AQUACON-MedBas project

AQUACON-MedBas project

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Subproject No. 5 : freshwater analysis : intercomparison 2000
Environmental research
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INSTITUTE FOR ENVIRONMENT AND SUSTAINABILITY
AQUACON-MedBas PROJECT
Subproject No. 5
FRESHWATER ANALYSIS
Intercomparison 2000
R. Mosello , G.A. Tartan, M. Bianchi*, M.C. Brizzio, R. Giuliano,
A. Marchetto, S. Polesello**, D. Rembges* and H. Muntati*
Istituto Italiano di Idrobiologia, Consiglio Nazionale delle Ricerche, Verbania Pallanza (Italy)
institute for Environment and Sustainability, Joint Research Centre, Ispra (Italy)
**Istituto di Ricerca sulle Acque, Consiglio Nazionale delle Ricerche, Brugherio (Italy)
'Corresponding author: r.mosello@iii.to.cnr.it
EUROPEAN COMMISSION
JOINT RESEARCH CENTRE
2002 EUR 20427 EN INSTITUTE FOR ENVIRONMENT AND SUSTAI NABI LITY
AQUACON-MedBas PROJECT
Subproject No. 5
FRESHWATER ANALYSIS
Intercomparison 2000
R Mosello , G.A. Tartari, M. Bianchi*, M.C. Biizzio, R Giuliano,
A. Marchetto, S. Polesello**, D. Rembges* and H. Muntau*
Istituto Italiano di Idrobiologia, Consiglio Nazionale delle Ricerche, Verbania Pallama (Italy)
institute for Environment and Sustainability, Joint Research Centre, Ispra (Italy)
**Istituto dì Ricerca sulle Acque, Consiglio Nazionale delle Ricerche, Brugherio (Italy)
'Corresponding author: r.mosello@iii.to.cnr.it
EUROPEAN COMMISSION
JOINTRESEARCH CENTRE
2002 I — 1 EUR 20427 EN LEGAL NOTICE
Neither the European Commission nor any person
acting on behalf of then is responsible for
the use which might be made of the following information.
A great deal of additional information on the
European Union is available on the Internet.
It can be accessed through the Europa server
(http://europa.eu.int).
EUR 20427 EN
© European Communities, 2002
Reproduction is authorised provided the source is acknowledged
Printed in Italy CONTENTS
ABSTRACT 3
1. INTRODUCTION 4
2. SAMPLE PREPARATION 6
3. SAMPLE HOMOGENEITY AND STABILITY
4. EXPECTED RESULTS 9
5. LABORATORIES PARTICIPATING AND ANALYTICAL METHODS USED.. 10
6. DATA ELABORATION 19
7. RESULTS 23
8. ION CHROMATOGRAPHY DETAILS 65
9. REPEATABILITY AND REPRODUCIBILITY IN ION CHROMATOGRAPHY. 86
10. COMPARISON OF CATIONS ANALYSIS WITH IC, AAS, AES, ICP 9
11. DISCUSSION 98
12. CONCLUSIONS 104
13. REFERENCES7 ABSTRACT
The intercomparìson exercise discussed in this report is the third AQUACON
exercise on samples with concentrations close to those of natural freshwater, and
including chemical variables which play a major part in eutrophication studies, such as
phosphate, total phosphorus, total nitrogen and silica A total of 155 laboratories sent
back results. Artificial surface water samples, with concentrations close to the values
ordinarily measured in nature, stabilised with chloroform (samples A, B), and solutions
of ammonium chloride, potassium di-hydrogen phosphate, creatinine, glucose 1-
phosphate di-sodium salt and sodium esqfluorosilicate, stabilised with chloroform and
sulphuric acid to pH 3.5 (solutions C, D), were prepared in September 2000 by the
Environment Institute of the Joint Research Centre of Ispra, and checked for
homogeneity and stability in time in collaboration with the C.N.R Istituto Italiano di
Idrobiologia, Verbania Ρ alianza.
Results showed a high number of outliers in the measurements of ammonium,
phosphate and nitrate, indicating a lack of precision which was more marked in the low
concentration samples. For other variables (e.g. pH, conductivity, alkalinity, silicate,
chloride, phosphate and total phosphorus) the number of outliers is relatively low, but
there is a wide dispersion of the values around the expected concentrations. Several
results showed marked differences in the ionic balance and between measured and
calculated conductivity. The results highlight the need for this kind of quality control of
analyses to improve analytical quality. An example of the checks is provided as an
Excel file, available on request, using the results of this exercise. The Youden graphs
showed the prevalence of systematic over random errors for most of the chemical
variables examined
A detailed study of the causes of errors in ion chromatography analyses for anions
and cations, was part of the present intercomparìson. Of the various technical aspects
considered, one important source of error was neglect of the non-linearity of
calibration curves. In a selected number of experienced laboratories (17), repeatability
and reproducibility tests of anion and cation measurements in IC were performed in
accordance with the ISO 5725. Relative repeatability (r%) ranges from 5.2 to 15.3 for
anions and from 3.5 to 13.1 for cations, while relative reproducibility (R%) ranges from
9.2 to 21.4 for anions and from 6.6 to 19.0 for cations. These results show that there
are no significant differences in precision and reliability between anion and cation
analyses, and that the best repeatability and reproducibility of IC methods of water
analysis that can be achieved are about 5% and 10% respectively.
Several other details of IC measurement are discussed; each of them should be
carefully considered by the laboratories to check and, if necessary, correct the
procedure used 1. INTRODUCTION
This report presents the results of the third intercomparìson exercise on surface
water samples performed in the framework of the project "Analytical Quality Control
and Assessment Studies in the Mediterranean Basin (AQUACON)", part of the
"Protection of the Environment" program executed by the Environment Institute of the
Joint Research Centre (JRC-EI), in collaboration with the Istituto Italiano di Idrobiologia
of the Italian National Research Council (CNR-JH). The AQUACON project aims at the
identification, quantification and reduction/elirnination of random and systematic errors
associated with the most important branches of environmental analysis. Topics include
the analysis of solute in aqueous solutions, mercury in sea food, toxic substances in
industrial discharge and in lake/sea sediments (Muntau et al. 1995).
Previous exercises comparing chemical methods on surface water samples were
carried out in 1996 and 1997 (Mosello et al 1997a, 1998b), closely related to the
exercises on rainwater samples which have been performed since 1991 (Mosello et al.
1992, 1993, 1994, 1995, 1996, 1997b, 1998a, 1999). The main differences are the
ranges of concentrations considered in the two types of samples (Tab. 1), and the
analysis of phosphate and total phosphorus, total nitrogen, silica and low concentrations
of ammonium performed in the surface water exercises, because of the importance of
these variables in limnologica! studies.
Tab. 1 - Main differences in concentration ranges between rain and surface water samples used
in AQUACON intercomparisons.
Atmospheric
Variables Unit Surface water
deposition
3.5-5.0 >7.0 pH
μ8 cm"1 20 °C <100 100-400 Conductivity
meql1 <0.2 >0.9 Alkalinity
0.2-2 2-10 mgr1 cr
mgl"1 <15 10-100 sor
mgr1 0.1-2 0.2-1.0 N-N03-
Ca- 0.2-5 15-50 mgl'1
Mg" mgl"1 0.2-2 2-10
0.2-5 Na+ mgl1 2-10
0.2-2 iC mgl1 2-10
mg NT1 0.4-2 <0.2 N-NEU*
μ8ΡΓ1 - 10-300 P-PO4
μδΡΓ1 - 10-300 Total Ρ
mgNl·1 - 1-5 Total Ν
mg Si r1 - 1-5 Si The laboratories invited to participate in the surface water intercomparìson are
broadly the same as those involved in the rainwater exercise, with the addition of several
public or research laboratories, mainly from Italy, involved in environmental control or in
eutrophication studies. Some of these laboratories already co-operate in other research
activities, so that eventually laboratories participating in the following projects were
involved:
• Analytical Quality Control and Assessment Studies in the Mediterranean Basin
(AQUACON);
• European Mountain lake Ecosystems: Régionalisation diaGnostics & Socio-Economie
Evaluation (EMERGE)
• International Co-operative Programme on Assessment and Monitoring of Air
Pollution Effects on Forests, in the framework of the "UN ECE Convention on Long-
Range Transboundary Air Pollution" (ICP Forests);
• South American laboratories involved in freshwater research.
The aim of this report is to describe the methods used in preparing and checking the
samples and to discuss the results of the exercise. Special emphasis will be given to algal
nutrients (phosphate and total phosphorus, total nitrogen and silicate), as well as to
ammonium nitrogen, considered at concentrations much lower than in the rainwater
samples and to ion chromatography analysis.
Special attention is paid to IC, as this technique is used for 60 and 30% of the
analyses of anions and cations, respectively: repeatability and reproducibility were
calculated in accordance with the ISO 5725 from a selected number of laboratories.
The importance of checking the correctness of the data through the ion balance and
by comparing measured and calculated conductivity is emphasised, as we think that these
techniques, although often described in papers (e.g. Miles and Yost, 1982), in analytical
handbooks (e.g. A.P.H.A., A.W.W.A., W.E.F. 1995a) and in previous AQUACON
reports (Mosello et al., 1992, 1997 a,b; 1998 a,b) are not yet sufficiently widespread in
routine analytical practice.