Liquid handling as the usual option in the field
Whenever precise analyses are required on an expedition, the list of feasible methods is very short. “Liquid handling is often the only appropriate handling in the field”, clarifies Kallmeyer. “A precision scale needs recalibration once it is moved. And more commonly, there is no way to properly set up a balance. A pipette is much more convenient, it keeps its calibration during transport and is much easier to pack. And in my experience the accuracy of normal pipettes is sufficient in the field.” If possible, the scientists carry solutions with them, or pre-weighed reagents to which they just add water.
Special challenges in the field of liquid handling
Lab work that requires delicate work like pipetting is not done in harsh environments, assures Kallmeyer: “If conditions become extreme, then operations are reduced to just sampling. In a heat protection suit, there is no way to operate anything more sensitive than a hammer and standing next to a 1.100°C hot lava lake, you will not even think about pipetting.” So, in general, all analyses are performed in environments much less challenging and there is a significant distinction between sampling, sample processing and sample analysis. “During field work accuracy is important, but perhaps not to the same degree as in the lab. We have to balance between the accuracy that possible in the field vs. how much time it takes to achieve this level, given the limited time available during a field trip. Thus, we try to avoid any measurements that are so sensitive that temperature or density fluctuations would bias the results.” On a field trip, Kallmeyer usually relies on air cushion pipettes. “In the home lab we use positive displacement pipettes for very small volumes, but I try to avoid doing such work in the field. The possibility for errors is just too big.”
What really matters when it comes to equipment
When planning a field trip, every single step of sampling, sample processing and sample analysis is carefully dissected into small increments and written down. “We define what tools and reagents are necessary for each step and how much you need for the number of samples or analyses planned, plus a safety margin”, explains Kallmeyer. “Reliability of the equipment, e.g., pipettes, is perhaps the most important point. In most cases re-calibration is not possible, so I have to be able to trust the results.” Resilience is another must have, as field equipment needs to withstand extreme conditions. “But luckily, most equipment is surprisingly robust.” And last but not least: Ergonomics. “There simply is no time for fiddling around. Thus, complicated use is usually the death sentence for any type of field equipment.” As many analyses have to be conducted in the home lab, transporting samples safely is always an issue. “For molecular biology we try to freeze the sample tubes as quickly and cold as possible, liquid nitrogen being the best option. But in many cases oxygen is our worst enemy, so storage must be in a protective atmosphere. We usually take gas-tight foil sleeves that we can heat-seal and flush with Nitrogen or any other inert gas.”