Study On Laser Induced Breakdown Spectroscopy Method For Detecting Key Elements In Liquid Milk

The mineral element content of liquid milk determines its quality directly as liquid milk is a high-quality protein and minerals source.The conventional detection methods of mineral elements in liquid milk often rely on laboratory technology,which has high accuracy but high cost and low detection efficiency.Thus,they are challenging to meet the detection needs of actual production and consumption of China's dairy industry.Therefore,it is urgent to develop a new and efficient method for the detection of mineral elements in liquid milk.In this thesis,a liquid detection system based on Laser-induced breakdown spectroscopy(LIBS)was developed for the measurement of K,Ca,Mg,and other mineral elements in liquid milk.On this basis,combined with the variable selection method,the intrinsic information of mineral elements in the LIBS spectrum signal is extracted accurately.Thus,the rapid detection method of key minerals elements in liquid milk was developed.The thesis mainly includes the following two aspects:(1)A liquid detection system(LIBS-LD)based on laser-induced breakdown spectroscopy was built.In this thesis,ultra-high frequency piezoelectric ceramics were used to oscillate the liquid samples into aerosols,and then the short focal laser-induced breakdown spectroscopy was used to detect the liquid milk aerosol.It significantly reduced the limit of detection and the related interference of the system.(2)A calibration method of partial least square modeling based on competitive adaptive re-weighted sampling is developed.Multivariate scattering correction,normalization,and high-density discrete wavelet transform were used as spectral pretreatment methods,and the PLS prediction model was established after variable selection.It significantly improves the accuracy and prediction capability of the model.The experimental results show that the RSD of the liquid detection system can be controlled under 10%,and the detection limit of Mg,K and Ca elements is about0.2ppm,5ppm and 30ppm,respectively.It not only meet the need of subsequent experiments but also satisfies the requirements of detection accuracy and speed in the actual production process.The R~2of K,Ca,and Mg in the prediction model were 0.91,0.95,and 0.97,respectively,and the prediction error could be basically controlled within 6%.These satisfactory results illustrate that laser-induced breakdown spectroscopy has great potential in the field of dairy products detection,and also provides a reference for the detection of other food safety fields.