Anti-plasmodial Property Of Moringa Oleifera Seed Extract On Swiss Mice

Figure 9: Schematic layout of a GC/MS instrument.
The stationary phase in Gas Chromatography is commonly a packing of inert, small diameter particles (such as diatomaceous earth) with a nonpolar liquid coating them, or just a liquid coating on the inner surface of the column. This liquid is a very thin layer (0.1 to 5 μm), usually a polydimethyl siloxane (shown below) where some of the –CH3 groups can be altered so as to match the polarity of the analytes. A parameter common in chromatography used for this is called the Partition Coefficient (or Ratio), K, which is the ratio of the concentration of the analyte in the stationary phase to that in the mobile phase.
The mobile phase is an inert gas such as Argon, Helium or Nitrogen that only carries the analyte molecules through the column. The carrier gas does not interact with the analyte and column packing material. In this lab, ultrahigh purity Helium is used as carrier gas.
The retention time (time it takes to pass through the column) for an analyte is based on the time spent in the stationary phase vs. the mobile phase, with longer retention times for analytes with polarities closer to that of the stationary phase. In the sample chromatogram shown in Fig. 2, two different molecules have distinct retention times, t1 and t2. Dead time, t0, is the time it takes for the carrier gas to go through the column.
The analyte peaks tend to broaden as they pass along the column, resembling Gaussian peaks. This is due to the random motions of molecules as they migrate down a column, passing in and out of the stationary phase. This peak broadening affects the efficiency of the column as well as its ability to distinctly separate the peaks of two different analytes (the resolution). Another common parameter used in chromatography is the Selectivity Factor, which is the ratio
of the migration rates between two different analytes, A and B, and provides a measure of how well the column separates A from B.Molecules 1 and 2 are well separated in spite of the substantial peak broadening.
In order to optimize the column resolution and efficiency, one can change the column dimensions and/or the stationary phase. However, altering the temperature has the greatest effect on column resolution and efficiency. Gradually increasing the temperature, manually or in a predetermined software program, can greatly increase scan speeds as well as increase resolution between peaks.
Samples are commonly injected in very small volumes through a septum or diaphragm into the column head to prevent evaporation of the sample. If the sample is a liquid, then it must be vaporized before being sent into the column. The chromatogram can be used for qualitative and quantitative analysis, but a better method is to direct the output of the chromatographic column into a mass spectrometer (or other identification method) which can then analyze each analyte as it elutes off the column.
 Mass Spectrometry
Mass Spectrometry refers to a group of analytical techniques that precisely measure masses of molecules, atoms and/or ions. Because each species is characterized by a unique mass, mass spectrometry is the most common identification technique used by chemists, biologists, forensic scientists, etc. There are many different types of mass spectrometry based on the various sections of the instrument and the application desired. In most approaches, vaporized samples are ionized (and commonly fragmented), and these ions are separated based on their mass to charge ratios (m/z) and then detected and processed.
1) Sample Injection: There are many different methods used to inject a sample into a mass spectrometer depending on the original phase of the sample. The main requirement is that the sample is converted into the gas phase at very low pressures (down to 10–10 atm) for the instrument to function properly. In this lab, the sample will be injected as a liquid with a syringe. The injected liquid will then be heated to convert it into a vapor.
2) Ionization: Of the numerous ways to ionize the sample, electron impact is the most commonly used. There are several methods that combine vaporization and ionization in one step, especially for solid samples. In electron impact ionization, a filament is used to