Monolithic columns cycle time

Current commercial silica-based columns have two important characteristics (1) they can produce efficiency similar to that of columns packed with 3.5 /tm particles and (2) they typically produce a pressure drop of half that caused by a column packed with 5 /tm particles.35 Monolithic columns have been shown to exhibit flat van Deemter curves, resulting in little loss of efficiency at high flow rates.36 As a result, high-throughput separations on conventional HPLC instruments can be achieved by increasing flow rate up to nine times (up to 9 ml/min) the usual rate in a conventional packed column. Cycle times for HPLC analysis as short as 1 min (injection-to-injection) have been reported by users of monolithic columns. Additional benefits of monolithic columns cited include... 

A high-throughput approach to HPLC-MS/MS for metabolite identify-cation was also described by Dear and co-workers [29], where up to six hydroxylated isomers were chromatographically resolved in 1 min with the overall cycle time reduced to 5 min on a monolithic column (4 mL/min). 

Figure 18.10 Two-dimensional separation of a mixture of phenolic and flavone antioxidants [after P. Jandera, University of Pardubice, Czech Republic see also F. Cacciola et a ., J. Chromatogr. A, 1149, 73 (2007)]. Conditions in the first dimension column, 15 cm x 4.6 mm i.d. stationary phase, PEG silica 5 pm mobile phase, 0.3 ml min" water-acetonitrile, gradient 1-55% acetonitrile in 200 min. Interface ten-port valve with two storage columns X-Terra Cl8 2.5 pm, 3 cm x 4.6 mm i.d. which concentrate the eluate. Cycle time, 5 min. Conditions in the second dimension column, 10 cm x 4.6 mm i.d. stationary phase, SpeedROD RP-18e (monolith) mobile phase, 2 ml min" water-acetonitrile, gradient 1-40% acetonitrile in 5min. Diode array detector with 254 + 260 + 280 + 320 nm. Of the numerous identified analytes only the most important ones are specified in the figure.

Because of the uncertainty of sample delivery times, rapid/fast IPC chromatographic methods are needed to maintain an efficient analytical laboratory and plant operation.Since many samples can be generated during the process development, IPC methods should be developed and optimized for the shortest analysis time possible. The need for a fast IPC method was demonstrated by Wu et al. who redeveloped an in-process method to shorten the run time for a reaction conversion HPLC analysis from 30 to 10 min using a monolithic HPLC column.The newly developed method could also be used to determine mother liquor concentrations and perform impurity profiles for the crude product. This optimized method reduced the process cycle time for lab instrumentation. The dual purpose for an IPC method (i.e., COR, impurity profiling, and/or concentration analysis) is another opportunity to improve the process and lab efficiency. Another example of a dual-purpose method use was demonstrated by Nageswara Rao et al. who developed a 15-min RP-HPLC method that could determine the COR and impurity profile (isolated product) for two different processes for production of 4-methoxyphenyl acetic acid." The dual-purpose method is a common theme for in-process analyses. It is also important to remember that a reduction in the analysis time and overall manufacturing time can reduce the cost of the API. 

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