Particle Size Distribution (PSD) Testing

Aerosol Science

NGI and Andersen cascade impactors and real-time platforms (APS, OPS, FMPS, and Spraytec), paired with HPLC, ELISA, or ddPCR quantitation selected for the active and matrix.

Multi-instrument PSD array — Malvern Spraytec, TSI FMPS, APS, Andersen cascade impactor, and NGI

Purpose & when to use

Particle Size Distribution (PSD) testing resolves how aerosol mass and number distribute across particle diameters — the central performance attribute behind how a drug, antimicrobial, or consumer aerosol behaves in the lung, on a surface, or through a filter. Cascade impactor methods (NGI, Andersen) deliver the regulator-aligned mass profile for MMAD and GSD under USP <601>; real-time platforms (APS, OPS, FMPS, Spraytec) add time-resolved sizing and droplet spectra. PSD is foundational for:

PSD for MDIs, DPIs, nebulizers, and nasal sprays — stage-by-stage mass, MMAD / GSD, and fine-particle dose for in vitro packages under USP <601>, USP <1601>, FDA MDI / DPI / nasal.
Lot-to-lot comparability and design-change control across nozzle, valve, formulation, propellant, or pump changes — predicate and reference comparisons under ICH Q5E and FDA change-control guidance, with documented statistical power and method controls.
Exposure and risk assessments for consumer aerosols, antimicrobial sprays, and room-applied disinfectants — fine-fraction and ultrafine particle screening informing EPA inhalation-safety dossiers and OECD test-guideline alignment.
Stability and accelerated-aging studies where particle-size drift is a critical quality attribute under USP <601>, ICH Q1A, and FDA stability guidance — supporting shelf-life justifications and container-closure decisions for inhalation products.
Fogging, misting, and ULV (ultra-low volume) droplet-spectrum characterization for room-disinfection and antimicrobial-spray applications — supporting EPA registration packages, ISO 27427 nebulizing-equipment alignment, and ASTM E2647 inhalation-exposure framing.

Use PSD testing when the project requires defensible size-fraction data traceable to a defined method setup. ARE Labs controls actuation, flow, and conditioning and documents replicates, blanks, and analytical controls throughout collection and reporting. The resulting dataset can support internal review, predicate comparison, or regulatory submission.

Built for inhalation, drug delivery, and consumer aerosols

PSD characterization spans the device categories that put particles into the air — pharmaceutical, medical, and consumer products under one analytical roof.

MDIMetered-dose inhalers
DPIDry-powder inhalers
NebulizerLiquid aerosol generators
Nasal sprayIntranasal delivery
Consumer aerosolSprays · fogs · disinfectants

Instrumentation & measurement ranges

We select the platform based on the device, aerosol physics, and the decision the data must support. Each sizing basis answers a different technical question.

0.4 – 11 µmaerodynamic

Cascade impactors (NGI / Andersen)

Size-fractionated mass collection across NGI stages or Andersen cuts — the regulator-aligned basis for aerodynamic diameter, MMAD, and GSD derivation. Strong lot-to-lot comparability and the foundation for cascade extraction analytics.

0.5 – 20 µmaerodynamic

APS (aerodynamic particle sizer)

Time-of-flight aerodynamic sizing in real time — number distributions and transient plume dynamics during actuation. Useful for screening, troubleshooting, and bridging cascade data with development decisions.

0.3 – 10 µmoptical

OPS (optical particle sizer)

Optical-equivalent diameter via laser scattering with low setup overhead. Useful when refractive index is well-characterized and aerodynamic detail isn't the primary requirement — common for room-applied aerosols and consumer-product screening.

5.6 – 560 nmmobility

FMPS (fast mobility particle sizer)

Fast-mobility number distributions across the fine and ultrafine regime — captures the sub-100 nm fraction cascade impactors miss. Charge-conditioning and dilution discipline mandatory for cross-lab comparability.

0.1 – 980 µmdiffractive

Malvern Spraytec (laser diffraction)

Volume-weighted droplet spectra via laser diffraction at high throughput — screening for nasal sprays, ULV applications, and consumer-aerosol development. Refractive-index and multiple-scattering corrections applied per study.

Test method options

Method	Strengths	Tradeoff	Aligned with
Regulator-aligned in vitro PSD (cascade impactor focus)	Stage-by-stage mass with derived MMAD, GSD, and fine-particle dose — from controlled actuations on NGI or Andersen impactors under documented flow. Strong lot-to-lot comparability; the canonical package for inhalation submissions under USP <601>, USP <1601>, and FDA MDI / DPI / nasal guidance.	More setup and analytical work than real-time screening — best when device and formulation are locked enough to justify the cost.	USP <601>USP <1601>FDA MDI / DPI / nasal
Real-time PSD screening (APS / OPS)	Fast iteration with time-resolved number distributions — supports troubleshooting and rapid formulation or device screening. Far less setup overhead than a cascade run — right when the program is moving and the decision is comparative, not regulatory.	Number-based sizing doesn't map directly to mass-based endpoints; bridge to cascade data when the program approaches submission.	—
Nanoparticle characterization (FMPS)	Captures the ultrafine and sub-100 nm fractions cascade impactors miss — essential when the ultrafine tail drives the safety question. High time resolution (1 Hz) reveals how the ultrafine spectrum evolves through actuation, not just the integrated dose.	Requires careful charge-conditioning, neutralization, and dilution assumptions — cross-lab comparisons depend on documented method parity.	—
Spray droplet sizing (Malvern Spraytec)	High throughput for spray and nasal-product development — full droplet spectra in seconds, ideal for formulation screening. Non-destructive and quick to reconfigure — pairs naturally with early device-design iteration and rapid lot comparisons.	Optical sizing basis doesn't substitute for aerodynamic measurement when regulators require mass-fraction data — bridge to cascade impactor results before submission.	ISO 27427FDA MDI / DPI / nasal
Hybrid method (cascade impactor + real-time monitor)	Links time-resolved plume behavior to stage-by-stage mass in a single dataset — explains what the device emits and how the emission evolves. Strong framing for comparability studies where the regulator wants the dynamic explanation behind the static stage mass.	More instrumentation, synchronization, and analyst time per condition; reserve for cases where the combined view materially changes the decision.	USP <601>USP <1601>FDA MDI / DPI / nasal

Setup configurations

Each PSD study uses a configuration matched to the device, formulation, and decision the data must support. A fit-for-purpose setup combines method rigor, including controlled flow, actuation, and conditioning, with the practical operating characteristics of the test device. During study planning, we define the dimensions below to keep the measured size distribution interpretable, reproducible, and defensible:

Device interfaces

Adapters for MDIs, DPIs, nebulizers, nasal sprays, and room-applied aerosols — geometry matched to the device under test.

Flow & actuation profiles

Controlled flow rates, actuation force and displacement, and shot counts that match the use conditions a patient or operator would apply.

Sample numbers

Replicates per condition plus method controls; power sized to device-to-device and shot-to-shot variability declared up front.

Media & handling

Coated impactor plates where applicable, extraction solvents, and documented storage for collected stages, filters, and analytical samples.

Calibration & verification

Flow meters, mass-flow controllers, and sizing instruments calibrated against traceable standards before each campaign and verified between runs.

Methods anchored to the standards that matter

Each PSD study follows a documented quality system aligned with regulatory frameworks for inhalation, intranasal, and consumer-aerosol products. The four anchors below define the study's data requirements.

ISO 17025AccreditedTesting-laboratory competence — documented methods, calibration traceability, and uncertainty contributors.
USP <601>AccreditedAerosols, nasal sprays, MDIs, and DPIs — performance quality tests.
USP <1601>AlignedProducts for nebulization — characterization tests.
FDA MDI / DPI / nasalAlignedChemistry, manufacturing, and controls for inhalation and intranasal products.

Key data outputs & reporting

Each PSD study provides documented primary results and the underlying datasets. Standard outputs include stage-by-stage mass, derived aerodynamic metrics such as MMAD, GSD, and fine-particle dose, summary statistics, figures, and traceable QA/QC controls. Files are formatted for regulatory submissions, internal change-control packages, or downstream modeling. The deliverables below make up the standard PSD report. Complex programs, including comparability studies, predicate studies, and stability time-courses, receive an extended package with the supporting artifacts listed beneath the table.

Primary outputs

Stage-by-stage mass from cascade impactors with derived metrics — MMAD, GSD, and fine-particle dose per actuation and per device.
Number or mass distributions from APS / OPS / Spraytec / FMPS with time stamps for transient plume behavior.
Summary statistics across replicates (mean, SD, CV) plus condition comparisons against predicate, control, or specification baselines.

Stage-by-stage deposition

Cascade impactor · APSD pilot · n=3 · % of total dose · stage cut-off µm

Deliverables

#	Format	Contents
01	PDF report	Methods, controls, and results tables.
02	CSV / XLSX datasets	Stage mass and derived metrics.
03	Figures	PSD curves, overlays, and stage-mass bar charts for internal reviews and submissions.

Extended deliverables · multi-arm comparability · stability · predicate studies

Comparability appendix — Side-by-side stage-mass overlays + statistical equivalence test per ICH Q1E or product-specific predicate framing.
Stability time-course pack — MMAD / GSD / fine-particle-dose trends across timepoints with predefined OOT criteria flagged.
Method-development notes — Documentation of method-selection rationale, control runs, and uncertainty contributors — for submission cover letters and inspection readiness.

QA / QC & data integrity

Each PSD study includes a documented QA/QC framework matched to the method plan. Controls and verifications are selected for the regulatory framework, analytical chemistry, and decision the data must support. These checks run alongside size-fraction collection, are audited under our ISO 17025 quality system, and remain traceable from sample receipt through the final result. Recovery, system-suitability, and environmental monitoring are added when required by the assay.

Blanks and background runs including stage and plate blanks where applicable.

Replicate runs and device-level repeats to quantify variability across actuations, devices, and lots.

Calibration and verification logs for flow control, mass-flow controllers, and sizing instruments.

Assay controls for HPLC, ELISA, and ddPCR quantitation — calibration standards, system-suitability checks per assay, and spike-recovery on matrix-challenging analytes.

Chain of custody from sample receipt through analysis and final reporting.

Why ARE Labs

ARE Labs connects technical topics to practical study design, method selection, controlled aerosol work, and reportable evidence without turning technical pages into sales pages.

Reviewed byJamie Balarashti (25 yrs - cascade & inhalation methods) - Weston Schaper (7 yrs - real-time sizing & nanoparticle work)

17025Accredited testing

900+Studies Performed

17+Years in operation

300+Clients supported

Common questions

These answers address the questions inhalation, antimicrobial, and consumer-aerosol teams commonly ask when planning a PSD study, including method selection, quantitation, replicate counts, comparability, and deliverables. They are starting points rather than study protocols. Most PSD programs require at least one custom configuration based on the device, formulation, or regulatory framework, and those choices are often easier to define during a call.

Q.Which PSD method should I choose?

A.Use cascade impactors when the study requires size-fraction mass and derived aerodynamic metrics such as MMAD and GSD. APS, OPS, and Spraytec support faster development screening, while FMPS is appropriate when the sub-100 nm fraction matters. We match the method to the decision during study planning.

Q.Can you quantify stages without gravimetry?

A.Yes. Depending on the active and matrix, ARE Labs can quantify collected mass using HPLC, ELISA, or ddPCR. Assay controls, system suitability, and recovery are documented with the results.

Q.How many actuations or runs are typical?

A.The required shot count and number of replicates depend on device output and assay sensitivity. We define both during study planning to meet the precision goals, including device-level repeats when device-to-device variability must be quantified.

Q.What affects comparability between lots or designs?

A.Actuation conditions, flow control, device-to-device variability, and assay recovery can each affect PSD results. We control flow with mass-flow controllers, record actuation force for each shot, and document assay recovery so the comparison remains interpretable.

Q.What do you deliver?

A.Deliverables include a PDF report with methods, controls, and results tables; CSV/XLSX datasets containing stage mass and derived metrics; and figures such as PSD curves, overlays, and stage-mass bar charts for internal review or submission appendices.

Standards & guidance

ARE Labs conducts PSD studies in alignment with the regulatory and consensus standards that apply to inhalation, intranasal, and consumer-aerosol products. When third-party accreditation covers the applicable scope, the method is documented as accredited under ISO 17025. When a standard is followed outside a formally accredited scope, the method is described as aligned or conformant where applicable. The cards below identify the standards most often used in PSD packages. Select a card to review the standard's role in the study, the deliverables it defines, and the tests that cite it.

Inhalation & Drug Delivery - Accredited

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