CHEK Proficiency study 664. Solvents in adhesive. Date 3 July 2017 Version 1. Report number CHEK Final CHEK proficiency study July 2017

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1 CHEK Proficiency study 664 Solvents in adhesive Date 3 July 2017 Version 1 Status Final Report number CHEK page 0

2 Colophon Number 664 Name Solvents in adhesive Contact Author Authorization 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 Krista Bouma (operational manager) page 1

3 Content 1 Introduction 1 2 Time-table 1 3 Sample preparation 1 4 Statistical results Benzene in adhesive samples uniform level Toluene in adhesive samples uniform level Chloroform in adhesive samples uniform level Summary solvents in adhesive 6 5 Methods of analysis 6 6 Remarks from participants 7 7 List of invited participants 7 8 Explanation of graphical presentations 8 9 Tables and graphical presentations 9-16 page 0

4 1 Introduction Proficiency study 664 as directed by the CHEK working group concerned the investigation of solvents benzene (CAS no ), toluene (CAS no ) and chloroform (CAS no ) contents of two adhesive samples. To get an impression of the performance of the quantitative determination of solvents in adhesive 21 laboratories were invited to join this proficiency study. 2 Time-table Homogeneity of samples 21 April 2017 Distribution of samples 15 May 2017 Deadline for the production of results 16 June 2017 Final report 3 July Sample preparation Adhesive samples A and B uniform level 500 g adhesive (PVC glue (solution of vinyl polymers in a mixture of solvents, not containing benzene, toluene and chloroform) was obtained from the local market. 1.4 g benzene (CAS no ), 1.4 g toluene (CAS no ) and 1.4 g chloroform (CAS no ) were added to the adhesive and thoroughly minced in a plastic container by shaking for 1 hour in a powder blender. After homogenisation approximately 80 sub-samples of about 5 g were prepared in plastic sachets. Homogeneity The homogeneity was checked by the laboratory of the Netherlands Food and Consumer Product Safety Authority, Groningen by randomly selected samples for the determination of the benzene (CAS no ), toluene (CAS no ) and chloroform (CAS no ) contents (see table II). The average contents were 0.281% m/m benzene, 0.373% m/m toluene and 0.265% m/m chloroform. Stability The stability was not checked yet. Samples are stored at room temperature (+20 C) in the dark until shipment. Samples are expected to be stable during the period between the distribution of samples and the deadline for the production of results. Instructions Samples were stored at room temperature (+20 C) in the dark until shipment. To each of the participants two samples coded A and B were sent. Participants were instructed to store the samples at room temperature in a dark place and to mix each samples before analyses. 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. Performance The performance of a determination is assessed as following: satisfactory = maximum allowable RSD R (including uncertainty) 2 questionable = 2< maximum allowable RSD R (including uncertainty) <3 unsatisfactory = maximum allowable RSD R (including uncertainty) 3 Target standard deviation For the target standard deviation in most of the cases Horwitz shows a good maximum allowable RSD R but does not include different levels of complexity of analytical method like migrations. If the target standard deviation is not chosen realistically the interpretation satisfactory, questionable and unsatisfactory is not valid. In this study it is more adequate to use the reproducibility standard deviation (s R ) as target standard deviation to calculate the Z-scores and maximum allowable RSD R. This proficiency study provides precision data for this specific analysis. page 2

6 4.1 Benzene in adhesive uniform level Benzene in adhesive samples A and B 21 labs : Results of all laboratories 19 labs : Results of laboratories 3 and 9 are rejected by the Grubbs test 21 labs 19 labs Unit Average % m/m Repeatability standard deviation (s r ') % m/m Repeatability rel. standard deviation (RSD r ') % Reproducibility standard deviation (s R ') % m/m Reproducibility rel. standard deviation (RSD R ') % Acceptable value for (RSD R ') % Repeatability r' % m/m Reproducibility R' % m/m Summary benzene in adhesive samples A and B The results of this and earlier performed proficiency studies are summarised in the table below. Prof. study Number of labs Average % m/m RSD R % Acceptable RSD R % Conclusions benzene in adhesive samples A and B The performance of the determination of benzene in adhesive is satisfactory. The results approach a normal distribution. No Cochran outliers are found in the datasets of sample A and B. The results of laboratories 3 and 9 are marked as outliers by the Grubbs test indicating systematic errors and are rejected. The absolute Z-scores of laboratories 3 and 9 are greater than 3 and suggest poor performance in terms of accuracy. page 3

7 4.2 Toluene in adhesive uniform level Toluene in adhesive samples A and B 21 labs : Results of all laboratories 21 labs Unit Average % m/m Repeatability standard deviation (s r ) % m/m Repeatability rel. standard deviation (RSD r ) 4.2 % Reproducibility standard deviation (s R ) % m/m Reproducibility rel. standard deviation (RSD R ) 18 % Acceptable value for (RSD R ) 18 % Repeatability r % m/m Reproducibility R 0.14 % m/m Summary toluene in adhesive samples A and B The results of this and earlier performed proficiency studies are summarised in the table below. Prof. study Number of labs Average % m/m RSD R % Acceptable RSD R % Conclusions toluene in adhesive samples A and B The performance of the determination of toluene in adhesive is satisfactory. The results approach a normal distribution. No Cochran or Grubbs outliers are found in the datasets of sample A and B. page 4

8 4.3 Chloroform in adhesive uniform level Chloroform in adhesive samples A and B 17 labs : Results of all laboratories 17 labs Unit Average % m/m Repeatability standard deviation (s r ') % m/m Repeatability rel. standard deviation (RSD r ') 4.4 % Reproducibility standard deviation (s R ') % m/m Reproducibility rel. standard deviation (RSD R ') 23 % Acceptable value for (RSD R ) 23 % Repeatability r' % m/m Reproducibility R' 0.18 % m/m Summary chloroform in adhesive samples A and B The results of this and an earlier performed proficiency study are summarised in the table below. Prof. study Number of labs Average % m/m RSD R % Acceptable RSD R % Conclusions chloroform in adhesive samples A and B The performance of the determination of chloroform in adhesive is satisfactory. The results are drawn from a normal distribution. No Cochran or Grubbs outliers are found in the datasets of sample A and B. page 5

9 4.4 Summary solvents in adhesive The results of this proficiency study are summarised in the table below. Number of accepted results Average [% m/m] RSD R [%] Benzene Toluene Chloroform Method of analysis Lab GC MS FID Extraction solvent Samples/year 1 x x ACE x x ACE x x x x MeOH - 5 x x x x DMI x x ACE 0 8 x x x MTBE < x x x H (for benzene and toluene) ca. 30 ACE/THF (for chloroform) 11 x x ACE x x ACE x x none x x DMF x x MTBE - 16 x x MTBE - 17 x x x x ACE x x DCM x x x ACE - ACE = acetone DCM = dichloromethane DMF = dimethylformamide H = hexane MeOH = methanol MTBE = methyl-tert-butyl ether THF = tetrahydrofuran page 6

10 6 Remarks from participants Lab 1 Lab 5 A series of test result shows that the concentration of the compounds is decreasing as time goes by when these samples were stored at the condition according to the test instruction. Our method reports accuracy to the second decimal digit. 7 List of invited participants Europe Cyprus - 1 participant Germany - 8 participants Italy - 1 participant The Netherlands - 1 participant Spain 1 participant Outside Europe Bangladesh 1 participant Brazil 1 participant China - 2 participants Hong Kong - 1 participant Korea - 1 participant Taiwan 1 participant Turkey 1 participant Vietnam 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: Z x Where: x = an (average) laboratory result. = the average result of all laboratories (calculated exclusive outliers). σ = an assigned precision standard or fixed target value. As a fixed target value the maximum allowable standard deviation is used at a given concentration-level (in this study s R is used, see explanation on page 2). 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 664: benzene, toluene and chloroform in adhesive [% m/m] Lab Benzene Toluene Chloroform Method Sample A Sample B Z-score Sample A Sample B Z-score Sample A Sample B Z-score ACE-GC_MS ACE-GC-MS (2) 0.38 (2) GC-MS MeOH-GC-MS GC-MS DMI-GC-MS ACE-GC-MS GC (2) (2) MTBE-GC-MS H or ACE/THF-GC-FID or MS ACE-GC-MS ACE-GC-MS GC-MS DMF-GC-FID MTBE-GC-MS MTBE-GC-MS GC-MS ACE-GC-MS DCM-GC-MS GC ACE-GC-MS σ (1) = Cochran outlier (2) = Grubbs outlier (3) = Results removed by hand page 9

13 Table II; Homogeneity of samples for solvents in adhesive [% m/m] Sample no 1st analysis Benzene Toluene Chloroform 2nd analysis 1st analysis 2nd analysis 1st analysis 2nd analysis average t-test t samples t critical,95% Homogeneity S between S within S R S between / S between /S R Based on the t-test there is no significant difference between the averages of 1st and the 2nd analysis of benzene and chloroform and there is a slight difference between the average of 1st and the 2nd analysis of toluene. The ratio of the sampling standard deviation and the target value for all solvents is higher than the recommended value of 0.3. The ratio of the sampling standard deviation and the reproducibility standard deviation S R chloroform is lower than the recommended value of 0.3. Samples are regarded as sufficient homogeneous for the purpose of the proficiency study. S between = between samples standard deviation S within = within samples standard deviation σ = target value calculated from the Horwitz equation or assigned precision standard. = reproducibility standard deviation S R page 10

14 Graphical presentations benzene in adhesive Figure Ia; Saw-tooth plot benzene in adhesive, calculated with target s. Figure Ib; Saw-tooth plot benzene in adhesive, calculated with group s (exclusive laboratories 3 and 9). page 11

15 Figure II; Youden plot benzene in adhesive. Figure III; Z-score benzene in adhesive. page 12

16 Graphical presentations toluene in adhesive Figure IVa; Saw-tooth plot toluene in adhesive, calculated with target s. Figure IVb; Saw-tooth plot toluene in adhesive, calculated with group s. page 13

17 Figure V; Youden plot toluene in adhesive. Figure VI; Z-score toluene in adhesive. page 14

18 Graphical presentations chloroform in adhesive Figure VIIa; Saw-tooth plot chloroform in adhesive, calculated with target s. Figure VIIb; Saw-tooth plot chloroform in adhesive, calculated with group s. page 15

19 Figure VIII; Youden plot chloroform in adhesive. Figure IX; Z-score chloroform in adhesive. page 16