Production of Raw and Ligand-modified Silica Monolith Particles in an Enhanced Scale and their Application in High Performance Liquid Chromatography

Development of Narrow-Bore C18 Column for Fast Separation of Peptides and Proteins in High-Performance Liquid Chromatography

Separation with high efficiency and good resolution is constantly in demand in the pharmaceutical industry. The fast and efficient separation of complex samples such as peptides and proteins is a challenging task. To achieve high efficiency with good resolution, chromatographers are moving towards small particles packed into narrow-bore columns. Silica monolith particles (sub-2 µm) were derivatized with chlorodimethyl octadecyl silane (C18) and packed into stainless steel columns (100 mm × 1.8 mm i.d) by a slurry-packing method. The developed columns were used for the separation of peptides and proteins. A separation efficiency (N) of 40,000 plates/column (400,000 plates/m) was achieved for the mixture of five peptides. Similarly, the fast separation of the peptides was carried out using a high flow rate, and the separation of the five peptides was achieved in one minute with high efficiency (N ≅ 240,000 plates/m). The limit of detection (DL) and the limit of quantification (QL) for each analyte were determined by developing a linear regression curve with relatively very low concentrations of the target compound. The average values of the QL for the peptide and proteins were 0.55 ng and 0.48 ng, respectively, using short C18 column (1.8 mm × 100 mm) UV (at 214 nm). The fast analysis of peptides and proteins with such high efficiency and good resolution has not been reported in the literature yet. Owing to high efficiency, these home-made columns could be used as an alternative to the expensive commercial columns for peptide and protein separation.

Preparation of mixed-mode stationary phase for separation of peptides and proteins in high performance liquid chromatography

Porous silica particles were prepared by sol–gel method with some modification to get wide-pore particles. These particles were derivatized with N-phenylmaleimide-methylvinylisocyanate (PMI) and styrene by reversible addition fragmentation chain transfer (RAFT) polymerization to prepare N-phenylmaleimide embedded polystyrene (PMP) stationary phases. Narrow bore stainless steel column (100 × 1.8 mm i.d) was packed by slurry packing method. The chromatographic performance of PMP column was evaluated for the separation of synthetic peptides mixture composed of five peptides (Gly-Tyr, Gly-Leu-Tyr, Gly-Gly-Tyr-Arg, Tyr-Ile-Gly-Ser-Arg, Leucine enkephalin) and tryptic digest of human serum albumin (HAS) respectively. Number of theoretical plates as high as 280,000 plates/m were obtained for peptides mixture at optimum elution condition. Separation performance of the developed column was compared with commercial Ascentis Express RP-Amide column and it was observed that separation performance of PMP column was better than commercial column in terms of separation efficiency and resolution.

Fabrication of permanent silver cement frit at the inlet of micro-columns: a significant progress toward realization of disposable micro-columns

The advent of disposable micro-columns will be a hope of workers of chromatography-related laboratories. A very critical and important requirement is the formation of affordable inlet frits. Welding a metal screen to a column inlet is not recommended because of the risk of damage to stationary phase. In this study, the Tollens probe (silver mirror reaction) was adopted to make affordable frits. Silver is reduced on the particle surface and in an empty space among the particles, forming a solid silver network structure at the column inlet area by injecting the reaction solution into the packed column at a depth of one third (10 cm) of the packed bed (0.5 mm × 300 mm). The silver cement structure was successfully formed, and the silver cement frit endured mobile phase flow well when C18 modified ground silica monolith particles were used to make the packed bed. The formation of the silver cement frit was not successful when the stationary phase based on conventional spherical silica particles was used. Negligible reduction of chromatographic performance by the silver cemented frit was observed. This study serves as the first step toward realization of disposable micro-columns.