Gas Chromatography

1
Gas Chromatography Refractive Index of
Distillates

• Text References
• Slayden p. 39, 41- 44, 45 - 47
• Pavia - 13.1 13.4 p. 723 724 729 - 731
• Pavia - Tech 14.1 - 14.3 p. 733 740 (Simple
  Distillation)
• Pavia - Tech 15.1 - 15.6 p. 744 755
  (Fractional Distillation)
• Pavia - Tech 22.1 22.12 p. 837 855 (Gas
  Chromatography)
• Pavia - Tech 24 p. 867 872 (Refractive
  Index)

2
Gas Chromatography Refractive Index of
Distillates

• Experiment Overview GC Acetates
• Simple Fractional Distillation
• GC Distillates
• The results of these 3 experiments are combined
  with the objective of evaluating the relative
  efficiencies of Simple Fractional Distillation
  to separate compounds in a mixture.
• Todays experiment will produce Mole values
  from Gas Chromatograms of the Distillate
  Fractions and the Standard Mixture (A or B)
  obtained from last weeks experiment.
• Mole values will also be determined from
  Refractive Index values of the Distillate
  Fractions and the standard mixture.

3
Gas Chromatography Refractive Index of
Distillates

• Mole Percent of Distillates by Gas Chromatography
• Work in the same groups of four (4) as last week.
• Use the same Chromatograph used in GC Acetates
  Exp.
• Obtain Gas Chromatogram of the Standard Mixture
  used in the Simple Fractional Distillation
  experiment (Ethyl Acetate Butyl Acetate). Use
  bottle A or B, whichever you used.
• Obtain Gas Chromatograms of the six (6) vials you
  collected last week, i.e., 3 from the Simple
  Distillation and 3 from the Fractional
  Distillation.

4
Gas Chromatography Refractive Indexof
Distillates

• Mole Percent of Distillates by Gas Chromatography
• Compute the Peak Areas using Triangulation
  method.
• Note There are two peaks on each Chromatogram
• Compute Total Area for each Chromatogram
• Compute the Mole Fraction
• Compute Mole Percent.
• Adjust the Mole for non-Linear Thermal
  Conductivity Response (Use results from Equimolar
  mixture in GC Acetates Experiment to set TRs
  TRI ratios)

5
Gas Chromatography Refractive Indexof
Distillates

• Mole Percent by Refractive Index
• Note Add to Experiment only if directed by
  Instructor
• Obtain temperature corrected Refractive Index
  values for the Unknown mixture (A or B) and the 6
  simple fractional distillation vials.
• Use MS Excel to create a scatter plot of
  Refractive Index(Y axis) versus Mole Ethyl
  Acetate (X axis) for mixtures of known Mole
  (see slide 4).
• Note You can Click on X axis scale, select the
  scale box, and then select the Reverse
  Axis option to put 100 on the left side.

6
Gas Chromatography Refractive Indexof
Distillates

• Add a trend (regression) line and regression
  equation to the plot (This is an option under the
  Chart Dialog Box in Excel.
• Use the regression equation to determine the Mole
  of standard mixture and 6 distillate vials from
  the measured values of Refractive Index

7
Gas Chromatography Refractive Indexof
Distillates

• Mole Analysis by Refractive Index
• The Mole of the components in a mixture can be
  computed using Refractive Index values in
  conjunction with a Regression Curve.
• The analysis is performed by comparing measured
  Refractive Index values from mixtures of unknown
  mole content against a Standard Regression Curve
  based on mixtures of the same compounds but of
  known mole content.
• Ex Use table on next slide to create a Scatter
  Plot (with Trend Line) by plotting Mole
  Ethyl Acetate on X Axis vs. Corrected R.I.
  on Y Axis.
• Note Reverse X axis to put 100 on
  left side

8
Gas Chromatography Refractive Indexof
Distillates

• Mole Analysis by Refractive Index
• Use the values in the following table to
  construct a scatter plotter of Mole Ethyl
  Acetate on the X Axis vs. Corrected R.I. on
  the Y Axis

Solutions of Known Mole and Refractive Index
9
Gas Chromatography Refractive Indexof
Distillates

• Mole Analysis by Refractive Index
• The Mole values of the unknown mixtures are
  computed either from the regression equation or
  obtained directly from the Regression Curve by
  noting the mole relative to its equivalent
  Refractive Index value.

Rearrange the equation as follows to compute the
Mole values x (Mole )
(1.3949 y (Measured R.I.) / 0.00022 Ex.
Measured R.I. 1.3850 ? Mole 45
Ethyl, 55 Butyl
10
Gas Chromatography Refractive Indexof
Distillates

• Combined Lab Report Setup
• The report for this lab combines the Simple and
  Fractional Distillation experiment and todays
  Gas Chromatography experiment.
• Simple Distillation Fractional Distillation
• Volume Recover and Recovery
• Volumes Volume of Distillate Fractions
• Mass, Moles, Mole Fractions, and Mole from
  Distillate Volume Calculations

11

• Combined Lab Report Setup (Cont)
• Gas Chromatograms of Distillate Fractions
  Standard Mixture
• Peak Areas, Total Area, Mole Fraction, Mole
  from Gas Chromatograms
• Refractive Index (corrected for temperature) of
  Distillate Fractions
• Standard (Regression) Curve of known Mole
  mixtures
• Mole of Distillate Fractions from Regression
  Curve

12
Gas Chromatography Refractive Indexof
Distillates

• Combined Lab Report Setup (cont)
• The report design should reflect careful
  attention to logical presentation of the results
• Keep related items together. All multiple sample
  results obtained from a given Procedure/Computatio
  n can be presented as a single procedure
• Each unique calculation is considered a new
  procedure and must be set up with applicable
  title, Equipment Materials and suitable
  Description. The Description includes the setup
  of the relevant equation with appropriate
  definition of the variables

13
Gas Chromatography Refractive Indexof
Distillates

• Combined Lab Report Setup (Cont)
• The Summary section is a paragraph presentation
  of the results obtained in logical order
• The Conclusion section should focus on a
  comparison of the Mole results obtained from
  the three methods with an evaluation of the best
  method to physically separate the mixture
  components and determine the Mole composition of
  the mixture