Monika Michel

High performance liquid chromatography of 1,1-diamino-2,2-dinitroethene and some intermediate products of its synthesis.

1,1-Diamino-2,2-dinitroethene (DADNE, FOX-7) is a novel explosive with low sensitivity and high performance. The unique combination of the valuable properties is a result of the structure of the compound. The molecular packing of DADNE consists of layers with strong intermolecular hydrogen bonds which stabilize the molecule. In the paper, the results of research the purity of DADNE in different recrystallization conditions and some intermediate products of its synthesis were presented. High performance liquid chromatography (HPLC) method based on the porous graphitic carbon (PGC) column packing material has been developed. Two variants of mobile phases in different pH values: acetonitrile-water and methanol-water with ammonia (NH(3)) and with trifluoroacetic acid (TFA) were used. The probable mechanism of interaction between the analyte, the stationary phase, and the mobile phase was suggested.

Influence of temperature on mass transfer in an incomplete trapping supported liquid membrane extraction of triazole fungicides.

The influence of temperature in a supported liquid membrane (SLM) extraction of triazole fungicides was investigated. The mass transfer parameters such as diffusion coefficient, flux and apparent viscosity were determined at temperatures ranging from 5 to 40 degrees C. Increase in temperature led to an increase in diffusion coefficient and flux with a flowing acceptor solution. The apparent viscosity also decreased with an increase in temperature. However, the increase in mass transfer parameters did not result in an overall increase in extraction efficiency with a stagnant or circulation acceptor phase. Stripping of the analytes from the membrane into the acceptor phase as well as the configuration of the extraction unit could have limited the influence of temperature on mass transfer. The partition coefficient of analytes from the acceptor solution to the membrane, K(A), was found to be much higher than that from the donor solution to the membrane K(D), thus triazole compounds preferred to remain in the membrane even with an increased extraction temperature.

Comparison of various extraction techniques to determine fungicide residue in wheat grain

Abstract Methods for the extraction, separation, detection, and quantification of benzimidazole fungicide carbendazim residue in wheat grain were evaluated. The extraction of the residue was achieved using liquid–liquid extraction (LLE), solid‐phase extraction (SPE), and matrix solid phase dispersion (MSPD). Their respective advantages and disadvantages were discussed. Determination was carried out by reversed‐phase high performance liquid chromatography (RP‐HPLC) with column switching and diode array detection (DAD). Recoveries, at spiked concentrations below the maximum acceptable residue levels established by the Polish Government, were between 71.2–76.5% for LLE, 82.2–83.2% for SPE, and 84.3–90.7% for MSPD. Relative standard deviations (RSDs) ranging from 5.2% for LLE, 3.1–4.6% for SPE, and 2.7–4.1% for MSPD. The limit of quantification (LOQ) at λ=279 nm was 0.02 µg/g for all the extractions. Results obtained by the methods were compared in terms of sensitivity and selectivity and the three methods were applied to analyze real samples. As MSPD is easier to perform, faster than the organic solvent extraction, and shows equal accuracy and resolution, its application for analyzing pesticides in wheat is recommended.

Influence of temperature on mass transfer in an incomplete trapping single hollow fibre supported liquid membrane extraction of triazole fungicides

The influence of temperature in a single hollow fibre supported liquid membrane extraction of triazole fungicides with a stagnant acceptor phase was investigated. The mass transfer parameters such as diffusion coefficient, flux and apparent viscosity were determined at temperature ranging from 278 K to 313 K. Increase in temperature led to an increase in diffusion coefficient and flux. The apparent viscosity also decreased with an increase in temperature. The degree of trapping in the acceptor phase influenced the mass transfer at higher temperature. At lower temperature, the transport of analytes from the donor solution through the donor-membrane interface and through the membrane mainly affected the transport of triazole fungicides. The effect of temperature in a single hollow fibre SLM extraction technique is therefore more pronounced where transport is donor controlled and/or membrane controlled. The partition coefficient of analytes from the acceptor solution to the membrane, K(A) was found to be much higher than that of from the donor solution to the membrane K(D), thus least trapped triazole fungicides preferred to remain in the membrane even with an increased extraction temperature.

HPLC DETERMINATION OF PESTICIDE RESIDUE ISOLATED FROM FOOD MATRICES

ABSTRACT Methods for the extraction, separation, detection, and quantification of ten herbicide, insecticide, and fungicide residues in fruits, vegetables, and cereal were evaluated. The extraction of the residues was achieved using liquid–liquid extraction (LLE), solid-phase extraction (SPE), and matrix solid-phase dispersion (MSPD). Determination was carried out by reversed-phase high performance liquid chromatography (RP-HPLC) with column switching and diode array detection (DAD). Recoveries, at spiked concentrations below the maximum acceptable residue levels established by the Polish Government, were between 68.7 and 105.0% with relative standard deviations ranging from 0.5 to 6.2%. The limits of quantification varied from 0.02 to 0.25 μg/g.

Isolation and Determination of Urea Herbicides in Soil by Hyphenated Chromatographic Techniques

Abstract Eight phenylurea herbicides (chlorotoluron, isoproturon, diuron, monolinuron, linuron, metobromuron, chlorbromuron, methabenzthiazuron) were isolated from soil by extraction. The extract was cleaned up using an SPE module. Elution with a methanol‐dichloromethane mixture resulted in total recoveries using this method, which included all losses during sample preparation, ranging from 79 to 97% recovery of the herbicides from the activated silica gel sorbent column. Separation of the eight herbicides was easily achieved working under liquid chromatographic conditions. The validation of the analytical processes was described and the parameters of the LC‐DAD method are as follows: limits of detection from 0.07 to 0.13 µg/g; precision (RSD) from 2.9 to 10.4%. The proposed LC‐DAD method offers good resolution and selectivity.

DETERMINATION OF NEW GENERATION PESTICIDES IN COMPLEX PLANT MATRICES BY HPLC USING VARIOUS STATIONARY PHASES

Author interest is focused on method optimization to determine the new compounds using stationary and mobile phases with different physicochemical properties. This work deals with 5 substances composed of nitrogen containing heterocycles, 1,2,4-triazoles. The relationships between the chromatographic retention factor (k) and those physicochemical properties which are relevant in quantitative structure retention relationship (QSRR) studies were investigated. The accuracy of the simple linear regressions between the chromatographic retention and the descriptors for all of the compounds was satisfactory (correlation coefficient, 0.8 ≤ r2 ≤ 1.0). The QSRR models of compounds could be predicted with a multiple linear regression equation having the statistical index, r2 = 1.000. Evaluation of chromatographic properties of the new stationary phases and description of the molecular separation mechanism using the QSRR method including molecular modeling will be suggested.

High Performance Liquid Chromatography of Benzyl Derivatives of ES‐Silanates

Abstract Presented in this paper are results of investigations concerning optimization of conditions of separation and determination of two newly obtained hyper coordinated silicates, which belong to the group of ES‐silanates. To this process were subjected: 1‐[N‐(phenylmethyl)aminiomethyl]spirobi(sila‐2,5‐dioxa‐4,4‐dimethylcyclopentane‐3‐on)ate and 1‐[N‐(phenylmethyl)aminiomethyl]spirobi(sila‐2,5‐dioxacyclopentane‐3‐on)ate. The analyzed compounds show biological activity. Three stationary phases (octadecyl, octyl and naphthylpropyl), two mobile phases (acetonitrile, dichloromethane) with various flow were tested. The highest selectivity and separation factors (α=1.27) were obtained using the naphthylpropyl column and the mobile phase consisting of pure acetonitrile. The octadecyl (which is recommended as standard) phase did not enable satisfactory results.

The QuEChERS Approach for the Determination of Pesticide Residues in Soil Samples: An Overview.

Soil samples are complex matrixes; therefore, soil sample preparation is a critical step, and one that is usually expensive, time-consuming, and labor intensive. The quick, easy, cheap, effective, rugged, and safe (QuEChERS) method, originally developed for the determination of pesticides in fruits and vegetables, has been recently modified and adopted for the analysis of pesticides in soil. This paper reviews all aspects of sample preparation, including extraction and clean-up, and describes the applications of conventional and modified QuEChERS techniques. It also presents a comparison of the QuEChERS method with other methods used for sample preparation for determination of pesticides in soil.

Prediction of extraction efficiency in supported liquid membrane with a stagnant acceptor phase by means of artificial neural network.

An artificial neural network model of supported liquid membrane extraction process with a stagnant acceptor phase is proposed. Triazine herbicides and phenolic compounds were used as model compounds. The model is able to predict the compound extraction efficiency within the same family based on the octanol-water partition coefficient, water solubility, molecular mass and ionisation constant of the compound. The network uses the back-propagation algorithm for evaluating the connection strengths representing the correlations between inputs (octanol-water partition coefficients logP, acid dissociation constant pK(a), water solubility and molecular weight) and outputs (extraction efficiency in dihexyl ether and undecane as organic solvents). The model predicted results in good agreement with the experimental data and the average deviations for all the cases are found to be smaller than ±3%. Moreover, standard statistical methods were applied for exploration of relationships between studied parameters.