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Dissociation constant

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Endpoint:
dissociation constant
Data waiving:
study technically not feasible
Justification for data waiving:
the study does not need to be conducted because the analytical method is not sensitive enough
other:
Endpoint:
dissociation constant
Type of information:
experimental study
Adequacy of study:
other information
Study period:
05MAY2010 - 12MAY2010
Reliability:
3 (not reliable)
Rationale for reliability incl. deficiencies:
unsuitable test system
Remarks:
The test concentration was not in line with OECD 112. The test method is not suited for UVCB substances.
Qualifier:
according to
Guideline:
OECD Guideline 112 (Dissociation Constants in Water)
Deviations:
no
GLP compliance:
no
Dissociating properties:
not determined

System check (20 °C):

KCl solution 0.01 mol/L, certified: 1380 - 1440 [µS/cm]

KCl solution 0.01 mol/L, measurement: 1410 [µS/cm]

Demineralized water: 0.2 [µS/cm]

Sample measurement (20 °C):

Sample, 17.7g / 200 mL: 136.8/136.5 [µS/cm]

Sample (dilution factor: 2): 69.7/69.5 [µS/cm]

Sample (dilution factor: 4): 35.8/35.9 [µS/cm]

Sample (dilution factor: 8): 18.2/18.3 [µS/cm]

Sample (dilution factor: 16): 9.419.5 [µS/cm]

Salt solution (20 °C):

NaCl (22.9 mg/L) + K2SO4 (0.5 mg/L) + CaCl2 x 2 H2O (1.3 mg/L): 51.3 [µS/cm]

The sample solution was analyzed for inorganic elements (ions) by Atomic Emission Spectrometry (ICP-OES). Significant amounts of the following elements where detected :

Sample solution : (17.7g / 200 mL)

Calcium (Ca): 0.35 mg/L = CaCl2 x 2 H2O: 1.3 mg/L

Sodium (Na): 9.0 mg/L = NaCl: 22.9 mg/L

Potassium (K): 0.25 mg/L = K2SO4: 0.5 mg/L

Additionally, the sample solution was analyzed for anions by Ion Chromatography (IC). Significant amounts of the following anions where detected :

Sample solution: (17.7g / 200 mL)

Chloride (Cl): 20 mg/L

Sulfate (SO4): 5 mg/L

Based on these concentrations the conductivity of a synthetic solution of NaCl, K2SO4 and CaCl2 in demineralized water was determined, such as:

Conductivity of salt solution: approx. 50 µS/cm

Conductivity of sample solution: approx. 140 µS/cm

The conductivity of the sample solution is partly caused from impurities (ions of the elements calcium , potassium, sodium and the anions sulfate and chloride). A new test item solution with a concentration of 1.03 g/L did still contain undissolved

particles. The conductivity measured in this solution was 2.5 µS/cm.

The conductivity caused from dissociated test item is too low to carry out the measurements of the dilution series for determination of the dissociation constant. Due to this fact the calculation of the dissociation constant was not possible.

Conclusions:
The conductivity of the sample solution is partly caused from impurities (ions of the elements calcium , potassium, sodium and the anions sulfate and chloride). The conductivity caused from dissociated test item is too low to carry out the measurements of the dilution series for determination of the dissociation constant. Due to this fact the calculation of the dissociation constant was not possible.

Description of key information

The dissociation constant(s) in water of the test substance could not be determined following the OECD 112 guideline. The test method is not suitable for UVCB substances. 

Key value for chemical safety assessment

Additional information

Attempts were made to determine the dissociation constant(s) of the substance in water, however the conductivity caused from dissociated test item is to low to carry out the measurements of the dilution series for determination of the dissociation constant. Due to this fact the calculation of the dissociation constant was not possible.