Managing the uncertainty and limit of quantification of parameters determined by the difference between independently measured values

Many chemical parameters are determined as the difference, d, between two measured values, designated as larger (g) and lower (w) inputs, (d = g – w; where g > w) determined from independent measurements such as:   Magnesium Hardness (mg/L of CaC03) = Total Hardness – Calcium Hardness Chromium (III) = Total Chromium – Chromium (VI)   The uncertainty associated with Read more about Managing the uncertainty and limit of quantification of parameters determined by the difference between independently measured values[…]

Eurachem/CITAC guide on assessing the performance and uncertainty in qualitative chemical analysis

Eurachem, together with CITAC, have published a guide on how to assess and report the performance of qualitative analyses. This guide describes some of the tools that can be used to check if qualitative analyses have fit for purpose uncertainty. The limitations of some approaches for quantifying performance are discussed. The quantification of false results Read more about Eurachem/CITAC guide on assessing the performance and uncertainty in qualitative chemical analysis[…]

The uncertainty evaluation should adapt to the available experimental data…not the other way around!

Talanta paper on the top-down evaluation of the measurement uncertainty from correlated validation data following regulated validation design.  Link: https://www.sciencedirect.com/science/article/abs/pii/S0039914020306779 #Metrology #Uncertainty #Validation #AnalyticalChemistry #Crossvalidation #Correlation   Research Novelty: This work presents and cross-validates a novel top-down measurement uncertainty evaluation adapted to a common method validation design for the quantification of an impurity in active Read more about The uncertainty evaluation should adapt to the available experimental data…not the other way around![…]

Using sampling uncertainty to distinguish small composition variations of a large river area!

Free share link: https://authors.elsevier.com/a/1bFkQ,ashxm80 (Until 7 August 2020) The assessment of long-term trends in river water composition is hampered by river composition heterogeneity, and sampling and sample analysis uncertainty. This work describes a novel methodology for the reliable detection of small river composition trends by taking all relevant uncertainty components into account. The methodology was Read more about Using sampling uncertainty to distinguish small composition variations of a large river area![…]

Instrumental Quantifications: Easy bottom-up uncertainty evaluations!

The paper “Monte Carlo Bottom-up Evaluation of Global Instrumental Quantification Uncertainty: Flexible and user-friendly computational tool” makes bottom-up uncertainty evaluations easy! (DOI doi.org/10.1016/j.chemosphere.2020.127285). This research presents a novel and flexible tool for the Monte Carlo simulation of global instrumental quantifications uncertainty applicable to determinations supported on low quality and correlated calibrators values, homoscedastic or heteroscedastic signals’ Read more about Instrumental Quantifications: Easy bottom-up uncertainty evaluations![…]

Use the uncertainty in conformity assessments because it is…honest!

The new requirement of the ISO/IEC 17025 standard for discussing with the customers the impact of the measurement uncertainty in the reliability of conformity decisions and for subsequently using it in conformity assessments is not just another novelty of the standard. It represents a very important evolution of laboratory accreditation that will generalise the quantification Read more about Use the uncertainty in conformity assessments because it is…honest![…]

Spreadsheet for outliers detection

Detecting single and paired outliers in replicate signals of calibration standards can be useful. Please find below a link for the spreadsheet.   Outliers are identified by cell colours. The test’s confidence level can be selected in W column. Single outliers should be removed first. Do not remove more data than reasonable. Link for the Read more about Spreadsheet for outliers detection[…]

Procedure (not method…) validation!

According to VIM3 [1], a method is: a “generic description of a logical organization of operations used in a measurement” (Entry 2.5) (e.g. standard addition method or gas-chromatography) …therefore, methods cannot be validated because are too general. The detailed description of the analytical methodology, subject to validation, is a procedure: Measurement procedure (Entry 2.6): “detailed Read more about Procedure (not method…) validation![…]

The measurement uncertainty was…?!

A measurement result is usually expressed as a (“measured quantity value” ± “measurement uncertainty”). The measured quantity value aims at estimating the “true” quantity value of a measurand (VIM3: Entry 2.10). On the other hand, the measurement uncertainty is evaluated “based on the information used” (VIM3: Entry 2.26) since there is no “true” value for Read more about The measurement uncertainty was…?![…]