Laboratory PT #1

September 2022

1st Round of Mercury Laboratory Proficiency Testing– Asia and the Pacific –Final Report

1 |Page1. Objective
This proficiency testing (PT) programme was to evaluate the performance of mercury analyses
conducted by the laboratories. It was expected to provide the individual proficiency levels ofparticipating laboratories and collective mercury monitoring capacity in the region.

2. Proficiency testing provider
This PT was organized by United Nations Environmental Programme, Regional Office for Asia-and
the Pacific (UNEP-ROAP) with the overall PT design by National Institute for Minamata Disease(NIMD). Asian Institute of Technology Regional Resource Centre for Asia and the Pacific (AITRRC.AP) distributed the test item and collected the analytical results. IDEA Consultants, Inc.
prepared the test item for this PT.

3. Implementation period
Call for participation:

August – December 2021

Test item distribution:

February – March 2022

Duration of test (analysis):

Until 8 April 2022

4. Participation feeFree.

5. Test item (sample) and parameter
One (1) human hair sample was used for analysing total mercury concentration.

5.1. Test item preparation
The hair was collected from multiple people who was not occupationally exposed of mercury.
Collected hair was cut (<1 mm) without crushing and mixed to ensure sufficient homogeneity. The
test item was also sterilized by gamma-ray.
Approximately 3 g each of the prepared hair was packed in brown glass bottle. The bottles of test
items were sealed in aluminium-lined laminate packs for distribution to the participants.

2 |Page5.2. Homogeneity testing
To ensure no significant differences of the mercury concentrations in the test items between thebottles, which might affect the result of the PT, following homogeneity testing of the test item wasconducted.
After the preparation of test item (packed in bottles), 10 bottles were selected and the total
mercury analysis (acid digestion – aeration CVAAS measurement) was performed twice per eachtest item in a bottle.
Homogeneity of the test item was then analysed from the results of the total mercury
concentrations. Because the analysis results contain the uncertainty by the (chemical) analysis
procedure, homogeneity was judged by following criterion:

Criterion: Ss ≦ √𝐹1 × (0.3 × 𝜎𝑒𝑝 )2 + 𝐹2 × 𝑆𝑤 2
Ss: relative standard deviation of homogeneity testing
σep: (expected) relative standard deviation of the reported results from participants
wi2 =Σ (xgm2 - x̄ g2) / (m-1)

xgm: result of m times analysis of the bottle

Sw2 =Σ wi2 / gx̄ g: average of the result of each bottle

F1 and F2 are values which are calculated from the probability distribution. In this homogeneity
testing (10 bottles testing), F1 and F2 were applied following numbers:
F1 = 1.88

F2 = 1.01(Even though these values are referred from the Annex B of ISO13528:2015, they are introduced
from the random variables of χ2 distribution and F distribution.)
Analysis results of this homogeneity testing are as follows:
Ss = 0.0256
Sw2 = 0.000897
Also, relative standard deviation of the results from the participants was as follows:
σep = 0.0837
This standard deviation should be used the value which was used for the performance evaluation
for participants. As described in 9.2, the performance of participants was evaluated from themedian and normalized interquartile range (NIQR) of the results, thus relative NIQR was used for theconfirmation of the criterion.
Therefore, above criterion was judged as follows:√𝐹1 × (0.3 × 𝜎𝑒𝑝 )2 + 𝐹2 × 𝑆𝑤 2
= √1.88 × (0.3 × 0.0837)2 + 1.01 × 0.0008972
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= 0.0344 > 0.0256 (Ss)
It was confirmed that the test item was sufficiently homogeneous to evaluate the performance ofparticipants’ results.

5.3. Stability testing
To ensure the concentration of the target parameter (total mercury) being maintained without
significant changes during the PT, following stability testing was conducted after the duration of theanalysis.
Stored (not distributed to participants) 10 bottles of test items were selected and the totalmercury analysis (acid digestion – aeration CVAAS measurement) was performed twice per eachtest items in a bottle.
Stability of the test item was then analysed by comparing the results before and after thedistribution of the test item. The stability of test item was judged by following criterion:

Criterion: | x̄ - ȳ | ≦ 0.3 × σpt + 2 × √𝑢(𝑥) 2 + 𝑢(𝑦) 2x̄ : average of the item before distributionȳ: average of the item after proficiency testingu(x): uncertainty of the item before distribution
u(y): uncertainty of the item after proficiency testing
σpt: standard deviation for the proficiency evaluation. In this program, NIQR was applied toevaluation of performance of the participant.
Analysis results of test items before and after the PT are as follows:x̄ = 1.289

u(x) = 0.0104

ȳ = 1.294

u(y) = 0.0157

Standard deviation of the result of all participants was as follows:
σpt = 0.122
This standard deviation should be used the value which was used for the performance evaluation
for participants. As described in 9.2, the performance of participants was evaluated from themedian and normalized interquartile range (NIQR) of the results, thus NIQR was used for theconfirmation of the criterion.
Therefore, above criterion was judged as follows:
0.3 × σpt + 2 × √(𝑢(𝑥) 2 + 𝑢(𝑦) 24 |Page

= 0.3 × 0.122 + 2 × √0.01042 + 0.01572= 0.0743 > 0.005 (| x̄ - ȳ |)It was confirmed that the concentration of total mercury in test item was not changed during thePT.

6. Target parameter
Target parameter of the PT was total mercury. Participants conducted 3 times of total mercury
analysis and reported all results of them. Participants also conducted analysis of the moisture in
the test item. The result of moisture was used for the analysis of reported data; however, it was not
the target of the PT, and the result of total mercury was not calculated by the moisture.
The analysis procedure of moisture was instructed to participants as follows:
1.

Take a hair sample of 100 mg or more and weigh it precisely.

2.

Dry the taken hair sample (85 °C, 4 hours)

3.

Weigh the dried hair sample again and calculate the moisture of sample from the reduced
mass.

Also, it was instructed that the sample used for moisture analysis should not be used for total
mercury analysis.

7. Participating institutions
The public laboratories or laboratories in universities that undertakes mercury analysis wereintended for this PT. Performance of the analysis that lower of detection limit than 0.1 mg/kg on 10mg test item was requested, however there was an institution who was unable to perform thatanalysis and report the result.
34 institutions registered in the PT and 26 institutions reported analysis results.
Table 1 Changes in number of laboratories per stepCategory

Number of laboratories

Registered

34Sample received

31

Result delivered

26

Most participating laboratories were from Asia and the Pacific region but a few laboratories fromother regions were also participated in the PT. Number of laboratories participated from eachregion is shown in Table 2.
5 |PageTable 2 Number of participating laboratories per region
UN Region

Number of laboratories

Africa2

Asia and the Pacific21Central and Eastern Europe

0Latin America and the Caribbean

2

Western Europe and Other Group1

8. Methods and procedures
The method of analysis was not specified for the PT and the participants performed analysis by
the method that they usually used in their routine analysis, or they were planning to use in the future.
The participants performed analysis of total mercury by the following methods:-Thermal decomposition Cold Vapour Atomic Absorption Spectrometry (TDAAS)-

Acid digestion, reduction or hydride generation aeration Cold Vapour Atomic Absorption
Spectrometry (CVAAS)-Acid digestion, Cold Vapour Atomic Fluorescence Spectrometry (CVAFS)-Acid digestion, Inductively Coupled Plasma Mass Spectrometry (ICP-MS)

In CVAAS method, there were participants who used chemical reduction (using by such as
stannous chloride) and who used hydride generation (using by such as borohydride).

6 |Page9. Result
9.1. Basic statistic data of the PT result (total mercury)
The basic statistics of the result of PT are shown in Table 3.
Table 3 Summary of the results of the PT
Statistic data of the results (unit: mg/kg)
Average:

1.405

Median:1.458

Standard deviation:

0.238

Minimum

0.720

Maximum

1.824

25 percentiles

1.339

75 percentiles

1.504Interquartile range (IQR)

0.165

Normalized IQR (NIQR)

0.122

Parameter related to distribution
Skewness of distribution-0.865

Kurtosis of distribution

1.880

The distribution of the results from the participants is shown in Fig. 1.

Fig. 1 Histogram of the report data (total mercury)
7 |PageSome registered participants were unable to receive the test item because of several issues suchas custom clearance, etc. Also, there were participants who were not able to report the analysis
results because of trouble or insufficient performance of measuring instrument.
These statistical data were calculated from the average of each participant. There wereparticipants who did not report 3 results (1, 2 or 4 results were reported), however all data wereused for the statistical analysis.
It was also shown in large kurtosis of distribution, a relatively many reported values wereconcentrated in a narrow range around the median, while some reported values deviate from themedian. Thus, the results in a relatively small interquartile range than the standard deviation.
There were more reported values lower than the median than larger, as evidenced by negativeskewness values.
There were few reported results that were far from the median, and it was considered that thereported data did not have a singular distribution. Since no results were reported which wereextremely different from other reported values and may affect the evaluation, the performance wasevaluated based on the data obtained from all reported values without processing outliers.

9.2. Performance evaluation for participantsMedian data of all laboratories was applied as agreement value. Performance of the results wasevaluated by the robust z score which was calculated from the median and normalized interquartile
range (NIQR).
z score of each participant was calculated from the following equation.
z = [(average of reported result) – (median of all participants)] / NIQR
Performance of the result is classified by z score as follows:|z| ≦2: Performance is satisfactory (satisfactory)
2 < |z| < 3: Performance is questionable (caution)|z| ≧ 3: Performance is unsatisfactory (action)

8 |PageThe results and performances of laboratories are shown in Fig. 2.

Fig. 2 Result of each participant
The numbers of laboratories disaggregated for each z score range are shown in Table 4.
Table 4 Number of the laboratories in the range of z scorez scorenz ≦ -3
2-3 <z< -2
3-2 ≦z≦ 2
182<z<33z ≧30

As described in 9.1, IQR of reported results were relatively small. Therefore, satisfactory range ofthe result (mercury concentration) was relatively close and results around 25 % difference from themedian was the classified range of unsatisfactory of the result.

9 |Page9.3. Regions of participating laboratories and the performances
Number of laboratories per region where the laboratories are located and the performance of thePT are shown in Fig. 3.

Fig. 3 Number of laboratories per regions and performances
Regional difference was not examined due to the limited numbers of laboratories participating fromregions other than Asia and the Pacific being insufficient for comparison.

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9.4. Types of laboratories and the performances
Number of laboratories per type (academic, government, or non-government) and the performanceof the PT are shown in Fig. 4.

Fig. 4 Number of laboratories per types and performance
Statistical differences among the types of laboratories were not detected from the reported
results (Kruskal-Wallis one-way ANOVA on ranks, p=0.44).

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9.5. Analysis methods and results
The distribution of the results from participants by analysis method is shown in Fig. 5.

Fig. 5 Distribution of the report data by analysis method
Most TDAAS results agreed with median, but noticeable differences were not detected among theanalysis methods employed (Kruskal-Wallis one-way ANOVA on ranks, p=0.12).

9.6. Moisture
The basic statistics of the reported moisture of test item is shown in Table 5.
Table 5 Summary of the result of moisture (Unit: %)Average

11.6

Median9.75

Standard deviation*1

16.3 (3.09)

Minimum

0.51

Maximum*2

88.4 (13.5)*1: Value in parentheses is standard deviations excluding the maximum result.
*2: Value in parentheses is second largest result.

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The distribution of the results of moisture is shown in Fig. 6.

Fig. 6 Histogram of the result of moisture

The plots of the relations of moisture and mercury concentration are shown in Fig. 7. (The largest
value of moisture (88.1 %) is not shown in this figure.)

Fig. 7 Total mercury and moisture
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The deviation of the moisture was larger than the mercury concentration, but noticeable relation
between moisture and mercury concentration was not detected. It was considered that theuncertainty of the analysis of moisture was larger than the change of the moisture during the PT
analysis duration.

10. Conclusion
Even the participants of this time PT were not so many, many of the reported results from theparticipants were concentrated around the median value and IQR of the results was relatively close.
Thus, it was considered that the difference among with many mercury analysis laboratories wererelatively small.
The range of moisture reported from the participants were larger than the deviation of the mercury
results even it was not the target of the PT. Also, the correlation between the mercury and moisture
was not detected. This result suggests that precise measurement of moisture for the small amountof sample such as the hair is not easy and there may be a challenge to correct the result of such
sample by the moisture.

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