It would be of interest to speculate on how those portable CE instruments meet the requirements outlined above for shock- and vibration proof. Unfortunately, to the present author's knowledge, no data is available about performance of those instruments in the conditions of shock and vibration. Frequently overlooked but one of the most difficult aspects of the design of portable instruments is packaging – how all the electronics, pumps, detectors and displays are located in the most compact and ergonomic way as pointed out by Turner [36]. He stresses that “The case has to provide electrical screening for both radiofrequency emissions from the instrument and to prevent external fields from affecting its operation. It has to be sealed against the elements, and it must be easy to assemble. It has to be as light as possible, and yet it must be robust” [36]. In conclusion, one can expect that if the portable instrument is encased in the shock-, dust-, and waterproof case (like Peli™) then it should well withstand environmental disturbances if the internal mount is performed in accordance with the requirements listed above. A challenge for the CE research community now is to further develop and test portable and in situ CE analysis systems, keeping in mind the demands imposed by the conditions of the harsh milieu in which the instrument will operate.
For the design of portability or in situ CE the use of proper material choice for manufacturing instrument components is an important issue. For in situ monitoring the material must be robust to ensure a good device lifetime. Portable instruments are not so constrained. Robustness is desirable but it may be traded against cost/convenience. For chip-based CE systems, particularly in recent years, the popularity of polymer materials compared to glass-based systems has grown significantly. This trend is attributed to the lower cost of the polymers and their ease of fabrication. Also, polymers can be more robust than glass, which is often too fragile for field use. Greater mechanical robustness of polymeric chips is even more important for in situ monitoring especially in the case of harsh environments. However, a big disadvantage of polymeric materials is the fact that they are not compatible with organic solvents and do not offer the same chemical inertness as glass or silicon and as such are prone to surface contamination. This affects their performance and lifetime. One approach to overcome this is to design the system in such way that the fluidic component is replaceable. This yields some flexibility in the design of non-chip based portable CE instruments. On the contrary, for in situ instruments based on a microfluidic chip, channel replacement is not an option and so a cleaning regime for the selected material needs consideration.
4.3. Ambient pressure and microgravity
There is no info on how the low/high ambient pressure may influence the performance of the analytical separation instrument. This is not a problem on terrestrial environments but this may pose an issue on extra-terrestrial environments: e.g. solvents might rapidly evaporate. This challenge can be tackled by using solvents that do not evaporate like dimethyl sulfoxide [37] or ionic liquids. Use of ionic liquids probably makes good sealing of the instrument unnecessary but at the moment it is not clear how suitable ionic liquids are to process the analytes of interest. Another solution is to simply create a pressurized shell that surrounds the CE instrument in a gas blanket, in order to control the pressure [37]. In this way, the spacecraft would create the necessary conditions for maintaining the working buffer in the liquid state.
Microgravity is a condition that is hardly encountered on earth but low gravity is encountered in environments of extra-terrestrial small bodies (like moons and comets). Physical processes that depend on the weight of a body act differently without a certain amount of gravity. It can cause serious problems on the work of instruments and can influence their performance. On the other hand, e.g. microgravity environment allows the observation of continuous-flow electrophoretic separations without the interference of natural convection that disturbs this process on earth [38]. Thus, the possible influence of microgravity on the work of analytical instrument used in extra-terrestrial environment requires attention. Testing the effects of microgravity on earth is possible in special planes executing parabolic flights for a short period of time. No info of such tests on a CE instrument has been available to the present author.