Spectrophotometric measurement of freshwater pH with purified meta-cresol purple and phenol red

Chun Ze Lai; Michael D. DeGrandpre; Brandon D. Wasser; Taymee A. Brandon; Daniel S. Clucas; Emma J. Jaqueth; Zachary D. Benson; Cory M. Beatty; Reggie S. Spaulding

doi:10.1002/lom3.10137

Spectrophotometric measurement of freshwater pH with purified meta-cresol purple and phenol red

Chun Ze Lai
, Michael D. DeGrandpre
, Brandon D. Wasser
, Taymee A. Brandon
, Daniel S. Clucas
, Emma J. Jaqueth
, Zachary D. Benson
, Cory M. Beatty
, Reggie S. Spaulding

Chemistry and Biochemistry

Research output: Contribution to journal › Article › peer-review

43 Scopus citations

Abstract

Impurities in indicator salts can significantly bias spectrophotometric pH determinations. In this work, two purified sulfonephthalein indicators, meta-cresol purple (mCP) and phenol red (PR), were tested for analysis of freshwater pH on the free hydrogen ion concentration scale. These two purified indicators were characterized for the first time under low ionic strength conditions, providing their molar absorption coefficients and dissociation constants along with their temperature dependence from 8°C to 30°C. At 25°C, the infinite dilution constants (pK_I °) were determined to be 8.6606 and 8.0642 for mCP and PR, respectively. The accuracy and precision of the method, evaluated with a variety of buffers with known pH, were found to be ±0.0014 pH units and ±0.0022 pH units, respectively (n530). The pH values of different freshwater samples were also determined using both indicators. The mCP and PR results were all within ±0.01 pH units of each other with three out of seven pH differences within ±0.001 pH units, indicating the high consistency between these two indicator methods. The work presented here is the first parallel comparison with two purified indicators used to determine pH of the same freshwater samples.

Original language	English
Pages (from-to)	864-873
Number of pages	10
Journal	Limnology and Oceanography: Methods
Volume	14
Issue number	12
DOIs	https://doi.org/10.1002/lom3.10137
State	Published - Dec 1 2016

Funding

This manuscript is presented in memory of Zachary Benson, a B.S. chemistry graduate of UM, who worked on this project as an undergraduate in its early stages. Zach passed away from complications due to leukemia in September 2008. Financial support was provided by the Montana University System Research Initiative (contract 51030-MUSRI2015-02), the M.J. Murdock Charitable Trust and the Montana Board of Research and Commercialization Technology. Undergraduate researchers (BW, TB, DC and EJ) were supported by the U.S. National Science Foundation under grants ARC-1107346 and OCE-1459255.

Funder number
ARC-1107346, OCE-1459255
51030-MUSRI2015-02

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10.1002/lom3.10137

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@article{5663527669544ecb83c2da5e240ac4d2,

title = "Spectrophotometric measurement of freshwater pH with purified meta-cresol purple and phenol red",

abstract = "Impurities in indicator salts can significantly bias spectrophotometric pH determinations. In this work, two purified sulfonephthalein indicators, meta-cresol purple (mCP) and phenol red (PR), were tested for analysis of freshwater pH on the free hydrogen ion concentration scale. These two purified indicators were characterized for the first time under low ionic strength conditions, providing their molar absorption coefficients and dissociation constants along with their temperature dependence from 8°C to 30°C. At 25°C, the infinite dilution constants (pKI °) were determined to be 8.6606 and 8.0642 for mCP and PR, respectively. The accuracy and precision of the method, evaluated with a variety of buffers with known pH, were found to be ±0.0014 pH units and ±0.0022 pH units, respectively (n530). The pH values of different freshwater samples were also determined using both indicators. The mCP and PR results were all within ±0.01 pH units of each other with three out of seven pH differences within ±0.001 pH units, indicating the high consistency between these two indicator methods. The work presented here is the first parallel comparison with two purified indicators used to determine pH of the same freshwater samples.",

author = "Lai, \{Chun Ze\} and DeGrandpre, \{Michael D.\} and Wasser, \{Brandon D.\} and Brandon, \{Taymee A.\} and Clucas, \{Daniel S.\} and Jaqueth, \{Emma J.\} and Benson, \{Zachary D.\} and Beatty, \{Cory M.\} and Spaulding, \{Reggie S.\}",

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AU - Lai, Chun Ze

AU - DeGrandpre, Michael D.

AU - Wasser, Brandon D.

AU - Brandon, Taymee A.

AU - Clucas, Daniel S.

AU - Jaqueth, Emma J.

AU - Benson, Zachary D.

AU - Beatty, Cory M.

AU - Spaulding, Reggie S.

PY - 2016/12/1

Y1 - 2016/12/1

N2 - Impurities in indicator salts can significantly bias spectrophotometric pH determinations. In this work, two purified sulfonephthalein indicators, meta-cresol purple (mCP) and phenol red (PR), were tested for analysis of freshwater pH on the free hydrogen ion concentration scale. These two purified indicators were characterized for the first time under low ionic strength conditions, providing their molar absorption coefficients and dissociation constants along with their temperature dependence from 8°C to 30°C. At 25°C, the infinite dilution constants (pKI °) were determined to be 8.6606 and 8.0642 for mCP and PR, respectively. The accuracy and precision of the method, evaluated with a variety of buffers with known pH, were found to be ±0.0014 pH units and ±0.0022 pH units, respectively (n530). The pH values of different freshwater samples were also determined using both indicators. The mCP and PR results were all within ±0.01 pH units of each other with three out of seven pH differences within ±0.001 pH units, indicating the high consistency between these two indicator methods. The work presented here is the first parallel comparison with two purified indicators used to determine pH of the same freshwater samples.

AB - Impurities in indicator salts can significantly bias spectrophotometric pH determinations. In this work, two purified sulfonephthalein indicators, meta-cresol purple (mCP) and phenol red (PR), were tested for analysis of freshwater pH on the free hydrogen ion concentration scale. These two purified indicators were characterized for the first time under low ionic strength conditions, providing their molar absorption coefficients and dissociation constants along with their temperature dependence from 8°C to 30°C. At 25°C, the infinite dilution constants (pKI °) were determined to be 8.6606 and 8.0642 for mCP and PR, respectively. The accuracy and precision of the method, evaluated with a variety of buffers with known pH, were found to be ±0.0014 pH units and ±0.0022 pH units, respectively (n530). The pH values of different freshwater samples were also determined using both indicators. The mCP and PR results were all within ±0.01 pH units of each other with three out of seven pH differences within ±0.001 pH units, indicating the high consistency between these two indicator methods. The work presented here is the first parallel comparison with two purified indicators used to determine pH of the same freshwater samples.

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DO - 10.1002/lom3.10137

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AN - SCOPUS:84992603253

SN - 1541-5856

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EP - 873

JO - Limnology and Oceanography: Methods

JF - Limnology and Oceanography: Methods

IS - 12

ER -

Spectrophotometric measurement of freshwater pH with purified meta-cresol purple and phenol red

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Corrigendum to: Spectrophotometric measurement of freshwater pH with purified meta-cresol purple and phenol red: Freshwater pH with purified indicators (Limnology and Oceanography: Methods, (2016), 14, 12, (864-873), 10.1002/lom3.10137)

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