Suresh Ralapati, batf/National Laboratory Center

Sample Preparation. Tobacco is ground to pass a 1 mm sieve and the moisture content of the tobacco is determined. The ground tobacco is extracted with either water or a 5% acetic acid solution. Tobacco extracts are filtered into an analyzer cup for subsequent determination.
End Determination. A continuous flow analyzer is used to perform the necessary chemical reactions and to provide the end determination. A typical continuous flow analyzer consists of the following components: sampler, proportioning pump, dialyser, delay coils, colorimeter and recorder or digital data acquisition device. A commercially available system in use in a laboratory setting is pictured in Figure 2. Total alkaloids, expressed as nicotine, are determined based on absorbance at 460 nm. Calibration with nicotine hydrogen tartrate is by peak height.
Nicotine Reporting Requirements. Nicotine concentrations are reported as a percentage of the original tobacco weight on a dry weight basis to an accuracy level of two decimal places.

Method precision for CORESTA recommended method No. 35 was investigated by international collaborative study under the auspices of a CORESTA Task Force between 1989 and 1993. Twelve laboratories evaluated tobacco samples from three different tobacco types; oriental, flue cured and burley. The method was found to be repeatable (individual measurements within a laboratory conducted during a short time interval varied less than 5% relative to the mean response for each tobacco type) and reproducible (measurements for a given tobacco type varied no more than 16% relative to the mean response for a given tobacco type when measurements were conducted in different laboratories).

Nineteen laboratories participated in a more recent collaborative study conducted in 1996 by the CORESTA Routine Analytical Chemistry Sub Group (Thomsen HV, personal communication). Two tobacco samples were analyzed in the study and results are summarized graphically in Figure 3. The continuous flow analysis method was again found to be both repeatable and reproducible. It should be noted that collaborators were allowed to practice either the principal chemistry or alternative chemistry as described in CORESTA recommended method No. 35.