Temperature-dependent schlieren effect in liquid flow for chemical analysis

Area of Science:

• Analytical Chemistry
• Physical Chemistry

Background:

• The schlieren effect arises from light refraction at liquid interfaces with differing refractive indices.
• This effect is influenced by both analyte concentration and temperature variations.

Purpose of the Study:

• To quantitatively investigate the schlieren signal generated by temperature differences for enthalpimetric measurements.
• To develop and apply a flow analysis system exploiting the temperature-dependent schlieren effect for chemical analysis.

Main Methods:

• A thermally insulated flow manifold was constructed using deionized water as the carrier.
• A heat exchanger unit (HEU) was designed to manage temperature changes during reactions.
• Exothermic oxidation reactions (acid dichromate with ethanol or ascorbic acid) were used to demonstrate the system's applicability.

Main Results:

• A direct correlation was established between the schlieren signal and sample temperature.
• Linear calibration curves (r² > 0.99) were achieved for ethanol and ascorbic acid determination.
• The system demonstrated good precision (RSD < 5%) and a sample throughput of 4 samples per hour.

Conclusions:

• The temperature-dependent schlieren effect can be effectively utilized for quantitative chemical analysis in a flow system.
• The developed method accurately determined ethanol in Thai white spirit and ascorbic acid in vitamin C tablets, showing agreement with comparative techniques.