Methods for determining ethanol concentration in water.
NIR gas analysis
Paper on measuring ethanol from head gas, link. Uses a Binos 100 gas analyzer, see the manual, principal of operation on p59-60. Uses two interference filters, one for ethanol absorbance region (4300nm), other for reference (4000nm) where no absorbance is expected.
FTIR liquid analysis
Using ATR with a zinc selenide crystal. ZnSe crystals are farily expensive and hard to source.
This usually is a infrared spectroscopy technique, so a diffraction grating is necessary and moving parts to scan over the frequency range. This reduces source light intensity and increases complexity. The solution is more general.
IR LED system patent using a tunable IR dichromic / interference filter: link. This filter is expensive and hard to source.
Enzymatic / fluorescent
College chem lab