Anal. Chem. 1909, 65, 2229-2235
2229
Closed-System, Solid-Phase Extraction Cleanup Method for Removal of Normal Paraffin Hydrocarbon from Samples Prior to Purge-and-Trap Volatile Analysis Richard B. Lucke, James A. Campbell,' Gerald A. Ross, Steven C. Goheen, and Eric W. Hoppe Pacific Northwest Laboratory, Box 999, Richland, Washington 99352
A novel approach has been developed to separate potential semivolatile interferences from volatile analytes prior to purge-and-trapanalysis. This technique involves a closed system with solidphase extraction which provides a simple, inexpensive method with minimal loss of volatile components. In addition, the separation method minimizes the potential adsorption of unwanted volatile species from the surrounding air during the cleanup procedureand reduces the radioactive level in actual tank waste samples. This cleanup method has been applied to radioactive, hazardous mixed waste samples containing normal paraffin hydrocarbon (NPH) from a Hanford single-shell tank. NPH, present at the percent level in actual tank wastes either as a native component or introduced as a hydrostatic fluid, interferes with the purge-and-trap gas@chromatography/mass spectrometry (GC/MS) analysis of volatile components. Validation of the procedure was performed by analyzing blank spikes and actual, spiked single-shell tank waste samples. The NPH removal from actual waste samples and blank samples was better than 99%. This methodology could be easily extended to a sample matrix, such as water, sorbents, or soils, that contains excessive quantities of normal paraffin hydrocarbons.
INTRODUCTION Nuclear waste was generated a t the Hanford defense complex (Richland, WA) over its nearly 50 years of operation. The varied chemical operations that have taken place over that period have generated a wide variety of chemically heterogeneous wastes. For 35 years, the bulk of the aqueous waste was stored in 149 single-shelltanks (SSTs). For a little over a decade, waste has been stored in 28 double-shell tanks (DSTs), four of which contain double-shell slurry (DSS) that was produced by transferring and concentrating supernate from SSTs to minimize environmental intrusions caused by leaking SSTs. The wastes in DSTs and SSTs are highly radioactive and generally are mixtures of one aqueous phase and a large number of solid phases. The aqueous phase is generallyalkaline and contains varying amountsof complexing agents and other organics. Many of the SSTs are now being analyzed for volatile and semivolatile components. Volatile organic analysis of environmental samples by purge-and-trap gas chromatography/mass spectrometry (GC/ MS) is commonly used throughout many analytical laboratories.'-7 The EPA test method 8240-Gas Chromatography/ Mass Spectrometry (GC/MS) for Volatile Organics from SW8461-is applicable to nearly all types of samples, including 0003-2700/93/0385-2229$04.00/0
groundwater, aqueous sludges, caustic liquors, acid liquors, waste solvents, oily wastes, mousses, tars, fibrous wastes, polymeric emulsions, filter cakes, spent carbons, spent catalysts, soils, and sediments, regardless of water content. However, this method is not a good indicator of potential interferences from semivolatile components such as normal paraffin hydrocarbon (NPH). Attempts to employ typical methods for volatile analysis of waste samples from the Hanford tanks have resulted in substantial degradation of the analytical systems. In order to anticipate difficulties with the sample matrix, screening methods such as EPA method 3820-Hexadecane Extraction and Screening of Purgeable Organics-have been employed. This method involves extracting an aliquot of the sample with hexadecane and analyzing using gas chromatography/flame ionization detection (GC/FID) to determine whether the sample requires dilution prior to purge-and-trap GC/MS analysis. Both volatile and semivolatile analyses of SST waste samples have been plagued by the presence of NPH. NPH is a hydrocarbon oil, consisting primarily of n-C12, n-C13, and n-C14. NPH has been found in radioactive mixed waste from Hanford waste tanks at Richland, WA. either as a native component or introduced as a hydrostatic fluid. The hydrocarbon oil is used as the hydrostatic fluid to prevent the borehole from collapsing while core drilling for samples. These components interfere with the purge-and-trap GC/MS analysis such that the quantitative results can be compromised. The presence of large amounts of NPH significantly alters the retention times and response factors of targeted volatile organics. NPH contamination can occur throughout the purge-and-trap gas chromatographic system, acting as a liquid stationary phase, in the sampler bubbler, transfer lines, multiport valves, and desorption trap. In addition, semivolatiles take a considerably longer time to elute off a GC column system configured to analyze volatile components; as a result, the analysis time is longer. In the case of packedcolumn GC, it can take several hours to requilibrate a column. The common solution to reducing this interference is to dilute the sample. However, in some cases the NPH interference is so high a lOOOOX dilution is required. As a result, the detection limits are changed from the ppm level to the percent (1) Test Methods for Evaluating Solid Waste. Volume l B ,Laboratory Manual Physical Chemical Methods; SW 846, 3rd ed.; Unitad States Environmental Protection Agency, Office of Solid Waste and Emergency Response: Waehington, DC, Nov 1986. (2) Griest,W.H.;Schenley,R.L.;Tomkins,B.A.;Caton,J.E.;Fleming, G. S.; Harmon, S. H.; Garcia, M. E. Presented at Environmental American Chemical Society Exposition and 6th Annual Waste Testing and Quality Assurance Symposium, 1990; CONF-900758-2. (3) Word, W. E. Enuiron. Lab. 1991, (Feb/Mar), 42-45. (4) Washall, J. W.; Wampler, T.P. Am. Lab. 1990, (Dec), 38-44. (5) Charles, M. J.; Simmons, M. S. Anal. Chem. 1987,59,1217-1221. (6) Olynnyk, P.; Budde, W. L.; Eichelberger, J. W. J. Chromatogr. Sci. 1981,19,377-382. (7) Tomkins, B. A.; Caton, J. E.; Edwards, M. D.; Garcia, M. E.; Schenley, R. L.; Wachter, L. J.; Griest, W. H. Anal. Chem. 1989, 61, 2751-2756. 0 1993 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 05, NO. 17, SEPTEMBER 1, 1993
level. The interference may be reduced by optimizing the purge-and-trap unit so that NPH is less likely to contaminate the system. In addition, the presence of NPH also creates a problem for the analysis of semivolatile components.8 In this paper, we discuss a novel approach to separating potential semivolatile interferences from volatile analytes. A closed-system, solid-phase extraction is utilized as the cleanup method. This method is simple and inexpensive and minimizes loss of volatile components. The separation method also minimizes the potential adsorption of unwanted volatile species from the surrounding air during the cleanup procedure. The applicabilityof the method is demonstrated using blanks saturated with NPH and spiked with the 35 targeted EPA volatiles contained in method 8240. In addition, the separation method was also applied to actual SST samples. This method also provides a technique for reducing the radioactive level present in the SST samples prior to analysis by GUMS. The intent of this work is not to provide recoveries and precision for volatile organics over a range of conditions and analyte concentrations,but is rather a proof of principle. This methodology could be easily extended to any sample matrix, such as water, sorbents, or soils, that contains excessive quantities of normal paraffin hydrocarbons.
EXPERIMENTAL SECTION Reagents. The methanol used in this work was purge-andtrap quality or equivalent. The target compounds for the spikes and instrument calibration were prepared from Restek (Bellefonte, PA) analytical reference standards for EPA Contract Laboratory Program Methods mixes. The NPH was obtained from Westinghouse Hanford Co., Richland, WA. The area percentages, obtained from analysis by GUMS for the NPH constituents, were 18, 48, 33, and 1% for dodecane, tridecane, tetradecane, and pentadecane, respectively. Spiked blanks were prepared by adding each of the volatile analytes at a concentration of 50 pg/L X 625 dilution factor and with NPH at saturation. Solid-Phase Extraction Cartridge and Apparatus. An Environmental Cl8 Sep-Pak (Waters, division of Millipore Corp., Milford, MA) was utilized to separate the NPH. The closed cleanup system apparatus was modified somewhat during the final development. The initial study used 10-mL gas-tight syringes (Hamilton, Reno, NV); these were eventually replaced with 5-mL gas-tight syringes from the same manufacturer. The three-way valve, originally nylon, was replaced with a stainless steel valve and finally replaced with a Hamilton HV 1-1 two-way valve for use with radioactive samples. In the initial development, a 1-mL aliquot of the extract was introduced through the sample syringe, through the cartridge column, and into the volatile fraction receiving syringe while the eluent syringe valve was closed. The sample syringe was then closed,the eluent syringevalve opened, and a volume of methanoV water passed from the eluent solvent syringe into the receiving volatile fraction syringe to form a final volume of 5 mL. A 200pL aliquot was dispersed in a pure water matrix (5 mL) and analyzed by purge-and-trap GC/MS. However, in the final development, a 2-mL aliquot of the extract was introduced into the sample syringe and eluted with 3 mL of methanol/water to form a fiial volume of 5 mL. In addition, in the final development the volume analyzed by purge-and-trap GUMS was l00pL rather than 200 bL. SST Sample Preparation. Prior to use, an Environmental cl8 Sep-Pak cartridge was preconditioned by passing 5 mL of methanol, followed by 5 mL of 9010 methanol/water through the cartridge from a clean 5-mL Luer-lok, gas-tight syringe. The eluant was discarded. Approximately 1 g of sample was accurately weighed into a 20-mL volatile organic analysis (VOA) vial. A 5.0-mL solution of 90:10methanol/waterwhich had been spiked with the surrogate (8) Hoppe, E. W.; Campbell,J. A,; Stromatt, R. W. Development and Validation of a Cleanup Method for the Separation of Normal Paraffin Hydrocarbon(NPH)and SemivolatileOrganicCompoundsinRadioactive Tank Waste Samples. Submitted to Enuiron. Sci. Technol.
compoundsat the concentration specified in the defined analysis method was added to the sample. The compounds were spiked at a level equivalent to 50 pg/L X 625 dilution factor and with NPH to saturation. The vial was capped, shaken for 1min, and centrifuged. The mixture was transferred to a 5-mL vial and then stored for cleanup. A 2-mL aliquot of the sample mixture was slowly removed with a 5-mLsyringe. The needle was removed from the syringe; the sample syringe was then connected to a preconditionedSep-Pak cartridge. The other side of the cartridge was connected to a three-port, Luer-lok, two-way valve. A clean 5-mL syringe was attached to the other port on the valve. The 2-mL sample mixture was slowly pushed through the cartridge and into the receiving syringe. The cartridge was eluted with 3 mL of methanol/water to form a final volume of 5 mL. A 100-pL aliquot of the sample was then dispersed in 5 mL of pure water and analyzed by purge-and-trap GUMS. The preparation of the SST samples was performed in the hot cell facilities. The hot cell facilities are used for the preparation, e.g., sample dissolution, dilution, and solvent extraction and, occasionally,the analysisof nuclear wastes. For highlyradioactive wastes, e.g., 3-11 R/h, the hot cell must be used. This room is composed of thick walls (=1.3 m) equipped with a sample entry port, viewing windows (leaded glass and oil filled), and remote manipulators, which are operated by a highly trained specialist. When a radioactive sample is processed in the hot cell, the procedure is both time consumingand tricky. These procedures cannot be performed by just anyone, anywhere,in any laboratory, when highly radioactive samples are involved; special training is required. Sample turnaround is much lower when using the hot cell facilities. Wastes with low-to-moderate specific or total radioactivity, 51R/h, may be prepared and analyzed outside the hot cell in a radiation hood or glovebox. The actual cutoff levels which differentiate laboratory bench work, glovebox work, and hot cell work are usually based n local practice or the judgment of the resident health p h y s i c r Instrumentation. HPLC. The Waters Associates HPLC system was connected to an Environmental Sep-Pak CIScolumn andelutedwith 2.0mL/minmethanol/water (80:20). Theeffluent of the column was monitored using a Waters UV detector at 254 nm, intended for detecting acetone and the xylenes, and a Waters refractive index detector for detecting high concentrations of NPH. GC and GCIMS. The gas chromatograph flame ionization detector used for NPH analysis during the initial phase of development was a Hewlett Packard 5880A gas chromatograph equipped with a DB-5 column (J&W Scientific, Folsom, CA; 30 m X 0.25 mm i.d. capillary column 0.25-pm film thickness). A typical temperature program used was the following: 50 "C for 1 min, 50-280 "C at 8 "C/min, and then 280 OC for 10 min. Volatileanalyte analysiswas performedon a HP5880 GC (using a DB-624,30 m X 0.53 mm i.d., 3.0-pm film thickness, capillary column) and a HP 5987 mass spectrometer with an RTE-6 data system. Sample introduction was performed with a Tekmar LSC-2 purge-and-trap instrument. Analysis of radioactive tank waste was performed using a Tekmar LSC-3 purge and trap. Following the procedure, the trap was removed from the LSC-3 and replaced on the LSC-2 for desorption into the GUMS for analysis. The following temperature program was used: purge time 10 min, desorb 4 min at 180 "C, and then bake out for 5 min at 200 "C. The GC/FID used for NPH analysis was calibrated using a single-levelcalibration. The mass spectrometer mass calibration and tune parameters were adjusted using perfluorotributylamine (PFTBA)as a tuning compound. The linearity of the instrument was verified from an initial four-point calibration. A single-level continuing calibration was performed for a partial contract laboratory procedure (CLP) volatile target list of compounds each day of operation. Typical mass spectrometric parameters include source temperature 200 "C, interfaces 280 "C, 70-eV electron impact, and the electron multiplier at 2100 V. A 30 m X 0.25 mm i.d. (0.25-pmf i i thickness) DB-5gas chromatographic with a flow rate Of mL/min was used. The Oven temperature Was held at 40 "cfor 1min, Programmed to 280 "c at 8 "C/min, and held at 280 "C for 10 min.
ANALYTICAL CHEMISTRY, VOL. 65, NO. 17, SEPTEMBER 1, 1993
2231
2
u 12
16
20
24
28
Tlme (mlnutes)
32
36
40
44
48
52
Time (minutes) 57
40
.s .-
60
I
@
120
140
160
180
200
21 71
43
5
100
80
CI
E
141 I,
40
60
120
100
80
140
.
1u
71
1M I
160
I L 180 d
I
40
60
80
100
120
140
160
180
200
MIZ Flgure 1. (a) Total Ion chromatogram of NPH standard and (b) mass spectra of NPH.
RESULTS AND DISCUSSION The following discussion includes the initial development modifications to include the final development, and application of the cleanup procedure to spiked, actual waste samples. Initial Development. Figure l a is a total ion chromatogram of a sample containing NPH, and (b) is the corresponding mass spectra of NPH for C12-Cl4. Figure 2a is a total ion chromatogram after several samples containing large amounts of NPH have been analyzed by purge-and-trap GUMS. The degradation in chromatography is evident by the large hump from approximately 32 to 52 min as a result of residual NPH. Figure 2b is the mass spectrum characteristic of the broad hump. It is readily apparent from Figure 2a that NPH certainly affects the chromatography and must be removed to provide quantitative data for volatile analytes that elute with retention times in the range of 32-52 min. As illustrated in Figure 3, separation of acetone and xylene from NPH by high-performance liquid chromatography with a Cle cartridge column was obtained. Detection was accomplished with both UV for acetone and xylene and refractive index (RI) for NPH. Acetone and xylene were chosen because they represent the range of the EPA method 8240 targeted volatile compounds; acetone is one of the most volatile and xylene the least volatile. This indicated that substantial cleanup of NPH, at the solvent composition methanol/water (80:20),could be expected. Analysisof the same column eluent by GC/MS verified the removal of NPH.
85
j~h
98
99
/
Ah fib112I
.
127 141 151 170 dl II I d
I
20
I
hlvz Flgure 2. (a) Total Ion chromatogramafter several samples contalnlng NPH were analyzed and (b) mass spectrum representatbe of broad hump with retentlon tlme from 32 to 52 mln.
Time (rnlnutes)
Flgure 3. Chromatogram of acetone, xylene, and NPH eluted from a CIS column.
The closed-system apparatus is illustrated in Figure 4. In the initial development, the system was assembled using 10mL gas-tight Hamilton syringes. Two of the syringes are Luer-lok attached to a nylon three-way valve. The remaining Sepvolatile fraction syringe is Luer-lok connected to a Pak cartridge, which is in turn connected to the three-way valve. The sample is introduced through the sample syringe, through the cartridge column, and into the volatile fraction receiving syringe while the eluent solvent syringe valve is closed. The sample syringe is then closed, the eluent solvent syringe valve opened, and methanoVwater ( a 2 0 1passed from the eluent solvent syringe into the receiving volatile fraction syringe to form a final volume of 5 mL. The valve for the volatile fraction syringe is closed, and the contents are ready
2232
ANALYTICAL CHEMISTRY, VOL. 65, NO. 17, SEPTEMBER 1, l9Q3 26
Sample
+
1
Eluent Solvent
C 18 SepPak
Volrtlle Fractlon
4-
II
Figure 4. Closed system for volatile cleanup procedure.
Table I. Percent Recovery Results of a Partial Target List Standard after Cleanup Using the Initial Closed System 80% methanol compd std std + NPH name no, 1 2 3 4 5 6 7 8 9 10 11 12 13 14 16 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
bromochloromethane0 chloromethane bromomethane vinyl chloride chloroethane methylene chloride acetone carbon disulfide 1,l-dichloroethene 1,l-dichloroethane trans-l,2-dichloroethene
cis-1,2-dichloroethene chloroform 1,2-dichloroethane-ddc 1,8dichloroethane 2-butanone l,l,l-trichloroethane carbon tetrachloride vinyl acetate bromodichloromethane 1,4-difluorobenzenea 1,2-dichloropropane cis-1,3-dichloropropene trichloroethene dibromochloromethane 1,1,2-trichloroethane benzene trane-1,3-dichloropropene
bromoform chlorobenzene-ds0 4-methyl-2-pentanone 2-hexanone tetrachloroethene
100.0 NAb 332.8 NA 62.4
82.0 133.8
10.2 19.0 34.0
100.0 NA
97.2 NA
78.4 104.2 177.4 17.2
35.8
NA
64.4 48.4 NA 72.4 NA
48.8
86.6
218.2 12.4 7.0 103.4
298.0
24.4 NA
39.2
38.0 100.0 27.2 32.6
12.0 33.6 39.8
26.0 NA NA
100.0 51.0
1,1,2,2-tetrachloroethane
28.8 18.2 26.2
toluene toluene-dsc chlorobenzene ethylbenzene styrene p-xylene o-xylene bromofluorobenzenec
NA 10.4 9.2 8.2 NA 2.0 NA
10.0
22.8
11.4 132.6
70.0
100.0
52.6 61.4
20.8 63.8
70.8 49.2 NA NA
100.0 86.2
51.8 20.5 54.6 17.6 NA 19.8
5.2
7.6 NA 0.0 NA
a Compound is an internal standard. b NA, not analyzed. Compound is a surrogate spike.
for analysis. The closed-system apparatus was modified somewhat during the final development. The 10-mLsyringes were replaced with 5-mL syringes and the three-way nylon valve was subsequently replaced with a stainless steel valve. Table I showsthe recoveries obtained from the partial target list standards with and without NPH. The standards used the initially developed cleanup procedure and employed a 1-mLsample introduction. They were eluted with methanol/ water (8020) to a fiial volume of 5 mL. The results show that generally the compounds with lower relative polarity exhibit lower recovery, indicating the need for a less polar eluting solvent composition. However, the presence of NPH
20
40
80
80
100
%methanol
Figure 5. Solubility of NPH solutions at 21 O C .
measured in various methanoVwater
during this experiment apparently improved recoveries. This could indicate a stationary-phase loading effect from NPH. The NPH competes for the less polar adsorption sites of the stationary phase in leaving the polar mobile phase. This in turn forces more of the analyte to the mobile phase. This also introduces a differing equilibrium between the new stationary phase and the mobile-phase components. This effect is most conspicuous when the loading capacity of the column is approached. The recoveries exceeding 100%, found primarily among the ketones, are presumably from contaminated methanol. Ketones are typical contaminants of methanol and the relatively large quantity of this solvent employed during this analysis magnifies the complication. Final Development. Initial familiarization and testing during this phase of the study revealed that a portion of the analyte losses were due to the use of a nylon valve employed in the closed cleanup system. Prior to solvent optimization studies,replacement with a stainless steel valve and eventually a Hamilton Teflon-lined valve improved recoveries. Blank spikes containing the full volatile target compound list were loaded onto the C18 cartridge cleanup column and eluted using 80,85,and 90% methanol in water to determine the optimum column mobile-phasecompositionfor maximum analyte recovery. The best recoveries were obtained with 90% methanol. The recoveries of the compounds with relatively lower polarity, such as the xylenes and benzenes, improved substantially. A solubility study was performed by saturating various methanol/water compositions and measuring the NPH present to determine the potential loading of NPH onto the cleanup column. Figure 5 shows the results of the solubility study. At 80 % methanol, the solubility of the NPH was very low. The capacity of the cartridge column, as provided by the manufacturer, is -10 mg and will not be exceeded until the concentration of methanol is -96 % . Blanks were spiked with NPH and eluted through a cartridge column to assess the ability of the cartridge column to remove NPH in various methanol/water solvent compositions. The elution solvent composition was varied a t five different levels between 80and 100% methanol. The amount of NPH present in the column eluent was then measured. Figure 6 shows that no measurable quantity of NPH was present a t 90 % or less methanol in water. At 95% methanol, 0.43 % recovery of the NPH was measured. The purge-andtrap and GC/MS system would receive -600 ng of NPH per sample based upon the following considerations: (1) The solubility of NPH in 95% methanol at 21 O C is -7000 pg/mL. (2) The amount of the extractant employed in the cleanup process is 1mL. (3)The amount of methanol that is currently used in the analysis is 200pL, which is dispersed in the normal 5 mL of pure water matrix for purge-and-trap GC/MS.
ANALYTICAL CHEMISTRY, VOL. 65, NO. 17, SEPTEMBER 1, 1993
R
P
8
e
Table 11. Percent Recovery Results Obtained from a Blank Spike Extraction, Followed by the Cleanup Procedures Using 90% Methanol. high
compd
MeOH blk
extracted blk spike
cleaned
no.
blk spike
procedure effect
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
100.0 0.0 0.0 0.0 0.0 0.0 29.9 0.0 0.0 0.0 0.0 0.0 0.0 104.5 0.5 35.8 0.0 0.0 0.0 0.0 100.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.9 100.0 9.2 11.6 0.0 3.4 0.0 107.0 0.0 0.0 0.0 0.0 0.0 103.9
100.0 91.0 98.0 91.9 96.5 90.3 72.1 85.6 96.3 102.8 104.7 105.6 106.8 107.8 106.1 71.2 102.5 101.3 101.7 103.4 100.0 101.5 102.2 100.2 95.1 103.0 99.1 90.8 85.0 100.0 93.8 92.0 111.8 102.3 110.2 111.6 110.8 109.1 111.5 109.8 105.4 105.4
100.0 70.3 78.7 59.2 73.6 96.6 133.0 47.4 60.5 99.8 97.7 104.6 108.1 108.4 109.0 107.6 99.5 96.4 105.5 108.3 100.0 99.3 104.9 96.4 94.9 104.2 90.8 92.3 91.9 100.0 104.5 110.1 113.8 110.1 113.7 114.2 115.5 114.5 112.6 115.0 108.9 111.6
0.0 -20.7 -19.3 -32.7 -22.9 6.4 60.9 -38.2 -35.9 -3.0 -7.0 -1.0 1.3 0.6 2.9 36.4 -3.1 -4.8 3.8 4.9 0.0 -2.1 2.7 -3.9 -0.2 1.2 -8.3 1.5 7.0 0.0 10.7 18.1 2.0 7.8 3.5 2.5 4.7 5.5 1.1 5.2 3.6 6.2
I
t 60
8 40
20
75
80
85
80
85
100
Yo methanol
Flgure 6. Percent recovery results after column cleanup for various methanollwater solutions.
Retention of this amount of NPH would be cumulative and therefore devastating to the purge-and-trap GUMS over time. Therefore, 90% methanol in water was chosen as the composition of the mobile phase. No measurable amount of NPH should be observed using the 90% methanol solvent composition. Table I1 shows the results for a blank, extracted blank spike, and the same blank spike after performing the cleanup procedure using 90% methanol as the eluting solvent and analyzing 200 pL of the eluent. The difference is presented as the effect of the cleanup procedure. The most volatile and polar analytes show the greatest losses, as much as 38%, although most recoveries are quite satisfactory. The ketone recoveries show an increase due to their presence in the methanol. This contamination is best identified by inspection of the corresponding blank results. It was also necessary to determine the maximum amount of methanol that could be introduced into the purge-andtrap G U M S system without measurable chromatographic degradation. This is related to the maximum volume of cleaned extract that may be analyzed. Figure 7 shows the effect of 10, 100, 200, and 300 p L of methanol on the chromatography of chloroform. The results are quite obvious: less methanol in the purge vessel results in better chromatography. Based on these results and the chromatographic performance of other compounds, the amount of methanol extract that is purged should not exceed 100 pL. Additionally, the same limit exists for the EPA mediumlevel analysis. Rather than allow the dilution of the method to become higher, it was proposed that 2 mL (instead of 1mL) of the extraction mixture would be introduced into the cleanup cartridge column. The amount of methanol for analysis could then be reduced from 200 pL, as used previously, to 100 pL; the overall dilution would remain the same, 625 for a 1-g sample. This would also reduce the rnethanoVketone contamination difficulties as described earlier. The results indicated the contamination was reduced as expected. The dilution factor is obtained by taking a 1-g sample and extracting with 5 mL (1:5), 2 mL of extraction mixture and diluting to 5 mL (2:5), and then removing 100 p L for purgeand-trap analysis (100 pL/5 mL). The total dilution factor obtained was 625. When 2 mL of the extract was used, the small 0.5-mL rinses of the sample syringe became even more important in order to flush the compounds through the cartridge in a narrow band to yield good recovery. The 90 % methanol worked very well at eluting the target compounds while permitting the Environmental Cle Sep-Pak cartridge to retain the NPH, even though high levels of NPH were present in the original sample. The 90% methanol ratio permits use of a 1-g sample with 0-100% moisture. For example, if the sample consisted of
2239
a
A 200-pLaliquot wm used for analysis.
f 12.0
11d
13.0
12.0
12.6
13.0
13.5
14.0
14.6
16.0
15.6
12.0
12.6
13.0
13.5
140
14d
16.0
16.5
11.0
121)
13.0
11.6
14.0
14d
16.0
16d
13d
14.0
14d
16.0
16d
2
f
n m (minutni
n m (mrrut"1
Flgure 7. Chromatograms Illustrating effects of (a) lo-, (b) 10% (c) 200-, and (d) 3 0 0 - ~ Lpurge volumes of methanol on chromatography
of chloroform.
100% moisture, the extraction mixture would be 75% methanol, which will still permit good recovery of the target compounds during the extraction process. In contrast, if a
ANALYTICAL CHEMISTRY, VOL. 65, NO. 17, SEPTEMBER 1, 1993
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Table 111. Percent Recovery Results and Matrix Effect for BllO Sample
compd. no.
sample
spike
spike duplicate
matrix effect
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
100.0 22.1 8.7 0.0 0.0 0.0 6.5 0.0 0.0 0.0 0.0 0.0 0.0 87.4 0.0 0.0 0.0 0.0 0.0 0.0 100.0 0.0 0.0 0.0 0.0 0.0 0.3 0.0 0.0 100.0 0.0 0.0 0.0 0.0
100.0 4.6 35.1 41.2 51.4 85.0 45.0 38.1 65.3 87.4 76.9 92.0 95.1 84.9 83.1 36.0 88.6 84.6 0.0 90.9 100.0 88.1 90.1 93.7 73.9 70.6 80.0 70.6 70.5 100.0 35.7 28.9 69.7 38.6 80.8 76.1 85.5 79.0 78.3 75.9 89.8 85.9
100.0 34.8 42.6 48.2 57.9 94.8 45.4 44.0 74.4 95.8 87.5 102.7 106.3 96.0 96.5 43.8 95.3 90.1 0.0 102.9 100.0 95.4 97.0 99.9 84.2 80.4 89.7 76.9 81.9 100.0 38.2 31.0 73.4 40.1 80.9 78.1 88.0 82.1 82.4 74.4 78.1 80.0
0.0 -60.1 -43.7 -22.7 -18.1 4.6 -67.7 -12.6 5.4 7.6 -5.7 6.5 6.7 -5.1 -1.8 -71.0 4.5 3.1 -81.1 7.4 0.0 -4.2 -9.7 1.0 -21.5 -21.9 -8.2 -13.3 -17.6 0.0 -70.8 -70.9 -21.6 -64.8 -36.1 -29.0 -14.0 -17.8 -19.1 -20.7 -13.5 -20.6
16 17
18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
5.1 75.6 0.0 0.0 0.0 0.0 0.4 78.4
sample with 0% moisture is extracted, the 90% methanol extract will still allow the NPH to remain on the Sep-Pak cartridge.
APPLICATION Evaluation of the initial and final development yielded a set of parameters for use in the column cleanup procedure. These empirically derived parameters were verified experimentally by analyzing spiked blanks and measuring recoveries. Application of the cleanup procedure was performed on actual waste samples by analyzing blank spikes and spiked SST samples. The results obtained from G U M S analysis of SST sample BllO are provided in Table 111. The matrix effect is supplied as well. The matrix effect is calculated by subtracting the blank spike results from the mean of the sample spikes results. Therefore, a negative number represents the loss that can be expected as a result of the matrix effect of this sample relative to analysis of a blank spike. Figure 8a is a total ion chromatogram of the blank spike with 90 % methanol through the cleanup procedure, and (8b) is a total ion chromatogram of spiked core sample with 90 % methanol through the cleanup procedure. The chromatography is much improved compared to the chromatography illustrated in Figure 2a. The constituentsa t the retention times of 9,14, and 16min and marked by asterisks are siloxanes, presumably from the silicone lubricant used during drilling operations. Complete loss of vinyl acetate (19) was observed for SST sample BllO and is
4
8
12
4
8
12
16 20 Time (minutes)
20
rime (minutes)
24
32
28
I B
32
Figure 8. Total ion chromatogramsfrom (top)purge-and-trapGC/MS of blank spike through Sep Pak and (bottom)spiked core sample. Peak numbers refer to compounds listed in Tables I-IV. Siloxanes.
illustrated in Figure 8b. Similar results were obtained for SST sample U110 and are shown in Table IV. The matrix effect was substantial for both samples, although the effect of UllO was noticeably more severe. Essentially complete loss of 1,1,2,2-tetrachloroethane,carbon disulfide, and vinyl acetate was observed in sample U110. Under the alkaline conditions for this sample, approximately pH 12, it is postulated that 1,1,2,2-tetrachloroethaneunderwent base elimination of HCl to yield trichloroethylene (TCE). This is substantiated by the elevated recovery of TCE of =185 % . This was also observed in the same-day and 12-day analyses for sample U110. Results from analysis after 12 days also indicated that 1,1,2-trichloroethanehad undergone similar degradation to form 1,l-dichloroethene. The 1,l-dichloroethene yield is not as quantitative as the TCE, so it must be assumed that a competing reaction or further degradation is taking place. The reaction kinetics of the tetrachloroethane to TCE conversion are much faster than with the trichloroethane to dichloroethene conversion. In addition to these elimination reactions, other decompositions were observed. Chloromethane and bromomethane exhibited low spike recoveries, more so under the alkaline conditions of sample U110. Interestingly, the recovery for bromomethane was lower than for chloromethane. This observation is consistent with the expectation that the bromide ion is a better leaving group than is the chloride ion. Chloromethane and bromomethane were also observed in the extracts of sample B110. However, this observation may be an artifact due to the possibility of degradation of the first internal standard, bromochloromethane,to these compounds. Responses for bromochloromethane were as much as 20% low during analysis of B110. This effect cannot be directly associated with alkalinity because the pH of sample BllO was 9.5. Sample UllO was more alkaline, pH 12, but the bromochloromethane response was not noticeably affected; however, both chloromethane and bromomethane were not observed. Other compounds that seem to exhibit alkali sensitivity are vinyl acetate, vinyl chloride, and carbon
ANALYTICAL CHEMISTRY, VOL. 65, NO. 17, SEPTEMBER 1, 1993
Table IV. Percent Recovery Results and Matrix Effect for SST UllO S a m ~ l e compd no. sample spike spike duplicate matrix effect 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
100.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
89.0 0.0 3.0 0.0 0.0 0.0 0.0
100.0 0.0 0.0 0.0 0.0 0.0 0.5 0.0 0.0 100.0 0.0 0.0 0.0 0.0
15.4 101.2 0.0 0.0 0.0 0.0 0.8 103.0
100.0 58.5 57.4 43.5 71.8 103.6 44.7 0.0 118.7 97.9 89.5 99.8 102.4 90.7 90.3 38.3 98.5 97.2 0.0 99.6 100.0 99.9 104.2 188.6 83.1 30.7 97.8 80.4 57.4 100.0 46.3 37.2 95.0 0.0 99.9 101.4 103.9 99.6 102.1 100.7 113.9 104.9
100.0 57.1 67.0 48.4 71.8 105.0 52.8 0.4 91.6 99.6 91.5 102.6 105.2 95.3 92.8 44.4 98.4 98.0 0.5 101.6 100.0 101.8 106.7 183.8 87.4 60.2 98.2 83.5 65.5 100.0 50.2 43.0 100.3 0.0 102.5 105.3 104.7 103.0 104.6 101.1 117.7 104.7
0.0 -42.2 -37.8 -54.0 -28.2 4.3 -51.3 -99.8 5.1 -1.3 -9.5 1.2 3.8 -7.0 -8.4 -58.7 -1.6 -2.4 -99.7 0.6 0.0 0.8 5.4 86.2 -14.8 -54.6 -2.0 -18.1 -38.6 0.0 -51.8 -60.0
-2.4 -100.0 1.2 3.4 4.3 1.3 3.3 0.9 15.8 4.8
disulfide, which were decomposed by the tank sample matrix. The effect of chelation is beyond the scope of this work; however, chelators are known to exist in many of the tank wastes, are typically used to complex with metal cations, and will thereby increase the effective alkalinity (and nucleophilicity) of anions. Additionally, to assess extractant storage possibilities, same-day analyses of a blank spike and SST-spiked sample UllO were compared to analyses performed 12 days later on the same residue (data not shown). Methylene chloride showed the greatest loss, although all the compounds compare adequately with the original analysis. Toluene showed an increase of almost 27 9%. These data are viewed as an anomaly as calibration data seem reasonable for each day of analysis and holding blanks from the refrigerated storage have not revealed toluene contamination problems. The same storage time study was performed using a residue from SST sample U110. This sample showed a substantial change in results between the two analyses. While there are considerablelosses for many compounds, it seems unreasonable to believe that an analyte native to this sample would not have undergone similar processes long before this analysis.
CONCLUSIONS Samples obtained from the Hanford SSTsare contaminated
2235
sampling process or native to the tank waste. The contamination is usually high enough that a dilution of up to 4 orders of magnitude was required before the sample could be analyzed by the conventional methodology of purge-and-trap concentration followed by gas chromatography/mass spectrometry. To eliminate this problem, use of this sample extraction and cleanup method is encouraged and is summarized as follows: an aliquot (nominally 1g) of the sample was extracted with 5 mL of methanol/water (90:lO) containing the EPA CLP surrogate compounds. A 2-mL aliquot was eluted through a CU Sep-Pak cartridge and followed by 0.5mL rinses until a final volume of 5 mL was obtained. A 100p L sample of the eluent was transferred to a purge vessel containing 4.9 mL of water. Internal standards were added to the purge vessel and purge and trap extracted following the EPA method or a similar procedure. The final dilution incorporated into this method was 625-fold. The effectiveness of this cleanup method was demonstrated for all of the volatile target list compounds in the Contract Laboratory Program Statement of Work (CLPSOW).g Both blanks and SST samples spiked with all of the target compounds and NPH were used in the development and validation studies. The NPH removal for samples and blank spikes was better than 99 % . The recoveries were excellent for most of the target compounds in blank spikes and satisfactory for all compounds, although lower for the more volatile compounds. The blank spike residues were shown to store well for up to 12 days. The SST sampleswere observed to have a substantial matrix effect on recovery of the gases, ketones, and saturated compounds that are halogenated. Advisory quality control limits from tank waste data were established for the surrogate and matrix spike compounds. There are several advantages to employing this procedure. The first and most obvious was the removal of NPH. The cleanup method has worked well to remove large amounts of NPH from the samples. According to G U M S analysis, tank sample extracts analyzed by this procedure had less than detectable amounts of NPH in them. These samples originally contained a level of NPH that analysis without this cleanup would require a t least a 5000-1OOOOX dilution factor. A second advantage was that the methanol extracts of the samples contain a much lower radioactivity level than the original samples. For example, the radioactivity of some of the samples was measured at ;=lo00 mR/g. In contrast, the 5-mL extracts of these samples were less than 1mR each in radioactivity. A third advantage was that, following extraction, the residue may be stored for up to 12 days. This allows for better optimization of analytical batch sizes and resource planning. As more data are obtained using this cleanup method, required quality control limits will be implemented and a better definition of cleanup effectiveness can be established. If this technique is to become an accepted methodology, each laboratory would determine precision and recoveries for each volatile analyte at several concentrations. This method should be applicable to other matrices, such as water, adsorbents, or soils, that contain excessive amounts of NPH.
ACKNOWLEDGMENT This work was supported by the Department of Energy under Contract DE-AC06-76RLO 1830. Pacific Northwest Laboratory is operated by Battelle Memorial Institute. The authors also thank Scott Harvey and for many helpful suggestions. In addition, the authors thank Westinghouse Hanford Co. for support of this work.
with NPH either introduced as hydrostatic fluid from the (9) PNL-LO-335,GCIMS Analysis of Volatile Organic Compounds;
Rev. 0, Pacific Northwest Laboratory, Technical Procedure, 1989.
RECEIVED for review February 1, 1993. Accepted May 27, 1993.
