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Innovations and Future Trends in HPLC Column Technology
Editor's Note: This is an expanded version of an article that appeared in the August 2014 issue of Pharmaceutical Technology.
An average high performance liquid chromatography (HPLC) instrument uses 6-8 columns per year; as the number of instruments grows, so does the market for columns. The overall market for columns (analytical, preparative/process, capillary/nano, bulk packing, and accessories) is now estimated to be $1.3 B with an overall growth of 3.5%, with higher growth in the ultra high performance liquid chromatograpy (UHPLC) segment (1). Developments in column technology to deliver greater efficiency, speed and inertness benefit the entire drug development process from discovery to manufacturing and quality control.
For new methods, superficially porous particle (SPP) columns have become the favoured column type in pharmaceutical laboratories thanks to the lower pressure, enhanced efficiency and equal loadability offered in comparison to smaller totally porous particles. The development of even smaller SPP particles can also be anticipated. If SPP columns continue to dominate, the need to further increase instrument pressure limits may not be necessary but in chromatography, pressure is always a useful commodity.
If researchers are able to improve efficiency without great increases in backpressure and can make longer length columns for difficult separations, monolithic columns still have great promise. In particular, polymeric monoliths could be quite attractive since their wider operating range gives them some advantages. Monoliths may become the favoured approach for laboratory-on-a-chip systems since they can be synthesized in situ inside the narrow channels where efficient packing of particulates may prove exceedingly difficult.
With its orthogonal separation power, supercritical-fluid chromatography (SFC) has made a comeback in the rapid analysis of small pharmaceutical compounds. Initially, SFC made its contributions in the preparative arena for chiral drugs but now has been applied to more general small-molecule applications. For many separations, SFC can be superior to HPLC/UHPLC, especially in the speed of analysis. The phases used for SFC are different than those used for LC so additional polar phases are required to further exploit this technology.
The trend in the production of monoclonal antibodies and peptide-based compounds in drug development requires columns capable of providing high-recovery separations of biologically derived compounds, oligonucleotides and biosimilars, both neat and in biological fluids. Column manufacturers are already responding with biocompatible columns that provide more selective separations with higher recovery.
Tremendous strides have been made in particle and stationary phase technology over the years. Users in the drug industry are looking for productivity improvements and these demands continue to push further development in columns that are more efficient and provide symmetrical peak shapes, are faster and more inert. These needs stretch from the drug discovery phase and all phases of development up to manufacturing and quality control accuracy.
Stationary phases have come a long way and seldom are complaints heard about column-to-column and batch-to-batch non-reproducibility. Approaches to increase and predict chromatographic resolution with improved stationary phases that show better control of selectivity for critical separations will be needed in the future. Small changes in selectivity provide the biggest changes in overall resolution--much bigger than particle size effects alone.
Instruments will undoubtedly see improvement in lowering band dispersion to handle smaller SPPs. Closer integration of the column hardware and instrument connections may emerge, such that dead volumes may be almost nil. Although systems can be built to go to even higher pressure, work has shown that ultrahigh pressures in the thousands of bar causes changes in molecular physiochemical parameters that may compromise chromatographic results.
In the race to discover the next promising biotherapeutic, or develop a reliable biosimilar, analytical accuracy and efficiency cannot be compromised. Reducing process development time, having the ability to make procedural changes quickly, and minimizing variability in analyses are challenges faced daily when trying to characterize proteins, antibodies, conjugated, new biological entities and biopharmaceuticals. Reversed phase (RP) is one of the key techniques in biochromatography. Small particle improvements in the columns make RP an attractive choice for biopharmaceutical applications.
As biopharmaceuticals such as monoclonal antibodies and peptide-based compounds continue to make inroads in the drug market, columns capable of providing high recovery separations of biologically-derived compounds, oligonucleotides and biosimilars, both neat and in biological fluids, will be in big demand. Column manufacturers are already responding with biocompatible columns that provide more selective separations with higher recovery. Oligonucleotide purity requires columns that separate a wide range of oligomers, sometimes at high pH so chromatographers in that field are always on the lookout for high efficiency, high pH tolerant columns.
Although column lifetimes are much longer now than formerly, many users, especially in the pharmaceutical environment, consider columns expendable. When dealing with precious, high-activity, high-value pharmaceuticals, compound purity and accuracy of analysis is of utmost importance and a column that has been used for thousands of injections may have some degree of contamination that may affect retention and peak shape as well as compound purity, not worth risking in quantitative analysis.
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