HACH 9187sc Online Chlorine Dioxide Analyzer

Overview

The HACH 9187sc Online Chlorine Dioxide Analyzer is an electrochemical amperometric instrument engineered for continuous, real-time monitoring of chlorine dioxide (ClO₂) concentration in potable water distribution systems and industrial process streams. It operates on a selective, membrane-covered amperometric sensor principle: ClO₂ diffuses through a gas-permeable hydrophobic membrane into an electrolyte-filled electrochemical cell, where it undergoes a stoichiometric reduction at the cathode (ClO₂ + 4H⁺ + 5e⁻ → Cl⁻ + 2H₂O), while silver oxidation occurs at the anode (Cl⁻ + Ag → AgCl + e⁻). The resulting current is linearly proportional to dissolved ClO₂ concentration. Integrated temperature sensing enables automatic temperature compensation across the full operational range (0–45 °C), ensuring measurement stability under variable field conditions. Designed for unattended operation in municipal water treatment plants, food & beverage processing lines, and pharmaceutical utilities, the 9187sc delivers trace-level detection down to 10 ppb with high reproducibility and minimal drift.

Key Features

• Amperometric sensor with selective ClO₂-permeable membrane—rejects common oxidants including free chlorine, combined chlorine, bromine, and hydrogen peroxide
• Integrated Pt1000 temperature probe for real-time thermal compensation and improved accuracy across ambient and process temperature fluctuations
• Low-maintenance design: calibration required only every two months; membrane and electrolyte replacement every six months under typical operating conditions
• Rugged IP66/NEMA 4X-rated enclosure suitable for indoor and outdoor installation in humid, dusty, or splash-prone environments
• Fast response time (t₉₀ < 90 seconds) enabling timely feedback for automated dosing control loops
• Wide dynamic range (0.010–2.000 mg/L ClO₂) with 0.01 ppm resolution supports both low-dose residual monitoring and higher-concentration process verification

Sample Compatibility & Compliance

The 9187sc is validated for use with clarified, filtered, non-abrasive aqueous samples—including drinking water, secondary effluent, cooling tower make-up, and purified process water. It is not intended for raw surface water with high turbidity (>5 NTU), suspended solids, or strong reducing agents that may foul the membrane or poison the electrode surface. The analyzer complies with EPA Method 300.1 (amperometric determination of residual disinfectants) and aligns with ISO 7888 (water quality — determination of chlorine dioxide) for field-deployable electrochemical methods. Its stable baseline and documented repeatability support GLP-compliant data acquisition when paired with HACH’s SC1000 controller or third-party SCADA systems meeting IEC 62443-3-3 cybersecurity requirements.

Software & Data Management

The 9187sc interfaces seamlessly with HACH’s SC1000 Multi-Parameter Controller or SC200 Universal Controller via 4–20 mA analog output and Modbus RTU over RS-485. All measurements are timestamped and stored locally with configurable logging intervals (1 min to 24 h). When integrated into a HACH Asset Manager or enterprise LIMS environment, the system supports audit-trail-enabled data export compliant with FDA 21 CFR Part 11 requirements—including electronic signatures, user access controls, and immutable change history. Firmware updates are performed remotely via secure HTTPS connection, minimizing onsite service visits.

Applications

• Real-time monitoring of ClO₂ residuals in municipal drinking water distribution networks to ensure regulatory compliance (e.g., U.S. EPA Stage 2 Disinfectants and Disinfection Byproducts Rule)
• Closed-loop control of ClO₂ generators in food processing facilities for surface sanitation and equipment rinse validation
• Verification of disinfectant efficacy during pharmaceutical water-for-injection (WFI) system sanitization cycles
• Performance validation of point-of-use ClO₂ injection systems in hospitals and laboratories
• Troubleshooting oxidant demand anomalies in cooling water treatment programs

FAQ

Does the 9187sc require zero or span calibration with standard solutions?
No—calibration is performed using a certified laboratory reference method (e.g., iodometric titration or DPD spectrophotometry) on a grab sample collected simultaneously with the online measurement. This “field comparison” approach eliminates reliance on unstable ClO₂ standards.
Can ozone (O₃) interfere with the measurement?
Yes—ozone is cross-sensitive and will produce a positive interference. However, O₃ is rarely present in ClO₂-based disinfection systems, making this interference negligible in typical applications.
What maintenance tasks are required beyond membrane and electrolyte replacement?
Routine inspection of flow path integrity, cleaning of inlet/outlet fittings, and verification of sample pressure and flow rate (200–250 mL/min) are recommended quarterly. No optical alignment or internal electronics servicing is required.
Is the sensor compatible with aggressive cleaning agents used in CIP cycles?
The sensor body and housing are constructed from PVDF and 316 stainless steel, resistant to sodium hypochlorite (≤500 ppm), citric acid (≤5%), and phosphoric acid (≤2%). Direct exposure to hot alkaline cleaners (>80 °C, pH >12) is not recommended.
How does the analyzer handle fluctuating sample pH?
The amperometric reaction is pH-dependent below pH 5.5. For optimal accuracy, the 9187sc is specified for use in samples with pH 5.5–8.5. Outside this range, buffering or inline pH adjustment upstream of the analyzer is advised.