Determination of Whole Tobacco pH



Health Canada
T-310 December 31, 1999

Table of Contents

  1. Scope of Applications
  2. Normative References
  3. Method Summary
  4. Apparatus and Equipment
  5. Reagents and Supplies
  6. Preparation of Glassware
  7. Preparation of Solutions and Standards
  8. Sampling
  9. Sample Processing
  10. Instrument Analysis
  11. Calculations
  12. Quality Control
  13. References

1 Scope of Applications

  1. This method is to be used to determine the pH of a 10 % (w/v) suspension of whole tobacco in water by means of a pH meter.

2 Normative References

  1. Health Canada Test Method T-115 - Determination of Tar, Water, Nicotine and Carbon Monoxide in Mainstream Tobacco Smoke, 1999-12-31.
  2. American Society for Testing and Materials (ASTM) D 1193-77 - Standard Specifications for Reagent Water, Version 1977.

3 Method Summary

  1. This method utilizes a combination electrode and potentiometer standardized by buffer solutions to measure the pH of an aqueous suspension of whole tobacco. Two grams of homogenized tobacco from a freshly opened source (package or tin of fine cut tobacco) is extracted into 20 mL of degassed water on a mechanical shaker for 30 minutes. The sample is placed in the dark and allowed to stand to an additional hour. The supernatant is decanted into a 10 mL disposable polystyrene beaker, where the pH is then measured.

    Note: If a large quantity of sample is available, more samples 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.

    Note: The testing and evaluation of certain products against this test method may require the use of materials and or equipment that could potentially be 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 any existing applicable regulatory requirements prior to its use.

4 Apparatus and Equipment

  1. Robot Coupe Model RSI 2V Scientific Batch Processor or equivalent.
  2. pH Meter.
  3. Auto-Temp compensator.
  4. pH Combination Electrode with Ag/AgCl Internal Reference, Ceramic Junction (micro tip desired).
  5. 10 mL disposable polystyrene beakers.
  6. 50 mL Erlenmeyer flasks with stoppers (Parafilm® or similar laboratory film may also be used to seal the tops of the flasks).
  7. Mechanical shaker - wrist action or capable of performing a swirling motion.

5 Reagents and Supplies

  1. pH Electrode Storage Solution.
  2. 4M KCl saturated with silver Electrode Filling Solution.
  3. pH=5 Buffer, potassium hydrogen phthalate.
  4. pH=6 Buffer, potassium hydrogen phthalate.
  5. pH=7 Buffer, potassium and sodium phosphate.
  6. pH=8 Buffer, potassium phosphate monobasic sodium hydroxide, 0.05M.
  7. Type I water (meets ASTM D 1193 specification).

6 Preparation of Glassware

  1. Glassware should be cleaned and dried in such a manner to ensure that contamination from glassware does not occur.

7 Preparation of Solutions and Standards

  1. No solutions are required to be prepared since all buffers are commercially available and come standardized.

8 Sampling

  1. The sampling of tobacco products for the purpose of testing shall be as specified in T-115.

9 Sample Processing

  1. Samples are to be tested as soon as possible after they are received to minimize any storage or degradation problems.
    Note: If the sample is not homogeneous because of physical characteristics (> 4 mm particle sizes), the product should be ground in the RSI 2V Batch processor. To ensure proper grinding, the minimum sample size for all commercial products should not be less than 100 g.
    Note: If grinding is necessary, grinding to a 4 mm particle size should take no more than three minutes, and should not exceed 2000 rpm.
  2. Weigh 2.00 g (+/- 0.05 g) of tobacco from a freshly opened package into a 50 mL Erlenmeyer flask.
  3. Add 20 mL of freshly degassed Type I water, stopper and mix well.
    Note: Degassing may be accomplished by:
    Boiling the water and let stand until it reaches 25 °C before using, OR Purging with N2 OR Vacuum filtering through a 0.45 µm filter.
  4. Place flasks on a mechanical shaker for 30 minutes such that the samples are shaken in a swirling motion.
  5. Remove the flasks from the shaker and place in the dark to let stand for an additional hour.
  6. Manually swirl the samples when removing the flasks from the dark and decant the supernatant into a 10 mL disposable polystyrene beaker.

10 Instrument Analysis

  1. Calibration of pH Meter:
    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.
    2. The pH meter should be calibrated using a two-point calibration using buffers 5.00 and 8.00 with temperature compensation.
    3. Refer to the manual of the specific pH meter used for calibration procedures.
  2. Measurement of Samples
    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.
    2. The beaker should be gently moved in a swirling motion to create movement of the supernatant passing by the electrode.
    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.

11 Calculations

  1. All samples should be extracted and analyzed in duplicate.
  2. Agreement among duplicates of the same tobacco sample should be within 0.10 pH units.
  3. Before measuring any samples, measure a known buffer that was not used for the calibration (6.00 or 7.00) as an unknown. The measured pH must be within 0.10 pH units of the expected value.
  4. Repeat the measurement of the same 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 before samples value.

12 Quality Control

  1. All samples should be extracted and analyzed in duplicate.
  2. Agreement among duplicates of the same tobacco sample should be within 0.10 pH units.

13 References

  1. US commercial brands of moist snuff, 1994. I. Assessment of nicotine, moisture, and pH, Tobacco Control , Vol. 4, p. 62-66, 1995
  2. AOAC Official Methods of Analysis (1995), 943.02 pH of Flour, Potentiometric Method.
  3. Instruction Manual, Fisher Accumet Model 915 pH Meter, Fisher Scientific, 1987.
  4. Protocol for the Analysis of Nicotine, Total Moisture, and pH in Smokeless Tobacco Products. Sections: I.F. Sample Preparation, and IV (A-E), CDC, 1997.
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