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Dissociation constant

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Reference
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
Qualifier:
according to guideline
Guideline:
EPA OPPTS 830.7370 (Dissociation constants in water)
GLP compliance:
yes
Dissociating properties:
no

- The only difference in each overlay is the absorbance level at approximately 249 nm at each pH level. This difference is attributable to dilution effect in making pH adjustments (as expected, the pH adjusted spectrum provides the lowest absorption in each figure) .

- The principal requirements for determining a pKa by UV-vis are that the test material should absorb ultraviolet or visible light and that the absorption of the ion should differ from that of the molecule in wavelength and intensity (preferably both). The overlays indicate that the test material exhibits neither a wavelength difference across the pH range 2-10, nor does it exhibit an

absorbance difference due to ionisation. The test material does not demonstrate pKa activity by UV-vis absorption technique .

- The sharp inflection on the representative potentiometric titration (pHvs. mL, NaOH titrant) plot at approximately 10 mL is due to the expected HCl: NaOH (strong acid:strong base) equivalence point. No other inflections are evident. The reverse plot from approximately pH 2 to approximately pH 12 showed only the same expected matrix inflection and no other evident inflections. The duplicate test material solutions exhibited the same response. The absence of inflections other than matrix would indicate

that the test material does not exhibit pKa activity by potentiometric titration.

- The titrants, 0.1 N NaOH and 0.1 N HCI, were each checked prior to use. Inflections were noted within 10 ± 0.02 mL versus 10.00 mL theoretical.

- No pKa activity was observed for the test material. Differences in UV spectra were found to irreversible, and titrations revealed

only one expected matrix (strong acid/strong base) inflection and no observable inflections due to the test material.

Conclusions:
Under the conditions of this study, no pKa activity was observed for the test material.
Executive summary:

The dissociation constant of the test material was investigated in accordance with the standardised guideline OPPTS 830.7370, under GLP conditions.

Under the conditions of this study, no pKa activity was observed for the test material.

Description of key information

Under the conditions of this study, no pKa activity was observed for the test material.

Key value for chemical safety assessment

Additional information

The dissociation constant of the test material was investigated in accordance with the standardised guideline OPPTS 830.7370, under GLP conditions. The study was awarded a reliability score of 1 in accordance with the criteria set forth by Klimisch et al. (1997).

Under the conditions of this study, no pKa activity was observed for the test material.