Application of micro- and nano-HPLC to the determination and characterization of bioactive and biomarker peptides

This article reviews the works published since 2001 (included) on the micro/nano-HPLC analysis of bioactive and biomarker peptides. The main achievements related to the improvement of the detection sensitivity, quantitation repeatability and reproducibility, and separation selectivity are highlighted. A wide attention is paid to the application of micro/nano-HPLC to the analysis of bioactive peptides in biological matrices. The uses of micro/nano-HPLC in peptidomics to discover new endogenous bioactive peptides and to develop quantitation procedures to compare the levels of peptides of interest in two different biological samples are also considered. Finally, the application of micro/nano-HPLC to the analysis of biomarker peptides for various diseases is also included in this review.

Determination of bradykinin and arg-bradykinin in rat muscle tissue by microdialysis and capillary column-switching liquid chromatography with mass spectrometric detection

Quantification of bradykinin peptides in limited amounts of rat muscle tissue dialysate has been performed using a packed capillary LC-ESI-TOF-MS method. The micro dialysate samples (450 microL) with added internal standard were loaded onto a 1 mm x 5 mm loading column packed with 5 microm Kromasil C18 particles by a carrier solution of 0.1% formic acid in ACN/water (5:95, v/v) at a flow rate of 250 microL/min for online preconcentration of the analytes. Back-flushed elution onto a 150 mm x 0.5 mm Zorbax C18 column packed with 5 microm particles was conducted using a linear solvent ACN/H2O gradient containing 0.1% formic acid. (Tyr8)-bradykinin was used as an internal standard and was added to the dialysis sample prior to injection. Baseline separation of bradykinin, arg-bradykinin and (tyr8)-bradykinin was achieved within 10 min. Positive ESI was performed in the m/z range of 200-1300. The method was validated in the range 0.2-1.0 ng/mL dialysate, yielding correlation coefficients of 0.995 and 0.990 for bradykinin and arg-bradykinin, respectively. The within-assay and between-assay precisions were between 4.3-9.6% and 6.2-10.6%, respectively. Both arg-bradykinin and bradykinin were detected in dialysate from rat muscle tissue, at concentrations of 0.1 and 0.4 ng/mL for bradykinin and arg-bradykinin, respectively, confirming the presence of arg-bradykinin in rat muscles.

Large-bore particle-entrapped monolithic precolumns prepared by a sol–gel method for on-line peptides trapping and preconcentration in multidimensional liquid chromatography system for proteome analysis

The present report describes the preparation and characterization of large-bore particle-entrapped monolithic precolumns, which are suitable for incorporation into a two-dimensional liquid chromatography (2D-LC) system for proteome analysis. The fritless precolumns with different inner diameter (i.d.) (320 and 530 microm) were rapidly and successfully prepared by entrapping octadecylsilica (ODS) particles (5 microm, 300 A) prepacked into fused silica capillaries with a sol-gel network, which was formed by hydrolysis and polycondensation of methyltriethoxysilane (MTES). By optimizing the composition of the sol solution, the resulting large-bore monolithic precolumns of 5 mm length allow a flow rate of 20 microL/min loading buffer at a reasonable low back pressure of 25 bar or less and are capable of withstanding up to 300 bar inlet pressure. Scanning electron micrograms of the precolumns profile showed that the evolving sol-gel network joined particles to each other and onto the column wall, and no cracking or shrinkage of the column bed was observed even in 530 microm-i.d. capillary. The performance of the particle-entrapped monolithic precolumns used for preconcentration and desalting of proteolytic digest was evaluated by on-line coupling the large-bore precolumns with a capillary reversed-phase liquid chromatographic (RPLC) column followed by UV detection. The laboratory-made monolithic precolumns with 320 and 530 microm i.d. were characterized by using BSA tryptic digest or peptide standards as the analytes with respect to sample loading capacity, linearity, recovery and reproducibility, etc. The results indicate that the large-bore and short precolumns (5 mm x 320 microm i.d. or 5 mm x 530 microm i.d.) allow sample fast loading at a flow rate of 30 or 60 microL/min. The precolumns also have a mass loading capacity for BSA peptides of about 70 microg and for standard peptides of about 80 microg. Good linear calibration curves (R2 > 0.99) were obtained and the limits of detection (signal-to-noise ratio, S/N = 3) were improved by more than 60-fold and were between 0.53 and 1.32 ng/microL even with a UV absorbance detector. The total recovery was found to be approximately 90-100% for BSA digest and standard peptides. The day-to-day relative standard deviation (RSD) values for recoveries of BSA peptides on a single precolumn ranged from 4.66 to 7.56% and 2.68 to 3.05% for precolumn back pressure, while the column-to-column RSD values were 3.51-6.13% and 1.22-1.26% for recoveries of BSA peptides and precolumn back pressure, respectively. With good precolumn reproducibility, no significant degradation or decrease in precolumn performance was showed even after approximately 150 preconcentration/desorption cycles. The precolumns also proved to be resistant to salt buffer with high concentration and low-pH mobile phase. The large-bore particle-entrapped monolithic precolumns will be further used in a high-throughput 2D-LC array system coupled with tandem matrix assisted laser desorption/ionization-time of flight-time of flight-mass spectrometry (MALDI-TOF-TOF-MS) detection for proteome analysis.

Quantitation of the large polypeptide glucagon by protein precipitation and LC/MS

We present a method for the quantitation of glucagon from rat plasma by protein precipitation and LC/MS. No internal standard was used, as a labeled standard was not available and similar peptides did not show comparable extraction characteristics to glucagon. The LC system included a Keystone C18, 300 A pore size column; a linear gradient was used with a mobile phase consisting of water and acetonitrile, each with 0.2% acetic acid and 0.02% trifluoroacetic acid. Glucagon was detected with the mass spectrometer in positive ion mode monitoring the 4+ charge state at m/z 871.7. The method had an approximated limit of detection of 1 ng/mL. The lower limit of quantitation (LLOQ) was 25 ng/mL (7.2 fmol/mL), which could be reduced with an appropriate internal standard. External calibration was used and calibration curves were found to be linear over the range from 25 to 1000 ng/mL (7.2 to 290 fmol/mL). The method showed a high degree of precision and accuracy both within and between runs at four validation points, including the LLOQ.