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COMPARISM OF GC AND HPLC METHODS
More info:
Practical gas chromatography
GCdetectors
GC troubleshooting
HPLC troubleshooting
INSTRUMENT CHOICE
It is important to understand the difference between the separation techniques in order to select the best method to suit your application.
Both GC and HPLC are separation techniques that have applications in which HPLC is best suited for pharmacueticals and polymers, and GC is significant in petroleum and prtrochemicals.
GC for your lab depends on various factors - your specific analytical needs, the types of sample you will be analysing, and your budget.
General purpose GC instrument - versatile, wide range of applications.
GC combined techniques - some of the most popular hybrid techniques used in chemistry and biochemistry are GC/MS, LC/MS, GC/IF, and LC/NMR.
Detectors
You must choose the correct detector to measure your determinations. Learn about the different type of detectors and their analytical properties.
Good detector examples for hydrocarbons and electro-negative compounds are FID and ECD.
High sensitivity analysis - MS hybrid types
Low sensitivity analysis - TCD
Qualitative and quantitative GC analyses - GC hybrid detector systems or FID.
HPLC detectors - Generate signals proportional to sample mixture as it emerges from column.
The UV UV-VIS detector is the most widely used in HPLC. It is highly sensitive to light absorbing molecules up to picogram levels.
Fixed wavelength - operate at 254nm
Variable wavelength - sample absorption and multiple wavelengths.
Photo diode array detector - PDA - record absorbance in a single wavelength or in a wavelengh range.
In addition, consideration must be given to the following :
Mobile phase
Column packing
Column size
Nature of compounds
Operating Temperature
Research
You can obtain information on these factors from manufacturers and suppliers.
Seek feedback and technical support from potential suppliers and receive recommendations, technical literature, and user manuals on the instrument you prefer to use.
Some good brand name instrument makers are :
Agilent technologies
Thermo Fisher Scientific
Shidmadzu
Perkin Elmer
Bruker
A summary of the methods of HPLC and GC is given in the table below.
Difference Liquid chromatography Gas chromatography METHOD Difference PUMP Gas flow Mobile phase Liquid-solvent resevoir Gas N2 or Helium Separation Polar Volatile Compound type Soluble - volatile/non volatile Volatile Temperature Room temp. 20-25 degrees C HIgh temp. 150 - 350 degrees C Speed Slow Faster Resolution Low for polarity Low for molecular weights EQUIPMENT Column length Short and wide Long and thin Solvent Polar Volatizable Detection non destructive Destructive Cost High Lower APPLICATIONS inorganic ions,polymers,vitamins,poteins,lipids,sugars,tetra cyclines,peptides,insecticides plant pigments,faty acids,drugs,oils,pesticides,toxns,air samples DETECTORS Detection Fluorescence,Chiral detector,conductivity monotor,RID FID,UV_VIS,Diode array,TCD,Thermal ion detctor,Fpp,MS