Hi khelz, welcome here!
Some data for viscosity at Engineeringtoolbox as usual:
http://www.engineeringtoolbox.com/absolute-viscosity-liquids-d_1259.htmlSome non-conductive liquids here, thin, and decently safe - I ignore what an ion mobility spectrometer demands more.
Simple alkanes, slightly longer than hexane, are decently safe yet can be thinner than water.
n-decane would be such one;
ramified alkanes around C
12 maybe;
White spirit is a combination of such alkanes, and the thinnest variants woud fit:
http://en.wikipedia.org/wiki/White_spiritdon't expect any kind of reproducibility with this petroleum distillate. Viscosity is easily measured with home-made means.
Toluene and the
xylene isomers fit your query:
http://en.wikipedia.org/wiki/Xylenethey are all good solvents as well. Safe enough to be paint thinners. Ortho-xylene's flash point is only +17°C, toluene's is +6°C, less than perfect. m- and p- xylene have +25°C.
Many freons would be excellent... But their use and availability are restricted.
Fluorocarbons are, up to now, less restricted than CFC. Perfluorodecalin is reasonably available, but I have no viscosity data.