2904
Anal. Chem. 1904, 56,2984-2987
Oxidative Losses of Anthracene, Acenaphthylene, and Benzo[ a Ipyrene during Florisil and Silica Gel Cleanup Using Diethyl Ether Containing Peroxides Sir: In the analysis of samples for nonpolar trace organic compounds, a cleanup procedure is often required to remove interfering compounds. Columns of Florisil (magnesium silicate) and silica gel (silicic acid, Si02.nH20) are frequently used for this purpose. Many procedures based on these materials have been reported which allow the cleanup of samples containing compounds such as the polychlorinated biphenyls (PCBs) (1,2).If samples are to be analyzed with a capillary gas chromatograph/mass spectrometer/data system (GC/MS/DS), however, it may not be necessary to completely eliminate all compounds which coelute with the target analytes during the GC chromatogram. Rather, the selectivity of the MS may allow less stringent cleanup, and it may be advantageous to modify the solvent elution step in the cleanup procedure so as to allow the recovery of a wider range of neutral compounds (e.g., pesticides to polycyclic aromatic hydrocarbons (PAHs)). As always, however, any such modifications must be carefully examined to ensure that the recoveries of all target and internal standard compounds remain high. Good recoveries for the latter are of obvious particular importance. Occasionally, the occurrence of unexpected and undesired processes may be detected and eliminated before the modification is incorporated into ongoing analytical protocols. This paper describes such an experience involving acenaphthylene, benzo[a]pyrene, anthracene, and anthracene-dlo. The last compound has been recommended for use as an internal standard (IS) compound (3). Toward the goal of the development of a cleanup method which would allow the recovery of a range of neutral compounds following the extraction of filters used to sample ambient air, Florisil column chromatography was tested using solvent mixes of pentane and diethyl ether. Hexane:diethyl ether has been recommended for use in the cleanup of pesticide-containing extracts (4). Pentane was substituted here for hexane because of its greater volatility. It was hoped that the pentane:diethyl ether solvent mix ratio could be adjusted to allow the simultaneous recovery of the PAH compounds in the same eluent fraction. Recovery studies were carried out using a standard solution of pesticides and PAHs. EXPERIMENTAL SECTION All solvents were glass-distilled (Burdick and Jackson, Muskegon, MI). The 60/80 mesh, PR grade Florisil (Alltech ASSOC., Deerfield, IL) was activated by heating for 16 h at 150 OC. The 100/200 mesh silica gel (Fisher Scientific, Fairlawn, NJ) was activated in the same manner. The anthracene-dIo and acenaphthene-dlo (KOR Isotopes, Cambridge, MA) possessed a stated purity of greater than 99%. The PAH and pesticide standard materials were obtained from Chem Service (West Chester, PA). Peroxide test strips were obtained from EM Science (Gibbstown, NJ). The glass fiber filters (GFFs) (Gelman, Inc., Ann Arbor, MI) were precleaned by solvent extracting for 24 h in 5050 acetone:methylene chloride, and then baking for 3 h at 400 "C in a muffle furnace. Two sets of experiments were conducted. In the f i t set, a 200-pLaliquot of recovery standard in acetone containing 20 pg of the compounds listed in Table I was injected onto a GFF. The compounds acenaphthene-dlo, phenanthrene, fluoranthene, and chrysene were chosen to serve as internal standards, due to their comparative stability toward oxidation. These compounds demonstrated aveiage absolute recoveries of 62,78,84, and 68% over the entire extraction/cleanup procedure to be described. After being loaded with the recovery standard, 0003-2700/84/0356-2984$01.50/0
the GFF was Soxhlet extracted with 5050 acetone:methylene chloride for 1 h. The extract was concentrated to 1 mL with a Kuderna-Danish apparatus and then to 200 pL by nitrogen blowdown. Recoveries were determined for the extraction step by analyzing the extract at this stage by GC using a HewlettPackard 5880A capillary GC equipped with a flame ionization detector (FID) set at 325 O C . A 30 m, 0.25 mm i.d. SE-54 fused silica capillary column (J&W Scientific, Rancho Cordova, CA) was used with a carrier gas linear velocity of 30 cm/s (at ambient temperature). A 2.0-wL portion of the extract was injected splitless (injector temperature, 275 O C ) . The GC temperature program used was as follows: hold at 100 "C for 0.7 min and then program to 300 O C at 7 OC/min. The extract was then applied to the top of a 1.0 cm diameter, 8.0 cm long Florisil or silica gel column and eluted with 20 mL of 5050 pentane:diethyl ether. The eluent was reconcentrated to 200 pL and analyzed again as described above. Most runs were carried out under bright lighting conditions. "Dim lighting" constituted being shielded in a hood with both hood and room lights off. Elutions were carried out with two separate bottles of diethyl ether, one of which was freshly opened. Similar experiments were conducted with 60:40 pentane:methylene chloride as the elution solvent. In the second set of experiments, the stabilities of the PAH compounds in 5050 pentane:diethyl ether solution and in acetone were monitored for a period of 1week. Separate solutions were prepared with the two bottles of ether described above. Solutions were stored in either clear 3-mL Reacti-vials (Pierce Chemical, Rockford, IL), or amber Reacti-vialsto protect them from room light. Aliquots of the solutions were analyzed periodically by GC/FID as described above. Analyses by GC/MS/DS involved a 30 m, 0.25 mm i.d. SE-54 fused silica capillary column (J&W Scientific) in a Finnigan 4000 GC/MS/DS (Sunnyvale, CA). The chromatographic conditions used were as follows: carrier gas linear velocity, 50 cm/s (at ambient temperature); MS scanning from 60 to 450 amu in 1s; splitless injection (injector temperature, 300 "C); and GC temperature program, 50 OC to 320 "C at 10 OC/min. The transfer line, source, and MS manifold temperatures were maintained at 250 O C , 250 O C , and 100 "C, respectively. The electron multiplier was set at 1700 V.
RESULTS AND DISCUSSION Although the diethyl ether was preserved with ethanol against the formation of peroxides, testing revealed a peroxide level of -0.5 mg/L in the bottle which had been open for approximately 4 months. No peroxides could be detected in the freshly opened ether bottle. Recovery data from the extraction and cleanup experiment with 5050 pentane:diethyl ether containing peroxides are presented in Table I. The recoveries of all the PAH and pesticides were very good for the 5050 acetone:methylene chloride GFF extraction step, but losses of up to 75% occurred during the cleanup step for the compouads acenaphthylene, benzo[a]pyrene, anthracene, and anthracene-dlo. A single run carried out with 50:50 pentane:diethyl ether/silica gel gave very similar results. Since no differences were observed between the results obtained under bright and dim lighting conditions with Florisil, photochemically induced degradation does not seem to provide an explanation for the losses here. The 10 mL of diethyl ether used in the 50:50 pentane:diethyl ether experiments corresponds to 5 Kg of peroxides per cleanup. Since this level is comparable to the 20 pg per compound involved in the recovery studies, there would have been adequate peroxides to cause the types of losses observed during the cleanup procedure. 0 1984 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 56, NO. 14, DECEMBER 1984
2985
Table I. PAH and Pesticide Recoveries after GFF Extraction with 5050 Acetone:Methylene Chloride and Subsequent Florisil Cleanup with 5050 Pentane:Diethyl Ethera
compound acenaphthylene acenaphthene
1 1 2 2, 2 2 2 3 3 4
fluorene Q-HCH
9-fluorenone anthracene anthracene-d,, pyrene P,P'-DDE benzo [a]pyrene
recovery (%) after cleanup f 1s bright light dim light
recovery (%) after extraction f 1s bright light dim light
int std
94 f 10 (6)
101 (1)
101 f 3 (5) 106 f 11 (6) 102 f 7 (4) 98 f 9 (5) 101 f 4 (5) 98 f 2 (6) 102 f 5 (6) 103 f 12 (5) 95 i 22 (6)
NI
41 f 12 (5) 95 f 5 (5) 86 f 13 (5) 97 f 7 (5) 98 f 4 (5) 52 f 12 (5) 50 f 11 (5) 98 f 11 (15) 110 f 8 (5) 24 f 13 (5)
112 (1)
NI NI NI 102 (1) 104 (1)
NI 106 (1)
Diethyl ether contained 0.5 mg/L peroxides. Internal standard compounds: 1, acenaphthene-d,,; 2, phenanthrene; 3, fluoranthene; 4, chrysene. Recovery values are fl standard deviation. The numbers in parentheses after the recoveries are the numbers of recovery experiments. NI = not included in the recovery standard for that run. Table 11. Dependence of PAH Recoveries during Florisil Cleanup Step on Pentane:Diethyl EthecMethylene Chloride Proportions and Peroxide Content of the Ethera
31.57
321
i\
recovery (%) compound acenaphthylene anthracene-dlo
int std
fluorene pyrene
1 2 2 3
benzo[a]pyrene
4
50500 0.5 mg/L perox (6) 40 i 10
51 f 10 86 f 12 96 i 10 24 i 13
50:500
60040
