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Diss Factsheets

Physical & Chemical properties

Dissociation constant

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Administrative data

Endpoint:
dissociation constant
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
according to OECD 112

Data source

Reference
Title:
Unnamed
Year:
2021
Report date:
2021

Materials and methods

Test guidelineopen allclose all
Qualifier:
according to guideline
Guideline:
OECD Guideline 112 (Dissociation Constants in Water)
Qualifier:
according to guideline
Guideline:
other: Regulation (EC) 2017/735, A.25.
GLP compliance:
no

Test material

Constituent 1
Test material form:
solid: nanoform

Results and discussion

Dissociating properties:
yes
Dissociation constant
pKa:
9
Temp.:
20 °C
Remarks on result:
other: mean of 23 measurements

Any other information on results incl. tables

Table 3: Results of the 3 main tests


 


quantities between 0.1 and 0.5 mL of 0.01 mol/L sodium hydroxide solution were added respectively to the samples of the stock solutions


1) unionized form dm


2) ionized form di


main test I: pka = 9.00, standard deviation 0.35


main test II: pka = 9.00, standard deviation 0.41


main test III: pka = 8.89, standard deviation 0.42



 




























































































































































 



Main test I



Main test II



Main test III



Experiment



pH value



Absorption
at 393 nm



pKa



pH value



Absorption
at 393 nm



pKa



pH value



Absorption
at 393 nm



pKa



I-1(dm)



5.7



1.1570



1)



5.7



1.1519



1)



5.4



1.1381



1)



I-2 (di)



10.5



0.9796



2)



10.5



0.9742



2)



10.5



0.9647



2)



I-3



8.6



1.0921



8.82



7.6



1.1178



8.18



7.3



1.1170



8.18



I-4



9.3



1.0525



9.13



8.6



1.0728



8.73



7.9



1.0977



8.43



I-5



9.5



1.0522



9.29



9.2



1.0567



9.18



8.2



1.0933



8.67



I-6



9.5



1.0444



9.27



9.5



1.0257



9.11



8.7



1.0725



8.93



I-7



8.0



1.1151



8.51



9.7



1.0264



9.28



9.4



1.0292



9.21



I-8



9.6



1.0350



9.29



9.9



1.0115



9.29



9.7



1.0115



9.22



I-9



9.9



1.0103



9.19



10.0



1.0020



9.23



9.9



0.9914



9.15



I-10



7.9



1.1227



8.47



 



-



-



9.3



1.0490



9.31



 



 



 



9.00



 



 



9.00



 



 



8.89



 

Applicant's summary and conclusion

Executive summary:

The dissociation constant of C.I. Pigment Yellow 191 (nanoform) was determined according to OECD 112 and regulation (EC) 2017/735.

Based on the results of a preliminary test (low water solubility) the spectrophometric method was chosen to investigate the dissociation behaviour of the test item. Three main tests, 7 to 8 measurements respectively, where performed. Small quantities of 0.01 mol/L sodium hydroxide solution were added to samples prepared from stock solutions. The absorption spectra were recorded at 393 nm. The pka values were calculated using the determined pH values and measured absorptions of the unionised form, the ionised form and the test solutions at several intermediate pH values.

The mean pka value was 9.0