Interlaboratory Proficiency Test 12/2020. Metals in waste water and sludge

Interlaboratory Proficiency Test 12/2020

Metals in waste water and sludge

Mirja Leivuori, Päivi Grönroos, Riitta Koivikko, Timo Sara-Aho, Teemu Näykki, Mika Sarkkinen,

Keijo Tervonen, Sari Lanteri, Ritva Väisänen and Markku Ilmakunnas

REPORTS OF THE FINNISH ENVIRONMENT

INSTITUTE 13 | 2021

Helsinki 2021

Finnish Environment Institute

Interlaboratory Proficiency Test 12/2020

Metals in waste water and sludge

Mirja Leivuori, Päivi Grönroos, Riitta Koivikko, imo Sara-Aho, Teemu Näykki, Mika Sarkkinen, Keijo Tervonen, Sari Lanteri, Ritva Väisänen and Markku Ilmakunnas

T

SYKE

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

ISBN 978-952-11-5379-2 (pbk.) ISBN 978-952-11-5380-8 (PDF) ISSN 1796-1718 (print)

ISSN 1796-1726 (Online)

Author(s): Mirja Leivuori, Päivi Grönroos, Riitta Koivikko, Timo Sara-Aho, Teemu Näykki, Mika Sarkkinen, Keijo Tervonen, Sari Lanteri, Ritva Väisänen and Markku Ilmakunnas

Publisher and financier of publication: Finnish Environment Institute (SYKE) Latokartanonkaari 11, FI-00790 Helsinki, Finland, Phone +358 295 251 000, syke.fi.

Year of issue: 2021

and sludge in October-November 2020. In total, there were 24 participants in the PT. The measurands for the synthetic sample, industrial and municipal waste water samples as well as sludge sample were Al, As, B, Ba, Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, S, Sb, Se, Sn, Sr, Ti, U, V and Zn. Also, dry weight (Drw), N and P were analysed for the sludge sample.

In total, 91 % of the results evaluated with z scores were satisfactory when total deviation of 10–30 % from the assigned value was accepted. Of the results evaluated with E

n

scores, 88 % were satisfactory. 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 measurands.

Warm thanks to all the participants in this proficiency test!

Keywords: water analysis, metals, waste waters, sludge, Al, As, B, Ba, Cd, Co, Cr, Cu, Drw, Fe, Hg, Mn, Mo, N, Ni, P, Pb, S, Sb, Se, Sn, Sr, Ti, U, V, Zn, water and environmental laboratories, proficiency test, interlaboratory comparison

TIIVISTELMÄ

Laboratorioiden välinen pätevyyskoe 12/2020

Proftest SYKE järjesti loka-marraskuussa 2020 pätevyyskokeen laboratorioille, jotka määrittävät metalleja ja elohopeaa jätevesistä ja lietteestä. Pätevyyskokeessa määritettiin synteettisistä näytteistä, teollisuuden ja viemärilaitoksen jätevesinäytteistä sekä lietteestä testisuureet Al, As, B, Ba, Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, S, Sb, Se, Sn, Sr, Ti, U, V ja Zn. Lisäksi lietteestä määritetiin Drw, N ja P. Pätevyyskokeeseen osallistui yhteensä 24 laboratoriota.

Koko aineistossa oli 91 % hyväksyttäviä tuloksia z-arvoilla arvioituja, kun tulosten sallittiin poiketa vertailuarvosta 10–30 %. Tuloksista, jotka arvioitiin E

n

-arvoilla, hyväksyttyjä oli 88 %. Testisuureen vertailuarvona käytettiin metrologisesti jäljitettävää pitoisuutta, laskennallista pitoisuutta tai osallistujien raportoimien tulosten robustia keskiarvoa, keskiarvoa tai mediaania.

Kiitos pätevyyskokeen osallistujille!

Avainsanat: vesianalyysi, metallit, jätevesi, liete, Al, As, B, Ba, Cd, Co, Cr, Cu, Drw, Fe, Hg, Mn, Mo, N, Ni, P, Pb, S, Sb, Se, Sn, Sr, Ti, U, V, Zn, vesi- ja ympäristölaboratoriot, pätevyyskoe, laboratorioiden välinen vertailumittaus

SAMMANDRAG Provningsjämförelse 12/2020

Proftest SYKE genomförde en provningsjämförelse i oktober-november 2020, som omfattade bestämningen av Al, As, B, Ba, Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, S, Sb, Se, Sn, Sr, Ti, U, V och Zn i syntetiska provet, industri- och avloppsvattenprov och slam. Tillsammans 24 laboratorier deltog i jämförelsen.

I jämförelsen 91 % av resultaten som värderades med hjälp z värdet var acceptabla, när totalavvikelsen på 10–30 % från referensvärdet tillåten. Resultaten som värderades med hjälp av E

n

-värdet var 88 % acceptabla. Som referensvärde av analytens koncentration användes mest det metrologiska spårbara värdet, teoretiska värdet eller robust medelvärdet, medelvärdet eller median av deltagarnas resultat.

Ett varmt tack till alla deltagarna i testet!

Nyckelord: vattenanalyser, metaller, avloppsvatten, slam Al, As, B, Ba, Cd, Co, Cr, Cu, Drw, Fe, Hg,

Mn, Mo, N, Ni, P, Pb, S, Sb, Se, Sn, Sr, Ti, U, V, Zn, provningsjämförelse, vatten- och miljölaboratorie

CONTENTS

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 ... 10

2.6.3 Proficiency assessment procedure ... 11

3 Results and conclusions ... 12

3.1 Results ... 12

3.2 Analytical methods ... 16

3.3 Uncertainties of the results ... 18

4 Evaluation of the results ... 19

5 Summary ... 21

6 Summary in Finnish ... 22

References ... 23

APPENDIX 1 : Participants in the proficiency test ... 24

APPENDIX 2 : Sample preparation ... 25

APPENDIX 3 : Homogeneity of the samples ... 27

APPENDIX 4 : Feedback from the proficiency test ... 28

APPENDIX 5 : Evaluation of the assigned values and their uncertainties ... 29

APPENDIX 6 : Terms in the results tables ... 32

APPENDIX 7 : Results of each participant ... 33

APPENDIX 8 : Summary of the z scores ... 63

APPENDIX 9 : Summary of the E

n

scores ... 66

APPENDIX 10 : z scores in ascending order ... 67

APPENDIX 11 : Results grouped according to the methods ... 104

APPENDIX 12 : Significant differences in the results reported using different methods ... 152

APPENDIX 13 : Examples of measurement uncertainties reported by the participants ... 155

1 Introduction

Proftest SYKE carried out a proficiency test (PT) for analysis of metals and mercury in waste waters and sludge in October-November 2020 (MET 12/2020). The measurands for the synthetic sample, industrial and municipal waste water samples as well as sludge sample were: Al, As, B, Ba, Ca, Cd, Co, Cr, Cu, Fe, Hg, K, Mg, Mn, Mo, Ni, Pb, Sb, Se, Sn, Sr, Ti, V, and Zn. Also, dry weight (Drw), N, and P were analysed for the sludge sample. In the PT the results of the national laboratories providing environmental data for Finnish environmental authorities were evaluated.

Additionally, other water and environmental laboratories were welcomed to participate 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 standard ISO/IEC 17043 [1] and applying ISO 13528 [2] and IUPAC Technical report [3]. 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 Mustialankatu 3, FI-00790 Helsinki, Finland

Phone: +358 295 251 000, Email: proftest@syke.fi The responsibilities in organizing the proficiency test Mirja Leivuori coordinator

Riitta Koivikko substitute for coordinator

Päivi Grönroos coordinator trainee

Keijo Tervonen technical assistance

Markku Ilmakunnas technical assistance

Sari Lanteri technical assistance

Ritva Väisänen technical assistance

Timo Sara-Aho (SYKE) metals, ID-ICP-MS Teemu Näykki (SYKE) Hg, ID-ICP-MS Mika Sarkkinen (SYKE) Hg in sludge

2.2 Participants

In total 24 laboratories participated in this proficiency test (Appendix 1), 22 from Finland and 2 from abroad. 75 % of the participants reported that they have accredited quality management system based on ISO/IEC 17025, while 2 participants did not report the accreditation status of their management system. 58 % of the participants reported to used accredited analytical methods at least for a part of the measurements.

For this proficiency test, the organizing laboratory (T003, www.finas.fi/sites/en) has the code 8 (SYKE, Helsinki) in the result tables.

2.3 Samples and delivery

Four types of samples were delivered to the participants: synthetic, industrial waste water, municipal waste water and sludge samples. The synthetic sample M1A was prepared from the NIST traceable commercial reference material produced by Inorganic Ventures. The synthetic sample Hg1A was prepared by diluting from the NIST traceable AccuTrace

^TM

Reference Standard produced by AccuStandard, Inc. The sample preparation is described in detail in the Appendix 2. The synthetic sample M1A was acidified with nitric acid and the synthetic mercury sample Hg1A with hydrochloric acid.

The industrial waste water samples M2T (after analysis: M2TN – no digestion / M2TY – digestion with acid or with acid mixture) and T3Hg for Hg measurements were prepared with additions of single element standard solutions (AccuStandard for Hg and Merck CertiPUR

^®

for other elements, Appendix 2). The municipal waste water samples M3V and Hg3V were prepared with additions of the same single element standard solutions (Appendix 2).

The tested sludge sample M4L (after analysis: M4LN – digestion with HNO3 / M4LO – digestion with HNO3+HCl /M4LT – digestion with HNO3+HF, for Hg also: M4LC – oxygen combustion) was reused sludge sample from the previous PT MET 08/2015 [4]. The sample was from sewage treatment plant from southern Finland. The sludge was manually rehomogenized and divided into subsamples. The homogeneity of the sludge 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 3 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 5 October 2020 to some of the participants (national and abroad)

and on 6 October 2020 to most of the national participants. The samples arrived to the participants

mainly on 7 October 2020 and all participants had received the samples on 8 October 2020.

Mercury in water samples latest on 16 October 2020 The other measurands and samples latest on 30 October 2020 The results were to be reported latest on 4 November 2020. Participants delivered the results mainly accordingly with the exception of one who delivered the results on 5 November 2020.

The preliminary results report was delivered to the participants via ProftestWEB and email on 13 November 2020.

2.4 Homogeneity and stability studies

The homogeneity of the samples was tested by analyzing Cd, Cr, Cu, Hg, Pb, Se, Ti, and Zn.

According to the homogeneity test results, all samples were considered homogenous. The synthetic samples were prepared from traceable certified reference materials, and thus known to be homogenous. However, homogeneity of these was checked by three measurements of two samples and they were considered homogenous. More detailed information of homogeneity study is shown in Appendix 3.

The sludge used for the sample M4L was of the same material than in the previous PT MET 08/2015 [4]. The homogeneity of the sludge sample was tested after rehomogenization by parallel measurements (Cd, Cu, Hg, Mn, Zn) of three samples and the test confirmed the homogeneity of the sample (Appendix 3).

Further, based on the earlier similar PTs, the samples are known to be stable over the given schedule of the PT.

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 delayed sample delivery and reporting of their results. The comment from the provider focused on the missing sample arrival documents. All the feedback from the proficiency test is valuable and is exploited when improving the activities.

2.6 Processing the data

2.6.1 Pretesting the data

To test the normality of the data the Kolmogorov-Smirnov test was applied. 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 50 % from the robust mean were rejected before the statistical results handling.

If the result has been 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].

The calculated values (NIST traceable) were used as the assigned values for measurements of synthetic sample M1A, with the exception of Pb and Hg. The results based on isotope dilution (ID) ICP-MS technique were used as assigned value for Hg and Pb in samples M1A, M2TN, M3V, Hg1A, Hg2T, and Hg3V. 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 SYKE calibration laboratory (K054; www.finas.fi/sites/en). For the other samples and measurands the robust mean of the results reported by the participants was used as the assigned value.

In this PT, due to the small size of the data set (n

stat

<12), the median or the mean of the participants’ results was used as the assigned value.

The median was used as the assigned value in the following cases:

• Sample M2TN: S, Sb, Se, Sn, Sr, Ti, U, V

• Sample M2TY: Al, B, Ba, Cd, Cu, Fe, Mn, Mo, Ni, Pb, S, Sb, Se, Sn, Sr, Ti, U, V, Zn

• Sample M3V: Al, B, Cu, Sb, Se, Sn, Sr, Ti, U

The mean was used as the assigned value in the following cases:

• Sample M2TN: Ba, Co

• Sample M2TY: As, Cr, Co

• Sample M3V: As, Mo

For the sludge samples the median was used as the assigned value for all other measurands except in the sample M4LO: Fe and the sample M4LN: V, in which the mean value was used. The used assigned values based on the robust mean, the mean or the median of the results reported by the participants are not metrologically traceable values. As it was not possible to have metrologically traceable assigned values, the best available values were selected to be used as the assigned values. The reliability of the assigned values was statistically tested (Appendix 5) [2, 3].

The expanded uncertainty for the calculated assigned values (k=2) was evaluated 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 mean was used as the assigned value, the uncertainty was calculated using the robust standard deviation or standard deviation, respectively [1, 2, 5]. For the metrologically traceable mercury and lead results used for assigned values, the uncertainty is the expanded measurement uncertainty of the ID-ICP-MS method.

The expanded uncertainty of the calculated and metrologically traceable assigned values for metals in the synthetic samples varied between 0.5 and 3 %. When using the robust mean, the mean or the median of the participants’ results as the assigned value, the expanded uncertainties of the assigned values were between 1 and 37 % (Appendix 5).

The assigned value for Hg in the sample M4LN was changed from the preliminary results

evaluation (0.76 mg/kg) to final results evaluation (0.68 mg/kg). Only few participants reported

preliminary results no other changes have been done for the assigned values.

2.6.3 Proficiency assessment procedure

The results of this proficiency test were evaluated both with the z and E

n

scores.

Performance evaluation was not given for Hg (samples M4LC and M4LN), Sb (M4LN), Sn (M4LN) and Ti (sample M4LO) due to low number of results (2 or 3) and variation between the results.

The standard deviation for proficiency assessment was evaluated based on 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. For performance evaluation based on z scores the standard deviation for the proficiency assessment (2×s

pt

, at the 95 % confidence interval) was set to 10–30 % depending on the measurement.

When the number of reported results was low (n

stat

<6) or there was variation between the results, (M2TY: B, Ba, Se, Sn, Sr, Ti, U; M4LC: Hg; M4LN: Al, As, B, Ba, Cd, Co, Cr, Fe, Mo, Ni, Pb, P, S Sn, Sr, Ti, U, V ; Hg, M4LO: B, Ni, U ) the standard deviation for proficiency assessment was not set. When the uncertainty was set for the assigned value, the performance evaluation was done 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:

(𝐸

_𝑛

)

_𝑖

=

^{𝑥𝑖−𝑥𝑝𝑡}

√𝑈_𝑖²+ 𝑈_𝑝𝑡²

, 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.

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. E

n

scores are not given when the participant has not reported uncertainties with their results.

After reporting the preliminary results no changes have been done for the proficiency assessment.

When using the robust mean, the median or the mean 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 [2, 3]. When testing the

reliability of the assigned value the criterion was mainly fulfilled and the assigned values were

considered reliable.

comparing the deviation for proficiency assessment (s

pt

) with the robust standard deviation (s

rob

) or standard deviation (s, n

stat

<12) of the reported results (the criteria) [3]. The criterion s

rob

or s / s

pt

< 1.2 was mainly fulfilled.

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

¹

and/or for the reliability of the target value for the deviation

²

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

Sample Measurand

M2TN Ni

¹

, Zn

¹

M2TY Al

¹

, Co

¹

, S

¹

, Se

¹

M3V Zn

¹

M4LN Cu

¹

, Zn

¹

M4LO Al

¹

, As

¹

, Cd

¹

, Pb

^1,2

, P

¹

, Sn

¹

3 Results and conclusions

3.1 Results

The summary of the results is presented in Table 1. The terms in the results tables are explained in Appendix 6. The results and the performance of each participant are presented in Appendix 7.

The summaries of the z and E

n

scores are shown in Appendices 8 and 9. In Appendix 10 the z scores are shown in the ascending order. The reported results grouped by the used analytical methods with their expanded uncertainties (k=2) are presented in Appendix 11.

The robust standard deviations of the results varied from 2.1 % to 37 % and the standard deviations varied from 3.2 % to 23 % (Table 1). The robust standard deviation or the standard deviation of results was lower than 10 % for 95 % and for 37 % of the results, respectively. The standard deviations higher than 10 % apply mainly to the sludge sample (M4L, Table 1). For the waste water samples the robust standard deviations of the results varied from 3.3 % to 11.9 % and for the sludge sample the variation was from 2.1 % to 44 % (Table 1).

The robust standard deviations for waste water samples were approximately in the same range as

in the previous similar PT MET 11/2019, where the deviations varied from 2.6 % to 28 % [6]. For

the sludge samples the robust standard deviations were somewhat higher than in the previous

similar PT MET 08/2015 [4], where the deviations varied from 1.1 % to 17.5 %.

Measurand Sample Unit Assigned value Mean Rob. mean Median s

rob

/ s s

rob

% / s % 2 x s

pt

% n

all

Acc z % / E

n %

Al M1A µg/l 325 326 328 329 27 8.1 10 17 76

M2TN µg/l 324 323 324 325 21 6.5 15 13 92

M2TY µg/l 324 335 335 324 40 11.9 20 7 100

M3V µg/l 36.0 36.1 36.1 36.0 1.2 3.3 20 14 69

M4LN g/kg 5.53 5.53 - 5.53

0.81 14.7

- 6

60

M4LO g/kg 6.74 6.58 6.60 6.74 0.67 10.1 20 7 100

As M1A µg/l 27.0 26.0 25.9 26.5 1.4 5.6 10 17 88

M2TN µg/l 21.4 21.5 21.4 21.2 2.1 9.6 20 13 92

M2TY µg/l 21.4 21.4 21.4 21.0 1.6 7.6 20 7 100

M3V µg/l 10.6 10.6 10.6 10.7 0.5 5.2 15 13 92

M4LN mg/kg 4.50 4.53 - 4.50

0.80 17.5

- 5

100

M4LO mg/kg 4.64 4.57 4.57 4.64 0.66 14.4 25 8 88

B M1A µg/l 48.0 48.4 48.5 48.9 3.2 6.6 10 12 73

M2TN µg/l 161 161 160 161 9 5.3 15 10 100

M2TY µg/l 157 159 - 157

11.7 7.3

- 4

100

M3V µg/l 70.5 69.7 69.7 70.5 4.2 6.0 15 13 92

M4LN mg/kg 11.0 11.4 - 11.0

2.5 22.0

- 5

67

M4LO mg/kg 11.5 12.2 - 11.5

1.9 15.6

- 8

75

Ba M1A µg/l 110 109 109 109 3 2.8 10 13 100

M2TN µg/l 67.2 67.2 67.3 67.2 2.5 3.7 15 11 100

M2TY µg/l 69.6 68.7 - 69.6

2.6 3.8

- 5

100

M3V µg/l 14.4 14.4 14.4 14.6 1.0 6.8 15 12 100

M4LN mg/kg 161 162 - 161

12.0 7.4

- 5

100

M4LO mg/kg 171 170 171 171 12 7.0 20 8 88

Cd M1A µg/l 6.40 6.23 6.30 6.27 0.27 4.3 15 16 100

M2TN µg/l 6.23 6.21 6.23 6.04 0.45 7.3 15 12 100

M2TY µg/l 6.34 6.33 6.44 6.34 0.44 6.8 20 7 86

M3V µg/l 3.07 3.06 3.07 3.08 0.21 6.7 15 13 85

M4LN mg/kg 0.74 0.72 - 0.74

0.13 17.5

- 5

100

M4LO mg/kg 0.72 0.72 0.72 0.72 0.08 11.7 20 8 100

Co M1A µg/l 32.0 32.0 31.9 31.8 2.2 6.8 10 15 87

M2TN µg/l 30.3 30.3 30.3 30.1 2.5 8.3 15 12 92

M2TY µg/l 30.8 30.8 - 30.2

2.9 9.4

20 6 100

M3V µg/l 10.7 10.7 10.7 10.8 0.8 7.1 15 13 92

M4LN mg/kg 5.53 5.58 - 5.53

0.7 12.4

- 5

100

M4LO mg/kg 5.32 5.40 5.59 5.32 0.88 15.6 25 8 88

Cr M1A µg/l 44.0 43.8 43.7 43.1 2.5 5.6 10 18 100

M2TN µg/l 46.1 46.4 46.1 45.8 3.0 6.6 15 13 85

M2TY µg/l 47.8 47.8 47.6 48.0 3.2 6.8 15 8 100

M3V µg/l 15.4 15.4 15.4 15.6 0.9 5.8 15 13 100

M4LN mg/kg 28.2 29.5 - 28.2

3.7 12.6

- 5

100

M4LO mg/kg 33.7 33.3 33.6 33.7 3.7 11.1 25 8 100

Cu M1A µg/l 79.0 79.4 79.2 78.6 3.9 4.9 10 19 95

M2TN µg/l 57.9 57.8 57.9 58.7 4.9 8.4 15 15 100

M2TY µg/l 58.1 57.9 58.0 58.1 5.7 9.8 20 7 100

M3V µg/l 5.80 5.8 5.8 5.8 0.6 10.3 20 14 79

M4LN mg/kg 395 402 - 395

45 11.1

20 6 100

M4LO mg/kg 418 416 416 418 38 9.1 20 9 100

Drw M4L % 88.9 89.1 89.4 88.9 1.8 2.1 5 12 83

Measurand Sample Unit Assigned value Mean Rob. mean Median s

rob

/ s s

rob

% / s % 2 x s

pt

% n

all

Acc z % / E

n %

Fe M1A µg/l 435 442 443 445 24 5.5 10 20 90

M2TN µg/l 418 420 418 419 26 6.1 15 15 87

M2TY µg/l 426 426 424 426 27 6.3 15 8 100

M3V µg/l 61.3 61.5 61.3 60.0 3.9 6.3 15 15 100

M4LN g/kg 117 117 117 3.9 3.3 - 6

60

M4LO g/kg 121 121 124 119 14 11.2 20 9 89

Hg Hg1A µg/l 0.35 0.35 0.36 0.35 0.03 9.8 20 15 80

Hg2T µg/l 1.54 1.47 1.47 1.44 0.09 6.1 20 16 94

Hg3V µg/l 0.25 0.25 0.25 0.25 0.02 6.2 20 11 82

M4LC mg/kg 0.66 0.66 - 0.66

0.2 25.7

- 2 -

M4LN mg/kg 0.68 0.68 - 0.68

0.3 34.8

- 2 -

M4LO mg/kg 0.82 0.84 - 0.82

0.06 7.5

20 6 100

Mn M1A µg/l 33.0 33.8 34.2 34.0 1.9 5.7 10 18 89

M2TN µg/l 27.2 27.3 27.2 27.0 1.9 7.0 15 15 87

M2TY µg/l 26.2 26.6 - 26.2

1.5 5.5

15 6 100

M3V µg/l 16.1 16.1 16.1 16.0 0.9 5.8 15 15 93

M4LN mg/kg 354 347 - 354

23 6.5

20 6 100

M4LO mg/kg 362 355 355 362 17 4.8 20 8 88

Mo M1A µg/l 54.0 52.8 53.0 52.6 2.5 4.8 10 15 93

M2TN µg/l 1171 1174 1171 1173 71 6.0 15 13 100

M2TY µg/l 1219 1211 1211 1219 72 5.9 15 7 100

M3V µg/l 22.8 22.8 23.2 22.6 1.5 6.3 15 14 79

M4LN mg/kg 4.95 4.92 - 4.95

1.1 23.1

- 6

100

M4LO mg/kg 5.66 5.75 5.75 5.66 0.70 12.1 25 8 100

Ni M1A µg/l 35.0 34.7 34.9 34.8 1.9 5.3 10 17 94

M2TN µg/l 37.3 37.3 37.3 36.3 3.3 8.8 15 13 92

M2TY µg/l 37.7 37.8 37.8 37.7 3.1 8.1 20 7 100

M3V µg/l 6.83 6.77 6.83 6.78 0.47 6.9 15 13 92

M4LN mg/kg 20.9 20.6 - 20.9

2.8 13.6

- 5

100

M4LO mg/kg 22.1 21.9 21.1 22.1 3.6 16.9 25 8 88

N M4L g/kg 34.3 33.8 33.8 34.3 1.8 5.4 15 8 100

Pb M1A µg/l 28.9 28.5 28.6 28.4 1.7 5.8 10 16 81

M2TN µg/l 30.6 28.8 28.9 29.5 3.1 10.8 15 12 75

M2TY µg/l 29.1 29.0 29.0 29.1 3.0 10.3 20 7 100

M3V µg/l 5.12 5.02 5.04 4.99 0.38 7.6 15 13 75

M4LN mg/kg 17.9 18.4 - 17.9

1.2 6.5

- 5

100

M4LO mg/kg 17.9 17.9 17.9 17.9 3.9 21.6 30 7 100

P M4LN g/kg 33.9 32.2 - 33.9

6.1 19.1

- 7

60

M4LO g/kg 36.3 35.7 35.7 36.3 4.0 11.2 20 7 100

S M1A µg/l 15000 14389 14488 14405 742 5.1 10 14 86

M2TN µg/l 150175 150829 149921 150175 4951 3.3 10 11 91

M2TY µg/l 152000 150782 - 152000

11983 7.9

15 6 100

M3V µg/l 31943 31916 31943 32100 946 3.0 10 13 92

M4LN mg/kg 10100 9927 - 10100

1203 12.1

- 6

60

M4LO mg/kg 11558 11161 11161 11558 1033 9.3 20 8 88

Measurand Sample Unit Assigned value Mean Rob. mean Median s

rob

/ s s

rob

% / s % 2 x s

pt

% n

all

Acc z % / E

n %

Sb M1A µg/l 59.0 57.3 57.1 57.3 1.6 2.7 10 14 93

M2TN µg/l 59.1 59.1 59.1 59.7 3.7 6.2 15 12 100

M2TY µg/l 59.2 58.8 - 59.2

3.3 5.6

15 6 100

M3V µg/l 5.21 5.19 5.26 5.21 0.40 7.5 15 12 82

M4LN mg/kg 36.6 36.5 - 36.6

12.3 33.7

- 3 -

M4LO mg/kg 66.6 67.9 - 66.6

6.4 9.4

25 7 86

Se M1A µg/l 29.0 28.4 29.0 28.3 2.7 9.4 10 13 69

M2TN µg/l 24.0 24.1 24.6 24.0 1.7 6.8 15 11 91

M2TY µg/l 25.8 25.4 - 25.8

3.0 12.0

- 6

100

M3V µg/l 5.62 5.63 5.66 5.62 0.39 6.8 15 12 91

M4LN mg/kg 85.4 85.6 - 85.4

13.6 15.9

- 5

100

M4LO mg/kg 82.1 82.3 82.3 82.1 10.4 12.7 25 8 100

Sn M1A µg/l 25.0 23.9 24.0 24.0 0.7 2.9 10 10 90

M2TN µg/l 20.7 20.4 - 20.7

1.2 6.1

15 9 75

M2TY µg/l 16.8 17.4 - 16.8

2.3 13.3

- 4

100

M3V µg/l 4.81 4.81 4.77 4.81 0.20 4.3 15 11 89

M4LN mg/kg 48.6 48.6 - 48.6

18.5 38.0

- 2 -

M4LO mg/kg 83.9 85.9 - 83.9

8.4 9.7

20 7 71

Sr M1A µg/l 125 123 123 125 7 5.7 10 12 92

M2TN µg/l 152 153 153 152 6 3.9 15 11 91

M2TY µg/l 152 153 - 152

13.2 8.6

- 4

100

M3V µg/l 78.6 78.3 78.0 78.6 3.6 4.7 10 12 83

M4LN mg/kg 95.1 95.3 - 95.1

9.6 10.1

- 4

100

M4LO mg/kg 95.3 96.4 96.2 95.3 9.2 9.6 20 9 78

Ti M1A µg/l 83.0 82.1 82.1 82.7 3.8 4.6 10 10 100

M2TN µg/l 79.8 79.5 79.5 79.8 4.4 5.6 10 10 90

M2TY µg/l 85.6 85.4 - 85.6

2.8 3.2

- 3

100

M3V µg/l 20.2 20.2 20.0 20.2 1.0 5.0 10 11 82

M4LN mg/kg 399 392 - 399

146 37.2

- 4

67

M4LO mg/kg 482 489 - 482

217 44.4

- 4 -

U M1A µg/l 2.30 2.24 2.23 2.24 0.10 4.7 10 10 100

M2TN µg/l 3.12 3.11 3.10 3.12 0.27 8.7 20 8 100

M2TY µg/l 3.17 3.05 - 3.17

0.31 10.2

- 3

100

M3V µg/l 1.19 1.20 1.20 1.19 0.08 7.1 15 10 100

M4LN mg/kg 71.7 71.9 - 71.7

3.3 4.5

- 3

100

M4LO mg/kg 65.3 66.4 - 65.3

8.9 13.4

- 6

83

V M1A µg/l 33.0 32.1 32.1 32.0 1.4 4.4 10 14 100

M2TN µg/l 51.8 52.5 52.9 51.8 2.6 4.9 15 10 90

M2TY µg/l 50.8 51.3 51.8 50.8 1.9 3.6 15 7 86

M3V µg/l 5.25 5.26 5.25 5.17 0.25 4.7 15 13 100

M4LN mg/kg 33.4 33.4 - 31.7

3.4 10.2

- 5

100

M4LO mg/kg 33.9 34.2 34.2 33.9 3.3 9.5 20 8 100

Zn M1A µg/l 331 342 341 336 17 5.1 10 20 90

M2TN µg/l 267 266 267 271 22 8.1 15 15 87

M2TY µg/l 282 281 281 282 16 5.7 15 8 100

M3V µg/l 34.9 34.9 34.9 35.1 2.7 7.6 15 15 87

M4LN mg/kg 612 598 - 612

65 10.9

20 6 100

M4LO mg/kg 583 589 589 583 61 10.4 20 9 100

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, 2×s

pt

%: the standard deviation for proficiency assessment at the 95 % confidence level, n

all

: the total number of the participants, Acc z %: the results (%), where z  2, E

n

%: the results (%), where

 E

n

 <1.

3.2 Analytical methods

The participants could use different analytical methods for the measurements in the PT. The used analytical methods and results of the participants grouped by methods are shown in more detail in Appendix 11. The statistical comparison of the analytical methods was possible for the data where the number of the results was ≥ 5. The statistically significant differences are shown in Appendix 12.

Effect of sample pretreatment on elemental concentrations in waste waters

Elements in waste water were mainly measured from acidified samples without sample pretreatment with the exception of the industrial waste water sample (M2TN/M2TY). The participants measured the acidified industrial waste water mostly without sample pretreatment (M2TN), and a smaller part of the participants measured the industrial waste water after acid digestion (M2TY). The results of these samples were evaluated separately (Table 1).

The difference between the average concentrations of elements measured by different sample pretreatment methods was tested using the t-test. Statistically significant difference was observed for aluminium analyses where no pretreatment approach gave statistically significantly lower results compared to the pretreatment with acid digestion (Appendix 12). For an unfiltered waste water sample the results are as expected, acid digestion should give similar or higher results than without digestion.

Effect of sample pretreatment on elemental concentrations in sludge sample

Acid soluble elements in the sludge sample were measured mainly after acid digestion (M4LN/M4LO). In average, 39 % of the participants measured the sludge sample after nitric acid digestion (M4LN), and the other participants (61 %) measured the sample after aqua regia digestion (M4LO). The results of these were evaluated separately. Both treatments can be considered as partial digestions only. For total element content other acid mixtures including hydrofluoric acid must be used.

The digestion method in general can highly influence the recoveries depending on digestion temperature and hold times as can the sample weight and acid amount ratio. The difference between the average concentrations of elements measured by different acid digestions was tested using the t-test. Statistically significant difference was not observed.

Effect of measurement methods on elemental results

The most commonly used analytical method was ICP-MS, followed by ICP-OES. FAAS or GAAS technique was used by one participant for some measurements. Hydride generation ICP-OES was used by three participants for some measurements (Appendix 11). N-Kjeldahl or similar method was used by six participants and CHN-analyzer by two participants for nitrogen determination.

The difference between the average concentrations of metals measured by different measurement

methods was tested using the t-test. Statistically significant differences were noticed for barium,

lower results than ICP-OES technique (Appendix 12). The concentrations of these elements were high enough to be successfully measured by both techniques. ICP-MS is more sensitive, especially for Cr and Mo. The differences were 4-6 %, which is close to half of a typical expanded measurement uncertainty for ICP-MS.

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. The best solution to minimize matrix effects is to use robust plasma conditions, which applies to both ICP-MS and ICP-OES.

Internal standardization is traditionally used in ICP-MS to correct for both short- and long-term drift during the measurement. It may even correct for matrix effects to some degree, if the ionization potential matches that of the analyte. In environmental ICP-MS analysis commonly used internal standard elements are Sc, Ga, Ge, Y, Rh, In and Ir. The internal standard elements should not be present in the sample and should not cause spectral interferences on the analytes.

They should also be checked for any possible spectral interferences caused by matrix or analyte elements.

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. Also, some participants (1-2) reported to measure mercury with CV-AAS, CV-ICP-OES, CV-ICP-MS or direct combustion (O

2

flow + AAS) techniques (Appendix 11).

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. BrCl is commonly used for oxidation of mercury species. Microwave assisted HNO

3

digestion is very efficient in breaking up organic species in the sample matrix and thus reducing carry-over effects.

Generally, the differences in mercury results are most likely due to different pretreatment

procedures, provided a measurement technique sensitive enough is used. Cold vapor techniques

are recommended, especially for samples with low concentrations. CV-AFS and CV-ICP-MS

have superior detection capability compared to CV-AAS or CV-ICP-OES.

3.3 Uncertainties of the results

At maximum 79 % of the participants reported the expanded uncertainties (k=2) with their results for at least some of their results (Table 2, Appendix 11). Several approaches were used for evaluating the measurement uncertainty (Appendix 13). The most used approach was based on the method validation data or using the internal quality data in different ways. MUkit measurement uncertainty software for the estimation of the uncertainties was used by at maximum three participants (Appendix 13) [7, 8]. The free software is available on 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-evaluated their expanded (k=2) measurement uncertainty. In this proficiency test several high measurement uncertainties were reported, i.e. 50 % or higher, marked as bold in Table 2. Further, in this PT many very high measurement uncertainties (up to 100 %) were reported. Very high measurement uncertainties should not exist, unless the measured concentration is near to the limit of quantification.

Table 2. The range of the expanded measurement uncertainties (k=2, U

i

%) reported by the participants.

Measurand M1A/Hg1A % M2TN/Hg2T % M2TY % M3V/Hg3V % M4L/M4LN/M4LC % M4LO %

Al 5-50 5-40 8-25 10-50 15-40 15-30

As 4-50 4-20 12-50 10-100 15-35 15-30

B 12-60 12-40 15-25 12-60 20-45 20-70

Ba 10-20 10-20 10-20 10-50 17-30 15-30

Cd 10-60 10-60 15-33 10-100 20-25 20-25

Co 10-20 10-20 12-30 10-100 15-40 15-40

Cr 1.49-20 9-20 1.49-30 10-50 20-30 18-30

Cu 10-40 10-40 10-34 10-100 15-30 15-30

Drw - - - - 2-30 -

Fe 5-40 5-40 12-33 10-40 15-30 15-30

Hg 12-28 12-24 12-40 20-30 15-40

Mn 8-40 8-40 9-18 8-50 10-23 10-30

Mo 5-40 5-20 12-35 10-50 20-35 18-35

Ni 9-50 9-50 12-27 10-100 15-25 15-35

N - - - - 10-25 -

Pb 10-50 10-40 12-50 10-100 15-20 15-35

P - - - - 10-25 14-30

S 8-35 5-30 10-35 8-35 10-40 14-40

Sb 10-20 10-20 12-27 10-50 30-35 20-30

Se 14-50 14-30 15-50 14-50 20-40 16-40

Sn 15-50 15-30 15-50 15-50 40-40 17-35

Sr 10-25 10-25 15-25 10-25 20-40 15-40

Ti 10-80 10-20 15-15 15-80 30-40 20-30

U 10-20 10-20 15-20 10-20 15-40 15-40

V 8-50 10-20 12-25 8-100 17-30 17-30

Zn 5-25 5-20 10-30 10-40 12-25 15-25

traceability, the national quality recommendations for data included into water quality registers have been published in Finland [9]. The recommendations for measurement uncertainties for most of the tested measurands in waste water are 20 %. In this proficiency test some of the participants had their measurement uncertainties within these limits, while some did not achieve them. Harmonization of the uncertainty’s estimation should be continued.

4 Evaluation of the results

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

n

scores, which were calculated using the assigned values and the standard deviation for the performance assessment.

The z and E

n

scores were interpreted as follows:

Criteria Criteria

Performance 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

In total, 91 % of the results evaluated with z scores were satisfactory when total deviation of 10–30 % from the assigned value was accepted (Appendix 8). Of the results evaluated with E

n

scores, 88 % were satisfactory (Appendix 9). Altogether 58 % of the participants used accredited analytical methods at least for a part of the measurements and 95 % of their results were satisfactory. The summary of the performance evaluation and comparison to the previous similar PT is presented in Table 3. In the previous similar PT, MET 11/2019, the performance was satisfactory for 89 % of the participants result of waste waters when standard deviation of 10–25 % from the assigned values was accepted [6].

In general, the share of satisfactory results varied between 85 % and 100 %, based on evaluation with z scores, for the tested sample types (Table 3). In total the share was slightly better compared to the previous similar proficiency test in 2019 (Table 3) [6]. The share of satisfactory results in the synthetic sample M1A was the lowest for Se and B, 69 % and 73 %, respectively.

For the industrial waste water sample (M2TN and T3Hg) 88/94 % of the results were satisfactory, when deviation of 10–20 % from the assigned value was accepted (Table 3). For B, Ba, Cd, Cu, Mo, Sb and U in the sample M2TN all the results were satisfactory. For the industrial waste water sample digested with acid or with acid mixture, M2TY, the performance evaluation was done with z and E

n

scores. For E

n

score, the performance was better than in the previous similar PT, MET 11/2019 (Table 3) [6].

For the municipal waste water samples M3V the number of satisfactory results evaluated based

on z scores was lower than in the previous similar PT MET 11/2019 (Table 3) [6]. For Ba, Cr,

Fe, U, and V in the sample M3V all the results were satisfactory.

Sample

Satisfactory results (mean, %)

Accepted deviation from the assigned value (%)

Remarks

M1A / Hg1A 86 / 80 10-20 - Difficulties in measurements for Al, B, Se

< 80% satisfactory results.

- In the MET 11/2019 the performance was satisfactory for 84 / 79 % of the results [6].

M2TN/

Hg2T

88 / 94 10-20 - Somewhat approximate performance evaluation for Ni, Zn.

- Difficulties in measurements for Pb, Sn

< 80% satisfactory results.

- In the MET 11/2019 the performance was satisfactory for 93 / 93 % of the results [6].

M2TY z score: 92 E

n

score: 100

15-20 - Somewhat approximate performance evaluation for Al, Co, S, Se.

- Many results were evaluated based on E

n

scores due to low number of results.

- In the MET 11/2019 the performance was satisfactory based on z scores for 93 % of the results when accepting deviation of 15-25 % from the assigned value and based on E

n

scores 91 % [6].

M3V / Hg3V 85 / 82 10-20 - Somewhat approximate performance evaluation for Zn.

- Difficulties in measurements for Al, Cu, Mo, Pb

< 80% satisfactory results.

- In the MET 11/2019 the performance was satisfactory for 92 / E

n

40 % of the results [6].

M4L/M4LC 92 5-15 - In the MET 08/2015 the performance was satisfactory based on z score evaluation for 88 % of the results.

- Due to low number of results Hg in the sample M4LC was not evaluated.

M4LN z score: 100 E

n

score: 86

20 - Somewhat approximate performance evaluation for Cu, Zn.

- Many results were evaluated based on E

n

scores due to low number of results.

- Due to low number of results and high variation between the results Hg, Sb and Sn were not evaluated.

- In the MET 08/2015 the performance was satisfactory based on z score evaluation for 96 % of the results when accepting deviation of 15-30 % from the assigned value [4].

M4LO z score: 93 E

n

score: 79

20-30 - Somewhat approximate performance evaluation for Al, As, Cd, Pb, P

- Due to low number of results and high variation between the results Ti was not evaluated.

- In the MET 08/2015 the performance was satisfactory based

on z score evaluation for 94 % of the results when accepting

deviation of 15-30 % from the assigned value [4].

of participants analysing the sample was low. For the sludge sample, standard deviations of 5–30 % from the assigned value were accepted when using z score evaluation (Table 3). Of the results obtained after nitric acid digestion (M4LN), 100 % of the results were satisfactory when the standard deviation of 20 % from the assigned value was accepted. Further, 93 % of the results obtained after aqua regia digestion (M4LO), were satisfactory when the standard deviation of 20–30 % from the assigned value was accepted. The E

n

scores were 79 % and 86 % in M4LO and M4LN, respectively. The sludge sample was of the same material than in the PT MET 08/2015. The performance evaluation based on z scores was mostly in the same range in both PTs (Table 3) [4]. For dry weight (Drw) of the sludge sample M4L, 83 % of the results were satisfactory when the accepted standard deviation from the assigned value was 5 %. For N from the sample M4L the accepted standard deviation from the assigned value was 15 % and 100 % of the results were satisfactory. In the previous PT MET 08/2015 100 % of Drw results and 89 % of nitrogen results were satisfactory [4].

5 Summary

Proftest SYKE carried out a proficiency test (PT) for the analysis of metals and mercury in waste waters and sludge in October-November 2020 (MET 12/2020). The measurands for the synthetic sample, industrial and municipal waste water samples as well as sludge sample were Al, As, B, Ba, Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, S, Sb, Se, Sn, Sr, Ti, U, V, and Zn. Also, dry weight (Drw), N, and P were analysed for the sludge sample. In total 24 laboratories participated in the PT.

The calculated concentration (the NIST traceable) or the robust mean, the mean or the median of the results reported by the participants was chosen as the assigned value for the measurands, with the exception of Pb and Hg where the used assigned values were based on the metrologically traceable isotope dilution (ID) ICP-MS technique for some samples. The uncertainty for the assigned value was estimated at the 95 % confidence level (k=2) 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 and 37 %.

The evaluation of the performance was based on the z or E

n

scores. In total, 91 % of the results

evaluated with z scores were satisfactory when total deviation of 10–30 % from the assigned

value was accepted. Of the results evaluated with E

n

scores, 88 % were satisfactory. Altogether

58 % of the participants used accredited analytical methods at least for a part of the measurements

and 95 % of their results were satisfactory.

6 Summary in Finnish

Proftest SYKE järjesti loka-marraskuussa 2020 pätevyyskokeen laboratorioille, jotka määrittävät metalleja ja elohopeaa jätevesistä ja lietteestä (MET 12/2020). Pätevyyskokeessa määritettiin synteettisistä näytteistä, teollisuuden ja viemärilaitoksen jätevesinäytteistä sekä lietteestä testisuureet Al, As, B, Ba, Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, S, Sb, Se, Sn, Sr, Ti, U, V ja Zn. Lisäksi lietteestä määritetiin Drw, N ja P. Pätevyyskokeeseen osallistui yhteensä 24 laboratoriota.

Testisuureen vertailuarvona käytettiin laskennallista pitoisuutta tai osallistujien tulosten robustia keskiarvoa, keskiarvoa tai mediaania. Lyijylle ja elohopealle käytettiin metrologisesti jälji- tettävää vertailuarvoa osassa testinäytteistä. Vertailuarvolle laskettiin epävarmuus 95 % luottamusvälillä. Vertailuarvon laajennettu epävarmuus oli 0,5 – 3 % laskennallista tai metrolo- gisesti jäljitettävää pitoisuutta vertailuarvona käytettäessä ja muilla välillä 1 – 37 %.

Pätevyyden arviointi tehtiin z- tai E

n

-arvojen avulla. Koko aineistossa hyväksyttäviä z-arvoilla

arvioituja tuloksia oli 91 %, kun tulosten sallittiin poiketa vertailuarvosta 10 – 30 %. Tuloksista,

jotka arvioitiin E

n

-arvoilla, hyväksyttyjä oli 88 %. Noin 58 % osallistujista käytti akkreditoituja

määritysmenetelmiä ja näistä tuloksista oli hyväksyttäviä 95 %.

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. Koivikko, R., Leivuori, M., Sara-Aho, T., Näykki, T., Tervonen, K., Lanteri, S., Väisänen, R., Ilmakunnas, M., Interlaboratory Proficiency Test 08/2015. Metals in waste waters and sludge. Reports of the Finnish Environment Institute 11/2016.

http://hdl.handle.net/10138/160817

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., Ilmakunnas, M. 2019. Interlaboratory proficiency test 11/2019. Metals in waste waters.

Reports of Finnish Environment Institute 10/2020. http://hdl.handle.net/10138/313601.

7. 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.

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. 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, storage times and methods

associated with analytes determined from waters). Suomen ympäristökeskuksen raportteja

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

Country Participant Finland Boliden Kokkola Oy

Eurofins Ahma Oy, Oulu

Eurofins Environment Testing Finland Oy, Lahti

Eurofins Labtium Oy, Kuopio

Fortum Waste Solutions Oy, Riihimäki

Hortilab Ab Oy

KVVY Tutkimus Oy, Tampere

Kymen Ympäristölaboratorio Oy

Lounais-Suomen vesi- ja ympäristötutkimus Oy, Turku

MetropoliLab Oy

Neste Corporation, Technology Center, Kilpilahti

Norilsk Nickel Harjavalta Oy

Outokumpu Stainless Oy, Tutkimuskeskus, Tornio Savo-Karjalan Ympäristötutkimus Oy, Kuopio

SGS Finland Oy, Kotka

SSAB Europe Oy, Analyysilaboratorio, Hämeenlinna

SSAB Europe Raahe, Raahe

STUK, Ympäristön säteilyvalvonta, Mittaus ja Analyysit (MIT)

SYKE, Helsingin toimipaikka

UPM Tutkimuskeskus, Lappeenranta

Venator

Yara Suomi Oy, Uusikaupunki

Sweden Fortum Waste Solutions AB

INOVYN Sverige AB

The synthetic samples M1A was prepared by diluting from the NIST traceable certified reference materials produced by Inorganic Ventures. The synthetic sample Hg1A was prepared by diluting from the NIST traceable AccuTrace

^TM

Reference Standard produced by AccuStandard, Inc. The water samples M2T (M2TN/M2TY), M3V, Hg2T and Hg3V were prepared by adding some separate metal solutions (Merck CertiPUR

^®

or AccuStandard) into the original water sample, if the original concentration was not high enough.

The tested sludge sample L4M (after analysis: M4LN, M4LO, M4LT) was reused sludge sample from the previous PT MET 08/2015 [4]. The sludge was rehomogenized and divided into sub- samples.

Measurand M1A µg/l

M2TN/

M2TY µg/l

M3V µg/l

M4LN/

M4LO/

M4LT mg/kg

Measurand M1A µg/l

M2TN/M2TY µg/l

M3V µg/l

M4LN/

M4LO/

M4LT mg/kg Al Original

Dilution Addition Ass. value

3250 10

- 325

55 - 270 324/324

9.2 - 20 36.0

6.17 g/kg - - 5.53/6.74/-

Fe Original Dilution Addition Ass. value

4350 10

- 435

120 - 305 418/426

62 - - 61.3

128 g/kg - - 117/121/- As Original

Dilution Addition Ass. value

270 10

- 27.0

0.85 - 20 21.4/21.4

0.27 - 10 10.6

5.24 - - 4.50/4.64/-

Mn Original Dilution Addition Ass. value

330 10 - 33.0

26 - - 27.2/26.2

15 - - 16.1

374 - - 354/362/- B Original

Dilution Addition Ass. value

480 10 - 48.0

170 - - 161/157

73 - - 70.5

13.0 - - 11.0/11.5/-

Mo Original Dilution Addition Ass. value

540 10 - 54.0

1200 - - 1171/1219

1.7 - 20 22.8

6.38 - - 4.95/5.66/- Ba Original

Dilution Addition Ass. value

1100 10

- 110

69 - - 67.2/69.6

4.4 - 10 14.4

169 - - 161/171/-

N Original Dilution Addition Ass. value

- - - -

- - - -

- - - -

32 g/kg - - 34.3 Cd Original

Dilution Addition Ass. value

64 10 - 6.40

0.38 - 6 6.23/6.34

0.01 - 3 3.07

0.75 - - 0.74/0.72/-

Ni Original Dilution Addition Ass. value

350 10 - 35.0

17 - 20 37.3/37.7

6.9 - - 6.83

23.8 - - 20.9/22.1/- Co Original

Dilution Addition Ass. value

320 10 - 32.0

0.98 - 30 30.3/30.8

0.66 - 10 10.7

6.31 - - 5.53/5.32/-

P Original Dilution Addition Ass. value

- - - -

- - - -

- - - -

34.6 g/kg - - 33.9/36.3/- Cr Original

Dilution Addition Ass. value

440 10 - 44.0

17 - 30 46.1/47.8

0.48 - 15 15.4

35.1 - - 28.2/33.7/-

Pb Original Dilution Addition Ass. value

290 10 - 28.9

0.23 - 30 30.6/29.1

0.05 - 5 5.12

19.3 - - 17.9/17.9/-

Cu Original Dilution Addition Ass. value

790 10 - 79.0

9.1 - 50 57.9/58.1

5.6 - - 5.80

446 - - 395/418/-

S Original Dilution Addition Ass. value

150000 10

- 15000

170000 - - 150175/

152000

36000 - - 31943

11610 - - 10100/

11558/-

Measurand M1A µg/l

M2TN/

M2TY µg/l

M3V µg/l

M4LN/

M4LO/

M4LT mg/kg

Measurand M1A µg/l

M2TN/M2TY µg/l

M3V µg/l

M4LN/

M4LO/

M4LT mg/kg Sb Original

Dilution Addition Ass. value

590 10 - 59.0

9.0 - 50 59.1/59.2

0.26 - 5 5.21

76.9 - - 36.6/66.6/-

U Original Dilution Addition Ass. value

23 10 - 2.30

0.11 - 3 3.12/3.17

0.18 - 1 1.19

72.5 - - 71.7/65.3/- Se Original

Dilution Addition Ass. value

290 10 - 29.0

4.0 - 20 24.0/25.8

0.07 - 5.43 5.62

96.0 - - 85.4/82.1/-

V Original Dilution Addition Ass. value

330 10 - 33.0

3.4 - 50 51.8/50.8

0.09 - 5 5.25

36 - - 33.4/33.9/- Sn Original

Dilution Addition Ass. value

250 10 - 25.0

0.02 - 20 20.7/16.8

0.03 - 5 4.81

39.1/89.3/- - - 48.6/83.9/-

Zn Original Dilution Addition Ass. value

3310 10

- 331

77 - 200 277

35 - - 34.9

669 - - 612/583/-

Sr Original Dilution Addition Ass. value

1250 10

- 125

150 - - 152/152

74 - - 78.6

99.9 - - 95.1/95.3/-

Measurand Hg1A

µg/l

Hg2T µg/l

Hg3V µg/l

M4LN/

M4LO/

M4LT/

M4LC mg/kg Ti Original

Dilution Addition Ass. value

830 10 - 83.0

0.8 - 80 80.8

0.1 - 20 20.2

406 - - 399/482

Hg Original Dilution Addition Ass. value

- - 0.35 0.35

0 - 1.50 1.54

0 - 0.25 0.25

0.72 - - 0.76/0.82/-/

0.66 Original = the original concentration

Dilution = the ratio of dilution

Addition = the addition concentration

Ass. value = the assigned value

Homogeneity was tested from duplicate measurements of selected measurement from six samples of each sample types (see table below).

Criteria for homogeneity

s

anal

/s

h

< 0.5 and s

sam2

<c, where

s

h

= standard deviation for testing of homogeneity

s

anal

= analytical deviation, standard deviation of the results within sub samples

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].

Measurement/

sample

Concentration [µg/l]

[mg/kg]

n s

pt

% s

h

% s

h

s

anal

s

anal

/s

h

Is

s

anal

/s

h

<0.5? s

sam2

c Is s

sam2

<c?

Cd/M2T 6.80 3 7.5 2.5 0.17 0.09 0.49 Yes 0 0.04 Yes

Cr/ M2T 47.2 3 7.5 1.1 0.52 0.25 0.49 Yes 0.10 0.35 Yes

Cu/ M2T 57.8 3 7.5 1.5 0.87 0.42 0.49 Yes 0.003 0.96 Yes

Se/ M2T 24.1 3 7.5 3.5 0.84 0.42 0.50 Yes 0.19 0.95 Yes

Zn/ M2T 273 3 7.5 1.8 4.92 2.33 0.47 Yes 0 29.6 Yes

Cd/M3V 3.18 3 7.5 2.3 0.07 0.04 0.49 Yes 0 0.007 Yes

Cr/ M3V 15.8 3 7.5 2.6 0.41 0.20 0.48 Yes 0 0.22 Yes

Cu/ M3V 5.75 3 10 4.2 0.24 0.12 0.49 Yes 0 0,08 Yes

Se/ M3V 5.44 3 7.5 2.8 0.15 0.07 0.49 Yes 0 0.03 Yes

Zn/ M3V 35.4 3 7.5 1.4 0.50 0.24 0.48 Yes 0.12 0.31 Yes

Cd/M4L 0.75 3 10 5.5 0.04 0.02 0.49 Yes 0 0.002 Yes

Cu/ M4L 446 3 10 0.9 4.01 1.93 0.48 Yes 7.55 20.2 Yes

Hg/ M4L 0.72 3 10 8.0 0.06 0.03 0.50 Yes 0 0.004 Yes

Mn/ M4L 374 3 10 0.8 2.99 1.44 0.48 Yes 2.25 11.3 Yes

Zn/ M4L 669 3 10 2.1 14.1 6.94 0.49 Yes 18.7 259 Yes

Hg/Hg2T* 1.54 3 10 1.3 0.02 0.009 0.47 Yes 0 0.005 Yes

Hg/Hg3T* 0.25 3 10 1.6 0.004 0.002 0.47 Yes 0 0.00002 Yes

Pb/M2T* 30.6 3 7.5 1.1 0.34 0.16 0.49 Yes 0 0.14 Yes

Pb/M3V* 5.11 3 7.5 0.6 0.03 0.02 0.49 Yes 0 0.001 Yes

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

pt

% = standard deviation for proficiency assessment

Conclusion: All criteria for homogeneity were fulfilled and the samples could be considered

homogenous.

FEEDBACK FROM THE PARTICIPANTS

Participant Comments on technical excecution Action / Proftest All The pretreatments for industrial waste water and

sludge samples were missing from the cover letter of the samples. The reporting date for the results was also incorrect.

The provider contacted the participants by email. The letter was corrected and uploaded to ProftestWEB.

10, 13, 16 The participant informed that the delivery of

samples was delayed. According to the distributor's (Posti) tracking system, the samples arrived to the participant on time. The provider recommends to check the internal package delivery procedures.

19 The participant received the samples with one day

delay. The used distributor (Posti) did not deliver the

samples according to the agreed schedule.

Participant Comments to the results Action / Proftest 22 The participant informed that their Hg result for the

sample M4LN was incorrect in the preliminary report. The corrected result was: 0.8489 mg/kg.

Hg in the sample M2LN was not evaluated in the preliminary result evaluation due to the low number and high variation of reported results. However, in the final result evaluation this participant result was removed. The assigned value changed from 0.76 to 0.68 mg/kg. This caused no change to the evaluation of participants’ performance.

FEEDBACK TO THE PARTICIPANTS Participant Comments

15, 18, 21 The participants did not return the sample arrival document to the provider or delivered it late. The participants should follow the instructions of the provider.

All The preliminary results report was missing in the ProftestWEB. The provider apologizes this and

will be more carefully in the future PTs.