Kjeldahl vs Dumas vs NIR

NIR versus Kjeldahl, FTIR and Raman: where each method fits, what each costs in time and sample prep, and what to ask before buying an NIR analyzer.

The short answerKjeldahl and Dumas are reference methods that destroy the sample and take minutes to hours. NIR is a secondary method: results in under a minute, no chemicals, but it must be calibrated against a reference and only predicts what it was trained on.

Key numbers

4-6 hSoxhlet fat extraction
Glossary
under 1 mintypical NIR result
Grain FAQ
3 methodsKjeldahl, Dumas, NIR
This page

Reference methods

Kjeldahl: acid digestion, distillation and titration for nitrogen to crude protein. Dumas: combustion in oxygen with nitrogen measured by thermal conductivity. Soxhlet: solvent extraction for fat over 4-6 hours. Karl Fischer: titration for moisture in low-water powders and oils.

Where NIR fits

NIR replaces the routine runs, not the reference. You still need the reference method to build and check calibrations, and the wet chemistry for disputes.

One sample, three ways to look at it

Same sample, three methods. Each draws a different kind of spectrum.

NIR
Light reflects off or passes through the sample
FTIR
An interferometer scans all wavelengths at once
Raman
A laser hits the sample and scattered light is read
At a glanceNIRFTIRRaman
Speed
Sample prep
Water sensitivity
Cost band
Typical useMoisture, protein, fat in bulk food, feed, grainIdentification and chemical labsIdentification, packaging, lab and field checks

The ratings are relative and simplified. More bars is better for speed, easy prep, water tolerance and low cost.

Before you buy an analyzer

Ask which of your products and constituents are covered, who builds the calibration, how it is transferred across instruments, and what ongoing support costs. Course lessons 20 and 28 cover choosing an instrument and working with vendors.

Go deeper in the course

L9
NIR vs. Wet Chemistry
Week 3 · 24 min
See in curriculum
L11
NIR and Lab Reference Methods
Week 3 · 16 min
See in curriculum
L20
Choosing the Right Instrument
Week 5 · 24 min
See in curriculum

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Questions

Can NIR replace Kjeldahl?

For routine screening in many products, yes. The reference still anchors the calibration and settles disputes.

Is Dumas better than Kjeldahl?

Dumas is a modern alternative that measures total nitrogen by combustion. Both are reference methods, so the choice is about speed, chemicals and lab setup.