Focus
Electrophoresis in Space For the past year or so, the McDonnell Douglas Corporation has been testing a unique gravity-free electrophoretic separation unit on flights of the U.S. space shuttle (Figure 1). The project, code-named EOS (electrophoretic operations in space), is directed at separating substances from complex mixtures, such as blood serum samples. Although the biologically active materials McDonnell Douglas seeks to isolate—such as important enzymes and hormones—are already available on Earth in small quantities, the gravity-free environment of space makes it possible to scale up the process by a large factor. In the first two tests, the device separated over 700 times more material than a similar electrophoresis unit could on Earth, and purity levels were up by a factor of four. Electrophoresis involves the differential displacement of mixture components under the influence of an electric field. The type of electrophoresis commonly used in laboratories is called static electrophoresis (Figure 2), because the sample is placed on a stationary medium, such as a porous gel plate. An electric field applied across the medium induces charged mixture components to migrate differentially across the face of the plate. Since static electrophoresis is not suitable for production-scale separations, the EOS project uses continuous-flow electrophoresis (Figure 3). In this process, a stream of sample is continuously introduced into a flowing buffer solution (called the carrier fluid) that carries the sample from the bottom to the top of a rectangular chamber. As the sample flows through the chamber, an electric field is applied, causing components with varying charges to migrate laterally at different rates. This differential migration splits the sample into separate particle streams that exit the chamber through collection outlets at the top. On Earth, gravity seriously limits the output and purity of separation in continuous-flow electrophoresis. For example, in a gravity environment, a sample that is too concentrated (dense) will tend to collapse around its inlet port. Thus, sample concentration is limited on Earth. In addition, gravity causes convection currents and
Figure 1. A McDonnell Douglas engineer and a NASA quality control inspector examine the EOS device after its installation on the Challenger orbiter for June's shuttle flight Courtesy of NASA
bandspreading that make particle streams overlap, limiting the purity levels that can be attained. In the weightlessness of space, the problems associated with limited sample concentrations, convection currents, and bandspreading are virtually eliminated. Thus, operation in space has made it possible to scale up production and to improve separation resolution considerably. At least one analytical instrument company is involved in the EOS project: Princeton Instruments is currently working on a multichannel imaging detector for McDonnell Douglas that will make it possible for scientists on Earth to continuously monitor the protein output from each
Figure 2. Static electrophoresis Adapted from company literature courtesy of McDonnell Douglas
ANALYTICAL CHEMISTRY, VOL. 55, NO. 12, OCTOBER 1983 · 1187 A
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Figure 3. Continuous-flow electrophoresis Adapted from company literature courtesy of McDonnell Douglas
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channel of the electrophoretic separator. If space shuttle testing continues to be successful, McDonnell Douglas plans to design and fabricate an EOS unit with 24 times the capacity of the single-chamber unit flying now. The larger unit is currently scheduled for an initial shuttle flight in 1985. The company has benefited from a National Aeronautics and Space Administration (NASA) program, the Joint Endeavor Policy, that encourages private investment in space industrialization by offering free shuttle flight time during the R&D phase of a commercial venture. McDonnell Douglas will have to pay for shuttle flights once commercial operation begins. Later still, perhaps in the late 1980s, the company plans to start fullscale production on an unmanned space platform orbiting in space. Such a plant, which could operate continuously for months at a time, would be serviced by shuttle crews, who would deliver raw materials and collect separated pharmaceuticals for return to Earth. Business Week (Aug. 29,1983, pp. 52-53) reports that Fairchild Industries plans a 1987 launch of "Leasecraft" platforms that could be rented out for research and manufacturing operations. McDonnell Douglas may buy time on an orbiting station from such a company, or it may decide to launch its own manufacturing station. Either way, the company expects the EOS operation to be generating a positive cash flow within a few years of production start-up. Stuart A. Borman
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