Interlaboratory Proficiency Test 05/2018

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INTERLABORATORY PROFICIENCY TEST SYKE 05/2018FINNISH ENVIRONMENT INSTITUTE

Metals in natural waters and soil

Mirja Leivuori, Riitta Koivikko, Timo Sara-Aho, Teemu Näykki, Keijo Tervonen, Sari Lanteri,

Ritva Väisänen and Markku Ilmakunnas

REPORTS OF THE FINNISH ENVIRONMENT INSTITUTE 22 | 2018

SYKE

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Helsinki 2018

Finnish Environment Institute

Interlaboratory Proficiency Test 05/2018

Metals in natural waters and soil

Mirja Leivuori, Riitta Koivikko, Timo Sara-Aho, Teemu Näykki, Keijo Tervonen, Sari Lanteri,

Ritva Väisänen and Markku Ilmakunnas

SYKE

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The publication is also available in the Internet: www.syke.fi/publication | helda.helsinki.fi/syke

ISBN 978-952-11-4959-7 (pbk.) ISBN 978-952-11-4960-3 (PDF) ISSN 1796-1718 (print)

ISSN 1796-1726 (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) P.O. Box 140, FI-00251 Helsinki, Finland, Phone +358 295 251 000, syke.fi.

Year of issue: 2018

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soil in April-May 2018. The measurands for the synthetic, ground and lake water as well as soil samples were: Al, As, Ba, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, Sr, Ti, V, and Zn. In addition to the aforementioned, also measurands Ca and Mg were analysed from the soil sample. In total 20 participants joined in the PT. In this proficiency test 88 % of the results were satisfactory when deviation of 10–35 % from the assigned value was accepted.

Basically, either the metrologically traceable concentration, the calculated concentration, the robust mean, the mean or the median of the results reported by the participants was used as the assigned value for the measurands. The evaluation of the performance of the participants was carried out using z scores. In some cases the performance evaluation based on z scores was not possible e.g. due to the low number of the participant results or the high deviation of reported results. There, the evaluation of performance was carried out by E

n

scores.

Warm thanks to all the participants of this proficiency test!

Keywords: water analysis, metals, Al, As, Ba, Cd, Ca, Co, Cr, Cu, Fe, Hg, Mg, Mn, Ni, Pb, Se, Sr, Ti, V, Zn, water, environmental laboratories, proficiency test, interlaboratory comparisons

T IIV IS T E LM Ä

Laboratorioiden välinen pätevyyskoe 05/2018

Proftest SYKE järjesti pätevyyskokeen ympäristönäytteitä analysoiville laboratorioille huhti- toukokuussa 2018. Pätevyyskokeessa testattiin Al, As, Ba, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, Sr, Ti, V ja Zn synteettisestä näytteestä, pohja- ja järvivedestä sekä maasta. Maanäytteestä testattiin myös Ca ja Mg. Pätevyyskokeeseen osallistui yhteensä 20 osallistujaa. Koko tulosaineistossa hyväksyttäviä tuloksia oli 88 %, kun vertailuarvosta sallittiin 10–35 %:n poikkeama.

Osallistujien pätevyyden arviointi tehtiin z-arvon avulla. Testisuureen vertailuarvona käytettiin metrologisesti jäljitettävää pitoisuutta, laskennallista pitoisuutta, osallistujien ilmoittamien tulosten robustia keskiarvoa, keskiarvoa tai mediaania. Joissain tapauksissa tulosten vähäisen määrän tai suuren hajonnan vuoksi pätevyyden arviointi z-arvojen avulla ei ollut mahdollista. Tällöin, mikäli mahdollista, arviointi tehtiin E

n

-arvon avulla.

Kiitos pätevyyskokeen osallistujille!

Avainsanat: vesianalyysi, metallit, Al, As, Ba, Cd, Ca, Co, Cr, Cu, Fe, Hg, Mg, Mn, Ni, Pb, Se, Sr, Ti, V, Zn, vesi- ja ympäristölaboratoriot, pätevyyskoe, laboratorioiden välinen vertailumittaus

S AMM AND R AG Provningsjämförelse 05/2018

Proftest SYKE genomförde en provningsjämförelse i april-maj 2018, som omfattade bestämningen av Al, As, Ba, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, Sr, Ti, V och Zn i syntetik sample, natur och grundvatten och jorden, också Ca och Mg var bestämde i jorden. Tillsammans 20 laboratorier deltog i jämförelsen. I jämförelsen var 88 % av alla resultaten tillfredsställande, när avvikelsen 10–35 % från referensvärdet accepterades.

Som referensvärde av analytens koncentration användes mest det metrologiska spårbara värdet, teoretiska värdet, robust medelvärdet, medelvärdet eller median av deltagarnas resultat. Resultaten värderades med hjälp av z- eller E

n

-värden.

Ett varmt tack till alla deltagarna i testet!

Nyckelord: vattenanalyser, metaller, Al, As, Ba, Cd, Ca, Co, Cr, Cu, Fe, Hg, Mg, Mn, Ni, Pb, Se,

Sr, Ti, V, Zn, provningsjämförelse, vatten- och miljölaboratorier

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Abstract • Tiivistelmä • Sammandrag ... 3

1 Introduction ... 7

2 Organizing the proficiency test ... 7

2.1 Responsibilities ... 7

2.2 Participants ... 8

2.3 Samples and delivery... 8

2.4 Homogeneity and stability studies ... 9

2.5 Feedback from the proficiency test ... 9

2.6 Processing the data ... 9

2.6.1 Pretesting the data ... 9

2.6.2 Assigned values ... 9

2.6.3 Standard deviation for proficiency assessment and z score ... 10

3 Results and conclusions ... 11

3.1 Results ... 11

3.2 Analytical methods ... 14

3.3 Uncertainties of the results ... 15

4 Evaluation of the results ... 16

5 Summary ... 18

6 Summary in Finnish ... 19

References ... 19

: Participants in the proficiency test ... 21

APPENDIX 1 : Preparation of the samples ... 22

APPENDIX 2 : Homogeneity of the samples ... 23

APPENDIX 3 : Feedback from the proficiency test ... 24

APPENDIX 4 : Evaluation of the assigned values and their uncertainties ... 25

APPENDIX 5 : Terms in the results tables ... 27

APPENDIX 6 : Results of each participant ... 28

APPENDIX 7 : Summary of the z and E

n

scores ... 52

APPENDIX 8 : z scores in ascending order ... 55

APPENDIX 9 : Results grouped according to the methods ... 77

APPENDIX 10 : Significant differences in the results reported using different methods ... 107

APPENDIX 11 : Examples of the measurement uncertainties reported by the participants .... 108

APPENDIX 12

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Proftest SYKE carried out in April-May 2018 (MET 05/18) the proficiency test (PT) for analysis of elements in ground and natural waters and in soil. The measurands for the synthetic sample, ground and lake water samples as well as soil sample were: Al, As, Ba, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, Sr, Ti, V, and Zn. In addition to the aforementioned, also measurands Ca and Mg were analysed from the soil sample. In total 20 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 was carried out in accordance with the international guidelines ISO/IEC 17043 [1], ISO 13528 [2]

and IUPAC Technical report [3]. The Proftest SYKE is accredited by the Finnish Accreditation Service as a proficiency testing provider (PT01, ISO/IEC 17043, www.finas.fi/sites/en). The organizing of this proficiency test is included in the accreditation scope of the Proftest SYKE.

2 Organizing the proficiency test

2.1 Responsibilities

Organizer:

Proftest SYKE, Finnish Environment Institute (SYKE), Laboratory Centre Ultramariinikuja 4 (formerly Hakuninmaantie 6), FI-00430 Helsinki, Finland Phone: +358 295 251 000, Email: proftest@environment.fi

The responsibilities in organizing the proficiency test were as follows:

Mirja Leivuori coordinator

Riitta Koivikko substitute for coordinator Keijo Tervonen technical assistance Markku Ilmakunnas technical assistance Sari Lanteri technical assistance Ritva Väisänen technical assistance

Timo Sara-Aho analytical expert (metals, ID-ICP-MS)

Teemu Näykki analytical expert (Hg, ID-ICP-MS)

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participants used accredited analytical methods at least for a part of the measurands. For this proficiency test, the organizing laboratory (T003, ISO/IEC 17025, www.finas.fi/sites/en) has the codes 2 and 21 (SYKE, Helsinki) in the result tables.

2.3 Samples and delivery

Four types of samples were delivered to the participants: synthetic, ground and lake water as well as soil samples. The sample preparation is described in details in the Appendix 2.

The synthetic sample A1M was prepared from the NIST traceable commercial reference material produced by Inorganic Ventures. The synthetic sample A1Hg was prepared by diluting from the NIST traceable AccuTrace

^TM

Reference Standard produced by AccuStandard, Inc.

The sample G2M was ground water collected from the southern Finland and the sample N3M was lake water collected from the Lake Lohjanjärvi, located in southern Finland. To these samples additions of single element standard solutions (Merck CertiPUR

^®

) were done when needed (Appendix 2). The water samples were acidified with nitric acid with the exception of samples for mercury, which were acidified with the hydrochloric acid.

The tested soil sample M4M (after analysis: MC4 – oxygen combustion (only Hg) / MN4 – digestion with HNO

3

/ MO4 – digestion with HNO

3

+ HCl) was moorland soil sample used in the previous SYKE PT 05/2003 [4 ]. Soil was manually rehomogenized and divided into sub- samples. The homogeneity of the soil 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 23 April 2018 to the participants abroad and on 24 April 2018 to the national participants. The samples arrived to the participants mainly on 25 April 2018.

One participant received the samples on 27 April 2018.

The samples were requested to be measured as follows:

Mercury (A1Hg, G2Hg and N3Hg) latest on 4 May 2018

The other samples latest on 11 May 2018

The results were requested to be reported latest on 14 May 2018. Participants delivered the

results mainly accordingly, one participant reported the results on the following day. The

preliminary results were delivered to the participants via ProftestWEB and email on 21 May

2018.

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More detailed information of the homogeneity studies is shown in Appendix 3. 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 soil sample was the same as in the previous SYKE PT 05/2003 [4]. The homogeneity of the soil sample was tested after rehomogenization by parallel measurements (Cd, Cr, Cu, Hg, and Zn) of three samples and they confirmed the homogeneity of the sample.

Based on the earlier similar proficiency tests the water samples are known to be stable over the given time period for the test.

2.5 Feedback from the proficiency test

The feedback from the proficiency test is shown in Appendix 4. The comments from the participants mainly dealt with some clarification for their performance in the PT. The comment from the provider is focused to the lacking conversancy to the given information with the samples. All the feedback is valuable and is exploited when improving the activities.

2.6 Processing the data

2.6.1 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 s

rob

× 5 or 50 % 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].

2.6.2 Assigned values

For the synthetic sample A1M the NIST traceable calculated concentrations were used as the assigned value, with the exception of Al, Cr, Hg, and Pb. The robust mean of the results was used as the assigned value for Al and Cr in A1M. The assigned values for Hg and Pb are based on the results of the metrologically traceable isotope dilution (ID) ICP-MS technique for the samples A1M, A1Hg, G2M, G2Hg, N3M and N3Hg. The assigned value based on the ID-ICP- MS method is the mean of the homogeneity results and the test result. The ID-ICP-MS method is accredited for soluble lead in synthetic and natural waters and for soluble mercury in synthetic, natural and waste water in the scope of calibration laboratory (K054;

www.finas.fi/sites/en). In this PT the ID-ICP-MS results for the samples A1Hg and N3Hg are

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variation in the results, basically the mean value or median was reported as the assigned value (MN4 and MO4: all measurands, G2M: Cr, Mn, Ni, Se, Ti, V, Zn, N3M: As, Fe, V). For some measurands assigned value is not given due to the low number of results and high variability within the results (e.g. MM4: Ca, Ti, MO4: Se, Ti).

The robust mean, the mean or the median is not metrologically traceable assigned value. As it was not possible to have metrologically traceable assigned value, the robust mean, the 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 [2, 3].

The expanded uncertainty (k=2) 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 using the robust mean, the mean or the median as assigned value, the uncertainty of the assigned value was calculated using the robust standard deviation or standard deviation of the reported results [2, 5]. For the metrologically traceable mercury and lead results, the uncertainty is the expanded measurement uncertainty of the ID-ICP-MS method.

The uncertainty of the calculated assigned value and the metrologically traceable value for metals in the synthetic samples varied between 0.5 and 3 %. When using the robust mean, the mean or the median of the participant results as the assigned value, the uncertainties of the assigned values were between 1 and 32 % (Appendix 5).

The assigned values have not been changed after reporting the preliminary results.

2.6.3 Standard deviation for proficiency assessment and z score

The standard deviation for proficiency assessment was estimated on the basis of the uncertainty of the assigned values, the concentrations of the measurands, the results of homogeneity and stability tests, and the long-term variation in the former proficiency tests. If the number of reported results were low, the standard deviation for proficiency assessment and the assigned value were not set (MN4: Ca,Ti, MO4: Se, Ti). The standard deviation for the proficiency assessment (2×s

_pt

at the 95 % confidence level) was set to 10–35 % depending on the sample and measurand. The standard deviations for the proficiency assessment have not been changed after reporting the preliminary results.

When the number of reported results was low 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

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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.

Scores of E

n

-1.0 < E

n

< 1.0 should be taken as an indicator of successful performance when the uncertainties are valid. Whereas scores E

n

1.0 or E

n

-1.0 could indicate a need to review the uncertainty estimates, or to correct a measurement issue.

When using the robust mean, the mean or the median as the assigned value, the reliability was tested according to the criterion u

pt

/ s

pt

0.3, where u

pt

is the standard uncertainty of the assigned value and s

pt

is the standard deviation for proficiency assessment [3]. 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 z score was estimated by comparing the deviation for proficiency assessment (s

pt

) with the robust standard deviation (s

rob

) or the standard deviation (sd) of the reported results [3]. The criterion s

rob

/ s

pt

< 1.2 was mainly fulfilled, also in the case of using the standard deviation.

In the following cases, the criterion for the reliability of the assigned value

¹

and/or for the reliability of the deviation for proficiency assessment

²

was not met and, therefore, the evaluation of the performance is weakened in this proficiency test:

Sample Measurand

G2M Al

¹

, Ba

¹

, Ni

¹

, Ti

¹

MO4 Al

¹

, As

¹

, Cd

¹

, Fe

¹

, Hg

¹

, Mn

¹

, Ni

¹

, Sr

¹

, V

¹

N3M Al

¹

, Cu

¹

, Mn

¹

, Ni

¹

, Se

^1,2

, Ti

¹

, V

¹

, Zn

¹

3 Results and conclusions

3.1 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 1. The summaries of the z and E

n

scores are shown in Appendix 8. In Appendix 9 the

z scores are shown in the ascending order. The reported results with their expanded

uncertainties (k=2) grouped according to the methods are presented in Appendix 10.

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MN4 g/kg 23.6 23.6 22.9 - 6 -

MO4 g/kg 24.2 24.2 24.2 24.5 3.3 13.5 25 9 78

N3M µg/l 1425 1425 1425 1383 126 8.9 15 17 94

As A1M µg/l 2.50 2.50 2.48 2.47 0.19 7.7 15 14 85

G2M µg/l 0.32 0.32 0.32 0.32 0.03 9.2 30 14 77

MN4 mg/kg 9.01 9.01 9.99 - 6 -

MO4 mg/kg 10.7 10.7 10.7 11.0 1.4 13.2 25 9 89

N3M µg/l 0.77 0.77 0.77 0.79 0.07 9.0 25 13 83

Ba A1M µg/l 34.0 33.8 34.1 33.8 1.7 5.0 15 12 92

G2M µg/l 4.50 4.51 4.50 4.44 0.41 9.0 20 13 100

MN4 mg/kg 134 132 134 - 5 -

MO4 mg/kg 123 123 122 120 12 9.7 25 9 78

N3M µg/l 25.6 25.4 25.6 25.4 1.0 3.9 10 12 83

Ca MN4 g/kg 4.09 4.61 - 5 -

MO4 g/kg 5.41 5.41 5.44 - 8 -

Cd A1M µg/l 0.45 0.44 0.44 0.44 0.03 6.8 15 16 100

G2M µg/l 0.22 0.22 0.22 0.22 0.02 8.1 20 16 87

MN4 mg/kg 0.73 0.69 0.73 - 6 -

MO4 mg/kg 0.75 0.75 0.75 0.74 0.14 18.1 20 10 70

N3M µg/l 0.54 0.54 0.54 0.54 0.04 8.1 20 15 100

Co A1M µg/l 1.25 1.24 1.24 1.25 0.06 4.5 10 13 100

G2M µg/l 0.80 0.79 0.80 0.81 0.06 8.2 20 13 92

MN4 mg/kg 10.3 9.98 10.30 - 5 -

MO4 mg/kg 10.2 11.1 10.9 10.2 3.1 28.6 - 9 -

N3M µg/l 1.39 1.38 1.39 1.40 0.08 5.6 15 13 92

Cr A1M µg/l 1.35 1.34 1.35 1.35 0.09 6.6 15 14 100

G2M µg/l 0.76 0.76 0.76 0.76 0.09 12.2 20 14 92

MN4 mg/kg 58.0 56.0 58.0 - 6 -

MO4 mg/kg 57.5 57.5 57.5 55.8 6.0 10.5 25 10 80

N3M µg/l 2.41 2.41 2.41 2.40 0.20 8.2 20 14 100

Cu A1M µg/l 7.35 7.17 7.17 7.20 0.42 5.9 10 15 87

G2M µg/l 20.3 20.2 20.3 20.6 1.6 7.7 15 17 94

MN4 mg/kg 116 113 116 - 6 -

MO4 mg/kg 115 115 115 113 10 8.5 20 9 78

N3M µg/l 7.06 7.06 7.06 7.25 0.53 7.5 15 15 93

Fe A1M µg/l 335 339 337 338 20 6.0 10 17 88

G2M µg/l 333 333 333 332 14 4.1 10 18 78

MN4 g/kg 33.6 33.8 33.6 - 6 -

MO4 g/kg 35.9 37.0 36.6 35.9 3.5 9.7 25 9 78

N3M µg/l 1573 1592 1592 1573 99 6.2 10 17 100

Hg A1Hg µg/l 0.44 0.44 0.44 0.44 0.04 10.1 20 13 92

G2Hg µg/l 0.088 0.089 0.088 0.089 0.015 16.6 25 14 77

MC4 mg/kg 0.27 0.27 0.27 - 3 -

MN4 mg/kg 0.23 0.23 0.23 - 5 -

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Mn A1M µg/l 2.25 2.20 2.21 2.22 0.10 4.7 15 17 94

G2M µg/l 81.5 80.9 80.9 81.5 4.9 6.0 10 18 83

MN4 mg/kg 426 426 416 - 6 -

MO4 mg/kg 423 423 423 420 58 13.8 25 9 78

N3M µg/l 101 101 101 100 6 5.7 10 17 100

Ni A1M µg/l 4.25 4.13 4.15 4.14 0.24 5.9 15 14 93

G2M µg/l 0.98 0.98 0.97 0.96 0.13 13.6 25 14 69

MN4 mg/kg 21.6 19.1 21.6 - 6 -

MO4 mg/kg 20.6 20.6 20.6 19.3 3.2 15.4 25 10 90

N3M µg/l 3.04 3.04 3.04 3.11 0.30 9.9 20 13 85

Pb A1M µg/l 1.27 1.21 1.22 1.24 0.08 6.7 15 15 93

G2M µg/l 1.02 0.96 0.96 0.98 0.06 6.5 15 15 86

MN4 mg/kg 27.5 27.0 27.5 - 6 -

MO4 mg/kg 24.2 24.2 24.2 23.5 2.8 11.5 25 10 80

N3M µg/l 0.84 0.80 0.80 0.80 0.05 5.7 15 14 92

Se A1M µg/l 3.25 3.23 3.14 3.22 0.29 9.4 15 12 82

G2M µg/l 1.36 1.36 1.38 1.36 0.08 5.5 15 12 82

MN4 mg/kg 2.00 2.02 2.00 - 5 -

MO4 mg/kg 2.39 2.04 - 7 -

N3M µg/l 0.53 0.52 0.54 0.53 0.08 15.4 25 11 70

Sr A1M µg/l 8.75 8.83 8.81 8.75 0.37 4.2 10 12 92

G2M µg/l 140 140 140 140 8 6.0 15 13 92

MN4 mg/kg 22.4 25.0 22.3 - 6 -

MO4 mg/kg 33.2 34.1 33.2 30 8 75

N3M µg/l 44.8 44.9 44.8 44.6 2.3 5.2 15 12 100

Ti A1M µg/l 45.0 45.3 45.2 45.1 2.3 5.1 10 13 100

G2M µg/l 10.1 10.2 10.2 10.1 1.0 10.1 15 13 83

MN4 mg/kg 1348 982 - 5 -

MO4 mg/kg 2165 2165 2196 2109 97.5 - 8 -

N3M µg/l 63.2 61.8 61.6 63.2 7.9 12.8 20 12 75

V A1M µg/l 10.3 10.0 10.0 9.9 0.4 4.3 10 13 92

G2M µg/l 1.42 1.42 1.42 1.40 0.13 9.3 20 13 92

MN4 mg/kg 69.8 69.3 - 5 -

MO4 mg/kg 65.6 64.9 64.9 65.6 14.6 22.6 35 9 78

N3M µg/l 2.80 2.76 2.77 2.80 0.22 8.1 15 12 83

Zn A1M µg/l 5.25 5.41 5.92 5.50 1.04 17.5 20 15 73

G2M µg/l 13.7 13.7 13.9 13.5 1.3 9.3 15 15 87

MN4 mg/kg 77.9 77.3 77.9 - 6 -

MO4 mg/kg 73.7 73.7 73.6 73.7 8.3 11.2 25 9 89

N3M µg/l 9.37 9.36 9.37 9.46 0.65 6.9 15 14 79

Rob. mean: the robust mean, s

rob

: the robust standard deviation, s

rob

%: the robust standard deviation as percent, 2×s

pt

%: the total standard deviation for proficiency assessment at the 95 % confidence level, Acc z %: the results (%), where

z 2, n(all): the total number of the participants.

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the soil sample (MO4, Table 1). The robust standard deviations for water samples (4.1 % – 16.6 %) were approximately the same than in the previous similar proficiency test MET 04/2017 [6], where the deviations varied from 3 % to 21 % for the water samples. For the soil sample the robust standard deviations were in the same range (8.5 % – 29 %) as in the previous similar proficiency test Proftest SYKE MET 04/2015 [7], where the deviations varied from 2.5 % to 28 %. The robust standard deviation was not calculated when the number of results within the statistical evaluation was low (< 7, Table 1).

3.2 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 10. 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 11.

Effect of sample pretreatment on elemental concentrations in soil sample

The soil sample M4M was measured using pretreatment and the results from different pretreatment procedures were processed separately in data handling. Mostly the participants (from 5 to 6 depending on measurand) measured the soil sample after nitric acid digestion (MN4, Table 1, Appendix 10). The other participants used acid mixture of HNO

₃

+HCl for the digestion (MO4). For Hg measurements five participants used the nitric acid digestion (MN4), eight used acid mixture of HNO

3

+HCl (MO4) for the digestion and three participants used the oxygen combustion pretreatment (MC4).

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 Pb analyses where acid digestion with nitric acid (MN4) gave significantly higher results (27.0 mg/kg) than acid digestion with acid mixture of HNO

3

+HCl (MO4, 24.2 mg/kg, Appendix 11).

Effect of measurement methods on elemental results

The most commonly used analytical method was ICP-MS and ICP-OES. Only few participants (1-2) used FAAS or GAAS techniques for some measurands (Appendix 10). 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 difference was observed, when the number of results were high enough for the statistical comparison.

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

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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 remained lower than the assigned values of Ni, Pb and V for the sample A1M. However, the differences were generally within the reported measurement uncertainties of the participants.

Effect of measurement methods on mercury results

For the analysis of mercury, ICP-MS was the most often used method of analysis. That was followed by CV-AFS and CV-AAS. Other used methods were CV-ICP-MS, ICP-OES, and direct combustion (Appendix 10). No significant differences between the used measuring methods were found. For the sludge sample, aqua regia digestion (MO4) was more often used than nitric acid digestion (MN4).

As for other metal determinations, also mercury results are 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 to be used for sample preservation and BrCl is recommended to be used for oxidation of mercury species.

Generally, the differences in mercury results may be mainly due to different pretreatment procedures. Analytical techniques does not have so much effect on the results, but the fact is that for example using CV-AFS lower detection limits can be achieved compared to CV-AAS.

CV-ICP-MS technique is known have very competent detection limits as well.

3.3 Uncertainties of the results

At maximum 76 % of the participants reported the expanded uncertainties (k=2) with their results for at least some of their results (Table 2, Appendix 10). Several approaches were used for estimating the measurement uncertainty (Appendix 12). 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 12) [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 2, some of the participants have over-estimated their expanded (k=2)

measurement uncertainty. Very high measurement uncertainties (i.e. 50 % or higher) should not

exist, unless the measured concentration is near to the limit of quantification. In this PT the

participants did not report expanded uncertainties below 5%, which could commonly be

considered unrealistic uncertainty value for routine laboratories.

(18)

Al 10-41 6-41 5-41 17-51

As 10-23 10-30 10-30 10-25

Ba 10-20 10-25 10-20 10-30

Ca - - - 14-30

Cd 7-22 7-22 7-22 20-50

Co 9-20 10-20 9-20 14-50

Cr 9-27 9-25 9-30 12-30

Cu 9-20 9-20 9-20 10-30

Fe 8-35 8-35 5-35 15-30

Hg 10-30 15-30 15-30 16-30

Mg - - - 15-30

Mn 10-44 7-20 5-20 15-30

Ni 10-39 10-32 10-39 10-27

Pb 10-30 10-30 10-30 15-30

Se 10-30 10-30 10-50 20-30

Sr 9-30 9-30 9-30 15-35

Ti 10-30 10-30 10-30 20-35

V 10-22 10-50 10-22 20-30

Zn 10-35 8-35 8-35 15-41

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 [10]. The recommendation for measurement uncertainties for all tested measurands in natural waters is 15 %. 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.

4 Evaluation of the results

The evaluation of the participants was based on the z and E

n

scores, using the assigned values and the standard deviation for performance assessments (Appendix 6). The z and E

n

scores were interpreted as follows:

Criteria Performance

z 2 Satisfactory

2 < z < 3 Questionable

| z 3 Unsatisfactory

-1.0 < E

n

< 1.0 Satisfactory

E

n

- 1.0 or E

n

1.0 Unsatisfactory

(19)

Altogether 81 % of the participants used accredited analytical methods at least for a part of the measurands and 93 % of their results were satisfactory. In the previous similar kind PT MET 04/2015, the performance was satisfactory for 89 % of the results when deviation 10–35 % from the assigned value was accepted [7]. The summary of the performance evaluation and comparison to the previous performance is presented in Table 3.

Table 3. Summary of the performance evaluation in the proficiency test MET 05/2018.

Sample Satisfactory

results (%) Accepted deviation from the

assigned value (%) Remarks A1M,

A1Hg

90 10 – 20 Mainly good performance.

Difficulties in measurements for Zn, < 80%

satisfactory results.

In the previous PTs MET 04/2017 and MET 04/2015 and the performance was satisfactory for 90 and 88 % of the results, respectively [6, 7].

G2M,

G2Hg 86 10 – 25 Only approximate assessment for Al, Ba, Ni, Ti.

Difficulties in measurements for Hg, As, Fe, and Ni,

< 80% satisfactory results.

In the previous PT MET 04/2015 and the

performance was satisfactory for 91 % of the results, respectively [7].

N3M,

N3Hg 90 10 – 25 Mainly good performance.

Only approximate assessment for Al, Cu, Mn, Ni, Se, Ti, V, Zn.

Difficulties in measurements for Se and Ti, < 80%

satisfactory results.

In the previous PTs MET 04/2017 and MET 04/2015 the performance was satisfactory for 94 % of the results, respectively [6, 7].

MN4 80

based on E

n

score

In the previous PT MET 04/2015 the performance was satisfactory based on z scores for 80 % of the results when accepting the deviation of 10-30 % from the assigned value [7].

MO4 71 20 – 35 Only approximate assessment for Al, As, Cd, Fe, Hg,

Mn, Ni, Sr, V.

In the previous PT MET 04/2015 the performance was satisfactory for 85 % of the results when accepting the deviation of 15-30 % from the assigned value [7].

The satisfactory results based on z scores varied between 71 % and 90 % for the tested sample types (Table 3). The share of satisfactory results in the synthetic sample A1M was the lowest for Zn, about 73 %. Totally the share was in the same level as in the previous proficiency tests in 2017 and 2015 (Table 3) [6, 7].

For the ground water sample G2M all results for Ba were satisfactory. For the natural (lake)

water sample N3M all results for Cd, Fe, Mn and Sr were satisfactory. In this proficiency test

the share of satisfactory results was almost in the same level as in the previous proficiency tests

(Table 3) [6, 7].

(20)

(HNO

3

+HCl, MO4), was satisfactory based on z scores for 71 % of the results when accepting the deviation of 20–35 % from the assigned value. The performance was lower than in the previous PT MET 04/2015 where 85 % of results were satisfactory when the deviation of 15–30 % from the assigned value was accepted [7].

5 Summary

Proftest SYKE carried out the proficiency test (PT) for analysis of elements in natural waters and soil in April-May 2018 (MET 05/18). The measurands for the synthetic sample, ground and lake water samples as well as for soil sample were: Al, As, Ba, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, Sr, Ti, V, and Zn. In addition to the aforementioned, also measurands Ca and Mg were analysed from the soil sample. In total 20 participants joined in the PT.

For the synthetic sample A1M the NIST traceable calculated concentrations were used as the assigned value, with the exception of Al, Cr, Hg, and Pb. The robust mean of the results was used as the assigned value for Al and Cr in A1M. The assigned values for Hg and Pb are based on the results of the metrologically traceable isotope dilution (ID) ICP-MS technique for the samples A1M, A1Hg, G2M, G2Hg, N3M and N3Hg. Basically, for the other samples and measurands the robust mean value was used as the assigned value. If the number of results was low or there was high variation in the results, basically the mean value or median was reported as the assigned value (MN4, MO4: all measurands, G2M: Cr, Mn, Ni, Se, Ti, V, Zn, N3M: As, Fe, V). For some measurands assigned value is not given due to the low number of results and high variability within the results (e.g. MM4: Ca, Ti, MO4: Se, Ti).

The uncertainty for the assigned value was estimated at the 95 % confidence level and it was between 0.5 and 3 % for the calculated and metrologically traceable assigned values and for assigned values based on the robust mean, the mean or the median it was between 1–32 %.

The evaluation of the performance was based on the z scores, which were calculated using the

standard deviation for proficiency assessment at 95 % confidence level. In this proficiency test

88 % of the data was regarded satisfactory when the results were accepted to deviate from the

assigned values 10 to 35 %. The evaluation of the performance of the soil sample results

obtained by the digestion with nitric acid (MN4) was based on the E

n

scores and 80 % of the

results were satisfactory. About 81 % of the participants used accredited methods and 93 % of

their results were satisfactory.

(21)

Proftest SYKE järjesti ympäristönäytteitä analysoiville laboratorioille pätevyyskokeen huhti- toukokuussa 2018. Pätevyyskokeessa testattiin Al, As, Ba, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, Sr, Ti, V ja Zn synteettisestä näytteestä, pohja- ja järvivedestä sekä maasta. Maanäytteestä testattiin myös Ca ja Mg. Pätevyyskokeessa oli yhteensä 20 osallistujaa.

Testisuureen vertailuarvona käytettiin laskennallista pitoisuutta, osallistujien tulosten robustia keskiarvoa, keskiarvoa tai mediaania. Lyijylle ja elohopealle käytettiin metrologisesti jäljitet- tävää tavoitearvoa osalla testinäytteistä. Vertailuarvolle laskettiin laajennettu epävarmuus 95 % luottamusvälillä. Vertailuarvon laajennettu epävarmuus oli 0,5 ja 3 % välillä laskennallista tai metrologisesti jäljitettävää pitoisuutta vertailuarvona käytettäessä ja muilla välillä 1–32 %.

Pätevyyden arviointi tehtiin z-arvon avulla ja tulosten sallittiin poiketa vertailuarvosta 10–35 %. Koko aineistossa hyväksyttäviä z-arvotuloksia oli 88 %. Maanäytteen typpihappo- hajotuksella saadut tulokset (MN4) arvioitiin E

n

-arvoilla ja näistä 80 % oli hyväksyttyjä. Noin 81 % osallistujista käytti akkreditoituja määritysmenetelmiä ja näistä tuloksista oli hyväksyttäviä 93 %.

R E FE R E NC E S

1. SFS-EN ISO 17043, 2010. Conformity assessment – General requirements for Proficiency Testing.

2. ISO 13528, 2015. Statistical methods for use in proficiency testing by interlaboratory comparisons.

3. Thompson, M., Ellison, S. L. R., Wood, R., 2006. The International Harmonized Protocol for the Proficiency Testing of Analytical Chemistry laboratories (IUPAC Technical report).

Pure Appl. Chem. 78: 145-196, www.iupac.org.

4. Mäkinen, I., Huhtala, S., Järvinen, O., Näykki, T. and Ilmakunnas, M. 2004.

Laboratorioiden välinen pätevyyskoe 5/2003. Metallit ja elohopea vesistä ja maasta.

Suomen ympäristökeskuksen moniste 295 (In Finnish). Helsinki.

(http://hdl.handle.net/10138/178240).

5. Proftest SYKE Guide for laboratories: www.syke.fi/proftest/en Current proficiency tests www.syke.fi/download/noname/%7B3FFB2F05-9363-4208-9265-1E2CE936D48C%7D/39886 . 6. Leivuori, M., Koivikko, R., Sara-Aho, T., Näykki, T., Tervonen, K., Lanteri, S., Väisänen,

R. and Ilmakunnas, M. 2017. Interlaboratory Proficiency Test 04/2017. Metals in natural waters. Reports of Finnish Environment Institute 25/2017. Helsinki.

(http://hdl.handle.net/10138/217482).

(22)

(http://hdl.handle.net/10138/156303).

8. Magnusson B., Näykki T., Hovind H., Krysell M., Sahlin E., 2017. Handbook for Calculation of Measurement Uncertainty in Environmental Laboratories. Nordtest Report TR 537 (ed. 4). (http://www.nordtest.info)

9. Näykki, T., Virtanen, A. and Leito, I., 2012. Software support for the Nordtest method of measurement uncertainty evaluation. Accred. Qual. Assur. 17: 603-612. MUkit website:

www.syke.fi/envical.

10. Näykki, T. and Väisänen, T. (Eds.) 2016. Laatusuositukset ympäristöhallinnon

vedenlaaturekistereihin vietävälle tiedolle: Vesistä tehtävien analyyttien määritysrajat,

mittausepävarmuudet sekä säilytysajat ja –tavat. - 2. uudistettu painos. (Quality

recommendations for data entered into the environmental administration’s water quality

registers: Quantification limits, measurement uncertainties, strorage times and methods

associated with analytes determined from waters). Suomen ympäristökeskuksen raportteja

22/2016. 57 pp. (In Finnish). (http://hdl.handle.net/10138/163532).

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: Participants in the proficiency test APPENDIX 1

Country Participant

Finland Eurofins Ahma Oy, Oulu

Eurofins Environment Testing Finland Oy, Lahti Eurofins Nab Labs Oy Jyväskylä

Freeport Cobalt Oy

HY/Ympäristötieteidenlaitos/Almalab KVVY Tutkimus Oy, Tampere Kymen Ympäristölaboratorio Oy

Lounais-Suomen vesi- ja ympäristötutkimus Oy, Turku Luonnonvarakeskus, Viikki B2-laboratorio

MetropoliLab Oy

SeiLab Oy Haapaveden toimipiste SeiLab Oy Seinäjoen toimipiste SGS Finland Oy, Kotka

STUK, Ympäristön säteilyvalvonta, Valvonta ja Mittaus (VAM) SYKE Ympäristökemia Helsinki

SYNLAB Analytics & Services Finland Oy

Teknologian tutkimuskeskus VTT Oy, Ydinturvallisuus Luxembourg Laboratoire National de Sante

Norway Eurofins Environment Norway A/S, Moss, Norway

Sweden ACES, Stockholm University

(24)

The synthetic sample A1M was prepared by diluting from the NIST traceable certified reference materials produced by Inorganic Ventures. The synthetic sample A1Hg was prepared by diluting from the NIST traceable AccuTrace

^TM

Reference Standard produced by AccuStandard, Inc. The water samples G2M and N3M were prepared by adding some separate metal solutions (Merck CertiPUR

^®

) into the original water sample, if the original concentration was not high enough. Samples G2Hg and N3Hg 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 soil sample (after analysis: MC4, MN4, MO4) was reused soil sample from the previous SYKE PT 05/2003 [4].

Measurand A1M µg/l

G2M µg/l

N3M µg/l

MN4/MO4 mg/kg

Measurand A1M µg/l

G2M µg/l

N3M µg/l

MN4/MO4 mg/kg Al Original

Dilution Addition Ass. value

125 10 - 16.8

93 - - 200

810 - - 1425

26 g/kg - - 23.6/24.2

Fe Original Dilution Addition Ass. value

3350 10

- 335

180 - - 333

860 - - 1573

37 g/kg - - 33.6/35.9 As Original

25 10 - 2.50

0.27 - - 0.32

0.72 - - 0.77

6.8 - - 9.01/10.7

Mg Original Dilution Addition Ass. value

- - - -

12 g/kg - - 11.4/12.3 Ba Original

340 10 - 34.0

4.6 - - 4.5

22 - - 25.6

130 - - 134/123

Mn Original Dilution Addition Ass. value

22.5 10

- 2.25

47 - - 81.5

77 - - 101

440 - - 426/423 Ca Original

- - - -

5.4 g/kg - - -/5.41

Ni Original Dilution Addition Ass. value

42.5 10

- 4.25

1.5 - - 0.98

4.9 - - 3.04

21 - - 21.6/20.6 Cr Original

12.5 10

- 1.35

0.17 - 0.3 0.76

1.2 - - 2.41

59 - - 58.0/57.5

Sr Original Dilution Addition Ass. value

87.5 10

- 8.75

140 - - 140

44 - - 44.8

38 - - 22.4/33.2 Cu Original

73.5 10

- 7.35

20 - - 20.3

7.8 - - 7.06

120 - - 116/115

Ti Original Dilution Addition Ass. value

450 10 - 45.0

2.2 - - 10.1

29 - - 63.2

510 - - - V Original

102.5 10

- 10.3

1.2 - - 1.42

1.7 - - 2.80

42 - - -/65.6

Hg Original Dilution Addition Ass. value

- - 0.45 0.44

0.0008 - 0.089 0.088

0.004 - 0.246

0.25

0.27 - - 0.27/0.23/

0.27 Zn Original

52.5 10

- 5.25

14 - - 13.7

5.8 - - 9.37

75 - - 77.9/73.7 Original = the original concentration

Dilution = the ratio of dilution Addition = the addition concentration Ass. value = the assigned value

(25)

: Homogeneity of the samples APPENDIX 3

The homogeneity was checked for the selected samples and measurands as duplicate measurements.

Criteria for homogeneity:

s

anal

/s

h

<0.5 and s

sam

2

<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 = F1 × s

all2

+ F2 × s

anal2

, where s

all2

= (0.3 × s

h

)

²

,

F1 and F2 are constants of F distribution derived from the standard statistical tables for the tested number of samples [2, 3].

Measurand/Sample Concentration

[µg/l, mg/kg] n s

pt

% s

h

% s

h

s

anal

s

anal

/s

h

s

anal

/s

h

<0.5? s

sam2

c s

sam2

<c?

Cd/G2M 0.24 3 7.5 2.0 0.005 0.002 0.356 Yes 0.00001 0.00002 Yes

Cr/G2M 0.82 3 10 3.5 0.029 0.004 0.136 Yes 0.0003 0.0003 Yes

Cu/G2M 21.7 3 7.5 0.9 0.195 0.096 0.491 Yes 0.034 0.049 Yes

Se/G2M 1.48 3 7.5 1.3 0.019 0.009 0.470 Yes 0 0.0004 Yes

Ti/G2M 9.68 3 7.5 1.0 0.097 0.017 0.173 Yes 0.004 0.004 Yes

Zn/G2M 15.2 3 7.5 2.4 0.365 0.181 0.495 Yes 0.038 0.176 Yes

Cd/N3M 0.58 3 10 0.8 0.005 0.0004 0.084 Yes 0.000006 0.000007 Yes

Cr/N3M 2.79 3 10 0.8 0.022 0.011 0.480 Yes 0.0004 0.0006 Yes

Cu/N3M 7.69 3 7.5 0.4 0.031 0.014 0.445 Yes 0.001 0.001 Yes

Se/N3M 0.53 3 12.5 4.4 0.024 0.012 0.492 Yes 0 0.0007 Yes

Ti/N3M 68.7 3 10 3.1 2.129 1.060 0.498 Yes 0 6.024 Yes

Zn/N3M 10.0 3 7.5 6.4 0.642 0.050 0.078 Yes 0.121 0.122 Yes

Cd/M4M 0.68 3 10 2.0 0.014 0.007 0.489 Yes 0 0.0002 Yes

Cr/M4M 55.0 3 12.5 1.0 0.550 0.249 0.454 Yes 0.120 0.348 Yes

Cu/M4M 106 3 10 0.9 0.953 0.233 0.244 Yes 0.451 0.478 Yes

Hg/M4M 0.26 3 17.5 3.1 0.008 0.004 0.489 Yes 0 0.0001 Yes

Zn/M4M 67.9 3 12.5 0.5 0.340 0.163 0.480 Yes 0.010 0.145 Yes

Hg/G2Hg* 0.09 3 12.5 2.2 0.002 0.0002 0.108 Yes 0 0 Yes

Hg/N3Hg* 0.25 3 10 1.2 0.003 0 0 Yes 0.000002 0.000002 Yes

Pb/G2M* 1.03 3 7.5 0.7 0.007 0.004 0.483 Yes 0 0.0001 Yes

Pb/N3M* 0.84 3 7.5 1.2 0.010 0.001 0.134 Yes 0.00004 0.00004 Yes

n= number of tested sub-samples

*) result based on the ID-ICP-MS measurement s

pt

% = standard deviation for proficiency assessment

Conclusion: The criteria were fulfilled for the tested measurands and the samples were regarded

as homogenous

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FEEDBACK FROM THE PARTICIPANTS

Participant Comments on technical execution Action / Proftest 10 The participant asked the reason for sample

delivery without cool packs, thus the samples were guided to be stored at the temperature + 4 °C.

In the proficiency tests of heavy metals the sample delivery is optimized: we use acidified samples and the sample delivery time to participants is as fast as possible.

The delivery protocol has been the same for over 15 years without any sign of sample changes during the used transport protocol. Also based on the earlier knowledge the possible short time warming of acidified samples during the transportation has no influence to the stability of the samples when the participant stores them after arrival for the longer period in refrigerator.

Participant Comments to the results Action / Proftest 9 The result of the mercury was unsatisfactory in the

synthetic sample A1Hg. The participant ordered a new sample A1Hg, from which they measured satisfactory result. They asked the reason for the unsatisfactory result and remeasurement of the original sample A1Hg in the laboratory of SYKE.

The provider evaluated the sample preparation protocol and no clear reason for the abnormal result was found.

With the remeasurement of the participant’s orginal sample A1Hg (bottle number 23) also the sample bottle number 22 (stored at +4 °C), and bottle number 29 (stored at room temperature and light several weeks) were measured for Hg. The result of the partcipant’s original sample was 50 % lower than expected. The result from the bottle number 22 was same as the used assigned value for Hg. The result of the sample stored at the room temperature was about 50 % lower than expected. It was evident that storing of the sample in the light and room temperature decreased the concentration of mercury in the samples. As there was not found a clear reason from the provider’s sample preparation protocol for the abnormal result, the performance evaluation of the participant’s result was kept in the final data handling.

16 The participant asked about their high

concentration for some metals in the soil sample MO4.

The participant used aqua regia digestion with the addition of 0.5 ml HF. With this acid combination their soil digestion is much stronger for some measurands (e.g. Al, Ba, Cr, Sr V, Ca), and thus higher concentrations are expected. The abnormal results were excluded from the calculation of the assigned value.

20 The participant reported erroneously their result for Ti in the sample MO4.

The corrected result was 2410 mg/kg.

Due to high variation in the results Ti in the sample MO4 were not evaluated.

FEEDBACK TO THE PARTICIPANTS

Participant Comments

18 The participant informed that they are accredited for several measurands. However they did not report

measurement uncertainty with their results. The measurement uncertainty should be reported with the results

obtained by accredited method.

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: Evaluation of the assigned values and their uncertainties APPENDIX 5

Measurand Sample Unit Assigned value Upt Upt, % Evaluation method of assigned value upt/spt

Al A1M µg/l 16.8 0.9 5.1 Robust mean 0.26

G2M µg/l 200 10 4.8 Robust mean 0.32

MN4 g/kg 23.6 1.6 6.6 Mean

MO4 g/kg 24.2 2.2 9.0 Mean 0.36

N3M µg/l 1425 78 5.5 Robust mean 0.37

As A1M µg/l 2.50 0.02 0.7 Calculated value 0.05

G2M µg/l 0.32 0.03 8.5 Mean 0.28

MN4 mg/kg 9.01 2.25 25.0 Mean

MO4 mg/kg 10.7 0.9 8.8 Mean 0.35

N3M µg/l 0.77 0.04 5.0 Mean 0.20

Ba A1M µg/l 34.0 0.2 0.6 Calculated value 0.04

G2M µg/l 4.50 0.28 6.3 Robust mean 0.32

MN4 mg/kg 134 7 5.1 Median

MO4 mg/kg 123 9 7.2 Mean 0.29

N3M µg/l 25.6 0.7 2.8 Robust mean 0.28

Ca MN4 g/kg

MO4 g/kg 5.41 0.05 1.0 Mean

Cd A1M µg/l 0.45 0.00 0.7 Calculated value 0.05

MN4 mg/kg 0.73 0.23 32.0 Median

MO4 mg/kg 0.75 0.05 7.3 Mean 0.37

Co A1M µg/l 1.25 0.01 0.7 Calculated value 0.07

MN4 mg/kg 10.3 0.82 8.0 Median

MO4 mg/kg 10.2 2.0 20.0 Median

Cr A1M µg/l 1.35 0.06 4.4 Robust mean 0.29

G2M µg/l 0.76 0.05 6.1 Median 0.31

MO4 mg/kg 57.5 3.7 6.5 Mean 0.26

Cu A1M µg/l 7.35 0.04 0.6 Calculated value 0.06

MN4 mg/kg 116 16 14.0 Median

MO4 mg/kg 115 7 5.7 Mean 0.29

Fe A1M µg/l 335 2 0.5 Calculated value 0.05

MN4 g/kg 33.6 1.5 4.4 Median

MO4 g/kg 35.9 2.8 7.9 Median 0.32

N3M µg/l 1573 42 2.7 Median 0.27

Hg A1Hg µg/l 0.44 0.01 3.0 ID-ICP-MS 0.15

G2Hg µg/l 0.088 0.003 3.0 ID-ICP-MS 0.12

MC4 mg/kg 0.27 0.01 5.0 Median

MO4 mg/kg 0.27 0.04 13.0 Median 0.37

N3Hg µg/l 0.25 0.01 3.0 ID-ICP-MS 0.15

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Mg MN4 g/kg 11.4 0.5 4.0 Median

MO4 g/kg 12.3 0.9 7.7 Median 0.39

Mn A1M µg/l 2.25 0.01 0.5 Calculated value 0.03

G2M µg/l 81.5 2.2 2.7 Median 0.27

MN4 mg/kg 426 26 6.2 Mean

MO4 mg/kg 423 39 9.2 Mean 0.37

N3M µg/l 101 3 3.4 Robust mean 0.34

Ni A1M µg/l 4.25 0.03 0.6 Calculated value 0.04

G2M µg/l 0.98 0.09 8.7 Mean 0.35

MO4 mg/kg 20.6 1.9 9.1 Mean 0.36

Pb A1M µg/l 1.27 0.03 2.5 ID-ICP-MS 0.17

G2M µg/l 1.02 0.03 2.5 ID-ICP-MS 0.17

MO4 mg/kg 24.2 1.7 7.1 Mean 0.28

N3M µg/l 0.84 0.03 3.0 ID-ICP-MS 0.20

Se A1M µg/l 3.25 0.02 0.7 Calculated value 0.05

G2M µg/l 1.36 0.04 2.8 Mean 0.19

MN4 mg/kg 2.00 0.28 14.0 Median

MO4 mg/kg

N3M µg/l 0.53 0.05 10.0 Median 0.40

Sr A1M µg/l 8.75 0.04 0.5 Calculated value 0.05

MN4 mg/kg 22.4 Median

MO4 mg/kg 33.2 3.7 11.0 Median 0.37

Ti A1M µg/l 45.0 0.3 0.7 Calculated value 0.07

G2M µg/l 10.1 0.5 5.4 Median 0.36

MN4 mg/kg

MO4 mg/kg

N3M µg/l 63.2 4.4 6.9 Median 0.35

V A1M µg/l 10.3 0.1 0.7 Calculated value 0.07

G2M µg/l 1.42 0.07 4.7 Mean 0.24

MN4 mg/kg

MO4 mg/kg 65.6 9.8 15.0 Median 0.43

N3M µg/l 2.80 0.13 4.8 Median 0.32

Zn A1M µg/l 5.25 0.03 0.5 Calculated value 0.03

G2M µg/l 13.7 0.6 4.2 Mean 0.28

MO4 mg/kg 73.7 5.3 7.2 Median 0.29

Upt = Expanded uncertainty of the assigned value

Criterion for reliability of the assigned value upt/spt < 0.3, where spt= the standard deviation for proficiency assessment upt= the standard uncertainty of the assigned value

If upt/spt < 0.3, the assigned value is reliable and the z scores are qualified.

(29)

: Terms in the results tables APPENDIX 6

Results of each participant

Measurand The tested parameter

Sample The code of the sample

z score 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 2 × s

pt

% The standard deviation for proficiency assessment (s

pt

) at the 95 %

confidence level

Participants’s result The result reported by the participant

Md Median

sd Standard deviation

sd% Standard deviation, %

n (stat) Number of results in statistical processing Summary on the z scores

S – satisfactory ( -2 z 2)

Q – questionable ( 2< z < 3), positive error, the result deviates more than 2 × s

pt

from the assigned value q – questionable ( -3 < z < -2), negative error, the result deviates more than 2 × s

pt

from the assigned value U – unsatisfactory (z 3), positive error, the result deviates more than 3 × s

pt

from the assigned value u – unsatisfactory (z -3), negative error, the result deviates more than 3 × s

pt

from the assigned value Robust analysis

The items of data are sorted into increasing order, x

1

, x

2

, x

i

,…,x

p

. Initial values for x

^*

and s

^*

are calculated as:

x

^*

= median of x

i

(i = 1, 2, ....,p)

s

^*

= 1.483 × median of x

i

– x

^*

(i = 1, 2, ....,p) The mean x

^*

and s

^*

are updated as follows:

Calculate = 1.5 × s

^*

. A new value is then calculated for each result x

i

(i = 1, 2 …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:

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 [2].

p x x

^* _i^*

/

) 1 /(

) (

134 .

1 x x

²

p

s

_i

(30)

Participant 1

Measurand Unit Sample z score Assigned value 2×spt % Participant's result Md Mean sd sd % n (stat)

Al µg/l A1M 0.12 16.8 20 17.0 17.0 16.6 1.6 9.8 15

µg/l G2M 1.13 200 15 217 198 200 14 6.9 17

µg/l N3M 1.72 1425 15 1609 1383 1425 111 7.8 16

As µg/l A1M -0.69 2.50 15 2.37 2.47 2.50 0.22 8.6 13

µg/l G2M 0.21 0.32 30 0.33 0.32 0.32 0.04 13.5 10

mg/kg MO4 0.97 10.7 25 12.0 11.0 10.7 1.3 12.4 8

µg/l N3M 0.73 0.77 25 0.84 0.79 0.77 0.06 8.0 10

Ba µg/l A1M -0.93 34.0 15 31.6 33.8 33.8 1.3 3.9 11

µg/l G2M -0.44 4.50 20 4.30 4.44 4.51 0.37 8.2 13

mg/kg MO4 -0.20 123 25 120 120 123 12 9.5 7

µg/l N3M -0.16 25.6 10 25.4 25.4 25.4 0.4 1.7 12

Cd µg/l A1M -0.59 0.45 15 0.43 0.44 0.44 0.03 6.5 15

µg/l G2M 0.00 0.22 20 0.22 0.22 0.22 0.01 5.7 15

mg/kg MO4 1.87 0.75 20 0.89 0.74 0.75 0.07 9.7 7

µg/l N3M 0.19 0.54 20 0.55 0.54 0.54 0.04 7.7 14

Co µg/l A1M 0.48 1.25 10 1.28 1.25 1.24 0.05 4.0 13

µg/l G2M 0.37 0.80 20 0.83 0.81 0.79 0.08 10.4 13

mg/kg MO4 10.2 7.7 10.2 11.1 3.1 28.0 8

µg/l N3M 0.58 1.39 15 1.45 1.40 1.38 0.08 5.6 12

Cr µg/l A1M 0.20 1.35 15 1.37 1.35 1.34 0.08 6.0 14

µg/l G2M 0.39 0.76 20 0.79 0.76 0.76 0.08 11.0 13

mg/kg MO4 -0.49 57.5 25 54.0 55.8 57.5 5.3 9.2 8

µg/l N3M 1.37 2.41 20 2.74 2.40 2.41 0.19 8.0 14

Cu µg/l A1M 0.08 7.35 10 7.38 7.20 7.17 0.39 5.4 15

µg/l G2M 0.30 20.3 15 20.8 20.6 20.2 1.3 6.5 17

mg/kg MO4 -0.43 115 20 110 113 115 9 7.5 7

µg/l N3M 0.53 7.06 15 7.34 7.25 7.06 0.46 6.6 14

Fe µg/l A1M -0.90 335 10 320 338 339 17 5.1 16

µg/l G2M -0.18 333 10 330 332 333 14 4.2 14

µg/l N3M 0.34 1573 10 1600 1573 1592 88 5.5 17

Hg µg/l A1Hg 0.23 0.44 20 0.45 0.44 0.44 0.04 8.9 12

µg/l G2Hg 2.91 0.088 25 0.120 0.089 0.089 0.015 16.6 12

mg/kg MO4 0.27 35 <0,5 0.27 0.28 0.04 15.3 6

µg/l N3Hg 0.40 0.25 20 0.26 0.25 0.24 0.02 8.0 12

Mn µg/l A1M -0.12 2.25 15 2.23 2.22 2.20 0.11 4.8 16

µg/l G2M 0.93 81.5 10 85.3 81.5 80.9 4.4 5.4 16

µg/l N3M 0.79 101 10 105 100 101 5 5.0 17

Ni µg/l A1M -0.25 4.25 15 4.17 4.14 4.13 0.28 6.7 14

µg/l G2M 0.57 0.98 25 1.05 0.96 0.98 0.14 13.8 10

mg/kg MO4 0.93 20.6 25 23.0 19.3 20.6 2.8 13.6 9

µg/l N3M 0.26 3.04 20 3.12 3.11 3.04 0.33 10.8 13

-3 0 3

(31)

Participant 1

Pb µg/l A1M -1.36 1.27 15 1.14 1.24 1.21 0.07 5.5 13

µg/l G2M -1.31 1.02 15 0.92 0.98 0.96 0.05 5.7 13

mg/kg MO4 -0.40 24.2 25 23.0 23.5 24.2 2.4 10.1 8

µg/l N3M -0.95 0.84 15 0.78 0.80 0.80 0.04 5.0 12

Se µg/l A1M -1.15 3.25 15 2.97 3.22 3.23 0.17 5.4 9

µg/l G2M 0.59 1.36 15 1.42 1.36 1.36 0.06 4.2 9

µg/l N3M 0.91 0.53 25 0.59 0.53 0.52 0.07 14.3 8

Sr µg/l A1M -0.80 8.75 10 8.40 8.75 8.83 0.38 4.3 12

µg/l G2M -0.38 140 15 136 140 140 8 5.4 12

µg/l N3M -0.33 44.8 15 43.7 44.6 44.9 2.2 4.8 12

Ti µg/l A1M -0.80 45.0 10 43.2 45.1 45.3 2.1 4.7 13

µg/l G2M -0.53 10.1 15 9.7 10.1 10.2 0.9 8.9 11

µg/l N3M 0.03 63.2 20 63.4 63.2 61.8 7.4 12.0 12

V µg/l A1M -0.58 10.3 10 10.0 9.9 10.0 0.5 4.9 13

µg/l G2M 1.27 1.42 20 1.60 1.40 1.42 0.12 8.2 12

mg/kg MO4 -0.49 65.6 35 60.0 65.6 64.9 12.9 19.9 7

µg/l N3M 1.43 2.80 15 3.10 2.80 2.76 0.22 7.9 11

Zn µg/l A1M 4.90 5.25 20 7.82 5.50 5.41 0.21 3.8 11

µg/l G2M 3.92 13.7 15 17.7 13.5 13.7 1.0 7.5 13

mg/kg MO4 -0.08 73.7 25 73.0 73.7 73.7 7.6 10.2 8

µg/l N3M -0.18 9.37 15 9.24 9.46 9.36 0.79 8.4 13

Participant 2

Al µg/l A1M 0.48 16.8 20 17.6 17.0 16.6 1.6 9.8 15

µg/l G2M -0.13 200 15 198 198 200 14 6.9 17

g/kg MN4 23.6 24.9 22.9 23.6 1.7 7.3 5

µg/l N3M -1.47 1425 15 1268 1383 1425 111 7.8 16

As µg/l A1M -0.16 2.50 15 2.47 2.47 2.50 0.22 8.6 13

µg/l G2M 0.35 0.32 30 0.34 0.32 0.32 0.04 13.5 10

mg/kg MN4 9.01 7.04 9.99 9.01 2.56 28.4 5

µg/l N3M -0.15 0.77 25 0.76 0.79 0.77 0.06 8.0 10

Ba µg/l A1M 0.24 34.0 15 34.6 33.8 33.8 1.3 3.9 11

µg/l G2M 0.51 4.50 20 4.73 4.44 4.51 0.37 8.2 13

mg/kg MN4 134 134 134 132 7 5.1 4

µg/l N3M 0.00 25.6 10 25.6 25.4 25.4 0.4 1.7 12

Ca g/kg MN4 5.42 4.61 4.09 1.59 39.0 5

Cd µg/l A1M 0.18 0.45 15 0.46 0.44 0.44 0.03 6.5 15

µg/l G2M 0.55 0.22 20 0.23 0.22 0.22 0.01 5.7 15

mg/kg MN4 0.73 0.76 0.73 0.69 0.27 39.4 6

µg/l N3M 0.72 0.54 20 0.58 0.54 0.54 0.04 7.7 14

Co µg/l A1M 0.16 1.25 10 1.26 1.25 1.24 0.05 4.0 13

µg/l G2M 0.16 0.80 20 0.81 0.81 0.79 0.08 10.4 13

mg/kg MN4 10.3 10.40 10.30 9.98 0.79 8.0 4

µg/l N3M 0.38 1.39 15 1.43 1.40 1.38 0.08 5.6 12

-3 0 3

(32)

Cr µg/l A1M -0.49 1.35 15 1.30 1.35 1.34 0.08 6.0 14

µg/l G2M -0.09 0.76 20 0.75 0.76 0.76 0.08 11.0 13

mg/kg MN4 58.0 61.6 58.0 56.0 6.6 11.9 5

µg/l N3M -0.08 2.41 20 2.39 2.40 2.41 0.19 8.0 14

Cu µg/l A1M 0.33 7.35 10 7.47 7.20 7.17 0.39 5.4 15

µg/l G2M 0.46 20.3 15 21.0 20.6 20.2 1.3 6.5 17

mg/kg MN4 116 116 116 113 18 16.0 5

µg/l N3M 0.43 7.06 15 7.29 7.25 7.06 0.46 6.6 14

Fe µg/l A1M 0.12 335 10 337 338 339 17 5.1 16

µg/l G2M 0.66 333 10 344 332 333 14 4.2 14

g/kg MN4 33.6 35.4 33.6 33.8 1.7 4.9 5

µg/l N3M -0.01 1573 10 1572 1573 1592 88 5.5 17

Hg µg/l A1Hg 0.09 0.44 20 0.44 0.44 0.44 0.04 8.9 12

µg/l G2Hg 0.05 0.088 25 0.089 0.089 0.089 0.015 16.6 12

mg/kg MN4 0.23 0.26 0.23 0.23 0.02 9.5 4

µg/l N3Hg 0.28 0.25 20 0.26 0.25 0.24 0.02 8.0 12

Mg g/kg MN4 11.4 11.5 11.4 11.2 0.5 4.0 4

Mn µg/l A1M 0.12 2.25 15 2.27 2.22 2.20 0.11 4.8 16

µg/l G2M 1.03 81.5 10 85.7 81.5 80.9 4.4 5.4 16

mg/kg MN4 426 464 416 426 30 6.9 5

µg/l N3M 0.59 101 10 104 100 101 5 5.0 17

Ni µg/l A1M 0.22 4.25 15 4.32 4.14 4.13 0.28 6.7 14

µg/l G2M 0.57 0.98 25 1.05 0.96 0.98 0.14 13.8 10

mg/kg MN4 21.6 21.8 21.6 19.1 4.6 24.2 5

µg/l N3M 0.23 3.04 20 3.11 3.11 3.04 0.33 10.8 13

Pb µg/l A1M 0.00 1.27 15 1.27 1.24 1.21 0.07 5.5 13

µg/l G2M -0.48 1.02 15 0.98 0.98 0.96 0.05 5.7 13

mg/kg MN4 27.5 27.9 27.5 27.0 1.9 7.2 5

µg/l N3M -0.35 0.84 15 0.82 0.80 0.80 0.04 5.0 12

Se µg/l A1M 0.16 3.25 15 3.29 3.22 3.23 0.17 5.4 9

µg/l G2M 0.69 1.36 15 1.43 1.36 1.36 0.06 4.2 9

mg/kg MN4 2.00 1.72 2.00 2.02 0.28 14.0 4

µg/l N3M -0.15 0.53 25 0.52 0.53 0.52 0.07 14.3 8

Sr µg/l A1M 0.05 8.75 10 8.77 8.75 8.83 0.38 4.3 12

µg/l G2M 0.38 140 15 144 140 140 8 5.4 12

mg/kg MN4 22.4 39.4 22.3 25.0 12.8 51.4 6

µg/l N3M 0.09 44.8 15 45.1 44.6 44.9 2.2 4.8 12

Ti µg/l A1M -0.09 45.0 10 44.8 45.1 45.3 2.1 4.7 13

µg/l G2M -1.04 10.1 15 9.3 10.1 10.2 0.9 8.9 11

mg/kg MN4 526 982 1348 967 71.7 5

µg/l N3M -2.07 63.2 20 50.1 63.2 61.8 7.4 12.0 12

V µg/l A1M 0.00 10.3 10 10.3 9.9 10.0 0.5 4.9 13

µg/l G2M 0.77 1.42 20 1.53 1.40 1.42 0.12 8.2 12

mg/kg MN4 44.6 69.3 69.8 1.9 2.7 3

µg/l N3M -0.05 2.80 15 2.79 2.80 2.76 0.22 7.9 11

-3 0 3

(33)

Participant 2

Zn µg/l A1M 4.25 5.25 20 7.48 5.50 5.41 0.21 3.8 11

µg/l G2M 0.49 13.7 15 14.2 13.5 13.7 1.0 7.5 13

mg/kg MN4 77.9 76.8 77.9 77.3 3.9 5.0 4

µg/l N3M 0.54 9.37 15 9.75 9.46 9.36 0.79 8.4 13

Participant 3

Measurand Unit Sample z score Assigned value 2×spt % Participant's result Md Mean sd sd % n (stat)

Al µg/l G2M -1.47 200 15 178 198 200 14 6.9 17

µg/l N3M 0.98 1425 15 1530 1383 1425 111 7.8 16

As µg/l A1M 2.35 2.50 15 2.94 2.47 2.50 0.22 8.6 13

µg/l G2M 10.42 0.32 30 0.82 0.32 0.32 0.04 13.5 10

µg/l N3M 19.84 0.77 25 2.68 0.79 0.77 0.06 8.0 10

Cd µg/l A1M 0.59 0.45 15 0.47 0.44 0.44 0.03 6.5 15

µg/l G2M 5.91 0.22 20 0.35 0.22 0.22 0.01 5.7 15

µg/l N3M 0.37 0.54 20 0.56 0.54 0.54 0.04 7.7 14

Cr µg/l A1M 0.99 1.35 15 1.45 1.35 1.34 0.08 6.0 14

µg/l G2M 1.32 0.76 20 0.86 0.76 0.76 0.08 11.0 13

µg/l N3M 0.71 2.41 20 2.58 2.40 2.41 0.19 8.0 14

Cu µg/l A1M -1.20 7.35 10 6.91 7.20 7.17 0.39 5.4 15

µg/l G2M -1.25 20.3 15 18.4 20.6 20.2 1.3 6.5 17

µg/l N3M -1.02 7.06 15 6.52 7.25 7.06 0.46 6.6 14

Fe µg/l A1M -4.30 335 10 263 338 339 17 5.1 16

µg/l G2M -5.35 333 10 244 332 333 14 4.2 14

µg/l N3M -1.69 1573 10 1440 1573 1592 88 5.5 17

Mn µg/l A1M -1.66 2.25 15 1.97 2.22 2.20 0.11 4.8 16

µg/l G2M -2.06 81.5 10 73.1 81.5 80.9 4.4 5.4 16

µg/l N3M -1.80 101 10 92 100 101 5 5.0 17

Ni µg/l A1M -2.35 4.25 15 3.50 4.14 4.13 0.28 6.7 14

µg/l G2M -3.10 0.98 25 0.60 0.96 0.98 0.14 13.8 10

µg/l N3M -2.11 3.04 20 2.40 3.11 3.04 0.33 10.8 13

Pb µg/l A1M 4.72 1.27 15 1.72 1.24 1.21 0.07 5.5 13

µg/l G2M 10.59 1.02 15 1.83 0.98 0.96 0.05 5.7 13

µg/l N3M 34.29 0.84 15 3.00 0.80 0.80 0.04 5.0 12

Participant 4

Al µg/l A1M -0.89 16.8 20 15.3 17.0 16.6 1.6 9.8 15

µg/l G2M -0.71 200 15 189 198 200 14 6.9 17

µg/l N3M -0.41 1425 15 1381 1383 1425 111 7.8 16

Cd µg/l A1M -0.40 0.45 15 0.44 0.44 0.44 0.03 6.5 15

µg/l G2M -0.54 0.22 20 0.21 0.22 0.22 0.01 5.7 15

µg/l N3M -0.57 0.54 20 0.51 0.54 0.54 0.04 7.7 14

Cu µg/l A1M -0.15 7.35 10 7.29 7.20 7.17 0.39 5.4 15

µg/l G2M -0.46 20.3 15 19.6 20.6 20.2 1.3 6.5 17

µg/l N3M -0.61 7.06 15 6.74 7.25 7.06 0.46 6.6 14

Fe µg/l A1M 0.76 335 10 348 338 339 17 5.1 16

µg/l G2M -0.09 333 10 332 332 333 14 4.2 14

µg/l N3M -0.62 1573 10 1524 1573 1592 88 5.5 17

-3 0 3