GC Advantages
Download
1 / 22

GC Advantages Very Large N (Very Long Columns) No Packing Material (A=0) - PowerPoint PPT Presentation


  • 77 Views
  • Uploaded on
  • Presentation posted in: General

GC Advantages Very Large N (Very Long Columns) No Packing Material (A=0) Simple Mobile Phase (Compressed Gas) Universal Detectors (FID) Easy to Change k’ (Temperature Program). GC Limitations Analytes must be Thermally Stable Analytes must be Relatively Volatile MW < 400

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha

Download Presentation

GC Advantages Very Large N (Very Long Columns) No Packing Material (A=0)

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


  • GC Advantages

  • Very Large N (Very Long Columns)

  • No Packing Material (A=0)

  • Simple Mobile Phase (Compressed Gas)

  • Universal Detectors (FID)

  • Easy to Change k’ (Temperature Program)


  • GC Limitations

  • Analytes must be Thermally Stable

  • Analytes must be Relatively Volatile

  • MW < 400

  • Not possible to operate at biological

  • conditions

  • If these limitations are not critical, then GC is probably the BEST means for analyzing a complex sample


  • GC Limitations

  • Analytes must be Thermally Stable

  • Analytes must be Relatively Volatile

  • MW < 400

  • Not possible to operate at biological

  • conditions

  • If at least one of these is a serious concern, then another technique must be employed.


Modern Liquid Chromatography

(post 1969)

HPLC

High Performance Liquid Chromatography

(originally High Pressure Liquid Chromatography)


LIQUID CHROMATOGRAPHY


HPLC INSTRUMENTATION

1. Mobile Phase Supply

2. Sample Injector

3. Column (Stationary Phase)

4. Detector


HPLC Stack Configuration


Mobile Phase Supply: Solvent Reservoirs


Mobile Phase Supply: Solvent Reservoirs

To Pump


Mobile Phase Supply: Syringe Pump

Provides a constant, smooth, high pressure flow.

Difficult to mix or change solvent (reservoir is inside the pump)


Mobile Phase Supply: Reciprocating Pump

Draws solvent(s) from an external reservoir.

Flow is not as uniform, dissolved gas can be troublesome.

Pump only works if liquid is in chamber (must be primed)


Mobile Phase Composition

Reversed Phase ≡Retention decreases as mobile phase

polarity decreases

Aqueous Mobile Phases

Normal Phase ≡Retention decreases as mobile phase

polarity increases

Organic Mobile Phases


  • Advantages of Reversed Phase HPLC

  • Weak Attractive Forces

  • Aqueous mobile phase, sometimes with added liquid organic modifiers (MeOH, Acetonitrile), dissolved salts, and/or buffers.

  • Wide scope: may separate polar, non-polar, ionizeable, and ionic compounds (perhaps at the same time).

  • Elution occurs in order of decreasing polarity (but not at predictable as GC Retention Index).


Mobile phase: Water + % MeOH + 0.5% H3PO4

Effect of Organic Modifiers

(separation of common analgesics)


Mobile phase: 20 mM KH2PO4 : acetonitrile (95:5)

Effect of pH

(separation of sulfa drugs)


Isocratic:

constant 0.055 M sodium nitrate

Gradient:

0.01 to 0.1 M sodium nitrate in 25 min

Separation of aromatic carboxylic acids


Separation of amino acids with

pH Gradient Elution


Sample Injection


Sample Injection


Auto-injection


Stop Here for now!


ad
  • Login