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Day 3
Vendor/Exhibitor Session
Expanding the Versatility of Automated On-Line Extraction and
Multiplexed LC-MS Systems
Joseph M. Di Bussolo, Cohesive Technologies, Inc.
Turbulent-flow liquid chromatography (TFLC) has been successfully
applied for on-line extractions of biological fluids prior to LC-MS
analysis. Turbulent flow conditions can be achieved in 1.0 mm i.d.
columns packed with particles greater than 50 um diameter at a flow rate
of at least 4.0 mL/min. Turbulent flow eliminates one contribution to
peak band broadening and tailing which results from radial diffusion
between the flow streams.
Turbulent flow chromatography actually involves a combination of
size-exclusion and adsorption phenomena. If the analyte fraction has a
high enough affinity for the stationary phase inside the pores, then it
will remain there until a solvent with the appropriate strength desorbs
it.
It was found that by decreasing the inside diameter of the TurboFlow
column from 1 mm to 0.5 mm, turbulent flow can be achieved at a flow
rate of just 1.0 mL/min and the eluting flow can be reduced by a factor
of four. The result is a reduction in total solvent consumption by a
factor of four. To properly operate the 0.5 mm i.d. column it was
necessary to reduce the dead volume of the system by using smaller
diameter tubing, valve stators, and rotors. An added bonus from these
diameter reductions is that the analyte fraction is diluted less, and
therefore, results in an increase in sensitivity.
The versatility of this technique has been expanded with the recent
introduction of TurboFlow columns packed with silica-based
ion-exchangers: strong and weak cation exchangers and strong and weak
anion exchangers. Ion exchangers are useful to selectively capture
analytes of interest or to scavenge interfering sample components. A
typical flow diagram of their use as a scavenger column is shown below.
Since on-line extraction typically adds a few extra minutes to the
overall LC method, the technique is often multiplexed to maximize sample
throughput, as shown below.
To expand the versatility of the Aria™ systems, the version 1.4
operating system can now be installed on the same computer that controls
the mass spectrometer. The choice of pumping systems has been expanded
to include Agilentıs low-flow and high-flow pumps as well as Flux Rheos
and Shimadzu pumps. An extra pump can also be added to provide a makeup
flow to the MS source during times when no peaks are emerging from any
of the Aria channels to keep the spray more consistent. Aria version 1.4
can also send sample information to the MassLynx 4.0 queue, eliminating
the need to write a sample list for MassLynx and QuanLynx.
Contact Information
Cohesive Technologies, Inc.
101 Constitution Boulevard
Franklin, MA 02038
Tel: 508-528-7989
Fax: 508-528-8699
info@cohesivetech.com
www.cohesivetech.com
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