| RMAL HOME | Techniques
Complete metals analysis at the RMAL is accomplished by using up to four different analytical techniques. These four techniques are:
The EPA's "Test Methods for Evaluating Solid Waste Physical/Chemical Methods" (SW846) is used as guidance for all samples requiring regulatory analysis The RMAL has developed in house standard analytical methods (SAM) based on SW846 methods with necessary modifications to take into account the complex matrices and radioactive nature of the samples. The current SAMs kept on file at the RMAL are as follows:
Each instrument is either located in a radiochemical hood or interfaced with a hood system for radioactive containment. Each instrument is described below with a list of typical analytes and their detection limits. Pictures of the instruments are also included.
Inductively Coupled Plasma - Atomic Emission Spectroscopy (ICP-AES) Type: SpectroFlame ICP-AES. Operation: A liquid sample is passed through a nebulizer to create an aerosol. The aerosol is transported via an argon gas stream to a gas plasma (medium temperature of the plasma is 8,000 to 10,000 Kelvin). As the aerosol passes through the plasma it is dried, melted, evaporated, atomized, then excited. When the excited atoms pass through the cooler part of the plasma they de-excite releasing photons at specific wavelength dependent on the element. The wavelength emissions are passed to the optical system which measures the intensities of the emitted light. The wavelength intensities are directly proportional to the concentrations of the analytes. The SpectroFlame uses fiber optics to pass the emitted light from the plasma to the optic system for analyte qualification and quantitation. With this configuration the RMAL was able to place the sampling system and torchbox of the ICP in a radiochemical hood and place the optics outside the hood on the benchtop with a computer workstation for data collection and reduction. Typical metals and their
detection limits: The SpectroFlame ICP-AES is equipped with three polychromators
(allows for simultaneous detection of two or more wavelengths) and one
monochromator (can sequentially scan a set number of wavelengths). The
polychromator is configured for the simultaneous detection of the 22 elements
listed in the table below. The monochromator can scan any wavelength from
180 nm to 800 nm. Only the typical metals analyzed using the monochromator
are shown with their detection limits. RCRA metals are in bold and the
cell is shaded yellow (proposed metals are shaded brown).
Inductively Coupled Plasma - Mass Spectroscopy (ICP-MS) Type: VG Elemental Fisons PlasmaQuad II interfaced with a CETAC MCN 6000 desolvating nebulizer. Operation: A liquid sample is nebulized to create an aerosol. The aerosol is passed through a membrane chamber and stripped of moisture before being transported via an argon gas stream to a gas plasma. The atomized and ionized sample is then directed from the plasma into a quadrapole mass spectrometer via a series of cones and charged lens. The mass filter then transmits ions of specific mass-to-charge ratios to a detector where they are detected as electronic pulses. The number of registered ions from a given isotope is directly proportional to the concentration. The PlasmaQuad is interfaced with a radiochemical hood system such that only the sample introduction system and the ion source, including the sampling and skimmer cones, are contained within the hood. All other components are located outside of the hood boundaries. This allows for convenient maintenance and upkeep of all major components of the instrument while providing adequate rad protection for laboratory personnel. The CETAC desolvating autosampler strips the nebulized sample of moisture prior to reaching the plasma resulting in a "dry plasma". This technique significantly lowers oxide formation and increases sensitivity when compared to conventional spray chamber equipped sample introduction systems. Since the installation of the MCN 6000 the RMAL has reduced the oxide levels to less than 0.04% and have increased sensitivity up to a factor of ten resulting in significantly lower instrument detection limits with reduced interferences. Lastly, another advantage is that no radioactive waste is produced during the analysis. Typical metals and their detection limits: The RMAL uses the ICP-MS for a variety of metal and isotopic analysis and a list of detection limits would be too large to present here. Instead suffice it to say that the typical detection limits are in the parts per trillion range for analytes with clean mass lines. For some analytes, such as the non-metals sulfer and phosphorus, which have interferences at their mass lines the detection limits will be increased to the parts per billion range. Some examples of how the
RMAL uses the ICP-MS for waste characterization studies are listed below.
Graphite Furnace - Atomic Absorption Spectroscopy (GFAA) Type: Perkin-Elmer SIMAA 6000. Operation: A sample with a matrix modifier is placed onto a graphite platform contained within a graphite tube. The sample is taken through a series of increasing temperatures using a temperature program to atomize the sample. The temperature program first removes moisture using a number of drying steps. Next, the temperature is raised to char the sample. This char (or pyrolysis) step is used to volatilize the sample's matrix while maintaining the analyte on the platform. The sample is then subject to an instantaneous step up in temperature (typically up to 2100 degrees centigrade) to atomize it and form an atomized vapor cloud in the graphite tube. Light of a specific wavelength and known intensity is passed through the vapor cloud. The analyte will absorb some of the light and the difference in the starting intensity and final intensity is used to determine the analytes concentration using Beer's law and comparing absorption values to that of standards of known concentrations. The SIMAA 6000 allows for
the simultaneous detection of up to six analytes with one sample burn.
This is accomplished using prisms to combine multiple analytical wavelengths
so that they form a single beam of light which is then passed through the
graphite tube when the sample is atomized. An Echelle polychromator system
is then used to separate and detect each analytical wavelength for analyte
quantitation.
Cold Vapor - Atomic Absorption Spectroscopy (CVAA) Type: CETAC M-6000A Operation: The RMAL uses the cold vapor instrument primarily for the detection of mercury. A liquid sample is introduced into the instrument via a peristaltic pump were it is mixed with a stannous chloride (SnCl2) solution. The tin reduces the oxidized mercury (Hg II) in the sample to the elemental state forming mercury vapor. The mixture is passed through a gas/liquid separator were the mercury vapor is entrained into a dry argon gas stream. The gas stream transports the mercury vapor through a drying tube to remove moisture then to a sample cell for measurement. In the sample cell the mercury vapors will absorb the 253.6 nm radiation focused through the cell to a solid state silicon detector. The incident radiant power is measured and compared to a reference cell to obtain the mercury concentration using Beer's law and comparing absorption values to that of standards of known concentrations. Typical metals and their detection limits: The CETAC M-6000A analyzer can be operated using three ranges for mercury detection. Using its most sensitive range the instrument detection limit for mercury is one part per trillion (ppt). |
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