Deciphering the Jargon of the Analytical Lab, Chapter 3

Welcome to the third installment of this terminology trilogy. I hope the first two raps were useful, and not just relegated to soliloquy.

Trend lines are a beautiful thing. Graphing your data points can elicit euphoria when you connect the dots, especially should that line stick to those points like static cling.

Consider when calibrating your instrument, for example, by measuring the response of a few concentrations, perhaps 5, or better yet, 9. That trend line can be described by an equation, y = mx + b. How many 9s are on your curve? I’ve got four on mine.

Image Citation: Kkmurray

Those 9s portray the R-squared (R2), or coefficient of determination, a measure of the goodness-of-fit of your points to that straight line. Don’t use a different function though, Jack, like quadratic, or your R2 will lose all meaning since by the straight line is that R2 defined.

Just listen to the root word when designing your plan; your method doesn’t need special super(script) powers, you see. The points, and lines, and stats all are used to define a method’s linearity, another piece of validating defendability.

Moving on… there’s a cage match at hand, analyst 1 versus analyst 2. Who will stand victorious in the battle of standard deviations, your colleague or you? Each analyst tries their best to be the other’s clone. By conducting some choreographed chromatography (or insert method), a method’s ruggedness will be shown.

The samples are bombarded with conditions from every direction. The dance between the analysts can stretch across multiple days, or instruments, or even a rival lab — how’s that for a little analytical perfection? A rugged method is a surviving one (regardless of what’s thrown at it), an insensitive juggernaut, a powerhouse of reproducibility. Lab-to-lab, analyst-to-analyst… ah yes, but what about its selectivity?

Of interfering agents, is your method free? Can your method pick analytes out of a vast molecular sea? You can quantify this, and should you find that your method has zero interfering agents, you’ll have ensnared the rare, elusive, interferent-free specificity.

If that’s the case, well done, my friend. But most of us live on Earth with interfering agents. The End.

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About the author

Jason S. Lupoi, Ph.D.

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