Online FTIR Graph Plotter and Spectrum Analysis Tool

Online FTIR Plotting and Analysis Features

Online FTIR Matching, Functional-Group Analysis, and Composition Estimation

The dedicated FTIR Analysis panel compares your measured spectrum with reference spectral patterns over the visible X-axis range. Start with a broad view of the measured bands, run Match FTIR Spectrum, and review the candidate preview before activating full analysis for the sample.

Compare reference spectra and chemical information

Full matching provides ranked reference names, InstaNANO IDs, match scores, spectrum overlays, and available metadata. The top reference opens automatically after activation; other reference spectra and details load when you open or select them. Use Add to graph to retain useful overlays, and narrow the search with Filter By: Name or CAS when the sample chemistry suggests particular candidates. The match score describes spectral similarity, not the probability of chemical identity.

Inspect possible functional-group assignments

Select Estimate Functional Groups to display markers at detected peaks and review the suggested assignments. The tool considers characteristic wavenumber ranges, related bands, relative peak strength, and selected-reference information when available. You can also investigate a smaller feature by adding a marker on the sample graph. Functional-group estimation can be used without selecting a reference after sample access is activated.

Estimate spectral composition and investigate additional bands

Select chemically plausible reference overlays and use Estimate Composition & Impurities. The tool fits the selected spectra to your sample in absorbance space and reports FTIR spectral contribution (semi-quantitative) and Residual spectral mismatch. These results help compare candidate components and investigate bands that remain unexplained.

Interpreting composition: The percentages describe fitted spectral contributions, not calibrated mass fractions or sample purity. Residual mismatch is a fit diagnostic rather than an impurity concentration. Evaluate it with the band pattern, selected references, sample preparation, and measurement conditions.

Free preview and full FTIR analysis

One credit activates full FTIR analysis for one sample for up to 30 days, within the applicable plan validity and usage allowances. Opening another reference or using the functional-group and composition tools does not require a separate analysis credit for each action. Save the project to continue the same sample analysis later.

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.

• Supported FTIR instrument files

  Open compatible SPA or ISPD files directly to import their measured wavenumber and signal 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.

Instrument exports: For other vendor formats, including native OPUS files, export the numerical spectrum as CSV, TXT, ASC, DAT, XY, or Excel data before importing it.

How to Plot an FTIR Spectrum

1. 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.

2. 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.

3. 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.

4. 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.

5. 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.

6. Analyze selected spectral regions.

   Measure area and FWHM or fit overlapping bands within a selected interval. For reference matching and functional-group estimation, use the dedicated FTIR Analysis panel.

7. Compare reference spectra when needed.

   Keep one sample enabled, open FTIR Analysis, and select Match FTIR Spectrum. Follow the matching workflow below to review candidate references and use the advanced interpretation tools.

8. 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 Match an FTIR Spectrum and Review Its Results

1. Check the sample data and visible range.

   Assign wavenumber to the X-axis and absorbance or transmittance to the Y-axis. Keep exactly one sample spectrum enabled. Matching uses the visible measured range, so begin with a broad view of the spectrum; the comparison needs at least 32 valid points and a usable span of 2000 cm⁻¹.

2. Run the free matching preview.

   Open FTIR Analysis and select Match FTIR Spectrum. Review the leading InstaNANO IDs and preview similarities.

3. Activate full analysis when required.

   Sign in with an eligible analysis credit plan and use the one-credit full-match button. The top reference is automatically selected under Add to graph, with its overlay and details available for comparison.

4. Compare chemically relevant references.

   Open other results to inspect their spectra and metadata. Keep useful references checked under Add to graph. If needed, add a name or CAS tag in Filter By: Name or CAS, choose Match Mode, and run the match again.

5. Inspect functional groups and spectral composition.

   Select Estimate Functional Groups to review peak assignments. For composition estimation, retain relevant reference overlays and select Estimate Composition & Impurities. Compare the reported spectral contributions with the remaining unexplained features.

6. Save the analysis and record its basis.

   Use Save Project to continue later, or Download Graph to export a PNG. Record the reference names and InstaNANO IDs, comparison range, and signal representation alongside your interpretation.

Convert FTIR Transmittance and Absorbance

With one recognizable spectrum enabled, the conversion control displays T → A or A → T according to the signal. It adds a converted column and retains the original data. For percent transmittance, the relationship is A = −log₁₀(%T/100), consistent with the IUPAC definition of absorbance.

Conversion is free. Using the built-in conversion on the same activated sample does not require another analysis credit. Select Match FTIR Spectrum again after switching representations, and check that the graph axes describe the displayed signal.

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