Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
D1013-93 – Standard Test Method Technical Guide
ASTM D1013-93 (Reapproved 1998) is the standard test method for determining total nitrogen in nitrogen-containing resins and plastics. It is widely used for quality control and purity assessment in the production of amine resins and other nitrogenous polymers.
📌 Scope and Significance of the Test
This test method covers the determination of total nitrogen in nitrogen-containing plastics, resins, and resin solutions. It is not applicable for materials containing nitro-groups. The total nitrogen content indicates the level or purity of nitrogen-containing materials, such as amine resins. This is critical for quality control and ensures proper formulation of products. The standard has been approved for use by agencies of the Department of Defense.
⚙️ Essential Apparatus and Reagents
The test requires specific apparatus and high-purity reagents. Below are the key components.
| 🟦 Apparatus | 📏 Specification | 🎯 Purpose |
|---|---|---|
| Kjeldahl Flask | 800 mL, hard glass | Digestion and distillation |
| Connecting Bulb | Davisson type | Prevent mechanical carry-over |
| Heating Unit | Electric or gas | Heating for digestion and distillation |
| Connecting Tube | Glass, 150-200 mm | Conduct distillate to receiver |
| Weighing Tube | For liquid resins | Weigh without volatile loss |
| 🟦 Reagent | 📏 Specification | 🎯 Application |
|---|---|---|
| HCl or H₂SO₄ | Standard 0.5 N | Titration of distilled ammonia |
| Mercury (metal/oxide) | Reagent grade | Catalyst in digestion |
| Methyl Purple Indicator | Solution | pH indication with sharp color change |
| Potassium Sulfate | Reagent grade | Elevate boiling point for digestion |
| NaOH Solution | 760 g/L (technical grade) | Alkaline digestion medium |
| NaOH Standard | 0.5 N (carbonate-free) | Acid standardization and titration |
All reagents conform to reagent grade specifications as recommended by the American Chemical Society. Water used is Type II of Specification D1193.
📊 Procedure and Analytical Measurements
The Kjeldahl procedure involves digestion, distillation, and titration. The sample is digested with sulfuric acid, potassium sulfate, and mercury catalyst to convert nitrogen to ammonium sulfate. After cooling, the solution is made alkaline with 760 g/L NaOH, and ammonia is distilled into a standard 0.5 N acid solution. The excess acid is titrated with standard 0.5 N NaOH using methyl purple indicator. The endpoint is indicated by a color change from purple to green.
Total nitrogen content is calculated based on the volume of acid neutralized by the distilled ammonia, considering the sample weight. The methyl purple indicator is recommended for its abrupt and clear color change, enhancing titration accuracy.
⚠️ Caution: This test method is not suitable for materials containing nitro-groups. Always use fume hoods and protective gear during digestion and distillation.
💡 Tip: Standardize the 0.5 N NaOH solution against the standard acid using the same indicator as used in the sample titration to ensure consistency.
❓ Frequently Asked Questions
🔍 What types of samples are suitable?
Nitrogen-containing plastics, resins, and resin solutions. Materials with nitro-groups cannot be tested.
💡 Why is methyl purple recommended?
It provides an abrupt color change from purple to green in the presence of ammonium salts, which improves endpoint detection during titration.
⚡ What is the role of potassium sulfate?
It raises the boiling point of sulfuric acid during digestion, ensuring complete decomposition of organic matter and conversion of nitrogen to ammonium sulfate.
📌 How is total nitrogen calculated?
The calculation is based on the difference between the acid added and the acid titrated, multiplied by the normality and the nitrogen equivalent factor, expressed as a percentage of the sample weight.