Chlorine determination in cement paste samples using laser-induced breakdown spectroscopy and non-matching matrix calibration samples†

This paper deals with determining the chlorine content in cement matrixes using non-matching calibration samples made from microsilica and potassium chloride. We aimed to make easy-to-prepare calibration samples and determine the chlorine content in cement paste samples. To create proper cement paste samples, it is necessary to allow the concrete to mature for 28 days. Also, this methodology enables faster calibration and higher throughput in routine analysis. To suppress the matrix effect, we tested several strategies of signal normalization and then compared the reference (known) and the predicted chlorine content. Best results were obtained when we normalized the intensity of the chlorine line by a parameter proportional to the particle number density which was a priori determined by the intensity of the hydrogen emission line (H_α) and full width at half-maximum (FWHM). With this parameter, we obtained a high-reliability coefficient for the calibration curve (R² = 0.99) and the best prediction for total chloride content in cement paste, with a sum of mean squares of the prediction error of 0.22 wt%.