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8/2/2019 Quality Control2[1]
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Quality Control in TestingLaboratories
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Quality Control Samples
In every test series should be used acontrol sample
The control sample MUST beindependent from the calibrationsolution!
Examples: Prepared from other chemical Another lot of solution
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Quality Control Samples
Quality control samples maybe:
Standard solutions Ready prepared reference
materials In-house reference materials Certified reference materials
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Quality Control Samples
Use of standards as quality control sample: Only the calibration standard and the stability of
the analytical system is controlled Use of CRM as quality control sample:
The calibration standard and the stability of theanalytical system is controlled
The sample preparation is controlled as well
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Quality Control Samples
Requirements for quality controlsamples:
Long time stability Available in big amounts Concentration of the analyt equal to the
analytical problem Matrix equal to the analytical problem
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Quality Control Samples
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Control Charts
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Control Charts
Statistical calculation for the x-chart Pre-period is made by 12 or 20 measurements of
a quality control sample from different workingdays
The average is calculated The standard deviation (s) is calculated 2 s (95% confidence interval) warning limits 3 s (99% confidence interval) control limits
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Control Charts
Use of the X-chart in the daily routine: Every day at minimum the same control sample is
measured If the control sample is measured more than one
time a day All measurements can be used or Always the same has to be used!!
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Control Charts
Out-of-control-situations: One point out of 3 s Two of three points out of 2 s Seven points continuously increasing Seven points continuously decreasing Seven points continuously above the average Seven points continuously below the average Ten of eleven points below / above the average
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Control Charts
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Control Charts
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Control Charts
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Control Charts
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Control Charts
Target Value Chart Range Chart
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R- Chart
Preparation of the Range Chart In every sequence one natural sample is
analysed twice The deviation of the results in % will be put
into the range chart If often the samples give negative results it is
possible to use the quality control sample
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R- Chart
Preparation of theRange Chart
The mean of the rangesis calculated
The upper control limitis
3,267 times the meanof the range forduplicates
2,574 times the meanof the range fortriplicates
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R- Chart
Out of control criteria
One point above the control limit 7 points in a row above the central line 7 points in a row steadily increasing or
decreasing
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Target Value Chart
For the target value chart the targetvalue is used instead of the average ascentral line.
The limits are defined by the laboratory. There should be some objective evidence
for the limits: proficiency test results Limits from normative documents or laws experience
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Target Value Chart
The only out- of control criteria is out of the limits
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Target Value Chart
The target value chart may be used forthe statistical evaluation of the analysis ofcertified reference materials.
In that case it is sufficient if the result ofthe reference material is within the givenlimits of the reference material producer.
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Blank Chart
Where blanks have an significant influenceon the test result, blanks should be
Analyzed daily Documented in a blank chart
For this purpose a X-chart can be used!
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Recovery Chart
If the recovery is analysed on routinebasis, the results can be documented in aRecovery Chart
For this purpose also a X-chart can beused!
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Control Charts
How to react upon out-of-controlsituations??
Stop the analyses
Start root cause analyses Only go on with producing results after
corrective action and when the system is incontrol again
Complete documentation as nonconformingwork may be necessary!!!
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Reference Materials
Periodical use of Certified ReferenceMaterials CRM is necessary.
Use of in-house RM is possible. The used in-house RM should be traceable
to CRM or proficiency tests (PT)
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Reference Materials
The analytes and the matrix analyzed inthe laboratory should be covered by the
CRM available in the laboratory. The available CRM / RM shall be listed
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Reference Materials
The policy of the use of CRM / RM mustbe described in a procedure.
Who is allowed to use RM? Who is responsible? Under which conditions the CRM have to be
stored? How have the CRM to be handled?
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Reference Materials
This policy is very important forlaboratories that use CRM for calibration
of measuring equipment! For them the written procedure must be
very precise (e.g. mechanical testing)
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Reference Materials
In-house RM may be:
Self-made materials Old PT-samples Spiked samples
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Reference Materials
In-house Reference Materials In-house RM should have the following
characteristics: Defined and known values homogeneous Long-time stability Available in a big quantity Matrix should cover the analytical problem
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Reference Materials
COMAR Database for certified reference
materials www.comar.bam.de
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Proficiency Tests
The Proficiency Tests should cover thefield of accreditation in a specified time
period with respect to: Matrix Parameters
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Proficiency Tests
The participation in Proficiency Testsshould mirror the main-fields of the workof the laboratory.
Special regulations of the accreditationbody and governmental requirementsshall be taken in account.
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Proficiency Tests
The laboratory must have apolicy for the participation inproficiency tests.
The participation has to beplanned.
The results of the Proficiencytests have to be listed.
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Proficiency Test Provider
FAPAS several languages, every kind of food,
water, GMO, microbiology, chemistry www.fapas.com
EPTIS Database for PTs
www.eptis.bam.de
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