Posts Tagged 'methods'

Purification and characterization of thymol blue for spectrophotometric pH measurements in rivers, estuaries, and oceans


  • Thymol blue (TB) was purified using flash chromatography.
  • TB is useful for pH measurements above the range of meta-cresol purple (mCP).
  • Paired pH measurements directly link the equilibrium characteristics of TB and mCP.


Thymol blue (TB) is one of a suite of indicator dyes appropriate for spectrophotometric determinations of the pH of aqueous solutions. For measurements of seawater pH, meta-cresol purple (mCP) is most often used, but TB is especially well suited for measurements in surface or shallow waters where the pH may exceed the optimal indicating range of mCP (e.g., due to photosynthesis). This work presents flash chromatography procedures for purifying commercially available TB and describes physical–chemical characteristics of the purified dye, thus enabling the acquisition of spectrophotometric pH measurements over a wide range of practical salinities (SP) and temperatures (T). The essential TB characteristics for 0 ≤ SP ≤ 40 and 278.15 ≤ T ≤ 308.15 K are described by:





e1 = −0.00132 + 0.00001600T

e4 = −0.005042 + 0.0002094T + 0.01916SP0.5/T

where pHT is pH determined on the total hydrogen ion concentration scale; R is the ratio of TB absorbances (A) at 435 and 596 nm (596A/435A); K2T is the equilibrium constant for the second TB dissociation step on the total scale; and e1, e2, and e4 are TB molar absorptivity ratios. This characterization was developed in a manner that ensures consistency with the primary TRIS buffer standards used in previously published characterizations of mCP. With this characterization, TB joins mCP as a sulfonephthalein indicator that has been characterized over the ranges of salinity and temperature required to make high-quality pH measurements in rivers, estuaries, and the open ocean. The full characterization of purified TB reported here extends the upper range of pHT that can be accessed with precise spectrophotometric measurements by approximately 0.50 pH units.

Continue reading ‘Purification and characterization of thymol blue for spectrophotometric pH measurements in rivers, estuaries, and oceans’

Metered reagent injection into microfluidic continuous flow sampling for conductimetric ocean dissolved inorganic carbon sensing

Continuous and autonomous measurement of total dissolved inorganic carbon (TCO2) in the oceans is critical for modelling important climate change factors such as ocean uptake of atmospheric CO2 and ocean acidification. Miniaturised chemical analysis systems are therefore required which are small enough for integration into the existing Argo ocean float network for long-term unattended depth profiling of dissolved CO2 with the accuracy of laboratory bench analysers. A microfluidic conductivity-based approach offers the potential for such miniaturisation. Reagent payload for >3 yr operation is a critical parameter. The precise injection of acid into sample, liberating CO2 from seawater, is addressed here. Laser etched microfluidic snake channel restrictors and asymmetric Y meters were fabricated to adjust the metering ratio between seawater and acid simulants. Laser etching conditions were varied to create a range of channel dimensions down to ~75 microns. Channel flow versus pressure measurements were used to determine hydrodynamic resistances which were compared with finite element simulations using a range of cross-section profiles and areas. Microfluidic metering circuits were constructed from variable resistance snake channels and dimensionally symmetric or asymmetric Y-junctions. Sample to acid volume ratios (meter ratio) up to 100:1 have been achieved with 300 microns wide snake channel for lengths > 1m. At the highest pattern resolution, this would require a footprint of > 600 mm2 (6 x10-4 m2). Circuits based solely on asymmetric Y-junctions gave meter ratios up to 16:1 with a footprint cost of < 40 mm2 and precision values of ~0.2%. Further design and fabrication refinements will be required to ensure the structural and dimensional integrity of such small channels in future integration of metering units into full TCO2 analysis microfluidic circuits.

Continue reading ‘Metered reagent injection into microfluidic continuous flow sampling for conductimetric ocean dissolved inorganic carbon sensing’

CO2 and HCl-induced seawater acidification impair the ingestion and digestion of blue mussel Mytilus edulis


1. The effect of two acidifying treatments, CO2 enrichment and HCl addition, on Mytilus edulis manifests different degrees of damage.

2. The effect of seawater acidification on mussels is not from a single factor (H+) but other action factors related to CO2.

3. Seawater acidification might inhibit the energy intake of mussels through interfering with the processes of ingestion and digestion.


Anthropogenic CO2 emissions lead to seawater acidification that reportedly exerts deleterious impacts on marine organisms, especially on calcifying organisms such as mussels. A 21-day experiment focusing on the impacts of seawater acidification on the blue mussel, Mytilus edulis, was performed in this study, within which two acidifying treatments, CO2 enrichment and HCl addition, were applied. Two acidifying pH values (7.7 and 7.1) and the alteration of the key physiological processes of ingestion and digestion were estimated. To thoroughly investigate the impact of acidification on mussels, a histopathological study approach was adopted. The results showed that: (1) Seawater acidification induced either by CO2 enrichment or HCl addition impaired the gill structure. Transmission electron microscope (TEM) results suggested that the most obvious impacts were inflammatory lesions and edema, while more distinct alterations, including endoplasmic reticulum edema, nuclear condensation and chromatin plate-like condensation, were placed in the CO2-treated groups compared to HCl-treated specimens. The ciliary activity of the CO2 group was significantly inhibited simultaneously, leading to an obstacle in food intake. (2) Seawater acidification prominently damaged the structure of digestive glands, and the enzymatic activities of amylase, protease and lipase significantly decreased, which might indicate that the digestion was suppressed. The negative impacts induced by the CO2 group were more severe than that by the HCl group. The present results suggest that acidification interferes with the processes of ingestion and digestion, which potentially inhibits the energy intake of mussels.

Continue reading ‘CO2 and HCl-induced seawater acidification impair the ingestion and digestion of blue mussel Mytilus edulis’

Characterization of a novel autonomous analyzer for seawater total alkalinity: results from laboratory and field tests

High‐quality seawater total alkalinity (AT) measurements are essential for reliable ocean carbon and acidification observations. Well‐established manual multipoint potentiometric titration methods already fulfill these requirements. The next step in the improvement of these observations is the increase of the spatial and temporal measuring resolution with minimal personnel and instrumental effort. For this, a rapid, automated underway analyzer meeting the same high requirements as the traditional method is necessary. In this study, we carried out a comprehensive characterization of the flow‐through analyzer CONTROS HydroFIA® TA (Kongsberg Maritime Contros GmbH, Kiel, Germany) for automated seawater AT measurements in the laboratory and in field with overall more than 5000 measurements. Under laboratory conditions, the analyzer featured a precision of ± 1.5 μmol kg−1 and an accuracy of ± 1.0 μmol kg−1, combined in an uncertainty of 1.6 – 2.0 μmol kg−1. High precision (± 1.1 μmol kg−1) and accuracy (−0.3 ± 2.8 μmol kg−1), and low uncertainty (2.0 – 2.5 μmol kg−1) were also achieved during field trials of 4 and 6 weeks duration. Although a linear drift appears to be the typical behavior of the system, this can be corrected for by regular reference measurements giving consistent measurement results. Another advantage of regular reference measurements is the early detection of any kind of malfunction due to its direct impact on the measurement performance. Based on the present study, recommendations for automated long‐term deployments are provided in order to gain optimal performance characteristics, aiming at the requirements for AT measurements.

Continue reading ‘Characterization of a novel autonomous analyzer for seawater total alkalinity: results from laboratory and field tests’

Established and emerging techniques for characterising the formation, structure and performance of calcified structures under ocean acidification

Ocean acidification (OA) is the decline in seawater pH and saturation levels of calcium carbonate (CaCO3) minerals that has led to concerns for calcifying organisms such as corals, oysters and mussels because of the adverse effects of OA on their biomineralisation, shells and skeletons. A range of cellular biology, geochemistry and materials science approaches have been used to explore biomineralisation. These techniques have revealed that responses to seawater acidification can be highly variable among species, yet the underlying mechanisms remain largely unresolved. To assess the impacts of global OA, researchers will need to apply a range of tools developed across disciplines, many of which are emerging and have not yet been used in this context. This review outlines techniques that could be applied to study OA-induced alterations in the mechanisms of biomineralisation and their ultimate effects on shells and skeletons. We illustrate how to characterise, quantify and monitor the process of biomineralisation in the context of global climate change and OA. We highlight the basic principles, as well as the advantages and disadvantages, of established, emerging and future techniques for OA researchers. A combination of these techniques will enable a holistic approach and better understanding of the potential impact of OA on biomineralisation and its consequences for marine calcifiers and associated ecosystems.

Continue reading ‘Established and emerging techniques for characterising the formation, structure and performance of calcified structures under ocean acidification’

Observing the global ocean with Biogeochemical-Argo

Biogeochemical-Argo (BGC-Argo) is a network of profiling floats carrying sensors that enable observation of as many as six essential biogeochemical and bio-optical variables: oxygen, nitrate, pH, chlorophyll a, suspended particles, and downwelling irradiance. This sensor network represents today’s most promising strategy for collecting temporally and vertically resolved observations of biogeochemical properties throughout the ocean. All data are freely available within 24 hours of transmission. These data fill large gaps in ocean-observing systems and support three ambitions: gaining a better understanding of biogeochemical processes (e.g., the biological carbon pump and air–sea CO2 exchanges) and evaluating ongoing changes resulting from increasing anthropogenic pressure (e.g., acidification and deoxygenation); managing the ocean (e.g., improving the global carbon budget and developing sustainable fisheries); and carrying out exploration for potential discoveries. The BGC-Argo network has already delivered extensive high-quality global data sets that have resulted in unique scientific outcomes from regional to global scales. With the proposed expansion of BGC-Argo in the near future, this network has the potential to become a pivotal observation system that links satellite and ship-based observations in a transformative manner.

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A BGC-Argo guide: planning, deployment, data handling and usage

The Biogeochemical-Argo program (BGC-Argo) is a new profiling-float-based, ocean wide, and distributed ocean monitoring program which is tightly linked to, and has benefited significantly from, the Argo program. The community has recommended for BGC-Argo to measure six additional properties in addition to pressure, temperature and salinity measured by Argo, to include oxygen, pH, nitrate, downwelling light, chlorophyll fluorescence and the optical backscattering coefficient. The purpose of this addition is to enable the monitoring of ocean biogeochemistry and health, and in particular, monitor major processes such as ocean deoxygenation, acidification and warming and their effect on phytoplankton, the main source of energy of marine ecosystems. Here we describe the salient issues associated with the operation of the BGC-Argo network, with information useful for those interested in deploying floats and using the data they produce. The topics include float testing, deployment and increasingly, recovery. Aspects of data management, processing and quality control are covered as well as specific issues associated with each of the six BGC-Argo sensors. In particular, it is recommended that water samples be collected during float deployment to be used for validation of sensor output.

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Ocean acidification in the IPCC AR5 WG II

OUP book