1718
Anal. Chem. 1981, 53, 1718-1719
Loss of Phthalic Acid Esters and Polychlorinated Biphenyls from Seawater Samples during Storage Sir: In the analyses of trace organic compounds from natural waters, it is common to store the water in glass containers. During the storage of the sample, loss of the analyte can occur via vaporization, degradation, and/or adsorption. Adsorption of trace organic and inorganic species in seawater to container walls can severely affect the accuracy of their determination. The loss of trace metals by adsorption onto storage containers has been reported for mercury ( I ) and lead and cadmium compounds in water samples (2). The adsorption of dichlorodiphenyltrichloroethane(DDT) (3)and hexachlorobiphenyl (4) onto glass containers has been observed. We discuss here some factors affecting the loss of other prevalent organic pollutants, phthalic acid esters and polychlorinated biphenyls (5,6),from water while stored in glass containers. EXPERIMENTAL SECTION The containers were 16 X 125 borosilicate screw-cap test tubes whose cap liners had been replaced with Teflon liners. Tenmilliliter aliquots of an aqueous solution spiked with di-n-butyl phthalate (DBP), bis(2-ethylhexyl) phthalate (BEHP),or polychlorinated biphenyls (PCB) were placed into replicate test tubes. The test tubes were kept at 25 "C and were inverted repeatedly during the 12-h equilibration time. A previous kinetics study had shown that the vast majority of phthalate adsorption occurred within the first hour and that equilibrium was essentially reached after 12 h (7). The aqueous phases were transferred to other test tubes and were extracted with two 2-mL aliquots of isooctane. The amount of water not removed from the test tubes was estimated from the differences in the weights of four test tubes before the addition of the water and after its removal. To determine whether phthalates or PCB which best absorbed on the test tubes can desorb into seawater, 10 mL of unspiked seawater was added to empty test tubes which previously contained spiked seawater. The unspiked water was then analyzed as before. After three seawater rinses, the test tubes were ex-
tracted with two 2-mL aliquots of acetonitrile. The acetonitrile and isooctane extracts were taken to dryness with a stream of nitrogen and were redissolved in isooctane or liquid scintillation cocktail depending on the method of quantitation. A Tracor MT 220 electron-capturegas chromatograph was used to quantitate the nonradioactive phthalates and to check the cleanliness of test tubes prior to use. A 6 ft glass column packed with 3% SE-30 on Gas-Chrom Q (100-120 mesh) was used at 190 "C. The carrier gas was nitrogen at a 60 mL/min flow rate. The glass containers used in the experiments were cleaned by sequential rinses with acetone and petroleum ether. The final petroleum ether rinse was concentrated under a stream of nitrogen and injected into the gas chromatograph. The detection of less than 1ng of phthalate per piece of glassware was required before the glassware was used. A Beckman LS 7000 liquid scintillation counter was used to quantitate the 14C labeled phthalates and polychlorinated biphenyls. Radiolabeled compounds were used so that low concentrations of the test compounds could be conveniently monitored. The samples were counted for a minimum of 20 min or until enough data had been accumulated so that there was only a 2% probability that the actual counts per minute were greater than twice the sample standard deviation away from the sample counts per minute. The seawater was cleaned of interfering organic material prior to spiking and use by passing it through a column containing Amberlite XAD-2 and charcoal. The water was collected in the Gulf of Mexico and had a pH of 8.1 and salinity of 3 6 % ~ The ~ seawater was spiked with less than 100 p L of a phthalate-acetone solution or of a benzene solution of the 14Clabeled compounds. Small amounts of sodium azide were added to the aqueous solutions to prevent microbial degradation of the phthalates. Possible synergistic interactions between bis(2-ethylhexyl) phthalate and 14CAroclor 1254, a commercial mixture of polychlorinated biphenyls, were investigated by adding aqueous solutions spiked with the different compounds sequentially to the same test tubes. One pair of replicate test tubes had a PCB-spiked solution and unspiked water added to them. Another set of replicates had a BEHP-spiked solution followed by a PCB-spiked
Table I. Distribution of Solutes among Original Solutions and Subsequent Water and Solvent Rinses of Containers % of solute recovered initial aqueous original water rinses acetonitrile rinses solutea concn, pg/L spiked water of test tubes of test tubes 4420 (+140)
DBP DBP
28.9 (i 2.2)
14CDBP
19.2 (i 2.0)
BEHP
407 (i.9)
BEHP
229 ( i 7 ) 15.5 (1.0.3)
I4C BEHP
6.8
I4C PCB (alone) I4C PCB (after BEHP) a
(k 0.5)
6.8 (k0.5)
94.6 85.4 95.8 97.0 96.2 97.8 68.0 72.1 74.1 56.2 73.0 56.0 50.1 54.6 71.1 81.1
n.d. n.d. 4.1 2.9 3.6 2.1 20.5 19.5 17.5 3.1 2.0 21.8 31.2 30.4 5.5 0.6
55.2 55.3
11.4 4.4
DBP = dibutyl phthalate; BEHP = bis( 2-ethylhexyl) phthalate; PCB = polychlorinated biphenyls. 0003-2700/81/0353-1718$01.25/00 1981 American Chemical Society
5.4 14.6 < 0.1
