Title : Determination of alcohol using Gas Chromatography ( GC ). Instrument ( Model ) : Agilent Technologies 7820A ( GC System ) Detector : Flame Ionization Detector ( FID ) Mobile phase : Gas Stationary Phase : Liquid Column : HP-5 ( 5% Phenyl Methyl Siloxane ) Injection volume : 0.1 ml Standard : Standard mix ( butanol : methanol , 1 : 1 ) Sample : Methanol , Butanol , Unknown sample , standard mixture .
Introduction :
Gas chromatography is a process by which a mixture is separated into its constituents by a gas phase moving over a stationary phase. For a gas chromatograph (GC) is an analytical instrument that measures the content of various components in a sample. The analysis performed by a gas chromatograph is called gas chromatography. Typical uses of GC include testing the purity of a particular substance, or separating the different components of a mixture (the relative amounts of such components can also be determined). In some situations, GC may help in identifying a compound. In preparative chromatography, GC can be used to prepare pure compounds from a mixture. In gas chromatography, the mobile phase or moving phase is a carrier gas, usually an inert gas such as helium or an unreactive gas such as nitrogen. The stationary phase is a microscopic layer of liquid or polymer on an inert solid support, inside a piece of glass or metal tubing called a column (a homage to the fractionating column used in distillation). The instrument used to perform gas chromatography is called a gas chromatograph. The gaseous compounds being analysed interact with the walls of the column, which is coated with a stationary phase. This causes each compound to elute at a different time, known as the retention time of the compound. The comparison of retention times is what gives GC its analytical usefulness.
Gas chromatography is also similar to fractional distillation, since both processes separate the components of a mixture primarily based on boiling point (or vapour pressure) differences. However, fractional distillation is typically used to separate components of a mixture on a large scale, whereas GC can be used on a much smaller scale. Gas chromatography is also sometimes known as vapour-phase chromatography (VPC), or gas–liquid partition chromatography (GLPC). These alternative names, as well as their respective abbreviations, are frequently used in scientific literature. Strictly speaking, GLPC is the most correct terminology, and is thus preferred by many authors.
Objective : a) To determine retention time ( tr ) of the methanol and butanol. b) To identify the components present in a standard mixture based on the retention time. c) To identify the components present in an unknown sample.
Methods : A. Start Up the GC. 1. The computer was switch on. 2. The gas (CDA, Nitrogen , and Hydrogen ) was check , around 60-80 psi source pressures. 3. The carrier and the detector gases was turn on at their sources. 4. The GC power was turn on. 5. Then , double click Agilent 7820 AC Remote Controller . ( Automatic connects PC to GC ). Wait for Power on Successful to be displayed. 6. The EZ Chrom Elite >GC>OK was double click. 7. The method was load.
B. Running Methods from the Software Keypad. 1. Go to [ File ] → Method → Open → Method A CHM260. 2. Go to [Control ] > Download Method ( transfer the data from PC to GC ). 3. Go to [ Control ] > Instrument status : check the instrument (ready/not ready). 4. Wait for STATUS Ready for Injection to be displayed on GC Instrument. 5. The number of sample that we have was check. 6. Go to [ File ] → Sequence → Edit/New. 7. Follow the table below. Run
Status
Level
Conc override
Custom paramete r
Reps
Vial
Volume Etc. (ul)
1
1
201
2
1
201
Use method method
etc Etc
8. Go to [ File ] → Sequence →Save As → Write your File Name → Save. 9. The sample was prepare for injection. 10. The sample vial was load into the assigned location in the ALS turret. 11. Go to [ Control ] → Sequence Run → Start. 12. Wait until all the analysis complete. ( propanol, methanol , standard mixture & unknown .) 13. The analysis of standard mixture with METHOD B CHM260 was repeat . 14. Step 1-8 was repeated. The sample only standard mixture. 15. Wait until all the analysis complete. 16. The analysis of standard mixture with METHOD C CHM260 EDIT was repeated. 17. Step 1-8 was repeated. The sample only standard mixture. 18. Wait until all the analysis complete.
Results : Tabulate data obtained.
Table A : Table of standard and retention time for GC sample Standard / sample
Retention time (tR )
Methanol
0.440
Butanol
0.843
Unknown
0.440
Standard mixture
Butanol 1 0.770
Methanol :
1 0.437
Discussion: In this experiment, we need to determine of alcohol using gas chromatography by using sample Methanol , Butanol , Standard mixture , and unknown sample. There are few objectives that we must achieve on this experiment which is to determine retention time of
methanol and butanol, to identify the components present in a standard mixture based on the retention time and also to identify the components present in an unknown sample. The volatile compound can define are organic chemicals that have a high vapor pressure at ordinary room temperature. Their high vapor pressure results from a low boiling point, which causes large numbers of molecules to evaporate or sublimate from the liquid or solid form of the compound and enter the surrounding air. Retention time is the time required for a compound to come off the column (that is , the time it takes to travel from the injection chamber to the detector. ) We use methanol and butanol as sample. The boiling point for methanol is 148.5◦ F or 64.7◦ C. For the butanol is a 243.9◦F or 117.7 ◦ C .Gas chromatography (GC) is one of these techniques. It is estimated that 10-20% of the known compounds can be analysed by GC. To be suitable for GC analysis, a compound must have sufficient volatility and thermal stability. If all or some of the compound molecules are in the gas or vapour phase at 400-450◦ C or below, and they do not decompose at these temperatures, the compound can probably be analysed by GC. The detector for gas chromatography is a Flame Ionization Detector (FID). The FID is a suitable detector for GC because a carrier gas is required with a low water and oxygen impurities since water and oxygen can interact with the stationary phase and cause significant problems such as high baseline noise and column bleed in the output gas chromatogram which both reduces the analyser sensitivity and decreases column lifetime. The FID is also extremely sensitive to hydrocarbon impurities in the hydrocarbon and air supply for the flame. Hydrocarbon impurities can cause increased baseline noise and reduce the detector sensitivity. There are two types of column, packed and capillary (also known as open tubular). Packed column contain a finely divided, inert, solid support material (commonly based on diatomaceous earth) coated with liquid stationary phase. Most packed column are 1.5-10 m in length and have an internal diameter 0f 2 – 4mm.There are few factors which can increase the efficiency of a GC column. The selection of the proper capillary column for any application should be based on four significant factors which is stationary phase, column I.D, film thickness and column length.
Conclusion : For this experiment, it took about 40 minutes to finish the determination of alcohol. Gas chromatography is one most important tools in chemistry because of its simplicity, sensitivity and effectiveness in separating components of mixtures. It is widely used for
quantitative and qualitative analysis of mixtures and for the purification of compounds. Chromatography in general has another main branch which is liquid chromatography. It is a widely used separation technique using also sample partition between two phases a stationary phase of large surface area and a mobile liquid which percolates over the stationary bed. In contrast to Gas chromatography, traditional liquid chromatography is a rather slow technique taking hours and days to run a sample. We manage to do this experiment successfully with the helping from our lecturer. We also get to learn how to handle the instrument Agilent Technologies 7820A ( GC System ) correctly.
References : 1. AACC.,2000.Approved Methods of Analysis, 10th Edition. American Association of Cereal Chemists, St Paul,MN. 2. Bradley, R.L.,2003.Moisture and Total Solids Analysis, In Food Analysis,3rd Edition. Nielsen ,S.S.(ed.) New York: Kluwer Academic. 3. Brownsell, V.L., Griffith, C.J & Jones, E. 1985. Basic Science for Food Studies. London: Longman.
