CERTIFICATION REPORT

Transcription

1 CERTIFICATION REPORT The certification of the mass fractions of As, Br, Cd, Cl, Cr, Hg, Pb, S and Sb and the assignment of indicative values for Sn and Zn in two polyethylene reference materials Certified Reference Materials ERM -EC680k and ERM -EC681k Report EUR EN

2 The mission of IRMM is to promote a common and reliable European measurement system in support of EU policies. European Commission Directorate-General Joint Research Centre Institute for Reference Materials and Measurements Contact information CRM Sales European Commission Directorate-General Joint Research Centre Institute for Reference Materials and Measurements Retieseweg 111 B-2440 Geel Belgium jrc-irmm-rm-sales@ec.europa.eu Tel.: +32 (0) Fax: +32 (0) Legal Notice Neither the European Commission nor any person acting on behalf of the Commission is responsible for the use which might be made of the following information. EUR Report EN ISSN ISBN Luxembourg: Office for Official Publications of the European Communities European Communities, 2007 Reproduction is authorised provided the source is acknowledged Printed in Belgium

3 CERTIFICATION REPORT The certification of the mass fraction of, As, Br, Cd, Cl, Cr, Hg, Pb, S and Sb and the assignment of indicative values for Sn and Zn in two polyethylene reference materials Certified Reference Materials ERM -EC680k and ERM -EC681k T. Linsinger, A. Liebich, E. Przyk, A. Lamberty European Commission, Joint Research Centre Institute for Reference Materials and Measurements (IRMM) Geel (BE) Report EUR EN

4 SUMMARY This report describes the preparation and certification of the polymer certified reference materials (CRM) ERM-EC680k and ERM-EC681k. They replace the exhausted predecessors, ERM-EC680 and ERM-EC681. The CRMs have been certified by the European Commission, Directorate General Joint Research Centre, Institute for Reference Materials and Measurements (IRMM), Geel, Belgium. The CRM was prepared from a low-density polyethylene (LDPE) granulate spiked with inorganic pigments (As 2 O 3, Green 36, ZnS/CdS, Green 7, Cr 2 O 3, PbCrO 4 /PbSO 4, HgS, Sb 2 O 3, SnO 2 ). Certification of the CRM included testing of the homogeneity and stability of the material as well as the characterisation using an intercomparison approach. The new CRMs have been certified for their content of As, Br, Cd, Cl, Cr, Hg, Pb, S, Sb and indicative values have been established for Sn and Zn. Additional information about acid digestible Cr is given. These CRMs are intended for use in quality assurance of measurements of elements in polymers and related matrices. The following values were assigned: Certified and indicative values. Assigned uncertainties are expanded uncertainties estimated in accordance with the Guide to the Expression of Uncertainty in Measurement (GUM) with a coverage factor k = 2.78 for Cr and k = 2 for all other elements, corresponding to a level of confidence of about 95 %. ERM-EC680k ERM-EC681k As 4.1 ± 0.5 mg/kg 29.1 ± 1.8 mg/kg Br 96 ± 4 mg/kg 0.77 ± 0.04 g/kg Cd 19.6 ± 1.4 mg/kg 137 ± 4 mg/kg Cl ± 3.0 mg/kg 0.80 ± 0.05 g/kg Cr 20.2 ± 1.1 mg/kg 100 ± 5 mg/kg Hg 4.64 ± 0.20 mg/kg 23.7 ± 0.8 mg/kg Pb 13.6 ± 0.5 mg/kg 98 ± 6 mg/kg S 76 ± 4 mg/kg 0.63 ± 0.04 g/kg Sb 10.1 ± 1.6 mg/kg 99 ± 6 mg/kg Indicative values ERM-EC680k ERM-EC681k Sn 15.3 ± 2.8 mg/kg 86 ± 6 mg/kg Zn 137 ± 20 mg/kg 1.25 ± 0.07 g/kg 1

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6 TABLE OF CONTENTS Summary...1 Table of contents...3 Glossary Introduction Time table of the project Participants Processing Homogeneity Between-unit homogeneity Minimum sample intake Stability Stability of the previous materials Tests on the current materials Uncertainty of stability Characterisation Technical evaluation Statistical evaluation Assigned Values and their uncertainties Certified values Indicative values Additional material information Metrological Traceability and commutability Metrological Traceability Commutability Instructions for use Storage conditions Safety and protection of the environment Use of the certified values Acknowledgements Annexes References

7 GLOSSARY AAS Atomic absorption spectrometry AFS Atomic fluorescence spectrometry ANOVA Analysis of variance CRM Certified reference material CVAAS Cold vapour AAS CVAFS Cold vapour AFS DMA Direct mercury analyser ETAAS Electrothermal AAS HG Hydride generation HPA High pressure asher IC Ion chromatography ICP Inductively coupled plasma ICP-AES Inductively coupled plasma atomic emission spectrometry ICP-MS Inductively coupled plasma mass spectrometry ID -TIMS Thermal ionization mass spectrometry using isotope dilution INAA Instrumental neutron activation analysis IPAA Instrumental photon activation analysis IR Infrared spectrometry k Coverage factor k 0 NAA Neutron activation analysis using the k 0 -method for quantification MS among Mean square among bottles from an ANOVA MS within Mean square within a bottle from an ANOVA NAA Neutron activation analysis RoHS Directive 2002/95/EC (restriction of the use of certain hazardous substances in electric and electronic equipment) RSD Relative standard deviation rel Relative (as subscript) s bb Between-unit variability s wb Standard deviation within bottle SF Sectorfield SI Système International d'unités (International System of Units) SS-ZAAS Solid sampling Zeeman AAS u bb Uncertainty related to a possible between-bottle heterogeneity u * bb Heterogeneity that could be hidden by method repeatability u c Combined uncertainty of the certified value u char Uncertainty of the characterisation U CRM Expanded uncertainty of a certified value u lts Uncertainty of long-term stability u sts Uncertainty of short-term stability WDXRF Wavelength-dispersive X-ray fluorescence spectrometry XRF X-ray fluorescence spectrometry 4

8 1 INTRODUCTION Most countries have adopted legislation to monitor the mass fraction of elements in consumer products in order to protect human and animal health. From an environmental perspective, the flow of heavy metals to the environment should be monitored well to avoid adverse health effects due to excessive load. To this end, the European Union has passed legislation to limit the load of certain elements in various products, amongst them Directive 94/62/EC (packaging directive), Directive 2002/95/EC (restriction of the use of certain hazardous substances in electric and electronic equipment RoHS) and Directive 2000/53/EC (end of live vehicles). Directive 94/62/EC concerns plastics packaging and packaging material and regulates the amounts of metals (Cd, Cr, Hg and Pb) in plastics used for packaging. Article 11 of this directive states that the maximum element content should be decreased in three consecutive steps, namely to 600 mg/kg before June 30, 1998, to 250 mg/kg before June 30, 1999 and to 100 mg/kg before June 30, Directive 2002/95/EC aims at reducing the amount of hazardous substances in electric and electronic equipment. Use of Pb, Hg, Cr(VI), Cd and polybrominated flame retardants is prohibited unless not alternatives exist for certain applications. Commission Decision 2005/618/EC sets a limit of maximum 0.1 g/kg in homogeneous materials for Pb, Hg, Cr(VI) and 0.1 g/kg for Cd. Similarly, Directive 2000/53/EC aims at reducing the amount of hazardous substances entering the environment from old vehicles. Council Decision 2005/673/EC sets a limit of maximum 0.1 g/kg in homogeneous materials for Pb, Hg, Cr(VI) and 0.1 g/kg for Cd. In support of these directives, two sets of certified reference materials (CRMs) have been produced by the European Commission, namely a set of four polyethylene (PE) materials (on behalf of the German Verband der Automobilindustrie e.v. (VDA), Frankfurt) [1] and two additional PE materials, BCR-680 and BCR-681 [2]. BCR-680 and BCR-681 were re-labelled as ERM-EC680 and ERM-EC681 in Due to the high need for these materials, stocks of ERM-EC680 and ERM-EC681 were exhausted in 2006 and new batches were produced. This report describes the production of the two replacement batches ERM-EC680k and ERM-EC681k. 2 TIME TABLE OF THE PROJECT Processing...March 2006 June 2006 Homogeneity study...july 2006 September 2006 Stability study...july 2006 October 2006 Characterisation study...august 2006 December

9 3 PARTICIPANTS Processing DSM Resolve, Geleen (NL) EC-JRC, Institute for Reference Materials and Measurements (IRMM), Geel (BE) Homogeneity study Vlaamse Instelling voor Technologisch Onderzoek (VITO), Mol (BE) European Commission, Joint Research Centre, Institute for Reference Materials and Measurements (IRMM), Geel (BE) All measurements were performed by wavelength-dispersive X-ray fluorescence spectrometry (WDXRF) except for Hg in EC680k, for which a direct-mercury analyser was used. Stability study Vlaamse Instelling voor Technologisch Onderzoek (VITO), Mol (BE) European Commission, Joint Research Centre, Institute for Reference Materials and Measurements (IRMM), Geel (BE) All measurements were performed by wavelength-dispersive X-ray fluorescence spectrometry (WDXRF) except for Hg in EC680k, for which a direct-mercury analyser was used. Characterisation measurements Bundesanstalt für Materialforschung und prüfung (BAM), Berlin (DE) (accredited for the measurements performed according to ISO DAP-PL ) DSM Resolve, Geleen (NL) GSF, Neuherberg (DE) Institut Jozef Stefan, Ljubljana (SI) Solvias, Basel (CH) Studiecentrum voor Kernenergie (SCK), Mol (BE) Umweltbundesamt, Vienna (AT) (accredited for the measurements performed according to ISO BMWA /0191-I/12/2005, PSID 200) Vlaamse Instelling voor Technologisch Onderzoek (VITO), Mol (BE) Methods used included methods without sample preparation (XRF, NAA) as well as digestion methods (acid, oxygen) with different quantification steps (ICP methods, IC with conductivity detection, AAS, XRF). Project Management and evaluation European Commission, Joint Research Centre, Institute for Reference Materials and Measurements (IRMM), Geel (BE) 6

10 4 PROCESSING A survey among customers was conducted to come up with potential improvements of the previous material. Amongst ideas of a different format (e.g. plates), the additional certification of the mass fraction of Sb and Sn was mentioned. Therefore, Sb and Sn were added to the range of elements. Preparation of the batches was performed by DSM Resolve, Geleen (NL). Low-density polyethylene (LDPE) was used as base material without addition of plasticisers and softeners. The target elements had to be added as LDPE itself does not contain them. Most frequent use of the target elements is as colourant, i.e. in the form of pigments. Therefore, inorganic pigments were added to achieve the target contents for the various elements. Due to the nature of the production process, these pigments cannot be present in the initial polymerisation process but have to be blended into the final LDPE granulate. Pigments were ground to particle sizes < 1 µm if necessary. For each material, a master batch of a higher element concentration was produced by mixing with PE powder in a nail mill and subsequent extrusion. The granulate obtained was mixed, blended with blank LDPE to yield the desired element concentrations and extruded. The granulate from this step was mixed again and extruded a second time. Pigments used and the desired target element mass fractions are listed in Table 1. Table 1: Pigments used and element target concentrations. Element Pigments Element target mass fractions ERM-EC680k ERM-EC681k As As 2 O Br Cl/Br phthalocyanine (Green 36) Cd ZnS/CdS Cl Cl-phthalocyanine (Green 7), Cl/Br phthalocyanine (Green 36) Cr Cr 2 O 3 (Green 17), PbCrO 4 /PbSO 4 (Yellow 34) Hg HgS 5 25 Pb PbCrO 4 /PbSO 4 (Yellow 34) S ZnS/CdS, PbCrO 4 /PbSO 4 (Yellow 34) Sb Sb 2 O Sn SnO The same pigments and target concentration levels as for the previous batches were used. However, the coding was reversed: while ERM-EC680 was previously the high level material, ERM-EC680k is the low level material. This is clearly indicated on the label. About 300 kg of each batch were produced and delivered to IRMM. Material was filled into drums of about 100 kg (maximum capacity of the mixer) and homogenised in a turbula mixer. One hundred grams were filled into amber glass jars, which were ed according to the filling sequence. The relationship between drums and sample s is given in Table 2. Table 2: Drums and sample s. For ERM-EC681k, samples were labelled , i.e. samples 1-52 do not exist. Bottle s ERM-EC680k Bottle s ERM-EC681k Drum Drum Drum

11 5 HOMOGENEITY 5.1 BETWEEN-UNIT HOMOGENEITY Thirty units of each batch were selected using a random stratified sampling scheme and analysed by VITO (ERM-EC680k) and IRMM (ERM-EC681k) for all elements. Three plates (diameter about 4 cm; height about 5 mm) were pressed from each bottle and the plates were analysed in a randomised manner to be able to separate potential analytical drift from a trend in the filling sequence. The methods used were WDXRF for all elements except Hg in ERM-EC680k, where a direct mercury analyser (combustion with subsequent quantification by AAS) was used Descriptive evaluation Grubbs-tests were performed to detect potentially outlying individual results as well as outlying bottle averages. For ERM-EC680k, outlying individual values were found for Pb, Cl, S and Sb. The ones for Pb and Sb were only significant on a 95 %, but not on a 99 % confidence level whereas the ones for Cl and S were also significant on a 99 % level. Four outlying bottle averages (one for As and Br and two for Cl) were found, all significant at 95 %, but not at 99 % confidence levels. Bottle 1222 was found an outlier both for As and Br, whereas the two outlying averages for Cl came from bottles 316 and For ERM-EC681k, one outlying result each was found for Br and Cl. These outlying results made the bottle average an outlier as well. Both measurements concerned the same result, namely measurement 36 of bottle Measurement 36 was also an outlying result for S. Additionally, measurement 16 (bottle 1523) was an outlier for S as well. The other measurements of the other plates from the same bottle did not confirm the deviating result for this bottle, so the outliers are most likely statistical artefacts. As no technical reason for the outlier could be found and outlying bottle averages were not significant at 99 % confidence levels, all data were retained for statistical analysis. Regression analyses were performed to evaluate potential trends in the analytical sequence as well as trends in the filling sequence. In ERM-EC680k, the apparent mass fractions of Br and Sn increased with increasing bottle s. These trends were significant on a 95 % confidence level, but not on a 99 % confidence level. The same was true for Cd in EC681k. All data were retained. Uncertainty of homogeneity is very low (see below), despite the fact that any potential trend is reflected in this uncertainty. For EC681k, some trends in the analytical sequence were visible, pointing at instability of the analytical system. These were again only significant on a 95 %, but not on a 99 % confidence level and no drift correction was applied. It was furthermore checked whether the individual data and bottle averages follow a normal distribution using normal probability plots and whether the individual data are unimodally distributed using histograms. For ERM-EC680k and ERM-EC681k, most individual results and sample means follow normal distributions. Sample means are unimodally distributed for all elements. A special case is Pb in EC681k: as can be seen in Annex A, individual results fall clearly into three groups with Pb mass fractions around 96.5, 101 and 107 mg/kg respectively. This grouping is not visible in the sample means. Fifteen plates were measured again, yielding a similar pattern, but with different plates. It was therefore concluded that this grouping is due to some instrumental artefact and not due to some real variation in the Pb mass fractions. All values were therefore retained as the higher variation between the individual measurement results 8

12 is reflected in the estimate of the uncertainty of homogeneity. Retention of the values therefore does not result in an underestimation of potential heterogeneity. The result of the descriptive evaluation is given in Table 3 and Table 4. Table 3: Results of the descriptive evaluation of the homogeneity results of ERM-EC680k. None of the trends is significant on a 99 % confidence level. Only the outliers for S and Cd are significant on a 99 % confidence level. For the individual values with indication of outliers, see Annex A. Individual values Outliers Bottle average Significant trends (95 % confidence) Analytical sequence Filling sequence Distribution of individual results Distribution of bottle means Normal Unimodal Normal Unimodal As no 1 no no yes yes approx. yes Br no 1 no yes approx. hint of bimodal approx. yes Cd no no no no yes yes yes yes Cl 1 2 no no no yes no yes Cr no no no no yes yes yes yes Hg no no no no yes yes yes yes Pb 2 no no no yes yes yes yes S 1 no no no no yes no yes Sb 1 no no no no yes no yes Sn no no no yes yes yes yes yes Table 4: Result of the descriptive evaluation for the homogeneity results of ERM-EC681k. None of the trends is significant on a 99 % confidence level. Only the outlier for the individual value for Br is significant on a 99 % confidence level. For the individual values with indication of outliers see Annex A. Individual values Outliers Bottle average Significant trends (95 % confidence) Analytical sequence Filling sequence Distribution of individual results Distribution of bottle means Normal Unimodal Normal Unimodal As no no no no yes yes yes yes Br 1 1 no no no yes no yes Cd no no yes yes yes yes yes yes Cl 1 1 no no no yes no yes Cr no no no no yes yes yes yes Hg no no yes no yes yes yes yes Pb no no no no no no no approx. S 2 no yes no no yes yes yes Sb no no no no yes yes no yes Sn no no no no yes yes yes yes Between-drum homogeneity Samples were produced in three batches due to restraints in the maximum mixing capacity. Therefore the equivalence of the three batches was checked. Mean values for all elements were grouped by the batch and differences were evaluated using one-way analysis of variance (ANOVA) with the batch as grouping variable. 9

13 For ERM-EC680k, the differences between drums were significant for Br on a 95 %, but not on a 99 % confidence level and were therefore regarded as statistical artefact. No significant difference between drums was found for any of the other elements on a 95 % confidence level. For Br, the difference between the highest and the lowest drum average was 1.50 %. For ERM-EC681k, differences between batch averages were significantly different on a 95 % significance level for Br and Cr. The differences between the highest and the lowest average were 0.34 % for Br and 0.24 % for Cr. The uncertainty of variation between drums, u drum, was estimated assuming a rectangular distribution of results between the highest and lowest drum average. In line with the Guide to the Expression of Uncertainty in Measurement (GUM) [3], uncertainty was estimated as halfwidth of this difference divided by 3. This gives uncertainty contributions of 0.43 % for Br in ERM-EC680k and 0.10 % and 0.07 %, respectively, for Br and Cr, respectively, in ERM- EC681k Variation between bottles Key requirement for any reference material is equivalence between the various units. In this respect, it is not relevant whether the variation between units is significant compared to the analytical variation, but whether this variation is significant to the certified uncertainty. Consequently, ISO Guide 35 demands RM producers to quantify the between bottle variation. This quantification is most easily done by ANOVA, which can separate the between-bottle variation (s bb ) from the within-bottle variation (s wb ). The latter is equivalent to the analytical variation if the individual subsamples are representative for the whole bottle. Evaluation by ANOVA is only possible if data follow unimodal distributions. One has to bear in mind that s bb and s wb are estimates of the true standard deviations and therefore subject to random fluctuations. This can result in negative estimates for the between-bottle variation, whereas the natural lower limit is naturally zero. In this case, u * bb, the maximum heterogeneity that could be hidden by method repeatability, was calculated as described by Linsinger et al. [4]. u * bb is comparable to the limit of detection of an analytical method, yielding the maximum amount of a substance that might be undetected by any given analytical test. Because all individual values and sample means followed unimodal distributions, results could be evaluated using ANOVA. Standard deviations within units (s wb ) and between units (s bb ) as well as u * bb were calculated. The results of these evaluations are shown in Table 5 and Table 6. Table 5: Results of the homogeneity test for ERM-EC680k. n.c.= cannot be calculated as MS among < MS within. Average s wb s bb u * bb [%] [%] [%] As Br n.c. n.c Cd n.c. n.c Cl Cr Hg n.c. n.c Pb n.c. n.c S n.c. n.c Sb n.c. n.c Sn

14 Table 6: Results of the homogeneity test for ERM-EC681k. n.c.= cannot be calculated as MS among < MS within Average s wb s bb u * bb [%] [%] [%] As n.c. n.c Br Cd Cl Cr n.c. n.c Hg n.c. n.c Pb n.c. n.c S Sb Sn n.c. n.c As can be seen in Table 5 and, the estimates for s bb or u bb * are above the between-drum variation, confirming expectations that the between-drum variation is already included in the variation between units. The between-drum variation therefore does not have to be added to the between-bottle variation. 5.2 MINIMUM SAMPLE INTAKE The minimum sample intake defines the minimum amount of sample that is representative for the whole unit. Samples above the minimum sample intake therefore guarantee the certified value, which is not true for subsamples smaller than the minimum sample intake: intrinsic microhomogeneity may result in deviations from the certified value for such very small samples. Minimum sample intake was estimated using two approaches, namely conducting measurements with solid-sampling atomic absorption spectrometry (SS-AAS) and its assessment from the characterisation study. Cd, Pb and Cr were measured by SS-AAS. In this method, minute sample amounts (0.43 to 4.3 mg) are analysed by direct atomisation. The assumption is that at these small sample intakes, analytical variation becomes negligible compared to variation due to microheterogeneity. The observed standard deviation can therefore be used to estimate a minimum sample amount necessary for a given measurement repeatability as described by Pauwels et al [5]. Fifty measurements were performed for each element and the minimum sample intakes necessary for a repeatability of 5 % are given in Table 7. It should be emphasised that these are conservative estimates, as the variation has not been corrected for the intrinsic analytical variability. For all other elements, the minimum sample intakes were estimated from the characterisation studies: a sample intake is automatically sufficient if a laboratory achieved satisfactory repeatability with a given sample intake. The lowest sample intake that resulted in satisfactory repeatability was therefore used as minimum sample intake. 11

15 Table 7: Minimum sample intakes. Sample intakes for Cd, Cr and Pb from SS-AAS for a repeatability of 5 %, for all other elements from the characterisation study. Two values are given for elements for which different minimum sample intakes have been used. ERM-EC680k [mg] ERM-EC681k [mg] As 100 Br 150 Cd 28 2 Cl 150 Cr Hg Pb S 150 Sb 100 Sn 150 As shown above, minimum subsamples for all elements were 150 mg or below. Data for Cd, Cr, Hg and Pb suggest that the material can be used for microanalytical techniques for some elements. While this may also be true for the other elements, no positive proof for this is available. Sample intakes of 150 mg, approximately 7 granules, are therefore representative for both materials and all analytes. This sample intake is suitable for all digestion based methods. 12

16 6 STABILITY Possibilities to reduce the time needed for the initial stability study were sought in order to decrease time until release, Where possible, the same pigments were used for the preparation of the new material as for the old material, the only difference being that BaCrO 4 was replaced by Cr 2 O 3, which is also very stable against radiation and heat. Two new stable pigments have been used, namely SnO 2 and Sb 2 O 3. All materials, ERM-EC680/ERM-EC681 and ERM-EC680k/ERM-681k consist of polyethylene. High-density polyethylene is used in the first case whereas low density polyethylene is used for the new batch. However, both materials show similar resistance to oxidative degradation. As the pigments as well as the matrix are very similar, stability of the new batch can be inferred from stability of the previous batch. Stability could therefore be inferred from two sources, namely stability of the EC680 and EC681 and stability tests on EC680k and EC681k. Extreme conditions were chosen for testing the current materials in order to have good confidence on their stability. 6.1 STABILITY OF THE PREVIOUS MATERIALS In November 2005, measurements were performed on EC680 and EC681 in the frame of IRMM's stability monitoring program. k 0 NAA was chosen as analytical method for this test as it can determine multiple elements simultaneously with high accuracy. Twelve subsamples of about 350 mg were taken from one bottle of each material. Irradiations lasted 9 hours for the determination of long-lived isotopes (As, Br, Cd, Cr and Hg) and 900 seconds for the determination of Cl. The results are compared to the certified values in Table 8. Additional confirmation of stability comes from the results of the characterisation study of the current material: participants received one unit each of EC680 and EC681 as quality control sample. As these samples are used for quality control purpose, stability is a prerequisite and the results cannot be used for a rigorous stability test. However, as the laboratories used validated methods, results still give additional indication of stability. 13

17 Table 8: Comparison of the certified values of EC680 and EC681 with the results of the stability test 2005 and the results obtained during the characterisation study for the new batches. Error ranges are expanded uncertainties (k=2) for the certified values 1999, single standard deviations of the results for the stability test 2005 and single standard deviation of the laboratory means accepted for the characterisation for the characterisation ERM-EC680 ERM-EC681 Element Certified value 1999 Stability test 2005 As 30.9 ± ± ± 1.0 Br 808 ± ± ± 38 Cd ± ± ± 5.5 Cl 810 ± ± ± 81 Cr ± ± ± 1.8 Hg 25.6 ± ± ± 1.1 Pb ± ± 3.2 not tested Characterisation 2006 S 670 ± ± 60 As 3.93 ± ± ± 0.25 Br 98 ± ± ± 5.4 Cd 21.7 ± ± ± 1.3 Cl 92.9 ± ± ± 10.3 Cr 17.7 ± ± ± 0.7 Hg 4.50 ± ± ± 0.18 Pb 13.8 ± ± 3.6 S 78 ± 17 not tested 71.1 ± 5.91 As can be seen in Table 8, all results from 2005 with the exception of As and Cl in ERM- EC681 agree with the certified values. Furthermore, all averages obtained during characterisation study 2006 agreed with the certified values, confirming stability. 6.2 TESTS ON THE CURRENT MATERIALS Stability of the new materials was tested under stress conditions to confirm the assumption of equal behaviour of the old and the new batches in a short time. The main potential degradation factors were thought to be temperature-dependent, thus testing at elevated temperature was performed. Also the influence of UV radiation was investigated as polyethylene is known to be sensitive to UV-irradiation. Samples were stored for 0, 2 and 4 months at +60 C and 4 months at +18 C in an isochronous study [6]. Samples were shifted to -20 C after the respective times at +60 C and 18 C. In this way, the degradation status of the materials is maintained. At the end of the study, all materials can be analysed in one run under repeatability conditions, thus minimising analytical variation. After 4 months, samples were analysed by WDXRF (4 bottles per time point; three measurements per bottle). In addition, samples were put on flat Petri dishes and irradiated for 544 hours by a lowpressure Hg UV-lamp (254 nm; 30 W; max 15 cm distance to the lamp) in a laminar flow hood to avoid contamination. The samples were spread in a single layer of granules and were mixed approximately every 24 hours. After irradiation, samples were analysed in triplicate together with the samples from the isochronous study. On visual inspection, no significant change in colour was visible as shown in Figure 1. 14

18 Figure 1: Comparison of ERM-EC680k and ERM-EC681k following 0 and 544 hours of UV irradiation. Data obtained by WDXRF were screened for outlying values. Some outlying individual values were found (Grubbs-test at 95 % and 99 % confidence level). These were retained as no technical reason for exclusion was found. Moreover, tentative removal of the outliers did not significantly influence the outcome of the subsequent analysis, therefore outliers were retained. Subsequently the regression lines for samples stored at 60 C were calculated and tested for significance. If found not significant, the uncertainty of stability during dispatch was calculated for 1 week (u sts ) as uncertainty of the slope of a regression line with a slope of 0 multiplied with the time (1 week) using the equation below [7]. u sts s = 2 ( x x) t Equation 1 with u sts being the uncertainty of short-term stability, s the standard deviation of results, x and x the time points and average time of the study, respectively and t the duration for which the uncertainty is evaluated (1 week). In addition, the results for the irradiated sample and the samples stored at +18 C were compared to the result obtained on the samples stored at +4 C throughout using a t-test. The results of these evaluations are shown in Table 9 and Table 10, graphs of the study are given in Annex B. Table 9: Results of stability test EC680k. Test temperature+ 60 C; reference temperature 4 C. 60 C Difference with t = 0 (4 C) significant? Average ± s Slope ± s Slope u sts for t = 1 18 C Irradiated [mg/kg/month] significant week [%] As 4.5 ± ± 0.06 no 0.34 no no Br ± ± 0.36 no 0.08 no no Cd 19.0 ± ± 0.18 no 0.23 no no Cl ± ± 0.88 no 0.21 no no Cr 24.5 ± ± 0.03 no 0.04 yes (95 %), no (99%) no Hg 4.0 ± ± 0.12 no 0.27 no no Pb 14.2 ± ± 0.05 no 0.08 no no S 86.3 ± ± 0.62 no 0.18 no no Sb 2.2 ± ± 0.06 no 0.72 no no Sn 10.5 ± ± 0.05 no 0.13 no no 15

19 Table 10: Results of stability test EC681k. Test temperature +60 C; reference temperature +4 C 60 C Difference with t = 0 (4 C) significant? Average ± s Slope ± s Slope u sts for t = 1 18 C Irradiated [µg/kg] [mg/kg/month] significant week [%] As 28.3 ± ± 0.18 no 0.16 no no Br ± ± 0.23 no 0.01 no no Cd ± ± 0.21 no 0.04 no no Cl ± ± 0.26 yes (95 %), yes (95 %), 0.01 no (99 % ) no (99 %) yes (99 %) Cr ± ± 0.06 no 0.01 no no Hg 20.6 ± no 0.06 no yes (95 %), no (99 %) Pb ± ± 0.41 no 0.10 no no S ± ± 0.31 yes (95% ), no (99 % ) 0.01 no no Sb 96.0 ± ± 0.30 no 0.08 no no Sn ± ± 0.31 no 0.08 yes (99 %) yes (99 %) None of the slopes of the regression lines was significantly different from zero on a 95 % confidence level for ERM-EC 680k. For ERM-EC681k, two slopes were found significant at a 95 %, but not at a 99 % confidence level. The significance of the slope for Cl depends on retaining an individual value that is actually flagged as outlier on a 99 % confidence level removal makes the slope not significant, which casts some doubts on the validity of the significance of this slope. Because in total 20 studies were evaluated, one significant slope on a 95 % confidence level can be expected on statistical grounds. It was therefore concluded that the two significant slopes were most likely statistical artefacts. In any case, uncertainty of stability for these two analytes is also higher (see section 6.3), so that even if the slope was indeed real, shelf lives of more than 40 months are obtained for these two analytes. The observed slopes therefore do not indicate significant degradation. Mass fractions of samples stored at +18 C and of irradiated samples were not significantly (99 % confidence) different from samples stored at +4 C in the case of ERM-EC680k. The apparent change for Cr at 18 C is contradicted by the stability at 60 C and was therefore regarded as statistical artefact. Some significant differences exist for ERM-EC681k, especially for irradiated samples. This indicates some changes during irradiation, which are presumably hidden by the higher relative standard deviation of the measurements for ERM- EC680k. The indication of changes during irradiation is also confirmed by the appearance of the platelets prepared for XRF: boundaries between grains are clearly visible for irradiated samples, possibly caused by surface oxidation. The tests of ERM-EC680k and ERM-EC681k at +60 C therefore confirm the assumption that the stability of the new batches is equivalent to the stability of the old batches. 6.3 UNCERTAINTY OF STABILITY Tests of the current material gave no indication of degradation. Uncertainty of stability (u lts ) was evaluated from the previous batches as follows: u t shelf 2 2 lts = uconf + bias Equation 2 t study with t shelf the chosen shelf life, t study the duration of the stability study, u conf the uncertainty of the confirmation of stability and bias the observed bias in the confirmation of result. This approach of combining bias has been shown not to underestimate uncertainties [8] while 16

20 retaining symmetric uncertainties. Bias is only included if the bias is indeed significant, i.e. if 2*u conf < bias. t shelf is the arbitrarily chosen shelf life for which stability can be guaranteed and is closely related to the further stability monitoring: stability must be confirmed before t shelf ends. An initial shelf life of 2 years was chosen for EC680k and EC681k. The factor t shelf /t study derived from the fact that the square root of equation 2 gives the potential degradation of the complete duration of the study. Assuming as first approximation linear degradation as proposed in [7], potential degradation for e.g. half of the time is half as severe. u conf, the confirmation of stability comprises uncertainty of the certified values and the measurement uncertainty and was estimated as 2 smeas u conf = ucrm + Equation 3 nmeas 2 with u CRM the standard uncertainty of the certified values (U/2), n meas and s meas the of results and their standard deviation of the stability tests. The uncertainty components and the uncertainty of stability are listed in Table 11. Table 11: Estimation of u lts for ERM-EC680k and ERM-EC681k. t shelf = 2 years; t study = 6 years; u lts in % is based on the certified value; * significant bias; # bias included in u lts. Element u CRM s meas / n u conf Bias u lts [%] As Br Cd Cl Cr Hg As * # Br Cd Cl * # Cr Hg ERM-EC680k ERM-EC681k No completely independent data for Pb and S are available. However, the pigments containing Pb and S are chemically very stable and no degradation is expected. In addition, agreement of the results obtained during the characterisation study for the previous batches of the material also indicates stability. As conservative estimates, u lts for Pb and S were therefore set equal to the largest relative uncertainty for each material. The same reasoning was used for Sb and Sn. These uncertainties are given in Table

21 Table 12: u lts for Pb, S, Sb and Sn in ERM-EC680k and ERM-EC681k. Uncertainties of stability were set equal to the highest uncertainty obtained for any of the other elements in the respective material (see Table 11). Material Element u lts [%] ERM-EC680k Pb 0.68 S 0.68 Sb 0.68 Sn 0.68 ERM-EC681k Pb 2.18 S 2.18 Sb 2.18 Sn

22 7 CHARACTERISATION The participants received two bottles of each material and were requested to provide 3 independent results from each bottle. Measurements had to be spread over two days. Characterisation of the material was based on intercomparison between expert laboratories for randomisation of individual laboratory bias. Methods used included methods without sample preparation (XRF, NAA) as well as digestion methods (acid, oxygen) with different quantification steps (ICP methods, IC with conductivity detection, AAS, XRF). Quantification was based on completely different principles: neutron capture, atomic emission by thermal excitation, atomic emission after ionisation by X-rays, mass spectrometry after different ionisation techniques, atomic absorption as well as chromatographic separation. It is unlikely that all these results are biased in the same way. Tables and graphs showing the submitted values are given in Annex D. As a quality control measure, the participants also received a bottle of the previous batches ERM-EC680 and ERM-EC681. One digestion (if applicable) had to be performed for each of these samples and the digest had to be analysed in triplicate. The results for this sample are not reported here but have been used to support the evaluation of results to identify and substantiate outliers. 7.1 TECHNICAL EVALUATION The methods used in the characterisation study are described in Annex C. Individual results of the participants, grouped per element and material are displayed in tabular and graphical form in Annex D. All laboratories had received samples of the previous materials (EC680 and EC681) as quality control samples. It was checked whether the data set result on the original material agreed with the certified values within the stated uncertainties. In addition, a meeting was held in which the results of the participants were discussed. This meeting identified several inexplicable deviations for the two WDXRF datasets. In some cases, such unexplainable deviations had been observed by one laboratory also in other intercomparisons. These deviations were not of a systematic nature, i.e. in some cases the result of one dataset was above, in other cases below the other results. While these deviations were usually not large in absolute terms and well within what can be expected from the method, they were significant in comparison with the agreement among the other datasets. It was therefore concluded that WDXRF, while in general a valid method, did not show the accuracy required for the certification of the two reference materials. The results from WDXRF therefore confirm the applicability of the materials for WDXRF, but were not used for the calculation of the certified values. Therefore, "all results" should read as "all results with the exception of WDXRF" in the subsequent text. The detailed outcome of the technical discussion is given below Arsenic All results agree within their stated uncertainties and the datasets for the previous materials agree with the certified values. Therefore, all datasets were accepted for characterisation. Results from WDXRF agree with the other values, thus confirming both applicability of the method as well as the assigned values within the accuracy of the method. 19

23 7.1.2 Bromine Results from titration, IC, ICP-AES using two different digestion techniques, k 0 NAA, INAA and IPAA agree with each other within the stated uncertainties. Result for the previous materials agree with the certified values. There is therefore no reason to expect any bias. However, the Br-concentration of EC680k is close to the limit of quantification for the titration method, resulting in a large uncertainty. While this dataset confirms the values of the other methods, it was excluded from the calculation of the certified value due to its high uncertainty. The result for WDXRF is a little above the other values, indicating the general applicability of the method as well as confirming the assigned value within the accuracy of the method Cadmium For EC680k, 15 datasets agree within their stated uncertainties. Three datasets seem to be on the low side, but fall within a normal distribution. The results were therefore retained. For EC681k, results of 14 datasets agree within their stated uncertainty and most results on the previous material agree with the certified values. The result of one dataset, obtained by ETAAS, is significantly above the certified value. The laboratory reported that the standard deviation of this dataset was significantly above what would be normally expected from the method. As the value for this dataset was above the certified value in the old material by about the same amount and as the precision was also significantly worse than that of the other laboratories, the value was excluded from the calculation of the certified value. Laboratory 16 observed significant differences between the Cd mass fractions of the two bottles. This observation was not confirmed by any of the other laboratories, not even by the laboratories that had received bottle s close to those analysed by laboratory 16. This observation is therefore most likely an analytical artefact. Results from WDXRF agree with the other values, thus confirming both applicability of the method as well as the assigned values within the accuracy of the method Chlorine The 6 (EC680k) and 7 (EC681k) datasets, respectively, agree within their stated uncertainties and the results for the previous material agree with the certified value. The laboratory concerned reported that the method for dataset 21 (HPA-ICP-AES) was close to the limit of quantification for EC680, resulting in a large uncertainty. While this dataset confirms the values of the other methods, it was excluded from the calculation of the certified value due to the high uncertainty. Results from WDXRF agree with the other values, thus confirming both applicability of the method as well as the assigned values within the accuracy of the method Chromium A clear pattern is visible for Cr with instrumental methods giving significantly higher results than methods based on acid digestion. This is due to the presence of Cr 2 O 3, which is very difficult to dissolve in acids. While one laboratory reported complete dissolution of pure Cr 2 O 3 in a mixture of HClO 4 /H 2 O 2, the presence of the polymer, maybe by consumption of the acid, apparently makes complete digestion with acids impossible. Laboratory 18 achieved complete digestion, but only after filtration of the undissolved residue, ashing of the filter and fusion melting of the ash. Laboratory 22 used very harsh digestion conditions and reported increasing Cr-results with decreasing sample intake. At a sample intake of 30 mg a result close to the ones from instrumental methods was obtained for EC680k. However, the higher amount of Cr 2 O 3 to be 20

24 digested resulted in less complete digestion in the higher level material EC681k. A uniform sample intake of 200 mg was used for the ICP-MS set of results (code 22), which explains the lower values for the same digestion method. All other datasets obtained by acid digestion achieved varying digestion efficiencies, depending on the sample intake, digestion medium and digestion conditions. It was therefore concluded that the value of 4 datasets obtained by 3 instrumental methods (INAA, IPAA and twice k 0 NAA) together with the value obtained by ID-TIMS after fusion melting was the best estimate of the true value. These values agree with each other and also agree with the nominal content. A certified value can be assigned as results from one primary method (ID-TIMS) and a candidate primary method (k 0 NAA) are confirmed by two other independent methods. Both datasets obtained by WDXRF are about 25 % above the results from the other instrumental methods as well as above the nominal values, indicating some unresolved measurement bias. No explanation for these high results could be given by the participants Mercury The results agree within their stated uncertainties and the datasets for the previous materials agree with the certified values. Therefore, all datasets were accepted for characterisation. The dataset obtained by WDXRF is below those obtained by the other methods for EC680k, but is in agreement with some of the other datasets for EC681k. This confirms the general applicability of the method and the assessment that the accuracy is lower than for the other methods Lead Results from ETAAS, ICP-MS, ICP-AES, ID-TIMS and IPAA agree within their stated uncertainties and the datasets for the previous materials agree with the certified values. However, IPAA is not very sensitive for Pb. The concentrations are close to the limits of quantification, resulting in large uncertainties. While this dataset confirms the values of the other methods, it was excluded from the calculation of the certified value due to the high uncertainty. The dataset obtained by WDXRF is in agreement with the results obtained by other methods for EC680k while being 10 % above the other results for EC681k. This is in agreement with some of the other datasets, thus confirming both applicability of the method as well as the assigned values within the accuracy of the method Sulfur Results from ICP-AES, IC and ID-TIMS agree within their stated uncertainties and the laboratories' results for the previous materials agree with the certified values. Therefore, all datasets were accepted for characterisation. The method using combustion-ir resulted in extensive soot formation. Therefore, no complete dataset could be delivered and the dataset was therefore not used for certification, but it confirms the certified value. One result from WDXRF agrees with the values whereas one WDXRF-dataset gives values significantly above the other laboratories and the nominal value Antimony Most results agree with one another at reasonably low uncertainties. The only exception is the result of Laboratory 23 for EC681k, which is significantly below the other values. However, no explanation could be given for this deviation. The result was therefore retained. 21

25 Results from WDXRF are 22 % (EC680k) and 12 % (EC681k) below the other datasets, respectively, but in agreement with other datasets confirming both applicability of the method as well as the assigned values within the accuracy of the method Tin The two datasets from k 0 NAA agree with the datasets obtained by WDXRF while results for digestion based methods are below these. The reason is, as for Cr, that the pigment used (SnO 2 ) is hardly digestible by acid mixtures. As for Cr, laboratory 21 achieved complete digestion with small sample intakes for EC680k, due to the smaller amount of SnO 2 present, while only incomplete digestion was achieved for EC681k. The higher sample intake used for dataset 23 explains the lower values obtained in this dataset although the same digestion method had been used. The low of methods ruled out certification of the Sn content, but indicative values can be assigned. As indicative values require less accuracy, results obtained by WDXRF can be included in the value assignment. Indicative values for Sn are therefore based on results by WDXRF, k 0 NAA and, in the case of EC680k, ICP-AES dataset Zinc Zn was not intended for certification. However, three datasets for Zn analysed by instrumental methods were submitted. These results, obtained by k 0 NAA and IPAA agree with each other. No certified values can be assigned as neither homogeneity data nor stability data are available. In addition, the of results and method variability is rather low for assigning certified values. Indicative values are therefore assigned based on the available results. 7.2 STATISTICAL EVALUATION The datasets accepted on technical grounds were tested for outlying means using the Grubbs and Nalimov procedures, for outlying standard deviations using the Cochran test, (both at a 99 % confidence level) as well as for normality of dataset means using the normal probability plot. Standard deviation within (s within ) and between (s between ) laboratories were calculated using one-way ANOVA. The results of these evaluations are shown in Table 13 and Table 14. Table 13: Statistical evaluation of the technically accepted datasets for ERM-EC680k; p: of accepted sets of results; s: standard deviation of dataset means; averages and standard deviations in mg/kg. Element p Outliers Normally Statistical parameters Means Variances distributed Average s s between s within As 10 no no yes Br 7 no yes yes Cd 15 no yes yes Cl 5 no yes approx n.c Cr 5 no no yes Hg 9 no no no Pb 12 no no yes S 6 yes yes no Sb 11 no yes yes Sn 5 no yes no Zn 3 too few data