Environ. Sci. Technol. 1980, 22, 565-570
(21) Tan, C. W.; Hsu, C.-J. J. Aerosol Sci. 1971, 2, 117. (22) Tan, C. W. Heat Mass Transfer 1969, 12, 471. (23) Sparrow, E. M.; Lin, S. H.; Lundgren, T. S. Phys. Fluids 1964, 7, 338. (24) Finlayson, B. A. In Finite Elements in Fluids; Gallagher, R. H., et al., Eds.; Wiley: London, 1975; Vol. 1, p 1. (25) Becker, E. B.; Carey, G. F.; Oden, J. T. Finite Elements: An Introduction; Prentice-Hall: Englewood Cliffs, NJ, 1981; VOl. 1, p 10.
Aoki, T.; Uemura, S.; Munemori, M. Anal. Chem. 1983,55, 1620.
Hallowell, A.; Pacey, G. E.; Gordon, G. Anal. Chem. 1985, 57, 2851. Kiani, A.; Bhave, R. R.; Sirkar, K. K. J.Membr. Sci. 1984, 20, 125. Carlson, R. M. Anal. Chem. 1978, 50, 1528. Dasgupta, P. K. Anal. Chem. 1984, 56, 96. Davies, C. N. J. Aerosol Sci. 1973, 4, 317. Gormley, P.; Kennedy, M. Roc. R. Zr. Acad., Sect. A 1949, 52A, 163. Ingham, D. B. J. Aerosol Sci. 1975, 6, 125.
Received for review September 8,1986. Accepted November 3, 1987.
Development and Evaluation of a Procedure fo'r Determining Volatile Organics in Water Larry C. Michael and Edo D. Pelllzzari" Research Triangle Institute, Research Triangle Park, North Carolina 27709
Roger W. Wlseman National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709
organic compounds from various waters was developed through the use of representative volatile organic compounds as part of the EPA Master Analytical Scheme. Preliminary recoveries were determined for a broad range of analytes in distilled water, municipal wastewater effluent, and industrial (energy-related)wastewater effluent. The apparatus for isolation of the compounds from water was interfaced directly to a gas chromatograph/mass spectrometer/computer, and recoveries were determined for compounds comprising different functional groups in drinking water and municipal/industrial wastewater.
per sample and was inherently freer from interferences than closed-loop gas stripping analysis. In particular, the carbon disulfide used for desorption of the carbon trap in CLSA chromatographically obscured early-eluting analytes. Consequently, extensive method optimization was performed only on the purge and trap method. This was accomplished with 14C-labeledcompounds and is too extensive for inclusion here (2). This paper addresses method refinement, interface of the purge and trap apparatus to the GC/MS/COMP, and the method evaluation. Nonradiolabeled purgeable compounds, encompassing a broad range of compound types, were employed for method evaluation.
Introduction
Experimental Section
Analysis of organic compounds in water has traditionally been approached by selecting analytical methods on the basis of the target compounds. Examples of such an approach are the 600 series methods presented in the Federal Register (1). Alternatively, broad spectrum analytical methods provide a comprehensive assessment of all sample components. This philosophy was embraced by the U.S. EPA "Master Analytical Scheme" program (2). Analytical methods developed under this program were designed to encompass all gas chromatographable compounds with the fewest analytical methods. The overall approach to development of a comprehensive analytical scheme for purgeables in water was to employ gas chromatography/mass spectrometry/computer (GC/MS/COMP) in conjunction with an isolation technique which would include the volatile (bp < 150 "C), water-insoluble compounds and also many compounds considered to be semivolatile and semi water soluble. An additional objective was to detect and quantitate these compounds at 0.1 pg/L in drinking water, 1pg/L in surface waters, and 10 pg/L in effluent waters. On the basis of a comprehensive review of the current literature (3),only two techniques possessed adequate sensitivity to warrant experimental investigation of their range of applicability: (1)purge and trap (4) and (2) closed-loop gas stripping (Grob) analysis (CLSA) (5-7). Preliminary evaluation of both of these methods revealed that the conventional purge and trap method had a significantly shorter analysis time
Method Refinement Studies. Recovery determinations with representative compounds followed the analytical protocol outlined below: (1)Organic-free water was prepared by purging deionized water for 2 h at 90 "C with 100 mL/min helium followed by continued purging while cooling to 30 "C. (2) Aliquots (200 mL) were transferred to purge flasks containing 60 g of anhydrous Na2S04and were shaken to dissolve the salt. (3) The 30% Na2S04solution was spiked with 5 pL of the appropriate standard mixture in methanol, mixed gently, and equilibrated at 30 "C for 10 mins. (4) After the Tenax GC cartridge was attached, 500 mL of helium was passed through the solution at 25 mL/min. (5) Exposed cartridges were analyzed by thermal desorption gas chromatography with flame ionization detection (GC/FID) on either a 180 X 0.2 cm Tenax GC (80/100 mesh) packed column or a 65 m X 0.5 mm SE-30 WCOT column. (6) Recoveries were calculated by comparison to standard cartridges using electronic peak height measurements. (7) In experiments involving municipal and energy effluent samples, 20 mL of effluent was combined with 180 mL of distilled water prior to introduction into the purge flask. Evaluation of an Integrated GC/MS/COMP Purge and Trap System. A purge and trap system (Figure 1) consisting of a purge and trap module (A), an injection
A comprehensive procedure for isolation of volatile
0013-936X/88/0922-0565$01 SO10
0 1988 American Chemical Society
Environ. Sci. Technol., Vol. 22, No. 5, 1988 565
Table I. Component Identification: Purge a n d T r a p System item
description
1 2 3 4 4A 4B 4c 5 6 7 8 9
rope heaters-Hotwatt Inc., 250 W, 120 V, 60 in. insulation-glass wool sleeve ' i Zin. X ' / 6 in. thick glass fiber tape-Scotch 27 (3M Co.) sorbent trap--1.5 g of Tenax GC (Enka Research Institute, The Netherlands); 35/60 mesh in. stainless steel, fritted (10 pm) reduction union 3/8 3/8-in. stainless steel nut 10 in. X 3/8 in. 0.d. X '/56 in. i.d. stainless steel tubing heated/insulated nickel transfer line from six-port valve to GC injection system, in. 0.d. X 0.040 in. i.d. x 30 in. heated/insulated nickel transfer line from six-port valve to sorbent trap, '/I6 in. 0.d. X 0.040 in. i.d. x 14 in. support and heater for six-port valve, Valco HA-1 (Valco Instruments Co., Inc.) six-port valve, Valco C-6-T, '/I6 in. zero dead volume fittings support bracket for sample valve sample valve, Tekmar 14036 (Tekmar Co.) sample introduction needle, Tekmar 14217 Teflon (E. I. du Pont de Nemours and Co.) tubing (l/16 in. 0.d. X 0.040 in. i.d. X 20 in.) with needle (18 gauge X 55 in.) Teflon tubing ('/I6 in. 0.d. X 0.040 in. i.d. X 8 in.) with Cheminert (LDC/Milton Roy) connector for connecting to item 20 sampler union, Tekmar 14049 same as item 14 sample container, 243 mL, glass, 24-mm septum cap three-finger clamp, Fisher 05-742 (Fisher Scientific Co.) clamp holder, Fisher 05-754 aluminum rod, l/z in., Fisher 14-666 heated/insulated nickel transfer line from purge flask connecting line to six-port valve, in. 0.d. X 0.040 in. i.d. X 14 in. heated/insulated nickel transfer line from six-port valve to sorbent trap, '/le in. 0.d. X 0.040 in. i.d. X 20 in. heated/insulated nickel transfer line from sorbent trap to six-port valve, '/I6 in. 0.d. X 0.040 in. i.d. X 5 in. clamp soap bubble flowmeter purge flask approximate dimensions-18 in. X 1.5 in. purge gas in. 0.d. frit porosity-medium material-borosilicate glass (A) Microflex valve, Kontes K-749100-21 (Kontes Scientific Glassware/Instruments) (B)Chromaflex column valve, Kontes K-423600 (C) Chromaflex column valve, Kontes K-423600 spring, 1.5 in. dry purge valve, four-port, Valco C-4-T, '/I6 in. zero dead volume fittings aluminum panel, 16 in. X 26 in. X in. Flexframe Foot plate, Fisher 14-666-'25 purge gas line, Teflon tubing (1/16 in. 0.d. X 0.040 in. i.d. X 20 in.) with Cheminert fitting Teflon tubing (1/16 in. 0.d. X 0.040 in. i.d.) with stainless steel needle (18 gauge X 1 in.) purge gas flow metering valve, Nupro SS-2SG (Nupro Co.), in. fittings temperature controller/readout no. 1
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
26 27 28 29 30 31 32 33
port/cryofocusing trap (B), and other ancillary devices was evaluated for analysis of volatile organic compounds. Parts listings are given in Tables I and 11. Organic-freewater was transferred into a 250-mL bottle equipped with a magnetic stirrer and a silicone-Teflon septum closure until the bottle was filled to capacity (no head space). Compounds of interest were introduced through the septum in 2 ELLof a methanol solution containing 200-300 ng/pL of each compound and deuteriated internal standards ( [2H5]bromoethane; [2H3]anisole; [2H5]chlorobenzene)and then stirred for 2 min. Gaseous solutions of the external standard perfluorotoluene (PFT)were prepared in a 1-L gas bulb which had been flushed with helium and heated with a heating mantle to 35 "C. With continual magnetic stirring, P F T was injected into the bulb through a septum to produce 200 ng of P F T / 1 mL of gas; the system was equilibrated for 30 min. Sixty grams of anhydrous powdered sodium sulfate (Baker) was added to the dry 200-mL purge vessel. The vessel was equipped with a foam trap on the purge gas exit and Teflon valves on the purge gas inlet and exit lines. Following the introduction of salt, the vessel was purged (with the exit line disconnected from the Tenax trap) at 25 mL/min for 20 min to simultaneously purge the salt and displace the void volume of the flask. The Teflon valves on the flask were then closed, and the flask was 566
Environ. Sci. Technol., Vol. 22, No. 5, 1988
Table 11. Component Identification: Injection System 1 2 3 4 5 6 7 8
9 10
11 12
13 14
injection block, containing six-port valve liquid nitrogen cooled, nickel capillary trap gas chromatograph carrier gas inlet to injector septum purge outlet (closed during operations) injection splitter exit (closed) vent heated/insulated transfer line inlet from purge and trap system, l/s in. 0.d. X 0.040 in. i.d. X 30 in. (other end of item 5, Table I) purge flask heater, 3 / 4 in. diameter X 8 in., Watlow 01808081 (Watlow Winona, Inc.) electrical connection to injector body electrical connection to cryogenic trap heater gas chromatograph bulkhead gas chromatograph injection port fused-silica capillary column temDerature controller /readout no. 2
shaken to redistribute the salt for easier dissolution. After the valve on the exit line leading to the Tenax trap was opened (to allow head-space displacement), 200 mL of sample was introduced into the vessel by a pressurized delivery system (Figure 2) using helium. When delivery was complete, the valves on the flask were closed, and the flask was shaken to dissolve the salt. The foam trap and Teflon valves prevent water from entering the system lines during the shaking procedure. After the salt was dissolved,
Flgure 1. (A) h r g e an
system; (B) injection system
Flgw 2. pressurized Sample delivery system.
the valves were reopened, and the sample was purged for 20 min a t 25 mL/min. A t the conclusion of the normal purge cycle, the purge gas was diverted (part 27, Figure 1)around the purge flask for an additional 5 min to remove residual water vapor from the Tenax trap. During this "dryx purge (18 min into the cycle), 1mL of gaseous PFT in helium was injected with a 5-mL gas-tight syringe into the cold cryogenic trap. Trapped compounds were desorbed from the Tenax trap at 200 "C onto the cryogenic trap for 8 minutes at 15 mL/min. The cryofocused eluent was then flash evaporated onto the capillary column by balliitic heating of the cryotrap to 200 OC. All experiments were conducted in triplicate.
Results and Discussion Method Refinement Studies. Recovery studies with representative compounds were performed in triplicate at 1ppb in tap water and 100 ppb in municipal and energy effluents. These studies encompassed ten different functional group classifications including aldehydes, ketones, esters, ethers, aromatic hydrocarbons, aliphatic hydrocarbons, halogenated aromatic hydrocarbons, halc-
genated aliphatic hydrocarbons, miscellaneous nitrogen compounds, and miscellaneous sulfur compounds. The two effluent waters were diluted 1:lO prior to purging to minimize foaming. Recovery data (Table 111) indicate compound classes which are amenable to purge and trap as described here. Recoveries for aldehydes, ketones, esters, and miscellaneous nitrogen compounds were extremely low (
