Experiment:

Experiment: Date:

Gas Chromatography: Acetates10/27/15

NamePartnersDrawer No.Course / Section

Katheryn SotoN/A#21CHEM 315/204

Purpose:

The purpose of this experiment is to identify an unknown organic compound based on its retention time via gas chromatography and calculate the molar percentage of compounds in a mixture based on their relative peak areas.

Approach:

Using the gas chromatograph, Obtain a chromatogram for a standard equimolar solution of four esters (Ethyl acetate, Propyl acetate, Butyl acetate, and Pentyl acetate) and determine the retention times for each compound. Obtain a second chromatogram for an unknown mixture of the aforementioned esters and determine the retention times for each compound. Calculate the peak areas for each chromatogram. Using the values collected from the standard equimolar solution; adjust the peak area values of the unknown solution for thermal response. Calculate the total area from adjusted area values. Calculate mole fraction for each ester present in the unknown solution. Calculate mole percentage for each compound from the mole fraction.

References

Text Pavia, D.L., Lampman, G.M., Kriz, G.S., Engel, .G.R., 2011, Introduction to Organic Laboratory Techniques, A Small Scale Approach, GMU Edition, Chem 315/318, Cengage Learning: pp. 817-836

Slayden, S., Stalick, W., Roth, R, 2014, Organic Chemistry Laboratory Manual, 2nd Edition: Pearson Custom Publishing: pp. 51-54

Web Site URL

Dr Schornicks Website: http:/mason.gmu.edu/~jschorni/gaschromatography

Unknown or Synthesized Compound

Ethyl acetate, 141-78-6, CRC Handbook of Chemistry & Physics, 84th Edition, Lide, D.R., Editor-in-chief, 2003-2004, CRC Press, p 3-250, 4871.

Propyl acetate, 109-60-4, CRC Handbook of Chemistry & Physics, 84th Edition, Lide, D.R., Editor-in-chief, 2003-2004, CRC Press, p 3-468, 9203.

Butyl acetate, 123-86-4, CRC Handbook of Chemistry & Physics, 84th Edition, Lide, D.R., Editor-in-chief, 2003-2004, CRC Press, p 3-80, 1487.

Pentyl acetate, 628-63-7, CRC Handbook of Chemistry & Physics, 84th Edition, Lide, D.R., Editor-in-chief, 2003-2004, CRC Press, p 3-440, 8662.

Proc # 1Gas ChromatographyResultsUnk No.B

MaterialsEquipmentInstrument ReadingsInjection port temp.

120oC

Column temp.

120oC

Detector temp.

120oC

Chart Speed25.0mm/minGas flow rate

10 mL/min (He @ 7PSI)Moving liquid phase

Supelco Carbowax 20m, 6 ftObservations: Acetone was not used to rinse the syringe to prevent residual/incorrect readings.

Complete reading of compound took approximately 5 minutes.

2L Standard ether sample

2L Unknown ether sample Gas chromatography microsyringe

Desc:

Begin a new chromatogram.

Rinse the microsyringe several times with the sample solution.

Insert the syringe into the sample solution and raise and depress the plunger several times to remove any air bubbles from the syringe.

Load the microsyringe with a small amount of sample (2L). Insert the syringe into the chromatograph port through the rubber septum. Quickly inject the sample and withdraw the syringe from the port Wait approximately 5 minutes to allow the sample to be analyzed. Print resulting chromatogram. Rinse the syringe with the sample solution several times.

Repeat steps with additional samples.

Equation Setup:

Proc # 2Retention TimeResults

MaterialsEquipmentChart Speed = 25.0mm/min

Retention Times Standard Solution

Peak

Distance (mm)Retention Time (min)

C2

37.01.48C3

45.51.82C4

64.02.56C5

94.53.78R.T.C2 = 37.0 / 25.0 = 1.48R.T.C3 = 45.5 / 25.0 = 1.82R.T.C4 = 64.0 / 25.0 = 2.56R.T.C5 = 94.5 / 25.0 = 3.78Retention Times Unknown Solution

Peak

Distance (mm)

Retention Time (min)

C2------C3

46.01.84C4

68.52.74C5

---

---

R.T.C3 = 46.0 / 25.0 = 1.84R.T.C4 = 68.5 / 25.0 = 2.74

Calculator

Desc:

Computed from the chart speed and the distance on the chart from the time of injection to the point on the chart when the perpendicular line drawn from the maximum pen deflection intersects the base line. Mark starting point on chart (t = 0)

Draw vertical line from peak top to base line

Measure distance from starting point to each peak.

Equation Setup:

Where v = velocity, d = distance, and t = time:

Therefore, where t= retention time:

Proc # 3Peak AreaResults

MaterialsEquipmentPeak Areas-Standard SolutionPeakHeight (mm)(mm)Peak Area (mm2)C2176588C31716103C41497104C51328106AreaC2 = 176 * 5 = 880AreaC3 = 171 * 6 = 103AreaC4 = 149 * 7= 104AreaC5 = 132 * 8 = 106

AreaC3 = 59 * 6 = 35Peak Areas-Unknown Solution

Peak

Height (mm)

(mm)Peak Area (mm2)C2

000C3

59635C4

97

768C5

000AreaC4 = 97 * 7 = 68

Chromatographs for known and unknown solutions Ruler Calculator

Desc:

Measure the height of the peak (in mm.) from the baseline

Measure the width of the peak at half the height Multiply the two measurements to determine the peak areas.

Equation Setup:

Where h = peak height from baseline and = width of peak at the peak height:

Proc # 4Adjusted Peak AreasResults

MaterialsEquipment*It is assumed that the unknown mixture is missing Ethyl acetate (C2) and Propyl acetate (C3) will be used for the basis of the calculations.Adjusted Peak AreaC3

C4

C5

Standard

Peak Area (mm2)

103

104

106

TRs/TRi=As/Ai (s=C2 )

1.001.011.03Unknown

Peak Area (mm2)

35

68

0

A1/As(s=C2)

1.001.960

Standard Solution:TR3 = AreaC3/ AreaC3 = 103 / 103 = 1.00TR4 = AreaC4 / AreaC3 = 104 / 103 = 1.01TR5 = AreaC5 / AreaC3 = 106 / 103 = 1.03Unknown Solution:AAC3 = (35 / 35) * 1.00 = 1.00AAC4= (68 / 35) *1.01 = 1.96

Calculator

Desc:

Thermal response factors (TR) are computed as ratios of the areas of one peak in the known mixture (base peak) to the area of each of the other peaks in the mixture There must be at least two similar compounds in the known and unknown mixtures

TR values will be calculated from the areas under the peaks in the standard equimolar mixture.

Equation Setup:

Where s refers to the base peak (ethyl acetate), I refers to the number of carbons in each component in the mixture, area refers to the peak area measured, and TR refers to the thermal response factor:

AA= Adjusted Area

Proc # 5Total Peak Area Results

MaterialsEquipmentTotal Peak Area

EtAc (2)

ProAc (3)

BuAc (4)

PtAc (5)

A1/As(s= 2)

01.001.960

= 2.96

Calculator

Desc:

The areas of gas chromatogram peaks are proportional to the molarity of the compound. Varying thermal conductivity based on the structure and substituent groups of different compound causes deviations in this relationship Determined from the adjusted peak areas and add them to determine the total peak area

Equation Setup:

Add adjusted peak area values calculated for each of the components of the solution to determine the total peak area.

Proc # 6Mole FractionResults

MaterialsEquipmentMole Fraction: Unknown

1.00 / 2.960.338

1.96 / 2.960.662

Calculator

Desc:

Computed by dividing the individual adjusted peak areas by the sum of the adjusted peak areas in the chromatogram.

Equation Setup:

Where areai represents a component of the mixture and represents the adjusted total peak area:

Proc # 7Mole PercentResults

MaterialsEquipmentMole Percent

Mole FractionMole %ProAc

0.338x 100 =33.8BuAc

0.662x 100 =66.2

Calculator

Desc:

Computed by multiplying the Mole fraction values by 100. Represents the percentage of moles of a component that is present in a compound.

Equation Setup:

Summary of Results:

The injection port temperature was 120 oC. The column temperature was 120oC. The detector temperature was 120oC. The gas flow rate was 10mL/min. The chart speed was 2.5cm/min. The moving liquid phase was SUPELCO CARBOWAX 20m, 6ft. The retention times for the standard ester solution were as follows: C2=1.5; C3=1.8; C4=2.6; C5=3.8. The retention times for the unknown ester solution were as follows: C3=1.8; C4=2.7. The peak areas for the standard ester solution were as follows: C2=8.80; C3=10.3; C4=10.4; C5=10.6. The peak areas for the unknown ester solution were as follows: C3=3.50; C4=6.80. The thermal response factors for the standard ester solution were as follows: TR3=1.00; TR4=1.01; TR5=1.03. The adjusted peak areas for the unknown ester solution were as follows: AAC3=1.18; AAC4=2.33. The total adjusted peak area for the unknown ester solution was 2.96. The mole fractions for the unknown ester solution were 0.338 and 0.662. The mole percentages for the unknown ester solution were 33.8% and 66.2%.

Analysis & Conclusions:

Gas chromatography is used to separate and analyze organic compounds that can be vaporized without decomposing. It is a useful technique for determining both the quantity and the identity of a compound(s) in a solution.

This analysis assumed that the detector was equally sensitive to all organic compounds and responded in a linear fashion. As such, the area from the baseline of a gas chromatogram to a peak represents the number of moles of a compound present in a solution. It, however, is not valid to assume that peak area and number of moles are directly proportional for every organic compound. To increase the accuracy of this measure, a chromatogram of a standard equimolar solution of similar compounds must first be measured and analyzed. This preliminary measurement can be used to calculate the Thermal Response factor for each component of the unknown solution and adjust the measurements for the unknown compound accordingly.

The separation of esters by the gas chromatograph was based on the differences in boiling points (and thus the vapor pressures) of each of the compounds. Compounds with lower boiling points typically display shorter retention times because they have higher vapor pressures and spend more time in the vapor phase than they do in the liquid phase. This validates that the first peak furthest to the left (the peak with the shortest retention time) on the chromatogram for the standard ester solution represents Ethyl acetate, as it had the lowest boiling point and was the most volatile of the fours esters in the solution and the shortest retention time (C2=1.5). It is also safe to assume that each subsequent peak represents the ester before it +1C, as the more carbon atoms a molecule contains correspond to a higher boiling point and a higher molecular weight. This is only reasonable when the components of a solution of alkenes are very similar in structure (i.e. contain similar functional groups like the acetates analyzed).

The number of moles for each compound on the chromatograms was determined based on the measured areas beneath each peak. The standard solution contained approximately 1 mol of each ethyl, propyl, butyl and pentyl acetate.After identifying each peak for the standard equimolar mixture, the retention times were compared to those of the unknown chromatogram. The distance of the peaks on the unknown chromatogram were closest to that of the peaks that represented propyl acetate and butyl acetate. This is a sound conclusion as all other conditions of the chromatograph remained constant for both readings.

Literature Summary (Unknowns, Synthesized Compounds)

Unknown No.

CAS No.141-78-6109-60-4123-86-4628-63-7

Name (IUPAC)Ethyl acetatePropyl acetateButyl acetatePentyl acetate

SynonymsAcetic acid ethyl ester; Acetic ether; Acetoxyethane; Ethyl Acetic Ester; Ethyl ethanoateAcetic acid propyl ester 1-Acetoxybutane, Butyl ethanoateAmyl acetate

Melting Point (oC)

Lit-83.8oCExp

Lit-93.0oCExp

Lit-77.0oC

Exp

Lit-61.0oCExp

Boiling Point (oC)

Lit77.1oCExp

Lit101.0oCExp

Lit126.0oCExp

Lit149.4oCExp

Refractive Index (nD20)Lit1.372320Exp

Lit 1.382825Exp

Lit1.394120Exp

Lit1.402320Exp

Solubility(Rel to Water)LitsExp

Lit slExp

Lit slExp

LitslExp

Density

Rel to WaterLit0.900320g/cm-3Exp

Lit0.882025g/cm-3Exp

Lit0.882520g/cm-3Exp

Lit0.875620g/cm-3Exp

Molecular FormulaC4H8O2C5H10O2C6H12O2C7H14O2

Structural Formula