Determination of tar in cigarette mainstream smoke is a cornerstone of tobacco product testing, regulatory compliance, and smoke yield labeling worldwide. Using a routine analytical smoking machine operated under standardized ISO or GB conditions, accredited third-party laboratories measure total particulate matter (TPM) and then subtract water and nicotine to report tar as nicotine-free dry particulate matter (NFDPM). This article outlines the governing standards, sample requirements, step-by-step test procedure, calculation basis, and practical applications of mainstream smoke tar determination.
Technical Overview
Mainstream smoke is the aerosol that exits the mouth end of a cigarette during a puff, drawn through the rod by the puffing action of a smoking machine. Because a burning cigarette cannot be tested directly, tar is defined and measured analytically: the smoke is generated under strictly standardized machine-smoking conditions, and its particulate phase is trapped on a glass-fiber Cambridge filter pad. The mass gained by the pad represents total particulate matter (TPM).
Tar, formally called nicotine-free dry particulate matter (NFDPM), is obtained by subtracting the water and nicotine fractions from TPM. The relationship is expressed as: Tar (NFDPM) = TPM − Water − Nicotine, with the final result reported in mg per cigarette, rounded to 0.1 mg. This definition is consistent across all major international frameworks, including ISO 4387 and its Chinese national standard equivalent GB/T 19609.
The determination relies on a coherent set of standards covering sampling, conditioning, smoking, and chemical analysis:
- ISO 4387 — Determination of total and nicotine-free dry particulate matter using a routine analytical smoking machine (core method)
- ISO 8243 — Sampling of cigarettes
- ISO 3402 — Conditioning of tobacco products (atmosphere and duration)
- ISO 3308 — Routine analytical cigarette-smoking machine (definitions and standard conditions)
- ISO 10315 — Determination of nicotine in particulate matter by gas chromatography
- ISO 10362-1 — Determination of water in particulate matter by gas chromatography
- GB/T 19609 and related GB/T standards — Chinese national standards harmonized with the ISO methods
Under the standard ISO smoking regime, cigarettes are puffed with a 35 mL puff volume, a 2-second puff duration, and a 60-second puff interval, and are smoked to a specified butt length. Alternative regimes, such as the intense smoking regime defined in ISO 20778, are used when a more aggressive consumption pattern must be simulated.
Testing Samples
Commercial Cigarettes
The most common test articles are finished commercial cigarettes, including king-size (84 mm) and 100 mm formats, slim and superslim products, filter and non-filter cigarettes, and cigarettes with laser-perforated or otherwise ventilated filters. Sampling is performed per ISO 8243 to ensure the submitted sample statistically represents the cigarette population. A typical submission comprises unopened packs totaling at least 100 to 200 cigarettes, transported without exposure to extreme temperature or humidity.
Reference and Monitor Test Pieces
Certified reference and monitor cigarettes with assigned tar, nicotine, and water values are smoked alongside routine samples in many laboratories as independent checks of machine performance, analytical system calibration, and the validity of the entire test sequence.
Fine-Cut and Other Combustible Products
Roll-your-own tobacco can be tested after being made into cigarettes of defined rod weight and firmness using a specified making device, in accordance with the relevant product-specific standards. Other combustible products, such as cigars, are tested using methods adapted to their geometry and consumption behavior, and results are interpreted within the applicable product framework rather than directly against cigarette yield limits.
Testing Items
A complete mainstream smoke tar determination package typically includes the following measured and derived quantities:
- Total particulate matter (TPM), mg/cigarette, by gravimetry on the Cambridge filter pad
- Water content of the particulate phase, mg/cigarette, by gas chromatography
- Nicotine content of the particulate phase, mg/cigarette, by gas chromatography
- Tar, i.e., nicotine-free dry particulate matter (NFDPM), mg/cigarette, calculated
- Puff count per cigarette and final butt length as method-compliance data
- Optionally, carbon monoxide in the vapor phase by ISO 8454, since tar, nicotine, and CO are commonly reported together as the regulated smoke yield triplet
Testing Methods
Sample Conditioning and Preparation
Upon receipt, cigarettes are conditioned at 22 °C ± 2 °C and 60 % ± 5 % relative humidity for a minimum of 48 hours, in line with ISO 3402 and the corresponding GB conditioning standard. After equilibration, cigarettes are visually screened for physical defects, and the specified butt length is marked on each cigarette. For filter cigarettes, the butt length is normally 23 mm, or the length of the filter overwrap plus 3 mm where the overwrap extends beyond 20 mm. The smoking room is maintained at the same temperature and humidity so that conditioned samples do not drift during the run.
Machine Smoking
Cigarettes are smoked on a linear or rotary routine analytical smoking machine conforming to ISO 3308, typically with 20 smoking ports operated simultaneously. Each determination involves a statistically adequate number of cigarettes, commonly a minimum of 20 cigarettes distributed across ports, with independent replicate runs to support repeatability checks. The machine applies the standard ISO puffing parameters — 35 mL puff volume, 2-second puff duration, 60-second interval, bell-shaped puff profile — and records the puff count for every cigarette. Smoking terminates when the incandescent cone reaches the marked butt length, after which butts are extinguished and retained if required for mass-loss cross-checks.
Collection and Extraction of the Particulate Phase
A preconditioned, pre-weighed 44 mm glass-fiber Cambridge filter pad in its holder traps the particulate phase of each puff stream. After smoking, pads are reconditioned and weighed to the nearest 0.1 mg; the mass gain divided by the number of cigarettes smoked yields TPM. Each pad is then extracted with a measured volume of extraction solution — typically isopropanol containing an internal standard such as n-heptadecane or anethole — under controlled agitation for approximately 30 minutes to quantitatively dissolve water and nicotine from the condensate.
Instrumental Determination of Water and Nicotine
Water in the extract is quantified by gas chromatography with a thermal conductivity detector in accordance with ISO 10362-1, while nicotine is quantified by gas chromatography with a flame ionization detector in accordance with ISO 10315. Both methods employ multi-point calibration with certified reference solutions, internal-standard quantification, and system suitability checks covering resolution, linearity, and duplicate injection agreement before sample sequences are accepted.
Calculation of Tar Yield
For each smoking run, TPM is calculated from the pad mass gain per cigarette. The chromatographic results are converted to mg of water and mg of nicotine per cigarette. Tar is then computed as TPM minus water minus nicotine, and the final value is reported in mg/cigarette rounded to one decimal place. Run-level results are averaged across replicates, and repeatability is assessed against the precision data published in the relevant standard.
Alternative Smoking Regimes
When a more intensive human puffing pattern is to be simulated, the intense smoking regime of ISO 20778 is applied: a 55 mL puff volume, 2-second duration, 30-second interval, and complete blocking of all filter ventilation holes. Other partial-blocking regimes exist for specific regulatory or research purposes. Yields obtained under different regimes are not interchangeable, and the regime must always be stated alongside the reported tar value.
Quality Assurance
Accredited third-party laboratories support the validity of tar data through documented equipment qualification (smoking machines, humidities, balances, gas chromatographs), regular verification with certified reference cigarettes, participation in interlaboratory smoke proficiency schemes, control charting of reference yields, and estimation of measurement uncertainty for the reported NFDPM value.
Applications
Mainstream smoke tar determination serves multiple technical and regulatory purposes across the tobacco value chain:
- Regulatory compliance and yield labeling, where tar values printed on packs and checked by market surveillance authorities must be substantiated by standardized machine-smoking data
- Product design and development, evaluating how filter ventilation, paper porosity, rod density, and blend changes influence smoke yields
- Manufacturing quality control, monitoring lot-to-lot consistency of tar delivery against internal specifications and trend limits
- Harm-reduction and comparative research, quantifying yield differences between product formats, generations, or design iterations
- Certification of reference cigarettes and support of interlaboratory studies that underpin method standardization
FAQ
What is the difference between TPM and tar?
TPM (total particulate matter) is everything retained on the Cambridge filter pad, including water and nicotine. Tar (NFDPM) is the portion of TPM remaining after subtracting water and nicotine, which is why a tar determination always requires three measurements: gravimetric TPM plus chromatographic water and nicotine.
Why are the puffing parameters fixed so precisely?
Machine-smoking yields are conditional values whose meaning depends entirely on how the smoke is generated. Fixing puff volume, duration, interval, butt length, and conditioning atmosphere makes results comparable between laboratories and over time, which is the entire basis of the ISO and GB reporting systems.
How many cigarettes are needed for a test?
A single determination typically consumes at least 20 cigarettes, and laboratories generally request 100 or more conditioned cigarettes so that replicate runs, confirmatory testing, and any repeat analyses can be completed from one representative sample.
Why do tar results sometimes differ between reports?
Differences usually arise from the smoking regime used. Intense regime testing (larger puffs, shorter intervals, blocked ventilation holes) yields substantially higher tar values than the standard ISO regime. Conditioning deviations, cigarette selection, and normal measurement variability also contribute smaller differences.
How is the result reported?
Tar is reported as nicotine-free dry particulate matter in mg per cigarette, rounded to 0.1 mg, together with TPM, water, nicotine, puff count, and an explicit statement of the smoking regime and standards followed.
How long does the test take?
Conditioning requires at least 48 hours, followed by smoking, extraction, chromatographic analysis, and data review. Most routine determinations are completed within five to ten working days after samples are received and stabilized.