validation procedure for existing and emerging screening methods

Validatio fand emeC. Gonzalez, E. Pr .

The approach used for standar

in-house should be adapted

objective of this article is to s

a more relevant validation pr

range of methods.

2007 Elsevier Ltd. All rights

Keywords: Performance criteria; S

dation of methods.The WFD does not set out any specific

quality and comparability. with a reference method (standard meth-

C. Gonzalez*,

S. Spinelli,

J. Gille, E. Touraud

Ecole des Mines dAle`s,

Centre LGEI,

6 avenue de Clavie`res,

30319 Ale`s, France

E. Prichard

LGC, Queens Road,

Teddington,

Middlesex TW11 0LY, UK

Trends in Analytical Chemistry, Vol. 26, No. 4, 2007 TrendsE-mail: catherine.gonzalez@The reliability (QA) and comparability ofmeasurement results is a key issue of theWFD. Various factors (e.g., seasonalchange, matrix effects, flow rate and bio-fouling) can lead to errors in observed dataand those may influence the accuracy ofcontinuous water-quality monitoring, inparticular for field-measurement devicesor tools. These errors could lead to wrongdecisions being made based on such

od). The evaluation procedure is based onstatistical tests in order to assess the per-formance of both methods (alternative andreference). Finally, the measurement re-sults for test samples using both methodsare compared to identify statistically sig-nificant differences.The current situation may well prevent

new technologies being accepted. Toovercome this problem, the US Environ-

*Corresponding author.

Tel.: +33 0 4 66 78 27 65;

Fax: +33 0 4 66 78 27 01;provision of data of an equivalent scientific alternative methods and their comparisonmonitoring requirements nor does it rec-ommend specific QA. It indicates that allmonitoring should conform to the relevantstandards on the national, European orinternational scale (e.g., developed by theEuropean Committee for Standardization(CEN) and the International Organizationfor Standardization (ISO)) to ensure theema.fr

0165-9936/$ - see front matter 20070165-9936/$ - see front matter 2007n procedurerging screeninichard, S. Spinelli, J. Gille, E

d methods and laboratory methods developed

for field-measurement systems. The main

pecify for such alternative screening methods

ocess that should be appropriate for a wide

reserved.

creening method; Validation

1. Introduction

The Water Framework Directive (WFD)of the European Union (EU) aims to preventthe deterioration and maintain the qualityof all community waters. For WFD to besuccessful requires methods of monitoringwater quality that give reliable, comparabledata. This can be achieved via sound ana-lytical quality assurance (QA) and qualitycontrol (QC) procedures that include vali-water-monitoring data.

Elsevier Ltd. All rights reserved. doi:10.1016/j.trac.2007.01.0Elsevier Ltd. All rights reserved. doi:10.1016/j.trac.2007.01.0or existingg methodsTouraud

The aim of an appropriate QAprogramme is to quantify and to controlerrors. QA procedures may take the formof standardization and validation ofsampling procedures and analyticalmethods, use of reference materials, andlaboratory-accreditation schemes. SomeCEN or ISO procedures concern specificissues of QA: appropriate sampling procedures [1]; methods of writing clear procedures [2]; validation of analytical methods [3].

The extent of the validation differs fordifferent situations. Published standardmethods may have detailed validationinformation available, so all that is re-quired is evidence that the published per-formance can be achieved (i.e.verification). However, when such meth-ods are used outside their scope, they re-quire full validation. The standard alsorequires the implementation of a pro-gramme of QA/QC.Concerning alternative or screening

methods, in particular for field studies,there is very little available in terms ofrecommended validation procedures.There is a standard that focuses on on-linestudies using sensors [4]. In France, theAFNOR standard method, T 90210 [5],presents the performance evaluation ofmental Protection Agency (EPA) set up an

03 31503 315

Trends Trends in Analytical Chemistry, Vol. 26, No. 4, 2007Environmental Technology Verification (ETV) Program[http://www.epa.gov/etv] that develops testing protocolsand verifies the performance of innovative technologiesthat have the potential to improve protection of humanhealth and the environment. ETV was created to accel-erate the entrance of new environmental technologiesinto the domestic and international marketplace. Thisverification program is applied to various devices forwater analysis (e.g., chemical-test kits (arsenic tests),multi-parameter water-quality probes, immunoassay-test kits, field-portable gas chromatography-mass spec-trometry (GC-MS) and infrared (IR) monitors). The ETVpublishes the verification report for each system tested.The report sets out clearly the experimental approachand test objectives used, comparing the equipment undertest with standard methods. It also outlines the QA/QCprocedures that the testing laboratory has used. The EPAhas also published a report on technologies for biologicalearly warning systems (BEWSs) [6].In addition, AOAC International has a method-vali-

dation program designed specifically for test-kit meth-ods. Performance-tested certified kits are thoroughlyreviewed and independently tested by the AOACResearch Institute, a subsidiary of the AOAC Interna-tional. Performance-tested certified kits are evaluatedfor accuracy (trueness), precision, limit of detection(LoD), false-positive and false-negative rates, rugged-ness, cross-reactivity, stability, lot-to-lot consistency,and matrix effects, and compared to an existingmethod. In addition, the AOAC Research Institute hasa database of test kits providing information suppliedby the manufacturers of test kits (e.g., microbiology,antibiotics, and hormones) [www.aoac.org/testkits].These have not necessarily been verified by the AOACResearch Institute.Finally, the EU METROPOLIS project [http://

www.metropolis-network.net] developed a database forbio-monitoring assays and analytical chemical methodsthat provides, in a structured, comprehensive form,information about the state of the art and the currentgaps in methodology in the bio-monitoring strategiesapplied to the environmental monitoring field and givesinformation on standard methods. The toxicity test(Microtox) is described in IS0 11348 [79]. Themethod concerns bioassays usually applied in thelaboratory.Due to the poor state of the art in the validation of

alternative or screening methods, there is an obviousneed to develop validation procedures in order to assessthe performances of these methods for water monitoringto satisfy WFD requirements. The lack of an acceptedvalidation process and performance-evaluation planis the main constraint on the acceptance of newtechnologies and their integration into water-monitoringstrategies.316 http://www.elsevier.com/locate/trac2. Validation process: general concepts

Method validation is the confirmation, by examinationand the provision of objective evidence, that the requirementsfor a specific intended use are fulfilled [2].Method validation is a process of sufficiently develop-

ing a picture of the performance of a method to dem-onstrate that it is fit for an intended purpose. The processis based on determination of a range of performancecharacteristics of the method (e.g., trueness, precision(repeatability, reproducibility), linearity, LoD, limit ofquantitation (LoQ), ruggedness and selectivity). Thesecharacteristics are, in general, well defined in manystandard documents [1012]. The validation process isshown in Fig. 1.Before validation can begin, it is necessary to define

the analytical requirements of the method (which pol-lutant or parameter, which type of water, the concen-tration range to be covered, the uncertainty acceptablein the result) in accordance with WFD requirements andmonitoring objectives. The next step is to check if there isa suitable alternative or screening method available or ifit is necessary to develop a new method.A validation plan comprises experiments that have to

be carried out to determine the relevant performanceparameters of the method (e.g., linearity, working range,LoD and LoQ).The main issues concerning the validation of alter-

native or screening methods are to: specify the more relevant performance parameters; develop an experimental plan; and, design the testing strategy in accordance with the

measurement objectives.When values of the quantitative parameters are ob-

tained, the fitness for purpose of the method is deter-mined. The values obtained during the experiment arecompared, using statistical techniques, with the valuesrequired. If they meet the requirements, then a state-ment of validation can be produced. If not, the methodhas to be modified or another method has to be chosenand the process repeated.The main objective of this article is to specify for

alternative or screening methods a more relevantvalidation process that should be appropriate for awide range of methods (e.g., physico-chemical, bio-sensor and bioassay). These methods can deliverquantitative data (parameters level, pollutant concen-tration) or semi-quantitative data. For each specificcase, a validation plan should be developed on thebasis of the classical approach generally applied forlaboratory analytical methods. In the case of qualita-tive methods, the goal is to propose a procedure toensure the quality of the data obtained (e.g., specificthreshold values, false-negative and false-positive rates,and ruggedness).

N canhod/sc

yticent

N

canhod/sc

yticent

N

canhod/sc

yticent

lid

Trends in Analytical Chemistry, Vol. 26, No. 4, 2007 Trends3. Existing and emerging field devices (screeningmethods)

In the frame of SWIFT-WFD project [European UnionSixth Framework Programme, funded by DG Research,www.swift-wfd.com], a technical report, Directory ofexisting and emerging techniques for water qualitymonitoring, has been produced [13]. This inventoryaims to summarize existing and emerging methodssupporting the WFD in the assessment of physico-chemical, biological and chemical quality elements and

Chemical parameters

Pollutants/EQS

Choice ofmet

(alternative

Analrequirem

Statement of validation

YES

Monitoring objectives/ WFD requirements

Chemical parameters

Pollutants/EQS

Choice ofmet

(alternative

Analrequirem


YES

Chemical parameters

Pollutants/EQS

Choice ofmet

(alternative

Analrequirem


YES

Monitoring objectives/ WFD requirements

Figure 1. Vaparameters (excluding hydromorphological elements).These tools (some commercially available and some indevelopment) include: equipment for measuring physico-chemical character-

istics (e.g., Total Organic Carbon, pH, temperatureand nitrogen);

sampling devices and chemical analytical methods(e.g., passive-sampling devices, laboratory-basedmethods, sensors, chemical-test kits, and immuno-assays) and

biological assessment techniques (e.g., biomarkers,bioassays or biosensors and BEWS).Among these techniques and tools, some are on-site

systems (portable or transportable equipment, chemical-test kits and immunoassay-test kits) and require asampling step (spot sampling). Some other methods allowin-situ measurements (sensors, probes, on-line systemsand BEWS). In this case, the pollutants are measuredcontinuously and data can be stored on-line.For commercial chemical methods, the manufacturer

indicates, in general, specifications concerning calibra-tion range, LoD, LoQ and the potential interferences. Themain issue for water-monitoring requirements is therelevance of these specifications in relation to the qual-ity objective (reliable data for various environmentalsituations).To ensure the quality of the data obtained, the alter-

native or screening tools need to be validated as fit-for-purpose for water monitoring. Fig. 2 summarizes themethodology developed that comprises three main steps: laboratory validation (evaluation of classical perfor-

mance criteria); field validation (evaluation of key performance criteria

and comparison with classical methods) and

O

didate

reening)Plan validation

experiments

Use data to assess fitness for purpose

al met?

Carry out experiments

O

didate


experiments


al met?


O

didate


experiments


al met?


ation process. performance evaluation of the devices in order toassess fitness-for-purpose in relation to monitoring.The first step is dedicated to validation in the labora-

tory; this is based on a best-practice approach. Table 1sets out the main performance criteria that should beinvestigated for each type of alternative or screeningmethod. For quantitative methods or devices (test kits,portable laboratory-based instruments, probes, sensors,and immunoassays), the performance criteria to beevaluated are the same as those used for laboratory-method validation (in particular, selectivity, workingrange, LoD, LoQ, precision, bias, and ruggedness).The performances of field devices are compared with

accepted classical analytical methods using a statisticalapproach [5]. The main goal, in this case, is to demon-strate the equivalence of data obtained by field devices ortools to those obtained by analytical methods used in thelaboratory.The performances of two methods have been evalu-

ated and compared to a reference method (laboratorymethods) according to the AFNOR Standard [5]. Forboth methods, the evaluation procedure was based onseveral steps:

http://www.elsevier.com/locate/trac 317

cess

nstrum

Trends Trends in Analytical Chemistry, Vol. 26, No. 4, 2007 check data are normally distributed (Shapiro-Wilk Wtest);

linearity range; calibration line; repeatability (CV%); LoD; LoQ;

Manufacturers specifications

Recommendationsfor field use

Manufacturers specifications

Recommendationsfor field use

Figure 2. Validation pro

Table 1. Performance criteria for laboratory validation

Test kits Portable lab. i

Precisionp p

Selectivityp p

Bias/recoveryp p

Ruggednessp p

Linearity/working rangep p

LoD,LoQp p selectivity and ruggedness

Concerning determination of the linearity range, theAFNOR Standard specifies a homogeneity test based onvariance. In this case, it is necessary to choose the lowestand the highest concentrations corresponding to thesupposed linearity range. The two concentration limitsare measured under repeatability conditions (n > 5). Theratio of the two variances (Fcal) is compared to F0.99(Snedecor law) [14]. If Fcal < F0.99, it means that thelinearity range is acceptable.The calibration line drawn (y = a1x + b1) comprises

the results of at least 5 independent standard solutions.The residual standard deviation, sy1, of the calibrationline, and the standard deviation of the slope (sa1) arecalculated, and finally, the standard deviation of themethod is defined by the following formula:

sx0 sy1a1

The correlation coefficient (r) of the calibration line isevaluated and tcal is calculated:

tcal r2N1 21 r2

318 http://www.elsevier.com/locate/tracIf tcal > t0.975, there is a linear relationship between yiand xi. We recognize that this is not a measure of line-arity but of correlation. It is important that the data arealso plotted and visualized.The repeatability is evaluated with several standard

solutions, one corresponding to a concentration at 10%of the calibration range, another corresponding to 90%

Performance evaluation

Fitness for purpose

Laboratory Field validation

Validation procedure

Laboratory Field validationLaboratory Field validation

Validation procedure

Performance evaluation

Fitness for purpose

for screening methods.

ents Probes Sensors Immunoassays

p p pp p pp p pp p pp p pp p pof the calibration range and at least two solutions be-tween 10% and 90% of the calibration range. Eachsolution is measured (n > 5). The variance, the standarddeviation, the coefficient of variance and the limit ofrepeatability are calculated for each concentration.For the LoD and LoQ, a blank test solution is measured

(n > 5) under repeatability conditions yb average re-sponse for blank solution). Standard deviation sb is cal-culated and the LoD is defined by the following formula:

LoD yb kdsbwhere kd 2

2p

t1a, if t1a and t1b are equal.The LoQ is calculated by the classical formula:

LoQ yb 10sbThe selectivity is assessed using water samples spiked

with a known amount of potential interferences (stan-dard-addition method). The linear calibration is plotted(y = a2x + b2) and the standard deviation of the slope sa2is compared to the standard deviation of the calibrationline sa1 using the Snedecor F test.The trueness (accuracy) can be assessed using certified

reference materials (CRMs), if available. An alternative isto spike a clean water with the analyte of interest andmeasure the recovery factor.

For bioassay methods, the minimum performancecriteria are precision (repeatability from triplicate mea-surements), accuracy (frequency of positive response),toxicity threshold, false-negative or false-positive re-sponse (presence or absence of contamination in variousmatrices), working range and ruggedness (Table 3). Inorder to specify the matrix effects, the performanceshould be evaluated in various matrices and in thepresence of potential interferences.For bioindicators, the performance criteria are reduced

to toxicity threshold, false-negative and false-positive

( )alty

refalt zy =Theoretical line

Experimental lineAlte

rnat

ive

met

hod

refalt zbay +=

Confidence interval

=

refalt zbay +=

=

refalt zbay +=

Trends in Analytical Chemistry, Vol. 26, No. 4, 2007 TrendsFinally, the comparison of alternative method (yalt)and analytical method (zref) could be carried out onseveral samples (e.g., with a range of sample matrices,environmental conditions, and anthropogenic pressures)and focused on two main performance criteria (repeat-ability and trueness). Fig. 3 illustrates the theoreticalcomparison yalt a bzref .The validation in field conditions (second step) is more

or less based on the same criteria as those defined forchemical methods (e.g., working range, LoD, LoQ,repeatability, selectivity, and precision). In accordancewith field constraints, some additional parametersshould be evaluated in order to assess the performancesof field devices in real conditions. They are illustrated inTable 2. These criteria mainly depend on external con-ditions (e.g., temperature, seasonal change, flow rateand biofouling effects) and on the type of monitoringdevices (in particular, on-line systems (memory effect,short-term drift)). ISO 15839 Standard specifies partic-ular criteria to be assessed in field conditions (e.g., bias,long-term drift and response time) [4]. The operationalfactors (field portability) are, in this case, important andmainly concern the ease of use, and response stability in

( )refzAnalytical method

0z

Figure 3. Comparison of alternative or screening methods withclassical methods.various conditions (e.g., perturbations and interfer-ences).Finally, the performance criteria evaluated (laboratory-

scale and field conditions) are then compared and theirfitness-for-purpose assessed.

Pastel UV is an on-site physico-chemical tool, easy to useand providing, at the same time, many parameters (e.g.,

Table 2. Additional criteria for field validation

Test kits Portable lab. instrume

Tp

Seasonal changep p

Flow rateEffect of biofoulingMatrix effect

pShort-term drift

pMemory effectField portability

p pchemical oxygen demand (COD), biological oxygendemand (BOD), total organic carbon (TOC), total sus-pended solids (TSS), nitrate (NO3) and surfactants

nts Probes Sensors Immunoassays

p pp p

pp

p pp p pp pp p presponse. In general, these tools are dedicated more towater-contamination diagnosis (e.g., BEWS and toxicityestimation).

4. Examples and applications

Two of these methods or tools have been tested in realconditions in several European river basins (RibbleEstuary (UK), River Aller (Germany), Daugava River(Latvia), Tevere River (Italy), Upper Rhine (France), Or-lice River (Czech Republic)). The data obtained werecompared with results obtained from classical analysis inorder to demonstrate their equivalence, their robustnessand the relevance of the tools for water-monitoringrequirements under WFD.Their relative performances were assessed in labora-

tory-based (tank experiments) and field studies in natu-ral conditions in order to identify a sub-set of robust, fit-for-purpose methods that can provide monitoring tosupport the implementation of the WFD. On the basis ofQA/QC procedures, the performance of these methodswas assessed under laboratory conditions as well as infield conditions. In parallel, case studies based on differ-ent scenarios were also performed in order to assess theirpotential integration into monitoring systems.

4.1. Evaluation of nitrateshttp://www.elsevier.com/locate/trac 319

(dodecyl benzene sulfonate (DBS)). During SWIFT-WFDfield trials, Pastel UV was used to measure nitrate.The performance of Pastel UV was evaluated and

compared to a reference method (ion chromatography(IC)) according to the AFNOR Standard [5]. In addition,performance criteria were verified in field conditions inorder to assess the impact of these conditions and todemonstrate the portability of the instrument.Table 4 shows the results obtained (calibration range,

accuracy, LoD and LoQ), which show good agreementwith laboratory data. The results obtained indicated thatthe environmental conditions did not adversely affect theperformance of the device. In general (laboratory andfield conditions), the LoDs obtained were higher than thespecification value declared by the manufacturer

Moreover, reference material RM13 (produce by theSWIFT-WFD Consortium) was used as a check sample inorder to verify Pastel UV performance in field conditions(e.g., temperature and climatic conditions). Table 6indicates that the coefficients of variance (CVs) obtainedfor field measurements are acceptable compared to thoseobtained for laboratory measurements.

4.2. Evaluation of orthophosphatesThe orthophosphates were measured by the HACH sys-tem, which is based on a colorimetric reaction (forma-tion of phosphomolybdate complex, blue color). Themanufacturers specification was compared with the re-sults obtained during the validation procedure in thelaboratory. All the performance criteria were evaluatedaccording to the standard procedure based on a statis-tical approach [5].The linearity is in the same concentration range but is

precisely defined using the statistical approach(0.242.4 PO34 mg=L).The repeatability was evaluated for seven standard

solutions, each measured 10 times (Table 7). The resultsshow that the coefficient of variance (CV%) increaseswhen the concentration decreases; this is not unusual

UV

togra

O3 =L

3)3 =L3 =L

Table 3. Performance criteria for biosystems

Bioindicators Bioassays

Precisionp

Accuracyp

Toxicity thresholdp p

False negative/positivep p

Working rangep

Ruggednessp p

Trends Trends in Analytical Chemistry, Vol. 26, No. 4, 2007(LoD = 0.2 mg NO3 =L).Four reference materials (spring water, two river

waters and lake water) were measured in the laboratoryusing both methods. Table 5 shows the results obtainedwith Pastel UV and the IC method. The values obtainedagree within the uncertainty of the results.

Table 4. Performance comparison of ion chromatography and Pastel

Ion chroma

Linearity range 115 mg NCalibration line r2 = 0.99Accuracy (Bias) RM Hamilton 20 (10.8 0.2 NO3 =L) 10.85(0.2LoD 0.7 mg NOLoQ 0.8 mg NO

Table 5. Performance evaluation using several reference materials

Reference materials Reference value (mg NO3 =L)

SWIFT RM06 (spring water) 62.2 (2.4)a

SWIFT RM13 (river water) 4.06 (0.9)a

LGC6020 (River Thames) 39.4 (0.5)

Hamilton 20 (lake water) 10.85 (0.23)

aMean of inter-laboratory exercise.bMean and standard deviation obtained from 12 measurements.

Table 6. Use of SWIFT-RM13 to test repeatability in laboratory and field

Laboratory Field (1)

Average (mg NO3 =L) 4.6 5.4CV (%) 2.2 2.5

320 http://www.elsevier.com/locate/tracconditions

Field (2) Field (3) Field (4)

5.5 5.2 5.32.8 2.0 1.1although in this case it does not follow a regular trend.The repeatability was also assessed in field conditionswith five concentrations, each measured 15 times (Table8). A similar trend is observed.In this study, the LoD and the LoQ were measured in

demineralized water and in natural water (without

(laboratory and field conditions)

phy Pastel UV (lab. conditions) Pastel UV (field conditions)

0.515 mg NO3 =L 0.515 mg NO3 =L

r2 = 0.99 r2 = 0.9810.7(0.1) 11.0 (0.1)0.5 mg NO3 =L 0.6 mg NO

3 =L

0.9 mg NO3 =L 0.7 mg NO3 =L

Ion chromatography (mg NO3 =L)b Pastel UV (mg NO3 =L)

b

62.9 (0.6) 61.2 (1.4)5.1 ( 0.7) 4.6 (0.1)

39.6 ( 0.2) 40.3 (0.3)10.7 ( 0.1) 10.7 (0.1)

orthophosphates) using a clean-up step (HCl) specified bythe manufacturer. In this case, the results are quitesimilar and are in good agreement with manufacturersspecification (Table 9).The selectivity was tested using several spiked

natural waters (Galeizon River and Tevere River

(Trasimeno, Italy)). Fig. 4 shows clearly that no matrixeffect was observed; the calibration line slopesare similar. This was confirmed by a statisticaltest.A reference material (LGC RM Thames River,

1.1 0.1 mg/L) was used as a QC tool in order to

Table 7. Repeatability of standard solution measurements (laboratory conditions, 10 measurements)

Concentration (mg/L) 0.24 0.48 0.8 1.2 1.5 2 2.4

% of concentration range 10 20 33.3 50 62.5 83.3 100CV (%) 4.8 4.5 1.9 2.4 1.5 0.8 0.5

Table 8. Repeatability of standard solution measurements (field conditions, 15 measurements)

Concentration (mg/L) 0.23 0.46 0.77 1.53 2.3

% of concentration range 10 20 33 66 100CV (%) 3.31 1.14 0.60 0.99 0.94

Table 9. Limits of detection and quantitation (clean up with HCl)

HACH specification Demineralized water Natural water

Laboratory Field

LoD (mg/L) 0.05 0.07 0.04 0.04LoQ (mg/L) 0.13 0.08 0.08

Trends in Analytical Chemistry, Vol. 26, No. 4, 2007 Trends0.3

0.4

0.5

orba

nce

0.3

0.4

0.5

orba

nce0.0

0.1

0.2

0 0.5 1 1.PO4

3-concentration mg/L

Abs

0.0

0.1

0.2

0 0.5 1 1.PO4

3-concentration mg/L

Abs

Figure 4. Selectivity assessment (

Table 10. Quality control RM to test repeatability in laboratory and field

Laboratory Field (

Average concentration (mg/L) 1.12 1.13CV (%) 1.7 1.0

Table 11. Comparison of HACH method with reference method using ref

HAC

Average concentration (mg/L) 1.11CV (%) 2.7y = 0.2907x + 0.0018Demineralized water

Tevere River-Trasimeno

y = 0.2907x + 0.0018Demineralized water

Tevere River-Trasimeno

y = 0.2787x + 0.0295

y = 0.293x + 0.0263

5 2

Galeizon Rivery = 0.2787x + 0.0295

y = 0.293x + 0.0263

5 2

Galeizon River

standard-addition method).

conditions

1) Field (2) Field (3) Field (4)

1.17 1.15 1.192.1 1.6 1.9

erence material

H method Reference method

1.191.0

http://www.elsevier.com/locate/trac 321

material (LGC RM Thames River). Table 11 shows theresults obtained with the HACH system and the value

toring requirements, if the concentration is well above theLoD.

needs to be given to seasonal variations, whatever theconcentration of the pollutant.

C. Gonzalez, Talanta 69 (2006) 302.

[14] International Organization for Standardization (ISO), ISO 8466-

Trends6. Websites

http://www.epa.gov/etvhttp://www.epa.gov/nhsrchttp://www.aoac.org/testkitshttp://www.metropolis-network.nethttp://www.swift-wfd.com

Acknowledgement

We acknowledge financial support from the EuropeanUnions 6th Framework Programme (SWIFT-WFD,5. Conclusion

In order to produce data that will be useful for monitoringthe quality of water to meet the requirements of the WFD,only fully validated methods should be used. This articleindicates an approach that can be used for proceduresused for on-site monitoring. For this to work, it is essentialthat the principles of laboratory-method validation arewell understood before starting to develop the validation ofon-site technologies. It is appreciated that, in this study,short-term estimates of precision were used, whereas abetter estimate of likely variability would be obtained froma long-term study. Using QC data collected on-site over aperiod of time would provide such an estimate. The cor-relation coefficient was used as a measure of correlation,but, during the validation procedure, it may be better toapply more rigorous linearity tests (e.g., a statistical testcomparing the residual variance with the variance of themethod, as indicated in the text).The approach outlined can be applied where the pol-

lutant levels are well above the LoD. However, attentionquoted by the manufacturer. The results are in goodagreement, even though stored calibration data wereused. In this example, the laboratory validation led to re-sults that were not significantly different from thosespecified by the manufacturer. These results indicatedthat there is no significant bias between the two methods.Thus, this system seems reliable enough for water-moni-compare measurements obtained in laboratory and fieldconditions. The results are shown in Table 10.Finally, the HACH system was compared to a reference

method (colorimetric method) using the same referencecontract no: SSPI-CT-2003-502492) and all the SWIFT-

322 http://www.elsevier.com/locate/trac1:1990, Water Quality Calibration and Evaluation of Analytical

Methods and Estimation of Performance Characteristics Part 1:

Statistical Evaluation of the Linear Calibration Function, ISO,WFD partners who were involved in the production ofreference materials.

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[4] International Organization for Standardization (ISO), ISO

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Geneva, Switzerland, 2003.

[5] Association Francaise de Normalisation (AFNOR), XPT 90-210

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[6] US Environmental Protection Agency, Technologies and

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[10] CITAC (The Cooperation on International Traceability in Analyt-

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[12] International Organization for Standardization (ISO), International

Vocabulary of Basic and General Terms in Metrology, second ed.,

ISBN 92-67-01075-1, ISO, Geneva, Switzerland, 1993.

[13] I.J. Allan, B. Vrana, R. Greenwood, G.A. Mills, B. Roig,

Trends in Analytical Chemistry, Vol. 26, No. 4, 2007Geneva, Switzerland, 1990.

Validation procedure for existing and emerging screening methodsIntroductionValidation process: general conceptsExisting and emerging field devices (screening methods)Examples and applicationsEvaluation of nitratesEvaluation of orthophosphates

ConclusionWebsitesAcknowledgementReferences

validation procedure for existing and emerging screening methods

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