FAPAS Report 2095 Sulphur Dioxide in Apricots September-October 2012 Page 1 of 23
PARTICIPANT LABORATORY NUMBER Participants can log in to FAPAS SecureWeb at any time to obtain their for this proficiency test. Laboratory numbers are displayed in SecureWeb next to the download link for this report. REPORT INTEGRITY Since 2006 all FAPAS reports have been distributed as Adobe Certified Document Services (CDS) Adobe PDF documents [1]. The use of Adobe CDS allows the PDF files to certify that the author of the report is FAPAS and that the document has not been altered in anyway. A blue ribbon and information bar indicates this validation when the document is opened using Adobe Reader v7 or later. Hard copies of FAPAS reports can never incorporate this level of integrity and consequently when a FAPAS report is printed a watermark, stating that printed copies are not controlled, appears on every page. End users of FAPAS reports should ensure that either the opened PDF file displays a valid FAPAS digital signature or that the content of any hard copy exactly matches the content of a PDF file that displays a valid FAPAS digital signature. QUALITY SYSTEMS FAPAS is accredited by UKAS as complying with the requirements of ISO/IEC 17043:2010 [2]. The Food and Environment Research Agency is an ISO 9001 certified organisation. 0009 PT Whereas this report has been produced in good faith and in accordance with best industry practice, neither The Food and Environment Research Agency nor the Secretary of State for Environment, Food and Rural Affairs accepts any liability whatsoever as to the application or use of the information contained therein. Crown Copyright 2012 Page 2 of 23
SUMMARY 1. The test material for FAPAS proficiency test 2095 was dispatched in September 2012. Each participant received an apricot slurry test material to be analysed for sulphur dioxide. 2. An assigned value (x a ) was determined for sulphur dioxide and in conjunction with the standard deviation for proficiency (σ p ) was used to calculate a z-score for each result. 3. Results for this proficiency test are summarised as follows: analyte assigned value, x a mg/kg number of scores, z 2 total number of scores % z 2 Sulphur Dioxide 1483 119 157 76 4. Surplus test materials are available for sale, see APPENDIX II. Page 3 of 23
CONTENTS 1. INTRODUCTION 5 1.1. Proficiency Testing 5 2. TEST MATERIAL 5 2.1. Preparation 5 2.2. Homogeneity 5 2.3. Dispatch 5 3. RESULTS 5 4. STATISTICAL EVALUATION OF RESULTS 6 4.1. Calculation of the Assigned Value, x a 6 4.2. Standard Deviation for Proficiency, σ p 6 4.3. Individual z-scores 6 5. INTERPRETATION OF SCORES 7 6. REFERENCES 7 TABLES Table 1: Results and z-scores 8 Table 2: Participants Comments 15 Table 3: Assigned Values and Standard Deviations for Proficiency 15 Table 4: Number and Percentage of z-scores where z 2 15 FIGURES Figure 1: z-scores for Sulphur Dioxide 16 APPENDICES APPENDIX I: Analytical Methods Used by Participants 17 APPENDIX II: FAPAS SecureWeb, Protocol and Contact Details 23 Page 4 of 23
1. INTRODUCTION 1.1. Proficiency Testing Proficiency testing aims to provide an independent assessment of the competence of participating laboratories. Together with the use of validated methods, proficiency testing is an essential element of laboratory quality assurance. Further details of the FAPAS protocols [3, 4]. 2. TEST MATERIAL proficiency testing scheme are available in our 2.1. Preparation Preparation of the samples for this proficiency test was sub-contracted to a laboratory meeting the quality requirements of the scheme s accreditation [2]. The apricot slurry was prepared from dried apricots and water. Sulphur dioxide was spiked into the test material by adding sodium metabisulphite into the test material ingredients. Samples were stored at -20 C until dispatch. 2.2. Homogeneity To test for homogeneity, randomly selected test materials were analysed in duplicate. Testing was sub-contracted to a laboratory meeting the quality requirements of the scheme s accreditation [2]. These data showed sufficient homogeneity and were not included in the subsequent calculation of the assigned values. 2.3. Dispatch The start date was 11 September 2012. Test materials were sent to 160 participants. 3. RESULTS The instructions for reporting results were as follows: Determine the level of sulphur dioxide as (SO 2 ) present in the test material in mg/kg. Do not report your result as a salt. Results were submitted by 157 participants (98%) before the closing date for this test, 23 October 2012. Each participant was given a, assigned in order of receipt of results. The reported analyte concentrations are given in Table 1. Participants comments are given in Table 2. The analytical methods used by each participant are summarised in APPENDIX I. Page 5 of 23
4. STATISTICAL EVALUATION OF RESULTS The results submitted by participants were statistically analysed in order to provide an assigned value for sulphur dioxide. The assigned value was then used in combination with the standard deviation for proficiency, σ p, to calculate a z-score for each result. The procedure follows that recommended in the IUPAC International Harmonised Protocol for the Proficiency Testing of Analytical Chemistry Laboratories [5]. Further details on the procedure followed can be found in the relevant protocols [3, 4]. 4.1. Calculation of the Assigned Value, x a The assigned value, x a, for sulphur dioxide was derived from the consensus of the results submitted by participants. The following results were excluded from the calculation of the assigned value: i) results reported as approximately 10, 100 or 1000 greater or smaller than the majority of submitted results (as these were considered to be reporting errors). For sulphur dioxide, this procedure was straightforward and the robust mean was chosen as the assigned value. The assigned value for sulphur dioxide is shown in Table 3. 4.2. Standard Deviation for Proficiency, σ p The standard deviation for proficiency, σ p, was set at a value that reflects best practice for the analyses in question. For sulphur dioxide, σ p was derived from the appropriate form of the Horwitz equation [6]. The value for σ p used to calculate z-scores from the reported results of this test is given in Table 3. 4.3. Individual z-scores Participants z-scores were calculated as: ( x z = σ p x a ) where x = the participant s reported result, x a = the assigned value and σ p = the standard deviation for proficiency. Participants z-scores for sulphur dioxide are given in Table 1 and shown as a histogram in Figures 1. It is possible for the z-scores published in this report to differ slightly from the z-score that can be calculated using the formula given above. These differences arise from the necessary rounding of the actual assigned value and standard deviation for proficiency prior to their publication in Table 3. The number and percentage of z-scores in the range -2 z 2 for sulphur dioxide are given in Table 4. Page 6 of 23
5. INTERPRETATION OF SCORES In normal circumstances, over time, about 95% of z-scores will lie in the range -2 z 2. Occasional scores in the range 2 < z <3 are to be expected, at a rate of 1 in 20. Whether or not such scores are of importance can only be decided by considering them in the context of the other scores obtained by that laboratory. Scores where z >3 are to be expected at a rate of about 1 in 300. Given this rarity, such z-scores very strongly indicate that the result is not fit-for-purpose and almost certainly requires investigation. The consideration of a set or sequence of z-scores over time provides more useful information than a single z-score. Examples of suitable methods of comparison are provided in the IUPAC International Harmonised Protocol for the Proficiency Testing of Analytical Chemistry Laboratories [5]. 6. REFERENCES 1 Adobe Certified Document Services, http://www.adobe.com/security/partners_cds.html, accessed 08/05/2012. 2 ISO/IEC 17043:2010, Conformity assessment General requirements for proficiency testing. 3 FAPAS, 2012, Protocol for Proficiency Testing Schemes, Part 1 Common Principles, Version 3, Issued January 2012. 4 FAPAS, 2012, Protocol for Proficiency Testing Schemes, Part 2 FAPAS, Version 2, Issued January 2012. 5 Thompson, M., Ellison, S.L.R. and Wood, R., 2006, The International Harmonised Protocol for the Proficiency Testing of Analytical Chemistry Laboratories, Pure Appl. Chem., 78, No. 1, 145 196. 6 Thompson, M., 2000, Recent trends in inter-laboratory precision at ppb and sub-ppb concentrations in relation to fitness for purpose criteria in proficiency testing, Analyst, 125, 385-386. Page 7 of 23
Table 1: Results and z-scores analyte Sulphur Dioxide assigned value 1483 mg/kg result mg/kg z-score 001 1572 1.1 002 1420-0.8 003 1745.0 3.3 004 1514.90 0.4 005 1536 0.7 006 876-7.7 007 1411-0.9 008 1580 1.2 009 1469-0.2 010 1434-0.6 011 1205-3.5 012 1550 0.9 013 1660 2.2 014 1473-0.1 015 1544 0.8 016 137-17.0 017 1402-1.0 018 1621 1.7 019 1570 1.1 020 1658 2.2 021 1558.96 1.0 022 1500 0.2 023 1560 1.0 024 1616 1.7 025 1549 0.8 z-scores outside z >2 are shown in bold, see Section 5 Page 8 of 23
Table 1 (continued): Results and z-scores analyte Sulphur Dioxide assigned value 1483 mg/kg result mg/kg z-score 026 1565 1.0 027 889.139-7.5 028 1465.5-0.2 029 1715 2.9 030 1402-1.0 031 1482 0.0 032 918-7.1 033 1516.40 0.4 034 1529 0.6 035 1480 0.0 036 1281.90-2.5 037 1288-2.5 038 1358-1.6 039 665-10.3 040 1600 1.5 041 1590 1.4 042 1500 0.2 043 1638.19 2.0 044 1536 0.7 045 1389.11-1.2 046 1580 1.2 047 1100.8-4.8 048 1306-2.2 049 1426-0.7 050 1561.67 1.0 z-scores outside z >2 are shown in bold, see Section 5 Page 9 of 23
Table 1 (continued): Results and z-scores analyte Sulphur Dioxide assigned value 1483 mg/kg result mg/kg z-score 051 1767.32 3.6 052 1280-2.6 053 1259-2.8 054 1504 0.3 055 1518.40 0.5 056 1368-1.5 057 225-15.9 058 1718 3.0 059 1478-0.1 060 1479.6 0.0 061 1405-1.0 062 1484 0.0 063 1220-3.3 064 1405.14-1.0 065 1136-4.4 066 1422-0.8 067 1492 0.1 068 1364.13-1.5 069 2092.2 7.7 070 1440.72-0.5 071 1800 4.0 072 1440-0.5 073 1596.7 1.4 074 1456.75-0.3 075 1360-1.6 z-scores outside z >2 are shown in bold, see Section 5 Page 10 of 23
Table 1 (continued): Results and z-scores analyte Sulphur Dioxide assigned value 1483 mg/kg result mg/kg z-score 076 1297-2.3 077 1524 0.5 078 1531.27 0.6 079 1391-1.2 080 1420.96-0.8 081 1552.96 0.9 082 1436.79-0.6 083 1544.601 0.8 084 1737.6 3.2 085 1392-1.1 086 1381-1.3 087 1519 0.5 088 1340-1.8 089 1468-0.2 090 1503.96 0.3 091 63.75-18.0 092 1498 0.2 093 1452.4-0.4 094 1430-0.7 095 1490 0.1 096 1829.3 4.4 097 1731.26 3.1 098 1577.42 1.2 099 1430-0.7 100 1560 1.0 z-scores outside z >2 are shown in bold, see Section 5 Page 11 of 23
Table 1 (continued): Results and z-scores analyte Sulphur Dioxide assigned value 1483 mg/kg result mg/kg z-score 101 1541.3 0.7 102 1430-0.7 103 1535.1 0.7 104 1690 2.6 105 758.5-9.2 106 1578.36 1.2 107 1607.09 1.6 108 1508 0.3 109 1580 1.2 110 1510 0.3 111 1580 1.2 112 1600 1.5 113 1362-1.5 114 1383-1.3 115 1255-2.9 116 1582.12 1.3 117 1570 1.1 118 2250 9.7 119 1575 1.2 120 1410-0.9 121 1360-1.6 122 1506 0.3 123 1578.0 1.2 124 1512 0.4 125 1762 3.5 z-scores outside z >2 are shown in bold, see Section 5 Page 12 of 23
Table 1 (continued): Results and z-scores analyte Sulphur Dioxide assigned value 1483 mg/kg result mg/kg z-score 126 1356-1.6 127 1360-1.6 128 1550 0.9 129 1590 1.4 130 1340-1.8 131 1536 0.7 132 1431-0.7 133 1568 1.1 134 1502 0.2 135 1604 1.5 136 1700 2.7 137 1493.2 0.1 138 1327.80-2.0 139 1511.81 0.4 140 1408.7-0.9 141 1004-6.1 142 153.8-16.8 143 1275-2.6 144 1390-1.2 145 1592 1.4 146 1447.8-0.4 147 1366.83-1.5 148 1644 2.0 149 1533.38 0.6 150 1515 0.4 z-scores outside z >2 are shown in bold, see Section 5 Page 13 of 23
Table 1 (continued): Results and z-scores analyte Sulphur Dioxide assigned value 1483 mg/kg result mg/kg z-score 151 1600 1.5 152 1556 0.9 153 1608 1.6 154 1455-0.4 155 1443.98-0.5 156 1471.7-0.1 157 786-8.8 z-scores outside z >2 are shown in bold, see Section 5 Page 14 of 23
Table 2: Participants Comments participant number comments 064 The sample be placed in the freezer immediately on receipt then kept there until analysis, and homogenised the whole material before taking a representative sample. 066 Method used: Monier-Williams 125 recovery was counted in result 134 Recovery Factor of 0.946 applied to result comments are as submitted by participants Table 3: analyte Assigned Values and Standard Deviations for Proficiency data points, n assigned value, x a, mg/kg uncertainty, u standard deviation for proficiency, σ p, units Sulphur Dioxide 155 1483 10.9 Horwitz [6] 79.0 Table 4: Number and Percentage of z-scores where z 2 analyte number of scores where z 2 total number of scores % z 2 Sulphur Dioxide 119 157 76 Page 15 of 23
z-score 10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0-1.0-2.0-3.0-4.0-5.0-6.0-7.0-8.0-9.0-10.0 118 69 96 71 51 125 3 84 97 58 29 136 104 13 20 148 43 18 24 153 107 135 151 112 40 73 145 129 41 116 111 109 8 46 106 123 98 119 1 117 19 133 26 50 100 23 21 152 81 128 12 25 83 15 101 131 5 44 103 149 78 34 77 87 55 33 150 4 124 139 110 108 122 54 90 134 42 22 92 137 67 95 62 31 35 60 59 14 156 9 89 28 74 154 93 146 155 70 72 82 10 132 102 99 94 49 2 80 66 7 120 140 64 61 30 17 85 79 144 45 114 86 56 147 68 113 127 121 75 38 126 130 88 138 48 76 37 36 52 143 53 115 63 11 65 47 141 6 27 32 157 105 39 57 142 16 91 Figure 1: z-scores for Sulphur Dioxide Laboratory Number 1641 mg/kg 1483 mg/kg 1325 mg/kg Page 16 of 23
APPENDIX I: Analytical Methods Used by Participants Methods are tabulated according to the information supplied by participants, but some responses may have been combined or edited for clarity. Accredited Method Used yes 001 002 004 005 010 011 012 013 018 019 024 025 026 028 029 030 031 032 036 038 041 042 043 046 049 050 051 052 054 056 057 058 059 061 063 067 068 069 073 075 079 080 081 082 089 090 093 094 097 098 099 101 103 104 107 108 109 110 111 114 115 116 118 119 120 121 123 124 126 127 130 131 133 134 136 138 139 140 142 147 148 151 153 154 155 156 157 no 003 008 014 015 016 017 020 021 023 027 037 039 040 044 045 048 053 055 064 065 066 070 071 077 078 083 084 088 091 092 096 102 129 132 135 143 144 145 152 Reference 1983 157 1987 078 1989 133 1990 104 1998 040 123 131 1999 092 2000 055 2003 115 118 2006 051 2009 126 2010 098 116 2011 103 129 139 AFNOR 023 AFNOR 1998 NF EN 1988-1 084 Analytical Chemistry 1988 029 066 AOAC Methods 1990 104 AOAC Official Methods 013 014 099 AOAC Official Methods 962.16 037 054 073 101 111 134 AOAC Official Methods 963.20 153 AOAC Official Methods 990.28 051 090 109 116 132 154 156 AOAC Official Methods 990.31 056 Page 17 of 23
Reference (continued) AOAC Official Methods 1984 14 20. 123-20.125 048 AOAC Official Methods 1986 14/7 62 082 AOAC Official Methods 1990 027 AOAC Official Methods 1990 1 1157, 1158 069 AOAC Official Methods 1990 1 93-95 068 AOAC Official Methods 1994 097 AOAC Official Methods 2000 041 AOAC Official Methods 2000 II / 17 29-30 004 AOAC Official Methods 2003 151 AOAC Official Methods 2005 17 29-31 043 AOAC Official Methods 2005 18th 038 064 081 AOAC Official Methods 2009 011 AOAC Official Methods 2011 028 119 BS EN 1998 1: 152 dionex 096 DM 03/02/1989 1989 133 EN 1988 029 030 075 EN 2001 135 EN 2001 1988-1 143 FAO Food and Nutrition Paper 1986 14/7 61-64 FAO Food and Nutrition Paper 1986 14/7 62 Food Additives Analysis in Food 2000 2nd 71 036 082 127 Gazetta Ufficiale 1989 052 Gazetta Ufficiale 1989 D.M. 03/02/1989 031 Gazetta Ufficiale 1989 S.O.G.U.168 del 20/07/1989 99 065 GB/T 5009.34 2003 115 118 in house 021 058 083 121 129 131 iodometric method 053 ISO 1981 050 ISO 1981 5522 046 124 J. AOAC Int. 1986 69 827 045 088 J. Food Science 2005 067 Japanese law 057 Page 18 of 23
Reference (continued) JORF 1987 13003 010 KFDA 2011 103 LFRA Analytical Methods 002 LI00.882-1 2010 098 LMBG Method 019 063 094 120 LMBG Method 1998 L00.00-46/1 012 LMBG Method 1999 024 025 136 LMBG Method 1999 64 LFGB 00.00-46/1 1-5 026 LMBG Method 1999 00.00-46/2-032 LMBG Method 1999 L 00.00-46/1 107 MEBAK 2002 Band II 139 108 modified method Monnier williams 1987 078 nation official method 1983 157 NEN-EN 1988-1 1998 040 ofiical method of Japan 042 OIV 2009 126 Pearson's Composition and Anal 1976 30-31 Pearson's Composition and Anal 1991 9th Ed 73-74 080 Ph.Eur 7.5 138 PN-90/A-75101/23 1990 I 1-4 070 Reith Willems 1999 092 SLMB 1992 110 SOP 155 TFDA 142 049 061 TFDA NO.:1011902184 2011 139 The Japan Pharmaceutical Society 2000 055 UNI EN 1988-1:1998 1998 123 Time (hrs) sample allowed to defrost before analysis. none 004 045 068 070 080 093 097 103 151 <1 012 021 028 032 036 038 041 048 050 051 054 058 066 069 073 079 081 084 107 114 120 127 133 135 138 139 140 142 156 1 - <1.5 016 020 037 049 056 077 082 090 101 102 111 116 136 Page 19 of 23
Time (hrs) sample allowed to defrost before analysis. (continued) 1.5 - <2 013 027 029 030 043 065 104 121 123 126 129 2 - <5 002 005 031 042 055 061 067 088 092 108 130 134 152 154 155 157 5 - <10 018 019 064 078 overnight 014 015 023 024 026 039 040 046 053 057 071 075 091 094 110 115 124 131 143 147 Sample Weight (g) <1 010 021 051 113 129 1 - <2 036 039 043 055 058 097 099 116 118 127 139 154 2 - <5 002 015 017 026 029 042 049 054 056 057 084 090 103 114 115 121 124 126 130 131 135 140 157 5 - <10 012 013 014 016 018 020 023 028 030 031 032 037 040 046 052 053 066 073 075 078 079 081 082 093 098 101 102 104 108 110 119 120 132 133 136 142 143 147 151 152 10 - <25 001 008 019 027 038 044 045 050 059 065 067 070 071 077 092 094 111 148 25 - <50 003 024 025 041 061 068 069 080 083 088 091 096 107 134 138 145 155 50 004 005 011 048 064 123 156 Modified Monier-Williams Method e.g. AOAC 962.16 used yes 001 002 003 004 005 011 012 013 014 016 018 020 021 023 024 025 027 037 038 039 041 043 044 048 054 061 064 066 067 071 073 078 082 084 093 101 103 104 107 111 116 119 120 123 132 134 135 142 147 151 152 156 157 no 010 015 026 028 029 030 031 032 040 042 045 046 049 050 051 053 055 056 057 058 065 069 070 075 077 079 080 081 083 088 091 092 096 097 102 108 109 114 115 118 121 126 127 129 130 131 133 138 139 140 143 145 153 154 155 Page 20 of 23
Total Refluxing Time - once steady refluxing is reached (mins) <10 012 020 029 030 044 045 071 077 119 131 152 10 - <20 003 057 067 078 088 114 127 130 142 157 20 - <30 015 027 042 059 070 101 102 108 115 120 139 30 - <40 002 005 010 036 049 055 061 079 082 092 135 140 40 - <60 019 031 037 039 064 065 084 110 126 133 138 155 60 - <80 001 016 018 038 040 048 054 068 069 090 094 134 80 - <100 011 013 028 107 129 143 100 004 008 014 021 023 024 026 041 043 046 051 066 073 081 083 093 097 098 099 103 104 111 116 123 132 136 147 151 154 156 Basis of other sulphur dioxide method used distillation into H2O2 002 003 004 008 010 014 015 016 018 019 020 023 028 031 036 037 038 039 040 041 043 044 046 048 049 050 051 054 055 056 057 059 061 064 065 066 070 077 079 084 092 093 094 096 097 101 103 108 109 110 111 113 116 119 120 123 124 126 129 130 132 134 135 136 138 139 142 143 147 148 151 152 154 155 156 distillation (other) 024 045 053 071 088 091 102 104 127 131 acidify with HCl 003 004 008 018 021 023 028 029 030 031 037 038 040 050 051 053 054 058 065 068 069 071 073 078 084 088 091 097 101 102 103 104 111 116 119 123 132 138 143 148 151 154 156 acidification (other) 002 010 020 045 059 061 077 079 092 110 120 126 127 130 131 134 147 152 titration with iodine 029 030 045 058 071 080 088 091 102 titration (other) 027 052 053 054 067 titration with sodium hydroxide 002 003 004 005 008 010 014 016 018 021 023 025 026 028 031 037 038 040 042 050 051 057 059 061 065 077 079 081 084 092 093 097 101 103 108 110 111 114 116 119 120 123 126 132 133 134 138 140 143 144 145 147 151 152 154 155 156 157 Page 21 of 23
Basis of other sulphur dioxide method used (continued) enzymatic method 017 032 063 075 spectrophotometric 032 075 098 104 121 127 131 UV 115 Recovery Correction Included yes 004 017 020 026 036 038 043 064 067 069 071 082 096 102 115 129 134 135 148 no 001 002 003 005 008 010 011 012 013 014 015 016 018 019 021 023 024 025 027 028 029 030 031 032 037 039 040 041 042 044 045 046 048 049 050 051 052 053 054 055 056 057 058 061 065 066 068 070 073 075 077 078 079 080 081 083 084 088 090 091 092 093 094 097 098 099 101 103 104 107 108 109 110 111 114 116 118 119 120 121 123 124 126 127 130 131 132 133 138 139 140 142 143 144 147 151 152 154 155 156 157 Source of recovery data reference material 015 018 021 027 032 042 046 053 068 069 077 082 115 119 151 sample spiked with metabisulphate 004 017 020 036 037 038 043 055 056 058 064 067 080 081 088 092 094 096 102 103 110 123 129 134 135 148 157 HMS 026 051 098 156 laboratory riferiment material 052 Na2SO3 075 none 048 sodium sulphite 003 040 049 061 071 079 Page 22 of 23
APPENDIX II: FAPAS SecureWeb, Protocol and Contact Details 1. FAPAS SECUREWEB Access to the secure area of our website is only available to participants in our proficiency tests. Please contact us if you require a UserID and Password. FAPAS SecureWeb allows participants to: Obtain their s for the proficiency tests in which they have participated. View the results they submitted in past and current proficiency tests. Submit their results and methods for current tests. Review future tests they have ordered. Order proficiency tests and quality control materials. Freely download copies of reports (PDF file), of proficiency tests in which they have participated. 2. PROTOCOL The Protocols [3, 4] set out how FAPAS is organised. Copies can be downloaded from our website. 3. CONTACT DETAILS This report was prepared and authorised on behalf of FAPAS by Simon Hunter (Round Coordinator). Participants with any comments or concerns about this proficiency test should contact: FAPAS The Food and Environment Research Agency Sand Hutton York YO41 1LZ UK Tel: +44 (0)1904 462100 Fax: +44 (0)1904 500440 info@fapas.com testmaterials@fapas.com www.fapas.com Page 23 of 23