Basic Course Experiments to Demonstrate Validation

Abstract

Undoubtedly, nowadays modem instrumental Analytical Chemistry (AC) is one of the most important interdisciplinery sciences. Therefore teaching AC at university should have a very high priority - also in undergraduate and graduate courses. In this connection both fundamental analytical strategies - accurate results and obtaining their quality - should be implemented from the very beginning into the chemistry curriculum. One approach in this context is the introduction of fundamental analytical terms in such a manner that the results of measurements performed by students are used to highlight a specific analytical problem and the concept - condensed in the selected term - to solve it. One pivotal analytical problem can be formulated as “How can one be sure that a method produces accurate, i.e. precise and true results?”. This problem is embedded in the context of the term “validation of a method” which is linked with the question “What has to be done to assure that a method is fit for the intended analytical purpose?”

The ability of an analytical method to produce true results can be evaluated by means of the application of independent comparison methods. In this case subsamples of a sufficient homogeneous material are analysed using the method under investigation and methods based on different measurement principles. To illustrate this approach a simple experimental arrangement was worked out utilizing gravimetric determinations of inorganic ions (Fe³⁺, AI³⁺, SO₄ ^2-and PO ₄ ^3-) as methods under investigation and photometry resp. flow injection analysis as independent comparison methods. In order to avoid the use of a “black box” method and to enhance the learning effect a “didactic” photometer was constructed which enables the students to have a close look at all relevant components of the instrument and to realize the measurement process in detail. The whole exercise is aimed at students in the first year and can be performed e.g. within the first laboratory course. The students can work together in small groups and in a subsequent tutorial the obtained data can be used to draw conclusions about the specific performance characteristics of the employed methods.