Performance and lifetime of slurry packed capillary columns for high performance liquid chromatography (original) (raw)
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Journal of Chromatography A, 2006
A method is proposed for the comprehensive characterization and comparison of columns in the high-performance liquid chromatographic (HPLC) and capillary electrochromatographic (CEC) modes. Using this approach, column parameters such as the number of plates, the eddydiffusion and mass-transfer contributions to peak broadening, the permeability, and the analysis time are incorporated in a single graph and a comparison in terms of efficiency and speed is obtained. The chromatographic performance of silica-based and polymer-based monolithic capillary columns is discussed and a comparison is made with the performance of packed columns. Also, the potential of ultra-high-pressure liquid chromatography is discussed in this context. In the HPLC mode, the best results were obtained with silica monoliths; in the CEC mode, the low-density methacrylate-ester-based monoliths showed the best performance.
Comparison of different packing methods for capillary electrochromatography columns
Journal of Chromatography A, 2000
A study was carried out in which 50 mm I.D. fused-silica capillaries were packed with 3 mm octadecylsilane bonded silica, from the same batch, by four methods; liquid slurry and carbon dioxide supercritical carrier, each with and without the use of an ultrasonic probe. A neutral test mixture was analysed by capillary column in reversed-phase mode, and the reproducibility of the electroosmotic flow and of migration time, column efficiency and retention factors, was determined. Initially results suggested that there was no significant difference between properties of columns packed by different methods, and a more thorough statistical evaluation confirmed this; differences observed in the column performance were attributed to random variations between replicate columns, and not between packing methods. However, the variation was least when applying the ultrasonication during liquid slurry.
Journal of Chromatography A, 2008
The review highlights the fundamentals and the most prominent achievements in the field of high-performance liquid chromatography (HPLC) column development over a period of nearly 50 years. After a short introduction on the structure and function of HPLC columns, the first part treats the major steps and processes in the manufacture of a particle packed column: synthesis and control of particle morphology, sizing and size analysis, packing procedures and performance characterization. The next section is devoted to three subjects, which reflect the recent development and the main future directions of packed columns: minimum particle size of packing, totally porous vs. core/shell particles and column miniaturization. In the last section an analysis is given on an alternative to packed columns-monolithic columns, which have gained considerable attraction. The challenges are: improved packing design based on modeling and simulation for targeted applications, and enhanced robustness and reproducibility of monolithic columns. In the field of miniaturization, particularly in chip-based nano-LC systems, monoliths offer a great potential for the separation of complex mixtures e.g. in life science.
Journal of Chromatography A, 2002
Reduction of through-pore size and skeleton size of a monolithic silica column was attempted to provide high separation efficiency in a short time. Monolithic silica columns were prepared to have various sizes of skeletons (|1-2 mm) and through-pores (|2-8 mm) in a fused-silica capillary (50-200 mm I.D.). The columns were evaluated in HPLC after derivatization to C phase. It was possible to prepare monolithic silica structures in capillaries of up to 200 mm I.D. from a 18 mixture of tetramethoxysilane and methyltrimethoxysilane. As expected, a monolithic silica column with smaller domain size showed higher column efficiency and higher pressure drop. High external porosity (.80%) and large through-pores 214 212 2 resulted in high permeability (K58?10 -1.3?10 m ) that was 2-30 times higher than that of a column packed with 5-mm silica particles. The monolithic silica columns prepared in capillaries produced a plate height of about 8-12 mm with an 80% aqueous acetonitrile mobile phase at a linear velocity of 1 mm / s. Separation impedance, E, was found to be as low as 100 under optimum conditions, a value about an order of magnitude lower than reported for conventional columns packed with 5-mm particles. Although a column with smaller domain size generally resulted in higher separation impedance and the lower total performance, the monolithic silica columns showed performance beyond the limit of conventional particle-packed columns under pressure-driven conditions.
Monolithic silica columns for high-efficiency chromatographic separations
Journal of Chromatography A, 2002
Generation of a large number of theoretical plates was attempted by capillary HPLC. Monolithic silica columns having small skeletons (ca. 2 mm) and large through-pores (ca. 8 mm) were prepared by a sol-gel method in a fused-silica capillary (50 mm I.D.), and derivatized to C phase by on-column reaction. High external porosity (.80%) and large through-pores 212 2 resulted in high permeability (K51.2310 m ). The monolithic silica column in the capillary produced a plate height of about 12 mm in 80% acetonitrile at a linear velocity of 1 mm / s. Separation impedance, E value, was found to be as low as 200, that was about an order of magnitude lower than reported values for conventional columns packed with 5 mm particles. Reproducibility of preparation within 615% was obtained for column efficiency and for pressure drop. It was possible to 2 generate 100,000 plates by using a 130-cm column at very low pressure (,7 kg / cm ). A considerable decrease in column efficiency was observed at high linear velocity, and for solutes with large retention factors due to the slow mobile-phase mass transfer in the large through-pores. The monolithic silica columns, however, showed performance beyond the limit of conventional particle-packed columns in HPLC under favorable conditions. 0 2 of ca. 350-400 kg / cm . Many researchers have widely used in routine applications due to practical been trying to overcome the problem of high pres-difficulties including frit failure, or bubble formation. The problems associated with particle-packed columns for CEC were alleviated by using a mono-*Corresponding author. Tel.: 181-75-724-7809; fax: 181-75lithic column that was either prepared from mono-724-7710.
Journal of Chromatography A, 1997
The packing behavior of a typical 10 Ixm C~ stationary phase was studied in terms of the resultant column efficiency and capacity factor. The column-to-column reproducibility of these parameters under identical packing procedures is assessed. Correlation of these parameters and the column void volume to the column packing density is reported. Two regimes were studied; that of poor-and well-packed columns. For poorly packed columns, the column-to-column variability is high, but a concomitantly poor same-column reproducibility of measurement suggests that little statistically significant difference exists between different columns packed with the same procedure. There is also no statistically significant correlation between the column parameters and the packing densities, however, the poorest columns showed a degradation of performance after the drying procedures used to obtain the column masses. Well-packed columns showed much less degradation upon drying. For the well-packed columns, statistically significant column-to-column differences were observable, mainly due to a high same-column precision of measurement. Analysis of the results suggests that even well-packed columns are not optimally packed and that regions of high and low density coexist along the column. The results are compared to those achieved with semi-preparative columns packed with the same slurry procedure and preparative columns packed under dynamic axial compression. Poor day-to-day, same-column reproducibility (degradation) under ambient conditions was observed in conjunction with a high column-to-column variability for the semi-preparative columns.
Journal of Chromatography A, 2006
In order to reduce the analysis time and maintain good efficiency in liquid chromatography, it is advisable to simultaneously decrease the column length and the particle size of the chromatographic support. Therefore, several manufacturers have developed and commercialized short columns filled with particles that have a diameter smaller than 2 m. The focus of this work was to check the chromatographic performance of such columns and compare possibilities offered by sub-2 m supports with conventional columns in terms of analysis time reduction and efficiency improvements. For this purpose, different parameters were discussed namely: separation impedance (E), Knox curves (h, v), and number of plates by time unit (N/t 0 ). Kinetic plots were also drawn. It appeared that sub-2 m supports were well adapted to improve chromatographic performance and to reduce the analysis time. Furthermore, it was also demonstrated that the best chromatographic performances were reached with high pressure systems (up to 1000 bar).
Column packings for high performance liquid chromatography: Present state and future development
Journal of Radioanalytical and Nuclear Chemistry Articles, 1994
A short overview of HPLC column packings is presented. The properties of chromatographic carriers and the possibilities to combine the solid matrices with organic polymeric stationary phases are elucidated in detail. The latest achievements and anticipated future developments in the area are outlined. Column packings belong to the most important and the most rapidly developing constituents of liquid chromatographs. The properties of the column packings determine several important parameters of the chromatographic processes, namely their selectivity, efficiency and sample capacity thus setting the limits of performance, throughput and speed of separation. High performance liquid chromatography (HPLC) column packings consist of a chromatographic carrier and of a stationary phase. The stationary phase is chemically or physically immobilized on the carrier and its most important part represent(s) the chromatographic function(s). The chromatographic function is a ligand either electroneutral or ionic, attached to the carrier either directly or via a spacer. Alternatively, the chromatographic functions can be carried by macromolecules. Sometimes the molecules provided with the chromatographic functions are attached to the carrier only temporarily, being in dynamic equilibrium with the same molecules added to the mobile phase. ~ Some LC column packings are chemically uniform, i.e., the chemical compositions of the chromatographic carrier and of the stationary phase including chromatographic functions are identical. More often, however, the composition of the carrier matrix differs from the composition of the stationary phase. The stationary phases in general and chromatographic function in particular are responsible for the adsorption, ion interactions, associations including chelation and other kinds of complexation, affinity interactions, partition between stationary and mobile phase, etc., of the separated molecules. The differences in the above interactions
Journal of Chromatography A, 2007
We here report a new type of stationary phase for microcolumns. C18 modified silica monolith particles were prepared by grinding and sieving the silica monolith followed by C18 modification and end-capping, and were used as packing material. Ground silica monolith particles were not spherical but irregular with some residual monolithic network structure. The separation efficiency of the stationary phase made of sieved monolith particles (5-10 m) was better than that of the stationary phase made of unsieved particles. The microcolumn packed with the sieved C18 ground monolith particles (5-10 m) showed quite good separation efficiency (height equivalent to theoretical plate, HETP, as low as 15 m) and it was even superior to the microcolumn packed with a commercial spherical 5 m C18 stationary phase. The column pressure drop of C18 monolith particles was about two-third of that of the commercial spherical C18 phase. The preparation method of C18 stationary phase with ground and sieved silica monolith particles presumably suggests advantages of simplicity and convenience in modification and washing procedures compared to bulk silica monolith. It also showed both improved separation efficiency and low back pressure.