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8/10/2019 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
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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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
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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UncertaintyProbability of95% ; k=2
Mean MEASURAND
15
U=kuk=2
-U +U
U
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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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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
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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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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Which is its working range?
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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Which is its working range?
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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Which is its working range?
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
15.00
20.00
25.00
30.00
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
9.00
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
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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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
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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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