Analysis of large experimental datasets in electrochemical impedance spectroscopy

An approach for the analysis of large experimental datasets in electrochemical impedance spectroscopy (EIS) has been developed. The approach uses the idea of successive Bayesian estimation and splits the multidimensional EIS datasets into parts with reduced dimensionality. Afterwards, estimation of the parameters of the EIS-models is performed successively, from one part to another, using complex nonlinear least squares (CNLS) method. The results obtained on the previous step are used as a priori values (in the Bayesian form) for the analysis of the next part. To provide high stability of the sequential CNLS minimisation procedure, a new hybrid algorithm has been developed. This algorithm fits the datasets of reduced dimensionality to the selected EIS models, provides high stability of the fitting and allows semi-automatic data analysis on a reasonable timescale. The hybrid algorithm consists of two stages in which different zero-order optimisation strategies are used, reducing both the computational time and the probability to overlook the global optimum. The performance of the developed approach has been evaluated using (i) simulated large EIS dataset which represents a possible output of a scanning electrochemical impedance microscopy experiments, and (ii) experimental dataset, where EIS spectra were acquired as a function of the electrode potential and time. The developed data analysis strategy showed promise and can be further extended to other electroanalytical EIS applications which require multidimensional data analysis.     

Ultrasonic Studies of Binary Mixtures of p-Chlorotoluene with l-Alcohols at 303.15 K

Abstract

Ultrasonic sound velocities and densities were measured for the binary mixtures of p-chlorotoluene with l-alcohols. The alcohols included: l-propanol, l-butanol, l-pentanol, l-hexanol and l-heptanol. Isentropic compressibilities, k_s and deviation in isentropic compressibility, K_s from ideal behaviour have been calculated from the results. The deviation in isentropic compressibility has been ascribed to competition between structure-breaking and structural effects to different extents.     

A study of the precision and accuracy of peak quantification in comprehensive two-dimensional liquid chromatography in time

Simulated chromatographic data were used to determine the precision and accuracy in the estimation of peak volumes (i.e., peak sizes) in comprehensive two-dimensional liquid chromatography in time (LC × LC). Peak volumes were determined both by summing the areas in the second dimension chromatograms and by fitting the second dimension areas to a Gaussian peak. The Gaussian method is better at predicting the peak volume than the moments method provided there are at least three second dimension injections above the limit of detection (LOD). However, when only two of the second dimension signals are substantially above baseline, the accuracy and precision of the Gaussian fit method become quite poor because the results from the fitting algorithm become indeterminate. Based on simulations in which the modulation ratio (M_R = 4¹σ/t_s) and sampling phase (?) were varied, we conclude for well-resolved peaks that the optimum precision in peak volumes in 2D separations will be obtained when the M_R is between two and five, such that there are typically four to ten second dimension peaks recorded over the eight σ width of the first dimension peak. This sampling rate is similar to that suggested by the Murphy–Schure–Foley criterion. This provides an RSD of approximately 2% for the signal-to-noise ratio used in the present simulations. The precision of the peak volume of experimental data was also assessed, and RSD values were in the range of 4–5%. We conclude that the poorer precision found in the LC × LC experimental data as compared to LC may be due to experimental imprecision in sampling the effluent from the first dimension column.     

Preparative purification of gentamicin components using high-speed counter-current chromatography coupled with electrospray mass spectrometry

We developed a useful and preparative method based on high-speed counter-current chromatography with mass spectrometry (HSCCC/MS) to purify gentamicin C1a, C2/2a and C1 from standard powder. The analytes were purified on the HSCCC model CCC-1000 (multi-layer coil planet centrifuge) with a volatile two-phase solvent system composed of n-butanol/10% aqueous ammonia solution (50:50, v/v) and detected on an LCMS-2020EV quadrupole mass spectrometer fitted with an electrospray ionization (ESI) source system in positive ionization following scan mode (m/z 100-500). The HSCCC/ESI-MS peaks indicated that gentamicin C1a (m/z 450: [M+H](+)), C2/2a (m/z 464: [M+H](+)) and C1 (m/z 478: [M+H](+)) have the peak resolution values of 1.3 and 1.7 from 30 mg of loaded gentamicin powder. The HSCCC yielded 3.9 mg of gentamicin C1a, 12.6 mg of gentamicin C2/2a and 12.0 mg of gentamicin C1. These purified substances were analyzed by LC/MS with scan positive-mode. Based on the LC/MS chromatograms and spectra of the fractions, analytes were estimated to be over 95% pure. These gentamicin isomers of C1a, C2/2a and C1 were evaluated for their antibacterial activities. The overall results indicate that this approach of HSCCC/MS is a powerful technique for the purification of gentamicin components.     

东天山的一次暴雨洪水中心最大雨量的估算

本文通过对新疆天山东部地区一次罕见的大暴雨洪水的特征分析，应用水箱模型法和最大熵原理等方法推算出本次大暴雨的中心最大雨量和流域面平均降水量．     

RP-HPLC-DAD method for the determination of phenylepherine,paracetamol, caffeine and chlorpheniramine in bulk and marketed formulation

A simple, specific and accurate isocratic RP-HPLC-DAD method was developed for the simultaneous determination of phenylephrine, paracetamol, caffeine and chlorpheniramine in bulk and tablet dosage form. The four contents are present in variable concentrations and have variable chromatographic behavior making the process of analysis very difficult. For present studies a reversed-phase C-18 column (150 mm × 4.5 mm i.d., particle size 5 μm) with mobile phase consisting of acetonitrile, methanol and 10 Mm phosphate buffer 16:22:62 (v/v) (pH of buffer 2.5 ± 0.02, adjusted with ortho phosphoric acid) was used. The flow rate was 1.0 ml/min and eluents were monitored at 280 nm. The mean retention times of phenylephrine, paracetamol, caffeine and chlorpheniramine were found to be 1.8, 3.1, 5.2 and 10.9 min, respectively. The method was validated in terms of linearity, range, specificity, accuracy, precision and robustness. The proposed method was successfully applied to the estimation of phenylephrine, paracetamol, caffeine and chlorpheniramine in combined tablet dosage form.