonporous silica in packed capillary electrochromatography and application in pharmaceutical analysis

Reversed-phase nonporous silica (RP-NPS) of 1.5 microm dp is employed to demonstrate rapid and efficient separations in packed capillary electrochromatography (CEC). Two methods for packing capillaries and two techniques to manufacture frits used to hold the packing in place are evaluated for their effect upon separation performance using polyaromatic hydrocarbons (PAHs) and polar neutral pharmaceutical compounds. Attention is given to conditioning of the packed capillaries for high efficiency separations without necessity for sodium dodecyl sulfate (SDS). Separation conditions for the nonporous materials were modified from those previously determined on porous reversed-phase silica. Feasibility for method development and validation of a parent pharmaceutical compound and related impurities in the range of 0.1-120% of a 5 mg/mL concentration was assessed and reported. An approach to improving detection sensitivity through use of large-bore capillaries is briefly discussed.

Peptide separation in normal-phase liquid chromatography. Study of selectivity and mobile phase effects on various columns

An experimental procedure for peptide separation by normal-phase liquid chromatography (NPLC) was proposed in previous papers. In the present study, the chromatographic behavior of amino, cyano, amide, diol and silica columns, which have been used in non-aqueous NPLC, is investigated anew. The amino column was not appropriate for peptide separation because of poor recovery. The cyano column could not be used due to lack of retention. The amide, diol and silica columns were useful for peptide separation. The chromatograms on amide, diol and silica columns were a little different when the mobile phase composition was changed. The recovery of peptides was good: diol > amide > silica. Repeatability and reproducibility using amide, diol and silica columns was satisfactory.

Protein separation using non-porous sorbents

This article overviews the development of non-porous sorbents having small particle diameters which have proven effective for rapid analysis and micropreparative separation of proteins by liquid chromatography. Much attention is given to the preparation and application of silica- and polystyrene-based non-porous packings for various chromatographic modes, especially affinity chromatography. Modeling works on the prediction and parameter estimation for the dynamics of protein adsorption using non-porous sorbents are reviewed and briefly described. To conclude this review, future prospects of the application of non-porous sorbents are also presented.

Peptide separation in normal phase liquid chromatography

A new method is established for separating peptides in normal phase liquid chromatography using TSK gel Amide-80, carbamoyl groups bonded to a silica gel matrix, and an acetonitrile-water solution containing 0.1% trifluoroacetic acid. Peptide retention time increased with acetonitrile concentration in the initial eluent. Hydrophilic peptides with no retention in a reversed phase column were retained and separated in the present method. Separation selectivities in the present and reversed phase methods differed significantly. Two-dimensional separation of protein digest using reversed and normal phases was conducted, taking advantage of the differences in selectivities. All peptides obtained from the digest could be separated completely. The present method is useful for separating peptide mixtures in conjunction with reversed phase liquid chromatography. Peptide recovery from the Amide-80 column exceeded 80%, as with the reversed phase column, and repeatability and reproducibility were satisfactory.

Effect of mobile phase additives on peptide retention in reversed-phase chromatography with pellicular and totally porous sorbents

The effect of two mobile phase additives, trifluoroacetic acid and phosphoric acid, on the energetics of peptide retention in reversed-phase chromatography was investigated using Hy-Tach C18 micropellicular and Vydac C4 and C18 totally porous stationary phases. The effect of the relatively low phase ratio of columns packed with micropellicular sorbents was also examined. The logarithmic retention factors, of two model peptides, Ac-RGGGGLGLGK-amide and Ac-RGAGGLGLGK-amide, were evaluated with different columns and additives in a practical range of eluent strength. The dependence of the logarithmic retention factor on the concentration of acetonitrile in the mobile phase was linear in all cases. The higher sensitivity of the retention to the organic modifier concentration in the case of the Hy-Tach C18 column is attributed to the relatively low phase ratio of this column. Pairwise plots of the logarithmic retention factors were linear. The plots of data obtained with the two additives has unit slopes and thus reveal homoenergetic retention behavior. On the other hand data obtained on two different columns manifest homeoenergetic retention, the slopes of plots are different from unity. The analysis has yielded consistent results and validated the assumption that the retention free energy can be divided into two components arising from mobile phase and stationary phase contributions. The approach also allowed an estimation of the relative phase ratios of the columns and the Vydac C18 column was found to have an 3 and 8 times higher phase ratio than the Vydac C4 and the Hy-Tech C18 column, respectively.

Performance of wide-pore silica- and polymer-based packing materials in polypeptide separation: effect of pore size and alkyl chain length

The effects of pore size and alkyl chain length of silica- and polymer-based packing materials in the elution of polypeptides with an acetonitrile gradient in the presence of trifluoroacetic acid were studied. Considerable differences were found in the performance of alkylsilylated phases prepared from various wide-pore silica particles assumed to have 30-50-nm pores. The pore size of such silica gels was found to be the critical factor in determining the efficiency for high-molecular-weight polypeptides. Silica C18 phases having small pore volumes below 20 nm pore diameter showed comparable performances to C4 and C8 phases for polypeptides with molecular weights of up to 80,000, and were more stable. Polymer-based packing materials with adequate pore size provided excellent column efficiencies and recoveries for polypeptides with higher chemical stabilities than silica-based materials.