Gas Chromatography: Identifying Unknown Compounds

In a test known as solid phase micro-extraction, SPME, a phase-coated fiber that is contained within a syringe is exposed to the sample being tested². In this case, when Jones³ had collected all of the polyacrylate for that particular time of day, she would take the fibers back to the lab in a cooler full of ice. This was to ensure that none of the chemicals escaped from the cloth while in transit to be analyzed. In order to analyze the fibers, the chemicals were extracted by withdrawing the fiber from the needle, the needle is then removed from the sample vial and introduced into the gas chromatography injector⁴. After Jones had analyzed the fibers using Gas Chromatography (GC), she had determined that the major contributors to decomposition were cadaverine, putrescine, skatole, and indole [Figure 1]. Each of these chemicals produce their own distinct odor⁵ and is present at different stages of the decomposition

Please Note: This lab involves a lot of waiting for the gas collection. Make sure you allot yourself the full three hours to perform the experiments.

Purpose: To use indicators to test for the presence of organic compounds in certain substances.

This experiment was done in order to understand both fractional distillations and gas chromatography. In addition, this experiment was done to separate and identify two liquids that made up an unknown mixture. Gas chromatography was used to figure out the ratio of these two liquids.

Answer: Gas chromatography (GC) – utilized by scientists in order to be able to separate the volatile

Spectrophotometers are quite precise instruments allowing for five significant figures to be obtained. The major source of error in this lab is how small the concentration of the reagents are.

During this investigation the question we looked to answer was: what are the identities of the unknown compounds? In an effort to answer the question, our group designed a method in which the relationships between the unknown compounds in plastic bags were compared so that their identities could be determined. The mole (mol) provides a measure of the number of atoms present in the sample of a compound. One mole of an element or compound contains

Identifying an unknown substance can be accomplished with the use of multiple scientific tests, which help narrow down the possibilities of the unknown compound. The unknown substance that I was given was unknown number A84841BIR, and posed to be a real challenge since I needed to test two different molecular combinations for this specific substance. Once the number of moles in substance was calculated using the ideal gas law, I divided it from the sample mass number after heating and obtained that the molarity of my unknown chemical was 58.93 g/mol. To find my molecular formula I calculated the mass of each element, then the moles, lastly I took the smallest whole-number ratio. Using the molarity calculated I was able to do some research to get a better understanding about what my unknown chemical could possibly be. Once I’ve collected all my data together and strenuously researched the web for articles relating to understanding Infa-Red spectroscopy, I should be able to make an educated guess upon what my unknown solution could be.

Through this experiment, I used IR and NMR to identify several unknown compounds. In order to identify my pure unknown compound, IR-12, I first looked for any medium to strong peaks on my IR spectra. The peaks that were useful in identifying my unknown were: a C-O bond of an ester at 1043.8, a C-O bond of an ester at 1243.6, a stretching C=O bond at 1743.2, a stretching alkyl C-H bond at 2860.4, and a stretching alkyl C-H bond at 2958.7. When figuring out which IR unknown was my compound, I first looked to see if my IR spectra showed an alcohol or an amine. Since my IR spectra didn’t show an alcohol or an amine, I was able narrow down my choices of possible compounds to twelve. Next, I looked for an aromatic ring in my IR spectra and since my IR didn’t show an aromatic ring, I was able to narrow down my choices to six possible compounds. Then I looked for any nitriles in my IR and since my IR didn’t contain any nitriles, I was able to narrow down my choice to five possible compounds. Then, I looked to see if my IR contained a ketone, an aldehyde, or an ester. My IR spectra didn’t contain a ketone or an aldehyde, however, it did contain an ester, which is how I was able to identify my unknown, IR-12.

Aim: To classify unknown substances according to their structure type and to observe how the structure of materials affects their uses.

By correlating the retention time of pure compounds to the retention time of the sample, the compound in the sample can be identified. As seen in Figure 1, there were 2 peaks seen in the GC graph, which indicates there were 2 compound made up in the product. Since cyclohexane was added into the product, it is safe to assume that the peaks were cyclohexane and bromocyclohexane. According to table 2, their retention times were 2.469 and 2.780mn, respectively from 1-2. The first peak was most likely to be cyclohexane since it is less polar compared to bromocyclohexane; therefore, the nonpolar compound will come out first at 2.469mn. If so, the second peak that came out second at 2.780mn was surely bromocyclohexane, the wanted product. According to both figure 1 and table 2, cyclohexane was responsible for 73.78% of the total sample used for analysis whereas bromocyclohexane only accounted for 26.22%. Even though the graph suggested the product was pure when the cyclohexane was neglected, some bumps could be seen within range of 3 to 4mn, which indicated that the product was not 100%

The molecular relationships consists of the bonding vibrations between specific elements. Carbon, hydrogen, and oxygen bonds are commonly witnessed in IR spectra. The focus on the bonding vibrations associated with these elements leads to IR’s use in organic chemistry. A key use of IR spectra is to determine functional groups within compounds and also to verify compound purity. For this experiment, the IR spectra will be used to determine plausible functional groups that exists in the samples. These functional groups will be verified or disregarded by the MS spectra ion fragment weights and the spectra produced by Hydrogen-1 and Carbon-13 Nuclear Magnetic Resonance Spectroscopy

In this study, the unknown compound (No. 55) was obtained, and its identity was determined using three methods: the solubility testing, the melting point analysis, and Thin Layer Chromatography (TLC) method.

The guiding question of this ADI lab was, “What are the identities of the unknown compounds?” The goal of this lab was to understand the relationships between moles and molar mass to find the identity of unknown compounds. The mole can be used to measure small amounts of a substance or is used to convert from unit to unit using dimensional analysis. One mole is equivalent to the molar mass in grams of that substance. If you start with the moles of an unknown substance, multiply it by a given compound’s molar mass, and then divide it by however many moles are in the compound of your choice, you will get the mass of the compound. With that answer you can then compare with mass of the compound in the bag to determine its identity. We first started

8. In order confidently determine what substance my “G9R” was I would have to do over the boiling point experiment a couple of more times. I would turn the gas off and take the Bunsen burner away from the apparatus when the stream of bubbles started coming out from the mouth of the capillary tube. This would allow me to correctly determine when the atmospheric pressure was equal to the vapour pressure.