Please do your own homework, find probes that would be suitable for your specific use and budget, and we'll be happy to comment on specific types and help getting them to work with Arduino.
I know the things exist and at least some work like regular pH probes, which are quite straightforward to get working with Arduino. You can buy a pH sensor amplifier or you can build your own (I did just that on a piece of protoboard just for the fun of it - it actually worked the first time), and that in turn can be read easily by an Arduino, usually through the analog port.