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
Related item, precision CO2 sensor using NDIR, $60
MH-Z19 carbon dioxide gas sensor (hereinafter referred to as the sensor) is a generic type, small sensors, using non dispersive infrared (NDIR) principle to detect the air in the presence of CO2, with good selectivity and no oxygen dependence and long service life. Built in temperature compensation, with digital output and waveform output, easy to use. The sensor is a high performance sensor which is combined with the mature infrared absorption gas detection technology and the precise optical path design and the excellent circuit design.