ANALYTICAL CHEMISTRY, VOL. 50, NO. 7, JUNE 1978
contribute to lack of reliability in the analytical method.
CONCLUSIONS T h e methodology involving HPLC with fluorescence detection as described allows measurement of all PAH of interest except chrysene and perylene in a single injection by using the optimal fluorescence conditions a t A,, 280 and ,A, >389 nm. This satisfies the requirements of UICC/IARC Joint Working Group (16)which specifies that a n acceptable method should separate and quantitate B[a]A, B[a]P, B[e]P, B[k]F, benz[ghi]perylene, fluoranthene, and coronene. The system conditions are simple and no gradient elution technique is involved. The elapsed time to carry out a complete analysis of the extract/aqueous system is about 60 to 90 min. However, analysis time would increase two- or threefold if chrysene and/or perylene are t o be determined. The method would then necessitate separate injections for chrysene and perylene a t fluorescence conditions of A,, 250, ,A, >370 and A, 240, ,A, >470 nm, respectively. I t is concluded that the system described offers considerable promise as a simple, rapid, and sensitive method with a high degree of precision for the determination of PAH.
ACKNOWLEDGMENT The authors express thanks to the following: D. Wang and A. A. Nicholson of the Laboratory Services Branch, Ministry of Environment, Ontario for helpful discussion and advice in the initial stages of this work; D. Mozzon of the Air Resources Branch, Ministry of Environment, Ontario, for providing the environmental and process samples; S. Morton of the Health Protection Branch, Ministry of Labour, Ontario, for the
973
personal monitoring sample; R. C. Lao of the Air Pollution Control Directorate, Environment Canada, Ottawa, Ontario, for the reference PAH standards; and J . Brady and T. Cooper of the Ontario Research Foundation for technical assistance.
LITERATURE CITED International Agency for Research on Cancer, "IARC Monographs on the Evaluation of Carcinogenic Risk of Chemicals to Man, Vol. 3, Certain Polycyclic Aromatic Hydrocarbons and Heterocyclic Compounds", IARC, Lyon, France, 1973. C. G. Vaughan, B. B. Wheals, and M. J. Whitehouse, J . Chromatogr., 78. 203 (1973). B. 6 . Wheals. C,G. Vauahan. and M. J. Whitehouse. J . Chromatour.. 106, 109 (1975). B. L. Karger, M. Martin, J Lohead, and G. Guiochon, Anal. Chem., 45, 496 (1973). M. Popl, M. Stejskal, and J. Mostecky, Anal. Chem., 46, 1581 (1974). M. Novotny, M. L. Lee, and K. D.Bartle, ,/. Chromatogr. Sci., 12, 606 (1974). M. Dong, D. C. Locke, and E. Ferrand, Anal. Chem., 48, 368 (1976). M. A. Fox and S.W. Staley, Anal. Chem., 48, 992 (1976). H. Boden, J . Chromatogr. Sci., 14, 392 (1976). A. M. Krstulovic, D.M. Rosie, and P. R. Brown, Anal. Chem., 48, 1383 (1976). T. Panalaks, J . Environ, Sci. Health, B77 (4), 299 (1976). Fed. Regist., 36 (247), 24888 (1971). "Report on Analytical Methods used in a Coke Oven Effluent Study", Publication No. (NIOSH) 74-105 (1974). T. W. Stanley, J. W. Meeker, and M. J. Morgan, Environ. Sci. Techno;., 1, 927 (1967). "Emergency Temporary Standard for Occupational Exposure to Benzene", Fed. Regist., 42, No. 85, May 3 (1977). UICC Technical Report Series 4 (1970): [ARC Internal Tech. Rep. No 71/002 (1971).
RECEIVED for review December 13, 1977. Accepted March 27, 1978. Financial support from the Ministry of Industry and Tourism, Province of Ontario is gratefully acknowledged.
Phenylfluorone Method for the Determination of Tin in Submicrogram Levels with Cetylt rimethylammonium Bro mide V. H. Kulkarni and Mary L. Good* Department of Chemistry, University of New Orleans, Lakefront, New Orleans, Louisiana 70 722
I n an attempt to improve the phenyifiuorone method for determining tin, the modification of the visible spectrum of tin(1V) fluorone complex has been studied by adding cetyitrimethyiammonium bromide. The band maximum observed at 530 nm for the tin(1V)-fiuorone complex does not show any bathochromic shift but the absorbance of the band maximum is significantly enhanced compared with previous methods. The tin(1V)-fiuorone complex is formed at pH 1.2. The color development takes about 60 mln and the color is stable for about 2 h. Beer's law is obeyed up to 3.0 pg, giving a working range of 0.20 to 3.00 pg Sn/50 mL with a standard deviation of 7.42 x 10-3.
Efforts in our laboratory have been focused on the improvement of colorimetric methods for the determination of tin leached from marine coatings into seawater. A variety of marine antifouling coatings have been developed using organotin toxicants. The successful coatings have low leach rates and various hydrolysis mechanisms have been postulated for the dissolution of the tin moieties ( I , 2). In order to determine leach rates and to evaluate the proposed leaching mechanisms, 0003-2700/78/0350-0973$0 1.OO/O
one must be able to determine tin accurately in the submicrogram range in seawater. Thus, this study was undertaken to evaluate and optimize the fluorone method for tin analysis. Since the introduction of phenylfluorone for the spectrophotometric estimation of tin in various matrices by Luke (3), many modifications have been suggested for the improvement of sensitivity and reproducibility (4-10). Recently, Smith (11) has reported a modified method for determining tin in the range of 0.3 to 3.0 kg, where he has abandoned the use of gelatin as well as the acetate buffer, and developed the color at pH 1.0. He claims that the method is reproducible. Russian workers have reported that the use of phenylfluorone (Po with antipyrine (Ap) in the presence of mineral acid anion (anion) in the molar ratio 1:2:1, viz., PfAp:anion, yields a fourcomponent complex which can readily be extracted into chloroform (12). These reactions are reported to be highly sensitive and are recommended for determining microgram quantities of tin. Sensitizers, such as cetyltrimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPyB) have been used with catechol violet and xylenol orange to increase the sensitivity of these colorimetric methods (23-15). A considerable bathochromic shift and an increase in the absorbance are C 1978 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 50, NO. 7, JUNE 1978
Table I. Calibration Figures Obtained by the Proposed Method Amt of Sn in 0.20 0.40 0.60
0.80 1.00 1.40 2.00 2.50 3.00
Absorbances observed for four replica tesD I I1 I11 IV 0.0120 0.1060 0.0190 0.0255 0.0263 0.0370 0.0470 0.0440 0.0640
0.0110 0.0160 0.0200 0.0235 0.0270 0.0299 0.0370 0.0520 0.0540
0.0100 0.0155 0.0201 0.0230 0.0280 0.0355 0.0450 0.0450 0.0520
Mean absorbances 0.0113 0.01 56 0.0200 0.0237 0.0265 0.0331 0.0427 0.0467 0.0555
0.0125 0.0150 0.0210 0.0230 0.0250 0.0420 0.0420 0.0460 0.0520
a Absorbances were measured at 5 3 0 nm using 1-cm Pyrex cells. Total solution volumes of all samples were 50 mL.
Table 11. Comparison with Absorbances for Other Reported Methodsa A
pH 1.2 1.0
%A
Absorb- Absorb- absorbance ance ance 0.215 0.160
,..
0.055
34.77 19.44 14.36
Ref. Present work 7
0.180 0.035 1 3.5 0.188 0.027 2 a 1.0 X M Solution of tin(1V) is taken for the measurements. 1.8
observed in the spectrum of the tin(1V)-catechol violet complex. No such attempts have been reported in the case of the phenylfluorone method. The success of the sensitizers tried in the case of catechol violet indicated that it should be worthwhile to try one of these sensitizers for the fluorone method and study its impact on the Sn determination limit. From these investigations it has been found that CTAB does not produce any bathochromic shift in the absorption maximum of tin(1V)-fluorone complex a t 530 nm. However, the intensity of the band maximum is markedly improved. EXPERIMENTAL Reagents. All reagents used were of analytical grade. Sulfuric Acid (1 M). Concentrated sulfuric acid, 55.5 mL, (Sp. gr. 1.84) was diluted to 1 L. Sodium Acetate (4 M). Sodium acetate trihydrate, 136.0 g, was dissolved in about 150 mL of distilled water by heating; after cooling the solution was diluted to 250 mL. Sodium Hydroxide (4 M). Sodium hydroxide pellets, 160.0 g, were dissolved in distilled water and diluted to 1 L after cooling. Tin(1V) Stock Solution. Pure granulated tin, 0.1000 g, was dissolved in 20 mL of concentrated sulfuric acid by heating to fumes. After cooling, the solution was added cautiously to about 150 mL of ice-cold distilled water and an additional 65 mL of concentrated sulfuric acid was introduced with stirring. The solution was cooled, transferred to a 1-L volumetric flask, and diluted to mark with distilled water.
1 mL of solution
=
100 p g Sn
Tin(1V) Standard Solution. Tin(1V) stock solution, 1.00 mL, was diluted to 1Ml mL, with 1 M sulfuric acid. This solution was prepared fresh when required.
Phenylfluorone. Phenylfluorone, 10 mg (Aldrich analyzed sample), was dissolved in about 25 mL of ethanol containing 0.2 mL of concentrated sulfuric acid, and diluted to 100 mL with ethanol. The solution stored in the dark is stable for at least 2 months. A 1.0 X lo4 M solution prepared from the stock solution was used for the measurements. Cetyltrimethylamrnonium Bromide (CTAB). CTAB, 0.10 g, was dissolved in distilled water by warming, and diluted to 100 mL. A 1.0 X M solution of CTAB was used in the color development. Apparatus. A Beckman Zeromatic I1 pH meter equipped with glass and reference electrodes was used for measuring the pH of the solutions. The pH meter was standardized using Beckman standard solutions of pH 4.01 and 7.00 and then verified for pH’s 1.48, 2.07, and 4.64 using the supplementary standards recommended for the calibration of the glass electrode (16). A Beckman spectrophotometer model DU with 1-cm matched Pyrex cells was used t o measure the optical densities of the solutions. Preparation of Calibration Graph. Transfer by pipet, standard tin(1V) solution (from 0.20 to 4.00 pg) to a series of 50-mL beakers. To each beaker add the following in the order shown, mixing thoroughly at each addition. Add 4.5 mL of CTAB, 20 mL of 2 N sulfuric acid and mix them thoroughly. Adjust the pH of the solution to 1.2 by adding 4 M NaOH dropwise. Add 2 mL phenylfluorone solution and mix thoroughly. Transfer the solutions quantitatively to the 50-mL calibrated volumetric flasks, and dilute to mark with distilled water, having the pH adjusted to 1.2 with 1 M sulfuric acid. Leave for 40 min at room temperature and then measure the optical density of each solution in 1-cm Pyrex cells at wavelength 530 nm with water as reagent blank. The graph of absorbance vs. the amount of tin in pg is a straight line over a range from 0.20 to 3.00 wg of tin (see Table I). The least squares fit obtained for this calibration graph has an intercept of 1.36 X lo-*and a slope of 1.37 X W2.The computed standard deviation amounts to 7.42 X
RESULTS A N D D I S C U S S I O N S p e c t r a l Characteristics. T h e absorption spectra of phenylfluorone and its tin(1V) complex are shown in Figure 1. Phenylfluorone in ethanol shows a broad maximum in the range of 460-480 nm. The aqueous solution of phenylfluorone containing CTAB at p H 1.2 displays an intense band maximum a t 460 nm and a shoulder inflection in the region 430-440 nm. The absorption a t 460 nm is more intense than that noted for ethanol solution. This enhancement in the absorbance is apparently due to the presence of CTAB which is capable of bonding with fluorone. In the tin(1V) complex, the band a t 460 nm is sufficiently suppressed and a high-intensity band maximum appears exactly at 530 nm. We have repeated the experiments of Luke ( I ) , Bennett and Smith ( 2 ) ,and Smith ( 7 ) to compare with our results. The optical densities observed at the optimum wavelength and percentage increase in the optical densities observed are given in Table 11. It is obvious from the results that in the present work the intensity of the band maximum of the tin(1V)-fluorone complex is significantly increased compared with the other methods. Effect of pH. T h e effect of p H on the Sn determination has been examined by adding various amounts of 4 M sodium acetate to a series of solutions containing 2 m L of 1.0x M solution of Sn, 4.5 mL of CTAB, and 20 mL of 1 M of sulfuric acid. Fluorone, 4 mL of 1.0 X M, is then added to each solution and the solutions are diluted to 50 mL. The
Table 111. Effect of Variation of pH on the Color Intensity of the Complexa PH 0.5 0.85 1.0 1.2 1.6 Absorbance for blank 0.005 0.013 0.013 0.012 0.021 Absorbance for Sn(1V)phenylfluorone complex 0.012 0.0142 0.163 0 . 2 13 0.209 a Absorbances are measured at the oDtimum wavelength as determined bv soectral scanning.
1.8
2.0
0.023
0.024
0.207
0.209
ANALYTICAL CHEMISTRY, VOL. 50, NO. 7, JUNE 1978
1
nm Figure 1. Absorption spectra of: (I) 4 mL of 0.0001 M phenylfluorone 4.5 mL in 5 0 mL of ethanol; (11) 4 mL of 0.0001 M phenylfluorone M of CTAB at pH 1.2 in 50 mL of solution; (111) 2 mL of 1.0 X Sn 4 mL of 1.0 X M phenylfluorone 4.5 mL of CTAB at pH
+
+
1.2 in 5 0 mL of solution
+
optical densities measured a t the optimum wavelength reveal t h a t maximum sensitivity is obtained a t pH 1.2 (Table 111). The use of 4 M sodium hydroxide in the place of 4 M sodium acetate does not appreciably affect the optical densities and, hence, in further experiments 4 N sodium hydroxide has been used. Measurements at pH > 2 have not been attempted since the absorbance of the anionic form of the ligand becomes significant ( I 7). Effect of Reagent. Various volumes of 1.0 X M phenylfluorone are added to a series of solutions containing 2 mL of 1.0 x M solution of Sn, 4.5 mL of CTAB, and 20 mL of 1 M sulfuric acid a t pH 1.2, and diluted to 50 mL with water having pH 1.2. The absorbances measured at 530 nm indicate a rapid increase with increasing amounts of phenylfluorone up to 4 mL of phenylfluorone. The increase in the absorbance for the next successive additions is gradual. T h e excess of phenylfluorone does not decrease the absorbance. I t can, therefore, be concluded that for 0.0 to 2.0 mL of 1.0 X M Sn, 4.0 mL of phenylfluorone should be optimum.
975
Effect of CTAB. The effect of the variation of CTAB concentration on the absorbance of tin(1V)-fluorone complex indicates that maximum absorbance is obtained for CTAB volumes in the range of 4-5 mL. The volume has been fixed a t 4.5 mL (0.0001 M) to produce maximum color for the tin(1V)-fluorone complex. Stability of Tin-Fluorone Complex. It has been reported in Smith's method that 2 h are required for the development of complete color and that the color fades a t the rate of 1% per hour for the following 4 h. In the present method it is observed that the complete color development occurs in about 60 min and the color is stable for about 2 h. After 2 h, a gradual decrease in the color intensity is observed. This decrease amounts to about 1.14%/h. Nature of the Complex. The composition of tin(1V)fluorone complex in the presence of CTAB has been determined by continuous variation and mole ratio methods. Both methods indicate that the ratio of tin to fluorone is 1:2. LITERATURE CITED (1) A. W. Sheldon, J . faint Techno/., 47, 54 (1975). (2) C. P. Monaghan, J. F. Hoffman, E. J. O'Brien, L. M. Frenzel, and M. L. Good, in "hoceedings of 1977 Contrdled Release Pesticide Symposium", R. L. Goulding. Ed., August 1977, Oregon State University, Corvallis, Ore. (3) C. L. Luke, Anal. Chem., 28, 1276 (1956). (4) R. L. Bennett and H. A. Smith, Anal. Chem., 31, 1441 (1959). (5) E. N. Pollock and L. P. Zopatti, Anal. Chem., 37 290 (1965). ( 6 ) S. Kanno and H. Ogura, J . FoodHyg. SOC. Jpn., 5 , 116 (1964); Anal. Abstr., 12, 5448 (1965). (7) E. Ruf, Fresenlus' Z. Anal. Chem., 162, 9 (1958). (8) E. Asmus, and J. Kraetsch, Fresenlus' Z. Anal. Chem., 222 401 (1966). (9) E. Asmus, 8. Kropp. and F. M. Moczko, Fresenius' Z. Anal. Chem.. 256, 276 (1972). (10) N. L. Olenovich and G. I.Seivenko. Zavod. Lab., 41, 658 (1975): Anal. Abstr., 30, 1833 (1976) (11) J . D Smith, Analyst(London), 95, 347 (1970), Anal. Chim. Acta, 57, 371 (19711 (12) A.sh'. ShakhabudiwvandO. A. Tataev, Zh. Anal. Khim., 27, 2382(1972). (13) R. M. Dagnall, T S. West, and P. Young, Analyst(London). 92, 27 (1967). (14) H. Corbin, Anal. Chem., 45, 534 (1973). (15) V. Svoboda and V. Chromy, Talanta, 13, 237 (1966). (16) A. 1. Vogel, "Quantitative Inorganic Analysis", Longmans Green, London, 2nd ed., 1958, p 868. (17) A. K. Babko and N. N. Karnaukhova, Zh. Anal. Khim., 22, 868 (1967).
RECEIVED for review November 28, 1977. Accepted March 30, 1978. This work is a result of research sponsored by the Office of Naval Research and the NOAA Office of Sea Grant, Department of Commerce, under Grant No. R/MTR-1.
