Determination of the pH of whole tobacco: T-310
1 Scope of application
1.1
This method is to be used to determine the pH of a 10% (w/v) suspension of tobacco in water by means of a pH meter.
2 Normative references
2.1
Health Canada Official Method T-115. Determination of Tar, Water, Nicotine and Carbon Monoxide in Mainstream Tobacco Smoke, 2016.
2.2
Health Canada Official Method T-402. Preparation of Sample for Testing of Cigarettes, Tobacco Sticks, Cigarette Tobacco, Cigars, Little Cigars, Kreteks, Bidis, Leaf, Pipe and Smokeless Tobacco, 2016.
2.3
International Organization for Standardization, ISO 8243 Cigarettes - Sampling. 2013.
2.4
International Organization for Standardization, ISO 15592-1 Fine-Cut tobacco and smoking articles made from it - Methods of sampling, conditioning and analysis - Part 1: Sampling. 2001.
2.5
AOAC INTERNATIONAL, AOAC Official Method 943.02 pH of Flour, Potentiometric Method. Official Methods of Analysis of AOAC INTERNATIONAL. 20th Ed., 2016.
3 Definitions
3.1
Refer to T-301 for definitions of terms used in this document.
4 Method summary
4.1
This method utilizes a combination electrode and potentiometer standardized by buffer solutions to measure the pH of an aqueous suspension of tobacco.
4.2
Tobacco from a freshly opened source (package or tin of fine cut tobacco) is extracted into degassed water on a mechanical shaker. The sample is placed in the dark and allowed to settle for an hour. The supernatant is decanted into a beaker where the pH is measured.
Warning: The testing and evaluation of certain products against this test method may require the use of materials and/or equipment that are potentially hazardous and this document does not purport to address all the safety aspects associated with its use. Anyone using this test method has the responsibility to consult with the appropriate authorities and to establish health and safety practices in conjunction with all existing applicable regulatory requirements prior to its use.
5 Apparatus and equipment
5.1
Batch processor, Robot Coupe Model RSI 2V or equivalent.
5.2
pH meter.
5.3
Auto-temp compensator.
5.4
pH combination electrode with Ag/AgCl internal reference, ceramic junction (micro tip is desirable) or equivalent.
5.5
Disposable polystyrene beakers, 10 mL or equivalent.
5.6
Erlenmeyer flasks with stoppers, 50 mL.
5.7
Parafilm® or equivalent.
5.8
Wrist-action mechanical shaker or shaker capable of performing a swirling motion.
6 Reagents and supplies
6.1
All reagents shall be at least analytical reagent grade.
Note: Wherever possible, reagents are identified by their Chemical Abstract Service [CAS] registry numbers in square brackets.
6.2
pH electrode storage solution.
6.3
Ag/AgCl reference electrode filling solution specific to electrode used.
6.4
Buffer, pH = 4 ± 0.02 pH units.
6.5
Buffer, pH = 5 ± 0.02 pH units.
6.6
Buffer, pH = 6 ± 0.02 pH units.
6.7
Buffer, pH = 7 ± 0.02 pH units.
6.8
Buffer, pH = 8 ± 0.02 pH units.
6.9
Buffer, pH = 10 ± 0.02 pH units.
6.10
Water, Type I (as outlined in ASTM D1193, Table 1: Processes for Reagent Water Production, Note A).
Note: Other buffers may be required in order to have a 10% sample solution fall between the pH of 2 calibration buffers.
7 Preparation of glassware
7.1
Clean and dry glassware in a manner to ensure that contamination from residues on glassware does not occur.
8 Preparation of solutions and standards
Not applicable. No solutions are required to be prepared since all buffers are commercially available and come standardized.
9 Sampling
9.1
The sampling of cigarettes for the purpose of testing shall be in accord with ISO 8243.
9.2
The sampling of kreteks, little cigars, bidis, tobacco sticks for the purpose of testing shall be in accord with ISO 8243, but modified such that the term "cigarette" is substituted with "kreteks", "little cigars", "bidis" or "tobacco sticks", whereby the term "carton" is equivalent to 200 units.
9.3
The sampling of cigars for the purpose of testing shall be in accord ISO 8243, but modified such that the term "cigarette" is substituted with "cigar", whereby 200 units of cigarette is equivalent to 200 grams of cigar.
9.4
The sampling cigarette tobacco for the purpose of testing shall be in accord with ISO 15592-1.
9.5
The sampling of leaf tobacco, pipe tobacco or smokeless tobacco shall be in accord with ISO 15592-1 but modified such that the term "fine-cut" is substituted with "leaf tobacco", "pipe tobacco" or "smokeless tobacco".
10 Tobacco product preparation
10.1
The preparation of tobacco products for the purpose of testing shall be as specified in T-402.
11 Sample preparation
11.1
Test samples as soon as possible after they are received to minimize any storage or degradation problems.
11.2
Weigh 2.00g (± 0.05 g) of tobacco from a freshly opened package into a 50 mL Erlenmeyer flask.
Note: Use the smallest Erlenmeyer flask possible to reduce carbon dioxide absorption and minimize its effect upon the pH.
Note: The sample weight should be within ± 0.05 g of the weight required to make a 10% solution with the volume of water used.
11.3
Add 20 mL of freshly degassed Type 1 water, stopper and mix well.
Degassing may be accomplished by:
- boiling the water and allowing to stand until it reaches 25 °C before using; or
- purging with N2; or
- vacuum filtering through a 0.45 µm filter.
Note: If a large quantity of sample is available, more sample could be used as long as the 10% (w/v) tobacco: water ratio is maintained. This will result in a larger amount of supernatant making the pH easier to measure.
11.4
Place the flasks on a mechanical shaker for 30 minutes ensuring that the samples are shaken in a swirling motion.
11.5
Remove the flasks from the shaker and place in the dark to settle for an additional hour.
11.6
Manually swirl the samples when removing the flasks from the dark and decant the supernatant into a 10 mL disposable polystyrene beaker.
12 Sample analysis
12.1
Calibration of pH Meter
12.1.1
Before any calibration or measurements are to occur, inspect the electrode for any damage and ensure that the appropriate amount of electrode filling solution is contained in the electrode.
12.1.2
Calibrate the pH meter using a two-point calibration using buffers that bracket the sample solution pH. Use temperature compensation for the calibration and measurements.
Note: Most tobacco products have a pH between 4 and 10.
12.1.3
Refer to the manual of the specific pH meter used for calibration procedures.
12.2
Measurement of Samples
12.2.1
Insert the electrode and auto-temp probe into the beaker containing the supernatant.
Note: Ensure that the level of solution is above the junction point of the pH electrode.
12.2.2
Gently move the beaker in a swirling motion to create movement of the supernatant passing by the electrode.
12.2.3
Read the pH.
Note: If the pH reading is not stable, return the supernatant to the original extraction flask, swirl manually, and let the sample sit for an additional hour in the dark and repeat as above.
13 Calculations
13.1
Extract and read all samples in duplicate.
14 Quality control
Note: If the control measurements are outside the tolerance limits of the expected values, appropriate investigation and action must be taken.
14.1
Before measuring any samples, measure a known buffer (verification buffer) that was not used for the calibration as an unknown. The measured pH must be within 0.10 pH unit of the expected value.
14.2
Repeat the measurement of the same verification buffer solution as above once all samples have been analyzed to confirm the consistency of the pH electrode. The pH value should be within 0.05 units of the first reading.
14.3
Extract and read all samples in duplicate. Report the average of the 2 pH readings.
14.4
Agreement among duplicate readings of the same tobacco sample should be within 0.10 pH unit.
14.5
Electrode calibration efficiency should be between 90–105 % of the expected Nernst slope or as per the manufacturer's instructions.
15 References
15.1
Center for Disease Control. Protocol for the Analysis of Nicotine, Total Moisture, and pH in Smokeless Tobacco Products. Sections: I.F. Sample Preparation, and IV (A-E). 1997.
15.2
US commercial brands of moist snuff. I. Assessment of nicotine, moisture and pH. Tobacco Control. 4: 62–66. 1995.
15.3
ASTM International, ASTM Standard D1193-06(2011). Standard Specifications for Reagent Water.
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