High sensitivity thermal lens microscopy: Cr-VI trace detection in water

Area of Science:

• Analytical Chemistry
• Spectroscopy
• Environmental Science

Background:

• Hexavalent chromium (Cr-VI) is a toxic heavy metal pollutant found in water.
• Existing detection methods often lack the sensitivity required for regulatory compliance and public health protection.
• Low detection limits are crucial for monitoring Cr-VI below toxicity thresholds and international drinking water standards.

Purpose of the Study:

• To develop a highly sensitive method for detecting hexavalent chromium in water.
• To achieve detection limits in the parts-per-trillion range for Cr-VI analysis.
• To validate the method's effectiveness in real-world water samples like bottled and tap water.

Main Methods:

• Utilized a micro-spatial thermal lens spectroscopy (TLS) setup.
• Employed coaxial counter-propagating pump and probe laser beams.
• Integrated a passive optical Fabry-Perot resonator and the diphenyl carbazide colorimetric method.

Main Results:

• Achieved an ultra-low detection limit of 21 ng/L (parts per trillion) for hexavalent chromium.
• Measured Cr-VI concentrations in the µg/L range in bottled and tap water samples.
• Demonstrated direct detection of Cr-VI in potassium dichromate solutions without colorimetric aids.

Conclusions:

• The developed TLS system offers unprecedented sensitivity for Cr-VI detection in aqueous samples.
• The method is suitable for monitoring Cr-VI levels well below toxicity and regulatory limits.
• The system's capability for direct detection simplifies Cr-VI analysis in certain applications.