Real-Time Underway Mapping of Nutrient Concentrations of Surface Seawater Using an Autonomous Flow Analyzer

Autocalibration based on dilution of a single concentrated standard is used for the determination of silicate in sea water by the modified molybdenum blue method

The silicate (Si) molybdenum blue method was modified by combining oxalate and ascorbic acid into a single reagent and was used for determining Si in sea water samples. The first step of this automated assay protocol was designed to perform either a calibration by a single Si standard prepared in deionized (DI) water, or to dilute samples in the range of 0-160 μM Si to fit into 0-20 μM Si calibration range using a 20 cm flow cell. By designing the assay protocol to function in batch mode, the influence of salinity on calibration was eliminated, thus making the method suitable for analysis of samples collected in the open ocean, coastal areas, or rivers. Reproducibility and accuracy of this method were evaluated by analysis of certified sea water reference materials. Phosphate (P) does not interfere significantly if the Si:P ratio is 4:1 or larger. The limit of detection was 514 nM Si, r.s.d. 2.1 %, sampling frequency 40 s/h, reagent consumption 700 μL/sample, and using deionized water as the carrier solution.

Relevant insights and concepts overlooked throughout the development of flow analysis. A tutorial

The conceptual expansion, fast development, and general acceptance of flow analysis are consequence of its adherence to the principles of green and white analytical chemistry, and chemical derivatization plays an essential role in this context. Through the flow analysis development, however, some of its potentialities and limitations have been overlooked. This is more evident when the involved modifications in flow rates, timing and/or manifold architecture deteriorate the analytical signals. These aspects have not always been systematically investigated, and are addressed here in relation to flow analyzers with UV-Vis spectrophotometric detection. Novel strategies for solution handling, guidance for dealing with the aforementioned analytical signal deterioration, and an alternative possibility for exploiting differential aspiration are presented. The concept of blank reagent carrier stream is proposed.

Portable instrument based on color sensor chip for on-site rapid detection of dissolved sulfides in environmental water samples

To ensure real-time validity of the detection of unstable toxic environmental pollutants, such as dissolved sulfides, we developed a portable on-site rapid analysis instrument. Through novel design of the color sensor chip-based core sensing components and the conversion between color signal and absorbance by Lambert's law, the instrument showed great performance for rapid (within 3 min) and sensitive on-site detection of sulfides in the environment. It is easy to achieve user-friendly, sample in-answer out, one-stop operation due to the touch-screen-integrated user interface of the instrument's data terminal. The detection limit of this method is 2.24 μg/L, the linear operation range is 0-1000 μg/L, and the coefficient of determination is 0.999. This instrument has been successfully applied to the on-site determination of sulfides in the Yellow River Delta and the Yantai Guangdang River in China. The portable instrument showed excellent anti-interference, good stability, and simple operation, which showed great prospects for the on-site rapid analysis of unstable targets in the environment.