Looking for a portable particle counter that can withstand corrosive chemical solutions, pH range 0 to 12, need to see down to 0.1 microns or better.
Will you be looking at suspensions / powders / droplets ?
What volume of sample will you have available?
What is the upper range of particle size?
What do you mean by portable - not mains operated?
There are a number of laser diffraction devices which take samples in disposable cuvettes - just like a spectrophotometer which might be suitable - for small particle suspensions, no larger than ~micron.
Your best bet would be to talk to a rep from Beckman Coulter:http://www.beckmancoulter.com/products/Discipline/Life_Science_Research/pr_disc_gen_partchar.asp?bhcp=1
I don't think you're going to find a very portable solution though.