Page 23 - Modern Analytical Chemistry

1400-CH01 9/9/99 2:20 PM Page 6

6 Modern Analytical Chemistry

1. Identify the problem
Determine type of information needed 5. Propose a solution
(qualitative, quantitative, Conduct external evaluation
characterization, or fundamental)
Identify context of the problem

2. Design the experimental procedure
Establish design criteria (accuracy, precision, 4. Analyze the experimental data
scale of operation, sensitivity, selectivity,
cost, speed) Reduce or transform data

Identify interferents Analyze statistics
Select method Verify results
Establish validation criteria Interpret results

Establish sampling strategy Feedback
loop

3. Conduct an experiment
Calibrate instruments and equipment

Standardize reagents
Figure 1.3
Gather data
Flow diagram for the analytical approach to
solving problems; modified after Atkinson. 7c

analysis. Finding an appropriate balance between these parameters is frequently
complicated by their interdependence. For example, improving the precision of an
analysis may require a larger sample. Consideration is also given to collecting, stor-
ing, and preparing samples, and to whether chemical or physical interferences will
affect the analysis. Finally, a good experimental procedure may still yield useless in-
formation if there is no method for validating the results.
The most visible part of the analytical approach occurs in the laboratory. As
part of the validation process, appropriate chemical or physical standards are used
to calibrate any equipment being used and any solutions whose concentrations
must be known. The selected samples are then analyzed and the raw data recorded.
The raw data collected during the experiment are then analyzed. Frequently the
data must be reduced or transformed to a more readily analyzable form. A statistical
treatment of the data is used to evaluate the accuracy and precision of the analysis
and to validate the procedure. These results are compared with the criteria estab-
lished during the design of the experiment, and then the design is reconsidered, ad-
ditional experimental trials are run, or a solution to the problem is proposed. When
a solution is proposed, the results are subject to an external evaluation that may re-
sult in a new problem and the beginning of a new analytical cycle.