Determination of nitrogen-containing pesticides in soil using vacuum-assisted headspace solid-phase microextraction

Wed, 20 Dec 2023 00:00:00 +0600

Pesticides are one of the largest groups of environmental pollutants used to protect agricultural plants from different pests and weeds. Soil is the initial area of accumulation of pesticides after their release into the environment. Determination of pesticides in soil is complicated by matrix effects and laborious sample preparation which generally involves the use of large amounts of organic solvents. Development of accurate green analytical methods for determination of pesticides in soil is an urgent task in environmental and analytical chemistry.

In this study a method based on vacuum-assisted headspace solid-phase microextraction (Vac-HSSPME) coupled with gas chromatography-mass-spectrometry (GC-MS) was developed for the quantification of nitrogen-containing pesticides in soil samples. The pesticides atraton, simazine, atrazine, propazine, diazinon, metribuzin, prometryn, and oxyfluorfen were target analytes. The effects of water addition, reduced pressure, salting-out and pH adjustment on the extraction efficiency of target pesticides from soil were studied.

Using Vac-HSSPME, the increase in the responses for all target pesticides by 3-7 times compared to ambient-pressure HSSPME was observed. Addition of water resulted in 2 to 380 times increase of the peak areas of analytes obtained using Vac-HSSPME. Optimum Vac-HSSPME performance was achieved using 60 min extraction at 60 °C. The proposed method can be recommended for quantification of atraton, atrazine, propazine, diazinon, prometryn, and oxyfluorfen in soil. Under optimum conditions the weighted linear regressions with R² > 0.949 were obtained for most analytes in the concentration range 25-200 ng/g. The limits of detection and quantification ranged from 0.1 to 4 ng/g, and from 0.4 to 12 ng/g, respectively.

Kinetic model of photocatalytic oxidation of dye (Orange II) by superoxide radicals

Zhandos K. Orazov, Yerzhigit Tulebekov, Askar M. Bakhadur, Bolat M. Uralbekov — Mon, 20 Nov 2023 00:00:00 +0600

The kinetics of photocatalytic decomposition of dye (Orange II) in the presence of titanium (IV) dioxide was studied. A presented kinetic model takes into account the active forms of particles involved in the process of photocatalytic oxidation. By adding various scavengers, it was found that superoxide radicals (O₂^•-) play the most significant role in dye photodegradation. Tert-butanol (t-BuOH), ammonium oxalate (OA), sodium azide (NaN₃), 4-hydroxy-TEMPO (TEMPOL) and dimethyl sulfoxide (DMSO) were used as scavengers with a final concentration of 10 mM of hydroxide radicals (•OH), holes (h⁺), singlet oxygen (¹O₂), superoxide radicals (O₂^•-) and electrons (e^-) in 40 ml of Orange II solution. The proposed kinetic model includes the following stages: photogeneration of particles, formation of superoxide radicals and their interaction with organic dye, products and inactive surfaces. Studies were conducted to determine the kinetic parameters of the reaction, particularly the order of Orange II photodegradation, showed that the reaction follows a pseudo-first-order kinetics, which is consistent with the proposed kinetic model. The resulting linear dependence of ln(C₀/C) with time shows that the photodecomposition reaction of Orange II is a pseudo-first order reaction, the rate constant of which is (35.1 ± 1.3)^.10^-3 min^-1.

Chemical Bulletin of Kazakh National University

Determination of nitrogen-containing pesticides in soil using vacuum-assisted headspace solid-phase microextraction

Kinetic model of photocatalytic oxidation of dye (Orange II) by superoxide radicals