Correction of C–Fe line interference for the measurement of unburned carbon in fly ash by LIBS

Abstract

For the serious interference between the Fe 247.98 nm and the C 247.86 nm lines in the analysis of fly ash when using a poor-resolution spectrograph, this paper presents a correction method that uses Fe lines to correct the C–Fe line interference. The integrated intensity of the spectral lines is chosen as the input intensity to obtain the intensity ratio of non-interference Fe lines and the Fe 247.98 nm line by LIBS measurements, and to obtain the C 247.86 nm line integrated intensity from the overlapping peak. Fe 248.33 nm, Fe 250.11 nm, and Fe 251.08 nm lines were used as correction lines to predict the unburned carbon (UC) content in fly ash. We applied multivariate calibration methods to establish the calibration curve of UC in the measured samples, and used quantitative analysis to further verify the effect of Fe lines as correction lines on the detection accuracy of UC in fly ash by LIBS. The results show that the correlation coefficients R² of multivariate calibration all have improved based on Fe 248.33 nm, Fe 250.11 nm, and Fe 251.08 nm line correction. In terms of the overall evaluation from the calibration curve fitting and predictive accuracy of quantitative analysis, the Fe 248.33 nm line has the best performance as a correction line to correct C–Fe line interference when measuring UC content in fly ash. The correlation coefficients R² of the multivariate calibration and the averaged prediction absolute error of the UC content are 0.998 and 0.002 wt%, respectively, which is significantly improved compared with that without correction.