Coordinated Instrumentation Facility
Inorganics Lab
Page Contents
- Welcome
- X-ray dispersive powder diffractometer
- X-ray fluorescence spectrometers, energy- and wavelength-dispersive
- Inductively-Coupled Plasma (ICP) Atomic Emission Spectrometer
- Sediment-dating radiometer *
- Sample preparation
- Personnel
Also, an Inductively-Coupled Plasma/Mass Spectrometer (ICP/MS) is located in the CIF Organics Laboratory.
Welcome
The CIF Inorganic Laboratory is located in room 105 of the Science and Engineering Facility (Bldg. #16). The instruments in this laboratory are used to analyze, identify, and describe a wide variety of solids and solutions. CIF personnel are available to train students in the safe preparation of samples and operation of the instruments. The Inorganic Laboratory analyzes a wide variety of samples including environmentally related samples and recycled catalysts. Samples are not limited to rocks, soil, and inorganic chemicals; organic materials such as tree cores, polymers, and fish tissue can be analyzed for many of the heavy metals. The instruments can be used individually, but are of greater use when they complement one another. They provide us with knowledge of a previously invisible world. The laboratory can determine what elements a sample contains, the sample concentration, the type of crystalline material components and obtain a measure of the physical size and distribution of particles within a sample.X-ray Diffractometer (XRD)
The x-ray powder diffractometer is used to identify crystalline compounds. Most solids are crystalline, and their diffraction pattern can be computer matched to a database of more than 115,000 known patterns. XRD is often used for qualitative identification of compounds. If standards are available, it can perform quantitative analysis. The laboratory uses a Scintag XDS2000 equipped with an automated sample changer and a high resolution solid state detector.
The Scintag diffactometer was purchased in 1990. Jade, a user-friendly software package, was first purchased in 1993, and upgraded in 1999, to speed up the computerized search/match of the database. To improve our research capabilities, a CD-ROM containing the full database was purchased in October 1994 from the International Centre for Diffraction Data, ICDD. The 2003 ICDD files are used for our current search/match database. Typical XRD samples being run include recycled catalysts and special polymer films from the Chemical Engineering Department. Also, environmentally related reaction products from the Chemistry Department are being verified. Occasionally the minerals present in rock samples are identified.
The characteristic atoms of a particular crystal are oriented in a set way, and the spacing between these atoms is very specific. The x-ray powder diffraction instrument uses the structure of the crystal to identify the compound. The electron fields around the atoms can diffract an x-ray beam. As the beam rotates about the sample, the diffracted beam is reinforced at angles that depend on these atomic spaces. Each crystalline compound has a unique diffraction pattern, like a fingerprint. The diffraction information is tracked graphically. The peaks' angles in this graphical information are converted into numerical values called d-spacing, and the relative peak intensities are measured on a scale of 1 to 100. To identify the sample, this numerical information must be matched in an organized search of as many as 157,000 known files of compounds.
Fast identification of sample components using a PC-based system is now made possible by having over 157,000 powder diffraction files on a single CD-ROM disk. The ICDD is the main source of these known files. The number of patterns to be searched may be reduced by restricting the search. For example, restricting the file to minerals excludes organic and other inorganic data files. Restricting the search to certain elements also reduces the search time. Many samples contain more than one compound, which may result in peak overlaps and other problems. The Jade software makes easy work of problem search/matches.
Normally only solid samples have crystalline patterns. The sample to be analyzed is ground to a fine powder to randomly orient the crystals and equally expose all the crystal faces to the x-ray beam. Samples should be ground to less than 40 mm. When preparing a sample, preferred orientation should be avoided because orientation affects peak intensities. The ICDD files are based on the sample's random crystal orientation.
The x-ray beam is generated by a finely focused x-ray tube, with a water-cooled copper anode. Ideally, the x-rays should be one wavelength, copper K-a1. However, Cu K- a2, Cu K-b and background x-rays are also generated. The sample may also produce fluorescence radiation, which results in a high background; samples high in iron may cause this problem. All of the radiation from the sample could be picked up by the detector. The XRD uses a high-resolution solid-state detector to stop some of the unwanted radiation, while some is stopped by electronic discrimination. The computer, leaving only the K-a1 peaks, strips out the K- a2 peaks and the background that normally appear in the raw pattern.
The x-ray tube, sample holder, and detector are mounted on a goniometer. The sample is horizontal on a vertical goniometer. The detector and x-ray tube turn, and the sample is stationary. This type of goniometer operates in what is called theta/theta mode. The angles from the sample of the incident beam and the diffracted beam are equal.
X-ray Fluorescence (XRF)
These instruments have not yet been re-installed in the new location. 
Two types of XRF analyzers are available, a wavelength XRF (or WDXRF) and an energy dispersive XRF (or EDXRF). Both of these XRFs provide a non-destructive analysis method for solid samples with a minimum of sample preparation. Fine powder samples are mixed with a wax binder and pressed into a pellet. This instrument is capable of a rapid qualitative analysis of a sample for elements with atomic weights greater than sodium. The WDXRF will also do percentage concentrations of fluorine. Both instruments are equipped with a computer which controls the automatic sample chamber, calculates the elemental concentrations, and prepares a report.
The WDXRF is a Siemens SRS 200. The instrument was installed in 1982 and received new software in December 1994. The new software improved our development capabilities for this instrument. The EDXRF (Spectro X-lab), made by Spectro, was installed in November 1994. Bruker now makes the Siemens WDXRF and Ametek makes the Spectro EDXRF.
Samples currently being run on the EDXRF are tree cores and soils for heavy metal content and recycled catalyst samples. Recently, a total chemical analyses on rock samples from Arizona State University, the University of New Orleans, and Tulane University were done using both fluorescence instruments.
In the operation of either XRF instrument, the sample is bombarded by x-rays causing the various elements to fluoresce with their characteristic x-ray energy in proportion to their concentration. The way in which the x-ray information is handled on these two XRFs is very different.
On the EDXRF, a very specialized solid-state detector and the analyzer system sort out the x-ray energies that are displayed for evaluation. Sensitivity of the instrument for specific elements can be accomplished by using the computer to select either the various secondary x-ray targets or the polarizing x-ray targets between this source and the sample. The optimum x-ray tube voltage potential and current are set automatically to improve sensitivity. A number of elements can be analyzed simultaneously by the EDXRF. Spectro precalibrated the EDXRF with more than 194 standards to make the pellets method file. Specialized analysis files like the tree core and catalyst use only similar matrix standards for their calibrations.
The WDXRF uses crystals to separate the x-ray wavelengths. Direct excitation of the sample is done with a chrome or molybdenum anode x-ray tube. The proper crystal and angle on that crystal are selected by the computer for each element. One element is detected at a time making this a sequential spectrometer. The resolution on the WDXRF is better than the EDXRF.
Inductively-Coupled Plasma (ICP) Atomic Emission Spectrometer
The ICP, a Perkin Elmer Optima 3000 installed in December 1993, can
simultaneously perform analysis of over 75 elements. The ICP, using Argon gas, takes the liquid and atomizes and ionizes the sample. As the atoms emit electrons, the UV and visible radiation is characteristic of a specific atom and is utilized in the detection. The advantages of
using the ICP are its rapid analysis of samples, freedom from most
interference, and sensitivity to analyze three to four orders of
magnitude.
Samples must be dissolved in an acidic matrix for uptake by the Ultrasonic Nebulizer (USN). Solutions with a total dissolved salt content greater than 1.0 mg/ml will plug the USN. Any undissolved solids may also plug the fine capillaries in the USN.
The ICP regularly analyzes samples from the Departments of Chemistry, Earth and Environmental Sciences (EES), Biology (EEOB), Biomedical Engineering, and Chemical Engineering. The use of the ultrasonic nebulizer allows trace elements to be seen in drinking water and biological tissue samples. Typical samples run by the ICP are soils, sediments, tree cores, catalysts, synthetic chemicals, and biomedical implants. All samples analyzed by the ICP must be aqueous and totally free of undissolved particles. The Inorganic Laboratory has digestion capabilities to assist you in sample preparation.
Sample Preparation
The Inorganic Laboratory has several options for sample preparation. Two CEM closed vessel microwave sample preparation systems and microwave ashing furnace system are available. The units were purchased in December 1993 and May 1995. The microwave digesters have pressure and temperature sensors to monitor the sample decomposition. They use pressure, temperature, and acids to digest the samples. The microwave ashing furnace offers a quick way to ash samples, up to 97% faster than conventional muffle furnaces. Most of the samples that are run on the ICP and ICP/MS are first digested by the microwave. The microwave systems have many advantages that make them useful. They reduce sample preparation time, offer control of the reaction, and are easy to use. A digestion program can be set up for each individual sample. High and low pressures are available. Typically, the high pressure vessels are used for biological and organic samples while the low pressure vessels are sued for soil/sediment, environmnental samples, and catalysts. If you have any questions about how to prepare your samples, do not hesitate to call.Sample contamination is prevented by using high-purity deionized water and low trace metal digestion acids. The digestion vessels and glassware are acid cleaned and washed before use.
All the necessary safety equipment, such as gloves, lab coats, and safety glasses are available in the Inorganic Laboratory. It is extremely important that users of the microwave systems are safety trained.
Additionally, there is a hot plate digestion table and a cleanroom available in the Organic Laboratory.