ALTERNATIVER TIL SITEANALYZER PLUS
ALTERNATIVER TIL SITEANALYZER SERIES

Įlectrochemical techniques for nutrient measurements facilitate sensor miniaturization, require low power, and in some cases eliminate the need for reagents.

Optical UV sensors have shown promise for long-term in situ deployment, but their application is limited by low sensitivity and accuracy due to optical interfering factors such as bromide and dissolved organic material. These systems do not require chemical reagents, can measure over a wide range of concentrations, and are easy to use due to their small size and robustness.

In particular, various ultraviolet (UV) optical sensors for routine measurement of NO 3 − have been developed and deployed on different platforms. In the last 20 years, a number of studies have been conducted on on-site monitoring of nutrients in marine waters using mainly three analytical approaches: optical, electrochemical, and wet chemical techniques. Therefore, there is an urgent need for technologies that enable on-site measurements for long-term monitoring and are equipped to cope with challenging conditions during sporadic and transient environmental events. However, such methods are labor intensive, expensive, and yield datasets with a low temporal and spatial resolution. Nutrient data obtained from discrete samples usually collected at operational intervals and analyzed using laboratory techniques based on automated colorimetric approaches or ion chromatography. To study these biogeochemical processes, real-time and long-term monitoring of macronutrient concentrations is required to determine the spatial trends and temporal variations in their distributions. In tropical and subtropical regions, H 4SiO 4 is depleted to low levels of ≈0.6 μM, which limits the diatom productivity and thus carbon export from the surface mixed layer. In the open ocean, oligotrophic regions are subject to N and P limitation, which restricts biological productivity. However, excessive input of PO 4 3− and NO 3 − into estuaries and coastal waters leads to eutrophication, deoxygenation, and other processes that damage aquatic environment. In particular, PO 4 3− and NO 3 − are the bioavailable forms utilized by phytoplankton and autotrophic bacteria, H 4SiO 4 exerts a strong influence on the productivity of silicifying phytoplankton such as diatoms, which are estimated to account for 40% of the total primary production in the oceans. Macronutrients such as phosphate (PO 4 3−), nitrate (NO 3 −), and silicic acid (H 4SiO 4) play key roles in the regulation of ocean productivity and thus the marine biogeochemical carbon cycle.

ALTERNATIVER TIL SITEANALYZER SERIES

Time series data agreed well with data obtained from the analysis of discretely collected samples using standard reference laboratory procedures and showed clear correlations with key hydrographic parameters throughout the deployment period.

The system successfully collected 443, 440, and 409 on-site data points for PO 4 3−, Σ(NO 3 − + NO 2 −), and H 4SiO 4, respectively. The analyzer performed well in the field during a 46-day deployment on a pontoon in the Kiel Fjord (located in the southwestern Baltic Sea), with a water supply from a depth of 1 m.

ALTERNATIVER TIL SITEANALYZER PLUS

The analyzer showed good precision with a relative standard deviation of 8.9% for PO 4 3−, 4.8% for H 4SiO 4, and 7.4% for NO 2 − plus NO 3 − during routine analysis of certified reference materials (KANSO, Japan). The instrument showed wide linear ranges, from 0.2 to 100 μM PO 4 3−, between 0.2 and 100 μM H 4SiO 4, from 0.5 to 100 μM NO 3 −, and between 0.4 and 100 μM NO 2 −, with detection limits of 0.18 μM, 0.15 μM, 0.45 μM, and 0.35 μM for PO 4 3−, H 4SiO 4, NO 3 −, and NO 2 −, respectively. Here, we report the optimization of analytical conditions, including reaction time for PO 4 3− analysis, complexation time for H 4SiO 4 analysis, and analyte to reagent ratio for NO 3 − analysis. The sensor uses the phosphomolybdate blue method for PO 4 3−, the silicomolybdate blue method for H 4SiO 4 and the Griess reagent method for NO 2 −, modified with vanadium chloride as reducing agent for the determination of NO 3 −.

Here, we present improvements of a commercial automated sensor for nutrients (including PO 4 3−, H 4SiO 4, and NO 2 − plus NO 3 −), suitable for a variety of aquatic environments. The development of robust sensors for long-term on-site analysis of macronutrients in seawater is a great challenge. Accurate, on-site determinations of macronutrients (phosphate (PO 4 3−), nitrate (NO 3 −), and silicic acid (H 4SiO 4)) in seawater in real time are essential to obtain information on their distribution, flux, and role in marine biogeochemical cycles.

Alternativer til siteanalyzer