Device built-in

Agilent Nitrogen Chemiluminescence Detector (NCD) Technology and Applications

Agilent's Nitrogen Chemiluminescence Detector (NCD) is a high-sensitivity detection device specifically designed for nitrogen-containing compounds in gas chromatography (GC) systems. Based on chemiluminescence principles, this technology provides equimolar linear response for ammonia, hydrazine, hydrogen cyanide, nitrogen oxides (NOx), and various organic nitrogen compounds, achieving detection limits as low as parts-per-billion (ppb) levels. It plays a crucial role in environmental monitoring, petrochemical analysis, food safety, and pharmaceutical testing.

Working Principle and Core Technology

The core technology of Agilent's NCD lies in the highly specific chemical reaction combined with a precision optical detection system. The detection process consists of two key stages: First, nitrogen-containing compounds in the sample are converted into nitric oxide (NO) through high-temperature combustion (~800°C) in a stainless steel burner, operating in a hydrogen/oxygen-rich atmosphere with helium as the carrier gas to minimize background interference. Second, the generated NO reacts with ozone (O₃) in the reaction chamber, producing excited-state NO₂* molecules that emit light at specific wavelengths (600–2800 nm) upon returning to the ground state. A photomultiplier tube (PMT) captures and amplifies these photon signals, enabling ultra-sensitive detection.

The system incorporates several innovative designs:

• A dual-plasma burner configuration, compatible with dry pump or oil pump systems (G6600A/G6601A).
• Optimized combustion chamber temperature and gas flow rates (H₂: 25 mL/min, O₂: 10 mL/min), ensuring >99% conversion efficiency for nitrogen compounds.
• A unique backflush technique using a 10-port valve and dual-column system to eliminate high-boiling-point interferences, allowing only target analytes to enter the detector, significantly improving analytical efficiency.
• The Model 8255 includes specialized configurations for nitrosamine analysis, making it ideal for detecting nitrosamine migration in food-contact materials and rubber products.

Performance Characteristics and Advantages

Agilent’s NCD detector excels in exceptional selectivity and sensitivity. Unlike flame ionization detectors (FID), which respond to most organic compounds, the NCD only detects nitrogen-containing species, effectively eliminating hydrocarbon interference in complex matrices (e.g., gasoline, polymers, biological samples). Experimental data show that for nitrogen compounds such as nitrobenzene, 3-methylindole, and 9-methylcarbazole (at 25 ppm), the relative standard deviation (RSD) of response values is <2.5%, with long-term stability confirmed through 143 consecutive analyses over three days.

Key advantages include:

• Wide dynamic range and equimolar response, meaning different nitrogen compounds (e.g., primary amines, secondary amines, nitro compounds) produce similar response signals at the same nitrogen molar concentration, greatly simplifying quantification.
• The Model 8255 features an enhanced optical system and burner design, achieving sub-ppb detection limits, such as 10 ppb sensitivity for trace NO in ethylene.
• Unique NCD-FID parallel interface enables simultaneous nitrogen-specific detection and universal hydrocarbon detection, providing comprehensive data for unknown sample analysis.

Typical Applications

Petrochemical Industry

The NCD is used to monitor trace NOx contamination in high-purity olefins (e.g., ethylene, propylene), preventing the formation of explosive nitrate resins in cold-box equipment. A typical application involves an HP-5 column (30 m × 0.32 mm, 0.25 µm film thickness) with temperature programming (65°C for 3 min, then ramped at 25°C/min to 250°C), successfully separating and detecting nitrobenzene (218 ppm), 3-methylindole (234 ppm), and 9-methylcarbazole (326 ppm) in ethylene—with no solvent interference in the NCD chromatogram.

Food Safety

The NCD is the gold-standard method for detecting nitrosamine migration in rubber nipples and pacifiers. Its optimized ammonia and nitrosamine response, combined with advanced sample preparation, enables accurate quantification of carcinogenic N-nitrosodimethylamine (NDMA) in simulated saliva.

Environmental Monitoring

Applications include:

• Trace analysis of 2-ethylhexyl nitrate in diesel additives.
• Online monitoring of toxic nitrogen compounds (e.g., hydrogen cyanide, hydrazine) in industrial emissions.

Fuel Cell & Pharmaceutical Industries

• Fuel cell vehicles: The Agilent 8890 GC/8255 NCD system precisely measures ammonia impurities in high-purity hydrogen, protecting fuel cell stacks from nitrogen poisoning.
• Pharmaceuticals: The NCD is critical for controlling genotoxic impurities (e.g., nitrosamines) in active pharmaceutical ingredients (APIs), complying with stringent regulations (e.g., USP <1469>).

Conclusion

Agilent’s Nitrogen Chemiluminescence Detector (NCD) stands as the preferred solution for nitrogen-specific detection in modern analytical laboratories. From the basic Model 255 to the high-performance Model 8255, continuous innovation ensures this technology remains at the forefront of the industry, meeting increasingly complex analytical demands with unmatched selectivity, sensitivity, and stability.