were to be considered, it would result in a decrease in the apparent film thickness, to ca. 250 A or so. This cannot be carried out exactly, however, as we do not know the shape or halfwidth of the 1614 cm-' band. The observation that 7 min of fibrinogen deposition drove the open-circuit potential 100 mV in the cathodic direction could indicate that a t least some of the fibrinogen retains its normal negative charge while it is adsorbed on the surface, making the surface appear more negative than bare carbon; i.e., a change in the PZC. The observation that the open-circuit potential is 40 mV more negative in the I% fibrinogen solution than it is in buffer probably indicates some initial "spontaneous" adsorption, as noted by Baier et al. (3, 4 ) . Further support for the negatively charged adsorbed layer comes from noting that the first sign of enhanced adsorption took place a t +150 mV, which also happens to be very nearly the point of zero charge for carbon ( 5 ) ,and that subsequent deposition attempts required more positive potentials. After the 9.5 min of adsorption a t +150 mV reported above, an 3 h a t the open-circuit potential (-230 mV), no additional deposition would take place a t +150 mV. The potential had to be raised anodic to +300 mV before deposition would again take place a t a rate comparable to the initial rate. These results tend to support the theory that there are two forms of fibrinogen involved in charge-induced adsorption. It is conceivable that either there are two populations of fibrinogen exhibiting different secondary structures, indicated by the shifted Amide I and I1 peak positions and reversed intensity ratio, or the adsorbed fibrinogen molecules are exhibiting a strained secondary structure over part of each molecule, relaxing to the normal configuration after the externally applied charge is removed. While they employ a fibrinogen of higher purity (97.7% clottable vs. 90% clottable), we feel that the results of Stromberg et al. (9) tend to confirm these results. Stromberg et al. (9) found, using ellipsometry, that reversible conformation changes probably accompany the charge-enhanced adsorption of fibrinogen, serum albumin,
and y-globulin on platinum. Additional similarity exists between these experiments on carbon and Stromberg et a1.k (9) experiments on platinum when it is noted that the onset potential they observed for fibrinogen on platinum is very nearly at the PZC for platinum (IO), as is the case for these results on carbon.
LITERATURE CITED (1) L. Vroman, J. Biomed. Mater. Res., 3, 669 (1969). (2) L. Vroman and A. L. Adams, Thromb. Diath. Haemorrh., 18, 510 (1967). (3) R. C. Dutton, R . E. Baier, R. L. Dedrick, and R. L. Bowman, Trans. Am. Soc. Artif. int. Organs, 14, 57 (1968). (4) R. E. Baier and R. C. Dutton, J. Biomed. Mater. Res., 3, 191 (1969). (5) J. C. Bokros, E. Dalle-Molle, B. D. Epstein, F. J. Schoen, and D.P. Snowden, "Biocompatibility of Carbon", Annual Report, NIH Conrract PH43-67-1411, Feb. 19, 1971, Nat. Tech. Inf. Ser., Springfield, Va., Acc. No. PB198404. (6) P. N. Sawyer, Ann. N. Y. Acad. Sci., 146, 49 (1968). (7) N. Ramasamy, M. Ranganathan, L. Duic, S. Srlnivasan, and P. N. Sawyer, J. Electrochem. Soc., 120, 354 (1973). (8) J. S. Mattson and C. A. Smith, Science, 181, 1055 (1973). (9) R . R. Stromberg, B. W. Morrissey, L. E. Smith, W. H. Grant, and C. A. Fenstermaker, "Interaction of Blood Protein with Solid Surfaces", National Bureau of Standards, NBSlR 75-667, Washington, D.C. 20234, Jan. 15, 1975. (IO) E. A. Efimov and I. G. Erusalimchik, Zh. Fir. Khim., 33, 441 (1959); In "Modern Aspects of Electrochemistry, No. 5", J. O'M. Bockris and B. E. Conway, Ed., Plenum, New York, 1969, p 254. (1 1) J. S.Mattson and C. A. Smith, Anal. Chem., 47, 1122 (1975). (12) J. S.Mattson and C. A . Smith, Chapter 2 in "Computers in chemistry and Instrumentation,Vol. 7", J. S.Mattson, H. B. Mark, Jr., and H. C. MacDonald, Jr., Ed., Marcel Dekker, New York, in press. (13) A. Savitsky and M. J. E. Golay, Anal. Chem., 36, 1627 (1964); J. Steiner, Y. Termonia, and J. Deltour, Anal. Chem., 44, 1906 (1972). (14) W. N. Hansen, J. Opt. Soc. Am., 58, 380 (1968). (15) J. S. Mattson and H. B. Mark, Jr., "Activated Carbon. Surface Chemistry and Adsorption from Solution", Marcel Dekker, New York, 1971. (16) E. N. C. Randall and H. B. Mark, Jr., Chapter 2 in "Computers in Chemistry and Instrumentation, Vol. 3", J. S. Mattson, H. B. Mark, Jr., and H. C. MacDonald, Jr., Ed., Marcel Dekker, New York, 1973.
RECEIVEDfor review May 10,1976. Accepted September 7, 1976. This research was supported by the National Heart and Lung Institute, National Institutes of Health, Grant No. HL-15919.
Differential Pulse Polarographic Determination of Acrolein in Water Samples Lyman H. Howe Laboratory Branch, Division of Environmental Planning, Tennessee Valley Authority, Chattanooga, Tenn. 3740 1
A differential puke polarographic method has been developed for determination of acrolein from 0.05 to at least 0.50 mg/l. in nafural water samples. Acrolein is measured at about -1.2 V vs. SCE (NaCl) at pH 7.2 in phosphate buffer solution (0.09 M) with ethyienediaminetetraacetic acid added (0.09 % ) to prevent interference from zinc. The pH in the 6.8-7.6 range and zinc at 2.0 mg/l. do not affect the recovery of acroleln. Seven replicate anaiyses of standard solutions containing 0.10 and 0.30 mg/l. of acrolein give relative standard deviations of 7.6 and 4.3% and percentage accuracles of -2.9 and -3.3.
Acrolein is an olefinic aldehyde with the chemical name propenal. It is registered for use in controlling slime growths. I t also has potential for use as a molluscicide for controlling Asiatic clams in the heat exchangers and other service water
systems at steam-electric generating stations ( I ) ; however, it is not now registered for this application. For acrolein concentrations near 0.30 mg/l., which is the dosage that has been useful to control slime growths and that may be useful for controlling infestations of Asiatic clams ( I ) , the Betz Laboratories colorimetric method (2) frequently has produced erratic results. Furthermore, the distillation and color development steps are time-consuming. Moshier ( 3 )reports a polarographic method for assaying acrolein in water with a detection limit of 10 mgh. Van Sandt et al. ( 4 ) improves Moshier's method to achieve a detection limit of 1 mg/l., but this sensitivity is not adequate for monitoring an acrolein concentration of 0.30 mg/l. With differential pulse polarography, an extremely sensitive and economical analytical tool ( 5 ) ,it should be possible to improve the sensitivity of the Van Sandt method ( 4 )to 0.05 mg/l. The theory and practice of differential pulse polarography are given in the literature (5-8).
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Table I. Comparative T e s t Results f o r Acrolein Recovered a f t e r O n e H o u r f o r Split Samples of S u r f a c e W a t e r s w i t h 0.30 mg/l. Acrolein Added Acrolein recovered, mg/l. Location
L
.os
1-L-
I
-10
-11
VOLTS
.I2 v6
.I3
.I4
-1s
-16
S C E :NoCli
Flgure 1. Differential pulse polarograms for acrolein
EXPERIMENTAL Reagents. Nitrogen gas used to deaerate solutions for polarographic analysis was purged of oxygen by passing zero-grade nitrogen gas through a furnace containing a special catalytic converter that was heated to 600 "C. (This system was the Model 02-2315 Gas Purifier purchased from Supelco, Bellefonte, Pa.). The gaseous effluent from the furnace was then passed through sintered glass frits in three scrubbing towers, two containing 100 ml of 0.1 M chromous chloride in 2.4 M hydrochloric acid with amalgamated zinc and one containing 100 ml of reagent water. The amalgamated zinc was 0.8-3.2 mm pore size for a Jones reductor (Fisher Scientific Company, Fairlawn, N.J.). Details for preparing the chromous chloride scrubbers are given by Meites (9). The acrolein used in this study was purified by distillation, and the fraction that boiled at 51-53 O C was collected in sufficient hydroquinone to provide a final concentration of 0.1% (w/v) hydroquinone (Caution! Acrolein is a powerful lachrymator and irritates the skin. Handle with gloves in a ventilated hood. Acrolein, when hot and concentrated, may react explosively with oxidants, bisulfite, or other chemicals. It is also very flammable). The acrolein in the clear distillate was assayed by potentiometric titration with bisulfite (10).The end point appeared at pH 9.5. The analytical results revealed that one bisulfite molecule formed a complex with each molecule of acrolein. This information and the end point are not given in the literature (10,11).Both Baker and Eastman reagent grade acrolein contained about 65%acrolein by bisulfite assay, whereas the freshly distilled product inhibited with 0.1% (w/v) hydroquinone contained about 93%. The acrolein stock solution was prepared by transferring about 1 g of purified acrolein (weighed to the nearest 0.01 g) with a weighing pipet to a 1000-mlvolumetric flask containing reagent water, diluting to volume, and mixing. The stock solution was corrected for assay results. An acrolein standard solution containing 100 mg/l. was prepared by appropriate dilution of the stock solution. Stock and standard solutions were prepared fresh daily. The phosphate buffer solution (pH 7.4) was prepared by mixing 300 ml of 1.0 M dipotassium hydrqgenphosphate (174.18 gh.) and 100 ml of 1.0 M potassium dihydrogenphosphate (136.09 g/l.). These solutions were employed directly or combined to test the effects of pH on the polarographic behavior of acrolein. The 10% EDTA solution was prepared by dissolving 25 g of disodium ethylenediaminetetraacetate dihydrate (EDTA) in water and diluting to 250 ml. The solution was heated as necessary to complete the dissolution of the salt. When the dissolution was incomplete, the solution was filtered, and the first 10 ml of the filtrate discarded. Apparatus and Polarography. All measurements were made with the Princeton Applied Research (PAR) Model 174 Polarographic Analyzer with mechanical drop timer and Houston Omnigraphic X-Y Recorder Model 2200-3-3. The dropping mercury electrode was a 2to 5-s capillary from Sargent-Welch Company (Part No. S-29419). The height of the mercury column above the capillary was adjusted to provide a natural drop time of approximately 3 s in 0.09 M phosphate buffer solution (pH 7.4) at open circuit. The rest of the electrochemical accessories were obtained from PAR the carbon counter 2160
Duck River Mile 133.92 Duck River Mile 156.51 Duck River Mile 64.0 Duck River Mile 47.9 Holston River Mile 131.5 Holston River Mile 118.4 Paradise Towera Inlet Paradise Tower Outlet Holston River Mile 118.4 Holston River Mile 131.5 French Broad River Mile 54.3 French Broad River Mile 77.5 French Broad River Mile 71.4 Nolichucky River Mile 5.3 Cumberland River Mile 285 Tennessee River Mile 391.2
Polarographic Colorimetric 0.21 0.17 0.19 0.22 0.22 0.22 0.15 0.21 0.17 0.17 0.14 0.20 0.18 0.23 0.23 0.19
0.19 0.27 0.29 0.23 0.19 0.16 0.20 0.14 0.15 0.21 0.18 0.24
0.16 0.21 0.29 0.27
a Paradise Tower is located along the Green River, which discharges into the Ohio River.
electrode, the salt bridge with isolation frit, the calomel electrode filled with saturated sodium chloride, the outgassing tube, the cell holder, and the cell. The salt bridge was necessary to isolate the reference electrode from the test solution and prevent sloping baselines in the polarograms. The counter electrode was spectroscopic-grade graphite. The following typical settings were employed for the PAR 174 polarographic analyzer with mechanical drop timer: drop time, 2 s; scan rate, 2 mV/s; display direction, positive; scan direction, negative; initial potential, -0.900 V; range, 1.5 V; sensitivity, 0.5 pA for 0.10 mg/l. acrolein, 1 FA for 0.30 mg/l., and 2 PA for 0.50 mgh.; modulation amplitude, 100 mV, operation mode, differential pulse; output offset, negative settings as required. With the Houston Omnigraphic 2200-3-3 Recorder the following settings were used: recorder Y-axis was adjusted to 1 V/in. (0.039 V/mm) and X-axis to 100 mV/in. (3.94 mV/mm). Except when noted otherwise, 10.0 ml of the sample to be analyzed for acrolein was treated with 1.00 ml of phosphate buffer solution (pH 7.4) and 100 pl of 10%EDTA solution. Test solutions containing 0.10, 0.30, and 0.50 mg/l. of acrolein were prepared by spiking 10.0 ml of sample or reagent water with 10,30, and 50 ~1 of 100 mg/l. acrolein standard solution (Centaur micropipets were employed. These were obtained from Cole-Parmer Instrument Company, Chicago, Ill.). The solution was deaerated for 10 min with oxygen-free nitrogen. A minute was allowed for convection to cease, and a polarographic scan was made between -0.900 and -1.5 V vs. SCE (NaCl).
RESULTS AND DISCUSSION Typical polarograms a r e given in Figure 1for acrolein with conditions adjusted a s in t h e Experimental section. With t h e mercury electrode adjusted t o provide a natural drop time of 2.7 s in 0.09 M phosphate, standard solutions containing 0.10, 0.30, and 0.50 mg/l. of acrolein produce peak currents of 112, 392, a n d 630 nA, respectively. No measurable current is observed for a reagent blank. T h e peak currents have been d e termined by measuring height above extrapolations of t h e current just before and just after t h e wave. The detection limit of t h e method is found t o be 0.05 mg/l., approximately 20 times t h e sensitivity obtained by direct current polarography
(4). T h e precision a n d accuracy based on t h e analysis of seven replicate freshly prepared standard solutions containing 0.10 and 0.30 mg/l. of acrolein have been determined by comparison t o a standard curve prepared by polarographing a series of s t a n d a r d acrolein solutions. T h e standard deviations are, respectively, 0.008 a n d 0.013 mg/l., t h e relative s t a n d a r d de-
ANALYTICAL CHEMISTRY, VOL. 48, NO. 14, DECEMBER 1976
viations are 7.6 and 4.3%,and percentage accuracies are -2.9 and -3.3 (12). It is well known that 3% ethylenediaminetetraacetic acid (EDTA) eliminates electrochemical interference by zinc (Is), and EDTA in a concentration of 0.09%has been added for that purpose. The interference from 2.0 mg/l. of zinc in 0.09 M phosphate buffer (pH 7.4) is totally eliminated by addition of EDTA in a concentration of 0.09%. Many natural waters contain zinc, but most of them contain zinc in concentrations of less than 2.0 mg/l. The pH of the test solution affects both peak height and peak potential. The best pH is 7.2. Tests have been conducted at about 22 "C with 0.50 mgA. acrolein solutions at pH 4.3,6.8, 7.2, 7.6, and 8.3 in phosphate buffer solutions (0.09 M) with ethylenediaminetetraacetic acid added (0.09%). The height and potential of the acrolein reduction peak are the same at pH 6.8, 7.2, and 7.6. The pH of most water samples can be adjusted and maintained at pH values between 6.8 and 7.6 by the addition of 1.00 ml of 1.0 M phosphate buffer solution (pH 7.4) and 100 ~1 of 10% EDTA solution to a 10.0-ml sample. Adjustment may be required for strongly acidic samples, such as drainage from strip mines. At pH 4.3 the peak height for 0.50 mg/l. acrolein is 45%of the value at p H 7.2, and the potential is -1.10 V vs. SCE (NaC1) rather than -1.22 V. These shifts of peak potential and peak height found by differential pulse polarography agree with Moshier's observations by direct current polarography ( 3 ) .At pH 8.3 the peak height does not change appreciably, but the potential shifts to -1.25 V. The addition of bisulfite to the carbonyl group in acrolein destroys the peak but so does hydrogenation of the double bond: propionaldehyde is also not polarographically active at voltages less than -1.4 V vs. SCE. The direct current polarographic reduction wave for propionaldehyde in 0.1 M lithium hydroxide does not appear until about -1.9 V (9).The absence of differential pulse polarographic activity between -0.5 and -1.4 V has been observed for the acrolein-bisulfite complex in a test solution deaerated for 10 min and consisting of 10 ml of 0.50 mg/l. of acrolein, 22.5 mg/l. of sodium sulfite (sufficient to form the complex with 10 mg/l. of acrolein, as discussed in the Experimental section), 1.00 ml of 1.0 M phosphate buffer solution (pH 7.4) and 100 J of 10%EDTA solution. Since neither the double bond in the acrolein-bisulfite complex nor the carbonyl in propionaldehyde are polarographically active in the -0.5 to -1.4 V range, then the 9-electron system which includes both must be involved in the reduction of acrolein. But these observations do not contradict that the reduction may be represented by the equations:
-
+ 2H+ + 2e
CH2=C,H-CHO
+
+
CH3-CH2-CHO
(1)
CHz=CH-CHO 4H+ 4e CH3-CH2-CH20H (2) Equation 1represents the first peak, which is given by Figure 1,and Equation 2 represents the second peak. The polarographic method described in this paper has been compared with the colorimetric method for recovering acrolein
from samples of water taken in the Tennessee Valley. The colorimetric method is the Betz Laboratories test method (2) with spectrometric determination of absorbance a t 600 nm (14,15). Analytical results for acrolein recovered after 1 h for split samples of surface water with 0.30 mg/l. acrolein added and analyzed by the polarographic and colorimetric methods are given in Table I. The acrolein concentration by each method has been determined from a standard curve prepared by analyzing solutions containing 0.10, 0.30, and 0.50 mg/l. acrolein. According to the paired-sample t test (26),the mean of the differences (f0.0175) between these observations, is not significantly different from zero a t the 0.05 level of significance. The standard deviation employed in calculating the t value has been computed using n - 1weighting, where n is the number of observations. The calculated t value is 1.30, which is less than that of 1.75 given for t0.05 for 15 degrees of freedom in the t table (16). Thus, a t the 0.05 level there is only one chance in 10 of incorrectly concluding that the methods do not differ. Acrolein recovered at 0.10 and 0.50 mgA. concentrations also has been determined by both the colorimetric and polarographic methods. Approximately the same statistical comparisons are found at these levels as a t the 0.30 mg/l. level.
LITERATURE CITED J. F. Walko, J. M. Donohue, and B. F. Shema. Special Report 506, Betz Laboratories, Inc., Trevose, Pa., November 1971. Betz Laboratories, Inc., Trevose, Pa., Publication INS104, June 1967. R. W. Moshier, lnd. Eng. Chem., Anal. Ed., 15, 107 (1943). W. A. Van Sandt, R.J. Graui, and W. J. Roberts, Am. lnd. Hyg. Assoc. Q., 16, 221 (1955). Jud E. Flato, Anal. Chem., 44 (11). 75A-87A (1972). A. M. Bond and D. R Canterford, Anal. Chem., 44, 721 (1972). E. P Parry and R. A. Osteryoung, Anal. Chem., 37, 1634 (1965). J. H. Christie, J. Osteryoung, and R. A. Osteryoung, Anal. Chem., 45, 210 (1973). L. Meites, "Polarographic Techniques", 2d ed., lnterscience Publishers, New York, N.Y., 1967, pp 87-90, 705. S.Siggia, "Quantitative Organic Analysis via Functional Groups", 3d ed., John Wiley & Sons, New York, N.Y., 1963, pp 79-85. Beilstein, "Handbook of Organic Chemistry (in German)", Vol. 1, 2d supolement. Julius Sorinaer. Berlin, 1941, PD . . 782-786. (12) Editors, Anal. Chem.,-47, 2527 (!975). (13) American Public Health Assoc., Standard Methods for the Examination of Water and Waste Water", 13th ed., New York, N.Y., 1971, pp 448451. (14) I. R. Cohen and A. P. Altshuller, Anal. Chem., 33, 726 (1961). (15) R. G. Smith, R. J. Bryan, M. Feldstein, B. Levadie, F. A. Miller, E. R. Stephens, and N. G. White, Health Lab. Sci., 7 , 179 (1970). (16) I. Miller and J. E.Freund, "Probability and statistics for Engineers", Prentice-Hall Publishers, Inc., Englewood Cliffs, N.J., 1965, pp 169-170, 399.
RECEIVEDfor review July 28, 1976. Accepted September 3, 1976. Presented at the third annual meeting, Federation of Analytical Chemistry and Spectroscopy Societies, Philadelphia, Pa., November 1976. This material was taken in part from a report submitted to the U.S. Environmental Protection Agency. This work was supported in part by Energy Accomplishment Plan Subagreement No. 77BDH under interagency agreement by TVA under sponsorship of EPA. Mention of specific manufacturers and models is illustrative and does not imply endorsement by the Tennessee Valley Authority.
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