Analytical Techniques and Instrumentation

Gas chromatography or GC

GC is a separation technique. The instrument used is called a gas chromatograph or GC. Three main components of a simple GC are injector, column & detector. Mostly used for separation, identification and quantification of mixture of hydrocarbons. Examples are pona/piano in gasoline, naphtha or other streams. Specially configured GCs can also separate, oxygenates, ethanol, benzene, toluene & aromatics in gasoline etc. GC technique has a vast list of compounds that can be separated in a mixture.

Atomic absorption spectrometry or AAS

Atomic absorption or AAS technique is used to determine elements (metals in our business) in petroleum products as well as in water by environmental labs. It is commonly used to detect vanadium, sodium, iron, nickel, aluminum, silicon and many more metals in crude oil, fuel oils, bunkers and other dirty fuels. The detection followed by quantification is limited to ppm levels. The instrument used is called atomic absorption spectrophotometer or AA. AA can be flame or graphite furnace based. Furnace based AA can selectively detect metals to ppb levels.

ICP - Optical Emission Spectroscopy with OES

Optical emission spectroscopy or OES is a technique to simultaneously determine the qualitative identification and determining the concentration of more than 60 elements in inorganic and organic matrices. The instrument used is called inductively coupled plasma or ICP. ICP has the capability of detecting and quantifying elements (metals in our business) to ppb levels. Argon gas is used to create a very high temperature plasma.

Comparison between AAS and ICP-OES

Both techniques are actually complementary and not competitive. AAS is an energy absorption technique while ICP-OES is energy emission technique. AAS use flame/furnace for atomization while ICP-OES uses high temperature plasma for atomization. AAS remains the least expensive technique while ICP-OES is 5-7 times more expensive. ICP-OES can be sequential as well as simultaneous technique. Chemical interferences are few in ICP due to the high temperatures involved.

Other techniques to follow are:

X-ray techniques, infrared and ultraviolet & visible technique, mass spectrometry and several others like GC-MS; ICP-MS, IC, combustions and detections etc.