[clrntrules]

I am new to this forum, but I hope you can help. I am attempting to find the peak width at half height for a series of Ion Mobility Spectra. If you are not familiar with IMS, the data is presented much like HPLC or GC. I have approximately 40 spectra and I need to find the peak width at half height for a peak on each one, but have thus far been unable to find a reliable method for doing so. I am using both Excel and IGOR Pro 5.03, and the problem is that the calculated half-height points are in between two of the actual data points and I cannot find a way to reproducibly measure this width. Any help would be greatly appreciated.

[invisiblegs]

There are a couple of ways that you might actually do this.  The peak width at half height is a useful approximation for systems that do not electronically integrate peaks from a baseline.  The simplest solution might be to take the average of the two widths that surround your half height point.  This would give you a good approximation provided that the half height point is close to half way between the other two data points, and that it falls close to the inflection point of the rising or falling peak slope.  Another way would be to find the equation of the line between the two data points that lie on either side of your half height point.  Using the equation of that line, you can more accurately calculate the width at half height.  Yet another alternative is to integrate the peaks themsleves using a computer program such as Excel.  From your post, it seems as though you have a data file of some sort, and if you can establish a nice flat baseline, a numerical integration algorithm may be the easiest and most accurate way to find what you need.

[ARGOS++]

Dear Clrntrules;


Why not use simple “Linear Interpolation”?

As it seems you have the data in Excel you can automate or at least “semi automate” it, especial if your time axes is equal spaced.
You have only to use the “Intercept Theorem” between the measured “Neighbour Points”.

This is allowed, reproducible, and reliable also in cases if the Peaks are not completely divided, because around the half height the measuring curve is becoming very close to linear shape.

But for future help knowledge of your data organisation in Excel is required.


Good Luck!
                    ARGOS⁺⁺