By Anonymous on Tuesday, March 30, 2004 - 07:17 am:
I do remember a formula (x = h/wB), but cann't remember whether or not the formula is a good description for the symmetry of a peak or not.
I know the formula for peak symmetrie: T = b(0.1)/a(0.1) [T=1, symmetric peak]
Does anyone can help me?
By tom jupille on Tuesday, March 30, 2004 - 12:22 pm:
You need to define your terms.
Assuming that h = peak height, and wB = baseline width, then their ratio will not provide information about symmetry.
Two symmetry measurement are commonly used. For both, assume that a = distance from front slope to centerline, and b = distance from centerline to back slope, then:
Asymmetry Factor (As or ASF) = b/a (with measurements made at 10% of the maximum peak height). This is the formula you cite, and is the standard measurement according to IUPAC or ASTM
Tailing Factor (T or TF) = (a+b)/2a (with measurements made at 5% of the maximum peak height). This is the standard measurement for USP.
For most (but not all!) peaks, the magnitudes of the two measurements will be similar with ASF numbers being a bit larger, but there is no general way to compute one from the other.