1、TAPPI/ANSI T 406 om-13 OFFICIAL STANDARD 1926 TENTATIVE STANDARD 1960 SUGGESTED METHOD 1972 OFFICIAL TEST METHOD 1982 REVISED 1988 REVISED 1994 REVISED 1999 REVISED 2004 REAFFIRMED 2008 REVISED 2013 2013 TAPPI The information and data contained in this document were prepared by a technical committee
2、 of the Association. The committee and the Association assume no liability or responsibility in connection with the use of such information or data, including but not limited to any liability under patent, copyright, or trade secret laws. The user is responsible for determining that this document is
3、 the most recent edition published. Approved by the Standard Specific Interest Group for this Test Method TAPPI CAUTION: This Test Method may include safety precautions which are believed to be appropriate at the time of publication of the method. The intent of these is to alert the user of the meth
4、od to safety issues related to such use. The user is responsible for determining that the safety precautions are complete and are appropriate to their use of the method, and for ensuring that suitable safety practices have not changed since publication of the method. This method may require the use,
5、 disposal, or both, of chemicals which may present serious health hazards to humans. Procedures for the handling of such substances are set forth on Material Safety Data Sheets which must be developed by all manufacturers and importers of potentially hazardous chemicals and maintained by all distrib
6、utors of potentially hazardous chemicals. Prior to the use of this method, the user must determine whether any of the chemicals to be used or disposed of are potentially hazardous and, if so, must follow strictly the procedures specified by both the manufacturer, as well as local, state, and federal
7、 authorities for safe use and disposal of these chemicals. Reducible sulfur in paper and paperboard 1. Scope 1.1 This method describes two procedures for the determination of reducible sulfur in paper and paperboard within the context of the given definitions. 1.1.1 The quantitative procedure found
8、in Section 9 gives a measure of the reducible sulfur with the precision shown in Section 12. 1.1.2 The semi-quantitative test described in section 13 indicates the general level of reducible sulfur with limited accuracy. 2. Significance 2.1 The procedures are not necessarily a measure of how much a
9、given test material will tarnish polished metals. When tested by these procedures, paper which has less than 0.0008% reducible sulfur may be assumed to be nontarnishing as far as sulfur is concerned, but if more than 0.0008%, this does not necessarily mean that tarnishing will occur, because sulfur
10、compounds which may not cause staining are reduced by the treatment with the subsequent evolution of hydrogen sulfide. If more than 0.0008% reducible sulfur is found, or if the effect of that or other materials causing stains on silver is desired, the paper should be subjected to an accelerated tarn
11、ishing test (see TAPPI T 444 “Silver Tarnishing by Paper and Paperboard”). NOTE 1: If the pH of the paper is low, e.g., 4-4.5 (cold extraction), as little as 0.0002% of reducible sulfur may cause tarnishing of imitation gold bronze prints; whereas, if the pH were higher, e.g., on brush-coated art pa
12、per, a much higher quantity of sulfur might be tolerated. 2.2 The procedures described do not give the total sulfur content, nor the total reducible sulfur content, nor are they intended to. They are limited to the reducible sulfur content determined under the conditions of the test (i.e., a fairly
13、mild reduction system) (1). T 406 om-13 Reducible sulfur in paper and paperboard / 2 2.2.1 Those forms of sulfur believed to be “reducible” under the test conditions are (1) sulfide (released by the acid, not actually reduced), (2) elemental sulfur, (3) thiosulfate, (4) other polythionates or polysu
14、lfides, and (5) perhaps sulfite. Sulfate is excluded. 3. Summary 3.1 The semi-quantitative method (see section 13.3) involves the reduction of various forms of sulfur to hydrogen sulfide and the development of a dark spot of lead sulfide on the filter paper impregnated with lead acetate. The intensi
15、ty of the spot is compared with spots developed from standards and is proportional to the concentration. No colorimeter or spectrophotometer is needed for this method. 3.2 The quantitative method uses the identical reduction system to generate H2S, but the sulfide is precipitated by alkaline cadmium
16、 sulfate and then converted to methylene blue by reaction with acidic p-aminodimethylaniline in the presence of ferric chloride. The methylene blue is measured spectrophotometrically, and the intensity is compared with standards prepared in a similar manner. 4. Definitions 4.1 Reducible sulfur is th
17、at sulfur content of a specimen which is released as hydrogen sulfide gas under the conditions of the test. 4.1.1 The conditions of the test are fairly mild reducing conditions intended to predict tarnishing tendency. They are designed to simulate normal atmospheric or environmental conditions (e.g.
18、, high humidity or wetting, acidic conditions, high temperature, high concentrations of reducing gases in the atmosphere, etc.) which may be encountered in the use of paper or paperboard as a packaging material. 5. Apparatus 5.1 Reaction apparatus1(Fig. 1), consisting of a 500-mL roundbottomed 3-nec
19、ked flask as illustrated, equipped with a gas inlet tube adapter with perforated bulb, a 60-mL pear-shaped funnel, a 200-mm condenser, a side-arm adapter, and a heating mantle with variable power supply. Fig. 1 . Reaction apparatus (quantitative determination). 5.2 Absorption apparatus1(Fig. 1), con
20、sisting of a 100-mL amber or low-actinic flask in a suitable ice bath. 5.3 Colorimeter or spectrophotometer, to read at 660-670 nm equipped with 20-50-mm cuvettes. 5.4 Pipets, 1-, 2-, 5-, 10-mL serological or bacteriological (blow-out). 5.5 Other equipment, 100- and 1000-mL volumetric flasks; medici
21、ne droppers; 10- and 100-mL graduated cylinders; forceps; 10.0-mL volumetric pipets. 1Names of suppliers of testing equipment and materials for this method may be found on the Test Equipment Suppliers list, available as part of the CD or printed set of Standards, or on the TAPPI website general Stan
22、dards page. 3 / Reducible sulfur in paper and paperboard T 406 om-13 5.6 Disintegrator, a blender or other such rotating-blade device with a small volume container, if possible. 5.7 Constant temperature bath, at 20-25C (optional). 6. Reagents and materials 6.1 Aluminum foil1, 1145 Alloy, plain (or a
23、luminum weighing pans), not over 0.25 mm thick, sulfur-free. 6.2 Phosphoric acid, concentrated, 85% H3PO4, sulfur-free. 6.3 Cadmium hydroxide absorption suspension: dissolve 4.3 g of cadmium sulfate, 3CdSO4 8H2O in water; add 0.3 g of sodium hydroxide, NaOH, dissolved in water and 10 g of arabinogal
24、actan; dilute to 1000 mL and stir well. This is a saturated solution of cadmium hydroxide; the suspension is swirled before pouring off an aliquot. 6.4 Ferric chloride solution: dissolve 100 g of ferric chloride hexahydrate (FeCl3 6H2O) in water and dilute to 100 mL. 6.5 Amine solutions 6.5.1 Stock
25、amine solution: dissolve 25 g of p-aminodimethylaniline sulfate (i.e., N,N-dimethyl-p-phenylenediamine sulfate) in 75 mL of cold 1:1 sulfuric acid and dilute to 100 mL with the 1:1 acid. NOTE 2: Use as high a purity reagent as possible for best reagent blank results. 6.5.2 Dilute amine solution: pip
26、et 2.5 mL of the stock solution into a 100-mL volumetric flask and dilute to the mark with 1:1 sulfuric acid. 6.6 Sodium sulfide standard solutions (use water deaerated with nitrogen). 6.6.1 Stock solution: dissolve 0.4 g sodium sulfide nonahydrate, Na2S 9H2O (use large crystals which appear dry) in
27、 the deaerated water and dilute to 250 mL. After the solution has been diluted to volume, add 5-10 mL of cyclohexane to protect the solution from air oxidation. This solution should be stable for 1 month. 6.6.1.1 The stock solution shall be at least 90% of its intended strength as made (6.6.1) when
28、used to prepare the calibration standards (9.3). The exact concentration of NaS in the stock solution may be determined by potentiometric titration with silver nitrate solution using a sulfide-specific electrode using the following procedure which was previously found in TAPPI T 625, which has been
29、withdrawn 6.6.1.2 To an 800-mL beaker, add 100 mL of 20% NaOH solution, 35 mL of 1:99 ammonia, and a 100 mL aliquot of 200 ppm stock sulfide solution. Adjust the beaker contents to 500 mL with water. Titrate immediately with standardized AgNO3using magnetic stirring to cause just the beginning of a
30、vortex. 6.6.1.3 Follow the course of the titration potentiometrically, using a silver-silver sulfide indicator electrode and the high pH glass reference electrode. Add the titrant in fixed increments of volume and record the indicated steady emf after each addition. As the end point approaches, ther
31、e will be an increase in E/V, that is, there will be an increase in the change of observed emf per increment of titrant. In the immediate vicinity of the end point, a large and sudden change in the observed emf will occur, to the extent of 100 mV or more. When this happens, add two more increments o
32、f the titrant and stop the titration. 6.6.1.4 Plot the data on linear coordinates with mL of AgNO3as the x axis and emf on the y axis to obtain the usual S-shaped titration curve. Determine the exact amount of AgNO3used at the end point by projecting the inflection point in the curve to the abscissa
33、. Calculate: g/L Na2S = (titre in mL) (N AgNO3) (0.039)(1000) aliquot in mL 6.6.2 Working solution (prepare daily): pipet 10.0 mL of stock solution into a 1000 mL volumetric flask and dilute to the mark with the deaerated water. One milliliter of this solution contains 2 g of sulfur (i.e., solution
34、is 2 ppm in sulfur). NOTE 3: This solution or the stock solution may be standardized by potentiometric titration with silver nitrate solution using a sulfide-specific electrode (see TAPPI T 625 wd-99 “Analysis of Soda and Sulfate Black Liquor” now withdrawn); the sulfide standard should be at least
35、90% pure. 6.7 Nitrogen gas, sulfur free. 7. Sampling T 406 om-13 Reducible sulfur in paper and paperboard / 4 7.1 Obtain a sample in accordance with TAPPI T 400 “Sampling and Accepting a Single Lot of Paper, Paperboard, Containerboard, or Related Product.” 7.2 A minimum of 8 g of sample is required
36、to provide triplicate test specimens, including 2 g for moisture determination. 7.3 Do not touch the test area of sample or test specimens with the fingers; handle with clean forceps only. 8. Test specimens 8.1 From each test unit of the sample, cut three test specimens, each approximately 2 g and w
37、eigh to the nearest milligram. Upon agreement between the users of the method, where the interest is only the presence or absence of reducible sulfur and this method is preferred over the semi-quantitative method in Section 13, a single test may be made and reported upon each sample using the quanti
38、tative procedure, section 9 of this test method. 8.2 Determine moisture content according to TAPPI T 550 “Determination of Equilibrium Moisture in Paper and Paperboard for Chemical Analysis.” 9. Quantitative procedure 9.1 Disintegrate the test specimen in the blender with 75 mL of water and transfer
39、 the test specimen from the disintegrator quantitatively to the 500 mL reaction flask using additional aliquots of 5 mL of water to assist in the transfer. Add 2 g of aluminum foil (or 1 aluminum foil weighing dish) which has been cut into 13 mm squares and complete the assembly of the reaction appa
40、ratus. 9.2 Precipitation of cadmium sulfide 9.2.1 Measure 10 mL of the concentrated (85%) phosphoric acid into the dropping funnel and 75 mL of the cadmium hydroxide absorption suspension (which is swirled before pouring and should include some solids) into the darkened 100 mL volumetric collecting
41、flask. Start bubbling the nitrogen at the rate of about 5 bubbles per second, taking care to ensure that there are no leaks. Use top quality sulfur-free stopcock grease at the joints and if necessary tie the joints with clamps or rubber bands. After the nitrogen has been adjusted, submerge the deliv
42、ery tube into the absorption suspension in the 100 mL volumetric flask and put the ice bath in place, taking care to assure that the tip is to the bottom of the flask (i.e., submerged as deeply as possible). 9.2.2 Add the 10 mL of concentrated phosphoric acid from the dropping funnel. Leave a small
43、amount of acid in the tip, close the stopcock on the funnel, and start heating the mixture to a boil. Take care that the absorption solution does not back up in the delivery tube while the mixture is heating. It may be necessary to adjust the nitrogen flow to prevent this. 9.2.3 Discontinue heating
44、after 45 min, remove the volumetric flask together with the side-arm adapter by dislodging it at the condenser, and stop the nitrogen flow. Keep the adapter together with the flask until the amine reagent is added in the color development step because the cadmium sulfide often hangs up in the tube t
45、ip. The test specimen should not be stored in this manner for more than an hour. 9.3 Preparation of calibration standards (prepare each time the analysis is performed). 9.3.1 Add 75 mL of the cadmium hydroxide absorption suspension to each of five 100-mL darkened volumetric flasks and place in the c
46、onstant temperature bath (at 20to 25C). 9.3.2 Pipet 1, 2, 5, and 10 mL, respectively, of the sodium sulfide standard working solution into four of the volumetric flasks. 9.3.2.1 The “blow-out” (clause 5.4) pipets are used to pipet the sodium sulfide working solution aliquots. They are immersed into
47、the absorption solutions and allowed to drain slowly while the tips are below the surface. When drainage is complete, gently blow out the last drops while still immersed and then remove the flask. “Blow out” pipettes have been used for 9.3.2 in earlier editions of this standard test method to minimi
48、ze introduction of oxygen into the sodium sulfide stock solution and the diluted calibration standards. A digital pipet may be used for preparation of the calibration standards, provided the solutions are protected from air oxidation durng the transfer step. 9.3.3 Swirl gently but adequately. The fl
49、ask containing no sulfide solutions is the reagent blank. The standards contain 2, 4, 10, and 20 g sulfur per 100 mL. 9.4 Color development and read-out 9.4.1 To the test specimen, reagent blank, and calibration standard 100-mL volumetric flasks, add 2 mL of the dilute amine solution. Allow the dense amine solution to flow down the side of the flask to the bottom of the absorption solution. Stopper the flask and swirl gently but adequately a few times without shaking (heat will be regenerated). Immediately add 10 drops of the ferric chloride solution and shake
