[PDF] IAEA-158 Report final 03 december 2009

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Report No. IAEA/AL/187

IAEA/MEL/82

World -Wide Intercomparison Exercise

On The Determination Of Trace Elements

In IAEA-158 Marine Sediment

M. J. Campbell, S. Azemard and J. Oh

March 2008

International Atomic Energy Agency

Marine Environment Laboratories

4 quai Antoine 1

er

MC 98000 Monaco

Prepared in collaboration with:

UNEP 2 3

CONTENT

1. INTRODUCTION ...............................................................................................5

2. SCOPE OF THE INTERCOMPARISON...........................................................6

3. DESCRIPTION OF THE MATERIAL...............................................................7

4. HOMOGENEITY TESTS...................................................................................9

5. Stability..............................................................................................................10

6. ANALYSES AND REPORTING......................................................................10

7. EVALUATION OF THE RESULTS ................................................................11

7.1 Data Table Term:.........................................................................................11

7.2 Statistical and technical evaluation..............................................................13

7.3 Certification criteria.....................................................................................14

8. RESULTS AND DISCUSSION........................................................................17

8.1 Overview of the results................................................................................17

8.1.1. Moisture content ..................................................................................17

8.1.2. Analytical methods ..............................................................................18

8.1.3. Laboratory performances.....................................................................21

8.2 Laboratory performance for selected trace elements...................................32

8.2.1. Aluminium...........................................................................................33

8.2.2. Arsenic.................................................................................................34

8.2.3. Cadmium..............................................................................................35

8.2.4. Chromium............................................................................................36

8.2.5. Copper, Cobalt, Nickel and Zinc .........................................................37

8.2.6. Lead......................................................................................................40

8.2.7. Manganese and Iron.............................................................................41

8.2.8. Mercury................................................................................................43

8.2.9. Strontium and Vanadium:....................................................................44

9. METHYLMERCURY.......................................................................................46

10. RECOMMENDATIONS...................................................................................50

11. CONCLUSIONS................................................................................................51

12. ACKNOWLEDGEMENTS...............................................................................51

13. REFERENCES ..................................................................................................51

APPENDIX I

Data report of the individual laboratory results sorted by element......54

APPENDIX II

Graphical presentation of results sorted by element...........................82

APPENDIX III

List of participants............................................................................115

APPENDIX IV

Reference Sheet for IAEA-158.......................................................124 4

LIST OF TABLES

Table 1. Within- and between- bottle homogeneity for IAEA-158...............................9

Table 2. Method codes for IAEA-158 .........................................................................12

Table 3. Results of intercomparison exercise IAEA-158 marine sediment.................16 Table 4. Frequency of use for different analytical techniques.....................................20

Table 5. Summary of performance by element............................................................24

Table 6. Assessment of laboratories based on z-scores...............................................25

Table 7. Overall assessment of laboratory performance..............................................30

Table 8. List of laboratories and analytical methods used for methylmercury

LIST OF FIGURES

Figure 1. Particle size distribution profile for IAEA-158..............................................8

Figure 2: Proportional distribution of analytical techniques used

to analyse IAEA-158...................................................................................................18

Figure 3.Aluminium results derived from different methods......................................33

Figure 4. Total vs Partial reported mean for Aluminium.............................................34

Figure 5: Arsenic results derived from different methods...........................................35

Figure 6: Cadmium results derived from different methods........................................36 Figure 7: Chromium results derived from different methods......................................37

Figure 8. Copper results derived from different methods............................................38

Figure 9. Cobalt results derived from different methods.............................................38

Figure 10. Nickel results derived from different methods...........................................39

Figure 11. Zinc results derived from different methods..............................................39

Figure 12: Lead results derived from different methods .............................................40

Figure 13. Manganese results derived from different methods ...................................42

Figure 14. Iron results derived from different methods...............................................42

Figure 15: Mercury results derived from different methods........................................43 Figure 16. Strontium results derived from different methods......................................45 Figure 17. Vanadium results derived from different methods.....................................45 Figure 18: Plot extracted of the automatic generated report of the

BWE Cofino model.....................................................................................................48

Figure 19: Reported means and sample preparation procedure...................................49 5

1. INTRODUCTION

For nearly thirty years, the Marine Environmental Studies Laboratory (MESL) of International Atomic Energy Agency-Marine Environment Laboratories (IAEA- MEL) has conducted worldwide laboratory performance studies, also known as intercomparison exercises

1, 2. The results have been used to characterise both

laboratory performance and the materials themselves with respect to a wide range of organic

3, 4 and inorganic constituents, including methylmercury5-8. Thus, test samples

can subsequently be used as reference materials (RMs) for organic and inorganic marine pollution studies. This work, a contribution to the IAEA Analytical Quality Control Services (AQCS), has been conducted in collaboration with the UNEP Regional Seas Programme. In the past, such exercises were also carried out in association with the IOC Global Investigation of the Pollution in the Marine

Environment (GIPME) programme

9. Quality assurance and quality control (QA/QC) cover a very broad discipline; there are numerous factors and protocols that must be employed to validate data and ensure reliable analytical performance. A good QA/QC programme should include internal performance checks for day-to-day validation

10, 11, as well as regular external

performance evaluations for an independent assessment of analytical proficiency

9, 12.

In the first case, a routine method of quality control entails the concurrent processing of a material of known composition that is of similar matrix to the sample, i.e., a reference material, to confirm the accuracy of the analytical process. This should be a continuous and regular process, not only to maximize the confidence in a particular data set, but also to maximize the confidence in an analytical process, and indeed, in how the laboratory routinely operates in the longer term

10, 11. An intercomparison

exercise, such as this interlaboratory study, serves as such an independent external assessment. Interlaboratory comparisons are not only essential for checking the accuracy of a laboratory"s analytical results, but also serve to stimulate better analytical performance

11, 12.

The present interlaboratory study was designed in order to evaluate the measurement performance of participating laboratories for the analysis of trace elements in fish homogenate samples. Following the statistical evaluation obtained results were used to assign a reference value for several trace elements and methyl mercury in the test material and to fulfil the increased demand for marine reference materials characterised for trace elements and methyl mercury (MeHg). The test material was distributed to 140 laboratories worldwide and the results from 93 laboratories in 41 countries were received by end 2006. 6 The data reported by laboratories, together with the technical and statistical evaluations of the results for each element, are given in this report. As statistical and technical criteria to assign the reference value of a number of elements were fulfilled, the sample can now be used as a reference material for quality control in the determination of trace elements and methyl mercury in marine sediment. The performance of the participant laboratories was assessed through evaluating Z-scores. These results should assist chemists to make appropriate modifications to laboratory analytical procedures in order to improve data quality. All results were treated confidentially and each laboratory was identified with a code number for anonymity. Further information concerning this report and the IAEA quality assurance programme can be obtained from the Marine Environmental Studies Laboratory,

IAEA-MEL, 4 Quai Antoine 1

er, MC 98000, Monaco or the web site: http://www- naweb.iaea.org/naml/.

2. SCOPE OF THE INTERCOMPARISON

In February 2006, 308 letters of invitation were sent out to laboratories that had expressed a wish to participate, or previously participated, in an IAEA intercomparison exercise on the determination of trace elements in marine samples, soliciting interest in this exercise. Positive responses were received from 140 laboratories in 59 IAEA Member States and samples were duly dispatched to them. Each participating laboratory received one sample of the marine sediment material, designated IAEA-158, accompanied by an information sheet and a reporting form. Using the procedures routinely applied in their laboratories, participants were requested to determine as many elements as possible from the following 18 elements: Al, As, Cd, Co, Cr, Cu, Fe, Hg (total and methylmercury), Li, Mn, Ni, Pb, Sb, Se, Sn, Sr, V and Zn. The IAEA was also interested to receive results for any other elements that participating laboratories were willing to provide to enhance the characterisation of the matrix. The deadline for returning the results was initially set at September 2006, but was later extended to the end of November 2006 due to delays in dispatching the samples from Monaco. In total 93 laboratories from 41 countries participated to this intercomparison exercise and reported results for up to 51 elements (including methylmercury). 7 The distribution of participants belonging to countries included in the UNEP

Regional Seas Programmes was as follows:

Number of laboratories Number of countries

Mediterranean Action Plan 30 14

Kuwait Action Plan 4 4

West and Central Africa Action Plan 1 1

Caribbean Action Plan 1 2

East Asian Seas Action Plan 3 2

South-East Pacific Action Plan 6 2

Eastern African Action Plan 2 2

South Asian Seas Action Plan 4 2

Black Sea Environmental Programme 14 5

South-West Atlantic 4 1

3. DESCRIPTION OF THE MATERIAL

In November 2004, a large quantity of marine sediment was collected from Kilbrannan Sound, south east of the island of Arran, in the Clyde River estuary, Scotland, UK. The material was collected and supplied to the IAEA through collaboration with the QUASIMEME Laboratory Performance Studies Programme. The material was freeze dried by QUASIMEME and sent to IAEA MEL for further processing and bottling. The dried material was hand sieved (315 μm) by MESL staff. The sieving cut-off value chosen was a compromise value selected to ensure that the physical properties of the material should be sufficiently uniform whilst retaining sufficient material to make an adequate number of units. The particle size distribution profile of the bottled material was measured using a MALVERN Mastersizer Micro v2.12 instrument. This device uses the diffraction of laser light to determine the range of particle sizes in the sample. The particle size distribution profile for IAEA-158 is presented in Figure 1. Approximately 70% of particles had sizes below 100 μm. In the context of a reference material, it is important that the substance is finely divided and physically as "homogeneous" as possible, such that sub-samples are as representative as possible and physical processes such as digestion (and moisture determination) will be reproducible. Aliquots of about 25 g were packed into glass bottles with polyethylene caps and sealed in plastic bags. Approximately five hundred units of the material were prepared, providing adequate supplies to be used as a reference material at the 8 conclusion of the interlaboratory study. The homogeneity of this material for trace elements was tested using a standard protocol and found to be satisfactory for the purposes of this intercomparison exercise (at or above an intake mass of 200 mg). Metal concentrations are expected to match the range normally found in the marine environment in this region.

Particle Diameter (μm.)Volume (%)

0 10 0 10 20 30
40
50
60
70
80

90 100

0.1 1.0 10.0 100.01000.0

Figure 1. Particle size distribution profile for IAEA-158 9

4. HOMOGENEITY TESTS

A homogeneity test was conducted after bottling the sample material. The between- bottle homogeneity was tested by the determination of the concentration of some typical elements (Cd, Cu, Fe, Hg, Mn, Pb and Zn) in sample aliquots of 0.25 g taken from nine bottles, which were set aside at regular intervals during the whole period of bottling. The within- bottle homogeneity was assessed through 6 determinations of the contents of one bottle. The uncertainty of the analytical methods was assessed for each element by 5 replicate measurements from one standard solution or on one digest solution. For the determination of trace elements, the samples were mineralized with HNO

3, HF and boric acid using a microwave digestion system prior to dilution to

volume with appropriate amounts of deionised water. The final determination was performed by F-AAS for Cu, Mn, Fe and Zn, and by ZGF-AAS for Cd and Pb. The total mercury (Hg) was determined by Solid-AAS (AMA 254, Altec). The coefficients of variation (CV) obtained for the studied elements are presented in Table 1. Table 1. Within- and between- bottle homogeneity for IAEA-158

Element

Within-bottle 1

CV (%) Between-bottle

2

CV (%) Method

3

CV (%)

Cd 4.6 5.4 2.9

Cu 5.8 8.6 4.2

Fe 2.9 2.0 4.1

Pb 6.1 4.3 4.6

Mn 2.4 2.1 3.7

Hg 10.5 13.8 1.5

Zn 4.2 3.4 3.2

1 6 replicate determinations on the content of 1 bottle.

2 Single determinations on the content of 6 bottles.

3 5 replicates of a digested solution and reference material (for Hg)

CV = Coefficient of variation.

10 An F-test was performed for the different metals and revealed no significant differences between the within- and between- bottle variances at a significance level of 0.05, indicating that the heterogeneity observed was relatively consistent. However, for Hg it appears that the variance is clearly much greater than the analytical variability of the method. It was observed that the relatively high variation was due to "high" values that would be considered as outlier if tested statistically. The experiment for Hg was repeated 3 times, using different bottles and different weights and similar results were achieved. It was hypothesised that very fine particulates in the material may be associated with the high Hg values. The fact that analysis of additional units of IAEA-158 returned the same result suggests that the probability to obtain extreme values is the same for all bottles. It was concluded that this artefact should not be a problem for the intercomparison exercise.

5. STABILITY

Previous IAEA trace element reference material (biological and sediment) have been continuously tested for stability. Sets of bottles are stored under different conditions (+20°C, -20°C and +60°C) and are regularly analysed for trace elements. No significant changes were found until now. IAEA 158 is expected to have similar stability. The stability of this CRM will continue to be monitored and customers will be notified if any significant irregularity occurs prior to the expiry date, which as been set at January 2019.

6. ANALYSES AND REPORTING

The participants in this worldwide intercomparison exercise were requested to determine the trace metal amount content in marine sediment sample IAEA-158 using the techniques routinely employed in their laboratories. They were requested to make at least three, but preferably six, independent replicate determinations for each element and to record all results on the reporting form. They were also asked to provide both a summary of the quality control procedures routinely employed (if any)quotesdbs_dbs46.pdfusesText_46

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