Mobile phase MeCN/ 1 mM NH 3 80/20 10.47 9.75 MeCN/ 1 mM NH 3 50/50 10.07 9.75 MeCN/ pH 5 80/20 8.93 5.00 MeOH/ 1 mM NH 3 80/20 8.89 9.75 MeOH/ 1 mM NH 3 50/50 8.70 9.75 MeCN/ pH 5 50/50 7.50 5.00 MeOH/ pH 5 80/20 7.49 5.00 pH 7 (diluted) 7.22 7.16 MeOH/ pH 5 50/50 6.47 5.00 MeCN/ 0.1% HCOOH 80/20 5.37 2.68 MeOH/ 0.1% HCOOH 80/20 4.79 2.68 MeCN/ 0.1% HCOOH 50/50 4.39 2.68 pH 4 (diluted) 4.09 4.15 MeOH/ 0.1% HCOOH 50/50 3.89 2.68 Uni fi ed pH values of liquid chromatography mobile phases Agnes Heering 1 , Rasmus Born 1 , Sofja Tshepelevitsh 1 , Lauri Jalukse 1 , Jaanus Liigand 1 , Anneli Kruve 1 , Daniel Himmel 2 , Ingo Krossing 2 , Martí Rosés 3 , and Ivo Leito 1, * 1 University of Tartu, Institute of Chemistry, Ravila 14a, Tartu, 50411, Estonia 2 Institute for Inorganic and Analytical Chemistry and Freiburger Materialforschungszentrum (FMF), Albert‐Ludwigs‐Universität Freiburg, Albertstrasse 21, 79104 Freiburg, Germany 3 Departament de Química Analítica, Universitat de Barcelona, Martí í Franquès, 1‐11, E‐08028 Barcelona, Spain [email protected] www.uniphied.eu pH measurement of LC mobile phases is not trivial pH measurement in mixed solvents is not well established, the most widespread approach is ୵ ୵ There is the concept of Unified pH scale (pH abs * scale)! * Here we used pH abs in the meaning of ୟୠୱ ୌଶ , i.e. "aligned" with the aqueous pH scale [1] Is there a rigorous way? How to measure that in practice? Differential potentiometry [1] [1] Anal. Chem. 2015, 87, 2623–2630, http://dx.doi.org/10.1021/ac504692m. pH abs of mobile phases? Possible in any mobile phase Anchoring: Aqueous std buffers This work was supported by the EMPIR programme (project 17FUN09, UnipHied) co‐financed by the Participating States and from the European Union’s Horizon 2020 research and innovation programme, by the EU through the European Regional Development Fund (TK141) and by Institutional Funding IUT20‐14 from the Estonian Research Council. Which works better in practice, or pH abs ? Degree of ionization: pH abs is better with bases, with acids Retention: Neither is perfect 0 10 20 30 0.0 1.5 3.0 4.5 6.0 0 5 10 15 0 5 10 15 Signal Time (min) COOH pK a (H 2 O) = 4.2 N N H pK aH (H 2 O) = 5.6 N pK aH (H 2 O) = 6.7 OH NO 2 O 2 N pK a (H 2 O) = 4.1 Numbers on peaks: extents of ionization Void time . % / , : , ൌ . ൌ . ~ / , : , ൌ . ൌ . ~ / , : , ൌ . ൌ . 0 9 100 100 52 9 95 79 100 100 0 0

UnifiedpH values of liquid chromatography mobile phases · chromatography mobile phases Agnes Heering 1 , RasmusBorn 1 , SofjaTshepelevitsh 1 , Lauri Jalukse 1 , JaanusLiigand 1 ,AnneliKruve

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Page 1: UnifiedpH values of liquid chromatography mobile phases · chromatography mobile phases Agnes Heering 1 , RasmusBorn 1 , SofjaTshepelevitsh 1 , Lauri Jalukse 1 , JaanusLiigand 1 ,AnneliKruve

Mobile phase 𝐩𝐇𝐚𝐛𝐬𝐇𝟐𝐎 𝐩𝐇𝐰

𝐰

MeCN/ 1 mM NH3 80/20 10.47 9.75MeCN/ 1 mM NH3 50/50 10.07 9.75

MeCN/ pH 5 80/20 8.93 5.00MeOH/ 1 mM NH3 80/20 8.89 9.75MeOH/ 1 mM NH3 50/50 8.70 9.75

MeCN/ pH 5 50/50 7.50 5.00MeOH/ pH 5 80/20 7.49 5.00

pH 7 (diluted) 7.22 7.16MeOH/ pH 5 50/50 6.47 5.00

MeCN/ 0.1% HCOOH 80/20 5.37 2.68MeOH/ 0.1% HCOOH 80/20 4.79 2.68MeCN/ 0.1% HCOOH 50/50 4.39 2.68

pH 4 (diluted) 4.09 4.15MeOH/ 0.1% HCOOH 50/50 3.89 2.68

Unified pH values of liquid chromatography mobile phases

Agnes Heering1, Rasmus Born1, Sofja Tshepelevitsh1, Lauri Jalukse1,Jaanus Liigand1, Anneli Kruve1, Daniel Himmel2, Ingo Krossing2, Martí Rosés3, and Ivo Leito1,*

1 University of Tartu, Institute of Chemistry, Ravila 14a, Tartu, 50411, Estonia2 Institute for Inorganic and Analytical Chemistry and Freiburger Materialforschungszentrum (FMF),

Albert‐Ludwigs‐Universität Freiburg, Albertstrasse 21, 79104 Freiburg, Germany3 Departament de Química Analítica, Universitat de Barcelona, Martí í Franquès, 1‐11, E‐08028 Barcelona, Spain

[email protected] www.uniphied.eu

pHmeasurement of LC mobile phases is not trivial

pH measurement in mixed solvents is not well established,the most widespread approach is

There is the concept of Unified pH scale (pHabs

* scale)!* Here we used pHabs in the meaning of , i.e. "aligned" with

the aqueous pH scale [1]

Is there a rigorous way?

How to measurethat in practice?

Differential potentiometry[1][1] Anal. Chem. 2015, 87, 2623–2630, http://dx.doi.org/10.1021/ac504692m.

pHabs of mobilephases?

Possible in any mobile phaseAnchoring: Aqueous std buffers

This work was supported by the EMPIR programme (project 17FUN09, UnipHied) co‐financed by the Participating States and from the European Union’s Horizon 2020 research and innovation programme, by the EU through the European Regional Development Fund (TK141)and by Institutional Funding IUT20‐14 from the Estonian Research Council.

Which works betterin practice, or

pHabs?

Degree of ionization: pHabs is betterwith bases, with acidsRetention: Neither is perfect

0.0 1.5 3.0 4.5 6.0

Sign

Time (min)

COOH

pKa(H2O) = 4.2

HpKaH(H2O) = 5.6

pKaH(H2O) = 6.7

NO2O2N

pKa(H2O) = 4.1