Page 278 - Vogel's TEXTBOOK OF QUANTITATIVE CHEMICAL ANALYSIS

9 CAS CHROMATOCRAPHV

Reagents and apparatus required. Ethyl acetate (1), octane (II), ethyl n-propyl
ketone (III) and toluene (IV), al1 GPR or comparable grade.
Mixture A containing compounds (1), (II), and (III) in an unknown ratio.
Micros yringe.
Gus chromatograph. Preferably equipped with a flame ionisation detector and
a digital integrator.
Column. Packed with stationary phase containing 10 per cent by weight of
dinonyl phthalate.
Procedure.
1. Prepare a mixture B which contains equal amounts by weight of the
compounds (1), (II), and (III).
2. Set the chromatograph oven to 75 OC and the carrier gas (pure nitrogen)
flow rate to 40-45 mL min- '.
3. When the oven temperature has stabilised, inject a 0.3 pL sample of mixture
B and decide from the peak areas whether the detector response is the same
for each component.
4. If the detector response differs, make up by weight a 1: 1 mixture of each of
the separate components (1, II, and III) with compound (IV). Inject a 0.1 pL
sample of each mixture, measure the corresponding peak area, and hence
deduce the factors which will correct the peak areas of components (1), (II),
and (III) with respect to the interna1 standard (IV).
5. Prepare a mixture, by weight, of A with compound (IV). Inject a 0.3 pL
sample of this mixture, measure the various peak areas and, after making
appropriate corrections for differences in detector sensitivity, determine the
percentage composition of A.

9.8 DETERMINATION OF SUCROSE AS ITS TRIMETHYLSILYL DERIVATIVE USlNG
GAS-LIQUID CHROMATOGRAPHY
The purpose of the experiment is to illustrate the application of derivatisation
in the analysis of sugar and related substances by gas-liquid chromatography.
The silylation method described is an almost universal derivatisation procedure
for carbohydrate analysis by GC.79
Reagents and apparatus. The reagents and solvents should be pure and dry,
and should be tested in advance in the gas chromatographic system which is
to be used in the experiment.
Pyridine. Purify by refluxing over potassium hydroxide, followed by distillation.
Store the purified pyridine over the same reagent.
Trimethylchlorosilane ( TMCS), (CH,) ,SiCl.
Hexamethyldisilazane (HMDS), (CH,),Si-NH-Si (CH,),.
Reaction uessel. Use a small tube or vial fitted with a Teflon-lined screw cap.
Gus chromatograph. Operate the column isothermally at 210 OC using a flame
ionisation detector.

Procedure. Treat 10 mg of sucrose with 1 mL of anhydrous pyridine, 0.2 mL of
HMDS, and 0.1 mL of TMCS in the plastic-stoppered vial (or similar container).
Shake the mixture vigorously for about 30seconds and allow it to stand for
10 min at room temperature; if the carbohydrate appears to remain insoluble