China Residual Chlorine Analyzer Factories & Pricelist

Free Chlorine refers to dissolved hypochlorous acid (HOCl) and hypochlorite ions (OCl⁻), which represent active, rapid disinfection capacity. Combined Chlorine results when free chlorine reacts with ammonia or organic nitrogen compounds to form chloramines (monochloramine, dichloramine, trichloramine), which are slower disinfectants that produce offensive odors and eye irritation. Total Chlorine is the sum of both (Total = Free + Combined). If your regulatory permit mandates chloramine tracking (such as in municipal chloramination or indoor swimming pools), specify a dual-cell Total/Free analyzer or a DPD colorimeter; for potable distribution, a Free Chlorine constant-voltage or polarographic membrane system is standard.

In aqueous solutions, free chlorine exists in chemical equilibrium: HOCl ⇌ H⁺ + OCl⁻. Amperometric sensors directly reduce hypochlorous acid (HOCl), which is up to 80 times more effective as a biocide than OCl⁻. As sample pH rises from 6.5 to 8.0, the percentage of HOCl plummets from ~90% to ~20%. Without automated pH compensation, an amperometric sensor will interpret this shift as a catastrophic collapse in chlorine concentration even when total oxidant remains unchanged. BOQU analyzers utilize a high-precision dual-input channel that feeds measured pH into a dissociation equation, calculating accurate Free Chlorine across fluctuating pH environments.

Amperometric reduction consumes reactant molecules right at the cathode surface. If the sample is stagnant, a depletion boundary layer quickly forms, driving measured current to zero. Consequently, bare electrode systems require a stable sample flow between 30 and 60 L/h across the sensing surface. BOQU provides custom acrylic flow-through assemblies equipped with integrated float flow meters and constant-head overflow weirs to eliminate velocity variations. Membrane-covered polarographic sensors feature reduced flow sensitivity because the diffusion membrane controls mass transfer, but they still require a minimum linear face velocity (> 0.15 m/s).

Chlorine calibration cannot be performed using stable bottled reference standards because dissolved chlorine degrades rapidly in the presence of air and light. Calibration must be carried out in-situ using a freshly drawn sample quantified with a certified DPD-1 portable photometer (e.g., standard colorimetric pocket test). Enter the photometer reading into the BOQU transmitter's single-point calibration menu. The zero-point is calibrated using zero-chlorine water (chlorine-free distilled water or water treated with activated carbon). For bare-electrode constant-voltage sensors, zero-point calibration is typically required only during initial commissioning, followed by single-point slope calibration every 30 to 60 days.

All BOQU online analyzers carry a comprehensive 12-month factory warranty against manufacturing defects. Replacement electrodes, pre-stretched membrane caps, and internal electrolytes are maintained in perpetual stock in Shanghai, shipping via DHL/FedEx within 24 to 48 hours. Commercial terms support T/T bank transfer, confirmed irrevocable Letters of Credit (L/C) at sight for large EPC contracts, and major credit cards for sample evaluation orders.