Organic Process Research & Development 2007, 11, 870–876
Mobile Tool for HPLC Reaction Monitoring
Wes A. Schafer,*,† Steve Hobbs,*,‡ Jason Rehm,‡ David A. Rakestraw,‡ Charles Orella,† Mark McLaughlin,† Zhihong Ge,† and
Christopher J. Welch*,†
Separation & Analysis Technologies, Merck Process Research, Rahway, New Jersey 07065, U.S.A., and Eksigent Technologies,
Inc., Dublin, California 94568, U.S.A.
Abstract:
In general, online reaction monitoring using HPLC provides
more specific information than online spectroscopic techniques.
For example, online HPLC analysis can be used to simulta-
neously monitor a variety of minor impurities, and can even
be used for monitoring enantiopurity, both challenges for
existing online spectroscopic techniques. While online chro-
matographic analysis has been known for some time,14,15 most
of the applications in this area have been focused on bio-
processes and ion analysis, with many examples confined to
pilot plant applications where custom designed and permanently
installed equipment are used. Online HPLC analysis is rarely
used by the typical chemist “at the bench”; this is despite the
fact that off-line HPLC, along with NMR, is by far the most
commonly used analytical tool for reaction progress analysis
among organic process research chemists. When considering
the benefits of a recently developed microfluidic HPLC system
(small size, fast run times, and extremely low mobile phase
usage and waste generation), we were struck with the possibility
of using such an instrument for a mobile HPLC reaction
monitoring system. We reasoned that such a tool could replace
the sporadic off-line HPLC analysis typically performed by
process chemists to monitor reaction progress, allowing more
complete data coverage while eliminating the need for scientists
to carry out tedious sampling, dilution, HPLC analysis, data
transfer, and graphing functions. Ideally, such a tool would
operate in the background, requiring only minimal input from
A mobile HPLC reaction monitoring tool consisting of a cart-
mounted microfluidic HPLC instrument equipped with a tethered,
automated sampling and dilution module is described. Several
examples of the use of the instrument for carrying out reaction
progress analysis are presented. Reaction aliquot size is typically
only a few microliters, allowing extensive sample monitoring from
small volume reactions. Reaction quenching is possible, and aliquot
dilution is adjustable, with suitable precision and accuracy even
at hundredfold dilution. A sampling capillary with a chemically
inert stainless steel fritted terminus allows sampling from some
heterogeneous reactions. The sampling interval is adjustable, from
a minimum of about 4 min, upwards. Visualization of an ongoing
or completed study as either stacked “waterfall” chromatograms
or as graphs of integrated peak areas (or any derived function,
such as percent ee or percent conversion) vs time affords the
process chemist valuable information on reaction kinetics and a
useful record of reaction progress over time. While online HPLC
analysis has been known for some time, the compact and mobile
nature of this instrument renders it especially useful for carrying
out reaction progress monitoring in the laboratory environment.
Introduction
Online/inline analysis is a powerful tool for monitoring
organic reactions during process development and scaleup. The
kinetic information obtained from such studies allows improved
monitoring and control of reactions during routine production
and also facilitates the design of robust processes and the
understanding of reaction mechanisms. By eliminating the need
for manual sampling and off-line analysis, online/inline analysis
greatly reduces the labor requirement for reaction monitoring.
The technique is especially useful in situations where some of
the reaction components are labile or where the reaction matrix
may be hazardous to the operator. Blackmond has recently
commented on the value of reaction progress analysis in
developing a greater understanding of organic reactions,1 and
the recent use of online/inline spectroscopic tools such as React
IR, UV, and Raman probes as well as calorimetry by process
chemists has led in many instances to improved understanding
of reaction mechanism, which in turn may lead to better
chemical manufacturing processes.2–13
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* Corresponding author. Telephone: (732) 594-0032. Fax: (732) 594-2020.
E-mail: Christopher_welch@merck.com.
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† Separation & Analysis Technologies, Process Research, Merck & Co., Inc.
‡ Eksigent Technologies, Inc.
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Vol. 11, No. 5, 2007 / Organic Process Research & Development
10.1021/op7000854 CCC: $37.00
2007 American Chemical Society
Published on Web 08/08/2007