A novel multi-walled carbon nanotubes (MWCNTs) dispersive solid phase extraction (d-SPE) method which combined with gas chromatography (GC) coupled with electron capture detector (ECD) was developed for the determination of five pyrethroid pesticides in liquid milk for the first time. The effect of d-SPE conditions on the kinds of sorbent, MWCNTs and magnesium sulfate anhydro mass ratio, and extraction condition were researched, and then, the suitable method was found. Under the optimal conditions, the linear range was from 20 to 500 μg kg−1. The recoveries were from 81.8% to 112.1%, with the corresponding relative standard deviations (RSDs) less than 6%, correlation coefficients from 0.9978 to 0.9990, and limits of detection and quantification from 2.62 to 4.86 μg kg−1 and 8.73 to 16.2 μg kg−1. The proposed method is simple, fast, safe, and has high recovery and sensitivity applicable to analyze pyrethroid pesticides in liquid milk sample.
The present study explores the feasibility of the determination of phosphorus at the extreme trace levels in high-purity silicon by radioreagent method. After silicon dissolution with hydrofluoric and nitric acids and matrix volatilization, 12-molybdophosphoric acid (12-MPA) is formed by the addition of the radioreagent,99MoO
, in nitric acid medium and then extracted into isobutyl acetate. By plotting the phosphorus content against the radioactivity of99Mo in the organic phase, a linear relationship persisting down to 5 ng is obtained. Special effort has been made to the elimination of the unreacted99MoO
reagent and the optimal control of phosphorus blank introduced through the multistage analytical procedure in order to ensure reliable determination of phosphorus at the ppb level.
Authors:B. Liu, Z. Tan, Z. Nan, P. Liu, L. Sun, F. Xu, and X. Lan
A solid complex of rare-earth compounds with alanine, [ErY(Ala)4(H2O)8](ClO4)6 (Ala=alanine), was synthesized, and a calorimetric study and thermal analysis for it was performed through adiabatic calorimetry
and thermogravimetry. The low-temperature heat capacity of [ErY(Ala)4(H2O)8](ClO4)6 was measured with an automated adiabatic precision calorimeter over the temperature range from 78 to 377 K. A solid-solid
phase transition was found between 99 and 121 K with a peak temperature at 115.78 k. The enthalpy and entropy of the phase
transition was determined to be 1.957 Kj mol-1, 16.90 j mol-1 k-1, respectively. Thermal decomposition of the complex was investigated in the temperature range of 40~550C by use of the thermogravimetric
and differential thermogravimetric (TG/DTG) analysis techniques. The TG/DTG curves showed that the decomposition started from
120 and ended at 430C, completed in three steps. A possible mechanism of the thermal decomposition was elucidated.
Authors:F. Xu, L. Sun, Z. Tan, X. Lan, P. Yu, and T. Zhang
The heat capacities of berberine sulphate [(C20H18NO4)2SO43H2O] were measured from 80 to 390 K by means of an automated adiabatic calorimeter. Smoothed heat capacities, HT-H298.15 and ST-S298.15 were calculated. The loss of crystalline water started at about 339.30.2 K, and its peak temperature was 365.80.6 K. The
peak temperature of decomposition for berberine sulphate was at about 391.40.4 K by DSC curve. TG-DTG analysis of this material
was carried out in temperature range from 310 to 970 K. TG and DSC curves show that there is no melting in the whole heating
Authors:J. Yao, Y. Liu, Z. Gao, P. Liu, M. Sun, S. Qu, and Z. Yu
A microcalorimetric technique based on the bacterial heat-output was explored to evaluate the effect of Mn(II) on Bacillus thuringiensis. The power-time curves of the growth metabolism of B. thuringiensis and the effect of Mn(II) on it were studied using an LKB-2277 BioActivity Monitor, ampoules method, at 28C. For evaluation
of the results, the maximum peak-heat output power (Pmax) in the growth phase, the growth rate constants (k), the log phase heat effects (Qlog ), and the total heat effect in 23 h (QT) for B. thuringiensis were determined. Manganese has been regarded as the essential biological trace element. Mn(II) of different concentration
have different effects on B. thuringiensis growth metabolism. High concentration (800-1600 μg mL-1) of Mn(II) can promote the growth of B. thuringiensis; low concentration (500-800 μg mL-1) can inhabit its growth.
Authors:P. Yu, Z. Tan, S. Meng, S. Lu, X. Lan, L. Sun, F. Xu, T. Zhang, and S. Hu
Isoproturon [N'-(p-cumenyl)-N,N-dimethylurea] was synthesized, and the low-temperature heat capacities were measured with a small sample precise
automatic adiabatic calorimeter over the temperature range from 78 to 342 K. No thermal anomaly or phase transition was observed
in this temperature range. The melting and thermal decomposition behavior of isoproturon was investigated by thermogravimetric
analysis (TG) and differential scanning calorimetry (DSC). The melting point and decomposition temperature of isoproturon
were determined to be 152.4 and 239.0C. The molar melting enthalpy, and entropy of isoproturon, ΔHm and ΔSm, were determined to be 21.33 and 50.13 J K-1 mol-1, respectively. The fundamental thermodynamic functions of isoproturon relative to standard reference temperature, 298.15
K, were derived from the heat capacity data.