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Are the Tailing factor, Symmetry factor, and Asymmetry factor the same?



Introduction:

Understanding the differences and similarities between the tailing factor, symmetry factor, and asymmetry factor is crucial for accurate interpretation. Let's explore how these terms are interpreted in different pharmacopoeias and their acceptance criteria in chromatographic practices.


USP General Chapter Chromatography- <621>:

According to the USP, the symmetry factor is also known as the asymmetry factor and the tailing factor, suggesting these terms are interchangeable.



The symmetry factor (As) is defined by the formula,


As = W0.05/2d


W = Width of the peak at one-twentieth of the peak height (Width at 5% height)

d = Distance between the perpendicular dropped from the peak maximum and the leading edge of the peak at one-twentieth of the peak height (front width at 5% height)


European Pharmacopoeia (Ph. Eur) General Chapter 2.2.46:

In contrast, Ph. Eur doesn't mention the asymmetry or tailing factors, focusing solely on the symmetry factor.


As per Ph. Eur, the symmetry factor (As) of a peak is calculated using the following equation:


As = W0.05/2d


W0.05 = Width of the peak at one-twentieth of the peak height (width at 5% height)

d = Distance between the perpendicular dropped from the peak maximum and the leading edge of the peak at one-twentieth of the peak height (front width at 5% height)


Acceptance criteria for symmetry factor:


1. Ph. Eur (Edition 11.0, previously due was- 1st Jan 2023): Unless otherwise stated, in a test or assay, the symmetry factor (tailing factor) of the peak used for quantitation is 0.8-1.8


2. USP (USP–NF 2023, USP–NF 2023, previously due was- 1st Dec 2022): Peak Symmetry: Unless otherwise stated, in a test or assay, the symmetry factor (tailing factor) of the peak used for quantification is 0.8–1.8.



Are the acceptance criteria other than as proposed above acceptable?

Both pharmacopoeias provide similar acceptance criteria for the symmetry factor, typically in the range of 0.8 to 1.8. This range is generally applicable unless specific monographs or tests dictate otherwise, demonstrating a common ground in the standards set by these authoritative bodies.


Example from Ph. Eur (Edition 10) for symmetry factor other than 0.8-1.8:



Example of USP (USP–NF 2023, USP–NF 2023 for symmetry factor other than 0.8-1.8:



Tailing factor: NMT 2.0, Standard solution (for Assay)


While USP groups the symmetry, asymmetry, and tailing factors together, Ph. Eur maintains a distinct approach, emphasizing the need for careful consideration of context in chromatographic analysis.


Your thoughts and insights on this topic are invaluable. Please share your experiences and perspectives on how these factors are interpreted and applied in your chromatographic practices


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