HELP creating sensor system for concentration of soluble oils in water

[asdfs]

I brought this question to thye forum because of the diverse measurement crowd revolving around DAQ.  I have a unique problem in which we need to monitor the % concentration of soluble cutting oil in water.  The problem right now is not a daq isue, but rather how to sense the concentration accurately??  I am concerned with variation of water hardness as well as different oil SGs causing issues.  I can probably install a tuning pot for some of this.  We would build the sensor from the component level once we know how to attack this. 

We will also need to measure PH but I see that as a little easier issue.  

Can anyone help or direct me?  

[AnalogKid2DigitalMan]

I don't have any specifics, but refractometers are typically used for such measurements.

http://en.wikipedia.org/wiki/Refractometer

-AK2DM

[asdfs]

Yes, I realize refract testing is mostly used but we need a real time meter on this and certain shops that run a lot of machines, that would be a full time job. 

[AnalogKid2DigitalMan]

That is what in-line units are used for, they are frequently used for real-time monitoring or for closed loop control, here is such an example:

http://www.atago.net/english/images/catalog/PRM-85.pdf

-AK2DM