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Select an article below to understand the options for processing acquired FTIR data.
You can perform basic equations (add, subtract, multiply and divide) with acquired sample spectra. There are a number of reasons why you might want to do this, especially for subtracting a reference spectrum. For more information, see the sections that follow.
To perform spectral math, the sample and reference spectra must have the same spectral resolution and be in the same Y-axis unit. If they are not, the software automatically converts the selected reference spectrum to match the selected sample spectrum. In order to subtract, multiply or divide spectra, at least a portion of the spectral range (X-axis) of the two spectra must overlap.
Note Use the bottom bar to change the Factor’s adjustable range.
Use Subtract to subtract one spectrum from another. Spectral subtraction is useful in a variety of situations. Here are some examples:
Use Add to add two spectra together. Adding spectra can be useful in the following situations:
Use Multiply to multiply two spectra. Most people use divide rather than multiply for most applications. But multiplying spectra can be useful for reprocessing a spectrum with a different background. For example, if you measure a sample that is adhered to a matrix, you can acquire a single beam spectrum of just the matrix and use that spectrum to cancel out the original background and replace it with the new one. Here is the equation:
S * B1/B2
Where:
S= sample spectrum (processed with original background)
B1 = original background
B2 = new background
Use Divide to divide one spectrum by another. Dividing spectra can be useful for reprocessing a spectrum with a different background. For example, if you measure a sample that is adhered to a matrix, you can acquire a single beam spectrum of just the matrix and use that spectrum to cancel out the original background and replace it with the new one. Here is the equation:
S / (B2/B1)
Where:
S= sample spectrum (processed with original background)
B1 = original background
B2 = new background
When “Require reason for change for Spectral Math” is enabled in the Thermo Scientific Security Suite, Spectral Math requires a change reason and signature before the results can be saved, and the following change event is recorded in the audit log:
Advanced Spectral Math provides more flexibility and power than standard spectral math. While standard spectral math supports spectral subtraction, addition, multiplication, and division using a single reference spectrum, Advanced Spectral Math allows you to build custom equations using up to 10 reference spectra and using a wider range of operations.
For many applications, using the standard subtract, add, multiply, and divide functions in spectral math is simple and sufficient. However, if your analysis requires a more complex equation, Advanced Spectral Math may be required.
Both forms of spectral math are available only in the Desktop interface of OMNIC Paradigm software.
When choosing between the two methods, consider the following differences to decide which tool is right for you:
When you use Advanced Spectral Math, you will typically add spectra that you will use in the equation, build your equation, preview the results, and finally review the result in the Spectral View.
You can add up to 10 spectra, and you do not need to use every spectrum that you open. You may find that it is easier to add the spectra first so that they are available while you focus on the equation, or you may prefer to add them only as needed.
The resulting spectrum is listed in the Results pane. Spectra used in the equation are shown in the sub-panes below the result spectrum with a label indicating their use in the equation.
Functions | Description |
---|---|
k | Constant |
? + ? | Addition |
? - ? | Subtraction |
? * ? | Multiplication |
? / ? | Division |
log(?) | Logarithm. Returns the base 10 log |
exp(?) | Returns the result of the constant e (2.7182818) raised to the power of the specified value |
sqrt(?) | Square root of the value |
deriv(?) | Derivative |
savderiv(?) | Savitsky-Golay derivative |
norderiv(?) | Norris derivative |
You can transform the original interferogram data for your spectrum with new settings by using Reprocess.
When comparing your spectrum to a reference, you can get a more accurate comparison if both spectra were processed using the same settings. For example, if your spectrum was collected using a broader range than the reference or if it used a different apodization technique, your comparison may be inaccurate. Reprocessing allows you to transform the original data to match your reference spectrum, resulting in better results for your correlation, QCheck, or quantification analyses.
You cannot reprocess to a finer resolution than was originally used. Reprocessing can transform your data but cannot fill in data that was never collected.
If you reprocess multiple spectra, the options show only the values that they share. For example, if one spectrum was measured at a finer resolution, you can select only the shared, lower resolution for reprocessing. This is also true for range. You can set the max and min values for Truncate to only the shared, overlapping range.
Reprocess is available only in the Desktop view of the software.
You can undo the reprocessing by viewing the History panel and reverting to an earlier state. If you reprocessed more than one spectrum, you will have to revert each one individually.
Clear data from a region of your spectrum with the Blank Regions tool in the Process menu. You can also blank regions in workflows with the Processing tile.
The Blank Regions tool is a great way to get rid of noisy data that would interfere with your analysis. For example, blanking a region helps in the following situations:
You can blank regions on one or more spectra.
To undo the change, view the spectrum's history and revert to a previous state.
To find the average or standard deviation of spectra, use the Statistical Spectra tool in the Process menu.
For each X value of your spectrum, you can find the average or standard deviation of the Y value. This creates a new spectrum.
You can also use the standard deviation to compare spectra of a standard sample that you measured at different times. This is a useful way to test the repeatability of the measurement.
You can calculate statistical spectra only in the Desktop view of the software. Use the Processing tile to calculate statistical spectra in workflows.