Application of flame gas chromatography and GC-MS

Application of gas chromatography and gas chromatography-mass spectrometry in the analysis of pesticide residues

at present, there are many methods for the analysis of pesticide residues, mainly chromatographic technology. Common chromatographic methods include gas chromatography, gas chromatography mass spectrometry, liquid chromatography, liquid chromatography mass spectrometry, and emerging chromatographic technologies such as immunoaffinity chromatography, gel permeation chromatography, etc. Gas chromatography mass spectrometry (GC-MS) not only has high separation efficiency of gas chromatography, but also has the characteristics of accurate identification of compound structure by mass spectrometry [1], which can simultaneously, accurately and quickly determine trace amounts of various pesticide residues

structural (substrate) characteristics

1 current situation and harm of pesticide residues

since the 1950s, the wide application of chemical synthetic pesticides in the world has undoubtedly played a decisive role in the prevention and control of diseases and pests, the eradication of weeds, and the increase of agricultural production, and has played a huge role in promoting and promoting the progress of human society and the development of productivity. However, pesticides are a kind of toxic chemicals, and they are actively put into the environment by people [2]. Long term massive use has had a great adverse impact on environmental biosafety and human health. In recent years, there have been frequent reports of poisoning of people and livestock caused by pesticide pollution, especially poisoning of vegetables and fruits. At present, pesticides have become one of the major sources of pollution in the world. Only 10% - 30% of pesticides sprayed in the field adhere to crops, and most of the others are dispersed through various ways, polluting the atmosphere, soil and water [3]

2 pesticide residue analysis technology

pesticide residue analysis is the analysis of Trace Pesticide parent compounds, toxic metabolites, degradation products and pesticide impurities in complex mixtures. It is a trace detection technology that requires fine micro operation means and high sensitivity [2]. With the increasing attention to food and environmental safety and the introduction of new and higher requirements of pesticide residue limit standards, pesticide residue analysis technology has developed rapidly. Modern pesticide residue analysis technology usually includes sample pretreatment and determination

2.1 sample pretreatment technology

at present, the new technologies that have been reported or have been widely used mainly include solid phase extraction (SPE), solid phase microextraction (SPME), supercritical fluid extraction (SFE), accelerated solvent extraction (ASE), microwave assisted extraction (MAE) [4]

2.1.1 solid phase extraction (SPE). Solid phase extraction is the development of the combination of liquid-solid extraction and liquid chromatography column technology. Its basic principle is to use solid adsorbents to adsorb the target compounds or impurities in liquid samples, and select appropriate elution solvents to selectively elute or retain the target compounds on the column and separate them from the sample matrix and interfering substances, so as to achieve the purpose of separation and enrichment. Solid phase extraction saves time, reduces the introduction of impurities, is safe for operators, has good reproducibility, and can quickly enrich pesticide residues

2.1.2 solid phase microextraction (SPME). Solid phase microextraction is a new solvent-free sample pretreatment technology, which was first reported by pawliszyn in 1989. Solid phase microextraction uses a specific solid (usually fibrous extraction material) as a solid phase extractor, immerses it in the sample solution or extracts it from headspace, and then directly analyzes it by GC, HPLC, etc. [5]. This technology integrates sampling, extraction, concentration and injection. It has high sensitivity, low cost, less sample quantity, good reproducibility and linearity, and simple, convenient and fast operation. Through adsorption/desorption technology, it enriches volatile and semi volatile components in samples, overcomes the shortcomings of some traditional sample processing technologies, and has been widely used in the analysis of water, food, environment and biological samples. SPME technology is widely used in food analysis, such as wine, fruit juice, vegetables, meat, eggs and so on. It is also used for the analysis of other harmful residual components in food, such as sulfonamides and tetracycline antibiotic residues in milk; Carcinogen N-nitrosamine in smoked ham; Analysis of propylene phthalein residues in grains and polychlorinated biphenyls and other chlorinated organic compounds in human milk [6]

2.1.3 supercritical fluid extraction (SFE). Supercritical fluid (SCF) is a high-density fluid at critical temperature (TC) and critical pressure (PC). Supercritical fluid not only has the characteristics of large solubility of liquid to solute, but also has the characteristics of easy diffusion and movement of gas. Because the viscosity, density, diffusion coefficient, solvation capacity and other properties of supercritical fluid vary greatly with temperature and pressure [7], it is very sensitive to selective separation. As early as 1879, Hannay et al. Found that supercritical ethanol fluid has significant solubility in inorganic salt solids, but supercritical extraction technology (SFE) is a new material separation and refinement technology that has developed rapidly in recent 30 years [8]. Fu Yujie et al. [9] used SCF-CO2 technology to extract glycyrrhetinic acid from licorice, and compared it with Soxhlet extraction method and ultrasonic method. The extraction rate was 13 times that of Soxhlet extraction method and 5 times that of ultrasonic method, with small solvent consumption and short cycle. At present, SFE has been applied to extract a variety of pesticides, fungicides and herbicides from plant samples, animal tissues, soil, water and other samples

2.1.4 gel permeation chromatography (GPC). Gel permeation chromatography is a rapid purification technology, which is based on the separation mechanism of volume exclusion. Through the stationary phase with molecular sieve property, it is used to separate substances with relatively small molecular weight, and can analyze polymer homologues with different molecular volumes and the same chemical properties. GPC has been widely used in the separation of lipid extracts and pesticides in the analysis of pesticide residues. It is the main purification method for the analysis of pesticide residues in fatty food samples [10]. Lu Jiwei et al. [11] determined the residues of 24 organophosphorus pesticides in Ganoderma lucidum after ice bath ultrasonic extraction and GPC purification. The recovery rate was 75.28% - 117.18%, RSD was 3.19% - 15.57%, and the effect was good

neat layout, clean, no external receiving path, space saving 2.1.5 accelerated solvent extraction (ASE). Accelerated solvent extraction is a new sample pretreatment method for extracting solid or semi-solid samples with solvent at elevated temperature (50 ~ 200 ℃) and pressure (1000 ~ 3000pa). Compared with other extraction methods, ASE method has the advantages of fast, less solvent consumption, high extraction efficiency and safety [12], and has been listed as one of the standard methods for processing solid samples by the United States EPA. ASE has been widely used in environment, medicine, food and other fields, especially in residue detection. It is used for the extraction of PCB, polycyclic aromatic hydrocarbons, organophosphorus pesticides, phenoxy herbicides and other harmful substances in soil, animal and plant tissues, vegetables and fruits

2.1.6 microwave assisted extraction (MAE). Microwave assisted extraction (MAE) is a new extraction method formed by the combination of microwave and traditional solvent extraction. It is a newly developed technology that uses microwave energy to improve the extraction rate. Microwave extraction has the advantages of simple equipment, high extraction efficiency, good reproducibility, fast, reagent saving, little pollution and so on, which has great promotion value. Onuska et al. [13] used a variety of solvents to microwave extract organochlorine pesticide residues from sludge. The results of Soxhlet extraction method for 6h were obtained in only 3.5min. Lo some of these projects have become local benchmark projects. PEZ Avila et al. [14] used ethane acetone (volume ratio of 1:1) as solvent to extract organics from soil at 115 ℃ for 15min. The recovery rate of 38 of 45 organochlorine pesticides was 80% - 120%, and proved that the recovery rate of organochlorine pesticides obtained by microwave extraction method was at least 7% higher than that by Soxhlet extraction or ultrasonic extraction method

2.2gc and the application of GC-MS in sample determination

2.2.1 gas chromatography (GC). In the 1950s, pesticide residue analysis was limited to chemical methods, colorimetry and bioassay, and the detection methods lacked specificity and sensitivity. In the early 1960s, gas chromatography began to be used in the analysis of pesticide residues. The use of many high-sensitivity detectors promoted the development of pesticide residue analysis technology and greatly improved the detection accuracy of pesticide residues. Because gas chromatography has the advantages of high separation efficiency, fast analysis speed, good selectivity, less sample consumption and high detection sensitivity, it is widely used to separate gases and volatile or volatile liquid and solid samples. At present, this method has become the most commonly used and main method in the analysis of pesticide residues

the detectors of gas chromatograph have various kinds of sensitivity and selectivity. Through the flexible application of these detectors, they can be used for the analysis of various samples. Electron capture detector (ECD) can realize the separation and determination of many organochlorine and pyrethroid pesticides; Flame photometric detector (FPD) has a good response value to organophosphorus pesticides; The response of nitrogen and phosphorus detector (NPD) to nitrogen, phosphorus and other compounds is greatly improved, and it has become an effective detector for the determination of organophosphorus and carbamate pesticides [15]

Wang Jianhua et al. [16] used acetonitrile homogeneous extraction, PSA solid phase extraction column purification, and then GC-ECD and FID to detect organophosphorus, organochlorine and pyrethroid pesticide residues in Sulfur-containing Vegetables. The recovery rate of the sample was 70% - 110%, RSD was 3.5% - 14.2%. Lihuidong et al. [17] extracted the pre prepared cabbage samples by high-speed homogenization method and purified the Florisil soil column, and then detected the residue of acetamiprid by GC-ECD. Quantitative by external standard method, the recovery rate was 80.2%~99.8%, the minimum detection concentration was 0.001mg/kg, and the RSD of the determination result was not greater than 3.4%. Songjiayu et al. [18] established a capillary gas chromatography method for the determination of organochlorine pesticide residues in food and traditional Chinese medicine. The samples were extracted by organic solvent ultrasound, purified by sulfuric acid, used ov-1701 capillary column, undivided injection, temperature programmed separation, ECD detection, and quantified by external standard method. The average recovery was 84.3% - 100.6%, RSD was 1.28% - 3.56%. Ren Hongbo [19] established a gas chromatography method for the detection of cyfluthrin. The honey sample was dissolved in water and extracted by hexane dichloromethane. The extract was purified by C18 solid phase extraction column and determined by gcd-ecd. The recovery was more than 80% and the detection limit was 0.0013mg/kg. Lu Fen et al. [20] extracted trace pyrethroids from vegetables and fruits with petroleum ether, concentrated and purified by Florisil solid phase extraction column, and determined by gas chromatography ECD. The results showed that the average recovery rate in Chinese cabbage was 86.2% - 93.4%, RSD was 3.4% - 8.6%; The recovery rate of apple is 87.3% - 92.8%, RSD is 2.8% - 8.1%

2.2.2 gas chromatography mass spectrometry (GC-MS). The combination of high-efficiency separation and high-performance identification instruments is a major technological progress in the field of instrumental analysis at the end of the 20th century. Among them, modern GC-MS combined technology is the most mature and widely used combined mode at present

mass spectrometry has the advantages of high sensitivity and strong qualitative ability, but it requires pure injection and complex quantitative analysis. Gas chromatography has high separation efficiency and simple quantitative analysis, but its qualitative ability is poor. Therefore, the combination of these two methods can learn from each other and give full play to both the high separation ability of chromatography and the high identification ability of mass spectrometry. It is suitable for qualitative identification of unknown substances in multi-component mixtures. It can determine the molecular structure of compounds, accurately determine the relative molecular mass of unknown components, and identify partially separated or even non separated chromatographic peaks

Zhu Jing et al. [21] purified thiazophos pesticide residues in environmental water by SPE and determined them by GC-MS. the minimum detection mass concentration of thiazophos in environmental water is 56.4ng/l, the recovery rate of samples is greater than 85.5%, and the RSD is less than 4.42%, which is suitable for the monitoring of trace pesticides in environmental water. Eijiueno et al. [22] first extracted 89 pesticides from vegetables with acetonitrile, and then dissolved ethyl acetate after salting out. The co solutes automatically passed through gel chromatography and activated carbon double columns in series. Then 2. The friction was relatively large, and the service life was short. GC-MS analysis was used. The recovery rate was 70%~120%, RSD was less than 5%. The method has been applied to the daily detection of 188 kinds of fruits and vegetables.