Aerosol Science

Particle Size Distribution (PSD) Testing

Cascade impactor and real-time sizing measure aerosol size distributions, providing size-fraction data for inhalation, exposure, and comparability decisions.

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

ISO 17025USP <601>USP <1601>FDA MDI / DPI / nasalReviewed 2026-10-20
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Multi-instrument PSD array — Malvern Spraytec, TSI FMPS, APS, Andersen cascade impactor, and NGI

Fig 01 · PSD instrument suite — diffraction, mobility, aerodynamic, and cascade methods.

Purpose & when to use

Particle Size Distribution (PSD) testing measures how aerosol mass and number distribute across particle diameters. Size distribution helps explain how a drug, antimicrobial, or consumer aerosol behaves in the lung, on a surface, or through a filter. For applicable inhalation products, cascade impactors (NGI, Andersen) provide regulator-aligned mass profiles for MMAD and GSD under USP <601>. Real-time platforms (APS, OPS, FMPS, Spraytec) add time-resolved sizing and droplet spectra. PSD supports:

  1. 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.
  2. Lot-to-lot and design-change studies compare nozzle, valve, formulation, propellant, or pump changes under a defined protocol; ISO 17025 quality records document reference products, replicates, and method controls.
  3. 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.
  4. 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.
  5. Fogging, misting, and ULV (ultra-low volume) droplet-spectrum characterization for room-disinfection and antimicrobial-spray applications, supporting EPA registration programs where applicable, with aerosol sizing and sampling defined by the study protocol.

Use PSD testing when you need size-fraction data traceable to a defined method setup. We control actuation, flow, and conditioning and document replicates, blanks, and analytical controls from collection through reporting. This documentation supports review of the results for internal decisions, 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 platforms by device type, aerosol physics, and the decision the data need to support. Each sizing basis answers a different 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

MethodStrengthsTradeoffAligned 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

We configure each PSD study around the device, formulation, and intended use of the results. Controlled flow, actuation, and conditioning must account for how the device operates in practice. The configurations below are defined during study planning to support reproducible measurements and give reviewers a documented basis for interpreting the size distribution:

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

PSD studies follow a documented laboratory quality system. USP and FDA references apply to relevant inhalation or intranasal drug products; consumer-aerosol sizing follows a separately defined measurement protocol. The references below describe those distinct roles.

  • 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

PSD studies report results for the selected platform and endpoints, along with underlying datasets, summary statistics, figures, and traceable QA / QC controls. Cascade-impactor results can include stage-by-stage mass, MMAD, GSD, and fine-particle dose; real-time sizing reports distributions on the instrument's stated measurement basis. When scoped, reports are formatted for regulatory submission, internal change-control, or downstream modeling. Comparability, predicate, and stability programs also receive the method-specific records listed below.

Primary outputs

  • Stage-by-stage mass from cascade impactors with derived metrics — MMAD, GSD, and fine-particle dose per actuation and per device.
  • Size distributions from the selected APS / OPS / Spraytec / FMPS platform, with time stamps and the weighting basis stated.
  • Summary statistics across replicates (mean, SD, CV) plus condition comparisons against predicate, control, or specification baselines.

Deliverables

#FormatContents
01PDF reportMethods, controls, and results tables.
02CSV / XLSX datasetsResults for the selected sizing platform and endpoints.
03FiguresPSD 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 overlays with protocol-defined statistical comparisons and product-specific predicate or comparator 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 documented QA / QC controls and verifications matched to the method plan. The regulatory frame, analytical chemistry, and intended use of the data guide these checks. They run alongside size-fraction collection, are audited under our ISO 17025 quality system, and are traceable from sample receipt through the final result. We add recovery checks, system-suitability checks, and environmental monitoring when the assay requires them.

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.

RESEARCH / THIS WORK IN PRACTICE

Real studies. Measured evidence.

Explore published studies connected to particle size distribution testing. Each explains the study question, approach and findings.

View related studies (2)
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Data Center Particle Deposition: Surface Contamination

The client needed a measured baseline for surface particle accumulation across operating spaces, with enough spatial detail to compare buildings, halls, and sampling heights.

Selected finding
Across 123 primary slides, mean and median mass deposition rates were 14.7 and 7.5 mg/m²/day.
Related context

Optical microscopy size measurements complement ARE Labs particle-sizing capabilities.

Data centerParticle depositionField study
Aerosol Characterization

Fragrance aerosol testing: particle size and chamber counts

The study compared the tested fragrance aerosols by spray particle-size distribution and time-resolved chamber counts under defined conditions.

Selected finding
Group-average D[4,3] was 31.49 µm for Test Article A and 75.03-89.77 µm for Comparator groups B-D.
FragranceParticle sizingProduct evaluation

Study-specific findings do not guarantee performance for another product.

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

The questions below cover method selection, quantitation choices, replicate counts, comparability framing, and deliverables for inhalation, antimicrobial, and consumer-aerosol studies. These answers are starting points, not protocols. Most PSD studies need at least one custom configuration choice. If your device, formulation, or regulatory frame differs from what is described here, a call can help work through those choices.

Q.Which PSD method should I choose?
A.Use cascade impactors when you need size-fraction mass and derived aerodynamic metrics, including MMAD and GSD. APS, OPS, or Spraytec can provide faster development screening; use FMPS 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. Validated chemical assays can quantify collected analyte mass; ELISA reports assay-specific immunoassay response, and ddPCR quantifies target nucleic-acid copies. We match the assay to the active and matrix and document units, controls, suitability, and recovery.
Q.How many actuations or runs are typical?
A.It depends on device output and assay sensitivity. During study planning, we set shot counts and replicates to meet precision goals, including device-level repeats to quantify variability.
Q.What affects comparability between lots or designs?
A.Actuation conditions, flow control, device-to-device variability, and assay recovery can all shift PSD results. We control flow with mass-flow controllers, log actuation force per shot, and document recovery for each assay so the comparison remains interpretable.
Q.What do you deliver?
A.A PDF report with methods, controls, and results tables; CSV / XLSX datasets for the selected sizing platform and endpoints; and relevant PSD curves, overlays, or stage-mass figures for internal reviews and submission appendices.

Standards & guidance

We select references for PSD studies according to the product and measurement objective. USP, FDA, and ISO nebulizer references below apply to relevant inhalation or intranasal drug products and nebulizing equipment. Consumer-aerosol sizing uses a separately defined protocol, rather than automatic alignment to those drug-product methods. Reports distinguish accredited scope, applicable reference methods, protocol adaptations, and analytical controls for the selected endpoint.

Inhalation & Drug Delivery - Accredited

USP <601>

Inhalation and nasal drug products: aerosols, sprays, and powders — performance quality testsView standard ->Inhalation & Drug Delivery - Aligned

USP <1601>

Products for nebulization — characterization testsView standard ->QA & Regulatory - Aligned

FDA MDI / DPI / nasal

Nasal sprays, MDIs, DPIs — chemistry, manufacturing, and controlsView standard ->Inhalation & Drug Delivery - Aligned

ISO 27427

Anaesthetic and respiratory equipment — nebulizing systems and componentsView standard ->

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