Use of Uncertainty Calculation Software as a Didactic Tool to Improve the Knowledge of Chemistry Students in Analytical Method Validation

Calculating
analytical uncertainties as a part of method validation
is a relevant aspect of field and laboratory practices in instrumental
analytical chemistry subjects, which usually require complex algorithms.
This work describes the development and didactic use of an automatic
and straightforward informatics tool, implemented in an Excel macro,
for calculating and interpreting the uncertainty of an analytical
method against a reference method on field measurements. The software
was initially developed for field testing of low-cost air quality
monitoring analytical methods against reference methods, and the present
work shows its adaptation to a didactic environment. The uncertainty
calculation software was implemented through an Excel macro based
on Visual Basic as a graphical user interface. It finds a best-fit
line that describes the relation between concentrations determined
by the candidate and reference methods. The software generates the
analytical validation results (slope and intercept with their respective
confidence limits, and expanded uncertainty of a concentration determined
by the candidate method), hiding the intermediate functions and calculations.
The Excel interface eases uncertainty calculations for undergraduate
students, although the background mathematics can be quickly unveiled
to students for didactic purposes. This tool has been applied to a
laboratory exercise focused on validating experimental results obtained
in the measurement of ozone levels in ambient air by passive sampling
and spectrophotometric detection. The uncertainty calculation software
has proved valuable by providing the student a resource to check the
analytical quality of the data generated in the laboratory, while
assimilating the fundamentals behind the calculations.