Isotherm Analysis in Phenol Solution Using Granular Activated
Carbon and High Performance Liquid Chromatography
Abstract:
Varying quantities of phenol stock and granular activated carbon were measured into eight
tubes for analysis using High Performance Liquid Chromatography. Isotherm equations were
then used to calculate two lines of best fit compared to the Cs isotherm curve found using the
HPLC method. The purpose of the lab was to determine whether the solution behaved like a
Freundlich Isotherm or a Langmuir Isotherm. In conclusion, we found that the solution behaved
like both Isotherms, and that more data points would make the results more conclusive in
future experiments.
Introduction:
Sorption is a very important property in the world of chemistry. Different types of sorption and
different rates of sorption can affect the transport and degradation of many molecules in the
environment. (Rodenburg, 2008) Sorption isotherms are what we use to describe the
equilibrium partitioning between sorbed and desorbed phases for these particles in question.
(Rodenburg, 2008) Two such relationships that can arise from equilibrium partitioning are
known as Freundlich isotherms and Langmuir isotherms. (Rodenburg, 2008) For this experiment
we utilized a High Performance Liquid Chromatograph to analyze the samples of phenol for their
sorptive properties.
HPLC utilizes a liquid mobile phase to separate the
components of a mixture. These analytes are first dissolved in
a solvent, and then forced to flow through a chromatographic
column under a high pressure. In the column, the mixture is
resolved into its components. The amount of resolution is
important, and is dependent upon the extent of interaction
between the solute components and the stationary phase. (Rodenburg, 2008)
Therefore, our purpose is to use HPLC, the Freundlich equations, and the Langmuir equations to
determine the identity of the isotherm in the samples.
Procedure:
We began this procedure on November 21st, 2008 at approximately 10am.
We first made a stock solution for the experiment using 0.0508g GAC/500mL of Phenol. We then
created eight solutions with varying concentrations of GAC sorbate in order to determine a
relationship between concentrations. The after measuring the standard solutions (containing 5,
10, 25, 50, and 100mg/L stock) using HPLC, we then measured the eight sample solutions for
their areas using the HPLC. The area of the standards was graphed and the slope and intercept
were used to determine the Cw and Cs for the samples. 1/Cw was plotted against 1/Cs to get
the Langmuir isotherm relationship and the log Cs was plotted against log Cw in order to get the
Freundlich isotherm relationship.
Equations used:
Freundlich Equation:
Linearization:
Log Cis = nLog Ciw + Log KiF
Langmuir Equation:
Linearization:
Cis = KiF * Cniw
Cis 
max  K iL  Ciw
1  K iL  Ciw
 1
1 
1
1



Cis  Cis,max  K iL  Ciw Cis,max
Results:
Graph I: Freundlich Linearization
We used this linearization to find “n”, which was the slope of the line, and to find log KF, which
was the intercept. With these values, we were able to predict Cs using the Freundlich equation.
Graph II: Langmuir Linearization
We used this linearization to find Csmax, which was 1/intercept, and to find KL, which was equal
to (1/slope)/ Csmax. With these values, we were able to predict Cs using the Langmuir equation.
Graph III: Sample Curve Experimental Data
This curve shows the relationship of Cs vs. Cw for the samples used in HPLC. Sample bottle #8
was exempt from the graphing.
Graph IV: Comparing Freundlich vs. Langmuir vs. Cs
This graph shows the relationship between the experimental curve and the calculated
Freundlich and Langmuir curves. The experimental Cs curves exhibits traits from both calculated
isotherm types.
Conclusion:
Based on our results, we find that the identity of the sorption isotherm remains inconclusive.
The Langmuir isotherm relationship works well for the low concentrations, however the results
afterwards were more closely related to the Freundlich isotherm. It may be possible that there
were sources of error in the HPLC. But regardless of propagated error, there needs to be more
data points to observe, especially at higher Cw levels. This should help make future
experimental results more concise and comprehendable. Due to the inconclusive nature of our
results, we did not achieve our purpose for this lab.
References:
Rodenburg, L. Introduction to Chromatography. Lecture. 2008.
Rodenburg, L. Sorption to organic matter. Power Point Presentation. 2008.
Acknowledgements:
I would like to thank Professor Rodenburg, and her assistant Jia for helping the class with this
experiment.