ANALYTICAL CHEMISTRY, VOL. 60, NO. 17, SEPTEMBER 1, 1988
1840
1
clogged probes can simply be repaired by replacement of the low-cost aperture or removal and ultrasonication of clogged aperatures. Although we have not used these probes with LC/MS, we anticipate no significant problems for this application. An additional modification may be the requirement of a silver solder between the 6.4-mm tube and the reducing union for vacuum considerations as described elsewhere (6). Further, the modified ferrules should be constructed to minimize dead volume, a criterion that was not particularly relevant to our initial work but would be for chromatographic or low volume flow injection applications. 3. oc
B. 00
15.0
TIME
21.0
27.0
kin.)
Figure 3. Calibration data for 1.0, 0.6, and 0.3 pglmL Ca (two injections each) using a 50-pm aperture-based thermospray (- - -) and 150 p m capillary thermospray (-); flow injection of 0.5 mL samples at 1.5 mL/min with 0.1% HN03 carrier; 393.3-nm Ca I1 line: 0.49 Llmin Ar aerosol carrier.
stable, long-term performance with laser-drilled apertures. This allows the user to rapidly change aperture sizes in order to optimize a chosen experiment. The apertures also provide extremely low pressure drops at typical HPLC flow rates (1-2 mL/min). For example, with a 50-pm aperture mounted on a 40 cm X 1.6 mm X 150 pm i.d. capillary, pump pressures (-3.5 MPa) are similar to those for the system in the absence of the aperture (-2.5 MPa) with 1 mL/min flow at the optimum temperatures for ICP-AES (160 "C for 150 pm and 190 "C for 50 ,um). Therefore, much smaller thermospray exit diameters may be explored before exceeding the pressure limitations of conventional HPLC pumps (typically -40 MPa). For example, we have recently found this approach useful with 25-pm apertures and found additional SNR enhancement and operating pressures of 6-7 MPa. Furthermore,
ACKNOWLEDGMENT We thank Hans Bank for assistance in the design and construction of the specialized components employed herein. Helpful discussions with M. L. Vestal are also appreciated. LITERATURE CITED ( 1 ) Vestal, M. L.; Fergusson, G. J. Anal. Chem. 1985, 5 7 , 2373. (2) Covey, T. R.; Lee, E. D.; Bruins, A. P.; Henion, J. D. Anal. Chem. 1988, 58, 1451A. (3) Meyer, G. A,; Roeck, J. S.; Vestal, M. L. ICP I n f . News/. 1985, 10, 955. (4) Koropchak, J. A.; Winn, D. H. Anal. Chem. 1986, 58, 2558. (5) Koropchak, J. A.; Winn. D. H. Appl. Spectrosc. 1987. 4 1 , 1311. (6) Unger, S. E.;McCormick, T. J.; Bolgar, M. S.:Hunt, J. B. Anal. Chem. 1987, 59, 1242. (7) Koropchak, J. A. Midwest University Analytical Chemistry Conference, Columbus, OH, 1987. (8) Vestal, M. L. University of Houston and Vestec Corp., personal communication, 1987. (9) Koropchak, J. A.; Aryamanya-Mugisha, H.; Winn, D. H. J. Anal. A t . Specbom., in press.
RECEIVED for review December 29, 1987. Accepted May 2, 1988. Supported in part by the Office of Research, Development and Administration of SIU-C and the Department of Energy through Grant DE-FC22-87PC79863.
CORRECTIONS Characterization and Automation of Sample Introduction Methods for Capillary Zone Electrophoresis Donald J. Rose, Jr., and James W. Jorgenson (Anal.Chem. 1988, 60, 642-648). On p 643, eq 10 should include the concentration of analyte, C. pgar4Aht =
817L
C
Conductivity and Resistivity of Water from the Melting to Critical Points Truman S. Light and Stuart L. Licht (Anal. Chem. 1987, 59, 2327-2330). On p 2329 in Table 111, the C constant for the range 0-100 "C should be -0.11599 X lo6 instead of 0.11599 X lo6.
