John Siller
Laboratory 8
Supercritical Fluid Extraction
Introduction:
Supercritical fluid extraction (SFE) is a separation technique that utilizes the unique properties of
supercritical fluids at high temperatures and pressures. CO2 is the most common compound used as a
supercritical fluid to separate the extractant from the matrix. SFE can extract analytes from solid or
liquid matrices. Supercritical fluid chromatography (SFC) works similarly to SFE with the end product
than being analyzed by one of a variety of analytical instruments. SFC has a wide range of applications
from removing unwanted compounds from a matrix to extracting specific compounds for further use.
SFC has a number of advantages over other forms of extraction such as liquid extraction. In general SFC
is quicker than other extraction techniques and less product is lost or contaminated than in liquid
extraction. In this lab we used SFC to extract wax from wax paper. The final wax product was massed to
determine its content in wax paper and the efficiency of the extraction technique. We ran solo wax
through the SFC to determine its purity and efficiency of the system.
Method:
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Pack the column with glass wool (tightly for samples, loosely for cleaning)
Turn on the switches
Assure the valves are closed
Turn on the CO2
Set the parameters on the SFC
Open the inlet valve to bring CO2 to the column
Turn on the pump and wait 5-10 minutes
Turn off the pump and close the valves
To analyze samples pack column with steel wool and solid
Open the inlet and outlet valves
Allow enough time for separation and extraction
Once extraction is complete close all of the valves
Vent pressure before detaching the column.
Results:
The following table lists the starting mass of the wax/wax paper, the mass of the final product
extracted, and the percent mass of the product in the starting wax/wax paper. Out of the three wax
paper samples 2 had known concentrations while 1 had an unknown concentration. Calculations for this
data can be found in my lab notebook.
Sample
Starting Mass (g)
Final Mass (g)
% Mass
Wax 1
1.0111
0.6611
65.38 %
Wax 2
1.0007
0.593
59.26 %
Wax 3
1.0188
0.8002
78.54 %
Wax Paper A (unknown)
0.9437
0.4263
45.17 %
Wax Paper 2
0.9689
0.2307
23.81 %
Wax Paper 4
0.9522
0.2226
23.38 %
Table 1: Mass percent data for wax samples and wax paper knowns and unknown.
The results for the two known wax papers are higher than the reported 13.5 % and 16.4 %
concentrations written on the envelopes. This could be because the wax is heavier than the paper so it
accounts for a greater percentage to the mass than the paper. I’m not sure if the concentrations written
on the envelopes were % mass or concentration values. Either way the calculated values are closer than
the given values. This error could be due to the SFE not running for long enough to produce all of the
wax on the paper. Another possibility of error could be from other compounds being extracted along
with the wax that we were trying to extract. While the SFE was running I noticed that some product was
being lost out of the Erlenmeyer flask as it was coming out of the SFE. The Parafilm that was covering
the Erlenmeyer flask was loosened due to the pressure coming out of the SFC blowing the Parafilm up.
There was no way to collect all of the wax coming out of the SFE without the use of a very large
collection flask because the wax is being carried out by the supercritical fluid. When the wax comes out
it is being carried by gas and goes everywhere with the gas. The gas was reflecting off the bottom of the
Erlenmeyer flask and back up and out of the flask. When placing a microspatula near the opening the
amount of wax being lost was apparent by the buildup of wax on the microspatula.
Conclusion:
This lab was one of the best labs that we ran due to the simplicity and ease of running the SFE. It
was very interesting working with supercritical fluid, but caution had to be taken due to the high
temperatures needed to produce supercritical fluid. Thermally insulated gloves were worn when
handling and installing the column. Difficulty arose in trying to connect the column with the big heavy
gloves on, because there are small screws that need to be turned to secure the column. This difficulty
was not too bad however and it was still a relatively easy instrument to use. The SFE is a very useful
instrument when trying to extract certain organic analytes from solid and liquid matrices. When coming
up with our real world project one method we thought of was attempting to extract gunshot residue
from a solid soil matrix to analyze it with the AA, ICP, or XRF. Ultimately we were not able to do this
because there was no way of shooting into the ground at the indoor range where we shot our t-shirt
samples. It would be an interesting idea for future research projects and I am curious to see if it could be
a useful technique or if the elements that characterize gunshot residue could be extracted on the SFE.
The SFE is a nice instrument and I would not hesitate to use it again in any kind of research involving an
extraction technique.