Determination of metal ion content in animal feed by atomic absorption spectrophotometer - Master's thesis - Dissertation

Determination of metal ion content in animal feed by atomic absorption spectrophotometer

Key words: atomic absorption spectrophotometer; animal feed; heavy metal; US analysis ; 1 instrument AA1800 atomic absorption spectrophotometer 1.1 AA1800 atomic absorption spectrophotometer with air-acetylene flame and a calibration device or The background absorption device is measured. 1.2坩埚: Platinum, quartz or porcelain, without potassium or sodium, the inner layer is smooth and not corroded, the upper diameter is 4cm-6cm, the lower diameter is 2cm-2.5cm, the height is about 5cm, and it is boiled with hydrochloric acid (2.3) before use. . 1.3 Hard glassware: boil with hydrochloric acid (2.3) before use and rinse with water. 1.4 electric heating plate or gas furnace. 1.5 water bath. 1.6 muffle furnace: temperature can be controlled at 550 ° C ± 15 ° C 1.7 analytical balance, weighing accuracy to 0.1 mg 1.8 Determination of Ca, Cu, Fe, K, Mg, Mn, Na, Zn used in hollow cathode lamps. 1.9 Quantitative filter paper. 2 Reagents and solutions Unless otherwise specified, only analytically pure reagents are used. 2.1 Water, should comply with GB/T 6682 three-level water. 2.2 Hydrochloric acid: c (HCl) = 12 mol / L (ρ = 1.19 g / mL). 2.3 hydrochloric acid solution: c (HCl) = 6 mol / L. 2.4 hydrochloric acid solution: c (HCl) = 0.6 mol / L. 2.5 cerium nitrate solution: Dissolve 133g of La(NO3).6H20 in 1L of water. If the prepared solution has the same strontium content, other strontium salts can be used. 2.6 Barium chloride solution: Dissolve 100 g of cyanide (CsCl) in 1 L of water. If the prepared solution has the same content of strontium, you can use other standard solutions of bismuth salt 2.7 Cu, Fe, Mn, Zn: Take 100mL of water, 125mL of hydrochloric acid (2.2) in a 1L volumetric flask, mix and weigh the following reagents: - 392.9 mg of copper sulfate (CUS04·5H20); - 702.2 mg of ammonium ferrous sulfate [(NH4)2SO4·FeS04·6H20]; - 307.7 mg of manganese sulfate (MnS04·H2O); - 439.8 mg of zinc sulfate (ZnS04·7H20); The above reagent was added to a volumetric flask, dissolved in water and made up to volume. The content of Cu, Fe, Mn and Zn in this stock solution is 100ug/mL. 2.8 Cu, Fe, Mn, Zn standard solution: Take 20.0mL of stock solution and add 100mL volumetric flask, dilute to volume with water. The content of Cu, Fe, Mn, and Zn in the standard solution was 20 ug/mL. The standard solution was prepared on the same day. 2.9 Standard stock solution of Ca, K, Mg, Na: Weigh the following reagents: - 1.907g potassium chloride (KCl); - 2.028g magnesium sulfate (MgS04 · 7H20); - 2.542g sodium chloride (NaCl) The reagent is added to a 1L volumetric flask. Weigh 2.497g of calcium carbonate (CaC03) into a beaker, add 50mL of hydrochloric acid (2.3), heat on a hot plate for 5min, and after cooling, transfer the solution to a volumetric flask containing K, Mg, Na salt, with hydrochloric acid ( 2.4) Constant volume. The content of Ca, K, and Na in the stock solution was 1 mg/mL, and the content of Mg was 200 ug/mL. 2.10 Standard solution of Ca, K, Mg, Na: Take 25.0mL of stock solution (2.9) and add 250mL volumetric flask, and make up to volume with hydrochloric acid (2.4). The content of Ca, K, and Na in the standard solution is 100 ug/mL, and the content of Mg is 20 ug/mL. The prepared standard solution is stored in a polyhexene bottle and can be used within one week. 2.11 镧 / 铯 blank solution: Take 5mL lanthanum nitrate (2.5) solution, 5mL cesium chloride solution (2.6) and 5mL hydrochloric acid (2.3) into a 100mL volumetric flask, and make up to volume with water. 3 Analysis step 3.1 Detection of the presence of organic matter Some samples were taken on a flat spoon to heat on the flame. If the sample melts without smoke, there is no organic matter. If the sample color changes and does not melt, the sample contains organic matter. 3.2 Samples According to the estimated content, weigh 1g-5g of prepared sample, accurate to 1mg, put into the crucible. If the sample contains organic matter, operate as in 2.3. If the sample does not contain organic matter, follow 2.4. 3.3 Dry Ashing Place the crucible on a hot plate or gas stove until the sample is completely charred (to avoid burning the sample). The crucible was transferred to a muffle furnace preheated at 550 ° C for 15 min for 3 h, and after cooling, the contents of the crucible were infiltrated with 2 mL of water. If there are many carbon particles, the crucible is dried on a water bath, then placed in a muffle furnace for 2 h, allowed to cool and then added with 2 mL of water. 3.4 Dissolve 10 ml of hydrochloric acid (2.3), start slowly adding one drop and one drop, while rotating, until it does not bubble (may produce carbon dioxide), then add it quickly, turn the crucible and heat until the contents are almost dry. Always avoid spilling contents during heating. After dissolving the residue by heating with 5 mL of hydrochloric acid (2.3), the sample solution was transferred to a 50 mL volumetric flask with about 5 mL of water. After cooling, it was then diluted to volume with water and filtered through a filter paper. 3.5 Blank solution Each time, the blank solution was prepared according to the procedures of 3.2, 3.3 and 3.4. 3.6 Determination of copper, iron, manganese and zinc 3.6.1 Measurement conditions The instrument conditions of the atomic absorption spectrophotometer are adjusted according to the requirements of the instrument, so that the sensitivity of the instrument in the air-acetylene flame measurement is optimal. The measurement wavelengths of Cu, Fe, Mn, and Zn are as follows: Cu: 324.8 nm; Fe: 248.3 nm; Mn: 279.5 nm; Zn: 213.8 nm, 3.6.2 Calibration curve preparation Standard solution (2.8) is diluted with hydrochloric acid (2.4), A suitable set of calibration solutions is prepared. The absorbance of hydrochloric acid (2.4) was measured, and the absorbance of the solution was corrected. The absorbance of the calibration solution was subtracted from the absorbance of hydrochloric acid (2.4) to obtain a calibration curve for the absorbance correction values ​​for Cu, Fe, Mn, and Zn, respectively. 3.6.3 Measurement of sample solution Under the same conditions, the absorbance of the sample solution (3.4) and the blank solution (3.5) was measured, and the absorbance of the sample solution was subtracted from the absorbance of the blank solution. Calculate the content according to Chapter 9. If necessary, dilute the sample solution and the blank solution with a hydrochloric acid solution (2.4) so ​​that the absorbance is within the linear range of the calibration curve. 3.7 Determination of calcium, magnesium, potassium and sodium 3.7.1 Measurement conditions The instrumental conditions of the atomic absorption spectrophotometer are adjusted according to the requirements of the instrument, so that the sensitivity of the instrument in the air-acetylene flame measurement is optimal. The measurement wavelengths of Ca, K, Mg, and Na are as follows: Ca: 422.6 nm; K: 766.5 nm; Mg: 285.2 nm; Na: 589.6 nm. 3.7.2 Calibration curve Preparation Standard dilution solution (2.10) with water, standard dilution per 100 mL A suitable set of calibration solutions was prepared by adding 5 mL of cerium nitrate solution (2.5), 5 mL of cerium chloride solution (2.6) and 5 mL of hydrochloric acid (2.3). The absorbance of the 镧/铯 blank solution (2.11) was measured. The absorbance of the calibration solution was measured and the absorbance of the 镧/铯 blank solution (2.11) was subtracted. Correction curves were plotted for the Ca, K, Mg, and Na contents with corrected absorbance. 3.7.3 Measurement of sample solution Quantitatively dilute the sample solution (3.4) and the blank solution (3.5) with water, add 5 mL of cerium nitrate (2.5), 5 mL of cerium chloride (2.6) and 5 mL of hydrochloric acid per 100 mL of the diluted solution. (2.3), under the same conditions, measure the absorbance of the sample solution and the blank solution. The absorbance of the sample solution was subtracted from the absorbance of the blank solution. If necessary, the sample solution and the blank solution were diluted with a ruthenium/iridium blank solution (2.11) so that the absorbance was within the linear range of the calibration curve. 4 The results show that the contents of Ca, Cu, Fe, Mn, Mg, K, Na, and Zn are calculated from the calibration curve, the mass of the sample, and the dilution. Revised according to Table 1 and expressed in mg/kg or g/kg. Table 1 results of the revised contract