Table of Contents
What is an asymmetry factor?
The asymmetry factor is a fundamental property of a scattering medium that affects the transfer of radiant energy through the medium. Particles that are small compared to the wavelength of the radiation, such as air molecules, have asymmetry factors close to zero.
What is asymmetry factor in chromatography?
Definition: Asymmetry factor The asymmetry factor is a measure of peak tailing. It is defined as the distance from the center line of the peak to the back slope divided by the distance from the center line of the peak to the front slope, with all measurements made at 10% of the maximum peak height.
What is the meaning of tailing in chromatography?
Tailing is basically the inverse of fronting. The peak is presented asymmetrically, with a broader second half and a narrower first half – breaking away from the ideal peak shape, with its symmetrical Gaussian profile. While the effect is similar, the circumstances of tailing are different from those of fronting.
What does it mean when a GC peak appears asymmetrical?
A peak is considered asymmetric when the distance from the start of the peak to the centre (A) and from centre to the end (B) of the peak differs (Fig 1). It is best to measure these distances at about 10% of the peak height. Within asymmetric peaks, there are two possibilities that could exist; Fronting and Tailing.
What is USP tailing factor?
The tailing factor is determined by drawing a perpendicular line from the peak centre to the baseline of the peak. Then the peak width and the front half-width are measured for the peak at 5% of the height of the peak. The tailing factor is simply the entire peak width divided by twice the front half-width.
What is peak tailing?
Peak tailing is the most common chromatographic peak shape distortion. Compounds possessing amine and other basic functional groups interact strongly with such ionised silanol groups, producing tailing peaks.
What causes tailing?
The primary cause of peak tailing is the occurrence of more than one mechanism of analyte retention. Secondary analyte interactions, with ionised silanols on the silica surface, give rise to peak tailing. These interactions need to be minimised to achieve acceptable peak shapes.
What is column asymmetry?
Peak asymmetry — the asymmetry factor (AS), defined as the distance from the center line of the peak to the back slope divided by the distance from the center line of the peak to the front slope. In general, the AS is a measure of the quality of column packing. Well-packed columns will have an AS of close to 1.
How do you increase peak tailing in GC?
How do I improve early eluting peak shape for GC?
- Use a split injection. This limits the amount of solvent that gets onto the column and reduces how much analyte dissolves in pooled solvent.
- Decrease the injection volume.
- Use a pressure pulsed injection.
- Use a guard column.
- Increase the column film thickness.
How do you measure tailing factor?
How can tailing factor be reduced?
There are a few methods that can be used to avoid peak tailing:
- Operate at a lower pH.
- Use a highly deactivated column.
- Consider the possibility of mass overload.
- Consider the possibility of column bed deformation.
- Work at high pH when analyzing basic compounds.
- Use a sample clean-up procedure.
How is the tailing factor used in asymmetry?
The USP tailing factor is widely accepted and differs from other asymmetry calculations in that it uses the peak width at 5% of peak height divided by 2x the front width at 5%. Asymmetry is commonly calculated as the ratio of back to front width at a specified % of peak height, normally at 10%.
How is the tailing factor and peak width measured?
Then the peak width and the front half-width are measured for the peak at 5% of the height of the peak. The tailing factor is simply the entire peak width divided by twice the front half-width while asymmetry factor measured at 10% of the peak height.
How is the asymmetry factor defined in ASTM?
The Asymmetry Factor is defined by ASTM as the distance from the centerline to the back edge divided by the distance from the centerline to the front edge, with all distances measured at 10% of the maximum peak height. Because the measurements are made at different levels on the peak, the two parameters cannot be exactly converted.
How to calculate the peak asymmetry factor in Excel?
Peak Asymmetry Factor. Peak Asymmetry Factor, often presented as A s is calculated with the following equation As = b/a where b is the distance from the peak midpoint ( perpendicular from the peak highest point) to the trailing edge of the peak measured at 10% of peak height and a is the distance from the leading edge…