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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:
10 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 / 1733181
- Expiration date of the lot/batch: 01 Nov 2020
- 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 place
- 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
1.0000 g test substance was weighed into a 100 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:
11.476
Temp.:
20.9
Remarks on result:
other: pKa of EQP1
No.:
#2
pKa:
8.44
Temp.:
20.9
Remarks on result:
other: pKa of EQP2

The calculation results of the pKa/ pKbare presented in the following table.

Table 4. Calculated pKaand pKbvalues of the Main Test EQP1

Determination

Volume half consumption in mL*

pKa

pKb

Main test 1

1.488

11.481

2.519

Main test 2

1.499

11.463

2.537

Main test 3

1.494

11.485

2.515

Mean

-

11.476

2.524

Standard Deviation

-

0.012

0.012

 

Table 5.         Calculated pKaand pKbvalues of the Main Test EQP2

Determination

Volume half consumption in mL*

pKa

pKb

Main test 1

3.072

8.447

5.553

Main test 2

3.086

8.438

5.562

Main test 3

3.078

8.436

5.564

Mean

-

8.440

5.560

Standard Deviation

-

0.006

0.006

 

* In these tables only the extrapolated half consumptions were stated. The calculations are stated in the study 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 TSP TG are stated:
pKa of EQP1= 11.476
pKb of EQP1= 2.524

pKa of EQP2= 8.440
pKb of EQP2= 5.560

Description of key information

Study performed in accordance with OECD 112.

Key value for chemical safety assessment

Additional information

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 pKaand pKbvalues ofPrayphos TSP TGare stated:

pKof EQP1= 11.476

pKbof EQP1= 2.524

 

pKof EQP2= 8.440

pKbof EQP2= 5.560