Aerosol Mass Output (Gravimetric Testing)

Overview

Gravimetric aerosol mass measurement is the simplest and most widely accepted method for quantifying how much aerosol a vapor product delivers. The principle is straightforward: capture the emitted aerosol on a filter, weigh the filter before and after collection, and calculate the mass difference. That difference represents the total particulate matter (TPM) captured during the test. Dividing by the number of puffs gives the evaporated mass per puff (EMP) — a fundamental performance metric for any vapor product.

Unlike optical or spectroscopic methods that require calibration against reference standards, gravimetric measurement is self-calibrating. A balance reads mass directly. There is no conversion factor, no response curve, and no matrix effect to account for. This makes it the reference method for aerosol output characterization in most regulatory frameworks, including CORESTA guidelines for e-cigarette testing and Health Canada's cannabis vape product requirements.

The UVM's multi-channel architecture allows gravimetric testing of up to four products simultaneously under identical puff conditions. Each channel can be fitted with its own inline filter, enabling direct side-by-side comparison of aerosol mass output across products, formulations, or power levels — all from a single test run.

Why It Matters

Aerosol mass output is the most direct measure of what a vapor product actually delivers to the user. While puff count tells you how many puffs a product lasts, and vapor density tells you the relative aerosol concentration on each puff, gravimetric data tells you the actual mass of material that was aerosolized and would have been inhaled.

For product development, EMP data answers critical questions. Does a formulation change increase or decrease aerosol delivery? Does a new cartridge design deliver more or less material per puff than the previous revision? Does power level affect total mass delivery proportionally, or is there a diminishing return at higher wattages?

For regulatory submissions, gravimetric data is often required. Health Canada's cannabis vape product characterization protocols specify TPM measurement. CORESTA Recommended Method 81 defines a gravimetric procedure for e-cigarette aerosol collection. Having instrument-generated, protocol-documented EMP data from a standardized testing platform satisfies these requirements directly.

For quality control, EMP provides a quantitative acceptance criterion. If your reference testing establishes that a product should deliver 5.0 mg per puff under standard conditions, a batch sample delivering 3.2 mg per puff indicates a problem — underfill, coil malfunction, wicking deficiency, or formulation error — that warrants investigation before the batch ships.

Equipment Needed

Gravimetric testing with the UVM requires minimal additional equipment beyond the machine itself:

• Universal Vaping Machine (UVM): Provides controlled, standardized puffs at defined volume, flow rate, and timing. Multi-channel operation enables parallel testing.
• Inline filter cartridges: PTFE membrane filter cartridges (available from Gram Research) or Cambridge filter pads in appropriate holders. PTFE filters offer low background mass, high capture efficiency for sub-micron aerosol particles, and chemical inertness. Cambridge filter pads (44 mm glass fiber) are the traditional standard for tobacco and e-cigarette aerosol collection.
• Analytical balance: A balance with 0.1 mg (100 microgram) readability. A 0.01 mg balance is preferred for low-output products or short puff regimens where the total captured mass may be small. The balance should be located in a stable, draft-free environment.
• Forceps: For handling filters without introducing fingerprint oils or moisture that could affect the mass measurement.
• Desiccator or conditioning chamber (optional): For equilibrating filters to a consistent temperature and humidity before weighing.

Protocol

1. Condition the Filter

Remove the filter from its packaging and place it in the laboratory environment — or in a desiccator — for at least 30 minutes to equilibrate to ambient temperature and humidity. Filters can absorb or release moisture depending on storage conditions, and this moisture contributes to the measured mass. Conditioning ensures the pre-test and post-test weighing conditions are consistent.

2. Weigh the Filter (Pre-Test)

Using forceps, place the conditioned filter on the analytical balance and record the mass to the precision of the instrument (0.1 mg minimum). Record this as M_pre. For best accuracy, take the average of three consecutive readings to account for balance drift. If using a filter in a holder or cartridge assembly, weigh the entire assembly — the same assembly will be weighed after the test.

3. Install the Filter Inline

Install the weighed filter cartridge in the flow path between the vapor product and the UVM's exhaust. The filter should be downstream of the vapor sensor (if vapor density data is also being collected) so that the aerosol passes through the sensor first and is then captured by the filter. Ensure all connections are airtight — any bypass air that does not pass through the filter represents uncaptured aerosol and will cause the gravimetric measurement to underreport.

4. Run the Puff Regimen

Configure the puff parameters — volume, flow rate, duration, rest interval, and power level — in the UVM software. For gravimetric testing, a fixed number of puffs is typically used rather than running to endpoint. Common regimens range from 10 to 50 puffs, depending on the product's output level and the balance's sensitivity. Too few puffs may produce a mass difference that is within the balance's uncertainty range. Too many puffs may overload the filter, increasing its flow resistance and potentially affecting the puff profile.

Start the test. The system executes the defined number of puffs automatically.

5. Remove and Weigh the Filter (Post-Test)

After the test completes, carefully remove the filter cartridge. Allow it to equilibrate to room conditions for 5-10 minutes — the filter may be slightly warm from the aerosol and may carry residual volatile compounds that will evaporate during this conditioning period. Using forceps, place the filter on the same analytical balance and record the mass as M_post.

6. Calculate Total Captured Mass

The total aerosol mass captured is simply:

TPM = M_post − M_pre

This value represents the total particulate matter deposited on the filter during the puff regimen.

7. Calculate Evaporated Mass per Puff

Divide the total captured mass by the number of puffs in the regimen:

EMP = TPM ÷ N_puffs

This is the evaporated mass per puff — the average mass of aerosol delivered on each puff under the tested conditions.

Filter Pressure Drop Consideration

As aerosol accumulates on the filter, the filter's resistance to airflow increases. This additional pressure drop can affect the puff profile — if the combined resistance of the product and the loaded filter exceeds the UVM's flow capacity, the actual delivered puff volume may fall below the target, producing lower-than-expected aerosol mass readings on later puffs.

To monitor for this, measure the filter's pressure drop before and after the test. A clean PTFE filter cartridge typically adds 5-15 mbar of resistance at standard test flow rates. After a 50-puff collection from a high-output product, this may increase to 30-50 mbar or more. If the post-test filter pressure drop is significantly elevated, consider using fewer puffs per filter or switching to a filter with a larger active area.

The UVM logs pressure drop data on every puff, so an increasing trend in total system pressure drop during the test is immediately visible in the data — even before the filter is removed and inspected.

Multi-Channel Gravimetric Testing

Running four products in parallel with individual inline filters on each channel produces four independent gravimetric datasets from a single test run. Because all four channels share the same puff timing, the comparison is genuinely controlled — every product received the same number of puffs, at the same intervals, at the same flow rate.

This is particularly valuable for formulation comparison (same hardware, different oils), hardware comparison (same oil, different cartridges), and batch QC (same product from different production lots). The gravimetric data can be correlated with the per-puff vapor density and pressure drop data that the UVM collects simultaneously, providing a complete picture of each product's performance from a single test run.

Data Output

The gravimetric measurement itself is an offline calculation — the balance reading is not connected to the UVM software. However, the UVM logs all parameters and sensor data from the test run, which you combine with the gravimetric result for a complete record:

• Total particulate matter (TPM): The filter mass difference, recorded manually from the balance.
• Evaporated mass per puff (EMP): TPM divided by puff count.
• Per-puff vapor density: The IR sensor reading for each puff, providing a relative aerosol output curve that can be correlated with the gravimetric total.
• Per-puff pressure drop: Useful for confirming that filter loading did not compromise the puff profile during the test.
• Puff parameters: Volume, flow rate, duration, power level, and rest interval — essential for reproducing the test or comparing results across facilities.