Plot and Analyze FTIR Spectra Online
Plot FTIR spectra directly in your browser without installing desktop graphing software. Import numerical data from CSV, TXT, Excel, XY, XYE, ASC, or DAT files, or paste the values into the editable data table. The FTIR page automatically applies Wavenumber (cm−1) and Transmittance (%) axis titles and displays the wavenumber axis from higher to lower values.
After plotting the spectrum, use the available tools for graph customization, local-polynomial smoothing, FTIR baseline correction, peak-area and FWHM measurement, multi-peak fitting, and free reference-based peak lookup. Graphs can be exported as high-resolution PNG files for reports, presentations, and publication-oriented figure preparation.
Important: The FTIR reference lookup suggests possible assignments near a selected peak. It does not independently identify a compound, material, or complete molecular structure.
Online FTIR Plotting and Analysis Features
| Feature | Current FTIR functionality |
|---|---|
| FTIR axis preset | Automatically applies Wavenumber (cm−1) and Transmittance (%) labels and displays the x-axis from higher to lower wavenumber. |
| Data import | Imports supported numerical text, spreadsheet, and tabular scientific data or accepts values pasted directly into the editable table. |
| Graph customization | Adjusts series names, colors, line and marker appearance, fonts, axis ranges, graph dimensions, aspect ratio, annotations, and legend presentation. |
| Spectrum smoothing | Applies local-polynomial smoothing with a selectable window and preview before the processed series is added. |
| Baseline correction | Uses an arPLS-based baseline-estimation routine adapted to FTIR transmittance data and adds the estimated baseline and corrected spectrum to the graph. |
| Area and FWHM | Calculates the integrated area and full width at half maximum within a selected spectral region using the FTIR transmittance reference. |
| Multi-peak fitting | Fits overlapping spectral bands using Gaussian, Lorentzian, Voigt, asymmetric pseudo-Voigt, and right- or left-tailed exponentially modified Gaussian models. |
| FTIR peak lookup | Compares a selected peak position with the free FTIR reference table and returns nearby group, class, position, and reported intensity information. |
| Project and graph export | Saves editable InstaNANO project files and downloads the graph as a PNG at a selected resolution and DPI. |
Supported FTIR Data Inputs
Text and numerical files
Import CSV, TXT, XY, XYE, ASC, or DAT files containing numerical x-y data. Files may contain one or more plotted data series when their tabular structure is supported.
Excel spreadsheets
Import XLS or XLSX worksheets containing wavenumber values and the corresponding transmittance or other spectral values.
Manual data entry
Paste copied columns directly into the data table or add, remove, and edit individual rows and series before plotting.
Saved projects
Reopen an .instanano project to continue editing previously prepared graph data and settings.
Vendor-file note: Proprietary FTIR formats such as SPA and native OPUS files are not direct FTIR inputs in the current tool. Export the spectrum from the instrument software as CSV, TXT, ASC, DAT, XY, or Excel data before importing it.
How to Plot an FTIR Spectrum
- Import or paste the FTIR data.
Drag a supported file into the upload area, select the file manually, or paste the wavenumber and spectral values into the table.
- Verify the plotted data.
Check that the imported values reproduce the expected FTIR spectrum and that no header rows or non-numerical values have been interpreted as data.
- Confirm the FTIR axes.
The FTIR page starts with Wavenumber (cm−1) on the x-axis, Transmittance (%) on the y-axis, and the conventional high-to-low wavenumber direction.
- Customize the graph.
Change the series name, color, line style, graph size, font, axis limits, annotations, and legend position as required for the intended report or publication.
- Apply processing only when needed.
Preview smoothing or baseline correction and confirm that genuine spectral bands are not removed, broadened, shifted, or replaced by processing artifacts.
- Analyze selected spectral regions.
Measure area and FWHM, fit overlapping bands, or use the FTIR reference lookup to investigate possible assignments near an experimental peak.
- Save or export the result.
Save an editable InstaNANO project for continued work or download the completed graph as a high-resolution PNG.
FTIR Baseline Correction and Smoothing
Baseline variation can obscure weak bands and affect peak-area or fitting results. The baseline tool estimates a smooth FTIR background using an asymmetrically reweighted penalized least-squares approach and calculates corrected transmittance relative to the estimated baseline. The stiffness control determines how closely the estimated baseline can follow broad curvature in the experimental data.
The smoothing tool uses a local-polynomial calculation with a selectable window size. Use the smallest window that sufficiently reduces random noise while preserving narrow peaks, shoulders, and overlapping bands. Excessive smoothing can change band width, intensity, and apparent resolution.
Calculation note: FTIR-specific baseline correction and area/FWHM calculations are configured for transmittance data with a 100% reference. Verify the spectral representation before applying these calculations to absorbance or other y-axis quantities.
The baseline implementation follows the general arPLS method described by Baek and co-workers.
Multi-Peak Fitting for Overlapping FTIR Bands
Overlapping FTIR bands can be fitted within a selected spectral interval using Gaussian, Lorentzian, Voigt, asymmetric pseudo-Voigt, or exponentially modified Gaussian peak shapes. The graph can display the combined fitted curve, individual components, background contribution, and fitting residual.
Choose the model according to the observed band shape and the physical purpose of the analysis. A mathematically improved fit does not, by itself, demonstrate that every fitted component corresponds to a separate vibration or chemical species. The fitted components should remain consistent with spectral resolution, expected vibrational behaviour, and the broader chemical context.
How to Check Possible FTIR Peak Assignments
- Plot the experimental FTIR spectrum.
Import the numerical data and confirm that the wavenumber scale and spectral orientation are correct.
- Open Other Match.
Select the Other Match panel from the left-hand tool menu. FTIR is available as one of the reference-search options.
- Select an experimental peak.
Choose the relevant plotted peak or its nearest experimental data point.
- Review the reference entries.
Examine the nearby reference positions together with their possible group, class, and intensity descriptions.
- Evaluate the complete spectral context.
Compare the proposed assignment with neighbouring bands, band shape, relative intensity, sample composition, preparation method, and expected molecular structure.
Scientific Interpretation of FTIR Results
The conventional mid-infrared region extends approximately from 4000 to 400 cm−1, although the tool can plot other imported ranges. This commonly used range is consistent with the mid-infrared terminology summarized by IUPAC.
Peak position alone is rarely sufficient for an unambiguous functional-group assignment. Band position and intensity can vary with chemical environment, hydrogen bonding, phase, concentration, sampling mode, spectral resolution, and instrumental processing. Overlapping absorptions may also produce one broad feature or shift an apparent maximum.
The NIST Quantitative Infrared Database also notes that differences in instrumental line functions can make individual point-intensity comparisons misleading. Whenever possible, consider the complete band profile and related spectral features rather than relying on one peak or one reference value.
Frequently Asked Questions
Is the online FTIR graph plotter free?
Yes. FTIR plotting, graph customization, baseline correction, smoothing, area/FWHM calculation, multi-peak fitting, and the selected-peak reference lookup are available within the online graph tool.
Can I upload an FTIR SPA file directly?
No. SPA and other proprietary FTIR vendor formats are not directly imported in the current version. Export the spectrum from the instrument software as CSV, TXT, ASC, DAT, XY, XLS, or XLSX data before uploading it.
Can the tool plot FTIR absorbance data?
Numerical absorbance values can be plotted and the y-axis title can be changed manually. However, FTIR-specific baseline and area/FWHM calculations currently use transmittance-oriented behaviour, so the calculation method should be verified before applying them to absorbance data.
Does the FTIR lookup identify the material automatically?
No. It returns possible reference assignments near the selected wavenumber. Material identification requires evaluation of the complete spectrum, sample composition, experimental conditions, and suitable reference data.
Can I fit overlapping FTIR peaks?
Yes. Select the relevant spectral interval and use multi-peak fitting with Gaussian, Lorentzian, Voigt, asymmetric pseudo-Voigt, or exponentially modified Gaussian peak models.
What graph format can I download?
The completed graph can be downloaded as a PNG at a selected resolution and DPI. The editable graph project can also be saved in the InstaNANO project format.
Can the graph be used in a research publication?
The graph can be prepared at high resolution with editable fonts, axes, series styles, annotations, and dimensions. Authors should still follow the figure-format, resolution, and reporting requirements of their selected journal.
Continue Your FTIR Analysis
Use the FTIR tool above to plot and process the experimental spectrum. For specialist data interpretation or comparison beyond the free peak-reference lookup, professional FTIR data-matching support is also available.