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--------------------------- Scientific research at the service of safe food production and animal health --------------------------------

Central office

Veterinary Operational Directions:

Groeselenberg 99, B-1180 Brussels

Tel. +32 (0)2 379 04 00

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+32 (0)2 379 04 01 (director))

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CODA-CERVA

Veterinary and Agrochemical Research Centre

Belgian National Reference Laboratory for Trace Elements in Food and Feed

PT-2016-NRL-TE-FASFC Determination of As, Asi, Cd, Pb, Cu and Zn in rice wafers

Final report on the 2016 Proficiency Test organised by the

National Reference Laboratory for Trace Elements in Food

and Feed

29 September 2016

Dr ir Karlien Cheyns and Dr ir Nadia Waegeneers

PT-2016-NRL-TE-FASFC: Determination of As, Asi, Cd, Pb, Cu and Zn in rice wafers 2

------------------------- Scientific research at the service of safe food production and animal health -------------------------


Summary From the 1st of January 2008, the laboratory for Trace Elements in the Veterinary and Agrochemical

Research Centre (CODA-CERVA), Tervuren, operates as National Reference Laboratory for Trace

Elements in Food and Feed (NRL-TE). One of its core tasks is to organise proficiency tests (PTs) among

laboratories appointed by the Federal Agency for the Safety of the Food Chain. This report presents

the results of the proficiency test organised by the NRL-TE which focused on the determination of

trace elements rice wafers. The results from the PT were treated in CODA-CERVA, Tervuren.

The 2016 PT was obligatory for all laboratories approved for the analysis of heavy metals in foodstuff

by the Federal Agency for the Safety of the Food Chain (FASFC). Ten laboratories registered for and

participated in the exercise.

The test material used in this test was a rice wafer, bought in a local supermarket. The choice for this

matrix was based on the implementation of maximum levels for inorganic arsenic in rice and rice

products from the 1st of January 2016 (Commission Regulation (EC) No 2015/1006 [1]). The material

was homogenized and used as such as PT material. Each participant received approximately 15 mg of

homogenized test material.

Participants were invited to report the mean value and measurement uncertainty on their results for

arsenic (As), inorganic arsenic (Asi), cadmium (Cd), lead (Pb), copper (Cu) and zinc (Zn).

The assigned values (xa) and their uncertainty (u(xa)) were determined as the consensus of

participant’s results. Standard deviations for proficiency assessment were calculated using the

modified Horwitz equation.

Of the ten laboratories that registered for participation, ten submitted results for As, Cd, Cu and Zn;

nine submitted results for Pb and four submitted results for Asi. The laboratories performed excellent

with only one z-score which was questionable. Only three of the calculated ζ-scores were

unsatisfactory.

It was a successful exercise and the laboratories have proven their competence to measure the

concerned trace elements in the matrix.




Introduction Trace elements occur in varying amounts as natural elements in soils, plants and animals, and

consequentially in food and feed. Concerning food and feed of plant origin, the characteristics of the

soil on which the plants are grown have a considerable influence on the content of trace elements in

the plant. The concentration of trace elements in plants is often correlated to the corresponding

concentrations in the soil on which they were grown, but also soil texture, soil pH and soil organic

matter content influence the trace element content in the plants. To ensure public health, maximum

levels for trace elements in foodstuff have been laid down in the Commission Regulation (EC) No

1881/2006 [2]. Scientific opinions of the European Food Safety Authority (EFSA) Panel on

Contaminants in the Food Chain (CONTAM Panel) have led to developments of this commission

regulation.

The EFSA CONTAM Panel adopted an opinion on arsenic in food on 12 October 2009. The scientific

opinion concluded that with the estimated dietary exposure to Asi in Europe there was a possibility

of a risk to some consumers. Rice waffles, rice wafers, rice crackers and rice cakes can contain high

levels of inorganic arsenic and these commodities can make an important contribution to the dietary

exposure of infants and young children. Therefore, a specific maximum level for these commodities

should be envisaged (Figure 1, [1]).

Figure 1 : Snapshot of maximum limits of Asi (mg/kg) in foodstuff as published in [1].

An extra note was added by Commission Regulation (EC) No 333/2007[3] which states that ‘Methods

for analysis for total arsenic are appropriate for screening purpose for control on inorganic arsenic

levels. If the total arsenic concentration is below the maximum level for inorganic arsenic, no further

testing is required and the sample is considered to be compliant with the maximum level for inorganic

arsenic. If the total arsenic concentration is at or above the maximum level for inorganic arsenic,

follow-up testing shall be conducted to determine if the inorganic arsenic concentration is above the

maximum level for inorganic arsenic.’

The EFSA CONTAM panel scientific opinion of 2009 concluded that the mean dietary exposures to

cadmium in European countries are close to or slightly exceeding the Tolerable Weekly Intake (TWI)

of 2,5 µg/kg body weight. Certain subgroups of the population may exceed the TWI by about 2 fold.

The CONTAM Panel further concluded that, although adverse effects on kidney function are unlikely

to occur for an individual exposed at this level, exposure to cadmium at the population level should

be reduced. This opinion resulted in lower maximum limits for Cd in certain matrices [4]. The panel

also concluded that processed cereal based foods and other baby foods for infants and young

children are an important source of exposure to cadmium for infants and young children. A particular

maximum level of cadmium (0.040 mg/kg) was therefore established for processed cereal based and




other baby foods for infants and young children (Figure 2). This maximum level is thus applicable on

rice wafers if they are intended and labeled for infants and young children.

The maximum limit for cadmium in rice is 0.20 mg/kg.

Figure 2 : Snapshot of maximum limits of Cd (mg/kg) in processed cereal-based foods and baby foods for infants and young children as published in [4].

The EFSA CONTAM panel scientific opinion of 2010 identified a need to reduce exposure of Pb due to

concern over possible neurodevelopmental effects in young children. This resulted in a specific

maximum limit for Pb in processed cereal-based foods and babyfoods for infants and young children.

So when rice wafers are processed and labeled for infants and young children, a specific maximum

limit is applicable according to Commission Regulation (EU) 2015/1005 [5], (Figure 3). The maximum

limit for Pb in cereals is 0.20 mg/kg.

Figure 3 : Snapshot of maximum limits of Pb (mg/kg) in processed cereal-based foods and baby foods for infants and young children as published in [5].

There is currently no European legislation regarding Cu or Zn in rice wafers.

The scope of this PT was to test the competence of the participating laboratories to determine the

total mass fraction of As, Asi, Cd, Pb, Cu and Zn in rice wafers.




Time frame, test material and instructions to participants Invitation letters to this PT were sent to participants in April (Annex 1). The 2016 PT was obligatory

for all laboratories approved for the analysis of heavy metals in foodstuff by the Federal Agency for

the Safety of the Food Chain (FASFC). Ten laboratories, which were approved for these foodstuffs,

registered for and participated in the exercise. The samples were dispatched to the participants by

the end of May 2016. Reporting deadline was the 24th of June.

This year the test material was a sample of rice wafers. The rice wafers were purchased in a local

supermarket and were not specifically labeled for infants and young children. The material was

milled and homogenized for 24 hours and divided in small portions of about 15 g. These portions

were dry and dark stored at room temperature.

The homogeneity of the test materials was tested following the recommended procedure according

to IUPAC [6]. All the trace elements appeared to be homogeneously distributed in the samples

(Annex 2). Each participant received the test material samples, an accompanying letter (Annex 3)

with instructions on sample handling and reporting (Annex 4), a form that had to be sent after

receipt of the samples to confirm their arrival (Annex 5) and a reporting form (Annex 6).

Participants were instructed to store the materials in a dark and dry place until analysis. Before

starting the analyses, the samples had to be re-homogenized by shaking for about 30 seconds. The

procedure followed for the exercise, had to be as close as possible to the method used by the

participant in routine sample analysis. Nevertheless participants were instructed to perform three

independent measurements per parameter and to report measurement uncertainty.

A questionnaire was attached to the reporting form. The questionnaire was intended to provide

further information on the measurements and the laboratories. A copy of the questionnaire is

presented in Annex 6.

Laboratory codes were given randomly and communicated confidentially to the corresponding

participant.




Assigned values The assigned values for the different trace elements in the rice wafer sample were determined as the

consensus of participant’s results [6]. The major advantages of consensus values are the

straightforward calculation and the fact that none of the participants is accorded higher status. The

disadvantages are that the consensus values are not independent of the participant’s results and,

especially in the current case with ten participants, that the uncertainty on the consensus (identified

as the standard error) may be high and the information content of the z-scores will be

correspondingly reduced. However, the IUPAC guide of 2010 on the selection and use of proficiency

testing schemes for a limited number of participants [7] states that if the standard uncertainty of the

assigned value u(xa) is insignificant in comparison to the fit-for-intended-use target standard

deviation σp (u(xa)2 <0.1* σp2), then z-scores can be calculated in a small scheme in the same matter

as recommended in IUPAC 2006 for a large scheme. A minimum of eight quantified results is

accepted to calculate z- and ζ-scores (eight is the minimum number to create a Kernel density

distribution).

The robust statistic approach is a convenient modern method of handling results when they are

expected to follow a near-normal distribution and it is suspected that they include a small proportion

of outliers. There are many different robust estimators of mean and standard deviation [8]. The

median and MAD (median absolute difference) were chosen here as robust estimators.

The modified Horwitz equation was used to establish the standard deviation for proficiency testing

(σp) [6][9]. It is an exponential relationship between the variability of chemical measurements and

concentration. The Horwitz value is widely recognized as a fitness-for-purpose criterion in proficiency

testing.

a) Results that were identifiable invalid or extreme outliers were excluded.

b) A visual presentation of the remaining results was examined. It was checked whether

the distribution was apparently unimodal and roughly symmetric, possible outliers aside. If so

c); else d).

c) The robust mean rob̂ and standard deviation rob̂ of the n results were calculated as

rob̂ = median and rob̂ = 1.4826*MAD. If rob̂ was less than about 1.2σp, then rob̂ was used

as the assigned value xa and rob̂ /√n as its standard uncertainty u(xa).

d) A Kernel density estimate of the distribution was made using normal kernels with a

bandwith h of 0.75σp. If this resulted in a unimodal and roughly symmetric kernel density, and

the mode and median were nearly coincident, then rob̂ was used as the assigned value and

rob̂ /√n as its standard uncertainty; else e).

e) If the minor mode could be safely attributed to an outlying result, then rob̂ was still

used as the assigned value and rob̂ /√n as its standard uncertainty; else no consensus value

could be derived.

Scheme 1 : Scheme followed to calculate the assigned value according to [6]




The scheme that was followed to estimate the consensus and its uncertainty is outlined in Scheme 1.

In the current case, steps (a) and (e) were not needed. Only for As, the visual presentation of the

results appeared not to be unimodal (step b). In this case, the Kernel density plot (step d) was made

and resulted in a unimodal and roughly symmetric kernel density.

For As, Cd, Cu and Zn the assigned value was calculated as rob̂ = median and the standard deviation

as rob̂ = 1.4826*MAD. Because of the low number of data, only informal scores were given for Asi

and no scores were given for Pb.

The consensus values, their standard uncertainty and some other statistical parameters are

summarised in Table 1.

Table 1 : Summary of statistical parameters for the test material.

As

mg/kg

Asi

mg/kg

Cd

mg/kg

Pb

mg/kg

Cu

mg/kg

Zn

mg/kg

N 10 4 9 3 10 10

Mean 0.188 0.156 0.118 0.009 3.33 21.4

SD 0.029 0.023 0.010 0.003 0.23 1.3

Robust mean (median) 0.177 0.160 0.120 0.009 3.28 21.3

Robust SD ( rob̂ ) 0.010 0.021 0.010 0.004 0.18 0.4

Assigned value xa 0.177 0.160 0.120 3.28 21.3

Standard uncertainty of the

assigned value u(xa) 0.003 0.010 0.003 0.06 0.1

σp 0.037 0.034 0.026 0.44 2.1

Assigned value xa: median of the reported results; σp: standard deviation for proficiency assessment.




Scores and evaluation criteria Individual laboratory performances are expressed in terms of z-scores and ζ-scores in accordance

with ISO 135283 and the International Harmonised Protocol [6], [10].

p

alab xxz

)()( 22

laba

alab

xuxu

xx

where:

xlab is the mean of the individual measurement results as reported by the participant

xa is the assigned value

σp is the standard deviation for proficiency assessment

u(xa) is the standard uncertainty for the assigned value

u(xlab) is the reported standard uncertainty on the reported value xlab. When no uncertainty was

reported by the laboratory, it was set to zero.

The z-score compares the participant's deviation from the reference value with the standard

deviation accepted for the proficiency test, σp. Should participants feel that these σ values are not fit

for their purpose they can recalculate their scorings with a standard deviation matching their

requirements.

The z-score can be interpreted as:

|z| ≤ 2 satisfactory result

2 < |z| ≤ 3 questionable result

|z| > 3 unsatisfactory result

The ζ-score states if the laboratory result agrees with the assigned value within the uncertainty

claimed by this laboratory (taking due account of the uncertainty on the reference value itself). The

interpretation of the ζ-score is similar to the interpretation of the z-score.

| ζ | ≤ 2 satisfactory result

2 < | ζ | ≤ 3 questionable result

| ζ | > 3 unsatisfactory result




Results

Arsenic (As) xa = 0.18 ± 0.01 mg/kg (k = 2)

All ten laboratories submitted results for total As concentrations. Nine laboratories obtained

satisfactory z-scores for As against the standard deviation accepted for the proficiency test (Table 2,

Figure 4). The z-score of L10 was questionable. Nine laboratories obtained satisfactory ζ-scores

against their stated measurement uncertainty. The ζ-score of L10 was unsatisfactory.

Table 2 : values reported for As (mg/kg) by the participants and scores calculated by the organizer

Lab

co

de

Re

sult

1 (

mg

kg-1

)

Re

sult

2 (

mg

kg-1

)

Re

sult

3 (

mg

kg-1

)

Me

an (

mg

kg-1

)

Exte

nd

ed

un

cert

ain

ty (

k =

2)

(u

lab; m

g kg

-1)

z-sc

ore

s

ζ-sc

ore

s

1 0.206 0.224 0.200 0.210 0.033 0.9 2.0

2 0.175 0.167 0.169 0.170 0.011 -0.2 -1.1

3 0.167 0.159 0.168 0.165 0.038 -0.3 -0.6

4 0.178 0.170 0.186 0.178 0.080 0.0 0.0

5 0.174 0.182 0.180 0.044 0.1 0.1

6 0.185 0.171 0.171 0.176 0.065 0.0 0.0

7 0.196 0.195 0.200 0.200 0.050 0.6 0.9

8 0.190 0.159 0.170 0.170 0.040 -0.2 -0.3

9 0.169 0.176 0.172 0.172 0.043 -0.1 -0.2

10 0.260 0.260 0.260 0.260 0.051 2.3 3.2




Figure 4 : (a) Results with expanded uncertainty for As, as reported by the participants (dashed lines: xa ± 2 u(xa), dotted lines: xa ± 2 σp and (b) z (blue bars) and ζ-scores (orange bars)

(A)

(B)




Inorganic arsenic (Asi) xa = 0.160 ± 0.02 mg/kg (k = 2)

Only four laboratories submitted results for Asi concentrations. The relative standard deviation of the

values of the results was less than 15%. Therefore, the median of these four results was used as

informal consensus value. The four laboratories obtained satisfactory informal z-scores for Asi against

the standard deviation accepted for the proficiency test (Table 3, Figure 5). These laboratories did

also obtain good informal ζ-scores against their stated measurement uncertainty.

Table 3 : values reported for Asi (mg/kg) by the participants and scores calculated by the organizer.

Lab

co

de

Re

sult

1 (

mg

kg-1

)

Re

sult

2 (

mg

kg-1

)

Re

sult

3 (

mg

kg-1

)

Me

an (

mg

kg-1

)

Exte

nd

ed

un

cert

ain

ty (

k =

2)

(u

lab; m

g kg

-1)

Info

rmal

z-s

core

s

Info

rmal

ζ-s

core

s

1

2

3 0.176 0.180 0.177 0.178 0.044 0.5 0.7

4

5

6 0.142 0.107 0.130 0.126 0.041 -1.0 -1.5

7 0.153 0.156 - 0.150 0.030 -0.3 -0.5

8

9

10 0.170 0.170 0.160 0.170 0.037 0.3 0.5




Figure 5 : (a) Results with expanded uncertainty for Asi, as reported by the participants (dashed lines: xa ± 2 u(xa), dotted lines: xa ± 2 σp and (b) informal z (blue bars) and ζ-scores (orange bars)

(A)

(B)




Cadmium (Cd) xa = 0.12 ± 0.01 mg/kg (k = 2)

Ten laboratories submitted results for Cd concentrations. One laboratory could not produce results

above their limit of quantification. The median of the nine results was used as assigned value. All

nine laboratories obtained satisfactory z-scores for Cd against the standard deviation accepted for

the proficiency test (Table 4, Figure 6). The laboratories did also obtain good ζ-scores against their

stated measurement uncertainty. The quantification limits of L02 was not lower than the

corresponding xa-3 u(xa) value, so the statements is satisfactory.

Table 4 : values reported for Cd (mg/kg) by the participants and scores calculated by the organizer

Lab

co

de

Re

sult

1 (

mg

kg-1

)

Re

sult

2 (

mg

kg-1

)

Re

sult

3 (

mg

kg-1

)

Me

an (

mg

kg-1

)

Exte

nd

ed

un

cert

ain

ty (

k =

2)

(u

lab; m

g kg

-1)

z-sc

ore

s

ζ-sc

ore

s

1 0.125 0.116 0.113 0.118 0.018 -0.1 -0.2

2 <0.6 <0.4 <0.6 <0.5

3 0.105 0.103 0.104 0.104 0.026 -0.6 -1.2

4 0.120 0.120 0.124 0.121 0.042 0.0 0.1

5 0.120 0.117 0.120 0.031 0.0 0.0

6 0.103 0.098 0.104 0.102 0.026 -0.7 -1.3

7 0.126 0.119 0.125 0.120 0.030 0.0 0.0

8 0.141 0.121 0.135 0.130 0.030 0.4 0.6

9 0.113 0.114 0.113 0.113 0.028 -0.3 -0.5

10 0.130 0.130 0.130 0.130 0.015 0.4 1.2




Figure 6 : (a) Results with expanded uncertainty for Cd, as reported by the participants (dashed lines: xa ± 2 u(xa), dotted lines: xa ± 2 σp, red bars represent the limits of quantification of the corresponding labs with the y-axis cut-off at 0.2 mg/kg) and (b) z (blue bars) and ζ-scores (orange bars)

(A)

(B)




Lead (Pb) Nine laboratories submitted results for Pb concentrations. Only three laboratories could produce

results above their limit of quantification. It was not possible to calculate an assigned value from

these results. The median value was 0.009 mg/kg.

Table 5 : values reported for Pb (mg/kg) in by the participants

Lab

co

de

Re

sult

1 (

mg

kg-1

)

Re

sult

2 (

mg

kg-1

)

Re

sult

3 (

mg

kg-1

)

Mea

n (

mg

kg-1

)

Exte

nd

ed u

nce

rtai

nty

(k

= 2

)

(u

lab; m

g kg

-1)

1 <0.020

2

3 <0.020

4 0.015 0.011 0.010 0.012 0.004

5 <0.050

6 <0.020

7 0.007 0.005 0.007 0.006 0.002

8 <0.016

9 0.010 0.009 0.009 0.009 0.005

10 <0.040




Copper (Cu) xa = 3.28 ± 0.12 µg/kg (k = 2)

Ten laboratories submitted results for Cu concentrations. The median of these ten results was used

as assigned value. All ten laboratories obtained satisfactory z-scores for Cu against the standard

deviation accepted for the proficiency test (Table 6, Figure 7). And all of these laboratories did also

obtain good ζ-scores against their stated measurement uncertainty.

Table 6 : values reported for Cu (mg/kg) by the participants and scores calculated by the organizer

Lab

co

de

Re

sult

1 (

mg

kg-1

)

Re

sult

1 (

mg

kg-1

)

Re

sult

1 (

mg

kg-1

)

Mea

n (

mg

kg-1

)

Exte

nd

ed u

nce

rtai

nty

(k=

2)

(u

lab; m

g kg

-1)

z-sc

ore

s

ζ-sc

ore

s

1 3.10 3.26 3.18 3.18 0.70 -0.2 -0.3

2 4.20 2.60 3.70 3.50 1.10 0.5 0.4

3 3.27 3.29 3.22 3.26 0.98 0.0 0.0

4 3.43 3.43 3.40 3.42 0.85 0.3 0.3

5 3.27 3.35 3.30 0.94 0.0 0.0

6 3.27 3.04 3.19 3.17 0.79 -0.3 -0.3

7 3.62 3.47 3.70 3.60 0.60 0.7 1.0

8 3.84 3.41 3.94 3.70 0.70 1.0 1.2

9 3.27 3.28 3.24 3.26 0.82 0.0 0.0

10 2.90 2.90 3.00 2.90 0.59 -0.9 -1.3




Figure 7 : (a) Results with expanded uncertainty for Cu, as reported by the participants (dashed lines: xa ± 2 u(xa), dotted lines: xa ± 2 σp, and (b) z (blue bars) and ζ-scores (orange bars)

(A)

(B)




Zinc (Zn) xa = 21.3 ± 0.3 mg/kg (k = 2)

Ten laboratories submitted results for Zn concentrations. The median of the ten results was used as

assigned value. All laboratories obtained satisfactory z-scores for Zn against the standard deviation

accepted for the proficiency test (Table 7, Figure 8). Eight laboratories did obtain also satisfactory ζ-

scores against their stated measurement uncertainty. Two laboratories (L09 and L10) obtained

unsatisfactory ζ-scores of which one laboratory (L10) did not report a measurement uncertainty

value.

Table 7 : values reported for Zn (mg/kg) by the participants and scores calculated by the organizer

Lab

co

de

Re

sult

1 (

mg

kg-1

)

Re

sult

1 (

mg

kg-1

)

Re

sult

1 (

mg

kg-1

)

Me

an (

mg

kg-1

)

Exte

nd

ed

un

cert

ain

ty (

k =

2)

(u

lab; m

g kg

-1)

z-sc

ore

s

ζ-sc

ore

s

1 21.1 21.7 21.1 21.3 4.1 0.0 0.0

2 20.0 20.4 20.5 20.3 1.0 -0.5 -1.9

3 21.6 21.3 20.9 21.3 3.2 0.0 0.0

4 22.1 21.4 31.4 21.6 5.4 0.1 0.2

5 21.2 21.2 - 21.0 4.0 -0.1 -0.1

6 22.2 21.0 21.5 21.6 4.6 0.1 0.1

7 21.2 20.3 21.6 21.1 3.2 -0.1 -0.1

8 26.5 21.0 23.9 23.8 3.4 1.2 1.5

9 19.0 19.5 19.3 19.3 1.0 -0.9 -3.9

10 24.0 21.0 23.0 23.0 0.0 0.8 12.5




Figure 8 : (a) Results with expanded uncertainty for Zn, as reported by the participants (dashed lines: xa ± 2 u(xa), dotted lines: xa ± 2 σp, and (b) z (blue bars) and ζ-scores (orange bars)

(A)

(B)




Discussion and conclusion The most commonly used technique for the analysis of As, Cd, Pb, Cu and Zn was ICP-MS (Inductively

Coupled Plasma-Mass Spectrometry). Only one exception was noticed by a lab which uses INAA

(Instrumental Neutral Activation Analysis). For Cu and/or Zn some laboratories used ICP-OES

(Inductively Coupled Plasma-Optical Emission Spectrometry).

As for inorganic As, the samples were all analysed by ICP-MS. Three laboratories used HPLC (High

Performance Liquid Chromatography), coupled to the ICP-MS as separation method and one

laboratory used SPE (Solid Phase Extraction). The measurement results seem to be similar for both

approaches, although the results with SPE method were slightly lower compared with the HPLC-ICP-

MS method. Already four laboratories participated successfully for Asi in this PT.

The laboratories were asked to state if the samples are compliant according to the current

legislation. In Commission Regulation (EC) 333/2007 [3] it is described when a sample is accepted:

“The lot or sublot is accepted if the analytical result of the laboratory sample does not exceed the

respective maximum level as laid down in Regulation (EC) No 1881/2006 taking into account the

expanded measurement uncertainty and correction of the result for recovery if an extraction step

has been applied in the analytical method used. The lot or sublot is rejected if the analytical result of

the laboratory sample exceeds beyond reasonable doubt the respective maximum level as laid down

in Regulation (EC) No 1881/2006 taking into account the expanded measurement uncertainty and

correction of the result for recovery if an extraction step has been applied in the analytical method

used.”

For the concerned matrix there are clear maximum limits for Asi (0.30 mg/kg). The organizers gave no

information as would the wafers be intended for infants and young children, but if this was the case

the maximum limit for Cd and Pb in this matrix is 0.040 and 0.050 mg/kg, respectively.

Table 8 : Compliant statements of the participating laboratories (no(N) or yes(Y)) compared with the measured values minus the expanded measurement uncertainty (xa-U(xa)) for As, Asi, Cd and Pb.

As* Asi Cd Pb

xlab-U(xlab) (mg/kg) stated by lab

L01 0.18

0.100 <0.020 Y

L02 0.16

<0.5 -

L03 0.13 0.13 0.078 <0.020 Y

L04 0.10

0.079 0.008 Y

L05 0.14

0.089 <0.05 Y/N**

L06 0.11 0.09 0.076 <0.05 Y

L07 0.15 0.12 0.090 0.005 Y

L08 0.13

0.100 <0.016 Y

L09 0.13

0.085 0.005 -

L10 0.21 0.13 0.115 <0.04 Y

ML 0.30 0.30 0.040** 0.050**

*as screening method **only if matrix is intended for infants and young children




So the measured concentration should be compared with these MLs, taking into account the

expanded measurement uncertainty. This means that a sample is non-compliant if xlab-U(xlab)>ML.

Table 8 shows this exercise for the participants. All laboratories stated this sample as compliant and

this was right in case the wafers were not intended especially for infants and young children (note:

information about the intended use was not given by the organizers). No calculated xlab-U(xlab)

exceeded the ML for Asi. This conclusion could also be drawn when only As was measured as the

total concentration did also not exceed the ML. However, when the wafers should be intended for

infants and young children, the sample would be non-compliant regarding the Cd concentration;

there was only one laboratory that noticed this nuance.

To conclude, this was a very successful exercise. Of the ten laboratories that registered for

participation, ten submitted results for As, Cd, Cu and Zn; nine submitted results for Pb and four

submitted results for Asi. The laboratories performed excellent with only one z-score which was

questionable. The laboratories have thus proven their competence to measure the concerned trace

elements in the matrix.




Bibliography

[1] European Commission, “Commission Regulation (EU) 2015/1006 of 25 June 2015 amending Regulation (EC) No 1881/2006 as regards maximum levels of inorganic arsenic in foodstuffs,” Off. J. Eur. Union, vol. L161, no. 14, pp. 1993–1995, 2015.

[2] European Commission, “Commission Regulation (EC) No 1881/2006 of 19 December 2006 setting maximum levels for certain contaminants in foodstuffs,” Off. J. Eur. Union, vol. L364, no. 78, pp. 5–24, 2006.

[3] European Commission, “Commission Regulation (EC) No 333/2007 of 28 March 2007 laying down the methods of sampling and analysis for the official control of the levels of lead, cadmium, mercury, inorganic tin, 3-MCPD and benzo(a)pyrene in foodstuffs,” Off. J. Eur. Union, vol. L88, no. 333, pp. 29–38, 2007.

[4] European Commission, “Commission Regulation (EU) No 488/2014 of 12 May 2014 amending Regulation (EC) No 1881/2006 as regards maximum levels of cadmium in foodstuffs,” Off. J. Eur. Union, vol. L138, no. 75, pp. 75–79, 2014.

[5] European Commission, “Commission Regulation (EU) 2015/1005 of 25 June 2015 amending Regulation (EC) No 1881/2006 as regards maximum levels of lead in certain foodstuffs,” Off. J. Eur. Union, vol. 161, no. 9, pp. 8–12, 2015.

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[8] AMC, “Robust statistics: a method of coping with outliers,” AMC Tech. Br., no. 6, 2001.

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Annexes

Annex 1: Invitation letter to laboratories




Annex 2: Results of the homogeneity studies

As Cd Pb Cu Zn

Cochran test for variance outliers

Cochran test statistic 0.423 0.281 0.504 0.987 0.482

Critical (99%) 0.718 0.718 0.718 0.718 0.718

Cochran < critical use complete

dataset

use complete

dataset

use complete

dataset

Remove

outlier

use complete

dataset

Cochran test statistic

(9 samples)

0.532

Critical (99%)

(9 samples)

0.754

Test for sufficient homogeneity

San² 39 656 1.2 8764 336004

Ssam² 182 118 0.3 46453 800433

σall² 159 84 0.5 22238 416074

F1 1.88 1.88 1.88 1.88 1.88

F2 1.01 1.01 1.01 1.01 1.01

Critical 339 223 2.1 52870 1121582

Ssam² < critical? accept accept accept accept accept




Annex 3: Letter accompanying the sample




Annex 4: Instructions to participants




Annex 5: Materials receipt form




Annex 6: Reporting form and questionnaire

belgian national reference laboratory for trace elements ...€¦ · trace elements in food and...

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