ISSN 0386-4049

TECHNICAL REPORTS OF THE METEOROLOGICAL RESEARCH INSTITUTE No. 50

2003 Intercomparison Exercise for Reference Material for
Nutrients in Seawater in a Seawater Matrix
Michio Aoyama

気象研究所技術報告第50号
栄養塩測定用海水組成標準の2003年国際共同実験報告
青山道夫

気象研究所
METEOROLOGICAL RESEARCH INSTITUTE, JAPANDECEMBER 2006

dummy2003 Intercomparison Exercise for Reference Material for
Nutrients in Seawater in a Seawater Matrix
栄養塩測定用海水組成標準の2003年国際共同実験報告

Michio Aoyama
青山道夫

dummyPreface
The analysis of nitrate, nitrite, phosphate, and silicic acid, in seawater has been carriedout for more than 50 years. The concentrations of nutrients in seawater are important forvarious oceanographic uses. The climatological distribution of nutrients in the ocean has
been established over the past 4 decades. In the 1990s, accurate concentration data fornutrients in seawater were required by oceanographers to detect the temporal variabilityof ocean nutrients derived from climate change. Although high-accuracy, high-precision
methods for nutrient analysis were available in the 1990s, such methods were notapplied to analysis of nutrients in seawater, primarily because of a lack of a suitablereference material. In this study, Aoyama et al. have succeeded in preparing a referencematerial based on natural seawater. This reference material has passed homogeneity andlong-term stability tests. To evaluate the reference material, an intercomparison between
18 laboratories was conducted. The results of the intercomparison, summarized in thisreport, indicate that a reference material is needed to establish traceability of nutrient
data from laboratories and that comparable nutrient data sets sufficient for detecting
variability can be established in the field of oceanography.

Katsumi Hirose
Director
Geochemical Research Department

dummyAbstract
Autoclaved natural seawater was used to prepare samples for an interlaboratorycomparison exercise for a reference material for nutrients in seawater. Sample
homogeneity was confirmed by repeatability of measurement. Sets of 6 samples
covering a concentration range greater than that in previous intercomparisons wereprepared. Concentrations were 0 –38 µmol kg–1 for nitrate, 0.0–0.9 µmol kg–1 for nitrite,
0.1–2.7 µmol kg–1 for phosphate, and 2–136 µmol kg–1 for silicic acid. A total of 18 setsof samples were distributed to 18 laboratories in 5 countries. Results were returned by
17 laboratories in 5 countries. Although consensus concentrations were obtained for the
6 samples, the standard deviations were 4.5 times and more than 10 times greater thanthose of the homogeneities for phosphate and silicic acid, respectively. For nitrate, thestandard deviations were only about double the homogeneities. These results indicatethat variability in in-house standards of the participating laboratories — rather thananalytical precision — is the primary source of interlaboratory discrepancy. Therefore
use of a certified reference material for nutrients in seawater is essential for establishing
nutrient data sets that can be compared across laboratories, especially for silicic acid andphosphate in seawater.

dummyContents
1
2
3
4
5
6

Introduction …………………………………………...
Samples ………………………………………………..
Participants and response ……………………………...
Statistical treatment …………………………………...
Results ………………………………………………...
Conclusions …………………………………………...

1
2
4
6
7
43

Appendices
I
II
III
IV

List of participating laboratories ……………………...
Results submitted by participating laboratories ………
Documents ……………………………………………
History of intercomparison exercises ………………...

47
51
77
85

List of Tables and Figures
TablesTable 1

Homogeneity of sample 3 and analytical precision

2

Table 2

Summary of responses from participants

4

Table 3

Median, mean, and standard deviation for the 6 samples

7

Table 4Comparison between consensus standard deviation of sample 3 and homogeneityof sample 3

8Table 5

Summary of Z-scores

9

FiguresFigure 1

Samples sent to participants

3

Figure 2

Nitrate results for sample 6: concentration versus laboratory number sorted byconcentration.

10

Figure 3

Phosphate results for sample 6: concentration versus laboratory number sorted byconcentration.

11

Figure 4

Silicic acid results for sample 3: concentration versus laboratory number sorted
by concentration

12

Figure 5-1

Nitrite results for sample 1: concentration versus laboratory number (upper panel)Frequency distribution of concentration (lower panel).

13

Figure 5-2

Nitrite results for sample 2: concentration versus laboratory number (upper panel)Frequency distribution of concentration (lower panel).

14

Figure 5-3

Nitrite results for sample 3: concentration versus laboratory number (upper panel)Frequency distribution of concentration (lower panel).

15

Figure 5-4

Nitrite results for sample 4: concentration versus laboratory number (upper panel)Frequency distribution of concentration (lower panel).

16

Figure 5-5

Nitrite results for sample 5: concentration versus laboratory number (upper panel)Frequency distribution of concentration (lower panel).

17

Figure 5-6

Nitrite results for sample 6: concentration versus laboratory number (upper panel)Frequency distribution of concentration (lower panel).

18

Figure 6-1

Nitrate results for sample 1: concentration versus laboratory number (upper
panel)
Frequency distribution of concentration (lower panel).

19

Figure 6-2

Nitrate results for sample 2: concentration versus laboratory number (upper
panel)
Frequency distribution of concentration (lower panel).

20

Figure 6-3

Nitrate results for sample 3: concentration versus laboratory number (upper
panel)
Frequency distribution of concentration (lower panel).

21

Figure 6-4

Nitrate results for sample 4: concentration versus laboratory number (upper
panel)
Frequency distribution of concentration (lower panel).

22

Figure 6-5

Nitrate results for sample 5: concentration versus laboratory number (upper
panel)
Frequency distribution of concentration (lower panel).

23

Figure 6-6

Nitrate results for sample 6: concentration versus laboratory number (upper
panel)
Frequency distribution of concentration (lower panel).

24

Figure 7-1

Nitrate + nitrite results for sample 1: concentration versus laboratory number(upper panel)Frequency distribution of concentration (lower panel).

25

Figure 7-2

Nitrate + nitrite results for sample 2: concentration versus laboratory number(upper panel)Frequency distribution of concentration (lower panel).

26

Figure 7-3

Nitrate + nitrite results for sample 3: concentration versus laboratory number(upper panel)Frequency distribution of concentration (lower panel).

27

Figure 7-4

Nitrate + nitrite results for sample 4: concentration versus laboratory number(upper panel)Frequency distribution of concentration (lower panel).

28

Figure 7-5

Nitrate + nitrite results for sample 5: concentration versus laboratory number(upper panel)Frequency distribution of concentration (lower panel).

29

Figure 7-6

Nitrate + nitrite results for sample 6: concentration versus laboratory number(upper panel)Frequency distribution of concentration (lower panel).

30

Figure 8-1

Phosphate results for sample 1: concentration versus laboratory number (upper
panel)
Frequency distribution of concentration (lower panel).

31

Figure 8-2

Phosphate results for sample 2: concentration versus laboratory number (upper
panel)
Frequency distribution of concentration (lower panel).

32

Figure 8-3

Phosphate results for sample 3: concentration versus laboratory number (upper
panel)
Frequency distribution of concentration (lower panel).

33

Figure 8-4

Phosphate results for sample 4: concentration versus laboratory number (upper
panel)
Frequency distribution of concentration (lower panel).

34

Figure 8-5

Phosphate results for sample 5: concentration versus laboratory number (upper
panel)
Frequency distribution of concentration (lower panel).

35

Figure 8-6

Phosphate results for sample 6: concentration versus laboratory number (upper
panel)
Frequency distribution of concentration (lower panel).

36

Figure 9-1

Silicic acid results for sample 1: concentration versus laboratory number (upper
panel)
Frequency distribution of concentration (lower panel).

37

Figure 9-2

Silicic acid results for sample 2: concentration versus laboratory number (upper
panel)
Frequency distribution of concentration (lower panel).

38

Figure 9-3

Silicic acid results for sample 3: concentration versus laboratory number (upper
panel)
Frequency distribution of concentration (lower panel).

39

Figure 9-4

Silicic acid results for sample 4: concentration versus laboratory number (upper
panel)
Frequency distribution of concentration (lower panel).

40

Figure 9-5

Silicic acid results for sample 5: concentration versus laboratory number (upper
panel)
Frequency distribution of concentration (lower panel).

41

Figure 9-6

Silicic acid results for sample 6: concentration versus laboratory number (upper
panel)
Frequency distribution of concentration (lower panel).

42

2003 RMNS Intercomparison

1. Introduction
The objective of this effort was to develop a reference standard for analysis ofnutrients in seawater that would ensure comparability of analytical data collected bydifferent laboratories and facilitate onboard analysis of nutrients in seawater. Highly
accurate nutrient data could thus become available. We have focused on developing acertified reference material for nutrients in seawater in a seawater matrix. The
IOC–IAEA–UNEP Group of Experts on Standards and Reference Materials (UNESCO,
1991, 1992) have clearly stated the need to place a high priority on developing areference material for nutrients in seawater (hereafter RMNS).
Currently, the only way to ensure comparability among nutrient analyses performedby different laboratories is to conduct interlaboratory comparison experiments thatprovide consensus values plus uncertainties for nutrient concentrations. The ICES
Nutrient Intercomparison has been done 5 times since 1965 (UNESCO, 1965, 1967;
ICES, 1967, 1977; Kirkwood et al., 1991; Aminot and Kirkwood, 1995), and efforts toensure comparability among analyses in this field have been carried out for 30 years. In
2000 and 2002, NOAA/NRC intercomparisons between laboratories in the UnitedStates and Canada were carried out to certify a seawater certified reference material for
nutrients as MOOS-1 provided by National Research Council Canada (Willie andClancy, 2000; Clancy and Willie, 2003). The first certified reference material for
nutrients in seawater in a seawater matrix was provided as MOOS-1 in 2003 by the
National Research Council of Canada (Clancy and Willie, 2004). However, the nutrient
concentrations of MOOS-1 were too low for analysis of nutrients in Pacific Ocean
seawater and did not cover the concentrations of nutrients in other seawater samples.
Thus, in 2003 the present exercise was planned and conducted to make progress inthis field. This intercomparison has two advantages over previous intercomparisons.
First, nutrient concentrations of the distributed samples were set to cover theconcentration range of nutrients in the Pacific Ocean, which has the highest nutrient
concentrations among the open oceans of the world. Second, the distributed samples
were prepared in a natural seawater matrix in a single bottle so that 4 determinands(nitrate, nitrite, phosphate, and silicic acid) could be simultaneously analyzed.
This report describes the exercise in detail and summarizes the results reported by theparticipants.

1

2003 RMNS Intercomparison

2. Samples
2.1 Sample preparation and timetable for intercomparison
Progress in preparing RMNS samples has been made over the past 10 years (Aoyama
et al., 2006). For this study, seawater in a stainless steel container (volume 40 to 200 L)
was autoclaved twice at 120 ºC for 2 h. A sample for analysis consisted of 90 mL of the
autoclaved seawater in a polypropylene bottle. This procedure for preparing samples isbased on a previously reported method for preparing a reference material for thedetermination of nutrients in seawater (Aminot and Kerouel, 1991, 1995). Sample
homogeneity was confirmed by repeatability of measurement. Long-term storage of our
RMNS samples for up to 4 years showed that the homogeneities and concentrations of
nutrients were maintained for about 4 years (Aoyama et al., 2006).
The samples sent to the participants were prepared in 2001 and 2002. The nutrient
concentrations in the samples were confirmed to be stable for at least several months
before the samples were sent to the participants between March 2002 and December
2002. All participants had analyzed the samples and returned their results by April
2003.
2.2 Selection of determinands
The determinands of interest were Nitrate (or Nitrate + Nitrite), Nitrite, Phosphate,and Silicic acid.
2.3 Sample homogeneity
The homogeneities of the samples were measured separately. The homogeneities for
30 bottles of sample 3 are listed in table 1. Analytical precision was also estimated for
30 samples of natural seawater whose nutrient concentrations were similar to those ofsample 3.
Table 1 Homogeneity of sample 3 and analytical precision

Homogeneity of sample 3 (%)
Analytical precision (CV %)Nitrate + nitrite
0.44
0.34

Phosphate
0.80
0.32

Silicic acid
0.15
0.16

Note: The concentrations of nutrients in natural seawater for the simultaneous analyses
were 43 µmol kg–1 for nitrate + nitrite, 3.1 µmol kg–1 for phosphate, and 148 µmol kg–1
for silicic acid.

2

2003 RMNS Intercomparison

Figure 1 Samples sent to participants
For sample 3, the homogeneities for nitrate + nitrite, phosphate, and silicic acid
were good considering the analytical precision for the analysis of natural seawater (table1). Since the concentrations of nutrients in sample 3 were similar to those in the natural
seawater used in this study, the homogeneities for nitrate + nitrite and silicic acid wereof the same order of magnitude as, or better than, the analytical precision. The
homogeneity for phosphate had a larger scattering, which was attributed to the nature of
the RMNS sample itself, and not any analytical problem.
Samples 1, 2, 4, 5, and 6 were not analyzed due to a limited number of samples. It is,however, safe to assume that these samples were similar in nature to sample 3, since all
samples were prepared by the same process.

3

2003 RMNS Intercomparison

3. Participants and response
By November 2002, 18 laboratories in 5 countries had replied to the call forparticipants. A total of 18 sets of samples were distributed. Appendix I lists theparticipants.
Results were submitted by 17 laboratories; a set of samples was returned by 1laboratory because it was unable to meet the deadline for submission of results. One
participant did not report results for nitrite. Four participants did not report results fornitrate, but did report results for nitrate + nitrite. In these cases, nitrate concentrations
were calculated from the nitrate + nitrite and nitrite concentrations. Four participants did
not report results for silicic acid.
The responses from the participants are summarized in table 2.

4

2003 RMNS Intercomparison

Table 2 Summary of responses from participants
Nutrient

Sample ID

Number of results
Received
Statistically treated
15
16
15
17
15
17
15
16
15
17
15
17

Nitrate + nitrite

1
2
3
4
5
6

Nitrite

1
2
3
4
5
6

16
16
16
16
16
16

15
16
14
14
16
16

Nitrate

1
2
3
4
5
6

13
13
13
13
13
13

15
16
15
15
16
16

Phosphate

1
2
3
4
5
6

17
17
17
17
17
17

17
17
17
17
17
17

Silicic acid

1
2
3
4
5
6

13
13
13
13
13
13

13
13
13
13
13
13

5

2003 RMNS Intercomparison

4. Statistical treatment
4.1 Consensus mean, median, and standard deviation
Successive t-tests at the 95% confidence level were applied to the results to remove
outliers before estimating the consensus mean, median, and standard deviation. Tests
were applied until a stable mean was reached, and stable means were obtained at thesecond test for all sets of results.
4.2 Calculation of Z-scoresZ-scores were used to evaluate the performance of laboratories.
The Z-score for each analysis is defined as
Zpar = ABS((Cpar – Cconsensus)/Ppar)(1)

where Zpar is the Z-score for an analysis; Cpar is the concentration of an RMNS sample
measured by a laboratory for the parameter of interest (nitrate, phosphate, or silicate);
Cconsensus is the consensus sample concentration for the parameter of interest, describedin section 4.1; and Ppar is the standard deviation at the sample concentration for theparameter of interest.
Averages of the Z-scores for the 6 samples were calculated for nitrate (ZNO3), nitrite(ZNO2), phosphate (Zp), and silicic acid (Zs).
Averages of Z-scores for each laboratory were calculated for ZNO3 + Zp and
ZNO3 + Zp + Zs.

6

2003 RMNS Intercomparison

5. Results
5.1 Raw results
Results reported by the participants are summarized in Appendix II.
5.2 Consensus medians, means, and standard deviations
The consensus medians, means, and standard deviations (table 3) were calculatedusing the data that passed the successive t-test applications described in section 4.1. The
consensus means and medians are in excellent agreement for all parameters for all
samples.
Table 3 Consensus medians, means, and standard deviations for the 6 samples
Nitrite(µmol kg–1)
Sample Median MeanSD

Nitrate(µmol kg–1)
Median MeanSD

Nitrate + nitrite(µmol kg–1)
Median Mean
SD

1

0.02

0.02

0.01

0.05

0.04

0.03

0.07

0.06

0.04

2

0.14

0.13

0.06

17.50

17.40

0.70

17.70

17.60

0.60

3

0.01

0.01

0.01

35.40

35.30

0.30

35.40

35.40

0.30

4

0.02

0.02

0.02

0.02

0.02

0.03

0.04

0.04

0.04

5

0.90

0.91

0.02

13.00

13.10

0.20

14.00

14.00

0.20

6

0.24

0.23

0.09

38.40

38.20

1.10

38.50

38.40

1.00

SamplePhosphate(µmol kg–1)
Median MeanSD

Silicic acid(µmol kg–1)
Median Mean
SD

1

0.09

0.09

0.02

2.03

2.06

0.23

2

1.25

1.25

0.04

66.30

66.40

2.00

3

2.14

2.14

0.07

136.00135.70

2.30

4

0.09

0.09

0.03

2.09

2.09

0.31

5

1.10

1.10

0.04

73.40

73.80

2.40

6

2.74

2.74

0.10

134.00133.802.50

7

2003 RMNS Intercomparison

5.3 Scatter plots and histograms of the results
Scatter plots for nitrate, phosphate, and silicic acid are shown in figures 2–4,
respectively. For nitrate and phosphate, laboratories were sorted by order of reported
concentration of nitrate and phosphate in sample 6, for which the nitrate and phosphateconcentrations were the highest in the 6 samples sent to the participants. For silicic acid,laboratories were sorted by order of reported silicic acid concentration in sample 3, forwhich the silicic acid concentration was the highest in the 6 samples. In figures 2–4,
error bars appear when they were reported.
Scatter plots and histograms for each parameter of each sample are shown in figures
5-1 to 9-6. The consensus value is shown at the top of each figure. In the scatter plots,
error bars appear when they were reported. Each histogram interval is set to equal thecorresponding standard deviation shown in table 4.
5.4 Comparison between consensus standard deviation of sample 3 and homogeneity ofsample 3
For nitrate, the consensus standard deviations were only about double thehomogeneities (table 4). For phosphate, the consensus standard deviations were 4.5
times greater than that of the homogeneities, and for silicic acid, the consensus standard
deviation was more than 10 times greater than that of the homogeneities.
Table 4 Comparison between consensus standard deviation of sample 3 andhomogeneity of sample 3
NitratePhosphate

Silicic acid

Homogeneity (%)

0.44

0.80

0.15

Standard deviation (CV %)

1.00

3.50

1.70

5.5 Z-scoresZ-scores, computed according to the method described in section 4.2, are summarized intable 5.
Laboratories 3, 5, 6, and 15 showed consistently good performance throughout therange of nutrients.

8

2003 RMNS Intercomparison

Table 5 Summary of Z-scores
Laboratory

ZNO3

ZNO2

Zp

Zs

1

22.970

2.07

1.02

1.34

11.99

8.44

2

3.710

1.43

1.24

6.04

2.48

3.66

3

0.370

0.44

0.41

0.65

0.39

0.48

4

1.020

0.63

0.97

0.52

1.00

0.84

5

0.460

0.41

0.95

no data

0.71

not available

6

0.330

0.39

0.63

0.08

0.48

0.35

7

0.710

0.77

1.16

0.96

0.93

0.94

8

0.900

0.97

0.38

1.02

0.64

0.77

9

0.580

0.77

2.12

1.80

1.35

1.50

10

1.020

1.46

0.68

no data

0.85

not available

11

2.130

0.96

0.77

0.63

1.45

1.18

13

0.690

0.50

0.61

1.27

0.65

0.86

14

0.860

1.08

1.19

no data

1.02

not available

15

0.890

0.81

0.78

no data

0.83

not available

16

1.190

0.84

2.28

0.79

1.74

1.42

17

2.650

1.84

0.65

0.53

1.65

1.27

18

0.36*

no data

0.96

2.58

0.66

1.30

(ZNO3+ Zp)/2 (ZNO3 + Zp + Zs)/3*ZNO3 for this laboratory was not available; the listed value corresponds to ZNO3+NO2.

9

2003 RMNS Intercomparison

30.00

20.00

Nitrateµmol kg -1

40.00

10.00

0.00

5
b#1
La 01
b#
La 14
b#
La 13
b#
La 08
b#
La 07
b#
La 9
b#0
La 05
b#
La 03
b#
La 06
b#
La 17
b#
La 10
b#
La 16
b#
La 11
b#
La 4
b#0
La 02
b#
La

Figure 2 Nitrate results for sample 6: concentration versus laboratory
number sorted by concentration.

10

2003 RMNS Intercomparison

3.50

Phosphateµmol kg -1

3.00

2.50

2.00

1.50

1.00

0.50

2
b#0
La 14
b#
La 15
b#
La 16
b#
La 8
b#0
La 05
b#
La 11
b#
La 3
b#0
La 01
b#
La 13
b#
La 7
b#0
La 18
b#
La 10
b#
La 17
b#
La 06
b#
La 9
b#0
La 04
b#
La

0.00

Figure 3 Phosphate results for sample 6: concentration versus
laboratory number sorted by concentration.

11

2003 RMNS Intercomparison

Silicic acidµmol kg -1

200.00150.00100.00

50.00

2
b#0
La
8
b#0
La
1
b#0
La
8
b#1
La
6
b#1
La
1
b#1
La
6
b#0
La
7
b#1
La
4
b#0
La
3
b#1
La
3
b#0
La
7
b#0
La
9
b#0
La

0.00

Figure 4 Silicic acid results for sample 3: concentration versus
laboratory number sorted by concentration.

12

2003 RMNS Intercomparison

Sample 1 — Nitrite
Consensus Value: 0.02 ± 0.01 µmol kg–1

0.05

Nitrite µmol kg-1

0.04
0.03
0.02
0.01
0.00
-0.01

0

5

10

15

20

Laboratory Number
10

Number

8
6
4
2
0

-0.01

0.00

0.01

0.02

0.03

0.04

0.05

0.06

µmol kg-1
Figure 5-1 Nitrite results for sample 1: concentration versus laboratory number (upper
panel)
Frequency distribution of concentration (lower panel).

13

2003 RMNS Intercomparison

Sample 2 — Nitrite
Consensus Value: 0.13 ± 0.06 µmol kg–1

Nitrite µmol kg-1

0.50
0.40
0.30
0.20
0.10
0.00

0

5

10

15

20

Laboratory Number
10

Number

8
6
4
2
0
0.00

0.06 0.12

0.18

0.24

0.30 0.36 0.42

0.48µmol kg-1
Figure 5-2 Nitrite results for sample 2: concentration versus laboratory number (upper
panel)
Frequency distribution of concentration (lower panel).
14

2003 RMNS Intercomparison

Sample 3 — Nitrite
Consensus Value: 0.01 ± 0.01 µmol kg–1

Nitrite µmol kg-1

0.50
0.40
0.30
0.20
0.10
0.00

0

5

10

15

20

Laboratory Number
10

Number

8
6
4
2
0
0.00

0.06 0.12

0.18

0.24

0.30 0.36 0.42

0.48µmol kg-1
Figure 5-3 Nitrite results for sample 3: concentration versus laboratory number (upper
panel)
Frequency distribution of concentration (lower panel).
15

2003 RMNS Intercomparison

Sample 4 — Nitrite
Consensus Value: 0.02 ± 0.02 µmol kg–1

0.06

Nitrite µmol kg-1

0.05
0.04
0.03
0.02
0.01
0.00
-0.01

0

5

10

15

20

Laboratory Number
10

Number

8
6
4
2
0
-0.02

0.00

0.02

0.04

0.06

0.08

µmol kg-1
Figure 5-4 Nitrite results for sample 4: concentration versus laboratory number (upper
panel)
Frequency distribution of concentration (lower panel).

16

2003 RMNS Intercomparison

Sample 5 — Nitrite
Consensus Value: 0.91 ± 0.02 µmol kg–1

Nitrite µmol kg-1

1.00

0.95

0.90

0.85

0.80

0

5

10

15

20

Laboratory Number
10

Number

8
6
4
2
0
0.82

0.84 0.86

0.88

0.90

0.92 0.94 0.96

0.98µmol kg-1
Figure 5-5 Nitrite results for sample 5: concentration versus laboratory number (upper
panel)
Frequency distribution of concentration (lower panel).

17

2003 RMNS Intercomparison

Sample 6 — Nitrite
Consensus Value: 0.23 ± 0.09 µmol kg–1

0.45

Nitrite µmol kg-1

0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05

0

5

10

15

20

Laboratory Number
10

Number

8
6
4
2
0
0.00

0.09

0.18

0.27

µmol kg

0.36

0.45

0.54

-1

Figure 5-6 Nitrite results for sample 6: concentration versus laboratory number (upper
panel)
Frequency distribution of concentration (lower panel).

18

2003 RMNS Intercomparison

Sample 1 — Nitrate
Consensus Value: 0.04 ± 0.03 µmol kg–1

Nitrate µmol kg-1

2.50
2.00
1.50
1.00
0.50
0.00
-0.50

0

5

10

15

20

Laboratory Number
10

Number

8
6
4
2
0

0.00

0.30

0.60

0.90

1.20

1.50

1.80

2.10

µmol kg-1
Figure 6-1 Nitrate results for sample 1: concentration versus laboratory number (upper
panel)
Frequency distribution of concentration (lower panel).
19

2003 RMNS Intercomparison

Sample 2 — Nitrate
Consensus Value: 17.4 ± 0.7 µmol kg–1

Nitrate µmol kg-1

19.00
18.50
18.00
17.50
17.00
16.50
16.00

0

5

10

15

20

Laboratory Number
10

Number

8
6
4
2
0
15.87

16.56

17.25

17.94

18.63

19.32

µmol kg-1
Figure 6-2 Nitrate results for sample 2: concentration versus laboratory number (upper
panel)
Frequency distribution of concentration (lower panel).

20

2003 RMNS Intercomparison

Sample 3 — Nitrate
Consensus Value: 35.3 ± 0.3 µmol kg–1

Nitrate µmol kg-1

38.00
37.00
36.00
35.00
34.00
33.00

0

5

10

15

20

Laboratory Number
10

Number

8
6
4
2
0
34.00

34.68

35.36

36.04

36.72

37.40

µmol kg-1
Figure 6-3 Nitrate results for sample 3: concentration versus laboratory number (upper
panel)
Frequency distribution of concentration (lower panel).

21

2003 RMNS Intercomparison

Sample 4 — Nitrate
Consensus Value: 0.02 ± 0.03 µmol kg–1

Nitrate µmol kg-1

2.00
1.50
1.00
0.50
0.00
-0.50

0

5

10

15

20

Laboratory Number
10

Number

8
6
4
2
0
0.00

0.30

0.60

0.90

1.20

1.50

1.80

µmol kg-1
Figure 6-4 Nitrate results for sample 4: concentration versus laboratory number (upper
panel)
Frequency distribution of concentration (lower panel).

22

2003 RMNS Intercomparison

Sample 5 — Nitrate
Consensus Value: 13.1± 0.2 µmol kg–1

Nitrate µmol kg-1

14.00
13.50
13.00
12.50
12.00
11.50
11.00

0

5

10

15

20

Laboratory Number
10

Number

8
6
4
2
0
11.50

11.96

12.42

12.88

13.34

13.80

µmol kg-1
Figure 6-5 Nitrate results for sample 5: concentration versus laboratory number (upper
panel)
Frequency distribution of concentration (lower panel).

23

2003 RMNS Intercomparison

Sample 6 — Nitrate
Consensus Value: 38.2 ± 1.1 µmol kg–1

Nitrate µmol kg-1

42.00
40.00
38.00
36.00
34.00
32.00

0

5

10

15

20

Laboratory Number
10

Number

8
6
4
2
0
32.86

34.98

37.10

39.22

41.34

µmol kg-1
Figure 6-6 Nitrate results for sample 6: concentration versus laboratory number (upper
panel)
Frequency distribution of concentration (lower panel).

24

2003 RMNS Intercomparison

Sample 1 — Nitrate + Nitrite
Consensus Value: 0.06 ± 0.04 µmol kg–1

Nitrate + Nitrite µmol kg-1

2.50
2.00
1.50
1.00
0.50
0.00
-0.50

0

5

10

15

20

Laboratory Number
10

Number

8
6
4
2
0
0.00

0.40

0.80

1.20

1.60

2.00

µmol kg-1
Figure 7-1 Nitrate + nitrite results for sample 1: concentration versus laboratory
number (upper panel)Frequency distribution of concentration (lower panel).

25

2003 RMNS Intercomparison

Sample 2 — Nitrate + Nitrite
Consensus Value: 17.6 ± 0.6 ? mol kg–1

Nitrate + Nitrite µmol kg-1

19.00
18.50
18.00
17.50
17.00
16.50
16.00

0

5

10

15

20

Laboratory Number
10

Number

8
6
4
2
0

15.86

16.47

17.08

17.69

18.30

18.91

19.52

µmol kg-1
Figure 7-2 Nitrate + nitrite results for sample 2: concentration versus laboratory
number (upper panel)Frequency distribution of concentration (lower panel).
26

2003 RMNS Intercomparison

Sample 3 — Nitrate + Nitrite
Consensus Value: 35.4 ± 0.3 µmol kg–1

Nitrate + Nitrite µmol kg-1

38.00
37.00
36.00
35.00
34.00
33.00

0

5

10

15

20

Laboratory Number
10

Number

8
6
4
2
0
33.90

34.50

35.10

35.70

36.30

36.90

37.50

µmol kg-1
Figure 7-3 Nitrate + nitrite results for sample 3: concentration versus laboratory
number (upper panel)Frequency distribution of concentration (lower panel).

27

2003 RMNS Intercomparison

Sample 4 — Nitrate + Nitrite
Consensus Value: 0.04 ± 0.04 µmol kg–1

Nitrate + Nitrite µmol kg-1

2.00
1.50
1.00
0.50
0.00
-0.50

0

5

10

15

20

Laboratory Number
10

Number8
6
4
2
0
0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80µmol kg-1
Figure 7-4 Nitrate + nitrite results for sample 4: concentration versus laboratory
number (upper panel)Frequency distribution of concentration (lower panel).

28

2003 RMNS Intercomparison

Sample 5 — Nitrate + Nitrite
Consensus Value: 14.0 ± 0.2 µmol kg–1

Nitrate + Nitrite µmol kg-1

15.00
14.50
14.00
13.50
13.00
12.50
12.00

0

5

10

15

20

Laboratory Number
10

Number

8
6
4
2
0
12.32

12.76

13.20

13.64

14.08

14.52

14.96

µmol kg-1
Figure 7-5 Nitrate + nitrite results for sample 5: concentration versus laboratory
number (upper panel)Frequency distribution of concentration (lower panel).

29

2003 RMNS Intercomparison

Sample 6 — Nitrate + Nitrite
Consensus Value: 38.4 ± 1.0 µmol kg–1

Nitrate + Nitrite µmol kg-1

41.00
40.00
39.00
38.00
37.00
36.00
35.00
34.00

0

5

10

15

20

Laboratory Number
10

Number8
6
4
2
0
33.66 34.68 35.70 36.72 37.74 38.76 39.78 40.80µmol kg-1
Figure 7-6 Nitrate + nitrite results for sample 6: concentration versus laboratory
number (upper panel)Frequency distribution of concentration (lower panel).

30

2003 RMNS Intercomparison

Sample 1 — Phosphate
Consensus Value: 0.09 ± 0.02 µmol kg–1

Phosphate µmol kg-1

0.20

0.15

0.10

0.05

0.00

0

5

10

15

20

Laboratory Number
10

Number

8
6
4
2
0

0.00

0.04

0.08

0.12

0.16

0.20

µmol kg-1
Figure 8-1 Phosphate results for sample 1: concentration versus laboratory number(upper panel)Frequency distribution of concentration (lower panel).

31

2003 RMNS Intercomparison

Sample 2 — Phosphate
Consensus Value: 1.25 ± 0.04 µmol kg–1

Phosphate µmol kg-1

1.35
1.30
1.25
1.20
1.15
1.10
1.05
1.00
0.95

0

5

10

15

20

Laboratory Number
10

Number

8
6
4
2
0
0.96

1.04

1.12

1.20

µmol kg

1.28

1.36

-1

Figure 8-2 Phosphate results for sample 2: concentration versus laboratory number(upper panel)Frequency distribution of concentration (lower panel).

32

2003 RMNS Intercomparison

Sample 3 — Phosphate
Consensus Value: 2.14 ± 0.07 µmol kg–1

Phosphate µmol kg-1

2.35
2.30
2.25
2.20
2.15
2.10
2.05
2.00
1.95

0

5

10

15

20

Laboratory Number
10

Number

8
6
4
2
0
1.96

2.03

2.10

2.17

µmol kg

2.24

2.31

2.38

-1

Figure 8-3 Phosphate results for sample 3: concentration versus laboratory number(upper panel)Frequency distribution of concentration (lower panel).

33

2003 RMNS Intercomparison

Sample 4 — Phosphate
Consensus Value: 0.09 ± 0.03 µmol kg–1

Phosphate µmol kg-1

0.25
0.20
0.15
0.10
0.05
0.00

0

5

10

15

20

Laboratory Number
10

Number

8
6
4
2
0
0.03

0.06

0.09

0.12

0.15

µmol kg

0.18

0.21

0.24

-1

Figure 8-4 Phosphate results for sample 4: concentration versus laboratory number(upper panel)Frequency distribution of concentration (lower panel).

34

2003 RMNS Intercomparison

Sample 5 — Phosphate
Consensus Value: 1.10 ± 0.04 µmol kg–1

Phosphate µmol kg-1

1.20

1.15

1.10

1.05

1.00

0

5

10

15

20

Laboratory Number
10

Number

8
6
4
2
0
0.96

1.00

1.04

1.08

1.12

µmol kg

1.16

1.20

1.24

-1

Figure 8-5 Phosphate results for sample 5: concentration versus laboratory number(upper panel)Frequency distribution of concentration (lower panel).

35

2003 RMNS Intercomparison

Sample 6 — Phosphate
Consensus Value: 2.74 ± 0.10 µmol kg–1

Phosphate µmol kg-1

3.10
3.00
2.90
2.80
2.70
2.60
2.50

0

5

10

15

20

Laboratory Number
10

Number

8
6
4
2
0
2.40

2.50

2.60

2.70

2.80

2.90

3.00

3.10

µmol kg-1
Figure 8-6 Phosphate results for sample 6: concentration versus laboratory number(upper panel)Frequency distribution of concentration (lower panel).

36

2003 RMNS Intercomparison

Sample 1 — Silicic acid
Consensus Value: 2.06 ± 0.23 µmol kg–1

Silicic acidµmol kg-1

3.00
2.50
2.00
1.50
1.00
0.50
0.00
-0.50

0

5

10

15

20

Laboratory Number
10

Number

8
6
4
2
0

0.00

0.46

0.92

1.38

1.84

2.30

2.76

µmol kg-1
Figure 9-1 Silicic acid results for sample 1: concentration versus laboratory number(upper panel)Frequency distribution of concentration (lower panel).

37

2003 RMNS Intercomparison

Sample 2 — Silicic acid
Consensus Value: 66.4 ± 2.0 µmol kg–1

Silicic acidµmol kg-1

110.0
100.0
90.0
80.0
70.0
60.0

0

5

10

15

20

Laboratory Number
10

Number

8
6
4
2
0
60.0

70.0

80.0

90.0

100.0

110.0

µmol kg-1
Figure 9-2 Silicic acid results for sample 2: concentration versus laboratory number(upper panel)Frequency distribution of concentration (lower panel).

38

2003 RMNS Intercomparison

Sample 3 — Silicic acid
Consensus Value: 135.7 ± 2.3 µmol kg–1

µmol kg-1

150.0

Silicic acid

155.0

140.0

145.0

135.0
130.0
125.0

0

5

10

15

20

Laboratory Number
10

Number

8
6
4
2
0
126.5

131.1

135.7

140.3

144.9

149.5

154.1

µmol kg-1
Figure 9-3 Silicic acid results for sample 3: concentration versus laboratory number(upper panel)Frequency distribution of concentration (lower panel).

39

2003 RMNS Intercomparison

Sample 4 — Silicic acid
Consensus Value: 2.09 ± 0.31 µmol kg–1

µmol kg-1

2.50

Silicic acid

3.00

1.50

2.00

1.00
0.50
0.00

0

5

10

15

20

Laboratory Number
10

Number

8
6
4
2
0
0.00

0.62

1.24

µmol kg

1.86

2.48

-1

Figure 9-4 Silicic acid results for sample 4: concentration versus laboratory number(upper panel)Frequency distribution of concentration (lower panel).
40

2003 RMNS Intercomparison

Sample 5 — Silicic acid
Consensus Value: 73.8 ± 2.4 µmol kg–1

µmol kg-1

78.0

Silicic acid

80.0

74.0

76.0

72.0
70.0
68.0

0

5

10

15

20

Laboratory Number
10

Number

8
6
4
2
0
67.2

69.6

72.0

74.4

76.8

79.2

81.6

µmol kg-1
Figure 9-5 Silicic acid results for sample 5: concentration versus laboratory number(upper panel)Frequency distribution of concentration (lower panel).

41

2003 RMNS Intercomparison

Sample 6 — Silicic acid
Consensus Value: 133.8 ±2.5 µmol kg–1

Silicic acidµmol kg-1

150.0
145.0
140.0
135.0
130.0
125.0

0

5

10

15

20

Laboratory Number
10

Number

8
6
4
2
0
125.0

130.0

135.0

140.0

145.0

150.0

µmol kg-1
Figure 9-6 Silicic acid results for sample 6: concentration versus laboratory number(upper panel)Frequency distribution of concentration (lower panel).

42

2003 RMNS Intercomparison

6. Conclusions
A total of 18 sets of 6 samples each were distributed in 5 countries. Results werereturned by 17 laboratories in 5 countries. Although consensus concentrations wereobtained for the 6 samples, the standard deviations were 4.5 times and more than 10times larger than those of the homogeneities for phosphate and silicic acid, respectively.
For nitrate, the standard deviations were only about double the homogeneities. These
results indicate that variability in in-house standards of the participating laboratories —rather than analytical precision — is the primary source of interlaboratory discrepancy.
Therefore use of a certified RMNS is essential for establishing nutrient data sets thatcan be compared across laboratories, especially for silicic acid and phosphate.

Acknowledgements
The author thanks all participants for their data submission and cooperation throughout
this intercomparison exercise. The author also thanks Wenjing Zhu and Mayako
Shimizu for data management and preparation of the many graphs and tables in thisreport.

43

2003 RMNS Intercomparison

References
Aminot, A. and R. Kerouel, 1991: Autoclaved seawater as a reference material for thedetermination of nitrate and phosphate in seawater. Anal. Chim. Acta, 248, 277–283.
Aminot, A. and R. Kerouel, 1995: Reference material for nutrients in seawater: stabilityof nitrate, nitrite, ammonia and phosphate in autoclaved samples. Mar. Chem., 49,
221–232.
Aminot, A. and D. S. Kirkwood, 1995: Report on the results of the fifth ICESIntercomparison Exercise for Nutrients in Seawater, ICES Cooperative Research Report
No. 213, 79 pp.
Aoyama, M., H. Ota, Y. Arii, S. Iwano, H. Kamiya, M. Kimura, T. Kitao, S. Masuda, N.
Nagai, K. Saito, 2006: Reference material for nutrients in seawater in a seawater matrix.
Pap. Meteorol. Geophys., in revise.
Clancy, V. and S. Willie, 2003: NOAA/NRC Intercomparison for Nutrients in Seawater,
NOAA Technical Memorandum NOS NCCOS CCMA 158, 32 pp.
Clancy, V. and S. Willie, 2004: Preparation and certification of a reference material forthe determination of nutrients in seawater. Anal. Bioanal. Chem., 378 (5), 1239–1242.
[ICES] International Council for the Exploration of the Sea, 1967: Report on theanalysis of phosphate at the ICES intercalibration trials of chemical methods held at
Copenhagen, 1966. ICES CM 1967/C:20.
[ICES] International Council for the Exploration of the Sea, 1977: The International
Intercalibration Exercise for Nutrient Methods, ICES Cooperative Research Report No.
67. 44 pp.
Kirkwood, D. S., 1992: Stability of solutions of nutrient salts during storage. Mar.
Chem., 38, 151–164.
Kirkwood, D. S., A. Aminot, and M. Perttila, 1991: Report on the results of the fourth
ICES Intercomparison Exercise for Nutrients in Seawater, ICES Cooperative Research
Report No. 174, 83 pp.
[UNESCO] United Nations Educational, Scientific and Cultural Organization, 1965:
Report on the intercalibration measurements in Copenhagen, 9–13 June 1965, UNESCO
Technical Papers in Marine Science, No. 3. 14 pp.
[UNESCO] United Nations Educational, Scientific and Cultural Organization, 1967:
Report on intercalibration measurements, Leningrad, 24–28 May 1966, Copenhagen,
September 1966, UNESCO Technical Papers in Marine Science, No. 9. 114 pp.
[UNESCO] United Nations Educational, Scientific and Cultural Organization, 1991:
44

2003 RMNS Intercomparison

IOC–IAEA–UNEP Group of Experts on Standards and Reference Materials (GESREM),
2nd session, 12 pp.
[UNESCO] United Nations Educational, Scientific and Cultural Organization, 1992:
IOC–IAEA–UNEP Group of Experts on Standards and Reference Materials (GESREM),
3rd session, 16 pp.
Willie, S. and V. Clancy, 2000: NOAA/NRC Intercomparison for Nutrients in Seawater,
NOAA Technical Memorandum NOS NCCOS CCMA 143, 176 pp

45

2003 RMNS Intercomparison

46

2003 RMNS Intercomparison

Appendix I
List of participating laboratories

47

2003 RMNS Intercomparison

48

2003 RMNS Intercomparison

Table A1 – List of participating laboratories
Laboratory

Name

Affiliation

Address

1

Minhan DAI

Marine Environmental
Laboratory,
Xiamen University, China

361005 Xiamen, China

2

Nurit KRESS

Israel Oceanographic andLimnological Research Institute,Israel

P.O. Box 8030, Tel-Shikmona,
31080 Haifa, Israel

3

Doug MASTEN /Susan BECKER

Scripps Institution of
Oceanography, STS/ODF, USA

8855 Biological Grade, 215 Isaacs Hall,
La Jolla, CA 92037

4Louis I. GORDON

College of Oceanic andAtmospheric Sciences, Oregon
State University, USA

College of Oceanic and Atmospheric
Sciences, Oregon State University,
104 Ocean Administration Building,Corvallis, OR 97331-5033

5Kazuhiro SAITO

Hakodate Marine Observatory,Japan

3-4-4 Mihara, Hakodate-shi,
Hokkaido 041-0806, Japan

6

Roger KEROUELIFREMER (Centre de Brest)

BP 70, 29280 Plouzane, France

7

Hiroshi OGAWA

Ocean Research Institute, The
University of Tokyo, Japan

1-15-1 Minamidai, Nakano-ku,
Tokyo 164-8639, Japan

8

Hiroaki SAITO

Tohoku National Fisheries
Research Institute, Japan

3-27-5 Shinhama-cho, Shiogama-city,
Miyagi 985-0001, Japan

Naoki NAGAI

Marine Division, Climate andMarine Department, Japan
Meteorological Agency, Japan

1-3-4 Otemachi, Chiyoda-ku,
Tokyo 100-8122, Japan

Hiroyuki TAKANO

Oceanographical Division,
Maizuru Marine Observatory,Japan

901 Shimofukui, Maizuru-city,
Kyoto 624-0946, Japan

9

10

49

2003 RMNS Intercomparison

Agnes. YOUENOU

IFREMER DEL/EC/PP

BP 70, 29280 Plouzane, France

13

Akihiko MURATA

Japan Marine Science andTechnology Center, Japan

2-15 Natsushima-cho,
Yokosuka-city,
Kanagawa 237-0061, Japan

14

Hideshi DAIMON

Kobe Marine Observatory,Japan

1-4-3 Wakinohamakaigan-dori, Chuo-ku,
Kobe-city, Hyogo 650-0073, Japan

15

Takao SHIMIZU

Nagasaki Marine Observatory,Japan

11-51 Minami-yamate,
Nagasaki-city, Nagasaki 850-0931, Japan

16

Hidekazu OTA

KANSO, Japan

3-1-1 Higashikurazi, Katano-city,
Osaka 576-0061, Japan

17

Atsushi TSUDA /Hiromi KASAI

Hokkaido National Fisheries
Research Institute116 Katsurakoi, Kushiro,
Hokkaido 085-0802, Japan

18

Katsumi
YOKOUCHI

Seikai National Fisheries
Research Institute3-30 Kokubu-machi,
Nagasaki 850-0951, Japan

11

50

2003 RMNS Intercomparison

Appendix II
Results submitted by participating laboratories

51

2003 RMNS Intercomparison

52

2003 RMNS Intercomparison

Laboratory 1
Report on Nutrient Intercomparison Results
April 29, 2003
LABORATORY: Ocean Carbon Group, Marine Environmental Laboratory, Xiamen
University, Xiamen, China
Contact: Minhan Dai, mdai@xmu.edu.cn
DATE OF RECEIPT OF SAMPLE: Jan. 18, 2003
NitriteNitratePhosphate

Silicic acid

Remarks

2.057

Nitrite +nitrate2.069

Sample 1

0.012

0.093

2.486

Shortage ofvolumeSample 2
Sample 3
Sample 4

0.448
ND*
ND*

16.37936.9361.855

16.82736.936
1.855

1.072
2.144
0.093

68.793139.093
2.572

Sample 5
Sample 6

0.896
0.362

13.49139.87214.38740.233

1.047
2.743

75.186137.229

Shortage ofvolumeUnit: mol kg–1
* Under detection limit
BRIEF DESCRIPTIONS OF ANALYSIS:
Nitrite (NO2), phosphate (PO4), and silicic acid (H2SiO3) were determinedcolorimetrically using a flow injection analyzer (Tri-223 autoanalyzer). Nitrate (NO3)plus NO2 was measured by reducing nitrate to nitrite using the same Tri-223
autoanalyzer with an on-line Cd coil.

COMMENTS;
1. Analysis date: April 28, 2003
2. We experienced a shortage of samples during the runs for samples 1 and 4.
3. Concentration units have been converted from µmol L–1 to µmol kg–1 according toMillero (1996) (Chemical Oceanography, 2nd edition).
4. We’d like to know more about the preparation procedure of the samples that were
provided for this intercomparison exercise. We are concerned about the way the
samples were stored.

53

2003 RMNS Intercomparison

Laboratory 2
Dr. Michio Aoyama
Geochemical Res. Dept.
Meteorological Res. Inst.
1-1 Nagamina, Tsukuba
305-0052, Japan
30 April 2003
Re: 2003 Intercomparison Exercise for Reference Material for Nutrients in Seawater ina Seawater Matrix
Dear Michio,
Below are the results of the analysis we performed on the six samples sent to us by the
Marine Chemistry Department of the Israel Oceanographic and Limnological ResearchInstitute, P.O. Box 8030, Tel-Shikmona, 31080 Haifa, Israel
The samples arrived in good shape on January 2003 and were analyzed on April 28,
2003. They were kept refrigerated during the whole time.
Comments:
1. Because we usually run samples with very low concentrations, samples 2, 3, 5,
and 6 were diluted before analysis with low-nutrient seawater from the eastern
Mediterranean
2. Samples 1 and 4 were run without dilution.
3. Triplicate samples were run and the average computed
4. Bdl – The detection limit for nitrate + nitrite and nitrite is 0.08 micromolar.
5. The concentrations in micromoles per liter were transformed to micromoles per
kilogram using the density calculated from the given salinity and thetemperature of the sample during analysis
Looking forward to the results of the intercomparison.
Sincerely,
Dr. Nurit Kress54

2003 RMNS Intercomparison

Table of results in micromoles per liter
SampleNO3 + NO2

NO2

PO4

Si(OH)4 Salinity Temp.

Density

34.75

20

1.0245734.65

201.024534.65

201.024534.8

201.0246134.6

201.0244634.5

201.02438

Micromoles per liter

S1

average

0.071

2.08

std. dev.

0.005

0.04

CV (%)

7

2

S2

Bdl

Bdl

average

17.4

0.20

1.28

110.9

std. dev.

0.2

0.00

0.02

0.7

CV (%)

10

1

1

average

35.1

Bdl

2.38

155.5

std. dev.

0.8

0.02

0.4

CV (%)

2

1

0

average

Bdl

0.094

2.16

std. dev.

0.005

0.03

CV (%)

5

1

S3

S4

S5

Bdl

average

12.8

0.87

1.17

80.3

std. dev.

0.2

0.03

0.02

0.9

CV (%)

2

4

2

1

average

35.3

0.25

3.09

152.9

std. dev.

0.3

0.01

0.02

0.2

CV (%)

1

2

1

0

S6

Table of results in micromoles per kilogram
SampleNO3 + NO2

NO2

PO4

Si(OH)4

Micromoles per kilogram

S1
S2
S3
S4
S5
S6

Average

Bdl

Bdl

0.069

2.03

Average

17.0

0.20

1.25

108.3

Average

34.3

Bdl

2.32

151.8

Average

Bdl

Bdl

0.091

2.11

Average

12.5

0.85

1.14

78.4

Average

34.5

0.24

3.02

149.2

A brief description of the methods used:
The nutrients were analyzed on a SANplus System autoanalyzer (Skalar, Breda, The
Netherlands) equipped with an automatic SA 1000 sampler, three colorimeters, and a55

2003 RMNS Intercomparison

data acquisition module with FlowAccess® software (Windows software for Skalar
SANplus systems). The peristaltic pump and the cartridges were from Bran+Luebbe.
The chemistries are as follows:
NO3 + NO2 — Nitrate is reduced to nitrite under alkaline conditions in a copperized
cadmium reductor coil. The nitrite reduced from nitrate, plus any free nitrite alreadypresent, reacts under acidic conditions with sulphanilamide to form a diazo compound,which then couples with N-1-naphthyl-ethylenediamine dihydrochloride to form a
reddish-purple azo dye, which is measured at 520 nm.
Si(OH)4 — Silicic acid reacts with ammonium molybdate in an acidic medium to form
silicomolybdic acid which is reduced to molybdenum blue with stannous chloride. The
absorption of the colored complex is measured at 630 nm.
PO4 — Phosphate reacts with ammonium molybdate in an acidic medium to form aphosphomolybdic acid, which is in turn reduced to phosphomolybdous acid byhydrazine sulfate. The intensity of the blue color of the latter compound is measured at
880 nm.
If you need any more information about the methods please let me know.

56

2003 RMNS Intercomparison

Laboratory 3
2003 Intercomparison Exercise for Reference Material for Nutrients in Seawater in a
Seawater Matrix
RESULTS REPORT FORMLABORATORY:
Scripps Institution of Oceanography
STS/ODFDATE OF RECEIPT OF SAMPLES:
13 Jan 2003
DATA OF ANALYSIS:All samples analyzed on 15 Jan 2003
Results in micromoles per kilogram = micromoles per liter/density
NitriteNitrateNitrite + nitrate

Phosphate

Silicic acid

0.03

0.06

0.09

0.10

2.2

0.14

17.60

17.74

1.26

66.8

0.01

35.36

35.37

2.14

133.2

0.03

0.07

0.10

0.13

2.3

0.90

13.08

13.98

1.09

73.4

0.27

38.11

38.38

2.7

130.9

Sample 1
Sample 2
Sample 3
Sample 4
Sample 5
Sample 6
Estimation of analytical error:
NO2
NO3 + NO2
PO4
SiO3

±0.005
±0.05
±0.04
±0.40

Brief description of analyses:
Samples were analyzed with a modified Technicon AAII.
1. A modification of the Armstrong et al. (1967) procedure was used for the analysis ofnitrate + nitrite and nitrite. Nitrate is quantitatively reduced to nitrite by passing the57

2003 RMNS Intercomparison

sample through a Cd/Cu reduction column. The sample is then passed through a
15-mm flowcell and absorbance measured at 540 nm.
2. Orthophosphate was analyzed using a modification of the Bernhardt and Wilhelms(1967) method using dihydrazine sulfate as a reductant of the sample in an acidified
ammonium molybdate solution. The sample was passed through a 50-mm flowcell
and absorbance measured at 820 nm.
3. Silicic acid was analyzed using a modification of the Armstrong et al. (1967)
method. Stannous chloride was used as a reductant of the sample in an acidified
ammonium molybdate solution. Tartaric acid was added to eliminate PO4interference. The sample was passed through a 15-mm flowcell and absorbancemeasured at 660 nm.
References:
Armstrong, F.A.J., C.R. Stearns and J.D.H. Strickland. 1967. The measurement of
upwelling and subsequent biological processes by means of the TechniconAutoanalyzer and associated equipment. Deep-Sea Research 14(3):381–389.
Bernhardt, H. and A. Wilhelms. 1967. The continuous determination of low level iron,soluble phosphate and total phosphate with the AutoAnalyzer. Technicon Symposium,
1967, Vol. I, p. 386.

58

2003 RMNS Intercomparison

Laboratory 4
Results for 2003 Intercomparison Exercise for Reference Material for Nutrients in Seawaterin a Seawater Matrix
RESULTS REPORT FORMLABORATORY:
College of Oceanic and Atmospheric Sciences, Oregon State University
DATE OF RECEIPT OF SAMPLES:
13-Jan-03
DATE OF ANALYSIS:
13-Jan-03
All samples
Results in micromoles per kilogram
NitriteNitrateNitrate + nitrite

Phosphate

Silicic acid

Mean

±

Mean

±

Mean

±

Mean

±

Mean

±

N

Sample 1

0.023

0.007

0.06

0.07

0.08

0.08

0.120

0.013

2.18

0.15

4

Sample 2

0.044

0.007

18.35

0.09

18.40

0.10

1.296

0.023

65.64

0.17

4

Sample 3

0.014

0.005

34.87

0.07

34.88

0.06

2.099

0.019

134.000.29

5

Sample 4

0.010

0.009

0.01

0.04

0.02

0.03

0.073

0.006

2.16

0.10

4

Sample 5

0.893

0.011

12.94

0.04

13.84

0.04

1.105

0.007

72.63

0.15

4

Sample 6

0.204

0.012

36.44

0.03

36.64

0.02

2.550

0.015

131.820.24

4± = 95% confidence level592003 RMNS Intercomparison

Brief descriptions of analysis:
All four nutrients were analyzed simultaneously on a hybrid autoanalyzer consisting of aTechnicon AAII for the determination of phosphate and an ALPKEM RFA 300 for thedetermination of silicic acid, nitrite, and nitrate + nitrite.
A description of the chemistries can be found in:
A suggested protocol for continuous flow automated analysis of seawater nutrients (phosphate,nitrate, nitrite and silicic acid) in the WOCE Hydrographic Program and the Joint Global Ocean
Fluxes Study.
WOCE Hydrographic Program Office, WHP Office Report WHPO 91-1, Part 3.1.3: WHP
Operations and Methods, WOCE Report No. 68/91, November 1994.

Comments:
Samples were in good shape prior to analysis and no problems occurred during the single run.
Prior to the analysis on March 19th, the samples were stored in the dark at room temperature.

60

2003 RMNS Intercomparison

Laboratory 5
2003 Intercomparison Exercise for Reference Material for Nutrients in Seawater in a
Seawater Matrix
RESULTS REPORT FORMLABORATORY:
KOHUMARU (HAKODATE)DATE OF RECEIPT OF SAMPLES:
2003/1/16 (Japan Standard Time)
DATE OF ANALYSIS: Sample 1
Sample 2
Sample 3
Sample 4
Sample 5
Sample 6

2003/2/20 17:22 (JST)2003/2/20 17:22 (JST)2003/2/20 17:22 (JST)2003/2/20 17:22 (JST)2003/2/20 17:22 (JST)2003/2/20 17:22 (JST)Results in micromoles per kilogram
NitriteNitrateSample 1
0.02 ± 0.00
0.05

Nitrite + nitrate
0.07 ± 0.01

Phosphate
0.08 ± 0.00

Sample 2

0.13 ± 0.01

17.62

17.75 ± 0.03

1.27 ± 0.01―

Sample 30.01 ± 0.00

35.07

35.08 ± 0.01

2.23 ± 0.00―

Sample 40.01 ± 0.00

0.03

0.04 ± 0.01

0.05 ± 0.01―

Sample 50.92 ± 0.00

12.81

13.73 ± 0.03

1.16 ± 0.01―

Sample 60.10 ± 0.01

38.44

38.54 ± 0.07

2.80 ± 0.01―

Silicic acid―

Brief descriptions of the methods of analysis:
Measurements were performed with an AutoAnalyzerTM-II (TechniconTM).
Distilled water was tightly sealed in clean bottles and opened just before use forzero-base. PO4 measurements were based upon the method of Murphy and Riley(1961). NO2 and NO3 were measured in accordance with the technique of Armstorng
et al. (1967), and NO3 concentrations were calculated by subtracting NO2 from NO3 +NO2. Since calibration curves of PO4 and NO3 were not linear at low concentrations,
we applied quadratic calibration curves.
61

2003 RMNS Intercomparison

Order of standard and RMNS was as follows:
0, 1/4, 2/4, 3/4, 4/4, 3/4, 2/4, 1/4, 0, Å standard for linearity check
RMNS-1, RMNS-1, RMNS-1, RMNS-1,
RMNS-2, RMNS-2, RMNS-2, RMNS-2,…………
RMNS-6, RMNS-6, RMNS-6, RMNS-6
Comments
No baseline drift occurred through the measurement. Peak shapes were neatenough.
We could not measure salinity values of RMNS because their remainders were too
small. Conversion of concentrations (from µmol L–1 to µmol kg–1) was carried out
using the given salinity values.

62

2003 RMNS Intercomparison

Laboratory 6
2003 Intercomparison Exercise for Reference Material for Nutrients in Seawater in a
Seawater Matrix
RESULTS REPORT FORMLABORATORY:
R. KEROUELIFREMER, Centre de Brest
Département DEL/EC/EB
BP 70, 29280 Plouzane
FranceDATE OF RECEIPT OF SAMPLES: 14 JAN 2003
DATA OF ANALYSIS:Sample 1
Sample 2
Sample 3
Sample 4
Sample 5
Sample 6

N & P: 23/01/03; Si: 27/01/03
N & P: 23/01/03; Si: 27/01/03
N & P: 23/01/03; Si: 27/01/03
N & P: 23/01/03; Si: 27/01/03
N & P: 23/01/03; Si: 27/01/03
N & P: 23/01/03; Si: 27/01/03

Note: after N & P analysis, the samples were immediately recapped and placed in arefrigerator until Si analysis.
Results in micromoles per kilogram
NitriteNitrateNitrite + nitrate

Phosphate

Silicic acid

Sample 1

0.023 ± 0.003 0.02 ± 0.03

0.04 ± 0.03

0.079 ± 0.004 2.03 ± 0.05

Sample 20.150 ± 0.003

17.6 ± 0.1

17.7 ± 0.1

1.23 ± 0.01

66.6 ± 0.3

Sample 30.012 ± 0.003

35.5 ± 0.2

35.5 ± 0.2

2.12 ± 0.01

136 ± 1

Sample 40.033 ± 0.003 0.02 ± 0.03

0.05 ± 0.03

0.113 ± 0.004 2.09 ± 0.05

Sample 50.918 ± 0.005

13.0 ± 0.1

13.9 ± 0.1

1.07 ± 0.01

73.7 ± 0.3

Sample 60.270 ± 0.003

38.1 ± 0.2

38.4 ± 0.2

2.65 ± 0.01

134 ± 1

Brief descriptions of analysis: automated analysis. Bran+Luebbe Autoanalyzer AA3 fornitrate and nitrite. Technicon Autoanalyzer AA2 for phosphate and silicic acid. Methods
proposed by Tréguer and Le Corre (1975) with only minor modifications.
Tréguer, P. and Le Corre, P., 1975. Manuel d’analyse des sels nutritifs dans l’eau demer. LOC-UBO, Brest, 110 pp.
Your comments: none

63

2003 RMNS Intercomparison

Laboratory 7
Unit: µmol kg–1

Results for RMNS

Sample

Ave

±SD

Ave

±SD

Ave

±SD

Ave

±SD

Silicic
acid
Ave

1

0.00

0.00

0.01

0.01

0.01

0.01

0.01

0.00

1.92

0.02

2

0.04

0.00

18.58

0.08

18.62

0.08

1.31

0.00

64.55

0.14

3

0.01

0.00

35.50

0.06

35.51

0.06

2.14

0.00

132.27

0.05

4

0.01

0.00

0.02

0.00

0.03

0.00

0.06

0.00

2.00

0.05

5

0.90

0.00

12.99

0.02

13.88

0.02

1.09

0.00

71.42

0.14

6

0.24

0.00

38.56

0.03

38.80

0.03

2.72

0.01

130.230.08

NitriteNitrateNitrite + nitrate

Phosphate

Analysis date: Apr 11, 2003
Analysts: Hiroshi Ogawa and Yoko Fujimoto, Ocean Research Institute, The University of Tokyo
Instrument: AACS III, BRAN+LUEBBE Co.
* Triplicate analyses for each sample

64

±SD

2003 RMNS Intercomparison

Laboratory 8
2003 Intercomparison Exercise for Reference Material for Nutrients in Seawater in a
Seawater Matrix

RESULTS REPORT FORMLABORATORY: Tohoku National Fisheries Research Institute, Fisheries Research
AgencyDATE OF RECEIPT OF SAMPLES:
Jan 2003
DATA OF ANALYSIS:Sample 1
Sample 2
Sample 3
Sample 4
Sample 5
Sample 6

March 5, 2003
March 5, 2003
March 5, 2003
March 5, 2003
March 5, 2003
March 5, 2003

Results in micromoles per kilogram
Nitrite Nitrate Nitrite + nitrate
Sample 1
0.04
0.1------------ ------------- -------------Sample 2
0.06
17.3
------------ ------------- -------------Sample 3
0.02
35.6
------------ ------------- -------------Sample 4
0.04
0.0------------ ------------- -------------Sample 5
0.91
13.6
------------ ------------- -------------Sample 6
0.29
39.0
------------ ------------- --------------

Phosphate
Silicic acid
0.09
1.9---------------------1.28
68.3---------------------2.16
139.5---------------------0.11
1.9---------------------1.10
75.8---------------------2.80
137.2----------------------

Brief descriptions of analysis:
Nutrients were analyzed using a Bran+Luebbe TRAACS 800 autoanalyzer following
the protocol for the JGOFS core measurements with low-nutrient seawater (LNSW)
base.

65

2003 RMNS Intercomparison

Laboratory 9
LABORATORY: R/V Ryofu-Maru
DATE OF RECEIPT OF SAMPLES:DATA OF ANALYSIS:Results in micromoles per kilogram
Sample 1
Sample 2
Sample 3
Sample 4
Sample 5
Sample 6

Nitrite Nitrate Nitrite + nitrate
Phosphate
Silicic acid0.01 ± 0.00
0.04 ± 0.04
0.08 ± 0.00
1.80 ± 0.06------------ ------------- ----------------------------------0.16 ± 0.00
16.39 ± 0.04
0.99 ± 0.00
62.99 ± 0.06------------ ------------- ----------------------------------0.00 ± 0.00
35.17 ± 0.04
2.03 ± 0.00 129.10 ± 0.06------------ ------------- ----------------------------------0.01 ± 0.00
0.03 ± 0.04
0.10 ± 0.00
1.89 ± 0.06------------ ------------- ----------------------------------0.90 ± 0.00
13.84 ± 0.04
1.02 ± 0.00
69.64 ± 0.06------------ ------------- ----------------------------------0.13 ± 0.00
38.57 ± 0.04
2.56 ± 0.00 127.06 ± 0.06------------ ------------- -----------------------------------

66

2003 RMNS Intercomparison

Laboratory 10
2003 Intercomparison Exercise for Reference Material for Nutrients in Seawater in a
Seawater Matrix

RESULTS REPORT FORMLABORATORY: Oceanographical Division, Maizuru Marine Observatory
DATE OF RECEIPT OF SAMPLES: 15 January 2003
DATA OF ANALYSIS:Results in micromoles per kilogram

Sample 1
Sample 2
Sample 3
Sample 4
Sample 5
Sample 6

NitriteNitrateNitrite +nitratePhosphate

Silicic acid

0.00 ± 0.01-----------0.06 ± 0.01-----------0.00 ± 0.01-----------0.00 ± 0.01-----------0.88 ± 0.01-----------0.42 ± 0.01------------

0.00 ± 0.14------------18.28 ± 0.14------------35.15 ± 0.14------------0.00 ± 0.14------------13.39 ± 0.14------------37.15 ± 0.14-------------

0.00 ± 0.14-------------18.34 ± 0.14-------------35.15 ± 0.14-------------0.00 ± 0.14-------------14.27 ± 0.14-------------37.57 ± 0.14--------------

0.10 ± 0.05-----------1.25 ± 0.05-----------2.00 ± 0.05-----------0.12 ± 0.05-----------1.09 ± 0.05-----------2.71 ± 0.05------------−----------−----------−----------−----------−----------−-----------

Brief descriptions of analysis:
We measured these samples with an AA-II system.
measurement dates: 17–18 March 2003
measurement place: R/V Seifu Maru (at Maizuru)

67

2003 RMNS Intercomparison

Laboratory 11
2003 Intercomparison Exercise for Reference Material for Nutrients in Seawater in a
Seawater Matrix
RESULTS REPORT FORMLABORATORY: IFREMER Centre de BREST
Département DEL/EC/PP
BP 70
29280 Plouzane, France
DATE OF RECEIPT OF SAMPLES: 15/01/2003
DATA OF ANALYSIS:Sample 1: Nitrate, Nitrite, Phosphate, 12/03/03; Silicic acid, 13/03/03
Sample 2: Nitrate, Nitrite, Phosphate, 12/03/03; Silicic acid, 13/03/03
Sample 3: Nitrate, Nitrite, Phosphate, 12/03/03; Silicic acid, 13/03/03
Sample 4: Nitrate, Nitrite, Phosphate, 12/03/03; Silicic acid, 13/03/03
Sample 5: Nitrate, Nitrite, Phosphate, 12/03/03; Silicic acid, 13/03/03
Sample 6: Nitrate, Nitrite, Phosphate, 12/03/03; Silicic acid, 13/03/03
Results in micromoles per kilogram

Sample 1
Sample 2
Sample 3
Sample 4
Sample 5
Sample 6

NO2
0.02 ± 0.01
0.22 ± 0.01
0.01 ± 0.01
0.02 ± 0.01
0.96 ± 0.01
0.39 ± 0.01

NO3
NO3 + NO2
PO4
Si
0.08 ± 0.1 0.10 ± 0.1 0.13 ± 0.02 2.1 ± 0.1
16.8 ± 0.1 17.0 ± 0.1 1.28 ± 0.02 70.1 ± 0.1
34.8 ± 0.1 34.9 ± 0.1 2.19 ± 0.02 136 ± 1
0 ± 0.1
0 ± 0.1
0.08 ± 0.02 2.08 ± 0.1
11.7 ± 0.1 12.7 ± 0.1 1.12 ± 0.02 77.5 ± 0.1
36.7 ± 0.1 37.0 ± 0.1 2.77 ± 0.02 134 ± 1

Brief descriptions of analysis:
Nitrate and phosphate were automatically analyzed with an Technicon AACE
Autoanalyser, and nitrite and silicic acid with an Technicon AAII Autoanalyser.
The technical reference manual for analysis is “Manuel d’analyse des sels nutritifs dansl’eau de mer” (Utilisation de l’Autoanalyser II Technicon) – P. Treguer, P. Le Corre,
1975.
Your comments: none

68

2003 RMNS Intercomparison

Laboratory 13
2003 Intercomparison Exercise for Reference Material for Nutrients in Seawater in a
Seawater Matrix

RESULTS REPORT FORMLABORATORY:The R/V Mirai
DATE OF RECEIPT OF SAMPLES:
Jan. 19, 2003
DATE OF ANALYSIS:Sample 1
Sample 2
Sample 3
Sample 4
Sample 5
Sample 6

Mar. 13, 2003
Mar. 13, 2003
Mar. 13, 2003
Mar. 13, 2003
Mar. 13, 2003
Mar. 13, 2003

Results in micromoles per kilogram
Nitrite Nitrate Nitrite + nitrate
Sample 1
0.02
0.07
0.09
------------ ------------- -------------Sample 2
0.19
17.32
17.51
------------ ------------- -------------Sample 3
0.01
35.23
35.24
------------ ------------- -------------Sample 4
0.01
0.05
0.05
------------ ------------- -------------Sample 5
0.90
12.86
13.76
------------ ------------- -------------Sample 6
0.14
38.83
38.97
------------ ------------- --------------

Phosphate
Silicic acid
0.09
1.38
---------------------1.19
65.62---------------------2.10
133.97---------------------0.08
1.48---------------------1.05
72.30---------------------2.74
131.50----------------------

Brief descriptions of analysis:
System used: BRAN+LUEBBE TRAACS 800
Your comments:
We feel uncertain as to the values of nitrite + nitrate and silicic acid forsample 4.
To evaluate the overall performance of our measuring system, we measured
concentrations of nutrients in the intermediate layer of the western North Pacific,
and calculated the repeatability (n = 5). The results are as follows:692003 RMNS Intercomparison

0.01 ± 0.003 (average ± 1 SD) for nitrite; 36.52 ± 0.047 for nitrate; 36.53 ± 0.044
for nitrite + nitrate; 2.52 ± 0.005 for phosphate; and 146.09 ± 0.267 for silicic acid.
This evaluation is close to that of the measuring system during the cruise of theMirai (MR03-K01).

70

2003 RMNS Intercomparison

Laboratory 14
2003 Intercomparison Exercise for Reference Material for Nutrients in Seawater in a
Seawater Matrix

RESULTS REPORT FORMLABORATORY:KEIFUMARUDATE OF RECEIPT OF SAMPLES:
1７APRIL 2003
DATA OF ANALYSIS:Results in micromoles per kilogram

Sample 1
Sample 2
Sample 3
Sample 4
Sample 5
Sample 6

NitriteNitrateNitrite +nitratePhosphate

0.00-----------0.22-----------0.00-----------0.00-----------0.89-----------0.23------------

0.02------------16.89------------35.66------------0.00------------13.29------------38.85-------------

0.02-------------17.11-------------35.66-------------0.00-------------14.19-------------39.08--------------

0.07-----------1.25-----------2.27-----------0.05-----------1.15-----------2.91------------

Silicic acid-------------------------------------------------------------

Brief descriptions of analysis: The analytical method is the oceanographic observation
guideline (JMA)
Samples were analyzed on an AAII instrument
Comments: 3 is analyzed, and it third.
Shown value the salinity used for the calculation.
Nitrite + nitrate of reduction is 98%
Water temperature 26 ºC (room temperature)71

2003 RMNS Intercomparison

Laboratory 15
RESULTS REPORT FORMLABORATORY:
Nagasaki Marine Observatory
DATE OF RECEIPT OF SAMPLES:DATA OF ANALYSIS:Results in micromoles per kilogram
NitriteNitrateNitrite + nitrate
Sample 10.00 ± 0.00
0.02 ± 0.18
0.02 ± 0.18------------ ------------- -------------Sample 2
0.16 ± 0.00 17.71 ± 0.18 17.87 ± 0.18------------ ------------- -------------Sample 3
0.01 ± 0.00 35.78 ± 0.18 35.79 ± 0.18------------ ------------- -------------Sample 4
0.02 ± 0.00
0.06 ± 0.18
0.08 ± 0.18------------ ------------- -------------Sample 50.94 ± 0.00 13.24 ± 0.18 14.18 ± 0.18------------ ------------- -------------Sample 6
0.15 ± 0.00 39.99 ± 0.18 40.14 ± 0.18------------ ------------- --------------

Phosphate Silicic acid
0.06 ± 0.01------------ ----------1.24 ± 0.01------------ ----------2.21 ± 0.01------------ ----------0.09 ± 0.01------------ ----------1.12 ± 0.01------------ ----------2.88 ± 0.01------------ -----------

Brief descriptions of analysis:
The sample subdivided to the sample cup of three, and analyzed six samples at the sametime.
The analytical error is a standard deviation of the standard.

72

2003 RMNS Intercomparison

Laboratory 16
RESULTS REPORT FORMLABORATORY: KANSODATE OF RECEIPT OF SAMPLES:
2003/1/17
DATA OF ANALYSIS:Sample 1
Sample 2
Sample 3
Sample 4
Sample 5
Sample 6

2003/4/16
2003/4/16
2003/4/16
2003/4/16
2003/4/16
2003/4/16

Results in micromoles per kilogram
NitriteNitrate Nitrite + nitrate
Sample 10.03 ± 0.00
0.12 ± 0.03------------ ------------- -------------Sample 2
0.13 ± 0.00 17.47 ± 0.04------------ ------------- -------------Sample 3
0.02 ± 0.00 35.80 ± 0.10------------ ------------- -------------Sample 40.04 ± 0.00
0.08 ± 0.00------------ ------------- -------------Sample 50.94 ± 0.00 13.07 ± 0.06------------ ------------- -------------Sample 6
0.18 ± 0.00 36.85 ± 0.14------------ ------------- --------------

Phosphate
Silicic acid
0.18 ± 0.01
1.71 ± 0.03---------------------1.17 ± 0.01
64.71 ± 0.34---------------------2.19 ± 0.02 136.30 ± 0.62---------------------0.20 ± 0.01
1.85 ± 0.07---------------------1.18 ± 0.01
73.03 ± 0.50---------------------2.82 ± 0.02 136.27 ± 0.19----------------------

Brief descriptions of analysis:
Nutrient analysis was performed on two Bran+Luebbe TRAACS 2000 systems with
4-channel analyzing systems for nitrate, nitrite, silicic acid, and phosphate.
Nitrite: Nitrite was determined by diazotizing with sulfanilamide and coupling with
N-1-naphthyl-ethylenediamine to form a colored azo dye whose absorbance wasmeasured at 550 nm using a 5-cm-long cell.
Nitrate: Nitrate in seawater was reduced to nitrite in a reduction tube (Cd–Cu tube), andthe nitrite determined by the method described above, but the flow cell used in nitrate
analysis was 3-cm-long cell.
Phosphate: The method of Murphy and Riley (1962) was used with separate additions73

2003 RMNS Intercomparisonof ascorbic acid and mixed molybdate–sulfuric acid–tartrate. The absorbance of thephosphomolybdate produced was measured at 880 nm using a 5-cm-long cell.
Silicic acid: The standard AAII molybdate–ascorbic acid method was used. The
temperature of the sample was maintained at 45–50 ºC using a water bath to reduce thereproducibility problems encountered when the samples were analyzed at different
temperatures. The absorbance of the silicomolybdate produced was measured at 660 nm
using a 3-cm-long cell.

74

2003 RMNS Intercomparison

Laboratory 17
RESULTS REPORT FORMLABORATORY:
Hokkaido National Fisheries Research Institute, Fisheries Research Agency(116 Katsurakoi, Kushiro, 085-0802 Hokkaido, Japan)
DATE OF RECEIPT OF SAMPLES:
March 2003
DATA OF ANALYSIS:Results in micromoles per kilogram
NitriteNitrateNitrite + nitrate
Sample 1
0.045
0.05------------ ------------- -------------Sample 2
0.118
18.10
------------ ------------- -------------Sample 3
0.048
37.10
------------ ------------- -------------Sample 4
0.050
0.23
------------ ------------- -------------Sample 5
0.968
13.71
------------ ------------- -------------Sample 6
0.241
37.74
------------ ------------- -------------Brief descriptions of analysis:
Samples were measured on April 22 and 23, 2003.
Each reported value is the mean of 4 measurements.

75

Phosphate
0.078-----------1.320-----------2.143-----------0.074-----------1.118-----------2.690------------

Silicic acid
2.29----------66.63----------135.19----------2.61----------73.74----------133.46-----------

2003 RMNS Intercomparison

Laboratory 18
RESULTS REPORT FORMLABORATORY:
Seikai National Fisheries Research Institute
DATE OF RECEIPT OF SAMPLES:
Maybe mid January 2003
DATA OF ANALYSIS:Results in micromoles per kilogram (mean ± standard deviation)
Nitrite Nitrate Nitrite + nitrate
Phosphate
Silicic acid
Sample 1------------ ------------- 0.07 ± 0.03
0.10 ± 0.02
0.12 ± 0.23
Sample 2------------ -------------17.78 ± 0.09
1.19 ± 0.01
66.08 ± 0.19
Sample 3------------ -------------35.41 ± 0.08 2.06 ± 0.01 136.83 ± 0.58
Sample 4------------ ------------ 0.05 ± 0.03
0.13 ± 0.02
0.32 ± 0.23
Sample 5------------ -------------14.09 ± 0.04
1.06 ± 0.02
73.21 ± 0.27
Sample 6------------ -------------38.47 ± 0.23 2.71 ± 0.01 134.95 ± 0.54

76

2003 RMNS Intercomparison

Appendix III
Documents77

2003 RMNS Intercomparison

78

2003 RMNS Intercomparison

Appendix III – Documents
III – 1 Call for participating
Dear Colleague,
This letter is to invite you to “Intercomparison Exercise for Reference Material of for
Nutrients in Seawater in a seawater matrix 2003”.
Progress in Reference Material for Nutrients in Seawater (RMNS) has done by ourgroup during these five years. The seawater in a stainless steel container of 40 liters was
autoclaved at 120 deg. C, 2 hours, 2 times. The autoclaved seawater of 90 ml was filledin polypropylene bottles. The homogeneity of the RMNS was confirmed as same
magnitude as a repeatability of the measurements of the same sample. The long-term
storage experiment of our RMNS for up to 4 years showed that homogeneity andconcentrations of nutrient are maintained for about 4 years. Our results, then, haddemonstrated that the RMNS for nitrate, nitrite, phosphate and silicic acid can beobtained using autoclaving and can be stored for about up to 4 years.
The objectives of this effort are to establish traceability on nutrient analyses inseawater and to become the onboard nutrients analyses more easy where more accurate
nutrients data could become available. We also focused to provide the certified
reference material in this field. Although the Group of Expert on standards andReference Material had clearly pointed out (UNESCO, 1991,1992) the necessity ofgiving high priority to developing production of RMNS, the Certified Reference
Materials which are in a seawater matrix are not available in this field at this moment.
The only way now is to conduct inter-laboratory comparison experiments bylaboratories, which would provide consensus values and their uncertainty of nutrientsconcentrations for nitrate, nitrite, phosphate and silicic acid.
The reply sheet in a document attached should be used to confirm your participationand following points should be clearly understood.
1. If you do not return the sheet by the end of November 2002, you will not receive any
RMNS samples.
2. I will acknowledge receipt of your reply and list of the participants on 3 Dec. 2002. If
you do not receive an acknowledgement by 7 Dec. 2002, please contact us in case yourreply has gone elsewhere.
3. A reply sheet will confirm that your wish to participate this comparison exercise andto analyzing the samples and submitting results before the reporting deadline,
tentatively end of April 2003, or returning the samples intact before the reporting
deadline, if for any reason you are unable to analyze them. I expect to receive nutrientsconcentrations for nitrate, nitrite, phosphate and silicic acid.
4. All results reported will be published with the name of data originator after the data79

2003 RMNS Intercomparisonin the publication is confirmed by each data originator.
Some documents are available at an anonymous ftp site of our Institute. You will find
three files, two of them are posters presented at Ocean Sciences Meeting at Hawaii in
Feb. 2002 and one of them are draft of manuscript entitled “Reference material for
nutrients in seawater in a seawater matrix”. The site is mri-2.mri-jma.go.jp, you canlogin as anonymous user using your e-mail address. The files are at/pub/geochem/outging/OSM.
Best regards,
Michio AOYAMAIntercomparison Exercise for Reference Material of for Nutrients in Seawater in aseawater matrix 2003
IMPORTANT DATESDEADLINE OF REPLY: 30 NOVEMBER 2002.
LIST OF PARTICIPANT: 3 DECEMBER 2002.
SAMPLES SHIPPED BY : 10 JANUARY 2003
REPORTING DEADLINE: 30 APRIL 2003
EXPECTED DRAFT OF INTERCOMPARIOSN SUMARY: 30 JUNE 2003
“Intercomparison Exercise for Reference Material of for Nutrients in Seawater in aseawater matrix 2003”.

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III – 2 Instructions for RMNS bottles
1. Package contents
1) Your package contains 6 bottles
2) You will see the sample IDs, from 1 to 6, and your name.
2. Preparations of samples
1) No preservatives have been added.
2) The details of preparation are given in the documents at our anonymous ftp site. You
will find three files, two of them are posters presented at Ocean Sciences Meeting at
Hawaii in Feb. 2002 and one of them are draft of manuscript entitled “Referencematerial for nutrients in seawater in a seawater matrix”. The site is mri-2.mri-jma.go.jp,
you can login as anonymous user using your e-mail address. The files are at/pub/geochem/outging/OSM.
3. Analysis
1) RMNSs are ready for analysis, then please use them without filtration just after you
open the bottles. Again, no preservatives have been added, when opened their sterility
will be lost.
2) Salinities are in the range 34.5-34.8.
Sample 134.75+-0.10
Sample 234.65+-0.10
Sample 3(assumed to be 34.65)
Sample 434.80+-0.10
Sample 534.60+-0.10
Sample 634.50+-0.10
I will determine the salinity of sample3 and deliver them to the participants later. Thenplease use 34.65 as the tentative salinity of sample3 to get the density of sample3.
3) Concentrations can be assumed to be in the following ranges in micromoles per
kilogram. Atlantic people may be surprised by high concentrations of sample 3 and 6,
however, these RMNS are Pacific origin.
NitriteNitrateNitrite + Nitrate Phosphate
Silicic acid
Sample 1
Sample 2
Sample 3
Sample 4
Sample 5
Sample 6<0.5-----------<0.5-----------<0.5-----------<0.5-----------<1.2-----------<1.0------------<5-----------<20-----------<45-----------<5-----------<20-----------<45------------<0.5-----------<1.5-----------<3.0-----------<0.5-----------<1.5-----------<3.0------------

4. Reporting of results
81<5-----------<80-----------<150-----------<5-----------<80-----------<150------------

2003 RMNS Intercomparison

1) Report concentrations in micromoles per kilogram using the reporting format
attached.
2) Please report one value for each parameter for each sample.
3) Participants are welcome to add your estimation on analytical error for eachparameter for each sample (ex. 1.23±0.04; 23.45±0.67).
4) REPORTING DEADLINE: 30 APRIL 2003

Intercomparison Exercise for Reference Material of for Nutrients in Seawater in aseawater matrix 2003

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Appendix III- 3 Results report form
LABORATORY:DATE OF RECEIPT OF SAMPLES:DATA OF ANALYSIS:SAMPLE 1
SAMPLE 2
SAMPLE 3
SAMPLE 4
SAMPLE 5
SAMPLE 6

Results in micromoles per kilogram
NitriteNitrateSAMPLE 1
SAMPLE 2
SAMPLE 3
SAMPLE 4
SAMPLE 5
SAMPLE 6

Nitrite + Nitrate Phosphate

Silicic acid------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Options;
Brief descriptions of analysis;Your comments;
THESE RESULTS SHOULD BE SENT TO:

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Michio AOYAMA
maoyama@mri-jma.go.jp
or mail toMichio AOYAMA
Geochemical Res. Dep.
Meteorological Res. Inst.
1-1
Nagamine,305-0052
JAPAN2003 RMNS Intercomparison

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Appendix IV
History of nutrients intercomprisons852003 RMNS Intercomparison

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Appendix IV

History of nutrient intercomparisonsThis history of nutrient intercomparisons is based on several reports of previous
intercomparison exercises. The histories of the first to fourth ICES exercises are derived
from Aminot and Kirkwood’s (1995) detailed report of the fifth ICES intercomparison,
which includes histories of the first to fourth ICES exercises. Histories of the fifth ICES
exercise and the first and second NOAA/NRC intercomparisons are also summarized inthis appendix.
1. First ICES Exercise
The first intercalibration to include nutrients was an entirely Baltic affair in June 1965,
when three research vessels met by private agreement in Copenhagen:ArandaHermann Wattenberg
Skagerak

Institute of Marine Research (IMR), Helsinki
Institut für Meereskunde, Kiel
Royal Fishery Board, Gothenburg

Each ship contributed freshly collected bulk samples to the experiment, which were
subsampled and analyzed on board each of the three participating ships on the same day.
Oxygen, salinity, chlorinity, alkalinity, and phosphate were determined.

2. Second ICES Exercise
The second ICES exercise, carried out in 1966 under the auspices of the newly formed
ICES Working Group on the Intercalibration of Chemical Methods, was still
predominantly a Baltic initiative and consisted of two parts: Part I, Leningrad, during
the 5th Conference of Baltic Oceanographers; and Part II, Copenhagen, at the 54th
ICES Statutory Meeting.
Part I, Leningrad (May 1966)
The participating research vessels were
Alkor
Okeanograf
Prof Otto Krammel
Skagerak

Institut für Meereskunde, Kiel
Institute of Marine Research, Leningrad
Institut für Meereskunde, Warnemünde
Fisheries Board of Sweden, Gothenburg

Research vessels delivered bulk samples, which were subsampled and analyzed almost
immediately for oxygen, salinity, chlorinity, pH, and phosphate.
Part II, Copenhagen (September 1966)
The list of interested parties continued to grow and, in addition to Baltic countries,
Norway and the UK were represented. Research vessels delivered bulk samples and the87

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various participants analyzed samples simultaneously in Copenhagen. The determinands
of primary interest included not only oxygen, salinity, chlorinity, and phosphate, as inPart I (Leningrad) and the previous year's exercise (Copenhagen, 1965), but also nitrate,
nitrite, and silicate.
The final report, edited by Grasshoff (UNESCO, 1966), makes no mention of nitrate or
nitrite but some of those who were present confessed that these results were "too terrible
to be included"! To be fair to those involved, 1966 was an early time in the developmentof heterogeneous cadmium-based nitrate/nitrite reduction techniques and some of theassociated problems were presumably not fully appreciated at the time.
Evidently nitrate analysis had some way to go to achieve the reliability and ease ofoperation of the Murphy and Riley (1962) phosphate technique, but it is worth notingthat intercomparison work on phosphate so far had consisted of simultaneous analysis
of freshly obtained subsamples by a small number of highly competent workers, inclose contact with each other, exchanging calibration solutions, ideas, technical details,
etc. Subsequent to the Copenhagen trial, Jones and Folkard (ICES, 1966) undertook adetailed laboratory examination of the individual methods used by the participants and,in their contribution to Grasshoff’s report, they announced, "There seems to be no needfor any further intercalibration in the determination of inorganic phosphate by thismethod."Clearly this happy state of affairs could and did not last. Along came the autoanalyzer!
3. Third ICES Exercise
The third ICES exercise was organized by the ICES Working Group on Chemical
Analysis of Sea Water under the joint auspices of ICES and SCOR and its official title,"The International Intercalibration Exercise for Nutrient Methods2”, shows that it set
out to be an ambitious project.
Samples were distributed in 1969–1970 and 45 laboratories from 20 countries submitted
results, but the final report on the results of the exercise was not published for several
years (ICES, 1977).
The time had come to study "nutrients" separately from oxygen, salinity, chlorinity, andpH, but with the awareness of problems arising from the instability of natural seawater
samples, the organizers chose to use standard solutions that were prepared anddistributed by the Sagami Chemical Research Center, Japan. [Note added by Aoyama:
The standard solutions used in this exercise were Cooperative Survey ofKuroshio(CSK) standards, which are solutions in artificial seawater for nitrate,
phosphate, and silicate and in pure water for nitrite.]In this exercise, participants performed the analyses in their own laboratories but,
despite being supplied (knowingly) with appropriate blank solutions for eachdetermination, the overall accuracy, particularly for phosphate and nitrate, wasdisappointing.

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The report concludes, "As methods did not diverge much, it is clear that variations must
be sought primarily in the standardization procedures. The results will also aid
participants in re-evaluating their analytical procedures by comparison of their methods
with those that appear most satisfactory from this exercise".
The names of the participating laboratories were listed, as were the tables of results, but
it was not possible to link them together. Hindsight suggests that this may have beencounterproductive; we now suspect that there is no greater incentive for a laboratory to
improve its performance than the knowledge that peer laboratories throughout the world
are aware that it is producing poor quality data.
4. Fourth ICES Exercise
Various "workshop" and multiship events following the ICES/SCOR exercise included
nutrient studies, but it was many years later (1988) before the ICES Marine Chemistry
Working Group produced volunteers (Don Kirkwood, Alain Aminot, and Matti Perttilä)
to organize the next large-scale intercalibration exercise, designated "NUTS I/C 4". This
exercise did not set out to be worldwide, beginning only with laboratories in ICES
Member Countries, but other laboratories who were interested in participating were notturned away.
The fourth exercise differed from the third exercise in three important respects.
1) The test samples were natural or near-natural seawater rather than standard solutions.
(Strictly speaking, this made the exercise an intercomparison rather than anintercalibration.)
2) Participants were unaware that "blank" samples were included.
3) Anonymity was abolished. Participants were made aware from the outset that the
final report would list identities of laboratories, results, and a means for any reader
to contact them.
Sixty-nine laboratories from 22 countries submitted results and, thanks in some measure
to the telefax machine, the final 83-page report (Kirkwood et al., 1991) was in the handsof participants within two years of the distribution of samples. Statistical treatment
identified 58 laboratories consistent in phosphate analyses, 51 consistent in nitrate
analyses, and 48 consistent in both phosphate and nitrate analyses, including a group of
12 whose results were especially close to the consensus concentrations.

5. Fifth ICES Exercise
Due to the generally perceived need for more and better quality control in analyticalmeasurement, a fifth ICES intercomparison exercise was carried out in 1993. A total of
142 sets of samples were distributed in 31 countries. Results were returned by 132
laboratories, 61 of which had participated in the fourth intercomparison and 56 of whichwere participating in QUASIMEME (Quality Assurance of Information for Marine892003 RMNS Intercomparison

Environmental Monitoring in Europe). The distribution of laboratories was as follows:
UK (22), Germany (18), Sweden (13), France (11), Spain (8), USA (7), Norway(5),Ireland(5), Australia(4) Canada(4), Netherlands(4), Denmark(3), Greece(3), Portugal(3),Belgium(2), Estonia(2), Finland(2), Italy(2), Poland(2), Argentina(1), Bermuda(1),China(1), Faroe Islands(1), Iceland(1), Japan(1), Latvia(1), Lithuania(1), New
Zealand(1), Qatar(1), South Africa(1), Turkey(1),The method of sample preparation, autoclaving, for the fifth intercomparison imposedconstraints that resulted in there being only two relevant determinands per sample(nitrate and nitrite in one series, and phosphate and ammonia in the other series).
A large volume of low-nutrient natural seawater was spiked with known concentrationsof nutrient salt. Although the concentrations in the distributed samples covered a greater
concentration range than that in the fourth intercomparison, the concentration levels
were representative of the Atlantic Ocean, 1–26 µmol L–1 for nitrate and 0.08–1.85µmol L–1 for phosphate.
6. 2000 NOAA/NRC Intercomparison
The test material distributed in this intercomparison was MOOS-1, a proposed certified
reference material for nutrients in seawater (Clancy and Willie, 2004). The sample
material was intended to be a certified reference material for silicate, phosphate, nitrite,
and nitrate + nitrite. Participating laboratories were each sent two bottles of MOOS-1
and requested to perform duplicate analyses on each of the bottles. The preparedsamples were sent to 36 participating laboratories. Thirty sets of results were returned.
The results of this intercomparison may, in several respects, have been compromised bysample homogeneity problems. The target standard deviation for measuring p-scores is
too broad and does not reflect the measurement precision that can be attained.
7. 2002 NOAA/NRC Intercomparison
An intercomparison exercise was undertaken to assess the current capabilities of a groupof laboratories to quantitate orthophosphate, silicate, nitrite, and nitrite + nitrate in aseawater sample. This was the second such exercise sponsored by the NOAA Center for
Coastal Monitoring and Assessment (CCMA) and coordinated by the Institute for
National Measurement Standards of the National Research Council of Canada. Two
seawater samples — one from Pensacola Sound, FL, and a proposed certified referencematerial for nutrients in seawater (MOOS-1) — were distributed to 31 laboratories.
Twenty-four laboratories submitted data. Methodologies were not prescribed to theparticipants; however, all reported results were obtained using traditional colorimetric
procedures. Generally, satisfactory agreement among participants was achieved, withresults within 10% of the assigned mean values.
The results from this exercise suggest that the homogeneity problem identified in thefirst NOAA/NRC intercomparison exercise was overcome, although the orthophosphatedata indicate a larger interlaboratory spread of results than expected.
Results for silicate, nitrite, and nitrite + nitrate in the distributed seawater samples were
acceptable for the majority of the participants and generally deviated <±10% from the90

2003 RMNS Intercomparison

assigned mean. All laboratories used methodology based on colorimetric principles.

8. 2003 MRI Intercomparison
Autoclaved natural seawater was prepared for intercomparison samples. Sample
homogeneity was confirmed by repeatability of measurement. Sets of 6 samples
covering a concentration range greater than that in previous intercomparisons were
distributed. The concentrations were 0–38 µmol kg–1 for nitrate, 0–0.9 µmol kg–1 fornitrite, 0–2.7 µmol kg–1 for phosphate, and 0–136 µmol kg–1 for silicic acid. A total of
18 sets of samples were distributed to 18 laboratories in 5 countries. Results werereturned by 17 laboratories in 5 countries. Although consensus concentrations wereobtained for the 6 samples, the standard deviations were 4.5 times and more than 10times greater than those of the homogeneities for phosphate and silicic acid,respectively. For nitrate, the standard deviations were only about double thehomogeneities. These results indicate that variability in in-house standards of theparticipating laboratories — rather than analytical precision — is the primary source ofinterlaboratory discrepancy. Therefore use of a certified RMNS is essential forestablishing nutrient data sets that can be compared across laboratories, especially forsilicic acid and phosphate.

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