Some standard content:
ICS 67. 160
Agricultural Industry Standard of the People's Republic of China
NY/T 273--2002
Replaces NY/T273.--1995
Green Food
Green food-Beer
Issued on 2002-12-30
Implemented on 2003-03-01
Issued by the Ministry of Agriculture of the People's Republic of China
NY/T273-2002
This standard is a revision of NY/T273--1995 "Green Food Beer". Green food is a safe, high-quality and nutritious food. This standard is formulated to ensure the quality of various types of green food beer, draft beer and fresh beer.
Compared with the national standard for beer, the green food beer standard pays more attention to the safety and nutrition of beer. Based on GB4927-2001 "Beer", this standard refers to foreign beer quality control standards and focuses on the content indicators of free sulfur dioxide, formaldehyde and nitrate in beer that exceed a certain limit and are harmful to the human body, as well as the detection methods and safety ranges of their contents. The main differences between this standard and the original standard NY/T273--1995 are as follows: a) "Terms" are changed to "Terms and Definitions", and the definitions of "cooked beer", "draft beer" and "fresh beer" are further improved. The lower limit of color of light beer is changed from 5EBC to 3EBC.
b) "Classification" and "Specification" are cancelled. c) Beer indicators are specified according to "superior grade" and "first grade". Foam retention of light beer: bottled premium and first-grade beer are changed to no less than 200s and 170s respectively, and canned premium and first-grade beer are changed to no less than 170s and 150s respectively; the foam retention of dark and black beer is the same as that of bottled light beer; there is no requirement for the foam retention of barrel beer.
The measurement unit of alcohol content is changed from mass percentage [% (m/m) to volume fraction (%). e
f) "Original wort concentration" is expressed by Plato (\P). The original wort concentration is determined by the manufacturer, but the allowable negative deviation is specified. g) The "total acid" index is tightened. The "total acid" of pale beer with a temperature of 14.1°P or more, 10.1°P to 14.0°P or less than 10.0°P shall not be greater than 3.5ml./100ml., 2.6mL/100mL and 2.2mL/100mL respectively; the "total acid" of dark and black beer shall not be greater than 4.0ml./100ml.
h) The upper limit of "carbon dioxide" has been added. The "carbon dioxide" of premium and first grade in bottles (cans) has been changed to: the mass fraction is 0.40%~0.65%.
The "diacetyl" index of premium pale beer has been changed to: not greater than 0.10mg/L: no requirement is made for dark and black beer.i)
j) The "free sulfur dioxide" index has been added, which is required to be less than 15mg/L.k) The "formaldehyde" index has been added, which is required to be less than 200μg/L. The "nitrate" index has been added, which is required to be less than 25mg/l. 1)
m) In the inspection rules, the sampling volume is appropriately increased. n) The "warning" requirements are specified in the label content. Appendix A, Appendix B and Appendix C of this standard are all normative appendices. This standard is proposed and managed by the China Green Food Development Center. The main drafting unit of this standard: School of Bioengineering, Jiangnan University. The main drafters of this standard: Gu Guoxian, Lu Jian, Li Qi, Sun Junyong. This standard was first issued in 1995.
1 Scope
Green Food
NY/T 273—2002
This standard specifies the terms and definitions, technical requirements, analysis methods, inspection rules and labels, packaging, transportation and storage requirements of green food beer.
This standard applies to all types of cooked, raw and fresh beers that have obtained the green food label. 2 Referenced Standards
The clauses in the following documents become the clauses of this standard through reference in this standard. For any dated referenced document, all subsequent amendments (excluding errata) or revisions are not applicable to this standard. However, parties that reach an agreement based on this standard are encouraged to study whether the latest versions of these documents can be used. For any undated referenced document, the latest version is applicable to this standard. GB/T191—2000 Pictorial signs for packaging, storage and transportation GB2758 Hygienic standards for fermented wine
GB 4544-1996 Beer bottles
GB4927—2001 Beer
GB/T4928-2001 Beer analysis methods
GB/T5009.49--1996 Analysis methods for the hygienic standards for fermented wine GB/T5738-1995 Plastic turnover boxes for bottled wine and beverages GB/T 6543—1986
Corrugated paper boxes
GB7718--1994 General standard for food labeling (neqCAC.CodexStan.1:1991) GB 9106—19941
Packaging containers Aluminum two-piece cans with easy-open lids
GB 10344—1989
Standard for labeling of alcoholic beverages
GB/T 17714-—1999Beer barrels (neq DIN 6647(T1):1978)NY/T391—2000Technical conditions for the production environment of green food3Terms and definitions
The following terms and definitions apply to this standard. 3.1
Green foodgreen food
Food that is pollution-free, safe, high-quality and nutritious and is produced in accordance with the principle of sustainable development and in a specific production method, approved by a specialized agency and permitted to use the green food logo.
Green food beergreen food beer
Beer with the green food logo
Light beerlight beer
Beer with a color of 3EBC to 14EBC.
NY/T 273--2002
dark beer
Beer with a color of 15EBC to 40EBC.
black beer
Beer with a color of 41EBC or more.
pasteurized beer
Beer that has been pasteurized or sterilized by high temperature. 3.7
draft beer
Beer that has been sterilized by physical filtration without being pasteurized or sterilized by high temperature to achieve a certain biological stability. 3.8
fresh beer
Beer that has been sterilized without being pasteurized or sterilized by high temperature and is allowed to contain a certain amount of live yeast in the finished product to achieve a certain biological stability. 3.9
Dry beer
In addition to meeting the technical requirements for pale beer, the actual fermentation degree shall not be less than 72%. The taste is refreshing. 3.10
Plato (°p)
An internationally accepted unit for expressing the original extract content, which means the number of grams of extract contained in 100 g of wort.
Ice crystallize
The process of super-freezing the beer before filtration through a special freezing equipment to form fine ice crystals. Technical requirements
4.1 Raw material production environment requirements
Must meet the requirements of NY/T 391.
4.2 Raw material requirements
Must meet the requirements of green food.
4. 3 Negative deviation of net content
4.3.1 When green beer is packed in bottles or cans (short for two pieces of aluminum easy-open lids) at 20℃, the negative deviation of its net content (net capacity) from the volume marked on the label is: less than 500mL/bottle (can), shall not exceed 8mL; equal to or greater than 500mL/bottle (can), shall not exceed 10mL. 4.3.2 When green beer is packed in barrels
20℃, the negative deviation of its net content from the volume marked on the label is: 1L~~14L/barrel, shall not exceed 2.0%; equal to or greater than 15L/barrel, shall not exceed 1.5%.
4.4 Sensory requirements
4.4.1 Green food pale beer
shall comply with the requirements of Table 1.
Transparency
Turbidity/EBC
Foam retention/s
Aroma and taste
Table 1 Sensory requirements for green food pale beer Excellent
NY/T 273--2002
Clear and transparent, fine suspended matter and sediment visible to the naked eye (not foreign matter) are allowed 0.9
Foam is white and delicate,Long-lasting cup hanging
With obvious hop aroma, pure taste, refreshing. The body of the wine is harmonious, soft, without strange aroma and odor
Green food dark color and black beer
Should meet the requirements of Table 2.
The foam is white and delicate, and lasts longer.
With obvious hop aroma, pure taste, refreshing, harmonious, without strange aroma and odor
Table 2 Sensory requirements for green food dark color and black beer Items
Transparency
Foam persistence/s
Aroma and taste
4.5 Physical and chemical requirements
Should meet the requirements of Table 3.
Alcohol content\/(%)
[Volume fraction
(Mass fraction)Gate
Original wort concentration/°P
Total acid/(ml/100mL)
Carbon dioxide/(%)Mass fraction
The body is shiny, and visible fine suspended matter and sediment (not foreign matter) are allowed. The foam is white and delicate, and it hangs on the cup for a long time
The foam is relatively white and delicate, and it hangs on the cup for a long time
It has obvious malt aroma, pure and refreshing taste, and has obvious malt aroma, pure and refreshing taste. The body is mellow and soft, and it has no odor. It has no odor.
Table 3 Physical and chemical indicators of green food beer
Light beer
≥14.1°P
12.1°P~14. 0°P
11. 1°P~~12. 0°P
10. 1°P~~11. 0°P
8. 1°P~10. 0°P
≥10.1°p
≥14.1'P
10. 1°P-~14. 0'P
Dense, black beer
5.5(4. 3)
0.40~0.65
NY/T 273—2002
Diacetyl/（mg/1.）
In sucrose invertase activity
Lead (Pb)/（mg/kg）
Monument (As)/（mg/kg）
Aflatoxin B, /(μg/kg）
Nitrate/（mg/L）
Free sulfur dioxide/（mg/L）
Formaldehyde/（μg/1.）
a Does not include low-alcohol beer.
Table 3 (continued)
bx is the original wort concentration marked on the label, "--0.3\ or "-0.2\ is the allowed negative deviation. C Only has requirements for "light beer".
d Only has requirements for "raw wine" and "fresh beer". 4.6 Hygiene indicators
Should comply with the provisions of GB2758.
Positive
4.7 Shelf life
The shelf life of bottled and canned (raw and cooked) wine shall not be less than 60 days, and the shelf life of barreled (raw and cooked) beer shall not be less than 30 days. The shelf life of fresh beer shall not be less than 5 days.
5 Analysis method
5. 1 Net content negative deviation, sensory requirements and physical and chemical index inspection shall be carried out in accordance with GB/T4928.
5.2 Inspection of hygiene indicators
According to GB/T5009.49.
5. 3 The determination of formaldehyde content, free sulfur dioxide content and nitrate content shall be carried out according to the methods in Appendix A, Appendix B and Appendix C. 6 Inspection rules
6.1 Acceptance
6.1.1 All beers produced with the same raw materials, the same formula and the same process, after mixed filtration, the same sake and the same packaging line are packaged and shipped out of the factory (or warehouse) on the same day, and the products with the sample quality inspection report are considered as one batch. 6.1.2 The manufacturer shall ensure the quality of the products and shall inspect the products batch by batch according to this standard and GB/T4928. The products shall be accompanied by a quality certificate signed by the quality supervision and inspection department, and unqualified products shall not be shipped out of the factory. 6.1. 3 The consignee has the right to take samples from the delivered batch of products upon receipt of the goods and conduct inspections in accordance with the provisions of GB/T4928 and this standard. In the inspection results, if one of the physical and chemical requirements and the microbiological requirements does not meet the requirements, the same batch of products may be re-sampled for re-inspection. If it still fails to meet the requirements, the batch of products shall be deemed unqualified.
6.1.4 When the supply and demand parties have a dispute over product quality, the two parties shall negotiate to resolve the dispute or entrust an arbitration unit to conduct a re-inspection, and the re-inspection results shall be the final basis for judgment.
6.1.5 The labeling and inspection of products for export may be carried out according to the agreement between the two parties. 22
6.2 Sampling
NY/T 273—2002
Draw samples according to Table 4, and then randomly draw the number of unit samples from each sample. After sampling, labels should be affixed immediately, indicating: sample name, variety, quantity, manufacturer name, sampling time and place, and sampler. One-third of the samples should be sealed and kept at 5℃~10℃ for 10 days for future reference. The remaining samples should be sent to the laboratory immediately for sensory, physical and chemical and hygiene index inspections. Table 4 Sampling arrangements for each batch of green food beer Batch range/box
Less than 50||tt| |51~1200
≥1201 and above
7 Marking, packaging, transportation, purchase and storage
7.1 Marking
Number of samples/box
Number of unit samples/can (bottle)/box
7.1.1 Sales packaging labels shall comply with the relevant provisions of GB10344 and GB7718, indicating: product name, raw materials, alcohol content, original wort concentration, net content (net capacity), manufacturer's name and address, canning (production) date, shelf life. Standard number and quality grade shall be adopted; "Warning: Do not hit to prevent bottle explosion" shall also be printed on the label, attached label or outer packaging. 7.1.2 In addition to indicating the product name, manufacturer's name and address, the outer packaging carton shall also indicate the net content and total quantity of the unit package. 7.1.3 The packaging storage and transportation graphic signs shall comply with the requirements of GB/T191. 7.2 Packaging
7.2.1 Glass bottles used for bottled beer shall comply with the requirements of GB4544. 7.2.2 Canned beer shall be packaged in packaging containers with sufficient pressure resistance, such as aluminum two-piece cans with easy-open lids that shall comply with the requirements of GB9106. 7.2.3 Barreled beer shall be packaged in beer barrels that comply with the requirements of GB/T17714. 7.2.4 (Bottles, cans, and barrels) Products shall be tightly packaged and shall not leak air or beer. 7.2.5 The outer packaging of bottled beer shall use corrugated paper boxes that comply with the requirements of GB/T6543, plastic turnover boxes that comply with the requirements of GB/T5738, or soft plastic overall packaging. Bottled beer shall not be tied with ropes for sale. Note: When using an automatic packaging machine for packaging, no partition material is allowed in the corrugated paper box. 7.3 Transportation, Purchase and Storage
7.3.1 When transporting beer, it should be handled with care, not thrown, and should be free from impact and squeezing. 7.3.2 Beer should not be mixed, stored or transported with toxic, harmful, corrosive, volatile or odorous items. 7.3.3 Beer should be transported and stored at 5℃～25℃; if the temperature is lower or higher than this range, appropriate antifreeze or heat protection measures should be taken. 7.3.4 Beer should be stored in a cool, dry and ventilated warehouse; it should not be piled in the open air, and should be strictly protected from sunlight and rain; it should not be in direct contact with wet ground.
NY/T 273—2002
A.1 Principle
Appendix A
(Normative Appendix)
Determination of trace formaldehyde in beer—AHMT colorimetric method Formaldehyde condenses with 4-amino-3-hydrazine-5-mercapto-1,2,4-triazole (AHMT for short) under alkaline conditions and is oxidized by potassium periodate to form a purple-red triazole condensate, the color depth of which is proportional to the formaldehyde content. A.2 Reagents
The preparation of various reagents is shown in Table A.1, and the calibration of formaldehyde is shown in Table A.2. Table A.1 Preparation of various reagents in AHMT colorimetry No.
Reagent name
5 g/L AHMT solution
15 g/L potassium iodate solution
Standard formaldehyde bath solution
100 g/L zinc acetate solution
0.5 mol/L hydrochloric acid solution
0. 2 mol/1. potassium hydroxide solution
5 mol/1. potassium hydroxide-EIDTA solution
Preparation method
Weigh 0.25 g AHMT and dissolve it in 0.5 mol/L hydrochloric acid, dilute to 50 ml.
Weigh 0.75 g potassium periodate and dissolve it in 0.2 mol/1. Potassium hydroxide, heat in a water bath to dissolve, and dilute to 50ml.
Pipette 2.8mL of formaldehyde solution (containing 36%
38%) into a 1L volumetric flask, add 0.5ml.sulfuric acid and dilute to the mark with water, shake well.
Take 10 g zinc acetate and dissolve it in water, make up to 100 ml.
Weigh 4.45 ml hydrochloric acid (35% ~ 37% hydrochloric acid) and make up to 100 ml.
Weigh 1.18 g potassium hydroxide and dissolve it in water, make up to 100 ml with distilled water.
Weigh 10. 0 g disodium ethylenediaminetetraacetate (EDTA-2Na) in 5 mol/1., potassium hydroxide solution, dilute to 100 ml.
Put it in a brown bottle and store it at room temperature for half a year.
The accurate concentration needs to be calibrated by iodine titration
Table A. 2 Calibration of formaldehyde standard solution
Sodium thiosulfate solution (c(NazS,O, 5H,0)=0. 05 mol/I) Weigh 26 Dissolve each sodium thiosulfate in boiled and cooled water and dilute to 1 000 mL. Add 0.4 g sodium hydroxide and store in a brown bottle. Accurately weigh the standard potassium dichromate (dried at 130℃～140℃ for 3h～4h, about 0.05g~0.06g is needed to standardize 0.05 mol/L solution) to be titrated with 18 ml~20 mL sodium thiosulfate solution, place it in an iodine volumetric flask, dissolve NY/T 273—2002
Standardized formaldehyde standard stock solution
Absorb 2.8 mL formaldehyde solution (containing 36%~38% formaldehyde), and dilute to 1 000 ml with water. This solution contains about 1 mg formaldehyde per liter. Pipette 20.0ml of formaldehyde stock solution into a 250mL iodine volumetric flask, add 50ml of 0.05mol/L iodine solution and 15ml of 4% sodium hydroxide solution, add a stopper, mix and place under a hood for 15min. Add 3% sulfuric acid to 50mL of water. Add 2mL of concentrated sulfuric acid and 1g of sodium carbonate, gently shake 20ml and mix. Place for another 15min. Dissolve the iodine volumetric flask with sodium thiosulfate to allow carbon dioxide to escape. Add 1g of potassium iodide and shake well, place in a dark place for 10min, add water to 100mL, and titrate with the sodium thiosulfate solution to be calibrated. When it is close to the end point (the solution is light yellow-green), add 2.5ml of 0.2% starch indicator and continue to titrate until the solution changes from blue to bright blue. Perform a blank test at the same time.
M= (V,=V) ×0. 049 03 ×2
Wherein:
G—mass of potassium dichromate, in grams (g); V,-amount of sodium thiosulfate solution used, in milliliters (ml.); Vz--
amount of sodium thiosulfate solution used in blank test, in millikelvin (mL);
actual concentration of sodium thiosulfate solution, in moles per M-
liter (mol/L);
A.3 Instruments and equipment
Mass of potassium dichromate in grams equivalent to 1. 00 mL sodium thiosulfate solution [c(Na2S,O,)=1. 000 mol/1.],
conversion factor of sodium thiosulfate.
A.3.1 Number of 10mL stoppered colorimetric tubes.
When the solution turns light yellow, add 1 ml of 0.2% starch solution and continue to titrate until the blue color just fades. At the same time, replace the formaldehyde solution with water, and do a blank test in the interlaced steps. Calculate the concentration of formaldehyde according to the following formula:
(Vl - V.) × MX 15 X 1 000
Where:
Concentration of formaldehyde in the standard stock solution of formaldehyde, in milligrams per milliliter (mg/1.);
Volume of sodium thiosulfate solution consumed in the blank, in milliliters (ml.);
Volume of sodium thiosulfate solution consumed for the calibration of formaldehyde, in milliliters (ml.);
Standard concentration of sodium thiosulfate solution, in M-
Moles per liter (mol/1.);
15-conversion value of formaldehyde.
A.3.2 Spectrophotometer: with a wavelength of 550nm and equipped with a colorimetric III with a 10mm optical path. A.4 Operation method
A.4.1 Drawing of standard curve
Dilute the formaldehyde standard stock solution to about 1 mg/L. Pipette 0 mL, 0.5 ml, 1.0 ml, 1.5 ml, 2.0 mL, 2.5 mL and 3.0 mL of the formaldehyde dilution solution into 10 mL stoppered colorimetric tubes respectively. Make up to 5 mL with pure water (equivalent to 0 μg/L, 114 μg/L, 229 μg/L, 343 μg/L, 458 μg/L, 573 μg/L and 687 μg/L formaldehyde). Then add 2.0 ml. 5 mol/L potassium hydroxide EDTA solution and 1.5 mL 5 g/L AHMT solution. Mix by inverting five times and place at room temperature (20°C) for 20 min. Add 0.5ml of 15g/l potassium periodate solution, mix it upside down 30 times, and let it stand for 5 minutes to allow the color reaction to be complete. Then use 10mm colorimetric blood, adjust the zero with the zero tube as the reference, measure the absorbance at a wavelength of 550nm, and draw a standard curve. A.4.2 Sample pretreatment
Because different beers have different chromaticities, the influence of chromaticity must be removed by distillation. Take 50ml of degassed beer, place it in a full glass distiller, add 10ml of water, 0.5ml of 10% sulfuric acid solution, 1ml of 100g/L zinc acetate solution and several glass beads. Distill at a distillation rate of 6mL/min~10mL/min, collect 45ml of distillate and make up to volume in a 50mL volumetric flask with distilled water.
NY/T273—2002
A.4.3 Determination of samples
Take 2.5mL of distillate (depending on the formaldehyde content in the sample) in a 10ml colorimetric tube, add water to make up to 5mL, then add 2.0ml5mol/L potassium hydroxide-EDTA solution, 1.5mL5g/L AHMT solution, turn upside down 5 times to mix, and place at room temperature (20℃) for 20min. Add 0.5mL15g/L potassium periodate solution, turn upside down 30 times to mix, and place accurately for 5min to complete the color reaction. Use 10mm colorimetric blood, adjust zero with the zero tube as reference, and measure the absorbance at a wavelength of 550nm (pay attention to the accurate control of the number of upside-down and color reaction time).
A.5 Calculation
A.5.1 Drawing of standard curve
Draw the standard curve with formaldehyde concentration as the horizontal axis and absorbance as the vertical axis. A.5.2 Calculation of formaldehyde content in samples
Find out the formaldehyde content from the standard curve according to the absorbance of the sample, and then multiply it by the dilution factor. A.6 Interference factors
Acetaldehyde, propionaldehyde, n-butyraldehyde, acrolein, crotonaldehyde, glyoxal, benzaldehyde, methanol, ethanol, n-propanol, n-butanol, sec-butanol, isobutanol, isopyrrolidone, and ethyl acetate have no effect on this method. Detection limit
The minimum detection concentration is 35ug/L.
A.8 Spiked recovery
The spiked recovery ranges from 97% to 101%.
B.1 Principle
Appendix B
(Normative Appendix)
Determination of free sulfur dioxide in beer—iodine titration method NY/T 273-—2002
The sample is acidified with sulfuric acid, starch is used as an indicator, and iodine standard solution is used for titration to determine the content of free sulfur dioxide. The titration reaction can be expressed as: SO2+I +2H20— SO2-+21-+4H+
B.2 Reagents
B. 2. 1 Sulfuric acid solution (25%).
B. 2.2 Iodine standard solution (0. 01 mol/L)First, prepare 0.05 mol/L iodine standard solution. Weigh a little more iodine than the theoretical amount (about 13g for preparing 0.05mol/L iodine standard solution) and add potassium iodide at a ratio of 25g potassium iodide per 13g iodine, dissolve in 100ml water, dilute to 1000ml, and shake. Then dilute 5 times with 0.05mol/L iodine standard solution and calibrate. B.2. 2. 10. 01 mol/L iodine standard solution calibration Use a basic burette to accurately measure 40.00mL of iodine solution to be calibrated, place it in an iodine volumetric bottle, and add 150mL of water. When titrating with a standard sodium thiosulfate solution of similar concentration to the near end point (the solution is very light yellow), add 5mL of 0.2% starch indicator solution and continue titrating until the blue color of the solution disappears. At the same time, use an equal amount of water to add 0.05mL. iodine solution and 5mL0.2% starch indicator solution for a blank test, and titrate with sodium thiosulfate solution until the blue color of the solution disappears.
B. 2. 2.2 Calculation
M=(Vi_V)×MWww.bzxZ.net
Where:
M——actual concentration of iodine standard solution, in mol/L; V. --Amount of sodium thiosulfate standard solution, in milliliter (mL); V. --Amount of sodium thiosulfate standard solution used in blank test, in milliliter (mL); M, ----actual concentration of sodium thiosulfate standard solution, in mol/L; V-Amount of iodine solution used, in milliliter (mL);
0.05 --Amount of iodine solution used in blank test, in milliliter (mL). B. 2. 3 Sodium thiosulfate standard solution
B. 2. 3. 1 Preparation of sodium thiosulfate standard solution Weigh more sodium thiosulfate than the theoretical amount (about 26 g of sodium thiosulfate pentahydrate or 16 g of sodium thiosulfate are needed to prepare 0.05 mol/L solution) and dissolve it in 1000 mL of water. Boil slowly for 10 minutes, cool, and add 0.2g of sodium carbonate. Transfer the solution to a reagent bottle (this reagent bottle needs to be washed with chromic acid solution and then fully rinsed with boiled and cooled water), place it in a dark place for two weeks, filter it and set it aside. B. 2. 3. 2 Standardization of sodium thiosulfate standard solution Use an alkaline burette to accurately measure 40 mL of sodium thiosulfate solution, place the titration standard potassium dichromate (dried at 130 ℃ ~ 140 ℃ for 3h ~ 4h, about 0.20g ~ 0.23g is required for standardization of 0.05mol/L solution) in an iodine volumetric bottle, and dissolve it in 100mL of water. Add 4mL of sulfuric acid and 2g of sodium thiosulfate and gently shake the phosphorus volumetric bottle to allow carbon dioxide to escape. Add 2g potassium iodide, shake well, place in the dark for 10min, add water to 200ml, titrate with the sodium thiosulfate solution to be calibrated, add 5mL 0.2% starch indicator solution when near the end point (the solution is light yellow-green), and continue titrating until the solution changes from blue to bright green. Perform a blank test at the same time. 27
NY/T 2732002
B, 2. 3. 3 Calculation
Wherein:
(V, - V,) × 0. 049 03 × 2
G-mass of potassium dichromate, in grams (g); V.-amount of sodium thiosulfate solution used for calibration, in milliliters (mL); amount of sodium thiosulfate solution used for blank test, in milliliters (mL); V2-
0. 049 03--
-actual concentration of sodium thiosulfate solution, in mol/L, (B.2)
the mass of potassium dichromate in grams equivalent to 1.00mL of sodium thiosulfate solution [c(Na,S,O.) = 1.000mol/L];
2 ~—Conversion factor of sodium thiosulfate.
B.2.4 Starch indicator solution (0.2%)
1.0g soluble starch, add a small amount of water to make a paste, pour into 400mL boiling water under constant stirring, boil slightly for 2min, cool, dilute with water to 500mL, a 0.2% solution. Add 0.5g thymol or 5mg mercuric iodide to the solution for preservation. B.3 Operation
Pull 50mL of the sample into a 250ml iodine volumetric flask, add 5mL sulfuric acid and 5mL starch indicator solution, and quickly titrate with 0.01mol/L iodine standard solution until the solution turns light blue and keeps it for 1min~2min without fading. Perform a blank test at the same time. B.4 Calculation
Free sulfur dioxide (SOa, mg/L) = (-Vo) × MX × 64 × 1 000V
Wu Zhong:
V——Amount of sample titration standard solution, in milliliters (mL) V. -Amount of blank test standard solution, in milliliters (mL) M--Actual concentration of iodine standard solution, in moles per liter (mol/L) V,----Sampling volume, in milliliters (mI),64-
-Conversion factor of sulfur dioxide.
B.5 Explanation
B.5.1 The sample should be kept away from air. The stopper of the iodine volume bottle should be opened only during titration to prevent sulfur dioxide from escaping and being oxidized. B.5.2 The titration temperature should be kept below 20℃. In hot seasons, a few ice cubes can be added to the test solution first, and then acidified with sulfuric acid. B.5.3 When approaching the titration endpoint, the solution begins to darken and then turns blue.
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