Chemiluminescence Nitrogen Analyzer (CLNA) – Principle & Applications
A Chemiluminescence Nitrogen Analyzer (CLNA) is used to measure total nitrogen (TN) content in petroleum products, lubricants, fuels, and other organic materials. It is widely applied in quality control, fuel research, and environmental testing.
1. Key Applications
✅ Lubricants & Fuel Analysis: Determines nitrogen content in diesel, gasoline, lubricants, and biofuels.
✅ Additive Testing: Evaluates nitrogen-containing detergents, dispersants, and anti-wear additives.
✅ Environmental Testing: Measures NOx emissions and nitrogen pollutants.
✅ Refinery & Petrochemical Industry: Ensures compliance with ASTM D4629, ASTM D5762, and EN 12260.
2. Working Principle – Chemiluminescence Detection (CLD)
1️⃣ Sample Introduction:
- Liquid samples (fuels, oils) are injected into a high-temperature furnace.
- Gaseous samples are directly introduced into the reaction chamber.
2️⃣ Oxidation (Combustion Process):
- The sample is burned at 900–1100°C in the presence of oxygen.
- Nitrogen compounds are converted into nitric oxide (NO).
3️⃣ Chemiluminescence Reaction:
- NO reacts with ozone (O₃) in a reaction chamber.
- The reaction produces *excited nitrogen dioxide (NO₂)**, which emits light (chemiluminescence) when returning to a stable state.
4️⃣ Detection & Quantification:
- A photomultiplier tube (PMT) detects the emitted light.
- The intensity of light is proportional to the nitrogen concentration.
- The instrument calculates total nitrogen content (mg/kg or ppm).
3. Applicable Test Standards
| Standard | Application |
|---|---|
| ASTM D4629 | Total nitrogen in liquid hydrocarbons (ppb to ppm levels) |
| ASTM D5762 | Total nitrogen in lubricating oils and fuels |
| ASTM D6069 | Nitrogen in aromatics and hydrocarbons |
| EN 12260 | Total bound nitrogen in water and petroleum products |
4. Typical Nitrogen Content in Fuels & Lubricants
| Sample Type | Nitrogen Content (ppm) |
|---|---|
| Gasoline | <0.5 – 5 |
| Diesel Fuel | 1 – 50 |
| Lubricating Oil (Base Oil) | 5 – 100 |
| Engine Oil with Additives | 100 – 2000 |
| Heavy Fuel Oil (HFO) | 500 – 5000 |
🔹 Lower nitrogen → Indicates better hydrotreating efficiency in refining.
🔹 Higher nitrogen → Suggests presence of additives, contamination, or incomplete refining.
5. Key Features of a Chemiluminescence Nitrogen Analyzer
✔ High Sensitivity: Detects <10 ppb to 10,000 ppm nitrogen.
✔ Wide Sample Compatibility: Suitable for fuels, lubricants, chemicals, and gases.
✔ Automated Calibration & Data Processing: Ensures accuracy & repeatability.
✔ Rapid Analysis: Results in less than 2 minutes per sample.
✔ Low Detection Limit (LOD): 0.01 – 0.5 ppm depending on the model.
6. Selection Guide: Choosing the Right CLNA Model
| Application | Recommended Model Features |
|---|---|
| Low-nitrogen fuels (gasoline, diesel) | LOD ≤ 0.1 ppm, automated sample handling |
| Lubricant base oils & additives | Wide dynamic range (0.1 – 5000 ppm), high-temperature combustion |
| Environmental testing (NOx, emissions) | Gas-phase analysis, real-time monitoring |
Detailed Testing Procedure for Chemiluminescence Nitrogen Analyzer (CLNA) – ASTM D4629 / ASTM D5762
This procedure describes how to determine total nitrogen content in lubricants, fuels, and petroleum products using a chemiluminescence nitrogen analyzer (CLNA) following ASTM D4629 (for hydrocarbons) and ASTM D5762 (for lubricating oils).
1. Equipment & Materials Needed
A. Instrumentation
✅ Chemiluminescence Nitrogen Analyzer (CLNA) – Must have:
- High-temperature combustion furnace (900–1100°C)
- Ozone (O₃) generator for chemiluminescence reaction
- Photomultiplier tube (PMT) for light detection
- Data acquisition system
✅ Carrier Gas System
- Oxygen (O₂), high purity (>99.99%) for combustion
- Argon (Ar) or helium (He), high purity, for sample transport
✅ Liquid Sample Injector
- Automated or manual injection system
- Microliter syringe (5–50 μL capacity)
✅ Calibration Gas Standards
- Certified nitrogen standard solutions for calibration (e.g., 100 ppm N in xylene)
B. Reagents & Consumables
✅ Solvent (Xylene or Toluene) – For dilution and cleaning
✅ Quartz Combustion Tube – Must withstand high-temperature oxidation
✅ Ozone Scrubber – Removes excess ozone from the system
2. Sample Preparation
A. Sample Types & Requirements
- Gasoline, diesel, or light hydrocarbons → ASTM D4629
- Lubricating oils, base oils, and additives → ASTM D5762
B. Sample Handling
- Ensure samples are homogeneous and free of particulate contamination.
- If viscosity is too high (e.g., for gear oils), dilute with xylene.
- Do not use nitrogen-containing solvents (e.g., amines) as they interfere with results.
C. Calibration Curve Preparation
- Prepare at least 5 calibration standards from 0.1 to 1000 ppm nitrogen using a certified nitrogen solution.
- Inject 5–50 μL of each standard into the CLNA and record responses.
- Plot a calibration curve of signal intensity vs. nitrogen concentration.
3. Testing Procedure
A. Instrument Setup & Optimization
1️⃣ Check Gas Flow Rates:
- Oxygen Flow: 300–500 mL/min
- Carrier Gas (He or Ar): 50–150 mL/min
2️⃣ Set Furnace Temperature:
- Typical range: 950–1100°C
- Ensure complete combustion of nitrogen compounds.
3️⃣ Ozone Generation & Detection System Check:
- Verify proper operation of ozone reactor and photomultiplier tube.
B. Sample Injection & Analysis
1️⃣ Baseline Check:
- Run a blank solvent (xylene/toluene) to confirm zero nitrogen contamination.
2️⃣ Sample Injection:
- Inject 5–50 μL of the sample into the analyzer.
- Ensure smooth injection to avoid air bubbles.
3️⃣ Combustion & Nitrogen Oxidation:
- The sample burns at >900°C, converting all nitrogen into NO gas.
4️⃣ Reaction with Ozone:
- NO reacts with O₃ to form excited NO₂, which emits chemiluminescent light.
5️⃣ Detection & Quantification:
- Light intensity is measured and correlated to total nitrogen content (ppm or mg/kg) using the calibration curve.
C. Quality Control & Validation
✅ Run a Calibration Check Standard every 5–10 samples to ensure instrument accuracy.
✅ Analyze a Duplicate Sample every 10 samples (repeatability check).
✅ Perform a Spike Recovery Test by adding a known nitrogen standard to the sample.
4. Interpretation of Results
A. Reporting Units
- Total Nitrogen Content (mg/kg or ppm) = Measured value from calibration curve.
B. Acceptable Precision & Accuracy
| Sample Type | Typical Nitrogen Range (ppm) | Repeatability (R) | Reproducibility (r) |
|---|---|---|---|
| Gasoline | <0.5 – 5 | ±0.1 ppm | ±0.5 ppm |
| Diesel Fuel | 1 – 50 | ±1 ppm | ±5 ppm |
| Lubricating Oils | 5 – 100 | ±2 ppm | ±10 ppm |
| Heavy Fuel Oils | 500 – 5000 | ±10 ppm | ±50 ppm |
5. Troubleshooting & Common Issues
| Issue | Possible Cause | Solution |
|---|---|---|
| Baseline Drift | Contaminated combustion tube | Clean or replace quartz tube |
| High Blank Values | Nitrogen in carrier gas or solvent | Use high-purity gases, fresh solvents |
| Low Sensitivity | Ozone generator issue | Check ozone scrubber & generator |
| Inconsistent Results | Sample not fully combusted | Increase furnace temperature to 1100°C |
6. Advantages of CLNA vs. Other Methods
| Method | Advantages | Disadvantages |
|---|---|---|
| Chemiluminescence Nitrogen Analyzer (CLNA) | Highly sensitive (ppb to ppm levels), rapid, automated | Requires high-purity gases & ozone generator |
| Kjeldahl Method | Simple, inexpensive | Time-consuming, low sensitivity |
| X-ray Fluorescence (XRF) | No sample combustion needed | Less sensitive for nitrogen detection |
7. Conclusion & Recommendations
- CLNA is the best method for low-level nitrogen detection in fuels & lubricants.
- ASTM D4629 is preferred for gasoline & diesel, while ASTM D5762 is used for lubricants & heavy oils.
- Regular calibration & quality control ensures accurate and repeatable results.