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D6016-17 – Standard Test Method Technical Guide
🧪 Scope and Significance
ASTM D6016-17 (Reapproved 2023) specifies a standard test method for the quantitative determination of water extractable nitrogen in leather. This method identifies nitrogen-containing water extractable materials such as excess and loosely bound tannins, ammonium salts, and nitrates. All values are stated in SI units to ensure international consistency.
This test method was developed in cooperation with the U.S. Army Natick Research Development & Engineering Center and the Defense Personnel Support Center, and it adheres to internationally recognized standardization principles established by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
⚠️ Safety Note: Users must establish appropriate safety, health, and environmental practices prior to use. The digestion procedure involves concentrated sulfuric acid (specific gravity 1.83) and high-temperature heating, requiring proper personal protective equipment and ventilation.
⚙️ Apparatus and Procedure
The test method requires specific laboratory apparatus and follows a controlled digestion procedure based on the Kjeldahl method.
| 🟦 Apparatus / Reagent | 📏 Specification |
|---|---|
| Volumetric Flask | 1 L capacity |
| Kjeldahl Flask | 800 mL capacity |
| Digestion Catalyst | 8 g (per D2868) |
| Sulfuric Acid | 20 mL, sp. gr. 1.83 |
| Sodium Thiosulfate | 25 mL of 8% solution |
The procedure begins with extraction per Test Method D3495. The extracted leather is saved and processed per section 7.1 of Test Method D2876. After collecting 1 L of extract in a volumetric flask, the contents are cooled to room temperature, adjusted to the 1 L mark with distilled water, and mixed thoroughly. A 500 mL aliquot is transferred to an 800 mL Kjeldahl flask. If using automated Kjeldahl instrumentation, sample size and reagent quantities may need adjustment.
| ⚡ Procedure Step | 🎯 Parameters |
|---|---|
| Extract volume collected | 1 L |
| Aliquot for digestion | 500 mL |
| Catalyst added | 8 g |
| H₂SO₄ added | 20 mL (sp. gr. 1.83) |
| Digestion after clearing | Minimum 1 h |
| Na₂S₂O₃ added | 25 mL of 8% |
| Hold time with stirring | 5–10 min |
Digestion begins over low heat until all organic matter is oxidized, indicated by cessation of foaming and clearing of the solution. Full heat is then applied for a minimum of 1 hour. After cooling to room temperature, 25 mL of 8% sodium thiosulfate is added and the flask is set aside for 5 to 10 minutes with occasional stirring. Distillation and titration follow section 7.3 of Test Method D2868.
💡 Automated Systems: When using automated Kjeldahl instrumentation, sample size and reagent quantities may need adjustment from the manual specifications. Always validate the automated method against the standard manual procedure to ensure equivalent results.
📊 Calculation and Key Parameters
The water extractable nitrogen content is calculated from the Kjeldahl distillation and titration results, accounting for the aliquot volume relative to the total extract volume. This test method detects water extractable nitrogen compounds including excess tannins, ammonium salts, and nitrates, providing valuable quality control data for leather processing operations.
Key referenced ASTM standards include:
- D2868 — Nitrogen Content (Kjeldahl) and Hide Substance Content of Leather, Wet Blue and Wet White
- D2876 — Water-Soluble Matter of Vegetable-Tanned Leather
- D3495 — Hexane Extraction of Leather
- D3790 — Volatile Matter (Moisture) of Leather by Oven Drying
❓ Frequently Asked Questions
🔍 What is the purpose of ASTM D6016-17?
This test method quantitatively determines water extractable nitrogen in leather, measuring compounds such as excess tannins, ammonium salts, and nitrates for quality control in leather processing.
💡 What is the minimum digestion time required?
After the solution has cleared, full heat is applied and digestion must continue for a minimum of 1 hour to ensure complete nitrogen conversion from all organic matter.
⚡ What safety precautions are needed?
The method uses concentrated sulfuric acid (sp. gr. 1.83) and high-temperature digestion. Users must establish appropriate safety, health, and environmental practices, including proper ventilation and personal protective equipment.
📌 Which referenced standards support this method?
This method references D2868 (Kjeldahl nitrogen and hide substance), D2876 (water-soluble matter), D3495 (hexane extraction), and D3790 (volatile matter by oven drying) as essential supporting procedures.