Liquid-Borne Particle Count (LPC)

Particle Size Distribution · Cleanliness Classification · ISO 16232 · VDA 19 · Light Obscuration Counting ISO/IEC 17025 Accredited Testing Where Applicable | LPC and Full Particle Analysis Capability | Automotive Cleanliness Specialist Gravimetric analysis tells you how much particle contamination is present by total mass. Liquid-borne particle counting tells you how that contamination is distributed across size ranges. In most automotive cleanliness specifications, it is the size distribution data, not the total mass, that determines whether a component passes or fails. Liquid-borne particle count (LPC) is the analytical step that generates this size distribution. It is a required element of technical cleanliness testing under ISO 16232 and VDA 19, and it is the method that translates extracted particle contamination into the cleanliness classification your OEM specification requires. What Liquid-Borne Particle Counting Measures LPC measures the number of particles present in a liquid suspension within defined size ranges. In automotive cleanliness testing, the liquid is the extraction solvent that has been used to remove particles from a component, filtered onto a membrane to collect the particles, and then re-suspended in clean solvent for analysis. The instrument passes this particle suspension through a measurement cell where a laser beam intersects the flow path. As each particle passes through the beam, it obstructs a portion of the light, causing a brief reduction in the light signal detected on the far side. The instrument measures the magnitude of this light reduction, which correlates with particle size, and records the event as a count in the appropriate size class. The result is a particle size distribution: the number of particles counted in each defined size range, expressed as particles per unit surface area of the component tested. This distribution is the core data used to assign the cleanliness classification under ISO 16232 or VDA 19. Why LPC and Gravimetric Analysis Are Used Together Gravimetric analysis and LPC are complementary measurements that answer different questions about the same particle contamination.   Measurement What it shows Limitation Gravimetric analysis Total mass of all extracted particles Cannot distinguish size distribution or individual large particles Liquid-borne particle count (LPC) Number of particles in each size class Does not show total mass or particle material   A component may pass the gravimetric mass limit while still containing one or two oversized particles that exceed the size class limit and trigger a cleanliness failure. A component may show a high total particle count in the smallest size class while all larger size classes are within specification, which may be entirely acceptable depending on the OEM requirement.   Neither measurement alone gives the complete picture that a cleanliness specification requires. ISO 16232 and VDA 19 require both, and the LPC size distribution data is what generates the cleanliness class that appears on the test report. How LPC Fits into the ISO 16232 and VDA 19 Workflow LPC is performed after particle extraction and filtration, and before or alongside microscopic particle classification.   The sequence is as follows. Particles are extracted from the component using the validated extraction method for that component type. The extraction solvent is filtered through a membrane with a defined pore size, collecting the particles. The membrane is dried and weighed for gravimetric analysis. The particles on the membrane are then re-suspended in a defined volume of clean solvent and the resulting suspension is run through the LPC instrument.   The LPC result, combined with the gravimetric mass and the microscopic classification data, forms the basis of the Component Cleanliness Code (CCC) that is reported to the OEM or customer. The size classes defined in ISO 16232 and VDA 19 cover a range from particles above 5 or 50 micrometres at the lower end, depending on the analysis type specified, up through multiple ranges to particles above 1,000 micrometres.   For a detailed explanation of the full cleanliness testing workflow, see our guide on particle analysis in automotive manufacturing. LPC in Fluid Cleanliness Testing LPC is also applied to fluid cleanliness monitoring in hydraulic systems, fuel systems, and cooling circuits, where the liquid tested is the operating fluid itself rather than an extraction solvent. Category Component Cleanliness Testing Fluid Cleanliness Monitoring Standard ISO 16232, VDA 19 ISO 4406 and equivalent Sample Extraction solvent from component Operating fluid drawn from system Purpose Characterises particles a component releases into a system on first assembly Characterises ongoing contamination level during service When applied Qualification and production testing Commissioning, service monitoring Result format Cleanliness classification (CCC) Three-number code per ISO 4406 Both use LPC as the core measurement, but the sample preparation, reference standards, and acceptance criteria are different. What Affects LPC Result Accuracy LPC results are sensitive to several factors that must be controlled during sample preparation and analysis. Re-suspension quality. Particles on the membrane must be fully and uniformly re-suspended. If re-suspension is incomplete, the count will be lower than the actual contamination level. Background particle counts. Solvent, glassware, and instrument must be verified clean. A blank count is performed before or alongside the sample to confirm the analysis environment is not contributing particles that would distort the result. Analysis volume accuracy. The volume of suspension analysed must be recorded and used correctly in calculating the final result per unit surface area. Errors in volume translate directly into errors in the reported count. Sample stability. Agglomeration of particles during any delay between extraction and analysis can shift the apparent size distribution toward larger sizes, reducing the count in smaller size classes. Frequently Asked Questions What is the difference between LPC and optical microscopy for particle counting?  LPC counts particles automatically using light obscuration as they pass through the measurement cell in liquid suspension, providing fast, statistically representative counts across the full size distribution. Optical microscopy examines particles on the filter membrane directly, allowing visual classification by type (metallic shiny, non-metallic, fibre) and morphology, but typically covers a smaller sample area. Both methods are required under ISO 16232 and VDA 19: LPC for the size distribution count and microscopic analysis for particle type classification.   Can LPC identify the type of particles counted?  No. LPC counts and sizes particles based on light obscuration but cannot identify whether a particle is metallic, non-metallic, a fibre, or any specific material type. Particle type classification requires microscopic examination of the filter membrane. Material identification of specific particles requires SEM-EDX or FTIR analysis.   What size particles does LPC detect in cleanliness testing?  The lower detection threshold in standard automotive cleanliness testing is typically 5 or 50 micrometres, depending on the analysis type specified by the applicable standard edition or OEM requirement. Particles smaller than the lower threshold are not individually counted and do not contribute to the cleanliness classification. The upper size limit is set by the largest size class defined in the specification, typically particles above 1,000 micrometres.   Does LPC replace gravimetric analysis in cleanliness testing?  No. Both are required under ISO 16232 and VDA 19 for a complete cleanliness test. Gravimetric analysis provides the total contamination mass, and LPC provides the size distribution. They answer different questions and neither substitutes for the other. Next Steps See our full Technical Cleanliness Testing services including LPC and particle analysis Read our guide on particle analysis methods, standards and applications Read our guide comparing ISO 16232 and VDA 19 Contact our team for a particle analysis or cleanliness testing quotation   ISO/IEC 17025 Accredited Testing Where Applicable | LPC and Particle Analysis Capability | Automotive Cleanliness Specialist