Determination of Oceanic Carbon Dioxide Using a Carbonate-Selective Electrode (original) (raw)
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Marine Chemistry, 1988
Bradshaw, A.L. and Brewer, P.G., 1988. High precision measurements of alkalinity and total carbon dioxide in seawater by potentiometric titration. 2. Measurements on standard solutions. Mar. Chem., 155-162. We have prepared standard solutions identical to those of Hansson for the validation of titration procedures used to determine the alkalinity and total carbon dioxide content of seawater. We show that both titrimetric and gas extraction (coulometry) procedures yield virtually identical results of 2140.5 _+ 2.7 ttm CO2 kg-1 for such solutions. In an earlier work we reported that measurements on natural seawaters yielded discrepancies of 21 ]tm C02 kg-1, which we tentatively ascribed to the presence of unknown organic acids masquerading as C02 in the titration scheme, and generally unrecognized in thermodynamic models of the proton condition of seawater. The results presented here tend to confirm this hypothesis.
Response properties, applications and limitations of carbonate-selective polymer membrane electrodes
Analytica Chimica Acta, 1982
The preparation and response characteristics of a carbonate-selective polymer membrane electrode are reported. The electrode is prepared by incorporating Aliquat 336, trifluoroacetyl-p-butylbenzene and di-2ethylhexyl sebacate or dioctyl phthalate in a poly(vinylchloride) membrane matrix. The effect of membrane composition and electrode response in various buffer systems are examined. Under buffer conditions appropriate for practical measurements, potentiometric data yield the following sclcctivity pattern: CIO; = salicylate > total carbon dioxide species > I-> NO; > acetate > Cl-> Br: The electrode can be readily fabricated in tubular form and utilized within a very simple flow-injection arrangement to determine total carbon dioxide species. The possible applications of the electrode to serum CO, measurements as well as within newly devised gas-sensing arrangements for dissolved CO, are also examined. The accurate and rapid determination of total carbon dioside species (e.g., CO?, hydrogencarbonate, and carbonate) in physiological, industrial, and environmental samples presents a formidable challenge_ At present,
Amperometric sensor for monitoring of dissolved carbon dioxide in seawater
Sensors and Actuators B: Chemical, 2001
Characteristics of an amperometric CO 2 sensor have been investigated for the measurement of CO 2 concentration in air and CO 2 partial pressure in seawater. Use of RuO 2 for the gas permeable pH-dependent electrode, in place of PtO, leads to improved sensitivity. The sensor showed good current response for a wide range of CO 2 concentrations in air. For seawater, the partial pressure of CO 2 can be measured continuously with the sensor. CO 2 from the sample solution permeates into the sensor electrolyte through the membrane in a similar manner as with gas sensing. The CO 2 concentration or partial pressure can be detected as a current of pH dependent RuO 2 reduction induced by hydrogen ions supplied from CO 2 .
Analytica Chimica Acta, 1999
A method for measuring three components of the CO 2 system, pH, alkalinity (A t) and total CO 2 (TCO 2) in coastal seawater is presented. The measurements are suf®ciently precise to register CO 2 changes of biological origin in sur®cial and coastal waters or in culture media. The method is based on a modi®ed potentiometric titration of seawater with acid in a custom-built cell with the data plotted as a difference derivative, giving two peaks from which total carbonate and alkalinity can be computed. pH is calculated directly from the initial millivolt reading of the sample. One important aspect of this technique is that, unlike a Gran titration, the measured values of pH, A t and TCO 2 are independent of any preconceived seawater model. In this work we demonstrate that the relative position of the two peaks (used for determining TCO 2) is relatively insensitive to interferences from dissolved organic matter to about 1 Â 10 À4 M, while peak height is sensitive to it. This last observation permits the detection of organic bases which might be included in the measurement of alkalinity.
Use of carbonic anhydrase in electrochemical biosensors for dissolved CO 2
Carbon dioxide is one of the most important gases in the environment. The methods for the detection of dissolved CO 2 presently in use are not satisfactory. In order to make the measurement of CO 2 easier and more reliable, new electrochemical biosensors based on the enzyme carbonic anhydrase (CA) are being developed. Potentiometric and amperometric transducers were tested. The immobilization of CA on a commercially available CO 2 potentiometric electrode substantially improved its response time. In the amperometric biosensor, the use of CA as the biological component, coupled to p-benzoquinone (PBQ) as a redox mediator, allowed to obtain response times 10-fold faster than in absence of the enzyme. The performance of the amperometric biosensor was optimized for mediator amount, enzyme loading, applied potential and temperature. The possibility of using highly stable and easily extractable algal CA was investigated. The stability, high activity and low cost extraction of Dunaliella salina CAs make these algal enzymes very promising for use in biosensors.
Bio-Electrochemical Sensor for Fast Analysis of Assimilable Organic Carbon in Seawater
Journal of Biosensors & Bioelectronics, 2014
A Microbial Fuel Cell (MFC) based biosensor for the determination of Assimilable Organic Carbon (AOC) in seawater was developed by establishing an anodophilic marine biofilm on the surface of an electrode poised at +250 mV (vs Ag/AgCl) rather than the traditionally used potentials of about-300 mV. A linear correlation (R 2 >0.99) between electrochemical signals (peak current) and acetate concentration ranging 10 to 55 μM was achieved.Using the positive anodic potential enabled the rapid establishment of the electrochemically active anodophilic biomass within a period of less than 8 days, a higher sensitivity (0.017 mA/μM acetate added) and a lower detection limit (2.5 μM acetate, 0.16 mg O 2 /L of Biological Oxygen Demand (BOD)) compared to the negative anodic potential. Further, it was shown that this bio-electrochemical AOC sensor could tolerate the presence of low concentrations of dissolved oxygen. The established potentiostat controlled MFC biosensor could be used for the purpose of online water quality monitoring for seawater desalination plants prone to biofouling of RO membranes.
Ciencias Marinas, 1999
During the Cither 3 cruise along WOCE section A14, where 107 full-water column stations were surveyed, pH and alkalinity were measured potentiometrically. Corrections carried out on the raw data set have allowed us to improve the data quality. The correction procedure was focused on monitoring: (i) calibrations, (ii) liquid junction potential and (iii) seawater sub-standards; CO2 reference material (CRM) has been used to check this procedure. Accuracy of pH15 measurements (NBS scale) and alkalinity was 0.004 and 1.4 µmol.kg–1, respectively. Certified total inorganic carbon on CRM, batch 24, is 1987.55 µmol.kg–1. A value of 1987.8 ± 2.2 µmol.kg–1 was obtained following the correction procedure. This improvement was independently verified by means of the covariances between nitrate and pH, and between silicate and normalized alkalinity in North Atlantic Deep Water.
Marine Chemistry, 1993
A global survey of the distribution of dissolved CO2 taking advantage of sampling opportunities provided by the World Ocean Circulation Experiment: World Hydrographic Program (WOCE-WHP) is being carried out through 1995. Goals include the measurement of oceanic inorganic carbon transport and the development of a data base from which future fossil-fuel CO2 build-up can be monitored. The analytical method selected for total carbon dioxide (CT) is gas extraction of acidified seawater with coulometric titration of the acid formed by the resultant carbon dioxide and monoethanolamine. To combine high accuracy and precision (+1.5 #mol/kg for CT > 2000/zmol/kg) with a high rate of analysis, we have modified an automated single-parameter system. Following prototype development between 1987 and 1990, an instrument emerged with the acronym SOMMA standing for single-operator multiparameter metabolic analyzer. Improved functional and operating procedures have integrated electronic calibration, CO2 gas calibration, and sample analysis with automated pressure, temperature, and conductivity (salinity) sensing into a single convenient transportable package.