Detection of calcium in rice using Laser-Induced Breakdown Spectroscopy (LIBS)

Abstract

LIBS is a very reliable technique for both qualitative and quantitative purposes. Detection of minerals composition is important to help consumer choose the right variety of rice. In this paper, an ungated Laser-Induced Breakdown Spectroscopy (LIBS) system was used to detect calcium in rice. An experimental setup was designed using Nd:YAG laser operating at 1064 nm (60 mJ per pulse) and a spectrometer connected to a fiber optic in order to collect the atomic emission which is displayed on a computer. Twelve samples of rice were purchased from local market which offered differences with regard to their rice varieties, grain size and polishing rate. The calcium concentration of each sample was initially evaluated by using Flame Atomic Absorption Spectroscopy (AAS) after acid digestion. Pellets of approximately 5 mm thick and 40 mm diameter were prepared by transferring 10 g of ground rice sample to a 40 mm die set and applying 40 MPa. For the LIBS analysis, Nd:YAG laser was used to ablate the surface of each pellets. Fifty spectra from different spots of the pellets were collected by the spectrometer from each sample. The spectra were then averaged and analyzed using OriginPro 8.5 for baseline removal and peak findings. Two calcium (Calcium II) lines with high intensity were observed at the wavelength of 393.37 nm and 396.85 nm. The study shows that LIBS can be an excellent tool for detecting calcium in rice.