Norsk akkreditering
Dok.id.: VII.1.2.1
NA Doc 26C: Requirements for calibration and control of
volumetric equipment for accredited testing laboratories
Mandatory/Krav
Utarbeidet av:
Sidenr:
Saeed Behdad
Godkjent av:
Morten Bjørgen
Versjon:
1.02
Gjelder fra:
01.03.2012
1 av 6
NA Doc 26C
Requirements for calibration and control of volumetric equipment
for accredited testing laboratories
Document category: Requirement
Accreditation type: Laboratories
Purpose
This document describes the requirements for calibration and control of volumetric equipment used in
accredited testing laboratories. Alternative methods can be used in the cases where the words should
and can is used in the document assumed the alternative methods gives equal results.
Content
1.
2.
3.
4.
5.
Definitions and explanations ................................................................................................................... 2
General .................................................................................................................................................... 3
Calibration of volumetric equipment ...................................................................................................... 4
Control of volumetric equipment............................................................................................................ 5
References / relevant literature .............................................................................................................. 6
NA Doc 26C: Requirements for calibration and control of
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1. Definitions and explanations
Traceability
The result of a measurement or value of a standard that can be related to specific references (usually
national or international standards) through an unbroken chain of comparisons, all of them with the
associated uncertainty stated (Ref 1).
Control
A set of operations performed under specified conditions which verify that equipment meets the
requirements of accuracy required. All types of controls that fall under this description shall be
performed in accordance with a documented procedure.
Balances
Balances used for calibration and control of volumetric equipment shall be calibrated according to
the requirements in NA Doc 26A (Ref 3). The balances shall be calibrated in the relevant range used
for the volumetric calibration or control. The measurement uncertainty given in the calibration
certificate shall be lower than the established requirements for the volumetric equipment.
Thermometers
Thermometers used for temperature measurements of liquids in relation to volumetric equipment
shall be calibrated by an accredited calibration laboratory or controlled according to the
requirements in
NA Doc 26B (Ref 4).
Calibration
A set of operations performed in order to establish, under specified conditions, the relationship
between values of the quantities indicated by a measuring system, or values represented by a
material measure or a reference material, and the corresponding values realized by standards (Ref
1).
Calibration shall primarily be performed by a calibration laboratory accredited by Norwegian
Accreditation (NA), other accreditation bodies who are signatories of the multilateral agreements
with EA (European Co-operation for Accreditation) or ILAC (International Laboratory Accreditation
Cooperation) or a national laboratory approved by NA. The calibration result shall be always stated
with the associated measurement uncertainty
NA Doc 26C: Requirements for calibration and control of
volumetric equipment for accredited testing laboratories
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2. General
Volumetric equipment
Many types of volumetric equipment are used in testing laboratories. Examples of such equipment
are:
 volumetric flasks and graduated cylinders
 glass pipettes, disposable pipettes and automatic pipettes (fixed and variable volume, multi
channel pipettes)
 dispensers and burettes
 auto-diluters and pipetting robots
 Volumetric filtration equipment
Requirements for volumetric equipment will vary according to the application. The laboratory has
the responsibility to show that the volumetric equipment meets the requirements. The laboratory
should take into account any recommendations issued by the equipment supplier.
External calibration
External calibration of volumetric equipment shall primarily be performed by a calibration laboratory
accredited for volumetric calibrations by:
 Norwegian Accreditation (NA)
 Other accreditation bodies who are signatories of the multilateral agreements with EA
(European Co-operation for Accreditation) or ILAC (International Laboratory Accreditation
Cooperation)
 National laboratory approved by NA
Internal calibration and control
NA does not require external calibration of volumetric equipment if calibration and control is
performed according to the requirements described in this document.
The following requirements apply to accredited laboratories performing internal calibration and
control of volumetric equipment:

The laboratory shall designate personnel who have knowledge and expertise to perform
internal calibration and control in a correct way. Training and approval of personnel shall be
documented.

Internal calibration of volumetric equipment shall be performed on an accredited calibrated
balance and with recently boiled water. The water temperature shall be controlled during
the internal calibration. Balances and thermometers shall meet the requirements described
in section 1. If the water density differs from 1 g/cm3 the laboratory has to adjust the
measurements accordingly (Ref 7).

Generally control of equipment shall be performed as described above. However liquid
adapted to the regular use of the equipment shall be used. If the equipment is sent to the
provider for control, the laboratory shall ensure that the requirements given above are met.
The calibration status of balances used for volumetric control performed by the provider
shall be documented.

Internal calibration and control of volumetric equipment shall be documented. Raw data
shall be archived.
NA Doc 26C: Requirements for calibration and control of
volumetric equipment for accredited testing laboratories
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Glass equipment
Glass equipment labeled as class A/AS can normally be used without calibration. The laboratory is
responsible to verify the validity, particularly for small volumes. Glass equipment labeled class B
should normally not be used for quantitative analysis.
Disposable equipment
There is no requirement for calibration of disposable equipment if the manufacturer is ISO 9001
certified and the quality certificate from the manufacturer shows a satisfactory volumetric
calibration/control. On receipt disposable equipment shall be controlled on the batch level by
random sampling.
“Black box” instruments with integrated volumetric equipment
There is no requirement to calibrate the volumetric units in the "black box" instruments containing
integrated volumetric units. Such instruments are controlled indirectly by the use of internal control
program for each method. In addition, such instruments shall have satisfactory service and
maintenance programs which are documented.
Others
For equipment delivering large volumes, such as dispensers, it is sufficient to control the volume by
volumetric flask class A / AS. It is the responsibility of the laboratory to determine if this is sufficient.
For small volumes where gravimetry is not suitable, photometry can be used.
3. Calibration of volumetric equipment
Calibration shall be performed on all volumetric equipment that may have an impact the analytical
result.
Calibration frequencies will depend on the type of equipment, how it is used, how often it is used,
maintenance requirements and the laboratory’s requirement of accuracy. It is up to the laboratory to
show that the selected calibration frequency is sufficient. A good rule of thumb is to carry out the
calibrations of new equipment with a high frequency in the beginning. The obtained results can be
used to establish a more adequate calibration frequency.
Internal calibration shall be performed according to a written procedure, and the measurement
results shall be documented. Internal calibration shall include at least the following elements:
 repeatability
 reproducibility
 determination of maximum error
For equipment with variable volumes shall calibration be performed in an adequate number of
volumes. Multichannel pipettes shall be calibrated on all channels.
Repeatability
The purpose of the determination of repeatability is to ensure that the equipment can deliver
repetitive measurements with satisfactory dispersion. The determination is done by performing
measurements under the same conditions using the same operator and the same equipment. When
controlling equipment with variable volume settings, the volume shall not be adjusted between the
measurements. The volume setting shall be fixed during all the measurements.
Reproducibility
NA Doc 26C: Requirements for calibration and control of
volumetric equipment for accredited testing laboratories
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The purpose of the determination of reproducibility is to ensure that the handling of the equipment
with different operators and different settings of the adjustable equipment does not affect the
results significantly. The determination is done by varying the mentioned parameters as much as
possible and to adjust the volume between each of the replicates.
Determination of maximum error
The laboratory shall determine the maximum error. Determination of maximum error for volumetric
measurements is performed either by weighing the equipment with and without liquid or by
weighing dispensed or delivered volume. For equipment weighed with and without liquid, the mass
of the liquid divided with the density * of the liquid will give the correct volume. Such weighing shall
be according to requirements specified described in Section 2, Internal calibration and control.
Vequipment 
m equipment
 liquid
* Density of the liquid shall be determined according to the descriptions in recognized publications,
e.g. Handbook of Chemistry and Physics (Ref 7).
The determination can advantageously be carried out in connection with the determination of
repeatability and reproducibility. When it is not suitable for adjustable equipment to determine the
repeatability of all volumes used, determination of the maximum error has to be carried out
separately.
4. Control of volumetric equipment
Purpose
The purpose of the volumetric control of equipment is to ensure that the volume does not change
over time and is no longer in compliance with the requirements. The control shall be performed
according to a written procedure.
Except for the number of measurements, shall the control be performed and documented in the
same manner as described in Section 3, Reproducibility. For volumetric control, it is normally
sufficient with one control measurement. Control data should be plotted in a trend chart (control
chart) to facilitate the monitoring of equipment stability. The laboratory shall have a written
procedure for performance of volumetric control and monitoring of control data.
Control frequency
Control frequencies will depend on the type of equipment, how it is used, how often it is used,
maintenance requirements and the laboratory’s requirement of accuracy. It is up to the laboratory to
show that the selected frequency is sufficient to prove that the volumetric equipment is functioning
satisfactorily. A good rule of thumb is to carry out the controls of new equipment with a high
frequency in the beginning. The obtained results can be used to establish a more adequate control
frequency. If the control interval of adjustable pipettes exceeds 1 week, the laboratory shall have
documentation available on the acceptance of the extended interval in relation to the accuracy
requirements. Based on the control results the laboratory shall be decide whether the equipment
should be approved or not.
Requirements for control results
Requirements for control results can be specified as an interval where the results shall be within. The
interval shall be based on scientific criteria related to the method where the volumetric equipment is
NA Doc 26C: Requirements for calibration and control of
volumetric equipment for accredited testing laboratories
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used. The laboratory shall specify the interval in accordance with the measurement uncertainty of
the test method.
5. References / relevant literature
1. ISO/IEC Guide 99 International vocabulary of metrology;
Basic and general concepts and associated terms (VIM)
2. NA Dok 52 Angivelse av måleusikkerhet ved kalibreringer (Norwegian translation of EA 4/02)
3. NA Doc 26a Requirements for calibration and control of balances in accredited testing
laboratories
4. NA Doc 26b Traceability requirements of the temperature measurement for accredited
laboratories
5. EURAMET/cg-19/v.01 Guidelines on the determination of uncertainty in gravimetric volume
calibration
6. NS-EN ISO/IEC 17025 General requirements for the competence of testing and calibration
laboratories
7. Handbook of chemistry and physics, http://www.hbcpnetbase.com/
8. NMKL procedure 13 Volumetric control
9. ISO 8655 Piston-operated volumetric equipment (Part 1-7)
Kryssreferanser
Eksterne referanser