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Anal. Chem. 1986, 58,2886-2888
Comparison of Jarrell-Ash, Perkin-Elmer, and Modified Perkin-Elmer Nebulizers for Inductively Coupled Plasma Analysis David E. Nixon*
Department of Laboratory Medicine, Mayo Clinic, Rochester, Minnesota 55905 Gordon A. Smith
Department of Engineering, Mayo Clinic, Rochester, Minnesota 55905 Performance characteristics of pneumatic nebulizers used with inductively coupled plasmas (ICP) have been critically reviewed in the recent past (1-9). Although the pneumatic nebulizer remains the most popular form of sample introduction because of its simplicity and expense, it also remains as the single most limiting factor in the transition of ICP from a laboratory curiosity to a routine tool (2-4,9). Although the original crossflow nebulizer designed by Kniseley et al. (11) gave adequate detection limit performance, sensitivity to solution composition or particulate matter and difficult routine maintenance have plagued this design (2,3,5). The nebulizer, whether concentric or crossflow design, must have a gas orifice small enough to produce a high velocity jet stream past the sample inlet ( 3 , 5 ,7, 9) and a sample orifice large enough to allow the free aspiration of material such as urine or diluted serum without clogging (3,5,9). In the case of the crossflow design, the proximity of the gas orifice behind the sample orifice is also critical (9). Second generation fixed crossflow nebulizers with large sample orifices and smaller gas inlets have now appeared (3, 5 ) . One model, available from Jarrell-Ash Division of Allied Analytical, produces excellent detection limits and is capable of aspirating most urine or serum samples without clogging. When a blockage does occur, however, the plasma must be stopped and the nebulizer unclogged or a replacement installed. While this device represents an improvement over previous designs, it precludes easy routine repair and a number of expensive replacements must be kept on hand. An alternate approach has been taken by Perkin-Elmer. Their crossflow nebulizer is completely demountable, with inexpensive gas and sample needles of molded plastic easily replaced. New needles simply fit prebored holes in the nebulizer body. Sample needle penetration and, therefore, alignment are predetermined by a stop ring molded on the needle. The proximity of the gas needle to the rear of the sample orifice is also preset. The disadvantage of this system is that when samples are pumped into the uptake orifice, signal to background ( S I B )ratios and detection limits are significantly poorer than those attained with the Jarrell-Ash design. In order to retain the performance of the Jarrell-Ash design and the serviceability of the Perkin-Elmer unit, the original gas orifice was replaced by a precision glass capillary with a significantly smaller diameter orifice. In this paper, we describe this modification in detail. Detection limit and signal to background ratio data for this device are compared with experimentally derived values for the stock Perkin-Elmer nebulizer and the Jarrell-Ash. Results for the analysis of urine and serum control specimens are compared to the certificate values.
EXPERIMENTAL SECTION Multielement ICP System. The components that comprise our six-element direct reading system are outlined in Table I. A complete description of this scanning/direct reading plasma facility can be found elsewhere (12). Operating parameters used in this study are listed in Table 11. Elements and their wavelengths fixed on the exit slitframe of the direct reader are listed in Table 111. All of the parameters listed
Table I. Inductively Coupled Plasma Facilities Plasma-Therm, Inc., Kresson, NJ Model HFS-2500E one piece quartz construction 18 mm i.d. plasma tube 14 mm i.d. auxiliary tube 1.2 mm i.d. aerosol tip Linde 201-4335; 201-4334 McPherson Model 216 (1 m focal length) 1200 grooves/mm; 300 nm blaze entrance, 25 km X 4 mm exit, ARL 6910-2 50 pm X 4 mm 25 mm X 200 mm focal length planoconvex Acton Research Model 395/BR Hamamatsu R760 13 m diameter computer interface, Mayo design multichannel readout, Mayo design HV and signal boards, Mayo design Jarrell-Ash Model 90-790 Perkin-Elmer Model N058-0368 Gilson Minipuls 2; 10 roller
plasma
HF generator torch
flow meters monochromater grating slits
optics filter
photomultipliers electronics nebulizers Pump
Table 11. Plasma System Operating Conditions forward power reflected power gas flow rates plasma auxiliary aerosol back pressure
1300 W
