NL2020339B1 - Method for the gc/ms/ms detection of pesticides in food products - Google Patents
Method for the gc/ms/ms detection of pesticides in food products Download PDFInfo
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- NL2020339B1 NL2020339B1 NL2020339A NL2020339A NL2020339B1 NL 2020339 B1 NL2020339 B1 NL 2020339B1 NL 2020339 A NL2020339 A NL 2020339A NL 2020339 A NL2020339 A NL 2020339A NL 2020339 B1 NL2020339 B1 NL 2020339B1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
- G01N1/34—Purifying; Cleaning
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D15/00—Separating processes involving the treatment of liquids with solid sorbents; Apparatus therefor
- B01D15/08—Selective adsorption, e.g. chromatography
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
- G01N1/40—Concentrating samples
- G01N1/405—Concentrating samples by adsorption or absorption
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/48—Biological material, e.g. blood, urine; Haemocytometers
- G01N33/50—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing
- G01N33/53—Immunoassay; Biospecific binding assay; Materials therefor
- G01N33/543—Immunoassay; Biospecific binding assay; Materials therefor with an insoluble carrier for immobilising immunochemicals
- G01N33/544—Immunoassay; Biospecific binding assay; Materials therefor with an insoluble carrier for immobilising immunochemicals the carrier being organic
- G01N33/548—Carbohydrates, e.g. dextran
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Abstract
The present invention relates to a method for the detection of pesticides in food products by means of gas or liquid chromatography in combination with mass spectrometry. More particularly, the present invention relates to the detection of pesticides in food products, wherein the method comprises the use of an extraction liquid mixture comprised of water and acetonitrile and an extraction salt composition comprised of magnesium sulphate, sodium chloride, trisodium citrate dihydrate, and disodium hydrogen citrate hexahydrate. Furthermore, the present invention relates to the method wherein an additional purification step of the acetonitrile phase is performed by means of a chemical filtration, which is especially suitable and preferred with the detection of pesticides in food using GC-MS analysis.
Description
Description
The present invention relates to a method for the detection of pesticides in food products by means of gas or liquid chromatography in combination with mass spectrometry. More particularly, the present invention relates to the detection of pesticides in food products., wherein the method comprises the use of an extraction liquid mixture comprised of water and acetonitrile and an extraction salt composition comprised of magnesium sulphate, sodium chloride, trisodium citrate dihydrate, and disodium hydrogen citrate hexahydrate. Furthermore, the present invention relates to the method wherein an additional purification step of the acetonitrile phase is performed by means of a chemical filtration, which is especially suitable and preferred with the detection of pesticides in food using GC-MS analysis.
Given the continuous growth of the world population, the demand for food is constantly growing. For the production of our food is often made use of various chemicals to ensure the quality and improve our food but also to increase the quantity of our food. Extensive use of chemical agents such as pesticides (insecticides, fungicides, herbicides) is adopted to control insects, weeds, microbes, etc. in order to improve the conditions for growth of vegetables and fruit and increase crop yield. The mode of action and toxicity of these agents used vary greatly and their use is not uncontro versial, since these substances can contaminate our food and there is a risk that these chemicals end up and build up in our bodies and therefore may pose a health risk.
The raw materials market for food products is becoming aware of the presence of pesticides, which may have consequences for the further use of these raw materials in the food chain. This awareness is translated into European guidelines, wherein the so-called maximum residue levels (MRLs) for pesticides in foods are determined. The trend in MRL for pesticides is a reduction in MRL. from ppm level to ppb level, which becomes a challenge to accurately measure these low levels of pesticides in a rapid and economically efficient manner.
Food or feed samples containing the pesticides need to be pre-treated using various separation and/or extraction steps to separate the pesticides from oil/fat residues and other contaminants that lead to a disturbance in a reliable detection of pesticides, such as the presence of sugars, protein and fatty acids. However the loss of pesticides in the various separation and extractions steps is a mayor bottleneck resulting in a yield loss of at least 60% of the pesticides and is not beneficiary to be able to detect these pesticides at low concentration levels as low as ppb in samples that are rich in oil and fat.
The physical and chemical characteristics of pesticides are very divers and many classes of pesticides exist. For example, there are a-polar pesticides which are insoluble in water, moderately polar to polar pesticides which are partly to completely soluble in water and highly polar and ionic pesticides which are sparingly soluble in an organic solvent to completely soluble in water.
In recent years a lot of effort has been put in the establishment and development of efficient, robust and sensitive analytical methods for the detection and determination of pesticides that are present in our food. Commonly used methods for analysing chemicals in food are for instance Gas Chromatography (GC) and Liquid Chromatography (LC). Chromatography has made a strong advance in recent years, wherein the chemicals are separated in a gas (by GC) or liquid (LC) phase on their selective distribution between the stationary (often a column or matrix), and the mobile phase (a earner gas (GC) or eluent (LC)). The substances that need to be separated or identified are carried along by the earner gas or eluent and interact with the column phase, in which molecules are bonded temporarily to the column, depending on the affinity of the molecules of the substance with the column phase. As a result, it is possible to separate substances from each other. Subsequently, the detection of the substances takes place by means of various detectors, such as, for example, mass spectrometry’.
However, chromatography is very’ sensitive to matrix effects, i.e. substances other than where one is interested in that are present in the sample, resulting in that systems are able to optimally measure only for a short period of time. Current technologies and methods allow for stable and reliable measurements with respect to the detection of pesticides in for example food from about one to a few days maximum. After this period, the columns and detector will become contaminated and/or clogged and are unusable for efficient and sensitive detection of chemicals and should either be cleaned or replaced. Therefore, it is currently of interest to inject on the column as little as possible of the extracts / samples. This can be achieved by means of extensive purification of the samples by means of extraction and / or diluting these samples, which can be a time-consuming undertaking. Bottleneck with such a diluent or purified sample is to achieve detection within the desired detection limits, in which the detection limits for chemicals in foods, such as insecticides and herbicides, continues to be lowered (adjusted) in order to monitor food safety and protect the health of the consumer.
Depending on the polarity of a pesticide, an extraction method may be selected. For example, the a-polar to polar pesticides can be extracted from the food product with a saltsaturated aqueous buffer and an organic solvent that is immiscible with water. The buffer should regulate the pH during the extraction and should make the polar pesticides medium-soluble in water, in order to achieve that all the pesticide after extraction will be present in the organic solvent. The extract is further purified before the analysis is carried out.
However, for the extraction of highly polar and ionic pesticides (or chemicals) the previously described extraction method does not work, and an aqueous extraction is more likely to be used because these compounds are all very' well soluble in water. However, this ·-> J extraction often results in suspensions that are difficult to separate into an aqueous portion and solid portion, and in the end, no stable chromatography will be obtained. In addition, there are many proteins, sugars, carbohydrates and fatty acids present in the extract which adversely affect the life time of the columns. As a result of this it was shown from the chromatographic analysis of the extract that many disturbing matrix is present through which retention times shifted from maximally a minute to more than a few minutes.
Another disadvantage of current methods for the detection and/or determination of these pesticides in food products is that they are often only suitable for one or more similar analytes. For example, glyphosate can be measured after a time-consuming derivatization process, and chlorate and perchlorate are measured by means of elaborate ion chromatography. In addition, known methods are mainly only suitable for aqueous samples.
Furthermore, most chromatography columns are often developed and suitable for use with w ater samples, in which no account is taken of the large amount of organic co-extracts, that arise as a result of the processing of the samples derived from foods. These organic co-extra.cts accumulate on to the column, causing the column to degenerate, resulting in a poor separation and reduced quality of the chromatographic analysis and detection of chemicals (i.e. the insecticides and herbicides). The end result is that the chromatography columns are rapidly aging”, the sensitivity of the columns fluctuates, and the retention time varies, which adversely affects an efficient and robust detection of pesticides. In addition, the maximum residue limit (MRL), which indicates how much pesticide may be left in or on the food product in recent years has been reduced from 500 pg/kg to 10 - 30 ug/'kg. Thus a very sensitive detection method is necessary. To achieve this, presently the highly polluted chromatographic columns are to be regenerated or replaced frequently.
In view of the above, there is a need in the art for a more reliable and rapid method for the detection of most of the pesticides in food and raw materials using one single method, without loss of pesticides during sample pre-treatment. There is a need for a robust, efficient and sensitive method that enables the detection of a great diversity (broad range) of pesticides in food products in a single chromatographic analysis (run) and to reduce matrix effects that occur during chromatography. A further object of the present invention is to provide an increased detection of a wide range pesticides by means of one extraction method.
It is an objective of the present invention, amongst other objects, to address the above need in the art. The object of present invention, amongst other objects, is met by the present invention as outlined in the appended clauses.
In particular, the above object is, amongst others, according to a first aspect achieved accordi ng to the present invention by a method for detection of pesticides in food products, wherein the method comprises the following steps;
a) contacting of a sample with an extraction liquid comprised of a mixture of water (H2O) and acetonitrile (C2H3N) and an extraction salt composition comprised of 55 - 65 wt% magnesium sulphate (MgSO<), 16.5 - 13.5 wt% sodium chloride (NaCI), 16.5 - 13.5 wt% trisodium citrate dihydrate (NasCfiHsO; . 2H2O), and 6-8 wt% disodium hydrogen citrate hexahydrate (Na 2C6H6O7.6H2O), based on the total weight of the extraction salt composition, to form a mixture A,
b) homogenizing of the mixture A to form a suspension A.
c) separating the suspension A into a water phase and an acetonitrile phase,
d) freezing of the acetonitrile phase, thereby solidifying residual compounds present in the acetonitrile phase, such as water, starch, fat, fatty acids, protein,
e) separating said solidified residual compounds and a purified acetonitrile phase,
f) isolating the purified acetonitrile phase.
g) determining pesticides in the purified acetonitrile phase by means of liquid chromatography - mass spectrometry' (LC-MS) or gas chromatography-mass spectrometry (GC-MS), thereby provid ing detection of pesticides in food products.
The method of present results in that a more stable chromatographic separation is obtained and matrix interference is minimized, resulting in a commodity independent method for the determination of a broad class of pesticides in food products by combining chromatography (LC or GC) arid mass spectrometry. Furthermore with the method of the present invention, an improved purified extract is obtained and therefore less sample can be used with increased detection sensitivity, within the pre-determined detection limits. In addition, the method according to the present invention has led to the fact that instead of stable detection was possible for only one day with liquid and Gas chromatography, stable detection is now possible for more than a week. The chromatography columns get less polluted, and thus last longer, resulting in an improvement in tlie detection of pesticides in both quantity and quality (detection sensitivity, detection rate).
According to yet another preferred embodiment, the present invention relates to the method, wherein between step f) and step g) an additional purification of the purified acetonitrile phase is carried out comprising the steps of
i) mixing of the purified aceton itrile phase with a composition comprised of 70 - 80 wt% of a matrix comprising silica gel base material with a matrix active group being ethylenediamine-N-propyl (PSA), 10 - 15 wt% magnesium sulphate (MgS04) and 10-15 wt% octadecyl-silyl-modified silica gei (C-18 sorbent), based on the total weight of the composition, to form a mixture B, ii) homogenizing of the mixture B to form a suspension B, iii) separating the suspension B into a solid phase comprising PSA, MgSO* arid C-18 sorbent, and a further purified acetonitrile phase, iv) isolation of the further purified acetonitrile phase,
v) extraction of the further pu rified acetonitrile phase by means of solid phase extraction (SPE) with a PSA column.
The further purification of the acetonitrile phase with a chemical filtration over a PSA elution column results to a further cleaned sample that is especially suitable and preferred with the detection of pesticides in food using GC-MS analysis.
According to a preferred embodiment, the present invention relates to the method the volume ratio water to acetonitrile in the extraction liquid is selected from the group consisting of about 5:1, about 3:1, about 2:1, about 1:1. preferably about 1:1. It has been investigated which extraction fluid results in optimal extraction of the pesticides from the food products. Eventually, a mixture of water and acetonitrile in the ratio of 1:1 seems to be most optimal. Water is also beneficial to accommodate the extraction of more polar pesticides of the sample. Mixture A is required to separate the water from the acetonitrile and make the w ater less favourable for the polar pesticides. Thus the polar pesticides will also be extracted to the acetonitrile. The extraction liquid as described in the method of the present invention results in a reduction in the occurrence of difficult to dissolve suspensions and reduces the number of contaminants such as organic coextracts present in the sample to be analysed after extraction, such as the presence of proteins and sugars.
According to another preferred embodiment, the present invention relates to the method wherein the weight ratio of sample to extraction liquid in the mixture of step a) is at least about 1:5, preferably at least about 1:10, most preferably at least about 1:20. In particular commodities with a high oil content the ratio betw een sample and acetonitrile is an important parameter since a-polar compounds prefer the oil over acetonitrile. The higher the ratio the better the a-polar compound will be extracted from the sample.
According to yet another preferred embodiment, the present invention relates to the method wherein the w eight ratio of extraction salt composition to extraction liquid is at least about 1:2, preferably at least about 1:3.
According to yet another preferred embodiment, the present invention relates to the method, wherein freezing of the acetonitrile phase is performed at a temperature of between -1 °C to -30 °C, preferably between -15 °C to -25 °C, for at least 30 min, preferably at least 45 min. By lowering the temperature several matrix compounds will dissolve less in the acetonitrile phase. This results in a better cleaning of the extract along the w hole procedure. The solidifying residual compounds, such as protein, fat, water, sugars, originate from the food products that have been processed and prepared to be analysed using the method of present invention.
According to another preferred embodiment, tire present invention relates to the method wherein said pesticides are one or more selected from the group consisting of organochlorine-based compounds, organophosphorous-based compounds, urea-based compounds, carbamates, anilinopyrimidine, aryioxyalkanoic acid, aryloxyphenoxypropionic acid, chloroacetamide, cyclodiene, phosphorothiolate, phthalimide, pyrethroid, triazine, and triazole.
According to a preferred embodiment, the present invention relates to the method wherein said food products is one or more selected from the group consisting of fruit, vegetables, seeds, oils, fat, fatty acids, grain, herbs, spices, meat, seafood, eggs and milk. Examples of food products can be analysed by the method of the present invention are fruits, vegetables, dried herbs such as chili powder, nutmeg, rapeseed, sunflower seed, sunflower oil, rapeseed oil. cereals, meat products such as minced meat and chicken fillet, milk powder, cheese, eggs, fish oil and fatty’ acids of animal or vegetable origin.
According to yet another preferred embodiment, the present invention relates to the method wherein said detection of pesticides in food products and/or raw materials thereof comprises a maximum residue limits (MRL) of at most 10 pg/kg, preferably of at most 5 pg/kg, most preferably of at most 1 pg/kg.
The present invention will be further detailed in the following examples;
Extraction for LC-MS or GC-MS analysis of pesticides
The equivalent of the weight of a sample according to table 1 ± 0.01 g is taken into consideration.
Table 1: Weighing and extraction fluid
Product | Sample (g) | Extraction Liquid (ml) |
Fatty' acids | 0.25 - 0.5 | 20 |
Oils and / or fats | 0.5 - 1 | 20 |
Lechifeed, Lecithine | 1-2 | 20 |
Acid oils. Organic anions (e.g. calcium soap) | 0.25-0.5 | 20 |
Dry- samples | 1-2 | 20 |
Depending on the type of sample, accurately weigh the quantity indicated in table to 0.01 grams of sample in a 50 ml centrifuge tube containing the extraction salt composition;
± 0.2 g magnesium sulphate, 1 ± 0.05 g sodium chloride, 1 ± 0.05 g trisodium citrate.2H2O and 0.5 ± 0.03 g disodium hydrogen citrate.6H2O, and mix. Add 10 ml of acetonitrile and homogenize. Then add water according to table 1 and mix the mixture on the vortex mixer for 5 minutes, making sure that the mixture is homogenized well. Centrifuge the mixture for 10 minutes at 3000 G and place the extract in the freezer for 45 minutes until the water is frozen. Then, centrifuge the extract for another 2 minutes at 3000 G and fill a vial from the acetonitrile portion for the LC-MS analysis.
For the GC-MS analysis die extract is additionally purified with PSA and Cl8.
Add 5 ml of the acetonitrile portion to a 15 ml centrifuge tube in which magnesium sulphate, PSA and CIS are weighed; 900 mg magnesium sulphate, 150 mg PSA (PSA SPE Bulk Packing, SigmaAldrich 52738-U) and 150 mg CIS (C-18 sorbent, octadecyl-silyl-modified silica gel, bulk material 50μηι). Mix the mixture on the vortex mixer for 5 minutes, making sure that the sample is well homogenized. Centrifuge the resulting mixture at 3000 G for 10 minutes. An additional purification with PSA tube is performed on the centrifuged extract. Transfer 2 ml of the purified extract to a PSA tube and allow it to elute under gravity. Then take 1 ml of the eluate and transfer it to a vial for the GC-MS analysis.
Chromatographic analysis of the extracts
The analysis of the extracts is performed by liquid chromatography (LC) and/or gas chromatography (GC) which is coupled to a triple quadrupole mass spectrometer. For the liquid chromatographic separation, use is made of column filled with a column of material of Octadecylsilane. The column is protected with a particle filter of 0.1pm. The chromatographic separation is performed under reversed phase conditions with an eluens consisting of methanol , water and formic acid.
The gas chromatographic separation is performed on a 25 m capillary column coated with a (5%-Phenyl)-methvlpolysiloxane phase. The chromatographic separation is performed with a temperature gradient.
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Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
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CN111024845A (en) * | 2019-12-21 | 2020-04-17 | 刘军虎 | Method for rapidly determining pesticide residues in vegetables, fruits and edible fungi |
Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
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CN103675175A (en) * | 2013-12-04 | 2014-03-26 | 广东出入境检验检疫局检验检疫技术中心 | Method for determination of pesticide residues in vegetable oils |
WO2016151947A1 (en) * | 2015-03-24 | 2016-09-29 | 三浦工業株式会社 | Method for preparing sample for residual pesticide analysis |
WO2016204854A1 (en) * | 2015-06-16 | 2016-12-22 | Agilent Technologies, Inc. | Compositions and methods for analytical sample preparation |
EP3168615A1 (en) * | 2015-11-13 | 2017-05-17 | Waters Technologies Corporation | Methods for detecting non-polar analytes with high sensitivity |
EP3184157A1 (en) * | 2014-08-19 | 2017-06-28 | Agricultural Chemicals And Toxic Substances Research Institute, Council Of Agriculture, Executive Yuan | Quick extraction kit for agricultural product pesticide residue detection procedure and method for obtaining stock solution of detection solution from agricultural product sample |
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Patent Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN103675175A (en) * | 2013-12-04 | 2014-03-26 | 广东出入境检验检疫局检验检疫技术中心 | Method for determination of pesticide residues in vegetable oils |
EP3184157A1 (en) * | 2014-08-19 | 2017-06-28 | Agricultural Chemicals And Toxic Substances Research Institute, Council Of Agriculture, Executive Yuan | Quick extraction kit for agricultural product pesticide residue detection procedure and method for obtaining stock solution of detection solution from agricultural product sample |
WO2016151947A1 (en) * | 2015-03-24 | 2016-09-29 | 三浦工業株式会社 | Method for preparing sample for residual pesticide analysis |
WO2016204854A1 (en) * | 2015-06-16 | 2016-12-22 | Agilent Technologies, Inc. | Compositions and methods for analytical sample preparation |
EP3168615A1 (en) * | 2015-11-13 | 2017-05-17 | Waters Technologies Corporation | Methods for detecting non-polar analytes with high sensitivity |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
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CN111024845A (en) * | 2019-12-21 | 2020-04-17 | 刘军虎 | Method for rapidly determining pesticide residues in vegetables, fruits and edible fungi |
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