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snow123
2 Posts 
Posted  07/09/2012 : 08:49:06 AM

Hi,
I am using Origin 8.1, SR2 under Windows 7.
I fit my spectrum with multiple Gaussian peaks over a spline baseline by using Analysis>Peaks and Baseline>Peak Analyzer, but wasn't very clear with the fitting results. I would be very appreciated if anyone can help me with the following questions:
1. For each Gaussian peak, the parameter table shows xc, A, w and their standard errors. It seems w=FWHM, because in Peak Analysis Report, FWHM has the same value as w, please confirm me with this. 2. The standard error is the standard deviation of each parameter? 3. How can I see the fitting function (Gaussian) as well as the baseline function (Spline line)?
Thanks a lot for your help


Hideo Fujii
USA
992 Posts 
Posted  07/09/2012 : 6:09:55 PM

Hi snow123,
> 1. For each Gaussian peak, the parameter table shows xc, A, w and > their standard errors. It seems w=FWHM, because in Peak Analysis > Report, FWHM has the same value as w, please confirm me with this.
Yes, the width (w) in the Gaussian function in the Peak Analyzer is the FWHM, as it uses the Origin buildin function "Gaussian".
(Note: Don't be confused with another builtin function "Gauss", where "w" indicates the sigma value(=FWHM/sqrt(ln(4))). )
To see the details of the function, go to the following section in the Origin help: UserGuide> Appendix3> Peak Analyzer Functions> Gaussian
> 2. The standard error is the standard deviation of each parameter? Yes, the parameter errors are standard errors of the mean. See the details: http://www.originlab.com/www/helponline/Origin/en/UserGuide/The_Fit_Results.html
> 3. How can I see the fitting function (Gaussian) as well as the > baseline function (Spline line)? In the graph output of the Peak Analyzer, it contains the baseline, individual peak curves, and cumulative curve as shown in the following screenshot. (To make more visible, I have here shown the legend in addition.)
Did I explain clearly?
Hideo Fujii Originlab 


snow123
2 Posts 
Posted  07/09/2012 : 11:18:59 PM

Hi Hideo,
Thanks a lot for the explanation. It's clear and helpful.
I am a little confused by the "Sample Curve" of the Gaussian function in Appendix3: parameter A should be the Aera (net counts) under the peak rather than the peak height, am I right?
Ideally I want to fit the spectrum with a spline baseline (based on selected anchor points) and multiple Gaussian peaks simultaneously, can I do it with Peak Analyzer? For now I can only create the spline baseline first, subtract the baseline from the data and then fit the subtracted data with Gaussian peaks. Although I can chose "Fitting" instead of "Interpolation" when I create baseline, but it seems there is no Spline baseline function provided.
Thanks



Hideo Fujii
USA
992 Posts 
Posted  07/10/2012 : 2:46:47 PM

Hi snow123,
> A should be the Aera (net counts) under the peak rather than the peak height, am I right?
First, our apology for the incorrect documentation. You are right  "A" in "Gaussian" is the area. I have reported this error description to our documentation team to fix.
Origin has three forms of Gaussian function: "Gaussian", "Gauss" and "GaussAmp". You can change the fit function from the default "Gaussian" to another by the "Fit Control" button in the "Fit Peaks stage. The summary of the parameters of these functions are:
Function A W Xc Derived Parameters

Gaussian(default) Area FWHM Center
Gauss Area Sigma*2 Center Sigma, FWHM, Amplitude
GaussAmp Amplitude Sigma Center FWHM, Area
> ...want to fit the spectrum with a spline baseline (based on selected anchor points) and multiple Gaussian peaks simultaneously, can I do it with Peak Analyzer?
Yes, Peak Analyzer (in OriginPro) can fit your multiplepeak curve as you like.
> I can chose "Fitting" instead of "Interpolation" when I create baseline, > but it seems there is no Spline baseline function provided.
I'm not sure what you meant. Spline is not an overall fitting, but an interpolation method to produce a "locally" smoothed curve around each data point. So, there is no single function formula. The Spline baseline data can be found in the "FitPeakCurve" sheet in the data workbook as well as in the result graph shown above. If I have misunderstood what you meant, please let me know.
Hideo Fujii OriginLab




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