Trace Moisture Analyzer by Karl Fischer Coulometric Titration XHWS180 Color Touch Screen 0-400mA 32-Bit

Karl Fischer coulometric titration (used by the XHWS180) generates iodine electrochemically at the anode, with the electrical charge consumed directly proportional to the water content per Faraday's law. This method is ideal for trace moisture analysis (microgram to low milligram range) as it eliminates the need for standardized titrant solutions and provides superior sensitivity down to 0.1μg H²O. Volumetric titration adds iodine via a burette and is better suited for higher water content samples (milligram to percentage range). For applications such as transformer oil, pharmaceutical raw materials, and chemical intermediates where moisture concentrations are typically very low, coulometric titration offers unmatched precision and requires no titrant standardization.

Calibration is performed using a 0.5μL microsyringe to inject exactly 0.1μL of pure water (equivalent to 100μg H²O) into the electrolyte. The displayed result should read 100±10μg. Calibration should be verified 2–3 times consecutively before testing samples. It is recommended to perform calibration: (a) at the start of each working day, (b) after replacing the electrolyte, (c) when measurement results appear inconsistent, and (d) after significant changes in ambient temperature or humidity. Regular calibration ensures continued accuracy within the specified ±10% tolerance for the 10μg–1000μg range.

Persistent high or unstable balance voltage (above 0.120V) typically indicates residual moisture in the system. Common causes include: moisture on the inner walls of the electrolytic cell (resolve by removing the cell, tilting and rotating it so electrolyte absorbs the moisture, then reassemble); atmospheric moisture intrusion through worn or improperly sealed ground-glass joints (check vacuum grease application, replace drying tube silica gel when saturated, inspect silicone rubber injection pad for oversized holes); and moisture adsorbed on the cathode chamber ceramic filter plate (ensure proper cleaning and drying with methanol). If voltage remains high after these steps, the electrolyte may be exhausted and require replacement with fresh reagent.

The XHWS180 accommodates liquid, solid, and gaseous samples with appropriate preparation. Liquid samples are most common — use a microsyringe to inject directly through the injection stopcock. Two injection modes are available: volume-based (enter the sample volume in mL, results calculated directly) and density-based (enter the sample density, results account for mass conversion). Select the appropriate formula from the 4 preset options via the parameter settings menu. For solid samples that dissolve in the electrolyte, use a solid sample injector accessory. Gas samples require a gas sampling apparatus with controlled flow rate. Avoid samples that react chemically with Karl Fischer reagent components (strong oxidizers, reducing agents) as they produce erroneous results.

Routine maintenance includes: regular replacement of color-changing silica gel in drying tubes (when color changes from blue to pink); cleaning the electrolytic cell components with methanol (never water on electrodes or cathode chamber); periodic inspection and reapplication of vacuum grease on ground-glass joints; and keeping the instrument in a clean, dry environment. Each XHWS180 ships as a complete kit including the main instrument, electrolytic cell assembly, measuring electrode, electrolysis electrode, drying tubes, injection stopcock, stirring bar, microsyringe, thermal printer paper, power cable, and user manual. Standard delivery time is 5–8 working days. The instrument carries a 1-year manufacturer warranty with lifetime technical support. Minimum order quantity is 1 unit with T/T payment terms.