A simple and brief presentation on the phenol coefficient with a video explanation of the test procedure.

1. PHENOL COEFFICIENT
Prepared By Rahit Singha
BMLT, MSc. Microbiology

2. INDEX
 INTRODUCTION
 DEFINITION OF PHENOL COEFFICIENT
 WHAT IS PHENOL COEFFICIENT
 CALCULATION OF PHENOL COEFFICIENT
 PHENOL COEFFICIENT TEST
 RIDEAL WALKER METHOD
 CHICK MARTIN TEST
 FACTORS AFFECTING PHENOL COEFFICIENT TEST
 CONCLUSION
 REFERENCES

3. INTRODUCTION
 Chemical disinfectants are categorized based on the power of their disinfection
for microbes and viruses. Strong disinfectants can kill fungi, vegetative cells, endospores,
and pathogens. Extended use of disinfectants can result in sterilization. Intermediate-level
disinfectants are less effective against certain viruses and endospores. Low-level
disinfectants are ineffective against endospores and can kill some enveloped viruses and
vegetative cells. The measure of the power of disinfection is required to appropriately suggest
the application of a particular disinfectant. The effectiveness of chemical disinfectants can be
measured using different methods, such as qualitative suspension test, quantitative
suspension test, Dilution test, Kelsey Sykes test, surface time kill test, etc. The phenol
coefficient is one of the methods to determine the effectiveness of a disinfectant.

4. DEFINITION OF PHENOL COEFFICIENT
 The measure of the disinfecting power of a substance, determined by dividing the figure indicating
the degree of dilution of the disinfectant that kills a microorganism within a given time by that
indicating the degree of dilution of phenol killing the microorganism under similar conditions.
 The number obtained by dividing the degree of dilution of test disinfectant by the degree of dilution
of phenol in a certain span of time.

5. • If the number is greater than 1, it
means that for given dilution, the
test disinfectant is more powerful
and can kill germs better than
phenol. If the number obtained is
less than 1, it means that for the
given dilution, phenol is better at
controlling germs

6. WHAT IS PHENOL COEFFICIENT
 Phenol is an aromatic compound and a carboxylic acid whose formula is C6H6O. Its structure is shown in
the figure below:
Figure :Structure of phenol

7. WHAT IS PHENOL COEFFICIENT
 Phenol is recognized as one of the oldest antiseptic agents with excellent antifungal and antibacterial
properties. At concentrations of 0.1 % to 1 %, it is bacteriostatic. At higher concentrations (from 1% to 2%),
2%), phenol is fungicidal and bactericidal. Phenol can kill Anthrax spores (which cause severe skin lesions,
lung infections, and intestine diseases) at 5% concentration within 48 hours.
 Although phenol has excellent antiseptic properties, it is not used as a common antiseptic due to its
systemic toxicity on the skin. Death can result from oral ingestion in significant quantities. Thus phenol is
used for comparison of the power of disinfection of other disinfectants such as chlorine, ozone, hydrogen
peroxide, etc.

8. CALCULATION OF PHENOL COEFFICIENT
 Phenol coefficient is a number obtained by dividing dilution ratio test disinfectant with the dilution ratio of
phenol under predetermined conditions.
 For instance, suppose phenol diluted to 1 part in 100 parts of diluent (1/100) is able to kill an organism in 10
minutes. Another disinfectant is diluted 1 part in 500 parts diluent (1/500) is able to kill organisms at the same
time. So the phenol coefficient can be calculated as follows:
 Thus, the phenol coefficient is 5. It means that the test disinfectant is stronger than phenol in terms of
disinfection.
Figure : Calculation of phenol coefficient

9. PHENOL COEFFICIENT TEST
 Two types of phenol coefficient tests are done:
1. Rideal Walker method for phenol coefficient determination
2. Chick Martin test

10. RIDEAL WALKER METHOD
 In 1903, Rideal Walker proposed a method to determine the power of a disinfectant in comparison with
phenol.

11. RIDEAL WALKER METHOD
 The phenol coefficient can be calculated as:
 The limitation of the Rideal Walker method is that it does not account for the presence of
any organic matter. Moreover, the time for disinfection testing is too short. This test is used only to
determine the power of phenolic type disinfectants only.

12. CHICK MARTIN TEST
 Chick martin test incorporates the presence of organic matter as the test is not carried out in the
water but yeast suspension or 4% dried human feces. The total time of the test is 30 minutes.
Both S. typhi and S. aureus cultures are used to test the efficacy of disinfectants. The calculation
method is the same as that Rideal Walker test.

13. FACTORS AFFECTING PHENOL
COEFFICIENT TEST
 Four major factors affect the disinfectants and thus produce wrong results for phenol coefficient
tests. These factors are temperature, pH, surface activity, and the presence of interfering
substances. An increase in temperature has shown increased disinfectant properties. Optimal
growth is achieved at pH between 6 to 8; thus, the recommended pH for the tests is 7.5. The
surface-active compounds in low concentrations may increase the disinfectant power. Interfering
substances such as certain salts may hinder disinfectant activity

14. CONCLUSION
 The phenol coefficient tests are designed specifically for determining the disinfection power of
phenol-like disinfectants. However, it has been observed that the phenol coefficient is used for
other purposes for which it is not applicable. Some chemicals whose structure and properties are
completely different from phenol but are germicides (such as chlorine, picric acid, hydrogen
peroxide, formalin, iodine, etc.) have been compared with phenol. In some cases, water-insoluble
compounds are compared with phenol either in their pure form or diluted in other kinds of
solvents. Such misuse of phenol coefficient creates confusion. It is also not recommended to use
phenol coefficient for testing antiseptics because antiseptics are not used to kill Bacillus
typhosus usually used in phenol tests. Different antiseptics kill different bacteria with varying
antiseptic power. One example is tincture iodine, which is 760 times more disinfecting compared to
5 % phenol solution. However, in reality, tincture iodine is not 760 times more germicidal than 5 %
phenol in practical conditions.

15. References
• Chem.Purdue. (2019). Phenol. Retrieved June 21, 2021, from
https://www.chem.purdue.edu/jmol/molecules/phenol.html
• Lakomia, L. & Fong, E. (1999). Microbiology for health careers. Albany, NY: Delmar Publishers.
• Ononugbo, C., Reward, E., & Ike, A. (2018). The Effect of pH and Temperature on Phenol
Coefficients of Two Common Disinfectants Using Clinical Isolates of Escherichia coli and
• Staphylococcus aureus. Journal of Advances in Microbiology, 10(2), 1–7.
https://doi.org/10.9734/jamb/2018/41376
• Reddish, G. F. (1937). Limitations of the Phenol Coefficient. Industrial and Engineering Chemistry,
29(9), 1044–1047. https://doi.org/10.1021/ie50333a017

16. THANK YOU