Anal. Chem. 1083, 5 5 , 744-749
LITERATURE CITED Mlchotte, Y.; Massart, D. L. J . Pharm. Sci. 1977, 66, 1630-1632. Buydens, L.; Massart, D. L. Anal. Chem. 1981, 53, 1990-1993. McGregor, T. R. J . Chromatogr. Sci. 1979, 17, 314-316. Mlllershlp, J. S.;Woolfson, A. D. J . Pharm. Pharmacal. 1978, 30, 483-485. Chrltien, J. R.; Dubois, J. E. Anal. Chem. 1977, 4 9 , 747-756. ChrOtlen, J. R.; Dubols, J. E. J . Chromatogr. 1976, 158, 43-56. Buydens. L.; Coomans, D.; Vanbelle. M.; Massart. D. L. J . Pharm. sC;'., in press. Hansch, C. In "Drug Design"; Arlens, E. J., Ed.; Academic Press: New York, 1971; Chapter 2. Martin, Y. C. "Quantitative Drug Design"; Marcel Dekker: New York and Basal, 1978. Kler, L. 8.; Hall, L. H. "Molecular Connectlvlty In Chemistry and Drug Research"; Academic Press: New York. 1976. Kler, L. B.; Hall, L. H. J . Pharm. Sci. 1981, 70, 583-584. Shorter, J. In "Correlation Analysis-Recent Advances"; Chapman, N.
B., Shorter, J., Ed.; Plenum Press: New York, 1978. (13) Amidon, G. L.; Anlk, S.T. J . Pharm. Sci. 1976, 65, 801-806. (14) Atklns, P. W. "Physical Chemistry"; Oxford Unlverslty Press: Oxford, 1978. (15) Pople, J. A.; Beveridge, D. L. "Approximate Molecular Orbital Theory"; McGraw-Hill: New York, 1970. (16) Roothaan. C. C. J. Rev. Mod. Phys. 1951, 23, 69-89. (17) Pople, J. A.; Gordon, M. J. J . Am. Chem. SOC. 1976, 8 9 , 4253-4261. (18) McReynolds, W. 0 . "Gas Chromatographlc Retentlon Data"; Preston Technical Abstracts Co.: IL, 1966. (19) Engleman, L.; Frane, J. W.; Jennrlch, R. I. In "BMDP-79"; Dlxon, W. J., Brown, M. B., Eds.; University of California Press: Berkeley-Los Angeles-London, 1979.
RECEIVED for review July 19, 1982. Accepted December 15, 1982. The authors thank F.G.W.O. for financial support.
Comparison of Gas Chromatography/High-Resolution Mass Spectrometry and Mass Spectrometry/Mass Spectrometry for Detection of Polychlorinated Biphenyls and Tetrachlorodibenzof uran Robert D. Voyksner' and J. Ronald #ass* National Institute of Environmental Health Sciences, P.0. Box 12233, Research Triangle Park, North Carolina 27709
G. Wayne Sovocool U.S. Environmental Protection Agency, EMSL-LV, QAD, P.O. Box 15027, Las Vegas, Nevada 891 14
Maurice M. Bursey Department of Chemlstty, Unlverslty of North Carolina, Chapel Hill, North Carolina 27514
Mass spectral techniques for environmental samples whlch receive little cleanup were evaluated. Analyses on identical samples of PCB's and TCDF by mass spectrometry/mass spectrometry (MSIMS) and gas chromatography/hlgh-resoiutlon mass spectrometry (GC/HRMS) were compared. For the TCDF samples the use of GC/MS/MS was also compared with these two techniques. On comparlson of the quantitative results, the direct probe MS/MS analysls was 2-10 times hlgher than the GC/HRMS or GC/MS/MS values. Matrlx effects, for a 10 pg/pL butyl stearate matrix, were shown to increase the signal intensity by a factor of 17 for GC Introduction of TCDF while the same sample by the direct probe showed a loss In Intensity relative to the nonmatrlx standard. The advantages and llmitatlons of the methods, the necessity of multllon or reaction detection to ensure speclflclty, the ability to detect Interferences, and the validity of the methodologles are discussed.
The validity of a technique for environmental analysis is dependent on its ability to obtain adequate sensitivity to detect the analyte and enough specificityto ensure the absence of interferences. This criterion is often impossible to satisfy because sensitivity is limited and the nature of possible interferences is unknown. The evaluation of a new technique can be based on the less rigorous criterion that another in'Also at the University
of N o r t h Carolina, Chapel Hill, NC. 0003-2700/83/0355-0744$01.50/0
dependent technique gives the same results. Though this approach is fallible (both procedures could detect the same interferences)it is useful in evaluating different methodologies for complex sample characterization. Most environmental analyses involving mass spectrometry as the detection method use one of two general approaches: (a) to employ extensive cleanup procedures which minimize the need for mass spectral selectivity ( I , 2), (b) to use specific mass spectral techniques to minimize the effect of interferences. The latter approach has the advantages of speed, smaller sample volumes, and fewer possibilities for analyte loss. These specific mass spectral techniques include chemical ionization (CI) mass spectrometry (3,4),atmospheric pressure ionization mass spectrometry (5), mass spectrometry/mass spectrometry (MS/MS) (6-8), gas chromatography/low- or high-resolution mass spectrometry (GC/LRMS or GC/ HRMS) (9-ll),and gas chromatography/mass spectrometry/mass spectrometry (GC/MS/MS) (12). The capability of MS/MS for structural elucidation and quantitative analysis has been investigated (6-8,13,14). The first analyzer provides nominal mass separation of the analyte from the matrix. The selected ion undergoes collisional activation (CA) to form structurally relevant fragments. The main advantage is fast analysis time; probe samples can take from a fraction of a minute to a few minutes. The analyses of cocaine in leaves; benzoylecgonine, cocaine, hippuric acid, and glucose in urine; and methylnaphthalenes, anthracene, quinoline, tetrahydroisoquinoline, and other polycyclic compounds in coal tar have been reported in recent literature (23-16). The initial mass analysis and the precursor/daughter 0 1983 Amerlcan Chemical Society
ANALYTICAL CHEMISTRY, VOL. 55, NO. 4, APRIL 1983
identification eliminate most of the chemical noise present and permit low nanogram to picogram detection limits. These advantages have made MS/MS an attractive technique for environmental analysis. GC/HRMS analysis provides an initial separation of the analyte from matrix by differences in the partition coefficient of the components between stationary and mobile phases, rather than by mass. This type of separation provides isomer information that would be lost if separation were based on mass alone. The HRMS detection adds specificity to the analysis by requiring the signal recorded to have the exact mass, within a narrow range, corresponding to the analyte. The removal of chemical noise by HRMS permits picogram detection limits. The GC/MS/MS analysis has all the advantages discussed for MS/MS, except for short analysis time. The use of the GC as the means of sample introduction increases specificity of the analysis with a sacrifice in time and is only appliable to gas chromatographable compounds. The specificity requirements are that if a compound in a certain retention time window shows a particular parent-daughter ion relationship, the technique should provide a valid environmental analysis. This paper compares the advantages and disadvantages of quantitative analysis by MS/MS and GC/HRMS of polychlorinated biphenyls (PCB's) and tetrachlorodibenzofuran (TCDF) in fat, blood, or oil matrix. For the TCDF sample GC/MS/MS analysis was performed for further evaluation of the mass spectrometric techniques. Polychlorobiphenyls are a widespread environmental contaminant detected in various biological fluids and tissues (I 7-19). These compounds and their associated impurities, polychlorodibenzofurans (20-22) have been investigated to determine their toxicological effects on humans. These samples provide a challenging test for the above MS techniques, because several types of interferences have been reported in GC/LRMS analysis (23-25). The methodology evaluated for the analyses was based on optimizing the mass spectral techniques to provide the best sensitivity and specificity. Since both classes of compounds gave intense molecular ions under electron impact (EI) conditions and many biological molecules do not, E1 was chosen over CI as the mode of ionization. The GC/HRMS analysis was performed by monitoring the [MI+. and [M 2]+. ions while observing the exact mass, retention time, and [M]+./[M 2]+. ratio. Deviations from the standard values indicated the presence of interferences. The MS/MS analyses carried out on the same samples monitored the loss of one and two chlorine atoms from the [MI+. ion for PCB's and the loss of COCl and C1. for TCDF. The analyses demanded that the ratio of the two observed losses be the same as that of a standard in order to demonstrate the presence of the analyte and the absence of interferences. Quantitation of PCB's has always presented problems (24-27). It is reasonable to assume that PCB quantitation will become validated when each relevant isomer is synthesized and its relative response measured. Such an undertaking is out of the scope of this paper. Rather, Aroclor 1254 standards were used because they resembled the isomer distribution of the fat samples. The TCDF sample presented no quantitation problems since only the one isomer (the 2,3,7,8 isomer) is present and the standard was available for it. EXPERIMENTAL SECTION To facilitate comparisons the same standards and samples were analyzed by each technique within days of each other and kept cold between analyses. The blood samples were extracted with hexane, the animal fat samples with benzene, and the human fat samples with ether. All samples were further purified by gel permeation chromatography. Each sample was evaporated to low volume then diluted with a known volume (0.1-1.0 mL) with the
+
+
745
respective solvent. Monsanto Aroclor 1254 was used for the PCB standards, which ranged from 1pg/pL to 100 ng/pL. The TCDF sample in an oil matrix, used for animal feed studies, was made from a certified isomeric pure 2,3,7,8-TCDFstandard and had a known concentration of 2 ng/KL. Standards ranging from 200 pg/pL to 13 ng/pL were made by spiking various amounts of pure 2,3,7,8-TCDFinto the blank and diluting to volume with toluene. Aliquots of 0.5-2.0 pL were used in the analyses. Analyses were performed on the VG Micromass ZAB-2F mass spectrometer equipped with a Finningan-INCOS 2300 data system. GC/HRMS Analysis. The samples were analyzed by oncolumn injection on a 20 M, OV-1 (Supelco, Inc.) or a 20 M, SE-30 (J+W Scientific) fused silica column inserted directly into the mass spectrometer source. After the solvent front eluted, the temperature was programmed ballistically to 150 "C and then programmed to 250 "C at 8 "C/min. The acquisition started 4 min after the temperature program was initiated. The mass spectrometer was operated at 5000 or 10000 resolution (10% valley), at 200 pA trap current, 8 keV accelerating voltage, 70 eV electron energy, and a source temperature of 220-240 "C. Either the C8Fll ion (for PCB's) or the C7Fll ion (for TCDF) of PFK was used as the lock ma98 for the VG digital multiple ion detection (MID) unit. The accelerating voltage scan of the MID unit was synchronized by a start of scan pulse from the data system (28, 29). A 200-300 ppm window was scanned for each monitored ion and the resulting signal stored in profile mode at a rate of 75 pslpoint. The positions of the centroids for the peak within the window enabled the determination of the exact mass of the signal. The MS/MS Analysis. The magnetic field was set to pass [MI+. ions of either m/z 358 (PCB's) or 304 (TCDF). The electrostatic analyzer (ESA)was scanned to observe the transitions [MI+. [M - C1]+ and [MI+. [M - 2C1]+- for the hexachlorobiphenyls and for TCDF the [MI+. [M - C1]+ and [MI+[M - COCl]+.transitions. The mass spectrometer was operated at a primary ion resolution of 800, 200 MAtrap current, 7 kV accelerating voltage, 70 eV electron energy, and at a source temperature of 200-240 "C. Helium was used as the collison gas at torr which was about 2 an analyzer gauge pressure of 1.5 X X torr in the collision cell (30). The GC/MS/MS Analysis. This analysis was performed under the same conditions described for the MS/MS analysis, but only the COCl loss was observed. The TCDF was chromatographed on a DB-5,20 M fused silica column (J+W Scientific), which was coupled directly into the mass spectrometer source. The column was temperature programmed from 200 to 280 "C at 16 "C/min. Acquisition began 3.5 min after the temperature program started. The HRMS Analysis. This analysis was performed under the same conditions as described for the GC/HRMS except the blood samples were introduced by direct probe. The C9FI3ion of PFK was used as the lock mass for the MID unit, and a 200 ppm window, centered on the exact mass for the [MI+-and [M + 2]+. ions of hexachlorobiphenyl, was scanned in 0.2 s for a total scan time of 0.7 s.
-
-
- -
RESULTS AND DISCUSSION PCB Analysis. The GC/HRMS analysis was performed by monitoring the [MI+.and the [M + 2]+-ions for the tetra-, penta-, and hexachlorobiphenyls. Each window was observed for 0.2 s with a total scan time of 1.68 s. The isomer resolution (Figure 1)for the Aroclor standards and samples permited quantitation of the individual isomers, but for this comparison only the total hexachlorobiphenyl concentration was determined. The amounts of the various hexachlorobiphenyls in Aroclor 1254 have been determined (3I),enabling the use of the Aroclor for a standard. The areas of all the hexachlorobiphenyls were summed and the [M]+./[M + 2]+-ratio was checked to confirm the expected ratio for a compound containing six chlorines. The quantitative results must depend on the similarity of the blood and fat samples to the Aroclor standard, because of different responses for the various isomers. This assumption was reasonable for the fat samples but not for the blood samples. The calibration curve was linear
748
ANALYTICAL CHEMISTRY, VOL. 55, NO. 4, APRIL 1983
Table I. Quantitafive Results for the Hexachlorobiphenyl Analysisa MS/MS
GC/HRMS
HRMS
amt, [M - 2C1]*+/ amt, FIl+*/ amt, cM3'*/ [M t 2]+* sample llglg [M - ClI+ Pg/g [M + 2]+* &/g fat no. 1 40.5 1.5 16.5 0.53 fat no. 2 35.9 1.7 14.5 0.50 fat.no. 3 58.6 1.4 14.9 0.53 fat no. 4 15.6 1.1 1.7 0.50 blood no. 1 0.06 2.4 0.003 0.50 0.02 0.47 blood no. 2 0.02 1.2 0.006 0.56 0.01 0.50 H-fat no. 1 0.53 1.7 0.10 0.53 standards 2.1 0.51 0.52 The standard deviations for direct probe work are usually less than 20%of the value and those for GC work are less than 5%of the value.
1:oo 100 35x
mlz 326
Intensity
Scan Tim ( min. )
2:m
'I
Int.
1
50
1
TIC
0
b
'
0
1 : ' ~
' Scan Time ( min. )
2:oo
LIA
Intensity
mlz 358 n h .
50
TIC
A 2:50
a:30
5:40 Scan Time
11:zo
( min. )
+
Flgure 1. Reconstructed ion chromatograms for the [M]'. and [M 2]+. windows for the tetra-, penta-, and hexachloroblphenyls: (a) response for the 1 ng standard of Aroclar 1254; (b) response for a
MIZ
0
fat sample.
The total ion current and peak profile for the loss of CISand 2CI. from the molecular Ion of hexachlorobiphenyl: (a) trace for 10 ng of Aroclor 1254 standard: (b) response for a blood sample.
from 100 ng to 20 pg, with a correlation coefficient of 0.998. The detection limits were determined to be about 2 pg in each case. The summary of the quantitative results is given on Table I. The similarity of the peak ratios and the lack of interfering signals in the 300 ppm window indicate that there were no interferences in the analysis. In the MS/MS analysis the m / z 358 ion of hexachlorobiphenyl was selected and the ESA was scanned to cover the mass range from 270 to 360 in 2.7 s. No information about the various isomers could be obtained since there is no way to resolve them. This presents problems if the quantity of a particular isomer is desired in a matrix of many isomers. The standards gave no signals other than the [MI+. [M C1]+ and [MI+. [M - 2C1]+-transitions (Figure 2). The calibration was linear from 100 ng to 100 pg with a correlation
coefficient of 0.995. The detection limits of 50 pg could be lowered to 10 pg when a 2 mass unit wide window was scanned in 0.5 s for each loss. The peak width was ignored because the kinetic energy release (KER) has been shown to depend on the chlorine substitution pattern of the biphenyls (32) and thus would vary because of different isomer content between samples and standards. Rather, the [MI+. [M - 2C1]+./ [MI+. [M - C1]+ ratio was taken to detect interferences and measure similarity of the isomer content in the sample with the standard. Ratios different than the standard ratio indicate there is an interference or a dissimilarity in isomer content between sample and standard. The ratio of [MI+- [M 2Cl]+./[M + 2]+. [M - 2C1]+. has been proposed to be more suitable for the detection of interferences since this ratio should remain independent of the hexachlorobiphenylisomer distribution. In principle it is straightforward to switch
-
-
Flgure 2.
-
-
-
-
ANALYTICAL CHEMISTRY, VOL. 55, NO. 4, APRIL 1983
primary ion beams by alteration of the acceleratingand electric sector potentials at fixed magnetic field strength to perform this multiple reaction monitoring (33). This type of switching only requires a few milliseconds and there is no increase in analysis time. While at first thought, this would seem to add specificity to the assay, it is not the case when you consider the probability that an interfering substance would be present which gave an [M - C1]+ and [M - 2Cl]+. peak. It is very unlikely any compound not containing C1 would give both those daughter ion peaks. Thus, if the first criteria were met, the compound would likely also give appropriate signals from the ion 2 daltons higher in mass. Therefore, the increase in experimental complexity would result in a reduction of S N (one must decrease the dwell time to increase the number of different m e s monitored) with the only apparent gain being that the analysis is independent of the hexachlorobiphenyl isomer distribution. The samples show a completely different elution profile (Figure 2) with possible interferences in the analyte windows. The comparison of the results (Table I) shows the values by MS/MS are 2 to 10 times larger than the GC/HRMS values. The results obtained by direct probe HRMS on the blood samples are higher than those obtained by GC/HRMS. This might indicate that the majority of the interferences are removed by the high-resolution techniques with prior chromatographic separation. These results suggest that the direct probe HRMS and MS/MS techniques are detecting more interferences, possibly due to aliphatics (cholesterol,etc.) in blood and fat (large [M - CH3]+present) or from hepta-, octa-, nona-, and decachlorobiphenyls. These higher mass compounds can undergo fragmentation in the source to produce ions that coincide with the molecular ion of hexachlorobiphenyl (m/z 358+). These ions are transmitted through the magnet and if they undergo the same dissociation as the [MI+.ion of hexachlorobiphenyl,the loss of C1 and 2C1, they can cause interferences in the analyses. For example an octachlorobiphenyl shows E1 fragment, [M - 2C1]+., ions of mlz 358+in the source. This fragment is transmitted through the magnet and undergoes the subsequent dissociations [M - 2C1]+. [M - 3C1]+ and [M - 2C1]+. -+ [M - 4C1]+. which will cause interferences in the hexachlorobiphenyl analysis. The GC/HRMS is presumed to be the more accurate method since it gave lower quantitative results, which indicates less influence from the matrix. The accuracy of the analysis cannot be checked since the true levels in the samples are not known a priori. Analysis of TCDF. The GC/HRMS analysis of TCDF in oil at 10000 resolution monitored the 200 ppm [MI+. and [M + 2]+. windows along with the PFK lock mass of 292.9824. The total scan time was 0.73 s. The retention time observed from the SE-30 column was 8.1 f 0.07 min (N = 15) after the temperature program initiation. In this time window there were no interferences or other isomers detected. The [M 2]+./[M]+-ratio was 1.3 f 0.05 (N = 15) which is the expected chlorine isotopic ratio for an ion with four chlorines. The centroid for the [MI+. and [M + 2]+. signals, calculated to be 303.9016 and 305.8986, respectively, did not deviate by more than 10 ppm from these values for all the runs (Figure 3). The calibration curve was linear from 200 pg to 13 ng, with a correlation coefficient of 0.996. The concentration of TCDF determined by this analysis was 2.1 f 0.1 ng/pL ( N = 31, in agreement with the known spiked concentration. The MS/MS analysis observe the [MI+. [M - C1]+ and [MI+. -* [M - COCl]+. transitions to give a total scan time of 1.45 s. The sample and standards produced similar recordings (Figure 4), but the sample eluted over a longer time span. The TCDF [MI+. [M - COCl]+-/[M]+. [M - C1]+ ratio for the standards had the value 1.4 f 0.1 ( N = 17). The sample ratio was 1.7 f 0.1 (N = 3) and, therefore, indicated
747
Flgure 3. GC/HRMS peak profiles for the [MI+. ions of TCDF at 10 000 resolution: (a) 4 ng of standard: (b) the sample.
a
i
-
+
-
-
-
-
-
-
Flgure 4. The total Ion current for [MI+. [M Ci]+[M]+. [M COCI]+-transitions of TCDF from the probe: (a) 4 ng standard; (b)
-
the sample.
the presence of interferences. The KER's at half height (34) for the loss of C1 and COG1 were 66 and 140 5 meV ( N = 6), respectively, for the TCDF standards. The sample showed a KER of 71 and 134 f 6 meV ( N = 3). The calibration over the same concentration range was linear with a correlation coefficient of 0.998. The results of the determination showed the concentration to be 3.4 f 0.3 ng/pL ( N = 3) and to differ significantly from those of the GC/HRMS determination. These differences in the determined concentrations for the GC sample introduction as oppossed to the direct probe
*
748
ANALYTICAL CHEMISTRY, VOL. 55, NO. 4, APRIL 1983
Int.
1W
b
Int.
C
50
Int.
Flgure 5. GC/MS/MS profile for the [MI+. + [M T C D F (a) 4 ng of standard; (b) the sample.
of
- COCI]+. transition
technique leave questions about the validity of the latter. To validate a technique, by the criterion defined above, the analysis was repeated by GC/MS/MS. Only the [MI+. [M - COCl]+. transition was observed to reduce the scan time to 0.61 s. The retention time for TCDF from a DB-5 column was 4.9 f 0.08 min (N = 15). The KER for the sample was 136 meV, which compared favorably with the standards (140 meV). Examination of the spectra did not reveal evidence of interference (Figure 5). The standard calibration curve was linear with a correlation coefficient of 0.997. From the calibration the concentration of TCDF was determined to be 1.9 f 0.15 ng/pL (N = 3). This value is in agreement with the GC/HRMS, and both are lower by a factor of 1.7 than the MS/MS value. Matrix Effects and Interferences. The validity of MS/MS for environmental analysis can be questioned in the limited number of cases examined. The advantages of speed and little sample preparation are, in our opinion, outweighed by the fact that the results were consistently and unpredictably high and did not agree with other techniques. It is not our opinion that GC/HRMS or GC/MS in void of interferences, but it seems clear that GC introduction reduces the probability of encountering interferences compared to direct probe techniques. The variance of the [MI+. [M COCl]+-/[M]+- [M - C1]+ ratio for TCDF by MS/MS analysis indicated that an interference was present and that the analysis needed to be performed by another method. The high resolution (1OOOO) observation of the mass window 303.4 to 304.4, which includes the masa range that would be selected by the first analyzer in MS/MS, reveals at least seven ions (Figure 6). The peaks at 303.9922 and 304.3082 are present in the blank. The 303.9016 ion is due to 2,3,7,8-TCDF present in the sample. The four peaks at 303.3221,304.2513,304.2883, and 304.2913 are interferences present in the sample but not found in the spiked blank. The GC/HRMS technique proves to be more analyte specific by comparison since it has been demonstrated that components 20 ppm apart can be distinguished (35). The specificity of HRMS can be shown by the fact there are 72 elemental compositions which satisfy the valence laws, contain
-
-
+
rigure o. nign-resoiurion \ 1 u uuu) scan over m e mass winaow transmttted dby MS/MS for the molecular ion of T C D F (a) blank; (b) 4 ng of TCDF spiked into blank: (c) sample.
tour chlorines, and are composed of C,H, N, 0,and S within 20 ppm of TCDF. This number is reduced to 20 when the compositions that give the proper [M 2]+./[M]+. ratio for a four chlorine compound are considered. On the other hand, the specificity of MS/MS analysis is partly dependent upon the particular instrumentation used in the analysis. For example in MIKES analysis, the daughter ion resolution, for the reaction 304+ 241+ of TCDF, is approximately 4 mass units wide. It is reasonable to assume that instrumentation which is capable of unit mass resolution of both parent and daughter ion (such as a triple quadrupole or BE linked scan techniques) would be subject to fewer interferences. Interferences also exist from high molecular weight matrix components undergoing metastable decompositions in the first field region and the flight tube. There are hundreds of compounds and metastable ions that could be within the unit mass window of TCDF that contain chlorine and oxygen. There is a high probability that these compounds will show losses of C1 and COCl similar to TCDF. Thus, it is speculated that there is a lower probability of exact mass interferences when compared to the probability of interference with separation based on reactions. The specificity of MS/MS should be enhanced by GC sample introduction because the analyte must now show a particular retention time and fragmentation reaction. The inability to obtain a true blank can greatly change the results for a direct probe analysis. Recent work showed the mlz 320 to m / z 257 transition for TCDD was reduced by one-third when 1pg of methyl stearate was added to 100 pg of sample (36). Another example showed a decrease of the mlz 322 ion current of TCDD by 85% with the addition of 25 pg of squalane to the probe cup (37). Our results (Table 11) showed a slight depression of ion current when 10 pg of butyl stearate was added to the cup with TCDF. The sample blank showed a drop in response of almost 50% compared to the standard in pure solvent. These matrix effects do no apply only to probe work but also to GC analysis as well: the sample blank (oil) doubled the response (area) of the TCDF signal over the response of TCDF in toluene (Table 11). The most significant change recorded was the peak height. The butyl
+
-
ANALYTICAL CHEMISTRY, VOL.
Table 11. Matrix Effects Observed for Both Mass Spectral Techniques for 4 ng of TCDF
matrix
MS/MS area
GC/HRMS re1 relpeak area height
toluene (no matrix)
1.0
1.0
1.0
10 pg of
0.85
2.0
17.5
0.56
2.0
2.3
butyl stearate 10 pg of oil
a
6
Int.
3
0
b
55, NO. 4, APRIL 1983
749
Registry No. TCDF, 30402-14-3; hexachlorobiphenyl, 26601-64-9;tetrachlorobiphenyl,26914-33-0;pentachlorobiphenyl, 25429-29-2. LITERATURE CITED ( I ) Langhorst, M. L.; Shadoff, L. A. Anal. Chem. 1080, 52, 2037-2044. (2) Lamparski, L. L.; Nestrick Y. J. Anal. Chem. 1080, 52, 2045-2054. (3) Jennings, K. R. “Gas Phase Ion Chemistry”; Academic Press: New York. 1979:Vol. 2. 123-151. (4) Hunt,’ D. F.. Harvey, T . MI; Russell, J. W. J. Chem. SOC.,Chem. Common. 1975. 5 . 151. (5) Mitchum, R. K.;’Mdec, G. F.; Korfmacher, W. A. Anal. Chem. 1980, 52, 2278-2282. (8) Kondrat, H. W.; Cooks, R. G. Anal. Chem. 1078, 50, 51A-92A. (7) McLafferty, F. W.; Bockhoff, F. M. Anal. Chem. 1078, 50, 69-75. (8) Yost, R. A.; Enke, C. G. Anal. Chem. 1070, 51, 1251A-1264A. (9) Gross, M. L. “High Performance Mass Spectrometry: Chemical Applications”; American Chemical Society: Washington, DC, 1978;pp 120-149. (IO) Kimble, B. J.; Gross, M. L. Science 1980, 207, 59. (11) Tindall, G. W.; Wininger, P. F. J. Chromatogr. 1080, 196, 109-119. (12)Harvan, D. J.; Hass, J. R.; Schraeder, J. L.; Corbett, 8. J. Anal. Chem. 1081, 53, 1755-1759. (13) Kondrat. R. W.; McCluskv, G. A.; Cooks, R. G. Anal. Chem. 1078, 50, 2017-2021. (14) Kruger, T. L.; Litton, J. F.; Kondrat, R. W.; Cooks, R. G. Anal. Chem. 1978, 48,2113-2119. (15) Zakett, D.; Shaddock, V. M.; Cooks, R. G. Anal. Chem. 1970, 51, 1849-1 . - . - .852. - - -. (18) McClusky, G. A.; Kondrat, R. W.; Cooks, R. G. J. Am. Chem. SOC.
int.
1078. 100. 6045-605 1. (17) Wasserman, M.; Wlsserman, D.; Cycos, S.; Miller, H. J. Ann. N . Y . Acad. Sci. 1070, 320, 69-124.
6.5 -
(18) Kutz, F. W.; Strassman, S. C. Proceedings of the National Conference on Polychioronated Biphenyls Nov 19-21, 1975, Chicago, IL, pp
100
-c
Int. 50
0
i
4:10
d (min.) Scan Time
8.20
Figure 7. The matrix effects observed for a 4 ng TCDF sample from the column: (a) no matrix; (b) spiked blank (oil matrix):(c) 10 fig of butyl stearate.
stearate, which elutes seconds before the TCDF, seems to carry the analyte through the column, reducing chromatographic band spread and enhancing peak height (Figure 7). This Grob type effect of chromatographic band narrowing was also noticed to a lesser extent for the oil matrix. Few components of the matrix elute from the column before the TCDF, and this observation may possibly explain the smaller enhancement for the TCDF. These observations indicate the importance of obtaining an accurate blank, the use of isotopically labeled internal standards, or the use of standard addition methods for quantitative analyses. ACKNOWLEDGMENT We are grateful to Donald J. Harvan for his insight into the instrumental aspects of the analysis.
139-143. (19) Risebrough, R. W.; Rieche, P.; Peakaii, D. B.; Herman, S. G.; Kirven, M. N. Nature (London)1088, 220, 1098. (20) Goklstein, J. A.; Hass. J. R.; Linko, P.; Harvan, D. J. Drug Metab. DisPOS. 1078, 6 , 258-264. (21) Buser, H. R.; Rappe, C.; Gara, A. Chemosphere 1078, 7 , 439-449. (22) Poland, A.; Glover, E.; Kende, A. S.; Decamp, M.; Giandomenlca, C. M. Science 1078, 194, 630. (23) Ast, T.; Bozorgzadeh, M. H.; Wiebers, J. L.; Beynon, J. H.; Brenton, A. G. Org. Mass Spectrom. 1070, 14, 313-318. (24) Cairns, T.; Siegmund, E. G. Anal. Chem. 1981, 53, 1183A. (25) Albro, P. W.; Parker, C. E. J. Chromatogr. 1080, 197, 155-169. (26) Aibro, P. W.; Parker, C. E. J. Chromatogr. 1979, 169, 161-166. (27) Eicheiberger, J. W.; Harris, L. E.; Budde, W. L. Anal. Chem. 1074, 46, 227-23 1. (28) Harman, D. J.; Hass, J. R.; Wood, D. Anal. Chem. 1082, 5 4 , 332-334. (29) Weiss, M.; Harvan, D. J.; Hass, J. R. 28th Annual Conference on Mass Spectrometry and Allied Topic, New York, NY, May 25-30, 1980, RPMP-6, p 602. (30) Murgan, R. P.; Beynon, J. H.; Bateman, R. H.; Green, B. N. Int. J. Mass. Spectrom., Ion Phys. 1978,28, 171-191. (31) Aibro, P. W.; Corbett, J. T.; Schroeder, J. L. J. Chromatogr. 1081, 205, 103-111. (32) Hass, J. R.; Bursey, M. M.; Levy, L. A.; Harvan, D. J. Org. Mass Spectrum. 1070, 14, 319-325. (33) Kondrat, R. W.; McClusky, G. A.; Cooks, R. G. Anal. Chem. 1078, 50, 2017-2021. (34) C0oks;R.G.; Beynon, J. H.; Caprioli, R. M.; Lester, G. R. “Metastable Ions”; Eisevier: New York, 1973;pp 97-128. (35) Hass, J. R.; Tondeur, Y., unpublished work NIEHS, Research Triangle Park, NC, 1981. (36) Harvan, P. J.; Hass, J. R.; Busch, K. L. 27th Annual Conference on Mass Spectrometry and Allied Topics, Seattle, WA, June 3-8, 1979; RAMOC-10, pp 529-530. (37) Baughman, R.; Meselson, M. “Chiorodioxins-Origin and Fate”; Blair, E. H., Ed.; American Chemical Society: Washington, DC, 1973;Chp. IO.
RECEIVED for review July 19,1982. Accepted January 6,1983.
