Effect of temperature on pH measurements and acid-base equilibria in methanol-water mixtures

Autores
Castells, Cecilia Beatriz Marta; Ràfols, Clara; Rosés, Martí; Bosch, Elisabeth
Año de publicación
2003
Idioma
inglés
Tipo de recurso
artículo
Estado
versión publicada
Descripción
The knowledge of the acid-base equilibria in water-solvent mixtures of both common buffers and analytes is necessary in order to predict their retention as function of pH, solvent composition and temperature. This paper describes the effect of temperature on acid-base equilibria in methanol-water solvent mixtures commonly used as HPLC mobile phases. We measured the δ-correction parameter (δ=swpH-sspH=Ē j-log swγH0) between two pH scales: pH measured in the solvent concerned and referred to the same standard state, sspH, and the pH measured in that solvent mixture but referred to water as standard state, swpH, for several methanol compositions in the temperature range of 20-50°C. These determinations suggest that the δ-term depends only on composition of the mixture and on temperature. In water-rich mixtures, for which methanol is below 40% (w/w), δ-term seems to be independent of temperature, within the experimental uncertainties, whereas for methanol content larger than 50% (w/w) the δ-correction decreases as temperature increases. We have attributed this decrease to a large increase in the medium effect when mixtures have more than 50% methanol. The pKa of five weak electrolytes of different chemical nature in 50% methanol-water at 20-50°C are presented: the effect of temperature on pKa was large for amines, pyridine and phenol, but almost no dependence was found for benzoic acid. This indicates that buffers can play a critical role in affecting retention and selectivity in HPLC at temperatures far from 25°C, particularly for co-eluted solutes.
Fil: Castells, Cecilia Beatriz Marta. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones en Tecnología de Pinturas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones en Tecnología de Pinturas; Argentina
Fil: Ràfols, Clara. Universidad de Barcelona; España
Fil: Rosés, Martí. Universidad de Barcelona; España
Fil: Bosch, Elisabeth. Universidad de Barcelona; España
Materia
ACID-BASE EQUILIBRIA
METHANOL-WATER MIXTURES
MOBILE PHASE COMPOSITION
PH
TEMPERATURE
WEAK ELECTROLYTES
Nivel de accesibilidad
acceso abierto
Condiciones de uso
https://creativecommons.org/licenses/by-nc-sa/2.5/ar/
Repositorio
CONICET Digital (CONICET)
Institución
Consejo Nacional de Investigaciones Científicas y Técnicas
OAI Identificador
oai:ri.conicet.gov.ar:11336/95471
Acceder
id CONICETDig_74356e84d3234a9ec89ab549d17cfe7e
oai_identifier_str oai:ri.conicet.gov.ar:11336/95471
network_acronym_str CONICETDig
repository_id_str 3498
network_name_str CONICET Digital (CONICET)
spelling Effect of temperature on pH measurements and acid-base equilibria in methanol-water mixturesCastells, Cecilia Beatriz MartaRàfols, ClaraRosés, MartíBosch, ElisabethACID-BASE EQUILIBRIAMETHANOL-WATER MIXTURESMOBILE PHASE COMPOSITIONPHTEMPERATUREWEAK ELECTROLYTEShttps://purl.org/becyt/ford/1.4https://purl.org/becyt/ford/1The knowledge of the acid-base equilibria in water-solvent mixtures of both common buffers and analytes is necessary in order to predict their retention as function of pH, solvent composition and temperature. This paper describes the effect of temperature on acid-base equilibria in methanol-water solvent mixtures commonly used as HPLC mobile phases. We measured the δ-correction parameter (δ=swpH-sspH=Ē j-log swγH0) between two pH scales: pH measured in the solvent concerned and referred to the same standard state, sspH, and the pH measured in that solvent mixture but referred to water as standard state, swpH, for several methanol compositions in the temperature range of 20-50°C. These determinations suggest that the δ-term depends only on composition of the mixture and on temperature. In water-rich mixtures, for which methanol is below 40% (w/w), δ-term seems to be independent of temperature, within the experimental uncertainties, whereas for methanol content larger than 50% (w/w) the δ-correction decreases as temperature increases. We have attributed this decrease to a large increase in the medium effect when mixtures have more than 50% methanol. The pKa of five weak electrolytes of different chemical nature in 50% methanol-water at 20-50°C are presented: the effect of temperature on pKa was large for amines, pyridine and phenol, but almost no dependence was found for benzoic acid. This indicates that buffers can play a critical role in affecting retention and selectivity in HPLC at temperatures far from 25°C, particularly for co-eluted solutes.Fil: Castells, Cecilia Beatriz Marta. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones en Tecnología de Pinturas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones en Tecnología de Pinturas; ArgentinaFil: Ràfols, Clara. Universidad de Barcelona; EspañaFil: Rosés, Martí. Universidad de Barcelona; EspañaFil: Bosch, Elisabeth. Universidad de Barcelona; EspañaElsevier Science2003-06info:eu-repo/semantics/articleinfo:eu-repo/semantics/publishedVersionhttp://purl.org/coar/resource_type/c_6501info:ar-repo/semantics/articuloapplication/pdfapplication/pdfhttp://hdl.handle.net/11336/95471Castells, Cecilia Beatriz Marta; Ràfols, Clara; Rosés, Martí; Bosch, Elisabeth; Effect of temperature on pH measurements and acid-base equilibria in methanol-water mixtures; Elsevier Science; Journal of Chromatography - A; 1002; 1-2; 6-2003; 41-530021-9673CONICET DigitalCONICETenginfo:eu-repo/semantics/altIdentifier/url/https://www.sciencedirect.com/science/article/pii/S0021967303006447info:eu-repo/semantics/altIdentifier/doi/10.1016/S0021-9673(03)00644-7info:eu-repo/semantics/openAccesshttps://creativecommons.org/licenses/by-nc-sa/2.5/ar/reponame:CONICET Digital (CONICET)instname:Consejo Nacional de Investigaciones Científicas y Técnicas2025-10-15T14:27:32Zoai:ri.conicet.gov.ar:11336/95471instacron:CONICETInstitucionalhttp://ri.conicet.gov.ar/Organismo científico-tecnológicoNo correspondehttp://ri.conicet.gov.ar/oai/requestdasensio@conicet.gov.ar; lcarlino@conicet.gov.arArgentinaNo correspondeNo correspondeNo correspondeopendoar:34982025-10-15 14:27:33.01CONICET Digital (CONICET) - Consejo Nacional de Investigaciones Científicas y Técnicasfalse
dc.title.none.fl_str_mv Effect of temperature on pH measurements and acid-base equilibria in methanol-water mixtures
title Effect of temperature on pH measurements and acid-base equilibria in methanol-water mixtures
spellingShingle Effect of temperature on pH measurements and acid-base equilibria in methanol-water mixtures
Castells, Cecilia Beatriz Marta
ACID-BASE EQUILIBRIA
METHANOL-WATER MIXTURES
MOBILE PHASE COMPOSITION
PH
TEMPERATURE
WEAK ELECTROLYTES
title_short Effect of temperature on pH measurements and acid-base equilibria in methanol-water mixtures
title_full Effect of temperature on pH measurements and acid-base equilibria in methanol-water mixtures
title_fullStr Effect of temperature on pH measurements and acid-base equilibria in methanol-water mixtures
title_full_unstemmed Effect of temperature on pH measurements and acid-base equilibria in methanol-water mixtures
title_sort Effect of temperature on pH measurements and acid-base equilibria in methanol-water mixtures
dc.creator.none.fl_str_mv Castells, Cecilia Beatriz Marta
Ràfols, Clara
Rosés, Martí
Bosch, Elisabeth
author Castells, Cecilia Beatriz Marta
author_facet Castells, Cecilia Beatriz Marta
Ràfols, Clara
Rosés, Martí
Bosch, Elisabeth
author_role author
author2 Ràfols, Clara
Rosés, Martí
Bosch, Elisabeth
author2_role author
author
author
dc.subject.none.fl_str_mv ACID-BASE EQUILIBRIA
METHANOL-WATER MIXTURES
MOBILE PHASE COMPOSITION
PH
TEMPERATURE
WEAK ELECTROLYTES
topic ACID-BASE EQUILIBRIA
METHANOL-WATER MIXTURES
MOBILE PHASE COMPOSITION
PH
TEMPERATURE
WEAK ELECTROLYTES
purl_subject.fl_str_mv https://purl.org/becyt/ford/1.4
https://purl.org/becyt/ford/1
dc.description.none.fl_txt_mv The knowledge of the acid-base equilibria in water-solvent mixtures of both common buffers and analytes is necessary in order to predict their retention as function of pH, solvent composition and temperature. This paper describes the effect of temperature on acid-base equilibria in methanol-water solvent mixtures commonly used as HPLC mobile phases. We measured the δ-correction parameter (δ=swpH-sspH=Ē j-log swγH0) between two pH scales: pH measured in the solvent concerned and referred to the same standard state, sspH, and the pH measured in that solvent mixture but referred to water as standard state, swpH, for several methanol compositions in the temperature range of 20-50°C. These determinations suggest that the δ-term depends only on composition of the mixture and on temperature. In water-rich mixtures, for which methanol is below 40% (w/w), δ-term seems to be independent of temperature, within the experimental uncertainties, whereas for methanol content larger than 50% (w/w) the δ-correction decreases as temperature increases. We have attributed this decrease to a large increase in the medium effect when mixtures have more than 50% methanol. The pKa of five weak electrolytes of different chemical nature in 50% methanol-water at 20-50°C are presented: the effect of temperature on pKa was large for amines, pyridine and phenol, but almost no dependence was found for benzoic acid. This indicates that buffers can play a critical role in affecting retention and selectivity in HPLC at temperatures far from 25°C, particularly for co-eluted solutes.
Fil: Castells, Cecilia Beatriz Marta. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones en Tecnología de Pinturas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones en Tecnología de Pinturas; Argentina
Fil: Ràfols, Clara. Universidad de Barcelona; España
Fil: Rosés, Martí. Universidad de Barcelona; España
Fil: Bosch, Elisabeth. Universidad de Barcelona; España
description The knowledge of the acid-base equilibria in water-solvent mixtures of both common buffers and analytes is necessary in order to predict their retention as function of pH, solvent composition and temperature. This paper describes the effect of temperature on acid-base equilibria in methanol-water solvent mixtures commonly used as HPLC mobile phases. We measured the δ-correction parameter (δ=swpH-sspH=Ē j-log swγH0) between two pH scales: pH measured in the solvent concerned and referred to the same standard state, sspH, and the pH measured in that solvent mixture but referred to water as standard state, swpH, for several methanol compositions in the temperature range of 20-50°C. These determinations suggest that the δ-term depends only on composition of the mixture and on temperature. In water-rich mixtures, for which methanol is below 40% (w/w), δ-term seems to be independent of temperature, within the experimental uncertainties, whereas for methanol content larger than 50% (w/w) the δ-correction decreases as temperature increases. We have attributed this decrease to a large increase in the medium effect when mixtures have more than 50% methanol. The pKa of five weak electrolytes of different chemical nature in 50% methanol-water at 20-50°C are presented: the effect of temperature on pKa was large for amines, pyridine and phenol, but almost no dependence was found for benzoic acid. This indicates that buffers can play a critical role in affecting retention and selectivity in HPLC at temperatures far from 25°C, particularly for co-eluted solutes.
publishDate 2003
dc.date.none.fl_str_mv 2003-06
dc.type.none.fl_str_mv info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
http://purl.org/coar/resource_type/c_6501
info:ar-repo/semantics/articulo
format article
status_str publishedVersion
dc.identifier.none.fl_str_mv http://hdl.handle.net/11336/95471
Castells, Cecilia Beatriz Marta; Ràfols, Clara; Rosés, Martí; Bosch, Elisabeth; Effect of temperature on pH measurements and acid-base equilibria in methanol-water mixtures; Elsevier Science; Journal of Chromatography - A; 1002; 1-2; 6-2003; 41-53
0021-9673
CONICET Digital
CONICET
url http://hdl.handle.net/11336/95471
identifier_str_mv Castells, Cecilia Beatriz Marta; Ràfols, Clara; Rosés, Martí; Bosch, Elisabeth; Effect of temperature on pH measurements and acid-base equilibria in methanol-water mixtures; Elsevier Science; Journal of Chromatography - A; 1002; 1-2; 6-2003; 41-53
0021-9673
CONICET Digital
CONICET
dc.language.none.fl_str_mv eng
language eng
dc.relation.none.fl_str_mv info:eu-repo/semantics/altIdentifier/url/https://www.sciencedirect.com/science/article/pii/S0021967303006447
info:eu-repo/semantics/altIdentifier/doi/10.1016/S0021-9673(03)00644-7
dc.rights.none.fl_str_mv info:eu-repo/semantics/openAccess
https://creativecommons.org/licenses/by-nc-sa/2.5/ar/
eu_rights_str_mv openAccess
rights_invalid_str_mv https://creativecommons.org/licenses/by-nc-sa/2.5/ar/
dc.format.none.fl_str_mv application/pdf
application/pdf
dc.publisher.none.fl_str_mv Elsevier Science
publisher.none.fl_str_mv Elsevier Science
dc.source.none.fl_str_mv reponame:CONICET Digital (CONICET)
instname:Consejo Nacional de Investigaciones Científicas y Técnicas
reponame_str CONICET Digital (CONICET)
collection CONICET Digital (CONICET)
instname_str Consejo Nacional de Investigaciones Científicas y Técnicas
repository.name.fl_str_mv CONICET Digital (CONICET) - Consejo Nacional de Investigaciones Científicas y Técnicas
repository.mail.fl_str_mv dasensio@conicet.gov.ar; lcarlino@conicet.gov.ar
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score 13.22299

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