Anal. Chem. 1988, 58, 2412-2414
2412
change separation. With the exception of Th, Zr, and Hf, which are not, and the lanthanides, which are partially eluted, they accompany titanium during elution with 2 M nitric acid. Since these elements are present only in trace concentrations, they easily can be complexed during the determination step by the addition of the reagents described and their interference avoided. The heavy alkalis also accompany titanium but do not interfere, while the light alkalis are retained only partially during the absorption step. Anion-forming elements such as vanadium and tungsten accompany molybdenum. Method of Determination. The method of determination with Tiron is an adapted version of that described by Clark (9). The sequence in the addition of EDTA and citrate has been reversed and the amounts of EDTA, dithionite, and thiourea have been considerably reduced because other elements are present only as traces. Molybdenum also forms a yellow color with Tiron. Though this color formation is suppressed by the presence of citrate, a small correction nevertheless had to be applied in some cases. The correction applied was 0.15 pg of titanium subtracted for every 10 pg of molybdenum present (as determined by atomic absorption). Corrections were only applied in cases where more than 10 pg of molybdenum was found to be present. Sample Dissolution. A small amount of nitric acid (5 mL of 2 M acid) plus hydrogen peroxide dissolved all samples analyzed. The excess acid will have to be removed by evaporation and the moist residue dissolved in water plus hydrogen peroxide to have a sufficiently low acid concentration, in cases where larger amounts of nitric acid should be required (large pieces of metal) (7)). The amount of phosphoric acid will also have to be controlled carefully and the concentration adjusted
by dilution because phosphoric acid mobilizes titanium on the column as shown in Figure 2. It should be pointed out that the presence of large amounts of molybdenum also contributes to the mobilization of titanium and causes it to be eluted even earlier than indicated on Figure 2 for the absence of molybdenum. Larger columns or even columns of AG50W-Xl2 resin may be required when the presence of considerable amounts of phosphoric acid cannot be avoided. Blank Values. While the values for titanium in blank runs for the analysis of synthetic mixtures and the molybdic acid sample were quite low at 0.4 f 0.1 pg, they increased markedly to about 2.2 f 0.2 pg when the blank run included the separation of a precipitate and ashing of a filter paper. The additional titanium could be traced to the filter papers. Ashing five filter papers in a platinum crucible and determining titanium in the ash gave a result of 9.8 pg of titanium or 2 pg per filter paper. Registry No. Moo3, 1313-27-5;HzOz,7722-84-1;Ti, 7440-32-6; Mo, 7439-98-7; Tiron, 149-45-1; molybdic acid, 27845-90-5.
LITERATURE CITED ,
(1) Bandi, W. R.; Buyok, E. G.: Lewis, G. G.; Melnick, L. M. Anal. Chem. 1981, 33, 1275. Shakashiro, Mouffac; Freund, Harry Anal. Chim. Acta 1985, 3 3 , 597. DonaMson, Elsie M. Talanta 1989, 16, 1605. Aiimarin, 1. P.; Medvedeva, A. M. Zavod. Lab. 1955, 21, 1416. Fritz, James S.;Abbink, J. E. Anal. Chem. 1962, 3 4 , 1080. Strelow, Franz W. E. Anal. Chem. 1963, 35, 1279. Spano, Ernest F.; Green. Thomas E. Anal. Chem. 1966, 38, 1341. Strelow, Franz W. E.: Rethemeyer, Ruthild; Bothma, C. J. C. Anal. Chem. 1965, 37, 106. (9) Clark, Lewis J. Anal. Chem. 1970, 42, 694.
(2) (3) (4) (5) (6) (7) (8)
RECEIVED for review March 13,1986. Accepted May 22,1986.
Determination of C,-C, Alcohols in Gasoline Using Multiple Ion Detection James H. Shofstahl and James K. Hardy*
Department of Chemistry, University of Akron, Akron, Ohio 44325
A method for the determination of C1-C4 alcohol content In gasoline by capillary column gas chromatography-ion trap detector system (GC-ITDS) Is described. The method Involves the direct Injectlon of gasdine into the GC-ITDS, and subsequent detectlon of the alcohols uslng the multiple Ion detection method. The detection method uses the rnass-tocharge ratio peaks at 31 and 45 for the quantlflcatlon of the alcohols. 1-Pentanoi Is used as an Internal standard. The method was evaluated over the range of 0-20 % for methanol and ethanol and 0-1% for 2-propanol, I-propanol, 2methyl-2-propanol, Imethylpropanoi, 2-methylpropanoi, and 1-butanol. Detectlon limits for each of the alcohols are less than 0.1 YO.
The characterization of oxygenated compounds added to gasoline has become more important as these compounds are used to boost the octane ratings in unleaded fuels. Although the presence of small amounts of alcohol in gasoline can be beneficial to the performance of the engine and can assist in
the elimination of water in gasoline, the presence of large amounts of alcohol in the gasoline can have a harmful effect (1). The state of Ohio, like other states ( Z ) , regulates the amount of alcohol added to gasoline. According to the Ohio Consumer Sales Protection Act and Substantive Rules, Section 109:4-3-18 (3) the total amount of alcohols in commercially retailed gasoline, methanol and ethanol, of any alcohol with a higher boiling point than these two alcohols, is limited to a maximum of 0.3% of the total volume in Ohio. If the dealer posts the alcohol content of the gasoline, then the gasoline may contain a total alcohol content not exceeding 10% of the gasoline’s volume (3). Of the previous methods of analysis for alcohol/gasoline mixtures, the majority involve the use of gas chromatography (4-7). Lockwood and Graddock described a method that uses multiple columns and back flushing to separate the alcohols from the remaining matrix (8). Another method of multidimensional chromatography is described by Johansen (9). A procedure involving liquid chromatography has been reported (10). Recently the determination of methanol in gasoline by NMR spectroscopy has been reported (2). A
0003-2700/86/0358-2412$01.50/0 0 1986 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 58, NO. 12, OCTOBER 1986
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Table I. Ion Trap Operation Conditions scan mode mass values seconds/scan multiplier voltage transfer iine temperature transfer line temperature peak threshold filament delay delta tune mass defect
multiple ion 31, 45 0.25 1350 250 "C 250 O C 2 300 s 0 dacs 100 amu/100 mmu
method proposed by the EPA (11) for the analysis of alcohols in gasoline involves the extraction of the alcohols into water containing 1.0% 2-butanone as an internal standard. The aqueous layer is then assayed by GC. While multidimensional chromatographic methods provide sufficient sensitivity and resolution, their operational complexity make their use difficult. Although the EPA method yields excellent detection limits, dilution of sample extracts exceeding 12% alcohol content by total volume is required. Further, the resolution of the butyl alcohols and the internal standard is poor. Since data from this type of analysis often lead to litigation, a more straightforward means of analysis is needed. The possibility for direct injection of gasoline into a gas chromatography-ion trap detector system (GC-ITDS) to analyze for the CI-C4 alcohols was investigated. To eliminate the very complicated chromatrogram normally associated with gasoline, the ITDS was configured to collect data in the multiple ion detecton (MIL)) mode, where the instrument only collects those chromatographic peaks that exhibit specific mass-tocharge ratios. Advantages of using the MID acquisition mode include a better signal-to-noise ratio, increased sensitivity as a result of the signal-to-noise ratio, and more reproducible peak ratios (13). For this study the m l e values of 31 and 45, that are commonly encountered in alcohols (12),were employed. The resulting chromatogram consists of nine peaks. The first eight peaks are due to the C1-C4 alcohols and the ninth peak is due to the internal standard, 1-pentanol.
EXPERIMENTAL SECTION Reagents and Standard Solutions. All reagents used were reagent grade (Fischer Scientific). a 1% solution of methanol, ethanol, 2-propanol, 1-propanol, 2-methyl-2-propano1, 1methylpropanol, 2-methylpropanol, 1-propanol, and 1-pentanol was prepared in a locally obtained regular grade unleaded gasoline that was determined to be alcohol free by the EPA method. One hundred microliters of internal standard was added to a 10-mL aliquot of each sample to be assayed. Instrumentation. The gas chromatography-mass spectrometry (GC-MS) system for this study was a Hewlett-Packard 5890A capillary column GC with a Finnigan-MAT 700 ion trap detector system (ITDS). The column used for the separation of the CL-C4alcohols was a Supelco SPB-1 fused silica capillary column 60 m by 0.32 mm id., with a film thickness of 1.00pm. A linear velocity of 1cm/min was employed providing a 1 mL/min flow to the open split interface of the ITDS. A split ratio of 5001 and injection volume of 0.1 pLL were used. Separations were accomplished with a temperature program consisting of an initial hold of 4 min at 40 OC, followed by an 8 OC/min ramp t o the final temperature of 220 "C. Table I shows the operating parameters of the ITDS. RESULTS AND DISCUSSION The total mass chromatogram shown in Figure l a is an example of the direct injection of gasoline as measured by an ITDS. As indicated by the MID chromatogram shown in Figure l b , the ability to interpret the total chromatogram, Figure la, resulting from the direct injection of gasoline is extremely difficult. The alcohol peaks are minor relative to
- 1
-
1
.
*
-
8
=
1 -me
'
c
5
*
'
,
'
~
Figure 1. Direct injection of gasoline: (a) total chromatogram of 1% alcohollgasoline blend, (b) MID chromatographic representation of (a) using m l e of 3 1 and 45.
-
e
Figure 2. MID chromatogram of 1 % alcohol/gasoRne blends: (a) combination of using m l e 31 and 45, (b) using m l e 31, (c) using m l e 45.
Table 11. Chromatography Data alcohols methanol ethanol 2-propanol
1-propanol 2-methyl-2-propanol 1-methylpropanol 2-methylpropanol 1-butanol 1-pentanol
peak no. 1 2 3 4
5 6 7 8 9
retention time, min:s
detection limit, 70
5:29 6:18 5:03 7:42 8:32
0.08 0.04 0.05 0.05 0.02 0.05 0.08 0.06
9:49 10:42
11:53 15:27
the other components in the spectrum. Table I1 lists the retention times and detection limits for each alcohol. Figure 2 contains the chromatograms associated with the MID acquisition mode. Figure 2a is the total chromatogram resulting from the use of both m l e peaks, 31 and 45. Figure 2b is the chromatogram that occurs if only the m l e ratio of 31 is used. Compared to the total chromatogram, Figure 2a, the MID acquisition chromatogram using m l e 31 exhibits lower sensitivity for 2-propanol and 1-methylpropanol than was expected. This occurred because the m l e ratio peak at 31, which is due to the CH20H+molecular fraction, is very weak for these two alcohols. T o overcome this problem another m l e ratio was added to the MID acquisition. Figure 2c shows the chromatogram that results from the use of only the 45 m l e ratio. As indicated by Figure 2c the peak that result from 2-propanol and 1-methylpropanol are both very prominent peaks. The m l e ratio peak at 45 results from the
Anal. Chem. 1986, 58, 2414-2420
2414
Table 111. Sample Data % by volume
sample
EPA
EPA-EOD-1 EPA-EOD-2 EPA-EOD-3 EPA-EOD-4 EPA-EOD-5 EPA-EOD-6 EPA-EOD-7 EPA-EOD-8 EPA-EOD-9 EPA-EOD-10
16.01 0.35" 9.87 f 0.11 19.46 f 0.46 NDb 4.55 f 0.30 0.44 0.04 8.37 f 0.46 1.18 f 0.03 10.72 0.32 16.15 f 0.52
* *
*
ITDS 16.10 f 0.04" 9.76 f 0.26 19.55 f 0.42 ND 4.88 f 0.08 0.33 f 0.04 8.32 f 0.13 1.26 f 0.15 10.84 f 0.27 16.17 f 0.17
% diff
0.56 1.11 0.46 7.26 25.00 0.60 6.78 1.12 0.13
"95% confidence limit. *ND, not detected.
molecular fraction of CH3CHOH+. By use of both the 31 and 45 m l e ratios the overall sensitivity and the detection limits were improved. Figure 2b,c is only shown for explanatory purposes, Figure 2a is the chromatogram used for quantification of the alcohol content of the gasoline. As indicated by Figure 2b,c, ethanol is present in both MID chromatograms. By use of both mle ratios, 31 and 45, ethanol could be determined a t the upper limit of 20% total volume. Twenty percent methanol or ethanol content was used as the upper limit since this value is well above the legal limit set by the Ohio Attorney General's Office. The remaining six alcohols are predominately found in concentrations of less than 1% since they are most commonly used as cosolvents for the other alcohols. T o evaluate the method, gasoline samples that had been assayed by the EPA method were reanalyzed by the GC-ITDS
procedure. Included in these samples were ten samples containing ethanol in concentrations up to 20% by volume that had been prepared for our laboratory by the EPA. The values that were obtained for the ten EPA samples by both methods are contained in Table 111.
ACKNOWLEDGMENT We wish to thank James Petroff of the Consumer Fraud Division of the Ohio Attorny General's Office for providing the gasoline samples used in the testing of this method. Registry No. Methanol, 67-56-1;ethanol, 64-17-5;2-propanol, 67-63-0; 1-propanol, 71-23-8; 2-methyl-2-propano1, 75-65-0; 2butanol, 78-92-2;2-methyl-1-propanol,78-83-1;1-butanol,71-36-3. LITERATURE CITED Thomas, K. The Aviation Consumer 1983, 13, 15-21. Renzoni, G. E.; Shankland, E. G.; Gaines, J. A,; Callis, J. B. Anal. Chem. 1985, 57, 2864-2867. "Ohlo Consumer Sales Practices Act and Substantive Rules", Ohio Attorney General's Office, pp 48-49. Pauls, R. E.; McCoy, R. W. J. J . Chromatogr. Sci. 1981, 79, 558-561. Sevick, J. HRC CC, J . High Resolut. Chromatogr. Chromatogr. Commun. 1980, 3 , 166-168. Durand, J. P; Petroff, N. Rev. Inst. F r . Pet. 1982, 3 7 , 575-578. Chem. Abstr. 1982, 9 7 , 112187a. Luke, L. A.; Ray, J. E. Analyst (London) 1984, 709, 989-992. Lockwood, A. F.; Craddock, B. D. Chromatographia 1983, 17, 65-68. Johansen, N. G. HRC CC , J High Resolut. Chromatogr Chromatogr . Commun. 1984, 8 , 487-489. Zinbo, M. Anal. Chem. 1984, 5 6 , 244-247. US EPA NEIC 1984, Ohio Attorney General's Office. Silverstein, R. M., Bassler, G. C., Morrill, T. C. Spectrometric Identification of Organic Compounds, 4th ed.; 1981. Ion Trap Detector Operation Manual, Revision 6 ,Finnigan-MAT Corp., San Jose, CA.
.
.
RECEIVED for review March 18,1986. Accepted June 1,1986.
Determination of Picogram per Cubic Meter Concentrations of Tetra- and Pentachlorinated Dibenzofurans and Dibenzo-p-dioxins in Indoor Air by High-Resolution Gas Chromatography/High-Resolution Mass Spectrometry R. M. Smith,* P. W. O'Keefe, D. R. Hilker, and K. M. Aldous Wadsworth Center for Laboratories and Research, New York State Department of Health, Empire State Plaza, Albany, New York 12201
An analytlcal method Is presented for the collectlon and quantlflcatlon of tetra- and pentachlorlnated dlbenrofurans (CDFs) and chlorinated dlbenro-pdbxlns (CDDs) In ambient alr. Thls method Is the first to deal with gaseous CDFs and CDDs as well as particulate-bound compounds and the first to validate and report the quantlflcatlon of these compounds at 1 pg/m3. Samples were collected with a glass flber filter followed by slllca gel contalned In a removable extraction thimble In a housing made of Teflon. The samples were Soxhiet extracted wlth benzene, cleaned up with alumlna and carbon adsorption llquld chromatography, and quantlfled with SP2330 caplllary GC/mass profile high-resolutlon mass spectrometry. A complex Isomer pattern of tetra- and penta-CDFs and tetra-CDDs lncludlng the 2,3,7,8-substltuted tetras was found in air samples taken from a contamlnated office building. Concentrations ranged from 0.23 pg/m3 2,3,7,8-tetra-CDD to 185 pg/m3 for total tetra-CDFs. Chlorlnated blphenylenes were also found. 0003-2700/86/0358-2414$01.50/0
Most of the interest concerning CDFs and CDDs in air has been related to incinerator stack emissions. Because no analytical method presently exists for the determination of picogram per cubic meter quantities of these compounds in indoor or outdoor air, risk assessment groups have been forced to use computer modeling or surrogate analyses (e.g., PCB) to estimate CDF and CDD concentrations. Although attempts have been made to analyze air particulate matter for CDFs and CDDs, no analytical method has dealt with the possibility of gaseous or desorbed compounds. Stack emission samples are commonly collected with a glass fiber filter followed by an XAD resin trap to collect both particulate and vapor-phase compounds. The filter and trap are contained in a complex water-cooled sampling train that is necessary to handle conditions of high temperature and moisture (1, 2); quantification is by GC/MS. For ambient air a simpler collection system can be used, but larger volumes (80 m3 or more) must be sampled. A high-volume ambient 0 1986 American Chemical Society
