A Micro Peristaltic Pump-Driven Step-Flow Autoanalyzer: Application to the Determination of Nitrite, Phosphate, and Silicate.

A simple, fast, and highly convenient autoanalyzer is proposed and demonstrated for the colorimetric measurement of nitrite, phosphate, and silicate in natural waters. The system employs individual micro peristaltic pumps controlled by integrated electric relay modules, allowing the main flow to be regulated in a stepwise manner. Activation is initiated by a single "start" button, which triggers a series of preprogramed actions, including sample loading, reagent mixing, refluxing of residual liquid, pausing for complete color development, and flushing the system with distilled water to reset the baseline to zero. Each measurement cycle is completed within 100 s with mild online heating. Real-time signals are captured via dynamic data exchange (DDE) and transferred to an Excel worksheet for instant calculation and display. Three systems are constructed and demonstrated for the determination of nitrite, phosphate, and silicate. Results indicate that over 99% completeness of the chemical reaction has been achieved with a precision better than ± 0.5% R.S.D. As each system is dedicated to a specific parameter, simplifying maintenance and minimizing troubleshooting, the system is highly convenient for use aboard research vessels or in busy laboratories, catering to users who need immediate measurements in either the "one-touch-one-sample" or "automatic-repeating" mode on a self-service basis.