Anal. Chem. 1987, 59, 1485-1488
1485
ammonium, and potassium ion chromatogram of a second aliquot of the urine sample in Figure 2B this time using indirect fluorescence detection. No interference of the separated cation peaks was noted. Quantitation of the peaks in Figure 4 resulted in the following values: Na+, 980 ppm; NH4+,490 ppm; K+, 850 ppm. While the concentration of sodium ion in this specimen was slightly low, the amounts of ammonium and potassium ions are well within expected values (19). A second urine specimen was found to contain values of 2400 ppm of Na+, 140 ppm of NHd', and 2270 ppm of K'. These values are also within normal accepted limits with the exception of the ammonium ion. Therefore, indirect fluorescence chromatography can be a rapid, viable method for determining the levels, of sodium, ammonium, and potassium ions in urine without prior sample cleanup.
ACKNOWLEDGMENT
Figure 4. Separation of (1) sodlum, (2) ammonium, and (3) potasslum ion In urine, indirect fluorescence detection: sample dilution, 1 to 1000; eluent, 0.01 mM Ce(II1); flow rate, 1.0 mL/min; sample volume, 20
Donation of the cation exchange column by James Benson of Interaction Chemicals, Inc., is gratefully appreciated. The authors thank Thomas Trosper of Kratos Analytical for the use of the fluorescence detector.
LITERATURE CITED
PL.
Ce(II1) mobile phase were acidified to convert any aromatic amines such as caffeine into cations which would then be retained on the column. Figure 3A shows a chromatogram of a third acidified urine sample analyzed by IPC using a cerium perchlorate mobile phase adjusted to pH 3.0. The perchlorate salt of cerium(II1) was used here, as acidification of the mobile phase sulfate salt with sulfuric acid results in the formation of sulfato-cerium complexes which changes the eluting characteristics of Ce(II1). The negative peak eluting a t 10 min was found to correspond to caffeine as shown by comparison to the chromatogram of a standard solution of caffeine (Figure 3B). A positive peak is still evident (Figure 3B) due to the unprotonated form of caffeine which, having a high UV absorbance, adds to the base-line absorbance of the Ce(II1) mobile phase. Although caffeine was identified as one possible interferent, it is likely other poorly retained compounds such as organic anions identified previously in urine (18)also will contribute substantially to the problem. In any case, quantitation of sodium, ammonium, and potassium was still not possible by IPC. Figure 4 shows a sodium,
(1) (2) (3) (4) (5) (6) (7) (8)
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36, 293. (12) Katz, S. S.; Pitt, W. W., Jr. Anal. Lett. 1972, 5(3),177-185. (13) Wolkoff, A. W.; Larose, R. H. J . Chromatogr. 1974, 99, 731-743. (14) Katz, S.; Pitt, W. W.. Jr.; Mrochek, J. E.; Dinsmore, S.J . Chromtogr. 1974, 101, 193-197. (15) Lee, S.H.; Field, L. R. Anal. Chem. 1984, 56, 2647. (16) Sherman, J. H.; Danielson, N. D. Anal. Chem. 1987, 59, 490. (17) Jupille, T. Am. Lab. (FairfeM, Conn.) 1988, 17, 114. (18) Miyagl, H.; Miura, J.; Takata, Y.; Kamitake, S.; Ganno, S.; Yamagata, Y. J . Chromatogr. 1982, 239, 733. (19) Modern Urine Chemistry; Ames Company, Division of Miles Laboratories, Inc.: Elkhart, IN, 1982; pp 96-98.
RECEIVED for review November 10,1986. Accepted February 17, 1987.
Low-Volume Fluorescence Detector for High-Performance Liquid Chromatography Alain Berthed,' Kuang Pang Li,2 Tiing Yu, and James D. Winefordner* Department of Chemistry, University of Florida, Gainesville, Florida 3261 1 The need for a variety of suitable detection techniques has induced many researchers to develop detectors for highperformance
