Researchers have developed a method combining thin-layer chromatography (TLC) and surface-enhanced Raman spectroscopy (SERS) to screen firefighting wastewater for hazardous aromatic compounds. The approach is designed for rapid, on-site analysis when laboratory instruments are not immediately available.
Water used to control chemical fires can collect pollutants from damaged materials, industrial chemicals, and combustion products. The resulting wastewater may contain several contaminants within a complex matrix, making individual compounds difficult to identify.
Laboratories commonly use gas chromatography-mass spectrometry or liquid chromatography-mass spectrometry for this type of analysis. Although sensitive and selective, these methods require laboratory equipment and may involve extraction, enrichment, or other sample-preparation steps.
The new method uses TLC to separate compounds on a silica-coated plate. SERS then produces a molecular fingerprint for each separated substance. The researchers used gold nanoparticles to enhance the Raman signals, allowing lower concentrations to be detected. The particles were produced through seed-mediated growth and had an average diameter of 121.93 ± 4.45 nanometers.
The team tested four substituted aromatic compounds: p-phenylenediamine, o-phenylenediamine, benzidine, and 4-chlorophenol. TLC separated the compounds within a standard mixture. The researchers then deposited gold colloid onto the corresponding areas of the plate and compared the resulting SERS spectra with spectra from individual reference standards.
Separating the compounds before Raman analysis helped address an important limitation of direct SERS. Structurally related aromatic compounds can produce overlapping Raman bands, while other wastewater components may cause fluorescence or compete for signal enhancement at the nanoparticle surface. TLC reduced this interference and allowed signals to be assigned to individual analytes.
The researchers also created separate calibration curves for each compound, supporting quantitative analysis after chromatographic separation. Sample preparation was limited to filtering the wastewater before applying it to the TLC plate.
In recovery experiments, known amounts of p-phenylenediamine, o-phenylenediamine, and 4-chlorophenol were added to firefighting wastewater. The method identified and quantified all three compounds, with measured concentrations agreeing with the amounts added.
The findings show that TLC-SERS can separate and measure selected aromatic pollutants added to a real wastewater matrix. However, the study does not establish performance across the wider range of chemicals that may be present after different fires.
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