Determination of heavy metals in food by AA-1800 atomic absorption spectrometry - Master's thesis - Dissertation

Determination of Heavy Metals in Food by AA-1800 Atomic Absorption Spectrometry

Key words: atomic absorption spectrometry; food heavy metals; aesthetic analyzer ; AA-1800 Atomic Absorption Spectrometer has been widely used in the determination of heavy metal content in foods in recent years. This method has sensitivity compared with traditional chemical analysis methods. Higher, more accurate measurement results. This paper reviews the progress in the determination of heavy metal elements such as lead (Pb), cadmium (Cd), chromium (Cr), mercury (Hg) and arsenic (As) in vegetables, food, seafood and beverages by atomic absorption spectrometry. The determination of the accuracy, sensitivity and recovery of different elements using flame atomic absorption (FAAS), graphite furnace atomic absorption (CTAAS) and hydride generation atomic absorption (HGAAS) methods, and the atomic absorption method in food heavy metals The application in the inspection is expected. Heavy metals are widely found in food and food processing. Most heavy metals have toxic effects on human body, and because they can accumulate in the human body, long-term intake of foods with high levels of heavy metals can endanger human health and even cause diseases. Pb, Cd, Cr, Hg and As are the main heavy metal elements that may be present in foods. Studies have shown that they can cause damage to various organs and tissues such as the human respiratory system, digestive system and nervous system. For example, Pb can cause lesions in the human nervous system, hematopoietic system, and blood vessels, and can lead to mental retardation and behavioral abnormalities in children. Cd damages the respiratory system, the digestive system, lungs, kidneys and other organs, and can cause bone pain and anemia, and can also induce cancer. Cr is widely present and accumulated in the environment and food chain, causing damage to the human respiratory tract, gastrointestinal tract, skin, and the like. Diet is an important channel for the intake of Hg into the human body. Especially in areas where seafood such as fish is the main food, Hg and alkyl Mercury compounds can cause poisoning. Among them, methylmercury and ethylmercury are extremely toxic. Appears in fish and aquatic mammals. As can cause health problems such as malignant tumors, cardiovascular diseases and diabetes. International standards impose strict limits on the content of heavy metals in food. For example, the international food law stipulates that the maximum Hg content in fish should not exceed 0.5 mg/kg. There are many methods for detecting heavy metals in food: instrument neutron activation analysis can detect trace elements in food, but can not accurately detect lower levels of Pb and Cd; inductively coupled plasma mass spectrometry is used to determine As in food. , Cd and Hg, but the working environment of the instrument is more demanding. Atomic absorption spectrometry has the advantages of high sensitivity, good analytical precision, high selectivity, and many types of elements. As the preferred method for the determination of trace metal elements, it has been widely used in the detection of heavy metals in foods in recent years. 1 Detection of heavy metals in grain Heavy metals in food are mainly from pollution sources such as the atmosphere, groundwater, soil, fertilizers and pesticides. Heavy metals can not only affect the growth and development of food crops, but also reduce production, and will cause harm to human health through enrichment. Togores et al. used the ET-AAS method to detect Cd and Pb from a total of 29 infant food products from 5 manufacturers in Spain. The sample was digested by dry method at 450 ° C for 24 - 48 h, and the ash was digested in concentrated nitric acid for 48-72 h and then determined by atomic absorption spectroscopy. The results are shown in Table 1. The contents of Cd and Pb in the milk-free infants were 3.8- 35.8 ng/g and 36.1-305.6 ng/g, respectively, while the Cd-containing and Pb-containing contents in the milk-containing cereals were 2.9-40.0, respectively. Ng/g and 53.5-598.3 ng/g. This study established an effective method for detecting the content of Cd and Pb in infant foods, which is of great significance for reducing Cd and Pb pollution in raw materials and production and processing. Wen Xiaodong et al. determined the content of Cd in rice and water by cloud point extraction-electrothermal evaporation atomic fluorescence spectrometry (CPE-ETAFS) and cloud point extraction-electrothermal atomic absorption (CPE-ETAAS). When the temperature of the extraction system is higher than the cloud point temperature of the surfactant Triton X-114, the Cd and dithizone complex are quantitatively extracted into the surfactant and separated from the aqueous phase by centrifugation. The results showed that the concentration, pH value, equilibrium temperature and reaction time of Triton X-114 and dithizone had significant effects on the CPE process. The detection limits of atomic fluorescence and atomic absorption methods were optimized after CPE conditions were 0.01. Gg/L and 0.03 μg/L. Parengam et al. used instrument neutron activation analysis (INAA) and GFAAS methods to determine metal elements in rice and beans. Experiments show that INAA has good accuracy and precision for the detection of metal elements such as Al, Ca, Mn and K. Sex, relative error and relative standard deviation (RSD) are less than 10%, and the sample does not need to be digested or extracted. However, the INAA method has lower sensitivity for Pb and Cd determination; the GFAAS rule is more suitable for the detection of Pb and Cd. The measured recoveries of both metals were higher than 80%, and the relative errors were only 1.54% and 6.06%, respectively. The results showed that the rice samples contained trace amounts of As (0.029-0.181 mg/kg) and Cd (0.010-0.025 mg/kg); the Cd content in soybean and peanut was higher, 0.022 mg/kg and 0.085 mg/kg. Hydride generation atomic absorption spectroscopy (HGAAS) is commonly used in the detection of As, Se and Hg, which is determined by reducing the metal elements in a sample to a hydride based on a selective chemical reduction reaction. Uluozlu et al. used the HGAAS method to determine the As content in foods such as rice, wheat, eggs, and tea. First, Sepabeads SP70 solid phase extraction method was used to separate and enrich As3+ and As5+ in the sample (the recovery rate of As3+ was more than 95%); then, As5+ was reduced to As3+ by potassium iodide and ascorbic acid to determine the total amount in the sample. As content. The results show that the quantitative method has good precision (RSD < 8%) and sensitivity (LOD = 13ng/L), which provides an effective method for detecting the content of different valence states of As in food. Sun et al. [26] proposed a new method for the direct determination of trace As in flour by suspension injection-HGAAS. A suspension was prepared using 0.3 g / 100 mL agar, 1 g / 100 mL of citric acid and n-octanol as stabilizers, sensitizers and antifoaming agents, respectively. The method was applied to the determination of As in five grains such as wheat and rice. The detection limit was 0.239 pg/L, the recovery was 95.5%-108%, and the RSD was 0.86%-3.02%. Three standard reference materials were analyzed and there was no significant difference between the measured results and the standard reference values. Table 1 Cd and Pb content in milk-free and milk-containing infants 1 Detection of heavy metals in vegetables and fruits Atmospheric sedimentation, pesticide use, fertilizer pollution and water pollution lead to the accumulation of heavy metals in vegetables and fruits, and through the food chain Causes damage to the human body. Since soil plays a key role in the pollution process of crops, the determination of heavy metals in vegetables and fruits is often accompanied by the determination of the metal content in the growing soil. Sharma et al. collected soil and vegetable samples around the highway in the Agra region of India, and detected the contents of Pb and Cd by atomic absorption spectrometry. The results showed that Pb in soil and vegetables near the road (0-5m) The content of Cd and Cd is higher than the distance (5-10m and 10-15m). Markovic et al. [15] collected soil, vegetable and fruit samples from the Belgrade agricultural region of Serbia, and determined the contents of Pb, Cd and Cu by atomic absorption spectrometry. The results showed that the heavy metal content of vegetables in the areas polluted by coal was higher. . Liu Hao et al. determined the contents of Pb, Cd, Mn, Cu and Zn in the soil of navel orange plantation around the railway by atomic absorption spectrometry. The results showed that the content of Pb and Mn in plantation soil was significantly higher than that of the control. Soil, but the difference between Cd, Cu and Zn content and control soil is not obvious. The above experiments show that the heavy metal content in vegetables and fruits is closely related to the soil in which it grows, and the heavy metal content in the soil is affected by the surrounding environment. For example, automobile exhaust gas and coal combustion on the road will increase the heavy metal content in the soil. And thus affect the level of metal in the crops grown in the soil. Wang Hui et al. used the soil and vegetables of the vegetable base in Luoyang as the research object. The contents of Cr, Pb, Cd and Hg in the samples were determined by atomic absorption spectrometry. The soil was evaluated by single factor pollution index and comprehensive pollution index method. Pollution status and vegetable quality. The results showed that the contents of Cr and Pb in the soil of Luoyang vegetable base were in line with the secondary standard limit of GB15618-1995 Soil Environmental Quality Standard; the main pollution element of vegetables was Pb, such as Pb content in rapeseed and lettuce. In addition, the average level of heavy metals in leafy vegetables exceeded the standard, while the root-stem vegetables were less polluted and at a safe level. In the detection of heavy metals in vegetables and fruits, the pretreatment methods of the samples often have a significant impact on the experimental results. Bakkali et al. determined the contents of Cd, Cr, Cu, Mn and Pb in tomato, pepper and onion by graphite furnace atomic absorption spectrometry (GFAAS). The samples were pretreated by closed microwave digestion. When different volumes of nitric acid were used, When hydrogen peroxide is used as the digestion solution, the measured results of the samples are different. As shown in Fig. 1, when the amounts of nitric acid and hydrogen peroxide are 6 mL and 2 mL, respectively, the measurement results reach a stable maximum value; the experiment established by the mortar The method has good sensitivity and accuracy for the determination of the above five elements. The limit of detection (LOD) and limit of quantitation (LOQ) are 0.05-2.20μg/kg and 0.15-7.34pg/kg, respectively. For samples with complex compositions, the pretreatment process usually involves separation and enrichment of the elements to be tested. Gunther et al. determined the content of Cd compounds of different molecular weights in spinach and radish by atomic absorption spectrometry. In this experiment, the samples were pretreated by gel permeation chromatography and polyacrylamide gel electrophoresis, and high molecular weight Cd compounds (150-700kD) and low molecular weight Cd compounds (< 150kD) were isolated. The quantitative analysis results showed The high molecular weight Cd compound is the main component, and the high molecular weight Cd compound in the two vegetables has a similar chemical structure. Xu Xiaoyan et al. established a method for the continuous determination of heavy metals Pb, Cr and Cd in fruits and vegetables by microwave digestion-GFAAS method in the same system. The effects of digestion reagent, digestion temperature and time on sample digestion were studied, and the GFAAS measurement conditions were optimized. Under the optimal experimental conditions, the detection limits of Pb, Cr and Cd were 0.293, 0.037 μg/L and 0.850 μg/L, respectively. The relative standard deviation was 2.1%-5.3%, and the recovery was 95.0%-101.9%. : 3 Detection of heavy metals in marine products Seafood is an important source of heavy metals in the diet of coastal residents. The content of heavy metals in the offshore waters and animals grown therein is often high. The detection of heavy metal content in 11 kinds of common foods showed that fish and other seafood had higher As, Cd, Hg and Pb contents than vegetables, cereals, fruits, eggs, meat, milk and oil. It can be seen that the detection of heavy metals in seafood is very important for food safety. Fish are very sensitive to pollutants and can be monitored by measuring the metal content of the fish. There are two kinds of fish measurement. One is the determination of fish food after canning. The source of metal is water source and processing. The other is the measurement of fresh fish. The source of metal is mainly water source. . Ashraf et al. studied heavy metals in canned salmon, sardines and tuna. The content of Pb and Cd was determined by GFAAS method. The contents of Ni, Cu and Cr were determined by FAAS method. The recovery was 90%-110%. The results showed that the content of Pb and Ni in sardines was 4 and 3 times higher than that of tuna, respectively. Shiber et al. used the GFAAS method to measure the contents of As, Cd, Pb and Hg in canned sardines purchased from eastern Kentucky, USA. The sample was directly digested with HNOs and H2O2, and the average result was As 1.06 μg, Cd 10.03 μg, and Pb 0.11 μg per gram of sample (wet mass). The study found that the metal content and ingredients in canned fish have a certain correlation. The sardines packed in tomato ingredients have higher Cd, the sardines packed in solution contain higher As, and the sardines packed in oil contain higher Pb. . Bilandzic et al. used microwave digestion-GFAAS method to study the contents of As, Cd, Cu, Hg and Pb in anchovy, carp, carp and black squid in the Adriatic. The results showed that there were significant differences in the content of heavy metals in different types of fish. For example, the As content in anchovies was 0.01-54.8 mg/kg, the Cd content was 0.001-0.02 mg/kg, and the Hg content was 0.001-0.52 mg/kg. The As content in the carp is 0.01-70.9 mg/kg, the Cd content is 0.002-0.85 mg/kg, and the Hg content is 0.002-2.07 mg/kg. The average content of Cd, Pb, Hg and Cu in different kinds of fish is lower than the relevant standards established by the European Community, such as the average Cd content is 0.002mg/kg, while the Cd content limit in the relevant European Community standards is 0.3. Mg/kg, red mullet 0.05mg/kg; As content determination results, except for As content in red mullet (5.91mg/kg) is higher than the legal limit (2mg/kg), the As content in other fish is not Excessive. Bivalve is a filter-feeding organism with strong enrichment ability for heavy metals. Many countries have adopted shellfish such as mussels and oysters as indicator organisms for heavy metal pollution. The pollution of shellfish products not only affects their exports, but also directly affects the health of consumers. Therefore, the safety limit monitoring of heavy metals in shellfish culture water is necessary to ensure the safety of consumers to eat shellfish. Jeng et al. studied the content of metal elements in mussel aquatic products produced in the west coast of Taiwan. The FAAS method and the GFAAS method were used to determine Cu, Zn and Pb, Cd, Hg and As. The results showed that the content of Cu and Zn in the oysters in Xiangshan District of Taiwan increased year by year with the environmental pollution brought by industrial growth. The Cu content in the oysters collected from the Errenxi estuary increased by more than 60 times in 10 years. Kwoczek et al. used atomic absorption spectrometry to determine 15 essential metal elements and harmful metal elements in seafood such as shrimp, mussels and crabs. The edible part is separated from the shellfish, and after drying and microwave elimination, Cu, Zn, Fe, Mn, Co, Ni, Cr, Mg and Ca are determined by FAAS method, and Cd is determined by GFAAS method. Pb, Se and Hg were determined by the HGAAS method, and the metal element levels of the shellfish were compared with those of the salmon, squid, pork, beef, chicken, and eggs. Analysis of the weekly tolerable intake of heavy metals (PTWI) showed that Hg, Cd and Pb levels were not harmful to humans in all shellfish products tested. Strady et al. used GFAAS and ICP-MS to study Cd in oysters. By measuring the Cd content in seawater, algae and oyster tissues, it was found that the Cd pollution of oysters mainly comes from the direct pollution of seawater, while the pollution generated by the food chain only accounts for 1%. Zheng Wei et al. determined the contents of metal elements such as Cd, Cr, Pb, Ni, Cu and Zn in the tetragonal scorpion of Haizhou Bay pond in Lianyungang by atomic absorption spectrometry. Five tissues of the mantle, the axillary, the axe, the occipital muscle and the visceral mass were examined. The results showed that the visceral mass was the main organ for selective enrichment of heavy metals. The single factor index evaluation showed that the main heavy metal pollutants in five tissues were Ni, the pollution index was 0.87 (axe foot) -10.73 (visceral mass), followed by Pb and Zn, and Cd was only slightly polluted in the visceral mass. Contaminated by Cr and Cu. 4 Detection of heavy metals in beverages In recent years, with the emergence of a large number of new varieties, new flavors and beverages with new functions, consumers are increasingly demanding the quality and safety of beverages, and the detection of harmful metal elements has become an important content. The source of heavy metals in beverages is not only related to the type of raw materials used, but also to factors such as processing, packaging and origin. Grembecka et al. used the FAAS method to measure the content of 14 metal elements such as Ni, Cu, Cr, Cd and Pb in commercially available coffee. Factor analysis of the concentration data of all metal elements in the measured coffee samples showed that the metal content in the coffee showed a significant correlation; as shown in Figure 2, different types of coffee (such as ground coffee, instant coffee and coffee) The content of metal elements in the immersion liquid, etc. is different, which provides a basis for distinguishing coffee varieties. Wang Shuo et al analyzed the Cu content in the beverage. The sample was extracted under acidic conditions by sodium pyrrolidine dithioformate-sodium diethylaminodithioformate-methyl isobutyl ketone (APDC-DDTC-MIBK) system, and then the content of Cu element was determined by GFAAS method. The detection limit of the method was 0.265 μg/L, the linear range was 1.5-10μg/L, the correlation coefficient was 0.9993, the recoveries were 95.79%-100.74%, and the relative standard deviation was 3.13%-5.06%. This method provides a new way for the detection of heavy metals in carbonated beverages. The metal elements in the wine not only have an effect on its sensory flavor, especially whether the content of heavy metals such as Pb in wine meets safety standards and is related to the health of consumers. Moreno et al. used the GFAAS method to determine the content of Pb and Ni in 54 commercially available red wines, and determined the contents of elements such as Cu, Al and Fe by inductively coupled plasma atomic emission spectrometry (ICP-AES). Linear discriminant analysis (LDA) and probabilistic neural network (PNN) analysis were performed on the results, and the correct discrimination between metal content and wine varieties reached 90% and 95%. Guo Jinying et al. used the GFAAS method to analyze trace Pb in red wine. The determination conditions were optimized. The red wine was adjusted with 0.15mol/L nitric acid, the ammonium dihydrogen phosphate was used as the matrix modifier, the ashing temperature was 700 °C, and the atomization temperature was 1800 °C. The rapid analysis method of Pb in wine was established. The spiked recovery of this method was 98% and the relative standard deviation of the assay was 3%. Milk is an important drink in daily life, but it may contain heavy metals such as As, Pb, Hg and Cd in addition to elements such as calcium which are beneficial to the human body. Especially in the case of frequent dairy safety accidents in recent years, the heavy metal content in milk has become an important indicator for dairy product inspection. Qm Liqiang et al. determined the trace elements in milk by atomic absorption spectrometry, plasma emission spectrometry and atomic fluorescence spectrometry, and compared the differences in heavy metal content between domestic milk and Japanese imported milk. The results showed that the content of Cr, Pb and Cd in domestic milk was in line with the national standard, but higher than that in Japanese milk. Li Xun et al. performed a morphological analysis of inorganic arsenic in fresh milk by electrochemical hydride generation and atomic absorption spectroscopy. The results show that under the conditions of current 0.6A and 1A, As3+ and As5+ have a good linear relationship in the range of 0-40 (μg/L mass concentration; the detection limits of As3+ and As5+ are 0.3 μg/L and 0.6 respectively). Gg/L; sample recovery is 96%-104%. This method avoids the pre-reduction step of As5+, which not only shortens the analysis time, but also reduces the contamination of the sample. 5 Prospective Determination of Heavy Metals in Food by Atomic Absorption Spectrometry It has the advantages of sensitivity, high efficiency and accuracy. According to the type and concentration of the metal to be tested, it is necessary to select atomic absorption spectra such as graphite furnace, flame and hydride generation, and combine appropriate pretreatment methods, including digestion equipment and improver. The digestion reagents and digestion temperature directly affect the accuracy of the determination results. However, due to the wide variety of foods, the development of relevant standards and regulations requires a larger number of detection experiments and more advanced detection methods. It can be seen that there are many food inspections. Unknown areas to be explored. In order to more accurately and quickly determine the metal elements in the sample, atomic absorption spectroscopy is often associated with other detection methods.