A high precision, fast response, and low power consumption in situ optical fiber chemical pCO2 sensor

Carbon Dioxide Sensing-Biomedical Applications to Human Subjects

Carbon dioxide (CO2) monitoring in human subjects is of crucial importance in medical practice. Transcutaneous monitors based on the Stow-Severinghaus electrode make a good alternative to the painful and risky arterial "blood gases" sampling. Yet, such monitors are not only expensive, but also bulky and continuously drifting, requiring frequent recalibrations by trained medical staff. Aiming at finding alternatives, the full panel of CO2 measurement techniques is thoroughly reviewed. The physicochemical working principle of each sensing technique is given, as well as some typical merit criteria, advantages, and drawbacks. An overview of the main CO2 monitoring methods and sites routinely used in clinical practice is also provided, revealing their constraints and specificities. The reviewed CO2 sensing techniques are then evaluated in view of the latter clinical constraints and transcutaneous sensing coupled to a dye-based fluorescence CO2 sensing seems to offer the best potential for the development of a future non-invasive clinical CO2 monitor.

Spectrophotometric determination of pH and carbonate ion concentrations in seawater: Choices, constraints and consequences

Accurate and precise marine CO₂ system measurements are important for marine carbon cycle research and investigations of ocean acidification. Seawater pH is important because it can be used to characterize a wide range of chemical and biogeochemical processes. Saturation states of calcium carbonate minerals, which are directly proportional to carbonate ion concentration ([CO₃^2-]), influence biogenic calcification and rates of carbonate dissolution. Spectrophotometric pH and carbonate ion measurements can both benefit greatly from the high sensitivity, stability, consistency and processing speed made possible through automation. Spectrophotometric methods are well-suited for shipboard, underway and in situ deployments under harsh conditions. Spectrophotometric pH measurements typically have a reproducibility of 0.0004-0.001 for shipboard and laboratory measurements and 0.0014-0.004 for in situ measurements. Shipboard spectrophotometric measurements of [CO₃^2-] are becoming common on research expeditions. This review highlights the development of methods and instrumentation for spectrophotometric pH and [CO₃^2-] measurements, and discusses the pros and cons of current technology. A comprehensive summary of the analytical merits of different flow analysis instruments is given. Aspects of measurement protocols that bear on the quality of pH and [CO₃^2-] measurements, such as indicator purification, sample pretreatment, etc., are also described. Based on three decades of experience with seawater analysis, this review includes method recommendations and perspectives directly applicable or potentially applicable to pH and [CO₃^2-] analysis of seawater.

Corrosion Sensors for Structural Health Monitoring of Oil and Natural Gas Infrastructure: A Review

Corrosion has been a great concern in the oil and natural gas industry costing billions of dollars annually in the U.S. The ability to monitor corrosion online before structural integrity is compromised can have a significant impact on preventing catastrophic events resulting from corrosion. This article critically reviews conventional corrosion sensors and emerging sensor technologies in terms of sensing principles, sensor designs, advantages, and limitations. Conventional corrosion sensors encompass corrosion coupons, electrical resistance probes, electrochemical sensors, ultrasonic testing sensors, magnetic flux leakage sensors, electromagnetic sensors, and in-line inspection tools. Emerging sensor technologies highlight optical fiber sensors (point, quasi-distributed, distributed) and passive wireless sensors such as passive radio-frequency identification sensors and surface acoustic wave sensors. Emerging sensors show great potential in continuous real-time in-situ monitoring of oil and natural gas infrastructure. Distributed chemical sensing is emphasized based on recent studies as a promising method to detect early corrosion onset and monitor corrosive environments for corrosion mitigation management. Additionally, challenges are discussed including durability and stability in extreme and harsh conditions such as high temperature high pressure in subsurface wellbores.

Spatial and temporal pCO2 marine monitoring near Panarea Island (Italy) using multiple low-cost GasPro sensors

The present paper describes the GasPro probe, a small, low-cost unit for in situ, continuous pCO2 monitoring. Laboratory tests defining its performance characteristics are reported, as are the results from a 60 h water-column deployment of 20 such units near a natural CO2 seep site off the coast of Panarea Island (Italy). The spatial-temporal evolution of dissolved CO2 movement is presented and possible origins and controlling mechanisms discussed. Results highlight the potential for this technology to be used for better understanding various dynamic physical and biochemical processes in marine environments, and for marine environmental monitoring of off-shore industrial sites. These experiments have allowed us to assess the advantages and disadvantages of the present GasPro prototype and to define areas for ongoing improvement.

Absorbance characteristics of a liquid-phase gas sensor based on gas-permeable liquid core waveguides

The absorbance characteristics and influential factors on these characteristics for a liquid-phase gas sensor, which is based on gas-permeable liquid core waveguides (LCWs), are studied from theoretical and experimental viewpoints in this paper. According to theory, it is predicted that absorbance is proportional to the analyte concentration, sampling time, analyte diffusion coefficient, and geometric factor of this device when the depletion layer of the analyte is ignored. The experimental results are in agreement with the theoretical hypothesis. According to the experimental results, absorbance is time-dependent and increasing linearly over time after the requisite response time with a linear correlation coefficient r(2)>0.999. In the linear region, the rate of absorbance change (RAC) indicates improved linearity with sample concentration and a relative higher sensitivity than instantaneous absorbance does. By using a core liquid that is more affinitive to the analyte, reducing wall thickness and the inner diameter of the tubing, or increasing sample flow rate limitedly, the response time can be decreased and the sensitivity can be increased. However, increasing the LCW length can only enhance sensitivity and has no effect on response time. For liquid phase detection, there is a maximum flow rate, and the absorbance will decrease beyond the stated limit. Under experimental conditions, hexane as the LCW core solvent, a tubing wall thickness of 0.1 mm, a length of 10 cm, and a flow rate of 12 mL min(-1), the detection results for the aqueous benzene sample demonstrate a response time of 4 min. Additionally, the standard curve for the RAC versus concentration is RAC=0.0267c+0.0351 (AU min(-1)), with r(2)=0.9922 within concentrations of 0.5-3.0 mg L(-1). The relative error for 0.5 mg L(-1) benzene (n=6) is 7.4±3.7%, and the LOD is 0.04 mg L(-1). This research can provide theoretical and practical guides for liquid-phase gas sensor design and development based on a gas-permeable Teflon AF 2400 LCW.

Automated spectrophotometric analyzer for rapid single-point titration of seawater total alkalinity

An automated analyzer was developed to achieve fast, precise, and accurate measurements of seawater total alkalinity (AT) based on single-point titration and spectrophotometric pH detection. The single-point titration was carried out in a circulating loop, which allowed the titrant (hydrochloric acid and bromocresol green solution) and a seawater sample to mix at a constant volume ratio. The dissolved CO2 in the sample-titrant mixture was efficiently removed by an inline CO2 remover, which consists of a gas-permeable tubing (Teflon AF2400) submerged in a sodium hydroxide (NaOH) solution. The pH of the mixture was then measured with a custom-made spectrophotometric detection system. The analyzer was calibrated against multiple certified reference materials (CRMs) with different AT values. The analyzer features a sample throughput time of 6.5 min with high precision (±0.33-0.36 μmol kg(-1); n = 48) and accuracy (-0.33 ± 0.99 μmol kg(-1); n = 10). Intercomparison to a traditional open-cell AT titrator showed overall good agreement of 0.88 ± 2.03 μmol kg(-1) (n = 22). The analyzer achieved excellent stability without recalibration over 11 days, during which time 320 measurements were made with a total running time of over 40 h. Because of its small size, low power consumption requirements, and its ability to be automated, the new analyzer can be adapted for underway and in situ measurements.

Teflon AF Materials

The unique combination of chemical, thermal, and mechanical stability, high fractional free volume, low refractive index, low surface energy, and wide optical transparency has led to growing interest in Teflon Amorphous Fluoropolymers (AFs) for a wide spectrum of applications ranging from chemical separations and sensors to bioassay platforms. New opportunities arise from the incorporation of nanoscale materials in Teflon AFs. In this chapter, we highlight fractional free volume - the most important property of Teflon AFs - with the aim of clarifying the unique transport behavior through Teflon AF membranes. We then review state-of-the-art developments based on Teflon AF platforms by focusing on the chemistry behind the applications.