This standard specifies the determination of water-soluble sulfate in pulp, paper and paperboard by conductivity titration. The minimum limit of sulfate ion in the material analyzed by this method is 20 mg/kg. GB/T 2678.6-1996 Determination of water-soluble sulfate in paper, paperboard and pulp (conductivity titration) GB/T2678.6-1996 Standard download decompression password: www.bzxz.net

GB/T 2678.6—1996
This standard is based on the number G94006 in the document No. 8 of the China Light Industry General Association (1994) on the "1994 National Standard and Industry Standard Planning Project for the Papermaking Industry". This standard amends the national standard GB5404--85 "Determination of water-soluble suiphates in paper, board and pulp".
This standard is equivalent to ISO 9198: 1989\Paper, board and pulp--Determination of water-soluble suiphates-Titrimetric method". It is also in accordance with GB 1.4--88 "Standardization Guidelines for Chemical Analysis Methods" and GB/T 1.1-1993 "Guidelines for Standardization Work Unit 1: Rules for Drafting and Presentation of Standards Part 1: Basic Provisions for Standard Writing" are revised.
In this revision, in addition to the modifications to the text, higher requirements are put forward for the sensitivity of the conductivity meter, and a method of using a calculator for linear regression to calculate the consumption of lithium sulfate in titration is added, which brings convenience to analysts. From the date of its entry into force, this standard will also replace GB5404-85. This standard was proposed by the China Light Industry Federation.
This standard was submitted by the National Technical Committee for Standardization of Paper Industry. The responsible drafting unit for this standard: China Pulp and Paper Industry Research Institute. The main drafters of this standard: Wei Pengyue and Yang Yanfei. 247
GB/T2678.6—1996
ISO Foreword
ISO (International Organization for Standardization) is a national standard research institute (ISO member) of a group of countries. Worldwide Federation. The preparation of international standards is carried out by ISO technical committees. Each member country interested in a topic established by a technical committee has the right to participate in the work of the committee. International organizations, governmental or non-governmental, in contact with ISO may also participate in its work. ISO maintains close cooperation with the International Electrotechnical Commission (IEC) on all matters of electrical technical standardization. Draft international standards adopted by the technical committee must be sent to member countries for review before being accepted as international standards by the ISO Council. According to ISO's procedural requirements, the review standards must be approved by at least 75% of the member countries. International Standard ISO9198 was proposed by ISO/TC6 Technical Committee on Paper, Board and Pulp. 248
1 Scope
National Standard of the People's Republic of China
Determination of water-soluble sulfate
salts in paper, board and pulp (conductometric titration)
Paper,board and pulp-Determination of water soluble sulphates (Conductimetric titration method)GB/T 2678.6-1996
eqv ISO 9198:1989
Replaces GB5404-85
This standard specifies the determination of water soluble sulfates in pulp, paper and paperboard by conductivity titration. The minimum limit of sulfate ions in the material analyzed by this method is 20 mg/kg. 2 Reference standards
The provisions contained in the following standards constitute the provisions of this standard through reference in this standard. When this standard is published, the versions shown are valid. All standards will be revised, and parties using this standard should explore the possibility of using the latest versions of the following standards. GB450-89 Paper and paperboard sample collection
GB46289 Determination of moisture content of paper and paperboard
GB740-89 Pulp sample collection
GB741-89 Determination of moisture content of pulp analysis sample 3 Principle
At least 4g of sheet sample is extracted with 100mL of hot water for 1h, the extract is filtered, and the sulfate ions therein are precipitated with excess barium ions, and the excess barium ions are determined by conductivity titration with lithium sulfate. 4 Reagents
In the analysis, analytically pure (AR) reagents and water specified in 4.1 are used. 4.1 Distilled water or deionized water; conductivity less than 1.0mS/m. 4.2 Ethanol (C,H.OH): 95% (V/V). 4.3 Barium chloride solution: c(BaCl·2H,0)～5mmol/L. Dissolve 1.25 g of two crystal waters of barium chloride in water (4.1) and dilute to 1 L. 4.4 Hydrochloric acid: c(HCl) 1 m mol/L solution. 4.5 Lithium sulfate standard solution: c(LizSO4· H,O) = 5 m mol/L. Dissolve 0.640 g of dry single crystal water lithium sulfate in water (4.1) accurately, transfer to a 1 L volumetric flask, and dilute to the mark with water.
5 Instruments
5.1 Conductivity meter, sensitivity 0.001 mS/m, 5.2 Microburette, 5 mL, scale 0.02 mL. If conditions permit, an automatic titration device can also be used. Approved by the State Administration of Technical Supervision on June 25, 1996, and implemented on January 1, 1997
GB/T2678.6—1996
5.3 Constant temperature water bath, capable of controlling and adjusting the temperature to 25℃±0.5℃ or other temperatures close to room temperature, and maintaining constant temperature during the titration process. It is essential for the accuracy of the experimental results to keep the temperature of the test solution constant throughout the titration process. 5.4 Agitator and automatic titration device, capable of controlling and adjusting the temperature. 6 Sample collection and preparation
Pulp samples shall be collected in accordance with the provisions of GB740, and average samples of paper and paperboard shall be collected in accordance with the provisions of GB450. During the sampling process, clean gloves should be worn to take samples and prepare paper sheets, and they should be taken carefully to prevent contamination of the samples. The samples should be kept away from acid mist and dust.
7 Test steps
Two tests shall be conducted for each sample. The blank test of the reagent should also be carried out completely according to the operating steps of the sample. 7.1 Extraction of paper sample
Weigh no less than 4g of air-dried sample (accurate to 0.01g), and weigh the sample to determine the moisture content. The moisture content of paper and paperboard samples shall be determined in accordance with GB462, and the moisture content of pulp samples shall be determined in accordance with GB741. Cut or tear the sample into pieces of about 5mmX5mm in size and put them into a 250mL conical flask with a standard interface. The thick paperboard should be dissociated and layered before extraction. Then use a pipette to transfer 100mL of water (4.1), connect the air condenser, put it in a water bath, fix the conical flask, heat and extract for 1h, and shake it from time to time.
When the extraction time reaches the end, remove it and cool it to room temperature, then filter it with a glass filter or Buchner funnel and pre-treated ash-free filter paper, and collect the filtrate in a clean conical flask with a stopper. 7.2 Determination of Sulfate
Use a pipette to draw 50.0 mL of the extracted filtrate and place it in a 250 mL beaker. Add 100 mL of 95% ethanol (4.2), 10 mL of hydrochloric acid (4.4), and accurately add 2.0 mL of barium chloride solution (4.3). Place the beaker in a constant temperature water bath (water bath temperature is 25°C ± 0.5°C) or at a relatively stable room temperature. Insert the electrode of the conductivity meter into the test solution. Use a glass rod or a stirring device to stir the test solution at a uniform speed. After the temperature stabilizes, use a microburette (5.2) to add 0.2 mL of lithium sulfate standard solution (4.5) each time. After each addition of lithium sulfate, record the conductivity indicator when it reaches a constant value. Repeat the addition of standard solution and read the corresponding conductivity value until the total volume of lithium sulfate added reaches 3.5 mL to 4.0 mL. If an automatic titrator is used, the rate of addition of lithium sulfate titrant should be controlled at about 0.2 ml/min. Note: In order to ensure complete precipitation of sulfate ions, it is very important to have a sufficient excess of barium ions at the beginning of the titration. If the corresponding consumption of lithium sulfate is less than 1 ml, a small amount of extract (less than 50 ml, such as 20 ml or 10 ml, etc.) should be taken, and then distilled water should be added to make the total volume 50 ml, and the measurement should be repeated. 7.3 Calculation of milliliters of lithium sulfate consumed in titration 7.3.1 Method 1: Draw a titration curve with the milliliters of lithium sulfate added as the horizontal axis and the conductivity reading of the solution as the vertical axis, and plot the test results. Draw straight lines through each point to form a "V" shape, and read the volume of lithium sulfate standard solution consumed at the intersection of the two straight lines.
7.3.2 Method 2: Use a calculator to discard 2 to 3 points at the intersection of the two straight lines, and then calculate the slope and intercept of the regression equations of the two straight lines:
Y+ b,X +ai
Where: br——-slope;
intercept.
Y2= b2X, + a2
Where: b2
—slope;
intercept.
GB/T 2678.61996
When two straight lines intersect at the coordinate (X,Y), Y=Y,-Y2,X=X,=X2. Solving the simultaneous equations yields:
8 Calculation of results
The water-soluble sulfate content of the sample is calculated by formula (4): (ay a2)
(b, - b,)
X = 96. 1c .Ve (V. - V)
Wherein: X-water extract sulfate content, mg/kg; the actual concentration of lithium sulfate solution (standard is 5mmol/L), mmol/I; 96.1
monosulfate (SO) molecular weight,
V. —the volume of lithium sulfate solution consumed during blank titration, mL; V. —the volume of lithium sulfate solution consumed during test solution titration, mL; V,
the volume of extract taken for titration (standard is 50mL), mL; V3 —the total volume of water added during the test (standard is 100 mL), mL; m —the mass of the absolute dry sample, g.
Substituting c, V2, V: into the standard values, the formula is simplified to: 961(V.Vi)
·（4）
（5）
Take the average of the two test results as the water-soluble sulfate content, expressed in milligrams per dry gram of absolutely dry sample, and round the result to the integer.
Test reportbzxz.net
The test report should include the following:
a) National standard number;
b) Date and place of the test;
c) Mark of the material tested;
d) Test results;
e) Any changes in the prescribed operating procedures or other details that may affect the test results. 251
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