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Characterization Techniques CHEM241-03B - Coggle Diagram
Characterization Techniques CHEM241-03B
Characterization via Melting Point Analysis
Melting point analysis is the process of analyzing the temperature or temperature range in which a solid sample transitions into the liquid phase. This technique can be accomplished through the usage of a MelTemp device which heats the sample and allows for a clear view of the sample as it melts. The melting point for a sample can explain the strength of the intermolecular forces inside of the sample as well as helping to explain what the sample may possibly be.
Pros
1- Helps to easily distinguish between compounds with varying intermolecular forces. 2- Can be performed very quickly to get a rough estimate of melting point. 3- Only requires a very small sample to complete analysis. 4- Relatively easy, quick, an inexpensive technique to run.
Cons
Uses of Techniques
Melting Point Characterization
https://www.youtube.com/watch?v=9RNRYLvlbXM
This technique can only be used with solid samples. The best results are obtained on pure samples due to the notion that impure sample will cause the depression of melting points, which will lead to error.
1- Melting points can be depressed if a sample is not pure. 2- Can only be used on samples that are in the solid phase. 3- Multiple different compounds can have the same melting point. 4- The sample has to be destroyed. 5- Can not analyzed quantitatively for the purity of a sample if it has more than one solute.
Characterization using Thin Layer Chromatography
Thin Layer Chromatography uses compound’s varying affinities for a stationary phase and a mobile phase to separate mixtures. These varying affinities for each phase can be used to create RF values which allow for the characterization of the compounds. To perform this technique, samples are added to the stationary phase which must be polar. Next, the mobile phase will be added and the molecules will unstick from the stationary phase to varying degrees due to their relative polarities. In class, this was performed using a developing jar with the stationary phase being silica gel. The less polar the molecule, the further distance it will travel as it has a lower affinity for the stationary phase. The opposite is true for more polar molecules. Polarity of each compound can then be characterized and analyzed based on the distance traveled by each analyte, this is the RF value.
Pros
Cons
Uses of Techniques
Thin Layer Chromatography
https://www.youtube.com/watch?v=462CmolEFhc
This technique should be used only with liquids. This technique should be used on a mixture of solutions to identify, which substances are apart of the solution.
1- Does not separate molecules with very similar polarities. 2- Is only used on molecules that are in the liquid phase. 3- Can not determine identity of unknown using this technique. 4- Non-volatile compounds only.
1- Simple and inexpensive process. 2- More than 1 compound can be separated on the TLC plate if the mobile phase is preferred. 3- Solvents can quickly and efficiently be changed depending on the results of the experiment. 4- The overall process is fast due to the quick analysis time.
Characterization via Gas Chromatography
Gas chromatography is a technique which utilizes varying affinities of compounds to separate them and then analyze them. This form of chromatography utilizes resin as the stationary phase and helium gas as the mobile phase. Specifically, a sample is placed in an oven to heat the sample into the gas phase which is then shot into the column. The compounds move through the column at varying rates and then are detected as they exit the column. This detector will assess the composition and purity of the sample that has passed through.
Pros
1- Allows for the analysis of the percent composition of a sample. 2- Can be completed much quicker than Thin Layer Chromatography. 3- Can analyze very complex components of one single sample. 4- Can resolve very closely related samples. 5- Samples can range from liquids, gases, and dissolved solids.
Cons
Uses of the Technique
Characterization via Gas Chromatography
https://www.youtube.com/watch?v=6Z61ezJFfyA
Can be used with samples in the liquid stationary phase and the gas mobile phase, especially if the samples are volatile.
1- It's limited only to volatile samples. 2- Samples tested must be soluble and must not react with the GC column. 3- It is destructive. The sample cannot be analyzed in a reverse reaction, since much of it is destroyed during.
Characterization via NMR Spectroscopy
NMR spectroscopy is used to determine content and purity of a sample, but in the lab performed in class it was mostly used to determine the molecular structure. To do this, the NMR observes and measures the nuclear spins when placed in a magnetic field. From the spectra that is created, information is given about the chemical shift. The chemical shift gives an insight into the composition of the atomic groups that are found in the molecule. By examining the peaks, the scientist can determine the structure of the molecules. It can also be used to determine which resonance structure was favored.
Pros
Cons
1- Weaker energies to ensure the sample stays intact, which makes it insensitive to giving accurate results of complex reactions. 2- May not identify all of the molecules due to insensitivity.
Uses of Technique
How to Analyze NMR Spectroscopy
https://www.youtube.com/watch?v=k0eR8YqcA8c
NMR Spectroscopy Visual
https://www.youtube.com/watch?v=RZLew6Ff-JE
This technique can be used on samples in the liquid or solid phase. The NMR can be used on pure or impure samples, due to the reason that one of the uses of NMR is to determine how pure a sample is.
1- NMR allows for the molecules to stay intact, allowing the sample to be used for future testing and observations. 2- There is no need to manipulate the sample in order to test. 3- Can be tested as either a solid or a liquid. 4- Simplify and speed up the data acquisition and analysis process. 5- Better ability to identify and quantify molecules.