Calcium 4-chloro-2-(5-hydroxy-3-methyl-1-(3-sulfonatophenyl)pyrazol-4-ylazo)-5-methylbenzenesulfonate

Dissociation constant

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 guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 112 (Dissociation Constants in Water)

Test guideline 2

Qualifier:

according to guideline

Guideline:

other: Regulation (EC) 2017/735, A.25.

GLP compliance:

no

Test material

Test material information

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 d_m

2) ionized form d_i

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