Water Analysis in an Alcohol-Brine Solution with a ClearView db Photometer

MEASURING WATER IN ALCHOHOL-BRINE SOLUTION

Measurement of water in a multiple alcohol and brine solution using our GUIDED WAVE™ ClearView® db Dual Beam Photometer.

Experimental

A fiber optic NIR Photometer and 2 low-OH optical fibers were used with a 5mm cuvette at 30°C to obtain absorbance data from the samples shown in Table 1. Near-infrared (NIR) spectra are rich in chemical information. These spectra are complex with overlapping peaks from water and alcohols, as shown in Figure 2.

Results – Measuring Water in Alcohol-Brine Solution

A careful analysis of the data reveals that a single wavelength at 1820 nm measures water with minimal interference from ethanol and isopropanol (see Figure 2). This wavelength is sensitive to water because it lies between the O-H peak from water at 1440 nm and the intense H-O-H peak near 1930 nm. It is, however, at a longer wavelength than the nearby alcohol peaks. It is also much less intense than the main water peak at 1440 nm, thereby allowing a probe to be used with a longer optical path, such as 5 mm, for better sensitivity.

Lastly, an added benefit in using this longer wavelength for water is its low sensitivity to sample temperature changes. Variation of ±5°C changes the predicted water content by less than 0.7% (without correcting for temperature). The GUIDED WAVE™ ClearView® db Dual Beam Photometer can measure the sample temperature input from an RTD and make this correction, if needed.

Conclusion

These results indicate that a ClearView db fiber optic filter photometer with an analyzing wavelength of 1820 nm and a reference wavelength near 1050 nm can analyze water in the presence of alcohols and salt.