Horwitz Iie 10

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Horwitz Equation

as Quality Benchmark in

Carlos Rivera

Rosario Rodriguez


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INDUSTRYFAO

WHO

Accreditation Requirements

17025S

essay lab

NISTCENAM

EMAOIML

WTO


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Experiment design ISO 5725-1

Data analysisISO 5725-2

17025 Labs Quality Assurance

Per ormance

Statistical testISO 5725-4

Referencesvalues

Proficient?

Yeah! Nei!


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The core question

Which reference values should be used tova ate s resu ts


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Objectives

1. Reproducibility and Uncertainty ofmeasurement?

2. Scope of testing laboratories quality control ? . orw tz equat on as qua ty enc mar

4. Uncertainty accreditation policies ?


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Objectives





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International Vocabulary of MetrologyVIM

Reproducibility

Repeatability


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VIM terms

2.25 measurement reproducibility

reproducibility measurement precision underreproducibility conditions of measurement

NOTE Relevant statistical terms are given in

ISO 5725-1:1994 and ISO 5725-2:1994.


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VIM terms

2.21 measurement repeatability

repeatability measurement precision under a set ofrepeatability conditions of measurement


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VIM terms

2.20 repeatability condition of measurement

same measurement procedure , same operators,same measuring system , same operating conditions andsame location, and replicate measurements on the sameor similar objects over a short period of time.


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Objectives





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UncertaintyProbability of95% ; k=2

Mean MEASURAND

15

U=kuk=2

-U +U

U


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Objectives





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17025s Quality Control

5.9.1. The laboratory shall have quality control procedures for monitoring the validity of tests

. . . ua ty contro ata s a e ana yze an ,where they are found to be outside

pre-defined criteria


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Equipment Environment

ISO/IEC 17025 Lab System

Item Measurement

Process

Measurementvalue U [k{n; p%}]

Personal Methods


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5.9 @ 17025

Measure the measurer!


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Objectives





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What does HorEq show?

Its an empirical number It is a CV

Comes from on analytical laboratoriesReproducibility of analytical processesCV Horwitz =

N > 1000 itemsData distribution were as standard


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How is it expressed?

-0.15

Where C, is the concentration of the analyteexpressed as a mass fraction


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How does it look?

HORWITZ ET.AL. Assoc. of Anal. Chem. (Vol. 63, No. 4, 1980); p. 1345


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When can it be used?

CANNOT

Physical measurement

Empirical analyte


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When can it be used?

NOT FOR

Humidity; ash; fiber; analyte defined by methodwhere its concentration depends on procedure.

Neither for undefined analytes such asenzymes, polymers and bimolecules.


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Which is its working range?

1.2 x 10-7

C 0.138This range was validated for mycotoxin in

milk, but


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Without further experimental confirmation ,similar conclusions have been incorporatedinto several recent EU Directives dealing

.

HORWITZ & ALBERT Journal of AOAC

International (Vol. 89, No. 4, 2006); p. 1103


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as the concentration decreases as thedetection limit is approached (at about 10 ppb),the number of false negatives increases.

HORWITZ & ALBERT, (Ibid.) page 1103


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1.2 x 10 -7 C 0.138 Limited scope of validation Accepted by EU regulations

100 ppb C Experimental finding by Horwitz et.al.


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Performance of Gas Chromatography

ASTM D3612 02 Analysis of GasesDissolved in Electrical Insulating Oil

na ys s o o yc or nateBiphenyls in Insulating Liquids


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Precision values at standards

ASTM D3612 02In (R) 95% = K n (R) 95% X C n

ASTM D4059 00

I(r) 0,95 = k(r) x (X media )0,75


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Comparision

ASTM Range Conc . (1) CVR%(95%)(2) CVH% (95%)

Ratio(1)/(2)

D3612 H 2 @ 90-710 90 38 16 2D3613 CO @ 110 - 930 110 79 16 5

D3614 CH 4 @ 35 - 620 35 72 19 4D3615 C 2H5 @ 40 - 400 40 75 18 4D3616 C 2H4 @ 30 - 800 30 82 19 4D3617 C 2H2 @ 25 - 335 25 64 20 3

D3618 CO 2 @ 25 - 335 25 76 20 4D4059 Megabore 5 30 25 1D4059 Megabore 50 30 18 2D4059 Megabore 500 17 13 1


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CVH vs CVR CV R control limits, too open to allow effective preventive actions.

os ng R m ts s a goo pract ce ut;

CV H closes limits of reproducibility to abenchmarked value


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+CV H

+CV R

Control Chart

*

*Preventive action

-CV R

-CV H

t1 t2 tnt3


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APPLICATIONS


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Control chart of BIAS withreproducibility limits

Evaluates BIAS of measurement process using acharacterized sample essayed; in different days.

Fixed limits on the Hor Eq value calculated;expanded 95% under standard probability curve.

Presents variance among results; on controls.


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35.00

40.00

C C

ASTM D4059 @ 1260

Control chart of BIAS with reproducibility limits

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09/01/05 09/01/16 09/02/09 09/02/11 09/03/05 09/03/18 09/03/20 09/04/02 09/04/14 09/04/21 09/05/19 09/05/28

p p m

d e t e c t a d a s e n

Valor

L.S.C.

L.I.C.

Valor (ppm)


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Control chart of variance withreproducibility limits

Evaluates CV of measurement process using acharacterized sample; essayed in different days.

Values come from standard deviation of the last threevalues at characterized sample.

Limits were fixed on the value calculated from HorwitzEquation expanded 95% under standard probability curve.


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Sample of control chart of reproducibility

6.00

7.00

8.00

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C C

ASTM D4059 @ 1254

0.00

1.00

2.00

3.00

4.00

5.00

23-08-2007 19-09-2007 13-11-2007 19-12-2007 18-02-2008 21-05-2008 09/01/05 09/02/12 09/03/17 09/05/05

p p m

d e t e c t a d a s e n

Valor

L.C.


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Uncertainty of Measurement

Laboratory controls shows stability. Performance on variance below Horwitz

limits and ASTM known reproducibility. a oratory ana yz ng orw tz quat on as t eequation of uncertainty.


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Objectives


2. Scope of testing laboratories quality control ? . orw tz equat on as qua ty enc mar 4. Uncertainty accreditation policies ?


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Policies for uncertainty in accreditation

International Laboratory AccreditationCooperation.

International coo erationamong various accreditationschemes throughout the world.


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Accreditation Bodies

Mutual RecognitionArrangement

Similar procedures Policies on uncertaint

aligned to ILACs guidelines


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ILAC G 17

The level of uncertainty that is acceptable:

Decided on the basis of fitness for purpose.Occasionally large uncertainty may beacceptable ; sometimes a small uncertainty is

required .


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G 17 about standardized methods

Well-recognized methods specifying limits of themajor sources of uncertainty require no special action.

Laboratories are allowed to uote the t icaluncertainty of measurement if they can demonstratefull compliance with the test method.


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Objectives





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Conclusions

Benchmarking with Horwitz allows scoped laboratoriesto track the performance of their processes;

A ro riate to ex ress CVat framed essa methods

Reporting uncertainty of measurement through

Horwitz Equation acceptable under ILACguidelines.


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Thank you!

Carlos Rivera

Rosario Rodrguez

Documents

Horwitz Iie 10