A Direct Bicarbonate Detection Method Based on a Near-Concentric Cavity-Enhanced Raman Spectroscopy System

Abstract

Raman spectroscopy has great potential as a tool in a variety of hydrothermal science applications. However, its low sensitivity has limited its use in common sea areas. In this paper, we develop a near-concentric cavity-enhanced Raman spectroscopy system to directly detect bicarbonate in seawater for the first time. With the aid of this near-concentric cavity-enhanced Raman spectroscopy system, a significant enhancement in HCO3− detection has been achieved. The obtained limit of detection (LOD) is determined to be 0.37 mmol/L—much lower than the typical concentration of HCO3− in seawater. By introducing a specially developed data processing scheme, the weak HCO3− signal is extracted from the strong sulfate signal background, hence a quantitative analysis with R2 of 0.951 is made possible. Based on the spectra taken from deep sea seawater sampling, the concentration of HCO3− has been determined to be 1.91 mmol/L, with a relative error of 2.1% from the reported value (1.95 mmol/L) of seawater in the ocean. It is expected that the near-concentric cavity-enhanced Raman spectroscopy system could be developed and used for in-situ ocean observation in the near future.

Feasibility Study of Real-Time Monitoring of Pin Connection Wear Using Acoustic Emission

“…Hay et al [71] applied an acoustic emission technique to monitor the connection parts of a bridge. In recent years, there is an emphasis on the monitoring of various structures in real time, and many innovative algorithms [72][73][74][75][76][77][78][79], sensors [14,80,81], and systems [82][83][84][85][86] have been developed for such a purpose. An AE sensor is normally small, and it can be easily attached to the host structure for real-time monitoring in a nondestructive way [81,[87][88][89][90].…”

Measurement of CO2 in Water from an Ultraviolet Oxidizer for a Space-Worthy Wastewater Recovery System Using Raman Spectroscopy

“…One team employed a 50 mW, 532 nm laser and a À100 °C TEC detector to measure 1080 mg/L CO 2 in 2.5 min within a two-chamber sample system that mixed liquid CO 2 and seawater at a depth of 500 m, representing one of the first Raman in-situ ocean measurements. 10 A second team employed a Raman system composed of a 300 mW, 532 nm laser, and a À40 °C thermo-electrically cooled (TEC) detector to measure bicarbonate with a limit of detection (LOD) of 22 mg/L in 50 s 11 This second team also measured gas phase CO 2 extracted from liquid water with an LOD of ∼1600 mg/L in 3 min 12 Essential to the second team's measurements was the use of two concave mirrors that reflected the laser beam through the liquid and gas phase samples 18 and 27 times, respectively. However, the TOCA concentration requirements to qualify water for drinking is 5 mg/L carbon, that is, TOC, with upper and lower detection limits of 10 and 0.25 mg/L carbon (36.6 and 0.92 mg/ L CO 2 ).…”

“…However, the TOCA concentration requirements to qualify water for drinking is 5 mg/L carbon, that is, TOC, with upper and lower detection limits of 10 and 0.25 mg/L carbon (36.6 and 0.92 mg/ L CO 2 ). 9 While the Raman system used to measure bicarbonate is closest to achieving these concentrations, it, like the other systems, is large and massive at ∼40 L and ∼30 kg, 11 far above NASA's next generation requirements.…”