Extraction and Identification of Organic Molecules from
Orange Peels
--- Using GC/MS --References Partially adapted from:
McKenzie, L. C.; Thompson, J. E.; Sullivan, R.; Hutchison, J. E. Journal of Green
Chemistry, 2004, 6, 355-358
www.wikipedia.org (components of orange oil and descriptions)
Objective
The purpose of this laboratory is to use separation techniques to extract organic
molecules from orange peels and use gas chromatography with mass spectroscopy
(GC/MS) to detect emissions of volatile organic compounds
Background
Orange oil, which can be extracted from orange peels, is composed of variety of organic
compounds which are part of the terpene family, shown below:
H3C
CH3
CH3
CH3
CH3
H3C
H3C
CH3
a-pinene
C10H16
136.23 g/mol
HO CH3
H3C
sabinene
C10H16
136.23 g/mol
myrcene
C10H16
136.23 g/mol
CH3
CH3
CH3
CH3
O
geranial
C10H18O
152.24 g/mol
O
citronellal
C10H18O
154.25 g/mol
CH3
H3C
CH3
H3C
linalool
C10H18O
154.25 g/mol
CH3
limonene
C10H16
136.23 g/mol
CH3
H3C
neral
C10H18O
154.25 g/mol
O
Many of the components are found in the rinds of a variety of citrus fruits and are responsible
for the smell of oranges and lemons. Orange oil has been used to rid a house of termites as an
alternative to other pesticides.
The individual components also have a variety of uses:

-Pinene is also found in coniferous trees, namely the pine tree, as well as rosemary and
is used as a fragrance.

Sabinene is one of the chemical compounds that contributes to the spiciness of black
pepper and is a major constituent of carrot seed oil, as well as nutmeg and tea tree oil.

Myrcene is another important chemical used for fragrances, and as an intermediate for
other flavor and fragrance chemicals.

Limonene is used in food manufacturing (flavor, for example), medicine, and as
precursors to other chemical compounds. It is also recently found use in “green”
cleaning products: since limonene is a hydrocarbon, it can be used to remove oil and
grease. Its abundance in the rinds of citrus fruits provides a renewable source, since the
rinds are considered ‘waste’ by most food manufacturers. Medicinally, limonene may be
a chemopreventative agent, and significant research is underway to determine it’s anticancer activity.

Linalool is used as a fragrance in many perfumed household products including soaps,
detergents, shampoos, and lotions. It can also be used as a flea and cockroach insecticide.
Other research shows that the oil can reduce stress.

Citronellal can be used as an insect repellent, and as the name suggests, is one of the
components found in citronella candles used outdoors in the summer to repel
mosquitoes.

Geranial and neral are structurally related: they are connected the same but differ in
their double bond geometry. Geranial has a strong lemon odor, while neral has a lemon
odor that is less intense, but sweeter. The combination is used for fragrance and flavor.
Many of these compounds have similar structures and identical molar masses. One tool that
can be used to tell the difference between these is a Gas Chromatograph/Mass Spectrometer.
Gas chromatography is a technique used to separate and analyze compounds. The technique
relies on the boiling points of the components. A sample is injected into the instrument, where
the components are vaporized and carried by an inert gas through a column (helium, in our
case), which is usually tightly packed with a polymer or solid support (stationary phase). The
different components will come out in order of boiling point, with the more volatile (lower
boiling) components eluting first.
In the case of a GC/MS instrument, each of the now separated components will then travel to
the mass spectrometer, where each compound is ionized to form positively charged particles,
which are then accelerated by the presence of a magnetic field in a curved tube; as the ions
travel through the tube, the angle at which they bend differs depending on the mass of the ion.
The charge to mass ratio can be determined based on where the ions hit the detector. Also,
when molecules are ionized and accelerated through the instrument, they can fragment into
smaller pieces; this fragmentation is often unique to the molecule and is related to the molecular
structure. In the case of molecules with the same molecular mass, the fragmentation pattern can
help identify which compound is present because the unique pattern of peaks observed in the
mass spectrum can be compared to authentic mass spectrum patterns for identification.
Apparatus
125 mL Erlenmeyer flasks ( x 2)
200 mL beaker ( x 1)
Scoopula
Paper Towels
Glass funnel
Filter paper
Pasteur pipets with bulb
Kimwipes
Autosampler GC vial with cap
Chemicals
Orange
Sodium sulfate
Dichloromethane
Procedure
1. Each team will need a ~quarter of the peels from one orange. Peel the orange.
2. Use the edge of a scoopula to scrape the white parts of the rind away and discard (Keep
the orange part of the rind); when this is done, the orange color should be visible on
both sides of the rind and you should be able to see some of the pores.
3. Tear the orange rind into small pieces (~ dime size). Put the peels into a 125 mL
Erlenmeyer flask.
4. Measure 50 mL of dichloromethane into a graduated cylinder and add it to the flask.
5. Swirl the rinds for ~ 2 minutes. The solvent should turn a pale yellow.
6. Place the flask onto a hot plate and heat it until the mixture starts boiling. Allow the
mixture to boil for ~ 5 min, swirling occasionally.
7. Allow the mixture to cool.
8. Fold a piece of filter paper as your instructor will show you and place it into a glass
funnel. Filter the mixture and collect the filtrate in another 125 mL flask.
9. Add a small amount of Na2SO4 to the liquid. This is a drying agent that is used to
remove water from the organic solvent and it clumps when it absorbs water. Swirl the
flask. If you have a significant amount of clumped solid, add another scoop. After ~ 5
minutes, if the drying agent is freely moving when swirled, move on to the next step. If
not, continue adding and swirling until it is dry.
10. Filter again as you did in step 8 to remove the Na2SO4.
11. Obtain a GC vial from your instructor. Using a sharpie marker, label it with your names
or initials.
12. Filter your sample through a Kimwipe into the vial, and bring it to the GC for analysis.
Post-Lab Report
The GC/MS will deliver a GC spectrum indicating different peaks for different components,
as well as corresponding mass spectrum for each of the peaks. Tape the spectrum into your
notebook. You should compare your mass spectrum with those known (see attached) and
indicate which of the compounds you see in your sample. Then, answer the questions in
your lab notebook.
Post-Lab Questions
1. Would you classify the sample you injected into the GC/MS as a pure element, pure
compound, homogeneous mixture or heterogeneous mixture? Explain your reasoning.
2. Briefly but clearly explain what happens in the GC component of the instrument when
the sample is injected. What gas is constantly flowing through the GC (this is called the
mobile phase)? Why is this specific gas used rather than using good old fashion “air”?
3. Provide an explanation of what happens to the sample when it travels through the MS
component of the instrument. Why are all the peaks obtained in MS due to cations even
if the injected sample was not ionic?
4. Describe in general what is plotted in a GC spectrum. Your description should include
what is plotted along the x- and y axis.
5. Describe in general what is plotted in a MS spectrum. Your description should include
what is plotted along the x- and y axis.
6. For the most abundant compound detected, what was its “elution time”? In the MS
spectra label the “parent peak” or “molecular ion peak”. Why is this peak useful?
7. Look up the percentages for the major components of orange oil. How do they orange
oil components compare with the spectrum you obtained from the experiment?
8. Draw a Lewis structure of limonene. Indicate the molecular geometry around each
carbon and the hybridization of each carbon. Indicate number of  and  bonds.
9. Is limonene polar or non-polar? Explain. Is linalool polar or non polar? Explain
10. We used dichloromethane to extract the components from the orange peels. We also
could have used hexane or pentane. However, using water would not be as effective.
Explain why.
11. Indicate which you would expect to have a higher boiling point, and briefly explain
why. You may check your choices by checking their bp online.
Limonene or myrcene? Sabinene or myrcene? Myrcene or linalool? Linalool or
geraniol?
12. In class, we talked about how the structure and shape of molecules has an effect their
uses and properties. Do you recognize any trends with the components of orange oil?
Explain.