Search

Three China trademarks of milk powder called Mengniu, Yili, Wandashan were taken as testing samples. Each of them mixed varied amount of starch in different gradient, which were consisted of 32 adulterated milk powder samples mixed with starch, was taken as standard samples for constructing predicted model. To those 32 samples, the reflecting spectrum characteristics in middle wave of near infrared spectrum with Near Infrared Spectrum Analyzer (Micro NIR 1700) produced by JDSU Ltd. USA were collected for five repeats in five different days. The time span was nearly two months. Firstly, we build the model used the reflecting spectrum characteristics of those samples with biomimetic pattern recognition (BPR) arithmetic to do the qualitative analysis. The analysis included the reliability of testing result and stability of the model. When we took ninety percent as the evaluation threshold of testing result of CAR (Correct Acceptance Rate) and CRR (Correct Rejection Rate), the lowest starch content of adulterate milk powder in all tested samples which the tested result were bigger than that abovementioned threshold was designated CAR threshold (CAR-T) and CRR threshold (CRR-T). CAR means the correct rate of accepting a sample which is belong to itself, CRR means correct rate of refusing to accept a sample which is not belong to itself. The results were shown that, when we constructed a model based on the near infrared spectrum data from each of three China trademark milk powders, respectively, if we constructed a model with infrared spectrum data tested in a same day, both the CAR-T and CRR-T of adulterate starch content of a sample can reach 0.1% in predicting the remainder infrared spectrum data tested within a same day. The three China trademarks of milk powder had the same result. In addition, when we ignored the trademarks, put the spectrum data of adulterate milk powder samples mixed with the same content of starch of three China trademarks milk powder together to construct a model, the CAR-T of mixed starch content of a sample may reach 0.1%, the CRR-T can reach 1%, if the model construction and predicting were performed with near infrared spectrum data tested in a same day. However, the CAR-T can just stably reach up to 5% and the CRR-T have the same result, if the model construction and predicting were crossly performed with mixed near infrared spectrum data tested in different days. Furthermore, the correct recognizing threshold mixed starch of a sample can stably reach up to 1% and the CAR-T can reach 5%, if the model construction was based on near infrared spectrum data combined the previous four days to predict the output of the another day. On the other hand, we also engaged quantitative analysis to the starch content in milk power with two kinds of arithmetic (PLSR, LS-SVR). In contrast with the testing outputs, the reliability of both the CAR-T and CRR-T in qualitative analysis was further validated.

In the present paper, the micro-NIR spectrometer with the splitter of linear variable filter was used to develop the recognition models of the West Lake Longjing tea and the ordinary flat tea of the year 2012 and 2013. The NIR spectral data of different years and different storage times were decomposed by PCA algorithm. The PLS-DA models were developed by the representative samples selected by the mathematical characteristics of PCA-scores' distribution in order to analyze the reason for the inadaptability of the models according to mathematical principles and find out the solution for its correction. Being examined by the external validation set, the adaptability of the authenticity identification model was enhanced effectively. The result of this research indicated that, for the West Lake Longjing tea and the ordinary flat tea, the correct recognition rate of the model developed by all different-year samples' NIR spectral data would be enhanced effectively. The model developed by the NIR spectral data of different storage time samples indicated that the physicochemical properties of the ordinary flat tea have changed remarkably after cryopreservation for 3 months, while the physicochemical properties of the West Lake Longjing tea are relatively stable. The model adaptabilities for different years and different storage times were studied according to the mathematical perspective of the principal component characteristics of spectral data. After the authenticity identification model of West Lake Longjing tea was developed, the prediction accuracy was enhanced effectively. This research would provide reference for not only the application of NIR spectroscopy in quality grading and safety of agricultural products, but also the enhancement of the prediction accuracy of the NIR grading models for agricultural products.

The interaction between umbelliferone (UMB) with tryptophan (Trp), tyrosine (Tyr) and phenylalanine (Phe) was studied by using fluorescence (FS) and ultraviolet (UV) spectroscopy. The results show that UMB can strongly quench the fluorescence of the three aromatic amino acids with the maximum quenching wavelengths at 347, 303 and 282 nm, respectively. Data analyses based on the Stern-Volmer curve and the UV spectroscopy show that static quenching occurred through the formation of the complexes of UMB with each aromatic amino acid in a molar ratio of 1 : 1. The binding constant K(c) of UMB with Trp, Tyr and Phe is 2.993 x 10(6), 7.858 x 10(4) and 1.186 x 10(3) L x mol(-1) (298.15 K) and 2.702 x 10(4), 1.063 x 10(5) and 8.352 x 10(3) L x mol(-1) (310.15 K), respectively. The thermodynamic parameters indicate that UMB has a strong interaction with the three aromatic amino acids. Hydrogen bond and Van der Waals force may play a major role in the reaction of UMB with Trp, whereas hydrophobic interaction should be responsible for the binding of UMB with Tyr and Phe. In addition, the dipole-dipole interaction may be another factor in the reactions between UMB and the three aromatic aminoacids.

Based on the scanning differential optical absorption spectroscopy (DOAS) system, field measurement of vertical profiles of HONO and NO2 was performed continuously from Aug. 27, 2007 to Sep. 4, 2007 in Chaoyang District of Beijing, and their vertical profiles were analyzed. Based on the acquired data, the typical vertical variation characteristics of HONO, NO2 and the ratio HONO/NO2 were discussed, and the possible formation sources of HONO were studied. The results indicated that the decrease of HONO with height was faster than the decrease of NO2. The study found good correlation between NO2 and HONO, as well as between the ratio HONO/NO2 and vapor, respectively. Therefore, the authors' conclusion is that HONO was formed by heterogeneous conversion of NO2 on surfaces or near ground and then transported to higher altitudes.

In the present study, beta-cyclodextrin(betaCD) was used as chiral selector to detect the proportion of chiral isomers of metalaxyl. The proportion of metalaxyl enantiomers can be detected by ultraviolet (UV)spectroscopy since the interaction between the R, S isomer of metalaxyl with beta-CD is different. The quantitative models were established by partial least squares regression (PLS) and the robust of models was evaluated by independent validation samples. The determination coefficient R2 of calibration set in the quantitative model was 0.999 0. The standard error of calibration set (SEC) and the relative standard deviation (RSD) of the model was respectively 0.006 7 and 0.89%; The correlation coefficient r of estimated value and specified value of the 6 independent validation samples was 0.998 5. The standard error of prediction (SEP) and RSD was respectively 0.008 9 and 1.17%. This method is rapid and easy to operate in practical applications.

Based on the differential optical absorption spectroscopy (DOAS) technology, the measurement of air pollutants (SOz, NO2, HONO and HCHO) was performed continuously from Jan 19, 2007 to Feb 8, 2007 in Peking University campus. The typical diurnal variation characteristic of SO2 concentration, the main source and the meteorological factors that influence the pollutants were analyzed. The results indicated that the typical diurnal variation of SO2 concentration has the same shape as the letter "V" when wind speed was low, and in the afternoon the SO2 concentration was the lowest, while in other time it was high. Coal-burning made prominent contribution to the concentration of atmospheric various pollutants in the heating period of Beijing. Wind speed played a leading role and other meteorological factors also have some effect, which resulted from the influence of the meteorology on diffusion, transmission, elimination of air pollutants.