Sensitivity and Calibration of the FT-IR Spectroscopy on Concentration of Heavy Metal Ions in River and Borehole Water Sources

Heavy metals in water sources can threaten human life and the environment. The analysis time, need for chemical reagents, and sample amount per analysis assist in monitoring contaminants. Application of the Fourier Transform Infrared (FT-IR) Spectroscopy for the investigation of heavy metal elements has significantly developed due to its cost effectiveness and accuracy. Use of chemometric models such as Partial Least Square (PLS) and Principle Component Regression Analysis (PCA) relate the multiple spectral intensities from numerous calibration samples to the recognized analytes. This study focused on the FT-IR calibration and quantification of heavy metals (Ag, Cd, Cu, Pb and Zn) in surveyed water sources. FT-IR measurements were compared with the atomic absorption spectrometer (AAS) measurements. Quantitative analysis methods, PCA and PLS, were used in the FT-IR calibration. The spectral analyses were done using the Attenuated Total Reflectance (ATR-FTIR) technique on three river and four borehole water sources sampled within two seasons in QwaQwa, South Africa (SA). The PLS models had good R2 values ranging from 0.95 to 1 and the PCA models ranged from 0.98 to 0.99. Significant differences were seen at 0.001 and 0.05 levels between the PLS and PCA models for detecting Cd and Pb in the water samples. The PCA models detected Ag concentrations more (˂0 mg L−1 on selected sites). Both the PLS and PCA models had lower detection only for Zn ions mostly above 45 mg L−1 deviating from the AAS measurements (<0.020 mg L−1). The FT-IR spectroscopy demonstrated good potential for heavy metal determination purposes.

Methodology for High-Accuracy Infrared Calibration in Environments with Through-Wall Heat Flux

This paper describes a new method for accurate in situ infrared (IR) calibration in environments with significant through-wall heat flux and surface temperature non-uniformity. In the context of turbine research environments, conventional approaches for in situ IR calibrations rely on thermocouples embedded in the surface or bonded to the surface using an adhesive layer. A review of the literature points to lack of emphasis on the uncertainty in the calibration arising from the effect of the adhesive substrate and paint on the temperature measured by the thermocouple, namely that under diabatic conditions (i.e. with through-wall heat flux) the measured temperature deviates from the true surface temperature. We present a systematic study of the sensitivity of the thermocouple temperature to installation conditions seen in typical laboratory IR calibration arrangements, and under realistic conditions of through-wall heat flux. A new technique is proposed that improves the calibration accuracy by reducing the difference between the thermocouple measurement and the external wall temperature seen by the infrared camera. The new technique has the additional advantage of reducing the uncertainty associated with selecting an appropriate pixel in the IR image, by providing a region with greater temperature uniformity especially in environments with significant underlying lateral surface temperature variation. The new approach is experimentally demonstrated and compared to more conventional measurement techniques on a heavily film-cooled nozzle guide vane assembly operated at highly engine-representative conditions. The proposed technique is demonstrated to significantly improve the measurement accuracy for IR in situ calibrations in environment with through-wall heat flux and surface temperature non-uniformity.