REPORTS OF THE FINNISH ENVIRONMENT INSTITUTE 4 7 Interlaboratory Proficiency Test /7 Chlorophyll a, colour, conductivity, nutrients, ph and turbidity in natural waters Mirja Leivuori, Riitta Koivikko, Mika Sarkkinen, Keijo Tervonen, Sari Lanteri, Ritva Väisänen and Markku Ilmakunnas Finnish Environment Institute
ABSTRACT Interlaboratory Proficiency Test /7 Proftest SYKE carried out the proficiency test for the determination of chlorophyll a, colour, conductivity, nutrients, ph and turbidity in natural waters in February 7. In total, participants joined in the proficiency test. Either the calculated concentration, the robust mean or the mean of the results reported by the participants was chosen to be the assigned value for the measurands. The performance of the participants was evaluated by using s. In this proficiency test 8 % of the results were satisfactory when the deviation % and. ph units from the assigned value was accepted. Warm thanks to all the participants! Keywords: water analysis, chlorophyll a, nutrients, ph, conductivity, colour, turbidity, water and environmental laboratories, proficiency test, interlaboratory comparison TIIVISTELMÄ Laboratorioiden välinen pätevyyskoe /7 Proftest SYKE järjesti luonnonvesiä analysoiville laboratorioille pätevyyskokeen helmikuussa 7. Pätevyyskokeessa määritettiin klorofylli a, ravinteet, ph sameus, sähkönjohtavuus ja väri luonnonvesistä. Pätevyyskokeessa oli yhteensä osallistujaa. Testisuureen vertailuarvona käytettiin laskennallista pitoisuutta, osallistujien tulosten robustia keskiarvoa tai keskiarvoa. Tulosten arviointi tehtiin z-arvon perusteella, jolloin määrityksissä sallittiin %:n ja. ph yksikön poikkeama vertailuarvosta. Koko aineistossa hyväksyttäviä tuloksia oli 8 %. Kiitos osallistujille! Avainsanat: vesianalyysi, klorofylli a, ravinteet, ph, sähkönjohtavuus, väri, sameus, vesi- ja ympäristölaboratoriot, pätevyyskoe, laboratorioiden välinen vertailumittaus SAMMANDRAG Provningsjämförelse /7 Under february 7 genomförde Proftest SYKE en provningsjämförelse, som omfattade bestämningen av a-klorofyll, näringsämnen (N NH4, N NO+NO, N tot, P PO4, P tot ), ph, ledningsförmåga, grumlighet och färg i naturvatten. Proven sändes ut till laboratorier. Som referensvärde av analytens koncentration användes det teoretiska värdet, robust medelvärdet eller medelvärdet av deltagarnas resultat. Resultaten värderades med hjälp av z-värden. I jämförelsen var 8 % av alla resultaten tillfredsställande, när % och, ph-mätetal avvikelsen från referensvärdet accepterades. Ett varmt tack till alla deltagarna! Nyckelord: vattenanalyser, klorofyll a, färg, grumlighet, näringsämne, N NH4, N NO+NO, N tot, P PO4, P tot, ph, ledningsförmåga, provningsjämförelse, vatten- och miljölaboratorier
CONTENTS Abstract Tiivistelmä Sammandrag... Introduction... 7. Responsibilities... 7. s... 8. Samples and delivery... 8.4 Homogeneity and stability studies... 9.5 Feedback from the proficiency test... 9.6 Processing the data... 9.6. Pretesting the data... 9.6. Assigned values... 9.6. Standard deviation for proficiency assessment and... Results and conclusions.... Results.... Analytical methods.... Uncertainties of the results... 5 Evaluation of the results... 7 4 Summary... 9 5 Summary in Finnish... 9 References... APPENDIX : s in the proficiency test... APPENDIX : Preparation of the samples... APPENDIX : Homogeneity of the samples... APPENDIX 4 : Stability of the samples... 4 APPENDIX 5 : Feedback from the proficiency test... 6 APPENDIX 6 : Evaluation of the assigned values and their uncertainties... 7 APPENDIX 7 : Terms in the results tables... 8 APPENDIX 8 : Results of each participant... 9 APPENDIX 9 : Results of participants and their uncertainties... 46 APPENDIX : Summary of the s... 57 APPENDIX : s in ascending order... 59 APPENDIX : Results grouped according to the methods... 7 APPENDIX : Examples of measurement uncertainties reported by the participants... 8 Proftest SYKE NW /7 5
6 Proftest SYKE NW /7
Introduction Proftest SYKE carried out the proficiency test (PT) for analysis of chlorophyll a, colour, conductivity (5), N NH4, N NO+NO, N tot, P PO4, P tot, ph, and turbidity in brackish and river waters in February 7 (NW /7). In the PT the results of Finnish laboratories providing environmental data for Finnish environmental authorities were evaluated. Additionally, other water and environmental laboratories were welcomed in the proficiency test. Finnish Environment Institute (SYKE) is appointed National Reference Laboratory in the environmental sector in Finland. The duties of the reference laboratory include providing interlaboratory proficiency tests and other comparisons for analytical laboratories and other producers of environmental information. The proficiency test provides an external quality evaluation between laboratory results, and mutual comparability of analytical reliability. The proficiency test was carried out in accordance with the international guidelines ISO/IEC 74 [], ISO 58 [] and IUPAC Technical report []. The Proftest SYKE is a proficiency testing provider PT accredited by FINAS Finnish Accreditation Service (www.finas.fi, ISO/IEC 74). The organizing of this proficiency test is included in the accreditation scope of the Proftest SYKE.. Responsibilities Organizer Proftest SYKE, Finnish Environment Institute (SYKE), Laboratory Centre Hakuninmaantie 6, FI-4 Helsinki, Finland Phone: +58 95 5 e-mail: proftest@environment.fi The responsibilities in organizing the proficiency test Mirja Leivuori coordinator Riitta Koivikko substitute for coordinator Keijo Tervonen technical assistance Markku Ilmakunnas technical assistance Sari Lanteri technical assistance Ritva Väisänen technical assistance Analytical experts Mika Sarkkinen analytical expert Proftest SYKE NW /7 7
. s In total laboratories participated in this proficiency test, 5 participants were from Finland, six from other European countries and two outside of Europe (Appendix ). Altogether 8 % of the participants used accredited analytical methods at least for a part of the measurements. For this proficiency test, the organizing laboratory (T, www.finas.fi, ISO/IEC 75) has the code 9 (SYKE, Oulu) in the result tables.. Samples and delivery Three types of samples were delivered to the participants; synthetic, brackish and river water samples for analysis of chlorophyll a, colour, conductivity, N NH4, N NO+NO, N tot, P PO4, P tot, ph, and turbidity. The synthetic samples AH, AJ, AN, and AP were prepared by diluting from NIST traceable certified reference materials produced by Merck or by BDH Prolab (ph). NIST traceable certified reference materials were not available for chlorophyll a, turbidity and colour determinations. The synthetic sample AK for chlorophyll a determination was prepared by dissolving the weighted green pigment (Sigma-Aldrich) in ethanol. The synthetic sample AS for turbidity determination was prepared by diluting Hach Formatzin Turbidity Standard produced by Hach Company. The synthetic sample AV for colour measurement was prepared from the colour standard produced by Reagecon. The brackish water was collected from the seashore of Helsinki. The river water was collected from Porvoo, Southern Finland. The sample preparation is described in detail in the Appendix. When preparing the samples, the purity of the used sample vessels was controlled. The randomly chosen sample vessels were filled with deionized water and the purity of the sample vessels was controlled after three days by measuring conductivity, N NH4 and P PO4. According to the test results all used vessels fulfilled the purity requirements. The samples were delivered on February 7 to the international participants and on 4 February 7 to the national participants. The samples arrived to the participants mainly on 5 February 7. The temperature control sample was placed into the sample package and the temperature was requested to be measured immediately after opening the package. The temperature of control sample was mainly C, while for participants,, 7, 8, and it was > C and at the highest 6.4 C. Based on earlier similar PTs, it is crucial to measure the temperature of the control sample as soon as possible after the sample package arrival, especially when the package is not stored in refrigerator after the arrival. The warming of samples was taken into account in the evaluation of results. The samples were requested to be measured as follows: chlorophyll a 6 February 7 conductivity, ph 6 February 7 N NH4, N NO+NO, P PO4 6 February 7 colour, turbidity 6 February 7 N tot, P tot latest on March 7 8 Proftest SYKE NW /7
The results were requested to be reported latest on March 7 and the participants mainly delivered the results accordingly. The preliminary results were delivered to the participants via ProftestWEB and email on 8 March 7..4 Homogeneity and stability studies The homogeneity of the samples was tested by analyzing ph, chlorophyll a, N NH4, N tot, P tot, and turbidity. Detailed information of homogeneity studies is shown in Appendix. According to the homogeneity test results, all samples were considered homogenous. The stability of the samples was tested by measuring chlorophyll a, N NH4, ph, and P PO4 from the samples stored at the room temperature for one day. The measurement values were checked against the results of the samples stored at 4 C. According to the test results, the concentration of N NH4 might slightly decrease and the concentration of P PO4 might slightly increase in the samples NN and NP, respectively, if the sample temperature increased during the sample distribution. According to the test other samples were considered stable..5 Feedback from the proficiency test The feedback from the proficiency test is shown in Appendix 5. The comments from the participants mainly dealt with their reporting errors with the samples or some difficulties in the result reporting. The comments from the provider were recommendations related to the reporting the sample arrival temperature. After the delivery of the preliminary results, the provider requested more detailed information of the pretreatment methods of the river water NS for the colour determinations. The participants informed even more results based on various pretreatment methods than they reported during the test. This is warmly thanked! All the feedback is valuable and is exploited when improving the activities..6 Processing the data.6. Pretesting the data The normality of the data was tested by the Kolmogorov-Smirnov test. The outliers were rejected according to the Grubbs or Hampel test before calculating the mean. The results which differed more than 5 % or 5 times from the robust mean were rejected before the statistical results handling. If the result has been reported as below detection limit, it has not been included in the statistical calculations. More information about the statistical handling of the data is available from the Guide for participant [4]..6. Assigned values The calculated values (NIST traceable) were used as the assigned values for N NH4, N NO+NO, N tot, P PO4, and P tot in the synthetic samples. For the other samples and measurements the robust Proftest SYKE NW /7 9
means or means (Colour Spectrophotmetric BS, n<) of the results reported by the participants were used as the assigned value. For the calculated assigned values the expanded measurement uncertainty (k=) was estimated using standard uncertainties associated with individual operations involved in the preparation of the sample. Mainly the individual source of the uncertainty was the uncertainty of the concentration in the stock solution. When the robust mean or mean was used as the assigned value, the uncertainty was calculated using the robust standard deviation or standard deviation. [, 4]. After reporting the preliminary results no changes have been done for the assigned values. The expanded uncertainty of the calculated assigned values (U pt, k=) was less or equal than. %. When using the robust mean or mean of the participant results as the assigned value, the expanded uncertainties of the assigned values were mainly between.5 and %, while for N NH4 in the river water and turbidity in the brackish water sample it was 4 % and for Colour Visual in the brackish water sample it was 6 % (Appendix 6)..6. Standard deviation for proficiency assessment and The standard deviation for proficiency assessment was estimated on the basis of the measurand concentration, the results of homogeneity and stability tests, the uncertainty of the assigned value, and the long-term variation in the former proficiency tests. The standard deviation for proficiency assessment ( s pt at the 95 % confidence level) was set to. ph units and to 5 % for the other measurements. After reporting the preliminary results no changes have been done for the standard deviations of the proficiency assessment values. When using the robust mean as the assigned value, the reliability was tested according to the criterion u pt / s pt., where u is the standard uncertainty of the assigned value (the expanded uncertainty of the assigned value (U pt ) divided by ) and s pt is the standard deviation for proficiency assessment []. When testing the reliability of the assigned value the criterion was mainly fulfilled and the assigned values were considered reliable. The reliability of the standard deviation for proficiency assessment and the corresponding was estimated by comparing the deviation for proficiency assessment (s pt ) with the robust standard deviation of the reported results (s rob ) []. The criterion s rob / s pt <. was mainly fulfilled. In the following cases, the criterion for the reliability of the assigned value and for the reliability of the target value for the deviation was not met and, therefore, the evaluation of the performance is weakened in this proficiency test: Sample AV, BS BN, NN BP, NP BS Measurand ColorVisual, ColorSpectophotometric NNH4 PPO4 Turbidity Proftest SYKE NW /7
Table. The summary of the results in the proficiency test NW /7. Measurand Sample Unit Assigned value Mean Rob. mean Median SD rob SD rob % x spt % n (all) Acc z % Chlorophyll a AK abs/cm.5.5.5.5.. 9 BK µg/l.5.4.5.. 9. 7 67 NK µg/l.7..7..6. 7 7 ColourVisual AV mg/l, Pt 4 4 4 4 4.8 5 4 87 BS mg/l, Pt 9 8 9. 5 79 NS mg/l, Pt 88 89 8 85 44.8-5 - ColourSpectrophotometric AV mg/l, Pt 9.7 9.8 9.7 9..4 6. 5 BS mg/l, Pt 9. 9. 9. 9.5.6 7. NS mg/l, Pt 9 9 9 4 54. - - Conductivity 5 AJ ms/m 6.54 6.56 6.54 6.54..8 5 86 BH ms/m 876 876 876 879.4 5 96 NH ms/m 4. 4. 4. 4... 5 4 88 NNH4 AN µg/l 5.5 5.9 6. 5.8. 4. 4 6 BN µg/l 8.8 8.9 8.8 8.9.4 7.9 5 74 NN µg/l.4.4.4. 5..8 64 NNO+NO AN µg/l 99 96 97 96 9 4.7 8 8 BN µg/l 9 9 5.5 87 NN µg/l 466 464 466 45 7 4.9 8 86 Ntot AN µg/l 5 7.9 5 8 BN µg/l 45 454 45 449 4.8 5 9 NN µg/l 88 8 88 8 84 4.6 95 ph AH 4.49 4.49 4.49 4.49.6. 4,5 5 96 BH 7.77 7.77 7.77 7.78.8.,6 4 8 NH 6.84 6.8 6.84 6.8..4,9 5 84 PPO4 AP µg/l 7.84 7.89 7.87 8..77 9.7 7 BP µg/l.4.4.4.5. 6. 7 NP µg/l 5.9 5. 5.9 5.4 7..6 7 Ptot AP µg/l.7.6.4..4 5 76 BP µg/l 5.6 5.7 5.6 5.4. 8.6 5 9 NP µg/l 5 6 5 5 8 7. 5 8 Turbidity AS FNU 4. 4. 4. 4.6. 8. 9 BS FNU...... 88 NS FNU 46. 46. 46. 46..8.8 95 Rob. mean: the robust mean, SD rob: the robust standard deviation, SD rob %: the robust standard deviation as percent, s pt %: the total standard deviation for proficiency assessment at the 95 % confidence level, Acc z %: the results (%), where z, n(all): the total number of the participants. Results and conclusions. Results The terms used in the results tables are shown in Appendix 7. The results and the performance of each participant are presented in Appendix 8 and the summary of the results in Table. The reported results with their expanded uncertainties (k=) are presented in Appendix 9. The summary of the s is shown in Appendix and s in the ascending order in Appendix. Proftest SYKE NW /7
The robust standard deviations for chrolophyll a, conductivity and ph in the synthetic samples were below.5 %. The river water sample NS was challenging for the colour measurements (robust standard deviation up to 54 %) due to the need of sample pretreatment, thus the sample was not evaluated (Table ). The robust standard deviation was lower than % for 64 % of the reported results and lower than % for 79 % of the results (Table ). The share of robust standard deviations was somewhat lower than in the previous similar proficiency test Proftest SYKE /5 [5].. Analytical methods The participants were allowed to use different analytical methods for the measurements in the PT. The statistical comparison of the analytical methods was possible for the data where the number of the results was 5. The used analytical methods and results of the participants grouped by methods are shown in more detail in Appendix. However, in this PT there were not enough results for statistical comparison. Thus, the comparison is based on the graphical result evaluation. Chlorophyll a Most of the participants determined chlorophyll a by spectrophotometry using the standard method SFS 577 or its application. Depending on the sample, one or two participants used fluorometric determination for the chlorophyll a measurements (Appendix ). Due to the low number of the results, the statistical comparison or visual evaluation of the used methods was not possible. Colour Colour determination was grouped into two groups: visual comparator method using a comparator (Colour Visual ) and spectrophotometric method (Colour Spectophotometric ). Depending on the sample 4 or 5 participants used visual method and or participants spectrophotometric method (mainly EN ISO 7887). Figure. In the left the tested river water sample NS in the PT NW /7, and in the right MQ-water sample for the comparison. Proftest SYKE NW /7
In this PT the river sample NS was coloured and its turbidity was 46 FNU (Figure, Table ). The properties of the sample caused some difficulties for the measurements. Basically, the sample needed pretreatment prior analysis. In the preliminary data handling it was noticed both from the visual and spectrophotometric results that different pretreatment methods might have been used, and thus the result were not evaluated (Appendix ). After the delivery of the preliminary results the provider requested more information of the pretreatment methods of the sample NS. The participants informed even more results based on various pretreatment methods than they reported during the test. This is warmly thanked! The given information by the participants is collected in Table. Different pretreatment methods were used for the river sample NS: settling or nothing, centrifugation or filtering the sample (Table ). From the given pretreatment information, the following summary could be concluded: By filtering the sample using a filter of porosity.45 µm the results varied from 8 to 9 mg/l Pt when using spectrophotometric method with one exception 97.6 mg/l Pt, whereas when using visual method the result was 8 mg/l Pt; using GF/C (porosity approximately. µm) the result was by spectrophotometric method mg/l Pt. With centrifugation the results varied from 5 (visual) / 55 (spectrophotometric) mg/l Pt to 8 (visual) / (spectrophotometric) mg/l Pt With settling, diluting or no pretreatment the results varied from 5 (visual) to (spectrophotometric) mg/l Pt; mostly the results were > mg/l Pt for both methods. Within the same company there were differences between the used pretreatment methods depending on the participants location. It is evident, that for colour measurements, the pretreatment procedures of high turbidity content and coloured samples need harmonization among the national laboratories. In the standard EN ISO 7887 [6] is pointed out that prior the spectrophotometric examination, the water sample should be filtered through a membrane filter of pore size.45 µm. While for comparator method also GF/C filtering is informed. Based on the results of the river water sample NS the filtration using a membrane filter of pore size.45 µm is crucially recommended, as it is mentioned in the standard EN ISO 7887. Proftest SYKE NW /7
Table. The pretreatment methods used for the colour measurements and participants result for the river sample NS. Pretreatment ColourSpectophotometric (mg/l Pt) ColourVisual (mg/l Pt) Filtering.45 µm polyethersulfone, PES filter 84 5 Filtering, GF/C( porosity approximately. µm) 6 Merck Mixed cellulosa ester filter.45 µm 97.6 8 Filtering.45 µm filter 9 85 Syringe filtering, Sartorius Minisart.45 µm 8. Syringe filtering VWR polyethersulfone.45 µm 86.4 8 Centrifugation 7 rpm, min 88 5 Centrifugation rpm 5 min 55 6 Centrifugation 4 rpm, 5 min 8 Centrifugation 4 rpm, min 5 Settling for - hours 77 No pretreatment 95 4 No pretreatment No pretreatment 5 4 Settling about hours.5 9 Settling Shaking and dilution of times 8 5 No pretreatment 9 No pretreatment or dilution 5 Conductivity 5 Most participants measured conductivity using the standard method EN 7888 (Appendix ). One laboratory reported the use of a sonde technique for the brackish water sample. Ammonium nitrogen Most participants (4 %) determined ammonium nitrogen using the standard method SFS (manual indophenol blue spectrophotometric method) and 6 % of the participants used the corresponding automatic standard method EN ISO 7 (Appendix ). Two participants used the spectrophotometric salicylate method modified for Aquachem technique and -4 participants used some other method (e.g. fluorometric or Hach Lange tube method). In the statistical comparison between the methods no statistically significant differences were observed (Appendix ). Nitrate + nitrite nitrogen Most participants (75 %) used the standard method EN ISO 95. The standard method SFS, the sulfanilamide spectrophotometric method after hydrazine or Cd/Cu reduction modified for Aquachem technique were used by - participants depending on the sample. Depending on the sample some other methods were used by or participants (e.g. colorimeter vanadium-chloride method with Aquachem technique). The statistical comparison between the methods was not carried out due to the low number of results. Based on the visual evaluation no differences between the methods were observed (Appendix ). Total nitrogen s mostly (88 %) determined the total nitrogen according to the standard method EN ISO 95. Depending on the sample or 4 participants used other methods (Appendix ). The other used methods were for example SFS-EN 6, SFS (withdrawn) or 4 Proftest SYKE NW /7
colorimeter vanadium-chloride method. In the visual method comparison no significant differences between the methods were observed. Phosphate phosphorus About 54 % of the participants determined phosphate phosphorus using the standard method EN 568. The withdrawn Finnish standard method 6 was used by % of the participants. The standard method EN ISO 6878 (manual spectrophotometric method) was used by two participants depending on the sample. The ammonium molybdate spectrophotometric method modified for Aquachem technique was used by -5 participants ( %) depending on the sample. One participant used some other method (Appendix ). In the visual method comparison no significant differences were observed between the methods. Total phosphorus About 45% of the participants determined total phosphorus using the standard method EN ISO 568. The withdrawn standard method SFS 6 was used by 6 % of the participants. The manual standard method EN ISO 6878 was used by three participants. Ammonium molybdate method modified for Aquachem technique was used by -4 participants (7 %) depending on the sample (Appendix ). Other methods (e.g. ICP) were used by - participants depending on the sample. In the visual comparison between the methods no statistically significant differences were observed. ph About 55 % of the participants measured ph using universal electrode and 4 % of the participants used an electrode for low ionic waters. Other electrodes (e.g. tris-electrode) were used by two or three participants (Appendix ). In the statistical method comparison no significant differences were observed between the electrode for low ionic waters and universal electrode as it was noticed in the previous similar proficiency test Proftest SYKE /5 [5]. Turbidity Most participants measured turbidity with an apparatus based on diffused radiation measurement. One participant reported used an apparatus based on attenuation of a radiation flus measurement and one some other method (Appendix ).. Uncertainties of the results At maximum 7 % of the participants reported the expanded uncertainties (k=) with their results for at least some of their results (Table, Appendix ). The range of the reported uncertainties varied between the measurements and the sample types. Several approaches were used for estimating of measurement uncertainty (Appendix ). The participants mainly used internal quality control (IQC) data from both synthetic control samples and routine sample replicates followed by the IQC data and the results obtained in proficiency tests. Also for some measurands the approach based on the data obtained from method validation was used. Depending on the sample, up to nine participants used MUkit measurement uncertainty software for the estimation of their uncertainties [8]. The free Proftest SYKE NW /7 5
software is available in the webpage: www.syke.fi/envical/en. Generally, the used approach for estimating measurement uncertainty did not make definite impact on the uncertainty estimates. In order to promote the enhancement of environmental measurements quality standards and traceability, the national quality recommendations for the data entered into the water quality registers have been published in Finland [7]. The recommendations for measurement uncertainties for the tested measurands in natural waters vary from 5 % to % (for ph measurement. ph units, see Table ). In this proficiency test some of participants had their measurement uncertainties within these limits, while some did not achieve them. Nevertheless, harmonization of the uncertainties estimation should be continued. Table. The range of the expanded measurement uncertainties (k=) reported by the participants and recommendations for natural waters [7]. Measurand/Water The range of the expanded Synthetic, U% Brackish, U% River, U% type measurement uncertainties, % [6] Chlorophyll a -6-6 -6 ColourVisual -5-5.9-5 ColourSpectrophotometric - -7 - Conductivity 5-8.89-8 -8 5 NNH4 8-94 8-58 8-54 5 NNO+NO 5-5- 5-5 Ntot 5-5 5-5 5-7 5 ph -6.6-5 -5. ph unit PPO4 8-4 8-8- 5 Ptot 8-5 8-8- 5 Turbidity 5-5-8 5-6 Proftest SYKE NW /7
Evaluation of the results The evaluation of the participants was based on the s, which were calculated using the assigned values and the standard deviation for performance assessment (Appendix 7). The z scores were interpreted as follows: Criteria z Performance Satisfactory < z < Questionable z Unsatisfactory In total, 8 % of the results were satisfactory when deviation of 5 % and. ph units from the assigned value was accepted (Appendix ). The brackish and river water samples were complicated for the measurements of N NH4 and P PO4. The variation of the colour results in the river water sample (NS) was high, and thus the performance evaluation was not done. Altogether 8 % of the participants used accredited analytical methods at least for a part of the measurements and 88 % of those results were satisfactory. The summary of the performance evaluation and comparison to the previous performance is presented in Table 4. In the previous similar proficiency test NW /5, the performance was satisfactory for 89 % of the all participants, when deviation of 5 % and. ph units from the assigned values were accepted [5]. Possible influences of temperature changes during the sample transport Altogether six participants reported increased (> C) temperatures at the sample arrival. According to the stability test results, the concentration of N NH4 might slightly have decreased and concentration of P PO4 might slightly have increased in the samples NN and NP, respectively, if the sample temperature increased during the sample distribution. Based on these changes the results of participants were evaluated and no clear performance influence was found due to the sample warming for these measurands and samples. It is known based an earlier PT that it is crucial to measure the temperature of the control sample rather soon after the sample package has arrived, especially when the package is not stored in refrigerator after the arrival. Proftest SYKE NW /7 7
Table 4. Summary of the performance evaluation in the proficiency test NW /7. Measurand spt, % Satisfactory results, % Assessment Chlorophyll a - 77 Difficulties in measurement of the samples BK and NK, < 8 % satisfactory results. In the PT NW /5 the performance was satisfactory for 84 % of the results when deviation of - % from the assigned value was accepted [5]. ColourVisual 5-5 8 The evaluation for the samples AV and BS is only approximate and the sample NS was not evaluated. In the PT NW /5 the performance was satisfactory for 8 % of the results [5]. ColourSpectophotometric 5- The evaluation for the samples AV and BS is only approximate and the sample NS was not evaluated. In the PT NW /5 the performance was satisfactory for 84 % of the results when deviation of 5-5 % from the assigned value was accepted [5]. Conductivity 5 5 9 Good performance. In the PT NW /5 the performance was satisfactory for 84 % of the results [5]. NNH4-66 The evaluation for the samples BN and NN is only approximate. The performance was weaker than in the PT NW /5, where the performance was satisfactory for 89 % of the results when deviation of 5- % from the assigned value was accepted [5]. NNO+NO 8-85 The performance was weaker than in the PT NW /5, where the performance was satisfactory for 97 % of the results with the same deviation [5]. Ntot -5 89 The performance was weaker than in the PT NW /5, where the performance was satisfactory for 97 % of the results with the same deviation [5]. ph.6 4.5 88 The performance was weaker than in the PT NW /5, where the performance was satisfactory for 95 % of the results with the same deviation [5]. PPO4-7 The evaluation for the samples BP and NP is only approximate. The performance was weaker than in the PT NW /5, where the performance was satisfactory for 84 % of the results when deviation of % from the assigned value was accepted [5]. Ptot 5 8 Difficulties in measurement of the sample AP < 8 % satisfactory results. The performance was weaker than in the PT NW /5, where the performance was satisfactory for 9 % of the results when deviation of -5 % from the assigned value was accepted [5]. Turbidity - 9 The evaluation for the sample BS is only approximate In the PT NW /5 the performance was satisfactory for 86 % of the results when deviation of 5- % from the assigned value was accepted [5]. 8 Proftest SYKE NW /7
4 Summary The Proftest SYKE carried out the proficiency test (PT) for analysis of colour, conductivity, N NH4, N NO+NO, N tot, P PO4, P tot, ph, and turbidity in brackish and river waters in February 7 (NW /7). In total, laboratories participated in this PT. Either the calculated concentration, the robust mean or the mean of the results reported by the participants was chosen to be the assigned value for the measurand. The uncertainty for the assigned value was estimated at the 95 % confidence level and it was less than. % for the calculated assigned values. For the assigned values based on the robust mean or the mean it was between.5 %, while for N NH4 in the river water and turbidity in the brackish water sample it was 4 % and for Colour Visual in the brackish water it was 6 %. The evaluation of the performance was based on the s, which was calculated using the standard deviation for the proficiency assessment at 95 % confidence level. In this proficiency test 8 % of the data was regarded to be satisfactory when the result was accepted to deviate from the assigned value. ph units for ph measurement and to 5 % for the other determinations. For the river water sample NS, which was colored and turbid, it was noticed that filtration by using a membrane filter of.45 µm pore size gave the most accurate results. Filtration is highly recommended pretreatment method for the colour measurements, i.e. the measurements should be carried out according the standard EN ISO 7887. 5 Summary in Finnish Proftest SYKE järjesti luonnonvesiä analysoiville laboratorioille pätevyyskokeen helmikuussa 7 (NW /7). Pätevyyskokeessa määritettiin klorofylli a, väri, sähkönjohtavuus, N NH4, N NO+NO, N tot, P PO4, P tot, ph ja sameus synteettisistä näytteistä, jokivedestä ja murtovedestä. Pätevyyskokeeseen osallistui yhteensä laboratoriota. Mittaussuureen vertailuarvona käytettiin laskennallista pitoisuutta, osallistujien tulosten robustia keskiarvoa tai keskiarvoa. Vertailuarvolle laskettiin mittausepävarmuus 95 % luottamusvälillä. Vertailuarvon laajennettu epävarmuus oli alle, % laskennallista pitoisuutta vertailuarvona käytettäessä ja muutoin välillä,5 %. Luonnonvedelle laajennettu epävarmuus N NH4 -määritykselle ja murtoveden sameuden määritykselle oli 4 % ja visuaaliselle värimääritykselle murtovedestä se oli 6 %. Pätevyyden arviointi tehtiin z-arvon avulla ja tulosten sallittiin poiketa vertailuarvosta, ph-yksikköä ja muilla testisuureilla 5 %. Koko aineistossa hyväksyttäviä tuloksia oli 8 %. Pätevyyskokeessa havaittiin, että värillisille ja sameille luonnonvesinäytteille suositellaan tehtäväksi membraanifiltterisuodatus huokoskoolla.45 µm värimäärityksille eli määritykset tulisi tehdä standardin EN ISO 7887 mukaan. Proftest SYKE NW /7 9
REFERENCES. SFS-EN ISO 74,. Conformity assessment General requirements for Proficiency Testing.. ISO 58, 5. Statistical methods for use in proficiency testing by interlaboratory comparisons.. Thompson, M., Ellison, S. L. R., Wood, R., 6. The International Harmonized Protocol for the Proficiency Testing of Analytical Chemistry laboratories (IUPAC Technical report). Pure Appl. Chem. 78: 45-96, www.iupac.org. 4. Proftest SYKE Guide for laboratories: www.syke.fi/proftest/en Current proficiency tests www.syke.fi/download/noname/%7bffbf5-96-48-965- ECE96D48C%7D/9886. 5. Leivuori M., Näykki, T., Koivikko, R., Björklöf, K., Tervonen, K., Lanteri, S., Väisänen, R. and Ilmakunnas, M. 5. Interlaboratory Proficiency Test /5 a-chlorophyll, colour, conductivity, nutrients, ph and turbidity in natural waters. Reports of Finnish Environment Institute 7/5. 89 pp. http://hdl.handle.net/8/5449. 6. EN ISO 7887,. Water quality- Examination and determination of colour. 7. Näykki, T. ja Väisänen, T. (toim.) 6. Laatusuositukset ympäristöhallinnon vedenlaaturekistereihin vietävälle tiedolle: Vesistä tehtävien analyyttien määritysrajat, mittausepävarmuudet sekä säilytysajat ja tavat.. uudistettu painos. (Quality recommendations for data entered into the environmental administration s water quality registers: Quantification limits, measurement uncertainties, storage times and methods associated with analytes determined from waters. nd edition). Suomen ympäristökeskuksen raportteja /6. 57 pp. http://hdl.handle.net/8/65. 8. Näykki, T., Virtanen, A. and Leito, I.,. Software support for the Nordtest method of measurement uncertainty evaluation. Accred. Qual. Assur. 7: 6-6. MUkit website: www.syke.fi/envical. 9. Magnusson, B. Näykki. T., Hovind, H. and Krysell, M.,. Handbook for Calculation of Measurement Uncertainty in Environmental Laboratories. NT Technical Report 57. Nordtest.. Ellison, S., L., R. and Williams, A. (Eds). () Eurachem/CITAC guide: Quantifying Uncertainty in Analytical Measurement, Third edition, ISBN 978--94896--.. ISO/IEC Guide 98-:8. Uncertainty of measurement -- Part : Guide to the expression of uncertainty in measurement (GUM: 995). Proftest SYKE NW /7
APPENDIX (/) APPENDIX : s in the proficiency test Country Estonia Finland Kyrgyz Republic Lithuania Sweden Estonian Marine Institute University of Tartu Marine Ecology Lab of Marine Systems Institute Ahma Ympäristö Oy, Rovaniemi Ahma ympäristö, Seinäjoki BotniaLab Oy Vaasa Eurofins Scientific Finland Oy Kokkolan yksikkö HSY Käyttölaboratorio Pitkäkoski Helsinki HY, Tvärminnen eläintieteellinen asema, Hanko Kokemäenjoen vesistön vesiensuojeluyhdistys ry, Tampere Kymen Ympäristölaboratorio Oy Lounais-Suomen vesi- ja ympäristötukimus Oy, Turku Luonnonvarakeskus, Viikki B-laboratorio Metropolilab Oy Nablabs Oy / Jyväskylä Neste Oyj, Tutkimus ja kehitys/vesilaboratorio, Kulloo Novalab Oy Ramboll Finland Oy, Ramboll Analytics, Lahti Saimaan Vesi- ja Ympäristötutkimus Oy, Lappeenranta Savo-Karjalan Ympäristötutkimus Oy, Joensuu Savo-Karjalan Ympäristötutkimus Oy, Kuopio ScanLab Oy SGS Inspection Services Oy, Kotka SYKE Oulun toimipaikka SYKE/Merikeskus Tampereen Vesi/Viemärilaitoksen laboratorio Yara Suomi Oy, Uusikaupunki ÅMHM laboratoriet, Jomala, Åland SAEPF, Issyk-Kul-Naryn, Cholpon-Ata City, Kyrgyz Republic Surface water pollution control Unit (Lab), Agency on Hydrometeorology of the Ministry of Emergency Situations of the Kyrgyz Republic Environmental Protection Agency,Klaipeda,Lithuania Environmental Protection Agency,Vilnius,Lithuania ACES, Stockholm University Medins Havs och Vattenkonsulter AB Proftest SYKE NW /7
APPENDIX (/) APPENDIX : Preparation of the samples Measurand 5 [µs/cm] ph ph unit Chlorophyll a [abs/cm] [µg/l] NNO+NO [µg/l] NNH4 [µg/l] Ntot [µg/l] PPO4 [µg/l] Ptot [µg/l] Turbidity [FNU] Colour [mg/l Pt] Addition (Dilution) Assigned value Sample AJ Initial - KCl 6.54 BH 96 5-876 NH 4.5-4. AH - NaHPO4/KHPO4 4.49 BH 7.7 4-7.77 NH 6.8-6.84 AK - Chlorophyll a 4 mg /.6 litres ethanol.5 BK..6.5 NK.5 5.7 AN - NaNO 99 BN 98.6 99 NN 8 (:) 466 AN - NH4Cl 5.5 BN 44 5.5-8.8 NN 6 (:).4 AN - NaNO BN 46.6 99 45 NN 8 (:) 88 AP - KHPO4 7.84 BP 7.8 -.4 NP 5-5.9 AP - KHPO4 BP 8 7.8-5.6 NP - 5 AS - 4.5 4. BS.4. NS 65-46. AV - 8 4 / 9.7 BS 5 9 / 9. NS - - First letter of the sample code indicates the sample type: A = Synthetic sample B = Brackish water N = Natural water (river water) Proftest SYKE NW /7
APPENDIX (/) APPENDIX : Homogeneity of the samples Homogeneity of the brackish and river water samples was tested by analyzing the concentration of the selected measurands from 5-8 subsamples. Criteria for homogeneity: s anal /s pt <.5 s sam <c, where s pt = standard deviation for testing of homogeneity s anal = analytical deviation, standard deviation of the results in a sub sample s sam = between-sample deviation, standard deviation of results between sub samples c = F s all + F s anal, where s all = (. s pt ) F and F are constants of F distribution derived from the standard statistical tables for the tested number of samples [, ]. Measurand/Sample Concentration n spt % spt sanal sanal/spt ssam c NNH4/BN 8.4 6.5.9..9 Yes.. Yes NNH4/NN 9.5 6 5.9.4.4 Yes.8. Yes Ntot/BN 49 6 7.5 6.9.64.4 Yes 76.5 76 Yes Ntot/NN 86 6 5 9. 5.7.6 Yes 8 77 Yes ph/bh 7.86 8....5 Yes.. Yes ph/nh 6.96 8.45..5.48 Yes.5.5 Yes Ptot/BP. 6 7.5.66.7.4 Yes..4 Yes Ptot/NP 6 7.5 7.6.7.7 Yes. 4. Yes Turbidity/BS. 5 5..4. Yes.7. Yes Turbidity/NS 45.9 6 5..8.8 Yes.. Yes Criterion for homogeneity: s sam/ s pt <.5, where s pt = standard deviation for proficiency assessment s sam = between-sample deviation, standard deviation of results between sub samples Measurand/Sample Concentration n spt % spt ssam ssam/spt ssam/spt <,5? Chlorophyll a/bk [µg/l] 5. 8.5.8.4 Yes Chlorophyll a/nk 4. 8.4.9. Yes Conclusion: The criteria were fulfilled for the tested measurands and the samples were regarded as homogenous. Proftest SYKE NW /7
APPENDIX 4 (/) APPENDIX 4: Stability of the samples The samples were delivered mostly on, or 4 February 7 and they arrived to the participants mainly on 5 February 7. The samples were requested to be analysed as follows: chlorophyll a 6 February 7 ph, conductivity 6 February 7 N NH4, N NO+NO, P PO4 6 February 7 colour, turbidity 6 February 7 N tot, P tot latest on March 7 Stability of chlorophyll a, ph, N NH4 and P PO4 was tested by analysing the samples stored at the temperatures 4 ºC and ºC. Criterion for stability: D <. s pt, where D = the difference of results measured from the samples stored at the temperatures 4 C and C s pt = standard deviation for proficiency assessment Chlorophyll a Sample Result, abs/cm Sample Result, µg/l Sample Result, µg/l Date [abs/cm] 6.. 6.. Date 6.. 6.. Date [µg/l] 6.. 6.. ( C) (4 C) ( C) (4 C) ( C) (4 C) AK.57.6 BK.84 4. NK 5.74 4.8 D.4 D.6 D.9. spt.4. spt.4. spt.98 D <. spt? No ) D <. spt? Yes D <. spt? Yes ph Sample Result Sample Result Sample Result Date 6.. ( C) 6.. (4 C) Date 6.. ( C) 6.. (4 C) Date 6.. ( C) 6.. (4 C) AH 4.46 4.48 BH 7.85 7.9 NH 6.9 6.9 D. D.6 D.. spt.. spt.. spt. D <. spt? Yes D <. spt? No ) D <. spt? Yes N NH4 Sample Result, µg/l Sample Result, µg/l Sample Result, µg/l Date [µg/l] 6.. ( C) 6.. (4 C) Date ple 6.. ( C) 6.. (4 C) Date 6.. ( C) 6.. (4 C) AN 7.8 7.5 BN 7.95 8.7 NN 7. 9.8 D. D.76 D.59. spt.48. spt.7. spt. D <. spt? Yes D <. spt? No ) D <. spt? No 4 Proftest SYKE NW /7
APPENDIX 4 (/) P PO4 Sample Result, µg/l Sample Result, µg/l Sample Result, µg/l Date [µg/l] 6.. ( C) 6.. (4 C) Date 6.. [µg/l] ( C) 6.. (4 C) Date 6.. ( C) 6.. (4 C) AP 7.7 8.5 BP 8.9 9.5 NP 55. 49.97 D.5 D. D 5.. spt.. spt.. spt.56 D <. spt? No ) D <. spt? Yes ) D <. spt? No ) The difference is within the analytic error. Conclusion: According to the test results, the concentration of N NH4 might slightly have decreased and concentration of P PO4 might slightly have increased in the samples NN and NP, respectively, if the sample temperature increased during the sample distribution. For the other measurands the noticed differences are within the analytic error or the test passed, and thus the samples could be regarded as homogenous. Proftest SYKE NW /7 5
APPENDIX 5 (/) APPENDIX 5: Feedback from the proficiency test FEEDBACK FROM THE PARTICIPANTS Comments on technical excecution Action / Proftest Bottles for nitrogen samples (AN, BN, NN) had leaked. The provider will be more careful when tightening the sample bottles.,8 The participants informed that they could not report the results via ProftestWEB. The provider noticed error in the last reporting day in the electronic interface and corrected the date. The provider will more carefully update the dates in the system. 5 The participant had problems in use of ProftestWEB. The coordinator solved out the problems with the participants via emails. Comments to the results Action / Proftest 7 reported the results for conductivity erroneously. The right results were: Sample AJ: 6.5 ms/m, Sample NH: 4. ms/m reported the results for N NH4 erroneously. The right results were: Sample AN:.4 µg/l Sample NN:. µg/l The participant reported the results for turbidity in FTU unit. The results were outliers in the statistical treatment, and thus did not affect the performance evaluation. If the results had been reported correctly, the results for would have been satisfactory. The participant can re-calculate the z scores according to the Guide for participants [4]. The results were outliers in the statistical treatment, and thus did not affect the performance evaluation. If the results had been reported correctly, the result for the sample AN would have been satisfactory and the result for the sample NN would have been questionable. The participant can re-calculate the z scores according to the Guide for participants [4]. The turbidity units NTU, FNU and FTU are all based on calibrations using the same formazin primary standards. There is numerical equivalence of the different unit. FEEDBACK TO THE PARTICIPANTS Comments,, 7, 9,, It is recommended that in the future the participant reports the sample arrival temperature.,, 9,,, 9, The participants (accredited) did not report the measurement uncertainties. The participants should follow up the instructions of the provider. 6 Proftest SYKE NW /7
APPENDIX 6 (/) APPENDIX 6: Evaluation of the assigned values and their uncertainties Measurand Sample Unit Assigned value Upt Upt, % Evaluation method of assigned value upt/spt Chlorophyll a AK abs/cm.5.. Robust mean. BK µg/l.5.8 6. Robust mean. NK µg/l.7. 7. Robust mean.6 ColourVisual AV mg/l, Pt 4 7. Robust mean.48 BS mg/l, Pt 9 6 Robust mean.46 ColourSpectrophotometric AV mg/l, Pt 9.7.7 4.4 Robust mean.9 BS mg/l, Pt 9..8 9 Mean. Conductivity 5 AJ ms/m 6.54.. Robust mean. BH ms/m 876 6.7 Robust mean.4 NH ms/m 4...6 Robust mean. NNH4 AN µg/l 5.5..8 Calculated value.4 BN µg/l 8.8.9 Robust mean.4 NN µg/l.4. 4 Robust mean.47 NNO+NO AN µg/l 99.6 Calculated value.8 BN µg/l 7. Robust mean. NN µg/l 466 8.6 Robust mean. Ntot AN µg/l 4. Calculated value.9 BN µg/l 45.6 Robust mean.7 NN µg/l 88 48.6 Robust mean.6 ph AH 4.49..6 Robust mean. BH 7.77.4.5 Robust mean.9 NH 6.84.5.7 Robust mean.6 PPO4 AP µg/l 7.84.. Calculated value. BP µg/l.4.7.6 Robust mean.6 NP µg/l 5.9 4.5 8.7 Robust mean.44 Ptot AP µg/l.. Calculated value.8 BP µg/l 5.6. 4.7 Robust mean. NP µg/l 5 4 4. Robust mean.8 Turbidity AS FNU 4.. 4.7 Robust mean.4 BS FNU.. 4 Robust mean.47 NS FNU 46... Robust mean. U pt = Expanded uncertainty of the assigned value Criterion for reliability of the assigned value u pt/s pt <., where s pt= target value of the standard deviation for proficiency assessment u pt= standard uncertainty of the assigned value If u pt/s pt <., the assigned value is reliable and the s are qualified. Proftest SYKE NW /7 7
APPENDIX 7 (/) APPENDIX 7: Terms in the results tables Results of each participant Measurand The tested parameter Sample The code of the sample Calculated as follows: z = (x i - x pt )/s pt, where x i = the result of the individual participant x pt = the assigned value s pt = the standard deviation for proficiency assessment Assigned value The reference value s pt % The standard deviation for proficiency assessment (s pt ) at the 95 % confidence level s result The result reported by the participant (the mean value of the replicates) Md Median SD Standard deviation SD% Standard deviation, % n (stat) Number of results in statistical processing Summary on the s S satisfactory ( - z ) Q questionable ( < z < ), positive error, the result deviates more than s pt from the assigned value q questionable ( - < z < -), negative error, the result deviates more than s pt from the assigned value U unsatisfactory (z ), positive error, the result deviates more than s pt from the assigned value u unsatisfactory (z -), negative error, the result deviates more than s pt from the assigned value Robust analysis The items of data are sorted into increasing order, x, x, x i,,x p. Initial values for x * and s * are calculated as: x * = median of x i (i =,,...,p) s * =.48 median of x i x * (i =,,...,p) The mean x * and s * are updated as follows: Calculate =.5 s *. A new value is then calculated for each result x i (i =, p): { x * -, if x i < x * - x * i = { x * +, if x i > x * +, { x i otherwise The new values of x * and s * are calculated from: * * x xi / p s.4 ( x i x ) /( p ) The robust estimates x * and s * can be derived by an iterative calculation, i.e. by updating the values of x * and s * several times, until the process convergences []. 8 Proftest SYKE NW /7
APPENDIX 8 (/7) APPENDIX 8: Results of each participant Measurand Unit Sample - Assigned value spt % 's result Md Mean SD SD% n (stat) Chlorophyll a abs/cm AK..5.5.5.5.. µg/l BK.4.5 4.9..4.5. 4 µg/l NK.64.7 4.8... 9.6 5 ColourVisual mg/l, Pt AV. 4 5 4 4 4 4. 4 mg/l, Pt BS -.95 9 5 8 8.7 mg/l, Pt NS 8 88 77 4.8 5 ColourSpectrophotometric mg/l, Pt AV.77 9.7 5 4. 9. 9.8. 5.5 mg/l, Pt BS.4 9. 9.5 9.5 9..4 5. Conductivity 5 ms/m AJ -.8 6.54 5 6.4 6.54 6.56..8 ms/m BH -.64 876 5 86 879 876 8.9 ms/m NH -.5 4. 5 4. 4. 4... NNH4 µg/l AN.7 5.5 5.6 5.8 5.9. 4. 9 µg/l BN -.84 8.8 5 4.5 8.9 8.9. 7.4 µg/l NN -..4 5.7..4 4.7. 7 NNO+NO µg/l AN -.68 99 8 86 96 96 9 4.4 µg/l BN -.9 6 9 9 5. µg/l NN -.75 466 8 4 45 464 74 5. Ntot µg/l AN -.7 5 4 5.8 µg/l BN -.7 45 5 446 449 454 4 5. µg/l NN -.6 88 77 8 8 8 4.4 ph AH.4 4.49 4,5 4.5 4.49 4.49.4. 5 BH -. 7.77,6 7.74 7.78 7.77.6.8 NH -. 6.84,9 6.8 6.8 6.8.9. 4 PPO4 µg/l AP.8 7.84 8.55 8. 7.89.75 9.5 9 µg/l BP -..4 8..5.4. 6. 9 µg/l NP.5 5.9 6.6 5.4 5. 6.. 5 Ptot µg/l AP -.69 5 8.8.4.7.. µg/l BP -.57 5.6 5.6 5.4 5.7. 8.5 µg/l NP.9 5 5 6 5 6 9 8.5 9 Turbidity FNU AS.74 4. 4.4 4.6 4.. 7.6 8 FNU BS.79..7... 8.8 4 FNU NS -. 46. 45.9 46. 46..8 4. Measurand Unit Sample - Assigned value spt % 's result Md Mean SD SD% n (stat) Chlorophyll a abs/cm AK -.6.5.5.5.5.. µg/l BK.7.5.6..4.5. 4 µg/l NK -.8.7 8.5... 9.6 5 ColourSpectrophotometric mg/l, Pt AV.4 9.7 5 4. 9. 9.8. 5.5 mg/l, Pt BS.8 9..8 9.5 9..4 5. mg/l, Pt NS 95 9 9 9 47.9 Conductivity 5 ms/m AJ -.4 6.54 5 6.5 6.54 6.56..8 ms/m BH.46 876 5 886 879 876 8.9 ms/m NH -.4 4. 5 4. 4. 4... Proftest SYKE NW /7 9
APPENDIX 8 (/7) Measurand Unit Sample - Assigned value spt % 's result Md Mean SD SD% n (stat) NNH4 µg/l AN. 5.5 7. 5.8 5.9. 4. 9 µg/l BN. 8.8 5 9. 8.9 8.9. 7.4 µg/l NN.95.4 5.6..4 4.7. 7 NNO+NO µg/l AN.6 99 8 9 96 96 9 4.4 µg/l BN.7 5 9 9 5. µg/l NN.87 466 8 57 45 464 74 5. Ntot µg/l AN.5 5 45 5.8 µg/l BN -.8 45 5 446 449 454 4 5. µg/l NN.66 88 888 8 8 8 4.4 ph AH. 4.49 4,5 4.5 4.49 4.49.4. 5 BH. 7.77,6 7.8 7.78 7.77.6.8 NH -.4 6.84,9 6.8 6.8 6.8.9. 4 PPO4 µg/l AP.96 7.84 9. 8. 7.89.75 9.5 9 µg/l BP.5.4.8.5.4. 6. 9 µg/l NP -.95 5.9 4.8 5.4 5. 6.. 5 Ptot µg/l AP -.97 5..4.7.. µg/l BP -. 5.6 5 5.4 5.4 5.7. 8.5 µg/l NP.6 5 5 5 6 9 8.5 9 Turbidity FNU AS.7 4. 4.4 4.6 4.. 7.6 8 FNU BS...... 8.8 4 FNU NS. 46. 46. 46. 46..8 4. Measurand Unit Sample - Assigned value spt % 's result Md Mean SD SD% n (stat) Chlorophyll a abs/cm AK..5.5.5.5.. µg/l BK.6.5 6.4..4.5. 4 µg/l NK..7 6.4... 9.6 5 ColourVisual mg/l, Pt AV -.67 4 5 5 4 4 4. 4 mg/l, Pt BS -.95 9 5 8 8.7 mg/l, Pt NS 75 8 88 77 4.8 5 Conductivity 5 ms/m AJ.94 6.54 5 6.86 6.54 6.56..8 ms/m BH -.95 876 5 8 879 876 8.9 ms/m NH. 4. 5 4. 4. 4... NNH4 µg/l AN. 5.5 5.5 5.8 5.9. 4. 9 µg/l BN -.94 8.8 5 6.6 8.9 8.9. 7.4 µg/l NN -.6.4 4.8..4 4.7. 7 NNO+NO µg/l AN -.5 99 8 79 96 96 9 4.4 µg/l BN.9 9 9 5. µg/l NN.9 466 8 5 45 464 74 5. Ntot µg/l AN.8 5 4 5.8 µg/l BN.89 45 5 56 449 454 4 5. µg/l NN -.6 88 77 8 8 8 4.4 ph AH.5 4.49 4,5 4.5 4.49 4.49.4. 5 BH -7.84 7.77,6 6.98 7.78 7.77.6.8 NH.6 6.84,9 7.6 6.8 6.8.9. 4 PPO4 µg/l AP.77 7.84 8.4 8. 7.89.75 9.5 9 µg/l BP.69.4..5.4. 6. 9 µg/l NP -.95 5.9 4.8 5.4 5. 6.. 5 Proftest SYKE NW /7