## ISO 8655 Reference Method

ISO 8655 is the most critical ISO standard for calibrating piston operated burets, outlining the required method, test conditions and equipment, reporting requirements and required measurement uncertainty values.

Designed to resemble everyday titrations, the ISO 8655 method is the globally accepted gravimetric test used by Metrohm USA’s calibration lab.

## Gravimetric Test

During the gravimetric test, dispensed water is weighed and the volume dosed is calculated using the specific density of water. As specified in the standard ISO 8655-3:2002 Piston-Operated Volumetric Apparatus, ten individual measurements are performed at three volumes across the buret range:

• 10% of the nominal buret volume
• 50% of the nominal buret volume
• 100% of the nominal buret volume

Water conforming with grade 3 as specified in ISO 3696 is used for measurements.

## Maximum Permissible Error

Error limits are clearly defined in ISO 8655:2002 for the maximum permissible systematic error and the maximum permissible random error for a buret at specific volumes. The systematic and the random measurement errors are calculated from the measured values.

To be considered valid by ISO 8655:2002, measurements must occur in a strictly controlled, vibration-free test environment. Explore the calibration lab to learn more about the specialized test tools and controlled environment that meet ISO requirements.