Anal. Chem. 1987, 59, 1089-1093
1089
Infrared Spectrophotometric Determination of Hydrogen-Containing Impurities in Silicon Tetrachloride Thomas Y. Kometani,* Darwin L. Wood, and Joseph P. Luongo AT&T Bell Laboratories, 600 Mountain Avenue, Murray Hill, N m tJwsey 07974
Analyses of IlquM samples of Slcl, by Infrared spectroscopy are described. Oualitatlve lnterpretatlon of the spectra of SICI, and its Impurities Is discussed. Partlcular emphasis Is given to the ldentmcatlon and measurement of hydrogencontalnlng lmpuritles contrlbutlng to the lncorporatlon of the -OH group Into optical wavegulde glass flbers made from SICI,. studies of the Mecl of moistwe on the staMtty of SICI, showed that SICI, storage In Teflon bottles under dry N, best prevents hydrolysis. The amblgultles of publlshed absorptlvitles of -OH in SICI, and glasses are discussed. Experlmentally determined absorptlvitles are reported for quantltatlve determlnatlons of -OH, HCI, and SIHCI, as well as for varlous -CH,, -CH2, and -CH groups In SICI,.
One of the important impurities contributing to signal attenuation in glass fiber light guides is the -OH functional group that has strong absorption in the near-infrared region where transmission is optimum for certain applications (1,2). There are many possible sources for -OH contamination during production of waveguide fibers by the modified chemical vapor deposition (MCVD) process (3). These may include diffusian from the cladding glass (4-6) or atmospheric moisture contamination during preform manufacture and subsequent drawing of the fiber (7, 8). A major source, however, is from hydrogen-containing impurities in the primary starting material, usually silicon tetrachloride (SiC14). One common impurity found in commercial SiC14 is trichlorosilane, HSiCl,, and the route taken by the hydrogen from the impurity into the finished fiber has been described previously (9, 10). Hydrogen is also readily introduced into SiCll from atmospheric moisture with the formation -OH compounds and HCl. To detect and measure such hydrogen-containing impurities infrared spectroscopy is particularly favorable because the molecular vibrations involving hydrogen give rise to highfrequency infrared transitions, while those of the heavier chlorinated molecules ordinarily used as starting materials occur a t much lower frequencies. The hydrogenic impurity absorption bands therefore absorb strongly in a region of the infrared where the starting materials hardly absorb at all. Rand (11)has shown that the use of liquid cell path lengths as long as 10 cm permits the detection of hydrogen-bearing impurities down to less than one part per million by weight (ppm) in favorable cases. Rand has also given approximate absorptivities from the literature for one or two absorption bands for some of the molecular species that might be found in silicon or germanium tetrachlorides. In this paper we report experimentally measured absorptivities for -OH, Si20C16, HSiC13, and HC1 in SiC14 and describe procedures for their determination.
EXPERIMENTAL SECTION Infrared spectra were recorded with Perkin-Elmer spectrophotometers, Models 397 and 421,that were continually purged with dry Nz in order to protect the optical surfaces from SiC14 fumes. A purged cell compartment was also constructed to hold 0003-2700/87/0359-1089$0 1.50/0
sample cells in a clean environment (12). Liquid cells were made by cementing 1.mm t,hick silver chloride windows with rapidsetting epoxy to 2.5-cm diameter stainless steel or monel tubes to which were soldered two I,uer-T,ok syringe fittings as filing and cleaning ports (13). Tapered Teflon phgs were used to seal the fittings during the recording of spert,ra,and cells with various path lengths were made to permit absorbance meRwrement,s over a wide range of impurity concentrations. For path lengths of less than 0.1 cm, standard infrared liquid cells with KRr windows were used. Sample cells were loaded by drawing liquid into a glass hypodermic syringe and transferring the sample into the cell through the Luer-Lok fitting. When precautions were taken to dry the cell and syringe by purging with nitrogen, it was found that an inert atmosphere was not necessary for the environment around the transfer operation. However, for storage of SiCl, samples and for transfer of liquids from one bottle to another, it was important to provide a plastic glovebox continually purged with Nz of less than 4% relative humidity. Samples were sealed in 30-mL Teflon bottles with screw caps that were carefully cleaned with concentrated HF, rinsed with HzO, and dried at 80 OC just before storage in the glovebox. Teflon bottles were chosen because they were not permeable to Sic& and were easy to clean and seal, although somewhat permeable to moisture. The infrared cells were cleaned by blowing out the sample with dry nitrogen and then flushing the chamber with reagent grade liquid chloroform several times. They were then dried with flowing nitrogen. After repeated use the cell windows became coated with hydrated silica that gave rise to a broad infrared absorption centered at 3300 cm-', which can be seen in curves A and B in Figure 1. There was also a larger absorption near 1070 cm-' that can badly distort the SiC14spectrum in that region. Such films of hydrated silica were easily removed from the silver chloride windows by rinsing briefly in dilute HF (19)followed by thorough rinsing with water and drying. In the case of KBr cells, however, it was necessary to repolish the windows by standard techniques.
RESULTS AND DISCUSSION Spectrum and SiC14. T o describe first the spectrum of relatively pure liquid SiCl,, we have reproduced in Figure 1 the infrared absorption for four cell path lengths: 0.0521, 0.386, 1.542, and 4.742 cm. In the thinnest sample essentially no absorption intrinsic to the SiCl, is observed for frequencies higher than 1300 cm-', and in several regions below 1300 cm-' there are windows between SiC14bands where impurity absorptions may be observed. As the sample thickness increases, the region from 400 to 1300 cm-' becomes less useful and the bands near 1820, 1632, and 1448 cm-' increase. The bar,ds near 3750,2840, and 2258 cm-' are due to -OH, CH, and SiH stretching vibrations from impurities in the SiC14,and these are the bands of most interest in selecting starting materials for making low-loss glass fibers, since these hydrogen-bearing impurities may later give rise to -OH in the glass fibers made from it (9, 10). The assignment of the absorption bands in Figure 1 to vibrations of the tetrahedral SiC14molecule has been made previously, and there are four fundamental modes of vibration (14) for a tetrahedral molecule, usually designated v1 to v4, with many overtones and combination bands derived from several of the fundamentals. Two of the fundamentals, v 2 and v4, are out of the range of wavelength covered by Figure 1, and the us fundamental at 606 cm-' gives by far the strongest infrared 0 1987 American Chemical Society
1090
ANALYTICAL CHEMISTRY, VOL. 59, NO. 8, APRIL 15, 1987 WAVELENGTH, MICRONS
WAVENUMBER, CM-I
Flgure 1. infrared spectra of a liquid SiCI, sample for various cell thicknesses. Curve A is for 47.4 mm. Curve B is for 15.42 mm. Curve C is for 3.86 mm. Curve D is for 0.521 mm. Absorption bands discussed in the text are labeled with their frequencies in cm-'. The characteristic -OH, CH, and SiH absorption regions are so indicated. This sample of SiCI, contained negligible HCi that absorbs in the region labeled "CH". WAVELENGTH MCRONS
Table I. Infrared Absorptivities for Impurities in SiCl,
molecular group or compd
freq, em-'
-OH
3670 2845 2260 497 3018 2395 2960 1110 1535 1837
HCl HSiC13 CHC13 CH3(CH,),CH$ SizOCl6
absorptivity, (ppm ern)-' 1.39 7.15 6.25 4.70 6.36 2.55 1.07 3.25 2.50 4.97
X X
x x x x
10-4 10-4
10-5 10-5
x 10-3
x 10-3 x 10-5
x 10-5
molar absorptivity,e, L (mol cm)-' 160 17.6 57.2 43.0 5.2 2.1 6.5 403 4.81 6.16
4 97
absorption. Each of the observed bands due to SiC14 is identified by frequency in Figure 1. Other bands in Figure 1such as those at 963,2260,2860,2930,2960, and 3670 cm-' are attributable to impurity vibrations including SiOH, HSiC13, HC1, and CH-containing compounds. They form the principal topic of discussion here. Absorptivities for Infrared Bands. In order to analyze SiC14samples quantitatively for the impurities giving rise to the infrared absorption bands observed as in Figure 1, it is necessary to know the absorptivity (a) (or molar absorptivity e) of each molecular species for each infrared band. These quantities relate the peak absorbance, A, with concentration, c, and cell thickness, b, through the Beer-Lambert law
Jpe ,
,
11603
WAVENUMBER ( C M - ' 1
I
'
'
'
8
I
'
'
8
,
,
' .
,
I
.
'
-
1
A / b = ac with cell thickness in cm, concentration in weight ppm (or in molarity), and a (or e) are then in (ppm cm1-l (or L (mol cm)-'). Trichlorosilane. Trichlorosilane, HSiC13, is a common contaminant of commercial SiC14. The spectrum in the gas phase is shown in Figure 2, with strong absorption bands a t 2260,808,603, and 497 cm-'. The spectrum in the liquid phase is essentially the same, but the bands at 808 and 603 cm-' overlap with those of SiC1, at 606 and 822 cm-' and cannot be used for analyses. The absorptitivies in Table I were obtained by measuring the peak absorbmces of the 2260 and 497 cm-' bands in carefully prepared standard solutions of HSiC13 in Sic&and calculating the slopes of the straight lines we obtair.ed for absorbance VR. concentration The band at 2258 cm-l is preferred €or HSiC13determinations because of its kola?ion from interfering absorption snd greater absorption strength relative to the 497 cm band Dissolved HCI. The vibrational shorption near 5845 cm for HCI dssdvod in SiCl, i s shnwn the lower ciiwc Tn Figure 3 measisred on a senple though which gaseom HCI had heen bubb!ee for ?O m r i . T h e absorptivity a t the maximum was
z
0 m m I
3
Flgure 3. Infrared absorption spectrum of HCI in solution in SiCi,: upper curve, gas phase, 10-cm path length; lower curve, liquid phase, 0.521-mm path length.
determined in two ways. In the first method a known volume (01 cm3) of liquid solution was completely volatilized in a IO-ern infrared gas cell of known volume. The gas spectrum was measured in the same wavelength ranged as the liquid, giving the top curve of Figure 3 that shows clearly the rota-
ANALYTICAL CHEMISTRY, VOL. 59, NO. 8, APRIL 15, 1987
1091
MICROMETERS
50 100 I
0
500
C, pprn H C I
1000
IN SlCP4
Figure 4. Calibration curve for spectrophotometric determination of HCI in liquid SiCI,.
tional fine structure lines of HC1 gas whose absorptivities are well-known (15). The concentration of HC1 was determined from these lines and that of SiCl, from the absorptivities of its bands at 760,1042, and 1235 cm-l also measured for the same gas sample. A value of a = 7.14 X lo4 (ppm cm)-' was thus determined a t 2845 cm-'. In the second method a set of known concentrations HC1 dissolved in liquid SiCl, were prepared and their infrared spectra were measured. For this purpose a 1-L expandable gas sampling bag was filled with pure HC1 at 1 atm from a gas cylinder. Known volumes of HCl gas were withdrawn from the bag with a syringe and slowly expelled into a long-necked 50-mL volumetric flask containing 100 mL of liquid SiCl,. The gas was introduced through a needle attached to the syringe and inserted through a glass wool plug in the neck of the flask. After the glass wool was replaced with a solid stopper, the contents of the flask were shaken for several minutes to assure complete solution, and then samples of liquid were transferred to the spectrophotometer cell and the spectra were run. The results of absorbance at 2845 cm-' vs. concentration of HC1, assuming complete dissolution, are shown in Figure 4, and the nonlinearity at greater concentrations is interpreted as the approach of saturation. The initial slope of the curve gives the absorptivity of 7.13 X lo-, (ppm cm)-' in agreement with the method described earlier. HC1 is frequently detected in SiC1, liquid samples since it can easily be formed by reaction with atmospheric moisture SiCl, xHzO = SiCl,,(OH), xHCl (1)
+
+
or by reaction with other sources of hydrogen. But it is necessary to be careful about interpretation of absorption at 2845 cm-' as simply due to HC1, since there are many other absorption bands in the same frequency range due to CH vibrations of various kinds (16), and molecular impurities containing these groups are commonly found in SiC1,. The spectra of CH-containing impurities is discussed in a later section. Hexachlorodisiloxane. A common impurity in SiC1, is hexachlorodisiloxane (Si,OC&), the lowest molecular weight member of a series of fully chlorinated siloxanes that can be thought of as forming polymers of SiC1, with oxygen. Although this molecule dose not contain hydrogen, the determination of its concentration in SiC1, was important to explain the mechanism of removal of -OH from SiC1, as will be discussed later. The infrared spectrum of Si20Cl, in SiC1, in Figure 5 shows characteristic absorption bands at 1837,1535, and 1110 cm-l. From the spectra of known concentrations of the compound in solution in SiCl, the absorptivities given in Table I were determined for these absorption bands. OH-Containing Impurities. There is confusion and uncertainty in the published literature on the absorptivity of -OH in MCVD starting materials and in the finished glass.
c
01 2000
60
eo
00
70
10
I
I
1800
I
1800
I
1400 1300 (PO0 WAVENUMBERS icmP
((00
1000
Flgure 5. IR spectrum of Si20ClEin SiCI, using 0.157- and 0.01-cm cell paths: ---, 6000 ppm Si,OCi, in SiCI,; -, SiCI, with no Si20C16
added. Table 11. Molar Absorptivities for OH in SiC14
OH-containing compd Ph3(OH)Siin CCll Ph,(OH)Si in CS2 Ph,(OH)Si in CS2 Si02 Si02 Si02
Si02 45 SiOz,35 BzO3, 20 Na20 B2°3
SiOHCla in SiC1,
e(OH),L (mol cm-') 160 134 93 77.5 77 25 86 (43) 29 70.5 102
ref
this work this work 23 23 25 26 27 28 29 34
The fact that the band at 3670 cm-' in Figures 1 and 3 is due to an -OH stretching vibration without hydrogen bonding or other association is well-documented (17). However, the exact molecular species giving rise to the -OH absorption is not well-known, and the molar absorptivity one should use to determine the amount of -OH present in SiCl, is equivocal. In fused silica glass there are several references to the strength of the SiOH absorption band at 3660 cm'(18-25). Stephenson and Jack (23) have been most often quoted (20-23) for the value o f t = 77.5 L (mol cm1-l obtained from measurements of weight gain and loss after treatment in HzO vapor for samples on which infrared measurements had been made. Hardy (25) also found a value of t = 77 L (mol cm)-' from weight loss measurements in fused silica. An older paper by Fry, Mohan, and Lee (26), who substituted -OD for -OH in fused silica, allows one to estimate the molar absorptivity to be t = 25 L (mol cm)-' from their Figure 2 and the stated concentration of -OD (1 deuterium atom/1000 Si atoms) determined from mass spectrometry. Williams et al. (27) found t = 86 L (mol cm)-' from exchange experiments in silica glass, but they plot linear absorption coefficient vs. % HzO (w/w) and convert to molar absorptivity on a one-to-one basis. Since each HzO molecule removed from SiOz comes from 2 -OH groups in the bulk, their molar absorptivity of -OH alone should be t = 43 L (mol cm)-'. There are other attempts to determine the molar absorptivities for -OH in glasses, but these are not for pure silica. In the case of sodium borosilicates, Pearson, Pasteur, and Northover (28) found t = 29 L (mol cm)-', and Pasteur (29) found E = 70.5 L (mol cm)-' for fused B,03. Other work for glasses (30-32) give generally low values, but the issue is clouded by the fact that the -OH may exist in more than one form or in more than one site (32, 33) in compound glasses with different absorption frequencies for the different forms. These results are collected in Table 11, and the value to be used for the determination of -OH in SiC1, lies somewhere
ANALYTICAL CHEMISTRY, VOL. 59, NO. 8, APRIL 15,
1092
1987
WAVELENGTH i M l C R O M E T E R S 1 5
2 5
100
7
6
REFLUXED
REFLUXED
5300pprn
Table 111. Effect of Exposure of SiC14 to Dry N2and Ambient Air
8
sicl4
......
Si20CO6
...q
P
treatment
v) (n
STARTING SlCP4
1
z c LL
'
' Z Y I N G
~
97pprn OH
0 4000
freshly opened open cap loose cap loose cap sealed Teflon bottle (15 ppm of
37ooppm
1
3500
3000 2000
IS00 FREOUENCY
1600
1400
I
IO
(cm-')
Flgure 6. Spectra of SEI,: -, starting material with 97 ppm of -OH; ---, same material after refluxing for 4 h contains 3 ppm of OH.
between the lowest t = 25 L (mol cm)-l and the highest t = 160 L (mol cm)-', which we determined in the manner to be described next. For our analytical work we use the value of c = 160 L (mol cm)-', based on the phenylsilanols and confirmed by further indirect experiments. When SiCl, is exposed to moisture, the infrared band at 3670 cm-' increases in intensity, presumably by reaction 1. The simplest reaction product containing -OH would be SiOHC1, (trichlorosilanol), and this could form according to reaction 2. We have not yet been able to prepare or obtain SiC1,
+ H20 = SiOHC13 + HC1
(2)
the pure compound SiOHC13to verify the assignment of the infrared band or to determine its molar absorptivity. Instead, we have used indirect methods to estimate the molar absorptivity, making the assumption that the R-SiOH group will absorb with approximately the same intensity in similar solvents and in molecules with different R groups. In the first indirect method we prepared solutions of two phenylsilanol model compounds and measured the molar absorptivity of the -OH band occurring at 3650 cm-', only 15 cm-' away from that for chlorinated silanol. The compound Ph3SiOH and a similar one, PhzSi(OH),, where P h is the phenyl group (-c6H6),are available as solids but are not very soluble in SiC1,. However, in CCl, which also had no overlapping absorption bands in the -OH region, the solubility is sufficient at room temperature to make satisfactory measurements. The results for both compounds agreed when reduced to molar absorptivity per -OH group, and the best fit to the plot of concentration vs. absorbance per centimeter of path length gave t(0H) = 160 L (mol cm)-'. Our value of e of Ph,SiOH measured in CS2was €(OH)= 134 L (mol cm)-' which roughly compares with 93 L (mol cm)-' obtained by Moulsen and Roberts (24) for the same system. Another indirect method for determining the molar absorptivity of SiOH is to convert it to Si,OCl, (hexachlorodisiloxane) by refluxing -OH-contaminated SiC1, according to reaction 3. After 4 h of refluxing at the boiling point (59 SiOHCl,
+ SiCl,re%3i,0C16 + HCl
(3)
"C), the -OH absorption at 3670 cm-' nearly disappeared, and as Figure 6 shows, the intensities of bands of SizOC1, a t 1837 and 1535 cm-' increased. With use of the molar absorptivity for -OH determined from the phenyl silanols in CCll (160 L mol-' cm-l), the starting SiC1, lost 94 ppm of -OH or 0.0082 mol/L while the increase in hexachlorodisiloxane during reflux was 1600 ppm or 0.0083 mol/L as expected from eq 3. We consider that the production of 1 mol of Si20CI,for each mole of SiOH consumed is confirmation of the value of the molar absorptivity of SiOH that was determined from the phenylsilanol model compounds. Gooden and Mitchell (34) have prepared solutions of SiOHCl, in SiCl, by quantitative photochemical oxidation of
-OH,ppm
duration of exposure, h
N,
0 0.17 24 48 240
25 25 31 28 15
ambient 40%
RH"
63 164 326 45
-OH) hydrolyzed hydrolyzed a
2 15
100 100
100
92
RH,relative humidity.
known concentrations of SiHC13 in SiCl,. They used these solutions to indirectly determine the absorptivity of the SiOH group at 3680 cm-' and found a lower value than ours, namely, t = 102 L (mol cm)-'. However, in their experiments there was the possibility that some SiOH could form Si20C1, by reaction with the SiCl, solvent and reduce the amount of SiOH produced by the photooxidation. They noted that no evidence for this side reaction was observed in their infrared spectra, but if the new values for the extinction coefficients of Si,OCI, in Table I are used, it can be shown that, for the conditions of their experiments, a significant quantity of that compound could not be detected. Thus, if a significant fraction of their SiHC13was converted to Si,OC&, and not detected, their value for t would be lower than the value if a correction had been made. This explains the lower value of E they obtained and lends credence to our higher value. CH Frequencies. An important source of hydrogen that converts to -OH in the finished glass during the MCVD process is the decomposition of CH groups in either organic compounds or organosilanes. The presence of CH-containing molecular groups is evident in the spectra of Figure 1 from the presence of absorption bands in the range from 2850 to 3100 cm-'. There are many molecules that have absorption bands in the CH region, and in general it is practical only to use the intensities of these bands for analyses after unequivocal identification by other methods. Nevertheless, the CH stretching vibrations occur in a region of the spectrum free of absorption from SiC1, even for the thickest samples, and some useful information can be obtained from them. The reader is referred to the literature (16) for details pertinent to their particular problems. It was possible to estimate very crudely the level of contamination of SiC1, samples from CH-containing species by measuring the strongest and the weakest CH molar absorptivities in likely compounds. We chose chloroform, CHC13, for the weakest absorber and found t = 5.2 L (mol cm)-' for the CH stretch at 3018 cm-'. Hexane was the strongest absorber with t = 65 L (mol cm)-' for the CH3group asymmetric stretching vibration at 2968 cm-'. Presumably any CH-containing compound would have an absorptivity between these extremes, and the level of contamination could be estimated to within a factor of about 15x without further detailed information. Storage of Silicon Tetrachloride. The reactivity of S i c 4 with moisture and its volatility require special handling and storage methods. The effects of exposure to dry N2 and to atmospheric moisture compared in Table I11 provided useful information on proper storage methods for SiCl,. In one experiment the seal on a fresh glass ampule of epitaxial grade SiC1, was broken under dry N, and the -OH level was found to be 25 ppm. Two samples were identically prepared, but one was stored without closure in dry N2 while the other was stored in air. The SiC1, exposed to N2 showed essentially no
Anal. Chem. 1987, 59, 1093-1095
change over a 48-h period, while the sample exposed to the moisture in room air increased significantly in -OH concentration. In another set of experiments samples of SiC14initially containing 15ppm of -OHwere stored in tightly closed Teflon bottles for 10 days in dry N2 and in room air. The SiC1, stored in N2 was unchanged, while that stored in air increased to 45 ppm of -OH. Clearly SiC1, even in Teflon bottles will hydrolyze unless stored in a dry atmosphere. Despite their porosity to moisture, however, Teflon bottles are useful because they effectively prevent volatilization of SiC1,.
ACKNOWLEDGMENT We gratefully acknowledge the assistance of W. G. French, S. S. DeBala, G. A. Pasteur, J. E. Kessler, J. B. MacChesney, A. D. Pearson, and S. R. Nagel. Registry No. SIC&, 10026-04-7; HCl, 7647-01-0; SiHCl,, 10025-78-2;Si,OC&, 14986-21-1;CHCl,, 67-66-3; CH3(CH2),CH,, 110-54-3; Ph,(OH)Si, 791-31-1. LITERATURE CITED Keck, D. B.; Schultz, P. C.; Zimer, F. Appl. Phys. Lett. 1072, 2 1 , 215.
Keck, D. B.; Tynes, A. R. Appl. Opt. 1872, 1 1 , 1502. MacChesney, J. 6. I€€€ 1080, 68, 1181. Nassau, K. Mater. Res. Bull. 1078, 13, 67-76. Ainsiie, B. J.; France, P. W.; Newns, G. R. Mater. Res. Bull. 1077, 122, 481.
Horiguchi, M.; Kawachi, M. Appl. Opt. 1078, 17, 2570. Horiguchi, M.; Osanai, H. Electron. Lett. 1078, 12, 310. Osanai, H.; Shioda, T.; Moriyama, T.; Aroki, S. Horiguchi, M.; Izawa, T.; Takata, H. Electron. Lett. 1076, 12, 549.
1093
Wood, D. L.; Kometanl, T. Y.; Luongo, J. P.; Saifi, M. A. J. Am. Ceram. SOC.1070. 6 2 , 638. Wood, D. L.; Shirk, J. S. J. Am. Ceram. SOC. 1081, 6 4 , 325. Rand, M. J. Anal. Chem. 1883, 3 5 , 2126. Luongo, J. P.; Wood, D. L.; Delbab, S. S. Appl. Spectrosc. 1081, 3 5 , 514. Wood, 0. L.; Luongo, J. P.; Debala, S. S. Anal. Chem. 1081, 5 3 , 1967. Herzberg, G. Infrared and Raman Spectra of Polyatomic Molecules ; Van Nostrand: New York, 1945; p 100. Benedict, W. S.; Herman, R.; Moore, G. E.; Silverman, S. Can. J. Phys. 1056, 34. 830. Smith, A. L. Spectrochim. Acta 1860, 16, 87. Adams, R. V. Phys. Chem. Glasses 1961, 2 , 39. Ernsberger, F. M. J . Am. Ceram. SOC. 1077, 6 0 , 91. Dodd. D. M.; Fraser, D. 0. J . Appl. Phys 1086, 3 7 , 39 11. Hertherington, G.; Jack, K. H. Phys. Chem. 1062, 3 , 129. Hertherington, 0.; Jack, K. H. Bull SOC. f r . Ceram. 1982, 55, 3. Elliott, C. R.; Newns, G. R. Appl. Spectrosc. 1071, 2 5 , 378. Stephenson, G.; Jack, K. H., discussion of; Moulson, A. J.; Roberts, J. P. Trans. Br. Ceram. SOC.1060, 5 9 , 388. Moulson, J.; Roberts, J. P. Nature (London) 1058, 182, 200. Hardy, L. E. PhD. Thesis, University of New Castle upon Tyne, 1970. Fry, D. L.; Mohan, P. V.; Lee, R. W. J. Opt. SOC. Am. 1060, 5 0 , 1321. Williams, J. P.; Su, Yao-sin; Strzegowski, W. R.; Butler, B. L.; Hoover, H. L.; Aitemos, V. 0. Am. Ceram. SOC.Bull. 1078, 55, 524. Pearson, A. D.; Pasteur, G. A.; Northover, W. R. J. Mater. Sci. 1070, 14, 869. Pasteur, 0. A. J. Am. Ceram. SOC.1075, 5 6 , 548. Gotz, J.; Vosohiova, E. Glastech. Ber. 1068, 4 1 , 47. Scholze, H. Glastech. Ber. 1050, 3 2 , 81. Scholze, H. Glastech. Ber. 1059, 3 2 , 142. Smith, A. L.; Angelotti, N. C. Spectrochim. Acta 1050, 15, 412. Gooden, R.; Mitchell, J. W. J. €lectrochem. SOC. 1082, 129, 1619.
.
RECEIVED for review September 29,1986. Accepted December 19, 1986.
Laser-Induced Room-Temperature Phosphorescence Detection of Benzo[ a Ipyrene-DNA Adducts Tuan Vo-Dinh* and Mayo Uziel
Advanced Monitoring Development Group, Health and Safety Research Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 -6101
The room-temperature phosphorescence (RTP) spectrum of benro[a]pyrene-r-7,t -8,9,1O-tetrahydrotetrol(BP-tetrol) has been measured uslng laser excltatlon. The BP-terol was obtalned by acid hydrolysls of the r-7,t -8-dlhydroxy-t -9,lO-epoxy-7,8,9,10-tetrahydrobenro[a]pyrene (BPDE)-DNA adducts. BPDE Is the ultimate carcinogenic metabolite of benro[a]pyrene (BP). The BP-tetrol sample was measured on a filter paper substrate pretreated wlth a heavy-atom salt, thallium acetate, used to Increase the phosphorescence slgnal of BP-tetrol. The detection llmlt of BPDE In In vltro modlfled BPDE-ONA was about 15 fmol. The results lndlcate the RTP would be useful as a simple and practical screening tool for monltorlng BPDE-DNA adducts and related BP metabolites In blologlcal samples.
The mutagenic and carcinogenic activity of many polynuclear aromatic (PNA) compounds (1)has been the focal point for concern about human exposure to these species in the workplace and in residential environments. Polynuclear aromatic compounds, which are products of incomplete combustion of organic materials, are widely distributed in the
environment. Since combustion processes occur frequently in many industries, PNA compounds have been found in a large number of workplace environments (2-4). Residential activities, including cooking, woodstove burning, and cigarette smoking, are indoor emission sources of PNA pollutants (5). An important PNA compound of great interest to toxicologists and cancer researchers is benzo[a]pyrene (BP). Studies have shown that BP is metabolically activated to electrophilic intermediates, which bind convalently to DNA (3). A specific diol epoxide derivative of BP, r-7,t-8-dihydroxy-t-9,lO-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE) was found as the major carcinogenic metabolite involved in binding to DNA (6). Metabolized B P is eliminated through the urine and feces (7). Since the carcinogenic activity of a compound could be associated with the degree to which it binds to DNA, there has been a great deal of interest in analytical techniques that are capable of detecting DNA-carcinogen interactions and monitoring human exposure to PNA compounds. Several techniques, including mass spectrometry (8),synchronous fluorescence (9,10,20),liquid chromatography (11, 12),fluorescence line narrowing spectroscopy (13),32P-postlabeling autoradiography (14), and enzyme-linked immunoassay (15),have been developed to detect carcinogen-DNA
0003-2700/87/0359-1093$01.50/0 0 1987 American Chemical Society
