The Ideal Analytical Method and Instrument

A number of characteristics can be used to define the utility of every analytical method or instrument; among these characteristics are the dynamic range, the typical signal-to-noise ratio, the sensitivity, and the selectivity associated with an instrument or technique. The hypothetical "ideal analytical method" can be described using these characteristics as well as others of a practical nature. The performance of a real analytical method such as Raman spectroscopy can be compared to the characteristics of the ideal method to establish the relative power of the real method in each characteristic area. An analyst can then weight each characteristic area according to his or her needs and capabilities to determine the best method to employ in a given analysis.

A convenient breakdown of the characteristics useful in describing an analytical method includes:

1. Wide dynamic range. The ability to determine concentrations from 10E-18 to 10E2 M would be a valuable asset on the resume of any method. Low detection limits and high sensitivity are important, but ideally a method should be able to count single atoms or molecules of a substance as well as determine concentrations of the substance ranging up to 100%. Analyses would be greatly simplified if every analytical signal were linear over this entire range.

2. Great Flexibility. Virtually every conceivable analyte and property could be determined using the ideal analytical instrument. Furthermore, these analytes and properties could be determined simultaneously and in any combination from the same sample of a substance. Any sort of sample, solid, liquid, or gas, could be directly analyzed with the instrument. The ideal analytical instrument would be the only instrument in every laboratory.

3. Durability. The ideal instrument is simple, rugged, and easy to maintain. Anyone can operate or repair it with little or no training. The device could act as a virtual "black box" that always produces the correct result regardless of the skill of the operator.

4. Accuracy and Precision. Measurements made with the technique would be free of systematic bias and highly reproducible.

5. Freedom from Interferences. The highest selectivity means that no characteristic of the sample or the environment will interfere with the measurement of any analyte or sample property. Furthermore, as an instrument approaches the "ideal analytical black box" it will need more and more "false-sample" detection capability; that is, the instrument will need to be able to recognize that it is examining a sample unlike any it has ever examined before, and will need to be able to respond appropriately. This response could take the form of a request for operator assistance, more samples of the same type, a "second opinion" analysis by another technique, or a library search for the best step to take.

6. Noninvasiveness and Nondestructiveness. The ideal method and instrument do not disturb the sample under analysis. Little or no sample preparation is required to use the technique. Very small sample sizes can be employed. The sample can be used for its originally intended purpose following the analysis, or it can be examined using another analytical technique.

7. Low cost. The ideal instrument and method are inexpensive in terms of the equipment, supplies, and personnel required to implement the technique.

8. Rapid. The ideal method is a fast one, resulting in increased sample throughput and cost savings.

Once again, the importance of each of these characteristics will vary from situation to situation, and each one of these areas should be weighted according to requirements and capabilities of the analyst.

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