Activities

Uncertainty calculation in chemical analysis
Uncertainty calculation in chemical analysis
02/02/2022

Activities

• Objective
• Background
• Definitions
• Types of Error
• Type A and Type B uncertainty
• Distribution
• Sources of uncertainty
• uncertainty calculations
• The use of uncertainty

Uncertainty calculation in chemical analysis
02/02/2022
02/02/2022
Uncertainty calculation in chemical analysis
Objective
To provide knowledge and to develop skill of participants in uncertainty calculations
02/02/2022
Uncertainty calculation in chemical analysis
Historical Background
1960: Error.
1977:
- no international consensus on the expression of Uncertainty in measurements.
- BIPM prepared questioner distributed to 32 NMIs and 5 international organizations.
1979: 21 feedback from laboratories.
1980: WG on the statement of Uncertainty, CIPM asked ISO to develop a guide.
1993: Guide to Expression of Uncertainty in Measurements (GUM).
1995: Quantifying Uncertainty in Analytical measurements (EURACHEM/CITAC).
02/02/2022
Uncertainty calculation in chemical analysis
Measurement
process of experimentally obtaining one or more quantity values that can reasonably be attributed to a quantity.
Metrology
science of measurement and its application.
Measurand
quantity intended to be measured.
Metrological traceability
property of a measurement result whereby the result can be related to a reference through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty.
Definitions
Definitions
Uncertainty calculation in chemical analysis
02/02/2022
Accuracy
closeness of agreement between a measured quantity value and a true quantity value of a measurand.
Precision
closeness of agreement between indications or measured quantity values obtained by replicate measurements on the same or similar objects under specified conditions.
02/02/2022
Uncertainty calculation in chemical analysis
Trueness
closeness of agreement between the average of an infinite number of replicate measured quantity values and a reference quantity value.
Bias
estimate of a systematic measurement error.
Repeatability
measurement precision under a set of repeatability conditions of measurement.
(same procedure, same location, same object over period of time)
Reproducibility
measurement precision under reproducibility conditions of measurement.
(different location, different operator, different system)
Definitions
02/02/2022
Uncertainty calculation in chemical analysis
Definitions
Coverage interval
interval containing the set of true quantity values of a measurand with a stated probability, based on the information available.
Coverage probability
probability that the set of true quantity values of a measurand is contained within a specified coverage interval.
Coverage factor (K)
number larger than one by which a combined standard measurement uncertainty is multiplied to obtain an expanded measurement uncertainty. (in many cases it is 2)