Question

Spectroscopy is an effective tool for characterizing molecules and, to date, many techniques are well established, especially UV, Mass Spec., NMR and Infrared (FTIR). These techniques are similar in that they are based on quantum mechanical properties/interactions of atoms and molecules with electromagnetic radiation. For UV, Mass Spec., NMR and FTIR please answer the following:

What elements of quantum mechanics enable spectroscopy?

Briefly describe the key underlying science for UV, IR, Mass Spec and NMR spectroscopy.

How do you interpret spectroscopic data and assess its accuracy and precision?

As a biomedical engineer with expertise in biomaterials why would you need these techniques (UV, IR, NMR, Mass Spec spectroscopy)?

If you lived in an alternative universe where all size scales of matter followed Newtonian physics, which spectroscopic technique, if any, could you still employ. You do know about the structure of atoms and molecules so atomic numbers, atomic weights, neutrons, protons and electrons are known.

Answer 1

1.

What elements of quantum mechanics enable spectroscopy?Briefly describe the key underlying science for UV, IR, Mass Spec and NMR spectroscopy.How do you interpret spectroscopic data and assess its accuracy and precision?

You have mentioned different analytical methods to characterize molecules present in a sample. However, the principles are much different. It varies from electronic structure of the atom or molecules and instrument.

The following is the explanation.

UV Spectroscopy - In this spectroscopy, the sample to be analyzed is subjected to ultraviolet light (UV). It excites molecules in the sample, and they undergo transition from their normal, ground state to excited state. The absorption of UV light causes change in their electronic, translational and rotational energy. The incident energy is refers as 'h x v', where h is Plank's constant and v is the frequency of incident radition. Different molecules have various absorption levels at different wavelenghts. Hence, the plot of absorbance vs wavelength shows the type of molecules/compounds present in a sample.

Mass Spectroscopy - In a mass spectroscopy (MS), it depends upon the type of molecule i.e. its atomic/molecular weight and its time of flight in a magnetic field applied. For example, a heavy molecule like benzene will take more more to travel through the path of magnetic field as compared to methane molecule. So in this technique, a time of flight differs from one molecule to another. It is also important to note that this refers to ionised molecules. In some special techniques such as ESI-MS (Electrospray Ionisation), the sample is mixed with solvents such as sodium hydroxide(NaOH) and the molecules to be detected are ionised with Na+ charge. The MS plot shows intensity vs mass-to-charge ratio. The appearance of a certain charged species is of course is differs by its time of flight. The lighter molecule will appear before the heavier ones in the plot.

FTIR - It is Fourier Transformed Infrared Spectroscopy. It used to analyse vibration of probe molecules on metal oxide. For example, binding of CO(carbon monoxide) on a metal oxide such as Alumina, Silica, Titania. In addition, this instrument can be used to analyze presence of Lewis and Bronsted acid sites on the metal oxides. The FTIR results are represented as intensity vs wavenumber. This technique, however, can be divided as : 1) Transmission IR; 2) DRIFTS IR i.e Diffuse Reflectance Infrared Spectroscopy. Moreover, the trasmission IR is mostly used in catalysis to identify interation/reativity or binding of probe moleculs with the metal oxides.The variables are intensity and wavenumber which depend on the tyep of proble molecule and metal oxide.

Nuclear Magnetic Resonance (NMR) - The variable in this technique is the type of nuclei of molecules present in a sample. In presence of magnetic field, nuclei of species attain certain direction (spin) with respect to the magnetic field. A high frequency wave is applied to the sample, and it shows change in the direction of nuclei. The instrument detects the change in the frequency of the wave applied. Thi will be different from one molecule to another.

2.

As a biomedical engineer with expertise in biomaterials why would you need these techniques (UV, IR, NMR, Mass Spec spectroscopy)?

In biomaterials or medical fields, the application of analytical tools varies from their application. For example, a combination of Mass Spectroscopy and NMR can be used to detect sample, if the sample contains mixture of complex molecules such phenols,alkylated benzene and paraffins (CnH2n+2; n=1,2,3..). There is hardly any way to analyze all molecules in a sample with a signle technique if the mixture contains hundreds of different molecules.

3.

If you lived in an alternative universe where all size scales of matter followed Newtonian physics, which spectroscopic technique, if any, could you still employ. You do know about the structure of atoms and molecules so atomic numbers, atomic weights, neutrons, protons and electrons are known.  

Based on our knowledge of above mentioned analytical tools, we try to charaterize molecules or atoms when subjected to incident known radition or magnetic field. Any deviation from the reference molecules could be difficult to analyze in case of alternative universe and it should be classified as 'new element'. But it could be possible to closely identify it in case it has orginated and resembled to the properties of periodic table elements and compounds known to us so far.