Environmental Analysis & Electrochemistry
Overview of perfl uorinated compounds residues in water analysis through profi ciency-testing scheme results
Frédéric Leccia1, Abdelkader Boubetra, Anne Tirard 1. Bureau Interprofessionnel d’Études Analytiques (BIPEA) - 189 rue d’Aubervilliers, 75018 PARIS - France. Corresponding author: fl
eccia@bipea.org
Interest for the detection of perfl uorinated compounds in water have increased in the past few years due to their harmful effect on the environment and human health [1, 2]. These molecules are also part of the list for the approval of the French Environment Ministry [3] with a diminution of their required quantifi cation limits since 2021. Thus, the BIPEA (Bureau Interprofessionnel d’Etudes Analytiques) decided to launch in 2015 a dedicated profi ciency testing scheme (PTS) for perfl uorinated compounds in surface water to allow the laboratories to test and enhance their abilities for these determinations, especially in the framework of laboratories accreditation according to ISO/IEC 17025 standard [4]. Other molecules were added in 2016, which led to an increase in the number of participants with better robustness of the statistical tests. Since 2018, twice a year, a profi ciency test with two series of samples spiked with 7 molecules is organised: perfl uorodecanoïque acid (PFDA), perfl uorodecane sulfonic acid (PFDS), perfl uoroheptanoïc acid (PFHpA), perfl uorohexane sulfonic acid (PFHxS), perfl uorohexanoïc acid (PFHxA), perfl uorooctanoic acid (PFOA), perfl uorooctane sulfonic acid (PFOS). Eleven rounds were performed so far, which allows now to draw an overview of the results and performance met in this PTS, especially regarding the number of results obtained for the different molecules, the related dispersion and some information about the recovery rate.
Materials and Methods. Sample production and shipment
The most crucial aspect for the implementation of a profi ciency-test program is the production of homogeneous and stable samples.
For this PTS, a batch of river surface water is homogenised in an adapted tank and distributed into one-litre brown glass bottles. Each bottle is then spiked individually with a solution containing all the molecules.
The homogeneity is checked through the analysis of a few molecules by an external accredited laboratory. Ten samples from the manufactured series are analysed in duplicate to determine the between-samples standard deviation (see Table 1).
Table 1. Example of homogeneity control for PFHxA (unit: µg.l -1; between-samples SD: Ss= 0,001). Sample number
1 2 3 4 5 6 7 8 9
10
Portion 1 0,027 0,029 0,030 0,030 0,039 0,022 0,023 0,014 0,031 0,030
Portion 2 0,030 0,032 0,028 0,038 0,040 0,042 0,038 0,027 0,035 0,024
Mean 0,029 0,031 0,029 0,034 0,040 0,032 0,031 0,021 0,033 0,027
For each series, a one-litre bottle is provided to the participants in order to provide to them enough volume to conduct their analytical process.
The parcel with the bottles is then shipped to all participants by express carrier under refrigerated conditions, using cooling gels, with a target temperature at (4±3) °C.
Analyses by laboratories
Laboratories are invited to analyse these samples using the technique or method they want, like the LC/MS or LC/MSMS and submit their analysis results via electronic reply forms, in which they can also provide additional information about their method and the date of analysis for example.
Statistical treatments
The statistical treatments of the quantitative returned results are carried out in accordance with ISO 13528 standard [5]. The assigned values (xpt) are estimated from the robust mean of all the results, except obviously erroneous values. The standard deviation for profi ciency
assessment (σpt) is set to 30% of the assigned value. The use of such a determined value, commonly used in the fi eld and discussed in participants meeting, allows to have an
assessment that is independent from the obtained results and consistent through time. This is especially useful when there is a limited number of results, which could lead to have a wide and fl uctuant dispersion of the results.
The quantitative results (x) could be evaluated and classifi ed through z-scores, where z = (x - xpt)
σpt
• for z ≤ |2|, the result is considered to be acceptable, • for |2| < z < |3|, the result is considered to be a warning signal, • for z ≥ |3|, the result is considered to be an action signal.
The interlaboratory comparison report is validated by both Bipea and an external technical expert, and is then circulated to the participant.
Results and Discussion
The fi rst important data is the participation and the number of results. There is an average of 18 registered participants since 2016. This number shows the interest for this kind of analyses. It is to be noted that the participants that give results usually do it for all the molecules offered, at the notable exception of the PFDS.
Below is Table 2 with the number of results per molecules over time.
Table 2. Participation over time for perfl uorinated compounds. Dec- 16
May- 17
PFDA PFDS
PFHpA PFHxS PFHxA PFOA PFOS
6 - -
7 -
8 8
9 - -
10 -
11 12
Dec- 17
8 3 -
8 -
10 10
May- 18
6 2 6 9 7 9 9
Dec- 18
11 3
10 10 9
11 11
Apr- 19
14 6
15 15 14 16 16
Dec- 19
14 7
16 16 16 16 17
Apr- 20
13 7
13 13 13 12 12
Dec- 20
14 11 15 15 15 15 16
Apr- 21
12 11 13 13 13 14 12
Dec- 21
15 13 17 17 17 17 17
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