Instrumentation

What is it?

An NMR spectrometer is an instrument that uses a high field (9T) superconducting magnet and frequency inputs to measure the energy required to change the magnetic alignment of nuclei that have magnetic dipole moments (typically spin = 1/2 nuclei such as 1H, 13C, 19F, 31P, and others). The energy depends on the type of nuclei and the chemical environment (i.e., connections to other atoms).

The high-resolution NMR at Bowdoin is used by students taking Organic Chemistry I and II, Molecular Structure Determination, Instrumental Analysis, and Physical Chemistry laboratory. The instrument is heavily used by students for their research projects.

Applications:

NMR spectroscopy is a powerful instrument that is used to verify structures (connectivity and geometries) of new molecules, to assess reaction yields, and to measure rates of dynamic processes. NMR is often used in conjunction with other techniques (mass spectrometry and infrared spectroscopy) for unknown structure determinations.

Bowdoin Users:

The high-resolution NMR at Bowdoin is used by students taking Organic Chemistry I and II, Molecular Structure Determination, Instrumental Analysis, and Physical Chemistry laboratory. The instrument is heavily used by students for their research projects.

What is it?

High performance liquid chromatography is a type of chromatography used to separate and identify chemicals in the liquid state. The sample is forced through a column (stationary phase) by liquid (mobile phase) at high pressure, which decreases the time that the separated components remain on the column.

Applications:

HPLC is used for structure determinations and is parcticularly useful when dealing with mixtures of compounds that may be present at low concentrations. This is also an important technique for quantitative measurements.

Bowdoin Users:

The HPLC instruments at Bowdoin are used by students taking Molecular Structure Determination, Quantitative Analysis, and Instrumental Analysis. The instrument is heavily used by students for their research projects.

What is it?

What is it?

GC/MS is a technique that uses the combination of a gas chromatograph (GC) to separate compounds in a mixture to a mass spectrometer (MS) for identification and quantification. The MS produces ions with a +1 charge in a vacuum that can be “weighed” to determine the mass of the original molecule.  Fragment ions can be used to determine molecular structure.

The GC/MS instruments at Bowdoin are used by students taking Molecular Structure Determination, Quantitative Analysis, and Instrumental Analysis. The instrument is heavily used by students for their research.

Applications:

GC/MS is used for structure determinations and is particularly useful when dealing with mixtures of compounds that may be present at low concentrations. This is also an important technique for quantitative measurements.

Bowdoin Users:

The GC/MS instruments at Bowdoin are used by students taking Molecular Structure Determination, Quantitative Analysis, and Instrumental Analysis. The instrument is heavily used by students for their research projects.

What is it?

Ultraviolet-visible spectroscopy is a type of spectroscopy that uses the visible and UV portion of the electromagnetic spectrum. In this region, molecules undergo electronic transitions. To obtain an absorption spectrum, a sample is placed in the spectrophotometer where ultraviolet and visible light are shined through the sample. The spectrophotometer measures how much of the light is absorbed by the sample. The intensity of light before passing through the sample is I0. The intensity of light remaining after it has passed through the sample is I. The fraction of light transmittance is (I / I0), which is usually expressed as a percent transmittance (%T).

What is it?

Infrared spectroscopy is a type of spectroscopy that uses the infrared portion of the electromagnetic spectrum. Infrared spectroscopy works because chemical bonds have specific frequencies at which they vibrate. These resonant frequencies are dependent on the length of the bond and the mass of the atoms connected by the bond. Therefore, the frequency of the vibrations can be associated with a particular bond type. Bonds can vibrate in six different ways, symmetrical and asymmetrical stretching, scissoring, rocking, wagging, and twisting.

Example project using this instrument:

Multiscale Analysis of Ciprofloxacin Reactions with Solid and Aqueous Ferric Species

• Researcher: Paras Triveda
• Abstract: Accurate risk assessment and effective management of aquatic and soil environments contaminated with human and veterinary antibiotics, such as ciprofloxacin, require systematic compilation of mechanistic and quantitative information on antibiotic speciation chemistry in the presence of ubiquitous sorbents, such as iron oxides. Combined results of ATR-FTIR and UV-VIS spectroscopic studies and computational molecular modeling suggest that ciprofloxacin mainly interacts electrostatically with ferric species via its carboxylate group. However, the extent of participation of these functional groups and thus the ultimate nature of the sorption reaction is predominantly a function of the physicochemical properties of the ferric species (surface charge density and degree of crystallinity). Complementary XAS studies, at Fe K-edge, reveal that the local structures of the ciprofloxacin-reacted ferric species are akin to those of unreacted ferric species, and thus corroborate the electrostatic interaction between them and cipro.

What is it?

Jasco FP-6500: Fluorescence is the process by which a molecule absorbs light energy of a given wavelength and emits most of that energy as light of a longer wavelength. The rest of the energy is lost via non-photon-emitting processes. Because fluorescence spectroscopy is both an absorption and emission process, it can be more selective than UV/visible absorption spectroscopy.

Example project using this instrument:

The Photocatalyzed Decomposition of Methanol to Formaldehyde and Molecular Hydrogen

• Researcher: Robert Adam Kinney
• Abstract: The photocatalytic capabilities of tetrakis(m-diphosphito)diplatinate(II) (Pt2), Pt2/HgII, and Pt2/TlIII were determined with respect to the decomposition of methanol to formaldehyde and molecular hydrogen. The relationships between reaction time, d10 metal concentration, and formaldehyde concentration were examined to elucidate the primary catalytic species in each system, as well as to completely determine the formaldehyde-generating processes that occur during the reaction. It was found that Pt2 acts photocatalytically on methanol to form formaldehyde. Addition of the d10 metals HgII and TlIII to methanolic Pt2 results in the formation of the photocatalytic species Pt2HgI and Pt2TlI, respectively. These species are in equilibrium with Pt2, meaning both contribute to the formation of formaldehyde during the reaction. Furthermore, Pt2TlI has a slower reaction rate relative to Pt2. A third process, the ligand to metal charge-transfer in the d10-solvato species, also results in formation of formaldehyde at a 1:1 molar ratio. The three processes combine to give the total formaldehyde yield for the system. Based on the observed degradation of the Pt2TlI photocatalyst over time, it is proposed that similar behavior occurs for the Pt2 system, except over a longer time frame. Such degradation does not occur for the Pt2HgI species. Rather, Pt2 is regenerated, as Hg0 is observed to form. Finally, preliminary studies on a hydrogen detection assay utilizing derivitization of Vaska’s complex were conducted. Early results suggest the method can reproducibly detect hydrogen, but the experimental setup needs to be refined to minimize atmospheric oxygen interference. The results of control experiments demonstrate that detection of hydrogen is possible with good sensitivity.

What is it?

Cyclic voltammetry measures the current (rate of electron flow) versus a varying applied potential (voltage or energy of electrons). The applied potential is the difference in energy of the working and reference electrodes, measured in volts (V) or millivolts (mV). Cyclic voltammetry is used to characterize how easily a compound is able to lose or accept an electron (i.e., undergo oxidation or reduction). It can be used to determine if these redox reactions are reversible, and to study the mechanism by which the reactions take place.

Bowdoin Users:

The cyclic voltammetry instrument at Bowdoin is used by students taking the Inorganic Chemistry course and by students who need to characterize the redox properties of a compound as part of their research.

What is it?