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EC number: 240-539-0 | CAS number: 16484-77-8
Partition coefficient
Administrative data
Link to relevant study record(s)
- Endpoint:
- partition coefficient
- Type of information:
- experimental study
- Adequacy of study:
- key study
- Study period:
- 02 February 1999 to 22 June 1999
- Reliability:
- 1 (reliable without restriction)
- Rationale for reliability incl. deficiencies:
- guideline study
- Qualifier:
- according to guideline
- Guideline:
- OECD Guideline 107 (Partition Coefficient (n-octanol / water), Shake Flask Method)
- Deviations:
- no
- Qualifier:
- according to guideline
- Guideline:
- EU Method A.8 (Partition Coefficient - Shake Flask Method)
- Deviations:
- no
- Qualifier:
- according to guideline
- Guideline:
- EPA OPPTS 830.7550 (Partition Coefficient, n-octanol / H2O, Shake Flask Method)
- Deviations:
- no
- GLP compliance:
- yes
- Type of method:
- HPLC method
- Partition coefficient type:
- octanol-water
- Analytical method:
- high-performance liquid chromatography
- Key result
- Type:
- Pow
- Partition coefficient:
- 156
- Temp.:
- 20 °C
- pH:
- 4
- Key result
- Type:
- Pow
- Partition coefficient:
- 0.64
- Temp.:
- 20 °C
- pH:
- 7
- Key result
- Type:
- Pow
- Partition coefficient:
- 0.23
- Temp.:
- 20 °C
- pH:
- 10
- Details on results:
- Measured partition coefficient results were:
pH 4 buffer solution; Pow = 156, log10Pow = 2.19
pH 7 buffer solution; Pow = 0.64, log10Pow = -0.19
pH 10 buffer solution; Pow = 0.23, log10Pow = -0.64 - Conclusions:
- Under the conditions of the study the partition coefficient of the test material was found to be 156 (log10 Pow = 2.19) in pH 4 buffer solution, 0.64 (log10 Pow = -0.19) in pH 7 buffer solution, and 0.23 (log10 Pow = -0.64) in pH 10 buffer solution.
- Executive summary:
The partition coefficient of the test material was assessed according to OECD Test Guideline 107 and EU Method A.8. and in compliance with GLP using the HPLC method.
Since the test material is an ionisable compound, the partition coefficient of the test material was determined in buffer solutions at pH 4, 7 and 10.
Measured volumes of test material in n-octanol (saturated with water) were shaken with measured volumes of each buffer solution (saturated with n-octanol) for 5 minutes. The mixtures were centrifuged (2 000 rpm) for 5 minutes at 20 °C, then equilibrated for 80 minutes at 20 °C and the phases separated.
The concentrations of test material in the n-octanol phases were determined by UV/visible spectrophotometry, following dilution of aliquots (1 mL) of the samples with n-octanol (20 mL).
The concentrations of test material in the aqueous phases were determined by high performance liquid chromatography (HPLC). The aqueous phases were either analysed directly (in the case of the pH 4 samples) or following dilution of aliquots (1 mL) of the samples with mobile phase (10 mL for the pH 7 samples, 20 mL for the pH 10 samples).
The pH values of the remaining aqueous phases were measured.
Under the conditions of the study the partition coefficient of the test material was found to be 156 (log10 Pow = 2.19) in pH 4 buffer solution, 0.64 (log10 Pow = -0.19) in pH 7 buffer solution, and 0.23 (log10 Pow = -0.64) in pH 10 buffer solution.
- Endpoint:
- partition coefficient
- Type of information:
- experimental study
- Adequacy of study:
- key study
- Study period:
- 11 April 1990 to 20 August 1990
- Reliability:
- 1 (reliable without restriction)
- Rationale for reliability incl. deficiencies:
- guideline study
- Qualifier:
- according to guideline
- Guideline:
- OECD Guideline 107 (Partition Coefficient (n-octanol / water), Shake Flask Method)
- Deviations:
- no
- Qualifier:
- according to guideline
- Guideline:
- EU Method A.8 (Partition Coefficient - Shake Flask Method)
- Deviations:
- no
- Qualifier:
- according to guideline
- Guideline:
- other: EPA FIFRA Subdivision D § 63-11
- Deviations:
- no
- GLP compliance:
- yes
- Type of method:
- flask method
- Partition coefficient type:
- octanol-water
- Analytical method:
- high-performance liquid chromatography
- Key result
- Type:
- log Pow
- Partition coefficient:
- 2.2
- Temp.:
- 20 °C
- pH:
- 4
- Key result
- Type:
- log Pow
- Partition coefficient:
- -0.391
- Temp.:
- 20 °C
- pH:
- 7
- Key result
- Type:
- log Pow
- Partition coefficient:
- -0.776
- Temp.:
- 20 °C
- pH:
- 9
- Details on results:
- It can be seen from the results that as one approaches the pKa value of the test material (PKa = 2.50) there is a greater tendency for the test material to partition into the n-octanol phase and this reflects the quantity of undissociated the test material.
The partition of undissociated the test material at pH 4, 7 and 9 are presented, but as the levels of undissociated the test material are not significant at pH 9 the errors involved in the calculation would be large. - Conclusions:
- Under the conditions of the study the measured partition coefficient (log10 Kow) between octanol and water was found to be 2.20 (pH 4), -0.391 (pH 7) and -0.776 (pH 9) at 20 °C.
- Executive summary:
The partition coefficient (log10 Kow) between octanol and water was assessed according to OECD guideline 107, EU Method A8 (flask method) and EPA FIFRA Subdivision D § 63 -11 and in compliance with GLP.
Values of log10 Kow for undissociated and dissociated forms of the test material were calculated by the Leo and Hansch procedure.
Determination of the partition coefficient of the test material was also carried out at 20 °C by shaking measured volumes of pH 4, 7 or 9 buffer solutions (saturated with n-octanol) with measured volumes of a solution in n-octanol (saturated with the appropriate buffer solution) of the test material (2.1 g/L). After shaking the two phases for approximately 2 minutes the samples were transferred to centrifuge tubes and equilibrated at 20 °C for 2 days. The samples were then centrifuged (2 500 rpm for 2 minutes at 20 °C), the phases separated and the pH of an aliquot of each of the aqueous phases measured.
Aliquots (1 mL) of each of the pH 7 and 9 buffer solutions were separately diluted to volume (100 mL and 200 mL respectively) with mobile phase. These solutions, together with the undiluted pH 4 buffer solutions, were analysed for the test material content by HPLC/UV analysis.
Aliquots (1 mL) of each of the n-octanol phases were separately diluted with portions (10 mL) of methanol, then diluted to volume (100 mL, 50 mL and 100 mL for n-octanol phases equilibrated with pH 4, 7 and 9 buffer solutions respectively) with mobile phase. These solutions were then analysed for the test material content by HPLC/UV analysis.
It can be seen from the results that as one approaches the pKa value of the test material (PKa = 2.50) there is a greater tendency for the test material to partition into the n-octanol phase and this reflects the quantity of undissociated the test material.
The partition of undissociated the test material at pH 4, 7 and 9 are presented, but as the levels of undissociated the test material are not significant at pH 9 the errors involved in the calculation would be large.
Under the conditions of the study the measured partition coefficient (log10 Kow) between octanol and water was found to be 2.20 (pH 4), -0.391 (pH 7) and -0.776 (pH 9) at 20 °C.
- Endpoint:
- partition coefficient
- Type of information:
- experimental study
- Adequacy of study:
- supporting study
- Study period:
- July to August 1991
- Reliability:
- 2 (reliable with restrictions)
- Rationale for reliability incl. deficiencies:
- guideline study without detailed documentation
- Qualifier:
- according to guideline
- Guideline:
- OECD Guideline 107 (Partition Coefficient (n-octanol / water), Shake Flask Method)
- Deviations:
- no
- GLP compliance:
- yes
- Type of method:
- HPLC method
- Partition coefficient type:
- octanol-water
- Analytical method:
- high-performance liquid chromatography
- Type:
- Pow
- Partition coefficient:
- >= 3.04 - <= 3.1
- Temp.:
- 25 °C
- pH:
- >= 2.36 - <= 2.44
- Details on results:
- The test material has a Pow of 3.10 and 3.04 respectively at 25 °C (room temperature). The Pow mean value is 3.07 and the corresponding Kow is 1175. The accuracy ranges s of the Pow values are 0.21 and 0.23 respectively.
Calculation of Pow at Different pH Values
The Pow and the Kow respectively are defined for nonionisable substances. In order to calculate the Pow of the nonionised acid or the Pow at other pH values, the PKa was used in the following equation:
Equation 6: Pows = Powe + lg [l0(pH - pKa) + 1]
Pows = Pow of the not ionised acid
Powe = Experimental determined Pow at experimental pH
pKa = Logarithm of the dissociation constant
The pH values under HPLC-conditions were 2.36 and 2.44 respectively. The PKa of the active ingredient is 3. 68.
The Pow at other pH values can be calculated by equation 7:
Equation 7: Pow = Pows - lg [l0(pH - pKa) + 1]
The mean value of Pows is 3.09 and the calculated Pow at pH 7 is -0.23. - Conclusions:
- Under the conditions of the study the test material has a Pow average of 3.07. The corresponding partition coefficient Kow is 1175. Under neutral conditions of pH 7 the Pow can be calculated to be -0.23.
- Executive summary:
The partition coefficient was assessed according to OECD test guideline 107 and in compliance with GLP.
The regression line of Pow = f(lg k') of eight reference substances, was used to determine the Pow value of the test material by linear interpolation. RP18-HPLC was used to receive the k' values. With the effluent mixture of methanol/ water/ lN H2SO4 = 550: 450: 10 the Pow was 3.10 at 25 °C (room temperature). With the mixture of methanol/ water/ lN H2SO4 = 600: 400: 10 the Pow was 3.04 at 25 °C (room temperature). The accuracy ranges s were 0.21 and 0.23 respectively.
Under the conditions of the study the test material has a Pow average of 3.07. The corresponding partition coefficient Kow is 1175. Under neutral conditions of pH 7 the Pow can be calculated to be -0.23.
Referenceopen allclose all
The calibration for the UV/visible spectrophotometric analysis was found to be linear over the range 0 to 120 mg/L of standard solutions in n-octanol with a regression coefficient of 0.9998.
The calibration for the HPLC analysis was found to be linear over the range 0 to 162 mg/L of standard solutions in mobile phase with a regression coefficient of 1.0000.
Standard Calibration for the Test Material by UV/Vis Spectrophotometry
Standard Concentration (mg/L) |
Absorbance |
7.525 |
0.063 |
15.05 |
0.127 |
30.10 |
0.245 |
60.20 |
0.494 |
90.30 |
0.762 |
120.4 |
0.990 |
Linear regression (including x = 0, y = 0)
y = 0.00828x + 0.000172
r = 0.9998
x = Concentration
y = Absorbance
Standard Calibration for the Test Material by HPLC.
Standard Concentration (mg/L) |
Peak Area |
10.10 |
147.7 |
20.19 |
291.2 |
40.38 |
574.6 |
80.76 |
1148 |
121.1 |
1724 |
161.5 |
2300 |
Linear regression (including x = 0, y = 0)
y = 14.2x + 1.75
r = 1.0000
x = Concentration
y = Peak area
Determination of the Partition Coefficient of the Test Material between n-Octanol and pH 4 Buffer Solution
Sample |
A |
B |
C |
D |
E |
F |
n-Octanol volume (mL) |
15 |
15 |
20 |
20 |
10 |
10 |
Compound in n-octanol (mg/L) |
2125 |
2144 |
2144 |
2134 |
2122 |
2101 |
Total compound in n-octanol (mg) |
31.9 |
32.2 |
42.99 |
42.7 |
21.2 |
21.0 |
Buffer volume (mL) |
15 |
15 |
10 |
10 |
20 |
20 |
Compound in the buffer (mg/L) |
13.63 |
13.63 |
13.77 |
13.74 |
13.47 |
13.69 |
Total compound in buffer (mg) |
0.204 |
0.204 |
0.138 |
0.137 |
0.269 |
0.274 |
Total compound added (mg) |
34.8 |
34.8 |
46.5 |
46.5 |
32.2 |
23.2 |
Total compound recovered (mg) |
32.1 |
32.4 |
43.0 |
42.8 |
21.5 |
21.3 |
pH of aqueous phase after partition |
4.02 |
4.00 |
4.00 |
4.01 |
3.98 |
3.98 |
Pow |
156 |
157 |
156 |
155 |
158 |
153 |
Log10Pow |
2.19 |
2.20 |
2.19 |
2.19 |
2.20 |
2.19 |
Mean Log10Pow = 2.19
Standard deviation = 0.004
Determination of the Partition Coefficient of the Test Material between n-Octanol and pH 10 Buffer Solution
Sample |
A |
B |
C |
D |
E |
F |
n-Octanol volume (mL) |
15 |
15 |
20 |
20 |
10 |
10 |
Compound in n-octanol (mg/L) |
465.7 |
439.1 |
716.8 |
699.9 |
243.5 |
258.0 |
Total compound in n-octanol (mg) |
6.99 |
6.59 |
14.3 |
14.0 |
2.44 |
2.58 |
Buffer volume (mL) |
15 |
15 |
10 |
10 |
20 |
20 |
Compound in the buffer (mg/L) |
1949 |
1925 |
3361 |
3339 |
1049 |
1052 |
Total compound in buffer (mg) |
29.2 |
28.9 |
33.6 |
33.4 |
21.0 |
21.0 |
Total compound added (mg) |
34.8 |
34.8 |
46.5 |
46.5 |
23.2 |
23.0 |
Total compound recovered (mg) |
36.2 |
35.5 |
47.9 |
47.4 |
23.4 |
23.6 |
pH of aqueous phase after partition |
9.53 |
9.55 |
9.22 |
9.21 |
9.73 |
9.76 |
Pow |
0.239 |
0.228 |
0.213 |
0.210 |
0.232 |
0.245 |
Log10Pow |
-0.622 |
-0.642 |
-0.671 |
-0.679 |
-0.634 |
-0.610 |
Mean Log10Pow = -0.643
Standard deviation = 0.027
UV/Visible Spectrophotometric Analysis of n-Octanol Phases from pH 4 Test
Sample |
Absorbance |
CA (mg/L) |
Dilution Factor |
CB (mg/L |
n-Octanol A |
0.880 |
106.2 |
20 |
2125 |
n-Octanol B |
0.888 |
107.2 |
20 |
2144 |
n-Octanol C |
0.888 |
107.2 |
20 |
2144 |
n-Octanol D |
0.884 |
106.7 |
20 |
2134 |
n-Octanol E |
0.879 |
106.1 |
20 |
2122 |
n-Octanol F |
0.870 |
105.0 |
20 |
2101 |
UV/Visible Spectrophotometric Analysis of n-Octanol Phases from pH 7 Test
Sample |
Absorbance |
CA (mg/L) |
Dilution Factor |
CB (mg/L |
n-Octanol A |
0.357 |
43.09 |
20 |
861.7 |
n-Octanol B |
0.364 |
43.93 |
20 |
878.6 |
n-Octanol C |
0.584 |
70.49 |
20 |
1410 |
n-Octanol D |
0.570 |
68.80 |
20 |
1376 |
n-Octanol E |
0.177 |
21.35 |
20 |
427.0 |
n-Octanol F |
0.171 |
20.63 |
20 |
412.5 |
UV/Visible Spectrophotometric Analysis of n-Octanol Phases from pH 10 Test
Sample |
Absorbance |
CA (mg/L) |
Dilution Factor |
CB (mg/L |
n-Octanol A |
0.913 |
23.28 |
20 |
465.7 |
n-Octanol B |
0.182 |
21.96 |
20 |
439.1 |
n-Octanol C |
0.297 |
35.84 |
20 |
716.8 |
n-Octanol D |
0.290 |
35.00 |
20 |
699.9 |
n-Octanol E |
0.101 |
12.17 |
20 |
243.5 |
n-Octanol F |
0.107 |
12.90 |
20 |
258.0 |
HPLC Analysis of pH 4 Buffer Phases
Sample |
Peak Area |
Cc (mg/L) |
Dilution Factor |
CD (mg/L) |
20.19 mg/L std |
290.8 |
- |
- |
- |
Aqueous A |
196.4 |
13.63 |
1 |
13.63 |
Aqueous B |
196.5 |
13.63 |
1 |
13.63 |
Aqueous C |
198.4 |
13.77 |
1 |
13.77 |
20.19 mg/L std |
291.1 |
- |
- |
- |
Aqueous D |
197.6 |
13.74 |
1 |
13.74 |
Aqueous E |
193.9 |
13.47 |
1 |
13.47 |
Aqueous F |
197.0 |
13.69 |
1 |
13.69 |
20.19 mg/L std |
289.8 |
- |
- |
- |
HPLC Analysis of pH 7 Buffer Phases
Sample |
Peak Area |
Cc (mg/L) |
Dilution Factor |
CD (mg/L) |
121.1 mg/L std |
1732 |
- |
- |
- |
Aqueous A |
1913 |
133.6 |
10 |
1336 |
Aqueous B |
1883 |
131.5 |
10 |
1315 |
Aqueous C |
2282 |
159.4 |
10 |
1594 |
121.1 mg/L std |
1736 |
- |
- |
- |
Aqueous D |
2271 |
158.5 |
10 |
1585 |
Aqueous E |
1308 |
91.29 |
10 |
912.9 |
Aqueous F |
1317 |
91.92 |
10 |
919.2 |
121.1 mg/L std |
1735 |
- |
- |
- |
HPLC Analysis of pH 10 Buffer Phases
Sample |
Peak Area |
Cc (mg/L) |
Dilution Factor |
CD (mg/L) |
121.1 mg/L std |
1735 |
- |
- |
- |
Aqueous A |
1395 |
97.44 |
20 |
1949 |
Aqueous B |
1378 |
96.24 |
20 |
1925 |
Aqueous C |
2506 |
168.0 |
20 |
3361 |
121.1 mg/L std |
1733 |
- |
- |
- |
Aqueous D |
2388 |
167.0 |
20 |
3339 |
Aqueous E |
750.2 |
52.46 |
20 |
1049 |
Aqueous F |
752.1 |
52.06 |
20 |
1052 |
121.1 mg/L std |
1731 |
- |
- |
- |
pH |
Measured Log10 Kow |
Equivalent Kow |
Log10 Kow (Undissociated Test Material) |
Equivalent Kow |
4 |
2.20 |
158.1 |
3.72 |
5216 |
7 |
-0.391 |
0.406 |
3.72 |
5232 |
9 |
-0.776 |
0.167 |
*5.56 |
*360861 |
*The level of undissociated test material is not significant at pH 9 and thus the error in this calculation would be large.
Mobile Phase: Methanol/ Water (Millipore) / Sulfuric acid 1 N = 550: 450: 10
Flow rate: 2.0 mL / min
pH- Wert: 2.36
Pressure: 200 bar
Temperature: 25 °C (room temperature)
Substance |
Tr |
Tt |
K’ |
Log K’ |
Po/w |
P/ow (b) |
Delta |
Test material |
7.77 |
0.59 |
10.261 |
1.0112 |
|
3.10 |
|
Anisole |
3.36 |
0.69 |
3.870 |
0.5877 |
2.10 |
2.35 |
-0.25 |
Methylbenzoate |
3.29 |
0.68 |
3.838 |
0.5841 |
2.12 |
2.34 |
-0.22 |
1-Napthole |
3.55 |
0.69 |
4.145 |
0.6175 |
2.71 |
2.40 |
0.31 |
2,3 – Dichloroaniline |
4.15 |
0.68 |
5.103 |
0.7078 |
2.78 |
2.56 |
0.22 |
Chlorobenzene |
6.61 |
0.68 |
8.721 |
0.9406 |
2.84 |
2.98 |
-0.14 |
Benzophenone |
7.98 |
0.69 |
10.565 |
1.0239 |
3.18 |
3.13 |
0.05 |
Thymole |
8.29 |
0.69 |
11.014 |
1.0419 |
3.30 |
3.16 |
0.14 |
1,4 – Dichlorobenzene |
12.33 |
0.68 |
17.132 |
1.2338 |
3.38 |
3.50 |
-0.12 |
Accuracy range s = 0.21
Regression function was calculated from the log k'-values and Pow-values.
Powb = slope x log k' + Pow-axis intercept
e.g. (Anisole): 2.35 = 1.782 x 0.5877 + 1.301
Slope m = 1.782
Pow-axis intercept b = 1.301
Corr. Coefficient r = 0.9041
The measured values (Tr and Td) are mean values of two injections (one injection was available)
Tr = Retention time (minutes)
Td = Dead time
Pow = Value from literature
Powb = Value calculated from the regression function
Delta = Pow - Powb
k' = (Tr - Td) / Td ; capacity factor of the substance in the given HPLC-system
Mobile Phase: Methanol/ Water (Millipore) / Sulfuric acid 1 N = 600: 400: 10
Flow rate: 2.0 mL / min
pH- Wert: 2.44
Pressure: 179 bar
Temperature: 25 °C (room temperature)
Substance |
Tr |
Tt |
K’ |
Log K’ |
Po/w |
P/ow (b) |
Delta |
Test material |
4.59 |
0.68 |
5.750 |
0.7597 |
|
3.04 |
|
Anisole |
2.50 |
0.68 |
2.676 |
0.4275 |
2.10 |
2.41 |
-0.31 |
Methylbenzoate |
2.38 |
0.68 |
2.500 |
0.3979 |
2.12 |
2.35 |
-0.23 |
1-Napthole |
2.43 |
0.68 |
2.574 |
0.4106 |
2.71 |
2.38 |
0.33 |
2,3 – Dichloroaniline |
2.86 |
0.68 |
3.206 |
0.5060 |
2.78 |
2.56 |
0.22 |
Chlorobenzene |
4.40 |
0.68 |
5.471 |
0.7381 |
2.84 |
3.00 |
-0.16 |
Benzophenone |
4.79 |
0.67 |
6.149 |
0.7888 |
3.18 |
3.10 |
0.08 |
Thymole |
4.96 |
0.68 |
6.294 |
0.7989 |
3.30 |
3.12 |
0.18 |
1,4 – Dichlorobenzene |
7.48 |
0.68 |
10.000 |
1.000 |
3.38 |
3.50 |
-0.12 |
Accuracy range s = 0.23
Regression function was calculated from the log k'-values and Pow-values.
Powb = slope x log k' + Pow-axis intercept
e.g. (Anisole): 2.41 = 1.901 x 0.4275 + 1.597
Slope m = 1.901
Pow-axis intercept b = 1.597
Corr. Coefficient r = 0.8773
The measured values (Tr and Td) are mean values of two injections (one injection was available)
Tr = Retention time (minutes)
Td = Dead time
Pow = Value from literature
Powb = Value calculated from the regression function
Delta = Pow - Powb
k' = (Tr - Td) / Td ; capacity factor of the substance in the given HPLC-system
Calculation of Pows and Pow at pH 7 for the Test Material
Powe |
pH |
pKa |
Pows |
Pow at pH 7 |
3.10 |
2.36 |
3.68 |
3.12 |
-0.20 |
3.04 |
2.44 |
3.68 |
3.06 |
-0.26 |
Mean values = |
3.09 |
-0.23 |
||
Powe = Experimentally determined Pow (Powb)
Pows = Pow of the not ionised acid
pKa = - Logarithm of the dissociation constant
Description of key information
Comb (2000b)
Under the conditions of the study the partition coefficient of the test material was found to be 156 (log10 Pow = 2.19) in pH 4 buffer solution, 0.64 (log10 Pow = -0.19) in pH 7 buffer solution, and 0.23 (log10 Pow = -0.64) in pH 10 buffer solution.
O'Connor (1990)
Under the conditions of the study the measured partition coefficient (log10 Kow) between octanol and water was found to be 2.20 (pH 4), -0.391 (pH 7) and -0.776 (pH 9) at 20 °C.
Supporting Study: Redeker (1991)
Under the conditions of the study the test material has a Pow average of 3.07. The corresponding partition coefficient Kow is 1175. Under neutral conditions of pH 7 the Pow can be calculated to be -0.23.
Key value for chemical safety assessment
- Log Kow (Log Pow):
- -0.19
- at the temperature of:
- 20 °C
Additional information
Comb (2000b)
The partition coefficient of the test material was assessed according to OECD Test Guideline 107 and EU Method A.8. and in compliance with GLP using the HPLC method. The study was awarded a reliability score of 1 in accordance with the criteria set forth by Klimisch et al. (1997).
Since the test material is an ionisable compound, the partition coefficient of the test material was determined in buffer solutions at pH 4, 7 and 10.
Measured volumes of test material in n-octanol (saturated with water) were shaken with measured volumes of each buffer solution (saturated with n-octanol) for 5 minutes. The mixtures were centrifuged (2 000 rpm) for 5 minutes at 20 °C, then equilibrated for 80 minutes at 20 °C and the phases separated.
The concentrations of test material in the n-octanol phases were determined by UV/visible spectrophotometry, following dilution of aliquots (1 mL) of the samples with n-octanol (20 mL).
The concentrations of test material in the aqueous phases were determined by high performance liquid chromatography (HPLC). The aqueous phases were either analysed directly (in the case of the pH 4 samples) or following dilution of aliquots (1 mL) of the samples with mobile phase (10 mL for the pH 7 samples, 20 mL for the pH 10 samples).
The pH values of the remaining aqueous phases were measured.
Under the conditions of the study the partition coefficient of the test material was found to be 156 (log10 Pow = 2.19) in pH 4 buffer solution, 0.64 (log10 Pow = -0.19) in pH 7 buffer solution, and 0.23 (log10 Pow = -0.64) in pH 10 buffer solution.
O'Connor (1990)
The partition coefficient (log10 Kow) between octanol and water was assessed according to OECD guideline 107, EU Method A8 (flask method) and EPA FIFRA Subdivision D § 63 -11 and in compliance with GLP. The study was awarded a reliability score of 1 in accordance with the criteria set forth by Klimisch et al. (1997).
Values of log10 Kow for undissociated and dissociated forms of the test material were calculated by the Leo and Hansch procedure.
Determination of the partition coefficient of the test material was also carried out at 20 °C by shaking measured volumes of pH 4, 7 or 9 buffer solutions (saturated with n-octanol) with measured volumes of a solution in n-octanol (saturated with the appropriate buffer solution) of the test material (2.1 g/L). After shaking the two phases for approximately 2 minutes the samples were transferred to centrifuge tubes and equilibrated at 20 °C for 2 days. The samples were then centrifuged (2 500 rpm for 2 minutes at 20 °C), the phases separated and the pH of an aliquot of each of the aqueous phases measured.
Aliquots (1 mL) of each of the pH 7 and 9 buffer solutions were separately diluted to volume (100 mL and 200 mL respectively) with mobile phase. These solutions, together with the undiluted pH 4 buffer solutions, were analysed for the test material content by HPLC/UV analysis.
Aliquots (1 mL) of each of the n-octanol phases were separately diluted with portions (10 mL) of methanol, then diluted to volume (100 mL, 50 mL and 100 mL for n-octanol phases equilibrated with pH 4, 7 and 9 buffer solutions respectively) with mobile phase. These solutions were then analysed for the test material content by HPLC/UV analysis.
It can be seen from the results that as one approaches the pKa value of the test material (PKa = 2.50) there is a greater tendency for the test material to partition into the n-octanol phase and this reflects the quantity of undissociated the test material.
The partition of undissociated the test material at pH 4, 7 and 9 are presented, but as the levels of undissociated the test material are not significant at pH 9 the errors involved in the calculation would be large.
Under the conditions of the study the measured partition coefficient (log10 Kow) between octanol and water was found to be 2.20 (pH 4), -0.391 (pH 7) and -0.776 (pH 9) at 20 °C.
Supporting Study: Redeker (1991)
The partition coefficient was assessed according to OECD test guideline 107 and in compliance with GLP. The study was awarded a reliability score of 2 in accordance with the criteria set forth by Klimisch et al. (1997).
The regression line of Pow = f(lg k') of eight reference substances, was used to determine the Pow value of the test material by linear interpolation. RP18-HPLC was used to receive the k' values. With the effluent mixture of methanol/ water/ lN H2SO4 = 550: 450: 10 the Pow was 3.10 at 25 °C (room temperature). With the mixture of methanol/ water/ lN H2SO4 = 600: 400: 10 the Pow was 3.04 at 25 °C (room temperature). The accuracy ranges were 0.21 and 0.23 respectively.
Under the conditions of the study the test material has a Pow average of 3.07. The corresponding partition coefficient Kow is 1175. Under neutral conditions of pH 7 the Pow can be calculated to be -0.23.
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