some eccentricity as well as a lack of accurate machining of the electrode surface to yield a perfect plane perpendicular to the axis of rotation. Above 6000 rpm, it was possible, however, to construct a working curve. DISCUSSION
The inert annulus so formed is significantly wider (approximately 1mm) than that normally encountered in commercial ring-disc electrodes and, hence, calculations based upon thin ring, thin gap electrodes were invalid. The wider annulus will, in addition, increase the average transit time (9) for the transport of a species from the disc to the ring. The transit time is further increased, relative to aqueous solution, as a result of working in molten salt media where greater viscosities and smaller diffusion coefficients usually prevail. In conclusion, despite the large annulus, this rotating ring-disc electrode is capable of definitive investigations of
electrochemical phenomena. It has proved particularly useful in this laboratory in the interpretation of molten salt transition metal chemistry, where complex adsorption phenomena are prevalent (IO). LITERATURE CITED (1) D. E. Bartak and R . A. Osteryoung, J. Nectroanal. Chem., in press. (2) G. L. Holleck. J. Electrochem. Soc., 119, 1159 (1972). (3) D. T. Napp, D. C. Johnson, and S. Bruckenstein, Anal. Chem., 39, 481 (1967). (4) I. D. Eubanks and F. J. Abbott, Anal. Chem., 41, 18 (1969). (5) L. G. Boxall, H. L. Jones, and R. A. Osteryoung, J. Electrochem. Soc., 121, 212 (19). (6) D. L. Maricle and D. N. Hume, J. Electrochem. Soc., 107, 354 (1960). (7) N. K. Gupta, Rev. Sci. Instrum., 42, 1368 (1967). (8) W. J. Albery and S. Bruckenstein, Trans. Faraday SOC.,62, 1920 (1966). (9) S.Bruckenstein and G. A. Feldman, J. Electroanai. Chem., 9, 395 (1967). (IO) J. Phillips and R. A. Osteryoung, forthcoming publication.
RECEIVEDfor review January 5 , 1976. Accepted March 15, 1976. This work was supported by the Air Force Office of Scientific Research.
Apparatus for in Situ Solvent Extraction of Nonpolar Organic Compounds in Sea and River Water Martin Ahnoff * and Bjorn Josefsson Department of Analytical Chemistry, University of Gothenburg, Fack, 5-402 20 Goteborg 5, Sweden
Sampling and enriching techniques are of primary importance in the analysis of trace organics in water. Often large sample volumes are required to obtain the desired sensitivity. This makes it inconvenient to transport the original sample to the laboratory. Also, because of the risk of sample loss and sample contamination, it is desirable to carry out the enrichment as close as possible to the sampling point. In on site techniques, the enrichment process is performed in close vicinity to the sampling point, e.g., on a ship or in a land-based station. The water is then transported from the sampling point, typically by means of a tubing and a pump. However, deposition of particles may occur in the tubing. The tubing walls and the inner surfaces of the pump may also contaminate the sample. The influence of the sampling process on the constituents of water may be further decreased by utilizing an in situ enrichment technique. Few examples of such procedures have been reported in the literature. At Kiel, the “Institut fur Meereskunde” has used a permanent marine station, “Perkeo buoy”, situated in the Kiel Bay, to enrich organics from sea water on Amberlite XAD-2 macroreticular resin filters ( I , 2). The same adsorbent was used by Roger Dawson ( 3 ) , who studied polychlorinated biphenyls and pesticides in sea water around the British Isles. A column with the resin was placed in a towed “fish” so that an integrated sample was taken while the ship was under way. The water, up to 30 l., was pumped by a peristaltic pump placed on board. For sampling in lakes, a diver-operated equipment was used. A 50-1. drum was placed a t 10-m depth and filled with air. When the air escaped it was continuously replaced by the same volume of water, which first had to pass through an Amberlite XAD-2 filter. Gether and Lunde ( 4 ) used an in situ apparatus for investigation of halogenated organic compounds in Norwegian coastal waters. Up to 200 1. of water was pumped downwards through a vertical glass cylinder, where a nonpolar solvent, n-hexane, was trapped by gravity. The cylinder was packed with small glass beads to increase the contact area between the solvent and the water passing through. A pump was connected to the outlet and was served by a car battery. The apparatus was used down to 10-m depth. 1268
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The in situ apparatus described here is designed to perform solvent extraction of large amounts of water. This is done continuously while the apparatus is situated a t the sampling point a t a desired depth. EXPERIMENTAL T h e in situ apparatus consists of a water-tight, nonmagnetic, stainless steel container equipped with one pump and two magnetic stirring motors. On the top of and outside the container, in direct contact with the surrounding water, are attached two extractors which are connected with the pump inlet as can be seen in Figure 1. The extractors are mixer-settlers, previously described in detail ( 5 )and tested in field studies ( 6 ) .The extractor is a separate plug-in unit, constructed with glass and P T F E as the only contacting materials. The water is drawn a t constant rate, typically 3 l h , directly into the first extractor. There, a rotating magnetic stirring bar produces a vortex mixing of the water with a stationary, nonpolar solvent. Phase separation occurs in two consecutive circular chambers located outside and below the mixing chamber. Droplets of the solvent, which is lighter than water, rise back into the mixing chamber. The water leaves the first extractor and passes through the second extractor, where the same extraction process is repeated. Finally, the water enters the pump and is expelled back into the surrounding water. Before an extraction is started, the pump and stirring motor speeds are set, as well as the timer, when used. The container is closed by means of band clamps (Figure 1).The extractors are filled with solvent, cyclohexane or cyclohexane-hexane, and distilled water in the laboratory, and are coupled to the container before it is lowered into the sea. The apparatus weighs about 50 kg and is held at the desired depth (0-50 m) by a 60-1. buoy. The depth is restricted by the type of pump arrangement. If ca. 150 1. of water is to be extracted, the apparatus will operate for 48 h. When the extraction is completed, the extraction units are brought to the laboratory, where the extracts are taken out and analyzed. In a prototype version, schematically shown in Figure 2, the in situ apparatus is served by an external 220-V ac power supply. The stirring motors are standard laboratory magnetic stirrers. The pump is a membrane pump which gives a constant flow within wide pressure limits. Another version of the in situ apparatus, also shown in Figure 2, has an internal 12-V dc storage battery source. The stirrers are driven by miniature direct current motors (Philips). The peristaltic pump (Struers, Denmark) consists of a pump head coupled to a standard windscreen wiper motor. The flexible tubing is of silicone rubber. The motors are fed with a pulsed current (200 Hz, variable
Figure 2. Left: 220-V ac version of apparatus. Right: 12-V dc internal power supply version of apparatus. (1) Inlet to first extractor, (2) extractor, (3) pump, (4) pulse dampener, (5) magnetic stirring motor, (6) storage battery, (7) timer, (8) 200-V ac cable
Figure 1. Exterior of in situ solvent extraction apparatus. Total height is 76 c m
pulse width) so that their speed can be regulated without unnecessary energy loss. The total energy consumption amounts to ca. 5 watts. The battery has a capacity for 48 h of continuous operation. RESULTS AND DISCUSSION
The in situ apparatus was used to take samples outside the harbor of Goteborg, Sweden. The gpparatus was placed in an area where dredging sludge was dumped in the beginning of 1975. The extracts were analyzed for polychlorinated biphenyls, PCB, using gas chromatography. The cleanup procedure included treatment with sulfuric acid, potassium hydroxide, and Florisil and concentration to a final volume of 1 ml. The analytical details have been described elsewhere (7). The result is shown in Table I. Some advantages can be pointed out for the in situ continuous solvent extraction technique when compared with other alternative methods to recover nonpolar organic compounds from water. Since significant short term variations in concentration of organics are common both in river and ocean water, a cumulative sampling technique will give a more representative sample than will a grab technique. Continuous sampling a t strategic places will also make possible estimates of mass transport between water basins. The in situ technique involves a minimum of manipulation with the sample before it is extracted, thus minimizing contamination and sample loss a t the sampling stage. Solvent extraction is a well known technique for the isolation of organic substances from water. Knowledge in classical batch extraction may be applied to the continuous extraction process (5). In contrast to techniques utilizing adsorbent filters, which often suffer from clogging and channeling effects ( 8 ) , the solvent extraction technique involves no filtering of the particles. Particles pass unhindered through the extractor together with the water solution, so that there is practically no pressure fall in the systems. Thus, it is quite easy to achieve a constant, well defined flow through the extractor. The pump may also be coupled to the outlet of the extractor, so that contamination from the pump is eliminated. Further, two or more extractors may be coupled in series with no change in flow rate. Since the particles are not filtered off, they are extracted by the solvent just as in a batch extraction in a separatory funnel. On the other hand, when adsorbents like Amberlite XAD-2 or polyurethane foam are used, small particles will
Table I. Amounts of PCBa Found in Estuarine Water in a Dredging Sludge Disposal Area outside Goteborg during and after Dumping in 1975 Using in Situ Solvent Extraction
PCB, 10-9 g/i. Extracted Second Date volume, 1. First extractor extractor April 22-23 66 1.3 April 23-24 75 1.7 April 27-28 90 1.2 April 29-30 84 2.8 May 29-28 70 0.35 0.10 May 29-31 140 0.40 0.14 g of PCB. The values a A procedural blank contained 4 X have not been corrected for this background level, amounting to g/l. for a 75-1. sample. 0.05 X pass through the column unaffected, while larger particles will be caught on top of the filter. Using serial extraction, the extraction efficiency can be studied by comparing the amounts in the first and the second extraction stage. This is useful since, in practice, recoveries often differ markedly from those obtained in model tests. Finally, one shortcoming may be observed for the technique described. The extraction efficiencies for organic substances adsorbed on particulate matter may certainly differ from the extraction efficiencies for these substances when they are in solution. This makes it more difficult to evaluate the overall recovery of compounds which are to some extent adsorbed on particles. If one wishes to study the dissolved and particulate matter separately, it is possible to connect a filter disc holder with, e.g., a glass fiber filter in front of the extractors. However, this makes the system more complicated. There will be a pressure fall over the filter so that a powerful and thus power-consuming pump must be used. The pump must not contain contaminating material, since it has to be installed on the inlet of the filter and the extractors. The maximum sample volume will be limited by the particle holding capacity of the filter. However, for more elaborate studies, when access to energy is not limited, this is an attractive technique for the investigation of dissolved contra particulate nonpolar organic matter in natural waters. LITERATURE CITED ( 1 ) M. Erhardt, lnstitut fur Meereskunde. Kiel. Lecture held at Nordic Research Course on the Chemistry of Sea Water, University of Gothenburg, 1975. (2) C. Osterroht, J. Chromatogr., 101, 289 (1974). (3) R. Dawson, Department of Oceanography, University of Liverpool. thesis, 1974. ANALYTICAL
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(4) J. Gether and G. Lunde, Technical Report No 6 from "Sentralinstitutt for industriell forskning", Osio, 1974. M. Ahnoff and E. Josefsson, Anal. Chem., 46 658(1974). M. Ahnoff and B. Josefsson, Ambio, 4, 172 (1975). M. Ahnoff and B. Josefsson, Bull. Env. Contam. ToxiCOl., 13, 159 (1975).
(6) T. A. Bellar and J. J. Lichtenberg, "Water Quality Parameters", ASTM STP 573, 1975, pp 206-219.
RECEIVEDfor review January 5, 1976. Accepted March 23, 1976.
Off-Line Coupling of Liquid Chromatograph and vass Spectrometer S. Elbert, B. Gruhn, E. Wipfelder, and H. lieusinger* lnstitut fur Radiochemie der Technischen Universifat Munchen, 8046 Garching, West Germany
The advantages of coupling liquid chromatography and mass spectrometry need scarcely be mentioned; in the absence of appropriate standard substances for any particular analysis, a mass spectrum provides the ultimate proof of identity. Additionally, because polymer molecular weight fractions can be compared to standards only with the introduction of a sometimes sizeable error, the mass spectrum approach provides a precise method of determining molecular weight ( d e < 1200) of substances at low concentrations. There have been at least two attempts to couple high pressure liquid chromatography (HPLC) and mass spectrometry in an on-line fashion ( 1 , 2 ) ,both successful, but either limited in applicability or somewhat difficult in practice. Jones and Yang ( I ) describe the use of a 3-stage dimethylsiloxane membrane to separate solvent from solute. However, the prerequisites that solvent be polar and solute be volatile make that technique uninteresting to most workers. Lovins and McKinney (2) describe a much more universal system, but with the unfortunate disadvantages that a) the chromatograph must be stopped in mid-analysis, increasing diffusion in the cblumn and reducing resolution between close peaks, and b) it requires a bellows assembly of considerable complexity. An on-line system necessitates that both instruments be situated together and that both function simultaneously, an arrangement which may be somewhat impractical. As an alternative, an off-line system is described which can be carried out expeditiously because of its inherent simplicity. The problems incurred by on-line systems are thereby practically solved.
inject
i
Figure 1. LC-separation of Kethylmaleimide homopolymer and cyclohexene-Kethylmaleimidecopolymer
nypodermic syrjngc
EXPERIMENTAL Apparatus. A Hewlett-Packard liquid chromatograph model lOlOB equipped with a variable wavelength detector and electronic flow control was used for the analysis. A Varian Mat CH 5 single focus mass spectrometer, equipped with magnetic scan, electron impact source, and variable probe temperature (0-480 "C) served for the mass spectra. Reagents. A mixture of N-ethylmaleimide (NEMI) homopolymer and cyclohexene-N-ethylmaleimide copolymer was prepared by subjecting N-ethylmaleimide and cyclohexene in cyclohexane to y radiation. The M,, of the resulting precipitate, determined by membrane osmosis, was 970, and represents an average molecular weight (3). Procedure. For the liquid chromatographic (LC) separation of N-ethylmaleimide homopolymer and cyclohexene-N-ethylmaleimide copolymer (Figure l),a single column (i.d. 4 mm, 50-cm length) of Porasil-C 100-120 mesh, with a-octyl groups permanently attached (Waters Associates, Framingham, Mass.) was used. The column was dry-packed by tapping, the ends plugged with silanized glass wool. Although the column material is actually intended for gas chromatography, it was eminently suitable for this analysis. The eluent was cyclohexane/isopropanol 1:5, isocratic a t 0.60 ml/min, with a column temperature of 25 "C. The spectrophotometer was set a t 245 nm throughout the analysis. Ten mg of the sample was dissolved in 1.00 ml of acetonitrile and injected 3 times in 5 - ~amounts. 1 To ensure that the mass spectrum is free of solvent peaks, the solvent must be distilled. Undistilled solvent, even spectral grade, resulted in fragments of high molecular weight. Masses of
