Analysis of pesticides in nuts by online reversed-phase liquid chromatography-gas chromatography using the through-oven transfer adsorption/desorption interface

Simultaneous determination of 106 pesticides in nuts by LC-MS/MS using freeze-out combined with dispersive solid-phase extraction purification

As a result of the low water content and high fat matrices in nuts, it is very difficult to simultaneously determine multi-pesticides in trace levels. Here, a sample pretreatment method was developed in which, microwave-assisted solvent extraction was firstly used to extract pesticides, and then a two-step cleanup method was conducted combining freeze-out with dispersive solid-phase extraction to remove the lipidic matrix. By this way, 106 pesticides were simultaneously determined in the complicated nut sample by using an ultra-high pressure liquid chromatography coupled with a tandem mass spectrometer. Average recoveries were 75.3-119.3% with relative standard deviations < 14% at three concentration levels. The limits of detection and quantification were in the ranges of 0.3-3.0 and 1.0-10.0 μg/kg, respectively. Furthermore, the method was successfully applied to the determination of pesticides in 180 commercial nut samples.

Residue levels and risk assessment of pesticides in nuts of China

The pesticide residue levels of three nuts (chestnut, walnut, pinenut) collected from seven main producing areas of China were investigated. Twenty-nine pesticides, including organophosphates (OPs), organochlorines (OCs), pyrethroids (PYs) and two fungicides (triadimefon and buprofezin) were analyzed by gas chromatography (GC). Four OPs (acephate, dimethoate, chlorpyrifos and parathion-methyl) were found in 11.4% samples, with the concentrations of 19.0 µg kg(-1) to 74.0 µg kg(-1). Six OCs (DDT, HCH, endosulfan, quintozene, aldrin and dieldrin) were found in 18.2% samples, with the concentrations of 2.0 µg kg(-1) to 65.7 µg kg(-1). Among OCs, p,p-DDE and α-HCH were the dominant isomer for DDT and HCH. Five PYs (fenpropathrin, fenvalerate, cypermethrin, bifenthrin and cyhalothrin) were found in 15.9% samples, with the concentrations of 2.5 µg kg(-1) to 433.0 µg kg(-1). Fenpropathrin was the most frequently detected pesticide. In addition, triadimefon and buprofezin were detected only in two samples. For the tested nuts, 25.0% samples with multiple residues (containing more than two pesticides) were noted, even up to 9.1% samples with five pesticide residues. The residue of 15.9% samples was higher than the maximum residue limits (MRLs) of China. The short-term risks for the tested nuts were below 1.2%, and the highest long-term risk was 12.58%. The cumulative risk (cHI) for the tested pesticides were 8.43% (OPs), 0.42% (OCs), 12.82% (PYs) and 0.15% (fungicides), respectively. The total cHI was 21.82%. There was no significant health risk for consumers via nuts consumption.

Simultaneous analysis of herbicides pendimethalin, oxyfluorfen, imazethapyr and quizalofop-p-ethyl by LC-MS/MS and safety evaluation of their harvest time residues in peanut (Arachis hypogaea L.)

This paper reports a simple and rapid method for simultaneous determination of the residues of selected herbicides viz. pendimethalin, oxyfluorfen, imazethapyr and quizalofop-p-ethyl in peanut by liquid chromatography-tandem mass spectrometry (LC-MS/MS). A modified approach of the QuEChERS methodology was used to extract the herbicides from the peanut kernel without any clean-up. The method showed excellent linearity (r(2) > 0.99) with no significant matrix effect. Accuracy of the method in terms of average recoveries of all the four herbicides ranged between 69.4 -94.4 % at spiking levels of 0.05, 0.10 and 0.25 mg kg(-1) with intra-day and inter-day precision RSD (%) between 2.6-16.6 and 8.0-11.3, respectively. Limit of quantification (LOQs) was 5.0 μg kg(-1) for pendimethalin, imazethapyr and quizalofop-p-ethyl and 10.0 μg kg(-1) for oxyfluorfen. The expanded uncertainties were <11 % for determination of these herbicides in peanut. The proposed method was successfully applied for analysis of these herbicide residues in peanut samples harvested from the experimental field and the residues were below the detection level.

On-line coupled reversed phase liquid chromatography and gas chromatography: a new sealing design for the TOTAD interface

Total elimination of the eluent resulting from the pre-separation step is the critical point when coupling LC to GC. As a helium flow is applied during transfer to eliminate the solvent, the interface used for linking the two chromatographic systems must be properly sealed to prevent gas leaks and to achieve an effective evaporation of the eluent. The aim of this work was to improve the performance of the Through Oven Transfer Adsorption Desorption (TOTAD) interface to remove the eluent coming from LC by modifying the way in which the injector sealing system is held in place. As with the original design, the new approach makes it possible to transfer high volumes at a high rate, but the proposed modification also simplifies the experimental work because the displacement risk of the sealing system is reduced. Analyses of an ester mixture by RPLC-GC were performed to confirm the applicability of the system modification. In this work, volumes of up to 5 ml, at flow rates as high as 2 ml/min, were transferred from LC to GC with almost complete solvent removal even when working in reversed phase mode in the LC step.

Miniaturization of Analytical Methods

This chapter highlights miniaturization in sample preparation as a valuable alternative for green analytical chemistry. The current state of the art is discussed on the basis of examples selected from representative application areas, including biomedical, environmental and food analysis, and involving conventional instrumental techniques for final determination of the target compounds. The emphasis is on those techniques and approaches that have already demonstrated their practicality by the analysis of real-life samples, and in particular on those dealing with the accurate determination of minor organic components. The potential of recent developments in this field for sample treatment simplification and complete hyphenation of analytical processes are discussed and the most pressing remaining limitations evaluated.