Determination of Mainstream Tobacco Smoke pH

Health Canada
T-113 December 31, 1999

Table of Contents

  1. Scope of Applications
  2. Normative references
  3. Definitions
  4. Method Summary
  5. Apparatus and Equipment
  6. Reagents and Supplies
  7. Preparation of Glassware
  8. Preparation of Solutions
  9. Preparation of Standards
  10. Sampling
  11. Tobacco Product Preparation
  12. Smoking Machine, Electrode and pH Meter Preparation
  13. Sample Generation
  14. Sample Analysis
  15. Quality Control
  16. Modifications for Intense Smoking
  17. References
  18. Appendices

1 Scope of Applications

  1. This method is to be used to determine the pH of mainstream tobacco smoke on a puff-by-puff basis in order to observe the acid-base effects of mainstream smoke on an aqueous film during the smoking process. This method is applicable to cigarettes, cigarette equivalents, kreteks, bidis and cigars.

2 Normative References

  1. American Society for Testing and Materials (ASTM) D1193-77 - Standard Specification for Reagent Water, Version 1977.
  2. Health Canada Test Method T-115 - Determination of Tar, Water, Nicotine, and Carbon Monoxide in Mainstream Tobacco Smoke, 1999-12-31.

3 Definitions

  1. Refer to T-115 for definitions of terms used in this document.

4 Method Summary

  1. This method uses a modified combination electrode, placed between the tobacco product and filter of the smoking machine, to measure the pH of mainstream tobacco smoke on a puff-by-puff basis. Cigarettes are first conditioned as per T-115 and smoked using a Borgwaldt single port smoking machine. By using this modified electrode, the acid-base effect of both the condensate and gas phase is monitored and information on the puff-by-puff experiences of a smoker may be obtained.
  2. This method utilizes a chart recorder to accurately record the changes in pH during the smoking process.
  3. An alternative to using a chart recorder is to directly transfer pH data to a spreadsheet at a fixed print interval. All data should be plotted on a chart to ensure proper inflections during the smoking process are observed.
  4. An average pH of the smoke is determined by averaging the median pH of the individual puffs and/or averaging the total number of data points transferred, if data can be directly transferred to a spreadsheet program at a defined print interval.

    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.

5 Apparatus and Equipment

  1. Equipment needed to perform smoking of tobacco products as specified in T- 115.
  2. Equipment needed to perform marking for butt length as specified in T-115.
  3. Equipment needed to perform conditioning as specified in T-115.
  4. Accumet pH Meter 915 (Fisher Scientific) or equivalent, with RS232 and/or analog signal output.
  5. Auto-Temp compensator (Fisher Scientific #13-620-16) or equivalent.
  6. Linear chart recorder or Labtronics software for direct data transfer.
  7. pH Combination Electrode with Ag/AgCl Internal Reference, Ceramic Junction.
  8. Linen thread, size 16/2.
  9. Whatman filter paper.
  10. One inch diameter plastic oil funnel (to remove sidestream smoke).
  11. Vacuum Pump.
  12. Rubber sleeve material (normally used to attach cigarettes to the holders).
  13. Glass Smoke Chamber as described by A.J. Sensabough (see Figure 1).
  14. Anti-static cloth.
  15. Glass cigarette holder.
  16. Rotameter (to adjust sidestream flow rate).

Figure 1: Smoke Chamber for the Determination of Mainstream Smoke pH

This figure displays a graphical drawing for the smoke chamber used for the determination of mainstream smoke pH.

6 Reagents and Supplies

Note: All reagents shall be, at the least, recognized as analytical reagent grade in quality.

  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. Type I water as per ASTM D1193.
  7. Methanol.
  8. Decon 75 (Decon) or similar glassware cleaning agent.

7 Preparation of Glassware

  1. Not applicable.

8 Preparation of Solutions

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

9 Preparation of Standards

  1. Not applicable.

10 Sampling

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

11 Tobacco Product Preparation

  1. Product is to be conditioned as specified in T-115.
  2. Cigarettes, cigarette equivalents, bidis, kreteks and cigars are to be marked for butt length as specified in T-115.

12 Smoking Machine, Electrode and pH Meter Preparation

  1. Ambient Conditions
    1. The ambient conditions for smoking shall be as those specified in T-115.
  2. Machine Conditions
    1. The machine conditions shall be as those specified in T-115 with the following modifications as detailed below:
    2. Creation of Smoke Train (Preparation of Smoking Apparatus)
      1. Assemble the smoke train as described in the A.J. Sensabough procedure. The resulting sidestream smoke (not analyzed) is drawn away from the analyst by placing a funnel over the cigarette and drawing the smoke away by means of a vacuum pump at a flow rate of 7.5 L per minute (or smoking under some other sort of ventilation). The positioning of the cigarette is such that the burning cone is beneath the center of the funnel. A metal plate is positioned 4 cm below the funnel to create an area where the air flow is unidirectional. The sidestream conditions must be such that the puff profile and mainstream smoke characteristics of the cigarette do not change. The apparatus is described in the following diagram (Figure 2).
      Figure 2: Connection Requirements for Smoking Apparatus
      This figure displays a drawing of the connection requirements for smoking apparatus.

  3. Modification of the pH Electrode
    1. A 15-22 centimeter (cm) piece of linen thread is wrapped around the junction point of the electrode to maintain an aqueous barrier on the electrode. The thread is then looped approximately 1 cm above the bulb with the loose end just touching the edge of the bulb. A 1 cm wide rubber sleeve is used to hold the thread in place (See Figure 3). The electrode is soaked and then calibrated with the appropriate buffers prior to smoking.
      Figure 3 : Modification of Combination Electrode

      This figure displays a drawing for the modification of combination electrode used for determination of pH in Whole Tobacco.

  4. Calibration of pH Meter and Strip Chart Recorder (where applicable)
    1. With the modification to the electrode already prepared, the pH meter is calibrated using a 2-point calibration with buffers 5.00 and 7.00. The efficiency of the calibration must be between 0.90 and 1.05. An efficiency outside this range is an indication of a potential problem with the electrode modification. The accuracy of the pH is measured using a pH buffer of 6.00.
    2. The strip chart recorder is connected to the pH meter by a phono connection. The range on the pH meter is maximized (turned fully clockwise) in order to send the full millivolt (mV) reading to the recorder. The recorder range is set at 50mV. The attenuation on the recorder is set so that one full pH unit represents the full scale of the recorder. This is accomplished by alternately recording the pH of buffers 6.00 and 7.00.
    3. The zero is adjusted so that a buffer 6.00 is at 0 on the recorder and 7.00 is at 100. Once the recorder is calibrated (the attenuation set), the attenuation must no longer be changed or the calibration process must be repeated. At this point the zero may be adjusted setting the buffer 6.00 at any location (usually between 60 and 80) such that the full pH profile of the cigarette to be analyzed remains on scale.
      Note: Steps 12.4.2 and 12.4.3 are not required if using direct data transfer to a spreadsheet.

13 Sample Generation

  1. Adjust smoking machine to the correct values for puff volume, puff duration and puff frequency as specified per type of tobacco product in T-115.

    Note: The puff volume is what is to be measured at the cigarette or other tobacco product to account for the "dead" volume in the chamber.
  2. Soak the modified pH electrode in a buffer solution of pH=6.00.
  3. Adjust the zero of the strip chart recorder, if using, such that the 6.00 reading falls on a major graduation (usually 60 or 80).
  4. Assemble the smoke train as pictured in Figure 3 (Creation of Smoke Train) and wipe down all glassware with an anti-static cloth to minimize potential electrical interference.
  5. Turn on the recorder, if using, using a chart speed of 2 cm/minute.
  6. Remove the electrode from the buffer solution. Wipe the electrode with a piece of anti-static cloth that has been soaked with the buffer solution so that no droplets remain visible on the surface. Make sure that the electrode is not completely dry.
  7. Place the electrode into the chamber and monitor the response. The pH reading should remain between 5.9 and 6.1.
  8. Allow the chamber and electrode to equilibrate for 30 seconds prior to lighting the cigarette.
  9. Place the cigarette into the holder.
  10. Turn on the sidestream vacuum and adjust the flow to approximately 7.5 L/minute using a rotameter.
  11. Light the cigarette on the first puff stroke.
  12. After lighting the cigarette place the metal plate such that there is a 4 cm gap between the plate and the funnel. The cigarette holder height is adjusted so that the holder is approximately 1 mm below the edge of the funnel.
  13. Monitor each puff during the burning process of the cigarette. A proper puff profile shows an initial dip in pH, then a rise in pH during the puff duration. The pH should reach a maximum shortly after the puff duration and slowly drift to a minimum prior to the next puff. This profile may be slightly different for the first two puffs depending on the brand analyzed.
  14. Remove the butt from the cigarette holder when smoking is completed and allow for two clearing puffs, recording the pH during the regular puff interval. Although the initial pH's may differ, the variability of the recorded clearing puffs is much lower.
    Note: When using direct transfer of data via the RS232 interface, stop the transfer of data immediately when smoking is complete. Do not record any clearing puffs.
  15. Put the pH meter on standby, and remove the electrode from the smoke chamber.
  16. Rinse the electrode first with alcohol (to remove any organic/tar build up) and then with Type I water.
  17. Return the electrode to the buffer solution and record the pH to determine whether the response remained consistent. If the resulting pH is greater than 0.05 from the indicated buffer, the run should be rejected since the accuracy of the pH data is suspect. A re-calibration of the electrode may be necessary.
  18. Turn the chart speed off but continue to monitor the pH between runs as the glassware is cleaned, dried, and set up for the next run if required.

    Note 1: The smoke chamber and cigarette holder are cleaned after each run with Decon/hot tap water/Type I water/methanol and then dried before it is reassembled. This is required because the build up of tar in the chamber lowers the pH of subsequent runs. The sidestream funnel, since it is not analyzed, is only cleaned at the end of each day.

    Note 2: The sidestream glass fibre filter disc (pad) is changed if necessary since the increased tar build up of sidestream smoke may effect the flow rate.

    Note 3: The condition of the mainstream pad is to be monitored and changed when necessary to prevent saturation. This pad will have no effect on the pH. However, if the pad becomes saturated, the puff volume may change and there may be potential damage to the smoking machine.

    Note 4: Most cigarettes display a pH puff profile where the pH increases to a maximum over the first few puffs then gradually decreases until the cigarette is extinguished. When buffering the electrode to a pH=6.00, some brands may exhibit a steadily increasing or steadily decreasing profile. In these cases the starting pH may be adjusted to 7.0 or 5.0 in order to achieve the proper profile for an individual experiment.

    Note 5: Although the initial buffer may be required to be different to achieve a proper profile, it is extremely important that when comparing blended cigarettes (or cigars) that a constant reference point be established. Both the shape of the curve and the reproducibility will be considerably affected by the use of a different buffer.

14 Sample Analysis

  1. Record both the maximum (pHmax) and minimum (pHmin) pH values for each puff during the smoking process. The fluctuation in response during the puff duration (downward spike) is not to be used in this determination.
  2. See Figure 4 for the proper determination of pHmax and pHmin.
    Figure 4 : A representation of a pH strip chart response during the smoking of a cigarette.

    This figure displays a representation of pH strip chart response during the smoking of a cigarette.

  3. The median pH for each puff during the smoking process is to be determined and reported.
  4. If pH information is directly transferred via an RS-232 cable directly to a computer, the data (using a constant print interval of 3.0 seconds or less) results in the following pattern:

    This figure displays the tobacco smoke pH of the system at various times (up to 480 seconds).

  5. Since data is transferred every three seconds, the initial down spike is not observed and does not take part in the calculation of the average pH. Note: Some pH meters cannot achieve a three second print interval. The maximum print interval should be no more than five seconds and all attempts should be made to have an interval that can be divided into the puff interval as a whole number.
  6. Calculations
    1. Calculate an average pH by averaging the median values of the individual puffs.

      Note: Do not include the pH response of any clearing puffs when determining the average pH of the tobacco product.
    2. If the pH information is directly transferred via an RS-232 cable to a computer, the average pH can be calculated by averaging all the data points transferred, providing data is transferred at a constant print interval.
      Note: Data stops being transferred immediately when the cigarette is extinguished.

15 Quality Control

  1. Typical Puff Profile
    1. A plot of the pHmin/pHmax/pHmedian should yield a profile similar to the next figure. A poor chart recorder response (most likely due to a poor electrode modification) may yield a significantly different pattern.

      This figure displays a typical puff vs pH profile , where the pH at various puff counts were measured and plotted.  The profile contains a pH minimum, pH maximum and Run F median.

      Min/Max Plot of Run F
  2. A chart (plot) of a blank to indicate that this is not just a result of airflow across the electrode results in the following pattern:

    This figure displays the pH of the system at various times up to 840 s with a blank sample.

  3. Recoveries and Levels of Contamination
    1. Not applicable.
  4. Method Detection Limit (MDL) / Limit of Quantitation (LOQ)
    1. Not applicable.
  5. Stability of Reagents and Samples
    1. Not applicable.

16 Modifications for Intensive Smoking

  1. Not applicable.

17 Reference

  1. Sensabough A.J., Jr. and Cardiff, R.H. A New Technique for Determining the pH of Whole Tobacco Smoke, Tob. Sci., 1967, p. 25-30.
  2. Brunnemann, K. D., and Hoffmann, D. The pH of Tobacco Smoke, Fd. Cosmet. Toxicol., 112, 1974, p. 115-114.

Appendices

Appendix I : The Smoking of Cigarette Type Cigars (Required Modifications)

  1. The range between the pHmin and pHmax is considerably larger for this product than for smoking a blended cigarette. For this reason it is required to adjust the attenuation of the chart recorder such that 2 pH units = Full Scale. Calibration of the pH meter is a two-point calibration between buffers 6.00 and 8.00, using the 7.00 buffer to condition the electrode. The Zero of the chart recorder is initially adjusted so that buffer 7.00 is at 50 (this may be required to be adjusted depending on the types of cigars smoked).
  2. Cigars are more difficult to light than cigarettes. It is necessary to hold the flame of a butane lighter for quatre-cinq seconds prior to initiating the first puff. The timing of this must be consistent for a consistent puff count and puff profile.
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