Tar yield is one of the most fundamental and tightly regulated measurements in cigarette testing, formally defined as nicotine-free dry particulate matter (NFDPM) in mainstream smoke. This article explains the complete laboratory workflow for cigarette tar determination, covering sample conditioning, machine smoking, Cambridge filter pad collection, gas chromatographic analysis, and yield calculation in accordance with ISO 4387 and GB/T 19609.
Technical Overview
Tar in cigarette smoke, formally known as nicotine-free dry particulate matter (NFDPM), is the residue of total particulate matter (TPM) retained on a glass-fiber filter pad during machine smoking, after the water and nicotine fractions have been subtracted. It is one of the core smoke chemistry measurements used for regulatory reporting, product labeling, and comparative assessment of cigarette designs. The internationally recognized procedure is specified in ISO 4387, which is adopted in China as the national standard GB/T 19609.
A complete tar determination is a multi-step analytical workflow that combines gravimetric and chromatographic techniques: conditioned cigarettes are smoked on a calibrated smoking machine under strictly defined puffing parameters, the particulate phase is trapped on a Cambridge filter pad, the pad is extracted with solvent, and gas chromatography quantifies the nicotine and water content. The final tar yield is then calculated by difference. Because every step directly influences the result, the procedure demands rigorous environmental control, instrument calibration, and documented quality assurance.
Testing Samples
Finished Commercial Cigarette Products
Manufactured cigarettes sampled from production lines or retail packages according to statistically valid sampling plans, such as those described in ISO 8243. These samples are tested for regulatory compliance, batch release, and verification of the tar value printed on the pack.
Prototype and R&D Samples
Experimental cigarette designs, including new filter configurations, blend variations, paper permeability changes, and ventilation levels, are submitted during product development to characterize how each design variable affects mainstream smoke delivery.
Monitor and Reference Cigarettes
Laboratory control cigarettes with assigned reference values are smoked alongside test samples in every analytical run. Their results are plotted on control charts to confirm that the smoking machine and analytical system remain within statistical control.
Testing Items
The cigarette tar determination experiment includes the following measurable outputs, all expressed in milligrams per cigarette:
- Total particulate matter (TPM), determined gravimetrically from the mass gain of the Cambridge filter pad.
- Water in the smoke condensate, determined by gas chromatography in accordance with ISO 10362-1.
- Nicotine in the smoke condensate, determined by gas chromatography in accordance with ISO 10315.
- Tar (NFDPM), calculated as TPM minus water minus nicotine in accordance with ISO 4387 and GB/T 19609.
- Average puff count, the mean number of standard puffs taken to the specified butt length.
- Vapor-phase carbon monoxide (optional), which can be collected simultaneously in the same smoking run using a dedicated analyzer.
Testing Methods
Sample Conditioning and Preparation
Cigarettes are conditioned at 22 °C ± 2 °C and 60 % ± 5 % relative humidity for at least 48 hours in accordance with ISO 3402. Test units are randomly selected and visually inspected, and any damaged cigarettes are rejected. Where required by the study design, weight-based selection retains only cigarettes within a narrow band around the average mass. The specified butt length, which is 23 mm or the filter overwrap length plus 3 mm where this is greater, is marked on each cigarette before smoking. Cambridge filter pads are equilibrated in the same laboratory atmosphere for a minimum of 12 hours and weighed on a calibrated analytical balance with 0.1 mg readability.
Machine Smoking Under Standard Conditions
A linear or rotary analytical smoking machine conforming to ISO 3308 is configured to the standard puffing regimen:
- Puff volume: 35 mL ± 0.3 mL
- Puff duration: 2.0 s ± 0.05 s
- Puff frequency: one puff every 60 s ± 0.5 s
- Butt length: 23 mm, or overwrap plus 3 mm, whichever is longer
Each Cambridge filter pad holder typically collects smoke from 20 cigarettes, and a complete test comprises at least five replicate determinations to establish a statistically sound mean. The smoking room is maintained at 22 °C ± 2 °C and 60 % ± 5 % relative humidity with controlled airflow over the pad holders. Puff volume, duration, and frequency are verified with calibrated flow-measuring devices before every run.
Collection and Extraction of Particulate Matter
After smoking, the pads are re-equilibrated and reweighed, and the mass gain is divided by the number of cigarettes smoked to obtain the TPM yield. Each pad is then transferred to an extraction vessel and mechanically agitated for approximately 30 minutes with a measured volume of isopropanol containing suitable internal standards. Blank pads are processed in parallel to confirm the absence of contamination. Because nicotine is highly toxic, all extracts are handled with gloves and under appropriate fume extraction.
Instrumental Analysis by Gas Chromatography
The pad extract is analyzed on two gas chromatographic channels: nicotine is quantified with a flame ionization detector against multi-point calibration standards in accordance with ISO 10315, and water is quantified with a thermal conductivity detector in accordance with ISO 10362-1. Calibration curves are verified with independent check standards, and monitor cigarette results must fall within established control limits before sample data are accepted.
Calculation and Reporting
Tar is obtained by difference: NFDPM = TPM − water − nicotine, with all quantities expressed in mg per cigarette. Replicate values are averaged, outliers are evaluated against the repeatability criteria of the standard, and the final yields are reported to the nearest 0.1 mg per cigarette together with the puff count and an explicit statement of the smoking regime used.
Quality Control and Method Assurance
Essential control elements include daily verification of puff parameters, leak testing of the smoking machine, continuous monitoring of laboratory temperature and humidity, scheduled balance and chromatograph calibration, inclusion of monitor cigarettes in every run, and participation in interlaboratory comparison programs. Laboratories operating under a quality management framework such as ISO/IEC 17025 document all of these controls to ensure traceable, defensible results.
Applications
- Regulatory compliance testing and tar-yield declarations for product registration and labeling.
- Product development support, including evaluation of filter efficiency, ventilation dilution, and paper permeability effects on delivery.
- Manufacturing quality control and batch-to-batch consistency monitoring.
- Market surveillance by authorities and accredited third-party laboratories to verify labeled smoke yields.
- Scientific research into mainstream smoke chemistry and comparative product assessment studies.
FAQ
What is the difference between TPM and tar?
TPM is the total mass of all particulate matter retained on the Cambridge filter pad, including water and nicotine. Tar (NFDPM) is TPM with the water and nicotine fractions subtracted, representing the remaining dry particulate residue.
Why are water and nicotine subtracted from TPM?
Water and nicotine are measured separately because they are chemically distinct fractions with their own reported yields. Removing them yields a consistent, comparable measure of the dry particulate residue, which is the quantity defined as tar in ISO 4387 and GB/T 19609.
How many cigarettes are required for one complete test?
A single determination typically uses 20 cigarettes collected on one filter pad. A full test with five replicate determinations therefore requires at least 100 conditioned cigarettes, plus additional units for monitor cigarettes and any retesting.
Does machine-measured tar equal what a smoker actually inhales?
No. Standard machine yields are comparative laboratory measurements obtained under fixed puffing parameters. They are not predictors of individual human exposure, which depends on smoking behavior, blocking of ventilation holes, and consumption patterns. Regulatory frameworks therefore require machine yields to be presented as standardized analytical values only.
Can the test be performed under alternative smoking regimes?
Yes. Some regulatory authorities specify more intense conditions, such as a 55 mL puff volume, a 30-second puff interval, and complete blocking of filter ventilation. Results obtained under any regime are not interchangeable, so the test report must always state the puffing parameters used.