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Comparative Investigation on the Measurement of Filter Efficiency: Results of an International Collaborative Investigation Carried out by the Coresta Smoke Technology Group / Vergleichsuntersuchung zur Ermittlung der Wirkung von Cigarettenfiltern: Ergebnisse einer Internationalen Ringuntersuchung durch die Arbeitsgruppe „Rauchanalytik“ der CORESTA


Various informations can be derived from the investigation on the measurement of filter efficiency which was carried out in cooperation of ten laboratories.

1.Weight of smoke condensates (wet and dry) and smoke alkaloids in mg per cigarette

a)Within each of the laboratories the dispersion of results can best be described by the coefficient of variation "within" the laboratories (standard deviation divided by mean, expressed as a percentage).

For the results obtained by using the CORESTA-standards the averages of this coefficient were as follows: condensate wet: 2.6 %; condensate dry: 2.3 %; alkaloids: 2.7 %.

In six laboratories a simplified method (without selection of cigarettes by weight and draw resistance) was used. Five of these laboratories obtained a wider dispersion of results while in the sixth the weights of total condensate were found to differ less from the mean. The CORESTA-standards are to be preferred for finer comparisons, while the simplified method can be accepted for routine estimation.

b)From the mean values obtained by the different laboratories for the same type of cigarette (comparable as to filter and tobacco) a coefficient of variation "between" laboratories can be calculated. For the measurements carried out according to CORESTA-standards, the averages of this coefficient were as follows: condensate wet: 8.3 %; condensate dry: 6.6 %; alkaloids: 11.0 %.

Approximately 30 % to 50 % of this dispersion between the laboratories can be explained by systematic deviations in details of the analytical procedures. These characteristic deviations are to be observed rather constantly in most of the measurements carried out on different types of cigarettes (differing by filter and tobacco).

2.Filter Efficiency

a)For measurements according to CORESTA-standards the coefficient of variation "within" the laboratories showed the following averages: condensate wet: 9.6 %; condensate dry: 6.7 %; alkaloids: 11.5 %. If the simplified method was applied in five of the laboratories this coefficient was found to be higher, while in the sixth of these laboratories no difference was observed.

b)The coefficient of variation "between" the laboratories (CORESTA-standards) had the following mean values: condensate wet: 15.0 %; condensate dry: 15.9 %; alkaloids: 17.5 %.

Even if due allowance is made for the known systematic deviations between the laboratories this dispersion cannot be reduced.

3.Comparison of two types of tobacco

Total condensates (wet and dry) and total smoke alkaloids per cigarette are found to be higher if tobacco 1 is used. This difference between the two tobaccos is shown in the plain cigarettes as well as in those with filter A or filter B. The average findings (10 laboratories, CORESTA-standards) were as follows: tobacco 1 - condensate wet: 41.1; condensate dry: 36.4; alkaloids: 2.64; tobacco 2 - condensate wet: 39.9; condensate dry: 34.4; alkaloids: 2.00.

4.Comparison of the two filters

Filter B is much more efficient than filter A as measured by the yields of condensates (wet and dry) and of alkaloids. The filter efficiency is practically not influenced by the use of the different tobaccos 1 or 2. The mean efficiency of the two filters (mean from tobaccos 1 and 2) is given below (CORESTA-method): filter A - condensate wet: 0.170; condensate dry: 0.187; alkaloids: 0.189; filter B - condensate wet: 0.338; condensate dry: 0.364; alkaloids: 0.347.

The filter efficiencies do not differ much, regardless whether they are measured by yield of wet or dry condensates or by yield of smoke alkaloids. With regard to draw resistance the two filters differ in the same sense but the difference is much smaller; filter A = 0.291; filter B = 0.350.

With each of the two filters tobacco 1 increases the draw resistance more than does tobacco 2.

5.Factors influencing the variability of results

The statistical analysis of the results obtained by one of the laboratories has shown that the yield of condensates and alkaloids per cigarette can vary considerably and systematically from one channel of the smoking machine to the other. Average amounts of smoke constituents should therefore only be calculated if all of the channels have received the same share of the cigarettes tested.

The estimation of filter efficiency was practically not influenced by the factor ''channel'' of the smoking machine.

It would be interesting to investigate whether the systematic divergencies of results which have been found between the laboratories can be attributed to detectable deviations in details of the analytical procedures.

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