How can we determine the concentration of sulfuric acid in a very small sample?
We are working on a “mechanical” process that transports a very small amount of sulfuric acid to an instrument and we need to provide the concentration of the acid on the output from our system tests (this does not need to be built into the system for operation, just bench testing validations). Our process involves levels of medium and high vacuum, I am considering the materials inside non-reactive (almost completely stainless steel), and the flow in the system is quick. I am assuming the only change to the acid is some amount of the water in the solution potentially boiling off from the vacuum, increasing the acid concentration. We know the acid solution at the input, and for safety and ease of testing at this point using a lower concentration, 0.12N solution. The output volumes are much lower than a drop of water, and I am guessing are in the 10s of microliters. We have access high quality balance and basic lab tools / glassware.
I had considered adding a drop of water to the test sample and then placing that in a refractometer to measure the diluted acid % w/w, specific gravity, and density. Then run the dilution calculations (how much water to add to concentrated acid to make low concentration acid) backwards to find the sample concentration before I added the drop of water. It seems too many things about the “concentrated acid” (the test sample) are unknowns to perform that calculation. I am also concerned that the concentration of the mixture would be too diluted to accurately measure with a refractometer.