GIFSQ Tools · Module 1 — Food Composition & Proximate Analysis · Tool 6 of 500
The Dumas analyser burns the sample and measures the nitrogen gas directly. Enter the instrument's nitrogen result, then correct it with the empty-tin blank and the calibration standard before applying the Jones factor.
Try sample values — fills the form with the worked example below.
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Crude protein (%)
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Nitrogen, corrected (%)
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Protein %, dry basis
Equation: Nitrogen % = instrument % − blank (mg) ÷ (sample (g) × 10), then × (standard theoretical ÷ standard measured)
Crude protein % = Nitrogen % × Jones factor
Dry basis: Protein % (dry) = Protein % ÷ (dry matter % ÷ 100).
Method: Dumas combustion, AOAC 992.15 (crude protein in meat) / AOAC 968.06 (protein in animal feed) — the sample burns at about 900–1000 °C in oxygen, nitrogen oxides are reduced to N2 over copper, and the N2 is measured by thermal conductivity. The empty-tin blank removes the nitrogen the tin and gases add; the standard (usually EDTA, 9.59 % N) checks the calibration for the run.
Assumptions: all nitrogen is protein nitrogen; the Jones factor matches the food; the blank and standard from the same run apply to this sample.
Limitations: same non-protein-nitrogen issue as Kjeldahl — urea, nitrates and free amino acids count as protein. Dumas measures total nitrogen including nitrate and nitrite, which Kjeldahl misses unless modified, so Dumas protein can read higher than Kjeldahl on nitrate-rich foods such as vegetables. Samples are small (100–200 mg), so heterogeneity is magnified — grind finely and run duplicates.
Rounding: results to 2 decimal places; intermediate values are not rounded.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Crude protein % = Nitrogen % × Jones factor
Dry basis: Protein % (dry) = Protein % ÷ (dry matter % ÷ 100).
Method: Dumas combustion, AOAC 992.15 (crude protein in meat) / AOAC 968.06 (protein in animal feed) — the sample burns at about 900–1000 °C in oxygen, nitrogen oxides are reduced to N2 over copper, and the N2 is measured by thermal conductivity. The empty-tin blank removes the nitrogen the tin and gases add; the standard (usually EDTA, 9.59 % N) checks the calibration for the run.
Assumptions: all nitrogen is protein nitrogen; the Jones factor matches the food; the blank and standard from the same run apply to this sample.
Limitations: same non-protein-nitrogen issue as Kjeldahl — urea, nitrates and free amino acids count as protein. Dumas measures total nitrogen including nitrate and nitrite, which Kjeldahl misses unless modified, so Dumas protein can read higher than Kjeldahl on nitrate-rich foods such as vegetables. Samples are small (100–200 mg), so heterogeneity is magnified — grind finely and run duplicates.
Rounding: results to 2 decimal places; intermediate values are not rounded.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Worked example: wheat flour, sample 0.150 g, instrument nitrogen 1.730 %, blank 0.002 mg, EDTA standard 9.59 % theoretical / 9.55 % measured, Jones factor 5.70. Blank = 0.002 ÷ (0.150 × 10) = 0.001 %; nitrogen after blank = 1.730 − 0.001 = 1.729 %; standard correction = 9.59 ÷ 9.55 = 1.0042; corrected nitrogen = 1.729 × 1.0042 = 1.74 %; crude protein = 1.74 × 5.70 = 9.89 %. With dry matter 87.00 %, protein on a dry basis = 9.89 ÷ 0.87 = 11.37 %.
Enter values above to see results.
Dumas or Kjeldahl? Dumas is faster, needs no strong acids, and measures nitrate nitrogen; Kjeldahl is the reference method most regulations name. For the same sample the two should agree within about 0.1–0.2 % protein — a bigger gap means the nitrate or the calibration needs checking. Tool 6 of 500 — GIFSQ
