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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:
11 October 2018
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:
no
Specific details on test material used for the study:
SOURCE OF TEST MATERIAL
- Source and lot/batch No.of test material: Lead Regsitrant / 1809481
- Expiration date of the lot/batch: 01 April 2021
- Purity test date: not reported

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: Store in a cool, dry place and well ventilated area; Store in original container
- Solubility and stability of the test substance in the solvent/vehicle: soluble

TREATMENT OF TEST MATERIAL PRIOR TO TESTING
- Final preparation of a solid: Test substance Solution 10 g/L
2.0000 g test substance was weighed into a 200 mL volumetric flask, deionised water was added and solved in the ultrasonic bath. After complete solution the volumetric flask was filled up to the mark with deionised water. No Tyndall effect (with a laser beam was not scattered when transmitted through the liquid) could be observed indicating that no colloidal dispersed particles were present.

FORM AS APPLIED IN THE TEST (if different from that of starting material) : solution

Dissociating properties:
yes
No.:
#1
pKa:
6.874
Temp.:
20.4 °C
No.:
#2
pKa:
6.836
Temp.:
20.4 °C
No.:
#3
pKa:
6.825
Temp.:
20.4 °C

Table 4. Calculated pKa and pKb values

Determination

Volume half consumption in mL*

pKa

pKb

Main test 1

3.486

6.874

7.126

Main test 2

3.477

6.836

7.164

Main test 3

3.499

6.825

7.175

Mean

-

6.845

7.155

Standard Deviation

-

0.026

0.026

* In this table only the extrapolated half consumptions were stated. The calculations are stated in the report

Note: All calculations are performed with unrounded values. Therefore, recalculation with rounded values may lead to slightly different results.

Conclusions:
The standard deviation of three independent performances of the determination of the dissociation constant was within ± 0.1 log units. The validity criterion was met.
The three evaluated main determinations showed good correlation.
The calculated pKa and pKb values of Prayphos DSP TG are stated:
pKa = 6.845
pKb = 7.155

Description of key information

Key value for chemical safety assessment

pKa at 20°C:
6.845

Additional information