Quick detection and quantification of iron-cyanide complexes using fourier transform infrared spectroscopy

Area of Science:

• Environmental Chemistry
• Analytical Chemistry
• Spectroscopy

Background:

• Persistent iron-cyanide (Fe-CN) complexes from industrial activities pose significant environmental hazards.
• Conventional cyanide (CN) determination methods like flow injection analysis (FIA) are time-consuming and expensive.
• There is a need for rapid and economical alternatives to quantify Fe-CN complexes in environmental matrices.

Purpose of the Study:

• To evaluate the feasibility of diffuse reflectance infrared Fourier spectroscopy (DRIFTS) for analyzing Fe-CN complexes in soil samples from a former Manufactured Gas Plant (MGP) site.
• To develop and validate a spectroscopic method for the rapid quantification of total cyanide (CN_tot) in soil.
• To assess the capability of FTIR spectroscopy in differentiating and quantifying various CN species present in soil.

Main Methods:

• Collection and analysis of 52 soil samples from a former MGP site.
• Application of diffuse reflectance infrared Fourier spectroscopy (DRIFTS) for spectral analysis.
• Development of partial least squares (PLS) calibration-validation models and leave-one-out cross-validation (LOO-CV) to determine the limit of detection (LOD) for CN_tot.

Main Results:

• Soil analysis indicated CN concentrations ranging from 8 to 14,809 mg kg^-1, with 97% present as solid Fe₄[Fe(CN)₆]₃.
• Initial PLS models showed an LOD of 2306 mg kg^-1 for CN_tot.
• LOO-CV improved sensitivity, reducing the LOD to 154 mg kg^-1 for samples with low CN_tot (<900 mg kg^-1) and 3751 mg kg^-1 for samples with high CN_tot (>900 mg kg^-1).

Conclusions:

• FTIR spectroscopy can provide information on different CN species in soil samples.
• The developed FTIR method is suitable for quantifying Fe-CN species in soils with CN_tot concentrations above 154 mg kg^-1.
• FTIR spectroscopy, coupled with statistical analysis, presents a feasible and rapid approach for screening Fe-CN contaminated sites.