GB/T 5009.11-2003 Determination of total arsenic and inorganic arsenic in food
Some standard content:
ICS67.040
National Standard of the People's Republic of China
GB/T5009.11—2003
Replaces GB/T5009.11--1996
Determination of total arsenic and abio-arsenic in foods
Determination of total arsenic and abio-arsenic in foodsPromulgated on August 11, 2003
Ministry of Health of the People's Republic of China
Standardization Administration of the People's Republic of China
Implementation on January 1, 2004
GB/T 5009.11-2003
This standard replaces GB/T 5009.11—1996 "Determination of total arsenic in foods". Compared with GB/T5009.11-1996, the main changes of this standard are as follows: the Chinese name of the standard has been changed to "Determination of total arsenic and inorganic arsenic in food"; - the determination of total arsenic has been added;
the determination of inorganic arsenic has been added;
- the structure of the original standard has been modified in accordance with GB/T20001.4-2001 "Standard Preparation Rules Part 4: Chemical Analysis Methods".
This standard is proposed and managed by the Ministry of Health of the People's Republic of China. The first method of determination of total arsenic in this standard was drafted by Sichuan Provincial Food Hygiene Supervision and Inspection Institute and Food Hygiene Supervision and Inspection Institute of the Ministry of Health, and Beijing Municipal Health and Epidemic Prevention Station and Beijing Imported Food Hygiene Supervision and Inspection Institute participated in the drafting. The second method of determination of total arsenic in this standard was drafted by the Institute of Nutrition and Food Hygiene of the Chinese Academy of Preventive Medicine and Qinghai Provincial Health and Epidemic Prevention Station.
The third method of determination of total arsenic in this standard was drafted by Food Hygiene Supervision and Inspection Institute of the Ministry of Health. The fourth method of determination of total arsenic in this standard was drafted by West China University of Medical Sciences. The first method for the determination of inorganic arsenic in this standard was drafted by the Food Sanitation Supervision and Inspection Institute of the Ministry of Health, with participation from the Jilin Provincial Health and Epidemic Prevention Station, Guangdong Provincial Food Sanitation Supervision and Inspection Institute, and Anhui Provincial Health and Epidemic Prevention Station. The second method for the determination of inorganic arsenic in this standard was drafted by the Jiangsu Provincial Center for Disease Control and Prevention, with participation from the Anhui Provincial Health and Epidemic Prevention Station and Nanjing Municipal Health and Epidemic Prevention Station.
The main drafters of the first method for the determination of total arsenic in this standard are: Qiang Weiguo, Yang Huifen, Mao Hong, and Yan Jun. The main drafters of the first method for the determination of inorganic arsenic in this standard are: Yang Huifen, Gu Wei, Bianjiang, Liang Chunsui, and Hu Jiaying. The main drafters of the second method for the determination of inorganic arsenic in this standard are: Cang Gongao, Teng Xiaopei, Ji Zhongshan, Ding Gang, and Hu Jiaying. This standard was first issued in 1985 and revised for the first time in 1996. This is the second revision. 72
1 Scope
Determination of total arsenic and inorganic arsenic in food
Determination of total arsenic
This standard specifies the determination method of total arsenic in various foods. This standard is applicable to the determination of total arsenic in various foods. GB/T 5009.11—2003
Detection limit of this method: hydride atomic fluorescence spectrophotometry: 0.01mg/kg, linear range is 0ng/mL~200ng/ml; silver salt method: 0.2mg/kg; arsenic spot method: 0.25mg/kg; borohydride reduction colorimetry: 0.05mg/kg. Method 1: Hydride Atomic Fluorescence Spectrophotometry
2 Principle
After wet digestion or dry ashing of food samples, sulfur glands are added to pre-reduce pentavalent arsenic to trivalent arsenic, and then sodium hydride or potassium borohydride is added to reduce it to generate arsenic hydrogen, which is decomposed into atomic arsenic in the argon-carried quartz atomizer. Atomic fluorescence is generated under the excitation of the emission light of a special arsenic hollow cathode lamp. Its fluorescence intensity is proportional to the arsenic concentration in the measured liquid under fixed conditions. It is quantitatively compared with the standard series. 3 Reagents
3.1 Sodium hydroxide solution (2g/L).
3.2 Sodium borohydride (NaBH4) solution (10g/L): Weigh 10.0g of sodium borohydride, dissolve it in 1000mL of 2g/L sodium hydroxide solution, and mix well. This solution can be stored in the refrigerator for 10 days and should be used on the same day after it is taken out (14g of potassium borohydride can also be weighed instead of 10g of sodium borohydride). 3.3 Thiourea solution (50 g/L).
3.4 Sulfuric acid solution (1+9): Measure 100 mL of sulfuric acid, carefully pour it into 900 mL of water, and mix well. 3.5 Sodium hydroxide solution (100 g/L) (for preparing arsenic standard solution, a small amount is enough). 3.6 Arsenic standard solution
3.6.1 Arsenic standard stock solution: containing 0.1 mg/mL arsenic. Accurately weigh 0.1320 g of arsenic trioxide (As2O) dried at 100°C for more than 2 hours, add 10 mL of 100 g/L sodium hydroxide to dissolve, transfer to a 1000 mL volumetric flask with appropriate amount of water, add 25 mL of (1+9) sulfuric acid, and dilute to the mark with water.
3.6.2 Standard solution for use: containing 1 μg/mL arsenic. Pipette 1.00 mL of standard stock solution into a 100 mL volumetric flask and dilute to the mark with water. This solution should be prepared and used on the same day.
3.7 Wet digestion reagents: nitric acid, sulfuric acid, perchloric acid. 3.8 Dry ash reagents: magnesium nitrate hexahydrate (150g/L), magnesium chloride, hydrochloric acid (1+1). 4 Instruments
Atomic fluorescence spectrophotometer.
5 Analysis steps
5.1 Sample digestion
5.1.1 Wet digestion: Weigh 1g~2.5g of solid sample and 5g~10g (or mL) of liquid sample (accurate to the second decimal place), place in a 50mL~100mL conical flask, and make two reagent blanks at the same time. Add 20mL~40mL nitric acid and 1.25mL sulfuric acid, shake well, leave overnight, and place on a hot plate for heating and digestion. If there are still undecomposed substances or the color becomes darker when the digestion solution is processed to about 10mL, remove the 73
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and let it cool. Add 5mL~10mL of nitric acid and digest it to about 10mL and observe. Repeat this two or three times, and be careful to avoid carbonization. If it is still not completely digested, add 1mL~2mL of perchloric acid, continue heating until the digestion is complete, and then continue to evaporate until the white smoke of perchloric acid dissipates and the white smoke of sulfuric acid begins to emerge. Cool, add 25mL of water, and evaporate until white smoke of sulfuric acid emerges. Cool, transfer the contents into a 25mL volumetric flask or colorimetric tube with water, add 2.5mL of 50g/L thiourea, add water to the scale and mix well, and prepare for measurement. 5.1.2 Dry ashing: Generally used for solid samples. Weigh 1g to 2.5g (accurate to the second decimal place) in a 50mL to 100mL crucible, and make two reagent blanks at the same time. Add 10mL of 150g/L magnesium nitrate and mix well. Evaporate to dryness at low heat. Carefully cover 1g of magnesium oxide on the dry residue, carbonize on an electric furnace until there is no black smoke, and transfer to a 550℃ high-temperature furnace for ash treatment for 4h. Take out and cool, carefully add 10mL of (1+1) hydrochloric acid to neutralize magnesium oxide and dissolve ash, transfer to a 25mL volumetric flask or colorimetric tube, add 2.5mL of 50g/L thiourea to the volumetric flask or colorimetric tube, rinse the crucible with (1+9) sulfuric acid in batches, transfer out and combine until the 25mL mark, mix well and prepare for measurement. 5.2 Preparation of standard series
Take 6 25mL volumetric flasks or colorimetric tubes, and accurately add 0, 0.05, 0.2, 0.5, 2.0, and 5.0mL of 1μg/mL arsenic standard solution in sequence (equivalent to arsenic concentrations of 0, 2.0, 8.0, 20.0, 80.0, and 200.0ng/mL, respectively). Add 12.5mL of (1+9) sulfuric acid and 2.5mL of 50g/L thiourea to each, add water to the scale, mix and prepare for measurement. 5.3 Determination
5.3.1 Instrument reference conditions: Photomultiplier tube voltage: 400V; Arsenic hollow cathode lamp current: 35mA; Atomizer: temperature 820℃~850℃; Height 7mm; Argon gas flow rate: carrier gas 600mL/min; Measurement method: Fluorescence intensity or concentration direct reading, reading method: peak area; Reading delay time: 1s; Reading time: 15s; Sodium borohydride solution addition time: 5s; Standard solution or sample solution addition volume: 2mL. 5.3.2 Concentration method measurement: If the fluorescence intensity is measured directly, after turning on the instrument and setting the instrument conditions, preheat and stabilize for about 20 minutes. Press the "B" key to enter the blank value measurement state, and continuously use the "0" tube of the standard series to inject samples. After the reading is stable, press the neutral key to record the blank value (that is, let the instrument automatically deduct the bottom) and start measuring. Measure the standard series in sequence first (you can no longer measure the "0" tube). After the standard series is tested, the sampler should be carefully cleaned (or replaced), and the "0" tube should be used to test the reading to basically return to zero before the blank and sample can be tested. The sampler should be cleaned before each test of a different sample, and the measurement data should be recorded (or printed). 5.3.3. Automatic instrument mode: The software function provided by the instrument can be used for direct reading of concentration. To this end, after turning on the instrument, setting conditions and preheating, it is necessary to enter the necessary parameters, namely: sample volume (g or mL); dilution volume (mL); injection volume (mL); concentration unit of the result; number of repeated measurements of each point in the standard series; number of points in the standard series (excluding zero point), and the concentration value of each point. First, enter the blank value measurement state, continuously use the standard series "0" tube to inject samples to obtain a stable blank value and perform automatic bottoming, then measure the standard series in turn (at this time, the "0" tube needs to be measured again). Before measuring the sample solution, you need to enter the blank value measurement state again, first use the standard series "0" tube to test to restore and stabilize the reading, then use two reagent blanks to inject samples once each, let the instrument take the average as the blank value for bottoming, and then test the samples in turn. After the measurement is completed, return to the main menu and select "Print Report" to print the measurement results. 6 Result calculation
If the fluorescence intensity measurement method is used, it is necessary to first perform regression calculation on the results of the standard series (because the "0" tube is forced to be 0 during measurement, the zero point value should be entered to occupy a point position), and then calculate the arsenic concentration of the reagent blank solution and the sample solution according to the regression equation, and then calculate the arsenic content of the sample according to formula (1):
In the formula:
X=C=C ×,25
X——Arsenic content of the sample, in milligrams per kilogram or milligrams per liter (mg/kg or mg/L); C,—Concentration of the sample test solution, in nanograms per milliliter (ng/mL); C. ——Concentration of the reagent blank solution, in nanograms per milliliter (ng/mL); The mass or volume of the sample, in grams or milliliters (g or mL). m
The calculation result shall retain two significant figures.
7 Precision
. (1)
The absolute difference between two independent determination results obtained under repeatability conditions by the wet digestion method shall not exceed 10% of the arithmetic mean. 74
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The absolute difference between two independent determination results obtained by the dry ashing method under repeatability conditions shall not exceed 15% of the arithmetic mean. 8 Accuracy
The recovery rate determined by the wet digestion method is 90%~105%; the recovery rate determined by the dry ashing method is 85%~100%. Second method Silver salt method
9 Principle
After the sample is digested, potassium iodide and stannous chloride are used to reduce the high-valent arsenic to trivalent arsenic, and then it reacts with zinc particles and acid to produce nascent hydrogen to generate arsenic hydrogen. After being absorbed by the silver salt solution, a red colloid is formed, which is compared with the standard series for quantitative analysis. 10 Reagents
10.1 Nitric acid.
10.2 Sulfuric acid.
10.3 Hydrochloric acid.
Magnesium oxide.
10.5 Arsenic-free zinc particles.
Nitric acid-perchloric acid mixed solution (4+1): Measure 80mL nitric acid, add 20mL perchloric acid, and mix well. 10.7
Magnesium nitrate solution (150g/L): Weigh 15g magnesium nitrate [Mg(NO)2*6HO, dissolve in water, and dilute to 100mL. 10.8
Potassium iodide solution (150g/L): Store in a brown bottle. Acidic stannous chloride solution: Weigh 40g stannous chloride (SnCl2·2H2O), dissolve in hydrochloric acid and dilute to 100mL, add 10.9
metal tin particles.
Hydrochloric acid (1+1): Measure 50mL of hydrochloric acid and dilute to 100mL with water. 10.11
Lead acetate solution (100g/L).
Lead acetate cotton: Soak the absorbent cotton with lead acetate solution (100g/L), press out the excess solution, and make it loose. After drying at 10.12
below 100℃, store in a glass bottle.
10, 13 Sodium hydroxide solution (200g/L). 10.14 Sulfuric acid (6+94): Measure 6.0mL of sulfuric acid and add it to 80mL of water. After cooling, dilute to 100mL with water. 10.15 Silver diethyldithiocarbamate-triethanolamine-chloroform solution: Weigh 0.25g silver diethyldithiocarbamate [(C2H.,NCSAg] into a mortar, add a small amount of chloroform to grind, transfer to a 100mL measuring cylinder, add 1.8mL triethanolamine, then wash the mortar with chloroform several times, transfer the washing liquid to the measuring cylinder, dilute to 100mL with chloroform, and leave overnight. Filter into a brown bottle
10.16 Arsenic standard stock solution: Accurately weigh 0.1320g of arsenic trioxide that has been dried in a sulfuric acid dryer or dried at 100℃ for 2h, add 5mL of sodium hydroxide solution (200g/L), add 25mL of sulfuric acid (6+94), transfer to a 1000mL volumetric flask, add freshly boiled and cooled water to dilute to the mark, and store in a brown glass bottle. Each milliliter of this solution is equivalent to 0.10m g arsenic. 10.17 Arsenic standard working solution: Pipette 1.0 mL arsenic standard stock solution, place in a 100 mL volumetric flask, add 1 mL combustible acid (694), and dilute to the mark with water. Each mL of this solution is equivalent to 1.0 μg arsenic. 11 Instruments
11.1 Spectrophotometer.
11.2 Arsenic measuring device: See Figure 1.
GB/T5009.11—2003
150m L conical flask;
-air guide tube;
lead acetate cotton;
10mL graduated centrifuge tube.
11.2.1100mL150mL conical flask: standard port No. 19. Figure 1
Unit is mm
11.2.2 Air guide tube: the tube port No. 19 standard port or the rubber stopper that has been cleaned after alkali treatment should not leak when it is tightly fitted with the conical flask. The diameter of the other end of the tube is 1.0 mm.
11.2.3 Absorption tube: 10mL graduated centrifuge tube is used as absorption tube. 12 Sample treatment
12.1 Nitric acid-perchloric acid-sulfuric acid method
12.1.1 Grain, vermicelli, vermicelli, dried bean products, cakes, tea, etc. and other solid foods with little water content: Weigh 5.00g or 10.00g of crushed sample, put it in a 250mL~500mL nitrogen determination bottle, add a little water to moisten it, add a few glass beads, 10mL~15mL nitric acid and perchloric acid mixture, let it stand for a while, heat slowly over low heat, wait for the effect to ease, and let it cool. Add 5mL along the wall of the bottle Or 10mL sulfuric acid, and then heat until the liquid in the bottle begins to turn brown, and then continue to drip nitric acid-perchloric acid mixture along the bottle wall until the organic matter is completely decomposed. Increase the firepower until white smoke is produced. After the white smoke from the bottle mouth is completely gone, the liquid in the bottle produces white smoke again, which means the digestion is complete. The solution should be clear and colorless or slightly yellow, and let it cool. (Care should be taken to prevent boiling or explosion during the operation) Add 20mL of water and boil, remove the residual nitric acid until white smoke is produced, and do this twice, and let it cool. Transfer the cooled solution to a 50mL or 100mL volumetric flask, wash the nitrogen determination bottle with water, and add the washing liquid to the volumetric flask, let it cool, add water to the scale, and mix. After the solution is fixed to volume, each 10mL is equivalent to 1g of the sample, which is equivalent to the amount of sulfuric acid added 1mL. Take the same amount of nitric acid-perchloric acid mixture and sulfuric acid as the digestion sample, and perform a reagent blank test according to the same method. 76
GB/T5009.11—2003
12.1.2 Vegetables and fruits: weigh 25.00g or 50.00g of the washed and homogenized sample, place it in a 250mL~～500mL nitrogen determination bottle, add several glass beads and 10mL～15mL nitric acid-perchloric acid mixture, and operate according to 12.1.1 from "let it stand for a while...", but every 10mL of the solution after volume determination is equivalent to 5g of sample, which is equivalent to adding 1.mL of sulfuric acid. 12.1.3 Sauces, soy sauces, vinegar, cold drinks, tofu, fermented bean curd, pickled vegetables, etc.: weigh 10.00g or 20.00g of sample (or absorb 10.0mL or 20.0mL of liquid sample), place it in a 250mL～500mL nitrogen determination bottle, add several glass beads and 10mL～15mL nitric acid-perchloric acid mixture, and operate according to 12.1.1 from "let it stand for a while..." Glass beads, 5mL~15mL nitric acid-perchloric acid mixture. The following operations are carried out according to 12.1.1 starting from "let it stand for a while...", but each 10mL of the solution after the volume is fixed is equivalent to 2g or 2mL of the sample.
12.1.4 Alcoholic beverages or beverages containing carbon dioxide: Pipette 10.00mL or 20.00mL of the sample, place it in a 250mL~500mL nitrogen determination bottle, add a few glass beads, first heat over low heat to remove ethanol or carbon dioxide, then add 5mL~10mL nitric acid-perchloric acid mixture, mix well, and the following operations are carried out according to 12.1.1 starting from "let it stand for a while...", but each 10mL of the solution after the volume is fixed is equivalent to 2mL of the sample.
12.1.5 Foods with high sugar content: Weigh 5.00g or 10.0g sample, place it in a 250mL~500mL nitrogen determination bottle, first add a little water to moisten it, add a few glass beads, 5mL~10mL nitric acid-perchloric acid, mix, and shake well. Slowly add 5mL or 10mL sulfuric acid, wait until the effect is relieved and the foam stops, first heat slowly with a low fire (sugar is easy to carbonize), and continue to add nitric acid-perchloric acid mixture along the bottle wall. After all the foam disappears, increase the fire again until the organic matter is completely decomposed and white smoke is generated. The solution should be clear and colorless or slightly yellow, and let it cool. The following operations are carried out according to 12.1.1 from "add 20mL water to boil..." 12.1.6 Aquatic products: Take the edible part of the sample and pound it into a homogenous slurry. Weigh 5.00g or 10.0g (the sampling amount of marine algae and shellfish can be appropriately reduced), place it in a 250mL~500mL nitrogen determination bottle, add a few glass beads and 5mL~10mL nitric acid-perchloric acid mixture, mix well, and then operate according to 12.1.1 from "add 5mL or 10mL sulfuric acid along the bottle wall..." 12.2 Nitric acid-sulfuric acid method
Use nitric acid instead of nitric acid-perchloric acid mixture for operation. 12.3 Ashing method
12.3.1 Grain, tea and other foods with little water content: Weigh 5.00g of ground sample, place it in a crucible, add 1g magnesium oxide and 10mL magnesium nitrate solution, mix well, and soak for 4h. Evaporate at low temperature or in a water bath, carbonize with low fire until smokeless, then transfer to a muffle furnace and heat to 550℃, burn for 3h~4h, and take out after cooling. After adding 5mL of water to moisten, stir with a thin glass rod, and then wash the ash attached to the glass rod with a small amount of water into the crucible. After evaporating on a water bath, transfer to a muffle furnace at 550℃ for 2h, and take out after cooling. Add 5mL of water to moisten the ash, then slowly add 10ml of hydrochloric acid (1+1), and then transfer the solution to a 50mL volumetric flask. Wash the crucible with hydrochloric acid (1+1) 3 times, 5mL each time, and then wash with water 3 times, 5mL each time. The washing liquid is added to the volumetric flask, and then water is added to the scale and mixed. After the solution is fixed to volume, each 10mL is equivalent to 1g of the sample, and the amount of hydrochloric acid added is not less than 1.5mL (excluding the amount required for neutralization). When the full amount is used for silver salt determination, no more hydrochloric acid is needed. Perform a reagent blank test according to the same operation method. 12.3.2 Vegetable oil: Weigh 5.00g of the sample and place it in a 50mL porcelain crucible. Add 10g of magnesium nitrate and cover it with 2g of magnesium oxide. Heat the crucible on a low fire until it starts to smoke. Immediately remove the crucible to prevent the contents from spilling out. When the smoke is small, heat it again until carbonization is complete. Move the crucible to a muffle furnace and burn it below 550℃ until it is completely ash-coated. Take it out after cooling. Add 5mL of water to moisten the ash, then slowly add 15mL of hydrochloric acid (1+1), then transfer the solution to a 50mL volumetric flask. Wash the crucible with hydrochloric acid (1+1) 5 times, 5mL each time. Add the washing liquid to the volumetric flask, add hydrochloric acid (1+1) to the scale, and mix. After the solution is fixed to volume, each 10mL is equivalent to 1g of the sample, which is equivalent to adding 1.5mL of hydrochloric acid (excluding the amount required for neutralization). Perform a reagent blank test in the same way. 12.3.3 Aquatic products: Take the edible part of the sample and pound it into a slurry. Weigh 5.00g and place it in a crucible. Add 1g of magnesium oxide and 10mL of magnesium nitrate solution, mix and soak for 4h. The following operations are carried out according to 12.3.1 starting from "evaporate to dryness at low temperature or in a water bath." 13 Analysis steps
Pick a certain amount of the digested fixed volume solution (equivalent to 5g of the sample) and the same amount of reagent blank solution, place them in 150mL conical flasks, add sulfuric acid to a total of 5mL, and add water to 50mL~55mL. 77
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13.1 Drawing of standard curve
Pipette 0, 2.0, 4.0, 6.0, 8.0, 10.0mL of standard working solution (equivalent to 0, 2.0, 4.0, 6.0, 8.0, 10.0g), respectively, and place in 150mL conical flasks, add water to 40mL, and then add 10mL sulfuric acid (1+1). 13.2 Use wet digestion solution
Add 3mL of potassium iodide solution (150g/L) and 0.5mL of acidic stannous chloride solution to the sample digestion solution, reagent blank solution and arsenic standard solution, mix well, and let stand for 15min. Add 3g zinc particles to each, immediately plug the airway tubes filled with lead acetate cotton, and insert the tip of the tube into the liquid surface of the centrifuge tube containing 4mL silver salt solution. After reacting at room temperature for 45 minutes, remove the centrifuge tube and add chloroform to make up to 4mL. Use a 1cm colorimetric cup and a zero tube to adjust the zero point, measure the absorbance at a wavelength of 520nm, and draw a standard curve. 13.3 Digestion solution using the ashing method
Put the ashing method digestion solution and the reagent blank solution in 150mL conical flasks respectively. Take 0, 2.0, 4.0, 6.0, 8.0, 10.0mL of arsenic standard working solution (equivalent to 0, 2.0, 4.0, 6.0, 8.0, 10.0μg arsenic), respectively, and put them in 150mL conical flasks, add water to 43.5mL, and then add 6.5mL hydrochloric acid. The following operations are carried out according to 13.2 starting from "In the sample digestion solution..." 14 Calculation of results
The content of arsenic in the sample is calculated according to formula (2). (A → A2) X1 000
m X Vz/V1 X 1 000
Wherein:
X—the content of arsenic in the sample, in milligrams per kilogram or milligrams per liter (mg/kg or mg/L); the mass of arsenic in the sample digestion solution for determination, in micrograms (ug); Ar
A2—the mass of arsenic in the reagent blank solution, in micrograms (μg); m
—the mass or volume of the sample, in grams or milliliters (g or mL); V.--the total volume of the sample digestion solution, in milliliters (mL); V2
—the volume of the sample digestion solution for determination, in milliliters (mL). The calculation result should be rounded to two significant figures.
15 Precision
The absolute difference between two independent determination results obtained under repeatability conditions shall not exceed 10% of the arithmetic mean. Method 3 Arsenic Spot Method
16 Principle
After the sample is digested, potassium iodide and stannous chloride are used to reduce the high-valent arsenic to trivalent arsenic, which is then converted into arsenic hydrogen with zinc particles and acid, and then into yellow to orange spots with mercuric bromide test paper, which are compared with standard arsenic spots for quantification. 17 Reagents
17.1 Same as silver salt method 10.1~~10.14, 10.16 and 10.17. 17.2 Mercuric bromide-ethanol solution (50g/L): Weigh 25g of mercuric bromide and dissolve it in a small amount of ethanol, then dilute to 500mL. 17.3 Mercuric bromide test paper: Cut a circular filter paper with a diameter of 2 cm, immerse it in a mercuric bromide ethanol solution (50g/L) for more than 1 hour, store it in a refrigerator, and take it out and dry it in a dark place before use. 18 Instruments
Arsenic test device is shown in Figure 2.
Conical flask;
- rubber stopper;
Test tube;
- tube mouth,
glass cap.
18.1 100mL conical flask.
18.2 Rubber stopper: with a hole in the middle.
GB/T5009.11—2003
18.3 Glass arsenic test tube: 18cm in total length, thick at the top and thin at the bottom, the inner diameter from the tube mouth to the 14cm section is 6.5mm, and it gradually narrows from there, with the inner diameter of the end being about 1mm~3mm. There is a hole 1cm near the end, with a diameter of 2mm. The narrow part is tightly inserted into the rubber stopper, so that the lower part extends to the small hole just below the rubber stopper. The thicker part at the top is filled with lead acetate cotton, 5cm~6cm long, and at least 3cm from the upper end to the tube mouth. The top of the arsenic test tube is a round flat tube mouth with a flat surface on the top and a hook on each side of the bottom for fixing the glass cap. 18.4 Glass cap: The bottom is flat, with a crescent-shaped groove on the top and a round hole in the center, with a diameter of 6.5mm. When in use, cover the glass cap on the mouth of the arsenic test tube so that the round holes fit together, sandwich the mercuric bromide test paper in the middle with the smooth side facing downward, and fix the glass cap and the arsenic test tube with a rubber ring or other appropriate method.
19 Sample digestion
Same as Chapter 12.
20 Analysis steps
Put the fixed volume solution of the quantitative sample after digestion (equivalent to 2g grain, 4g vegetables and fruits, 4mL cold drink, 5g vegetable oil, other samples refer to this amount) and the same amount of reagent blank solution into the arsenic test bottle, add 5mL potassium iodide solution (150g/L), 5 drops of acidic stannous chloride solution and 5mL hydrochloric acid (if the sample is digested with nitric acid-perchloric acid-sulfuric acid or nitric acid-sulfuric acid, the milliliters of sulfuric acid in the sample should be subtracted; if the sample is digested with ashing method, the milliliters of hydrochloric acid in the sample should be subtracted), and then add appropriate amount of water to 35mL (no water is added to vegetable oil). Pipette 0, 0.5, 1.0, 2.0mL of arsenic standard working solution (equivalent to 0, 0.5, 1.0, 2.0g arsenic) are placed in arsenic test bottles, 5mL potassium iodide solution (150g/L), 5 drops of acidic stannous chloride solution and 5mL hydrochloric acid are added to each, and water is added to 35mL (add water to 60mL when measuring vegetable oil). 3g zinc particles are added to the arsenic test bottles containing sample digestion solution, reagent blank solution and arsenic standard solution, and immediately plugged with arsenic test tubes pre-filled with lead acetate cotton and mercuric bromide test paper, placed at 25℃ for 1h, and the mercuric bromide test paper of the sample and reagent blank is taken out for comparison with the standard arsenic spot. 21 Result calculation
Same as Chapter 14.
GB/T5009.11—2003
22 Precision
The absolute difference between two independent determination results obtained under repeatability conditions shall not exceed 20% of the arithmetic mean. Method IV Borohydride Reduction Colorimetric Method
23 Principle
The sample is digested, and arsenic exists in pentavalent form. When the hydrogen ion concentration of the solution is greater than 1.0 mol/L, adding potassium iodide-sulfur hydride and heating can reduce pentavalent arsenic to trivalent arsenic. Under acidic conditions, potassium borohydride reduces trivalent arsenic to negative trivalent, forming arsine gas, which is introduced into the absorption liquid and is yellow. The depth of the yellow is proportional to the arsenic content in the solution. Quantitative comparison with the standard series. 24 Reagents
24.1 Potassium iodide (500g/L) + thiourea solution (50g/L) (1+1). 24.2 Sodium hydroxide solution (400g/L) and sodium hydroxide solution (100g/L). 24.3 Sulfuric acid (1+1).
24.4 Absorption liquid
24.4.1 Silver nitrate solution (8g/L): Weigh 4.0g of silver nitrate into a 500mL beaker, add appropriate amount of water to dissolve, then add 30mL of nitric acid, add water to 500mL, and store in a brown bottle. 24.4.2 Polyvinyl alcohol solution (4g/L): Weigh 0.4g of polyvinyl alcohol (1500-1800 wt%) into a small beaker, add 100ml of water, heat in a boiling water bath, stir until dissolved, keep warm for 10 min, take out and cool for later use. 24.4.3 Absorption liquid: Take one portion each of 24.4.1 and 24.4.2, add two volumes of ethanol (95%), mix well as the absorption liquid. Prepare it before use.
24.5 Potassium borohydride tablets: Mix potassium borohydride and sodium chloride in a mass ratio of 1:4 and grind them into fine powder. After fully mixing, make tablets with a diameter of 10mm and a thickness of 4mm on a tablet press. Each tablet is 0.5g. Avoid tableting in humid weather. 24.6 Lead acetate (100g/L) cotton: Soak the absorbent cotton in lead acetate solution (100g/L), squeeze out the excess solution after a few minutes, spread the cotton, dry it at 80℃ and store it in a wide-mouth glass bottle. 24.7 Citric acid (1.0mol/L)-ammonium citrate (1.0mol/L): Weigh 192g citric acid and 243g ammonium citrate, dissolve them in water and dilute to 1000mL.
24.8 Arsenic standard stock solution: Weigh 0.1320g of arsenic trioxide (As2O) dried at 105℃ for 1h and cooled to room temperature in a desiccator into a 100mL beaker, add 10mL sodium hydroxide solution (2.5mol/L), add 5mL perchloric acid and 5mL sulfuric acid after dissolving, heat on a hot plate until white smoke appears, cool, transfer to a 1000mL volumetric flask, and dilute to volume with water. This solution contains 0.100mg of arsenic (pentavalent) per milliliter.
24.9 Arsenic standard application solution: Pipette 1.00mL of arsenic standard stock solution into a 100mL volumetric flask, and dilute to volume with water. This solution contains 1.00μg of arsenic (pentavalent) per milliliter.
24.10 Methyl red indicator (2g/L): Weigh 0.1g of methyl red and dissolve in 50mL of ethanol (95%). 25 InstrumentsbzxZ.net
25.1 Spectrophotometer.
25.2 Arsenic hydrogen generator, see Figure 1.
26 Analysis steps
26.1 Sample treatment
26.1.1 Cereal food: Weigh 5.00g sample into a 250mL conical flask, add 5.0mL perchloric acid, 20mL nitric acid, 80
GB/T 5009.11—2003
2.5mL sulfuric acid (1+1), leave for several hours (or overnight), heat on a hot plate, if the solution turns brown, add nitric acid to completely decompose the organic matter, remove and cool, add 15mL water, heat again until white smoke appears, remove, and transfer the digestion solution quantitatively into a 100mL arsenic hydrogen generator bottle with 20mL water several times. At the same time, make a reagent blank. 26.1.2 Vegetables and fruits: weigh 10.00g-20.00g of sample into a 250mL conical flask, add 3mL perchloric acid, 20mL nitric acid, and 2.5mL sulfuric acid (1+1). Follow the steps in 26.1.1. 26.1.3 Animal food (except seafood): weigh 5.00g-10.00g of sample into a 250mL conical flask, follow the steps in 26.1.1.
26.1.4 Seafood: weigh 0.100g-1.00g of sample into a 250mL conical flask, add 2mL perchloric acid, 10mL nitric acid, and 2.5mL sulfuric acid (1+1). Follow the steps in 26.1.1. 26.1.5 Beverages containing ethanol or carbon dioxide: Pipette 10.0 mL of the sample into a 250 mL conical flask, heat at low temperature to remove the ethanol or carbon dioxide, then add 2 mL of perchloric acid, 10 mL of nitric acid, and 2.5 mL of sulfuric acid (1+1), and proceed as in 26.1.1. 26.1.6 Soy sauce foods: Pipette 5.0 mL~10.0 mL of a representative sample into a 250 mL conical flask, add 5 mL of perchloric acid, 20 mL of nitric acid, and 2.5 mL of sulfuric acid (1+1), and proceed as in 26.1.1. 26.2 Preparation of standard series
Into 6 100mL arsenic hydrogen generating bottles, add 0, 0.25, 0.5, 1.0, 2.0.3.0mL of arsenic standard application solution (equivalent to 0.0.25, 0.5, 1.0, 2.0, 3.0μg of arsenic) in sequence, add water to 3mL respectively, and then add 2.0mL of sulfuric acid (1+1). 26.3 Determination of Sample and Standard
Add 0.1 g ascorbic acid and 2.0 mL potassium iodide (500 g/L)-thiourea solution (50 g/L) to the sample and standard arsenic generation bottles, respectively. Heat in a boiling water bath for 5 min (the temperature in the bottle must not exceed 80°C at this time), take out and cool, add 1 drop of methyl red indicator (2 g/L), add about 3.5 mL sodium hydroxide solution (400 g/L), adjust with sodium hydroxide solution (100 g/L) until the solution just turns yellow, add 1.5 mL citric acid (1.0 mol/L)-ammonium citrate solution (1.0 mol/L), add water to 40 mL, add a potassium borohydride tablet, and immediately connect it to the absorption tube containing 4.0 mL absorption solution through a catheter plugged with lead acetate cotton. Shake the arsenic generation bottle from time to time. After reacting for 5 min, add another potassium borohydride tablet and continue to react for 5 min. Remove the absorption tube, use a 1cm colorimetric cup, adjust the absorbance of the standard tube zero tube to zero at a wavelength of 400nm, and measure the absorbance of each tube. Draw a standard curve or calculate the regression equation by comparing the arsenic content of each tube in the standard series with the absorbance.
27 Result calculation
The content of arsenic in the sample is calculated according to formula (3). Where:
X=AX1000
m×1000
X--the content of arsenic in the sample, in milligrams per kilogram or milligrams per liter (mg/kg or mg/L); A--the mass of the digestion solution obtained from the standard curve, in micrograms (ug); m-the mass or volume of the sample, in grams or milliliters (g or mL). The calculation result retains two significant figures.
28 Precision
The absolute difference between two independent determination results obtained under repeatability conditions shall not exceed 15% of the arithmetic mean. +（3）
GB/T 5009.11—2003
29 Scope
Determination of inorganic arsenic
This standard specifies the determination method of total inorganic arsenic in various foods. This standard is applicable to the determination of total inorganic arsenic in various foods. Detection limit of this method: atomic fluorescence spectrometry: solid sample 0.04 mg/kg, liquid sample 0.004 mg/L; silver salt method: 0.1 mg/kg. Linear range: 1.0 μg～10.0 μg. First method hydride atomic fluorescence spectrometry
30 Principle
Arsenic in food may exist in different chemical forms, including inorganic arsenic and organic arsenic. Inorganic arsenic is extracted in the form of chloride under 6 mol/L hydrochloric acid water bath conditions to achieve the separation of inorganic arsenic and organic arsenic. Total inorganic arsenic is determined under 2 mol/L hydrochloric acid conditions. 31 Reagents
31.1 Hydrochloric acid solution (1+1): Measure 250mL of hydrochloric acid, slowly pour it into 250mL of water, and mix well. 31.2 Potassium hydroxide solution (2g/L): Weigh 2g potassium hydroxide and dissolve it in water, dilute to 1000mL. 31.3 Potassium borohydride solution (7g/I): Weigh 3.5g potassium borohydride and dissolve it in 500mL 2g/L potassium hydroxide solution. 31.4 Potassium iodide (100g/L)-thiourea mixed solution (50g/L): Weigh 10g potassium iodide and 5g thiourea and dissolve them in water, dilute to 100mL and mix well.
31.5 Trivalent arsenic (As3+) standard solution: Accurately weigh 0.1320g arsenic trioxide, add 1mL 100g/L potassium hydroxide and a small amount of sub-boiling distilled water to dissolve, and transfer to a 100mL volumetric flask to make up the volume. This standard solution contains 1mg/mL trivalent arsenic (As3+). When using, dilute it step by step with water to a standard solution concentration of 1μg/mL trivalent arsenic (As3+). It can be used for 7 days if stored in the refrigerator. 32 Instruments
Glass instruments should be soaked in 15% nitric acid for 24 hours before use. 32.1 Atomic fluorescence spectrophotometer.
32.2 Constant temperature water bath.
33 Analysis steps
33.1 Sample treatment
Solid sample: Weigh 2.50g of dry sample that has been crushed and passed through an 80-mesh sieve (the sample weight should be increased or decreased as appropriate according to the sample content) into a 25ml. stoppered graduated test tube, add 20mL of hydrochloric acid (1+1) solution, and mix, or weigh 5.00g of fresh sample (the sample should be slurried first) into a 25mL stoppered graduated test tube, add 5mL of hydrochloric acid, and dilute to the scale with hydrochloric acid (1+1) solution, and mix. Place in a 60℃ water bath for 18 hours, shaking several times during this period to fully extract the sample. Take out and cool, filter with absorbent cotton, take 4mL of filtrate in a 10mL volumetric flask, add 1mL of potassium iodide-thiourea mixed solution, 8 drops of n-octanol (defoaming agent), and make up to volume with water. After standing for 10 minutes, test the inorganic arsenic in the sample. If it is turbid, filter it again and measure it. Perform a reagent blank test at the same time.
Note: After the sample is extracted and cooled, use hydrochloric acid (1+1) solution to make up to 25mL before filtering. Liquid sample: Take 4mL of sample in a 10mL volumetric flask, add 4mL of hydrochloric acid (1+1) solution, 1mL of potassium iodide-thiourea mixed solution, 8 drops of n-octanol, make up to volume and mix well, and determine the total inorganic arsenic in the sample. Perform a reagent blank test at the same time. 33.2 Instrument reference operating conditions
Photomultiplier tube (PMT) negative high voltage: 340V; arsenic hollow cathode lamp current: 40mA; atomizer height: 9mm; carrier gas flow rate: 82
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