Introduction to Chromatography

Chromatography, ohh the editor showing me this as a error !! But i am sure u must be known to aleast to this word that u can say such a word exist. This is a common and simple instrument in analytical instrumentation.

The technique is used for analysis of available chemical components in a fluid(gas or liquid) mixture. The technique adopt several methods to separate the components and then detecting the concentration of each component.

A Sample Chromatogram

The output is graph with time in x-axis and concentarion of different components on the Y-axis

What is the Principle and the method ?

when a fluid is allowed to pass through some another fluid or solid tunnel, the rate of flow for the components of mixture will be different. So at the other end of the tunnel the components will reach at different time.(the medium or the column called separator).

OK now our job turned easy becoz we know which component will come out at which time( its called retention time). we have to detect the gas coming out at different time.

Why different retention time?

Now the questions is why these components(our analyte is a mixture of different molecules and ions). The prime cause is the average speed. Acording to kinetic theory the average speed of gas molecules will depend upon its molecular mass.

except this there are different processes invloved in side the chromatography column/channel. The molecules may be adsorbed on the columns inner surface temporarily and then released. this stick and release may happen many times before it comes out of the column.

The terminology

Now its time to get some terminology things. i hate these from the begining as these may confuse the reader.

The gas (or liquid) is passed through the tunnel(chromatography column) which contains some material called the stationary phase. Again the analyte mixture may not pass through itself so we need some truck(we call it carrier gas) it acts as the mobile phase.

Simply we may say the mobile phase+analyte mixture is passed through the stationary phase which causes the separation of components. Separation caused by differntial partiotioning, selective adsorption, selective ion exchange...etc.