Progress 08/01/03 to 07/31/05
Outputs
Equipment was purchased and assembled to fabricate a programmable temperature vaporization - high-resolution gas chromatograph - mass selective detection (PTV-GC-MS) system. The system provides the means to transfer (semi-)volatile organic chemical ((S)VOC) analytes from commercially-available mini-sorbent tubes to the inlet of a high-resolution gas chromatograph-mass selective (GC-MS) for analysis. The PTV-GC-MS system will be used to measure masses of (S)VOCs collected from ambient air on filters or in sampling devices developed, fabricated, and tested in the PI's lab and transferred to mini-sorbent tubes. This final project report documents system components that were purchased, assembled, and tested, and successful transfer and analysis of one SVOC from a mini-sorbent tube. The analysis conditions utilized for the analysis, or similar ones, are applicable to analysis of hundreds of (S)VOCs present in ambient air at various concentrations. Although utilization of
supercritical fluid extraction (SFE) techniques was considered for transfer of analytes from sampling devices into the PTV inlet, it was decided that thermal extraction would be utilized as originally proposed. It was found that commercial SFE systems have decreased in availability in the past five years. The systems that are currently available were outside the price range of the grant for this project. In addition, the Project Director's research group has developed and utilized thermal extraction techniques for the past five years, and thus has developed a signicant knowledge base on its use. The viability of thermal extraction is high for analysis of numerous (S)VOCs of interest, and testing will be done to determine viability of analysis of thermally-labile (S)VOCs. Steps were also taken to minimize thermal degradation of analytes as described below. The system for thermal desorpton of analytes from mini-sorbent tubes and subsequent concentration in the PTV inlet was purchased
from Gerstel, Inc. (Baltimore, MD), assembled, installed, and the system conditioned and tuned. Items purchased included a TDS2 thermal desorption system, a CIS3 programmable temperature vaporization (PTV) inlet equipped with Peltier cooling, master software, and a mounting kit for the TDS2 on the GC. These items were installed on an Agilent 5890 Series II GC and an Agilent 5972 MS equipped with electron impact (EI) detection owned by Michigan Tech University, and the entire system assembled. Precautions taken to minimize thermal degradation of analytes included use of a Siltek-treated fused silica transfer line from Restek, Inc. (Bellefonte, PA) and a Siltek-treated glass wool liner packed by Restek, Inc. The system was utilized to analyze gamma-HCH deposited into a mini-sorbent tube. The total ion chromatogram exhibited a peak at 20.648 minutes, and the scan of this peak produced a spectrum having m/z values indicative of gamma-HCH (primary ion 183, secondary ions 181, 109; USEPA).
Analyses to determine detection limits and concentration precision and accuracy are presently underway for a mixture of six SVOCs.
Impacts
Mass selective detection rather than electron capture detection (ECD) or flame ionization detection (FID), as were the only detection methods available to us using gas chromatography, will greatly expand the ability to measure concentrations and fluxes of (S)VOCs of environmental significance using collection devices and techniques developed in the PI's group. For example, numerous pesticides and insecticides of interest in agriculture and forestry, and especially recently-commercialized ones such as alachlor, are not ECD or FID sensitive, yet can be analyzed by GC-MS. Also, analysis of compounds by PTV-GC-MS allows verification of compound identity when compound concentrations are routinely determined by GC-ECD or -FID. Determination of compound identity in ECD or FID is routinely carried out by comparison of the retention time of a compound in the sample with a retention time window determined using standards. Because determination of compound identity by mass
selective detection is based on comparison of m/z ratios of ionization products from the sample with those in published libraries of compound structure, chemical structure assignments can be carried out with no a priori information. This feature is highly advantageous when analyzing unknowns in environmental matrices. For ambient air samples collected using the novel techniques developed in the PIs group, the availability of a PTV-GC-MS system to measure analyte mass in mini-sorbent tubes greatly improves our ability to obtain grants and conduct studies that require use of such instrumentation.
Publications
- No publications reported this period
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Progress 10/01/03 to 09/30/04
Outputs
Progress to-date has been directed towards evaluating different options for each of the units that compose the system. An important development we made is identification of literature that suggests that we need to take special precautions to prevent thermal degradation of certain analytes. This development may require us to select a low-temperature extraction method over that proposed (thermal extraction), such as supercritical fluid extraction (SFE). Whether or not thermal extraction gives useful results is being evaluated now. The status of possible choices for purchase/fabrication of the units affected by this decision is discussed next. If thermal desorption is utilized for extraction, an analyte transfer unit and a mini-sorbent tube desorber unit will be built by us or a unit will be custom-built by CDS Analytical, Inc./Dynatherm Analytical Instruments, Inc. (Oxford, PA). The units built by us consist of (1) a deactivated stainless steel analyte transfer unit
consisting of a heated sleeve fit to the outer dimensions of high-volume diffusion denuders and a water-jacketed cold sleeve fit to the outer dimensions of mini-sorbent tubes with connections to nitrogen carrier gas will be built by us for ca. $1.5K. The temperature of the heated sleeve will be regulated with a controller, and helium carrier gas flowrate will be regulated with a pressure regulator, and (2) a mini-sorbent tube desorber fabricated by us for ca. $3K consists of a heated, deactivated, stainless steel sleeve with an outlet to a heated fused silica transfer line connected to the inlet fitting of a Programmable Temperature Vaporization (PTV) Inlet from Gerstel, Inc. (Baltimore, MD), and flow and temperature controllers. If CDS/Dynatherm can provide a unit within our project budget, this unit may be selected. CDS/Dynatherm has provided plans for a low-volume diffusion denuder thermal desorption unit that is connected to a cold trap and to the inlet of the gas chromatograph
for $23.6K. However, such a unit for extraction of high-volume diffusion denuders is required. Use of this unit obviates the need for a PTV Inlet. If low-temperature extraction is required, we will assemble a SFE system consisting of an extraction cell from Applied Separations (Allentown, PA) connected to a pump unit from Chrom Tech, Inc. (Apple Valley, MN) and heated jacket. SFE will be carried out off-line using supercritical carbon dioxide extraction at 40 degrees C into organic solvent or mini-sorbent tubes. The solvent will be concentrated by blow-down and injected into a PTV Inlet from Gerstel, Inc. If mini-sorbent tubes are used instead, they will be thermally extracted using the custom-built unit described above. The extraction cell costs ca. $1.5K and the pump unit $5.5K. The heated jacket and controller will cost an additional ca. $500. PTV Inlets from Gerstel, Inc., Apex Technologies, Inc. (Independence, KY), CDS/Dynatherm, PerkinElmer Instruments (Shelton, CT), and ATAS GL
International (Veldhoven, the Netherlands) were considered. The likely unit to be purchased is from either Gerstel, Inc. or CDS/Dynatherm as described above. The CIS-3 unit from Gerstel, Inc. is $12.8K.
Impacts
A mass spectrometer rather than an electron capture detector (ECD) will greatly expand our ability to measure concentrations and fluxes of pervasive bioaccumulative toxicants of environmental significance using diffusion denuders and extraction by thermal means or using supercritical fluid. For example, numerous pesticides and insecticides of interest in agriculture and forestry, and especially recently-commercialized ones such as alachlor, are not electron-capture sensitive, yet can be subjected to analysis by HRGC-MS. Accurate determination of fluxes to and emission from terrestrial and aquatic surfaces will be of substantial benefit to society.
Publications
- No publications reported this period
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