Environmental variability is often overlooked, but it can influence data confidence
When inhaler testing data varies unexpectedly, the first areas investigated are often the product, method, analyst technique or test equipment. But there is another potential contributor that can be harder to spot: the test environment.
Temperature, relative humidity and electrostatic charge can all influence orally inhaled and nasal drug product testing. These factors may affect dose emission, aerosol generation, particle behaviour and the performance of cascade impaction methods used for APSD measurement. They can also contribute to variability in delivered dose uniformity testing.
For laboratories working to improve reproducibility, reduce repeat testing and increase confidence in results, environmental control deserves closer attention.
Why environmental variability matters
Inhaler testing is already complex. Dose delivery is dynamic, cascade impaction is sensitive to multiple sources of variation, and small changes in test conditions can influence the quality and usefulness of data.
Poor control of environmental conditions can increase the risk of unexplained variability, out-of-specification or out-of-trend results, repeat investigations and reduced analytical discrimination. For R&D teams, this can make it harder to detect meaningful differences between formulations or devices. For QC teams, it can make it harder to confirm comparability with confidence.
In short, environmental variability can create uncertainty where laboratories need confidence.
The three environmental factors to consider:
1. Temperature
Changes in ambient temperature can influence formulation properties, aerosolisation behaviour and droplet evaporation. For cascade impaction, temperature effects can be particularly relevant for nebulisers and other droplet-based products such as soft mist inhalers.
2. Relative humidity
Relative humidity can affect particle or droplet behaviour, moisture-sensitive formulations and the tendency for electrostatic charge to build up. Low RH can make electrostatic effects more pronounced because there is less moisture in the air to help dissipate charge.
3. Electrostatics
Electrostatic charge can influence particle deposition, internal losses and dose delivery behaviour. These effects can be complex and unpredictable, especially where non-conductive surfaces, device materials, analyst handling or low-humidity conditions are involved.
When should environmental variability be investigated?
Environmental variability may be worth reviewing if your lab is experiencing:
- Unexplained variability in DDU or APSD results
- Poor reproducibility between runs, analysts, shifts or locations
- Out-of-specification or out-of-trend results with no clear root cause
- Seasonal changes in data behaviour
- Inconsistent temperature or RH readings around the test area
- Electrostatic issues during sample preparation or testing
- Pressure to improve control without investing in a dedicated climate-controlled room
These issues do not automatically mean the environment is the cause. But they are strong reasons to assess whether environmental conditions are contributing to test variability.
A practical alternative to full-room climate control
Dedicated climate-controlled laboratories can provide a stable working environment, but they may be costly, inflexible or difficult to justify for every testing requirement. EnviroMateā¢ offers a more focused approach. Designed specifically for inhaler testing, it provides controlled temperature and relative humidity in the immediate test area, with integrated electrostatic mitigation. It is a compact benchtop solution intended for laboratories dealing with variable conditions, inadequate climate control, poor reproducibility or unexplained OOS results. By controlling the immediate testing environment rather than the entire room, laboratories can take a practical step toward reducing avoidable variability and improving confidence in inhaler test data.
Air-conditioned does not always mean controlled
Many laboratories rely on general air conditioning or room-level climate control. However, this does not always guarantee stable conditions at the point of testing.
An EnviroMate application study compared temperature and RH variation in an air-conditioned laboratory with conditions inside the EnviroMate chamber. The surrounding lab showed clear variation across the test period, while conditions inside EnviroMate remained stable at the chosen set points. The study showed temperature control to within Ā±0.5Ā°C and RH control to within Ā±3%, within the quoted performance figures for the unit.
This highlights an important point: localised control of the immediate test environment may be more relevant than relying on room-level assumptions.
Recommended resources
White paper: Establishing a robust environment for inhaler testing
Understand how temperature, relative humidity and electrostatics can affect inhaler testing, and why environmental control matters for data integrity.
Download the white paperApplication note: Reducing variability in the inhaler testing environment with EnviroMate
See experimental data showing how EnviroMate controls temperature and RH compared with the surrounding air-conditioned laboratory.
View the application noteEnviroMateā¢ product information
Explore how EnviroMate provides cost-effective, benchtop environmental control for inhaler testing applications.
Learn more about EnviroMateEnvironmental Variability in Inhaler Testing: FAQs
Environmental variability refers to changes in the test environment that may influence inhaler testing results. The main factors are temperature, relative humidity and electrostatic charge. These can affect product behaviour, aerosol generation, particle or droplet behaviour, and the sampling process itself.
Temperature can influence formulation properties, aerosolisation behaviour and droplet evaporation. In cascade impaction testing, changes in temperature may also affect the behaviour of droplets or particles within the test set-up.
Relative humidity can influence moisture-sensitive formulations, particle or droplet behaviour and electrostatic charge dissipation. Low humidity can make electrostatic effects more pronounced, while higher humidity may affect products that are sensitive to moisture.
Electrostatic charge can influence particle deposition, internal losses and aerosol behaviour. In some cases, electrostatic effects may contribute to variability in delivered dose uniformity or aerodynamic particle size distribution measurements.
Controlling the immediate test environment can help reduce the influence of local temperature, humidity and electrostatic variation around the test setup. This may be more practical and cost-effective than relying solely on full-room climate control, particularly where the challenge is localised variability at the point of testing.
Speak to a specialist
Concerned that temperature, humidity or electrostatics may be affecting your inhaler testing data? Share a few details and one of our specialists will get back to you.
