This technical article addresses the issue of understanding the best way to obtain a limit of detection and quantification. The case discussed involves the quantification of an illicit drug using external calibration.
In developing analytical methods, it is important as part of the method validation to test the reliability and capabilities of the method. The list of related performance metrics is somewhat dependent on the intended use of the method and the environment in which it will be used (e.g., in a regulated environment under specific agency rules, must be legally defensible, must comply with international regulations, will be adopted by all labs within the company, etc.), but in general, the following are typically determined:
- Accuracy (how closely the average analytical result matches the actual)
- Precision (how tightly replicate results match each other; usually includes repeatability = same instrument and operator, intermediate precision = same lab but different operators and over extended time frame and reproducibility = different instruments and operators)
- Specificity (how well the method discriminates target analyte(s) from potential interferences)
- Limit of detection (the statistically valid lowest amount of target analyte that can be detected in a standard free of matrix)
- Limit of quantification (the statistically valid lowest amount of target analyte that can be identified and quantified in real samples)
- Linearity and range (the concentration/amount range over which target analyte can be quantified and the response curve shape over that range)
- Ruggedness (the ability to get the same answer when analysed in different laboratories, such as is determined in a round robin study = reproducibility)
- Robustness (ability to get the same answer if analytical conditions vary a bit)
- Stability (an evaluation of the short and long term stability of samples and standards, especially important for labile compounds and derivatives)
It should be noted that the questioner’s application involved a cocaine metabolite, benzoylecgonine. It is the primary target compound assayed in urinalysis for cocaine use.
By reading the full article, you will learn the best way to determine the limit of detection and limit of quantification.
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