edited: read next posts O'K, you are right. I didn't notice that analog +-10V limits, been happy to see +200V max voltage.
And also couldn't find any multiplexer, that operate higher than 80V. It's strange. :~
The only couple "improvements" I'd suggest, it replace electromechanical relay on solid state, that will minimize space and increase speed of the "homemade" mux front-end.
And second, opto-isolate analog input of the arduino, so processor or "core" would be on ground safe level, capable do other stuff - monitor some additional sensors, display info on LCD and take some commands from control panel or serial link. In order to do it, build a "floating" board, that would include own dc/dc convertor and analog opto-coupler that shown on:
http://ruggedcircuits.com/html/circuit__24.html
or
http://www.vishay.com/docs/83708/appn50.pdf
There is a SSR: