OECD Guideline for the Testing of Chemicals, 112 

Dissociation Constants in Water 

AUTHORS: 

Raymond L. Van Hoven, Ph.D. 

Frank J. Lezotte, B.S. 

Willard B. Nixon, Ph.D. 

STUDY INITIATION DATE: September 8, 2005 

STUDY COMPLETION DATE: October 6, 2005 

8598 Commerce Drive 

Easton, Maryland 21601 USA 

(410) 822-8600 

Page 1 of 25 
GOOD LABORATORY PRACTICE COMPLIANCE STATEMENT 

This study was conducted in compliance with Good Laboratory Practice Standards as published by 

the U.S. Environmental Protection Agency in 40 CFR Parts 160 and 792, August 17, 1989 and OECD 

Principles of Good Laboratory Practice, (ENV/MC/CHEM (98) 17), with the following exception: 

Test substance characterization and stability under storage conditions at the test site were not 

determined in accordance with Good Laboratory Practice Standards. 

STUDY DIRECTOR: \ 

/c>-6- 36- 

DATE 

Chemist 

SPONSOR APPROVAL: 

Sponsor's Representative DATE 
Wildlife httemati~nal, Ltd. Project Number 523~-113 

QUALITY ASSURANCE STATEMENT 

This study was examined for compliance with Good Laboratory Practice Standards as published by 

the U.S. Environmental Protection Agency in 40 CFR Parts 160 and 792, August 17, 1989 and OECD 

Principles of Good Laboratory Practice (ENV/MC/CHEM (98) 17). The dates of all inspections and audits 

and the dates that any findings were reported to the Study Director and Laboratory Management were as 

follows: 

DATE REPORTED TO: 

ACTIVITY: DATE CONDUCTED: STUDY DIRECTOR: MANAGEMENT: 

Protocol August 9,2005 August 10,2005 August 17,2005 

Sample Preparation September 9, 2005 September 9,2005 September 13,2005 

Raw Data and Draft Report September 28-29,2005 September 29,2005 October 5, 2005 

Final Report October 6, 2005 October 6,2005 October 6, 2005 

All inspections were study-based unless otherwise noted. 

# (-!! 

, io-6-og 

J&es H. Coleman 

- 

DATE 

Quality Assurance Representative 
-4 - 

REPORT APPROVAL 

SPONSOR: Infineurn USA, L.P. 

TITLE: 

WILDLIFE NTERNATIONAL, LTD. PROJECT NUMBER: 523C-113 

STUDY DIRECTOR: 

/3- 6-05 

 rank J. &od, BS. DATE 

Chemist 

MANAGEMENT: 

Willard B. Nixon, ~h.d DATE 

Director of Chemistry 
Wildlife International, Ltd. Project Number 523C-113

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TABLE OF CONTENTS 

Title/Cover Page ..................................................................................................................................... 1 

Good Laboratory Practice Compliance Statement .................................................................................. 2 

Quality Assurance Statement.................................................................................................................. 3 

Report Approval ..................................................................................................................................... 4 

Table of Contents.................................................................................................................................... 5 

Summary................................................................................................................................................. 7 

Introduction ............................................................................................................................................ 8 

Objective................................................................................................................................................. 8 

Experimental Design .............................................................................................................................. 8 

Materials and Methods............................................................................................................................ 8 

Test Substance................................................................................................................................ 8 

Reference Standard......................................................................................................................... 8 

Solvents and Reagents.................................................................................................................... 9 

Stock Preparation............................................................................................................................ 9 

Test Procedure................................................................................................................................ 9 

Results .................................................................................................................................................. 10 

Conclusions .......................................................................................................................................... 10 

References ............................................................................................................................................ 11 
- 6 - 

TABLE OF CONTENTS 

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TABLES 

Table 1 Typical Operating Parameters for Automatic Titrator ................................................ 12 

Table 2 pK Values of 

 

 

 
SUMMARY 
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INTRODUCTION

Tests were performed to determine the dissociation constant of the test substance in water at 20oC. 

This study was conducted by 

 

 
 

 

 
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was degassed with nitrogen to remove carbon dioxide prior to use. Each sample was equilibrated to 

20±1°C in a water bath then transferred into a beaker. The samples were then titrated against standardized 

0.001 N NaOH. At least ten incremental additions were made before the equivalence point and the 

titration was carried out past the equivalence point. Values of pK were calculated for a minimum of ten 

points on the titration curve. The dissociation constant (Ka) and pKa were determined as follows: 

 pKa = pH – log([B]/[HB]) 

 Antilog (-pKa) = Ka

 where pH = pH of test solution at any point 

 [B] = concentration of ionized species 

 [HB] = concentration of unionized species 

 

RESULTS 

The calculated pK value for 4-nitrophenol is summarized in Table 2, and a representative plot of the 

titration curve is presented in Figure 1. The pKa value for 4-nitrophenol was 7.15 at 20.0°C. The 

reference substance result was in good agreement with the literature value. 

The calculated pK values for the test substance are summarized in Table 2, and a representative plot 

of a titration curve is presented in Figure 2. The mean pKa value was 4.38 (SD = 0.0341, CV = 0.779%) at 

20±1°C. Representative titration data and pKa calculations for the test substance are summarized in Table 

3 

CONCLUSIONS 

The pKa value of the test substance was determined to be 4.38 (SD = 0.0341, CV = 0.779%) at 

20±1°C. 
3

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REFERENCES 

1. Organisation for Economic Cooperation and Development. 1981. Guideline for Testing of 

Chemicals, 112: Dissociation Constants in Water. 

2. Product Properties Test Guidelines. 1996. OPPTS 830.7370. Dissociation Constants in 

Water.

3. American Society for Testing and Materials. 1991. Standard Specification for Reagent Water. 

 D1193-91, ASTM Section II Water and Environmental Technology, Vol. 11.01:45-47. 

4. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
 

 

 
 
 

Appendix 1 

Protocol 



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Appendix 2 

Personnel Involved in the Study 

m

 1. Willard B. Nixon, Ph.D., Director of Chemistry 

2. Raymond L. Van Hoven, Ph.D., Scientist 

3. Frank J. Lezotte, B.S., Chemist