ACKNOWLEDGMENT The authors are grateful to W. Rahman for providing research facilities.
Received for review October 30, 1973. Accepted March 29, 1974. Financial assistance to R.K. and V.S. by the U.G.C. (India) is gratefully acknowledged.
Sampling Errors in the Quantitation of Petroleum in Boston Harbor Water S. M. Ahmed, M. D. Beasley, A. C. Efromson, and Ronald A. Hites' Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Mass. 02 139
The petroleum content of many effluents which are discharged into the environment (tanker ballast water and refinery waste water, for example) is limited by state or federal regulations. The enforcement of these regulations depends on the existence of reliable analytical methods for determining oil-in-water concentration. Many such methods are available: they make use of gravimetry (1);volumetry (2); infrared (3-6), ultraviolet (7) and fluorescence (7) spectrophotometry; and gas chromatography (4, 8, 9). Among these techniques, the infrared spectrophotometric method seems to be the most popular ( 5 ) .Despite its widespread use, however, there are no data available on its reliability in practice. Therefore, the precision and accuracy of this method have been studied using the Boston Inner Harbor as the test case and using two techniques of oil pre-concentration-namely, carbon tetrachloride extraction (1) and polyurethane foam adsorption (10).
RECOVERED O I L (mg/eI
Figure 1. Oil concentration as determined by infrared spectrophotometric technique vs. known concentration
EXPERIMENTAL All glassware was cleaned by washing with detergent and hot water followed by washing with concentrated chromic acid solution a t about 90 "C. The glassware was then thoroughly rinsed with distilled water, dried in an oven at 175 "C, and washed with carbon tetrachloride (ACS reagent grade, sulfur-free). Carbon Tetrachloride Extraction. The water samples (1 liter each) were obtained by submerging an open glass sample bottle upright to the desired depth and allowing it to fill. These bottles were then sealed with aluminum foil held secure with a screw cap. All samples were preserved with 3 ml of concentrated sulfuric acid, refrigerated, and extracted within 30 hours after being obtained. Once in the laboratory, the sample was poured into a 2 1. separatory funnel and 30 ml of carbon tetrachloride was used to wash the bottle from which the sample was removed. This same carbon tetrachloride was then used to extract the water sample. After 30-sec agitation and a 3-min settling period, the nonaqueous phase was drained through a funnel containing about 30 grams of anhydrous sodium sulfate over a glass wool plug and collected in a 100-ml vol'To whom correspondence should be addressed. ASTM Procedure No. D2778-70, "Solvent Extraction of Organic Matter from Water," ASTM Standards, Part 23. (2) L. E. Hearn, 164th National Meeting of the American Chemical Society, New York. N.Y., August 1972. (3) R. G. Shard, I. Hasegawa. W. Bandaruk, and C. E. Headington, Anal. (1)
Chem., 10, 1384 (1951). (4) R. Jeltes and W. A. M. den Tonkelaar, WaterRes., 6, 271 (1972). (5) R. A. Brown, T. D. Searl, J. J. Elliott, B. G. Phillips, D. E. Brandon, and P. H.Monaghan, Proceedings of 1973 Conference on Prevention and Control of Oil Spills, Washington, D.C.. p. 505. (6) M. Gruenfeld, Environ. Sci. Techno/., 7, 636 (1973). (7) E. M. Levy, WaterRes., 5 , 723 (1971). (8) R. Jeltes and R. Veldink, J. Cbromatogr.,27, 242 (1967). (9) R . Jeltes. Water Res., 3, 931 (1969). (10) P. Schatzberg and D. F. Jackson, U.S. Coast Guard Rep., No. 734209.9, Washington, D.C., November 1972.
1858
umetric flask. This rinsing and extraction procedure was repeated twice more. The sodium sulfate was rinsed with 5 ml of carbon tetrachloride which was added to the extracts and the volumetric flask was made up to 100.0 ml. Infrared spectra were taken of these extracts in a 10.0-mm cell with NaCl windows. Solutions were transferred via a Pasteur pipet, washing the cell twice with the solution to be observed before filling. Spectra were scanned from 3400 cm-' to 2500 cm-' using 5 to 10 times expansion of the percent transmission scale. The C-H stretching band a t 2930 cm-I was used for analysis. The absorptivity a t this wavelength as calibrated with a motor oil (SAE 30 weight) was 3.39 1. g-lcrn-'. A typical procedural blank corresponded to an oil concentration of less than 0.010 mg/l. Samples used in the recovery study were produced by adding known weights of the motor oil to sample bottles which were then filled about '14 full with distilled water and shaken. Concentrated sulfuric acid (2.5 ml) was added, the bottles were filled with distilled water and immediately processed as described above. Polyurethane Foam Adsorption. The foam adsorption method was implemented as described previously ( I O ) . In brief, 10 to 50 liters of sea water were passed through a foam disk (8-cm diameter, 4 cm thick, 100 pores/in.) and then the retained oil was extracted in a Soxhlet apparatus with carbon tetrachloride. This extract was measured as described above. I t was necessary to clean new disks by Soxhlet extraction with carbon tetrachloride for four to six hours to reduce blank analyses to acceptable levels. I t has previously been shown that recoveries of known concentrations of oil were greater than 85% for those concentrations above 5 mg/l. (10); lower concentrations were not studied ( I O ) .
RESULTS AND DISCUSSION To determine the performance of the carbon tetrachloride extraction method itself devoid of any sampling errors, a recovery study was carried out. Solutions of oil in water of known concentrations were prepared as described above
A N A L Y T I C A L C H E M I S T R Y , VOL. 46, NO. 12, OCTOBER 1974
Table I. Samples Taken from Boston Inner Harbor Sample No.
Station location'
1A 2A
a
1B 2B 3B
a b
1c
2c
b c a b
Date
Time
Sheen condition
July 26, 1973 July 26, 1973 Aug. 3, 1973 Aug. 3, 1973 Aug. 3, 1973 Aug. 16, 1973 Aug. 16, 1973
11:OO a.m. 11:30 a.m. 11:30 a.m. 10:30 a.m. 1 1 : O O a.m. 10:30 a.m. 11:30 a.m.
Light to heavy None Very heavy None None None to light None
a Station locations were a s follows: ( a ) 1.4 miles up Chelsea Creek (oil unloading site); ( b ) junction of Chel.sea Creek and Mystic River; ( e ) 0.4 miles up Chelsea Creek.
Table 11. Oil Concentration in Boston Harbor Water (mg/l.) Sample NO.^
1A
Surface (0-5 cm)
Subsurface (25-35 cm)
0.631 1.54 0.407 0.708 0.793
Av. 0 . 8 1 6 Re1 std dev* 53% Confid. lim.c 0 . 4 - 1 . 2 2A
0.213 0.030 0.197 0.320
Av. 0 . 1 9 0 Re1 std dev 6 3 % Confid. lim. 0 . 1 - 0 . 3
1c
0.546 0.256 0.306
