Yiping Du

Simultaneous determination of human serum albumin, γ-globulin, and glucose in a phosphate buffer solution by near-infrared spectroscopy with moving window partial least-squares regression

Near-infrared (NIR) spectra in the 12,000-4,000 cm(-1) region were measured for phosphate buffer solutions containing human serum albumin (HSA), gamma-globulin, and glucose with various concentrations at 37 degrees C. Five levels of full factorial design were used to prepare a sample set consisting of 125 samples of three component mixtures. The concentration ranges of HSA, gamma-globulin and glucose were 0.00-6.00 g dl(-1), 0.00-4.00 g dl(-1) and 0.00-2.00 g dl(-1), respectively. The 125 sample data were split into two sets, the calibration set with 95 data and the prediction set with 30 data. The most informative spectral ranges of 4648-4323, 4647-4255 and 4912-4304 cm(-1) were selected by moving window partial least-squares regression (MWPLSR) for HSA, [gamma]-globulin, and glucose in the mixtures, respectively. For HSA, the correlation coefficient (R) of 0.9998 and the root mean square error of prediction (RMSEP) of 0.0289 g dl(-1) were obtained. For [gamma]-globulin, R of 0.9997 and RMSEP of 0.0252 g dl(-1) were obtained. The corresponding statistic values of glucose were 0.9997 and 0.0156 g dl(-1), respectively. These statistical values obtained by MWPLSR are highly significant and better than those calculated by using the regions reported in the literature. The results presented here show that MWPLSR can select the informative regions with a simple procedure and increase the power of NIR spectroscopy for simultaneous determination of the concentrations of HSA, [gamma]-globulin and glucose in the mixture systems.

Temperature-dependent ideal strength and stacking fault energy of fcc Ni: a first-principles study of shear deformation

Variations of energy, stress, and magnetic moment of fcc Ni as a response to shear deformation and the associated ideal shear strength (τ(IS)), intrinsic (γ(SF)) and unstable (γ(US)) stacking fault energies have been studied in terms of first-principles calculations under both the alias and affine shear regimes within the {111} slip plane along the <112> and <110> directions. It is found that (i) the intrinsic stacking fault energy γ(SF) is nearly independent of the shear deformation regimes used, albeit a slightly smaller value is predicted by pure shear (with relaxation) compared to the one from simple shear (without relaxation); (ii) the minimum ideal shear strength τ(IS) is obtained by pure alias shear of {111}<112>; and (iii) the dissociation of the 1/2[110] dislocation into two partial Shockley dislocations (1/6[211] + 1/6[121]) is observed under pure alias shear of {111}<110>. Based on the quasiharmonic approach from first-principles phonon calculations, the predicted γ(SF) has been extended to finite temperatures. In particular, using a proposed quasistatic approach on the basis of the predicted volume versus temperature relation, the temperature dependence of τ(IS) is also obtained. Both the γ(SF) and the τ(IS) of fcc Ni decrease with increasing temperature. The computed ideal shear strengths as well as the intrinsic and unstable stacking fault energies are in favorable accord with experiments and other predictions in the literature.

Effects of alloying element and temperature on the stacking fault energies of dilute Ni-base superalloys

A systematic study of stacking fault energy (γ(SF)) resulting from induced alias shear deformation has been performed by means of first-principles calculations for dilute Ni-base superalloys (Ni(23)X and Ni(71)X) for various alloying elements (X) as a function of temperature. Twenty-six alloying elements are considered, i.e., Al, Co, Cr, Cu, Fe, Hf, Ir, Mn, Mo, Nb, Os, Pd, Pt, Re, Rh, Ru, Sc, Si, Ta, Tc, Ti, V, W, Y, Zn, and Zr. The temperature dependence of γ(SF) is computed using the proposed quasistatic approach based on a predicted γ(SF)-volume-temperature relationship. Besides γ(SF), equilibrium volume and the normalized stacking fault energy (Γ(SF) = γ(SF)/Gb, with G the shear modulus and b the Burgers vector) are also studied as a function of temperature for the 26 alloying elements. The following conclusions are obtained: all alloying elements X studied herein decrease the γ(SF) of fcc Ni, approximately the further the alloying element X is from Ni on the periodic table, the larger the decrease of γ(SF) for the dilute Ni-X alloy, and roughly the γ(SF) of Ni-X decreases with increasing equilibrium volume. In addition, the values of γ(SF) for all Ni-X systems decrease with increasing temperature (except for Ni-Cr at higher Cr content), and the largest decrease is observed for pure Ni. Similar to the case of the shear modulus, the variation of γ(SF) for Ni-X systems due to various alloying elements is traceable from the distribution of (magnetization) charge density: the spherical distribution of charge density around a Ni atom, especially a smaller sphere, results in a lower value of γ(SF) due to the facility of redistribution of charges. Computed stacking fault energies and the related properties are in favorable accord with available experimental and theoretical data.

Modified mesoporous silica materials for on-line separation and preconcentration of hexavalent chromium using a microcolumn coupled with flame atomic absorption spectrometry

A modified SBA-15 mesoporous silica material NH(2)-SBA-15 was synthesized successfully by grafting γ-aminopropyl-triethoxysilane. The material was characterized using transmission electron microscopy (TEM) and Fourier transform infrared/Raman (FT-IR/Raman) spectroscopy, and used for the first time in a flow injection on-line solid phase extraction (SPE) coupled with flame atomic absorption spectrometry (FAAS) to detect trace Cr (VI). Effective sorption of Cr (VI) was achieved at pH 2.0 with no interference from Cr (III) and other ions and 0.5 mol L(-1) NH(3)·H(2)O solution was found optimal for the complete elution of Cr (VI). An enrichment factor of 44 and was achieved under optimized experimental conditions at a sample loading of 2.0 mL min(-1) sample loading (300 s) and an elution flow rate of 2.0 mL min(-1) (24s). The precision of the 11 replicate Cr (VI) measurements was 2.1% at the 100 μg L(-1) level with a detection limit of 0.2 μg L(-1) (3s, n=10) using the FAAS. The developed method was successfully applied to trace chromium determination in waste water. The accuracy was validated using a certified reference material of riverine water (GBW08607).

Improvement of near infrared spectroscopic (NIRS) analysis of caffeine in roasted Arabica coffee by variable selection method of stability competitive adaptive reweighted sampling (SCARS)

Coffee is the most heavily consumed beverage in the world after water, for which quality is a key consideration in commercial trade. Therefore, caffeine content which has a significant effect on the final quality of the coffee products requires to be determined fast and reliably by new analytical techniques. The main purpose of this work was to establish a powerful and practical analytical method based on near infrared spectroscopy (NIRS) and chemometrics for quantitative determination of caffeine content in roasted Arabica coffees. Ground coffee samples within a wide range of roasted levels were analyzed by NIR, meanwhile, in which the caffeine contents were quantitative determined by the most commonly used HPLC-UV method as the reference values. Then calibration models based on chemometric analyses of the NIR spectral data and reference concentrations of coffee samples were developed. Partial least squares (PLS) regression was used to construct the models. Furthermore, diverse spectra pretreatment and variable selection techniques were applied in order to obtain robust and reliable reduced-spectrum regression models. Comparing the respective quality of the different models constructed, the application of second derivative pretreatment and stability competitive adaptive reweighted sampling (SCARS) variable selection provided a notably improved regression model, with root mean square error of cross validation (RMSECV) of 0.375 mg/g and correlation coefficient (R) of 0.918 at PLS factor of 7. An independent test set was used to assess the model, with the root mean square error of prediction (RMSEP) of 0.378 mg/g, mean relative error of 1.976% and mean relative standard deviation (RSD) of 1.707%. Thus, the results provided by the high-quality calibration model revealed the feasibility of NIR spectroscopy for at-line application to predict the caffeine content of unknown roasted coffee samples, thanks to the short analysis time of a few seconds and non-destructive advantages of NIRS.

Quantitative analysis of thymine with surface-enhanced Raman spectroscopy and partial least squares (PLS) regression

Silver sol surface-enhanced Raman spectroscopy (SERS) was considered as a technique in the quantitative analysis of low-concentration thymine. Because of the poor stability and reproducibility of SERS signal, a polymer of polyacrylic acid sodium was selected as a stable medium to add into silver sol in order to obtain a surface-enhanced Raman spectroscopy signal. Assignments of Raman shift for solid thymine, SERS of thymine, and SERS of thymine containing stable medium were given. The comparison of Raman peaks between them showed that the addition of stable medium had a little influence on the SERS of thymine and is suitable for the quantitative analysis of low-concentration thymine.

Effects of alloying elements and temperature on the elastic properties of dilute Ni-base superalloys from first-principles calculations

The variation of elastic properties, e.g., elastic constants, bulk modulus, and shear modulus of dilute Ni-base superalloys due to alloying elements (Xs) and temperature, has been studied via first-principles calculations. Here, 26 alloying elements are considered: Al, Co, Cr, Cu, Fe, Hf, Ir, Mn, Mo, Nb, Os, Pd, Pt, Re, Rh, Ru, Sc, Si, Ta, Tc, Ti, V, W, Y, Zn, and Zr. It is found that (i) both the bulk and shear moduli of Ni-X decrease approximately linearly with increasing equilibrium volume, especially within each group of 3d, 4d, or 5d transition-metal alloying elements; (ii) all alloying elements considered herein increase the ratio of bulk to shear modulus (i.e., the ductility) and the elastic anisotropy of the Ni-X alloys; and (iii) the largest decrease of elastic properties of Ni is caused by alloying element Y. It is observed that the change of elastic properties of Ni due to various alloying elements is traceable from the distribution of (magnetization) charge density, for instance the spherical...

Determination of Tricyclazole Content in Paddy Rice by Surface Enhanced Raman Spectroscopy

An ultrasensitive method based on Surface enhanced Raman scattering (SERS) has been developed to determine content of a pesticide which is tricyclazole in paddy rice using sliver colloid as a substrate and pyridine as an internal standard. The peaks at 424 and 1035 cm(-1) in a SERS spectrum were selected as analytic and internal peaks, respectively, and their intensity ratio I(t)/I(p) was used to calculate the regression concentration of tricyclazole. The correlation between I(t)/I(p) and concentration showed significant linear relationship with a correlation coefficient of R(2)= 0.995 in a concentration range of 0.05 to 0.70 mg/L and the tricyclazole solution can be detected to be low as 0.002 mg/L by SERS. The method was applied to determine tricyclazole contents of 3 real rice samples with a standard addition method in order to eliminate interference of matrix. The errors of SERS measurements for the 3 samples were 0.0008 to 0.0246, 0.0013 to 0.0028, and 0.0129 to 0.0304 mg/kg, respectively, compared with the results obtained by high performance liquid chromatography method. This also showed a good reproducibility with low values of relative standard deviation (n= 3) for the 3 samples ranged from 3.63% to 4.64%.

A comprehensive two-dimensional normal-phase × reversed-phase liquid chromatography based on the modification of mobile phases

A comprehensive orthogonal two-dimensional liquid chromatography (2D-LC) based on the modification of mobile phases was developed with a sample loop-valve interface. To improve the compatibility of mobile phases and analysis speed, some special solvents were chosen as the mobile phases, and the column temperature was elevated to decrease the viscosity of mobile phases of reversed-phase liquid chromatography (RPLC). Based on this principle, the first dimension was normal-phase liquid chromatography (NPLC) with a SiO2 column, and the second dimension was reversed-phase liquid chromatography containing two tandem C18 columns. 1,4-Dioxane was used in the NPLC mobile phase, and isopropyl alcohol was employed in the RPLC mobile phase. Moreover, the elevated column temperature enabled the reduction of the backpressure and using tandem C18 columns to improve the resolving power in RPLC. The new comprehensive 2D-LC system and applied strategy offered a novel idea for construction of 2D-LC system. A traditional Chinese medicine, Zhengtian pill, was used as the test sample to evaluate the constructed 2D-LC system. 876 peaks were detected, and the peak capacity reached 1740.

Preparation, characterization, and highly effective mercury adsorption of L-cysteine-functionalized mesoporous silica

A novel L-cysteine-functionalized mesoporous SBA-15 (SH-SBA-15) material was synthesized by an easy two-step post-grafting method of L-cysteine using poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) as a template under acidic conditions. The material maintained its well-ordered mesostructure after two-step modification as confirmed by powder X-ray diffraction and transmission electron microscopy analyses. X-ray photoelectron spectroscopy and 13C cross-polarization/magic angle spinning NMR revealed that L-cysteine was successfully introduced into SBA-15. The material showed excellent mercury adsorption capacity (429 mg g−1) at room temperature and mercury uptake time (<5 min). Adsorption isotherms and uptake kinetics were also investigated. Equilibrium data were found to be represented better by the Freundlich isotherm model than the Langmuir one. The pseudo-second-order kinetics model best described the kinetic adsorption process of Hg(II) ions onto SH-SBA-15. Moreover, the material possessed high selectivity for mercury and can be easily eluted with 5% thiourea in 1 mol L−1 aqueous HCl.