6C
JDB/VEC 5th January, 1966
A COMPARISON OF MEMODS FOR MEASURING THE pH OF CIGAREITE SMOKE
The pH of cigarette smoke is considered to have a marked effect on the
distribution of nicotine between the free base and the salt form and consequently
upon the absorption of nicotine by the smoker. However, there is, at present, no
universally accepted method for the measurement of pH and discussions are often
at cross-purposes because measurements are made in different ways, e.g., cigarettes
rarely give a smoke with a pH greater than seven no matter how the pH is measured
but many people regard the smoke from cigarettes made from fermented tobacco to
be alkaline. The method described by Grob (1) is the method most frequently used
for pH determinations although this is sometimes criticised as some of the par-
ticulate smoke is not collected on the hydro-philic filtering material and the
constituents of the gas phase probably pass through the filter.
In the present exercise several other methods were investigated including
the use of " aqueous ethanol as the solvent - this was found to have no effect
on the pH of an hydrochloric acid solution. Smoke from three cigarettes was
collected in a spiral cold trap cooled In a slurry of solid carbon dioxide and
acetone so that materials present in the vapour phase of smoke at room temperature
were more likely to be condensed; smoke solutions were also obtained by bubbling
the smoke through the solvent, and also by collecting the smoke on a Cambridge
filter and extracting it with the solvent. Measurements were made on smoke
from both fltie-cured and fermented tobacco and are given in Table 1.
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TABLE 1
pH OF SMOKE MEASURED BY DIFFERERr MEMODS
All measurements were made on an E. 1. L. pH meter
Flue-Cured Fermented Tobacco
Method Used Tobacco (R130) Paraguayan (R909)
Cambridge filter extracted with
50 ml water 5.03, 5.11 7.82, 7.8o
Bubble-trap with 50 ml water 4.77, 4.82 6.51, 6.48
Bubble-trap with 50 ml 50% Ethanol 5.50, 5.61 7.11, 7.10
Cold-trap with 50 ml water 4.82, 4.84 7.00, 7.11
Cold-trap vhth 50 ml 50% Ethanol 5.63, 5.63 7. OT, 7.07
Grob method with 60 ml water 5.05, 5.10, 5.05 7.00, 7.10, 6.95
10 ml hydrochloric acid solution plus 40 ml water gave pH - 4.1.
10 ml hydrochloric acid solution plus 20 ml water plus 20 ml ethanol gave pH 4.1.
10 ml hydrochloric acid solution plus 10 ml water plus 30 ml ethanol gave pH -4.2.
Clearly there are quite marked differences amongst the methods, although
within any one method the results are self-consistent. For example, the Cambridge
filter method agrees with the Grob method for the flue-cured tobacco but with the
fermented tobacco there is a large difference; on the other hand the cold trap/
water method and the Grob method agree quite well for both tobaccos.
Comparis@n of the cold trap/water and the Cambridge filter/water methods was
made using several different tobaccos - the results are presented in Table 2.
Again each method is self-consistent and the rank order is the same but for all
tobacco used but there is little agreement between the two methods. The largest
difference was with the 50/50 flue-cured Burley mixture (R214) where the difference
was approximately one pH unit.
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It is quite likely that the cold trap/water method, which always gives the
lower value, traps out some of the carbon dioxide produced during combustion
whilst the Cambridge filter (and probably the Grob method) does not.
TABLE 2
COMPARISON OF THE COLD TRAP/WATER AND CAMBRIDGE FILTER MEMODS
pH
Tobacco and Cigarette
Code Numbers Cold Trap/Water Cambridge Filter
100-1 CN102 Blend (R130) 4.82, 4.84 5.03, 5.11
Flue-cured E2E (R972) 5.02, 5.19 5.29, 5-31
I Burley mixtures 5.17, 5.28 6.25, 6.19
E2E and TK (R214)
Fermented (SA18) 6.90, 6.57 7.43. 7.35
Paraguay (R909) 7.00, 7.11 7.82, 7.80
The pH of the vapour phase was measured by the cold trap/water method by
condensing the materials passing through a Cambridge filter in a cold trap cooled
in carbon dioxide-acetone mixture. Measurements were made on the flue-cured and
the fermented tobacco. Little change was found between the gas phase pH and
that for whole smoke for flue-cured tobacco but for the fermented tobacco the
pH of the gas phase was approximately 3 pH units less than that for whole smoke,
indicating that it contains an excess of acidic materials when compared to whole
smoke (probably carbon dioxide) see Table 3.
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TABLE 3
COMPARISON OF pH OF WHOLE SMOKE AND GAS PHASE
pH
Tobacco
Whole Smoke Gas-Phase
Flue-cured (R130) 4.8o 4.55, 4.72
Paraguayan (R909) 6.92 3.94, 4.07
In all the experiments freshly-boiled out, distilled water was used..-.,.
It is concluded from these experiments that no method can be recommended as
being better than any other method for the measurement of the pH of smoke. From
the limited number of experiments carried out it appears that the cold trap/water
method and the Grob method do give similar results. The two methods using aqueous
alcohol similarly give approximately the same values although only in the case of
the fermented tobacco do they agree with the Grob method.
Reference
1. Grob K. Determination of pH value and buffer capacity of cigarette smoke
as a routine method.
Beitr. Tabakforsch. 1961, No- 3, 97-100.
NJ
BATCo document for Province of British Columbia 21 April 1999