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Dissociation constant

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Reference
Endpoint:
dissociation constant
Type of information:
experimental study
Adequacy of study:
other information
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
documentation insufficient for assessment
Remarks:
Method no.: SOP 00288 Version 1 This SOP corresponds to OECD Guidelines for Testing of Chemicals, Section 1 – Physical-Chemical Properties No: 112 “Dissociation Constants in Water”.
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 112 (Dissociation Constants in Water)
Version / remarks:
Method no.: SOP 00288 Version 1
This SOP corresponds to OECD Guidelines for Testing of Chemicals, Section 1 – Physical-Chemical Properties No: 112 “Dissociation Constants in Water”.
GLP compliance:
yes
Dissociating properties:
yes
pKa:
8.2
Temp.:
20 °C
Conclusions:
Bayscript Blaukomponente TEA-Salz has a pKa value of 8.2 at 20°C.
Executive summary:

The dissociation constant of Bayscript Blaukomponente TEA-Salz was investigated in accordance with the Guidline OECD 121. The determination of the dissociation constant was performed by titration. A defined amount of hydrochloric acid (0.1 mol/L) was added to convert the molecule completely into the acid form (nonionic form) and the solution was titrated with sodium hydroxide solution (0.1 mol/L). From the pH value of complete neutralization of the acid, the pH of half the neutralization (= pKa value) was calculated by the software of the titroprocessor. A pKa value of 8.2 was determined at 20°C by potentiometric titration (Currenta 2016).

As the UVCB substance Bayscript Blaukomponente TEA is a complex mixture composed of three main components and unknown impurities, no clear conclusion on dissociation state can be received. Effects of impurities and the ammonium counterion on the measured result can be assumed. In accordance with ECHA Guidance R.7a, for complex mixtures (e.g. UVCBs) containing ionisable components the assessment of pKa is clearly complicated. Estimation of the representative constituent’s pKa values, if applicable, should be considered.

Description of key information

The dissociation constant of Bayscripot Blaukomponente TEA-Salz was investigated in accordance with the Guidline OECD 121. A pKa value of 8.2 was determined at 20°C by potentiometric titration (Currenta 2016).

Key value for chemical safety assessment

pKa at 20°C:
8.2

Additional information