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Diss Factsheets

Physical & Chemical properties

Dissociation constant

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Administrative data

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Reference
Endpoint:
dissociation constant
Type of information:
experimental study
Adequacy of study:
key study
Study period:
From 2018-01-29 to 2018-03-30
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 112 (Dissociation Constants in Water)
Deviations:
no
GLP compliance:
yes
Specific details on test material used for the study:
Batch No.: 20170707
Purity: 99.13%
Dissociating properties:
yes
No.:
#1
pKa:
9.23
Temp.:
20 °C
Remarks on result:
other: pH 8-10
No.:
#2
pKa:
2.39
Temp.:
20 °C
Remarks on result:
other: pH 1-3
 pH Range  pH of solution

Absorbance (A)

  pKa  Mean ± SD
                

Replicate #1

Ai = 0.712

Au = 0.979

  8.53  0.946 9.38     9.23 ± 0.10
 8.77  0.901 9.15
 9.14  0.869 9.29
9.39   0.828 9.28
9.60 0.787  9.19
10.17 0.733 9.10
                

Replicate #2

Ai = 0.509

Au = 0.847

  1.38 0.821 2.46 2.39 ± 0.04
 1.63 0.797 2.39
 1.91 0.759 2.36
 2.33  0.682  2.35
 2.77  0.605  2.37
 3.26  0.552 2.42 
Conclusions:
The dissociation constant of this substance is 9.23 at pH 8-10, the dissociation constant is 2.39 at pH 1-3.
Executive summary:

The dissociation constant of the test substance was determined using the Spectrophotometric method according to OPPTS 830.7370 and OECD TG 112. This method is applicable to test substances which have appreciably different ultraviolet-visible (UV-vis) absorption spectra for the ionized and unionized forms. It may also be suitable for low solubility compounds and for non-acid/base dissociation (e.g. complex formation).

The test was carried out at a 20°C temperature. The absorbance and pH from each spectrum was tabulated. Six values for the pKa were calculated from the intermediate data points, and the mean and standard deviation of these results was calculated.

The dissociation constant of this substance is 9.23 at pH 8-10, the dissociation constant is 2.39 at pH 1-3.

Description of key information

The dissociation constant of this substance is 9.23 at pH 8-10, the dissociation constant is 2.39 at pH 1-3.

Key value for chemical safety assessment

pKa at 20°C:
9.23

Additional information