REPORTS OF THE FINNISH ENVIRONMENT INSTITUTE 5 9 Interlaboratory Proficiency Test /9 Metals in natural water and sediment Mirja Leivuori, Riitta Koivikko, Timo Sara-Aho, Teemu Näykki, Keijo Tervonen, Sari Lanteri, Ritva Väisänen and Markku Ilmakunnas Finnish Environment Institute
REPORTS OF THE FINNISH ENVIRONMENT INSTITUTE 5 9 Interlaboratory Proficiency Test /9 Metals in natural water and sediment Mirja Leivuori, Riitta Koivikko, Timo Sara-Aho, Teemu Näykki, Keijo Tervonen, Sari Lanteri, Ritva Väisänen and Markku Ilmakunnas SYKE Helsinki 9 Finnish Environment Institute
REPORTS OF THE FINNISH ENVIRONMENT INSTITUTE 5 9 Finnish Environment Institute SYKE Proftest SYKE Layout: Markku Ilmakunnas The publication is also available in the Internet: www.syke.fi/publication helda.helsinki.fi/syke ISBN 978-95--569- (pbk.) ISBN 978-95--57-8 (PDF) ISSN 796-78 (print) ISSN 796-76 (Online) Author(s): Mirja Leivuori, Riitta Koivikko, Timo Sara-Aho, Teemu Näykki, Keijo Tervonen, Sari Lanteri, Ritva Väisänen and Markku Ilmakunnas Publisher and financier of publication: Finnish Environment Institute (SYKE) Latokartanonkaari, FI-79 Helsinki, Finland, Phone +58 95 5, syke.fi. Year of issue: 9
ABSTRACT TIIVISTELMÄ SAMMANDRAG Interlaboratory Proficiency Test /9 Proftest SYKE carried out the proficiency test (PT) for analysis of elements in ground and domestic waters as well as in sediment in April 9. The measurands for the synthetic sample and domestic and ground water samples were: Al, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, Ti, U, V, and Zn. In addition to the aforementioned, also measurands N tot, P tot, S tot, TC, and dry weight (Drw) were analysed from the sediment sample. In total participants joined in the PT. In this proficiency test 9 % of the results valuated based on were satisfactory when deviation of 5 % from the assigned value was accepted. From the results evaluated with E n scores, 9 % were satisfactory. Basically, either the metrologically traceable concentration, the calculated concentration, the robust mean or the median of the results reported by the participants was used as the assigned value for the measurands. Warm thanks to all the participants of this proficiency test! Keywords: water analysis, sediment, metals, Al, As, Cd, Co, Cr, Cu, dry weight, Fe, Hg, Mn, Ni, N tot, Pb, P tot, Se, S tot, TC, Ti, U, V, Zn, environmental laboratories, proficiency test, interlaboratory comparisons TIIVISTELMÄ Laboratorioiden välinen pätevyyskoe /9 Proftest SYKE järjesti pätevyyskokeen ympäristönäytteitä analysoiville laboratorioille huhtikuussa 9. Pätevyyskokeessa määritettiin synteettisistä näytteistä sekä talous- ja pohjavesinäytteistä testisuureet Al, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, Ti, U, V ja Zn. Sedimenttinäytteestä määritettiin näiden lisäksi myös N tot, P tot, S tot, TC sekä kuivapaino (Drw). Pätevyyskokeeseen osallistui yhteensä osallistujaa. Koko tulosaineistossa hyväksyttäviä z-arvolla arvioituja tuloksia oli 9 %, kun vertailuarvosta sallittiin 5 %:n poikkeama. Tuloksista, jotka arvioitiin E n -arvolla, hyväksyttyjä oli 9 %. Testisuureen vertailuarvona käytettiin metrologisesti jäljitettävää pitoisuutta, laskennallista pitoisuutta, osallistujien ilmoittamien tulosten robustia keskiarvoa tai mediaania. Kiitos pätevyyskokeen osallistujille! Avainsanat: vesianalyysi, sedimentti, metallit, Al, As, Cd, Co, Cr, Cu, Fe, Hg, kuivapaino, Mn, Ni, N tot, Pb, P tot, Se, S tot, TC, Ti, U, V, Zn, ympäristölaboratoriot, pätevyyskoe, laboratorioiden välinen vertailumittaus SAMMANDRAG Provningsjämförelse /9 Proftest SYKE genomförde en provningsjämförelse i april 9, som omfattade bestämningen av Al, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, Ti, U, V och Zn i syntetik sample, hushålls- och grundvatten och sedimentet, också N tot, P tot, S tot, TC och torrvikt (Drw) var bestämde i sedimentet. Tillsammans laboratorier deltog i jämförelsen. I jämförelsen 9 % av resultaten som värderas med hjälp z värdet var acceptabla, när total deviation på 5 % från referensvärdet tillåten. Resultaten som värderades med hjälp E n värdet var 9 % acceptabla. Som referensvärde av analytens koncentration användes mest det metrologiska spårbara värdet, teoretiska värdet, robust medelvärdet, eller median av deltagarnas resultat. Ett varmt tack till alla deltagarna i testet! Nyckelord: vattenanalyser, sediment, metaller, Al, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, N tot, Pb, P tot, Se, S tot, TC, Ti, torrvikt, U, V, Zn, miljölaboratorier, provningsjämförelse
CONTENTS Abstract Tiivistelmä Sammandrag... Introduction... 7 Organizing the proficiency test... 7. Responsibilities... 7. s... 8. Samples and delivery... 8. Homogeneity and stability studies... 9.5 Feedback from the proficiency test... 9.6 Processing the data... 9.6. Pretesting the data... 9.6. Assigned values... 9.6. Standard deviation for proficiency assessment and results evaluation... Results and conclusions.... Results.... Analytical methods.... Uncertainties of the results... 5 Evaluation of the results... 6 5 Summary... 8 6 Summary in Finnish... 9 References... APPENDIX : s in the proficiency test... APPENDIX : Sample preparation... APPENDIX : Homogeneity of the samples... APPENDIX : Feedback from the proficiency test... APPENDIX 5 : Evaluation of the assigned values and their uncertainties... 5 APPENDIX 6 : Terms in the results tables... 7 APPENDIX 7 : Results of each participant... 8 APPENDIX 8 : Summary of the s... 8 APPENDIX 9 : Summary of the E n scores... 5 APPENDIX : s in ascending order... 5 APPENDIX : Results grouped according to the methods... 7 APPENDIX : Significant differences in the results reported using different methods... APPENDIX : Examples of measurement uncertainties reported by the participants... Proftest SYKE MET /9 5
6 Proftest SYKE MET /9
Introduction Proftest SYKE carried out the proficiency test (PT) for analysis of elements in ground and domestic waters and sediment in April 9 (MET /9). The measurands for the synthetic sample and domestic and ground water samples were: Al, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, Ti, U, V, and Zn. In addition to the aforementioned, also measurands N tot, P tot, S tot, TC, and dry weight (Drw) were analysed from the sediment sample. In total participants joined in the PT. In the PT the results of Finnish participants providing environmental data for Finnish environmental authorities were evaluated. Additionally, other water and environmental laboratories were welcomed in the proficiency test. Finnish Environment Institute (SYKE) is appointed National Reference Laboratory in the environmental sector in Finland. The duties of the reference laboratory include providing interlaboratory proficiency tests and other comparisons for analytical laboratories and other producers of environmental information. This proficiency test has been carried out under the scope of the SYKE reference laboratory and it provides an external quality evaluation between laboratory results, and mutual comparability of analytical reliability. The proficiency test has been carried out in accordance with the international standard ISO/IEC 7 [] and applying ISO 58 [] and IUPAC Technical report []. Proftest SYKE is accredited by the Finnish Accreditation Service as a proficiency testing provider (PT, ISO/IEC 7, www.finas.fi/sites/en). The organizing of this proficiency test is included in the accreditation scope of the Proftest SYKE. Organizing the proficiency test. Responsibilities Organizer Proftest SYKE, Finnish Environment Institute (SYKE), Laboratory Centre Ultramariinikuja, FI- Helsinki, Finland Phone: +58 95 5, email: proftest@environment.fi The responsibilities in organizing the proficiency test Mirja Leivuori coordinator Riitta Koivikko substitute for coordinator Keijo Tervonen technical assistance Markku Ilmakunnas technical assistance Sari Lanteri technical assistance Ritva Väisänen technical assistance Teemu Näykki analytical expert (Hg, ID-) Timo Sara-Aho analytical expert (other measurands, ID-) Proftest SYKE MET /9 7
. s In total participants joined in this proficiency test, 5 from Finland and 5 from other EU countries (Appendix ). Altogether 95 % of the participants used accredited analytical methods at least for a part of the measurands. For this proficiency test, the organizing laboratory has the code 5 (SYKE, Helsinki, T, ISO/IEC 75, www.finas.fi/sites/en) in the result tables.. Samples and delivery Four types of samples were delivered to the participants: synthetic, domestic and ground water as well as sediment samples. The sample preparation is described in details in the Appendix. The synthetic sample AM was prepared from the NIST traceable commercial reference material produced by Inorganic Ventures. The synthetic sample AHg was prepared by diluting from the NIST traceable AccuTrace TM Reference Standard produced by AccuStandard, Inc. The sample DM was domestic water collected from the Helsinki area and the sample GM was ground water collected from the southern Finland. To these samples additions of single element standard solutions (Merck CertiPUR ) were done when needed (Appendix ). The water samples were acidified with nitric acid with the exception of samples for mercury, which were acidified with the hydrochloric acid. The tested sediment sample SM (after analysis: SC oxygen combustion (only Hg) / SN digestion with HNO / SO digestion with HNO + HCl) was lake sediment from the Northern Savonia, eastern Finland used in previous Proftest SYKE PT MET / []. Sediment was manually rehomogenized and divided into sub-samples. The homogeneity of the sediment sample was retested. When preparing the samples, the purity of the used sample vessels was controlled. The randomly chosen sample vessels were filled with deionized water and the purity of the sample vessels was controlled after three days by analyzing Cd, Cu, Hg, and Zn. According to the test results all used vessels fulfilled the purity requirements. The samples were delivered on 8 April 9 to the participants abroad and on 9 April 9 to the national participants. The samples arrived to the participants mainly on April 9. The samples were requested to be measured as follows: Hg samples latest on 8 April 9 Other samples latest on 5 April 9 The results were requested to be reported latest on 5 April 9. s delivered the results accordingly. The preliminary results were delivered to the participants via ProftestWEB and email on 8 May 9. 8 Proftest SYKE MET /9
. Homogeneity and stability studies The homogeneity of the water samples was tested by analyzing Cd, Cr, Hg, Pb, Se, and Zn. More detailed information of the homogeneity studies is shown in Appendix. According to the homogeneity test results, all samples were considered homogenous. The synthetic samples were prepared from traceable certified reference materials. However, homogeneity of these was checked by parallel measurements of two samples. The sediment sample was the same as in the previous Proftest SYKE PT MET / []. The homogeneity of the sediment sample was tested after rehomogenization by parallel measurements (Cd, Cu, Hg, Mn, and Zn) of three samples and they confirmed the homogeneity of the sample. Based on the earlier similar proficiency tests the samples are known to be stable over the given time period for the test..5 Feedback from the proficiency test The feedback from the proficiency test is shown in Appendix. The comments from the participants mainly dealt with the sample delivery. The comments from the provider were focused on the lacking conversancy to the given information with the samples and the reported detection limits. All the feedback is valuable and is exploited when improving the activities..6 Processing the data.6. Pretesting the data The normality of the data was tested by the Kolmogorov-Smirnov test. The outliers were rejected according to the Grubbs or Hampel test before calculating the mean. The results, which differed from the data more than 5 s rob or 5 % from the robust mean, were rejected before the statistical results handling. If the result was reported as below detection limit, it has not been included in the statistical calculations. More information about the statistical handling of the data is available from the Guide for participant [5]..6. Assigned values The calculated values (NIST traceable) were used as the assigned values for the synthetic sample (AM), with the exception of Hg and Pb. For Hg and Pb in the samples AIM, AHg, DM, DHg, GM, and GHg the results based on metrologically traceable isotope dilution (ID) technique were used as assigned values. The assigned value based on the ID- method is the mean of the homogeneity results and the test result (9 results). The ID- method is accredited in the scope of calibration laboratory (K5; www.finas.fi/sites/en). For the other samples and measurands the robust mean value (n all ) Proftest SYKE MET /9 9
or the median value of the participants results (n all < ) was used as the assigned value. If only one participant result was reported, no assigned value was set (N tot : SO). The robust mean or the median of the participant results is not metrologically traceable assigned value. As it was not possible to have metrologically traceable assigned value, the robust mean or the median of the results was the best available value to be used as the assigned value. The reliability of the assigned value was statistically tested [, ]. The expanded uncertainty (k=) for the calculated assigned values was estimated using standard uncertainties associated with individual operations involved in the preparation of the sample. The main individual source of the uncertainty was the uncertainty of the concentration in the stock solution. When the robust mean or the median of the participant results was used as the assigned value, the uncertainty was calculated using the robust standard deviation or the standard deviation, respectively [, 5]. For the metrologically traceable mercury and lead results, the uncertainty is the expanded measurement uncertainty of the ID- method. The uncertainty of the calculated assigned value and the metrologically traceable value for metals in the synthetic samples varied between. and %. When using the robust mean or the median of the participant results as the assigned value, the uncertainties of the assigned values were between. and % (Appendix 5). The assigned values have not been changed after reporting the preliminary results..6. Standard deviation for proficiency assessment and results evaluation The standard deviation for proficiency assessment was estimated on the basis of the measurand concentration, the results of homogeneity and stability tests, the uncertainty of the assigned value, and the long-term variation in the former proficiency tests. The standard deviation for proficiency assessment based on evaluation ( s pt, at the 95 % confidence level) was set to 5 % depending on the measurement. If the number of the results was low (n all :, Hg: SC; Ti: SN, SO; Se: SO) and there was variability between the results, no standard deviation for proficiency assessment was given. The standard deviations for the proficiency assessment have not been changed after reporting the preliminary results. When the number of reported results was low (n stat < 6) or the variation between the results was high and the uncertainty was set for the assigned value, the performance was estimated by means of E n scores ( Error, normalized ).These are used to evaluate the difference between the assigned value and participant s result within their claimed expanded uncertainty. E n scores are calculated: ( ) =, where x i = participant s result, x pt = assigned value, U i = the expanded uncertainty of a participant s result and U pt = the expanded uncertainty of the assigned value. Proftest SYKE MET /9
Scores of E n. < E n <. should be taken as an indicator of successful performance when the uncertainties are valid. Whereas scores E n. or E n. could indicate a need to review the uncertainty estimates, or to correct a measurement issue. When using the robust mean or the median of the participant results the assigned value, the reliability was tested according to the criterion u pt / s pt., where u pt is the standard uncertainty of the assigned value (the expanded uncertainty of the assigned value (U pt ) divided by ) and s pt is the standard deviation for proficiency assessment [, ]. When testing the reliability of the assigned value the criterion was mainly fulfilled and the assigned values were considered reliable. The reliability of the standard deviation and the corresponding was estimated by comparing the deviation for proficiency assessment (s pt ) with the robust standard deviation (s rob ) or standard deviation (s, n stat < ) of the reported results (the criteria) []. The criterion s rob / s pt <. was mainly fulfilled. In the following cases, the criterion for the reliability of the assigned value was not met and, therefore, the evaluation of the performance is weakened in this proficiency test: Sample SN SO DM Measurement Ptot As, Ni, Pb, Ptot Fe Results and conclusions. Results The terms used in the results tables are presented in Appendix 6. The results and the performance of each participant are presented in Appendix 7 and the summary of the results in Table. The summaries of the z and E n scores are shown in Appendices 8 and 9. In Appendix the s are shown in the ascending order. The reported results with their expanded uncertainties (k=) grouped according to the methods are presented in Appendix. The robust standard deviations of the results varied mainly from.6 % to % and the standard deviations of the sediment sample varied from. % to % (Table ). The robust standard deviation of results was lower than % for 9 % of the results and lower than % for 98 % of the results (Table ). Standard deviations higher than % apply mainly to the ground water sample (GHg, Table ). The robust standard deviations for water samples (. 7 %) were approximately on the same level than in the previous almost similar proficiency tests MET /7 and MET 5/8, where the robust standard deviations varied from % to % for the water samples [6, 7]. For the sediment sample the robust standard deviations or the standard deviations were in the same range as in the previous similar PT MET / [], where the robust standard deviations varied from.6 % to 7 %. The robust standard deviation was not calculated when the number of results within the statistical evaluation was low (< 7, Table ). Proftest SYKE MET /9
Table. The summary of the results in the proficiency test MET /9. Measurand Sample Unit Assigned value Mean Rob. mean Median srob / s srob % / s % x spt % nall Acc z % Al AM µg/l 5 6.8 6 75 DM µg/l 7.9 7.9 7.9 7.6. 5.7 5 5 86 GM µg/l..... 8. 85 SN g/kg..8 -.. - - SO g/kg 5.9 5. - 5.9. 5 6 8 As AM µg/l.5....8 6.8 5 9 DM µg/l.98.98.98.98.7 7. 9 GM µg/l.8.8.8.8. 8.7 78 SN mg/kg 6.65 6.6-6.65.66-5 - SO mg/kg 6.89 6.8-6.89.95 5 6 Cd AM µg/l.75.7.7.7.6 8.6 5 5 79 DM µg/l..... 5. 5 9 GM µg/l.5.5.6.5. 5. 5 9 SN mg/kg.7.77 -.7. 6-5 - SO mg/kg.69.67 -.69. 6-6 - Co AM µg/l.5.7.8.7.. 9 DM µg/l..... 7.6 5 9 GM µg/l..... 5. 5 88 SN mg/kg.. -.. 6. - 5 - SO mg/kg 5.7 5. - 5.7.6 7. 6 Cr AM µg/l.5..8...8 5 5 9 DM µg/l.57.56.56.57.6. 5 9 GM µg/l.5.55.5.5. 5. 5 SN mg/kg 56. 55. - 56..9 8.9 5 6 SO mg/kg 58.9 58.9-58.9 6. 5 6 Cu AM µg/l.5.... 9. 5 8 DM µg/l 56.8 56.9 56.8 55.8. 5.6 5 GM µg/l.57.55.57.5.8 7.7 SN mg/kg 68. 66. - 68.. 5. 6 SO mg/kg 7. 69. - 7...6 6 Drw SM % 98. 98. 98. 98..6.6 5 Fe AM µg/l 75 76 75 7 8.8 7 88 DM µg/l 7.5 7.7 7.5 7.. 8. 5 6 87 GM µg/l 7.5 7.6 7.5 7..6 9. 9 SN g/kg.9. -.9.7 6 8 SO g/kg.5.6 -.5.7 7.7 6 Hg AHg µg/l.5.5.5.6..5 85 DHg µg/l.75.7.79.75. 7.6 5 7 GHg µg/l.5.5.56.5..5 5 7 SC mg/kg.67.67 -.67..8 - - SN mg/kg.7.7 -.7.. - 5 - SO mg/kg.7.7 -.7.6 8.7 7 86 Mn AM µg/l.5.5.5.7. 5. 5 DM µg/l 5.6 5.8 5.6 5.9. 6.8 5 5 87 GM µg/l..... 5. 5 SN mg/kg 6 69-6 7 5.7 5 6 SO mg/kg 7 75-7. 5 6 Proftest SYKE MET /9
Table. The summary of the results in the proficiency test MET /9. Measurand Sample Unit Assigned value Mean Rob. mean Median srob / s srob % / s % x spt % nall Acc z % Ni AM µg/l 7.5 7.8 7.5 7..5 7. 5 9 DM µg/l.5.55.55.5..8 78 GM µg/l.56.55.56.56. 7. 5 8 SN mg/kg 8.6 7. - 8.6.7 5.6-5 - SO mg/kg 7. 7.7-7.. 8.6 6 Ntot SN g/kg.7.6 -.7.6 5.6-6 - SO g/kg -.8 -.8 - - - - Pb AM µg/l..9...6.8 5 5 9 DM µg/l.8...8. 6. 5 GM µg/l.57.56.56.56. 5.8 5 9 SN mg/kg 8.7 8.5-8.7.9 6.7-5 - SO mg/kg 5.8 6. - 5.8. 5 6 Ptot SN g/kg.9...9.. 7 SO g/kg.. -.. 9. 6 Se AM µg/l.5.... 9. 5 8 DM µg/l.5.5.5.5. 5.7 5 GM µg/l.9.9.88.9. 5. 5 9 SN mg/kg.6.66 -.6.8-6 - SO mg/kg.8. -.8.9 6-6 - Stot SN g/kg.7.5 -.7.7 - - SO g/kg..8 -.99.8 9. - 5 - TC SM g/kg 87.7 87. - 87.7 6. 7. - 5 - Ti AM µg/l.5.7.7.6.9. 9 DM µg/l 5.6 5. 5.6 5.6.. 5 9 88 GM µg/l 6. 6. 6. 6.. 6.7 5 8 SN mg/kg 8 68-8 - - SO mg/kg 8 758-8 6 6 - - U AM µg/l.65.6.6.65. 5. 5 9 DM µg/l...... 5 9 GM µg/l.9.8.8.9.6 6.8 5 SN mg/kg..7 -.. 9.8-5 - SO mg/kg.6.9 -.6.59 7 - - V AM µg/l.5.5.5..5.8 DM µg/l..6.7..6 5. 5 GM µg/l.88.88.87.88.6 7. 5 SN mg/kg 58. 55. - 58. 6. - 5 - SO mg/kg 6.7 6. - 6.7 6.5-6 - Zn AM µg/l.5..... 5 8 DM µg/l.....5. 5 9 GM µg/l 5. 5.5 5. 5..7 6.8 5 9 SN mg/kg - 7.. 5 6 SO mg/kg 8-5.5-5 - Rob. mean: the robust mean, s rob : the robust standard deviation, s: the standard deviation, s rob %: the robust standard deviation as percent, s% : the standard deviation as percent, s p %: the total standard deviation for proficiency assessment at the 95 % confidence level, Acc z %: the results (%), where z, n(all): the total number of the participants. Proftest SYKE MET /9
. Analytical methods The participants were allowed to use different analytical methods for the measurands in the PT. The used analytical methods and results of the participants grouped by methods are shown in more detail in Appendix. The statistical comparison of the analytical methods was possible for the data where the number of the results was 5. The statistically significant differences between the results are shown in Appendix. Effect of sample pretreatment on elemental concentrations in sediment sample The sediment sample SM was measured using pretreatment and the results from different pretreatment procedures were processed separately in data handling. Almost equally the participants (from four to six participants depending on the measurand) measured the sediment sample after nitric acid digestion (SN) and after acid mixture of HNO +HCl for the digestion (SO Table, Appendix ). For Hg measurements five participants used the nitric acid digestion (SN), six used acid mixture of HNO +HCl (MO) for the digestion and two participants used the oxygen combustion pretreatment (MC). The difference between the average concentrations of elements measured after different sample preparation steps was tested using the t-test. Statistically significant difference was observed for Mn analyses where acid digestion with nitric acid (SN) gave significantly lower results (69 ± 7 mg/kg, mean ± standard deviation) than acid digestion with acid mixture of HNO +HCl (SO, 75 ± mg/kg, Appendix ). Effect of measurement methods on elemental results The most commonly used analytical methods were and ICP-OES. Only one participant used FAAS or GAAS techniques for some measurands (Appendix ). The difference between the average concentrations of metals measured by different measurement methods was tested using the t-test. In the statistical treatment no significant differences were observed, when the number of results were high enough for the statistical comparison. N tot in the sediment sample (SN, SO) was mainly measured using N-Kjeldahl or similar method or by C, H, N-analyzer. TC in the sediment sample SM was mainly measured by C, H, N-analyzer (Appendix ). As a general note, a low recovery may be an indication of loss of measurand which can occur during sample pretreatment (e.g. volatilization during acid digestion) or measurement (e.g. GAAS analysis). It may also be caused by incorrect background correction (ICP-OES) or matrix effects. Recoveries that are too high may be caused by spectral interferences (overlapping wavelengths in emission spectrometry, polyatomic or isobaric interferences in mass spectrometry), matrix effects or contamination. Matrix effects can often be overcome by matrix matching the calibration standards however; this is often difficult with environmental samples since the elemental concentrations vary a lot even within the same sample type. According to the results of this PT, majority of the participant s results of Co, Ti, and V remained lower than the assigned values for the sample AM. However, the differences were generally within the reported measurement uncertainties of the participants. Proftest SYKE MET /9
Effect of measurement methods on mercury results For the analysis of mercury, was the most often used method of analysis. That was followed by CV-AFS and CV-AAS. Other used methods were CV-, ICP-OES, and direct combustion (Appendix ). Based on visual estimation no differences between the used measuring methods were found. For the sediment sample, aqua regia digestion (SO) was slightly more often used than nitric acid digestion (SN). Like other metal determinations, mercury results are also affected by digestion procedures used (acids and oxidation reagents, their concentration, volumes and purities, digestion temperature and time). For water samples hydrochloric acid is recommended for sample preservation and BrCl is recommended for oxidation of mercury species. Generally, the differences in mercury results are most likely due to different pretreatment procedures, provided a measurement technique sensitive enough is used. Cold vapour techniques are recommended, especially for natural water matrices with low concentrations. CV-AFS and CV- have superior detection capability compared to CV-AAS or CV-ICP-OES.. Uncertainties of the results At maximum 75 % of the participants reported the expanded uncertainties (k=) with their results for at least some of their results (Table, Appendix ). Several approaches were used for estimating the measurement uncertainty (Appendix ). The most commonly used approach was based on the internal quality data with sample replicates and the method validation data [8]. MUkit measurement uncertainty software for the estimation of the uncertainties was used by at maximum five participants (Appendix ) [9]. The free software is available in the webpage: www.syke.fi/envical/en. Generally, the used approach for estimating measurement uncertainty did not make definite impact on the uncertainty estimates The range of the reported uncertainties varied between the measurements and the sample types. As can be seen in Table, some of the participants have over-estimated their expanded (k=) measurement uncertainty. Very high measurement uncertainties (i.e. 5 % or higher) should not exist, unless the measured concentration is near to the limit of quantification. The reported expanded uncertainties below 5 % commonly could be considered unrealistic uncertainty value for routine laboratories. In order to promote the enhancement of environmental measurements quality standards and traceability, the national quality recommendations for data entered into the water quality registers have been published in Finland []. The recommendation for measurement uncertainties in natural waters is 5 % for the measurands of this proficiency test. In this proficiency test some of the participants had their measurement uncertainties within this limit, while some did not achieve it. However, harmonization of the uncertainties estimation should be continued. Proftest SYKE MET /9 5
Table. The range of the expanded measurement uncertainties (k=, U i %) reported by the participants. Measurand AM/AHg, % DM/DHg, % GM/GHg, % SC/SM/SN/SO, % Al 6- - - - As -6 9-75 -.6 5-5 Cd -8-68 - -5 Co 9- - - 5- Cr -7-7 -5 5-6 Cu 9-9- - 5-5 Drw - - - - Fe 8-8- 8-5 - Hg 5-5- 5-5-5 Mn 7-7- 8-5 -5 Ni -5-5 -9 5-5 Ntot - - - 7- Pb -8-5 -5 5-5 Ptot -8-5 -5 5-5 Se 5-5- 5- -5 Stot - - - - TC - - - - Ti - - - 5-59 V 8-8-8 8-7- Zn 8-9 8- -9-5 Evaluation of the results The performance evaluation of the participants was based on the s, which were calculated using the assigned values and the standard deviation for the performance assessment (Appendix 6). Additionally, some of the results were evaluated using E n scores. The z and E n scores were interpreted as follows: Criteria Performance z Satisfactory < z < Questionable z Unsatisfactory. < En <. Satisfactory En. or En. Unsatisfactory In total, 9 % of the results were satisfactory, when deviation 5 % from the assigned value was accepted (Appendix 8). In total, 9 % of the E n score results were satisfactory for the sediment sample (Appendix 9). Altogether 95 % of the participants used accredited analytical methods at least for a part of the measurands and 9 % of their results were satisfactory. The summary of the performance evaluation and comparison to the previous performance is presented in Table. 6 Proftest SYKE MET /9
The satisfactory results based on s varied between 89 and 97 % for the tested sample types (Table ). The share of satisfactory results in the synthetic sample AM was the lowest for Al, about 75 %. Totally the share was in the same level as in the previous similar proficiency test in 8 (Table ) [7]. For the domestic water samples (DM, DHg) all results for Cu, Pb, Se and V were satisfactory, while for Hg the share of the satisfactory results was 7 %. For the ground water samples (GM, GHg) all results for Cr, Cu, Mn, Ti, U and V were satisfactory, and for Hg the recovery was the lowest 7 %. In this proficiency test the share of satisfactory results was almost in the same level as in the previous proficiency tests (Table ) [6, 7]. For the sediment sample digested with nitric acid (SN) the number of results was low, and thus the performance was evaluated based on the z or E n scores (Table, Appendix 9). In total, 89 97 % of the evaluated results were satisfactory (Table ). The performance of the sediment results obtained after aqua regia digestion (HNO +HCl, SO), was also evaluated based on z or E n scores depending the number of results (Table, Appendix 9). In this case 9 97 % of the results were satisfactory (Table ). The overall performance was slightly higher than in the previous PT MET /, where the same sediment sample was used []. However, in this PT there were less than half of participant results in the previous PT in. Table. Summary of the performance evaluation in the proficiency test MET /9. Sample Satisfactory results (%) Accepted deviation from the Remarks AM, AHg DM, DHg GM, GHg SN SC SO assigned value (%) 89 Difficulties in measurements for Al and Cd, < 8% satisfactory results. In the previous PT MET 5/8 the performance was satisfactory for 9 % of the results [7]. 9 5-5 Mainly good performance. Only approximate assessment for Fe. Difficulties in measurements for Hg and Ni, < 8% satisfactory results. In the previous PT MET /7 the performance was satisfactory for 9 % of the results, when accepting the deviation of -5 % from the assigned value [6]. 9 5-5 Mainly good performance. Difficulties in measurements for As, < 8% satisfactory results. In the previous PT MET 5/8 the performance was satisfactory for 86 % of the results, when accepting the deviation of -5 % from the assigned value respectively [7]. Based on : 97 Based on En score: 89 Based on : 97 Based on En score: 9 5-5 Mainly good performance. Only approximate assessment for Ptot. In the previous PT MET / the performance was satisfactory based on s for 8 % of the results when accepting the deviation of -5 % from the assigned value []. 5-5 Mainly good performance. Only approximate assessment for As, Ni, Pb, Ptot. In the previous PT MET / the performance was satisfactory based on s for 9 % of the results when accepting the deviation of 5- % from the assigned value []. Proftest SYKE MET /9 7
For the sediment sample digested with nitric acid, SN, all results for Cr, Cu, Mn, P tot, and Zn were satisfactory based on. Similarly for aqua regia digested sediment sample SO all results for As, Co, Cr, Cu, Fe, Mn, Ni, Pb and P tot were satisfactory. 5 Summary Proftest SYKE carried out the proficiency test (PT) for analysis of elements in ground and domestic waters and sediment in April 9 (MET /9). The measurands for the synthetic sample and domestic and ground water samples were: Al, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, Ti, U, V, and Zn. In addition to the aforementioned, also measurands N tot, P tot, S tot, TC, and dry weight (Drw) were analysed from the sediment sample. In total participants joined in the PT. The calculated values (NIST traceable) were used as the assigned values for the synthetic samples (AM) with the exception of Hg and Pb. For Hg and Pb in the samples AIM, AHg, DM, DHg, GM, and GHg the results based on metrologically traceable isotope dilution (ID) technique were used as assigned values. For the other samples and measurands the robust mean value (n all ) or the median value of the participants results (n all < ) was used as the assigned value. The uncertainties of the calculated assigned values and the metrologically traceable values for metals in the synthetic samples varied between. and %. When using the robust mean or the median of the participant results as the assigned value, the uncertainties of the assigned values were between. and % The evaluation of the performance was based on the z and E n scores. In this PT, 9 % of the results were satisfactory, when deviation 5 % from the assigned value was accepted. In total, 9 % of the E n score results were satisfactory for the sediment sample. About 95 % of the participants used accredited methods and 9 % of their results were satisfactory. 8 Proftest SYKE MET /9
6 Summary in Finnish Proftest SYKE järjesti ympäristönäytteitä analysoiville laboratorioille pätevyyskokeen huhtikuussa 9. Pätevyyskokeessa määritettiin synteettisistä näytteistä sekä talous- ja pohjavesinäytteistä testisuureet Al, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, Ti, U, V ja Zn. Sedimenttinäytteestä määritettiin näiden lisäksi myös N tot, P tot, S tot, TC sekä kuivapaino (Drw). Pätevyyskokeessa oli yhteensä osallistujaa. Testisuureen vertailuarvona käytettiin laskennallista pitoisuutta, osallistujien tulosten robustia keskiarvoa tai mediaania. Lyijylle ja elohopealle käytettiin metrologisesti jäljitettävää tavoitearvoa osalla testinäytteistä. Vertailuarvolle laskettiin laajennettu epävarmuus 95 % luottamusvälillä. Vertailuarvon laajennettu epävarmuus oli välillä, % laskennallista tai metrologisesti jäljitettävää pitoisuutta vertailuarvona käytettäessä ja muilla välillä, %. Pätevyyden arviointi tehtiin z- ja E n -arvojen avulla. Koko aineistossa hyväksyttäviä tuloksia z-arvoilla arvioituna oli 9 %, kun tulosten annettiin vaihdella 5 % vertailuarvosta. E n -arvoilla arvioiduista sedimenttinäytteen tuloksista 9 % oli hyväksyttyjä. Noin 95 % osallistujista käytti akkreditoituja määritysmenetelmiä ja näistä tuloksista oli hyväksyttäviä 9 %. Proftest SYKE MET /9 9
REFERENCES. SFS-EN ISO 7,. Conformity assessment General requirements for Proficiency Testing.. ISO 58, 5. Statistical methods for use in proficiency testing by interlaboratory comparisons.. Thompson, M., Ellison, S. L. R., Wood, R., 6. The International Harmonized Protocol for the Proficiency Testing of Analytical Chemistry laboratories (IUPAC Technical report). Pure Appl. Chem. 78: 5-96, www.iupac.org.. Leivuori, M., Korhonen-Ylönen, K., Sara-Aho, T., Näykki, T., Tervonen, K., Lanteri, S. and Ilmakunnas, M.. Proficiency Test /. Metals in waters and sediment. Reports of Finnish Environment Institute /. Helsinki. (http://hdl.handle.net/8/5). 5. Proftest SYKE Guide for laboratories: www.syke.fi/proftest/en Current proficiency tests www.syke.fi/download/noname/%7bffbf5-96-8-965-ece96d8c%7d/9886. 6. Leivuori, M., Koivikko, R., Sara-Aho, T., Näykki, T., Tervonen, K., Lanteri, S., Väisänen, R. and Ilmakunnas, M. 7. Interlaboratory Proficiency Test /7. Metals in natural waters. Reports of Finnish Environment Institute 5/7. Helsinki. (http://hdl.handle.net/8/78). 7. Leivuori, M., Koivikko, R., Sara-Aho, T., Näykki, T., Tervonen, K., Lanteri, S., Väisänen, R. and Ilmakunnas, M. 8. Interlaboratory Proficiency Test 5/8. Metals in natural waters and soil. Reports of Finnish Environment Institute /8. Helsinki. (http://hdl.handle.net/8/9). 8. Magnusson B., Näykki T., Hovind H., Krysell M., Sahlin E., 7. Handbook for Calculation of Measurement Uncertainty in Environmental Laboratories. Nordtest Report TR 57 (ed. ). (http://www.nordtest.info) 9. Näykki, T., Virtanen, A. and Leito, I.,. Software support for the Nordtest method of measurement uncertainty evaluation. Accred. Qual. Assur. 7: 6-6. MUkit website: www.syke.fi/envical.. Näykki, T. and Väisänen, T. (Eds.) 6. Laatusuositukset ympäristöhallinnon vedenlaaturekistereihin vietävälle tiedolle: Vesistä tehtävien analyyttien määritysrajat, mittausepävarmuudet sekä säilytysajat ja tavat. -. uudistettu painos. (Quality recommendations for data entered into the environmental administration s water quality registers: Quantification limits, measurement uncertainties, storage times and methods associated with analytes determined from waters). Suomen ympäristökeskuksen raportteja /6. 57 pp. (In Finnish). (http://hdl.handle.net/8/65). Proftest SYKE MET /9
APPENDIX (/) APPENDIX : s in the proficiency test Country Finland France Sweden Eurofins Ahma Oy Seinäjoki Eurofins Ahma Oy, Oulu Eurofins Environment Testing Finland Oy, Lahti Fortum Waste Solutions Oy, Riihimäki KVVY Tutkimus Oy, Tampere Kymen Ympäristölaboratorio Oy Lounais-Suomen vesi- ja ympäristötutkimus Oy, Turku Luonnonvarakeskus, Viikki B-laboratorio MetropoliLab Oy Savo-Karjalan Ympäristötutkimus Oy, Kuopio SeiLab Oy Seinäjoen toimipiste SGS Finland Oy, Kotka STUK, Ympäristön säteilyvalvonta, Valvonta ja Mittaus (VAM) SYKE, Helsingin toimipaikka SYNLAB Analytics & Services Finland Oy PearL, Limoges Cedex, France Erkenlaboratoriet INOVYN Sverige Ab Stockholm University, ACES Stockholm University, Department of Ecology, Environment and Plant Sciences Proftest SYKE MET /9
APPENDIX (/) APPENDIX : Sample preparation The synthetic sample AM was prepared by diluting from the NIST traceable certified reference materials produced by Inorganic Ventures. The synthetic sample AHg was prepared by diluting from the NIST traceable AccuTrace TM Reference Standard produced by AccuStandard, Inc. The water samples DM and GM were prepared by adding some separate metal solutions (Merck CertiPUR ) into the original water sample, if the original concentration was not high enough. Samples DHg and GHg were prepared by adding from the NIST traceable AccuTrace TM Reference Standard produced by AccuStandard, Inc., if the original concentration was not high enough.the tested sediment sample (after analysis: SC, SN, SO) was reused sediment sample from the previous PT MET / []. Measurand AM µg/l DM µg/l GM µg/l SN/SO mg/kg Measurand AM µg/l DM µg/l GM µg/l Al Original 5 9 5 Ni Original 7.5.57.6 Dilution - - - Dilution - - Addition - - - Addition - -.5 Ass. value 5 7.9../5.9 g/kg Ass. value 7.5.5.56 As Original.5..8 6.6 Ntot Original - - - Dilution - - - Dilution - - - Addition - - - - Addition - - - Ass. value.5.98.8 6.65/6.89 Ass. value - - - Cd Original 7.5..5.78 Pb Original.5..55 Dilution - - - Dilution - - Addition -.96.5 - Addition -.5 Ass. value.75..5.7/.69 Ass. value..8.57 Co Original.5. Ptot Original - - - Dilution - - - Dilution - - - Addition -.. - Addition - - - Ass. value.5.../5.7 Ass. value - - - Cr Original 5.7.7 57 Se Original.5 - - Dilution - - - Dilution - - Addition -.5.8 - Addition -.5.75 Ass. value.5.57.5 56./58.9 Ass. value.5.5.9 Cu Original 5 57.7 65 Stot Original - - - Dilution - - - Dilution - - - Addition - - - - Addition - - - Ass. value.5 56.8.57 68./7. Ass. value - - - Fe Original 75. TC Original - - - Dilution - - - Dilution - - - Addition - - 5 - Addition - - - Ass. value 75 7.5 7.5.9/.5 g/kg Ass. value - - - Mn Original 5.6. 68 Ti Original 5. - Dilution - - - Dilution - - Addition - - Addition - 5 5 Ass. value.5 5.6. 6/7/ Ass. value.5 5.6 6. U Original 6.5...6 Measurand AHg DHg GHg Dilution - - - µg/l µg/l µg/l Addition - - - - Ass. value.65..9./.6 V Original.5.5.9 59 Hg Original - - - Dilution - - - Dilution - - - Addition - - - Addition.5.75.5 Ass. value.5..88 58./6.7 Ass. value.5.75.5 Zn Original 5. 7 Dilution - - - Addition - - - Ass. value.5. 5. / Original = the original concentration; Dilution = the ratio of dilution; Addition = the addition concentration; Ass. value = the assigned value SN/SO mg/kg 8 - - 8.6/7..9 - -.7/- g/kg 9 - - 8.7/5.8. - -.9/. g/kg. - -.6/.8. - -.7/. g/kg 8. - - 87.7 g/kg - - 8/8 SC/ SN/ SO mg/kg.7 - -.67/.7/.7 Proftest SYKE MET /9
APPENDIX (/) APPENDIX : Homogeneity of the samples The homogeneity was checked for the selected samples and measurands as duplicate measurements. Criteria for homogeneity: s anal /s h <.5 and s sam <c, where s h = standard deviation for testing of the homogeneity s anal = analytical deviation, standard deviation of the results in a sub sample s sam = between-sample deviation, standard deviation of the results between sub samples c = F s all + F s anal, where s all = (. s h ), F and F are constants of F distribution derived from the standard statistical tables for the tested number of samples [, ]. Measurand/Sample Concentration [µg/l] n spt % sh% sh sanal sanal/sh sanal/sh<.5? ssam c ssam <c? [mg/kg] Cd/DM. 7.5.9...6 Yes.. Yes Cr/DM.6 7.5.7.8.. Yes.6. Yes Pb/DM.8 7.5.6..6.6 Yes.. Yes Se/DM.5 7.5.5.9..78 Yes..5 Yes Zn/DM. 7.5...6.85 Yes.5.6 Yes Cd/GM.6 7.5....9 Yes.. Yes Cr/GM.55 7.5...6.85 Yes. Yes Pb/GM.55 7.5..6..8 Yes. Yes Se/GM.95 7.5.6..5.7 Yes. Yes Zn/GM 5. 7.5..7.5.99 Yes.6 Yes Cd/SM.78 -.6...5 Yes.. Yes Cu/SM 6.6..9.68.9 Yes.9 Yes Hg/SM.7..5..6 Yes.. Yes Mn/SM 68 7.5. 6.98.56.57 Yes.8 55.5 Yes Zn/SM 7 7.5.9.86.65. Yes.. Yes Hg/DHg*.7.5..8..66 Yes.. Yes Hg/GHg*.5.5.5...86 Yes. Yes Pb/DM*.9 7.5.7.5.7.67 Yes.. Yes Pb/GM*.57 7.5...9. Yes..5 Yes n= number of tested sub-samples s pt % = standard deviation for proficiency assessment *) result based on the ID- measurement Conclusion: The criteria were fulfilled for the tested measurands and the samples were regarded as homogenous Proftest SYKE MET /9
APPENDIX (/) APPENDIX : Feedback from the proficiency test FEEDBACK FROM THE PARTICIPANTS Comments on technical execution Action / Proftest SYKE 6 informed receiving the samples two days after the estimated delivery day. received the samples one day after the estimated delivery day. According to the distributor s tracking system the samples arrived to the participant on time. It is recommended to check the in-house process for sample delivery. According to the distributor s tracking system the samples arrived to the participant on time. It is recommended to check the in-house process for sample delivery. FEEDBACK TO THE PARTICIPANTS Comments The participant informed that they are accredited for Hg (AHg). However they did not report measurement uncertainty with their result. The measurement uncertainty should be reported with the results obtained by accredited method. The participant reported lower than value for Co in the sample AM, though the tested concentration was high enough to be measured. The provider recommends the participant to revalidate their limit of detection value. The participant reported lower than value for Co in the sample AM, though the tested concentration was high enough to be measured. The provider recommends the participant to revalidate their limit of detection value. Proftest SYKE MET /9
APPENDIX 5 (/) APPENDIX 5: Evaluation of the assigned values and their uncertainties Measurand Sample Unit Assigned value Upt Upt, % Evaluation method of assigned value upt/spt Al AM µg/l 5.5 Calculated value.5 DM µg/l 7.9..8 Robust mean.5 GM µg/l..9 6. Robust mean. SN g/kg..5. Median SO g/kg 5.9.8. Median. As AM µg/l.5..7 Calculated value.5 DM µg/l.98.5 5.6 Median.8 GM µg/l.8..5 Median.8 SN mg/kg 6.65.6 9. Median SO mg/kg 6.89.76. Median. Cd AM µg/l.75..7 Calculated value.5 DM µg/l...7 Robust mean.5 GM µg/l.5.. Median.7 SN mg/kg.7. 5. Median SO mg/kg.69.9. Median Co AM µg/l.5..6 Calculated value.6 DM µg/l...8 Median. GM µg/l...6 Median.7 SN mg/kg..9 5.6 Median SO mg/kg 5.7. 6. Median. Cr AM µg/l.5..7 Calculated value.5 DM µg/l.57.. Median.5 GM µg/l.5.. Median. SN mg/kg 56.. 7. Median.9 SO mg/kg 58.9.9 8. Median. Cu AM µg/l.5.. Calculated value. DM µg/l 56.8..7 Robust mean.5 GM µg/l.57. 5.6 Robust mean.8 SN mg/kg 68..9. Median. SO mg/kg 7..7.8 Median.9 Drw SM % 98... Median.6 Fe AM µg/l 75.6 Calculated value.6 DM µg/l 7.5. 5.5 Robust mean.7 GM µg/l 7.5. 6.5 Robust mean. SN g/kg.9. 9. Median.6 SO g/kg.5. 6. Median. Hg AHg µg/l.5.. ID-.5 DHg µg/l.75.. ID-. GHg µg/l.5.. ID-. SC mg/kg.67 Median SN mg/kg.7..7 Median SO mg/kg.7.5 7. Median.6 Mn AM µg/l.5..6 Calculated value.6 DM µg/l 5.6.7. Robust mean.9 GM µg/l..6.9 Robust mean.6 SN mg/kg 6.7 Median. SO mg/kg 7 5.5 Median. Proftest SYKE MET /9 5
APPENDIX 5 (/) Measurand Sample Unit Assigned value Upt Upt, % Evaluation method of assigned value upt/spt Ni AM µg/l 7.5..6 Calculated value. DM µg/l.5..5 Median.8 GM µg/l.56.5.5 Median. SN mg/kg 8.6. 5. Median SO mg/kg 7.. 7. Median.6 Ntot SN g/kg.7. 5. Median SO g/kg Pb AM µg/l...5 ID-.7 DM µg/l.8.5.5 ID-.7 GM µg/l.57.. ID-.9 SN mg/kg 8.7.7 6. Median SO mg/kg 5.8.5 9.5 Median.8 Ptot SN g/kg.9.8 7.6 Median.8 SO g/kg..8 7. Median.7 Se AM µg/l.5..7 Calculated value.5 DM µg/l.5..5 Median. GM µg/l.9..6 Median. SN mg/kg.6.6. Median SO mg/kg.8 Median Stot SN g/kg.7.8. Median SO g/kg..7 9. Median TC SM g/kg 87.7 5.5 6. Median Ti AM µg/l.5..7 Calculated value.7 DM µg/l 5.6.. Median.7 GM µg/l 6..7. Median.8 SN mg/kg 8 Median SO mg/kg 8 Median U AM µg/l.65..6 Calculated value. DM µg/l.. 8. Median. GM µg/l.9.8.6 Median. SN mg/kg..9 8.8 Median SO mg/kg.6.7. Median V AM µg/l.5..6 Calculated value.6 DM µg/l..9. Median. GM µg/l.88..8 Median. SN mg/kg 58. 5.8 9.9 Median SO mg/kg 6.7 5. 8.6 Median Zn AM µg/l.5..6 Calculated value.6 DM µg/l... Robust mean. GM µg/l 5..6.9 Robust mean. SN mg/kg 6.7 Median.8 SO mg/kg.9 Median U pt = Expanded uncertainty of the assigned value Criterion for reliability of the assigned value u pt/s pt <., where s pt= the standard deviation for proficiency assessment u pt= the standard uncertainty of the assigned value If u pt/s pt <., the assigned value is reliable and the s are qualified. 6 Proftest SYKE MET /9
APPENDIX 6 (/) APPENDIX 6: Terms in the results tables Results of each participant Measurand The tested parameter Sample The code of the sample Calculated as follows: z = (x i - x pt )/s pt, where x i = the result of the individual participant x pt = the assigned value s pt = the standard deviation for proficiency assessment Assigned value The value attributed to a particular property of a proficiency test item s pt % The standard deviation for proficiency assessment (s pt ) at the 95 % confidence level s result The result reported by the participant (the mean value of the replicates) Md Median s Standard deviation s % Standard deviation, % n stat Number of results in statistical processing Summary on the s S satisfactory ( z ) Q questionable ( < z < ), positive error, the result deviates more than s pt from the assigned value q questionable ( < z < ), negative error, the result deviates more than s pt from the assigned value U unsatisfactory (z ), positive error, the result deviates more than s pt from the assigned value u unsatisfactory (z ), negative error, the result deviates more than s pt from the assigned value Robust analysis The items of data are sorted into increasing order, x, x, x i,,x p. Initial values for x * and s * are calculated as: x * = median of x i (i =,,...,p) s * =.8 median of x i x * (i =,,...,p) The mean x * and s * are updated as follows: Calculate =.5 s *. A new value is then calculated for each result x i (i =, p): { x * -, if x i < x * - x * i = { x * +, if x i > x * +, { x i otherwise The new values of x * and s * are calculated from: * * x xi / p s. ( x i x ) /( p ) The robust estimates x * and s * can be derived by an iterative calculation, i.e. by updating the values of x * and s * several times, until the process convergences []. Proftest SYKE MET /9 7
APPENDIX 7 (/) APPENDIX 7: Results of each participant Measurand Unit Sample - Assigned value spt % 's result Md Mean s s % nstat Al µg/l AM -.8 5 6.7 6 µg/l DM -.5 7.9 5 6.9 7.6 7.9.5. µg/l GM.7..... 8.6 g/kg SO -.7 5.9 5 5. 5.9 5... 6 As µg/l AM -..5 5....6 5. µg/l DM.98 <.5.98.98.8 8. 9 µg/l GM.8 <.5.8.8..6 7 mg/kg SO -.88 6.89 5 6. 6.89 6.8.95. 6 Cd µg/l AM.8.75 5.76.7.7.5 6.7 µg/l DM -.. 5.... 6.5 µg/l GM 5..5 5..5.5. 6. mg/kg SO.69.5.69.67. 6. 6 Co µg/l AM -.7.5..7.7.7. µg/l DM -.8. 5.... 6.8 9 µg/l GM. 5 <..... 7 mg/kg SO -.6 5.7 5.5 5.7 5..6 7. 6 Cr µg/l AM -.59.5 5.... 5. µg/l DM -.59.57 5.5.57.56.6.6 µg/l GM.5 5 <.5.55. 5. 9 mg/kg SO -.57 58.9 5 5.7 58.9 58.9 6.. 6 Cu µg/l AM -.6.5.... 8. 5 µg/l DM -.77 56.8 5 5.5 55.8 56.9.9 5. µg/l GM -.8.57..5.55.7 7.6 mg/kg SO.6 7. 7.6 7. 69...6 6 Drw % SM.77 98. 5. 98. 98..5.5 Fe µg/l AM.57 75 8 7 76 8.7 5 µg/l DM -. 7.5 5.7 7. 7.7. 8.6 µg/l GM -.5 7.5 6.6 7. 7.6.6 8.9 g/kg SO -.8.5.7.5.6.7 7.7 6 Hg µg/l AHg -..5..6.5. 9.8 µg/l DHg.75 5 <..75.7.6 8. 7 µg/l GHg.5 5 <..5.5.9 6. 8 mg/kg SO -.86.7..7.7.6 8.7 6 Mn µg/l AM..5..7.5..5 5 µg/l DM -.6 5.6 5 5. 5.9 5.8.7.6 5 µg/l GM -.. 5.... 5.7 mg/kg SO -.7 7 5 677 7 75. 6 Ni µg/l AM.9 7.5 5 7. 7. 7.8..8 µg/l DM.5 <.5.55.. 7 µg/l GM..56 5.56.56.55.8 5. 9 mg/kg SO -.8 7..7 7. 7.7. 8.6 6 Ntot g/kg SN.7.9.7.6.6 5.6 5 Pb µg/l AM -.. 5...9.5.6 µg/l DM -..8 5..8.. 5.6 µg/l GM -.9.57 5.5.56.56. 7.6 mg/kg SO -. 5.8 5.9 5.8 6...7 6 8 Proftest SYKE MET /9
APPENDIX 7 (/) Measurand Unit Sample - Assigned value spt % 's result Md Mean s s % nstat Ptot g/kg SO -.5..... 9. 6 Se µg/l AM..5 5.9....7 µg/l DM.5 5 <.5.5. 5. 9 µg/l GM..9 5.9.9.9.. 8 mg/kg SO.8..8..88 6.8 Stot g/kg SO..7.99.8.8 9. TC g/kg SM 87.7 95. 87.7 87. 6. 7. 5 Ti µg/l AM.8.5..6.7.9. 9 µg/l DM 5.6 5 < 5.6 5..9 5. 7 µg/l GM. 6. 5 7.6 6. 6..9 5.9 8 mg/kg SO 8 8 8 758 6 6. U µg/l AM -.8.65 5.6.65.6. 5. µg/l DM. 5 <,5....6 µg/l GM -.87.9 5..9.8. 6. mg/kg SO.6.6.6.9.59 7. V µg/l AM -.7.5.88..5.. µg/l DM -.. 5.8..6.5 5. µg/l GM -.6.88 5.8.88.88.6 7. 9 mg/kg SO 6.7 6. 6.7 6. 6.5.6 6 Zn µg/l AM.7.5 5.8...6 5. µg/l DM -.. 5 9.9....9 µg/l GM -. 5. 5 5. 5. 5.5.9 5. mg/kg SO 8 5.5 5 Measurand Unit Sample - Assigned value spt % 's result Md Mean s s % nstat U µg/l AM -..65 5.65.65.6. 5. µg/l DM.5. 5.....6 µg/l GM.5.9 5.5.9.8. 6. mg/kg SN..77..7. 9.8 5 Measurand Unit Sample - Assigned value spt % 's result Md Mean s s % nstat Al µg/l AM. 5 7 6.7 6 µg/l DM 7.9 5 < 7.6 7.9.5. µg/l GM. <... 8.6 g/kg SO.65 5.9 5 8. 5.9 5... 6 As µg/l AM.5 5 <....6 5. µg/l DM.98 <.98.98.8 8. 9 µg/l GM.8 <.8.8..6 7 mg/kg SO. 6.89 5 6.9 6.89 6.8.95. 6 Cd µg/l AM.75 5 <..7.7.5 6.7 µg/l DM. 5 <.... 6.5 µg/l GM.5 5 <..5.5. 6. mg/kg SO.69.65.69.67. 6. 6 Proftest SYKE MET /9 9