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Characterization of meta-Cresol Purple for spectrophotometric pH measurements in saline and hypersaline media at sub-zero temperatures

Characterization of meta-Cresol Purple for spectrophotometric pH measurements in saline and hypersaline media at sub-zero temperatures
Characterization of meta-Cresol Purple for spectrophotometric pH measurements in saline and hypersaline media at sub-zero temperatures
Accurate pH measurements in polar waters and sea ice brines require pH indicator dyes characterized at near-zero and below-zero temperatures and high salinities. We present experimentally determined physical and chemical characteristics of purified meta-Cresol Purple (mCP) pH indicator dye suitable for pH measurements in seawater and conservative seawater-derived brines at salinities (S) between 35 and 100 and temperatures (T) between their freezing point and 298.15 K (25 °C). Within this temperature and salinity range, using purified mCP and a novel thermostated spectrophotometric device, the pH on the total scale (pHT) can be calculated from direct measurements of the absorbance ratio R of the dye in natural samples as
pHT=−log(kT2e2)+log(R−e11−Re3e2)

Based on the mCP characterization in these extended conditions, the temperature and salinity dependence of the molar absorptivity ratios and − log(kT2e2)
of purified mCP is described by the following functions: e1 = −0.004363 + 3.598 × 10−5T, e3/e2 = −0.016224 + 2.42851 × 10−4T + 5.05663 × 10−5(S − 35), and − log(kT2e2) = −319.8369 + 0.688159 S −0.00018374 S2 + (10508.724 − 32.9599 S + 0.059082S2) T−1 + (55.54253 − 0.101639 S) ln T −0.08112151T. This work takes the characterisation of mCP beyond the currently available ranges of 278.15 K ≤ T ≤ 308.15 K and 20 ≤ S ≤ 40 in natural seawater, thereby allowing high quality pHT measurements in polar systems.
2045-2322
Loucaides, Socratis
5d0c31a4-269d-44a5-a858-13dc609ae072
Rerolle, Victoire M.C.
c30c1441-f55d-48c9-a9c6-659a7a125c60
Papadimitriou, Stathys
127a801b-c64a-4287-811b-e1c56407edd5
Kennedy, Hilary
932c7e9a-772b-4610-8d57-bdfcee9fd791
Mowlem, Matthew C.
6f633ca2-298f-48ee-a025-ce52dd62124f
Dickson, Andrew G.
225290d7-686a-4ce2-a960-18fa1447a611
Gledhill, Martha
da795c1e-1489-4d40-9df1-fc6bde54382d
Achterberg, Eric P.
685ce961-8c45-4503-9f03-50f6561202b9
Loucaides, Socratis
5d0c31a4-269d-44a5-a858-13dc609ae072
Rerolle, Victoire M.C.
c30c1441-f55d-48c9-a9c6-659a7a125c60
Papadimitriou, Stathys
127a801b-c64a-4287-811b-e1c56407edd5
Kennedy, Hilary
932c7e9a-772b-4610-8d57-bdfcee9fd791
Mowlem, Matthew C.
6f633ca2-298f-48ee-a025-ce52dd62124f
Dickson, Andrew G.
225290d7-686a-4ce2-a960-18fa1447a611
Gledhill, Martha
da795c1e-1489-4d40-9df1-fc6bde54382d
Achterberg, Eric P.
685ce961-8c45-4503-9f03-50f6561202b9

Loucaides, Socratis, Rerolle, Victoire M.C., Papadimitriou, Stathys, Kennedy, Hilary, Mowlem, Matthew C., Dickson, Andrew G., Gledhill, Martha and Achterberg, Eric P. (2017) Characterization of meta-Cresol Purple for spectrophotometric pH measurements in saline and hypersaline media at sub-zero temperatures. Scientific Reports, 7 (1). (doi:10.1038/s41598-017-02624-0).

Record type: Article

Abstract

Accurate pH measurements in polar waters and sea ice brines require pH indicator dyes characterized at near-zero and below-zero temperatures and high salinities. We present experimentally determined physical and chemical characteristics of purified meta-Cresol Purple (mCP) pH indicator dye suitable for pH measurements in seawater and conservative seawater-derived brines at salinities (S) between 35 and 100 and temperatures (T) between their freezing point and 298.15 K (25 °C). Within this temperature and salinity range, using purified mCP and a novel thermostated spectrophotometric device, the pH on the total scale (pHT) can be calculated from direct measurements of the absorbance ratio R of the dye in natural samples as
pHT=−log(kT2e2)+log(R−e11−Re3e2)

Based on the mCP characterization in these extended conditions, the temperature and salinity dependence of the molar absorptivity ratios and − log(kT2e2)
of purified mCP is described by the following functions: e1 = −0.004363 + 3.598 × 10−5T, e3/e2 = −0.016224 + 2.42851 × 10−4T + 5.05663 × 10−5(S − 35), and − log(kT2e2) = −319.8369 + 0.688159 S −0.00018374 S2 + (10508.724 − 32.9599 S + 0.059082S2) T−1 + (55.54253 − 0.101639 S) ln T −0.08112151T. This work takes the characterisation of mCP beyond the currently available ranges of 278.15 K ≤ T ≤ 308.15 K and 20 ≤ S ≤ 40 in natural seawater, thereby allowing high quality pHT measurements in polar systems.

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Accepted/In Press date: 13 April 2017
e-pub ahead of print date: 30 May 2017
Organisations: Ocean and Earth Science, Marine Biogeochemistry, National Oceanography Centre, Ocean Technology and Engineering, Southampton Marine & Maritime Institute

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Local EPrints ID: 411149
URI: https://eprints.soton.ac.uk/id/eprint/411149
ISSN: 2045-2322
PURE UUID: d981bc2d-6d84-48d5-9dcb-a1e1f77c82ac

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Date deposited: 15 Jun 2017 16:31
Last modified: 02 Dec 2019 19:02

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Contributors

Author: Socratis Loucaides
Author: Victoire M.C. Rerolle
Author: Stathys Papadimitriou
Author: Hilary Kennedy
Author: Matthew C. Mowlem
Author: Andrew G. Dickson
Author: Martha Gledhill

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