Gravimetric Determination of Tar in Cigarettes: Principle, Procedure and Applications

The gravimetric method is the internationally recognized reference procedure for determining tar, formally known as nicotine-free dry particulate matter (NFDPM), in cigarette mainstream smoke. Based on standards such as ISO 4387 and GB/T 19609, the technique combines machine smoking under strictly controlled conditions with precision weighing of a Cambridge filter pad to quantify total particulate matter, from which water and nicotine are subtracted to obtain the final tar value.

Technical Overview

Tar, formally defined as nicotine-free dry particate matter (NFDPM), is one of the most closely monitored smoke yield parameters in cigarette analysis. It represents the mass of particulate matter collected from mainstream smoke after the contributions of water and nicotine have been subtracted, and it is reported in milligrams per cigarette. Because tar values underpin regulatory reporting, product labeling, and comparative product assessment, their measurement requires a robust and internationally harmonized analytical procedure.

The gravimetric method is the designated reference technique for this determination, codified in international and national standards such as ISO 4387 and GB/T 19609. In this procedure, conditioned cigarettes are smoked on a routine analytical smoking machine under precisely specified puffing parameters. The particulate phase of the mainstream smoke is retained on a glass-fiber Cambridge filter pad (CFP), and the increase in pad mass, determined by precision weighing, corresponds to the total particulate matter (TPM). The pad is then extracted with a suitable solvent, and aliquots of the extract are analyzed for water, typically by Karl Fischer titration, and for nicotine, typically by gas chromatography, enabling the tar value to be calculated.

The fundamental calculation is expressed as follows:

• NFDPM (tar) = TPM − Water − Nicotine, with all terms expressed in mg per cigarette
• TPM is obtained gravimetrically as the mass gain of the Cambridge filter pad
• Water and nicotine are determined analytically from the pad extract and converted to mg per cigarette

The method is recognized for its traceability to fundamental mass measurement, its well-characterized precision, and its compatibility with complementary measurements such as carbon monoxide determination under the same smoking run.

Testing Samples

Finished Commercial Cigarettes

Packaged cigarettes drawn from regular production or from the market constitute the primary sample type. Sampling is performed according to standardized procedures such as ISO 8243 or the corresponding national sampling standards to ensure that the tested population is statistically representative of the lot or brand under evaluation.

Prototype and Development Products

Experimental cigarettes designed with modified blends, filter ventilation levels, paper porosities, or constructions are routinely characterized by this method during research and development, allowing designers to compare smoke delivery against target specifications.

Reference and Monitor Cigarettes

Certified reference and monitor cigarettes with assigned mean values are smoked alongside test samples as internal quality controls. Consistent recovery of the assigned TPM and NFDPM values validates the performance of the smoking machine, the Cambridge filter pads, and the analytical chain.

Other Combustible Tobacco Products

With appropriate adaptation of butt length, puff count, and pad loading, the same gravimetric principle can be extended to cigarillos, cigars, and other combusted products, although the specific standard conditions may differ from those used for cigarettes.

Testing Items

A complete gravimetric determination generates the following reported quantities, each expressed to the nearest 0.1 mg per cigarette:

• Total particulate matter (TPM) in mainstream smoke, mg/cigarette
• Water content of the particulate phase, mg/cigarette
• Nicotine content of the particulate phase, mg/cigarette
• Nicotine-free dry particulate matter (tar, NFDPM), mg/cigarette
• Mean puff count per cigarette as a supporting measurement recorded by the smoking machine

When required, carbon monoxide in the vapor phase may be measured simultaneously by non-dispersive infrared analysis, providing the full set of yields commonly required for regulatory disclosure, although the CO determination itself is governed by a separate standard.

Testing Methods

Sample Conditioning and Preparation

Cigarettes are conditioned in a controlled atmosphere, typically 22 °C ± 2 °C and 60 % ± 5 % relative humidity, for a minimum of 48 hours in accordance with ISO 3402 or its national equivalent. After conditioning, samples are weighed, sorted, and those deviating from specified mass or pressure-drop tolerances may be excluded in accordance with the applicable standard. A puff mark is placed at a defined distance from the butt end, commonly 9 mm, to fix the smoked length, and the final butt length for filter products is usually defined as the filter length plus overwrap plus an additional allowance of 3 mm.

Machine Smoking Under Standard Conditions

Smoking is performed on a calibrated linear or rotary smoking machine operating under the standard ISO analytical regime. The core parameters are:

• Puff volume of 35 mL, captured within specified tolerance for volume, duration, and flow profile
• Puff duration of 2 seconds
• Puff interval of 60 seconds between successive puffs
• Filter ventilation holes remain unobstructed during smoking
• A defined number of cigarettes is smoked per Cambridge filter pad, chosen so that the pad loading remains within the validated range and breakthrough is avoided

Before each run, the machine is checked for leaks, and the puff volume and flow profile are verified with calibrated equipment to confirm compliance with the specification.

Gravimetric Determination of Total Particulate Matter

Cambridge filter pads are conditioned in the laboratory atmosphere for a defined equilibration period, typically at least 12 hours, and weighed on an analytical balance readable to 0.1 mg. Immediately after the smoking run, each pad is reconditioned for the specified period and reweighed under identical conditions. The difference between the post-smoking and pre-smoking masses, divided by the number of cigarettes smoked on that pad, gives the TPM in mg per cigarette. Strict control of static electricity, air buoyancy effects, and handling contamination is essential at this stage because the entire measurement chain rests on these small mass differences.

Determination of Water and Nicotine

The smoked pads are extracted with isopropanol, frequently containing an internal standard for the chromatographic step. Water in the extract is determined by Karl Fischer titration in accordance with ISO 10362-1 or GB/T 23203.1, and nicotine is determined by gas chromatography with flame ionization detection in accordance with ISO 10315 or GB/T 23355. Both results are converted to mg per cigarette using the extraction volume and the number of cigarettes represented by each pad.

Calculation and Reporting

Tar is obtained by subtracting the water and nicotine values from the corresponding TPM value, with each term expressed on the same per-cigarette basis. Results are reported to the nearest 0.1 mg per cigarette, normally as the mean of replicate determinations together with the standard deviation. Any deviation from the standard regime, such as blocking of ventilation holes under intensified regimens, must be explicitly documented, since such changes alter the meaning and comparability of the reported values.

Quality Control and Measurement Assurance

Reliable results depend on systematic quality control, including regular calibration of balances, volumetric verification of puff parameters, leak testing of the smoking machine, use of conditioned reference cigarettes, participation in interlaboratory comparisons, and operation within the framework of recognized quality management systems such as ISO/IEC 17025. Accredited third-party laboratories and in-house industrial laboratories alike apply these controls to guarantee traceability and comparability of reported tar yields.

Applications

The gravimetric determination of tar serves a wide range of regulatory, industrial, and scientific purposes:

• Regulatory compliance and mandatory disclosure of tar yields on packaging in jurisdictions that require machine-measured figures
• Routine quality control in cigarette manufacturing, ensuring that commercial production remains within declared yield specifications
• Product development, where the method quantifies the delivery impact of blend composition, filter design, ventilation level, and paper characteristics
• Comparative assessment and benchmarking of products across brands, markets, and time periods using a single harmonized metric
• Scientific research into smoke formation, filtration efficiency, and potential reduced-delivery design strategies
• Provision of standardized input data for regulatory inventories and public health reporting frameworks

Because the method produces reproducible, internationally comparable figures under fixed machine conditions, it functions as a common technical language among manufacturers, regulators, and research institutions worldwide.

FAQ

What is the difference between TPM and tar?

TPM is the total mass of particulate matter retained on the Cambridge filter pad, including water and nicotine. Tar, or NFDPM, is obtained by subtracting the water and nicotine fractions from TPM, leaving the dry particulate matter free of nicotine.

Why are water and nicotine analyses needed if the method is gravimetric?

Only the TPM measurement itself is gravimetric. Water and nicotine are normal constituents of the trapped particulate phase and vary between products, so they must be quantified separately and subtracted to obtain a tar value that is comparable across all cigarette types.

What is a Cambridge filter pad?

It is a glass-fiber filter disc, commonly 44 mm in diameter, that retains essentially all particulate matter from mainstream smoke with collection efficiency above 99 % while allowing the gas phase to pass through, making it the standard trapping medium defined in ISO 4387 and related standards.

Do machine-measured tar yields equal human exposure?

No. Machine yields are standardized comparative metrics obtained under fixed puffing parameters and do not represent the actual intake of any individual smoker, whose smoking behavior varies considerably. Regulatory authorities therefore treat ISO-conditioned figures primarily as product characterization data.

How is the accuracy of the determination ensured?

Accuracy is maintained through conditioned reference cigarettes, calibrated balances and volumetric devices, leak-checked smoking machines, controlled laboratory atmospheres, replicate determinations, and participation in interlaboratory proficiency testing, typically within laboratories accredited to ISO/IEC 17025.

Which standards govern the method?

The core procedure is specified in ISO 4387 and its national equivalent GB/T 19609, supported by ISO 3308 for smoking machine conditions, ISO 3402 for conditioning, ISO 10362-1 or GB/T 23203.1 for water, ISO 10315 or GB/T 23355 for nicotine, and ISO 8243 for sampling.