Food analysis employing high energy nanosecond laser and low pressure He ambient gas

摘要

We report the results of an experimental study of food analysis using Nd:YAG nanosecond (ns) laser at various pulse energies in atmospheric ambient air and He ambient gas at different pressures. In contrary to previous results indicating the unfavorable applications of LIBS to food analysis using lower pulse energies and atmospheric ambient air, this study demonstrates clearly the excellent spectral quality obtained from a number of food samples of different hardnesses with high energy (132 mJ) ns laser pulses and 20 Torr He ambient gas. A series of energy dependent intensity measurements show that the intensities generally increase with higher laser energies and harder samples which can be attributed to the generation of stronger shock wave plasma and the subsequently induced He assisted excitation (HAE) mechanism which is responsible for the sharp emission lines and the very low spectral background. Using mochi samples with different Cu impurity contents, this experiment further reveals the existence of a linear calibration line and a detection limit of sub ppm level. The results of this study have thus suggested the promising development of low cost and practical technique for quantitative food analysis in place of more expensive and bulkies picosecond laser used before.