Ch27 Gas Chromatography

Gas Chromatography

Separation of polar/nonpolar, volatile, thermally stable (up to 400°C) compounds that can be vaporized w/o decomposition

What compounds work better for LC?

Nonvolatiles like proteins, salts, polymers

Gas Source of column

Inert gases (N2, H2, He) that must be pure, used to transport sample thru system, often uses traps for water/hydrocarbons/oxygen to increase purity

Different Inlet Types

Split/Splitless: most common, either all of sample goes to column or only a split part
Cool-on-Column: whole sample purged and trapped on to column
Programmable Temp: injected into inlet and heated to vaporize

Split Mode and Its Benefits

98% sample thrown away when injected, provides way to inject larger sample and only transport part to column

Splitless Mode and its Benefits

All of analyte used, suitable for low conc. samples

The GC Column

Highly T-dependent, in oven, may be ran isothermally or in ramped temp mode

Capillary GC Column

Glass tube fused w/ silica, column diameter influences efficiency, retention, pressure, carrier gas flow rate whereas column length influences retention, pressure, bleeding, and cost

Ideal GC Detector qualities

Adequate sensitivity, good stability and reproducibility, linear response, 0-400°C T, short response independent of flow rate, high reliability, easy use, selective response, NONDESTRUCTIVE

Detector Arrangements

Serial-nondestructive detector used before other detector
Parallel-splits column effluent to diff. detectors, usually used when both detectors destructive

GC Pros & Cons

✅easy, robust, many detectors, low cost
❌lack of data other than retention time, compounds must be thermally stable, needs injection control