ANALYTICAL CHEMISTRY, VOL. 50, NO. 2, FEBRUARY 1978
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Determination of Industrial Dyes in Water by Laser Excited Resonance Raman Spectrometry Laurent Van Haverbeke,' Patricia F. Lynch, and Chris W. Brown* Department of Chemistry, University of Rhode Island, Kingston, Rhode Island 0288 1
Industrial fabric dyes were detected in distilled water at concentrations below 100 ppb and identified at concentrations below 200 ppb using resonance Raman spectrometry. The method was tested on doped samples of river and seawater. I n both cases dyes could be detected and identified at the 200-ppb level. Detection and identification limits were higher in the natural samples because of an increase in the spectral background; however, the results show that the method is practical for "real world" samples.
In recent years, laser Raman spectrometry has been shown to be a promising method in water pollution studies. In the early 1970's, Bradley and Frenzel ( I ) reported the detection of benzene in water a t concentrations around 50 ppm, and Baldwin and Brown (2) found minimal detectable concentrations of 25 to 75 ppm for various inorganic anions. Later, Ahmadjian and Brown (3) demonstrated the use of Raman spectrometry in remote detection measurements. More recently, Cunningham, Goldberg, and Weiner ( 4 ) were able to reduce the detection limits to 5 to 40 ppm for various solutes. Up to now, the practical use of Raman spectrometry in pollution studies was restricted because, for most compounds, the minimum detectable concentration was too high. An important limitation is the Raman spectrum of the solvent, water, which shows u p as a background above which the spectrum of the compound of interest is observed ( 5 ) . It is possible to increase the strength of the Raman signal of the solute without increasing the one of water by taking advantage of t h e resonance Raman effect. When the excitation frequency approaches the frequency of an electronic absorption band, the resultant Raman signal may be enhanced several orders of magnitude. Since water does not have a n absorption band in or close to the visible region, enhancement of the water Raman signal is not observed. Because of their strong absorption in the visible region, dyes lend themselves readily to monitoring by resonance Raman spectrometry. In a recent study on FD&C dyes, Brown and Lynch (6) have shown that dyes can be detected and identified in commercial solutions such as juice mixes and sodas a t concentrations as low as 5 ppm without significant interference from other substances present. In t h e present contribution we have determined the detection and the identification limits for a number of red industrial fabric dyes. A comparison with visible spectral detection is also presented. Furthermore, we have tested the method on two natural water samples doped with a dye.
EXPERIMENTAL The Raman spectra of the dye solutions were recorded on a Spex Industries Model 1401 monochromator, equipped with a CRL Ar+ ion laser and a photon counting detection system. We Present address, Labortorium Anorganische Scheikunde, Rijksuniversitair Centrum Antwerpen, Groenenborgerlaan, 171, B2020 Antwerp, Belgium. 0003-2700/78/0350-0315$01 .OO/O
Table I. Resonance Raman Spectra of the Dyes in the Region 1100-1500 cm-' a Direct Superlitefast Procion Lyrazol Red 8 3 Rubine Red Fast Red 1277 ( 7 ) 1290 ( 9 ) 1334 ( 7 ) 1346 ( 8 ) 1387 ( 8 ) 1422 ( 1 0 ) 1451 ( 3 ) 1496 ( 2 )
1123 (2) 1180 ( 3 ) 1230 ( 4 ) 1251 ( 4 ) 1286 (10) 1344 ( 4 ) 1368 ( 2 ) 1430 ( 6 ) 1498 ( 2 )
1 1 9 6 (3) 1223 (3) 1257 ( 3 ) 1322 ( 4 ) 1357 (10) 1412 ( 4 ) 1439 (6)
1248 (3) 1317 (8) 1359 ( 1 0 ) 1421 ( 7 ) 1446 ( 6 ) 1482 ( 5 )
a The first figure gives the position of the band (in cm-'). The value in parentheses is the relative height (maximum =
10).
used both the 488-nm and 514.5-nm lines of the Ar+ laser as exciting sources with 1-W output at the sample. All samples were contained in a cylindrical cell (-10-mm diameter), mounted in the Spex standard illumination chamber. Instrumental conditions for obtaining maximum signal-to-noise (S/N) ratios were thoroughly investigated. For natural water samples, the maximum S / N ratio was obtained with a spectral slit-width of - 5 cm-'. A time constant (integration time) of 10 s was used for measuring the spectra; the S / K ratio was improved by using longer integration times, hut the time required to measure a spectrum was too long for a practical method. Spectra were scanned at 5 or 10 cm-'/min using a 10-s time constant. Visible absorption spectra were recorded on a Cary Model 15 UV-visible spectrophotometer using a standard 5-cm quartz cell. The fabric dyes used in this study were Superlitefast Rubine, Procion Red, Lyrazol Fast Red, and Direct Red 83. These commercial dyes were supplied by Kenyon Piece and Dye Works and by the Bradford Dyeing Association, and were used without further purification. They were dissolved in distilled water at concentrations around 200 ppm, diluted ten times to around 20 ppm, and then diluted consecutively to 50% to obtain lower concentrations.
RESULTS AND DISCUSSION T h e visible absorption spectra of Superlitefast Rubine, Procion Red, Lyrazol Fast Red, and Direct Red 83 are shown in Figure 1. All four dyes show a t least one absorption band in the vicinity of both the 514.5- and 488-nm lines of the Ar+ laser. Therefore, we used both lines as resonance Raman excitation frequencies. One of the dyes, however, (Procion Red) shows an intense fluorescence between 1000 and 2000 cm-' when the 514.5-nm line was used as exciting frequency. Since under these conditions a minimum concentration cannot be determined, we restricted our measurements on Procion Red to the 488-nm excitation. The most useful region of the Raman spectra of these dyes is the region between 1000 and 1500 cm-'. Below 1000 cm-', no intense bands are observed. On the other hand, intense bands in the region 1500 to 1800 cm-I will be masked by the water band a t 1640 cm-' upon dilution. Except for Procion Red, no major differences were observed between the spectra obtained with 488- and 514.5-nm excitation frequency. The C 1978 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 50, NO. 2, FEBRUARY I
1978
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Figure 1. Visible absorption spectra of fabric dyes. (a) Superlitefast Rubine (11.35 pprn), (b) Procion Red (6.32 pprn), (c) Lyrazol Fast Red (7.38 ppm), (d) Direct Red 83 (12.15 pprn)
Figure 2. Resonance Raman spectra of fabric dyes close to the identification level. (a) Superlitefast Rubine (88 ppb), (b) Procion Red (192 ppb), (c) Lyrazol Fast Red (210 ppb), (d) Direct Red 83 (190 ppb)
Table 11. Minimal Detection and Identification levelsa
RamaL Visible
a
Dye name
Detection
Superlitefast Rubine Procion Red Lyrazol Fast Red Direct Red 8 3
35 30 45 55
Identi- spectroficaphotion tometry 75 140
66 30
160 175
40
I
50
All values in parts per billion (ppb).
strongest bands in the 1000-1500 cm-' region for each of the dyes a t 488 nm excitation are listed in Table I. The table demonstrates very clearly that this region of the spectra is very characteristic and can be used as a fingerprint-like recognition pattern. More and more of the smaller bands are lost in the noise of the spectrum as the dye solutions are diluted. We considered the 1000-1500 cm-' region of the spectrum suitable for identification purposes at a certain concentration when at least three bands are visible, i.e., they have a signal-to-noise ratio >3. The lowest concentrations for which this occurs are given in Table 11. The spectra shown in Figure 2 are obtained from solutions close to these identification levels. In the same way, we consider a dye detectable at a certain concentration when a t least one band is visible with a signal-to-noise ratio of a t least three. The detection levels for the four dyes are also given in Table 11. From Table I1 we can see that there is a large variation in both the detection levels and the identification levels, but there is no relationship between them. The reason for this can be found in the pattern of the spectrum. If a large number of bands have the same intensity, both the level of detection and identification are similar. If, however, the spectrum is composed of one or two intense bands and a large number of smaller bands, there will be a significant separation between the two levels. Table I1 also contains the minimally detectable concentrations when using visible absorption spectrometry. A 5-cm pathlength cell was used and a minimally detectable absorption of 0.004 was assumed (7). As can be seen, the detection levels for resonance Raman spectrometry are of the same order as the ones obtained by visible spectrometry. The former has, however, the advantage of better identification capabilities.
600
cm-'
,zoo
Figure 3. Resonance Raman spectra of (a) Superlitefast Rubine in distilled water at 24.3 pprn; (b) Superlitefast Rubine in river water at 288 ppb
To investigate the practical use of the resonance Raman technique in pollution determinations, we simulated a real situation. A 250-mL water sample, collected from the nearby Pettaquamscutt River, was polluted with 3 mL of a 24.3 ppm solution of Superlitefast Rubine in distilled water, resulting in a dye concentration of 288 ppb in river water. From this sample, resonance Raman spectra were measured with both the 488- and 514.5-nm laser lines. The spectrum obtained using the 488-nm laser line showed a huge fluorescence, which made identification of the dye bands practically impossible. However, the 514.5-nm excited spectrum showed very little fluorescence. The region between 1200 and 1600 cm-' is shown in Figure 3b. For comparison, the spectrum of the same dye in distilled water a t a concentration of 24.3 ppm is displayed in Figure 3a. The spectral background level of the river water spectrum was -3000 counts/s (with an integration time of 10 s and a spectral slit-width of 5 cm-I), and the ratio of the Raman intensities to the background was -1:5. Seawater from Narragansett Bay was doped with the same dye and its spectrum measured. The water was collected from the Bay during August, doped with the dye, and the spectrum measured on the same day. The spectral background was -7500 counts/s (with an integration time of 10 s and a spectral slit-width of 5 cm-I), and the ratio of the Raman
ANALYTICAL CHEMISTRY, VOL. 50, NO. 2, FEBRUARY 1978
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intensities to the background was l : l 5 . Furthermore, suspended particles occasionally caused "spikes" in the spectrum as they moved through the laser beam. However, a spectrum with a signal-to-noise ratio of 10 was obtained a t a concentration of 444 ppb. Using the criterion of having three bands with a signal-to-noise ratio of >3, we can identify t h e dye in t h e seawater and t h e river water a t the 200-ppb level. T h e results of this study show t h a t Raman spectrometry is a viable method for detection and identification of chemicals in water when those chemicals exhibit resonance Raman scattering. The increased scattering caused by the resonance effect makes it possible to obtain reasonable spectra even when the spectral background is relatively high as in natural water samples.
317
LITERATURE CITED (1) (2) (3) (4)
-
F. B. Bradley and C. A. Frenzel, Waler Res., 4, 1 2 5 (1970). S. F. Baldwin and C. W. Brown, Water Res., 6, 1601 (1972).
M. Ahmadjian and C. W. Brown, Environ. Sci. Techno/.,7 , 452 (1973). K. M. Cunningham, M. C. Goldberg, and E. R. Weiner, Anal. Chem., 49, 70 (1977). ( 5 ) G. Brauniich, G. Gamer, and M. S. Petty, Water Res., 7 , 1643 (1973). (6) C. W. Brown and P. F. Lynch, J , FoodSci., 41, 1231 (1976).
(7) L. de Gdan, "Analytical Spectrometry", Adam Hilger Ltd., London, 1971.
RECEIVED for review April 2 7 , 1977. Accepted October 13, 1977. This research was partially supported by the National Sea Grant Program, National Oceanic and Atmospheric Administration. One of us (L.V.H.) gratefully acknowledges financial support from the State University Center of Antwerp and a N.A.T.O. Research Fellowship.
Analytical Chemistry of Amygdalin Thomas Cairns," Jerry E. Froberg, Steve Gonzales, William S. Langham, and John J. Stamp U S . Food and Drug Administration, Los Angeles, California 900 15
John K. Howie and Donald T. Sawyer Department of Chemistry, University of California, Riverside, California 9252 1
High performance liquid chromatography, carbon-13 nuclear magnetic resonance, chemical ionization mass spectrometry, and gas chromatography with flame ionization detection have been employed for the identification and quantitative determlnation of the epimers of amygdalin. The results indicate that a combination of techniques is required to understand total sample profiles and the pharmaceutical composition of current drug samples. Notably, injectable preparations of amygdalin are epimeric and below declared concentration, while tablet dosage forms contain epimerically pure (R)-amygdalin.
History. Amygdalin (I),a naturally occurring cyanogenetic glycoside (1) found in the kernels or seeds of members of the Rosaceae (almond, apple, apricot, cherry, peach, pear, plum, quince), was first isolated in 1830 (2). Subsequently it was discussed that amygdalin could be hydrolyzed by a nitrogenous enzyme associated with the glycoside in the almond. The hydrolysis product, "oil of bitter almonds", was in fact a mixture of benzaldehyde, hydrocyanic acid, gentiobiose, and glucose (3). T h e structural elucidation of amygdalin (I) and various synthetic approaches were first published in 1923/1924 by a number of workers ( 2 , 4 , 5 ) . About ten years later, the biochemistry of amygdalin as well as the physical, chemical, and physiological characterization of the compound and its hydrolysis products, notably HCN, was discussed by Viehoever and Mack (3). S t e r e o c h e m i s t r y . Amygdalin (I), a gentiobioside of mandelonitrile, contains several chiral (asymmetric) centers which potentially can give rise to a large number of epimeric species. The chiral centers of the gentiobiose moiety, however, are well defined (derived from P-D-glucose) and ai-e stable. The aglycone entity or nonsugar derived chiral center of mandelonitrile is susceptible to epimerization, particularly under basic conditions, because of the weakly acidic character of the benzylic proton. Because these epimers (derivatives of ( R ) 0003-2700/76/0350-0317$01 .OO/O
and (SI-mandelonitrile) will have different physiochemical properties and possible different pharmacological and toxicological properties, analytical procedures for amygdalin should be capable of their identification and quantitative determination. The naturally occurring amygdalin that is extracted from the kernels and seeds of members of the Rosaceae has the R configuration. Laetrile vs. Amygdalin. To avoid any risk of the further proliferation of confusion in nomenclature, amygdalin is not structurally synonymous with Laetrile. Amygdalin (I)
(I) Amygdalin cZOH27N011 0-nrndclonitrile- b e t a - O - g l r c o r l d o - 6 - b ~ t ~ - D - g l ~ c o r l d ~
,
COOH
(11)
Laetrile c14H151107 I-mandolonitrile-beta-glucuronic
acid
is a naturally occurring cyanogenetic glycoside that is present in the kernels of almonds and related fruits. Laetrile (111, according to the patents issued (6, 7 ) results (a) from hydrolysis of amygdalin and subsequent oxidation of the Lmandelonitrile-&glucoside product with platinum black, or C 1978 American Chemical Society
