ISO 8655-4:2022

Overview

ISO 8655-4:2022 specifies metrological and practical requirements for piston-operated volumetric dilutors. The standard covers dilutors with a sample uptake capacity (In) from 5 µl to 1 ml and a diluent capacity (Ex) from 50 µl to 100 ml, designed to deliver sample and diluent together in measured proportion and volume. It defines performance checks, adjustment procedures, marking and user information required for safe, accurate use and calibration.

Key Topics

• Scope and principle of operation: Describes how dilutors aspirate a measured sample and deliver it together with a measured diluent volume. Covers manual, electric, pneumatic and hydraulic drives, and bench-top, bottle-top and automated configurations.
• Metrological requirements: Sets maximum permissible errors (MPE) for sample uptake and diluent dispense (systematic and random errors). MPEs are tabulated by nominal volume (see Tables 1 and 2) and expressed as percentages; random error is expressed as a coefficient of variation based on tenfold gravimetric measurements.
• Adjustment procedures: Requires initial adjustment and, where provided, documented subsequent adjustments. Reference conditions for adjustment are either 20 °C or 27 °C, with 50% relative humidity and standard barometric pressure when using grade 3 water (ISO 3696).
• Measurement and calibration: Gravimetric measurement procedures per ISO 8655-6 or alternative procedures in ISO 8655-7 are required to determine trueness and precision of the complete dilutor system (pistons, valves, probes, tubing, change-over units).
• Calculation rules: Provides a formula to scale MPEs for selected volumes within the usable range and sets limits (e.g., an upper cap on calculated errors).
• Marking and user information: Mandates permanent markings (nominal volumes, units, brand/type, serial number) and comprehensive user information (nominal volumes, smallest deliverable volumes, error limits, maintenance, bubble-free filling, storage, and material compatibility).

Applications and Users

ISO 8655-4:2022 is directly applicable to:

• Manufacturers of pipettes and dilutors for product design, quality control and conformity declarations.
• Calibration laboratories, test houses and instrument service providers performing gravimetric verification and routine checks.
• Clinical, pharmaceutical, chemical and research laboratories that use dilutors in sample preparation and automated analyzers.
• Procurement and quality assurance teams who require traceable performance specifications for volumetric equipment.

Adoption of this standard helps ensure accurate dilution workflows, reproducible sample preparation, and compliance with laboratory quality systems.

Related Standards

• ISO 8655-1: Terminology, general requirements and user recommendations
• ISO 8655-6: Gravimetric reference measurement procedure for volume determination
• ISO 8655-7: Alternative measurement procedures for volume determination
• ISO 3696: Water for analytical laboratory use

Keywords: ISO 8655-4:2022, dilutors, piston-operated volumetric apparatus, maximum permissible errors, metrological requirements, gravimetric measurement, sample uptake, diluent dispense.