ANALYSIS OF HYDROCARBONS IN COMMON FUELS BY SOLID-PHASE MICROEXTRACTION (SPME) AND GAS CHROMATOGRAPHY- MASS SPECTROMETRY (GC-MS)

(EXPERIMENT 5) ANALYSIS OF HYDROCARBONS IN COMMON FUELS BY SOLID-PHASE MICROEXTRACTION (SPME) AND GAS CHROMATOGRAPHY- MASS SPECTROMETRY (GC-MS) NAME:

MOHAMAD NOR AMIRUL AZHAR BIN KAMIS

STUDENT ID:

2014647344

PARTNERS’ NAMES: 1.

MOHAMAD HAMIZAN BIN MOHD ISA

2.

MOHAMAD SHAFIQ BIN PARMAN

3.

MOHAMAD AZMIZAM BIN MOHAMAD NOOR

DATE OF EXPERIMENT: DATE OF SUBMISSION:

8/12/2014

INTRODUCTION: Solid-phase microextraction is a sample preparation technique that use fibre coated with extracting phase that extract different kinds of analytes for different fibre coating. The analytes can be in the form of liquid or gas either volatile or not. In this experiment, head space SPME is used where the fibre is exposed in the vapour phase above a gaseous sample. Head space SPME is suitable for the analysis of volatile organic compounds, and it is important to keep the headspace volume constant and keep the fibre position at the same depth for every analysis. The amount of analyte extracted by the fibre depends on the concentration of the analyte in the sample as long as equilibrium reached. After the extraction process was done, the fibre is transferred to the injection port of GC where desorption of the analyte takes place and the separation occur. The factors that affect the SPME performance are the coating material, thickness of fibre, sample agitation, sample pH, salt addition and the extraction procedure. The objective of this experiment is to identify the major hydrocarbons components in common fuels (diesel, petrol, thinner and an unknown) by using SPME-GC-MS.

EXPERIMENTAL: a. Instrument set-up: Injector temperature: 250˚C Detector temperature: 300˚C Carrier gas flow rate: 30mL/s Column temperature: 60˚C to 170˚C at 10˚C/min b. SPME procedure: 1. The fibre (100μm polydimethylsiloxane (PDMS)) was conditioned in the GC injector port for 10 minutes at 250˚C to remove any contaminants. 2. Diesel sample in a vial at 50˚C was heated constantly while the fibre was exposed to the headspace of the vial for 20 minutes.

3. The fibre was withdraw into the needle and was pulled out from the vial and was immediately injected into the GCMS with desorption time of 80 seconds. 4. Step 1 until 3 were repeated for petrol, thinner and an unknown sample. 5. Petrol sample was run for 15 minutes and thinner sample was run for 10 minutes, while the unknown sample was run for 25 minutes depending on the completion of separation. 6. By using the mass spectra library, the major compounds (4 spots) in each sample were identified.

RESULT AND DISCUSSION: A. Major compounds presence in petrol sample: Retention time, Area, % Quality min 2.57 16.95 90

Compound Benzeneacetamide

3.83

17.41

97

p-xylene

5.25

8.34

94

Benzene,1-ethyl-3methyl-

5.78

10.69

97

Benzene,1,2,3trimethyl-

B. Major compounds in diesel sample: Retention Area, % Quality time, min 8.94 5.60 93

Compound Dodecane

12.16

11.32

95

Naphthalene,1,4dimethyl-

13.01

5.23

97

Pentadecane

14.41

4.85

97

Hexadecane

C. Major compound in thinner sample: Retention time, Area, % min 2.54 100

Quality

Compound

91

Toluene

D. Compounds of unknown that match with compound in petrol: Retention time, Area, % Quality Compound min 5.21 6.91 93 Benzene,1-ethyl3-methyl-

5.73

9.89

93

Benzene,1,2,3trimethyl-

E. Compounds of unknown that match with compound I diesel: Retention Area, % Quality Compound time, min 8.94 5.44 94 Dodecane 12.17

7.38

94

Naphthalene,1,4dimethyl-

13.01

8.96

96

Pentadecane

From the analysis done, 4 major compounds presence in petrol sample are benzeneacetamide, p-xylene, benzene,1-ethyl-3-methyl-, and benzene,1,2,3trimethyl- that lie from retention time of 2 minutes to 11 minutes of analysis. Diesel sample show the trend of major compound peaks from 8 minutes to 15 minutes that correspond to dodecane, naphthalene,1,4-dimethyl-, pentadecane and hexadecane based on the mass spectra library.

It is outstanding result for the analysis of thinner that shows only one peak that is the toluene peak at 2.54 minutes with 100% area at 91 qualities. The unknown sample analysis shows that the unknown sample is the combination of diesel and petrol based on the similarities of some of the major compounds presence in diesel and petrol. The major compounds presence in the unknown are benzene,1-ethyl-3-methyl- and benzene,1,2,3-trimethyl- that is also presence in petrol while dodecane, naphthalene,1,4-dimethyl-, and pentadecane presence in diesel. There is a retention time that is presence in thinner and the unknown that at 2.54 minutes, but since the quality is lower that is 64, the assumption cannot be made because it has the possibilities to be other compounds. The advantages of using SPME is that the extraction is simple and fast, also can be done without any solvents. If the samples are properly stored, it can be analysed days later without much loss of volatiles.

CONCLUSION: The major compounds presence in petrol are benzeneacetamide, p-xylene, benzene,1-ethyl-3-methyl-, and benzene,1,2,3-trimethyl-. The major compounds presence in diesel are dodecane, naphthalene,1,4-dimethyl-, pentadecane and hexadecane. Thinner only show a single peak that corresponds to toluene. It can be concluded that the unknown sample is the mixture of diesel and petrol since there are some major compounds of diesel and petrol presence in the unknown.

REFERENCES: 1. Nor’ashikin S., Ruziyati T., Mardiana S. (2012), Analytical Separation Methods Laboratory Guide (2nd edition), 3/10/2014. 2. Solid-Phase Microextraction, 29/10/2014, http://en.wikipedia.org/wiki/Solid-phase_microextraction. 3. Mardiana Saaid, 29/10/2014, SPME sample preparation notes.