Objective: Measuring Water Content with High Precision
Accurately measuring water content in aromatic/acetone mixtures is essential for quality control and process efficiency. Using the GUIDED WAVE™ ClearView® db Dual-Beam Photometer, water levels can be measured to better than ±0.01% (wt.), ensuring reliable and repeatable results.
Experimental
Samples were measured in a 5 mm cuvette heated to 47 °C in the NIR with a spectrometer. Water concentrations were determined by KF titration. Samples contain isopropyl benzene, acetone and phenol in approximately constant ratios.
Water Absorption and C-H Activity
In aromatic/acetone mixtures, C-H absorption activity is prominent in the 1700–1800 nm and 1100–1200 nm wavelength regions. Notably, strong peaks appear near 1690 nm and 1150 nm due to aromatic C-H bonds.
On the other hand, water absorption is observed in two key regions:
- A moderate peak near 1430 nm
- A stronger peak at 1916 nm
To precisely measure water content, the photometer compares differential absorbance between a reference wavelength (set at 1850 nm, near the 1916 nm peak) and the water peak itself.
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Results: High-Precision Water Measurement
- Linear Regression Accuracy: The absorbance of all tested samples was plotted against water content, resulting in an excellent linear regression.
- Slope Measurement: The slope of the regression is 0.003% water/mAU.
- Stability: The long-term drift of the ClearView® db photometer is less than 500 μAU, indicating highly stable, precise online analysis.
Key Considerations for Optimal Accuracy
To achieve the best precision, it is important to:
- Minimize sample temperature fluctuations
- Prevent the presence of particulates in samples
Additionally, the ClearView db photometer can be equipped with an RTD temperature sensor, enabling automatic temperature compensation. For final calibration, we run samples at different temperatures, allowing us to fine-tune the analyzer for both absorbance and temperature coefficients.
Figure 2
It is important to minimize sample temperature fluctuations and the presence of particulates to achieve the stated precision. ClearView db can be equipped with an RTD temperature sensor for automatic temperature compensation. Thus, we can run your samples at several temperatures in a final calibration before shipping the analyzer. The resulting calibration would have coefficients for both absorbance and temperature.
Conclusion
A ClearView db photometer can measure water in complex mixtures to better than ±0.01% (wt.). It can utilize up to 2 fiber optic insertion probes flanged directly into a reactor or column, or flow cells on a slip stream for even better cost per sample point.