When Analytical Chemistry Needed a Raman Reference for Carbon Materials, It Chose Our MRI

Most of the research we feature chose our instruments to make a discovery. This one chose our MRI to be the yardstick everything else is measured against.

Carbon materials — fullerenes, diamond, graphene, carbon nanotubes — are notoriously hard to characterize by conventional infrared spectroscopy: they are opaque, strongly absorbing, and awkward to prepare as thin, transmissive samples. A 2024 study set out to solve that sampling problem with infrared photoacoustic spectroscopy (IR-PAS). But a new method is only as convincing as the reference it is checked against — and for the vibrational ground truth of these carbon materials, the authors turned to Raman.

The Obstacle — A New IR Method Is Only as Good as Its Reference

Infrared photoacoustic spectroscopy is attractive for carbon materials precisely because it sidesteps the sample-preparation headaches of transmission IR and diffuse reflectance (DRIFT): powders go straight into the sample cup, opacity stops being a problem, and minimal preparation is required. But demonstrating that a new technique reports the right structural information means comparing it, material by material, against established methods whose spectral assignments are already trusted. For sp²/sp³ carbon structure specifically, Raman spectroscopy — with its diagnostic D, G, and 2D bands — is the reference of record. The new IR-PAS results needed that anchor.

The Innovation — Independent Validation, With Raman as the Yardstick

In a study published in Analytical Chemistry (Tseng, Yang, Lu, Liu & Cheng, 2024, Anal. Chem., 96, 10732–10737, DOI: 10.1021/acs.analchem.4c01797), researchers at National Taipei University of Technology and Fu Jen Catholic University measured IR-PAS spectra of C₆₀, C₇₀, natural diamond powder, graphene, and multi-walled carbon nanotubes, and cross-checked each against conventional transmission IR, diffuse-reflectance IR (DRIFT), and Raman spectroscopy. The Raman spectra were recorded on a Micro Raman Identification (MRI) spectrometer, explicitly credited in the paper to Pro Trust Tech Co., at 532 nm excitation over an 186–3500 cm^-1 range at 1.8 cm^-1 resolution.

That instrument credit is the whole point of why we are featuring this paper. This is not a study that used our hardware to chase a headline result of its own — it is an independent, peer-reviewed analytical-chemistry paper that treated our MRI Raman spectrum as the reliable structural reference against which a new method had to prove itself.

Key Results — The Raman Fingerprints That Anchored the Comparison

Four carbon materials, one reference method: for each, the paper sets the new IR-PAS spectrum beside the trusted Raman or transmission-IR fingerprint that tells you what the material actually is.

The MRI Raman Spectrum Supplies Graphene’s D, G, and 2D Signature

For graphene, the MRI Raman spectrum (532 nm) resolved the material’s characteristic D, G, and 2D bands — the G band tracking the pristine sp²-bonded lattice, the D band signalling sp³-hybridized carbon and in-plane defects, and its intensity scaling with disorder. A clearly visible D band flagged defects in the sample. Crucially, these bands are Raman-active but IR-inactive, which is exactly why the paper needed Raman: it reports structural information the IR-PAS spectrum physically cannot, making the two techniques complementary rather than redundant.

For Carbon Nanotubes, the Raman D/G/2D Bands Land Exactly Where They Should

On 20–40 nm multi-walled carbon nanotubes, the MRI Raman spectrum recorded the D, G, and 2D bands at 1342.4, 1576.6, and 2679.7 cm^-1 — positions consistent with the established literature, with a pronounced D band indicating more structural disorder than in the graphene sample. Set beside the IR-PAS spectrum of the same material, the Raman reference is what lets the authors interpret the IR-PAS features (including their unusual negative bands relative to a carbon-black reference) with confidence about what material they were actually looking at.

IR-PAS Reproduces Fullerene Fingerprints Without the Sample Prep

For C₆₀, IR-PAS cleanly resolved the intramolecular vibrational bands (near 525, 575, 1182, 1429, and 1539 cm^-1, the F₁ᵤ modes), matching the transmission-absorption spectrum of a C₆₀ film — but straight from powder, with no need to spray a saturated xylene solution onto a KBr window and vacuum-bake it. The lower-symmetry C₇₀ (D_5h, 25 hexagons + 12 pentagons, versus C₆₀’s icosahedral I_h) showed its correspondingly richer band structure. This is the sampling advantage the whole paper is built on.

IR-PAS Types a Natural Diamond Straight From 10-µm Powder

On 10-µm natural diamond powder, the IR-PAS spectrum resolved the nitrogen-related lines (near 1282 and 1177 cm^-1) that classify the stone as a type IaAB diamond — again directly from powder, avoiding the specialized diffuse-reflectance accessory and vacuum operation the DRIFT comparison required.

Why ProTrusTech Is Featuring This Research

Almost everything else in our Featured Research is a story about what a researcher discovered with our instrument. This one is different, and arguably a stronger kind of endorsement: an independent group, publishing in Analytical Chemistry — one of the most rigorous analytical journals there is — chose our MRI Raman spectrometer to provide the reference spectra their new method would be judged against. When you are validating a novel technique, you do not benchmark it against an instrument you do not trust. The MRI’s Raman fingerprints of graphene and carbon nanotubes were the fixed point the whole comparison rested on.

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Why This Matters

There is a broader point here about where Raman sits in a materials-characterization workflow. For sp²/sp³ carbon systems, the Raman D/G/2D pattern is effectively the definition of “what this material is, structurally.” Any new spectroscopic method for carbon — IR-PAS here, but the principle generalizes — earns credibility by agreeing with that Raman reference. The same instrument plays exactly this structural-fingerprint role in our feature on carbon-shell magnetic nanoparticles, where the D/G bands verify the graphitic shell. An instrument that can reliably supply those reference spectra is not just a discovery tool; it is a metrology anchor — a role that recurs every time a lab needs to prove a new measurement is telling the truth.

What’s Next

• Extending IR-PAS across more carbon and carbonaceous solids — chars, cokes, graphites — where the same sampling advantages apply and Raman can again supply the structural cross-check.
• Exploiting the “negative band” phenomenon the authors observed in graphene and CNT IR-PAS spectra, which may encode information about defects, impurities, and production history not accessible to Raman alone.
• Pairing IR-PAS and Raman routinely as complementary techniques — IR-active and Raman-active modes together — for a fuller vibrational picture of carbon nanomaterials.

Working on carbon-material characterization, or need a Raman reference you can benchmark a new method against? Get in touch with our team.

Key Takeaways

• An independent Analytical Chemistry (2024) study used a ProTrusTech MRI Raman spectrometer (532 nm) as the trusted structural reference for validating a new infrared photoacoustic (IR-PAS) method on carbon materials.
• The MRI Raman spectra supplied the diagnostic D, G, and 2D bands of graphene and multi-walled carbon nanotubes (CNT bands at 1342.4, 1576.6, and 2679.7 cm^-1) — structural information IR spectroscopy cannot access.
• IR-PAS reproduced fullerene, diamond, graphene, and CNT fingerprints straight from powder, avoiding the sample-prep limitations of transmission IR and DRIFT.
• The paper is a rare “reference-grade” endorsement — our instrument chosen not to make a discovery, but to be the yardstick a new method is measured against.

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