United States Environmental Protection Agency Atmospheric Research and Exposure Assessment Laboratory Research Triangle Park NC 27711 Research and Development EPA/600/S3-90/091 Jan. 1991 EPA Project Summary Evaluation of Particle Beam Liquid Chromatography/Mass Spectrometry for the Analysis of Polar Semivolatile Organic Compounds in Air Samples Robert S. Whiton In the last few years, several Inter- faces have been developed for coupling high performance liquid chromatogra- phy (HPLC) and mass spectrometry (MS). Among the most recent is the particle beam interface. This report de- scribes the initial evaluation of a particle beam HPLC/MS system for the analysis of polar semivolatile organic com- pounds. The study focused on examin- ing and optimizing Instrumental operat- ing parameters, evaluating the ability of the Instrument to generate classical electron impact mass spectra of repre- sentative compounds, investigating the performance with chemical ionization, and evaluating the potential for quanti- tative analysis with selected com- pounds. Test compounds included hy- droxy-polycycltc aromatic hydrocarbons (PAH), nitro-PAH, amino-PAH, and hy- droxy-nltro-PAH. The report describes the results of these experiments and discusses several problems found in the current particle beam Interface de- sign. This Project Summary was devel- oped by EPA's Atmospheric Research and Exposure Assessment Laboratory, Research Triangle Park, NC, to an- nounce 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 Many current methods for the determi- nation of nonpolar organic compounds in air are based on gas chromatography/mass spectrometry (GC/MS), which utilizes the high resolution achievable with chromato- graphic separation and the sensitive, se- lective detection and compound identifica- tion of mass spectrometry. For analysis of polar semivolatile organic compounds (SVOCs), however, GC methods are limited by the requirement that the analytes be volatile and thermally stable. Compounds that do not meet these requirements can be analyzed by high performance liquid chromatography (HPLC), but standard de- tectors for HPLC lack the sensitivity and selectivity needed for analysis of air samples, and they do not provide the com- pound identification ability of the mass spectrometer. Efforts to couple HPLC and MS have been underway for more than 15 years. The LC/MS interfaces that have seen sig^ nificant use fall into several categories: direct liquid introduction, liquid ion evapo- ration, and solvent removal. Each of these categories has its characteristic areas of utility and its particular deficiencies. The particle beam interface introduced by Browner and co-workers is one of the most recent introductions. The particle beam interface uses a nebulizer and momentum separator to re- move the solvent vapor from the effluent with little sample contact with heated sur- faces. The analytes enter the MS ion source as a beam of dry particles and can be ionized by a variety of conventional pro- cesses, including electron impact (El) and chemical ionization (Cl) with any reagent gas. Since commercial versions of the in- Printed on Recycled Paper ------- terfaca were introduced in 1988, the tech- nique has been applied to a variety of compounds of environmental interest, with mixed results. In analysis of diazo dyes, the sensitivity was much worse than that obtained with thermospray. Other classes of compounds that have been analyzed by particle beam LC/MS include aromatic sutfonic acids, phenylurea and carbamate pesticides, and benzWines. Quantification has been problematic, with two groups reporting concave calibration curves and others reporting a carrier effect resulting in response enhancement by coeluting com- pounds. Procedures The particle beam LC/MS interface is optimized by adjusting the nebulizer posi- tion and helium gas flow while repeating injections of the compound of interest. The MS Is tuned with the particle beam interface inserted and solvent flowing. The tuning compound (perfluorotributylamine) and/or reagent gas are introduced through the interface. Manual tuning generally produces better results than the instrument auto- matic tuning procedure. Results The particle beam LC/MS interface was found to be reliable and relatively simple and straightforward to operate. Routine optimization involves only adjusting the position of the nebulizer capillary. It was beneficial to keep the ion source of the MS slightly hotter than would be normal for the corresponding GC/MS experiment. The instrument produces good classical El spectra for some classes of PAH deriva- tives, although the quality of the library matches is variable. It produces unaccept- able spectra for nitro-PAH compounds, which apparently are reduced to amines in the ion source,J"his.may-result from pro^_ longed contact with the ion source walls before the analytes are vaporized. The particle beam interface had diffi- culties with phenolic compounds due to adsorption in the interface. The adsorption problem is manifested as tailing peaks, carryover and reduced sensitivity for phe- Robert S. Wh'rton is with NSI Environmental Sciences, Research Triangle Park, NC 27709. Nancy K. Wilson Is the EPA Project Officer (see below). The complete report, entitled "Evaluation of Particle Beam Liquid Chromatography/ Mass Spectrometry for the Analysis of Polar Semivolatile Organic Compounds in Air Samples," (Order No. PB91-127746/AS; Cost: $15.00, 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: Atmospheric Research and Exposure Assessment Laboratory U.S. Environmental Protection Agency Research Triangle Park, NC 27711 nolic compounds. Hydroxy-nitro-PAHs could not be detected at levels of approxi- mately 100 ng. The adsorption problem was not alleviated by use of an acidic eiuent or the addition of a deactivated glass line to the desolvation chamber. The adsorption may be occurring in the overly long transfer line and the plastic cones of the momentum separator. The interface was compatible with electron capture negative ionization (ECNI) for nitro-PAHs, with no apparent interfer- ence from the solvent. Reduction reac- tions on the walls of the ion source are a problem when methane is used as the ECNI moderating gas. With carbon dioxide as the moderating gas, the instrument pro- duces good ECNI spectra for nitro-PAHs, ^._^,,^ but the response is nonlinear. Detection limits are approximately 1 ng by selected ion monitoring and 1 0 ng full scan. Conclusions and Recom mendations Overall, the performance of the particle beam interface has not lived up to expec- tations, although it is effective for certain compounds. Future modification and evaluation pf the system may make it a more reliable and versatile analytical tool. Some future activities to be carried out include: modification of the momentum separator to replace the plastic cones and shorten the transfer line, testing of a quartz plate in the ion source to minimize wall reactions, testing with pesticides such as carbamates and triazines, which are diffi- cult or impossible to analyze by GC, and testing of capillary column supercritical fluid chromatography/mass spectrometry as an alternative to LC/MS for hydroxy-PAH. United States Environmental Protection Agency Center for Environmental Research Information Cincinnati, OH 45268 BULK RATE POSTAGE & FEES PAID EPA PERMIT NO. G-35 Official Business Penalty for Private Use $300 EPA/600/S3-90/091 ------- |