SPE in Zero Gravity
At the University of Virginia, a lab, run by James Landers, Ph.D., is automating SPE for biological testing during extended space missions and has developed a fully integrated microfluidic genetic analysis system for unprocessed biological samples, like whole blood. “Astronauts take medications in flight for general pain, congestion, motion sickness, etc.,” said graduate student Daniel J. Marchiarullo.
Unfortunately the medications aren’t always as effective as on earth because space flight causes physiologic changes that alter a drug’s absorption, distribution, metabolism, and elimination properties. Therefore, a small, portable device to monitor the levels of medication in the body is needed, especially for long missions.
Marchiarullo, working with Lakshmi Putcha, Ph.D., at Johnson Space Center, is in the early stages of developing a prototype device to do just that. Ultimately, the device should integrate sample processing and analysis in one unit.
They have succeeded in using SPE to separate the anti-motion sickness medication promethazine and co-extract two hydroxyl free radical formation markers from saliva at recovery rates of 90–100%, reported Marchiarullo. “Concentration enhancements as high as 80-fold have been achieved by collecting only the fraction of eluent with the most analyte. Such high concentrations mean that solvent evaporation and reconstitution aren’t required because the eluent was compatible with electrophoretic separation.”
Landers’ lab already developed a glass microchip with three functional domains for genetic analysis—two for SPE and PCR and one for microchip electrophoresis—and are working on a gating device to control liquid transport through the microchip. The resulting device includes differential channel flow resistances, elastomeric valves, laminar flow, and electrophoretic mobility along with external fluid flow control using a syringe. Using this system, solid-phase extraction, PCR, and microchip electrophoresis, amplicon separation and detection takes less than 30 minutes. “This is one of the first systems with true sample-in-answer-out capability,” Marchiarullo said. It has detected Bacillus anthracis from 750 nL of whole blood from asymptomatic mice and Bordetella pertussis from 1 µL of nasal aspirate from a human patient. “Because the microfluidic device can use nanoliters or picoliters of fluid, quantities of reagents needed are dramatically reduced, which allows the device to be about the size of a shoe box.”
Integrating the microchannel with electrophoresis is in the beginning stages of development and is based on previous work with DNA analysis. Once a working prototype is developed, Marchiarullo said, it will be tested in collaboration with NASA, first in a hypergravity or microgravity environment and perhaps eventually in the space station.
Gilson (www.gilson.com) developed an automated approach to isolate capsaicin (the substance that produces the heat in chili peppers and topical analgesic creams) from a matrix, enhancing HPLC separation methods by automating method development for sample preparation, according to Mark E. Crawford, applications specialist. This allows chemists “to focus on the science, rather than on the mundane processes of manual SPE or HPLC,” he said.
This system is designed for bench work and can run one, four, or eight extractions simultaneously. Typically, SPE runs are 15 minutes, depending on the number of washes and the amount of sample to be captured. Gilson’s method runs in less than eight minutes and makes the wash step unnecessary, explained Crawford.
“The challenge was to optimize the method for several different matrices, while maintaining the same method for all.” To ensure that all of the compound was extracted from the solution, Crawford only collected the results when the capsaicin was present. His tests used hot sauce, pepper spray, two peppers, and a lotion. “The method extracted and eluted all the target analytes well.”
Crawford used a solution of 75% acetonitrile and 25% water to dilute the samples before solid phase extraction. “Acetonitrile incorporates well with lotion, helping draw the hydrophobic capsaicins into solution,” said Crawford. “Ethyl alcohol is effective too.”