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Dissociation constant

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Reference
Endpoint:
dissociation constant
Type of information:
experimental study
Adequacy of study:
key study
Study period:
From Oct 13, 2011 to Nov. 28, 2011
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 112 (Dissociation Constants in Water)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Remarks:
according to OECD and EU principles of GLP
Dissociating properties:
yes
No.:
#1
pKa:
7.82
Remarks on result:
other: Determined by titration method
Conclusions:
The pKa of MEA-LAS was therefore determined as 7.82± 0.5 (determined by titration method; OECD 112 guideline).
Executive summary:

The dissociation constant (pKa) value of MEA-LAS was determined following OECD Guideline 112 (Dissociation constants in water).

For the estimation of pKa, a 100 mL test solution was prepared using 1.833 g of the sample. 100 mL of 0.05 M acid solution was prepared using 0.232 g of formic acid. The solution in the flask was titrated with the acid solution, in 0.1 mL increments, until complete neutralisation had been achieved. The point of inflection was also determined from the ratio of change in pH of the test solution to change in volume after each addition of the acid; versus mean volume of the acid applied. From the point of inflection curve, the volume of the acid consumed was obtained. The volume of acid at the point of inflection was divided by 2 to obtain the mid-point of the point of inflection. The mid-point of the point of inflection was therefore obtained as the stage of the titration when 0.5 mL of the acid had been added to the test solution. The pH at the mid-point of the point of inflection was taken as the estimated pKa of the test material.

For the formal determination of pKa,the titration was repeated as in the pKa estimation stage but adding 0.05 mL of the acid at a time until 22 mL of the acid had been added to the test solution. The pH of the test solution observed at the point where the volume of acid consumed was 0.25 mL was then taken as the pKa of the sample.

The pKa of MEA-LAS was therefore determined as 7.82± 0.5. This value reflects the neutralization of free MEA ion, in the presence of LAS.  

This dissociation constant test is classified as acceptable, and satisfies the guideline requirements of the OECD 112 guideline).

Description of key information

The dissociation constant (pKa) value of MEA-LAS was determined following OECD Guideline 112 (Dissociation Constants in Water).

Key value for chemical safety assessment

pKa at 20°C:
7.82

Additional information