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D4629-24 – Standard Test Method Technical Guide
📐 Scope and Specimen Requirements
This test method covers the determination of trace total nitrogen in liquid hydrocarbons boiling from approximately 50 °C to 400 °C, with viscosities between 0.2 cSt and 10 cSt (mm²/s) at room temperature. It is applicable to naphthas, distillates, and oils containing 0.3 mg/kg to 100 mg/kg total nitrogen. For samples with higher nitrogen content, Test Method D5762 is more appropriate. The method can be applied to sample types outside these ranges through dilution, provided that solubility is verified and direct syringe introduction does not cause low results due to pyrolysis. The values stated in SI units are to be regarded as standard. Safety concerns are addressed in Sections 7.2, 7.4, 7.5, 7.9, and 8.
⚙️ Test Procedure and Detection Mechanism
The sample is introduced via a syringe or boat inlet system into a stream of inert gas (helium or argon). It is vaporized and carried to a high-temperature zone where oxygen is introduced, converting organically bound nitrogen to nitric oxide (NO). The NO contacts ozone, producing excited nitrogen dioxide (NO₂). As the NO₂ decays to its ground state, light is emitted and detected by a photomultiplier tube. The resulting signal is proportional to the nitrogen content in the sample. This method is significant because trace nitrogenous materials can poison catalysts in petroleum and chemical refining.
📊 Key Parameters and Referenced Standards
The following table summarizes the key parameters for this test method:
| 🟦 Parameter | 📏 Specified Range |
|---|---|
| Boiling Point of Hydrocarbons | 50 °C to 400 °C |
| Viscosity at Room Temperature | 0.2 cSt to 10 cSt (mm²/s) |
| Total Nitrogen Concentration | 0.3 mg/kg to 100 mg/kg |
Referenced ASTM standards for additional guidance include:
| 📐 Standard | 🎯 Purpose |
|---|---|
| D1298 | Density by Hydrometer Method |
| D4052 | Density by Digital Density Meter |
| D4175 | Terminology for Petroleum Products |
| D5762 | Nitrogen by Boat-Inlet Chemiluminescence |
| D6299 | Statistical Quality Assurance Practices |
💡 Tip: When diluting samples to meet the viscosity or concentration range, always verify complete solubility and ensure that the syringe introduction does not lead to pyrolysis of the sample or solvent.
⚡ Warning: This test method involves high temperatures and reactive gases. Refer to Sections 7.2, 7.4, 7.5, 7.9, and 8 for complete safety guidelines before proceeding.
❓ Frequently Asked Questions
🔍 What is the applicable concentration range for this test method?
The test method is applicable for total nitrogen concentrations from 0.3 mg/kg to 100 mg/kg. For higher concentrations, Test Method D5762 is recommended.
💡 How is nitrogen detected in the sample?
Nitrogen is converted to nitric oxide (NO) through oxidative combustion, which then reacts with ozone to produce excited nitrogen dioxide. The light emitted during decay is detected by a photomultiplier tube, providing a measure of nitrogen content.
⚡ Can this method be used for samples with viscosity higher than 10 cSt?
The method is specified for viscosities up to 10 cSt. However, samples with higher viscosity may be analyzed by dilution in an appropriate solvent, provided that solubility and absence of pyrolysis are verified.
📌 What safety precautions are mentioned in the standard?
Users must establish safety, health, and environmental practices and determine regulatory limitations. Specific sections to review include 7.2, 7.4, 7.5, 7.9, and 8.