Interlaboratory Proficiency Test 15/2020. VOC compounds in water and soil

Interlaboratory Proficiency Test 15/2020

VOC compounds in water and soil

Riitta Koivikko, Mirja Leivuori, Jari Nuutinen,

Keijo Tervonen, Sari Lanteri, Ritva Väisänen,

Helena Kutramoinen and Markku Ilmakunnas

REPORTS OF THE FINNISH ENVIRONMENT

INSTITUTE 14 | 2021

Helsinki 2021

Finnish Environment Institute

Interlaboratory Proficiency Test 15/2020

VOC compounds in water and soil

Riitta Koivikko, Mirja Leivuori, Jari Nuutinen, Keijo Tervonen, Sari Lanteri, Ritva Väisänen, Helena Kutramoinen and Markku Ilmakunnas

SYKE

Layout: Markku Ilmakunnas

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

ISBN 978-952-11-5381-5 (pbk.) ISBN 978-952-11-5382-2 (PDF) ISSN 1796-1718 (print) ISSN 1796-1726 (Online)

Author(s): Riitta Koivikko, Mirja Leivuori, Jari Nuutinen, Keijo Tervonen, Sari Lanteri, Ritva Väisänen, Helena Kutramoinen 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

ABSTRACT • TIIVISTELMÄ • SAMMANDRAG Interlaboratory Proficiency Test 15/2020

Proftest SYKE carried out the proficiency test (PT) for determination of volatile organic compounds from water and soil in November 2020. The provided samples in this PT included synthetic, surface water as well as soil samples. In total, there were 10 participants in the PT.

Either the calculated concentration or the median of the reported results was used as the assigned value for the measurands. The performance of the participants was evaluated by using z and E

scores. In this PT 82 % of the results evaluated with z scores were satisfactory when deviation of 15–35 % from the assigned value was accepted. Further, 80 % of the results evaluated with E

scores were satisfactory.

Warm thanks to all the participants in this proficiency test!

Keywords: water analysis, soil analysis, volatile organic compounds, VOC, water and environmental laboratories, proficiency test, interlaboratory comparisons

TIIVISTELMÄ

Laboratorioiden välinen pätevyyskoe 15/2020

Proftest SYKE järjesti marraskuussa 2020 pätevyyskokeen laboratorioille, jotka määrittävät haihtuvia orgaanisia yhdisteitä (VOC) vedestä ja maasta. Osallistujille toimitetiin synteettinen näyte, luonnonvesinäyte ja maanäyte. Pätevyyskokeessa oli yhteensä 10 osallistujaa.

Testisuureen vertailuarvona käytettiin laskennallista pitoisuutta tai osallistujien tulosten mediaania.

Osallistujien pätevyyden arviointi tehtiin z- ja E

-arvojen perusteella. Koko tulosaineistossa hyväksyttäviä tuloksia oli z-arvojen perusteella 82 %, kun vertailuarvosta sallittiin 15–35 %:n poikkeama. Tuloksista, jotka arvioitiin E

-arvoilla, oli hyväksyttäviä 80 %.

Kiitos pätevyyskokeen osallistujille!

Avainsanat: vesianalyysi, maa-analyysi, haihtuvat orgaaniset yhdisteet, VOC, vesi- ja ympäristölaboratoriot, pätevyyskoe, laboratorioiden välinen vertailumittaus

SAMMANDRAG Provningsjämförelse 15/2020

Under november 2020 genomförde Proftest SYKE en provningsjämförelse, som omfattade bestämningen av flyktiga organiska ämnen från ytvatten och från förorenad jord. Denna jämförelse hade totalt 10 deltagarna.

Som referensvärde av analytens koncentration användes det teoretiska värdet eller medianen av deltagarnas resultat. Resultaten värderades med hjälp av z- och E

-värden. I denna jämförelse var 82 % av resultaten som värderas med z-värden tillfredsställande. Resultatet var tillfredsställande, om det devierade mindre än 15–35 % från referensvärdet. Av resultaten som värderades med E

-värden 80 % var tillfredsställande.

Ett varmt tack till alla deltagarna i testet!

Nyckelord: vattenanalyser, jordanalyser, flyktiga organiska ämnen, VOC, provningsjämförelse,

vatten- och miljölaboratorier

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 ... 10

2.6.1 Pretesting the data ... 10

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 ... 15

3.3 Uncertainties of the results ... 16

4 Evaluation of the results ... 17

5 Summary ... 18

6 Summary in Finnish ... 18

References ... 19

APPENDIX 1 : Participants in the proficiency test ... 20

APPENDIX 2 : Sample preparation ... 21

APPENDIX 3 : Homogeneity of the samples ... 23

APPENDIX 4 : Stability of the samples ... 24

APPENDIX 5 : Feedback from the proficiency test ... 25

APPENDIX 6 : Evaluation of the assigned values and their uncertainties ... 26

APPENDIX 7 : Terms in the results tables ... 28

APPENDIX 8 : Results of each participant ... 29

APPENDIX 9 : Results of participants and their uncertainties ... 40

APPENDIX 10 : Summary of the z scores ... 61

APPENDIX 11 : Summary of the E

scores ... 63

APPENDIX 12 : z scores in ascending order ... 64

APPENDIX 13 : Results grouped according to the methods ... 83

APPENDIX 14 : Examples of measurement uncertainties reported by the participants ... 104

1 Introduction

Proftest SYKE carried out the proficiency test (PT) for determination of volatile organic compounds from water and soil in November 2020 (VOC 15/2020). In the PT participants determined aromatic VOC compounds (BTEXS), chlorinated VOC compounds and oxygenates from synthetic sample, surface water sample as well as from soil sample. The purpose of the PT was to ensure the comparability and accuracy of the results of the participants.

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 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 Riitta Koivikko coordinator

Mirja Leivuori substitute for coordinator Keijo Tervonen technical assistance Markku Ilmakunnas technical assistance Sari Lanteri technical assistance Ritva Väisänen technical assistance Helena Kutramoinen technical assistance Analytical expert Jari Nuutinen (SYKE)

Expert laboratory SYKE, Helsinki (T003, www.finas.fi/sites.en)

2.2 Participants

In total 10 laboratories participated in this proficiency test, 9 from Finland and one from abroad (Appendix 1). Altogether 80 % of the participants used accredited analytical methods at least for a part of the measurements. For this PT, the expert laboratory has code 4 in the result tables.

2.3 Samples and delivery

Three types of samples were delivered to the participants: synthetic sample (A1V), surface water sample (N2V) and soil sample (S3V). Sample preparation was done by the expert laboratory.

The measurands in the PT are listed with their CAS numbers in Table 1.

The sample A1V was prepared gravimetrically using NIST traceable commercial reference materials produced by Restek and Supelco. The surface water for sample N2V was collected from River Mustionjoki, Southern Finland and the water was spiked with the gravimetrically prepared VOC addition solution. The soil sample S3V was prepared gravimetrically into sandy soil with the gravimetrically prepared VOC addition solution. To ensure the used sample vessels did not contain any traces of VOCs, the sample vessels were heated at 200 ° for two hours prior use. The sample preparation is described in more detail in Appendix 2.

Table 1. Measurands with CAS numbers.

Aromatic

VOC compounds (BTEXS)

Benzene (71-43-2) Ethylbenzene (100-41-4) m/p-Xylene

o-Xylene (95-47-6) Styrene (100-42-5) Toluene (108-88-3)

Chlorinated VOC compounds 1,2,4-Trichlorobenzene (120-82-1) 1,2-Dichlorobenzene (95-50-1) 1,2-Dichloroethane (107-06-2) 1,4-Dichlorobenzene (106-46-7) cis-1,2-Dichloroethene (156-59-2) Dichloromethane (75-09-2) Tetrachloroethene (127-18-4) Tetrachloromethane (56-23-5) trans-1,2-Dichloroethene (156-60-5) Trichloroethene (79-01-6)

Trichloromethane (Chloroform) (67-66-3) Oxygenates ETBE, Ethyl-tert-butylether (637-92-3)

MTBE, Methyl-tert-butylether (1634-04-4) TAME, tert-Amyl methyl ether (994-05-8)

The samples were delivered on 6 November 2020 to the participants abroad and on 9 November 2020 to the national participants. The samples arrived to the participants at the latest on 10 November 2020.

The samples were requested to be measured at the latest on 13 November 2020. The results were

to be reported at the latest on 17 November 2020. Participants delivered the results accordingly,

except one participant who delivered the results on 18 November 2020. The preliminary results report was delivered to the participants via ProftestWEB and email on 24 November 2020.

2.4 Homogeneity and stability studies

The homogeneity of the samples was tested by analyzing three samples as replicate measurements. For all the tested measurands and samples the criterion for homogeneity between subsamples was fulfilled. The repeatability criterion was not fulfilled for trichloroethene in synthetic sample (A1V) and for tetrachloroethene in soil sample (S3V). For the former, the data supports sufficient repeatability and for the latter the difference is within the analytical error. In all other respects, the samples were tested homogenous and, thus, considered sufficiently homogenous. Detailed information of homogeneity studies is shown in Appendix 3.

The stability of the samples was tested by analysing VOCs from the samples stored at 20 ° C for one day. Those results were compared to the results of the samples stored all the time at 4 °C.

All the samples were analysed within the same sample series.

According to the stability test, the concentration of several measurands decreased in the synthetic sample A1V if the temperature of the sample rose to 20 °C. However, the observed differences were within the analytical error. Further according to the stability test, the concentration of styrene in the sample N2V could have been decreased if the temperature of the sample rose to 20 °C. Here also the data gave indication of the possible problems and performance evaluation is weakened. The stability results were taken into account when setting the standard deviation for proficiency assessment. For other measurands and samples the criterion for stability was fulfilled and those could be considered stable.

The transportation conditions were followed with a sample for temperature control. The participants were requested to measure the temperature of the control sample immediately after receiving the samples. The reported arrival temperatures were from 3.7 to 11.5 °C and their average was 8.2 °C. No evident effect of increased transportation temperature was shown in the results for this PT. This supports the sufficient stability of the sample A1V.

The stability of the samples A1V and S3V was controlled also by observing the possible loss of weight. Highest accepted change in weight was 1 %. For sample A1V the observed weight change was in average 0.41 % and the highest change was 0.7 %. For S3V no change in weight was observed. Based on the weight control the samples were considered stable over the transport.

2.5 Feedback from the proficiency test

The feedback from the proficiency test is shown in Appendix 5. The comments from the

participants mainly dealt with their results reporting. The provider commented the Cochran

outliers. 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 Hampel or the Grubbs test before calculating the mean. The results which differed from the data more than 5×s

or 50 % from the robust mean, were rejected before the statistical results handling. If the result had been reported as below detection limit, it was not included in the statistical calculations.

The participants were to report replicate results for all the measurements. The replicate results were tested using the Cochran’s test, which compares the within-laboratory deviation of each participant to the standard deviation of the replicate results of all the participants. The replicate results which differ significantly from others are outliers. The Cochran’s test rejects the results having significantly higher within-laboratory deviation than the results the average, regardless their z score evaluation. According to the Cochran’s test, the deviation of the replicate results is higher than the average for some of the results for 50 % of the participants (Appendix 5).

More information about the statistical handling of the data is available from the Guide for participant [5].

2.6.2 Assigned values

The calculated values (NIST traceable) were used as the assigned values for all the measurements of the synthetic sample (A1V). For the other samples and measurements, the median of the results reported by the participants was used as the assigned value. Detailed information of the assigned values, their uncertainties and their reliabilities are shown in Appendix 6.

The assigned values based on the median are not metrologically traceable. When 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 [2, 3].

For the calculated assigned values, the expanded uncertainty (k=2) was evaluated by using standard uncertainties associated with individual operations involved in the preparation of the sample. The main individual source of the uncertainty was the purity of the stock compound.

When the median was used as the assigned value, the uncertainty was calculated using the standard deviation [2, 5].

The uncertainty of the calculated assigned values was 2.2–9.2 % (at the 95 % confidence level).

When using the median of the participant results as the assigned value, the uncertainty of the

assigned value was 3.0–19.6 % (Appendix 6).

After reporting the preliminary results report the assigned value was recalculated in following cases:

Sample N2V: 1,2-dichloroethane – was 8.08 µg/l, changed to 7.87 µg/l

- Only small changes for z scores, no changes for participants performance evaluation.

Sample N2V: tetrachloromethane – was 7.02 µg/l, changed to 6.61 µg/l

- n

<6 and, therefore, the performance evaluation was not done with z scores but with E

scores.

- Changes in overall performance evaluation based on z scores for participant 1 (was 68 %, now 70 %) and for participant 3 (was 75 %, now 74 %).

No other changes have been done for the assigned values after the preliminary results report.

2.6.3 Proficiency assessment procedure

The standard deviation for proficiency assessment was estimated 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. The standard deviation for proficiency assessment (2 × s

at the 95 % confidence level) was set to 15–35 % depending on the measurand.

After the preliminary results report no changes have been done for the standard deviations of the proficiency assessment values.

When the number of reported results was low (n

<6), the assigned value was based on the participants’ results and the uncertainty was set for the assigned value, the performance evaluation was done by means of E

scores (’Error, normalized’, N2V: cis-1,2,-dichloroethene, ETBE, tetrachloromethane, and trans-1,2-dichloroethene). After the preliminary results report, the evaluation of tetrachloromethane has changed from z score to E

score. These are used to evaluate the difference between the assigned value and participant’s result within their claimed expanded uncertainty.

E

scores are calculated:

(𝐸

)

=

√𝑈_𝑖²+ 𝑈_𝑝𝑡²

, where

x

= participant’s result, x

= assigned value, U

= the expanded uncertainty of a participant’s result and U

= the expanded uncertainty of the assigned value.

Scores of E

–1.0 < E

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

≥ 1.0 or E

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

When using the median as the assigned value, the reliability was tested according to the criterion

u

/ s

≤ 0.3, where u

is the standard uncertainty of the assigned value and s

is the standard

deviation for proficiency assessment [3]. When testing the reliability of the assigned value the criterion was partly fulfilled.

The reliability of the standard deviation for proficiency assessment (s

) and also the corresponding z score was estimated by comparing s

with the standard deviation (s) of the reported results [3]. The criterion s / s

< 1.2 was partly fulfilled.

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

and of the standard deviation for proficiency assessment

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

Sample Measurement

N2V 1,2-Dichlorobenzene

, 1,2-Dichloroethane

, 1,4-Dichlorobenzene

, Dichloromethane

, MTBE

, Styrene

, Toluene

, Trichloroethene

S3V 1,4-Dichlorobenzene

, ETBE

, MTBE

, TAME

, Trichloroethene

3 Results and conclusions

3.1 Results

The summary of the results is presented in Table 2. The terms in the results table are explained in Appendix 7. The results and the performance of each participant are presented in Appendix 8 and the reported results with their expanded uncertainties (k=2) are presented in Appendix 9. The summaries of the z and E

scores are shown in Appendices 10 and 11 and z scores in the ascending order in Appendix 12.

Table 2. The summary of the results in the proficiency test VOC 15/2020.

Measurand Sample Unit Assigned

value Mean Rob.

mean Median s s % s

s

% 2 x s

% n

Acc z % /

1,2,4-Trichlorobenzene A1V µg/ml 2.44 2.23 2.19 2.22 0.41 18.3 0.37 16.7 25 7 86

N2V µg/l 10.3 10.3 10.8 10.3 1.2 11.5 1.9 17.2 30 7 86

S3V mg/kg 0.48 0.48 0.48 0.48 0.05 10.9 0.06 12.4 30 7 100

1,2-Dichlorobenzene A1V µg/ml 1.89 1.73 1.73 1.74 0.35 20.1 0.39 22.7 20 7 71

N2V µg/l 11.0 10.6 11.4 11.0 2.0 19.1 3.2 27.8 30 7 71

S3V mg/kg 0.91 0.90 0.89 0.91 0.11 12.6 0.11 12.8 30 7 100

1,2-Dichloroethane A1V µg/ml 1.71 1.74 1.74 1.64 0.23 13.0 0.25 14.6 15 9 78

N2V µg/l 7.87 7.93 7.92 7.87 1.04 13.2 1.15 14.6 30 8 88

S3V mg/kg 0.26 0.26 0.26 0.26 0.03 10.6 0.03 12.0 25 9 100

1,4-Dichlorobenzene A1V µg/ml 1.60 1.47 1.45 1.49 0.35 24.0 0.37 25.6 20 7 57

N2V µg/l 9.77 9.9 - 9.8 2.3 23.3 - - 30 7 57

S3V mg/kg 0.38 0.37 - 0.38 0.05 13.2 - - 30 7 86

Benzene A1V µg/ml 0.64 0.65 0.64 0.63 0.09 13.8 0.08 13.0 15 9 78

N2V µg/l 8.56 8.85 9.12 8.56 1.05 11.9 1.45 15.9 25 9 89

S3V mg/kg 0.17 0.17 0.17 0.17 0.03 14.6 0.03 14.7 30 9 89

Chloroform A1V µg/ml 1.71 1.82 1.79 1.81 0.32 17.4 0.30 16.8 20 9 78

N2V µg/l 7.75 7.81 - 7.75 1.00 12.7 - - 30 8 86

S3V mg/kg 0.25 0.26 0.26 0.25 0.03 12.6 0.04 14.3 30 9 100

Table 2. The summary of the results in the proficiency test VOC 15/2020.

Measurand Sample Unit Assigned

value Mean Rob.

mean Median s s % s

s

% 2 x s

% n

Acc z % /

cis-1,2-Dichloroethene

A1V µg/ml 1.91 1.91 1.90 1.88 0.18 9.6 0.19 10.0 15 7 86

N2V µg/l 11.0 11.6 - 11.0 1.4 12.1 - - - 6 - / 80

S3V mg/kg 0.88 0.91 0.90 0.88 0.08 8.5 0.07 7.7 25 7 100

Dichloromethane A1V µg/ml 4.06 4.46 4.42 4.03 0.94 21.2 0.99 22.4 15 8 63

N2V µg/l 32.2 33.0 - 32.2 5.5 16.6 - - 30 7 86

S3V mg/kg 1.43 1.42 1.55 1.43 0.05 3.7 0.28 18.0 30 8 75

ETBE A1V µg/ml 1.29 1.39 1.39 1.40 0.28 20.2 0.32 22.9 20 7 57

N2V µg/l 22.3 21.6 26.5 22.3 2.7 12.4 10.0 37.6 - 7 - / 60

S3V mg/kg 0.53 0.55 - 0.53 0.13 24.0 - - 30 7 71

Ethylbenzene A1V µg/ml 1.89 1.79 1.79 1.94 0.25 14.0 0.28 15.9 15 9 78

N2V µg/l 10.2 10.0 10.3 10.2 1.1 10.5 1.1 10.6 25 9 89

S3V mg/kg 0.95 0.97 0.97 0.95 0.08 8.8 0.09 9.6 25 9 100

m/p-Xylene A1V µg/ml 1.88 1.61 1.62 1.74 0.33 20.2 0.35 21.4 20 9 67

N2V µg/l 9.49 9.67 9.67 9.49 0.86 8.9 1.60 16.6 25 9 78

S3V mg/kg 0.96 0.95 0.92 0.96 0.10 11.0 0.14 15.6 25 9 89

MTBE A1V µg/ml 1.29 1.32 1.36 1.36 0.17 12.8 0.23 17.1 20 9 89

N2V µg/l 22.0 21.7 26.7 22.0 4.1 18.7 12.0 44.8 30 9 67

S3V mg/kg 0.60 0.64 0.63 0.60 0.18 28.7 0.19 30.0 35 9 78

o-Xylene A1V µg/ml 1.88 1.87 1.88 1.90 0.23 12.3 0.26 13.8 15 9 89

N2V µg/l 10.8 10.7 10.7 10.8 0.5 5.1 1.0 9.6 25 9 89

S3V mg/kg 0.91 0.92 0.92 0.91 0.06 6.1 0.06 6.9 25 9 100

Styrene A1V µg/ml 1.88 1.76 1.77 1.81 0.34 19.0 0.35 19.9 15 8 75

N2V µg/l 9.91 9.50 10.36 9.91 2.21 23.3 3.46 33.4 30 7 71

S3V mg/kg 0.91 0.92 0.89 0.91 0.10 10.7 0.14 16.0 25 8 88

TAME A1V µg/ml 1.29 1.30 1.30 1.28 0.22 16.6 0.23 17.8 20 8 88

N2V µg/l 22.4 22.5 24.8 22.4 1.7 7.8 5.4 21.9 25 9 78

S3V mg/kg 0.53 0.56 0.56 0.53 0.09 16.5 0.10 18.7 30 8 88

Tetrachloroethene A1V µg/ml 3.61 3.69 3.65 3.54 0.59 16.1 0.59 16.2 15 9 78

N2V µg/l 16.5 17.1 17.8 16.5 2.2 13.0 3.2 18.0 30 8 88

S3V mg/kg 1.20 1.16 1.17 1.20 0.14 11.9 0.14 12.0 25 9 89

Tetrachloromethane A1V µg/ml 1.72 1.56 1.77 1.50 0.14 9.3 0.48 26.8 20 8 75

N2V µg/l 6.61 6.88 - 6.61 1.26 18.4 - - - 7 - / 100

S3V mg/kg 0.24 0.23 0.23 0.24 0.04 17.4 0.05 19.7 30 8 86

Toluene A1V µg/ml 1.89 1.77 1.78 1.73 0.29 16.7 0.30 16.7 20 9 89

N2V µg/l 10.9 10.7 11.2 10.9 1.8 16.6 2.1 18.5 30 9 78

S3V mg/kg 0.85 0.86 0.87 0.85 0.07 8.5 0.08 8.7 25 9 100

trans-1,2-Dichloroethene

A1V µg/ml 1.89 1.82 1.82 1.78 0.22 11.9 0.25 13.5 15 7 71

N2V µg/l 10.3 10.9 - 10.3 1.5 14.1 - - - 6 - / 80

S3V mg/kg 0.78 0.78 0.80 0.78 0.05 6.8 0.08 10.3 25 7 86

Trichloroethene A1V µg/ml 1.72 1.79 1.79 1.81 0.19 10.8 0.18 10.2 15 9 78

N2V µg/l 7.45 7.44 7.80 7.45 1.15 15.4 1.66 21.3 30 8 75

S3V mg/kg 0.24 0.25 0.25 0.24 0.05 18.0 0.05 20.4 30 9 78

Rob. mean: the robust mean, s

: the robust standard deviation, s

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

%: the

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

: the number of the participants, Acc z %: the

results (%), where z  2, Acc E

%: the results (%), where E

 < 1.

The robust standard deviations of the results varied from 7 % to 45 % (Table 2). The robust standard deviations were approximately in the same range as in the previous similar PT VOC 11/2016, where the robust standard deviations varied from 5 % to 51 % [5]. For oxygenates, the robust standard deviations varied between 17 % and 45 % (7–41 % in the previous similar proficiency test), for BTEXS compounds they varied between 7 and 33 % (5–51 %), and for chlorinated VOC compounds they varied between 8 and 28 % (5–47 %).

In this PT the participants were to report replicate results for all the measurements. The repeatability of the replicate results was tested using the ANOVA statistical handling (Table 3).

The estimation of the robustness of the methods could be done by the ratio s

/s

. For robust methods the ratio s

/s

should not exceed 3. Only 7 % of the results fulfilled the criterion (Table 3).

Table 3. The summary of repeatability test based on replicate results (ANOVA statistics).

Measurand Sample Unit Assigned value Mean s

s

s

s

% s

% s

% s

/s

1,2,4-Trichlorobenzene A1V µg/ml 2.44 2.23 0.05 0.41 0.41 2.4 18 18 7.6

N2V µg/l 10.3 10.3 0.25 2.59 2.60 2.2 23 23 11

S3V mg/kg 0.48 0.48 0.02 0.05 0.05 3.5 11 11 3.0

1,2-Dichlorobenzene A1V µg/ml 1.89 1.73 0.03 0.35 0.35 1.5 20 20 13

N2V µg/l 11.0 10.6 0.22 4.46 4.46 1.8 37 37 20

S3V mg/kg 0.91 0.90 0.02 0.11 0.12 2.2 13 13 5.7

1,2-Dichloroethane A1V µg/ml 1.71 1.74 0.05 0.22 0.23 2.6 13 13 4.9

N2V µg/l 7.87 7.93 0.30 1.02 1.07 3.8 13 13 3.4

S3V mg/kg 0.26 0.26 0.01 0.03 0.03 3.4 10 11 3.0

1,4-Dichlorobenzene A1V µg/ml 1.60 1.47 0.03 0.35 0.35 1.7 24 24 14

N2V µg/l 9.77 9.9 0.27 2.29 2.31 2.7 23 23 8.6

S3V mg/kg 0.38 0.37 0.01 0.05 0.05 2.8 13 13 4.7

Benzene A1V µg/ml 0.64 0.65 0.02 0.09 0.09 2.8 14 14 4.9

N2V µg/l 8.56 8.85 0.24 2.59 2.60 2.5 27 27 11

S3V mg/kg 0.17 0.17 0.003 0.03 0.03 1.8 15 15 8.3

Chloroform A1V µg/ml 1.71 1.82 0.06 0.31 0.32 3.2 17 18 5.3

N2V µg/l 7.75 7.81 0.18 0.99 1.00 2.3 13 13 5.4

S3V mg/kg 0.25 0.26 0.01 0.03 0.03 3.5 12 13 3.5

cis-1,2-Dichloroethene

A1V µg/ml 1.91 1.91 0.04 0.18 0.19 2.3 9.5 9.8 4.1

N2V µg/l 11.0 11.6 0.40 3.50 3.53 3.1 27 27 8.8

S3V mg/kg 0.88 0.91 0.01 0.08 0.08 1.6 8.4 8.6 5.3

Dichloromethane A1V µg/ml 4.06 4.46 0.07 0.94 0.94 1.5 21 21 14

N2V µg/l 32.2 33.0 0.71 5.48 5.52 2.2 17 17 7.7

S3V mg/kg 1.43 1.42 0.07 0.24 0.25 4.6 16 16 3.4

ETBE A1V µg/ml 1.29 1.39 0.04 0.28 0.28 2.8 20 20 7.1

N2V µg/l 22.3 21.6 0.68 8.76 8.79 2.6 33 33 13

S3V mg/kg 0.53 0.55 0.01 0.13 0.13 0.9 24 24 27

Ethylbenzene A1V µg/ml 1.89 1.79 0.06 0.25 0.25 3.3 14 14 4.2

N2V µg/l 10.2 10.0 0.37 3.22 3.24 3.3 29 29 8.8

S3V mg/kg 0.95 0.97 0.02 0.08 0.09 1.9 8.7 8.9 4.6

m/p-Xylene A1V µg/ml 1.88 1.61 0.05 0.32 0.33 3.3 20 20 6.0

N2V µg/l 9.49 9.67 0.18 3.48 3.48 1.8 34 34 20

S3V mg/kg 0.96 0.95 0.02 0.18 0.18 2.2 20 20 9.1

Table 3. The summary of repeatability test based on replicate results (ANOVA statistics).

Measurand Sample Unit Assigned value Mean s

s

s

s

% s

% s

% s

/s

MTBE A1V µg/ml 1.29 1.32 0.10 0.27 0.29 6.8 20 21 2.9

N2V µg/l 22.0 21.7 0.98 10.9 11.0 3.7 41 41 11

S3V mg/kg 0.60 0.64 0.02 0.18 0.18 3.0 29 29 9.4

o-Xylene A1V µg/ml 1.88 1.87 0.03 0.23 0.23 1.8 12 12 6.8

N2V µg/l 10.8 10.7 0.26 2.83 2.84 2.3 25 25 11

S3V mg/kg 0.91 0.92 0.02 0.05 0.06 2.5 5.8 6.3 2.4

Styrene A1V µg/ml 1.88 1.76 0.04 0.33 0.34 2.1 19 19 9.1

N2V µg/l 9.91 9.50 0.21 4.64 4.64 1.9 42 42 22

S3V mg/kg 0.91 0.92 0.02 0.17 0.17 2.3 19 19 8.4

TAME A1V µg/ml 1.29 1.30 0.03 0.22 0.22 2.5 17 17 6.5

N2V µg/l 22.4 22.5 0.59 7.10 7.12 2.3 28 28 12

S3V mg/kg 0.53 0.56 0.01 0.09 0.09 2.4 16 17 6.7

Tetrachloroethene A1V µg/ml 3.61 3.69 0.17 0.58 0.61 4.5 16 16 3.5

N2V µg/l 16.5 17.1 0.42 5.18 5.19 2.3 28 28 12

S3V mg/kg 1.20 1.16 0.03 0.14 0.14 2.8 12 12 4.2

Tetrachloromethane A1V µg/ml 1.72 1.56 0.09 0.41 0.43 5.2 23 24 4.5

N2V µg/l 6.61 6.88 0.35 1.24 1.29 5.1 18 19 3.5

S3V mg/kg 0.24 0.23 0.01 0.04 0.04 5.1 17 18 3.4

Toluene A1V µg/ml 1.89 1.77 0.05 0.29 0.30 2.7 17 17 6.2

N2V µg/l 10.9 10.7 0.18 2.82 2.82 1.6 25 25 15

S3V mg/kg 0.85 0.86 0.02 0.07 0.07 2.0 8.4 8.6 4.2

trans-1,2-Dichloroethene

A1V µg/ml 1.89 1.82 0.06 0.21 0.22 3.5 12 12 3.3

N2V µg/l 10.3 10.9 0.34 1.52 1.56 3.1 14 14 4.4

S3V mg/kg 0.78 0.78 0.02 0.14 0.14 2.7 17 17 6.3

Trichloroethene A1V µg/ml 1.72 1.79 0.06 0.19 0.20 3.2 11 11 3.3

N2V µg/l 7.45 7.44 0.20 3.67 3.67 2.3 42 42 18

S3V mg/kg 0.24 0.25 0.01 0.05 0.05 2.8 18 18 6.4

Ass.val.: assigned value; s

: repeatability standard error; s

: between participants standard error; s

: reproducibility standard error.

3.2 Analytical methods

The participants could use different analytical methods for the measurements in the PT. The reported results grouped by used analytical methods are shown in Appendix 13. The statistical comparison of the analytical methods was possible for the data where the number of the results was ≥ 5.

Aromatic VOC compounds (BTEXS), chlorinated VOC compounds and oxygenates The measurements were mostly done with Headspace GC-MS (5–8 participants depending on the sample and measurand, Appendix 13). Depending on the sample and measurand, up to two participants used Headspace GC-FID and one participant used Purge&Trap GC-MS.

GC-FID technique is sensitive, and it is known to be good for hydrocarbons, but it is rather

unsensitive for halogenated compounds (chlorinated VOCs) as chloroform, tetrachloromethane

and trichloroethene. For those GC-ECD technique is more applicable. Further, with GC-MS

technique the identification is based both on retention time and separated ions and is, therefore,

more reliable. In this PT the concentration of some halogenated compounds was rather low and the results were below LOD when using GC-FID.

3.3 Uncertainties of the results

All but one participant reported the expanded uncertainties (k=2) with their results for at least some of their results (Table 4, Appendix 9). The range of the reported uncertainties varied between the measurands and the sample types.

Several approaches were used for evaluating the measurement uncertainty (Appendix 14). The most used approach was based on using the data obtained from method validation. The approaches based on the internal quality control (IQC) data from synthetic and routine sample replicates as well as the IQC data with proficiency test results were also used. One participant used MUkit measurement uncertainty software for the estimation of their uncertainties [6, 7].

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.

Within the optimal measuring range, the expanded measurement uncertainty (k=2) should typically be 20 – 40%. Close to the limit of quantification the relative measurement uncertainty is higher.

Table 4. The ranges of the reported expanded uncertainties by participants as percent (k=2, U

%).

Measurand Synthetic sample

A1V, % Surface water sample

N2V, % Soil sample

M3V, %

1,2,4-Trichlorobenzene 15–30 15–40 30–44

1,2-Dichlorobenzene 15–37 15–37 20-39

1,2-Dichloroethane 15–38 15–40 29–39

1,4-Dichlorobenzene 15–32 15–40 29–40

Benzene 15–37 15–37 30–40

Chloroform 15–34 15–40 27–39

cis-1,2-Dichloroethene 15–30 15–40 20–43

Dichloromethane 20–31 20–35 20–42

ETBE 10–30 10–35 30–50

Ethylbenzene 20–43 20–43 20–39

m/p-Xylene 15–38 15–40 20–39

MTBE 10–31 10–35 30–39

o-Xylene 20–33 20–35 20–39

Styrene 15–41 15–41 20–45

TAME 15–33 15–35 15–39

Tetrachloroethene 20–43 20–43 20–40

Tetrachloromethane 20–30 20–40 30–40

Toluene 17–37 17–37 20–39

trans-1,2-Dichloroethene 25–33 20–33 25–39

Trichloroethene 15–37 15–40 28–41

4 Evaluation of the results

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

scores, which were calculated using the assigned values and the standard deviation for proficiency assessment (Appendix 7). The z and E

scores were interpreted as follows:

Criteria Performance

 z   2 Satisfactory

2 <  z  < 3 Questionable

| z   3 Unsatisfactory –1.0 < E

< 1.0 Satisfactory E

 –1.0 or E

 1.0 Unsatisfactory

In total, 82 % of the results were satisfactory when total deviation of 15–35 % from the assigned value was accepted. Further, 80 % of the results evaluated based on E

scores were satisfactory.

Altogether 80 % of participants used accredited analytical methods at least for a part of the measurements. The summary of the performance evaluation and comparison to the previous PT is presented in Table 5. In the previous similar PT (VOC 11/2016) the performance was satisfactory for 81 % of the participant results [5].

Table 5. Summary of the performance evaluation in the proficiency test VOC 15/2020.

Sample /

Measurand 2×s

% Satisfactory

results, % Assessment A1V

Aromatic VOC

compounds 15–20 79

In the PT VOC 11/2016 80 % of the results were satisfactory when deviation of 15 % was accepted [5].

A1V

Chlorinated VOC compounds

15–25 75 In the PT VOC 11/2016 78 % of the results were satisfactory [5].

A1V

Oxygenates 20 78 In the PT VOC 11/2016 72 % of the results were satisfactory when deviation of 15 % was accepted [5].

N2V Aromatic VOC compounds

25–30 82 Only approximate performance evaluation for styrene and toluene as the criteria for the reliability of the assigned value and/or the s

were not met. In the PT VOC 11/2016 83 % of the results were satisfactory when deviation of 30 % was accepted [5].

N2V Chlorinated

VOC compounds 30

80 E

scores:

87

Only approximate performance evaluation for 1,2-dichlorobenzene, 1,2-dichloroethane, 1,4-dichlorobenzene, dichloromethane, and trichloroethene as the criteria for the reliability of the assigned value and/or the s

were not met. Also in the PT VOC 11/2016 80 % of the results were satisfactory when deviation of 25-35 % was accepted [5]. The results for cis-1,2-dichloroethene, tetrachloromethane, and trans-1,2-dichloroethene were evaluated with E

scores.

N2V

Oxygenates 25–30

73 E

scores:

60

Only approximate performance evaluation for MTBE as the criteria for the reliability of the assigned value and the s

were not met. In the PT VOC 11/2016 82 % of the results were satisfactory when deviation of 25-30 % was accepted [5]. The results of ETBE were evaluated with E

scores.

S3V Aromatic VOC

compounds 25–30 94

Good performance and for measurands ethylbenzene, o-xylene and toluene the performance was excellent (100 %). In the PT VOC 11/2016 74 % of the results were satisfactory when deviation of 30-35 % was accepted [5].

S3V Chlorinated

VOC compounds 25–30 91

Good overall performance. For 1,2,4-trichlorobenzene, 1,2-dichlorobenzene, 1,2-dichloro- ethane, chloroform, and cis-1,2-dichloroethene the performance was excellent (100 %).

Only approximate performance evaluation for 1,4-dichlorobenzene and trichloroethene as the criterion for the reliability of the assigned value was not met. In the PT VOC 11/2016 85 % of the results were satisfactory when deviation of 30-35 % was accepted [5].

S3V

Oxygenates 30–35 79 Only approximate performance evaluation as the criteria for the reliability of the assigned

value and/or the s

were not met. Also, in the PT VOC 11/2016 79 % of the results were

satisfactory [5].

5 Summary

Proftest SYKE carried out the proficiency test (PT) for analyses of volatile organic compounds water and soil in November 2020 (VOC 15/2020). A synthetic sample, a surface water sample and a soil sample were delivered to the participants. In total there were 10 participants in this proficiency test.

Either the calculated concentration (synthetic sample) or the median of the reported results was used as the assigned value for the measurands. The expanded uncertainty of the assigned value was estimated at the 95 % confidence level and it was 2.2–9.2 % for the calculated assigned values and 3.0–19.6 % for the assigned values based on the median of the reported results.

The performance of the participants was evaluated by using z and E

scores. In this PT 82 % of the results evaluated with z scores were satisfactory when deviation of 15–35 % from the assigned value was accepted. Further, 80 % of the results evaluated with E

scores were satisfactory. The performance of the participants was on the same level as in the previous similar PT in 2016 when 81 % of the results were satisfactory.

6 Summary in Finnish

Proftest SYKE järjesti marraskuussa 2020 pätevyyskokeen laboratorioille, jotka määrittävät haihtuvia orgaanisia yhdisteitä (VOC) vedestä ja maasta (VOC 15/2020). Osallistujille toimitettiin synteettinen näyte, pintavesinäyte sekä maanäyte. Pätevyyskokeeseen osallistui yhteensä 10 laboratoriota.

Testisuureiden vertailuarvona käytettiin laskennallisia pitoisuuksia (synteettinen näyte) tai osallistujien tulosten mediaania. Vertailuarvon laajennettu epävarmuus 95 %:n luottamusvälillä oli 2,2–9,2 % käytettäessä vertailuarvona laskennallista arvoa ja 3,0–19,6 % käytettäessä vertailuarvona osallistujatulosten mediaania.

Tuloksia arvioitiin z- ja E

-arvojen avulla. Koko tulosaineistossa hyväksyttäviä tuloksia oli

z-arvojen perusteella 82 %, kun vertailuarvosta sallittiin 15–35 %:n poikkeama. Tuloksista, jotka

arvioitiin E

-arvoilla, oli hyväksyttäviä 80 %. Hyväksyttävien tulosten määrä oli samalla tasolla

kuin edellisessä vastaavassa vertailussa vuonna 2016, jolloin hyväksyttäviä tuloksia oli 81 %.

REFERENCES

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. 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 . 5. Koivikko, R., Nuutinen, J., Tervonen, K., Lanteri, S., Kutramoinen, H., Väisänen, R. and

Ilmakunnas, M. 2017. Laboratorioiden välinen pätevyyskoe 11/2016. Haihtuvat orgaaniset yhdisteet vedestä ja maasta. Suomen ympäristökeskuksen raportteja 5/2017.

http://hdl.handle.net/10138/177657.

6. 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.

7. 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)

APPENDIX 1: Participants in the proficiency test

Country Participant

Finland Eurofins Ahma Oy, Oulu

Eurofins Environment Testing Finland Oy, Lahti Fortum Waste Solutions Oy, Riihimäki

KVVY Tutkimus Oy, Tampere

MetropoliLab Oy

Neste Oyj, Tutkimus ja kehitys/Vesilaboratorio, Kulloo

SGS Finland Oy, Kotka

SYKE, Helsingin toimipaikka

SYNLAB Analytics & Services Finland Oy

Germany UCL Umwelt Control Labor GmbH, QS

APPENDIX 2: Sample preparation

The samples were prepared by the expert laboratory. The addition solutions for the samples were prepared gravimetrically using NIST traceable certified reference materials from Supelco and Restek. The dilutions were prepared in methanol.

Table I. The commercial mixtures, chemicals, and solvent used for sample preparation.

Measurand / Solvent Code Producer, Product code, Concentration, Solvent ETBE, MTBE, TAME OXY Restek 30465, California Oxygenates Mixture #1, 2000

µg/ml in P&T Methanol Benzene, Ethylbenzene, p-Xylene,

o-Xylene, Styrene, Toluene,

Tetrachloroethene, cis-1,2-Dichloroethene, trans-1,2-Dichloroethene,

1,2-Dichlorobenzene

MIX8 Supelco 48803, Volatile Organic Compounds Mix8, 2000 µg/ml in Methanol

Trichloromethane, Tetrachloromethane, Trichloroethene, Tetrachloroethene, 1,2-Dichloroethane

HALO Supelco 48224, EPA 8010 Halogenated Volatileorganic Mix 1, 2000 µg/mL in Methanol

1,2,4-Trichlorobenzene 124TCB Supelco 40007, 1,2,4-Trichlorobenzene, 5000 µg/ml in Methanol

Dichloromethane DCM Supelco 40042, Dichloromethane, 5000 µg/ml in

Methanol

Benzene BZ Restek 30249, Benzene Standard, 2000 µg/ml in P&T

Methanol

1,4-Dichlorobenzene 14DB Supelco 40025, 1,4-Dichlorobenzene 5000 µg/ml in Methanol

Methanol Methanol J.T.Baker 9007-02, Methanol, Ultra Resi-Analyzed

Table II. Weighing results for the preparation of sample addition solutions.

Code A1V Addition solution for N2V Addition solution for S3V

OXY 0.07615 g 0.17149 g 0.23746 g

MIX8 0.11267 g 0.07484 g 0.40947 g

HALO 0.10232 g 0.04896 g 0.10314 g

124TCB 0.05791 g 0.03217 g 0.08068 g

DCM 0.09569 g 0.08850 g 0.24113 g

BZ 0.03746 g 0.06962 g 0.07085 g

14DB 0.03780 g 0.03160 g 0.07212 g

Methanol 118.5450 g 40.07959 g 39.55965 g

Synthetic sample A1V was prepared gravimetrically using commercial mixtures and chemicals to methanol.

The addition solution for sample N2V was prepared gravimetrically into methanol by using commercial mixtures and chemicals. Final sample N2V was prepared by weighing 50 ml of the addition solution N2V to 20 liter of surface water.

The addition solution for sample S3V was prepared gravimetrically into methanol by using commercial mixtures and chemicals. Final soil sample S3V was prepared gravimetrically by weighing 20 g of dry sandy soil (sieved < 0.5 mm), 4 ml of water, 1 ml of S3V addition solution and 20 ml of methanol.

Table III. Theoretical concentrations of measurands in the samples.

Code Measurand Stock solution

[µg/ml] A1V

[µg/ml] N2V

[µg/l] S3V [mg/kg]

OXY MTBE 2002.0 1.286 21.702 0.583

TAME 2004.4 1.288 21.728 0.584

ETBE 2001.6 1.286 21.697 0.583

Mix8 Toluene 1986 1.888 9.395 0.997

Ethylbenzene 1986 1.888 9.395 0.997

o-Xylene 1982 1.884 9.376 0.995

p-Xylene 1983 1.885 9.381 0.996

Styrene 1978 1.880 9.357 0.993

1,2-Dichlorobenzene 1992 1.893 9.424 1.000

trans-1,2-Dichloroethene 1990 1.891 9.414 0.999

cis-1,2-Dichloroethene 2010 1.910 9.509 1.009

Tetrachloroethene 1990 1.891 9.414 0.999

HALO Tetrachloromethane 1988 1.716 6.152 0.251

Trichloromethane 1985 1.713 6.143 0.251

1,2-Dichloroethane 1986 1.714 6.146 0.251

Tetrachloroethene 1986 1.714 6.146 0.251

Trichloroethene 1989 1.717 6.156 0.252

124TCB 1,2,4-Trichlorobenzene 5000 2.443 10.168 0.495

DCM Dichloromethane 5010 4.056 28.027 1.481

14DB 1,4-Dichlorobenzene 5001 1.595 9.989 0.442

BZ Benzene 2008 0.635 8.837 0.174

Total amount of

tetrachloroethene 3.606 15.560 1.250

APPENDIX 3: Homogeneity of the samples

Homogeneity was tested as replicate measurements of selected measurands from three samples of each sample type.

Criteria for homogeneity: s

/s

< 0.5 and s

<c, where s

= standard deviation for proficiency assessment

s

= analytical deviation, standard deviation of the results in a sub sample

s

= between-sample deviation, standard deviation of the results between sub samples c = F1 × s

+ F2 × s

, where

s

= (0.3 × s

)

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

Measurand

Concentration [µg/l]

[mg/kg]

n s

% s

s

s

/ s

s

/ s

< 0.5? s

c s

< c?

Sample A1V

1,2,4-Trichlorobenzene 2.35 3 12.5 0.29 0.04 0.15 Yes 0.000 0.032 Yes

Chloroform 1.83 3 10 0.18 0.06 0.33 Yes 0.000 0.025 Yes

Dichloromethane 4.11 3 7.5 0.31 0.14 0.45 Yes 0.000 0.107 Yes

MTBE 1.28 3 10 0.13 0.03 0.26 Yes 0.000 0.009 Yes

o-Xylene 1.76 3 7.5 0.13 0.06 0.49 Yes 0.000 0.022 Yes

Tetrachloroethene 3.86 3 7.5 0.29 0.14 0.49 Yes 0.000 0.107 Yes

Trichloroethene 1.72 3 7.5 0.13 0.07 0.57 No 0.000 0.028 Yes

Sample N2V

1,2,4-Trichlorobenzene 10.7 3 15 1.60 0.18 0.11 Yes 0.046 0.830 Yes

Chloroform 7.10 3 15 1.07 0.05 0.05 Yes 0.039 0.316 Yes

Dichloromethane 28.1 3 15 4.21 0.40 0.10 Yes 0.202 5.464 Yes

MTBE 23.1 3 15 3.46 0.24 0.07 Yes 0.217 3.477 Yes

o-Xylene 10.6 3 12.5 1.32 0.13 0.10 Yes 0.085 0.547 Yes

Tetrachloroethene 16.5 3 15 2.47 0.18 0.07 Yes 0.449 1.788 Yes

Trichloroethene 7.91 3 15 1.19 0.07 0.06 Yes 0.096 0.400 Yes

Sample S3V

1,2,4-Trichlorobenzene 0.49 3 15 0.07 0.02 0.28 Yes 0.000 0.003 Yes

Chloroform 0.26 3 15 0.04 0.02 0.41 Yes 0.000 0.001 Yes

Dichloromethane 1.39 3 15 0.21 0.08 0.40 Yes 0.000 0.042 Yes

MTBE 0.49 3 17.5 0.09 0.03 0.29 Yes 0.000 0.005 Yes

o-Xylene 0.87 3 12.5 0.11 0.05 0.49 Yes 0.000 0.015 Yes

Tetrachloroethene 1.23 3 12.5 0.15 0.08 0.52 No

0.000 0.034 Yes

Trichloroethene 0.21 3 15 0.03 0.02 0.49 Yes 0.000 0.001 Yes

1)

The difference is within the analytical error.

Conclusion: For all the tested measurands and samples the criterion for homogeneity between

subsamples was fulfilled. The repeatability criterion was not fulfilled for trichloroethene in

synthetic sample (A1V) and for tetrachloroethene in soil sample (S3V). For the former, the

data supports sufficient repeatability and for the latter the difference is within the analytical

error. In all other respects, the samples were tested homogenous.

APPENDIX 4: Stability of the samples

The samples were delivered to the participants on 6–9 November 2020 and they arrived to the participants at the latest on 10 November 2020. The samples were requested to be measured at the latest on 13 November 2020.

The stability of the samples was tested by analyzing samples stored at the temperatures 4 °C and 20 °C on 13 November 2020. For A1V one sample and for N2V as well as for S3V three samples were tested as replicate determinations for both temperatures.

Criteria for stability: D < 0.3 × s

, where

D = |the difference of results measured from the samples stored at the temperatures 4 °C and 20 °C|

s

= standard deviation for proficiency assessment

A1V N2V S3V

Measurand

Assigned value [µg/ml]

D 0.3 × s

D <

0.3 × s

?

Assigned value [µg/l]

D 0.3 × s

D <

0.3 × s

?

Assigned value [µg/l]

D 0.3 × s

D <

0.3 × s

? Aromatic VOC compounds

Benzene 0.64 0.023 0.014 No

8.56 0.16 0.32 Yes 0.17 0.002 0.008 Yes

Ethylbenzene 1.89 0.068 0.043 No

10.2 0.28 0.38 Yes 0.95 0.020 0.036 Yes

m/p-Xylene 1.88 0.065 0.056 No

9.49 0.24 0.36 Yes 0.96 0.018 0.036 Yes

o-Xylene 1.88 0.063 0.042 No

10.8 0.25 0.41 Yes 0.91 0.023 0.034 Yes

Styrene 1.88 0.052 0.042 No

9.91 1.01 0.45 No 0.91 0.013 0.034 Yes

Toluene 1.89 0.069 0.057 No

10.9 0.21 0.49 Yes 0.85 0.019 0.032 Yes

Chlorinated VOC compounds 1,2,4-

Trichlorobenzene 2.44 0.085 0.092 Yes 10.3 0.17 0.46 Yes 0.48 0.014 0.022 Yes

1,2-Dichlorobenzene 1.89 0.058 0.057 No

11.0 0.06 0.50 Yes 0.91 0.012 0.041 Yes

1,2-Dichloroethane 1.71 0.022 0.038 Yes 7.87 0.04 0.35 Yes 0.26 0.001 0.010 Yes

1,4-Dichlorobenzene 1.60 0.057 0.048 No

9.77 0.23 0.44 Yes 0.38 0.010 0.017 Yes

Chloroform 1.71 0.030 0.051 Yes 7.75 0.05 0.35 Yes 0.25 0.002 0.011 Yes

Dichloromethane 4.06 0.144 0.091 No

32.2 0.16 1.45 Yes 1.43 0.003 0.064 Yes

Tetrachloroethene 3.61 0.187 0.081 No

16.5 0.21 0.74 Yes 1.20 0.011 0.045 Yes

Trichloroethene 1.72 0.043 0.039 No

7.45 0.15 0.34 Yes 0.24 0.006 0.011 Yes

Oxygenates

MTBE 1.29 0.019 0.039 Yes 22.0 0.62 0.99 Yes 0.60 0.005 0.032 Yes

TAME 1.29 0.008 0.039 Yes 22.4 0.63 0.84 Yes 0.53 0.014 0.024 Yes

1)

The difference is within the analytical error

Conclusion: According to the stability test, the concentration of several measurands decreased in the synthetic sample A1V if the temperature of the samples rose to 20 °C. However, the observed differences were within the analytical error. Further, according to sample tracking, the arrival temperature was at highest 11.5 °C and in average 8.2 °C. Therefore, the sample A1V was considered sufficiently stable.

According to the stability test, the concentration of styrene in the sample N2V could have been decreased if the temperature of the sample rose to 20 °C. Here also the data gave indication of the possible problems and performance evaluation is weakened.

The stability results were taken into account when setting the standard deviation for

proficiency assessment. For other measurands and samples the criterion for stability was

fulfilled and those could be considered stable.

APPENDIX 5: Feedback from the proficiency test

FEEDBACK FROM THE PARTICIPANTS

Participant Comments to the results Action / Proftest SYKE 1 The result calculations for sample N2V were

done with wrong dilution factor. The corrected results were half of the reported ones.

The organizer does not correct the participant results after delivering the preliminary results report. Almost all erroneous results were handled as outliers in the statistical data treatment and they did not affect to the performance evaluation of the other participants. In the final data handling the results for 1,2-dichloroethane and

tetrachloromethane were set as manual outliers.

See more information from Chapter 2.6.2.

If the results had been reported correctly, they would have been satisfactory, except for the result for tetrachloromethane. The participant can re-calculate the z and E

scores according to the Guide for participants [4].

3 The result for cis-1,2-dichloroethene is the sum of cis- and trans-1,2-dichloroethene for all the samples. The isomers could not be separated.

The organizer thanks the participant for the additional information.

FEEDBACK TO THE PARTICIPANTS Participant Comments

10 The measurement uncertainty should be reported with the results obtained by accredited method.

1, 6, 7, 9, 10 The deviation of participant’s replicate results was significantly higher than the mean deviation of the replicate results, i.e. those results were Cochran outliers:

LAB 1: Trichloroethene (N2V) LAB 6: Benzene (A1V)

LAB 7: TAME (S3V), tetrachloroethene (A1V), trans-1,2-dichloroethene (A1V), trichloroethene (A1V)

LAB 9: Dichloromethane (N2V, S3V), MTBE (N2V) LAB 10: ETBE (S3V), MTBE (A1V)

The provider recommends the participants to re-validate their accepted deviation of replicate

measurements.

APPENDIX 6: Evaluation of the assigned values and their uncertainties

Measurand Sample Unit Assigned value U

U

, % Evaluation method of assigned value u

/s

1,2,4-Trichlorobenzene A1V µg/ml 2.44 0.18 7.2 Calculated value 0.29

N2V µg/l 10.3 1.0 9.4 Median 0.31

S3V mg/kg 0.48 0.04 8.3 Median 0.28

1,2-Dichlorobenzene A1V µg/ml 1.89 0.13 6.7 Calculated value 0.34

N2V µg/l 11.0 1.7 15.6 Median 0.52

S3V mg/kg 0.91 0.09 9.6 Median 0.32

1,2-Dichloroethane A1V µg/ml 1.71 0.11 6.6 Calculated value 0.44

N2V µg/l 7.87 0.78 9.9 Median 0.33

S3V mg/kg 0.26 0.02 7.5 Median 0.30

1,4-Dichlorobenzene A1V µg/ml 1.60 0.06 3.7 Calculated value 0.19

N2V µg/l 9.77 1.9 19.0 Median 0.63

S3V mg/kg 0.38 0.04 10.8 Median 0.36

Benzene A1V µg/ml 0.64 0.04 5.7 Calculated value 0.38

N2V µg/l 8.56 0.72 8.4 Median 0.34

S3V mg/kg 0.17 0.02 9.8 Median 0.33

Chloroform A1V µg/ml 1.71 0.12 7.2 Calculated value 0.36

N2V µg/l 7.75 0.81 10.4 Median 0.35

S3V mg/kg 0.25 0.02 8.9 Median 0.30

cis-1,2-Dichloroethene

A1V µg/ml 1.91 0.11 5.7 Calculated value 0.38

N2V µg/l 11.0 1.2 10.8 Median

S3V mg/kg 0.88 0.06 6.4 Median 0.26

Dichloromethane A1V µg/ml 4.06 0.14 3.4 Calculated value 0.23

N2V µg/l 32.2 4.4 13.6 Median 0.45

S3V mg/kg 1.43 0.04 3.0 Median 0.10

ETBE A1V µg/ml 1.29 0.03 2.2 Calculated value 0.11

N2V µg/l 22.3 2.5 11.1 Median

S3V mg/kg 0.53 0.10 19.6 Median 0.65

Ethylbenzene A1V µg/ml 1.89 0.14 7.4 Calculated value 0.49

N2V µg/l 10.2 0.8 7.5 Median 0.30

S3V mg/kg 0.95 0.06 5.8 Median 0.23

m/p-Xylene A1V µg/ml 1.88 0.14 7.7 Calculated value 0.39

N2V µg/l 9.49 0.64 6.7 Median 0.27

S3V mg/kg 0.96 0.07 7.8 Median 0.31

MTBE A1V µg/ml 1.29 0.03 2.2 Calculated value 0.11

N2V µg/l 22.0 3.1 14.2 Median 0.47

S3V mg/kg 0.60 0.11 19.1 Median 0.55

o-Xylene A1V µg/ml 1.88 0.13 6.8 Calculated value 0.45

N2V µg/l 10.8 0.4 3.9 Median 0.16

S3V mg/kg 0.91 0.04 4.1 Median 0.16

Styrene A1V µg/ml 1.88 0.14 7.3 Calculated value 0.49

N2V µg/l 9.91 1.88 19.0 Median 0.63

S3V mg/kg 0.91 0.07 8.1 Median 0.32

TAME A1V µg/ml 1.29 0.03 2.2 Calculated value 0.11

N2V µg/l 22.4 1.3 5.9 Median 0.24

S3V mg/kg 0.53 0.06 11.7 Median 0.39

Measurand Sample Unit Assigned value U

U

, % Evaluation method of assigned value u

/s

Tetrachloroethene A1V µg/ml 3.61 0.16 4.4 Calculated value 0.29

N2V µg/l 16.5 1.6 9.8 Median 0.33

S3V mg/kg 1.20 0.10 8.0 Median 0.32

Tetrachloromethane A1V µg/ml 1.72 0.16 9.2 Calculated value 0.46

N2V µg/l 6.61 1.08 16.4 Median

S3V mg/kg 0.24 0.03 13.1 Median 0.44

Toluene A1V µg/ml 1.89 0.15 7.8 Calculated value 0.39

N2V µg/l 10.9 1.3 11.7 Median 0.39

S3V mg/kg 0.85 0.05 5.7 Median 0.23

trans-1,2-Dichloroethene

A1V µg/ml 1.89 0.13 6.9 Calculated value 0.46

N2V µg/l 10.3 1.3 12.6 Median

S3V mg/kg 0.78 0.04 5.5 Median 0.22

Trichloroethene A1V µg/ml 1.72 0.13 7.4 Calculated value 0.49

N2V µg/l 7.45 0.87 11.7 Median 0.39

S3V mg/kg 0.24 0.03 12.7 Median 0.42

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.