Sample preparation is the single most critical factor governing the accuracy and reproducibility of cigarette tar (nicotine-free dry particulate matter) measurements. This technical article explains the complete preparation workflow — from representative sampling and climatic conditioning to cigarette selection, butt marking, and Cambridge filter pad handling — in accordance with ISO 4387, ISO 3308, ISO 3402, ISO 8243, and the corresponding GB national standards used by accredited third-party laboratories and tobacco manufacturers worldwide.
Technical Overview
Tar, formally defined as nicotine-free dry particulate matter (NFDPM), is the fraction of the total particulate matter (TPM) trapped from cigarette smoke after subtraction of the water and nicotine contents. It is one of the most closely regulated smoke yield metrics worldwide and must be determined under strictly standardized conditions. The governing method is ISO 4387, adopted in China as GB/T 19609, which specifies the use of a routine analytical linear smoking machine.
The analytical principle is straightforward: cigarettes are smoked under machine-controlled puffing conditions, the particulate phase is collected on a glass-fiber Cambridge filter pad (typically 44 mm in diameter), the pad is weighed to obtain TPM by gravimetry, and the collected matter is then extracted and analyzed by gas chromatography to quantify water (ISO 10362-1) and nicotine (ISO 10315). Tar is calculated as TPM minus water minus nicotine, expressed in mg per cigarette and rounded to the nearest 0.1 mg.
Although the final calculation is simple, most of the variability in tar results originates upstream of the smoking machine. Consequently, sample preparation encompasses the entire chain from sampling through conditioning, visual and physical selection, butt-length marking, pad conditioning, and extract preparation. Every step is performed inside a controlled atmosphere of 22 °C ± 2 °C and 60 % ± 5 % relative humidity as required by ISO 3402 (GB/T 16447), and each step is documented to preserve traceability.
Testing Samples
Commercial Cigarette Samples
Retail products are sampled according to ISO 8243 or GB/T 5606.1. A laboratory sample generally consists of no fewer than 200 cigarettes taken from multiple packs representing different production dates or retail points. Packaging must arrive intact, as broken wrappers alter moisture equilibrium and distort tar yields. Samples are transported protected from light, heat, and mechanical damage, and are logged into the laboratory information system on receipt.
Development and Pilot-Batch Samples
Prototype cigarettes from pilot production lines are prepared with the same rigor, supplemented by stricter traceability requirements: blend composition, filter ventilation, and rod physical parameters are recorded so that any yield deviation can be linked to a design variable rather than to preparation artifacts.
Reference and Monitor Cigarettes
Certified reference or monitor cigarettes are prepared alongside every smoking run. Their TPM, water, nicotine, and tar values are plotted on control charts, allowing the laboratory to demonstrate that the smoking machine, balance, and chromatographic systems remain in statistical control before unknown samples are reported.
Conditioning and Storage
Prior to conditioning, samples are held in sealed containers in a cool, dark environment. Unopened packs are then conditioned in the standard atmosphere for a minimum of 48 hours (ISO 3402). After packs are opened, individual cigarettes are equilibrated further and used promptly, and any cigarette removed from the conditioning room for more than a short, defined period is discarded.
Testing Items
The sample preparation procedure supports the following determinations, all reported in mg per cigarette:
- Total particulate matter (TPM) collected on the Cambridge filter pad, by gravimetry
- Water content of the smoke condensate, by gas chromatography (ISO 10362-1)
- Nicotine (transfer smoke nicotine) content of the condensate, by gas chromatography (ISO 10315)
- Nicotine-free dry particulate matter (tar, NFDPM), calculated as TPM minus water minus nicotine
- Supporting parameters: total puff count, cigarette mass, pressure drop (ISO 6565), butt-length compliance, and puff volume verification
Blank determinations, including unsmoked pad blanks and smoking machine blanks, are prepared with each batch to correct for background water and nicotine contributions from pads, solvent, and the laboratory environment.
Testing Methods
Sampling and Chain of Custody
Field sampling follows the randomization and minimum-quantity rules of ISO 8243. Each laboratory sample receives a unique identifier that follows it through conditioning, selection, smoking, extraction, and reporting, ensuring full chain of custody.
Climatic Conditioning
All cigarettes, Cambridge filter pads, and pad holders are equilibrated at 22 °C ± 2 °C and 60 % ± 5 % relative humidity for at least 48 hours. Conditioning cabinets are continuously monitored with calibrated sensors and data loggers, because even small humidity deviations measurably shift both burn rate and particulate transfer.
Cigarette Selection and Marking
Conditioned cigarettes are first screened visually; rods with manufacturing defects, damaged wrappers, or visible irregularities are excluded. Depending on the study protocol, cigarettes are then sorted by mass and, optionally, by pressure drop per ISO 6565, and only rods within a narrow tolerance band (for example ±0.05 g around the batch median) are retained to reduce between-run scatter. Each cigarette is finally marked at the specified butt length — the greater of 35 mm or the filter overwrap length plus 20 mm per ISO 4387 — so that the smoking endpoint is objective. Operators wear powder-free gloves or use tweezers throughout to prevent moisture transfer.
Cambridge Filter Pad Preparation
Glass-fiber pads are conditioned in the test atmosphere, weighed to 0.1 mg on a calibrated analytical balance, and loaded into clean holders. After smoking, pads are re-equilibrated and re-weighed under identical conditions; the mass gain divided by the number of cigarettes smoked gives TPM. For each determination at least 20 cigarettes are smoked, typically five per pad; the loading per pad is adjusted downward for high-delivery products to stay within validated pad capacity.
Smoking Conditions
Cigarettes are smoked on a linear (or rotary) smoking machine under the ISO 3308 standard regime: 35 mL puff volume, 2.0 s puff duration, one puff every 60 s, with a controlled laminar airflow (approximately 150–250 mm/s) across the burning cone. Puff volume, duration, frequency, and system leakage are verified before every run. Where regulatory or research programs require intense conditions, ISO 20778 is applied instead, but the preparation steps remain identical.
Extraction and Instrumental Analysis
Each smoked pad is transferred to an extraction vessel and shaken with a defined volume of isopropanol containing a suitable internal standard. An aliquot of the extract is injected into a GC-FID system for nicotine quantification per ISO 10315 and into a GC system for water per ISO 10362-1. Tar is then calculated, blank-corrected, rounded to 0.1 mg per cigarette, and reported together with puff counts and all preparation metadata. Accredited third-party laboratories operating under ISO/IEC 17025 additionally verify performance through control charts, replicate determinations, and interlaboratory comparisons.
Applications
Rigorous sample preparation for tar determination underpins a wide range of regulatory and industrial activities:
- Statutory tar and nicotine yield reporting and tar-band labelling for product registration and market surveillance
- Product development, including evaluation of filter ventilation, paper porosity, blend, and reconstituted tobacco changes
- Manufacturing quality control, where daily tar results feed statistical process control of delivery consistency
- Benchmarking of competitive products and support for scientific research on smoke formation and yield reduction
- Verification of conformity for export shipments to jurisdictions with differing yield disclosure requirements
In every application, the validity of the reported number depends directly on the discipline applied during sample preparation rather than on the analytical instrumentation itself.
FAQ
Why is conditioning so critical before tar testing?
Cigarette moisture content controls burn rate, puff count, and particulate transfer. Smoking unconditioned or unevenly conditioned cigarettes can shift tar results by a meaningful margin, which is why ISO 3402 mandates 48 hours minimum at 22 °C and 60 % relative humidity for both cigarettes and filter pads.
How many cigarettes are required for one determination?
ISO 4387 requires a minimum of 20 cigarettes per determination, normally smoked in groups of five per Cambridge filter pad, and the laboratory sample should contain at least 200 cigarettes to allow for selection losses and repeats.
What is the difference between TPM and tar?
TPM is everything the filter pad collects from the particulate phase. Tar (NFDPM) is TPM after subtracting the water and nicotine measured in the extract. Tar is always lower than TPM, and only tar is used for regulatory yield declaration.
Can cigarettes be selected by weight and draw resistance?
Yes. Excluding defect rods and restricting the population to a narrow mass band, and optionally a pressure-drop band per ISO 6565, reduces run-to-run variability without biasing the mean delivery, provided selection criteria are documented in the test protocol.
Which standards apply in China?
The Chinese national standards GB/T 19609 (TPM and tar), GB/T 16447 (conditioning atmosphere), and GB/T 5606.1 (sampling) are harmonized with ISO 4387, ISO 3402, and ISO 8243 respectively, so preparation practices are internationally comparable.
Do intense smoking regimes change the preparation?
No. Intense regimes such as ISO 20778 change only the smoking parameters (larger puffs, shorter interval, ventilation blocking); sampling, conditioning, selection, marking, pad preparation, and extraction follow exactly the same preparation workflow described above.