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National Bureau of Standards, Standard Reference Material No. 157 1, Orchard Leaves, 1971 (Revised 1976). Stary. J. "Solvent Extraction of Metal Chelates," Macmillan: New York,
1964
Lundquist, R.; Markle, G. E.; Boltz, D. F . Anal. Chem. 1955, 2 7 , 1731. Saltzman, B. E. Anal. Chem. 1955, 2 7 , 284. Cogan, E. Anal. Chem. 1960, 32, 973. Fassel. V. A.; Kniseley, 8.N. Anal. Chem. 1974, 46, lllOA. Varian Techtron Publication, #85-100044-00, Palo Alto, Calif., 1975. Olsen, K. W.; Haas, W. J.; Fassel, V. A. Anal. Chem. 1977, 49, 632. Sandell, E. B. "Colorimetric Determination of Traces of Metals", 3rd ed; Interscience: New York, 1959. Aiginger. H.; Wobrauschek, P.; Brauner, C. Meas., Detect. Controlhnviron. Pollution Proc. Int. Symp. 1976. 197;Chem. Abstr. 1977, 87, 11081Ot. Burrel, D. C. "Atomic Spectrometric Analysis of Heavy-Metal Pollutants in Water", Ann Arbor Science: Ann Arbor, Mich.. 1975. Evans, H. J.: Kliewer, M.; Lowe. R.; Mayeux, P. A. Plant Soil. 1964, 21.
153. Hovsepian, B. K.; Shain, I. J . Electroanal. Chem. 1966, 12, 397. Burdo. T . G.;Seitz, W . R . Anal. Chem. 1975, 47, 1639. Dubovenko, ._ L. I.; Beloshitskii, N. V. J . Anal. Chem. USSR. 1974, 29. 85
Babko, A. K.; Dubovenko, L. I.; Terletskaya, A. V. 1966, 32, 1326.
Sov. Prog. Chem.
(18) Bognar. J.; Sipos, L. Mlkrochim. Ichnoanal. Acta 1963, 3 , 442. (19) Babko. A. K.: Lukovskava. N. M. Zavod. Lab. 1963. 2 9 . 404: Chem. Abstr.'1963, 5 9 , 3301d. (20) Seitz, W. R.; Hercules, D. M.in "Chemiluminescence and Bioluminescence," Cormier, M. J.; Hercules, D. M.; Lee, J., Ed., Plenum Press: New York, 1973;pp. 427-449. (21) Hartkopf, A.; Deiumyea, R. Anal. Letf. 1974, 7 , 79. (22) Sheehan, T. L.; Hercules, D. M. Anal. Chem. 1977, 49, 446. (23) Nau, V.: Nieman. T. A. Anal. Chem. 1979, 51, 424. (24) Stieg, S.;Nieman, T. A. Anal. Chem. 1977, 49, 1322. (25) Ingle, J. D., Jr.; Wilson, R. L. Anal. Chem. 1976, 48, 1691.
RECEIVED for review October 20, 1978. Accepted February 12, 1979. ~ ~ k is made ~ to the~ NSF (grant ~ =CHE-76-16711)for partial support of this research and to the University Corporation for Atmospheric Research for fellowship support for one of us (L.A.M.). Presented in part a t the 1977 Northwest ACS meeting, Portland, Ore., and a t and the 29th Pittsburgh Conference On Applied Spectroscopy, Cleveland, Ohio.
Intracavity Absorption with External Fluorescence Measurement for Detection of Radioiodine Isotopes J. P.
Hohimer" and P.
J. Hargis, Jr.
Sandia Laboratories, Albuquerque, New Mexico 87 185
We report the use of intracavity absorption in a CW dye laser as a sensitive analytical method for the detection of iodine-129. With an external fluorescence detection scheme employing photon counting, quantitative isotope specific measurements of '"I2 and 2I'" have been made at concentrations in the Scaling esrange of 5 X 10" to 7 X ioi5 mo~ecu~es/cm~. timates indicate that a lower level may be achieved if desirable. I n addition, this method permits the simultaneous detection of a number of iodine isotopes.
Radioanalytical methods such as liquid scintillation counting and neutron activation analysis are presently used to measure trace concentrations of the long-lived radioisotope iodine-129. However, these methods are time-consuming and cannot be used for real-time measurements. New methods are needed which are capable of measuring iodine-129 in real time at or below the maximum permissible concentration of 2.0 x 10." Ci/cm3 (1). This concentration corresponds to an IBI2 number density of 7.9 X lo8 molecules/cm3. Laser-excited fluorescence spectroscopy is a sensitive method which has been studied for the real-time detection of trace iodine concentrations ( 2 ) . However, the severe quenching of the iodine fluorescence by atmospheric molecules (2-4) may limit the sensitivity of this fluorescence method for airborne radioiodine measurements. An alternative method for the detection of airborne iodine-129 is intracavity absorption spectroscopy. Intracavity absorption spectroscopy has been used to detect very weak absorption lines in a number of atomic and molecular species (5-10). This method involves placing a weakly absorbing species within the cavity of a broadband dye laser and measuring its effect on the spectral output of the laser. T h e wavelength-dependent loss introduced by even a very weak absorber dramatically decreases the intensity of the laser o u t p u t a t the absorber wavelength. T h e sensitivity of a broadband dye laser to small selective losses has been attributed to multiple passes of the laser beam through the absorbing medium as well as to t h e strong competition of simultaneously oscillating modes for the available energy in the homogeneously broadened gain medium (7, 8, 1 1 ) . An increase of absorption sensitivity by a factor of lo5,compared to a single-pass experiment, has been observed in an ex0003-2700/79/0351-0930$01 .OO/O
periment with an iodine-127 vapor cell inside the cavity of a CW dye laser (8).
EXPERIMENTAL A schematic diagram of the experimental apparatus used t o measure the sensitivity, linearity, and isotopic selectivity of the intracavity absorption of molecular iodine is shown in Figure 1. The 488-nm output from an argon ion laser (Spectra Physics, model 171-05)was used to pump a CW dye laser (Spectra Physics, model 375) which was amplitude stabilized by means of a feedback loop to the argon laser. Broadband emission was obtained when the dye laser was operated with all tuning elements removed from the laser cavity. This produced a laser output power of 50 mW with a spectral bandwidth of 0.75 nm fwhm (at 1.0-W argon pump power). However, under these conditions, the broadband cavity reflectors allowed the laser wavelength to shift as the wavelength dependent loss was modified by increasing the intracavity iodine vapor pressure. This caused large fluctuations in the experimental data. The reproducibility of the data was improved when the laser was operated with a tuning wedge in the cavity. This reduced the laser bandwidth to about 0.43 nm fwhm at the same output power level but greatly improved the laser wavelength stability. Even though small wavelength shifts were still observed, they had little effect on the reproducibility of the measurements. The intracavity iodine was contained in a quartz vapor cell with Brewster-angle windows and an internal pathlength of 5.0 cm. Because of the sensitivity of the CW dye laser to small wavelength dependent losses, wedged ( 2 30 in.) Brewster windows were required on the intracavity vapor cell to eliminate etalon effects in the dye laser output spectrum. The vapor cells used in these measurements were evacuated and subsequently filled with either iodine-127 or iodine-129. The iodine-129 vapor cells contained an unknown isotopic abundance of fission-produced iodine-127 estimated to be about 25% (12). The intracavity iodine number density could be varied from 5 X 10'l to 7 X 1015 molecules/cm3 by regulating the temperature of a cold finger on the vapor cell (-60.2 to 20.5 "C). External fluorescence detection was used for these intracavity absorption measurements since it gives a quantitative measure of the concentration of the intracavity absorbing species, takes full advantage of the many iodine absorption lines which lie within the laser bandwidth, and is more sensitive than other techniques which directly record the dye laser spectrum with either a high resolution spectrometer or a scanning Fabry-Perot etalon. In addition, the method is insensitive to fluorescence quenching 0 1979 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 51, NO. TO 12' l 2 CELL Y
CW DYE LASER
7, JUNE 1979
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lo------
I 2 CELL
*,*LASER
-
U
"
REFRIGERATOR FILTER VOLT TO FREQ CONVERTER
-
COMPENSATION CIRCUIT
AMPLIFIER
t COUNTER1 TIMER
LINE PRINTER
-
1011
,
1012
COUNTER
127
Figure 1. Schematic diagram of the experimental apparatus for iodine
Figure 3.
1~13
1014
1015
,
1
I -
lor--
I 1012 12' I
1013
1014
1015
1016
TOTAL
12 NUMBER DENSITY (mol
Cm3J
1017
NUMBER DENSITY 1 m o l ~ c m 3 )
Power dependence of analytical curves for iodine-127 intracavity absorption effects since the sealed external fluorescence detection cell is maintained in a fixed environment. The dye laser output was directed through both an iodine-127 vapor cell and an iodine-129 vapor cell external to the laser cavity as shown in Figure 1. These cells were identical to those described above, but were maintained a t room temperature. The Stokes-shifted iodine fluorescence from each monitor cell was collected with a lens and filtered (Corning 2-63 color filter) to minimize the scattered laser light reaching the photomultiplier tubes (RCA, 8850) which were used to detect the fluorescence radiation from each cell. The photomultiplier tubes (PMT) were operated in the photon counting mode. The output current pulses from each PMT were shaped by an amplifier/discriminator (Ortec, model 9302) and counted by a 100-MHz counter (Ortec, model 772). The response of each P M T was measured with calibrated neutral density filters inserted into the dye laser beam. The response was found to be linear over the range of signal levels in this experiment. A dual channel counter/timer (Ortec, model 9315) controlled the photon count time which was arbitrarily set a t 1.0 s. A temperature stabilized three-stage thermoelectric cooling module (Marlow Industries, model MI-3040) and a copperconstantan thermocouple (with a 0 "C reference point compensation circuit) were used to control the cold finger temperature of the intracavity absorption cell. A voltage-to-frequency converter (Molectron, model 156) and a discriminator (LeCroy Research Systems, model 161) were used to interface the thermocouple to the counter section of the counter/timer. This allowed the simultaneous measurement of the photon count rate (fluorescence signal) from each external vapor cell and the cold finger temperature (iodine number density) of the intracavity vapor cell. The cold finger was initially cooled to aproximately -60 "C, the lowest temperature available with the particular thermoelectric cooling module used. After thermal equilibrium was established (- 10 min when cooling from room temperature), the temperature of the cold finger was increased in discrete steps and the fluorescence signals were measured. Three minutes were allowed a t each temperature setting for an equilibrium vapor pressure Figure 2.
10l7
Isotopic selectivity of iodine intracavity absorption
intracavity absorption measurements
1011
1016
NUMBER DENSITY (mi cm31
Simultaneous measurement of iodine-127 and -129 by intracavity absorption Figure 4.
in the cell to be reached prior to measuring the fluorescence signal levels. After each 1-s measurement period, the data were recorded with a line printer (Ortec, model 777). The counters were then reset and restarted automatically. Ten consecutive measurements were made a t each temperature setting in order to obtain values for the mean and standard deviation of the photon count rates. Measurements were made at a number of temperature settings in the range of -60 to 20 "C. These data were subsequently used to construct an analytical calibration curve relating the mean photon count rate of the external fluorescence signals to the concentration of the intracavity absorbing species.
RESULTS AND DISCUSSION T h e effect of t h e dye laser output power on the shape of t h e analytical curves obtained with a n intracavity iodine-127 vapor cell is shown in Figure 2. In constructing these analytical curves, the normalized external fluorescence signal from t h e lZ7I2vapor cell was plotted as a function of the intracavity 1z712number density obtained from the cold finger temperature using the iodine vapor pressure relationship of Giauque (13). These measurements were made a t a laser wavelength of 551.6 n m using the dye Rhodamine 110 since X system is stronger here t h e iodine absorption in t h e B than a t Rhodamine 6G wavelengths ( 1 4 ) . Laser output power levels of 5, 50, and 250 m W were used corresponding to operation at 8, 64, and 391% above t h e threshold pumping power level for the dye laser, respectively. Calibrated neutral density filters were used to attenuate the dye laser output at the 50- and 250-mW power levels to prevent saturation of the iodine fluorescence. Polynomial fits t o t h e experimental data were computed and are shown as the solid lines in Figure 2. T h e shape of these curves and their power dependence is consistent with the behavior obtained by Tohma ( 1 5 ) using a rate-equation model for intracavity absorption. T h e lowest measurable intracavity iodine concentration, 5 X 10" molecules/cm3, was limited by the lowest cold finger temperature attainable with
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ANALYTICAL CHEMISTRY, VOL. 51,
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the three-stage thermoelectric cooling module. This concentration corresponds to a total of 3 x 10' iodine molecules within the sampled intracavity vapor cell volume (-0.4-mm laser beam diameter and 5.0-cm path length). T h e isotopic selectivity of iodine intracavity absorption was measured by using the intracavity l Z i I 2 vapor cell and the external fluorescence signal from the lZ912monitor cell. T h e normalized fluorescence signals from the external lm12cell were measured as a function of the intracavity '"12 concentration. These curves, shown in Figure 3, were measured simultaneously with those presented in Figure 2. Figure 3 shows that the isotopic selectivity of iodine intracavity absorption is relatively insensitive to both the laser output power and the intracavity absorber concentration. The small amount of lZ7I2impurity in the 12912 fluorescence monitoring cell is expected to fluoresce less intensely in Figure 3 when the l2;IZconcentration inside the cavity is high. This decrease is not observed, however, because an offsetting fluorescence signal is produced by the slight increase in laser power at the and 12i112sIabsorption wavelengths a t high intracavity 1z'12concentrations. The power dependence of the latter effect produces the scatter in the data shown in Figure 3. The isotopic selectivity of the intracavity absorption method allows the simultaneous and independent measurement of a number of iodine isotopes. This was demonstrated by placing an iodine-129 vapor cell (which also contained iodine-127) inside the laser activity. T h e measured fluorescence signal from a n identical external iodine-129 cell is plotted as a function of I? number density (see lower curve in Figure 4). T h e response of an external iodine-127 cell is shown as the upper curve. Both curves were normalized to unity a t the lowest measured intracavity iodine number density. T h e relative concentration of "'I2 in the intracavity vapor cell is given by
[lz'I,]/[TOTAL 12] = N l / N , where N , is the total intracavity iodine number density ('*'I2 127112sI lZ7I2)a t a given point on the lower curve in Figure 4 in its linear region, and N 2 is the apparent "'I2 number density a t the same external fluorescence signal level on the upper curve. When the data are normalized a t a point for which the external fluorescence signals are independent of the intracavity iodine concentration, this equation is independent of the relative response of the external fluorescence detection system. From this equation, the isotopic abundance of
+
+
iodine-127 in the intracavity iodine-129 vapor cell is given by (N1/N2)1/2.Using Figure 4, we determined the isotopic abundance of iodine-12'7 to be in the range 24-2870. This is in agreement with the estimated isotopic abundance of iodine-127 in this cell. I n conclusion, we have demonstrated the high sensitivity and large dynamic range of iodine intracavity absorption spectroscopy with a CW dye laser. Because the method is isotope specific, lZ9I2can be measured in the presence of fission-produced stable "'I2 and naturally occurring lZiIzin the atmosphere. T h e sensitivity of this technique can be increased by using a larger laser beam and a long sample cell. For example, with a 4-mm laser beam diameter and a 50-cm long intracavity sample cell, we expect the sensitivity of this measurement technique to be increased by a factor of -1000. This would permit a measurement of lZgI2a t levels below the maximum permissible concentration.
ACKNOWLEDGMENT T h e authors express their appreciation to M. E. Wilkins for providing technical assistance in making these measurements.
LITERATURE CITED Y. Wang, Ed., "CRC Handbook of Radioactive Nuclides", Chemical Rubber Co., Cleveland, Ohio, 1969, p 622. A. P. Baronavski and J. R. McDonald, " A Radioiodine Detector Based on Laser Induced Fluorescence", Nav. Res. Lab. (U.S.) Rep., 3514 (1977). R. L. Brown and W. Klemperer, J . Chem. Phys., 41, 3072 (1964). J. L. Steinfeld and W. Klemperer, J . Chem. Phys., 42, 3475 (1965). N. C. Peterson, M. J. Kurylo, W. Braun, A. M. Bass, and R . A. Keller, J . Opt. SOC.Am., 61, 746 (1971). R.J. Thrash, H. von Weyssenhoff, and J. S.Shirk, J . Chem. Phys., 55, 4659 (1971). R. A. Kelier, E. F. Zalewski, and N. C. Peterson, J . Opt. SOC.Am., 62, 319 (1972). T. W. Hansch, A . L. Schawlow. and P. E. Toschek, If€€ J . Quantum Electron., qe-8, 802 (1972). R. A. Keller. J. D. Simmons. and D. A. Jenninas. J . Oot. SOC.Am.. 63, 1552 (1973). W. J. Chiids, M. S. Fred, and L. S.Goodman, Appl. Opt., 13, 2297 (1974). W. Brunner and H. Paul, Opt. Cornmun., 12, 252 (1974). W. G. Schweitzer. Jr.. E. G. Kessler. Jr.. R. D. Deslattes. H. P. Laver. and J. R. Whetstone, Appl. Opt., 12, 2927 (1973). W. F. Giauque, J . Am. Chem. Soc.,53, 507 (1931). C. A. Goy and H. D. Pritchard, J . Mol. Spectrosc.. 12, 38 (1964). K. Tohma, J . Appl. Phys., 47, 1422 (1976).
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RECEIVED for review November 20, 1978. Accepted March 19, 1979. This work was supported by the United States Department of Energy.
Determination of Three Phenolic Compounds in Water by Laser Excited Resonance Raman Spectrometry Laurent Van Haverkeke and MCdard A. Herman" Rijksuniversitair Centrum Antwerpen, Laboratorium voor Anorganische Scheikunde, Groenenborgerlaan 171, B 2020 Antwerpen, Belgium
Three phenolic compounds are determined in aqueous solutions by resonance Raman spectrometry via the derivatiration with the diazonlum salt of 4-nitroaniline. The detection level of phenol in distilled water was 20 ppb. I n natural waters, the detection level of added phenol was 50 to 300 ppb, depending on the characteristics of the water sample. A calibration curve is set up and concentrations are measured within 10% or less. The spectra of three different phenols have been recorded to indicate the identification capabilities of the technique.
Several methods for the detection of phenols in water a t low concentrations have been described in the literature. The majority of these methods can be divided in two series. First,
there are the spectrophotometric analyses; the most commonly used coloring reactions are the ones that use 4-aminoantipyrine (1-4) and 3-methyl-2-benzothiazolinone hydrazone (3-6). The other important class of methods involves gas chromatography (7-11). For this method, the pollutants must, however, be taken out of their aquatic medium and transferred into an organic phase by an extraction procedure. Among the many other methods t h a t have been proposed, we mention polarography and ion-exchange liquid chromatography (12-14). T h e above cited methods all have least one factor t h a t inhibits their use in routine applications. Either the technique used is applicable only in nonaqueous media and, therefore, t h e pollutants have to be extracted into a n organic layer, or
0003-2700/79/0351-0932$01.00/0 1979 American Chemical Society
