G a s C h r o m a t o g r a p h y Deter mination of Ethanol in Wine

The characteristic of gas chromatography is that samples can move very rapidly to the stationary phase (and out). You can get narrower chromatogram and a sharper separation. Gas chromatography can only be used for aerial samples. The instrument consists in general of the carrier gas supplier, coarse pressure regulator, a fine pressure gage, an injection port (multi sampler),  column, detector and amplifier with analog-digital converter (Pomeranz, Meloan 1994).

The carrier gas respectively mobile phase is mostly helium, nitrogen or argon. The  pressure differential over the column  is responsible for the gas velocity down the column. If the pressure ratio is too low, molecular diffusion remixes the separated components and efficiency decreases. If the ratio is too high, the resistance to mass transfer increases and  the efficiency of separation  would decrease as well (Pomeranz, Meloan 1994).


Two systems for the column are normally used: preparative columns (stationary phase is solid material) and capillary columns (stationary phase is a thin film of not aerial, viscose fluid). It is necessary that the columns are heated to about two-thirds of the boiling point f the highest boiling material in the mixture to be separated. The heating has to be very constant so that the procedure can be reproducible. When the low boiling material is  separated, the column temperature can be raised for shortening the time of the separation of the remaining material. The advantage of the capillary column is the rapid and efficient analysis. However in this procedure you need a splitter. Because of the small capacity of the capillary column, only a sample of a few tenths of a micro liter is required. A splitter splits your injected sample into two parts. One small part is used for analysis and the rest is mostly discarded.
The stationary phases can divided into fife types: Nonpolar, polar, intermediate, hydrogen bonding and specific (Pomeranz, Meloan 1994). There is a wide range of detectors available, for example thermal conductivity detectors, cross-section detectors, argon ionization detectors  or electron capture detector.

Synthesis of Salicylic Acid

Throughout history, botanical extracts have been used as medicines. Approximately 30% of all medicines have a plant origin. This number increases to 60% if you consider medicines that at one time were derived from plants, but have more recently been synthesized in the laboratory. Salicylic acid is a white crystalline compound that can be isolated from the bark of birch trees. Since it is a valuable substance that can be isolated from nature, it is called a "natural product". Although it was used historically as an analgesic (pain reliever), today it is commonly used in ointments and plasters for the removal of warts from the skin. 

In this experiment you will synthesize salicylic acid from methyl salicylate. In this synthesis, methyl salicylate is the “starting material” or “precursor” and salicylic acid is the “synthetic target.” If the procedure goes well, we’ll be able to refer to salicylic acid as the “product.” Examine the structures pictured in Figure 1.  The difference in the two structures is a single functional group. In methyl salicylate (on the left) the benzene ring is substituted by two functional groups, a hydroxyl group (-OH) and an ester group (-COOCH₃). In salicylic acid (on the right), the ester group has been replaced by a carboxylic acid group (-COOH).

In this experiment to analyze the crystal we have gotten, we need to test. is it the crystal formed really salicylic acid compound or not, by using IR and UV instrumental. 

IR instrumental is a way to analyze the compound from the chemical structure not the chemical composition by figuring out the arrangement of each species in the compound. 

in this experiment, organic compound is not as difficult as inorganic compound. when the experiment was ongoing, we did recrystallization to make sure the compound really pure or the opposite and in the elucidation structure to analyze the matter, it has to be pure. if its not pure the others species will appear in the band of IR or UV (it affects the frequency of species).

Crystal is a form of solid to analyze with IR, it has to use Kbr pellet to triturate the sample.Trituration of Kbr is followed to avoid light scattering due to the large size of KBr crystal. KBr is an alkyl halide which doesn't show any absorption spectrum in infrared region. we also can use KCl. KBr doesn't absorb the infrared radiation in the region 4000-400 cm-1. 

The typical sample to KBr ratio used is 1 mg sample/900 mg KBr. This ratio was chosen so that the absorption bands are in the linear region of Beers Law, and so that the signal-to-noise ratio is maximized. Reliable quantitative analysis of samples depends on precise and reproducible sample preparation.