143
Anal. Chem. 1982, 5 4 , 143-146 -.6rnm+
-.-Reference
eiectrode
r=-\- -~
:>. Ailay
,_Contact wire
Ibl
-. LiTa03
=3-'IiIIflI --
Radiation
Flgure 1. (a) Top view aind (b) cross sectionial view of the sample.
4 OAV-+-&.Sec.+
I
resistor can be readily made. Third, the measured NEP in LiTaO, is 1.3 X 10-l" W/(Hz)'12 (14). Consequently, in principle, detection of heat exchange as low as a nanocalorie would be possible. Finally, in contrast with other thermal detectors, the pyroelectric current response depends on the rate of change of temperature rather than on the temperature itself. For this reason the maximum response is achieved at times shorter than the thermal relaxation time of the element, so that pyroelectrics are basically higher-frequency devices than other thermal detectors. The disadvantage of LiTaO, for DTA applications appears to be the low operational temperature, limited by Curie temperature (618 "C ( 7 ) ) . Yet, some pyroelectrics have been shown to have a higher Curie temperature (LiNbO,, for example, has a Curie temperature 1210 O C ( 7 ) ) .
CONCLUSION
n
The structure described in this study can be used to investigate phase transformations involving small amounts of material. Similar structures can be employed in various disciplines for thermal analysis and calorimetric measurement.
ACKNOWLEDGMENT The author thanks J. N. Zemel for useful discussion and for reading the original manuscript. LITERATURE CITED
1
heating
Flgure 2. Pyroelectric differential signal vs. time. Two low meting polnt alloy compositions were lplaced on the sample electrode.
there are several significant features of LiTaO, which should be mentioned at this point. First, LiiTaOs has favorable mechanical properties; it can be polished and cleaved into wafers, each wafer can be scribed and broken into small pieces as is commonly done with silicon wafers. Therefore, by chosing suitable dimensions for a specific purpose in thermal analysis, a desired heat transfer condition can be easily maintained. Moreover, the designed1 device can be mass produced. Second, the fabrication of thin metal film geometries using photolithography is a standard component of current integrated circuit technology. With this technique, (evaporatedNichrome and gold thin films on LiTaO, wafer are routinely etched into small elements to produce heater resistor and electrical contact, respectively (13). Thus, for DTA applications, the photolithographically defined electrode's areas and heater
Keulemans, A. I.M. "Gas Chromatography", 2nd ed.; Verver, C. G., Ed.; Reinholt: New York, 1969; p 91. Sandborn, W. A. "Resistance Temperature Transducers"; Metrology Press: Fort Collins, CO, 1972. Frost, W., Nlaulden, T. H., Eds. "Handbook of Turbulence, Vol. 7, Fundamentals and Applications"; Plenum Press: New York and London, 1977; p 315. Gorn, P. D. "Thermoanalytical Methods of Investlgation"; Academic Press: New York, 1965. Barthel, J. "Thermometric Titrations"; Wiley: New York, 1975; Chapter 9, p 159. Stevens, N. 8. I n "Semlconductor and Semimetals, Vol. 5, Infrared Detectors"; Wlllardson, R. D., Bear, A. G., Eds.; 1970; "Radiation Thermopiles", Chapter 7, p 287. Beerman, H. P. hfraredfhys. 1975, 15, 225. Landa, I.; Kremen, J. C. Anal. Chem. 1974, 4 6 , 1964. Llnes, M. E.: Glass, A. M. "Principles and Applications of Ferroelectrics and Related Materlals"; Clarendon Press: Oxford, 1977; Chapter 16, p 561. Lang, S. B. "XI1 Literature Guide to Pyroelectriclty 1980"; Ferroelectrics, 1961, 34, 71. Rahnamai, H.; Zemel, J. N., "Pyroelectric Anemometers-Preparation and Flow Vuiocity Measurements", Sensors and Actuators, Vol. 2, No. 1, Aug 198'1. Part of thls work is also published in the Proceedings of IEEE International Meetlng on Electron Devlces, Dec 1980, p 680. Brody, P. S. J. Solid State Chem. 1975, 12, 193. Young, J. C., Frederick, R., University of Pennsylvania, prlvate communication. Roundy, C. B.; Byer, R . L. J. Appl. Phys. 1973, 4 4 , 929.
RECEIVED for review May 29,1981. Accepted October 9,1981.
Sample Introduction System for Atmospheric Pressure Ionization Mass Spectrometry of Nonvolatile Compounds Hidekl Kambara central Research Laboratoty, Hltachi, Ltd., Kokubunll, Tokyo 785, Japan
Atmospheric pressure ionization (API) mass spectrometry is known to be a sensitive analytical method. Although it has been successfully applied to various analytical problems (1--7), the subjects for analysis have been restricted to volatile gaseous samples. Thiia is because samples are required to be
in a gaseous phase before ionization at atmospheric pressure. Thermal evaporation is frequently used to change samples from a liquid or solid state to a gaseous one (8). However, this method cannot be applied to nonvolatile thermolabile compounds, the analysis of which is one of the major subjects
0003-2700/62/0354-0143$01.25/0 0 1961 Amerlcan Chemical Society
144
ANALYTICAL CHEMISTRY, VOL. 54, NO. 1, JANUARY 1982
c H;
501
1
fl
CH2/," H-N-C, "2
' " 1 7 .+ MH 149
.-In
L
(b)
methionine
I
12
7-
~~-
0
9
COOH
lo
Figure 1. Schematic diagram of the API ion source: (1) needle electrode for corona discharge, (2) API ion source housing, (3) first aperture, (4) Intermediate region, (collision area), (5) second aperture, (6) first lens, (7) earth electrode, (8) quadrupole lens, (9) E1 ion source, (10) earth slit, (11) heater, (12) nebulizer.
for mass spectrometry these days. Several sample introduction methods for nonvolatile compounds into a chemical ionzation (CI) ion source have been reported, including a nebulizing method (9-11). It seems that the nebulizing method combined with CI has a serious droplet size problem and another in cleaning the ion source, which is easily contaminated by solvent and samples. These problems become serious mostly because the ion source is operated at low pressure, such as 1 torr or less. It is expected that the droplet size can be decreased more effectively at atmospheric pressure by mixing the droplets with heated gases. An atmospheric pressure ion source can be cleaned very easily, even when it is contaminated by solvents or samples. Many kinds of clusters are produced through API processes followed by adiabatic expansion into a low-pressure region. Such cluster formation is not favorable for analytical purposes. However, those clusters can be dissociated into quasi-molecular ions by a collisional excitation technique reported previously (12). The purpose of this paper is to demonstrate that a nebulizing sample introduction method combined with API can successfully provide quasi-molecular ions of nonvolatile compounds dissolved in various solvents. Amino acids, adenosine, inosine, guanosine, and kanamycin A and B are investigated. EXPERIMENTAL SECTION Apparatus. A single focusing mass spectrometer (Hitachi RMU-GM), equipped with an API ion source, was used. A schematic view of the apparatus is shown in Figure 1. The details of the apparatus will be published elsewhere (13). Sample solutions were nebulized to produce small droplets. A piezoelectric ultrasonic vibrator (2 MHz) was used as a nebulizer. The droplets were mixed with nitrogen gas and carried through a glass heating tube into the atmospheric pressure ion source. The glass tube and the ion source were heated to about 130 OC. Corona discharge was used to produce primary ions. The total discharge current was 5 PA. Clusters, produced in the API ion source, were introduced into the intermediate region of 0.1-0.2 torr through the first aperture (0.1 mm 4). This region was evaculated with a 1200 L/min rotary pump. Ions were accelerated under an electric field to excite them through multiple collisions with neutral gases. A drift voltage of 40 V was applied between the fist and second aperture electrodes. Clusters were dissociated into quasi-molecular ions by the collisional excitation. The ions, passing through the second aperture (0.4 mm 4), went through a quadrupole lens and an E1 ion source into the analyzing region. The acceleration energy was determined by the voltage applied to the second aperture electrode and was 2.8 keV. Dissociation of clusters after passing through the second aperture is not favorable. It will cause the increase of background
117
1 50
COOH
130
l
150
100
H-C-H COOH
~
~
200
Y!?z
Flgure 2. API spectra of amino acids: (a) arginine, (b) methionine, (c) glutamic acid.
signals, when the clusters dissociate during acceleration, or produce intense ghost peaks, when they dissociated in a field free region. Declustering in the intermediate pressure region is also effective to avoid this trouble. Ions were electrically detected with an electron multiplier (the gain was lo6) and an electrometer. Total ion current at the ion A (10' counts/s). Spectra were recorded collector was about with an UV recorder. Operation. About 10 pg of each sample was dissolved in 500 p L of methanol-water (150) or acetone-water and then injected into the nebulizer. Reactant ions were protonated methanol or acetone and their clusters. When organic solvents were not added to water, reactant ions were protonated water clusters (H+W,, n = 1, 2, 3, ...; W is water). Although a fairly large amount of the solution (20 pL) was spent for recording a spectrum in this experiment, the sample size can be diminished by improving sample introduction geometry. RESULTS AND DISCUSSION Amino Acids. Arginine, leucin, phenylalanine, methionine, and glutamic acid were investigated. Quasi-molecular ions (MH+) for all the investigated amino acids were observed as base peaks. Some of these API spectra are shown in Figure 2. The ions a t m f z 65 and 97 are protonated methanol clusters, which are the reactant ions for arginine and methionine. The ions at m / z 59 and 117 are protonated acetone clusters, which are the reactant ions for glutamic acid. Fragments due to loss of H 2 0 or NH:, appear for arginine (Figure 2a). The quasi-molecular ion (MH+) of methionine is very intense and the fragments at m / z 102 and 104 are due to bond ruptures a t "a", as shown in Figure 2b. Nucleosides. Adenosine, inosine, and guanosine were investigated. An API mass spectrum of adenosine is shown in Figure 3. The quasi-molecular ion (MH+) is the base peak and only one major fragment, at m / z 136, is observed. This fragment is due to the base moiety of the compound. No fragment from the saccharide moiety is observed in the API spectrum. API spectra of inosine obtained by both nebulizing sample introduction and for sample introduction by thermal evaporation are shown in Figure 4. The base peak at m / z 137 is due to the base moiety of the compound. MH+ is abundant;
ANALYTICAL CHEMISTRY, VOL. 54, NO. 1, JANUARY 1982
;I-
Adenosine m.w. 267
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:50
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I
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145
Guanosine
3
C
aJ c .-c 0
.-c 100
70
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Flgure 3. API spectrum
of
300
mh
~
I
-0aJ
I
I
a
133
1,
0
1'
,I, I , ,
,
,
,
,
,
,
,
,
,
,
.,
,
adenosine.
I nosine (m.w. 268)
100-
Flgure 5. API spectrum of guanosine. Kanamycin A m.w. 484
c
C
1
%
-
2731 269 265-k
1331
1
110
.-c
200
150
5
, I
'
250
I
I""
I
100
300
403
500
Figure 6. API spectrum of kanamycin A.
o
l
110
,
,
,
, ' ,
200
150
,
I
--JJ 250
"/Z
Figure 4. API spectra of inosine: (a) sample introduction by thermal evaporation, (b) nebulizing sample introduction.
however, the saccharide moiety is hardly observable in the nebulizing sample introduction (Figure 4b). On the other hand, saccharide moieties (S') a t m / z 133 and (2s - H)' a t m/z 265 are observed, together with (2BlH + H+) at m/z 273, in the sample introduction by thermal evaporation. Although ions a t m / z 269 are observed, they are lew abundant than the ions at m / z 273. It is likely that inosine decomposed into saccharide (S) and base (B) parts through heating and the ions at m / z 265,269, and 273 are reaction products, such as (2BH H)+, (S BH)+, and (2s - H)+, due to the ionization processes. It is interesting to compare these API spectra with FD and FD/CID spectra of inosine. Although the saccharide moiety was observed in an FD Eipectrum of inosine, it was not observed in its FD/CID spectrum for the molecular ions. This, together with the above API resudts, suggests that the saccharide moiety cannot be produced from MH+ by unimolecular reaction. An API spectrum of guanosine is shown in Figure 5. The base peak is due to the base moiety of guanosine at m / z 162. MH+ is also observed abundantly at m / z 284. However, the fragment due to sacchlaride moiety was3 hardly observable. Kanamycin A anal B. Kanamycin is nonvolatile and thermolabile. Quasi-molecular ions of kanamycin cannot be observed in E1 and CI spectra. API coupled with nebulizing sample introduction provides abundant quasi-molecular ions for kanamycin A and B, as shown in Figures 6 and 7. In both cases, the base peaks are MH+ and structurally informative
+
+
d
'
I
1611163
I
01 , . 100 ,
,
I
1. . , , , 200 ,
323.324
, ,
,I. '! , , .I. ,
,
300
, I
, , ,
"/.
.,, 400
,
1
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,
,
.I. , 500
1
, , ,
,
, , ,
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I
600
Figure 7. API spectrum of kanamycin B.
fragments due to glycosidic bond cleavages are observed. These include ions a t m / z 162, 163, and 324 for kanamycin A and m / z 161, 163, 323, and 324 for kanamycin B, which reflect their molecular structures well. Clusters produced by MeOH or water attachment to MH' are also observed. However, clusters between fragments and solvent molecules are hardly observable. It is likely that these fragments are not produced in the atmospheric pressure ion source but in the intermediate region by collisional excitation and dissociation. Otherwise, clusters between the fragments and solvent molecules would be more abundant, a t least as abundant as those between MH+ and solvent molecules.
CONCLUSION It has been successfully demonstrated that APIMS can be applied to obtaining molecular ion species of nonvolatile compounds using the nebulizing sample introduction method. Solvents, such as water or MeOH, can be used even if they include salts. These solvent molecules act as reagents in the chemical ionization a t atmospheric pressure. Contamination of the ion source was not serious because the ion source temperature was not very high and it seemed that nebulized solvent cleaned the ion source. These findings are very con-
Anal. Chem. 1082, 5 4 , 146-148
148
venient for direct connection of a liquid chromatograph and a mass spectrometer (24).
(7) Mltchum, R. K.; Moier, G. F.; Korfmacher, W. A. Anal. Chem. 1960, 52, 2278. (8) Carroll, D. 1.; Dzldic, 1.; Stlllwell, R. N.;Haegeie, K. D.;Horning, E. C. Anal. Cbem. 1975, 4 7 , 2369.
LITERATURE CITED
(9) Arpino, P.; Baidwin, M. A.; McLafferty, F. W. Biomed. Mass Specfrom. 1974, 1 , 80. (IO)Tsuge, S.;Hirata, Y.; Takeuchi, T. Anal. Chem. 1979, 51, 167. (11) Henion, J. D. Anal. Chem. 1978, 5 0 , 1687. (12) Kambara, H.; Mitsui, Y.; Kanomata, I. Anal. Cbem. 1979, 51. 1447. (13) Kambara, H.; Mitsui, Y.; Hirose, H., to be submitted for publication in Sbitsuryo Bunseki (14) Arpino, P. J.; Gulochon, G. Anal. Cbem. 1979, 5 1 , 682 A.
(1) Horning, E. C.; Carroll, D. I.; Dzidic, I.; Haegele, K. D.; Lin, S. N.;
Oertii, C. U.; Stillwell, R. N. Clin. Chem. (Winston-Salem N . C . ) 1977, 23, 13. (2) Gray, A. L. Anal. Cbem. 1976, 4 7 , 600. (3) Reid, N. M.; French, J. B.; Buckiey, J. A.; Lane, D. A.; Lane, A. M. Sclex Inc. Appllcatlon Note, 1977, No. 677. (4) Lovett. A. M.; Reld, N. M.; Buckiey, J. A.; French, J. B.; Cameron, D. M. Blomed. Mass Soectrom. 1979. 6 . 91. (5) Kambara. H.; KanGata, I. Anal. Chern. 1977, 4 9 , 270. (6) Kambara, H.; Ogawa, Y.; Mitsui, Y.; Kanomata, I. Anal. Cbem. 1980, 52, 1500.
.
for review August 4, l981- Accepted October 1, 1981.
Solvent Extraction of Low-Molecular-Weight Polycyclic Aromatic Hydrocarbons from Reversed-Phase Liquid Chromatographic Effluents I. Ogawa and C. D. Chrlswell" Ames Laboratory-USDOE,
Iowa State Universl~,Ames, Iowa 5001 1
High-performance liquid chromatography provides an effective means of separating constituents of samples of environmental origin, When suck samples contain large numbers of constituents a t low concentrations, retention times and detector responses provide insufficient data for component characterization. Coupling of HPLC fractionation with GC/MS characterization has proven to be a powerful technique for determining compounds of interest. Reversed-phase HPLC procedures are the most effective for separation of samples containing low-molecular-weight polycyclic aromatic hydrocarbons. However, the aqueous methanol or acetonitrile solvents used with reversed-phase HPLC are incompatible with high-resolution, high-sensitivity gas chromatography. Reversed-phase solvents can be removed from a sample by distillation or by evaporation with an inert gas. Both of these techniques also lead to significant losses of volatile analytes such as low-molecular-weight polycyclic aromatic hydrocarbons. Solvent extraction with large volumes of pentane has been used to isolate polycyclic aromatic hydrocarbons from HPLC effluents containing methanol (1) and from lowpressure liquid chromatographic effluents containing 2propanol (2). In the present work it has been demonstrated that low-molecular-weight polycyclic aromatic hydrocarbons can be isolated from reversed-phase HPLC solvents by a one-step solvent extraction using a small volume of solvent. The procedure is rapid and convenient and the use of a small volume of solvent eliminates the need for reducing the volume of extraction solvent by distillation or other techniques. The utility of the method has been demonstrated by the determination of biphenyl on fly ash.
EXPERIMENTAL SECTION Solvent Extraction. Separate solutions were prepared in 60-mL separatory funnels containing 50 mL of high-purity water (Millipore,Bedford, MA), 3 mL of either methanol or acetonitrile (Burdick and Jackson, Muskegon, MI), and 2,100, or 1000 pg of naphthalene, anthracene (Chem. Services, West Chester, PA), or acenaphthylene (Aldrich, Milwaukee, WI). Between 0.2 and 0.5 mL of a candidate extraction solvent was added to each separatory funnel, and the mixture was shaken vigorously for 2 min. After the phases separated, the aqueous layer was discarded and the organic layer drained into a collection vessel. The separatory funnel was rinsed with 0.1-0.2 mL of the same solvent which was then combined with the extraction solvent. The combined ex0003-2700/82/0354-0146$01.25/0
traction and rinse solvents were dried over anhydrous sodium sulfate (Fisher,Fair Lawn, NJ) which had been heated previously to 450 "C for 2 h. When dichloromethane was used as an extraction solvent, its solubility in water required the use of 1.3 mL for extraction in order to recover 0.5 mL. In addition, a second extraction was required with 0.2 mL of dichloromethane in order to obtain reproducible results. Recovery of Analytes from HPLC Effluents. Mixtures containing either 2 or 100 pg each of the dicyclic and tricyclic aromatic hydrocarbons naphthalene, acenaphthylene, and anthracene per 25 pL of solution were prepared in methanol and in acetonitrile. These solutions were separated with an SP8000 liquid chromatograph (Spectra Physics, Santa Clara, CA) equipped with a 25-pL injection loop, a 254-nm UV absorbance detector, and a 4.6 mm X 25 cm, 10 pm Lichrosorb RP-8 column (Jones Chromatography, Columbus, OH). Both linear gradient and isocratic separation modes were used with acetonitrile-water and methanol-water elution solvents. In all cases separations were performed at a flow rate of 1 mL/min at ambient temperature. Three-milliliter fractions containing the individual components of interest were collected manually. These fractions were diluted with 50 mL of water, extracted, and dried by using procedures described above. Determination of Analytes. Recovery of model compounds from standard mixtures and from HPLC effluents was determined by gas chromatography using a Tracor Model 560 gas chromatograph (Tracor, Austin, TX) equipped with a flame ionization detector and 6 ft X 2 mm i.d. glass column packed with 3% OV-17 on Chromosorb W-AW-DMCS. Quantitation was by comparison with an internal standard of 2-methylnaphthalene. Determination of Low-Molecular-Weight Polyaromatic Hydrocarbons on Fly Ash. A 50-g sample of electrostatic precipitator hopper ash from a local power plant coburning refuse and coal was subjected to ultrasonic extraction with 100 mL of 1:l dichloromethane-benzene. The volume of the extraction solvent was reduced to approximately 1mL by distillation, acetonitrile added, and the remaining dichloromethane-benzene removed by distillation. Constituents of the sample were separated by liquid chromatography using an SP8OOO instrument. Duplicate separations were performed by using a 250-pL injection loop, a 4.6 mm X 10 cm, 10-pm medium-performance RP-8 column (Brownlee Labs, Santa Clara, CA) at a flow rate of 1mL/min and ambient temperature. For these separations a linear gradient from an initial 20:80 acetonitrilewater t o 50:50 acetonitrile-water in 10 min was used. The final composition was held for 15 min and the composition was then raised to 100% acetonitrile to flush the column. In addition, duplicate separations were performed by 0 1981 American Chemical Society
