Mexican researchers use laser-induced breakdown spectroscopy to analyze water pollution

[ China Instrument Network Instrument Development ] A research team from Mexico has developed a method that uses laser-induced breakdown spectroscopy (LIBS) to detect extremely low concentrations of heavy metals in individual water droplets. LIBS technology is commonly used to analyze solid samples. Researchers used the technology they developed to suspend and pre-concentrate water droplets using acoustic suspension technology to achieve more accurate chemical analysis. The researchers obtained repeatable measurements of trace amounts of niobium, cadmium, mercury, and lead in deionized water-based samples. result.

A research group at the National Autonomous University of Mexico used sound waves to suspend water droplets and chemical analysis of liquid samples using laser-induced breakdown spectroscopy (LIBS) to study heavy metal contaminants. Credit: Jairo Peralta and Victor Contreras / National Institute of Natural Physics, National Autonomous University of Mexico.

The research team stated that they could use LIBS technology one day to quickly and economically monitor the quality of water supply and identify potential pollution in real time.

LIBS for liquid detection

LIBS is a method of atomic emission spectroscopy that was invented several decades ago. The main method is to use a laser to vaporize a small solid sample to generate a plasma. This laser-induced plasma can emit spectra that are related to the chemical composition of the sample. The recent miniaturization of LIBS equipment and the advantages of LIBS technology with little sample preparation make this technology increasingly used to provide real-time solid sample analysis.

Although the number of LIBS applications is increasing, this technology is difficult to use for liquid sample analysis. One of the reasons is that the laser-induced plasma formed by the liquid will rapidly cool down and quickly disappear, limiting the instrument's time window for capturing and measuring the plasma emission spectrum. Another disadvantage is that liquids can fluctuate, splash or form aerosols when they are disturbed, scattering light and destroying the spectrum.

A potential solution to these two obstacles is to dry the liquid sample for LIBS analysis on a solid substrate. The liquid sample is evaporated in this way to concentrate the elements and eliminate the problems associated with the physical properties of the liquid. However, irradiation laser pulses on the dried sample residue also excite atoms from the solid matrix, making the result inaccurate.

Acoustic suspension LIBS

In order to find another solution, a research team led by Victor Contreras of the National Institute of Natural Physics of the National Autonomous University of Mexico used the sonic suspension technology to suspend LIDS analysis of suspended water samples in the air. The suspension not only eliminates the problem of interference from the solid substrate, but also the suspended droplets produce a slight evaporation, concentrating any chemicals that may be contained. Moreover, because the position of the droplet is a definite small point, a compact and cost-effective low-energy laser can be used to generate the plasma.

Contreras and his research team demonstrated their LIBS technology using a water-based solution containing a small amount of heavy metals. First, they placed the water droplets in the sonic node of the uniaxial levitator. Once the water droplets begin to evaporate they will evaporate slightly and concentrate the heavy metals contained therein, making them easier to detect by spectroscopy. Next, the Nd:YAG laser system will supply the floating pre-concentrated water droplets with 532 nm laser pulses lasting 10 ns and 30 mJ of energy.

The laser pulse causes the water droplets to generate plasma, and the plasma emission spectrum is collected by a plano-convex lens and focused on the optical fiber coupled to the spectrometer and the computer for chemical analysis. The entire process from the start of water droplet suspension to complete chemical identification takes only a few minutes. The researchers reported that they detected as low as 0.2 mg / L of plutonium, 0.7 mg / L of cadmium, 1.0 mg / L of mercury, and 2.0 mg / L of lead in water drop samples and were able to provide multiple tests. Reproducible results. Contreras said: "Online analyzers based on our technology can someday help prevent environmental disasters and help improve water quality control technology."

Researchers are working hard to improve the instrument: They are optimizing the mechanical design of the acoustic levitation trap to provide more stable suspension conditions, and are also working to improve the detection sensitivity by further reducing the size of the water droplet sample.

(Original title: Mexican researchers use laser-induced breakdown spectroscopy to analyze water pollution)