Department of Chemistry Instrumentation Facility
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Instrumentation manager: Carol
A. Holden
Facility director: Sarah
C. Rutan
Atomic-absorption spectroscopy:
Atomic-absorption (AA) spectroscopy uses the absorption of light
to measure the concentration of gas-phase atoms. It is the most widely
used method for the determination of single elements in analytical samples.
Instrument: Varian - SpectrAA55 Atomic Absorption Spectrometer
Standards and samples are generally prepared in acid for best results. A “cookbook” is available for checkout from the manager, which provides suggested conditions for analysis of different elements.
Lamps available: Fe, Cu, Na, Mg, W, Mo, Tb, Gd, Co, P, Ir, Eu, Fe, Cd, Pt, Ni, Ca, Zn, Pb, Al and Pd.
Fluorescence spectroscopy:
Fluorescence spectroscopy is the optical emission from molecules
that have been excited to higher energy levels by absorption of electromagnetic
radiation. The main advantage of fluorescence detection compared to absorption
measurements is the greater sensitivity achievable because the fluorescence
signal has a very low background.
Instrument: Cary Eclipse Fluorescence Spectrophotometer
This instrument is equipped with a Xenon flash allowing the user to choose the collection mode of choice: fluorescence, phosphorescence or chemi/bio luminescence. The instrument has two monochromators, excitation and emission, and a photomultiplier tube detector.
Accessories available: A microplate reader accessory that measures 96 wells in less than 50 seconds and 384 in less than 90 seconds, and performs a full wavelength scan on each well within minutes. Also, a solid sample attachment, polarizers and a temperature-controlled cell holder are available for use.
User must provide cuvettes of choice.
FTIR and Raman spectroscopy:
In infrared spectroscopy, vibrational absorptions are measured. Fourier-transform
infrared spectrometers offer the advantage of high sensitivity, resolution
and speed of data acquisition.
Raman spectroscopy is based on the Raman Effect, which is the inelastic scattering of photons by molecules. Infrared (IR) and Raman spectroscopy both measure the vibrational energies of molecules but rely on different selection rules.
Instrument: Nicolet - Nexus 670 FT-IR and FT-Raman Module
This instrument has an Ever-Glo (black body radiation) light source and a XT-KBr beam splitter for near- and mid-infrared measurements and a polyethylene beam splitter for far-infrared measurements. The Raman module employs a Nd:YAG laser source at 1064 nm.
The detector for IR measurements is DTGS (deuterated triglycine sulfate) and for Raman, an InGaAs detector is used.
The user needs to provide IR-grade KBr for preparing pellet samples, or an appropriate liquid or mull-based cell.
Accessories: HATR (Horizontal Attenuated Total Reflectance): This accessory is ideal for highly absorbing materials such as aqueous solutions, rubbers and polymers (films).
Diffuse reflectance: The diffuse reflectance accessory can be used for most solids that can be put into a powder or crystalline state. Infrared KBr can be used for diluting solid samples and as a reference (supplied by user).
Mass spectrometry:
“Mass spectrometry is the art of ‘weighing’ individual
atoms and molecules to determine their masses or molecular weights. Such
mass or weight information is sometimes sufficient, frequently necessary
and always useful in determining the identity of a species.” –
John B. Fenn
Our instrumentation facility offers two GC-MS instruments, which are outlined below:
Hewlett-Packard G1800C Series II GCD System with HP ChemStation Software.
This instrument offers the following features:
Ion source: Electron Impact (EI)
Mass analyzer: Linear Quadrupole
Detector: Electron Multiplier (EM)
Varian Saturn 2000 GC/MS
Ion source: Electron Impact (EI) and Chemical Ionization
(CI)
Mass analyzer: Ion Trap
Detector: Electron Multiplier (EM)
Tandem mass spectrometry: (MS/MS)
Frequent users should provide their own GC syringes.
Liquid chromatography:
Instrument: Hewlett Packard, Series II, 1090 Liquid Chromatograph with HP ChemStation software.
This instrument has a diode array detector (200-600 nm) and a binary solvent delivery system.
Columns available: Waters C18, 4.6 x 150 mm column, Phenomenex C18, 4.6 x 300 (Bondapak & Bondclone), Chiral – AGP, 4.6 x 100 mm column, Agilent, Zorbax SB-CN, 4.6 x 150 mm column.
Available for use: solvent filtration system and filters (all mobile phases must be filtered), injection syringes.
User must provide solvents and mobile phases, and syringe filters for samples.
Ion exchange chromatography:
Ion exchange chromatography (IEC) is applicable to the separation of almost
any type of charged molecule, from large proteins to small nucleotides
and amino acids.
Instrument: Dionex ICS (Ion Chromatograph System) 1000
This instrument has a dual-piston pump, electrolytic suppression and digital conductivity detection. The AS14-A anion exchange column, with bicarbonate/carbonate eluent, provides sufficient separation of fluoride, chloride, bromide, acetate, nitrite, nitrate, phosphate and sulfate. In addition, there is an AS11-A anion exchange column that works with a sodium hydroxide eluent.
Columns available: Anion exchange column with membrane suppressor.
Inductively coupled plasma-optical emission spectroscopy (ICP-OES):
An ICP is a very high temperature (7000-8000K) excitation source that
efficiently desolvates, vaporizes, excites and ionizes atoms. Molecular
interferences are greatly reduced with this excitation source but are
not eliminated completely. ICP sources are used to excite atoms for optical
emission spectroscopy.
Instrument: Varian - Vista MPX, CCD Simultaneous ICP-OES
This instrument offers simultaneous measurement of approximately 75 elements from parts-per-billion to percent levels. Samples either can be introduced for analysis individually or by the use of an autosampler.
Available for use: Sample tubes for training and initial use. For additional use, sample tubes must be purchased by the user.
Scanning electron microscope:
The scanning electron microscope (SEM) uses electrons rather than light
to form an image. According to Skoog, Holler and Nieman in the fifth edition
of Principles of Instrumental Analysis, “. . . the surface of a
solid sample is scanned in a raster pattern with a beam of energetic electrons.”
There are many advantages to using the SEM as opposed to a light microscope.
Iowa State University Materials Science and Engineering Department summarizes
these advantages, stating that, “(t)he combination of higher magnification,
larger depth of focus, greater resolution and ease of sample observation
makes the SEM one of the most heavily used instruments in research areas
today.”
Instrument(s): The instrument facility has two SEMs.
They are:
1.) ABT, DS-130 Dual Stage Scanning Electron Microscope.
This instrument has the capability to do SEM (scanning electron microscopy),
STEM (scanning transmission electron microscopy) and EDX (energy dispersive
X-ray analysis).
The high resolution top stage positions the specimen
between the pole pieces of the objective lens and collects the imaging
electrons above the lens. The associated high electron efficiency collection
provides a resolution of 3nm with ideal samples. The lower stage is of
conventional design and allows specimens up to 10cm diameter to be examined
with a resolution of 6nm. Both stages are fitted with EDX Si/Li detectors.
2.) JEOL, JSM-T300 Scanning Microscope
Features:
• accelerated voltage from 1 – 35
• manual specimen stage X = 0-40 mm Y = 0-80 mm
• secondary and back scattered detectors
• fully automatic vacuum chambers
Capabilities:
• 6 mm resolution
• 15 by (WD = 48 mm) ~ 200,000 provided with automatic magnification
correction device
Thermal desorption for GC sample preparation:
The use of thermal desorption in conjunction with gas chromatography (GC)
assumes that some analytes of interest have been absorbed by some other
material and, by heating them, they can be liberated from their matrix.
Once desorbed, they are amenable to analysis by GC. This serves as a basis
for the analysis of a wide range of complex sample types including environmental
materials, fuel sources, foods, pharmaceuticals, polymers and many consumer
products.
One advantage of thermal desorption of sample compounds to GC permits analysis of 100 percent of the sample as opposed to an aliquot, which enables an immediate increase in sensitivity.
Instrument: Bulk Dynamic Headspace Sampler System, CDS 8000 Concentrator
This instrument comes with bulk sampling accessory that permits outgasing/thermal desorption of large or irregularly shaped materials. Samples can be heated up to 300∞C while the purge gas transfers the analytes to the built-in trap. After collection, the trap is heated to transfer analytes to the Varian Saturn 2000 GC-MS.
Accessory vessels: 95 mm x 110 mm vessel and a 38 mm x 128 mm bulk sampling vessel
UV-visible spectroscopy:
Molecular ultraviolet/visible absorption by molecules generally occurs
in one or more electronic absorption bands, each of which is made up of
numerous closely packed but discrete lines. Each line arises from the
transition of an electron from the ground state to one of the many vibrational
and rotational energy states associated with each excited electronic energy
state.
In condensed phase spectroscopy, these lines merge and appear as broad bands.
Instrument(s): The instrument facility has three Hewlett Packard 8453 UV-visible Spectroscopy Systems, each equipped with the latest version of HP ChemStation software.
One instrument is equipped with a HP 89090A Temperature Control so the user can control the sample temperature, and the other two are equipped with a Sipper System. As stated in the accompanying operator’s manual, written by Agilent Technologies, “(t)he Sipper System provides a simple method of improving the productivity and reproducibility of spectrophotometric analysis by eliminating the handling of cuvettes and the errors that can result in cuvette repositioning.”
These instruments offer:
UV-visible range: 200-780 nm
Light sources: deuterium and tungsten
Detector: diode array detector (2 nm/diode)
