What Does Specificity Mean in Chromatography?

Specificity is an important concept in chromatography. But it can also be one that’s hard to get your head around. In this post, we’ll discuss what exactly specificity means, why it’s important, how it’s demonstrated, and how it differs from selectivity.

What is specificity?

Generally speaking, specificity refers to the quality of being specific to a particular subject. In terms of chromatography, that refers to the accurate measurement of a specific analyte when other components are (or are expected to be) present in a given sample.

When looking at chromatography results, specificity can be demonstrated by the separation of analyte peaks compared to other peaks that have originated in the same sample. More specifically, it can be determined by the resolution of the two closest-eluting components.

Why does it matter?

Above all else, the essential purpose of chromatography is separation. Given that specificity is required to separate peaks and distinguish between them, it’s clearly vital to chromatography. But aside from the obvious, the benefits can be broken down as follows:

• Specificity ensures that the analyte of interest is identified n identification tests
• It allows methods to provide an accurate statement for impurities in purity tests
• It provides exact results when determining an analytes potency or content in assays

Demonstrating specificity

Given its importance, specificity must be demonstrated for suitable chromatographic methods. For identification, that’s done through a method’s ability to distinguish between compounds with closely related structures – or between a compound compared to a known reference material.

For assays, specificity can be demonstrated with the used of spikes samples. In doing so, you can show that a method’s results aren’t impacted by impurities.

A similar approach can be taken for impurity tests, where those impurities would be determined accurately based on the levels used to spike a substance.

Specificity vs selectivity

Given the definition above, it’s only natural that many confuse the concepts of specificity and selectivity. Selectivity also refers to how a detector or analytical method differentiates between an analyte of interest and other components in the sample.

It’s one of the key factors in the article ‘Selective and Robust UHPLC-MS/MS Assay for the Determination of Acrylamide Levels in Food Samples’, owing to the choice of an appropriate column with higher retention capacity for polar analytes.

So, how are they different? It comes down to the other components. Specificity is solely concerned the method’s identification of one specific analyte. On the other hand, selectivity still requires those other components to be identified – including the analyte of interest.