Determination of nitrite in food by UV-1200 spectrophotometry - Master's thesis - Dissertation

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Determination of Nitrite in Food by Spectrophotometry

Spectrophotometric Determination of Nitrite in Foods Keywords: Spectrophotometry; Food Additives; Nitrite; Metric Instruments http://; UV-1300 Abstract: This article comprehensively analyzes Asia The mechanism of nitrate poisoning; the symptoms of nitrite poisoning; the treatment measures to be taken for nitrite poisoning and how to prevent nitrite poisoning. The content of nitrite was determined by spectrophotometric method using naphthylethylenediamine hydrochloride. The method has the characteristics of wide application, high sensitivity, good selectivity, high accuracy, low analysis cost, simple and rapid operation. Key words: nitrite; poisoning mechanism; cause of poisoning; naphthylamine hydrochloride; spectrophotometry nitrite, commonly known as "nitrate", is a class of nitrogen-containing compounds. Common nitrites are potassium nitrite and sodium nitrite. They are white or light yellow crystal or granular powder. They are slightly salty, soluble in water, and are mostly white crystals. Their density is greater than water. They are hard and very brittle. The appearance is very similar to salt. It is widely found in natural environments, especially in gaseous water, surface water and groundwater, as well as in animal and plant bodies and food. Nitrite can be used in printing and dyeing, bleaching and other industries, and is widely used as a rust inhibitor. It is a concrete admixture commonly used in the construction industry. In some foods such as bacon, sausage, etc., a small amount of nitrite is often added as a preservative and a coloring agent, which not only can prevent corrosion, but also make the color of the meat bright [1] . However, nitrite is a potential carcinogen, which can induce diseases such as human gastric cancer, liver cancer, and esophageal cancer. Excessive or long-term consumption can cause harm to human body and even death. Therefore, the harm of nitrite to humans is worthy of attention. Part I: Nitrite poisoning 1. Mechanism of nitrite poisoning: Nitrite is a strong oxidant, which combines with hemoglobin after entering the bloodstream, causing oxygen and hemoglobin to become methemoglobin, thereby losing oxygen carrying capacity and causing tissue hypoxia. A series of poisoning symptoms of hypoxia occur, which can cause death in severe cases. In addition, nitrite has an expanding effect on peripheral blood vessels. Nitrite food poisoning, also known as intestinal bruising, purpura, and purpura, refers to the poisoning of nitrite-containing plants. Nitrate in food is non-toxic, but under the influence of some bacteria, it is reduced to toxic nitrite. According to the American Academy of Sciences, in the past 70 years, about 1 million Americans have obtained malignant tumors because of the application of nitrate fertilizers to certain agricultural products. In China, such major nitrite poisoning incidents occur almost every year. In the domestic search for “nitrite”, as many as 1,150 information about nitrite poisoning appeared immediately! In the past month alone, two incidents occurred in Beijing and a narcotics poisoning occurred in Chongqing. A total of 47 people were poisoned and 2 died. In the past 16 years, the literature reported as many as 130 cases of nitrite poisoning [3] . 2. Causes of nitrite poisoning [4] 2.1 The causes of acute poisoning are divided into: the "industrial salt" of nitrite or nitrite is mistaken for consumption as salt, noodle, etc.; doping, making fake; poisoning; eating Pickled meat products with high nitrous acid and nitrite, kimchi and spoiled vegetables. In the past, the disease was caused by the substitution of vegetables for food, which is a typical food-borne nitrite poisoning. Example: Pickled meat products: On May 26, 1996, 114 trains from Urumqi occurred passenger food poisoning incidents between West Anhui and Tianshui. 87 people were poisoned and 2 people died. Tracing found that the spicy beef slices sold for the smugglers in West Anhui Station contained a large amount of sodium nitrite, and the content of sodium nitrite in the stomach of the deceased was 75.70 mg/kg [5] . Kimchi: Freshly marinated vegetables (wine pickles) contain a lot of nitrite and disappear after about 20 days of salting. [6] Deteriorated vegetables: fresh vegetables, rotten vegetables and cooked vegetables that have been stored for too long. At this time, the nitrate in the original dish is converted into nitrite by the action of nitrate reducing bacteria; 80% of the nitrates ingested by the human body are from vegetables, and when the edible vegetables (especially leafy vegetables) are excessive, a large amount of nitrate enters the intestines. Road, if the intestinal digestive function is not good, the bacteria in the intestine can reduce nitrate to nitrite; 2.2 chronic poisoning (including cancer) causes are: drinking bitter water with high nitrate or nitrite content Steamer water. In some areas, drinking water contains more nitrate. When the porridge or food is used in the water, and then placed in an unclean pot overnight, the nitrate is reduced to nitrite under the action of bacteria. Water, due to the evaporation of water, increases the concentration of nitrate in the water. After drinking, some of the nitrate can be reduced to nitrite in the human body, which will also cause harm to the human body; the milk product contains Bacillus subtilis, which can restore nitrate For nitrite. 3. Symptoms of nitrite poisoning After 10 minutes to 3 hours of oral nitrite, headache, dizziness, fatigue, chest tightness, shortness of breath, palpitations, nausea, vomiting, abdominal pain, diarrhea, lethargy or irritability, difficulty breathing due to hypoxia , the whole body skin, mucous membrane purpura (lip lips, tongue tip, fingertips bruising, severe conjunctiva, facial and body skin bruising) and other symptoms. In severe cases, loss of consciousness, coma, convulsions, incontinence, respiratory failure, and even death. Laboratory tests revealed a marked increase in methemoglobin levels in the blood. 4. Nitrite poisoning to prevent nitrite poisoning is completely preventable [7] , but first of all to improve people's awareness of toxic substances, it is strictly prohibited to mix nitrite and salt together; packaging or storage of nitrite The container should have a conscious target; it is forbidden to use nitrite excessively in the processing of meat products. For the main causes of poisoning, the following preventive measures can be taken: 4.1 Vegetables should be properly preserved to prevent decay, fasting rotten vegetables or spoiled pickles; when eating cabbage, it should be noted that peeling off several layers containing a lot of nitrates Vegetable leaves. In addition, people should pay attention to observe the appearance when purchasing vegetables. If the appearance of cucumber, potato and zucchini oozes yellow spots, it reflects high nitrate content. 4.2 The leftover cooked vegetables should not be stored at high temperature for a long time before eating; 4.3 Do not eat a lot of freshly marinated vegetables. When pickles, the salt should be put more, at least for more than 15 days before eating; but the best dish is the best. Eat immediately, can not be stored for too long, use fresh vegetables when pickles; 4.4 not eat a lot of leafy vegetables in a short time, or first use boiling water for 5 minutes, discard the soup and then cook; 4.5 nitrate and salt in meat products The amount of nitrate should be strictly in accordance with the national health standards, not more than; the bitter well water should not be used for porridge, especially not to store overnight; 4.6 to prevent the wrong use of nitrite as salt or alkali. Of course, it is very difficult to completely avoid nitrate intake. 5. Treatment of nitrite poisoning After acute nitrite poisoning, as long as it is treated correctly and quickly, it can usually heal quickly. The main treatments include: vomiting, gastric lavage and catharsis as soon as possible. The application of the antidote, methylene blue (Memlan), vitamin C has a positive effect on the elimination of methemoglobinemia. Critically ill patients can enter a certain amount of fresh blood, timely treatment of hypotension shock, correction of acidosis, oxygen and other symptomatic treatment. The following is a simple and quick way to check for nitrite poisoning: nitrite poisoning by denatured hemoglobin test: Take 3-5 ml of venous blood from the patient, the blood color is blue-violet. Centrifugal sedimentation, the plasma was pale yellow, indicating that blue-violet is caused by abnormal cells. Shake well and shake in oxygen or air for 15 minutes. If it returns to bright red, it means that the original blue-violet is caused by oxidation of methemoglobin. Through the above simple tests, basically a preliminary judgment can be made. Thus, the determination of nitrite content is a very important item in food safety testing. Limits for nitrite in some foods (in terms of NaNO) Table 1-1

Product name limit standard mg/kg salt (fine salt), milk powder ≤ 2 sausage (sausage) fragrant belly, pickles, Cantonese-style bacon ≤ 20 fresh meat, fresh fish, food ≤ 3 meat products, ham, enema ≤30 Vegetables≤4 Other canned meat, other preserved canned food ≤50 Infant formula milk powder, fresh eggs ≤5 Western-style cooking, smoked ham and canned food, Western-style ham canned ≤70
The second part: rapid determination of nitrite 1 using nitrite rapid detection tube method principle: according to the national standard GB/T 5009.33 speed test tube, compared with the standard color card quantitative. 1.1 Rapid detection of nitrite in salt and rapid identification of salt and nitrite: use a small spoon to take 1 teaspoon of salt in the bag, add it to the test tube, add distilled water or purified water to the 1ml mark, cover The solid portion is shaken, and after 10 minutes, compared with the standard color plate, the value on the color plate multiplied by 10 is the content of nitrite in the salt of mg/kg, (the national standard specifies the nitrite in the salt (salt salt) Limited hygiene standards should be ≤ 2 mg / kg). When the sample appears blood red and precipitates or fades quickly to yellow, it can be determined that the nitrite content is quite high, or the sample itself is nitrite. 1.2 Liquid sample detection: directly take 1ml of clarified liquid sample into the detection tube, cover the lid, shake the reagent, and compare with the standard color plate after 10 minutes to find the color gradation of the same color as the solution in the detection tube. The value on the order is the nitrite content of the sample in mg/L (as NaNO2). (The milk and soy milk can also be directly tested, the result should not exceed 0.25mg / L, the color of the liquid sample can be added to some activated carbon decolorization filter after measurement). 1.3 Solid or semi-solid sample detection: Take 1.0g or 1.0ml to 10ml colorimetric tube of pulverized sample, add distilled water or deionized water (pure water) to the scale, shake it thoroughly, place it, take the supernatant (or Add 1.0 ml of the supernatant obtained by filtration or centrifugation to the test tube, cover the lid, shake the reagent, and compare it with the standard color plate after 10 minutes. The value on the color plate multiplied by 10 is the nitrous acid in the sample. The salt content is mg/kg, L (calculated as NaNO2). If the test result exceeds the highest value on the swatch, it can be quantitatively diluted and measured, and multiplied by the dilution factor (for example, take 1.0mL from the 10ml colorimetric tube and transfer it to another 10ml colorimetric tube, add water to The scale is taken from 1.0 mL and added to the test tube. The test result is multiplied by 100 (double dilution) to determine the content of nitrite in the sample. Part III: Determination of nitrite content in meat products - naphthyl hydrochloride Diamine photometric method [8] The nitrite in food is separated and diazotized with sodium p-aminobenzenesulfonate, and then coupled with naphthylethylenediamine hydrochloride to form red dye, its red shade and nitrite content. In proportion, the reaction formula is as follows 1. Reagents and instruments: borax solution ferrous solution zinc acetate solution p-aminobenzenesulfonic acid solution naphthalene diethylamine solution sodium nitrite solution UV-1500 spectrophotometer meat grinder electronic balance electric furnace suction filter bottle capacity bottle with match Color tube cuvette 2. Measurement procedure: 2.1 Sample treatment: The ham sausage was ground with a meat grinder, and 5 g was weighed into a beaker, and 12.5 ml of a saturated solution of borax was added and stirred well. The contents of the beaker were washed into a 500 ml volumetric flask with 300 ml of hot water of about 70, and heated in a boiling water bath for 15 minutes. After taking out, it was cooled to room temperature. Then, 5 ml of a zinc acetate solution was added dropwise while gently shaking to precipitate a protein. Shake well, add 5ml ferrous solution to remove the remaining zinc acetate. After completely cooling to room temperature, add water to the scribe line, shake well and let stand for 30min. The upper layer of fat was removed and the solution was filtered and an intermediate clear solution was taken for determination. 2.2 Determination: Accurately draw 40ml of filtrate into a 50 mL plugged colorimetric tube, and take 6 other colorimetric tubes, add 0.0 0.20 0.60.1.00 2.00 2.50ml sodium nitrite solution, add 2 mL 4g / L pair Aminobenzenesulfonic acid solution, mix. After standing for 5 min, add 1 mL of 2 g/L naphthylethylenediamine hydrochloride solution, add water to the mark, and let stand for 15 min. The absorbance was measured with a 1 cm cuvette at a wavelength of 540 nm with a zero tube zero point. The standard curve was drawn by linear regression for comparison. 2.3 Experimental data and processing: Absorbance values ​​measured with a 1 cm cuvette at a wavelength of 540 nm. Table 1-2 Sodium nitrite standard use solution volume (ml) 0.0 0.20 0.60 1.00 2.00 2.50 absorbance 0.015 0.040 0.061 0.095 0.165 0.215
Sample measurement results Table 1-3 Number of determinations Sample mass Total volume of sample Determination Volumetric absorbance 1 5g 500ml 40ml 0.046 2 5g 500ml 40ml 0.044 3 5g 500ml 40ml 0.047
Calculation results Table 1-4 Sodium nitrite standard use liquid volume (ml) 0.0 0.20 0.60 1.00 2.00 2.50 Sodium nitrite standard use liquid quality (ug) 0.0 1.00 3.00 5.00 10.00 12.50
0.0154x+0.0179=0.0457 solution x=1.805 ie m 1 =1.805ug m 1 sodium nitrite (mg∕kg) = ———————————— x 1000 mxv 2 /v 1 x 10001.805 = ———————————— x 1000 5 x 40∕500 x 1000 =4.51mg/kg Where: m 1 : The mass of sodium nitrite in the sample solution. Ug /kgm : the mass of the sample gv 1 : the total volume of the sample mlv 2 : the volume of the sample solution ml is obtained from Table 1-1. The content of nitrite in the ham is in accordance with the limit standard, and can be used within the range of safe use. .

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