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

The continuous release of persistent iron-cyanide (Fe-CN) complexes from various industrial sources poses a high hazard to the environment and indicates the necessity to analyze a considerable amount of samples. Conventional flow injection analysis (FIA) is a time and cost consuming method for cyanide (CN) determination. Thus, a rapid and economic alternative needs to be developed to quantify the Fe-CN complexes. 52 soil samples were collected at a former Manufactured Gas Plant (MGP) site in order to determine the feasibility of diffuse reflectance infrared Fourier spectroscopy (DRIFTS). Soil analysis revealed CN concentrations in a range from 8 to 14.809 mg kg^-1, where 97% was in the solid form (Fe₄[Fe(CN)₆]₃), which is characterized by a single symmetrical CN band in the range 2092-2084 cm^-1. The partial least squares (PLS) calibration-validation model revealed IR response to CN_tot which exceeds 2306 mg kg^-1 (limit of detection, LOD). Leave-one-out cross-validation (LOO-CV) was performed on soil samples, which contained low CN_tot (<900 mg kg^-1). This improved the sensitivity of the model by reducing the LOD to 154 mg kg^-1. Finally, the LOO-CV conducted on the samples with CN_tot > 900 mg kg^-1 resulted in LOD equal to 3751 mg kg^-1. It was found that FTIR spectroscopy provides the information concerning different CN species in the soil samples. Additionally, it is suitable for quantifying Fe-CN species in matrixes with CN_tot > 154 mg kg^-1. Thus, FTIR spectroscopy, in combination with the statistical approach applied here seems to be a feasible and quick method for screening of contaminated sites.