An article in The Scientist describes a "mini-mass spec" that can work 2500 meters below sea level, where the pressure can reach 250 atmospheres. To make such a device, researchers from Harvard and the Monterey Bay Aquarium Research Institute made a container from titanium that's about 1 meter long and 20 centimeters in diameter to hold the mass spec and had it rather than the mass spec deal with all that pressure.