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

High-frequency field nutrient analyzers offer a promising technology to solve time-consuming and laborious sampling problems in dynamic and complex river-estuarine-coastal ecosystems. However, few studies on the simultaneous underway analysis of five key nutrients (ammonium, nitrite, nitrate, phosphate, and silicate) in seawaters are available because of the limitations of the technique. In this study, a state-of-the-art autonomous portable analyzer for the shipboard analysis of nutrients in the environment of varied salinities and concentration ranges was reported. The analyzer consisted of compact hardware that was well suited for shipboard deployment with minimal maintenance. Moreover, a novel LabVIEW-based software program was developed, containing additional functions such as automated calibration curve generation, autodilution of high-concentration samples, and a user-friendly interface for multiparameter analysis using a single instrument. After the optimization of chemical reactions and work flow chart, the analyzer exhibited low limits of detection, a large linear range with automated dilution, and relative standard deviations of less than 2% (n = 11). Compared to other flow-based techniques, this analyzer is more portable and consumes less reagent with an autonomous data processing function and applicability within a broad salinity range (0-35). The analyzer was successfully applied for real-time analysis in the Jiulong River Estuary-Xiamen Bay with excellent on-site accuracy and applicability. The relationship between high spatial resolution nutrient concentrations and salinities showed very different patterns in estuarine and coastal areas, indicating the benefit of using an underway automated analyzer for chemical mapping in a dynamic environment.

An automated analyzer for the simultaneous determination of silicate and phosphate in seawater.

Accurate and automated determination methods for silicate and phosphate are in high demand to improve understanding of biogeochemistry and ecology in dynamic and complex estuarine-coastal ecosystems. Here, a portable automated analyzer is reported for the simultaneous determination of silicate and phosphate in water samples with varying salinity. After comprehensive optimization of the chemical reactions and flow manifold, the system demonstrated limits of detection of 0.09 and 0.05 µmol L-1 for silicate and phosphate, respectively, exhibiting linearity at concentrations up to 400 and 200 µmol L-1 with automated dilution, achieving relative standard deviations (n = 11) of 0.27% (20 µmol L-1 silicate), 0.51% (5 µmol L-1 phosphate) and 0.80% (1 µmol L-1 phosphate). Compared with similar automated flow analyzers, the system exhibited advantages, such as low consumption of reagents (10-20 µL/sample), portability (4.8 kg), rapid start-up (5 min), reliability (automated analysis of quality control sample) and applicability within a broad salinity range (from 0 to 35) allowing analysis of dynamic estuarine and seawater samples. The system was successfully applied to a routine monitoring program by a national marine station and is potentially suitable for installation on different observation platforms for on-line and real-time underway analysis of nutrients in coastal areas.

[Advances in On-site Analytical Methods for Inorganic Arsenic in Environmental Water].

Arsenic is a ubiquitous metalloid element in the environment. Arsenic is classified as a group A carcinogen and has caused serious impacts on human health. For example, chronic poisoning caused by arsenic in groundwater is a global health problem. The forms of arsenic in environmental water are diverse, which can easily be transformed into each other during the sampling process and transportation, resulting in errors in laboratory analysis results. Therefore, developing on-site analytical methods for arsenic and acquiring accurate data are the basis for the study of the morphological transformation and bio-absorption process of arsenic and accurately evaluating its toxicity. In the past few decades, laboratory-based analytical methods for arsenic have developed rapidly, but there are still huge challenges in the on-site analysis of arsenic. This review summarized the relevant reviews on analytical methods of arsenic in environmental water in the past decade (2011-2022); discussed the advances in on-site analytical methods such as colorimetric methods, luminescence-based methods, and electrochemical methods of arsenic; anticipated the future development of on-site analytical methods for arsenic in environmental waters; and provided references for the development and applications of new methods.

Towards citizen science. On-site detection of nitrite and ammonium using a smartphone and social media software.

Citizen scientists-based water quality surveys are becoming popular because of their wide applications in environmental monitoring and public education. At present, many similar studies are reported on collecting samples for later laboratory analysis. For environmentally toxic analytes such as ammonium and nitrite, on-site detection is a promising choice. However, this approach is limited by the availability of suitable methods and instruments. Here, a simple on-site detection method for ammonium and nitrite is reported. The chemistry of this method is based on the classic Griess reaction and modified indophenol blue reaction. Digital image colorimetry is carried out using a smartphone with a custom-made WeChat mini-program or free built-in applications (APPs). Using a simple and low-cost analytical kit, the detection limit of 0.27 µmol/L and 0.84 µmol/L is achieved for nitrite and ammonium, respectively, which are comparable to those achieved with a benchtop spectrophotometer. Relative standard deviations (n = 7) for low and high concentrations of nitrite are 3.6% and 4.3% and for ammonium are 5.6% and 2.6%, respectively. Identical results with a relative error of less than 10% are obtained using different smartphones (n = 3), color extracting software (n = 6), and with multiple individual users (n = 5). These results show the robustness and applicability of the proposed method. The on-site application is carried out in an in-campus wastewater treatment plant and at a local river. A total of 40 samples are analyzed and the analytical results are compared with that obtained by a standard method and a spectrophotometer, followed by a paired t-test at a 95% confidence level. This proposed on-site analytical kit has the advantages of simplicity and portability and has the potential to be popular and useful for citizen science-based environmental monitoring.