The rate of bacterial growth is assessed by the doubling time, the period required for the number of cells to double.

The shorter the doubling time, the faster the bacteria are growing.

Escherichia coli growth rates can range from doubling times as fast as 18 minutes to slower than 180 minutes.

#Id: 2778

#Unit 13. Methods in Biology

If the sample is hydrophobic Organic solvent is used, then to separat

Differing molecular size - Molecular exclusion system.

Weakly ionic or polar - Reversed-phase partition system.

Strongly ionic - Ion-exchange system or Reversed-phase partition system with lon-pairing is used.

#Id: 2779

#Unit 13. Methods in Biology

General structure and component of a chromatographic system

A stationary phase – typically an aqueous buffer with sufficient ionic strength to maintain a soluble protein.

A column -

An injector system: To deliver test samples to the top of the column in a reproducible manner.

A detector with data acquisition - To give a continuous record of the presence of the analytes in the eluate as it emerges from the column.

A fraction collector: For collecting the separated analytes for further biochemical studies.

#Id: 2780

#Unit 13. Methods in Biology

The basis of all forms of chromatography is the distribution or partition coefficient (Kd), which describes the way in which a compound (the analyte) distributes between two immiscible phases.

#Id: 2781

#Unit 13. Methods in Biology

A chromatogram is a pictorial record of the detector response as a function of elution volume or retention time, It consists of a series of peaks or bands.

#Id: 2782

#Unit 13. Methods in Biology

The retention time tR for each analyte has two components

 i - dead time, tM. &

ii - adjusted retention time, t’R.

#Id: 2783

#Unit 13. Methods in Biology

t’R is characteristic of the analyte and is the difference between the observed retention time and the dead time: