Determination of Nitrite,Phosphate, and Silicate by Valveless Continuous Analysis with a Bubble-Free Flow Cell and Spectrophotometric Detection

A continuous flow analysis system, composed of a 1.2-cm laboratory-made antibubble flow cell and a spectrophotometer, was established. The system was evaluated for the determination of nitrite, phosphate, and silicate. Different from flow injection analysis and other flow analysis modes, an injection or multiposition valve was not needed. Even better, the system was free from interferences from air bubbles without the use of a debubbler device or electronic bubble gate. Without the formation of air bubbles, the chemical reaction was accelerated using a water bath. The experimental parameters for nutrient analysis, including reagent concentration, flow strategy, flow rate, and reaction temperature, were optimized based on a univariate experimental design. The carry-over effect was comprehensively evaluated and may be ignored using this protocol. The established system and analytical methods were especially suitable for laboratories with only basic instruments and limited budgets. The system had the advantages of high sample throughput (>60?h^?1); great convenience without valve utilization; long linear dynamic ranges (0.2–80?µM for nitrite, 0.3–14?µM for phosphate, and 0.5–120?µM for silicate); low detection limits (0.06?µM for nitrite, 0.08?µM for phosphate, and 0.11?µM for silicate); and high recovery values (91.5?±?1.01 to 108.7?±?3.18%). In addition to water samples, national reference materials were analyzed, and the results were in good agreement with the certified values.