Determination of Cu, Mn, Cd and Pb in edible fungi by AA-1800 flame atomic absorption spectrometry - Master's thesis - Dissertation

Determination of Heavy Metals in Cu, Mn, Cd and Pb in Edible Fungi by AA-1800 Flame Atomic Absorption Spectrometry

Keywords: flame

Atomic absorption spectrometer

Cu, Mn, Cd, Pb in edible fungi; ; AA-1800C fresh shiitake mushroom, oyster mushroom sample washed, dried and ground, ashed by high temperature sintering furnace, and finally 5% dilute nitric acid Dissolved, the heavy metal elements Cu, Mn, Cd, Pb were determined by flame atomic absorption method. Results: The content of Cu and Cd in Pleurotus ostreatus and Lentinus edodes exceeded the national standard. Pb was not detected. The recoveries were 98% ~ 104%. , RSD is 0.1% ~ 0.9%. The method is simple in operation and high in sensitivity. It is found through experiments that the enrichment of heavy metals by different edible fungi is quite different, and the enrichment of heavy metals in different parts of the same edible fungi is completely different. China is one of the countries with the most abundant edible fungi. As a well-known food supplement, edible fungi are rich in protein, fat, vitamins and carbohydrates and are low-calorie, high-protein foods. It is rich in various minerals, vitamins, dietary fiber and free amino acids, trehalose, mannitol sugar and other nutrients. It is delicious and easy to eat. Modern medicine has proved that edible fungi also have good medicinal value, and it has the functions of enhancing the body's immune function, anti-tumor and blood fat reduction, and is a resource with good development prospects. However, due to the growing environment, the problem of heavy metals is particularly important. In recent years, with the massive discharge of industrial and urban pollutants, and the irrational use of clothing and chemical fertilizers, environmental heavy metal pollution has become increasingly serious, and heavy metal pollution in edible fungi has received increasing attention, such as in Beijing, Fujian and Chongqing. The investigation of the heavy metal content of edible fungi found that the content of heavy metals such as As, Pb and Cd in some samples exceeded the standard. From the data, it is reported that Mianyang has little research on the heavy metal content of edible fungi. Therefore, the content of heavy metal elements in Cu, Mn, Pb and Cd of edible mushrooms such as mushrooms and oyster mushrooms in Mianyang is determined, which provides a basis for people to choose edible fungi. . 1 Experimental part 1.1 Experimental materials, reagents and instruments 1. 1. 1 experimental materials and reagents Pleurotus ostreatus, mushrooms, Sichuan Mianyang; cadmium powder; copper powder; manganese powder; lead powder (all GR, content 99.9%), Tianjin Komio Technology Co., Ltd.; other chemical reagents (all AR), Chengdu Kelon Chemical Reagent Factory. 1.1. 2 experimental instrument AA-1800C flame atomic absorption spectrophotometer (American company); constant temperature drying oven (101 -2A type); electronic analytical balance; high temperature sintering furnace (SX2. 1.2 experimental method This experiment is to use flame atom Determination by absorption method. 1.3 Sample treatment 1.3.1 Sample pretreatment The sample is first washed with tap water and then washed with distilled water to remove impurities and metal ions attached to the surface of the sample. The water is then drained and placed in an oven (100 ~ 110). ^) Dry to constant weight, finally grind the sample with a pulverizer, and then pass through a 100 mesh nylon sieve, put it in a reagent dispensing bag, and put it into a desiccator for use. 1.3.2 Sample ashing, constant volume will sample 4 parts were accurately weighed and placed in a 25 mL porcelain crucible, placed in a high-temperature sintering furnace for 8 h ashing at 550 to remove organic matter, and the ashing was placed in a desiccator to be cooled and weighed. The ash weight is the weight of the crucible after cooling minus the weight of the crucible. All the weighing during the ashing process is accurate to 0.1 mg. Remove the beaker, transfer it to a 100.00 mL volumetric flask, dilute to volume with distillation, filter, and work according to the instrument. Condition Preparation of 1.4 standard solution 1.4.1 Preparation of standard stock solution Prepare standard stock solution of lead, manganese, copper and cadmium. Preparation of lead standard stock solution (1. 000 mg/mL): accurately weigh metal lead powder (Excellent grade, content 99.9% or more) 0. 500 0 g placed in a 25 mL beaker, add 10 mL of (1+1) hydrochloric acid, dissolve by heating, cool and transfer to a 500 mL volumetric flask, dilute with double distilled water Shake well and store in polyethylene bottle. Preparation of copper standard stock solution (1.000 mg/mL): Accurately weigh metal copper powder (excellent grade, content 99.9% or more) 0.500 0 g in 25 mL beaker Add 10 mL of (1+1) nitric acid, dissolve by heating, transfer to a 500 mL volumetric flask after cooling, dilute to the mark with double distilled water, shake well, and store in a polyethylene bottle. Standard stock solution of manganese (1. 000 Preparation of mg/mL): accurately weigh the manganese metal powder (excellent grade, content 99.9% or more) 0. 500 0 g in a 25 mL beaker, add a small amount of concentrated hydrochloric acid, and put it on a water bath to evaporate, then Add 5 mL of concentrated hydrochloric acid, then evaporate to dryness. Finally, add a few drops of concentrated hydrochloric acid and H:0 to heat and dissolve. After cooling, transfer to 500 m. L volumetric flask, diluted with double distilled water, shaken, stored in a polyethylene bottle. Preparation of cadmium standard stock solution (1. 000 mg / mL): Accurately weigh metal cadmium powder (excellent grade, content 99 9% or more) 0. 500 0 g in a 25 mL beaker, add 10 mL of (1+1) hydrochloric acid, dissolve by heating, cool and transfer to a 500 mL volumetric flask, dilute with double distilled water, shake well, store in In the polyethylene bottle. 1.4.2 Standard solution preparation of manganese standard solution: accurately transfer 10 μg / mL of standard stock solution 1.00 mL, 2.50 mL, 3. 50 mL, 5. 00 mL, 6. 50 mL In a 100 mL colorimetric tube, dilute with secondary distilled water to prepare a standard solution of 0.10 μg/mL, 0.25 μg/mL, 0.35 μg/mL, 0.50 μg/mL, and 0.65 μg/mL. Shake well and test. Preparation of standard copper solution: accurately transfer 10 μg/mL of standard stock solution 0. 50 mL, 1. 00 mL, 1.50 mL, 2. 00 mL, 2. 50 mL in a 25 mL colorimetric tube, The volume of the second distilled water was adjusted to 0.20 μg/mL, 0.40 μg/mL, 0.60 μg/mL, 0.80 μg/mL, and 1.00 μg/mL. Shake well and test. Preparation of standard solution of cadmium: accurately transfer 10 μg/mL of standard stock solution 0. 50 mL, 1. 00 mL, 1.50 mL, 2.00 mL, 2. 50 mL in 25 mL colorimetric tube, use twice The volume of distilled water was adjusted to 0.20 μg/mL, 0.40 μg/mL, 0.60 μg/mL, 0.80 μg/mL, and 1.00 μg/mL. Shake well and test. The formulation of Cu, Mn, Cd and Pb standard solutions is shown in Table 1. Table 1: Cu, Mn, Cd, Pb series standard solution 1.4.3 Standard curve drawing The atomic absorption spectrophotometer is used to determine the absorbance of the series standard solution according to the working conditions of the instrument, and then the absorbance is plotted against the concentration to obtain the linear equation and the correlation coefficient. Table 2. Table 2 Linear relationship of Element Table 2. Linear relationship of Element 1.4.4 Instrument working conditions Cu, Mn, Cd, Pb are determined by air-acetylene flame atomic absorption spectrophotometry, air compressor pressure is adjusted to 0.2 MP, the content of each element is measured by instrument Condition optimization, the selection of the best conditions are shown in Table 3. Table 3 Instrument best working conditions Table 3 Working conditions of the Instrument 1.4.5 Sample determination Sample preparation See 1.3 sample processing method, adjust the instrumental conditions of the corresponding elements, directly determine the different parts of Pleurotus ostreatus and mushroom by flame atomic absorption spectrometry , Mn, Cd, Pb content. 2 Results and discussion 2.1 Selection of sample processing methods Sample processing methods generally have dry digestion and wet digestion, wet digestion using nitric acid-perchloric acid in a ratio of 4:1, and the sample is digested at a certain temperature. , a process in which an acid vaporizes organic matter into two gasified carbon, water, and other volatile products, leaving inorganic acids and salts. The dry digestion is a process in which a sample is subjected to high-temperature ashing to remove organic matter by using a high-temperature sintering furnace. Although the wet digestion is fast, impurities are introduced by adding a reagent, which affects the measurement result. Therefore, the sample processing uses a dry digestion method. This method does not add a reagent, and both the macromolecular organic matter is efficiently and completely decomposed, and the introduction of impurities from the outside is avoided, and the method is simple. 2.2 Selection of ashing temperature The high-temperature ashing method is effective for destroying organic organisms in samples such as biochemical, environmental and food. Samples are typically dried 100 to 105 to remove moisture or volatiles. The ashing temperature and time are required to be selected. Food sample analysis generally controls the ashing temperature from 450 to 550 for dry ashing. If the ashing temperature is higher than 550, the sample will be lost, the ashing temperature should not be too low, and the ashing will be incomplete when the temperature is low. The residual small carbon particles are easy to adsorb metal elements, and it is difficult to dissolve with dilute acid, resulting in low measurement results. . The experiment firstly warmed the sample to 100 ^ in 30 min, then rose to 300 in 1 h, and maintained the temperature for 8 h. The results showed that under the experimental conditions, the ashing was incomplete and the residue was difficult to dissolve with dilute acid. . After repeated trials, the sample was heated to 100 in 30 min, then raised to 300 in 1 h, heated to 550 ^ in 2 h and maintained at this temperature for 8 h, under which conditions the ashing was complete. 2.3 The standard curve and the interference of each element adopt the standard curve method. In order to examine the mutual interference of each element, the standard curve and the standard addition curve of each element to be tested were respectively made, and the two curves were found to be parallel, and the results were consistent. It is shown that under the measurement conditions, the elements do not interfere with each other within the sample content, and each element can be measured in the same solution. 2.4 Recovery and precision The recovery of each element was determined by standard addition method, and 1 mL of a standard solution of 100 μg/mL was added to each 20 mL sample. Equivalent to the concentration increase of 5μgmL, measured in parallel 5 times, the experimental average recovery was 98%?104%, RSD was 0.1%?0.9%, indicating that the method is accurate and reliable, the experimental results are shown in Table 4. Table 4 Determination of recovery rate 2.5 Sample measurement results and over-standard conditions According to the working conditions of Table 3, the absorbance values ​​of four elements in the samples of Pleurotus ostreatus, Lentinus edodes and their different parts were determined and quantified by standard curve method. The results are shown in Table 5. . Table 5 Sample analysis results Figure 1 Element content histogram Fig. 1 Histogram element content The national safety range of heavy metal content of fresh mushrooms is shown in Table 6. Table 6 National safety standards According to the relevant national standards of Table 6, from the results of Table 5, in general, the content of heavy metals in the two common edible fungi is Mn>Cu>Cd>Pb, of which Cu and Cd are higher than National standard. The maximum content of manganese is 33.040 1 μg/g. Although there is no hygienic limit standard, it is still worth noting. Little lead was detected in fresh oyster mushrooms and mushrooms. 2.6 Enrichment of heavy metals by edible fungi As can be seen from Figure 1, the same heavy metal has a large difference in the content of different edible fungi. For example, the content of Cu and Mn in shiitake mushrooms is higher than that of Pleurotus ostreatus. In addition, the content of different heavy metals in the same edible mushroom is also different. The results show that the content of heavy metals is closely related to the varieties of edible fungi, and the reason may be related to the different ability of edible fungi to different heavy metals. In addition, this experiment also found that the heavy metal content of different parts of the same edible fungus is also different. For example, the content of Cu and Mn in the mushroom crown is slightly higher than that of the mushroom root. It indicates that the different parts of the same edible fungi have different degrees of absorption and enrichment of heavy metal elements. 3 Conclusion The contents of four heavy metal elements such as Pb, Cu, Mn and Cd in Pleurotus ostreatus and Lentinus edodes were determined by flame atomic absorption spectrometry. The results show that

Flame atomic absorption spectrometry

The method for measuring heavy metal content is simple and precise. It has been determined that Cu and Cd in oyster mushrooms and shiitake mushrooms are beyond the national food safety range, and environmental pollution may have certain effects. The two edible fungi have a good enrichment effect on heavy metals such as copper and cadmium, so it is necessary to prevent the pollution of heavy metals such as copper and cadmium in production. However, almost no lead residue was detected in oyster mushrooms and shiitake mushrooms, indicating that the lead residues in both samples were low.