trometric sources with minimal background emission, e.g., premixed 02-H2 flame, can be utilized. T h e use of continuum primary sources in AA is obviously also ruled out. T h e area where H T S might offer some real advantages is AF with low-emission background flames, but even there the advantage is limited. Assuming an ideal case where 1%of a 2047 slots mask are illuminated by AF analytical spectral lines of equal intensity (flame background emission is considered negligible), the FJ = 7 with a dynamic range of only 100. If 10% of the mask is illuminated (under similar conditions) FJ = 2 and the dynamic range is only 10. In addition, H T S will be incompatible for nonflame AF where fast pulse signals are obtained. The above predictions concerning the applicability of H T S to uv spectrometry were all based on the assumption t h a t the noise is white (time or frequency independent). These predictions have been confirmed both by using a computer-simulated (127 slots) H T S (1) and a real (255 slots mask) H T S (2). However, as the match between the Hadamard) mask movement frequency (samping frequency) and the noise frequency becomes closer, the degradation of the multiplex advantage by the noise becomes much more severe. A limiting case situation is demonstrated in Figure 16, where the entire noise in the spectrum has a frequency equal to the mask movement frequency. (The simulation technique used was described in Ref. 1 ) . Although the very strong features of the spectrum were reproduced by the HTS, the accuracy was seriously degraded because of the high fluctuations in the base line. In such cases, small spectral features could be easily masked beyond recognition and non-existing features could be falsely identified. Thus, as in the case of signal modulation, the correct prediction of the multiplex advantage requires an a priori knowledge of the noise spectrum characteristic of the spectrometric source used. These considerations should be taken into account when using other transform multiplex systems as well.
LITERATURE CITED (1) N. M. Larson, R . Crosmun, and Y. Talmi, Appl. Opt., 13,2662 (1974). (2) F. W. Plankey, T. H. Glenn, L. P. Hart, and J. D. Winefordner, Anal. Chem., 46, 1000 (1974). (3) L. D. Harmon, Sci. Am., 71, (Nov. (1973). (4) J. S. Bendat and A. G. Piersol, "Measurement and Analysis of Random Data", John Wiley and Sons, New York, N.Y., 1966. (5) J. W. Cooley and J. W. Tukey, Math. Corn., 19, 297 (1965). (6) A. J. McCormack. S. C. Tong, and W. D. Cooke, Anal. Chem., 37, 1470 (1965). (7) Y. Talmi and A. W. Andren, Anal. Chem., 46, 2122 (1974). (8) Y. Talmi and G. H. Morrison, Anal. Chem., 44, 1455 (1972). (9) R. S. Hobbs, G. F. Kirkbright, M. Sargent, and T. S. West, Talanta, 15, 997 (1968). (10) Equipment on loan from P. N. Keliher, Villanova University, Villanova, Pa. (11) K. W. Busch and T. J Vickers, Spectrochim. Acta, Part 8, 28, 85 (1973). (12) G. M. Hieftje and R . I. Bystroff, Spectrochim. Acta, Part 8,30, 187 (1975). (13) C. Th. J. Alkemade. H. P. Hooymayers, P. L. Lijnse, and T. J. M. J. Vierbergen, Spectrochim. Acta, Part 8. 27, 149 (1972). (14) Y. I. Belyaev. L. M. Ivantsov, A. V. Karagakin, P. H. Phi, and V. V. Shemet. J. Anal. Chem. USSR, 23, 855 (1968). (15) N. Marinkovic and T. J. Vickers, Anal. Chem., 42, 1613 (1970). (16) R. Herrmann, W. Lang, and K. Rudiger, Fresenius Z. Anal. Chem., 206, 241 (19641 > (17) G. M. Hiefije, B. E. Holder, A. S. Maddux, and R . Lim, Anal. Chem., 45, 238 (1973). (18) A. Antic-Janevic, V. Bojovic, and M. Marinkovic, Spectrochlm. Acta, Part E. 25. 405 119701. (19) V. G. Mossotti, 'F. N.'Abercrombie, and J. A. Eakin, Appl. Spectrosc., 25, 33 (1971). (20) S. Dobos and F. Till, Ann. Univ. Sci. Budapest, Sec. Chim., 6 , 47 (1964). (21) V. G. Mossotti. University of Minnesota, Minneapolis, Minn.. personal communication, 1973. (22) J. A. Decker, Jr.. and M. 0. Harwitt. Appl. Opt., 7, 2205 (1968). (23) E. D. Nelson and M. L. Fredman, J. Opt. SOC.Am., 60, 1664 (1970). (24) J. D . Ingle and S. R. Crouch, Anal. Chem., 44, 1375 (1972). ~~
RECEIVEDfor review July 22, 1975. Accepted November 6, 1975.By acceptance of this article, the publisher or recipient acknowledges the U.S. Government's right to retain a nonexclusive, royalty-free license in and to any copyright covering the article. Oak Ridge National Laboratory is operated by the Union Carbide Corporation for the U.S. Energy Research and Development Administration.
Pulsed Nitrogen Laser in Analytical Spectrometry of Molecules in the Condensed Phase T. F. Van Gee1 and J. D. Winefordner' Department of Chemistry, University of Florida, Gainesville, Fla. 326 1 1
Three laser fluorimeters (a pulsed N2 laser with an emission monochromator, a pulsed N2 laser pumped broadband dye laser with emission monochromator, and a pulsed N2 laser tunable dye laser with emission monochromator) are compared with a conventional spectrofluorimeter (Aminco-Bowman) with respect to analytical figures of merit. Detection limits for several organic molecules, including polynuclear aromatic hydrocarbons, are given for the four instrumental systems. The N2 laser was also used as a source in Raman spectrometry; the Raman spectrum of ethanol is given and linear analytical curves are obtained for alcohol in water and toluene in benzene. The Raman detection limits are reasonable, e.g., 0.1 vol YO of alcohol or toluene can be detected in their respective solutions.
In the past few years, lasers have been used more and more in analytical spectrometry and, for atomic and molecular fluorescence as well as in Raman spectrometry, the usefulness of laser sources has been demonstrated. A review of the uses of lasers and their applications in analytical chemistry has been given by Steinfeld (I) and Allkins (2). The pulsed N2 laser (in the present studies, the r\;r laser has a 100-kW peak pulsed output a t 337.1 nm with pulses approximately 10 ns wide) with or without the dye laser has not been frequently used as an excitation source in molecular spectrometry. However, because many molecules absorb strongly in the 337 nm region of the spectrum and because of the short (temporal) pulses of the N2 laser, it should be possible to excite most molecules with good
ANALYTICAL CHEMISTRY, VOL. 48,
NO. 2,
FEBRUARY 1976
335
MOLECTRON DYE LASER MODULE
I
Sample Cell
r
t
m
TRIGGER
m
m
PULSE
Figure 2. Block diagram of N2 laser (with or without dye) fluorimeter MOLECTRON DYE LASER MODULE
tration of 5 X M) was used to excite quinine and acridine, and the emission of coumarin 102 (at a concentration of IO-* M) was used to excite fluorescein. By tuning the dye-laser, most of the uncontrolled superradiation can be changed into lasing action. A schematic diagram of the three laser excitation systems and t h e configuration of the Molectron dye laser module is given in Figure I. T h e pulsed radiation was focused onto a 10 X 10 mmz quartz sample cuvette placed in front of the entrance slit of 250-mm focal length monochromator (EU-700 GCA/McPherson Instrument, Acton, Mass. 01720). An RCA 1P28 photomultiplier tube and a boxcar integrator (Model 160, Princeton Applied Research Corp., Princeton N.J. 08540) were used t o process t h e pulsed signals, and a potentiometric recorder (Servo/Riter 11, Texas Instruments, Inc., Houston, Texas 77008) was used as the readout. For all measurements except for the fluorescence decay study, the boxcar integrator had the following settings: repetition rate, 20 Hz; aperture time, 50 ns; gate time constant, 0.1 s; average time constant, 1 s. Plain front surface mirrors were used t o obtain an additional pass of t h e laser pulse through the sample solution and to increase the fluorescence signal. In Figure 2, a block diagram of the system is given. T h e commercial spectrofluorimeter used was t h e AmincoBowman Spectrofluorimeter (American Instruments Co., Silver Spring, Md. 20910). Reagents. High purity reagents and solvents were used in all studies. T h e chemicals acridine. fluorescein, and phenanthrene were obtained from Eastman Kodak Organic Chemicals (Eastman Kodak Co., Rochester, N.Y.): anthracene, chrysene, and fluoranthene were obtained from Chem Service (West Chester, Pa.); quinine sulfate was obtained from Pfaltz and Bauer, Inc. (Flushing, N.Y.); and pyrene was obtained from City Chemical Corp. (New York, N.Y.). T h e solvents used were: ethanol (USP reagent quality ethyl alcohol, Industrial Chemical Co., Kew York, N.Y.); water (deionized); toluene (GC-spectrophotometric grade, J. T. Baker Chemical Co., Phillipsburg, N.J.); cyclohexane (spectroquality grade, Matheson, Coleman and Bell, Norwood, Ohio); and sulfuric acid (analytical reagent grade, Mallinckrodt Chemical Works, St. Louis. Mo.). Procedure. Solutions were prepared from the above reagents and solvents. Successive dilution was utilized to prepare dilute solutions. No special precautions during measurement were employed, e.g., the solutions were not deaerated. All special experimental conditions are given in the appropriate part of the text.
Sample Cell
b
4
N2LASER
MOLECTRON DYE LASER MODULE
Flgure 1. Configuration of N2 laser fluorescence (Raman) spectrometric systems
( a ) N P laser-no dye excitation system. X = 337.1 nm; line width of laser output. 5 0 . 1 nm; peak power, ~ 1 0 kW 0 per pulse. ( 6 ) N2 laser-broadband dye emission-excitation system. 90% emission at -2 kW/pulse between 362-367 nm with PBD dye: 90% emission at 6 kW/pulse between 465-485 nm. (c) N2 laser narrowband tunable dye emission excitation system. For PBD, X = 365 nm; linewidth, 5 0 . 1 nm; and 6 kW/pulse. For Coumarin 102, X
= 470 nm, linewidth, 10.1 nm. and 15 kW/pulse
sensitivity and to discriminate between compounds with different fluorescence lifetimes (Measures ( 3 ) ,Brown ( 4 ) ) . Therefore, the N2 laser without an excitation monochromator will be compared with the N2 laser combined with either a broadband dye laser or with a narrow band (tunable) dye laser, particularly with respect to analytical detection limits; comparisons will also be made with a commercial spectrofluorimeter.
EXPERIMENTAL Apparatus. T h e experimental set-up consisted of a 100-kW pulsed N?laser, operated a t 20 Hz (C950, Avco Research Laboratory, Everett, Mass. 02149). A tunable dye laser (Molectron DL 200. Molectron Corporation, Sunnyvale, Calif. 94086) was placed in the Nz-laser beam. In the rotatable dye-cell holder of the tunable dye laser, one of the dye cells was replaced by a mirror and could be positioned t o reflect the Nz laser directly to the saniple cell by rotating the dye cell holder. By positioning the dye cell holder, laser emission of one of t h e dyes was produced (if the dye laser cavity was utilized, then tunable narrow band laser emission was produced; and if no dye laser cavity was utilized, then broadband laser emission was produced). T h e N?-Iaser (pulsed) beam consists mainly of superradiant emission a t 337.1 nm. When a dye is placed in t h e Ns-laser beam, broadband emission is observed. In this study, the emission of t h e dye 2-(4-biphenyl)-5 phenyl-1,3,4-oxadiazole (P.B.D. a t a concen-
RESULTS AND DISCUSSION Fluorescence Spectrometry. The detection limits (concentration of analyte producing a signal to noise = 2) for quinine in 1 M H2S04, acridine in ethanol, and fluorescein in water were determined. T h e results for the four different instrumental systems are given in Table I. For the two systems that gave the best results (the NPlaser beam and the Aminco-Bowman), detection limits (see Table 11) for several polynuclear aromatic hydrocarbons in cyclohexane were measured. T h e polynuclear aromatic hy-
________~
Table I. Fluorimetric Limits of Detection for Quinine, Acridine, alid Fluoresceill b> Three N,.Laser Systems and a Coaventional Spectrofluorimeter
hesc, nrn
Quinine Acridine Fluorescein
336
330 280
430
N 2 laser broadband
N, laser, narrow hand
Aminco-Bo\
