United States Environmental Protection Agency Environmental Monitoring Systems, Laboratory Research Triangle Park NC 27711 Research and Development EPA-600/S4-82-067 Jan. 1983 SEPA Project Summary Development of a Tunable Zeeman Spectrometer for Analysis of Toxic Organic Compounds T. Hadeishi, R. McLaughlin, and J. Millaud This program was undertaken to investigate the application of a new analytical technique called tunable atomic line molecular spectroscopy (TALMS) to the detection of a variety of volatile organic molecules of concern to the Environmental Protec- tion Agency. During the first phase of the study a prototype instrument was built and tested to demonstrate the detection of both small (i.e., less than four atoms) and complex molecules. During the second phase a more compact instrument was constructed for delivery to EPA, Research Triangle Park, NC before January, 1982. This second instrument was optimized for the detection of the more complex organic molecules benzene and chloro- benzene. TALMS is a high resolution, molec- ular differential absorption technique used in the ultraviolet-visible spectral region. It utilizes the splitting of an atomic emission spectral line from a lamp in a magnetic field (the Zeeman effect). One split line (Zeeman com- ponent) is made to overlap a rotational line associated with an electronic transition of the analyte molecule by proper adjustment of the magnetic field. Other Zeeman components of this same atomic line that do not overlap the absorption feature are used as reference lines. The concen- tration of the molecule is then deter- mined by differential intensity mea- surements of these two Zeeman components. TALMS was first devel- oped to detect inorganic diatomic and triatomic molecules which exhibit well defined rotational spectra in the visible and ultraviolet spectral regions, e.g., NO, SO2, NO2. Rationale for expected high specificity and high sensitivity with the TALMS instrument for large complex, organic molecules are discussed. Estimates of detection limits, resolution, selectivity, and linear range of the TALMS technique are also given. TALMS data on nitric oxide and formaldehyde are presented as a part of this study. The TALMS spectrum of formaldehyde near 3390 A is discussed since this data is the highest resolution data yet obtained on this compound and illustrates the selectivity attain- able with the technique. During the second phase of this work, the line shapes of the absorption features responsible for the benzene and chlorobenzene TALMS signals near 2537 A were obtained. Line shape information can be used to optimize the sensitivity of the instrument for a given compound. Using this informa- tion, it was possible to build a second instrument with a magnetic field strength that was optimum for the detection of benzene at 2537 A. Both ------- benzene and chlorobenzene give TALMS signals with the same mercury line at 2537 A. The line shape informa- tion for the compounds allowed a field strength and configuration to be chosen that effectively eliminated the interference of chlorobenzene on the benzene TALMS signal. Block dia- grams, photographs of the prototype instrument, and descriptions of its components are included. This Project Summary was developed by EPA's Environmental Monitoring Systems Laboratory, Research Triangle Park. NC, to announce key findings of the research project that is fully documented in a separate report of the same title (see Project Report ordering information at back). Introduction Increased utilization of advanced technologies has led to the need to monitor a large variety of toxic organic and inorganic species. The identifica- tion and quantification of almost all organic compounds are presently ac- complished using some type of chro- matographic technique, e.g., GC, GC/MS, HPLC, etc. These methods are time consuming, frequently not very selective, and, in the case of the GC-MS, require expensive equipment. A highly selective technique that depends on high resolution spectrometric principles would be faster and reducethe likelihood of incorrect qualitative analysis. The goal of this study, which was performed at the Lawrence Berkeley Laboratory, is to develop an instrument to be used for highly selective and sensitive organic analysis. This instrument should ideally be compact, relatively inexpensive, and easy to operate. Those methods that depend only upon the interaction of radiation with the sample most closely approach the ideal case. Contamination and loss problems are greatly reduced when the sample is only moved into a light beam. The technique whose development is de- scribed in this report represents a step in this direction for the determination of both organic and inorganic species. Although non-gaseous samples must be volatilized to use this technique, this alteration is common in other types of organic analysis, e.g., GC, GC-MS, LC- MS. An analytical technique called Tunable Atomic Line Molecular Spectroscopy (TALMS) has recently been developed at the Lawrence Berkeley Laboratory. It is capable of the detection and measure- ment of a large number of both organic and inorganic molecules with high sensitivity. The selectivity of TALMS is such that molecules can be identified and quantified even in the presence of a large amount and number of interfering substances. The number of compounds that can be detected is almost unlimited, depending only upon the presence of narrow, line-like features in the ultra- violet-visible absorption spectrum of the compound in the gas phase. This technique also requires minimal sample handling. TALM spectroscopy consists of splitting a source atomic emission spectral line by means of a magnetic field (Zeeman effect) and making a differential absorp- tion measurement between one Zeeman component that has been magnetically tuned to match an analyte absorption line and an unmatched Zeeman reference component. The difference in polariza- tion between the Zeeman components permits the matching and nonmatching wavelengths to be alternately selected and the absorption measured very rapidly with an electrooptical device called a Current Controlled Retardation plate (CCR). The TALM spectrometer detects the difference in absorption between the Zeeman components. The differential absorption is then propor- tional to the amount of molecular species whose absorption line is matched by one of the components of the source lamp. One remarkable feature of TALMS is its essential freedom from background interference Since the difference in wavelength between the Zeeman com- ponents of the source emission line is typically 0.04 nm, any particle scattering or semi-continuous absorption will affect both components equally. There- fore, the differential absorption mea- surement will remove this interference from the total signal. Hence, this type of interference, which is a problem in most spectroscopic methods, does not affect TALMS measurements. Conclusions and Recommendations Tests with the TALMS system on diatomic, triatomic, and tetratomic molecules indicate that these molecules contain rotational features similar in sharpness to that of atomic lines Larger molecules, e.g., benzene at certain wavelengths, also show large changes in absorption intensity within a small 60 GHz (2 cm ') spectral interval. TALMS data, limited available data from ultra- high resolution absorption experiments, and theoretical considerations make it evident that sharp line-like rotational structure and/or very sharp changes in the slope of absorption features are present in larger organic compounds and can be detected by TALMS. To demonstrate this detection capability, a benzene and chlorobenzene detecting instrument has been constructed and will be delivered to EPA, Research Triangle Park, NC, before January, 1982 The TALMS technique has a number of features that are useful for deter- mining toxic organic substances. It has an inherent resolution exceeding 500,000 It utilizes a principle of operation that is totally different from the currently used chromatographic methods Therefore it provides an independent confirming analysis. The sample pretreatment required for the TALMS method is much less than that required for chromato- graphic procedures. It should be possible to volatilize low boiling components from a solid or liquid sample directly into the light path of the instrument and perform the analysis with no further sample treatment Because the applica- tion of TALMS analysis is simpler than chromatographic procedures, it should be possible to develop an instrument that requires less skill and experience on the part of the analyst Samples may be sealed in previously evacuated cells and stored in the event another deter- mination is required at a later date. In order to utilize the TALMS tech- nique effectively, a data base of atomic emission lines which match molecular absorption features must be constructed. The most logical way to do this is simply to make magnetic scans using emission lines from atoms that have the highest possible density of spectral lines in the region where molecular absorption is intense Future efforts should be directed toward fabricating high inten- sity light sources that produce as many emission lines as possible, toward production of the data base required for qualitative and quantitative analysis; and toward analysis of complex en- vironmental air samples ------- T. Hadeishi, R. McLaughlin, and J. Millaud are with the University of California. Berkeley. CA 94720. D. R. Scott is the EPA Project Officer (see below). The complete report, entitled "Development of a Tunable Zeeman Spectrometer for Analysis of Toxic Organic Compounds," (Order No. PB 83-139 535; Cost: $10.00, subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield. VA 22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Environmental Monitoring Systems Laboratory U.S. Environmental Protection Agency Research Triangle Park, NC 27711 •f- U S GOVERNMENT PRINTING OFFICE 1983 659-O17/O892 United States Environmental Protection Agency Center for Environmental Research Information Cincinnati OH 45268 Postage and Fees Paid Environmental Protection Agency EPA 335 Official Business Penalty for Private Use $300 CHICAGO ------- |