We have a mangled mess of a spacecraft,” was the assessment of Dr. David Lindstrom of NASA following the unexpected parachute failure upon re-entry. At the same time, given the robust design of the spacecraft, there was optimism that some useful analysis could be performed on the solar wind samples collected in the Genesis program [1, 2]. In preparing samples for the relatively short journey to the analytical laboratory, it is prudent to anticipate and take steps to prevent unexpected mishaps, not all of them as obvious as a failed re-entry system.
Replicates
On initial examination, some of the samples of solar wind particulates appeared to be intact, others were pulverized. Replicates are important to assess variability in contamination levels and in analytical methodology. Further, in the event of sample damage, one is better than none.
It is not economically feasible to conduct multiple space missions. However, you do not have to put all your eggs in one basket. For large testing programs, it may be desirable to stage sample shipment. Such activities have to be coordinated with the testing lab to avoid introducing problems due to between-run bias.
What surrounds the sample?
How is the sample to be protected during shipment? Pro-active consideration of what might go wrong can help avoid ambiguous results as well as wasted time and money. Sample protection goes beyond using packing material to withstand failure of parachute deployment or use of your shipping crate in an impromptu game of catch. The sample container itself must not contribute to contamination during analysis. Particulates can be an issue as can molecular contamination. There is the temptation to ship components in plastic bags. However, plastic may outgas, resulting in addition of plasticizers to the sample. Experienced analysts can sometimes sort out phthalates from the contaminates you are interested in. However, the simpler or cleaner the mix of contaminates, the more likely you are to get a definitive answer. Appropriately cleaned aluminum foil is usually a better choice.
There is also the issue of whether sample contaminates will generate additional contamination. For example, residual moisture in a sealed container may accelerate substrate corrosion. If the contaminate of interest is not readily volatilized, drying the sample could be a wise move.
Shipment of liquids, coating, cleaning agent, lubricant, or a solvent wash or extract of a component, presents additional challenges. The container must be clean (free of thin-film residue and particulates). The expected contaminates must not be adsorbed by or react with the container walls (including lids and seals). These problems are exacerbated when low levels of contaminates are anticipated. In extreme cases or where reactivity cannot be well-documented, including blank (uncontaminated) samples and samples spiked with known levels of contaminates may be required, at least for initial analysis.
Sample Stability
There is a tendency to think of the sample as being inert. However, for critical applications, it is wise to think like a clinical chemist—that is, pretend the sample is not a piece of metal or deposition fluid. Instead, think of it as a sample of blood. All other things being equal, the potential for sample damage is related to shipping time and temperature.
Where oxidation or reactivity is a problem, such as with reactive metals, surrounding the sample with an inert atmosphere may be required; and the analyst should be notified of the potential reactivity problem. In fact, just as NASA analysts peered through the ports into the damaged re-entry module before moving anything, all you can do to illuminate and elucidate the nature of the sample will help your lab analyst to avoid unwittingly damaging the sample and to provide more definitive answers.
Location
In the case of NASA, returning the samples to this planet was the major goal. Where more direct shipment is an option, given equivalent capabilities, it is usually better to choose an analytical testing lab closer to your manufacturing facility. If the analytical instrumentation is close by, and you are uncertain about the experience of the analysts with your application, it is sometimes possible to arrange to be present during testing, or at least to obtain details about the testing protocol.
If the test is to be performed on a very routine basis, it may be appropriate to analyze on-site. On-site testing does not totally eliminate packing issues; it does often decrease sample transfer and may offer a greater measure of control.
“Measure Twice, Cut Once”
Transferring samples from your facility to the site of analysis requires planning and an understanding of potential contamination sources and of sample fragility. NASA prepared for the contingency of a bumpy (but not quite this bumpy) shipment process. With proper planning, you can minimize the bumps and increase the clarity of your analytical lab results.
References:
1 W. E. Leary. New York Times, Friday, September 10, 2004 p. A22.
2 Genesis Mission Status Report, RELEASE: 2004-228, September 10, 2004.
http://genesismission.jpl.nasa.gov/mission/status_report5.html
Barbara Kanegsberg trained in organic and biochemistry and Ed Kanegsberg, an electronics engineer, are consultants specializing in surface preparation and contamination control. Contact them at BFK Solutions LLC., 16924 Livorno Dr. Pacific Palisades, CA 90272, 310-459-3614; [email protected] Or visit their website at www.bfksolutions.com.
