Zhuochi AOX-S Microcoulometric Analyzer for Adsorbable Organic Halogens (AOX) in Water

Overview

The Zhuochi AOX-S Microcoulometric Analyzer is a dedicated, standards-compliant instrument engineered for the quantitative determination of Adsorbable Organic Halogens (AOX) in aqueous environmental samples—including surface water, groundwater, wastewater, and drinking water. It operates on the principle of high-temperature catalytic combustion followed by microcoulometric titration, as specified in China’s national standard HJ 1214–2021. In this method, organic halogen compounds are adsorbed onto activated carbon, thermally desorbed and combusted at controlled temperatures (500–1000 °C), converting halogens into hydrogen halides (e.g., HCl, HBr). The resulting halide ions are absorbed in an electrolyte solution and quantified via coulometric generation of silver ions (Ag⁺) at a working electrode, with charge integration providing direct mass-based quantification. This electrochemical detection mechanism ensures high selectivity for total halogen content and eliminates interferences from inorganic halides when proper sample pretreatment (e.g., acidification, filtration, and carbon adsorption) is applied.

Key Features

• Integrated dual-zone combustion furnace with precise gas-flow–controlled temperature regulation—enabling stable thermal decomposition across the full 500–1000 °C range with accuracy of ±1% ±5 °C
• Dedicated quartz combustion tube optimized for complete mineralization of refractory AOX compounds without memory effects or cross-contamination
• Automated sample introduction and effluent handling system to minimize operator exposure and ensure procedural consistency
• High-sensitivity microcoulometric detector featuring real-time charge integration, low-noise potentiostatic control, and drift-compensated baseline stabilization
• Modular column adsorption unit compatible with standardized activated carbon cartridges (e.g., 100–200 mg carbon loading), supporting both batch and continuous flow adsorption protocols
• Robust mechanical architecture with corrosion-resistant internal gas pathways (quartz and PTFE-lined) for long-term reliability in halogen-rich environments

Sample Compatibility & Compliance

The AOX-S system accommodates liquid samples within the pH 2–12 range following standard pretreatment per HJ 1214–2021, including acidification (to pH ≤2), filtration (0.45 µm), and adsorption on activated carbon under defined flow rates (typically 10–30 mL/min). It supports matrix types ranging from low-conductivity natural waters to high-salinity industrial effluents, provided chloride interference is mitigated via sodium nitrate masking or post-adsorption washing. While designed explicitly for compliance with HJ 1214–2021, its measurement principle aligns closely with internationally recognized methods such as DIN 38409-17 (Germany), ISO 9562 (Adsorbable Halogenated Organics), and EPA Method 1650 (though not EPA-validated out-of-the-box). For GLP/GMP-regulated laboratories, optional audit-trail-enabled software modules support 21 CFR Part 11–compliant data integrity requirements.

Software & Data Management

The AOX-S includes embedded firmware with intuitive touchscreen interface for method setup, real-time curve visualization (current vs. time), and automatic peak integration. Raw coulometric data (charge in coulombs) is exported in CSV format for traceability. Optional PC-based analytical software provides advanced features: calibration curve management (linear/nonlinear regression), QC sample tracking (spikes, duplicates, blanks), statistical reporting (RSD, recovery %), and customizable report templates compliant with laboratory information management systems (LIMS). All data files include embedded metadata (operator ID, timestamp, method version, instrument serial number), satisfying minimum ALCOA+ (Attributable, Legible, Contemporaneous, Original, Accurate) documentation criteria.

Applications

• Regulatory monitoring of AOX emissions from pulp and paper mills, chlor-alkali plants, and pharmaceutical manufacturing facilities
• Compliance verification for wastewater discharge permits under local ecological protection authorities
• Research-scale evaluation of halogenated disinfection by-product (DBP) formation during chlorination/chloramination of drinking water sources
• Assessment of adsorption efficiency in granular activated carbon (GAC) treatment trains
• Method validation studies comparing microcoulometric AOX against alternative techniques (e.g., GC-ECD, IC-MS)

FAQ

Does the AOX-S require external gas supplies?
Yes—it requires high-purity oxygen (≥99.995%) for combustion and nitrogen (≥99.99%) as carrier and purge gas. Gas flow rates and pressure settings are preconfigured and digitally regulated.

Can it measure individual halogens (Cl, Br, I) separately?
No—the AOX-S reports total adsorbable organic halogens as chlorine-equivalent (µg Cl⁻/L). Speciation requires coupling with hyphenated techniques such as IC-MS or GC-MS.

What maintenance is required for long-term operation?
Routine maintenance includes quarterly replacement of the electrolyte solution in the microcoulometric cell, annual calibration verification using certified AOX reference standards (e.g., chlorophenol solutions), and periodic inspection of quartz combustion tubes for cracking or soot accumulation.

Is the system compatible with automated sample changers?
Not natively—but the sample introduction module features standardized electrical and pneumatic interfaces, enabling third-party autosampler integration upon request and custom engineering support.