Quantitative Analysis in Gas Chromatography

Quantitative Gas Chromatography

1. Quantitative Gas
Chromatography

Chem 2223 Lab Prep

2. Goals and Objectives

« Goals

— To become familiar with basic methods of
quantitative analysis by gas chromatography

* Specific Objectives
— Use the standard additions technique to determine
the identities and concentrations of the
components in a mixture of volatile organic
compounds

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3. r
|
|
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Sample > injection

Carrier
gas tank

Y

Flow
regulators

Sample

chamber

Oven

© 2004 Thomson - Brooks/Cole

Setup

Display

Data
system

Detector

I
Thermostat

4. Solutes and Internal Standard

‘Compound Structure or Formula Boiling Point, °C Relative Polarity
Makel CH,OH 64.6 Polar
Golvent)
SS
Toluene Cy 110.6 Nonpolar
Z

~
Eihylbenzene 1352 Nonpolar

Br
Bromobenzene
internal standard) OÍ 156.0 Polar

5. Internal Standard Method

» Description
— In this approach, an internal standard is added to the
sample, and the response from the analyte peak is
compared to the internal standard. This approach
corrects for minor variations in the injection volume.

« Response Factor (RF)
— The response factor accounts for differences in the
detector response between the analyte and standard.

6. Sample Chromatogram and Integration Report

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in ethos 2 Erden em mere ——
Ré ea
zw 8
: IS
= El
& a
OZ
= alis — /
* | Cx [Cis
Peak RerTime Tye Width Area Beige Area
# twin} tain] [25 whe} [25 uv] 3
enla Va de 1
1 0. 0.0186 9.69921 8.67154 0.02960

762 3.25653e4 $463. 18750 99.65694

3.26724e4 5514.85485

7. Calibration Curve with Internal Standard

Standards GC Calibration Curve for Cocaine with Internal Standard
+ Each contains fixed mass of internal Games
standard, various masses of std Standard mont man en SE RER
analyte 2 5.00 5.00 1.000 241 601 0.401
+ Calibration curve shows linear te 5-3

response. Slope = response factor*

Cocaine with Interal Standard
r 1.0 microliter injections
Razo = fe 2
xlis y =03001 + 00018
2000
1800
Unknown i
+ Add known amount of internal standard me
+ Inject and measure A,/A,, Lu
+ Determine c,/c, for your unknown from 0.000
calibration curve. Since c;, is known, c, for Re ee oe se a 2
your unknown is simply

I “This expression for the response factor is not used directly in your

C, = (C,/ Cig) Cig calculations. The following expression which accounts for the intercept is
more rigorous (in practice the intercept is very near zero). Calculations
based on the calibration data do take the intercept into account.

i, = Be! = 0 intercept) 14

eis Ela