Anal. Chem. 1984, 56,601-602
: tloo\ 74\ W
g
o
2
1
3
TIME, hours
Flgure 1. Phosphorescence intensity at 495 nm plotted as a function of time for paper exposed to 285-nm light.
-
W I-
r W
601
batchwise well in advance of actual RTP analyses. Since RTP is a suitable detection method for compounds chromatographed on paper, entire sheets of paper could be illuminated prior to chromatography. Although no other cellulose supports were investigated, effective photolytic quenching is anticipated among different types of paper. We have found that the papers yield similar spectra, suggesting that the same impurities may be inherent in these papers. The importance of the background reduction is manifested in lower RTP detection limits for a vast number of phosphors absorbing and emitting light in the same spectral region. Recently, we implemented a sample drying technique and an instrumental modification (10) for RTP analysis. With those developments, the detection limit of p-aminobenzoic acid adsorbed on Whatman 3 MM chromatography paper was 12.9 pg. By utilization of the illuminated support described herein, the calculated detection limit has been reduced to approximately 0.5 pg or 200- to 20000-fold lower than previously reported on solid supports. With over an order of magnitude reduction in the background intensity, RTP has now matured into a more viable quantitative analytical technique.
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LITERATURE CITED
4I W K
300
200
500
400
600
W A V E L E N G T H , nm
Flgure 2. Phosphorescence excitation and emission spectra of paper before (---) and after (-) quenching with 285-nm light for 24 h. These spectra were recorded on the 100 nA and 10 nA scales, respectively.
previously illuminated supports were spotted with solutions of p-aminobenzoic acid and 4-biphenylcarboxylic acid. The samples were analyzed after 2 h of desiccation, and the analyte intensities were found to be identical with those obtained from the control samples.
DISCUSSION These results indicate that the background emission of cellulose papers can be diminished without the use of laborious techniques. The paper circles can be conveniently prepared
(1) Bateh, R. P.; Winefordner, J. D. J. Pharm. Sci. 1983, 72, 559-560. (2) Bateh, R. P.; Winefordner, J. D. Anal. Left. 1982, 15 (B4), 373-383. (3) Von Wandruszka, R. M. A.; Hurtubise, R. J. Anal. Chem. 1978, 48, 1784-1708. (4) Vo-Dinh, T.; Gammage, R. B.; Martinez, P. R . Anal. Chim. Acta 1980, 118, 313-323. ( 5 ) Vo-Dinh, T.; Gammage, R. B.; Martinez, P. R. Anal. Chem. 1981, 5 3 , 253-258. (6) Parker, R. T.; Freedlander, R. S.; Dunlap, R . B. Anal. Chim. Acta 1980, 119, 189-205. (7) Parker, R. T.; Freedlander, R. S.; Dunlap, R. B. Anal. Chlm. Acta 1980, 120, 1-17. (8) Ward, J. L.; Yen-Bower, E. L.; Winefordner, J. D. Talanta 1981, 28, 119-120. (9) McAleese, D. L.; Freedlander, R. S.; Dunlap, R. B. Anal. Chem. 1980, 52, 2443-2444. (10) McAleese, D. L.; Dunlap, R. B. Anal. Chem., in press.
RECEIVED for review September 6,1983. Accepted November 28,1983. These investigations were supported by NIH Grant CA 15645 from the National Cancer Institute. R. Bruce Dunlap is the recipient of a Faculty Research Award (FRA144) from the American Cancer Society.
Kinetic-Spectrophotometric Determination of Trace Levels of Iron Henri Rooze Universitd Libre de Bruxelles, Facultd des Sciences Appliqudes, 1050 Brussels, Belgium During a study of the kinetics of chlorite disproportionation (1,2) we observed that this process is catalyzed by traces of iron. o-Tolidine (biphenyl, 4,4’-diamino-3,3’-dimethyl-) is oxidized by intermediates of the reaction so that the overall stoichiometric reaction is given by eq 1. Here, o-tolidine is HClOz
+ 2NHzRNHz
Table I. Iron Content in Reagents 1.63 X 2.5 x T = 25.0
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M NaClO, M o-tolidine 0.2 “C amt of Fe, ppb
Fe(II1)
+
2NHRNH HC1+ 2H20 (1) represented by NH2RNH2and the imine resulting from its oxidation by NHRNH. In acid medium (pH
