Feasibility of Field Portable Near Infrared (NIR) Spectroscopy to Determine Cyanide Concentrations in Soil

Vicinities of manufactured gas plants were often contaminated with solid iron-cyanide complexes as a result of the coal gasification process. During the remediation of affected soils, knowledge about contaminant concentrations is crucial, but laboratory methods are often expensive and time consuming. Rapid and non-destructive field methods for contaminant determination permit an analysis of large sample numbers and hence, facilitate identification of 'hot spots' of contamination. Diffuse near infrared reflectance spectroscopy has proven to be a reliable analytical tool in soil investigation. In order to determine the feasibility of a Polychromix Handheld Field Portable Near-Infrared Analyzer (FP NIR), various sample preparation methods were examined, including homogenizing, sieving, drying, and grinding. Partial least squares calibration models were developed to determine near infrared (NIR) spectral responses to the cyanide concentration in the soil samples. As a control, the contaminant concentration was determined using conventional flow injection analysis. The experiments revealed that portable near-infrared spectrometers could be a reliable device for detecting cyanide concentrations > 2,400 mg kg(-1) in the field and > 1,750 mg kg(-1) after sample preparation in the laboratory. We found that portable NIR spectrometry cannot replace traditional laboratory analyses due to high limits of detection, but that it could be used for identification of contamination 'hot spots'.