Pure Carrier Gas Grades (subjective) Grade He H2 N2 Analytical 99.9999% N/A N/A Research 99.9999 99.9999 99.9995 UHP 99.999 99.999 99.9995 HP 99.995 99.99 99.99 Zero* 99.995 99.99 99.98 * “Instrument Zero”  usually no other impurities except THC (Total HydroCarbons) Often used as a zero gas for Total Hydrocarbon Analyzers.

Typical Impurities in Pure Gas Grades That Can Affect Detectors Electron Capture Detector ECD Oxygen and water can reduce detector response and halocarbons can give rise to baseline noise and negative peaks. Flame Ionization FID Hydrocarbons in carrier and Detector fuel gases can cause baseline noise and reduced detector sensitivity. Oxygen and water can cause column deterioration.

Gas Chromatography Applications: (two major roles) Performing separations Analysis using or peak height or peak area Qualitative Analysis using retention times, tR’s Limited by numerous variables May not lead to positive ID of species present, but rather to the absence of species e.g., absence of new peaks when evaluating purification of organics or in QC and QA

Quantitative Analysis Relative accuracy of < 1% (1) Based on Peak Height Variables closely controlled: temperature flow rate sample injection rate h

(2) Based on Peak Area Areas independent of: temperature flow rate sample injection rate Most GC’s have digital electronic integrators

Separation of Proteins Size Exclusion Chromatography Excellent for polymers and large biopolymers Detector response

Size Exclusion Chromatography Large molecules pass through column faster than small molecules Stationary phase: cross-linked polystyrene polymer Mobile Phase: varies Column: 0.62 X 25 cm (typical) Detector: UV absorption

Typical SEC Column Containing Polymerized “Fingers”

Gas Chromatography – Mass Spectrometry Hyphenated Methods GC is coupled with another technique: e.g., GC-MS, GC-FTIR, GC-NMR, etc. Gas Chromatography – Mass Spectrometry Problem: GC requires relatively high pressures (∼ 40 psi) MS requires very high vacuum (∼ μtorr) Solution: Use GC capillary column with jet separator or “skimmer” at the interface

Schematic of a Jet Separator Sample and He carrier gas from GC Sample to MS Entire chamber at He Silica nozzle

Jet Separator in Action

Schematic of Ion Trap Detector

2.5 cm

GC-MS Spectrum of Benzene (MW = 78)