Report of an interlaboratory comparison organised by the ......European Commission Joint Research...

2 0 1 3

Giorgia Beldì, Natalia Jakubowska, and Catherine Simoneau

Formaldehyde in 3%

acetic acid migration

solution -follow up

exercise

Report of an interlaboratory comparison

organised by the European Reference

Laboratory for Food Contact Materials

EUR 26206 EN

European Commission

Joint Research Centre

Institute for Health and Consumer Protection

Contact information

Catherine Simoneau

Address: Joint Research Centre, Via Enrico Fermi 2749, TP 260, 21027 Ispra (VA), Italy

E-mail: [email protected]

Tel.: +39 0332 78 5889

Fax: +39 0332 78 5707

http://ihcp.jrc.ec.europa.eu/

http://ihcp.jrc.ec.europa.eu/our_labs/eurl_food_c_m

http://www.jrc.ec.europa.eu/

This publication is a Report by the Joint Research Centre of the European Commission.

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JRC84500

EUR 26206 EN

ISBN 978-92-79-33525-9 (pdf)

ISSN 1831-9424 (online)

doi:10.2788/31739

Luxembourg: Publications Office of the European Union, 2013

© European Union, 2013

Reproduction is authorised provided the source is acknowledged.

Printed in Italy

http://ihcp.jrc.ec.europa.eu/

http://ihcp.jrc.ec.europa.eu/our_labs/eurl_food_c_m

EURL – FCM ILC04 2013- F&M follow up

Report of the interlaboratory comparison

ILC04 2013- Formaldehyde and Melamine in 3% acetic acid

migration solution - follow up exercise

EC-JRC-IHCP, CAT Unit, Action 15014, MDV, EURL-FCM

March 2013

SANCO 2012/FOOD SAFETY/076-Food Contact Materials

Giorgia Beldì, Natalia Jakubowska and Catherine Simoneau


4

Table of content

1. Summary ...................................................................................................................... 5

2. Introduction ................................................................................................................. 6

3. Scope ........................................................................................................................... 6

4. Planning ....................................................................................................................... 6

5. Questionnaire results ................................................................................................. 6

6. Test materials .............................................................................................................. 7

6.1 Preparation ........................................................................................................... 7

6.2 Homogeneity assessment .................................................................................... 7

6.3 Distribution ........................................................................................................... 8

7. Instructions to participants ........................................................................................ 8

8. Assigned values .......................................................................................................... 8

9. Target standard deviation .......................................................................................... 8

10. Evaluation of results ................................................................................................. 9

10.1 General observations ......................................................................................... 9

10.2 Statistical evaluation of results ........................................................................... 9

10.2.1. Determination of the consensus value and standard deviation of the

interlaboratory comparison ..................................................................................... 9

10.2.2. Scores and evaluation criteria ..................................................................... 9

10.3 Laboratory results and scores .......................................................................... 10

11. Conclusion .............................................................................................................. 14

12. References ............................................................................................................... 15

13. Annexes ................................................................................................................... 15


5

1. Summary

The Institute for Health and Consumer Protection (IHCP) of the European Commission’s Directorate-General Joint Research Centre hosts the EU Reference Laboratory for Food Contact Materials (EURL-FCM). One of its core tasks is to organise interlaboratory comparisons (ILCs) among appointed National Reference Laboratories (NRLs).

This report presents the results of the 2013 follow up of the EURL-FCM 2012 ILC on formaldehyde and melamine in food contact migration solution. In 2012, out of the 62 laboratories who submitted results, 23 laboratories (ca. 37%) had results that showed some discrepancies affecting the analysis of the highest concentration level sample. For the NRLs, 10 out of 27 laboratories (ca. 37%) had questionable or unsatisfactory scores for this test solution.

Therefore, as a follow up, the EURL sent a new high concentrated migration solution of 3% acetic acid for which a dilution step is necessary for analysis to the underperforming laboratories to repeat this part of the ILC and to improve their results. The test material used for preparation of the migration solution was melamine kitchenware (spoons) containing formaldehyde.

There were 23 participants to whom samples were dispatched and all laboratories submitted results (10 NRLs + 13 national control laboratories from European countries). The homogeneity study was performed by the EURL-FCM laboratory. Participants were invited to report 4 replicate results for the sample. Laboratory results were processed using DIN 38402 A45 (Q-Hampel) algorithm. The assigned values were obtained after applying the robust statistics to the results of the participants. Standard deviations for proficiency assessment (also called target standard deviations) were set based on the Horwitz equation.

The results of the quantification of formaldehyde in the migration solution showed an improvement for the problematic high concentration from 63% satisfactory in 2012 to 92% satisfactory for all laboratories indifferently of NRL or OCLs. For the NRLs the performance increased from 63% to 100%.


6

2. Introduction

ILC studies are an essential and very important element of laboratory quality assurance, which allow individual laboratories to compare their analytical results with those from other laboratories while providing them objective standards to perform against. This in turn allows them to demonstrate performance.

It is one of the core duties of the EU Reference Laboratories to organize interlaboratory comparisons, as stipulated in Regulation (EC) No 882/2004 of the European Parliament and of the Council [1].

In accordance with the above requirements the EU Reference Laboratory for Food Contact Material (EURL-FCM) a follow up exercise EURL-FCM ILC04 2013 on formaldehyde in food contact migration solution.

3. Scope

The scope of this follow up exercise was the remediation and improvement of unsatisfactory or questionable results which had affected the analysis of formaldehyde in the highest concentration level test material in the ILC exercise of 2012.

The assessment of the measurement results was undertaken on the basis of requirements laid down in international standards and guidelines [2 - 7].

4. Planning

The ILC04 2013 follow up was launched in July 2012. A questionnaire was sent to the underperforming laboratories (Annex 1).

Samples for a new exercise were prepared and homogeneity tests were performed. The samples were dispatched to participants together with instruction letter (Annex 2) and a format for the compilation of results to be sent in non-electronic format (Annex 4).The participants were asked to compile a letter of confirmation of the receipt of the samples (Annex 3).

5. Questionnaire results

The EURL prepared and sent a questionnaire to all laboratories which had an absolute value of the z-score higher than 2 in the determination of the concentration of formaldehyde in the high level sample of the exercise ILC 2012 (i.e. the sample of highest concentration where a dilution step was necessary, labeled F&M03). Fifteen laboratories out of 23 sent back the completed questionnaire. The input from the questionnaire indicated that the z-scores under -3 were likely caused primarily due to the dilution step which was not correctly made after the colorimetric reaction. The solvent used for the dilution did not play the key role in the determination of the formaldehyde concentration. No other conclusions could be made after the evaluation of the questionnaire results (Table 1).


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Table 1. Questionnaire results

*reaction with chromotropic acid or acetyl acetone reagent

6. Test materials

6.1 Preparation

The preparation of the test materials was done by the EURL-FCM laboratory.

The migration solutions were obtained after migration experiment from melamine spoons in 3% acetic acid for 2 hours at 70 °C (Table 2).

Table 2. Test materials

6.2 Homogeneity assessment

Laboratory code

z-score ILC04 2013

Dilution after

reaction*

Dilution before

reaction*

Solvent used for dilution Dilution

factor

water 3% acetic

acid

LC0004 -8.997

LC0005 2.812

LC0006 2.596 x x 1:10

LC0007 -12.408

LC0016 -2.117 x x 1:10

LC0020 6.563 x x 1:100

LC0025 4.004 x x 1:10 / 1:20

LC0033 -2.047 x x 1:10

LC0034 2.152 x 1:25

LC0040 -3.346 x x 1:10

LC0044 2.442

LC0061 -6.622 x 1:10

LC0064 -2.359 x x 1:10

LC0066 -9.507 x x 1:10

LC0067 -2.215

LC0078 -4.303

LC0080 2.884

LC0090 2.648

LC0093 2.124 x x 1:20

LC0095 3.695 x x 1:25

LC104 2.195 x x 1:50

LC0106 -2.129 x x 1:10

LC0111 -2.065 x x 1:10

Exercise Code Sample

ILC 01 2012 follow up F&M05 1 bottle of 3% acetic acid migration solution


8

The samples were tested for homogeneity by the EURL-FCM laboratory.

Ten randomly selected test specimens of F&M05 were analysed in duplicate for formaldehyde, using the CEN 13130-23 chromotropic acid method [8]. Homogeneity was evaluated using ProLab Software [9] according to IUPAC International Harmonised Protocol [3], to the F-test and to the method proposed in the ISO 13528 [2]. The results together with their statistical evaluation are given in Annex 5. All solutions showed sufficient homogeneity for the target standard deviation.

6.3 Distribution

The sample kits were dispatched to the participants by the EURL-FCM on 18th July 2012. Each participant received:

a) The box containing the test material;

b) The accompanying letters with instructions on sample handling, analysis and reporting of results (Annex 2);

c) The receipt form to confirm the sample arrival (Annex 3);

d) The form for reporting the results (Annex 4).

7. Instructions to participants

Detailed instructions were given to all participants in the documents that accompanied the sample (Annex 2).

Laboratories were asked to report 4 results. Participants were asked to follow their own procedures and to indicate their sample preparation method – CR-chromotropic acid, AA-acetyl acetone or other – and instrumental method of analysis – UV-VIS, HPLC-DAD, LC-MS or other. The results had to be reported using the unit of measure indicated in the instruction letter. The results were reported in a specific format sent to the participants (Annex 4).

8. Assigned values

As described earlier, the test materials used for this exercise was a migration solution of kitchenware in 3% acetic acid, prepared by the EURL laboratory.

As the “true” values could not be known, the assigned values were the robust mean value obtained after applying the robust statistics to the participants’ test results, using ProLab software [9].

9. Target standard deviation

The value of target standard deviation (p) determines the limits of satisfactory


9

performance in ILC test. It should be set as a value that reflects best practice for the analysis in question. The standard deviation of the reproducibility found in the collaborative trials is generally considered as an appropriate indicator of the best agreement that can be obtained between laboratories. However, it is not applicable to

all cases. In the absence of appropriate collaborative trial data, p can be derived from the appropriate form of the modified Horwitz equation [6].

For the sample of this ILC04 2013 follow up exercise the target standard deviation was set to the calculated by Horwitz formula.

10. Evaluation of results

10.1 General observations

There were 23 participants to whom samples were dispatched (10 NRLs + 13 national control laboratories from European countries) and all of them submitted results. Two laboratories sent the results using two different sample preparation methods. The ILC was closed on 17th September 2012 for statistical interpretation.

10.2 Statistical evaluation of results

10.2.1. Determination of the consensus value and standard deviation of the interlaboratory comparison

The statistical evaluation of the results was performed using ProLab software [9] according to Q/Hampel estimator (DIN 38402 A45) [4]. This was more robust to take into account outliers.

10.2.2. Scores and evaluation criteria

Individual laboratory performance was expressed in terms of z-scores (z) in accordance with ISO 13528 [2] and the International Harmonised Protocol [3]:

p

assignedlab Xxz

)( ,

Where x lab is the measurement result reported by a participant, X assigned is the assigned value and σ p is the target standard deviation for proficiency assessment .

The z- scores can be interpreted as follow:

|z|≤2 satisfactory result;

2<|z|≤3 questionable result;


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|z|>3 unsatisfactory result.

10.3 Laboratory results and scores

The results sent by the laboratories were first evaluated statistically using the DIN 38402 A45 all together (Figure 1). They were then evaluated a second time separately grouped according to the two sample preparation methods (CR and AA) (Figure 2 and 3). Some laboratories had noticed a difference in the formaldehyde concentration obtained using those two methods only in the high concentration solution when the dilution step was necessary.

Tables 3 and Figures 1-3. Represent the summary of the results of the laboratories for formaldehyde with their robust repeatability standard deviations and robust reproducibility standard deviations calculated according to Q/Hampel algorithm (ISO 20612:2007 [10] and DIN 38402 A45 [4] ) by ProLab software. The tables also contain the assigned values and target standard deviation of the ILC.

Summary of the calculated z-scores are reported in Tables 4 and Figures 1-3.

As the exercise was a proficiency test the laboratories where free to use their own method. The EURL evaluated the performance of the laboratories rather than the precision criteria of the methods used. For this reason the z-score which were kept into consideration was from all data submitted as a whole (Figure 1). Table 3. Summary of results for formaldehyde calculated according to DIN 38402 A45

Method DIN 38402 A45

ALL CR AA

Robust Mean = Assigned value , mg/kg 234.79 256.73 214.96

Robust Repeatability s.d., mg/kg 3.41 6.99 1.88

Robust Reproducibility s.d., mg/kg 28.82 30.62 19.48

Rel. target s.d., % 7.03 6.94 7.13

Rel. Reproducibility s.d., % 12.28 11.93 9.06

Rel. Repeatability s.d., % 1.45 2.72 0.87

Lower limit of tolerance, mg/kg 201.76 221.09 184.31

Upper limit of tolerance, mg/kg 267.83 292.37 245.61

No. of results 25 10 13


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Figure 1. Summary graph of the laboratory’s test results and the laboratory’s z-scores for formaldehyde (F&M05) for all laboratories


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Figure 2. Summary graph of the laboratory’s test results and the laboratory’s z-scores for formaldehyde (F&M05) for laboratories using Chromotropic acid method


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Figure 3. Summary graph of the laboratory’s test results and the laboratory’s z-scores for formaldehyde (F&M05) for laboratories using Acetyl acetone method


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Table 4. Laboratories’ z-scores for formaldehyde (F&M05)

Laboratory Code

ALL CR AA

LC0004 -0.20 -1.42 -

LC0005 4.22 - 5.84

LC0006 3.51 2.02 -

LC0007 3.61 2.11 -

LC0016 -1.66 - -0.49

LC0020 -1.55 - -0.37

LC0025 -1.16 - 0.04

LC0025b 3.71 2.21 -

LC0033 -0.90 - 0.32

LC0034 0.26 -0.99 -

LC0040 -2.10 - -0.97

LC0044 2.87 - -

LC0061 0.21 - 1.52

LC0064 -2.45 - -1.34

LC0066 0.58 -0.70 -

LC0067 -0.74 - 0.50

LC0078 -0.05 - -

LC0080 -1.42 -2.55 -

LC0090 -0.96 -2.12 -

LC0093 -1.41 - -0.22

LC0095 0.98 - 2.35

LC0095b 4.34 2.79 -

LC0104 0.09 -1.15 -

LC0106 -1.68 - -0.51

LC0111 -1.56 - -0.39

11. Conclusion

An overview of the ILC04 2013 follow up exercise outcome shows that the participation of the laboratories in the exercise was satisfactory and was 100%. All 23 participants reported results. In addition two laboratories sent the results using two different sample preparation methods.

The results of the quantification of in the migration solution of kitchenware in 3% acetic acid showed an improvement for the problematic high concentration from 63% satisfactory in 2012 to 92% satisfactory (for all laboratories indifferently of NRL or OCLs). For the NRLs, all results were satisfactory, thus the performance increased from 63% to 100%.


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12. References

[1] Regulation (EC) No 882/2004 of the European Parliament and of the Council of 29 April 2004 on official controls performed to ensure the verification of compliance with feed and food law, animal health and animal welfare rules

[2] ISO 13528:2005; Statistical Methods for Use in Proficiency Testing by Interlaboratory Comparisons

[3] The International Harmonised Protocol for the Proficiency Testing of Analytical Chemistry Laboratories by M. Thompson et al., Pure and Applied Chemistry (2006), 78, 145–196

[4] DIN 38402 A45 Ringversuche zur externen Qualitätskontrolle von Laboratorien

[5] ISO GUIDE 35:2006; Reference materials–General and statistical principles for certification

[6] M. Thompson, Analyst, (2000), 125, 385-386

[7] T. Linsinger et al., Accreditation and Quality Assurance in Analytical Chemistry (2001), 6, 20-25

[8] CEN 13130-23:2005, Determination of formaldehyde and hexamethylenete-tramine in food simulants

[9] ProLab Software – QuoData, Drezden – www.quodata.de

[10] ISO/TS 20612 Water quality – Interlaboratory comparison for proficiency testing of analytical chemistry laboratories

13. Annexes

Annex 1: Questionnaire ILC04 2013 follow up

Annex 2: Letters accompanying the sample ILC04 2013 follow up

Annex 3: Letter of confirmation of receipt of ILC04 2013 follow up

Annex 4: Form for the compilation of the results in non-electronic format

Annex 5: Results of the homogeneity study

http://www.quodata.de/


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Annex 1. Questionnaire ILC04 2013 follow up


17


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Annex 2. Letters accompanying the sample ILC04 2013


19

Annex 3. Letter of confirmation of receipt of ILC04 2013


20

Annex 4. Form for the compilation of the results in non-electronic format


21


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Annex 5. Results of the homogeneity study

Sample Measurand Unit Mean s(analytical) % Mode

s(target) HORRAT s(target) %

F-test Check for significant

heterogeneity

ISO 13528 Check for sufficient homogeneity

Harmonised Protocol - test on

significant heterogeneity

F&M05 Formaldehyde mg/kg 264.57 1.01 Horwitz 1 6.91 OK OK OK

European Commission

EUR 26206 – Joint Research Centre – Institute for Health and Consumer Protection

Title: Report of an interlaboratory comparison organised by the European Reference Laboratory for Food Contact Materials:

Formaldehyde in 3% acetic acid migration solution - follow up exercise.

Author(s): Giorgia Beldì, Natalia Jakubowska, and Catherine Simoneau

Luxembourg: Publications Office of the European Union

2013– 23 pp. – 21.0 x 29.7 cm

EUR – Scientific and Technical Research series – ISSN 1831-9424 (on-line)

ISBN 978-92-79-33525-9 (pdf)

doi:10.2788/31739

Abstract

This report presents the results of the 2013 follow up of the EURL-FCM 2012 ILC formaldehyde and melamine in food contact migration solution. In the 2012, out of the 62 laboratories who submitted results, 23 laboratories (ca. 37%) had results that showed some discrepancies affecting the analysis of the highest concentration level sample. For the NRLs, for this test solutions, 10 laboratories out of 27 (ca also 37%) had questionable or unsatisfactory scores. Therefore, as a follow up, the EURL sent prepared a new migration solution for underperforming laboratories to repeat this part of the ILC and improve their results.

There were 23 participants to whom samples were dispatched and all laboratories submitted results (10 NRLs + 13 national control laboratories from European countries) and all of them submitted results. The homogeneity study was performed by the EURL-FCM laboratory. Participants were invited to report 4 results. Laboratory results were processed using DIN 38402 A45 (Q-Hampel) algorithm. The assigned values were obtained after applying the robust statistics to the results of the participants. Standard deviations for proficiency assessment (also called target standard deviations) were set based on Horwitz equation.

The results of the quantification of in the migration solution of kitchenware in 3% acetic acid showed an improvement for the problematic high concentration from 63% satisfactory in 2012 to 92% satisfactory (for all laboratories indifferently of NRL or OCLs). For the NRLs, all results were satisfactory, and the performance increased from 63% to 100%.

z

As the Commission’s in-house science service, the Joint Research Centre’s mission is to provide EU policies with independent, evidence-based scientific and technical support throughout the whole policy cycle. Working in close cooperation with policy Directorates-General, the JRC addresses key societal challenges while stimulating innovation through developing new standards, methods and tools, and sharing and transferring its know-how to the Member States and international community. Key policy areas include: environment and climate change; energy and transport; agriculture and food security; health and consumer protection; information society and digital agenda; safety and security including nuclear; all supported through a cross-cutting and multi-disciplinary approach.

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