Anal. Chem. 1994,66, 905-908
Separation and Isolation of Volatile Organic Compounds Using Vacuum Distillation with GC/MS Determination Michael H. Hiatt' Environmental Monitoring Systems Laboratory, U.S. Environmental Protection Agency, P.0. Box 93478, Las Vegas, Nevada 89 193-3478 David R. Youngman and Joseph R. Donneiiy Lockheed Environmental Systems & Technologies Co., 980 Kelly Johnson Drive, Las Vegas, Nevada 89 1 19
Vacuum distillation of water, soil, oil, and fish samples is presented as an alternative technique for determining volatile organic compounds (VOCs). Analyses of samples containing VOCs and non-VOCsat 50 ppb concentrationswere performed to evaluate method limitations. Analyte recoverieswere found to relate closing with boiling point unless a compound's water solubility exceeded 5 g/L. Recovery, precision, and method detection limits for VOCs demonstrate this technology is appropriate for environmental samples. Determining volatile organic compound (VOC) cwcentrations in environmental matrices is one of the most important and routine analyses. VOCs are addressed as a major group of analytes for the Comprehensive Environmental Response Compensation and Liability Act (CERCLA), Resource Conversation and Recovery Act (RCRA), and the Clean Water Act (CWA). The widespread occurrence of VOCs in the environment and the potential of using VOCs as indicator parameters for contamination plumes from point sources make their accurate and routine measurement an important issue. These considerations make any improvements in VOC determinations worthwhile to the EPA and relevant to the analytical community. The most widespread technology used to determine VOCs is purge and trap, developed by the EPA to determine VOCs in water.lJ Purge and trap is incorporated into EPA methods for water and s0i1.~-~ This technique is optimal for drinking water, but has difficulties when purging is hindered by elevated organic content. The trapping material also introduces difficulties that have been summarized.6 Vacuum distillation was developed as an alternative technique for determining VOCs in nonwater environmental matrices. Thevacuum distillation of sediments and fish tissues provided greater VOC recoveries compared to purge and trap.7 (1) Bellar, T. A.; et al. J.-Am. Water Works Assoc. 1974, 66,739. (2) Bellar, T. A.; Lichtenberg, J. J.; Kroner, R. C. J.-Am. Water Works Assoc. 1974, 66,703. ( 3 ) US. Environmental Protection Agency. Contract Laboratory Program Statement of Workfor OrganicAnalysis, Multi-media, Multi-concentration. Document Number OLMOl .O, 1990. Including Revisions, OLMOl. 1OLM01.8, Dec 1990Sept 1991. US. Environmental Protection Agency, Cincinnati, OH. (4) US.Environmental Protection Agency. Test Methods for Determining Solid Waste, SW-846; 1992. ( 5 ) US. Environmental Protection Agency. Methods for the Defermination of Organic Compounds in Drinking Water; 1988. (6) Shirey, R. E. Cole, S . B. Supelco Rep. 1993, 12, 21.X3. (7) Hiatt, M. H. Anal. Chem. 1981, 53, 1541. 0003-2700/94/0366-0905$04.50/0 0 1994 Amerlcan Chemical Society
This approach was utilized by other investigators for analyzing larger water samples8 and algae.g A further refinement of vacuum distillation was the elimination of an adsorbent trap and direct interfacing of the apparatus to a gas chromatograph/mass spectrometer (GC/ M S ) . l 0 The removal of the adsorbent trapping material eliminated a major source of problems that plagued volatile compound determinatiom6 This new apparatus, however, was cumbersome and required continuous operator activity. The vacuum distillation apparatus described in this study provides further improvements for streamlining operation. The utilization of a single condenser coil facilitated temperature control and also eliminated a series of temperature control baths. This made vacuum distillation conduciveto automation and an attractive approach for determining volatilecompounds. This work was a result of EPA's investigation of vacuum distillation using the new apparatus to develop a method for determining volatile organic compounds in environmental samples and hazardous waste. A secondary goal was the development of a single distillation procedure for addressing multiple environmental matrices. Such a procedure may eliminate costs and confusion associated with matrix-specific apparatus and calibration. The vacuum distillation procedure used in this study is currently in the approval process for becoming an EPA test method.4 EXPERIMENTAL SECTION Vacuum Distillation Apparatus. The vacuum distillation apparatus (see Figure 1) consisted of a sample chamber connected to a condenser which was attached to a heated six-port sampling valve (V4). This sampling valve was connected to a condenser, vacuum pump, cryotrap, and gas chromatograph (GC). This study used a mass spectrometer, interfaced to the GC, for detection and quantitation. The circulating system which controlled the temperature for the condenser coils included a cryogenic cooler with a cold reservoir (Neslab ULT80DD) and an elevated (45 "C) temperature bath. The fluid for both baths was isopropyl alcohol,and the routing of isopropyl alcoholthrough the system was controlled by the bath fluidvalve (V2). The cold isopropyl alcohol (-5 "C) was pumped through the condenser by the cryogenic cooler. The warmed isopropyl alcohol was pumped
. (8) Kozloski, R. P. J. Chromatogr. 1985,346, (9) Ncwman, K. A.; Gschwend, P. M. Limnol. ceanogr. 1987, 32, 702. (10) Hiatt, M. H. Anal. Chem. 1983, 55, 506.
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Analytical Chemlsby, Vol. 66,No. 6, Mer& 15, 1994 905
Chromatography/ Mass Spectromete He
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through the condenser using a peristaltic pump (Cole Parmer 6-600 rpm). The valves, transfer lines, and condenser exterior were heated to 80 OC using thermal strips. This temperature was sufficient to prevent condensation of analytes onto condenser walls, valves, and connections. The temperature of the transfer line from the sampling valve to the gas chromatograph was maintained at 150 O C . Pirani gauges (Edwards Model 1001 with gauge head Made1 PRHlOK) were installed at the sample chamber, condenser, and vacuum pump (Alcatel Model ZM2012A) for pressure monitoring. Some key dimensions of the apparatus were as follows: (a) cyrotrap, 8 in. X 1/8 in. stainless steel tubing; (b) condenser, 12 in. X 2 in. with ground glass ends and Buna-N O-ring seals; (c) tubing between six-port valve and GC inlet, l/16-in. fused silica lined stainless steel; (d) a l/g-in. fitting six-port Valco sampling valve with (V4) port diameter (0.040 in.) stainless steel with Teflon internal parts; (e) 0.187-in.4.d. manual valves (Vl, V3); Whitey SS-43XS4, stainless steel with Teflon internal parts; and (f) a combination of multiple three-way Whitey B-43XS4 valves (V2). Reagents. Stock standard solutions were prepared in methanol using assayed liquids or gases, stored with minimal headspace at -10 to -20 OC, and protected from light. Fresh gas standards (chloromethane,bromomethane, vinyl chloride, chloroethane) were prepared weekly. Stock solutions in methanol were prepared from pure standard materials or purchased as certified solutions (Supelco, Bellefonte PA). These solutionswere used for calibration and for spikingsample matrices. Reagent water was generated by passing tap water through a carbon filter bed containing about 450 g of activated carbon 906 Ana&tlcalChemisiry, Vol. 66, No. 6, Marah 15, 1994
(Calgon Corp., Filtrasorb-300) or by using a water purification system (Millipore Super-Q). Purge and trap grade methanol (Burdick and Jackson, Muskegon, MI) was utilized for the study. Pharmaceutical grade Osco brand cod liver oil and food grade Starkist brand canned tuna in water were used for sample matrices. Spiked samples. Samples utilized in this study were spiked with 250 ng of each analyte dissolved in methanol. Water, soil, and tissue were spiked directly using a gas-tight syringe after the samplealiquot was transferred to the samplechamber. The methanol spike solutions, however, were not miscible with the oil matrix studied, and therefore, an intermediate spiking step was required. A 200-pL solution consisting of water saturated with lecithin was added to the oil in the sample chamber. The spike was then injected into the aqueous phase and the sample swirled until there was an even emulsion. When combinationsof oil and other matrices were to be investigated, the oil component was first spiked and then the additional matrix was added. Vacuum Distillation Procedure. The sample chamber, which contained the prepared spike sample, was first attached to the apparatus (Figure 1). The sampling valve (V4) was switched to the distillation position which allowed the cryotrap and condenser to be evacuated. The vacuum distillation began when sample chamber valve (V 1) was opened allowing sample vapors to pass over the condenser coil, (chilled to below -5 OC), resulting in the condensation of water vapor on the condenser coil. The vapors not condensed on the condenser coils were collected cryogenicallyin a section of 1/8-in. stainless steel tubing, chilled with liquid nitrogen (-196 OC). After 10 min of vacuum distillation, sampling valve (V4) was switched to the desorbing position, connecting the cryotrap to the gas chromatograph. The cryotrap condensate was then thermally desorbed and transferred to the gas chromatograph using helium carrier gas. During the cryotrapdesorption, a 10-min decontamination cycle was performed which required heating the condenser coil with 45 OC isopropyl alcohol and evacuating resultant vapors through the pump valve (V3). CC/MS Procedure. A fused silica capillary GC column (30 m X 0.53 mm i.d., 3- pm film thickness, DB-624 from JBCW Scientific, Folsom, CA) was used for this study. The
Tabh 1. Rea" and plw#on (a Om Standard DovlaUon)
=pound
oila
chlomethane N/A' N/A bromomethane N/A vinyl chloride N/A chlomthane 63f34 methylene chloride CONT acetone carbon dirulfide 98i40 1,l-dichlomthene 100f25 Wf21 1,l.dichlomthane t ~ n u - l , 2 ~ 0 m t h e n89 e f 22 ci8-1,2-diohloroe~ene 102 f 12 chloroform Wf12 1,2-dichloroethane 11Of 19 Im 2-btifmone l,l,l-trichlomthane 91t12 carbon tetrachloride 91f40 vinyl acetate INT bromodichloromethane 8 4 i 7 1,1,2,2-tetrachloroethane 62 i 10 1,2-dichloropropans 68f34 tranu-1,S-dichloropropene78 f 9 trichlomthene 81f7 dibromochloromethane 81 i 19 76f8 1,1,2-trichloroethane 116f6 ben" cl-1,3-dichloropropene 78 f 8 48i6 bromoform INT 2-hexanone 4-methyl-2-pentanone INT 68f8 tetrachlorethene 86i10 toluene 6Oi6 chlorobenzene ethylbenzene 48i6 66i7 rtyrene pxylme 26i10 0-xylene 46i7 38i4 bromofluorobelwne
wateP
milo
93f18 106t9 106i9 88f10 72f13 70f23 110i8
66f32 63f33 60i26 42f21 66f16
fiid
84 f 6 86 f 8 91t14 93t 16
6Of23 63f20 67f19 69 i 19 66 i 16 114i28 99t14
N/A N/A N/A N/A CONTf CONT 79t36 122i39 126i36 109 f 46 106 i 22 111t32 117i27
INT
INT
INT
96f13 91f 14 72f13 92f11 78 f 20 89f14 g4 16 86f8 90 f 12 87f 14 86f9 94 f 12 81f21 64f17 69 f 20 91f 11 8 9 i 11 88f12 90f12 89f9 86i8 86f10 94f 11
137t23 82f69 84i12 49t12 76 f 22 66i17 70 i 18 62i16 74 i 18 Mi20 64i12 64 i 20 68f 19 99t20 79 i 24 66f 16 60i 13 61f18 70f23 66i19 60i19 66i20 73i 19
106i30 83i34
84i6 96f11
*
CONT
INT 97i22 67 i 20 117i23 92 i 22 98i31 71 i 19 92i20 129f36 102 i 24 68t19
INT 113 i 37 66f20 CONT 66i19 74f19 67i14 46i13 83f20 62i16
e Cod live! oil 1 g, with lecithin and 6 I !& of water. b Water,6 mL. Soil, 6 g, m u d wlth 6 mL of water. d Fmh thue,10 g, mixed wth 6 mL of water. Concentration L 26 p b. No analyoen. f Exceuive concentration of anal@ in wnple &r to spiking. 1 w rpectral intsrfsroncwdue to concentrationo!coeluting hydrocsrboruprerent 0
compound
watep
(ppb) chloromethane 3.1 2.6 bromomethane vinyl chloride 4.0 chloroethane 6.1 3.1 methylene chloride 33.0 acetone carbon dieulfide 2.6 1,l-dichloroethene 3.4 2.3 1,l-dichloroethane t rane-2,3-dichloroethene 3.0 2.4 cl-l,%dichloroethene 2.7 chloroform 1,2-dichloroethane 1.6 67.0 2-butanone l,l,l-trichloroethane 1.6 carbon tetrachloride 1.6 23.0 vinyl acetate 2.0 bromodichloromethane 1,1,2,2-tetrachloroethane 3.6 1,2-dichloropropane 2.9 trane-1,3-dichloropropane 2.3 trichloroethene 2.6 2.1 dibromochloromethane 2.7 1,1,2-trichloroethene 1.7 benzene 2.1 cl-1,3-dichloropropne 2.3 bromoform 2-hemone 4.6 4-methyl-2-pentanone 3.8 tetrachloroethene 1.8 toluene 1.8 chlorobenzene 2.4 2.4 ethylbenzene 2.0 styrene 2.3 p-xylene 2.4 o-xylene
wilb (ppb) 8.6 4.9 7.1 7.6 3.3
tiMuee (PPb) 7.8 9.7 9.6 9.2
3.2 3.8 1.7 3.2 2.7 2.6 1.7
6.4 4.0 4.0 4.4 4.7 6.6 3.3 INT 1.1 3.2 INT 3.2 4.4 3.8 3.8 3.1 3.6 4.4 3.6 3.6 4.9 7.7 7.6 4.3 3.0 3.3 3.6 3.6 3.7 3.3
Oild
(PPm) N/AC N/A N/A N/A
CONTf 0.08 CONT CONT 0.12
IN?r 2.4 1.7 INT 2.3 3.2 3.7 2.4 3.0 2.9 2.8 2.9 2.6 2.6 4.6 3.9 2.6 4.4 2.6 4.1 2.6 3.9 4.1
0.19 0.19 0.13 0.09 0.08 0.06 0.08
INT 0.08 0.16
INT 0.06
0.09 0.12 0.08 0.06 0.04 0.07 0.03 0.06 0.10
INT INT 0.12 0.09 0.07 0.09 0.16 0.18 0.08
Water,6 mL. b Soil, 6 g. 0 Thue, 10 g. Cod liver oil, 1 g. No analyaw, flxcesoive concentration of anal@ in w n p b prior to spikm . I M W rpectralinterferonma due to elevated concentration Q
of coekting hydrocarbone prerent in wnple.
OUIplO,
GC column was temperature programmed from 10 (3 min) to 230 OC at 5 OC/min. The Hewlett-Packard 5970B mass spectrometer was operated in E1 mode at 70 eV, scanning 35-350 D at a rate of 0.82 s/scan. A heated jet separator was employed to interface the GC column to the mass spectrometer.
RESULTS AND DISCUSSION An analyte's presence in the vacuum distillate was found to be related to its boiling point. Samples were spiked with VOCs and semivolatile compounds representing a wide range of boiling points (-24 to 285 "C). The recovery of analytes compared to the analyte's boiling points was presented in Figure 2. Only compounds with water solubility less than 5 g/L were u r d to generate Figure 2. Recoveries were calculated by comparing against the recoveries of standards of the analytes transferred through the apparatus with the condenser coil at 45 "C. Volatile compounds that are very water soluble, such as alcohols, ethers, and amines, are not usually considered as VOCs due to their low volatility in the presence of water. To evaluate solubility effects during vacuum distillation, water
samples spiked with analytcs of varying solubilities (from less than 1g/L to infinitely miscible) were analyzed. Compounds with water solubilities greater that 5 g/L demonstrated lower recoveries than expected from their boiling points estimated using Figure 2. Compounds that were very soluble in water demonstrated the greatest drop in recovery making their detection difficult. We did not attempt to minimize analyte losses due to solubility; however, sample pretreatment, such as adding salt, would likely improve recoveries of miscible analytes. Spiked samples, representing the range of environmental matrices, were analyzed to determine the VOC recoveries and precision. Recovery data for the VOCs resulting from five replicate analyses of water, soil, and tissue samples were presented in Table 1. The effect of organic content on tho recoveries of VOCs from water and soil were also evaluated. When the organic content (emulsified cod liver oil) of water reached 20% the VOC recoveries were similar to those listed for oil in Table 1. These samples were successfully analyzed and were easily contained within the sample chamber using the vacuum distillation method. Generaly, when such high organic water samples are analyzed using a purge and trap procedure, an A ~ & t h GhmWy, l Vol. 88, No. 8, Mrch 16, 1@@4 907
uncontained frothfis produced which contaminates the adsorption trap. . Oil samples proved to be the most difficult matrix from which to recover VOCs; therefore, only l-g aliquots were analyzed. Heating, sample sonication, and extended distillation times were evaluated as possible means for improving VOC recoveries; however, only sample heating during the analyses improved the recoveries. Similar recovery improvements were also obtained by creating a water emulsion of the oil sample through the use of lecithin. Since sample heating could introduce artifacts and increase a potential to diffuse higher boiling nonanalyte compounds throughout the apparatus, sample heating was not utilized further. The recoveries of VOCs from the oil and water emulsion are among the data contained in Table 1. Fish tissue behaved similarly to cod liver oil in its impact on VOC distillation yields. As with oil, the addition of water did not substantially improve VOC recoveries but improvements were observed in precision, in ease of sample handling,
800 Anelytloel Chml.stry, Vol. 66, No. 6, March 15, 1994
and in minimization of mass spectral interferences by nonanalyte polar compounds in the distillate. Method detection limits for water, soil, oil, and tissue were determined in accordance to RCRA guideline^.^ These data are provided in Table 2.
ACKNOWLEWMENT Although the research described in this article has been funded by the United States EnvironmentalProtection Agency, through Contract 68-CO-0049to the Lockheed Environmental Systems and Technologies Co., it has not been subjected to Agency review. Therefore, it does not necessarily reflect the views of the Agency, and no official endorsement should be inferred. Mention of trade names or commercial products does not constitute an endorsement for use. Receivd for revbw September 7, 1993. Aocupted Doc” 6, 1993.. Abstract published in Advance ACS Abstracts, Februrry 1, 1994.
