MIPAES
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MIPAES |
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Tatiana Stoppe and Angela Zapata
Plasma spectroscopy has emerged as a primary method for elemental analysis of both organic and inorganic species. The Ar Inductively Coupled Plasma (ICP) has become the preferred technique for multielement metals analysis, offering excellent sensitivity, accuracy and precision. Another plasma source employed for elemental analysis is the Microwave Induced Plasma (MIP). Although MIPs are more commonly used for the analysis of gas streams (e.g., gas chromatography detection), analysis of nebulized metals solutions has also been demonstrated. The introduction of nebulized aqueous solutions into a plasma tends to diminish its stability and performance. Therefore, the plasma must be sustained at higher power and gas flow levels, thereby resulting in a more robust plasma.
The feasibility of employing a capillary MIP as an excitation source for metal contaminants is demonstrated. Atomization/excitation of analyte species is achieved by a plasma source which utilizes 0.5 L/min He at 50 W. These requirements are significantly lower than those of commercial ICPs (on average 14 L/min Ar at 1200 W) and experimental MIPs (on average 8 L/min He at 350 W). The capillary MIP employed, which was originally developed for gas chromatography applications, was taken from a commercial unit and modified to allow operation of a more stable plasma. Emission spectra were collected with a photo diode array spectrometer, and a photomultiplier tube sequential monochromator. Liquid samples were introduced as aerosols by using a peristaltic pump to deliver the solutions into a Hildebrand grid nebulizer.
Plasma characterization has included temperature and electron number density measurements under various experimental conditions. We have demonstrated that nebulized aqueous samples can be continuously introduced into the plasma without extinguishing it; further the stability of the plasma is evidenced by the good %RSD values (0.8-12%) of the linear dynamic ranges obtained. Various fundamental studies to characterize the plasma and to better understand the parameters which affect its optimization have been performed.
Recently, a variable attenuator, double stub tuner, and directional coupler have been added in order achieve a tunable source in which the forward and reflected power can be measured and controlled. Future developments include increasing the forward power. Our overall objective is the development of a field transportable instrument for on-site metals analysis. This instrument will be compact with low power and gas consumption.
For more information:
Zapata, Angela M., Bock, Christa L., Robbat, Albert Jr., Pittsburgh Conf. On Analyt. Chem. and Appl. Spectrosc. Abstract 424 (1998).
Angela Zapata and Zinovi Kataenko
Current demands on the government and private sector to remediate hazardous waste sites has resulted in the development of innovative assessment and remediation technologies which can reduce the time and cost associated with such practices. Field analytical techniques can significantly expedite site assessment by allowing on-site decision making, which in turn reduces the cost of traditional sampling and commercial laboratory services. Today, plasma sources are routinely used for the analysis of organic compounds (Gas Chromatography-Atomic Emission Spectroscopy (GC-AES)) and metals (Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES)). ICP instruments have been employed in field applications demonstrating excellent stability and performance. However, their size and amount of consumables required are far from the ideal for convenient field deployment.
A field practical Microwave Induced Plasma-Mass Spectrometer (MIP-MS) for the analysis of both metallic and organic pollutants present in gaseous and aqueous media has been investigated. Atomization/ionization of analyte species is achieved by a plasma source which utilizes 0.5 L/min He at 50 W. Because this capillary source has significantly lower consumable demands than commercially available ICPs (18 L/min Ar at 1000 W), it is a more practical source for field applications than ICP-AES or ICP-MS instruments. The capillary MIP employed was originally developed for gas chromatography applications, and was taken from a commercial unit without further modifications. The three-stage differentially pumped interface for coupling the atmospheric pressure MIP to the low pressure MS was designed and assembled in our laboratory. It comprises of a skimmer cone placed between the first and second chamber, and extraction lenses which direct the ions into the quadrupole manifold. The mass spectrometer consists of ion focusing lenses, a one-piece, metal-coated glass quadrupole, and an electron multiplier offset from the plasma axis.
The plasma's fundamental properties (e.g., Texc, Trot, Tion, and ne), as well as the background mass spectrum obtained is comparable to those of much larger MIP sources. SIM spectra of pesticide and PCB standard mixtures separated by gas chromatography have been collected. The stability of this capillary plasma in the presence of various media is evidenced by the successful continuous introduction of nebulized aqueous samples, and by the reproducibility and quantitability of the emission spectra of metals samples so far collected.
For more information:
Zapata, Angela M., Kataenko, Z., Robbat, Albert Jr., Pittsburgh Conf. On Analyt. Chem. and Appl. Spectrosc. Abstract 1356 (1998).
Over the past 15 years $26 billion has been spent, with little progress made, cleaning the nations hazardous waste sites. The U.S. General Accounting Office estimates $32 billion will be spent in long-term monitoring costs associated with the operation and maintenance of these sites through the fiscal year 2040. The DoE estimates between hundreds of billion to several trillion dollars cleaning its sites over the next 40 years. The need to provide faster, cheaper, and more accurate data for cleanup support thus becomes very evident.
We have developed a thermal extraction cone penetrometer (TECP) probe aimed at expediting site investigations. The TECP probe can provide semi-quantitative data about sub-surface soil-bound organic contaminants without the need to collect the actual soil sample. Such a device will better focus the soil sampling to maximize the information obtained increase the available information number of samples collected and analyzed on a daily basis, thereby reducing the uncertainty associated with any cleanup effort.
The overall goal of this research was to develop methods and technology that can couple a cone penetrometer (CP) with a field based analytical instrument. The specific aim was to design, laboratory test, and field validate an in situ thermal extraction (TE) device housed inside the cone penetrometer truck for the purpose of providing semi-quantitative data about sub-surface soil-bound organic contaminants without the need to collect the actual soil sample. Such a device would increase the number of samples collected and analyzed on a daily basis, thereby reducing the uncertainty associated with any cleanup effort.
Cone penetrometer system for in-situ thermal extraction of organics in soil.
Carrrier gas flows through a heated tranfer line and probe head which also is heated to about 300 ºC. The gas flows out of the probe head and is drawn back into the probe carrying volatilized organics through an inlet hole connected to a vacuum system. The oragnics are carried to the surface via the tranfer line which is connected to a cooled adsorption unit. The unit traps the hot organic vapor extracted from the soil onto either tennax tubes (VOCs) or empty glass tubes (SVOCs). The tubes can then be placed into a Thermal Desorption Gas Chromatograph-Mass Spectrometer (see below for details) for analysis.
Control panel for in-situ probe.
Rather than use standard syringe injections into a conventional GC/MS system, a thermal desorption system is used for large volume injections (1 µL-1mL). It is designed to rapidly concentrate dilute samples by ballistically heating them. The temperature of the thermal desorber first starts out at a temperature that is sufficient enough to volatilize the solvent. The solvent is then driven off and out a vent by carrier gas so that it does not go onto the column. Once gone, the temperature can quickly be ramped to a high enough temperature to thermally desorb what is now organic extract off of the wall of the glass sleeve which lines the desorber unit. From there, the vapor is driven to the column by the carrier gas.
One advantage to the thermal desorption unit is that higher molecular weight organics remained trapped on the glass sleeve. This helps to protect the instrument from the matrix. Another advatage is an increase in detection limits.
We have characterized the properties of tetranuclear complexes of the form (µ-O)L4Cu4-xNix(H2O)xCl6 that have led to novel electrodeposited metal alloys and oxides. Solution electrochemical mechanisms and kinetics have been determined as well. Work is in progress to determine liquid effects both on solution and deposition properties as well as transmetallated complexes containing cobalt and zinc. This work has the potential to lead to a more environmetally benign electrodeposition process for producing a wide variety of mixed metal alloy and oxide compositions.
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