Report CHEK proficiency study 658 - NVWA · Final | CHEK proficiency study 658 | 23 March 2017 page 0 Content 1 Introduction 1 2 Time-table 1 3 Sample preparation 1 4 Statistical

Final | CHEK proficiency study 658 | 23 March 2017

page 0

CHEK Proficiency study 658 Elements (Pb, Cd, Cr, Ni and Hg) in skin cream

Date 23 March 2017

Version 1

Status Final

Report number CHEK-17-658


page 1

Colophon

Number 658

Name Elements (Pb, Cd, Cr, Ni and Hg) in skin cream

Contact Netherlands Food and Consumer Product Safety Authority (NVWA)

Paterswoldseweg 1 | 9726 BA Groningen | The Netherlands

PO Box 43006 | 3540 AA Utrecht | The Netherlands

T +31 088 223 33 33

[email protected]

www.nvwa.nl/chek

ISBN 1380-51

Author Mariëlle van Vondel

Authorization Krista Bouma (operational manager)


page 0

Content

1 Introduction 1

2 Time-table 1

3 Sample preparation 1

4 Statistical results 2

4.1 Lead in skin cream 3

4.2 Cadmium in skin cream 4

4.3 Chromium (total) in skin cream 5

4.4 Nickel in skin cream 6

4.5 Mercury in skin cream 7

4.6 Summary elements in skin cream 8

5 Methods of analysis 9

6 Remarks from participants 10

7 List of invited participants 10

8 Explanation of graphical presentations 11

9 Tables and graphical presentations 12 - 22


page 1

1 Introduction

This proficiency study 658 as directed by the CHEK working group concerned the

investigation of elements lead, cadmium, chromium (total), nickel and mercury in skin

cream samples. To get an impression of the performance of the quantitative

determination of elements in skin cream 13 laboratories were invited to join this

proficiency study.

2 Time-table

Homogeneity test of samples 25 January 2017

Distribution of samples 13 February 2017

Deadline for the test samples 17 March 2017

Final report 23 March 2017

3 Sample preparation

Skin cream samples A and B

500 grams skin cream was weighed and 10 mL standard solution (containing 0,25 mg/ml

lead, 1 mg/mL cadmium, 1 mg/mL chromium, 1 mg/mL nickel, 0.10 mg/mL mercury, 1

mg/mL arsenic, 1 mg/mL barium and 1 mg/mL cobalt was added. Yielding the next

contents of elements 5 mg/kg lead, 20 mg/kg cadmium, 20 mg/kg chromium, 20 mg/kg

nickel and 2 mg/kg mercury. The skin cream and standard solutions were minced for 30

minutes using a mincer machine. After homogenisation approximately 100 sub-samples of

about 5 grams were prepared in plastic sachets.

Homogeneity

The homogeneity was checked by the laboratory of the Netherlands Food and Consumer

Product Safety Authority in Groningen by randomly selected samples for the

determination of elements lead, cadmium, chromium and nickel (see table II). The

average contents were 4.97 mg/kg lead, 18.6 mg/kg cadmium, 20.6 mg/kg chromium

and 20.3 mg/kg nickel. Mercury could not be tested, due to technical problems.

Stability

The stability was not checked yet. Samples are stored in a refrigerator at +4°C until

shipment. Samples are expected to be stable during the period between the distribution

of samples and the deadline for the production of results .

Instructions

Samples were stored in a refrigerator (+4°C) until shipment. To each of the participants

two samples skin cream coded A and B were sent. They were instructed to store the

samples in a refrigerator and mix each sample well before analysis by one analyst

singularly.


page 2

4 Statistical results

The results of the laboratories and the Z-scores are given in tables Ia and Ib. Figures I

to XXIV give graphical presentations of the results. One-way analysis of variance

(ANOVA), preceded by checking for normality and outlier checking of the results

(Cochran/Grubbs) is the statistical procedure for obtaining the estimates of within-

laboratory and between laboratory variability.

Performance

The performance of a determination is assessed as following:

satisfactory = maximum allowable RSDR ≤2

questionable = 2< maximum allowable RSDR <3

unsatisfactory = maximum allowable RSDR ≥3


page 3

4.1 Lead in skin cream uniform level

4.1.1 Lead in skin cream samples A and B

12 labs: Results of laboratory 11 are removed by hand

11 labs: Results of laboratory 2 are rejected by the Grubbs test

12 labs 11 labs Unit

Average 5.17 5.03 mg/kg

Repeatability standard deviation (sr') 0.18 0.18 mg/kg

Repeatability rel. standard deviation (RSDr') 3.5 3.5 %

Reproducibility standard deviation (sR') 0.62 0.39 mg/kg

Reproducibility rel. standard deviation (RSDR') 12 7.7 %

Horwitz acceptable value for (RSDR') 12 13 %

Repeatability r' 0.50 0.50 mg/kg

Reproducibility R' 1.7 1.1 mg/kg

4.1.2 Summary lead in skin cream samples A and B

The results of this and an earlier proficiency study are summarised in the table below.

Prof.

study

Number of

labs

Average

mg/kg

RSDR

%

Acceptable

RSDR %

658 11 5.03 7.7 13

645 17 5.10 6.6 13

619 14 11.8 12 11

4.1.3 Conclusions lead in skin cream samples A and B

� The performance of the determination of lead in skin cream is satisfactory.

� Results of laboratory 11 are removed by hand, because of non-quantitative results.

� The results are drawn from a normal distribution.

� No Cochran outliers are found in the datasets of sample A and B.

� The results of laboratory 1 are marked as stragglers by the Cochran test indicating

bad repeatability but are not rejected.

� The results of laboratory 2 are marked as outliers by the Grubbs test indicating

systematic errors and are rejected.


page 4

4.2 Cadmium in skin cream uniform level

4.2.1 Cadmium in skin cream samples A and B

13 labs: Results of all laboratories

13 labs Unit

Average 19.8 mg/kg

Repeatability standard deviation (sr') 0.75 mg/kg

Repeatability rel. standard deviation (RSDr') 3.8 %

Reproducibility standard deviation (sR') 1.8 mg/kg

Reproducibility rel. standard deviation (RSDR') 9.2 %

Horwitz acceptable value for (RSDR') 10 %

Repeatability r' 2.1 mg/kg

Reproducibility R' 5.1 mg/kg

4.2.2 Summary cadmium in skin cream samples A and B


Prof.

study

Number of

labs

Average

mg/kg

RSDR

%

Acceptable

RSDR %

658 13 19.8 9.2 10

645 18 20.8 10.5 10.1

619 15 46.7 14 9.0

4.2.3 Conclusions cadmium in skin cream samples A and B

� The performance of the determination of cadmium in skin cream is satisfactory.


� No Cochran or Grubbs outliers are found in the datasets of sample A and B.


page 5

4.3 Chromium (total) in skin cream uniform level

4.3.1 Chromium (total) in skin cream samples A and B


11 labs Unit

Average 20.5 mg/kg








4.3.2 Summary chromium (total) in skin cream samples A and B


Prof.

study

Number of

labs

Average

mg/kg

RSDR

%

Acceptable

RSDR %

658 11 20.5 4.7 10

645 14 20.6 5.1 10.1

619 13 47.8 10 8.9

4.3.3 Conclusions chromium (total) in skin cream samples A and B

� The performance of the determination of chromium (total) in skin cream is

satisfactory.




page 6

4.4 Nickel in skin cream uniform level

4.4.1 Nickel in skin cream samples A and B


10 labs Unit

Average 20.8 mg/kg








4.4.2 Summary nickel in skin cream samples A and B


Prof.

study

Number of

labs

Average

mg/kg

RSDR

%

Acceptable

RSDR %

658 10 20.8 5.8 10

645 14 20.5 5.4 10.1

619 14 49.2 16 8.9

4.4.3 Conclusions nickel in skin cream samples A and B

� The performance of the determination of nickel in skin cream is satisfactory.




page 7

4.5 Mercury in skin cream uniform level

4.5.1 Mercury in skin cream samples A and B


12 labs Unit

Average 1.09 mg/kg








4.5.2 Summary mercury in skin cream samples A and B


Prof.

study

Number of

labs

Average

mg/kg

RSDR

%

Acceptable

RSDR %

658 12 1.09 9.6 16

645 13 1.32 11 15

619 13 2.33 14 14

4.5.3 Conclusions mercury in skin cream samples A and B

� The performance of the determination of mercury in skin cream is satisfactory.




page 8

4.6 Summary elements in skin cream

The results of this proficiency study are summarised in the table below.

Number of

accepted results

Average

[mg/kg]

RSDR‘

[%]

Lead 11 5.03 7.7

Cadmium 13 19.8 9.2

Chromium (total) 11 20.5 4.7

Nickel 10 20.8 5.8

Mercury 12 1.09 9.6

5 Method of analysis

Lab Technique

Etraction/ microwave digestion

Samples/ year

1 AAVF (mercury) HNO3 and HF -

ICP-MS (remaining elements)

2 CV-AFS (mercury) HNO3 and HF 865

ICP-MS (remaining elements)

3 ICP-MS - -

4 ICP-MS HNO3 1

5 CV-AAS (mercury) - 400

GF-AAS (lead and cadmium)

6 ICP-MS - 2000

7 ICP-CCD HNO3 20

8 ICP-MS HNO3 -

9 ICP - -

10 ICP-MS HNO3 and HCL >500

11 ICP - -

12 AAS - 100

13 ICP-MS - -


page 9

6 Remarks from participants

Lab 6 Measurements were also performed with ICP-OES for Cd, P, Cr and Ni. Hg was

also measured with CV-AAS. All results were nearly identical.

Lab 13 Used method is accordance with Safety and Technical Standards for Cosmetics

(2015 version) Chapter 4 Physicochemical Analysis 1.6 ICP-MS method.

7 List of invited participants

Europe

France – 2 participant

Germany – 2 participants

Ireland – 1 participant

Switzerland – 1 participant

Outside Europe

China – 1 participant

Hong Kong – 1 participant

Iran – 1 participant

Taiwan – 1 participant

Thailand – 2 participants

Turkey – 1 participant


page 10

8 Explanation of graphical presentations

Z-score

As a criterion for evaluation of the performance of an individual laboratory a so-

called Z-score is used. The Z-score is given by the following equation:

σµ−= x

Z

Where:

x = an (average) laboratory result

µ = the average result of all laboratories (calculated exclusive outliers)

σ = an assigned precision standard or fixed target value

As a fixed target value the maximum allowable standard deviation is used

calculated according to Horwitz. The Z-score for an individual laboratory can be

compared with those of previous proficiency studies to determine whether the

laboratory performance has improved. Because Z is standardised, it is comparable

for all analytes, testmaterials and analytical methods.

In general, an absolute value of Z greater than three suggests poor performance in

terms of accuracy. When overall performance in a specific interlaboratory test is

graded as “good”, values of │Z│<1 would be very common and values of │Z│>3

would be very rare. It is possible to classify these scores:

Satisfactory = │Z│≤ 2

Questionable = 2 <│Z│< 3

Unsatisfactory = │Z│≥ 3

Saw-tooth plot

The results of the samples are presented in a so-called saw-tooth plot. In this figure

individual results of two (nearly) identical individual results are plotted. The

average of the sample, the 2s- and 3s-intervals of the target values (Horwitz plus

uncertainty) and the 2s- and 3s-intervals after removal of outliers are also included

(group s).

Youden-plot

Based on Youden statistics the calculated variance is split in a variance caused by

systematic and random errors of the individual laboratories. It is necessary that the

samples are similar. Generally the points form an elliptical pattern with the major

axis of the ellipse running diagonally at an angle of 45° to the X-axis. The lengths of

the perpendiculars drawn from the points to the 45° line are directly related to the

random errors. Systematic errors will be presented along the 45° line. The

perpendiculars intersect the 45° line at various distances from the point through

which the 45° line was drawn. These distances are directly related to the systematic

errors.


page 11

9 Tables and graphical presentations

Table I; Results lead, cadmium, chromium (total), nickel and mercury in skin cream [mg/kg]

Lab Lead Cadmium Chromium (total) Nickel Mercury

A B Z A B Z A B Z A B Z A B Z

1 5.00 4.34 -0.57 21.5 18.8 0.15 22.2 20.1 0.30 21.5 18.7 -0.34 0.99 0.90 -0.84

2 6.90(2) 6.60(2) 2.73 22.0 22.0 1.06 20.0 21.0 -0.01 20.0 22.0 0.09 1.10 1.20 0.35

3 5.32 5.12 0.31 21.0 20.1 0.35 20.8 19.0 -0.30 23.1 22.3 0.89 - - -

4 5.18 5.04 0.13 19.2 19.2 -0.32 21.0 20.5 0.11 20.9 20.4 -0.08 1.28 1.23 0.96

5 4.54 4.62 -0.71 17.0 16.9 -1.42 - - - - - - 1.11 1.01 -0.17

6 5.21 5.11 0.21 20.8 20.5 0.40 20.2 20.4 -0.11 20.3 20.2 -0.27 1.02 1.03 -0.37

7 5.06 5.27 0.22 20.5 22.0 0.69 20.6 22.2 0.42 20.5 22.1 0.23 1.12 1.04 -0.05

8 4.47 4.20 -1.10 17.0 18.6 -1.01 - - - - - - 0.953 0.953 -0.79

9 5.60 5.49 0.82 22.1 21.8 1.04 21.8 21.3 0.49 22.3 21.9 0.61 1.06 1.10 -0.05

10 4.86 4.89 -0.24 19.8 19.1 -0.20 20.5 20.4 -0.03 - - - 1.19 1.23 0.70

11 <10(3) <10(3) - 21.0 21.0 0.57 19.6 18.9 -0.61 20.5 20.3 -0.20 0.97 1.04 -0.49

12 5.21 5.42 0.46 17.1 16.3 -1.55 20.7 18.4 -0.47 18.8 19.6 -0.77 1.23 1.17 0.64

13 5.36 5.30 0.48 20.5 20.2 0.25 21.0 20.8 0.19 20.6 20.3 -0.18 1.10 1.12 0.12

μ 5.03 19.8 20.5 20.8 1.09

σ 0.63 2.0 2.1 2.1 0.17

(1) = Cochran outlier (2)= Grubbs outlier (3) = Results removed by hand


page 12

Table II; Homogeneity of samples for elements in skin cream [mg/kg]

Sample

no

Lead Cadmium Chromium (total) Nickel

1st

analysis

2nd

analysis

1st

analysis

1st

analysis

2nd

analysis

1st

analysis

1st

analysis

2nd

analysis

1 4.84 4.94 17.9 17.5 20.3 20.6 19.8 20.1

2 4.92 4.79 18.1 18.1 20.8 20.0 20.2 19.6

3 4.89 4.89 18.8 18.6 20.5 20.2 20.2 19.9

4 5.18 4.99 19.7 18.5 21.8 20.8 21.4 20.5

5 5.07 4.81 19.4 18.5 20.8 19.9 20.6 19.7

6 5.14 5.01 19.3 18.8 21.0 20.6 20.8 20.5

7 4.83 4.92 17.9 18.2 19.9 20.1 19.8 19.9

8 5.07 5.09 18.8 19.3 20.8 21.1 20.7 20.6

9 4.94 5.04 18.8 18.4 20.4 21.1 20.0 20.9

10 4.93 5.08 18.5 19.4 20.0 21.0 19.7 20.7

average 4.98 4.96 18.7 18.5 20.6 20.5 20.3 20.2

t-test

tsamples 0.56 0.87 0.46 0.44

tcritical,95% 2.26 2.26 2.26 2.26

Homogeneity

Sbetween 0.0592 0.398 0.160 0.204

Swithin 0.0971 0.440 0.471 0.450

σ 0.625 1.92 2.09 2.06

Sbetween/σ 0.0947 0.207 0.0766 0.0987

Based on the t-test there is no significant difference between the averages of 1st and the

2nd analysis for all elements, except for cadmium. The ratio of the sampling standard

deviation and the target value σ for all elements is lower than the recommended value of

0.3. Samples are regarded as sufficient homogeneous for the purpose of the proficiency

study.


page 13

Graphical presentations lead in skin cream

N.B. Results of laboratory 11 are not presented because of non-quantitative results.

Figure Ia; Saw-tooth plot lead in skin cream, calculated with target s

Figure Ib; Saw-tooth plot lead in skin cream, calculated with group s (exclusive

laboratories 2 and 11)


page 14

Figure II; Youden plot lead in skin cream

Figure III; Z-score lead in skin cream


page 15

Graphical presentations cadmium in skin cream

Figure IVa; Saw-tooth plot cadmium in skin cream, calculated with target s

Figure IVb; Saw-tooth plot cadmium in skin cream, calculated with group s


page 16

Figure V; Youden plot cadmium in skin cream

Figure VI; Z-score cadmium in skin cream


page 17

Graphical presentations chromium (total) in skin crème

Figure VIIa; Saw-tooth plot chromium (total) in skin cream, calculated with target s

Figure VIIb; Saw-tooth plot chromium (total) in skin cream, calculated with group s


page 18

Figure VIII; Youden plot chromium (total) in skin cream

Figure IX; Z-score chromium (total) in skin cream


page 19

Graphical presentations nickel in skin cream

Figure Xa; Saw-tooth plot nickel in skin cream, calculated with target s

Figure Xb; Saw-tooth plot nickel in skin cream, calculated with group s


page 20

Figure XI; Youden plot nickel in skin cream

Figure XII; Z-score nickel in skin cream


page 21

Graphical presentations mercury in skin cream

Figure XIIIa; Saw-tooth plot mercury in skin cream, calculated with target s

Figure XIIIb; Saw-tooth plot mercury in skin cream, calculated with group s


page 22

Figure XIV; Youden plot mercury in skin cream

Figure XV; Z-score mercury in skin cream

Documents

Report CHEK proficiency study 658 - NVWA · Final | CHEK proficiency study 658 | 23 March 2017 page 0 Content 1 Introduction 1 2 Time-table 1 3 Sample preparation 1 4 Statistical