Evaluation Report proficiency test. DLA 13/ Aflatoxins in Peanut. Waldemar-Bonsels-Weg Ahrensburg, Germany

Transcription

1 DLA Dienstleistung Lebensmittel Analytik GbR Evaluation Report proficiency test DLA 13/2015 Aflatoxins in Peanut Dienstleistung Lebensmittel Analytik GbR Waldemar-Bonsels-Weg Ahrensburg, Germany Coordinator: Dr. G. Wichmann Page 1 of 23

2 Inhalt / Content 1. Introduction Realisation Test material Homogeneity Test Results Evaluation Assigned value Standard deviation Outliers Target standard deviation General model (Horwitz) Precision experiment Value by perception z-score z'-score Quotient Standard uncertainty Results Aflatoxin B1 in µg/kg Total aflatoxins in µg/kg Documentation Primary data Aflatoxin B1 in µg/kg Aflatoxin B2 in µg/kg Aflatoxin G1 in µg/kg Aflatoxin G2 in µg/kg Total aflatoxins in µg/kg Homogeneity Repeatability standard deviation of participants Homogeneity testing before PT Comparison of sample number/test result Analytical methods Index of participant laboratories Index of literature...23 Page 2 of 23

3 1. Introduction The participation in proficiency testing schemes is an essential element of the quality-management-system of every laboratory testing food and feed. The implementation of proficiency tests enables the participating laboratories to prove their own analytical competence under realistic conditions. At the same time they receive valuable data regarding the validity of the particular testing method. The purpose of DLA is to offer proficiency tests for selected parameters in concentrations with practical relevance. Realisation and evaluation of the present proficiency test follows the principles of the DIN EN ISO/IEC (2010) and DIN ISO 13528: Realisation 2.1 Test material The test material with a natural content of aflatoxins is a mixture of various samples of peanut butter with additional app. 10% defatted almonds and app. 10% vegetable oil. Approximately 3 kg of the material were homogenized and then packaged lightproof in portions to approximately 50 g. The portions were numbered chronologically. The material was checked for homogeneity Homogeneity The homogeneity of the DLA-sample was verified by a 5-fold determination of the aflatoxin B1 content with the method ASU 64 LFGB The homogeneity is considered verified with a standard deviation of 10%, see documentation (5.2.2). A repeatability standard deviation of 3 10 % for the matrix peanut butter is given in the corresponding ASU 64 method. The results of the homogeneity test is given in the documentation. The calculation of the repeatability standard deviation of the participants for total aflatoxins was used as an indicator of homogeneity. The result is similar to the repeatability standard deviation of the official method ASU 64 LFGB (corresponds to EN 14123) for peanut butter (13). The repeatability standard deviation of the participants is given in the documentation. In the documentation the portion numbers are graphically assigned to the results of aflatoxin B1. There is no trend recognizable in the results which could suggest inhomogeneity. Page 3 of 23

4 2.2 Test Two portions of test material were sent to every participating laboratory in the 39 th week of The testing method was optional. The tests should be finished at 6 th November 2015 the latest. 2.3 Results The participants submitted their results in standard forms, which have been handed out with the samples (by ). The finally calculated concentrations of aflatoxin B1 and total aflatoxins as average of duplicate determinations of both numbered samples was used for the statistical evaluation. Queried and documented were single results, recovery and the used testing method for aflatoxin B1, B2, G1 and G2. All participants submitted at least one result. Page 4 of 23

5 3. Evaluation 3.1 Assigned value Because the analysed material was no certified reference material the robust mean of the submitted results was used as assigned value X. The distribution of submitted results showed no hint for bimodal distribution or other reasons for a higher variability. 3.2 Standard deviation For comparison to the target standard deviation a robust standard deviation (Sx) was calculated (6). 3.3 Outliers Statistical outliers were determined by Mandel s-h-statistic (significance level: 5%) (5). Detected outliers were stated for information only, when z-score simultaneously was < -2 or > Target standard deviation The target standard deviation of the assigned value is determined according to the following methods General model (Horwitz) The relative target standard deviation in % of the assigned value is calculated according to the following equation. σ (%) = 2 (1-0,5logX) Out of this is calculated the target standard deviation in µg/kg σ = X * σ (%) / 100. For analytes with a content below 120 µg/kg after the evaluation of a lot of mycotoxin-proficiency testing schemes after 1997 Thompson suggested for the target standard deviation a steady value of 22 % (11), analogical σ = 0,22 C / mr with σ = Target standard deviation for contents < 120 µg/kg C = measured value, expressed as a dimensionless mass ratio mr = dimensionless mass ratio. The target standard deviation according to Horwitz/Thompson (11/14/15) was used. Page 5 of 23

6 3.4.2 Precision experiment Using the reproducibility standard deviation σ R and the repeatability standard deviation σ r of a precision experiment the between-laboratories standard deviation ( σ L ) can be calculated : L = R 2 r 2. And then, using the number of replicate measurements n, each participant is to perform, the standard deviation for proficiency assessment is calculated: = L 2 r 2 /n. The precision data of the method ASU 64 LFGB (corresponds to EN 14123) for a comparable aflatoxin content/peanut butter (13) results in a relative target standard deviation of 18,7 % for aflatoxin B1. This target standard deviation is given for information in the evaluation. Because the method for this LVU was optional the target standard deviation according to Horwitz/Thompson (11/14/15) was used Value by perception The target standard deviation for proficiency assessment can be set at a value that corresponds to the level of performance that the coordinator would wish laboratories to be able to achieve (6). For the present evaluation of results the target standard deviation according to Horwitz/ Thompson was applied for aflatoxin B1 and total aflatoxins. 3.5 z-score To assess the results of the participants the z-score is used. It indicates about which multiple of the target standard deviation ( σ ) the result (x) of the participant is deviating from the assigned value (X)(6). Participants z-scores were derived as: z = (x X) / σ ; the requirements for the analytical performance are generally considered as fulfilled if -2 z 2. Page 6 of 23

7 3.6 z'-score The z'-score can be used for the valuation of the results of the participants, in cases the standard uncertainty has to be considered (s. 3.8). The z'-score represents the relation of the deviation of the result (x) of the participant from the respective assigned value (X) to the square root of quadrat sum of the target standard deviation ( σ ) and the standard uncertainty (Ux) (6). Participants z'-scores are derived as: In the following we define the denominator deviation σ '. as the target standard The requirements for the analytical performance are generally considered as fulfilled if -2 z' 2. Page 7 of 23

8 3.6 Quotient S x / Following the Horrat-value the results of a proficiency-test (PT) can be considered convincing, if the quotient of robust standard deviation and target standard deviation does not exceed the value of 2. A value > 2 means an insufficient precision, i.e. the analytical method is too variable, or the variation between the test participants is higher than estimated. Thus the comparability of the results is not given (11). In comparison to the year before for aflatoxin B 1 and for the total aflatoxins a sufficient comparability was achieved: proficiency test Aflatoxin B 1 Quotient S x / σ Total aflatoxins DLA (in nutmeg) 2,0 1,6 DLA (in nutmeg) 2,3 2,3 DLA (in nutmeg) 2,0 2,1 DLA (in peanut) 3,5 3,5 DLA (in nutmeg) 1,9 2,3 DLA (in peanut) 3,0 2,6 DLA (in peanut) 1,9 2,2 Using the target standard deviation of ASU 64 LFGB (corresponds to EN 14123) for a comparable aflatoxin content the quotient is similar. In this respect the results show a sufficient comparability. 3.7 Standard uncertainty The assigned value X has a standard uncertainty u X that depends on the analytical method, differences between the analytical methods used, the test material, the number of participant laboratories and perhaps on other factors. The standard uncertainty ( u X ) for this PT is calculated as follows (6). u X =1,25 S x / p If u X 0,3 the standard uncertainty of the assigned value needs not to be included in the interpretation of the results of the PT (6). The quotient u X / is reported in the characteristics of the test. In the present proficiency test a quotient > 0,3 was received. However the quotient S x / σ and the repeatability standard deviation of the participants gave no reason for an objection. Page 8 of 23

9 4. Results All following tables are anonymized. With the delivering of the evaluation-report the participants are informed about their individual evaluation-number. In the upper table test - the characteristics are listed: Number of results Number of outliers Mean Median Robust mean (X) Robust standard deviation (S x ) Target standard deviation( σ )(Horwitz/Thompson) Target standard deviation (ASU 64 LFGB / (corresponds to EN 14123)) for information Lower limit of target range (X - 2 σ ) Upper limit of target range (X + 2 σ ) Quotient S x / Standard uncertainty u x Quotient u X / Number of results in the target range In the lower table - Laboratories - the individual results of the participating laboratories are listed: Auswertenummer Parameter Evaluation [Einheit / Unit] number Abweichung z-score z-score Hinweis σ (Info) Deviation Remark Page 9 of 23

10 4.1 Aflatoxin B 1 in µg/kg Vergleichsuntersuchung / Proficiency Test Statistic Data Number of results 10 Number of outliers 1 Mean 3,18 Median 3,23 Robust Mean (X) 3,25 Robust standard deviation (S x ) 1,35 Target range: Target standard deviation σ (Horwitz/ Thompson) Target standard deviation ASU (L )for Information 0,714 0,606 lower limit of target range 1,82 upper limit of target range 4,67 Quotient S x / σ Standard uncertainty u x Quotient u x / σ 1,88 0,53 0,74 Results in the target range 8 Percent in the target range 80 6 Ergebnisse / Results Auswertenummer / evaluation number Aflatoxin B1 (µg/kg) obere Grenze upper limit rob. Mittelwert robust mean untere Grenze lower limit Abb. 1: Ergebnisse Aflatoxin B1 Fig. 1: Results aflatoxin B1 Page 10 of 23

11 Ergebnisse der teilnehmenden Institute: Results of Participants: Auswertenummer Evaluation Aflatoxin B1 (µg/kg) Abweichung [µg/kg] Deviation z-score σ z-score (Info) Hinweis Remark number [µg/kg] 1 3,20-0,0462-0,1-0, ,43-0,816-1,1-1,3 4 5,08 1,83 2,6 3,0 5 3,26 0,0138 0,0 0,0 6 2,00-1,25-1,7-2,1 7 0,59-2,66-3,7-4,4 Ausreisser / Outlier 8 4,63 1,38 1,9 2,3 9 2,84-0,411-0,6-0, ,10 0,854 1,2 1,4 12 3,70 0,454 0,6 0, z-score Auswertenummer / evaluation number Abb. 2: Fig. 2: Z-Scores Aflatoxin B1 Z-Scores aflatoxin B1 Page 11 of 23

12 4.2 Total aflatoxins in µg/kg Statistic Data Number of results 13 Number of outliers 0 Mean 5,81 Median 6,00 Robust Mean (X) Robust standard deviation (S x ) 5,80 2,78 Target range: Target standard deviation ( ) nach Horwitz/ Thompson 1,28 Target standard deviation ASU (L ) for Information 1,07 lower limit of target range 3,25 upper limit of target range Quotient S x / σ Standard uncertainty u x Quotient u x / σ 8,36 2,2 1,0 0,76 Results in the target range 8 Percent in the target range 62 σ 12 Ergebnisse / Results Auswertenummer / evaluation number Gesamt- Aflatoxin/ total aflatoxins (µg/kg) obere Grenze upper limit rob. Mittelwert robust mean untere Grenze lower limit Abb. 3: Ergebnisse Gesamt-Aflatoxin Fig. 3: Results total aflatoxins Page 12 of 23

13 Ergebnisse der teilnehmenden Institute: Results of Participants: Auswertenummer Evaluation Geamt-Aflatoxin/ Total Aflatoxins (µg/kg) Abweichung [µg/kg] Deviation z-score σ z-score (Info) number [µg/kg] 1 6,10 0,296 0,2 0,3 2 2,60-3,20-2,5-3,0 3 4,21-1,59-1,2-1,5 4 10,1 4,32 3,4 4,0 5 6,07 0,266 0,2 0,2 6 3,90-1,90-1,5-1,8 7 2,31-3,49-2,7-3,3 8 9,24 3,44 2,7 3,2 9 5,94 0,136 0,1 0,1 10 3,60-2,20-1,7-2,1 11 8,70 2,90 2,3 2,7 12 6,80 1,00 0,8 0,9 13 6,00 0,196 0,2 0,2 Hinweis Remark z-score Auswertenummer / evaluation number Abb. 4: Fig. 4: Z-Scores Gesamt-Aflatoxin Z-Scores total aflatoxins Page 13 of 23

14 5. Documentation 5.1 Primary data Aflatoxin B 1 in µg/kg Teilnehmer/ Participant Ergebnis/ Result DLA- Nr I/ no. I DLA- Nr II/ no. II Ergebnis Probe I/ Result sample I Ergebnis Probe II/ Result sample II Wiederfindung/ Recovery µg/kg µg/kg µg/kg in % 1 3, , , ,58 2,29 without recovery 4 5, ,06 5, , n.a. n.a. n.a. 6 2, ,2 1, , ,69 0,49 8 4, ,62 4,64 9 2, ,91 2,76 97, , ,2 3, , , Bemerkung/ remark n.a. = not analysed Page 14 of 23

15 5.1.2 Aflatoxin B 2 in µg/kg Teilnehmer/ participant Probe/ Probe/ sample A sample B µg/kg µg/kg 1 0,5 0, ,06 1,07 97 Wiederfindung/ recovery 5 0,77 n.a. 6 0,4 0, ,13 0,07 8 1,11 1,13 9 0,55 0,56 90, ,0 0, ,8 0, ,5 0,5 97 Bemerkung/ remark keine Einzelergebnisse/ no individual results mean median standard deviation 0,65 0,61 0,55 0,53 0,068 0,053 n.a. = not analysed Page 15 of 23

16 5.1.3 Aflatoxin G 1 in µg/kg Teilnehmer/ participant Probe/ sample A Probe/ sample B Wiederfindung/ recovery µg/kg µg/kg % 1 2,4 2, ,33 3, ,6 n.a. 6 1,0 0, ,87 0,76 8 2,62 2,64 9 2,03 1,89 70, , ,2 2, Bemerkung/ remark keine Einzelergebnisse/ no individual results mean median standard deviation 2,12 2,12 2,2 2,25 0,84 0,94 n.a. = not analysed Page 16 of 23

17 5.1.4 Aflatoxin G 2 in µg/kg Teilnehmer/ Probe/ Probe/ Wiederfindung/ participant sample A sample B recovery µg/kg µg/kg % 1 0,2 0, ,7 0, ,44 n.a. Bemerkung/ remark keine Einzelergebnisse/ no individual results 6 0,3 0, ,97 0,64 8 0,86 0,88 9 0,62 0,56 41, ,60 0, <0,4 <0, mean median standard deviation 0,59 0,58 0,61 0,64 0,26 0,22 n.a. = not analysed Page 17 of 23

18 5.1.5 Total aflatoxins in µg/kg Teilnehmer/ participants Ergebnis / result Ergebnis Probe I/ result sample I Ergebnis Probe II/ result sample II Wiederfindung/ recovery µg/kg µg/kg µg/kg in % 1 6,1 6,5 5, ,6 2,4 2,7 3 4,21 4,53 3,89 without recovery 4 10,12 10,15 10, ,07 n.a. n.a. n.a. 6 3,9 4,2 3, ,31 2,66 1,96 8 9,24 9,22 9,26 9 5,94 6,11 5, ,6 3,6 n.b. 66,5 11 8,7 12 6,8 6,4 7, ,33 6,65 95 Bemerkung/ remark n.a. = not analysed Page 18 of 23

19 5.2 Homogeneity Repeatability standard deviation of participants The repeatability standard deviations were calculated with the data documented in chapter 5,1. It is 0,51 µg/kg = 8,7 % of X (Total aflatoxins). In the ASU L the relative repeatability standard deviation of 5 % (Aflatoxin B 1 ) for a aflatoxin content x = 5,0 µg/kg was determined for peanut butter (13) Homogeneity testing before PT To verify the homogeneity of the test material aflatoxin B1 was analysed with HPLC in a 5-fold determination. Sample no. Aflatoxin B1 1 4,0 µg/kg 2 3,9 µg/kg 3 3,8 µg/kg 4 4,5 µg/kg 5 3,4 µg/kg mean standard deviation 3,9 0,40 10,1 % Page 19 of 23

20 5.2.3 Comparison of sample number/test result The comparison of the increasing sample-numbers and measured aflotoxin B1-results (*10) shows a sufficient homogeneity. Homogenität/ Homogeneity DLA Nr./ DLA no. Ergebnis*10/ result* Page 20 of 23

21 5.3 Analytical methods Teilnehmer/ participants 1 2 Methode/ method Wiederfindung mit gleicher Matrix/ recovery w ith same matrix Akkreditiert/ accredided 64 LFGB L mod. yes yes Veratox HS Aflatoxin-Kit no yes Sonstige Hinweise/ remarks 3 HPLC no no 4 Determination of aflatoxins in nut with HPLC and cobra cell yes yes Method AFLAREP (r-biopharm) no no P Determination of aflatoxin G1, G2, B1 and B2 as well as ochratoxin A with HPLC Determination: HPLC with IAC. no no Extraction with ACN/H2O (84/16 v/v), measurement with LC-MS/MS, internal standard: 13C17 Aflatoxin B1 yes yes yes yes 9 HPLC-methode with post-column-derivatization with cobra cell and fluorescence detection. no no Determination of aflatoxin B,G with ELISA yes yes 5 g sample, chloroform extraction, cleaning of 0,25 g sample with IAC form 5% methanol in aqua extract. IAC: EASI-EXTRACT from r- biopharm, derivatisation with LCTech UVE. HPLC separation: Nucleosil C18 250x4mm. fluorometric measurement: Ex=360nm, Em= 435nm. Reference material from r- biopharm. * yes no 64 LFGB L mod. yes yes ELISA from R-Biopharm yes yes The recovery was determined: spiking with 5g sample 49 and 68. Dope concentration = 2,5µg each of the 4 aflatoxins/kg. *IAC = Immuno Affinity Column * Further method information from participant no. 11: 2,5g sample 2,5g / 25 ml 0,25g / 5 ml weight: 0,25g / 2 ml 1 : 8 5 g dope solution.:4 x 250 µg/l 0,050 ml/5g = 4 x 2,5 µg / kg 1g NaCl, CHCl3 45ml, H2O 5 ml. 30 min., 20 C 10 min 4600g centrifugation, H2O and CHCl3 combine phase, remove solid parts. 25 ml H2O and CHCl3 phase Rotavap admit to 12,5 ml methanol, 12,5 ml n-heptan, 12,5 ml H2O 10 min 4600g centrifugation N-heptan phase removed, dilute 2,5 ml lower phase with 35 ml H2O Pump through IAC (1,6 ml/min) Elute with 2x 1ml methanol and 1 ml H2O Blow out methanol at 60 C and fill up with H2O to 2 ml. Page 21 of 23

22 6. Index of participant laboratories Teilnehmer/ Participant Ort/ Town Land/ Country Austria France Switzerland Germany Germany Germany Germany Germany Germany Germany Germany Germany Germany [The address data of the participants were deleted for publication of the evaluation report.] Page 22 of 23

23 7. Index of literature 1. DIN EN ISO/IEC 17043:2010; Konformitätsbewertung Allgemeine Anforderungen an Eignungsprüfungen / Conformity assessment General requirements for proficiency testing 2. Verordnung / Regulation 882/2004/EU; Verordnung über amtliche Kontrollen / Regulation on official controls 3. DIN EN ISO/IEC 17025:2005; Allgemeine Anforderungen an die Kompetenz von Prüf- und Kalibrierlaboratorien / General requirements for the competence of testing and calibration laboratories 4. Richtlinie / Directive 1993/99/EU; über zusätzliche Maßnahmen im Bereich der amtlichen Lebensmittelüberwachung / on additional measures concerning the official control of foodstuffs 5. ASU 64 LFGB : Planung und statistische Auswertung von Ringversuchen zur Methodenvalidierung 6. DIN ISO 13528:2009; Statistische Verfahren für Eignungsprüfungen durch Ringversuche / Statistical methods for use in proficiency testing by interlaboratory comparisons 7. The International Harmonised Protocol for the Proficiency Testing of Ananlytical Laboratories ; J.AOAC Int., 76(4), (1993) 8. The International Harmonised Protocol for the Proficiency Testing of Ananlytical Chemistry Laboratories ; Pure Appl Chem, 78, (2006) 9. Evaluation of analytical methods used for regulation of food and drugs;w. Horwitz; Analytical Chemistry, 54, (1982) 10.A Horwitz-like funktion describes precision in proficiency test; M. Thompson, P.J. Lowthian; Analyst, 120, (1995) 11.Protocol for the design, conduct and interpretation of method performance studies; W. Horwitz; Pure & Applied Chemistry, 67, (1995) 12.Recent trends in inter-laboratory precision at ppb and sub-ppb concentrations in relation to fitness for purpose criteria in proficiency testing; M. Thompson; Analyst, 125, (2000) 13.ASU 64 LFGB (Jan. 2012): Bestimmung von Aflatoxin B 1 und der Summe von Aflatoxin B 1, B 2, G 1 und G 2 in Erdnüssen, Pistazien, Feigen und Paprikapulver (: EN 14123:2007, Foodstuffs. Determination of aflatoxin B1 and the sum of aflatoxin B1, B2, G1 and G2 in hazelnuts, peanuts, pistachios, figs, and paprika powder. High performance liquid chromatographic method with post-column derivatisation and immunoaffinity column cleanup 14.EG-VO zur Festlegung der Probenahmeverfahren und Analysemethoden für die amtliche Kontrolle des Mykotoxingehalts von Lebensmitteln (COMMISSION REGULATION (EC) No 401/2006 laying down the methods of sampling and analysis for the official control of the levels of mycotoxins in foodstuffs) 15.EU-VO 519/2014 zur Änderung der Verordnung (EG) Nr. 401/2006 hinsichtlich der Probenahmeverfahren für große Partien, Gewürze und Nahrungsergänzungsmittel, der Leistungskriterien für die Bestimmung von T-2-Toxin, HT-2- Toxin und Citrinin sowie der Screening-Methoden für die Analyse (v. 16. Mai 2014) (COMMISSION REGULATION (EU) No 519/2014 amending Regulation (EC) No 401/2006 as regards methods of sampling of large lots, spices and food supplements, performance criteria for T-2, HT-2 toxin and citrinin and screening methods of analysis) Page 23 of 23