Development Of Novel Methods For Detecting Heavy Metals In Dairy Products

Among the techniques for detection of heavy metals,laser induced breakdown spectroscopy(LIBS)processes unique advantages for dairy products measurement,such as high sensitivity,simplicity and rapidity,etc.in which the samples require no pretreatment.This would definitely presents great potential in inspection of heavy metals contained in milk powder.This paper introduced LIBS into the field of safety inspection of dairy products.With the combination of efficient spectral pretreatment and accurate calibration algorithms,it is expected that LIBS provides a promising tool for rapid and accurate detection of heavy metals contained in milk powder.In this paper,a series of work was carried out on the detection of heavy metals in dairy products by LIBS.Following the principles of selection of representative samples and inspection of principal factors,the mostly common brands of milk powders were selected as the samples,and the heavy metal elements of Cr,Pb and Cu were selected as the detection indexes.In order to measure and analyze Cr,Pb and Cu in milk powder by LIBS,we prepared standard samples with low concentrations of heavy metals to evaluate the performance of LIBS.However,milk powder is a complex multi-component system,in which the presence of matrix greatly affects the signals of LIBS.It is therefore extremely important to optimize the measurement parameters of LIBS to achieve the best signals,resulting in a satisfactory quantification results.In LIBS measurement,it is very important to identify the spectral peaks of heavy metals.The characteristic analysis spectral peaks of the elements were calibrated as Cu I 324.75 nm?Cu I 327.40 nm?Pb I 368.35 nm?Pb I 405.78 nm?Cr I 425.43 nm?Cr I 427.48 nm,respectively.The spectral peaks were calibrated in the spectra of samples,and the linear relationship between the signal strength and the element concentration was verified.In this paper,the standard calibration curve method was used to establish the calibration curve of Cu,Cr and Pb,and the linear correlation coefficient(R2)was above 0.98.The calculation results showed that the limits of detection of Cu,Pb and Cr were 0.7432 ppm,0.2116 ppm and 0.5768 ppm respectively,which is lower than the concentration limits of heavy metal contaminations in milk powder.In the quantitative analysis of the validation samples,the relative errors between the analysis values and the actual values were kept within 5%,indicated the detection accuracy was satisfactory.Moreover,the results revealed that internal standard method could improve the linearity and the accuracy of quantitative analysis.In order to enhance the detection sensitivity and accuracy of LIBS spectroscopy,a new algorithm,named as the iterative wavelet transform(IWT),was developed.The IWT algorithm was utilized to overcome spectral noise and background interference simultaneously,thus enhancing the LIBS spectral peaks of individual heavy metal element.The results showed that the IWT algorithm significantly improved the prediction precision of the LIBS spectroscopy,thus decreasing the limit of detection.