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FAQ

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General questions | Use of RM | Handling of RM | ERM® | GMO CRMs | Terminology

Are CRMs generally produced under an accreditation scheme?

The appropriate standard for the production of reference materials is ISO Gu

ide 34 “General quality requirements for the production of reference materials”, but it is understood that measurements must comply with the provisions of ISO 17025. There are only very few reference material producers accredited to ISO Guide 34 yet. The Reference Materials Unit of IRMM was the first organisation in Europe to achieve accreditation to ISO Guide 34 for the production of CRMs.

Are ERM® materials only for Europeans?

No.

ERM-CRMs are suitable for any user who requires reference materials of the highest level of assurance. ERM® materials are available from a number of reference material distributors who make them available worldwide. But membership of reference materials producers in the ERM® co-operation is open only to producers located in the European Union, who can demonstrate that they meet certain defined membership criteria. Materials marketed under the ERM® brand have been produced in accordance with the principles laid down in ISO Guides 34 and 35 and have been subject to extensive review by all member organisations.

Are the GMO CRMs of IRMM checked for the presence/absence of other GM events than the one certified?

The GMO CRMs are gravimetric mixtures of pure GM and non-GM powders certifie

d for a specific GM event as mass fraction (g/kg). IRMM verifies the purity of the two raw materials used for production with respect to the presence of the particular GM event that is certified. The CRMs are not certified for the absence or adventitious presence of other (contaminating) GM events.

The GMO CRMs can be used as positive controls for the certified GM event for instance to validate a screening method. However, the GMO CRMs should not be used as negative controls for any other GM event than the one certified. Also the blank material of each series is certified to contain less than the certified amount for a given GM event and the absence of this event can not be guaranteed.

For additional information IRMM has conducted a study to verify the GM composition of 33 raw materials used for the production of the GMO CRMs. Those raw materials have been tested by quantitative PCR for the presence/absence of 39 single GM targets known for 7 plant species. It needs to be noted that adventitious presence of other GM events is likely to be heterogeneously distributed over the batch of raw material and needs to be taken into account when comparing the results obtained so far. These results are summarised in the  FAQ GMO_attachment.pdf and provide an indication about possible adventitious presence.

 

Can I purchase 100% GMO CRMs?

IRMM only produces for selected GMO events a pure certified GMO reference ma

terial (nominal 100%). However, such materials may be available from other organisations or the intellectual property owner of the GMO event.

Can I purchase bulk volumes of CRMs?

IRMM does not sell bulk volumes of reference materials, but rat

her individually labelled samples (‘units’) of CRMs.

Can I use the GMO CRMs to calibrate my ELISA measurements?

GMO reference materials from IRMM can be used as calibrants for DNA-based an

d protein-based methods. You should set-up a calibration with a reference material (calibrant) with known GM concentrations in order to be able to translate your test result into GM% m/m (mass fraction).

Do I have to throw my material away after the expiry date?

Producers of reference materials guarantee within a specified time (=shelf l

ife) the integrity of the material and the validity of the certificate accompanying the material, provided the sample is properly transported and stored. Furthermore, most producers guarantee this only for the unopened container. In other words, once the original material container is opened material integrity can no longer be guaranteed. This does not automatically mean that the user has to throw away the unused sample, but it only means that the producer can simply not guarantee stability forever.

Do you provide instructions how to perform PCR?

Event-specific detection methods submitted under the provision of Art.

47 of Regulation EC 1829/2003 and their validation reports are accessible on the web site of the EURL for GM food and feed (EURL-GMFF) under the section "Status of dossiers". Detection methods used during the certification of a GMO reference material are listed in the certification report.

How do I compare my result with the certified values?

The underlying principle is that one has to check whether the difference bet

ween the measured result and the certified value is larger than the expanded combined uncertainty of measurement and certified value. This is done as follows:

  1. Calculate the standard uncertainty of the certified value (uCRM). This is obtained by dividing the expanded uncertainty given on the certificate by the expansion factor (also stated on the certificate).
  2. Estimate the measurement uncertainty (um) of the result. As a very rough approximation, the reproducibility standard deviation can be used
  3. Combine the two uncertainties:
  4. Check whether 2*uc is larger than the difference between the certified and the measurement value. If this is the case, the measurement result agrees within the limits of the respective uncertainties with the certified values

For example: Certified reference material BCR-605 (road dust) with a trimethyllead-content of 7.9 ± 1.2 µg/kg has been used. The analytical result was 11.10 µg/kg and the standard measurement uncertainty as determined in the method validation (um) is 15 %, i.e. 1.67 µg/kg. The difference between analytical result and certified value is therefore 3.2 µg/kg. Prior to the determination of the combined uncertainty, the standard uncertainty of the certified value of the reference material must be determined. The uncertainty of the certified value (UCRM) is given as 95 % confidence interval with 6 degrees of freedom as stated on the certificate. The factor of the t-distribution (t95, 6) is 2.447. The confidence interval must be divided by this factor to obtain the standard uncertainty of the certified value. This standard uncertainty (uCRM) is therefore:

The combined uncertainty (uc) of measurement and certified value is the square root of the quadratic sum of the individual uncertainties:

The results show that the uncertainty of the certified value has almost no influence on the combined uncertainty. This combined uncertainty is now multiplied with a coverage factor of 2 to obtain the expanded uncertainty (here 3.48 µg/kg). This expanded uncertainty is bigger than the difference between analytical results and certified values (3.2 µg/kg). Within the limits of the uncertainties, no method bias is visible.

How do I know whether the certified value is valid for my method?

There are two CRM properties that describe the usefulness of a material for

a certain method, namely traceability and commutability. Traceability describes what the certified value actually refers to including the definition of the measurand: is it about total or extractable element content, Kjeldahl or Dumans N? Commutability describes whether a material behaves similarly as a certain routine sample for a given method.

Therefore, one should check whether the certified value of a CRM is traceable to the same reference as one’s method. If this is not the case, the material is unsuitable.

Example: Certified values for dietary fibre traceable to a certain ISO method are only valid, if exactly this method is used.

Additionally, one should check whether commutability is ensured. If this is not the case, the material may be unsuitable.

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