Application of mid-infrared photoacoustic spectroscopy in monitoring carbonate content in soils

Infrared photoacoustic spectroscopy provides an alternative to conventional infrared reflectance spectroscopy for rapidly estimating a wide array of soil properties. The objective of this study was to investigate the application of Fourier transform mid infrared (500–4000 cm−1)–photoacoustic spectroscopy (FTIR-PAS) to estimate soil carbonate content in samples collected from the Loess Plateau of China. Principal component analysis (PCA), partial least squares regression (PLSR) and generalized regression neural network (GRNN) models were used to calibrate and validate soil carbonate analysis using FTIR-PAS. Absorption bands for carbonate were observed in the FTIR-PAS spectra. Even though most bands associated with carbonate were subject to interference from other soil components, significant relationships were observed between carbonate content and FTIR-PAS spectral components, particularly in the range of 1000–2000 cm−1. Among the chemometric approaches applied, the GRNN model demonstrated the best performance [root mean square error (RMSEP) = 1.21% with a ratio of standard deviation to prediction error (RPD) = 3.83] for predicting soil carbonate content. This work demonstrates that FTIR-PAS is suitable for analyzing solid soil samples exhibiting great IR absorption, and the technique permits accurate and rapid determination of soil carbonate content.