2543
Anal. Chem. 1987, 59,2543-2544
Table 11. Vapor Deposition and Extraction Recoveries for Pyrene on Various Substrates substrate
Cd,wg/g“
silica TX ash AR ash WK ash graphite KA ash ET ash IL ash
58 62 45 31 54 60 53 47
C,,
pg/g
% recovery
60 64 41 23 28 30 10
103 103 91 74 52 50 19
0
0
=In all cases, the adsorbent was exposed to 60 pg of pyrene; several adsorbents failed to retain all of the pyrene to which they were exposed. Table 111. Extraction Recoveries of Solution- and Vapor-Deposited Pyrene from Various Adsorbents % recovery, % recovery,
soh
adsorbent
vapor deposition
Depositiona
silica TX ash AR ash
103 103 91 52
109 93 70 101 61 69 88
graphite K A ash ET ash IL ash a
50 19
0
Solvent: CH2C12.
(graphite, IL, ash, and KA ash) are much lower for “vapordeposited” than for “solution-deposited” pyrene, while the opposite is true for AR ash and silica. These results imply that the solvent used in “solution” depositions can significantly alter the affinity of an adsorbent for PAHs. Thus, it may be
inaccurate to use “solution-deposited standard” samples to infer extraction recoveries in the analysis of atmospheric particulate samples (in which the PAH deposits from the vapor phase, not from a liquid solution).
ACKNOWLEDGMENT We gratefully acknowledge the assistance of J. S. Krueger, Zhong Jinxian, R. A. Yokley, J. W. Taylor, and J. W. Gurley. Registry No. Pyrene, 129-00-0; graphite, 7782-42-5.
LITERATURE CITED (1) Schure, M. R.; Natusch, D. F. S. I n Polynuclear Aromatlc Hydrocarbons: Physicaland Eiobglcal Chemlstry;Cooke, M.. Dennis, A. J., Fisher, G. L., Eds.; Battelle Press: Columbus, OH, 1982; p 713. (2) Ryan, P. A.; Cohen, Y. Chemosphere 1986, 75, 21. (3) Yokley, R. A.; Garrison, A. A.; Wehry, E. L.; Mamantov, G. fnviron. Sci. Techno/. 1088, 20, 86. (4) Behymer, T. D.; Hltes, R. A. Environ. Sci. Technoi. 1085, 79, 1004. (5) Dlugi, R.; Gusten, H. Afmos. Environ. 1081, 17, 165. (6) Griest, W. H.; Yeatts, L. B., Jr.; Caton, J. E. Anal. Chem. 1980, 52, 199. (7) Grlest, W. H.; Caton, J. E. I n Handbook of Polycyclic Aromatic Hydrocarbons; Bjorseth, A., Ed.; Dekker: New York, 1983; Vol. 1, p 95. (8) Soltys, P. A.; Mauney, T.; Natusch, D. F. S.;Schure, M. R. fnviron. Sci. Techno/. 1088, 20, 175. (9) Stenberg, U.; Alsberg, T. E. Anal. Chem. 1081, 53,2067. (IO) Hawthorne, S. B.; Miller, D. J. J. Chromafogr. Scl. 1986, 2 4 , 258. (11) Wright, B. W.; Wright, C. W.; Gale, R. W.; Smith, R. D. Anal. Chem. 1987, 50,38. (12) Miguel, A. H.; Korfmacher, W. A,; Wehry, E. L.; Mamantov, G. fnvlron. Sci. Techno/. 1070, 73, 1229. (13) T. D. J. Dunstan, J. K. Sanders, R. J. Engelbach, E. L. Wehry, Mamantov, G., unpublished data, University of Tennessee, 1987.
RECEIVED for review May 14, 1987. Accepted July 7, 1987. This work was supported by the Department of Energy, Office of Health and Environmental Research, under Contract DEAS05-81ER60006.
Vibrating Tumblers as Cleaning Devices for Mass Spectrometer Ion Source Parts Louis R. Alexander,* Vince L. Maggio, Vaughn E. Green, James B. Gill, Elizabeth R. Barnhart, and Donald G. Patterson, Jr. Toxicology Branch, Environmental Health Laboratory Services, Center for Environmental Health, Centers for Disease Control, Atlanta, Georgia 30333 Lance C. Nicolaysen
Chemistry Department, Emory University, Atlanta, Georgia 30322 Maintaining clean ion source parts for a high-throughput laboratory can be a major task, even for highly motivated and skilled personnel. In our laboratory, an ion source used for analyzing adipose or serum extracts usually lasts from 1 to 2 weeks before it needs to be disassembled for cleaning. A source may perform adequately for longer periods on occasion, but a t any given time all mass spectrometer operators are involved at some stage in the source maintenance process. The usual source cleaning procedures include various scrubbing techniques, sandblasting, or electrochemical baths. These procedures are rigorous and erode the source parts to some extent, especially the more fragile sliding slits and beam center plates on the Vacuum Generator (VG) Instruments. The scrubbing action of rotary polishing tools, coupled with alumina paste, can result in surface scratches that produce a dull finish. Certain places in some of the parts, such as ion source blocks, are difficult to clean by any mechanical means. 0003-2700/87/0359-2543$01.50/0
Some of these more obstinate places can be reached by sandblasting which requires special equipment. However, one must carefully select the mesh size of the sandblasting medium. Even corn starch is too harsh for certain parts, because it can leave an etched or dull finish. In some cases, one can actually dislodge the chemical ionization restrictor from an ion source block or detach sliding slit guides from lens assemblies. The dull finish produced by sandblasting and abrasive cleaning induces rapid loss of sensitivity and expedites contamination causing degradation in source performance. Electropolishing, the reverse of electroplating, is a nonabrasive metal cleaning technique (I). Equipment is available from Vacumetrics (Ventura, CAI. It can also be assembled from items in the electrochemistry laboratory (2). Solutions for polishing various metals are easily prepared (3). During the polishing process, metal is removed from the source parts (anodic), and care must be exercised to control the amount 0 1987 American Chemical Society
2544
ANALYTICAL CHEMISTRY, VOL. 59, NO. 20, OCTOBER 15, 1987
of metal erosion. However, erosioa of the metal surfaces appears uneven and is most noticeable at the edges of the lenses and will vary with the amount of coating (contamination) present. As an alternative method of cleaning ion sources and other mass spectrometer parts, we have developed a cleaning procedure utilizing a vibrating ammunition case tumbler (polisher), crushed corn cobs, and a metal polish. This procedure allows practically effortless cleaning and produces a mirror finish on small metal parts, of various sizes and fragility, and in many usually inaccessible spots.
EXPERIMENTAL SECTION Apparatus. The vibrating ammunition case tumbler consists of a rubber bowl and lid attached to a motorized vibrator plate (Thumbler’s Tumbler, ULTRA-VIBE 18, Tru-Square Metal Products, Auburn, WA; others are also available from Buckeye Sports Supply, Canton OH, or local gun supply shops). The volume of the bowl is about 1 gallon which accommodates 5 lb of coated cleaning medium. These devices can be purchased for less than $150. The newer vibrating tumblers are less rigorous than the conventional rotating type which reduces the probability of scratches. Reagents and Chemicals. The cleaning medium consists of cr ished corn cobs pretreated with a fine polishing (abrasive) compound. Finely crushed walnut shells are also readily available and quite acceptable. These are procurable from gun shops which handle reloading supplies for about $2 per pound. A commonly available metal polish (Brasso, Airwick Industries, Inc., Carlstadt, NJ), was used to coat the cleaning medium. Other metal polishes, i.e. jeweler’s rouge or automotive rubbing (polishing)compound, may also be used. Commercially available reagent grade organic solvents were employed for rinsing. Procedure. The polishing medium consists of approximately 5 lb of crushed corn cobs and 4 oz of metal polish. The corn cobs can be reused many times, but the metal polish is replenished as indicated by the cleaning efficiency. Parts from one or more ion source assemblies are placed in the tumbler without any pretreatment. As a precaution, we install the shortest possible screws into all locations in ion source blocks and similar parts to prevent the polishing medium from entering the tapped screw holes. Longer screws increase the possibility of scratches on the other parts during the cleaning process. Other small metal parts may be cleaned by using this method, namely items that can be removed from ceramics and other nonmetal parts. Adjustable source slit components, screws, and other small metal parts have been successfully cleaned. The metal parts are usually tumbled overnight, although sometimes it takes longer to obtain the desired results. The parts are then removed from the polishing medium and excess dust is
evacuated using oil-free air. The parts are sonicated in several changes of deionized or distilled water until no trace of the polishing medium is visible. We continue sonication for three washes each in methanol, toluene, and finally acetone (total of nine washes; 10-15 min each). Other solvents may be used, provided they do not leave a residue on the metal parts. We have successfully used diethyl ether, methylene chloride, hexane, and ethanol with acceptable results. Sonication should be performed in a fume hood especially when using volatile and flammable solvents.
RESULTS AND DISCUSSION This procedure may seem long and laborious, since it requires more than 1 day to clean and assemble an ion source. However, the actual time the operator spends cleaning the ion source parts is rarely more than 10 min. Both the abrasive method using manual and rotary polishing and the sandblasting procedures require about an hour. Electropolishing requires somewhat less time, but it demands the operator’s undivided attention due to the widely dissimilar sizes of parts. An electropolishing apparatus is also considerably more expensive, about $500 for a basic unit compared to less than $150 for the tumbler. With the method described here, source parts can be tumbled while the analyst continues to run samples and rebuild the replacement source with a set of previously cleaned parts. We maintain two source assemblies and a supplementary set of source parts for each of our three high-resolution mass spectrometers. By exchanging the parts after cleaning, an analyst can reassemble an ion source in about 30 min. The total time lost due to an abrupt ion source failure is usually less than 1 h. ACKNOWLEDGMENT The authors thank the visiting scientists who viewed this operation in our laboratory and offered opinions on the feasibility and utility of this method. LITERATURE CITED (1) Damico, J. N.;Barron, R. P. Anal. Chem. 1971, 4 3 , 7 . ( 2 ) Peele, G. L.; Brent, D. A. Anal. &em. 1977, 4 9 , 4. ( 3 ) Rosenbury, F. Handbook of Electron Tube and Vacuum Techniques; Addison-Wesley: Reading, MA, 1967; pp 18-23.
RECEIVED for review May 18,1987. Accepted July 20,1987. Use of tradenames is for identification only and does not constitute endorsement by the United States Public Health Service or the United States Department of Health and Human Services.
CORRECTION Comparison of Inorganic Mobile Phase Counterions for Cationic Indirect Photometric Chromatography Jeffrey H. Sherman and Neil D. Danielson (Anal. Chem. 1987, 59, 490-493).
On p 492, Figures 3 and 4 should be switched. The figure captions are correct.
