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GB/T 13883-2023 English PDF (GB/T 13883-2008, GB/T 13883-1992)

GB/T 13883-2023_English: PDF (GB/T13883-2023)
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GB/T 13883-2023English230 Add to Cart 0--9 seconds. Auto-delivery Determination of selenium in feeds Valid GB/T 13883-2023
GB/T 13883-2008English85 Add to Cart 0--9 seconds. Auto-delivery Determination of selenium in feeds Obsolete GB/T 13883-2008
GB/T 13883-1992English199 Add to Cart 2 days [Need to translate] Method for the determination of selenium in feedstuffs. (DAN) fluorometrt Obsolete GB/T 13883-1992


BASIC DATA
Standard ID GB/T 13883-2023 (GB/T13883-2023)
Description (Translated English) Determination of selenium in feeds
Sector / Industry National Standard (Recommended)
Classification of Chinese Standard B46
Classification of International Standard 65.120
Word Count Estimation 14,140
Date of Issue 2023-08-06
Date of Implementation 2024-03-01
Older Standard (superseded by this standard) GB/T 13883-2008
Drafting Organization National Food Wuhan Scientific Research and Design Institute Co., Ltd., Changsha Xingjia Bioengineering Co., Ltd., Shandong New Hope Liuhe Group Co., Ltd., Yibin University
Administrative Organization National Feed Industry Standardization Technical Committee (SAC/TC 76)
Proposing organization National Feed Industry Standardization Technical Committee (SAC/TC 76)
Issuing agency(ies) State Administration for Market Regulation, National Standardization Administration

BASIC DATA
Standard ID GB/T 13883-2008 (GB/T13883-2008)
Description (Translated English) Determination of selenium in feeds
Sector / Industry National Standard (Recommended)
Classification of Chinese Standard B46
Classification of International Standard 65.120
Word Count Estimation 7,789
Date of Issue 2008-08-01
Date of Implementation 2008-11-01
Older Standard (superseded by this standard) GB/T 13883-1992
Quoted Standard GB/T 6682; GB/T 14699.1; GB/T 20195
Drafting Organization China Feed Industry Association
Administrative Organization National Standardization Technical Committee Feed Industry
Regulation (derived from) National Standard Approval Announcement 2008 No.12 (Total No.125)
Proposing organization National Feed Industry Standardization Technical Committee
Issuing agency(ies) Administration of Quality Supervision, Inspection and Quarantine of People's Republic of China; Standardization Administration of China
Summary This standard specifies the feed, concentrated feed and premix feed determination of selenium. This standard applies to feed, determination of feed and premix feed selenium concentration. Hydride generation atomic fluorescence spectrometry for quantitative limit 0. 01 mg/kg, fluorescence quantitative limit of 0. 02 mg/kg.

BASIC DATA
Standard ID GB/T 13883-1992 (GB/T13883-1992)
Description (Translated English) Method for the determination of selenium in feedstuffs. (DAN) fluorometrt
Sector / Industry National Standard (Recommended)
Classification of Chinese Standard B46
Classification of International Standard 65.12
Word Count Estimation 5,553
Date of Issue 1992/11/24
Date of Implementation 1993/6/1
Regulation (derived from) Announcement of Newly Approved National Standards No. 2008 (No. 125 overall) 12
Proposing organization People Republic of China Ministry of Commerce, Ministry of Agriculture
Issuing agency(ies) State Bureau of Technical Supervision


GB/T 13883-2023 GB NATIONAL STANDARD OF THE PEOPLE’S REPUBLIC OF CHINA ICS 65.120 CCS B 46 Replacing GB/T 13883-2008 Determination of selenium in feeds ISSUED ON: AUGUST 06, 2023 IMPLEMENTED ON: MARCH 01, 2024 Issued by: State Administration for Market Regulation; Standardization Administration of the People's Republic of China. Table of Contents Foreword ... 3 1 Scope ... 4 2 Normative references ... 4 3 Terms and definitions ... 4 4 Hydride generation-atomic fluorescence spectrometry (arbitration method) ... 4 5 Fluorescence spectrophotometry ... 9 6 Inductively coupled plasma mass spectrometry ... 13 Annex A (informative) Reference conditions for microwave digestion ... 18 Determination of selenium in feeds 1 Scope This document describes the determination of selenium in feeds by hydride generation- atomic fluorescence spectrometry, fluorescence spectrophotometry and inductively coupled plasma-mass spectrometry. In this document, hydride generation-atomic fluorescence spectrometry and fluorescence spectrophotometry are applicable to the determination of selenium in compound feed, concentrated feed, concentrate supplement, additive premix feed and feed raw materials. Inductively coupled plasma mass spectrometry is applicable to the determination of selenium in compound feed, concentrated feed, concentrate supplement and feed raw materials (except mineral feed raw materials). When the sample size is 1 g and the fixed volume is 50 mL, the detection limit of hydride generation-atomic fluorescence spectrometry and fluorescence spectrophotometry is 0.01 mg/kg and the quantification limit is 0.02 mg/kg. When the sample size is 0.5 g and the fixed volume is 50 mL, the detection limit of inductively coupled plasma mass spectrometry is 0.01 mg/kg and the quantification limit is 0.02 mg/kg. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. GB/T 6682, Water for analytical laboratory use - Specification and test methods GB/T 20195, Animal feed - Preparation of test samples 3 Terms and definitions There are no terms or definitions that require definition in this document. 4 Hydride generation-atomic fluorescence spectrometry (arbitration method) 4.1 Principle After the specimen is digested with acid, the selenium in the specimen digestion solution is reduced to tetravalent selenium in the hydrochloric acid medium. Potassium borohydride is used as a reducing agent to reduce tetravalent selenium to hydrogen selenide in the hydrochloric acid medium. It is carried into the atomizer by the carrier gas for atomization. Under the irradiation of the selenium hollow cathode lamp, the ground state selenium atoms are excited to a high energy state. When deactivated and returned to the ground state, fluorescence of a characteristic wavelength is emitted. Its fluorescence intensity is proportional to the selenium content and is quantitatively compared with the standard series. 4.2 Reagents or materials Warning -- All strong acids shall be handled with caution. Dilution and use shall be carried out in a fume hood. When using perchloric acid, be careful not to burn it dry. Be careful of explosion. Unless otherwise specified, only analytically pure reagents are used. 4.2.1 Water: GB/T 6682, Grade II. 4.2.2 Nitric acid: guaranteed reagent. 4.2.3 Perchloric acid: guaranteed reagent. 4.2.4 Hydrochloric acid: guaranteed reagent. 4.2.5 Sodium hydroxide: guaranteed reagent. 4.2.6 Hydrogen peroxide. 4.2.7 Potassium borohydride: guaranteed reagent. 4.2.8 Mixed acid solution: Measure 400 mL of nitric acid (4.2.2) and mix with 100 mL of perchloric acid (4.2.3). 4.2.9 Hydrochloric acid solution I: Measure 100 mL of hydrochloric acid (4.2.4) and mix with 100 mL of water. 4.2.10 Hydrochloric acid solution II: Pipette 5 mL of hydrochloric acid (4.2.4) and mix with 95 mL of water. 4.2.11 Sodium hydroxide solution (5 g/L): Weigh 5 g of sodium hydroxide. Dissolve it in water. Set volume to 1000 mL. Mix well. 4.2.12 Potassium borohydride solution (20 g/L): Weigh 20 g of potassium borohydride. Dissolve it in 1000 mL of sodium hydroxide solution (4.2.11). Mix well. 4.2.13 Potassium ferrocyanide solution (200 g/L): Weigh 20 g of potassium ferrocyanide. Dissolve it in 100 mL of water. Mix well. to an accuracy of 0.0001 g. Place in a 100 mL tall beaker. Add 15 mL of mixed acid solution (4.2.8) (10 mL of additive premix feed) and a few glass beads. Cover with a watch glass. Leave for more than 12 h. Place on a thermostatically adjustable hot plate and gradually heat [if the solution becomes darker during heating, remove it. After cooling to room temperature, add 5 mL of mixed acid solution (4.2.8). Continue heating]. When a large amount of white smoke is produced on the upper layer of the solution and the remaining solution volume is about 2 mL, remove it and cool to room temperature. Add 5 mL of hydrochloric acid solution I (4.2.9). Place on a thermostatically adjustable electric stove and heat until smoking. The remaining volume is about 2 mL. Remove it. Cool to room temperature. Transfer to a 50 mL volumetric flask with water. Add 8 mL of hydrochloric acid (4.2.4) and 2 mL of potassium ferrocyanide solution (4.2.13). Set to the volume with water. Mix well and use this as the specimen solution. Perform a blank test at the same time. 4.5.1.2 Microwave digestion Perform two tests in parallel. Weigh 0.5 g (accurate to 0.000l g) of the specimen into a polytetrafluoroethylene inner tank. Add 8 mL of nitric acid (4.2.2). Soak for 10 min. Then add 2 mL of hydrogen peroxide (4.2.6). Let stand for more than 2 h. Cover the safety valve. Install the protective cover. Place the digestion tank into the microwave digestion instrument. Set the microwave digestion conditions (see Annex A) and digest the sample. After the digestion is completed, open the tank cover to vent after cooling to room temperature. Rinse the inner cover with a small amount of water. Add the washing liquid to the tank. Place it on an adjustable temperature electric heating plate. Continue heating at 150℃ until the residual volume is about 2 mL. Remove. Cool. Add 5 mL of hydrochloric acid solution I (4.2.9). Continue heating until the residual volume is about 2 mL. Remove. Cool to room temperature. Transfer the digestion solution to a 25 mL volumetric flask. Add a small amount of water to wash the digestion tank 4~6 times. Add the washing solution to a volumetric flask. Add 4 mL of hydrochloric acid (4.2.4) and 1 mL of potassium ferrocyanide solution (4.2.13). Set to the volume with water. Mix well and use as the specimen solution. Perform a blank test at the same time. 4.5.2 Preparation of standard series solutions Accurately pipette 0 mL, 0.2 mL, 0.5 mL, 2 mL, 5 mL, 10 mL, 20 mL of selenium standard intermediate solution II (4.2.16). Place them in 50 mL volumetric flasks, respectively. Add water to 30 mL. Add 8 mL of hydrochloric acid (4.2.4) and 2 mL of potassium ferrocyanide solution (4.2.13). Dilute to the mark with water. Mix well. Prepare a series of selenium standard solutions with mass concentrations of 0 ng/mL, 0.4 ng/mL, 1 ng/mL, 4 ng/mL, 10 ng/mL, 20 ng/mL, and 40 ng/mL. Prepare when needed. 4.5.3 Instrument reference conditions The instrument reference conditions are as follows: a) Negative high voltage: 200 V~400 V; b) Selenium hollow cathode lamp current: 15 mA~100 mA; c) Atomizer temperature: 200℃; d) Atomizer height: 8 mm; e) Carrier gas flow rate: 400 mL/min; f) Shielding gas flow rate: 1000 mL/min. 4.5.4 Determination Adjust the instrument to the best working state. Start the measurement after stabilizing for 15 min~20 min. Use hydrochloric acid solution II (4.2.10) as the carrier and potassium borohydride solution (4.2.12) as the reducing agent. Use the carrier solution for continuous injection. After the fluorescence intensity is stable, measure the fluorescence intensity of the standard series solution, blank test solution and specimen solution in turn. Draw a standard curve with selenium concentration as the horizontal axis and fluorescence intensity as the vertical axis. The correlation coefficient r of the standard curve is not less than 0.99. From the standard curve, find the concentration of selenium in the specimen solution. If the fluorescence intensity of selenium in the specimen solution exceeds the linear range of the curve, take an appropriate amount of specimen solution for dilution. Add an appropriate amount of hydrochloric acid (4.2.4) and potassium ferrocyanide solution (4.2.13). Ensure that the concentrations of hydrochloric acid and potassium ferrocyanide in the diluted specimen solution are consistent with those of the standard series solution. Re-measure. NOTE: Before measuring the reagent blank solution and specimen solution, use hydrochloric acid solution II (4.2.10) to clean the sample until the fluorescence value is consistent with the reagent blank. 4.6 Test data processing The selenium content w1 in the specimen is expressed as mass fraction. The value is expressed in milligrams per kilogram (mg/kg), calculated according to formula (1): Where, ρ1 - the mass concentration of selenium in the specimen solution obtained from the standard curve, in nanograms per milliliter (ng/mL); ρ0 - the mass concentration of selenium in the blank test solution obtained from the 5.2.3 Nitric acid: guaranteed reagent. 5.2.4 Hydrochloric acid: guaranteed reagent. 5.2.5 Hydrogen peroxide. 5.2.6 Cyclohexane: guaranteed reagent. If there is interference at the measurement wavelength, it shall be redistilled. 5.2.7 Ammonia solution: Mix 100 mL of ammonia solution and 100 mL of water. 5.2.8 Hydrochloric acid solution III: Take 250 mL of hydrochloric acid (5.2.4) and mix with 750 mL of water. 5.2.9 Hydrochloric acid solution IV: Pipette 8.4 mL of hydrochloric acid (5.2.4) into a 1000 mL volumetric flask. Dilute with water, set to the volume, and mix well. 5.2.10 Hydroxylamine hydrochloride-ethylenediaminetetraacetic acid disodium solution: Weigh 10 g of ethylenediaminetetraacetic acid disodium and dissolve it in 500 mL of water. Add 25 g of hydroxylamine hydrochloride. Stir to dissolve. Dilute to 1000 mL with water. Mix well. 5.2.11 2,3-Diaminonaphthalene solution: Weigh 0.1 g of 2,3-diaminonaphthalene into a 250 mL beaker. Add 100 mL of hydrochloric acid solution IV (5.2.9) to dissolve it. Transfer to a 250 mL separatory funnel. Add 20 mL of cyclohexane (5.2.6). Shake for 1 min. After separation, discard the cyclohexane. Repeat the treatment of the aqueous phase with cyclohexane 2~3 times. Put the aqueous phase into a brown bottle. Cover it with 1 cm thick cyclohexane (5.2.6). Store it at 2℃~8℃. If necessary, purify it with cyclohexane before use. 5.2.12 Cresol red indicator (0.4 g/L): Weigh 0.04 g of cresol red into a 150 mL beaker. Add a small amount of ammonia solution (5.2.7) to dissolve it. Dilute to 100 mL with water. Mix well. 5.2.13 Selenium standard stock solution (100 μg/mL): Accurately weigh 100 mg of selenium powder (CAS No.: 7782-49-2, spectrally pure, purity not less than 99.9%) and dissolve it in a small amount of nitric acid (5.2.3). Add 2 mL of perchloric acid (5.2.2). Heat in a boiling water bath for 3 h~4 h. After cooling, add 8.4 mL of hydrochloric acid (5.2.4). Heat in a boiling water bath for another 2 min. Transfer to a 1000 mL volumetric flask with water. Dilute to the mark with water. Mix well. Store at 2℃~8℃. It shall be valid for 3 months. Or purchase certified standard substances. 5.2.14 Selenium standard intermediate solution (1 μg/mL): Accurately transfer 1 mL of selenium standard stock solution (5.2.13) into a 100 mL volumetric flask. Dilute to the volume with water. Mix well. Prepare when needed. 5.2.15 Selenium standard working solution (0.2 μg/mL): Accurately transfer 10 mL of selenium standard intermediate solution (5.2.14) into a 50 mL volumetric flask. Dilute with a small amount of water. Add the washing liquid to the digestion solution. Place on an adjustable temperature electric hot plate and continue heating at 150℃ until the remaining volume is about 2 mL. Remove. Cool to room temperature. Add 1 mL of water and 1 mL of hydrochloric acid solution III (5.2.8). Mix well. Let stand for 10 min. Transfer the digestion solution to a 50 mL stoppered colorimetric tube. Add a little water to wash the digestion tank 4~6 times. Add the washing solution to the stoppered colorimetric tube (For specimens with high selenium content, first transfer the digestion solution to a 100 mL volumetric flask. Dilute and set to the volume with water. After mixing, take an appropriate amount of solution into a 50 mL stoppered colorimetric tube). Add water to about 30 mL. Mix well. Set aside. Perform a blank test at the same time. 5.5.2 Extraction Add 2 drops of cresol red indicator (5.2.12) to the sample digestion solution. Adjust with ammonia solution (5.2.7) until the solution turns yellow. Adjust with hydrochloric acid solution III (5.2.8) until the solution turns orange (pH 1.5~2), then add 3 mL of hydroxylamine hydrochloride-ethylenediaminetetraacetic acid disodium solution (5.2.10). Shake well. Add 2 mL of 2,3-diaminonaphthalene solution (5.2.11). Cover the stopper. Shake well. Unscrew the stopper. Keep in boiling water for 5 min. Take out. Cool to room temperature. Dilute to the mark with hydrochloric acid solution IV (5.2.9). Add 5 mL of cyclohexane (5.2.6). Shake vigorously for 1 min. After standing for stratification, take the upper layer solution as the specimen solution for testing. 5.5.3 Preparation of standard curve Accurately pipette 0 mL, 0.1 mL, 0.5 mL, 2 mL, 3 mL, and 4 mL of selenium standard working solution (5.2.15) into 50 mL stoppered colorimetric tubes, respectively. The equivalent selenium masses are 0 μg, 0.02 μg, 0.1 μg, 0.4 μg, 0.6 μg, and 0.8 μg, respectively. Add water to about 30 mL. Perform the remaining steps in parallel with 5.5.2. 5.5.4 Determination Adjust the fluorescence photometer to the best working state. Use a 1 cm quartz cup to measure the fluorescence values of the upper cyclohexane solution in the standard series solution, reagent blank solution and specimen solution at an excitation wavelength of 376 nm and an emission wavelength of 520 nm. Draw a standard curve with the mass of selenium in the standard solution as the horizontal axis and the fluorescence value as the vertical axis. The correlation coefficient r of the standard curve is not less than 0.99. The mass of selenium in the specimen solution is obtained from the standard curve. 5.6 Test data processing The selenium content w2 in the specimen is expressed as mass fraction. The value is expressed in milligrams per kilogram (mg/kg), calculated according to formula (2): Warning -- All strong acids shall be handled with caution. Dilution and use shall be done in a fume hood. When using perchloric acid, be careful not to burn it dry. Be careful of explosion. Unless otherwise specified, only analytically pure reagents are used. 6.2.1 Water: GB/T 6682, Grade I. 6.2.2 Perchloric acid: guaranteed reagent. 6.2.3 Nitric acid: guaranteed reagent. 6.2.4 Hydrochloric acid: guaranteed reagent. 6.2.5 Hydrogen peroxide. 6.2.6 Nitric acid solution I: Take 5 mL of nitric acid (6.2.3) and add it to 95 mL of water. Mix well. 6.2.7 Nitric acid solution II: Measure 30 mL of nitric acid (6.2.3) and add it to 70 mL of water. Mix well. 6.2.8 Selenium standard stock solution (100 μg/mL): Accurately weigh 100 mg of selenium powder (CAS No.: 7782-49-2, spectrally pure, purity not less than 99.9%) and dissolve it in a small amount of nitric acid (6.2.3). Add 2 mL of perchloric acid (6.2.2). Heat in a boiling water bath for 3 h~4 h. After cooling, add 8.4 mL of hydrochloric acid (6.2.4). Heat in a boiling water bath for another 2 min. Transfer to a 1000 mL volumetric flask with water. Dilute to the mark with water. Mix well. Store at 2℃~8℃. It shall be valid for 3 months. Or purchase certified reference material. 6.2.9 Selenium standard intermediate solution (1.0 μg/mL): Accurately transfer 1 mL of selenium stock solution (6.2.8) into a 100 mL volumetric flask. Dilute to the mark with nitric acid solution I (6.2.6). Mix well. Prepare when needed. 6.2.10 Rhodium internal standard element stock solution (100 μg/mL): certified standard substance. 6.2.11 Rhodium internal standard element intermediate solution (1 μg/mL): Accurately transfer 1 mL of internal standard element stock solution (6.2.10) into a 100 mL volumetric flask. Dilute to the mark with nitric acid solution I (6.2.6). Mix well. Prepare when needed. 6.2.12 Selenium standard series solutions: Accurately pipette 0 mL, 0.1 mL, 0.2 mL, 0.5 mL, 1 mL, 2 mL, 5 mL of selenium standard intermediate solution (6.2.9). Place them in 100 mL volumetric bottles, respectively. Dilute with nitric acid solution I (6.2.6), set to the volume, and mix well. Prepare selenium standard series solutions with mass concentrations of 0 ng/mL, 1.0 ng/mL, 2.0 ng/mL, 5.0 ng/mL, 10 ng/mL, 20 ng/mL, 50 ng/mL. Prepare when needed. 6.2.13 Rhodium internal standard element working solution (10 ng/mL): Accurately transfer 1 mL of rhodium internal standard element intermediate solution (6.2.11) into a 100 mL volumetric flask. Dilute and set to the volume with nitric acid solution I (6.2.6). Mix well. Prepare when needed. 6.2.14 Microporous filter membrane: 0.45 μm, water system. 6.2.15 High-purity argon: purity is greater than 99.995%. 6.2.16 High-purity helium: purity is greater than 99.995%. NOTE: Before use, the containers shall be soaked in nitric acid solution (6.2.7) overnight and then rinsed with water. 6.3 Instruments and equipment 6.3.1 Inductively coupled plasma mass spectrometer. 6.3.2 Analytical balance: accuracy is 0.0001 g. 6.3.3 Microwave digestion apparatus. 6.3.4 Adjustable temperature electric heating plate. 6.3.5 Constant temperature water bath. 6.4 Sample Same as 4.4. 6.5 Test steps 6.5.1 Preparation of specimen solution Perform two tests in parallel. Weigh 0.5 g of the specimen (accurate to 0.0001 g) into a digestion tank. Add 8 mL of nitric acid (6.2.3). Soak for 10 min. Add 2 mL of hydrogen peroxide (6.2.5). Let stand for more than 2 h. Tighten the tank lid. Cover the safety valve. Place in a microwave digestion instrument. Set the microwave digestion conditions (see Annex A) according to the characteristics of the specimen for digestion. After digestion, take out. Cool to room temperature. Place on an adjustable temperature electric hot plate. Drive the acid solution to a volume of about 2 mL at 150℃. Remove. Cool to room temperature. Transfer the digestion solution to a 50 mL volumetric flask. Add a little water to wash the digestion tank 4~6 times. Add the washing solution to the volumetric flask. Set to the volume with water. Mix well. Filter with a microporous filter membrane (6.2.14). Set aside the filtrate. Perform a blank test at the same time. 6.5.2 Instrument reference conditions The instrument reference conditions are as follows: ......


GB/T 13883-2008 GB ICS 65.120 B 46 National Standard of the People’s Republic of China Replacing GB/T 13883-1992 Determination of selenium in feeds ISSUED ON. AUGUST 1, 2008 IMPLEMENTED ON. NOVEMBER 1, 2008 Issued by. General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China; Standardization Administration Committee. Table of Contents Foreword ... 3  1 Scope ... 4  2 Normative references ... 4  3 The first method -- Hydride generation atomic fluorescence spectrometry (Arbitration method) ... 4  4 The second method -- 2,3-diamino-naphthalene fluorescence ... 8  Foreword This Standard replaces GB/T 13883-1992 "Determination of selenium in feeds." Compared with GB/T 13883-1992, the main changes in this Standard are as follows. — INTRODUCE hydride generation atomic fluorescence spectrometry as arbitration method; — SPECIFY that the excitation wavelength of 2,3-diamino-naphthalene fluorescence is 376mm; the emission wavelength is 520nm. This Standard was proposed and shall be under the jurisdiction of the National Standardization Technical Committee of Feed Industry. Drafting organizations of this Standard. China Feed Industry Association, the National Feed Quality Supervision and Inspection Center (Wuhan). Main drafters of this Standard. He Yifan, Xin Shengpeng, Su Shenglan, Xu Jinping, Zou Daqiong, Liu Xiaomin, Gao Lihong. This Standard was first-time released in 1991 as the national standard GB 13883-1992. It was adjusted to non-mandatory standard in 1997, and renumbered as GB/T 13883-1992. This revision is the first revision of this Standard. Determination of selenium in feeds 1 Scope  This Standard specifies the determination method of selenium in compound feeds, concentrated feeds, and premixed feeds. This Standard applies to the determination of selenium in compound feeds, concentrated feeds, and premixed feeds. Quantitative limit of hydride generation atomic fluorescence spectrometry is 0.01mg/kg; quantitative limit of fluorescence is 0.02mg/kg. 2 Normative references  The provisions in following documents become the provisions of this Standard through reference in this Standard. For dated references, the subsequent amendments (excluding corrections) or revisions do not apply to this Standard, however, parties who reach an agreement based on this Standard are encouraged to study if the latest versions of these documents are applicable. For undated references, the latest edition of the referenced document applies.. GB/T 6682 Water for analytical laboratory use - Specification and test methods (GB/T 6682-1992, neq ISO 3696. 1987) GB/T 14699.1 Animal feeding stuffs - Sampling (GB/T 14699.1-2005, ISO 6497. 2002, IDT) GB/T 20195 Animal feeding stuffs - Preparation of test samples (GB/T 20195-2006, ISO 6498. 1998, IDT) 3  The  first  method  ‐‐  Hydride  generation  atomic  fluorescence  spectrometry (Arbitration method)  3.1 Principle After the sample is heated and digested by acid, in hydrochloric acid medium, REDUCE the hexavalent selenium in the sample TO tetravalent selenium. USE sodium borohydride as the reducing agent; REDUCE the tetravalent selenium to hydrogen selenide in hydrochloric acid medium; then it is carried by carrier gas into the atomizer to atomize. Under the irradiation of selenium hollow cathode lamp, the relative deviation ≤20%; When the mass fraction of selenium is more than 0.40mg/kg, the relative deviation ≤12%. 4 The second method ‐‐ 2,3‐diamino‐naphthalene fluorescence  4.1 Principle DIGEST the sample by mixed acid, so as to make the selenium free. In acidic solution, selenium (Se4+) and 2,3-diamino-naphthalene (DAN) generate 4,5-phenylbenzo selenadiazole. USE cyclohexane to directly extract in the solution of which the acidity is the same as that of generated complex. USE fluorescence spectrophotometer to determine the fluorescence intensity at an excitation wavelength of 376nm and an emission wavelength of 520nm. And then calculate selenium content in the sample. 4.2 Reagents The following reagents, unless otherwise stated, are of analytical purity. The water shall meet the Grade-2 water specified in GB/T 6682. 4.2.1 Perchloric acid. premium-grade pure. 4.2.2 Nitrate. premium-grade pure. 4.2.3 Ammonia solution. 1 + 1. 4.2.4 Hydrochloric acid solution. c (HCl) = 3mol/L. 4.2.5 Hydrochloric acid solution. c (HCl) = 0.1mol/L. 4.2.6 Cyclohexane. if there are fluorescent impurities, it shall be re-evaporated before being used. 4.2.7 Hydroxylamine hydrochloride-ethylene diamine tetraacetic acid (EDTA) solution. WEIGH 10g of EDTA and dissolve them in 500mL of water. ADD 25g of hydroxylamine hydrochloride and make them dissolved. DILUTE with water to 1L. 4.2.8 2,3-diamino-naphthalene (DAN) solution. WEIGH 10g of DAN in a 250-mL beaker. ADD 100mL of hydrochloric acid solution (4.2.5) to make them dissolved. TRANSFER into a 250-mL separating funnel. ADD 20mL of cyclohexane (4.2.6) and SHAKE for 1min. REMOVE cyclohexane after stratification. USE cyclohexane to repeatedly process aqueous phase for 2 to 3 times. PUT the aqueous phase into a brown bottle and cover with 1-cm-thick cyclohexane. KEEP in the dark. This solution can be used for several weeks. 4.5.1.2 Premixed feeds For premixed sample, WEIGH 1.0g of sample (accurate to 0.0001g). PLACE in a 100-mL high beaker. ADD 10mL of water and 15mL of nitric acid (4.2.2). COVER with a watch glass. PLACE on an electric hot plate and boiling at a low temperature for 30min. TAKE down and cool it down. USE water to transfer into a 100-mL volumetric flask. DILUTE to the scale. SHAKE well. MESURE some supernatant (Se≤0.4μg) into a 100-mL high beaker. ADD 5mL of perchloric acid (4.2.1). The following steps are conducted according to 4.5.1.1 - the analysis steps after perchloric acid is added. 4.5.2 Preparation of standard curves Accurately MEASURE 0.00, 0.50, 1.00, 2.00, 3.00, 4.00mL of selenium standard working solution (4.2.9) respectively into 50-mL colorimetric tubes with stoppers. ADD 2 drops of cresol red indicator (4.2.10). The following steps are conducted according to 4.5.1.1 - the analysis steps after “neutralize with aqueous ammonia solution (4.2.3)”. 4.5.3 Sample determination ABSORB the cyclohexane solution on the upper layer of the solution to be tested (4.5.1.1) INTO a 1-cm quartz cup. Use fluorophotometer to respectively determine the fluorescence intensity at the positions where excitation wavelength is 376nm and emission wavelength is 520nm. At the same time, DETERMINE the standard curves; DRAW the standard curves. OBTAIN the selenium content in the solution from the standard curves. Determination results of selenium in samples are calculated according to 4.6.1. 4.6 Calculation and presentation of analysis results 4.6.1 Calculation results Selenium content X in the sample, in mass fraction, of which the numerical value is expressed in milligrams per kilogram (mg/kg), is calculated according to equation (2). Where. m1 — Mass fraction of selenium in samples, obtained from the standard curve, in units of micrograms (μg); m2 — Mass fraction of selenium in blank, obtained from the standard curve, in units of micrograms (μg); V0 — Total volume of sample digestion solution, in units of milliliters (mL); m0 — Sample mass, in units of grams (g); V1 — Volume of dispensed solution, in units of milliliters (mL). The determination results are expressed in the arithmetic mean after parallel determination. The calculation results accurate to 0.01mg/kg. 4.6.2 Repeatability The results of two parallel determinations obtained in the same laboratory and by the same analyst shall meet the following requirements for relative deviation. When the mass fraction of selenium is less than or equal to 0.10mg/kg, the relative deviation ≤40%; When the mass fraction of selenium is more than 0.10mg/kg and less than 0.40 mg/kg, the relative deviation ≤20%; When the mass fraction of selenium is more than 0.40mg/kg, the relative deviation ≤15%. ......

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