FAPAS Report 20120 Sulphur Dioxide in Dried Apricot (water/fruit slurry) August-October 2015 Page 1 of 16
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 FAPAS reports are 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]. Fera is an ISO 9001 certified organisation. Fera hereby excludes all liability for any claim, loss, demands or damages of any kind whatsoever (whether such claims, loss, demands or damages were foreseeable, known or otherwise) arising out of or in connection with the preparation of any technical or scientific report, including without limitation, indirect or consequential loss or damage; loss of actual or anticipated profits (including loss of profits on contracts); loss of revenue; loss of business; loss of opportunity; loss of anticipated savings; loss of goodwill; loss of reputation; loss or damage to or corruption of data; loss of use of money or otherwise, and whether or not advised of the possibility of such claim, loss demand or damages and whether arising in tort (including negligence), contract or otherwise. This statement does not affect your statutory rights. Nothing in this disclaimer excludes or limits Fera liability for: (a) death or personal injury caused by Fera negligence (or that of its employees, agents or directors); or (b) the tort of deceit; [or (c) any breach of the obligations implied by Sale of Goods Act 1979 or Supply of Goods and Services Act 1982 (including those relating to the title, fitness for purpose and satisfactory quality of goods);] or (d) any liability which may not be limited or excluded by law (e) fraud or fraudulent misrepresentation. The parties agree that any matters are governed by English law and irrevocably submit to the non-exclusive jurisdiction of the English courts. Copyright Fera Science Ltd (Fera) 2015. All rights reserved. 0009 Page 2 of 16
SUMMARY 1. The test material for FAPAS proficiency test 20120 was dispatched in August 2015. Each participant received a dried 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 1891 106 132 80 Page 3 of 16
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 11 Table 3: Assigned Value and Standard Deviation for Proficiency 11 Table 4: Number and Percentage of z-scores where z 2 11 FIGURES Figure 1: z-scores for Sulphur Dioxide 12 APPENDICES APPENDIX I: Analytical Methods Used by Participants 13 APPENDIX II: FAPAS SecureWeb, Protocol and Contact Details 16 Page 4 of 16
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 proficiency testing scheme are available in our protocols [3, 4]. 2. TEST MATERIAL 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 value. 2.3. Dispatch The start date was 24 August 2015. Test materials were sent to 144 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 135 participants (94%) before the closing date for this test, 12 October 2015. 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 16
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) non numerical results i.e. qualitative or semi-quantitative results, For sulphur dioxide the major mode was chosen as the assigned value, due to the distribution of results being bi-modal. 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 values for σ p used to calculate z-scores from the reported results of this test are 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 are shown as a histogram in Figure 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 16
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/misc/pki/cds_cp.html, accessed 10/05/2015. 2 ISO/IEC 17043:2010, Conformity assessment General requirements for proficiency testing. 3 FAPAS, 2014, Protocol for Proficiency Testing Schemes, Part 1 Common Principles, Version 4, Issued May 2014. 4 FAPAS, 2014, Protocol for Proficiency Testing Schemes, Part 2 FAPAS, Version 3, Issued May 2014. 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 16
Table 1: Results and z-scores laboratory number analyte laboratory number analyte Sulphur Dioxide assigned 1891 mg/kg value Sulphur Dioxide assigned 1891 mg/kg value result mg/kg z-score result mg/kg z-score 001 1860-0.3 002 1885-0.1 003 1756-1.4 004 1909 0.2 005 1830-0.6 006 675.8-12.5 007 1832-0.6 008 1750-1.5 009 2117 2.3 010 1942 0.5 011 2044.08 1.6 012 1986.60 1.0 020 1942 0.5 021 500-14.3 022 1834-0.6 023 1838.0-0.5 024 1924 0.3 025 2056 1.7 026 2017 1.3 027 1060-8.6 028 1813-0.8 029 1885.34-0.1 030 1833-0.6 031 1779-1.2 032 1733-1.6 033 1418-4.9 034 1870-0.2 035 2035 1.5 036 1451.2-4.5 037 1992.22 1.0 038 1925 0.3 039 1746-1.5 040 1800-0.9 013 1869.5-0.2 041 1969 0.8 014 1890 0.0 042 1755-1.4 015 1897 0.1 043 1988 1.0 016 2061 1.7 044 1927 0.4 017 1803.36-0.9 045 1788-1.1 018 1950 0.6 046 1868.58-0.2 019 1945 0.6 047 2032 1.5 048 464-14.7 049 1915.60 0.3 050 1813.86-0.8 051 1935 0.5 052 1905 0.1 053 544-13.9 054 1867-0.2 055 2019 ± 141.7 056 1898 0.1 z-scores outside z >2 are shown in bold, see Section 5 Page 8 of 16
Table 1 (continued): Results and z-scores laboratory number analyte laboratory number analyte Sulphur Dioxide assigned 1891 mg/kg value Sulphur Dioxide assigned 1891 mg/kg value result mg/kg z-score result mg/kg z-score 057 1693.83-2.0 058 1837-0.6 059 1941 0.5 060 2020.7 1.3 061 1683.25-2.1 062 1901 0.1 063 629-13.0 064 1820-0.7 065 1888 0.0 066 1895 0.0 067 1287-6.2 068 1954 0.6 076 2040 1.5 077 2085 2.0 078 2000 1.1 079 1850-0.4 080 1884-0.1 081 1365-5.4 082 1743-1.5 083 1951.2 0.6 084 1880-0.1 085 1856.87-0.4 086 2024 1.4 087 258.07-16.8 088 2065 1.8 089 2172 2.9 090 1870-0.2 091 1858-0.3 092 1906.12 0.2 093 1860-0.3 094 1850-0.4 095 1944.9 0.6 096 1059-8.6 069 1070-8.4 097 1285-6.2 070 1920 0.3 098 1974.5 0.9 071 1839-0.5 099 1831-0.6 072 1929 ± 69 100 1780.584-1.1 073 1845.5-0.5 101 1846.74-0.5 074 1942.18 0.5 102 1920 0.3 075 1796-1.0 103 >101.6 104 1962 0.7 105 2000 1.1 106 1944 0.5 107 1944.7 0.6 108 1870-0.2 109 1872-0.2 110 1647-2.5 111 2079.19 1.9 112 1527-3.7 z-scores outside z >2 are shown in bold, see Section 5 Page 9 of 16
Table 1 (continued): Results and z-scores laboratory number analyte Sulphur Dioxide assigned value 1891 mg/kg result mg/kg z-score 113 1620-2.8 114 1863-0.3 115 1914.4 0.2 116 1828-0.6 117 2037 1.5 118 1957 0.7 119 1957 0.7 120 1772.6-1.2 121 734.8-11.9 122 1793-1.0 123 1800-0.9 124 1909.62 0.2 125 2133 2.5 126 1576-3.2 127 2064 1.8 128 1914 0.2 129 1990 1.0 130 1795-1.0 131 1650-2.5 132 1300-6.1 133 550.4-13.8 134 1958 0.7 135 1885.45-0.1 z-scores outside z >2 are shown in bold, see Section 5 Page 10 of 16
Table 2: Participants Comments participant number comments 010 Corrected for recovery (97.6%) 072 The data is reported as mean ± standard deviation for 2 replicates. 085 method not accredited 106 Method is accredited in the range 10-500ppm only. 126 Mean recovery 98.3% comments are as submitted by participants Table 3: analyte Assigned Value and Standard Deviation for Proficiency data points, n assigned value, x a, mg/kg uncertainty, u standard deviation for proficiency, σ p, mg/kg Sulphur Dioxide 132 1891 10.5 Horwitz [6] 97.2 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 106 132 80 Page 11 of 16
5.0 4.0 3.0 z-score 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 63 6121 53 133 21 48 87 42 39 8 82 32 57 61 131 110 113 36 112 126 33 81 67 132 97 69 27 96 Figure 1: z-scores for Sulphur Dioxide 92 4124 52 62 56 15 66 14 65 29 135 80 2 84 90 108 109 34 13 46 54 93 114 91 1 85 94 79 73 101 71 23 58 22 30 99 7 5 64 116 50 28 17 40 123 75 45 122 130 31 100 3 120 Laboratory Number 83 18 19 95 74 106 107 20 10 59 51 44 38 24 70 102 49 115 128 104 134 68 118 119 43 12 98 41 129 78 37 105 35 47 86 60 26 117 16 25 11 76 88 111 127 77 9125 89 2085 mg/kg 1891 mg/kg 1697 mg/kg Page 12 of 16
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. Method Used Accredited yes 003 010 011 012 014 015 018 019 020 022 025 028 030 031 032 034 037 041 043 048 054 056 058 059 065 068 069 071 074 076 079 087 088 089 093 094 095 097 098 105 108 112 113 114 115 117 119 121 123 125 128 132 133 135 no 005 006 007 021 023 024 027 029 035 038 044 046 055 067 072 073 075 077 083 085 099 111 116 118 126 127 131 Method Based On International Standard 010 012 014 018 021 022 024 025 029 032 035 037 038 041 044 059 067 069 071 074 077 083 085 087 095 098 105 111 118 125 128 133 National Standard 020 027 046 048 054 058 073 088 115 127 131 Paper Published In An International Journal Manufacturer/Kit Instructions/Technical Note 028 072 112 In house method 003 006 023 031 055 068 076 094 117 Time (hrs) sample allowed to defrost before analysis. 126 none 012 035 046 055 071 112 <1 003 011 015 018 022 030 032 044 048 069 073 083 098 114 116 118 131 1 - <1.5 014 019 025 031 034 058 059 067 072 074 077 087 088 095 105 125 126 127 135 1.5 - <2 037 075 094 111 133 2 - <5 010 028 029 043 054 065 068 079 099 overnight 006 007 020 023 024 027 041 056 076 085 093 097 108 115 117 132 Page 13 of 16
Sample Weight (g) <1 067 073 088 1 - <2 022 034 037 046 2 - <5 007 019 028 030 043 059 068 076 079 093 114 116 117 118 123 135 5 - <10 003 005 011 018 024 025 027 029 031 032 035 038 048 056 065 069 083 085 087 098 119 126 127 10 - <25 010 014 015 041 054 055 058 071 075 089 099 115 121 132 25 - <50 006 020 021 074 077 094 105 111 112 113 125 131 133 50 012 023 044 072 095 097 108 Modified Monier-Williams Method e.g. AOAC 962.16 used yes 003 006 010 012 018 020 021 023 028 029 032 034 035 037 038 041 043 044 046 056 059 067 069 071 073 076 077 083 095 098 105 108 111 113 116 118 119 123 125 127 131 no 007 011 014 015 022 024 025 027 030 031 048 054 055 058 065 068 072 074 075 079 085 087 088 094 097 099 112 114 115 117 126 132 133 Total Refluxing Time - once steady refluxing is reached (mins) <10 003 006 031 032 058 068 112 117 10 - <20 015 027 055 094 123 20 - <30 073 079 087 114 30 - <40 007 028 034 046 065 099 125 40 - <60 029 067 075 60 - <80 010 021 054 056 059 071 133 135 80 - <100 023 041 043 069 074 077 095 098 100 011 012 014 018 022 025 035 037 038 044 076 083 088 097 105 108 111 116 118 119 127 131 Page 14 of 16
Basis of other sulphur dioxide method used distillation into H2O2 005 006 007 010 014 018 019 021 023 025 027 028 029 032 035 037 038 041 043 046 055 059 065 067 068 071 073 075 087 088 089 095 097 099 111 114 115 118 123 125 131 distillation (other) 058 085 093 108 117 acidify with HCl 005 012 014 015 021 023 025 035 038 043 058 059 067 071 075 085 089 094 095 097 111 125 131 acidification (other) 010 028 055 065 073 093 099 117 123 titration with iodine 003 015 024 031 085 112 121 titration (other) 098 133 titration with sodium hydroxide 005 006 010 011 014 020 021 022 023 025 028 029 032 034 035 038 043 054 055 059 065 067 071 073 074 075 079 083 095 097 099 105 111 125 131 enzymatic method 048 126 132 spectrophotometric 072 093 117 126 UV 030 126 Recovery Correction Included yes 010 012 037 074 087 089 113 115 126 132 no 003 005 006 007 011 014 015 018 019 020 021 022 023 024 025 027 028 029 030 031 032 034 035 038 041 043 044 046 048 054 055 056 058 059 065 067 068 069 071 072 073 075 076 077 079 083 085 088 093 094 095 097 098 099 105 108 111 112 114 116 117 118 119 123 125 127 131 133 135 Source of recovery data reference material 018 019 032 056 079 087 097 127 sample spiked with metabisulphate 003 010 015 022 025 034 035 037 058 067 068 069 074 088 089 094 098 099 105 115 disulphite 093 formaldehyde sodium bisulfite 012 HMS 118 Na2SO3 073 Recovery solution run alone 043 sample spiked with sodium sulfite 065 126 Sodium hydrogen sulfite %39 113 Wine 132 Page 15 of 16
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, reference materials and quality control materials. Freely download copies of reports (PDF file), of proficiency tests in which they have participated. View charts of their z-scores obtained in previous FAPAS proficiency tests. 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 Jennifer Leak (Round Coordinator). Participants with any comments or concerns about this proficiency test should contact: FAPAS Fera Science Ltd (Fera) Sand Hutton York YO41 1LZ UK Tel: +44 (0)1904 462100 Fax: +44 (0)1904 500440 info@fapas.com www.fapas.com Page 16 of 16