report

Transcript

report

Consiglio Nazionale delle Ricerche
Istituto per lo Studio degli Ecosistemi
Ve r b a n i a P a l l a n z a
R E P O R T
CNR-ISE, 07.10 (E)
Quality Control IC Proficiency Test
QC-IC 2010-2
A. Marchetto, G. A. Tartari, P. Giacomotti
E. Zabiello & F. Abballe
2010
National Research Council of Italy
Institute of Ecosystem Study
Dionex S.p.A. – Milano
Quality Control IC Proficiency Test
QC-IC 2010-2
Aldo Marchetto, Gabriele A. Tartari, Paola Giacomotti
CNR – Institute of Ecosystem Study (ISE),
Largo Tonolli 50, 28922 Verbania Pallanza, Italy
e-mail corresponding author: [email protected]
web page: http://www.idrolab.ise.cnr.it
Eugenio Zabiello, Franco Abballe
Dionex S.p.A.
via XXV Aprile, 6, 20097 San Donato Milanese (Milano)
web page: http://www.dionex.com
24 November 2010
TABLE OF CONTENTS
1. INTRODUCTION
1
1.1.
Aims
1
1.2.
Description
1
1.3.
Participants
1
2. PROFICIENCY EVALUATION
2
2.1.
Assigned values
2
2.2.
Web site for result upload
3
3. SAMPLES
5
3.1.
Preparation and shipping
5
3.2.
Homogeneity
6
3.3.
Stability
7
3.4.
Expected values
8
4. RESULTS
9
4.1.
Data analysis
9
4.2.
Results
9
5. DISCUSSION
24
6. CONCLUSIONS
25
7. REFERENCES
26
1. INTRODUCTION
1.1.
Aims
This Quality Control IC Proficiency Test is organized by Dionex (Italy) S.p.A. supported by the
Institute of Ecosystem Study (ISE) of the National Research Council of Italy.
The aim of proficiency tests is to give to the participants a tool to evaluate the quality of their
results in order to improve them.
This program follows international ISO e ILAC rules.
The proficiency of each laboratory is evaluated by means of a z-score calculated using an assigned
standard deviation (SDa) for each analyte and sample. SDas were obtained using relative standard
deviation reported in official analytical methods or in previous exercises.
1.2.
Description
This test follows ISO/IEC 43-1:1997 e 43-2:1997, ILAC G13:2007 and ISO/IEC 17043:2010 rules.
A coordination team was formed, including:

Aldo Marchetto
CNR-ISE Verbania

Gabriele Tartari
CNR-ISE Verbania

Paola Giacomotti
CNR-ISE Verbania

Eugenio Zabiello
Dionex S.p.A. Milano

Franco Abballe
Dionex S.p.A. Milano
Leader
After registration, each laboratory received a code and a password to upload their results into the
website. To maintain each laboratory anonymous, its code is known exclusively by the laboratory
itself and the coordination team. In the report, laboratories are numbered, without any reference to
their codes.
Two 280-mL polyethylene bottles containing natural water samples (C1 and C2) were sent to each
participating lab. A single determination of chloride, nitrate, sulphate, sodium, potassium,
magnesium and calcium was requested, without replication.
Expected values were obtained by the robust average (x*) of the results, following point 5.6 of ISO
rule 13528:2005. Laboratory proficiency was evaluated using a z-score calculated using an assigned
standard deviation (SDa) for each analyze and sample. SDas were obtained using relative standard
deviation reported in official analytical methods or in previous exercises, following ISO rules 57255 (point 6.2) and ISO 13528.
Registration was open from June 2010 to September 27, 2010. Samples were sent on October 1st
and the deadline for result upload was set to November 8th, 2010.
1.3.
Participants
In February, 2010, a first proficiency test opened to Italian laboratories was organized. This second
test was opened to laboratories of different countries, namely 37 in Italy, 15 in the Netherlands, 2 in
Belgium and one each in Australia, Malaysia, Nigeria, Qatar, Russia, Switzerland and the Arab
Emirates. 50 laboratories uploaded the results.
-1-
2. PROFICIENCY EVALUATION
2.1.
Assigned values
Laboratory proficiency was evaluated using z-scores on the basis of the robust average of the results
and of assigned standard deviation.
Assigned standard deviation were estimated on the basis of method reproducibility reported in
official analytical methods APAT IRSA-CNR 4020 (Italy) and ISO 10304-1 (2007) for anions and
APAT IRSA-CNR 3030 for cations, and on the basis of other proficiency tests, such as Italian
UNICHIM proficiency tests for drinking water and wastewater and the previous QC-IC 2010-1 test.
Chloride
25
50
40
CVR %
CVR %
20
15
10
30
20
10
5
0
0
0
100
200
0
300
20
40
60
80
mg/L
mg/L
Sulphate
15
CVR %
Nitrate
ISO 10304-1
10
IRSA 4020
UNICHIM
5
QC-IC 2010-1
0
0
100
mg/L
200
300
Coefficients of variation of the reproducibility for anions, reported in analytical methods
(ISO 10304-1 and IRSA 4020) and in previous exercises (UNICHIM 2005-2009 and QCIC 2010-1).
-2-
IRSA 3030
Sodium
15
50
Potassium
UNICHIM
40
10
CVR %
CVR %
QC-IC 2010-1
5
30
20
10
0
0
25
50
75
0
100
mg/L
15
0
60
Magnesium
2
mg/L
4
mg/L
100
6
Calcium
50
10
CVR %
CVR %
40
5
30
20
10
0
0
10
20
30
40
0
50
0
mg/L
50
150
Coefficients of variation of the reproducibility for cations, reported in analytical methods
(ISO 10304-1 and IRSA 4020) and in previous exercises (UNICHIM 2005-2009 and QCIC 2010-1).
Assigned relative standard deviations (RSDa) are reported in the following table:
Anions
Chloride
Nitrate
Sulphate
Expected
value
mg/L
~ 1.8 – 2.2
RSDa
assigned
Cations
RSDa
assigned
Sodium
Expected
value
mg/L
~3–4
15
~3–4
10
Potassium
~ 1.5 – 2.5
10
~ 50 - 65
8
Magnesium
~ 7 - 12
8
Calcium
~ 40 - 50
8
8
2.2. Web site for result upload
In this proficiency test, a website has been used to upload the results. During data upload, each lab
can compare its results with provisional expected values. This comparison is possible after final
confirmation of results by the lab and when a minimum of 10 results have been uploaded for the
analyte.
Eight labs did not use the website and sent their results to the coordination team by e-mail.
-3-
In the following pictures, statistical plots and tables obtained by the laboratory of the Institute of
Ecosystem Study for sulphate are shown as an example. In the plots, the point referring to this
laboratory is in red.
Web page showing uploaded results and statistical tables
Web page with distribution plots of the results for the two samples
-4-
Web page with the Youden plot
3. SAMPLES
3.1. Preparation and shipping
Samples were prepared mixing different drinking waters
in 100-L containers two weeks before sample shipping.
Samples were sent in 250-ml polyethylene bottles,
washed with deionized water, left full of deionized water
for one day, and then washed twice with the samples.
No preservative was added and the samples were not
refrigerated during shipping.
Samples were sent on October the 1st (to Italian labs)
and September 28th (to the other labs) and in most cases
arrived to the participating laboratories before October
7th. However some labs received the samples later, up to
October 20th.
-5-
3.2.
Homogeneity
Sample homogeneity was evaluated following ISO e ILAC rules for proficiency tests, and in
particular Thompson et al. (2006) and Tholen et al. (2007).
Homogeneity tests were performed at the laboratory of the Institute of Ecosystem Study in
Verbania. For each sample (C1 and C2), twelve bottles were analyzed twice in a single batch but in
random sequence.
The presence of outliers was detected using Cochran test, with a critical value of 0.54, for p<0.05
and twelve samples.
Variance partitioning was then performed for analytical and between-sample variance. Between
sample variance was always lower than 30% of the assigned standard deviation for each variable, as
suggested by Thompson et al. (2006).
A single outlier was detected for calcium analysis of sample C2.
Variable
Sample
Chloride
C1
C2
C1
C2
C1
C2
C1
C2
C1
C2
C1
C2
C1
C2
Cochran
test for outliers
Overall
RSD
RSD
analysis
RSD
between
samples
0.26
0.19
0.18
0.14
0.25
0.21
*
0.18
0.09
0.22
*
0.10
*
0.09
0.26
0.76
0.71
0.30
0.31
0.25
Nitrate
0.51
0.40
0.36
0.50
0.15
0.07
Sulphate
0.43
0.63
0.58
0.46
0.26
0.15
Sodium
0.19
0.19
0.19
0.44
0.19
0.08
Potassium
0.39
0.22
0.21
0.23
0.26
0.15
Magnesium
0.35
0,22
0.23
0.28
0,10
0.03
Calcium
0.34
0,30
0.30
0,09
0.04
0.65
* denotes cases in which analytical variance was higher than overall variance.
-6-
% limit
(30% of SDa)
4.5
4.5
3.0
3.0
2.4
2.4
2.4
2.4
3.0
3.0
2.4
2.4
2.4
2.4
3.3.
Stability
Sample stability was evaluated by repeating the analysis of a bottle for each sample (C1 and C2)
preserved in the dark at 4°C. Analyses were performed on September 27th (two replicates), October
12th and 28th and November 9th (three replicates).
The resulting variability was again compared with a limit set to 30% of SDa.
During each analytical session, a second bottle, freshly opened, was analyzed.
The results are compared in the following table.
In general, stability was excellent and the relative standard deviation was lower than the limit.
However, in the case of sample C2, in November 8th the nitrate concentration in one of the three
analyzed samples was markedly lower than in the previous analyses.
Variable
Chloride
Nitrate
Sulphate
Sodium
Potassium
Magnesium
Calcium
Sample
C1
C2
C1
C2
C1
C2
C1
C2
C1
C2
C1
C2
C1
C2
RSD
sample preserved
in the dark at 4 °C
1.2
1.2
1.4
1.7
1.5
1.4
1.2
0.8
1.2
1.6
1.0
0.6
1.3
1.3
-7-
RSD
freshly opened
samples
1.0
0.9
1.3
3.7
1.2
1.2
0.2
0.3
0.4
0.5
0.2
0.2
0.2
0.5
% limit
(30% of SDa)
4.5
4.5
3.0
3.0
2.4
2.4
2.4
2.4
3.0
3.0
2.4
2.4
2.4
2.4
3.4.
Expected values
Expected values were obtained as robust average of the submitted results (consensus value),
following ISO rules for proficiency test (PT) (ISO/IEC 43-1:1997, UNI ISO 5725:1998, ISO
13528:2005, ISO/IEC 17025:2005, ISO/IEC 17043:2010).
Robust averages and standard deviations are reported in the following tables, together with assigned
standard deviation.
Expected values for sample 1, concentrations in mg/L
SAMPLE 1
Analyte
Number of
participating
laboratories
Robust
average
Robust
SD
Assigned
SD
Robust
RSD
Assigned
RSD
Chloride
48
1.95
0.20
0.29
10.2
15
Nitrate
45
3.142
0.244
0.314
7.8
10
Sulphate
48
62.87
3.13
5.03
5.0
8
Sodium
37
3.79
0.27
0.30
7.1
8
Potassium
38
2.38
0.19
0.24
8.0
10
Magnesium
37
7.09
0.29
0.57
4.1
8
Calcium
38
45.86
3.20
3.67
7.0
8
Expected values for sample 2, concentrations in mg/L
SAMPLE 2
Analyte
Number of
participating
laboratories
Robust
average
Robust
SD
Assigned
SD
Robust
RSD
Assigned
RSD
Chloride
46
2.00
0.19
0.30
9.7
15
Nitrate
42
3.728
0.239
0.373
6.4
10
Sulphate
46
51.11
2.40
4.09
4.7
8
Sodium
36
3.24
0.26
0.26
7.9
8
Potassium
37
1.73
0.15
0.17
8.4
10
Magnesium
36
11.78
0.46
0.94
3.9
8
Calcium
37
44.25
2.61
3.54
5.9
8
-8-
4. RESULTS
4.1. Data analysis
Laboratory proficiency is evaluated using the z-score (zi), calculated for each analyte as the
difference between the submitted result (xi) and the robust average, divided by the assigned
standard deviation (SDa), the fitness-for-purpose-based “standard deviation for proficiency
assessment”.
zi 
xi  average *
SDa
where:
xi is the submitted result,
average* is the robust average and
SDa the assigned standard deviation.
For interpreting the z-score it can be assumed that:
0<|z|<2
means that the results lye within the assigned variability
2<|z|<3
means attention level
|z| >3
means that some measure is needed




A score of zero implies a perfect result.
Approximately 95 % of z-scores will fall between -2 and +2. The sign (i.e., - or +) of the
score indicates a negative or positive error respectively. Scores in this range are commonly
considered as “acceptable” or “satisfactory”.
A score outside the range from -3 to 3 would be very unusual and is taken to indicate the
cause for this event should be investigated and solved. Scores in this class are commonly
designated as “unacceptable” or “unsatisfactory”.
Scores in the ranges -2 to -3 and 2 to 3 would be expected about 1 time out of 20. Scores in
this class are designated as “questionable”.
Robust averages, standard deviations and z-scores were verified independently using Tool4PT Pro
Cortez & Mermayde version 1.06.10 2009.
4.2. Results
In the following tables the results are listed for each analyte and sample, together with the statistics
and the z-scores. Distribution plots are also included, together with the Youden plots (Youden 1959;
Youden & Steiner 1975). The latter compares, for each laboratory, the results of the two samples,
allowing the identification of systematic and random errors: when systematic errors prevail, the
results are located along a diagonal line.
Results are numbered and laboratories can identify themselves on the basis of the submitted results.
-9-
CNR-ISE Verbania – Dionex S.p.A. Milano
Quality Control IC Proficiency Test - QC-IC 2010-2
Analyte: CHLORIDE
Unit: mg/L
Number of registered laboratories:
61
C1
48
1.95
1.96
0.21
0.29
11
15
Number of participating laboratories:
Robust average mg/L
Median mg/L
Robust standard deviation mg/L
Assigned standard deviation mg/L
Robust relative standard deviation
Assigned relative standard deviation
Lab.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
R.1
2.55
1.84
1.83
2.06
1.95
1.98
1.98
1.96
1.80
2.03
1.43
1.74
1.96
0.72
1.55
1.65
2.09
1.97
2.48
2.10
1.96
0.95
1.59
1.88
C1
z-score
2.1
-0.4
-0.4
0.4
0.0
0.1
0.1
0.0
-0.5
0.3
-1.8
-0.7
0.0
-4.2
-1.4
-1.0
0.5
0.1
1.8
0.5
0.0
-3.4
-1.2
-0.2
R.2
2.60
1.91
1.89
2.07
2.04
2.08
2.08
2.05
1.86
2.10
1.51
1.69
2.06
1.46
1.78
1.71
2.16
2.06
2.58
2.19
2.07
1.06
1.81
1.99
C2
z-score
2.0
-0.3
-0.4
0.2
0.1
0.3
0.3
0.2
-0.5
0.3
-1.6
-1.0
0.2
-1.8
-0.7
-1.0
0.5
Lab.
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
0.2
1.9
0.6
0.2
-3.1
-0.6
-0.0
- 10 -
R.1
1.98
1.97
1.92
2.07
1.90
4.98
2.14
2.09
1.94
2.00
1.92
4.74
2.02
1.89
1.12
1.80
1.81
3.59
2.04
1.89
1.95
2.00
2.25
1.92
C2
46
2.00
2.03
0.19
0.30
10
15
C1
z-score
0.1
0.1
-0.1
0.4
-0.2
10.4
0.7
0.5
-0.0
0.2
-0.1
9.6
0.3
-0.2
-2.8
-0.5
-0.5
5.6
0.3
-0.2
0.0
0.2
1.0
-0.1
R.2
1.99
2.05
2.00
2.14
C2
z-score
-0.0
0.2
-0.0
0.5
2.86
2.17
2.24
2.9
0.6
0.8
2.01
2.10
1.97
0.0
0.3
-0.1
2.10
2.02
1.14
1.86
1.87
3.53
2.11
1.95
2.03
2.00
1.82
1.84
0.3
0.1
-2.9
-0.5
-0.4
5.1
0.4
-0.2
0.1
-0.0
-0.6
-0.5
Analyte: CHLORIDE
Unit: mg/L
25
mg/L
Distribution plot
4.0
3.5
C2 (mg/L)
3.0
2.5
2.0
1.5
1.0
0.5
0.5
1.5
2.5
3.5
4.5
5.5
C1 (mg/L)
Youden plot
z-score
12
10
8
C1
C2
z +3
z +2
z 0
z -2
z -3
ClCl
6
4
2
0
-2
-6
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
-4
Lab.
Distribution plot of the z-scores
- 11 -
3.
6
2.
8
mg/L
3.
0
2.
4
2.
6
2.
0
2.
2
1.
6
1.
8
1.
0
5.0
0
3.
3.
2
4.7
6
8
2.
2.
2.
2
4
2.
8
1.
0
1.
2.
4
6
1.
0
2
0
1.
0
1.
5
6
5
8
10
0.
10
1.
2
15
1.
4
Lab.
15
0.
Lab.
C2
20
3.
2
C1
20
3.
4
25
Analyte: NITRATE
Unit: mg/L
51
C1
45
3.142
3.146
0.244
0.314
8
10
Robust average mg/L
Median mg/L
Lab.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
C1
R.1
z-score
C2
R.2
z-score
3.339
3.289
3.090
2.923
3.055
3.200
3.270
3.217
3.146
3.090
2.245
3.187
3.002
2.490
2.840
3.230
0.6
0.5
-0.2
-0.7
-0.3
0.2
0.4
0.2
0.0
-0.2
-2.9
0.1
-0.4
-2.1
-1.0
0.3
3.953
3.785
3.596
3.454
3.676
3.764
3.785
3.848
3.690
3.660
2.701
3.781
3.653
3.340
3.280
3.800
0.6
0.2
-0.4
-0.7
-0.1
0.1
0.2
0.3
-0.1
-0.2
-2.8
0.1
-0.2
-1.0
-1.2
0.2
6.378
3.660
3.180
2.680
3.600
2.791
3.009
10.3
1.6
0.1
-1.5
1.5
-1.1
-0.4
5.173
4.270
3.667
2.910
4.300
3.487
3.494
3.9
1.5
-0.2
-2.2
1.5
-0.6
-0.6
Lab.
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
- 12 -
C2
42
3.728
3.767
0.239
0.373
6
10
C1
R.1
z-score
3.585
1.4
3.443
1.0
3.088
-0.2
3.058
-0.3
2.916
-0.7
3.154
0.0
3.284
0.5
C2
R.2
z-score
4.706
2.6
4.008
0.8
3.653
-0.2
3.565
-0.4
3.826
3.842
0.3
0.3
3.400
3.221
3.270
2.995
2.812
3.261
3.116
0.8
0.3
0.4
-0.5
-1.1
0.4
-0.1
4.000
3.780
3.850
3.770
0.7
0.1
0.3
0.1
3.829
3.841
0.3
0.3
3.076
3.022
3.014
3.260
3.336
3.050
-0.2
-0.4
-0.4
0.4
0.6
-0.3
3.495
3.538
3.658
3.860
4.003
3.600
-0.6
-0.5
-0.2
0.4
0.7
-0.3
4.795
2.870
5.3
-0.9
3.550
-0.5
18
16
14
12
10
8
6
4
2
0
Unit: mg/L
16
14
C1
C2
Lab.
12
10
8
6
4
2
mg/L
mg/L
Distribution plot
5.5
C2 (mg/L)
5.0
4.5
4.0
3.5
3.0
2.5
1.5
2.5
3.5
4.5
5.5
6.5
7.5
C1 (mg/L)
Youden plot
z-score
12
10
8
C1
C2
z +3
z +2
z 0
z -2
z -3
NO3
NO3-
6
4
2
0
-4
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
-2
Lab.
- 13 -
5.
2
5.
0
4.
8
4.
6
4.
4
4.
0
4.
2
3.
6
3.
8
3.
2
3.
4
3.
0
2.
8
2.
6
6
4
4.
4.8 & 6.4
4.
0
2
4.
3.
4.
6
8
3.
2
3.
4
3.
3.
8
0
2.
4
6
2.
2.
0
2
2.
0
2.
Lab.
Analyte: NITRATE
Analyte: SULPHATE
Unit: mg/L
61
C1
48
62.87
63.40
3.13
5.03
5
8
Robust average mg/L
Median mg/L
Lab.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
C1
R.1
z-score
66.15
0.7
67.97
1.0
59.16
-0.7
64.81
0.4
62.50
-0.1
63.00
0.0
63.30
0.1
66.42
0.7
63.50
0.1
64.53
0.3
61.99
-0.2
63.72
0.2
62.93
0.0
64.83
0.4
54.21
-1.7
67.07
0.8
61.04
-0.4
C2
R.2
z-score
54.76
0.9
55.08
1.0
46.98
-1.0
51.87
0.2
51.00
-0.0
51.82
0.2
51.65
0.1
52.50
0.3
52.10
0.2
52.08
0.2
51.00
-0.0
48.27
-0.7
51.27
0.0
52.45
0.3
48.05
-0.7
52.61
0.4
49.73
-0.3
34.34
64.96
62.51
56.80
70.00
58.70
63.82
41.46
52.02
50.60
44.70
47.00
47.80
52.26
-5.7
0.4
-0.1
-1.2
1.4
-0.8
0.2
Lab.
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
-2.4
0.2
-0.1
-1.6
-1.0
-0.8
0.3
- 14 -
C2
46
51.11
51.44
2.40
4.09
5
8
C1
R.1
z-score
62.05
-0.2
63.62
0.1
63.98
0.2
63.49
0.1
56.95
-1.2
62.40
-0.1
64.16
0.3
62.15
-0.1
65.50
0.5
64.32
0.3
66.45
0.7
62.31
-0.1
60.11
-0.5
64.11
0.2
63.74
0.2
51.34
-2.3
56.32
-1.3
56.11
-1.3
62.35
-0.1
63.96
0.2
64.89
0.4
62.33
-0.1
C2
R.2
z-score
50.80
-0.1
51.34
0.1
52.05
0.2
51.43
0.1
69.30
59.76
1.3
-0.6
54.20
52.12
49.74
53.50
51.60
54.68
50.43
0.8
0.2
-0.3
0.6
0.1
0.9
-0.2
51.82
51.44
60.84
44.47
44.37
50.91
50.78
51.72
49.72
0.2
0.1
2.4
-1.6
-1.6
-0.0
-0.1
0.1
-0.3
55.43
49.89
1.1
-0.3
Unit: mg/L
Distribution plot
C2 (mg/L)
65
55
45
(34.3; 41.5)
35
40
50
60
70
80
C1 (mg/L)
Youden plot
z-score
4
2
C1
C2
z +3
z +2
z 0
z -2
z -3
=
SO4
SO
4
0
-2
-6
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
-4
Lab.
- 15 -
64
62
60
56
mg/L
58
52
54
48
50
44
mg/L
46
40
C2
38
70
68
66
64
62
60
58
56
54
52
50
48
436
6
Lab.
C1
18
16
14
12
10
8
6
4
2
0
42
20
18
16
14
12
10
8
6
4
2
0
434
4
Lab.
Analyte: SULPHATE
Analyte: SODIUM
Unit: mg/L
61
C1
37
3.79
3.82
0.27
0.30
7
8
Robust average mg/L
Median mg/L
Lab.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
C1
R.1
z-score
C2
R.2
z-score
3.82
4.05
0.1
0.9
3.23
3.45
-0.0
0.8
3.85
3.73
3.59
3.88
4.12
3.09
3.55
3.98
3.85
3.83
3.74
3.27
3.68
1.53
0.2
-0.2
-0.6
0.3
1.1
-2.3
-0.8
0.6
0.2
0.1
-0.2
-1.7
-0.3
-7.4
3.27
3.17
3.05
3.26
3.47
3.67
2.95
3.79
3.24
3.19
3.18
2.87
3.10
1.23
0.1
-0.3
-0.7
0.1
0.9
1.7
-1.1
2.1
0.0
-0.2
-0.2
-1.4
-0.5
-7.8
2.62
4.30
3.51
-3.8
1.7
-0.9
1.83
3.37
2.99
-5.4
0.5
-1.0
5.50
5.7
5.00
6.8
Lab.
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
- 16 -
C2
36
3.24
3.23
0.26
0.26
8
8
C1
R.1
z-score
C2
R.2
z-score
3.85
3.67
4.03
0.2
-0.4
0.8
3.20
3.06
3.45
-0.1
-0.7
0.8
3.95
3.58
0.5
-0.7
3.30
3.02
0.2
-0.8
3.90
3.67
3.81
3.91
3.50
0.4
-0.4
0.1
0.4
-0.9
3.20
3.09
3.80
3.34
-0.1
-0.6
2.2
0.4
3.50
4.33
3.89
3.78
-0.9
1.8
0.3
-0.0
2.92
3.71
3.23
3.22
-1.2
1.8
-0.0
-0.1
3.80
3.89
0.0
0.3
3.22
3.31
-0.1
0.3
4.07
0.9
3.38
0.6
8
6
4
-8
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
z-score
C2 (mg/L)
2
3.
1
2
4
4.
mg/L
mg/L
Distribution plot
6
5
4
3
2
1
3
- 17 4
5
C1
C2
z +3
z +2
z 0
z -2
z -3
Lab.
6
C1 (mg/L)
Youden plot
Na+
Na
2
0
-2
-4
-6
5.0
4.
0
4.8
3.
8
3.
6
3.
4
0
3.
0
2
0
3.
2
4
2
2.
8
4
2.
6
6
2.
2
10
2.
4
12
2.
0
C1
1.
8
8
Lab.
14
1.
6
1.4
1.
4
1.2
5.6
45.4
.6
0
2
4.
3.
4.
6
8
3.
4
3.
3.
8
0
2.
4
6
10
2.
12
2.
2.
0
1.4
21.6
.2
Lab.
Analyte: SODIUM
Unit: mg/L
14
C2
8
6
Analyte: POTASSIUM
Unit: mg/L
61
C1
38
2.38
2.39
0.19
0.24
8
10
Robust average mg/L
Median mg/L
Lab.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
R.1
2.25
2.46
2.52
C1
z-score
-0.6
0.3
0.6
R.2
1.62
1.81
1.85
C2
z-score
-0.6
0.5
0.7
2.43
2.25
2.42
2.34
2.50
2.17
2.34
2.22
2.39
2.49
2.38
6.14
2.08
2.55
0.2
-0.6
0.1
-0.2
0.5
-0.9
-0.2
-0.7
0.0
0.4
-0.0
15.8
-1.3
0.7
1.85
1.61
1.77
1.62
1.80
1.51
1.75
1.50
1.71
1.75
1.74
1.89
2.08
1.86
0.7
-0.7
0.2
-0.6
0.4
-1.3
0.1
-1.3
-0.1
0.1
0.1
0.9
2.0
0.8
2.57
2.28
2.84
0.8
-0.4
1.9
1.82
1.66
2.04
0.5
-0.4
1.8
2.96
2.4
1.92
1.1
Lab.
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
- 18 -
C2
37
1.73
1.74
0.15
0.17
8
10
C1
R.1
z-score
C2
R.2
z-score
2.18
2.35
2.47
-0.9
-0.1
0.4
1.54
1.71
1.85
-1.1
-0.1
0.7
2.57
2.10
0.8
-1.2
1.86
1.57
0.8
-0.9
2.50
2.33
2.36
2.53
1.77
0.5
-0.2
-0.1
0.6
-2.6
1.80
1.69
1.69
1.89
0.4
-0.2
-0.2
0.9
2.18
2.41
2.39
2.33
-0.9
0.1
0.0
-0.2
1.58
1.70
1.74
1.63
-0.9
-0.2
0.1
-0.6
2.34
2.13
-0.2
-1.1
1.70
1.05
-0.2
-3.9
2.89
2.1
1.58
-0.9
Analyte: POTASSIUM
Unit: mg/L
10
12
C1
10
Lab.
6
6
4
4
2
2
mg/L
mg/L
Distribution plot
2.4
2.2
C2 (mg/L)
2.0
(6.14; 1.89)
1.8
1.6
1.4
1.2
1.0
1.5
2.0
2.5
3.0
3.5
C1 (mg/L)
Youden plot
z-score
KK+
18
15
12
9
6
C1
C2
z +3
z +2
z 0
z -2
z -3
3
0
-6
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
-3
Lab.
- 19 -
2.
1
2.
2
2.
0
1.
9
1.
7
1.
8
1.
6
1.
5
1.
3
1.
4
1.
2
1.
1
0.
9
6.2
3.
1
6.1
3.
0
2.
9
2.
7
2.
8
2.
6
2.
5
2.
4
2.
2
2.
3
2.
1
2.
0
1.
9
1.
8
1.
0
0
0
1.
7
Lab.
C2
8
8
Analyte: MAGNESIUM
Unit: mg/L
61
C1
37
7.09
7.08
0.29
0.57
4
8
Robust average mg/L
Median mg/L
Lab.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
R.1
7.09
7.04
7.86
C1
z-score
0.0
-0.1
1.4
C2
R.2
z-score
11.85
0.1
11.63
-0.2
11.96
0.2
6.40
6.94
6.92
6.82
7.74
6.96
6.90
5.96
7.21
7.38
7.10
7.47
-1.2
-0.3
-0.3
-0.5
1.1
-0.2
-0.3
-2.0
0.2
0.5
0.0
0.7
10.85
11.53
11.50
11.40
12.86
11.52
11.43
8.77
11.95
12.29
11.60
13.18
-1.0
-0.3
-0.3
-0.4
1.2
-0.3
-0.4
-3.2
0.2
0.5
-0.2
1.5
6.68
-0.7
10.78
-1.1
7.23
7.30
7.30
0.2
0.4
0.4
13.30
12.37
12.05
1.6
0.6
0.3
6.87
-0.4
11.45
-0.3
Lab.
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
- 20 -
C2
36
11.78
11.74
0.46
0.94
4
8
C1
R.1
z-score
C2
R.2
z-score
7.11
7.07
7.12
0.0
-0.0
0.1
11.92
11.74
11.74
0.2
-0.0
-0.0
7.28
7.08
0.3
-0.0
12.06
12.03
0.3
0.3
7.10
7.19
7.02
6.81
12.69
0.0
0.2
-0.1
-0.5
9.9
11.80
12.03
12.14
11.57
0.0
0.3
0.4
-0.2
7.97
7.06
7.06
6.87
1.6
-0.1
-0.1
-0.4
13.03
11.65
11.43
11.60
1.3
-0.1
-0.4
-0.2
6.90
7.37
-0.3
0.5
11.36
11.96
-0.4
0.2
6.19
-1.6
11.23
-0.6
10
8
6
-4
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
z-score
C2 (mg/L)
8
6.
5
0
8.
6
9.
7
8.5
10
.0
8.8
10
.3
10
.6
10
.9
11
.2
11
.5
11
.8
12
.1
12
.4
12
.7
13
.0
13
.3
13
.6
12.8
8.
2
12.6
6
8
7.
7.
7.
2
4
7.
0
6.
7.
4
6
6.
0
2
6.
8
6
Lab.
10
6.
6
8
5.
5.
Lab.
Analyte: MAGNESIUM
Unit: mg/L
14
12
12
C1
10
8
4
2
0
7
- 21 -
C2
6
4
2
0
mg/L
mg/L
Distribution plot
15
14
13
12
11
10
9
8
8
C1
C2
z +3
z +2
z 0
z -2
z -3
Lab.
9
C1 (mg/L)
Youden plot
Mg++
Mg
4
2
0
-2
Analyte: CALCIUM
Unit: mg/L
61
C1
38
45.86
45.75
3.20
3.67
7
8
Robust average mg/L
Median mg/L
Lab.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
C1
R.1
z-score
45.92
0.0
45.06
-0.2
46.84
0.3
C2
R.2
z-score
44.12
-0.0
43.37
-0.2
46.11
0.5
41.40
46.64
45.31
44.28
50.93
45.81
45.98
49.01
45.17
46.34
44.50
50.10
43.99
38.52
-1.2
0.2
-0.2
-0.4
1.4
-0.0
0.0
0.9
-0.2
0.1
-0.4
1.2
-0.5
-2.0
42.30
45.55
43.62
43.20
49.08
44.03
44.25
50.10
43.51
44.68
42.80
50.73
42.13
37.00
-0.6
0.4
-0.2
-0.3
1.4
-0.1
-0.0
1.7
-0.2
0.1
-0.4
1.8
-0.6
-2.0
58.60
36.93
44.94
3.5
-2.4
-0.3
58.00
39.82
43.27
3.9
-1.3
-0.3
41.77
-1.1
41.31
-0.8
Lab.
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
- 22 -
C2
37
44.25
44.03
2.61
3.54
6
8
C1
R.1
z-score
C2
R.2
z-score
43.83
45.72
43.10
-0.6
-0.0
-0.8
43.25
44.07
41.99
-0.3
-0.1
-0.6
48.07
51.30
0.6
1.5
46.02
50.00
0.5
1.6
47.20
46.05
48.07
45.36
51.00
0.4
0.1
0.6
-0.1
1.4
45.40
44.24
46.85
43.86
0.3
-0.0
0.7
-0.1
52.20
44.65
47.06
45.78
1.7
-0.3
0.3
-0.0
50.00
42.87
44.39
44.53
1.6
-0.4
0.0
0.1
45.33
40.10
-0.1
-1.6
43.75
35.12
-0.1
-2.6
42.85
-0.8
41.94
-0.7
Analyte: CALCIUM
Unit: mg/L
14
16
C1
14
10
Lab.
10
8
6
8
6
mg/L
mg/L
Distribution plot
60
55
C2 (mg/L)
50
45
40
35
30
30
35
40
45
50
55
60
65
C1 (mg/L)
Youden plot
z-score
6
4
C1
C2
z +3
z +2
z 0
z -2
z -3
Ca++
Ca
2
0
-4
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
-2
Lab.
- 23 -
58
54
56
52
50
48
46
44
42
38
40
36
32
60
58
56
52
54
48
50
44
46
40
0
42
0
38
2
36
2
34
4
4
34
Lab.
C2
12
12
5. DISCUSSION
Fifty out of 61 registered laboratories submitted their results. The number of results received for
samples C1 and C2 for anions and cations is 42-48 and 36-38, respectively.
Ion chromatography was the most used analytical methods for anions (92-98%) and cations (ca.
70%). No comparison among the methods was performed.
Analytical
technique
Specific method
Chloride Nitrate Sulphate
Ion chromatography
APAT IRSA 4020
11
13
13
Ion chromatography
EPA 300.1 A
3
3
3
Ion chromatography
ISO 10304-1
8
7
8
Ion chromatography
ISS CBB 037
7
7
7
Ion chromatography
A.P.H.A. St. Methods. 2005 4110 B
3
3
3
Ion chromatography
Not available
13
11
13
Titration
APAT IRSA 4090 A1
1
Titration
ASTM D 512-04
1
Spectrophotometry
Not available
Not available
Not available
1
2
1
Analytical technique
Method
Sodium Potassium Calcium Magnesium
Ion chromatography
APAT IRSA 3030
10
10
10
10
Ion chromatography
ISO 14911
6
6
6
6
Ion chromatography
ISS CBB 038
3
3
3
3
Ion chromatography
Not available
9
9
10
9
ICP OES
APAT IRSA 3020
1
1
1
1
ICP OES
ISO 11885
2
2
2
2
ICP OES
Standard Methods
2005 3120 B
1
1
1
1
ICP OES
Not available
1
2
2
2
Atomic absorption
APAT IRSA 3270
1
Atomic absorption
APAT IRSA 3240
Atomic absorption
APAT IRSA 3180
Atomic absorption
APAT IRSA 3130
Atomic absorption
Not available
1
1
1
2
- 24 -
2
1
1
Anion and cation concentrations were representative of most drinking waters. Values were low, but
in the usual analytical range of ion chromatography.
Proficiency was good for nitrate, sulphate, calcium and magnesium, with only 1-2 laboratories
obtaining z-scores outside the range -3/+3. In the case of chloride, calcium and magnesium
variability was higher and 3-5 laboratories obtained z-scores higher than 3 or lower than -3.
Systematic errors prevailed, mainly for chloride, sodium and potassium, and may be related to
problems in standard preparation or in calibration, or to the contamination of standard solutions or
samples.
Sodium contamination may also be due to sodium release from glass containers and vials, while
potassium may suffer contamination from the potassium hydroxide used for the determination of
anions.
6. CONCLUSIONS
The overall proficiency of the laboratories was good, with a small number of z-scores outside the
range -3/+3, and robust standard deviations smaller than the assigned values, , which were
evaluated on the basis of the official analytical methods. In particular for sulphate and magnesium.
Youden plots showed that systematic errors prevail, indicating that further improvement is possible
by controlling the quality of standards, sample handling and instrument calibration.
The analysis of certified samples and the use of control charts may help to improve analytical
proficiency.
The use of a website for uploading the results allowed an immediate check of the results by each
lab, increasing the utility of the proficiency tests for improving analytical quality.
- 25 -
7. REFERENCES
A.P.H.A., A.W.W.A., W.E.F. 2005. Standard Methods for the examination of water and
wastewater. Method 4110 B. Determination of anions by ion chromatography. Am. Publ.
Health Ass., Washington.
APAT IRSA-CNR. 2003. Metodi analitici per le acque. 3030. Determinazione di cationi (sodio,
ammonio, potassio, magnesio, calcio) mediante cromatografia ionica. Vol. 1. 1153 pp.
APAT IRSA-CNR. 2003. Metodi analitici per le acque. 3020. Determinazione di elementi chimici
mediante spettroscopia di emissione con sorgente al plasma (ICP-OES). Vol. 1. 1153 pp.
APAT IRSA-CNR. 2003. Metodi analitici per le acque. 3180. Magnesio (F-AAS). Vol. 1. 1153 pp.
APAT IRSA-CNR. 2003. Metodi analitici per le acque. 3130. Calcio (F-AAS). Vol. 1. 1153 pp.
APAT IRSA-CNR. 2003. Metodi analitici per le acque. 3270. Sodio (F-AAS). Vol. 1. 1153 pp.
APAT IRSA-CNR. 2003. Metodi analitici per le acque. 3240. Potassio (F-AAS). Vol. 1. 1153 pp.
APAT IRSA-CNR. 2003. Metodi analitici per le acque. 4020. Anioni (fluoruro, cloruro, nitrito,
bromuro, nitrato, fosfato e solfato) in cromatografia ionica. Vol. 2. 1153 pp.
APAT IRSA-CNR. 2003. Metodi analitici per le acque. 4030. Azoto ammoniacale. Metodo A1.
Determinazione spettrofotometrica all’indofenolo. Vol. 2. 1153 pp.
EPA 300.1 1997. Determination of inorganic anions in drinking water by ion chromatography.
USEPA Office of Water.
ILAC-G13:08/2007. Guidelines for the Requirements for the Competence of Providers of
Proficiency Testing Schemes.
ISO/IEC 43-1:1997. Proficiency testing by interlaboratory comparisons. Part 1: Development and
operation of proficiency testing schemes.
ISO 14911:1998. Water quality. Determination of dissolved Li+, Na+, NH4+, K+, Mn2+, Ca2+, Mg2+,
Sr2+ and Ba2+ using ion chromatography. Method for water and waste water.
ISO 13528:2005. Statistical methods for use in proficiency testing by interlaboratory comparisons.
ISO/IEC 17025:2005. General requirements for the competence of testing and calibration
laboratories.
ISO 10304-1: 2007. Water quality. Determination of dissolved anions by liquid chromatography of
ions. Part. 1. Determination of bromide, chloride, fluoride, nitrate, phosphate and sulphate.
ISO/IEC 17043:2010. Conformity assessment. General requirements for proficiency testing.
ISS CBB 037. Istituto Superiore di Sanità. Metodi analitici di riferimento per le acque destinate al
consumo umano ai sensi del DL.vo 31/2001. Metodi chimici. Bromuro, clorito, cloruro,
fluoruro, fosfato, ioduro, nitrato, nitrito, solfato: metodo per cromatografia ionica. Rapporti
ISTISAN 07/31.
ISS CBB 038. Istituto Superiore di Sanità. Metodi analitici di riferimento per le acque destinate al
consumo umano ai sensi del DL.vo 31/2001. Metodi chimici. Calcio, litio, magnesio, potassio,
sodio: metodo per cromatografia ionica. Rapporto ISTISAN 07/31.
Thompson M., S. L. R. Ellison and R. Wood. 2006. The international harmonized protocol for the
proficiency testing of analytical chemistry laboratories (IUPAC Technical Report). Pure Appl.
Chem., 78: 1, 145-196.
Tholen D., N. Boley, J. Gun-Monro, J. Gust, W. Korth, M. Noble, P. Petions and D. Wruck. 2007.
ILAC discussion paper on homogeneity and stability testing. ILAC Proficiency testing
consultative group, task force on H&S testing.
- 26 -
Tool4PT Pro software for interlaboratory comparison tests. Proficiency testing (PT) schemes.
Cortez & Mermayde version 1.06.10 2009.
UNI ISO 5725:1998. Accuratezza (esattezza e precisione) dei risultati e dei metodi di misurazione.
Parte 5: Metodi alternativi per la determinazione della precisione di un metodo di misurazione
normalizzato.
UNICHIM 2005. Prova interlaboratorio UNICHIM – Fondazione AMGA “Acque di scarico” 15°
ciclo. Rapporto.
UNICHIM 2006. Prova interlaboratorio UNICHIM – Fondazione AMGA “Acque consumo umano”
19° ciclo. Rapporto.
Youden, W.J. 1959. Graphical diagnosis of interlaboratory test results. Industrial Quality Control,
15-24.
Youden, W.J. and E.H. Steiner. 1975. Statistical manual of the Association of Official Analytical
Chemists. Statistical Techniques for Collaborative Tests. Arlington.
- 27 -

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