The present protocol describes the utilization of ammonium formate for phase partitioning in QuEChERS, together with gas chromatography-mass spectrometry, to successfully determine organochlorine pesticide residues in a soil sample.
Currently, the QuEChERS method represents the most widely used sample preparation protocol worldwide for analyzing pesticide residues in a broad variety of matrices both in official and non-official laboratories. The QuEChERS method using ammonium formate has previously proven to be advantageous compared to the original and the two official versions. On the one hand, the simple addition of 0.5 g of ammonium formate per gram of sample is sufficient to induce phase separation and achieve good analytical performance. On the other hand, ammonium formate reduces the need for maintenance in routine analyses. Here, a modified QuEChERS method using ammonium formate was applied for the simultaneous analysis of organochlorine pesticide (OCP) residues in agricultural soil. Specifically, 10 g of the sample was hydrated with 10 mL of water and then extracted with 10 mL of acetonitrile. Next, phase separation was carried out using 5 g of ammonium formate. After centrifugation, the supernatant was subjected to a dispersive solid-phase extraction clean-up step with anhydrous magnesium sulfate, primary-secondary amine, and octadecylsilane. Gas chromatography-mass spectrometry was used as the analytical technique. The QuEChERS method using ammonium formate is demonstrated as a successful alternative for extracting OCP residues from a soil sample.
The need to increase food production has led to the intensive and widespread use of pesticides worldwide over the last few decades. Pesticides are applied to the crops to protect them from pests and increase crop yields, but their residues usually end up in the soil environment, especially in agricultural areas1. Furthermore, some pesticides, such as organochlorine pesticides (OCPs), have a very stable structure, so their residues do not decompose easily and persist in the soil for a long time2. Generally, the soil has a high capacity to accumulate pesticide residues, especially when it has a high content of organic matter3. As a result, the soil is one of the environmental compartments most contaminated by pesticide residues. As an example, one of the complete studies to date found that 83% of 317 agricultural soils from across the European Union were contaminated with one or more pesticide residues4.
Soil pollution by pesticide residues may affect non-target species, soil function, and consumer health through the food chain because of the high toxicity of the residues5,6. Consequently, the evaluation of pesticide residues in soils is essential to assess their potential negative effects on the environment and human health, particularly in developing countries due to a lack of strict regulations on the use of pesticides7. This makes pesticide multi-residue analysis increasingly important. However, the rapid and accurate analysis of pesticide residues in soils is a difficult challenge due to the large number of interfering substances, as well as the low concentration level and the diverse physicochemical properties of these analytes4.
Of all the pesticide residue analysis methods, the QuEChERS method has become the quickest, easiest, cheapest, most effective, robust, and safest option8. The QuEChERS method involves two steps. In the first step, a microscale extraction based on partitioning via salting-out between an aqueous and an acetonitrile layer is performed. In the second step, a cleaning process is carried out employing a dispersive solid phase extraction (dSPE); this technique uses small amounts of several combinations of porous sorbents to remove matrix-interfering components and overcomes the disadvantages of conventional SPE9. Hence, the QuEChERS is an environmentally friendly approach with little solvent/chemical going to waste that provides very accurate results and minimizes potential sources of random and systematic errors. In fact, it has been successfully applied for the high-throughput routine analysis of hundreds of pesticides, with strong applicability in almost all types of environmental, agri-food, and biological samples8,10. This work aims to apply and validate a new modification of the QuEChERS method that was previously developed and coupled to GC-MS to analyze OCPs in agricultural soil.
The original9 and the two official versions13,14 of the QuEChERS method use magnesium sulfate together with sodium chloride, acetate, or citrate salts to promote acetonitrile/water mixture separation during extraction. However, these salts tend to be deposited as solids on the surfaces in the mass spectrometry (MS) source, which causes the need for increased maintenance of liquid chromatography (LC)-MS-based methods. In terms of overcoming…
The authors have nothing to disclose.
I would like to thank Javier Hernández-Borges and Cecilia Ortega-Zamora for their invaluable support. I also want to thank the Universidad EAN and the Universidad de La Laguna.
15 mL disposable glass conical centrifuge tubes | PYREX | 99502-15 | |
2 mL centrifuge tubes | Eppendorf | 30120094 | |
50 mL centrifuge tubes with screw caps | VWR | 21008-169 | |
5977B mass-selective detector | Agilent Technologies | 1617R019 | |
7820A gas chromatography system | Agilent Technologies | 16162016 | |
Acetone | Supelco | 1006582500 | |
Acetonitrile | VWR | 83642320 | |
Ammonium formate | VWR | 21254260 | |
Automatic shaker KS 3000 i control | IKA | 3940000 | |
Balance | Sartorius Lab Instruments Gmbh & Co | ENTRIS224I-1S | |
Bondesil-C18, 40 µm | Agilent Technologies | 12213012 | |
Bondesil-PSA, 40 µm | Agilent Technologies | 12213024 | |
Cyclohexane | VWR | 85385320 | |
EPA TCL pesticides mix | Sigma Aldrich | 48913 | |
Ethyl acetate | Supelco | 1036492500 | |
G4567A automatic sampler | Agilent Technologies | 19490057 | |
HP-5ms Ultra Inert (5%-phenyl)-methylpolysiloxane 30 m x 250 µm x 0.25 µm column | Agilent Technologies | 19091S-433UI | |
Magnesium sulfate monohydrate | Sigma Aldrich | 434183-1KG | |
Mega Star 3.R centrifuge | VWR | 521-1752 | |
Milli-Q gradient A10 | Millipore | RR400Q101 | |
p,p'-DDE-d8 | Dr Ehrenstorfer | DRE-XA12041100AC | |
Pipette tips 2 – 200 µL | BRAND | 732008 | |
Pipette tips 5 mL | BRAND | 702595 | |
Pipette tips 50 – 1000 uL | BRAND | 732012 | |
Pippette Transferpette S variabel 10 – 100 µL | BRAND | 704774 | |
Pippette Transferpette S variabel 100 – 1000 µL | BRAND | 704780 | |
Pippette Transferpette S variabel 20 – 200 µL | BRAND | 704778 | |
Pippette Transferpette S variabel 500 – 5000 µL | BRAND | 704782 | |
Vials with fused-in insert | Sigma Aldrich | 29398-U | |
OCPs | CAS registry number | ||
α-BHC | 319-84-6 | ||
β-BHC | 319-85-7 | ||
Lindane | 58-89-9 | ||
δ-BHC | 319-86-8 | ||
Heptachlor | 76-44-8 | ||
Aldrin | 309-00-2 | ||
Heptachlor epoxide | 1024-57-3 | ||
α-Endosulfan | 959-98-8 | ||
4,4'-DDE-d8 (IS) | 93952-19-3 | ||
4,4'-DDE | 72-55-9 | ||
Dieldrin | 60-57-1 | ||
Endrin | 72-20-8 | ||
β-Endosulfan | 33213-65-9 | ||
4,4'-DDD | 72-54-8 | ||
Endosulfan sulfate | 1031-07-8 | ||
4,4'-DDT | 50-29-3 | ||
Endrin ketone | 53494-70-5 | ||
Methoxychlor | 72-43-5 |