Search

The trace element of Manganese element in the agricultural farm (Anhui Huaiyuan Nongkang) soil was quantitatively analyzed by Laser-induced breakdown spectroscopy. The line of 403.1 nm was selected as the analysis line of Mn. The matrix element of Fe in soil was chosen as the internal calibration element and the analysis line was 407.2 nm. Ten soil samples were used to construct calibration curves with traditional method and internal standard method, and four soil samples were selected as test samples. The experimental results showed that the fitting correlation coefficient (r) is 0.954 when using the traditional method, the maximum relative error of the measurement samples is 5.72%, and the detection limit of Mn in soil is 93 mg x kg(-1). While using the internal standard method to construct the calibration curve, the fitting correlation coefficient (r) is 0.983, the relative error of measurement samples is reduced to 4.1%, and the detection limit of Mn in soil is 71 mg x kg(-1). The result indicates that LIBS technique can be used to detect trace element Mn in soil. In a certain extent, the internal standard method can improve the accuracy of measurement.

Three feature extraction algorithms, such as the principal component analysis (PCA), the discrete cosine transform (DCT) and the non-negative factorization (NMF), were used to extract the main information of the spectral data in order to weaken the influence of the spectral fluctuation on the subsequent quantitative analysis results based on the SERS spectra of the pesticide thiram. Then the extracted components were respectively combined with the linear regression algorithm--the partial least square regression (PLSR) and the non-linear regression algorithm--the support vector machine regression (SVR) to develop the quantitative analysis models. Finally, the effect of the different feature extraction algorithms on the different kinds of the regression algorithms was evaluated by using 5-fold cross-validation method. The experiments demonstrate that the analysis results of SVR are better than PLSR for the non-linear relationship between the intensity of the SERS spectrum and the concentration of the analyte. Further, the feature extraction algorithms can significantly improve the analysis results regardless of the regression algorithms which mainly due to extracting the main information of the source spectral data and eliminating the fluctuation. Additionally, PCA performs best on the linear regression model and NMF is best on the non-linear model, and the predictive error can be reduced nearly three times in the best case. The root mean square error of cross-validation of the best regression model (NMF+SVR) is 0.0455 micormol x L(-1) (10(-6) mol x L(-1)), and it attains the national detection limit of thiram, so the method in this study provides a novel method for the fast detection of thiram. In conclusion, the study provides the experimental references the selecting the feature extraction algorithms on the analysis of the SERS spectrum, and some common findings of feature extraction can also help processing of other kinds of spectroscopy.

The fluorescence spectra of protoporphyrin IX (PPIX) solutions and human serum samples were measured and analyzed under physiological conditions. The experimental results showed that the fluorescence of PPIX in human serum was mainly derived from PPIX-serum albumin complex. Moreover, the effects of serum albumin and PPIX on the PPIX emission fluorescence were also investigated. Compared with pure PPIX solution, not only a red-shift of PPIX fluorescence peak was found for PPIX+albumin solution, but also albumin had a fluorescence enhancement effect on protoporphyrin IX. For the mixture of PPIX+albumin, with the increase of PPIX the wavelength of the PPIX emission peak will increased a little when its concentration was less than 0.8 x 10(-5) mol x L(-1), but was nearly invariable when its concentration was more than 0.8 x 10(-5) mol x L(-1).

In this paper, the Raman and difference FTIR spectra of NTO crystal, NTO solutions at different pH and saturated aqueous solution of Rb(NTO) x H2O have been studied. The determined structure of crystal suggests that the metal ion with oxygen and nitrogen atoms of [chemical structure see text] C-N, [chemical structure see text] C-NO2, [chemical structure see text] C=O and H2O formed bonds. The highest characterization peaks of Raman and FTIR spectra show that [chemical structure see text] C-NO2, [chemical structure see text] C=O and [chemical structure see text] C-N of NTO- formed week coordination bonds. The vibration spectra of saturation solution basically accord with those of the crystal. The bonds of saturation solution of the coordination compound have not changed. Therefore, the different vibration spectra of the saturation water solution of Rb (NTO) x H2O can be explicated by the formation of the bonds in crystal. The coordination compound formation mechanism of metal ion with NTO in alkali aqueous solution is discussed.