Frequently Asked Questions regarding ISO 8655, pipette calibration, and Artel’s photometric method
The answers to these FAQ’s were developed in consultation with Dr. Burkhard Winter of the German Standards Institute DIN, and are based on definitions given in International Standards. Dr. Winter is Secretary of ISO Technical Committee 48, which has jurisdiction over the ISO 8655 series of standards and was responsible for editing the 8655 series during its technical development.
Q: Does the photometric method satisfy ISO calibration requirements?
Yes. ISO 8655-7 states: “If the laboratories operate under ISO 9000 series regimes, or have accreditation to ISO 17025, the individually-adapted methods are usually validated to give results equivalent to those given by the gravimetric method specified in ISO 8655-6.”
Artel maintains a calibration and testing laboratory which is accredited to ISO 17025, and maintains accreditation for both gravimetric and photometric volume calibrations. Artel photometric systems have been validated in this laboratory, and each manufactured lot of reagents is tested by both photometric and gravimetric methods to ensure that results are fully equivalent to ISO 8655-6 as required.
Q: For what testing and in which situations can I use photometric methods to calibrate my pipette?
ISO 8655-7 says: “This part of ISO 8655 is applicable to the following types of testing:
- Of piston-operated volumetric apparatus for purposes other than type testing or the conformity testing which is required prior to declarations or certification of conformity;
- In user locations, where there may be no suitable balance or facilities to perform the reference method given in ISO 8655-6, but which may have at their disposal a suitable photometer or automatic titrator.”
In summary, photometry can be used for all common laboratory and calibration service activities.
Q: Do I need to calculate measurement uncertainty when using photometry?
ISO 8655-7 states, in reference to photometric methods: “If any of these methods is adapted, the expanded uncertainty of measurement needs to be calculated to enable comparison with the reference method.”
Artel PCS and MVS employ an adaptation of ISO 8655-7, and Artel has performed a comprehensive uncertainty analysis. Please click here for expanded measurement uncertainties for the Artel MVS instrument. These expanded uncertainty calculations fulfill the requirement of ISO 8655-7.
Q: When is it best to use the photometric method?
ISO 8655-7 notes on using the photometric method: “Photometric method: This may be the method of choice for laboratories having a UV/VIS photometer of suitable wavelength and bandwidth. Uncertainty with this method tends to become lower as test volumes decrease …”
The photometric method is applicable for all volume measurements and is particularly successful for small volumes. In contrast, the gravimetric method results in significantly increased measurement uncertainty with decreasing volumes.
Q: What is conformity testing and type testing?
Conformity testing is part of the product certification process by the manufacturer, and is normally done only once during the product life cycle as long as the product remains unchanged. For handheld pipettes, conformity testing is performed on a representative sample of product in what is called “type testing”. Type testing is performed either by the pipette manufacturer or by a third party test service, who then issues a “Declaration of Conformity” (by the manufacturer) or a “Certificate of Conformity” (by the third party test service) for that particular make and model of pipette. Customers and users of pipettes do not have to perform any of those tests.
For all other types of testing, such as routine calibration by the user or by a calibration service, photometry is fully permitted by ISO 8655-7, even if the calibration service is performed by the pipette manufacturer.