CHEK Proficiency study 642. Migration of formaldehyde from melamine kitchenware. Date 7 July 2016 Version 1 Status Final Report number CHEK

Transcription

1 CHEK Proficiency study 642 Migration of formaldehyde from melamine kitchenware Date 7 July 2016 Version 1 Status Final Report number CHEK page 1

2 Colophon Number 642 Name Migration of formaldehyde from melamine kitchenware Contact Author Netherlands Food and Consumer Product Safety Authority (NVWA) CHEK working group Paterswoldseweg BA Groningen The Netherlands PO Box AA Utrecht The Netherlands T chek@vwa.nl ISBN Mariëlle van Vondel Authorization Krista Bouma (operational manager) page 2

3 Content 1 Introduction 1 2 Time-table 1 3 Sample preparation 1 4 Statistical results Third migration of formaldehyde from melamine [mg/l] Third migration of formaldehyde from melamine [mg/kg] Contact area of migration of formaldehyde from melamine 5 5 Methods of analysis 6 6 Remarks from participants 6 7 List of invited participants 7 8 Explanation of graphical presentations 8 9 Tables and graphical presentations 9-15 page 3

4 1 Introduction Proficiency study number 642 as directed by the CHEK working group concerned the investigation of the migration of formaldehyde from two melamine bowls. To get an impression of the performance of the migration of formaldehyde from melamine 21 laboratories were invited to join this proficiency study. One laboratory was not able to submit results. 2 Time-table Homogeneity of samples 18 May 2016 Distribution of samples 24 May 2016 Deadline for the production of results 24 June 2016 Final report 7 July Sample preparation Melamine samples A and B uniform level 42 melamine bowls from the same batch were sampled during an import control and were tested positive for the migration of formaldehyde. The bowls were screened for the first migration of formaldehyde by filling them with 280 ml of pre-heated 3% acetic acid at 70 C, standing 2 hours at 70 C. The bowls were labelled A and B and packed together in a plastic sachet. The homogeneity was checked by the laboratory of the Netherlands Food and Consumer Product Safety Authority, Groningen by testing the bowl for the first formaldehyde migration (see table I, first column). The average formaldehyde migration was 3.4 mg/l with a standard deviation of 37%. Not enough data and experience are available yet to make a proper conclusion if samples are sufficiently homogeneous. Samples were stored at room temperature until shipment. To each of the participants two melamine samples coded A and B were sent. They were instructed to store the samples at room temperature after receipt. Each sample should be filled with 280 ml of pre-heated 3% acetic acid at 70 C. After the migration conditions (2 hours at 70 C for two times) the results of the formaldehyde migration of both first and second solution should be submitted, expressed as mg/l (surface is not included). Also the initial contact area of the samples (expressed as dm 2 ) that was filled with 280 ml 3% acetic acid should be submitted. page 1

5 4 Statistical results Results and Z-scores The results of the laboratories and the Z-scores are given in table I. Figures I to IX give graphical presentations of the results. One-way analysis of variance (ANOVA), preceded by checking for normality and outlier checking of the results (Cochran/Grubbs) is the statistical procedure for obtaining the estimates of withinlaboratory and between laboratory variability. Target standard deviation For the target standard deviation in most of the cases Horwitz shows a good maximum allowable (or acceptable) RSD R but does not include different levels of complexity of analytical methods and migration analysis. If the target standard deviation is not chosen realistically the interpretation satisfactory, questionable and unsatisfactory is not that reliable. Therefore in this proficiency study precision data of past three proficiency studies (no. 525, 549 and 581) were used to set a target reproducibility standard deviation (s R ). The acceptable RSD R for the migration of formaldehyde from melamine is set at 60%. For the contact area the reproducibility standard deviation is used as target value. These values were used as target standard deviation to calculate the Z-scores and the performances. Performance The performance of a determination is assessed as following: satisfactory = 0-2 x acceptable RSD R questionable = >2-3 x acceptable RSD R unsatisfactory = >3 x acceptable RSD R Results expressed as mg/kg All participants only were instructed to submit the migration of formaldehyde expressed as mg/l (surface is not included) and initial contact area. CHEK calculated results expressed as mg/kg - using the submitted results expressed as mg/l, the submitted contact area and standard volume of 280 ml - for all laboratories as below: Migration Migration [mg/kg] = [mg/l] Volume simulant [L] 6(Surface-to-volume 2 Contact area [dm ] ratio 2 [dm /kg]) page 2

6 4.1 Third migration of formaldehyde from melamine uniform level [mg/l] Third migration of formaldehyde from melamine samples A and B 19 labs: Results of laboratory 20 are removed by hand 16 labs: Results of laboratories 1, 4 and 16 are rejected by the Cochran test 19 labs 16 labs Unit Average mg/l Repeatability standard deviation (s r ') mg/l Repeatability rel. standard deviation (RSD r ') % Reproducibility standard deviation (s R ') mg/l Reproducibility rel. standard deviation (RSD R ') % Acceptable value for RSD R ' % Repeatability r' mg/l Reproducibility R' mg/l Summary third migration of formaldehyde from melamine samples A and B The results of this and earlier proficiency studies are summarised in the table below. Prof. study Number of labs Average mg/l RSD R % Acceptable RSD R % Conclusions third migration of formaldehyde from melamine samples A and B The performance of the determination of the third migration of formaldehyde from melamine expressed as mg/l is satisfactory. Results of laboratory 20 are removed by hand, because of non-quantitative results. The results are drawn from a normal distribution. The results of laboratories 1, 4 and 16 are marked as outliers by the Cochran test indicating bad repeatability and are rejected. No Grubbs outliers were found in the datasets of sample A and B. The results of laboratory 1 are also marked as stragglers by the Grubbs test indicating systematic errors. The absolute Z-scores of laboratories 1 and 2 are greater than 3 and suggest poor performance in terms of accuracy. page 3

7 4.2 Third migration of formaldehyde from melamine uniform level [mg/kg] Third migration of formaldehyde from melamine samples A and B 19 labs: Results of all laboratories 16 labs: Results of laboratories 1, 4 and 16 are rejected by the Cochran test 19 labs 16 labs Unit Average mg/kg Repeatability standard deviation (s r ') mg/kg Repeatability rel. standard deviation (RSD r ') % Reproducibility standard deviation (s R ') mg/kg Reproducibility rel. standard deviation (RSD R ') % Acceptable value for RSD R ' % Repeatability r' mg/kg Reproducibility R' mg/kg Summary third migration of formaldehyde from melamine samples A and B The results of this and earlier proficiency studies are summarised in the table below. Prof. study Number of labs Average mg/kg RSD R % Acceptable RSD R % Conclusions third migration of formaldehyde from melamine samples A and B The performance of the determination of the third migration of formaldehyde from melamine expressed as mg/kg is satisfactory. The results approach a normal distribution. The results of laboratories 1, 4 and 16 are marked as outliers by the Cochran test indicating bad repeatability and are rejected. No Grubbs outliers were found in the datasets of sample A and B. The results of laboratories 1, 2 and 15 are (also) marked as stragglers by the Grubbs test indicating systematic errors but are not rejected. The absolute Z-scores of laboratories 1 and 15 are greater than 3 and suggest poor performance in terms of accuracy. N.B. Participants only were instructed to submit results expressed as mg/l. CHEK calculated results expressed as mg/kg using the submitted results expressed as mg/l, the submitted contact area and standard volume of 280 ml (see page 2). page 4

8 4.3 Contact area of migration of formaldehyde from melamine uniform level Contact area of migration of formaldehyde from melamine samples A and B 19 labs: Results of laboratory 12 are removed by hand 18 labs: Results of laboratory 10 are rejected by the Cochran test 19 labs 18 labs Unit Average dm 2 Repeatability standard deviation (s r ') dm 2 Repeatability rel. standard deviation (RSD r ') % Reproducibility standard deviation (s R ') dm 2 Reproducibility rel. standard deviation (RSD R ') % Acceptable value for RSD R ' % Repeatability r' dm 2 Reproducibility R' dm Summary contact area of migration of formaldehyde from melamine samples A and B The results of this and earlier proficiency studies are summarised in the table below. Prof. study Number of labs Average mg/kg RSD R % Acceptable RSD R % Conclusions contact area of migration of formaldehyde from melamine samples A and B The performance of the determination of the contact area of the migration of formaldehyde from melamine is satisfactory. The results of laboratory 12 are removed by hand because of far outlying results. The results approach a normal distribution. The results of laboratory 10 are marked as outliers by the Cochran test indicating bad repeatability and are rejected. No Grubbs outliers were found in the datasets of sample A and B. The results of laboratories 15 and 17 are marked as stragglers by the Grubbs test indicating systematic errors but are not rejected. The absolute Z-score of laboratory 12 is greater than 3 and suggests poor performance in terms of accuracy. N.B. Horwitz is not applicable for results expressed as dm 2. Therefore the reproducibility relative standard deviation is set as assigned precision standard to calculate the performance and the Z-scores. page 5

9 5 Method of analysis Lab UV-VIS HPLC-DAD Remarks Samples/year 1 no details supplied - 2 x x x ca DIN CEN x - 7 no details supplied - 8 no details supplied - 9 x - 10 x DIN CEN/TS : x - 13 x x - 16 x x x x - 20 x - 21 no details supplied 10 6 Remarks from participants Lab 3 General annotation: Formaldehyde results from melamine samples are known to vary in quite wide ranges (depending on material quality). Therefore, usually always determination in triplicate is done in our lab routinely. Unfortunately, only two samples were available. We would like to have more samples (absolute minimum: 3 identical samples) to be tested in a proficiency testing. Lab 10 Results were adjusted for % recovery. Lab 17 First migration was discarded. Lab 20 Third release: sample A = 1.61 mg/l and sample B = 1.55 mg/l. page 6

10 7 List of invited participants Europe France 1 participant Germany - 4 participants Ireland - 1 participant Italy - 1 participant Luxembourg - 1 participant The Netherlands - 1 participant Spain - 1 participant Outside Europe China - 5 participants Hong Kong - 3 participants India - 1 participant Saudi Arabia - 1 participant Turkey - 1 participant page 7

11 8 Explanation of graphical presentations Z-score As a criterion for evaluation of the performance of an individual laboratory a socalled Z-score is used. The Z-score is given by the following equation: µ Z = x σ Where: x = an (average) laboratory result µ = the average result of all laboratories (calculated exclusive outliers). σ = an assigned precision standard (60% of average calculated stated after three proficiency studies for the migration of formaldehyde and s R for the contact area. As a fixed target value the maximum allowable standard deviation is used. The Z- score for an individual laboratory can be compared with those of previous proficiency studies to determine whether the laboratory performance has improved. Because Z is standardised, it is comparable for all analytes, testmaterials and analytical methods. In general, an absolute value of Z greater than three suggests poor performance in terms of accuracy. When overall performance in a specific interlaboratory test is graded as good, values of Z <1 would be very common and values of Z >3 would be very rare. It is possible to classify these scores: Satisfactory = Z 2 Questionable = 2 < Z < 3 Unsatisfactory = Z 3 Saw-tooth plot The results of the samples are presented in a so-called saw-tooth plot. In this figure individual results of two (nearly) identical individual results are plotted. The average of the sample, the 2s- and 3s-intervals of the target values and the 2sand 3s-intervals after removal of outliers are also included (group s). Youden-plot Based on Youden statistics the calculated variance is split in a variance caused by systematic and random errors of the individual laboratories. It is necessary that the samples are similar. Generally the points form an elliptical pattern with the major axis of the ellipse running diagonally at an angle of 45 to the X-axis. The lengths of the perpendiculars drawn from the points to the 45 line are directly related to the random errors. Systematic errors will be presented along the 45 line. The perpendiculars intersect the 45 line at various distances from the point through which the 45 line was drawn. These distances are directly related to the systematic errors. page 8

12 9 Tables and graphical presentations Table I; Proficiency study 642: Migration of formaldehyde from melamine kitchenware and contact area Lab First migration [mg/l] a Second migration [mg/l] b Third migration [mg/l] Third migration [mg/kg] c Contact area [dm 2 ] A B A B A B Z A B Z A B Z (1) 3.58 (1) (1) 3.17 (1) (1) 2.24 (1) (1) 1.76 (1) (1) 1.99 (1) (3) 6.18 (3) (1) 3.28 (1) (1) 2.89 (1) <1.5 <1.5 <1.5 (3) <1.5 (3) µ σ a. Results of first migration performed by the Netherlands Food and Consumer Product Safety Authority for screening. b. Results of second migration performed by participants, are only used for information about a possible relationship between first, second and third migration. c. Participants only were instructed to submit results expressed as mg/l. CHEK calculated results expressed as mg/kg (see page 2). (1) = Cochran outlier (2) = Grubbs outlier (3) = Results removed by hand page 9

13 Graphical presentations third migration of formaldehyde from melamine expressed as mg/l N.B. Results of laboratory 20 are not presented, because of non-quantitative results. Figure Ia; Saw-tooth plot third migration of formaldehyde from melamine, calculated with target s. Figure Ib; Saw-tooth plot third migration of formaldehyde from melamine, calculated with group s (exclusive laboratories 1, 4, 16 and 20). page 10

14 Figure II; Youden plot third migration of formaldehyde from melamine. Figure III; Z-score third migration of formaldehyde from melamine. page 11

15 Graphical presentations third migration of formaldehyde from melamine expressed as mg/kg Figure IVa; Saw-tooth plot third migration of formaldehyde from melamine, calculated with target s. Figure IVb; Saw-tooth plot third migration of formaldehyde from melamine, calculated with group s (exclusive laboratories 1, 4 and 16). page 12

16 Figure V; Youden plot third migration of formaldehyde from melamine. Figure VI; Z-score third migration of formaldehyde from melamine. page 13

17 Graphical presentations contact area of migration of formaldehyde from melamine Figure VIIa; Saw-tooth plot contact area of migration of formaldehyde from melamine, calculated with target s. Figure VIIb; Saw-tooth plot contact area of migration of formaldehyde from melamine, calculated with group s (exclusive laboratories 10 and 12). page 14

18 Figure VIII; Youden plot contact area of migration of formaldehyde from melamine. Figure IX; Z-score contact area of migration of formaldehyde from melamine. page 15