Gas Chromatographic Determination of Oil of Wintergreen in Rubbing Alcohol
Abstract
Gas chromatography is a technique that is used to separate isomeric butyl alcohols and finally the determinations of the portion of every mixture. This experiment sets out to determine the basic components of the chromatographic instrument and determine the importance of the process to the chemical analyst. By this way, we also set to understand the process by which the components are separated. We realize that the process of gas chromatography is very important to a number chemical process that contribute to the economic wellbeing and is one of the main enablers of modern day research.
Introduction
Chromatography is a very vital analytical tool since it enables the chemist to divide the various components in an assortment for successive use or quantification. Nearly all samples that chemists want to scrutinize are blends of many things. If the technique of quantification is discerning for a given element in the mixture, division is not required. The detectors is never sufficient therefore it is important to separate the components. There are numerous types of chromatography based on the type of sample to be used. In this test, gas chromatography will be used.
This technique makes it possible to split the volatile elements of a very small substance and to establish the amount of each element present. The necessities for the method include an injection port for the samples to be loaded, a “column” on which the elements are set apart, a synchronized flow of a mover gas in this case helium which carries the sample throughout the instrument, a detector, and a process.
Experiment
Injection of the sample
The sample to be analyzed was loaded at the injection port via a plunger syringe. The temperature of the injection port was raised through heating in order to ionize the sample. Once in the gas phase, the sample is transported onto the column by the transporter gas, typically helium, also known as mobile phase. Gas chromatographs, these are very sensitive instruments. Normally, liquid samples of one-microliter ware injected into the column.
The stationary phase
This is where the elements of the sample are separated. The phase contains dimethylsilicone gum coated on a substrate of silicate materials. Gas chromatography stationary phases are of two types, namely—packed and capillary this one is packed. Capillary columns are those in which the stationary phase is coated on the interior walls of a tubular column with a small inner diameter. Capillary column were used this experiment.
The stationary phase in our column is a dimethylsilicone material. Its basic structure of the polymeric molecules is shown below, where n is a variable number of recurring units and R stands for an organic active group. In our columns, 5% of the “R’s” are methyl groups (-CH3) and 95% of the “R’s” are phenyl groups (-C6H5)
This polymeric liquid has a high boiling point that prevents it from evaporating off the column during the experiment.
The components in the sample were separated on the column because they take different amounts of time to move through the column based on their affinity for the stationary phase. While the elements in the mixture are moving into the column from the injection port, they dissolve in the stationary phase and are retained. Upon re-ionization into the mobile phase, they are transported all the way down the column.
According to Ronald, (102), this process is repeated a number of times as the elements move through the column. Elements that have more affinity more strongly with the stationary phase spend proportionally less time in the mobile phase and therefore move through the column more slowly. Usually the column is selected such that it’s polarity resembles that of the sample. When this is the situation, the interaction with the elution times can be standardized according to Raoult’s law and the relationship linking vapor pressure and enthalpy of vaporization. The principle is that retention times are directly proportional to boiling points.
Detector
Monitor the mixture mechanism immediately following the elution from the gas chromatographic column; this is done by passing them through an equipment with the capability sensing their presence in the helium delivery gas. We will use a thermal conductivity detector as it can incorporate dual heated thermistors in helium steam and on the sample side (Chapman, p. 122).
The organic compounds used are poor conductors of heat from the thermistors as compared to the helium. Due to this, it is not bad if there is a slight change ion the temperature in the other sample thermistor. This change in the temperature is mostly experienced inn the bridge electronics. This is the chromatographic peak as it is at this point that an analyzed zone goes inside the detectors cell. Finally, it is advisable to convert the output of the detector from ac to volts and transmit it to the integrating recorder in order for it to store, plot and analyze the data.
Findings
After the experiment, the data that was collected was used to plot the following graphs with the peaks as indicated bellow. The graphs also had retention times as is shown in the graph below:
Figure: a plot of the samples
Figure 1: chromatogram for the experiment
Discussion
In the y-axis, we have the detector voltage and in the x-axis, we have the time function. Every peak in the graphs represents a separate component. The time between peaks is called the retention time. It is important to note that it is only easy to determine the retention time of each component after injection and is distinct from each sample. It is also important to inject pure sample and note their retentions times
From the experiment, it was realized that the level of voltage varies from each detector and is directly proportional to the quantity of molecules that go through the detector. It is also important to determine the proportionality factors that exist between the area and the volume by use of equipment used for calibration. Another notable thing is that in case of the separated peaks, the quantity of molecules that reaches the detectors is directly proportional to the area that is below the peak (Karasek, & Ray, p.170)
Relative Response Factors
In our case, the detectors were not evenly responsive to the diverse components; therefore, we multiply each of the peak area by an appropriate factor. This was carried out to resolve the differences in the responsiveness of the detectors. Finally, calculation was done on the corrected areas, by determining the percentages composition of the compound. The relative response factors are also employed while determining the proportion of the unknown mixture of similar portions
Symbols
ai = peak area of component;
pi = % composition of component;
qi = quantity of the component getting to the detector;
ki = the response factor;
fi = relative response factor of the component
The symbols are used in the derivation of the formula for calculating the output data to be plotted. The formula is deemed more accurate than the figure due to the ranges that the figure uses. There are minute ranges that cannot be shown in the figures (chromatograph). The formulas used on the calculations are as shown in the appendix and the methods used to derive the formula.
Calculations
1. Mark the peaks on the chromatograms of the standard and the mixtures that are not known. It is advisable to do this with the name of the substance related with the peaks
2. After calculating the runs of the standard mixture it is important to calculate the relative 95% confidence interval of means of the initial means
3. For every run on the standard mixture it is advisable to determine the relative response factor for every reagent and calculate the averages of each response factor based on the four different runs then calculate their relative 95% confidence interval of the averages.
Data collection
x y
0.0 0
0.4 0
0.8 0
1.2 0
1.6 0
2.0 2.039
2.2 0
2.4 2.345
2.5 0
2.6 2.844
3.2 0
Conclusion
From the experiment, the compounds used pass through the column peaks is dependent on the type of interactions between the different compounds and their stationary points. The rate is also affected by other various conditions such as column temperature and the rate at which the carrier gas flow
Works cited
Chapman, J., Practical Organic Mass Spectrometry, 2nd Ed. New York: Wiley, (2001).
Ronald A., Handbook of Mass Spectra Environmental Contaminants, 2nd ed. Boca Raton, FL: Lewis Publishers, (2003).
Karasek, W., and Ray E., Basic Gas Chromatography–Mass Spectrometry: Principles &Techniques. Amsterdam: Elsevier, (2000).
Appendix
