Measurements of Bicarbonate in Water Containing Ocean-Level Sulfate Using a Simple Multi-Pass Optical Raman System
The concentration of dissolved inorganic carbon in the oceans at depths of a few meters to thousands of meters is a critical parameter for understanding global warming. The concentration is both pH dependent and depth dependent. Current analysis that employs pH meters must account for several other...
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doaj-52977ed6e2dd4124916ad4f8bc8205392021-04-06T23:03:56ZengMDPI AGOceans2673-19242021-04-0121933033610.3390/oceans2020019Measurements of Bicarbonate in Water Containing Ocean-Level Sulfate Using a Simple Multi-Pass Optical Raman SystemChetan Shende0Stuart Farquharson1Duncan Farquharson2Carl Brouillette3Real-Time Analyzers, Inc., Middletown, CT 06457, USAReal-Time Analyzers, Inc., Middletown, CT 06457, USAReal-Time Analyzers, Inc., Middletown, CT 06457, USAReal-Time Analyzers, Inc., Middletown, CT 06457, USAThe concentration of dissolved inorganic carbon in the oceans at depths of a few meters to thousands of meters is a critical parameter for understanding global warming. The concentration is both pH dependent and depth dependent. Current analysis that employs pH meters must account for several other parameters, such as salinity, temperature, pressure, and the dissolved carbon’s form, carbon dioxide, bicarbonate, or carbonate. Recently, Raman spectroscopy has been used to measure these forms directly in water at ~1000 ppm, which is unfortunately insufficient for typical ocean concentrations, such as ~115 ppm bicarbonate near the surface. Here, we employed a simple multi-pass optical system, a flat mirror to reflect the laser back through the sample, and a concave mirror opposite the entrance slit that effectively doubled the laser power and the collected Raman photons, respectively. This multi-pass optical Raman system with a 1.5 W, 532 nm laser was used to measure 30 ppm bicarbonate in water that contained 2650 ppm sulfate to simulate ocean water, a bicarbonate concentration well below that near the ocean surface. Furthermore, spectral analysis employed the bicarbonate C=O symmetric stretch at 1360 cm<sup>−1</sup> instead of the C–OH stretch at 1015 cm<sup>−1</sup> to avoid the intense, overlapping sulfate SO<sub>4</sub> symmetric stretch at 985 cm<sup>−1</sup>. The calculated standard deviation of ~5 ppm for the described approach suggests that accurate measurement of bicarbonate in situ is possible, which has been, heretofore, either calculated based on pH or measured in a lab.https://www.mdpi.com/2673-1924/2/2/19ocean carbon dioxidebicarbonateRaman spectroscopy |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
Chetan Shende Stuart Farquharson Duncan Farquharson Carl Brouillette |
spellingShingle |
Chetan Shende Stuart Farquharson Duncan Farquharson Carl Brouillette Measurements of Bicarbonate in Water Containing Ocean-Level Sulfate Using a Simple Multi-Pass Optical Raman System Oceans ocean carbon dioxide bicarbonate Raman spectroscopy |
author_facet |
Chetan Shende Stuart Farquharson Duncan Farquharson Carl Brouillette |
author_sort |
Chetan Shende |
title |
Measurements of Bicarbonate in Water Containing Ocean-Level Sulfate Using a Simple Multi-Pass Optical Raman System |
title_short |
Measurements of Bicarbonate in Water Containing Ocean-Level Sulfate Using a Simple Multi-Pass Optical Raman System |
title_full |
Measurements of Bicarbonate in Water Containing Ocean-Level Sulfate Using a Simple Multi-Pass Optical Raman System |
title_fullStr |
Measurements of Bicarbonate in Water Containing Ocean-Level Sulfate Using a Simple Multi-Pass Optical Raman System |
title_full_unstemmed |
Measurements of Bicarbonate in Water Containing Ocean-Level Sulfate Using a Simple Multi-Pass Optical Raman System |
title_sort |
measurements of bicarbonate in water containing ocean-level sulfate using a simple multi-pass optical raman system |
publisher |
MDPI AG |
series |
Oceans |
issn |
2673-1924 |
publishDate |
2021-04-01 |
description |
The concentration of dissolved inorganic carbon in the oceans at depths of a few meters to thousands of meters is a critical parameter for understanding global warming. The concentration is both pH dependent and depth dependent. Current analysis that employs pH meters must account for several other parameters, such as salinity, temperature, pressure, and the dissolved carbon’s form, carbon dioxide, bicarbonate, or carbonate. Recently, Raman spectroscopy has been used to measure these forms directly in water at ~1000 ppm, which is unfortunately insufficient for typical ocean concentrations, such as ~115 ppm bicarbonate near the surface. Here, we employed a simple multi-pass optical system, a flat mirror to reflect the laser back through the sample, and a concave mirror opposite the entrance slit that effectively doubled the laser power and the collected Raman photons, respectively. This multi-pass optical Raman system with a 1.5 W, 532 nm laser was used to measure 30 ppm bicarbonate in water that contained 2650 ppm sulfate to simulate ocean water, a bicarbonate concentration well below that near the ocean surface. Furthermore, spectral analysis employed the bicarbonate C=O symmetric stretch at 1360 cm<sup>−1</sup> instead of the C–OH stretch at 1015 cm<sup>−1</sup> to avoid the intense, overlapping sulfate SO<sub>4</sub> symmetric stretch at 985 cm<sup>−1</sup>. The calculated standard deviation of ~5 ppm for the described approach suggests that accurate measurement of bicarbonate in situ is possible, which has been, heretofore, either calculated based on pH or measured in a lab. |
topic |
ocean carbon dioxide bicarbonate Raman spectroscopy |
url |
https://www.mdpi.com/2673-1924/2/2/19 |
work_keys_str_mv |
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