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A N A L Y T I C A L CHEMISTRY, VOL.
51, NO. 9, AUGUST 1979
n-alkanes. Such a combination of reactors will simplify the study of these components as a function of the reaction processes. ACKNOWLEDGMENT We are grateful t o Mark T. Atwood of the Oil Shale Corporation (Tosco) and Robert Heisand of the Paraho Corporation for providing samples of shale oil. LITERATURE CITED (1) "Shale Oil, Tar Sands and Related Fuel Sources", Yen, T. F., Ed.; (2) (3) (4)
(5)
"Advances in Chemistry", American chemical Society: Washington, D.C., 1976; Vol 151. Yen, T. F., "Science and Technology of Oil Shale", Ann Arbor Science Publishers; Ann Arbor, Mich., 1976. "Analytical Chemistry Pertaining to Oil Shale and Shale Oil", National Science Foundation Conference-Workshop, June 1974; Siggia, S.,Uden, P. C. Eds. Williams, I. H. Anal. Chem. 1965, 37, 1723. Innes, W. E., Bambrick, W. E., Andreatch, A. J. Anal. Chem. 1963, 35, 1198.
(6) Innes, W. B., Bambrick, W. E. J . Gas Chromatogr. 1964, 2 , 309. (7) Rowen, Jr.. R. Anal. Chem. 1961, 33, 658. (8) Barrall 11. E. M.. Baumann, F. J . Gas Chromatogr. 1984, 2 , 256. (9) Blytos, C., Peterson, D. L. Anal. Chem. 1967, 39, 1434. (IO) Cramers, C. A., Vermeer, E. A., Cranken, J. J. Chromafographia,1977, 10, 413. (11) "Analytical Chemistry of Liquid Fuel Sources", Uden, P. C., Siggia, S., Jensen. H. B., Eds.; "Advances in Chemistry", American Chemical Society: Washington, D.C., 1978; Vol. 170, pp 213-231. (12) DiSanzo, F. P., Uden, P. C., Siggia, S. unpublished observations. (13) Carpenter, Jr., A. P., Ph.D. Dissertation, University of Massachusettes, Amherst, Mass., 1978. (14) Scrima, D. A.. Yen, T. F., Warrent, P. L. Energy Sources 1974, 7(3), 321. (15) Robillard, M. V., Uden, P. C., Siggia, S. Anal. Chem. 1079, 51,435.
RECEIVED for review March 5, 1979. Accepted May 25, 1979. This work was supported by National Science Foundation grant CHE-74-15244 and instrumentation was obtained through Research Instrument grant GP 42542 to the University of Massachusetts.
Determination of Trace Level Ions by Ion Chromatography with Concentrator Columns R. A. Wetzel," C.
L. Anderson,
Helmut Schleicher, and G. D. Crook
Ion Chromatography Systems, Dionex Corporation, 1228 Titan Way, Sunnyvale, California 94086
Ion Chromatography (IC) is shown to be a reliable method for trace analysis down to 2 parts per billion for some common anions in solution. I C techniques used to perform such analyses are described. These include the use of a 3 X 50 mm concentrator column that can be loaded with various sample volumes by syringe or automatically by pump, either off or on-line. After concentration, chloride, phosphate, nitrate, and sulfate were analyzed from ppm to low ppb levels. It is shown that conductivity detector response vs. concentration is linear over this range and that the response for a given number of milliequivalents is independent of the concentration or volume loaded. It is also shown that concentrator columns can be loaded remotely and stored for at least seven days before analysis without significantly affecting ionic determinations.
Accurate determination of trace level ions is a common analytical problem in modern laboratories. Applications include: (1) monitoring corrosion-producing ions in feed, steam generator and turbine waters in the power production industry; ( 2 ) determination of rainwater composition; (3) analysis of fuel cell effluents. Although ion-specific electrodes and a limited number of conventional wet chemical techniques enable individual trace analysis of some ions, ion chromatography (IC) enables multispecific trace analysis for the first time. Small e t al. (1) described IC principles which use conductimetric detection to monitor ion-exchange separations as well as the ion-exchange resins used. This system enables very sensitive, accurate, and precise measurement of several ions during a single analysis. IC has also been shown to be accurate and precise when compared with conventional wet chemical 0003-2700/79/0351-1532$01.OO/O
techniques ( 2 ) . These features suggested that IC would be an ideal method for performing trace ion determinations. The 3 X 50 mm concentrator column enables trace ion determinations by retaining sample ions as measured volumes of sample liquid are pumped through the column. Concentrator resin is identical to that used in the ion-exchange separator column (i.e., a pellicular anion-exchange resin containing tetramethylammonium groups attached to a styrene/divinylbenzene backbone). Sample loading can be performed with the concentrator replacing the injection loop; sample is then loaded by syringe or by pump. Concentrators may also be loaded off-line, disconnected from the ion chromatograph. In the former case, activation of the injection valve automatically places the concentrator column in-line with the separator column. In the latter case, the concentrator must be manually connected to the flow path before the separator. After injection, sample ions are separated and detected in the usual manner. Normal multispecies analysis often requires less than 5 min per ion; trace analysis requires the same time as routine analysis once the concentrator is loaded. Concentrator loading requires 5-15 min per sample. EXPERIMENTAL Apparatus. A Model 14 Ion Chromatograph (Dionex Corporation, Sunnyvale, Calif. 94086) was used for all analyses using the three methods described below. A Linear Instruments strip chart recorder was used to monitor the analyses. Instrumental conditions were: eluent, 0.003 M NaHC03/0.0024 M Na2C03; flow rate, 30% X 460 mL/h = 138 mL/h; separator column, 3 X 500 mm anion separator; suppressor column, 3 X 250 mm anion suppressor; conductivity meter setting, variable; sample volume, variable; recorder speed, 0.5 cm/min. Methods Used for Trace Analysis. Pump Loading of Concentrator Columns. To eliminate any possibility of sample contamination, samples t o be loaded by pump were placed in a Wheaton flask under a purified nitrogen atmosphere. As supplied, 0 1979
American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 51, NO. 9, AUGUST 1979 Waste
t
+
m Separator Column
Suppressor Column 2 Concentrator
Suppressor Column 1
i
Separator Column Detector
Sample
h
Pump Sample
1533
Trap H,O
HZO Distilled
SUPPRESSOR VALVE
Figure 2. Dual suppressor column flow system
Figure 1. Sample loading and injection flow system the ion chromatograph has two analytical systems, including two eluent pumps. For this experiment, one of the eluent pumps was used to load the concentrator columns while the other was used for the chromatographic separation. The concentrators were loaded at a rate of 7 mL/min as determined by measuring the effluent from the concentrator wasteline. The sample loading and injection flow system is shown in Figure 1. The two valves constitute one injection valve (upper and lower halves). Solid lines indicate liquid flow connections; dotted lines indicate alternate flow paths used when the valve is in the load position. During trace analyses, the sample flask always contains water of extremely low ionic content. Attempts to clean the flask often resulted in contamination. AI1 glassware used was thoroughly rinsed and then soaked for a minimum of 24 h with triply-distilled water. Remote Loading of Concentrator Columns. All concentrators were flushed with eluent for 4 min before loading. A 10-mL glass syringe with a stainless steel Luer adaptor was used for remote loading of concentrator columns. A female Luer adaptor was attached to the column and the sample was forced through the column by manual pressure. Excessive force resulted in leakage along the plunger and through the Luer fitting. Remote loading by pump is also possible. Loaded concentrators were then placed in line before the separator column using the flared Teflon tubing connectors provided with each column. Suppressor Column Use f o r Trace Determinations. IC suppressor columns are used to remove highly conductive eluent ions from the separator column effluent before entering the conductivity cell. During anion determinations, the suppressor exchanges H+ for Nat, thus converting the highly conductive NaHC03/Na2C03eluent to a weakly conductive, dilute H2C03 solution. One consequence of suppressor column use is that solut,ions with lower conductance than the HZCO3 exiting the suppressor column cause a negative inflection in the detector output or base line. Because sample water is less conductive than the HzCO3 solution, it causes such a negative deflection, or “water dip,” approximately 2 min after injection during anion determinations. In order to obtain reproducible results, trace sample ions of interest must be separated from the water dip. Using the HC03-/C03’- eluent listed above, the chloride peak will not separate from the dip when using a concentrator column in conjunction with a fully regenerated (100% H form) 6 X 250 mm suppressor column. Acceptable precision is obtained, though, by converting approximately 50% of the H+ form suppressor resin to Na form. This causes the water dip to become narrower and to elute earlier, thus separating the dip from the C1- peak. Another method which permits C1- trace determination is to decrease the volume of the suppressor column. As with the partially exhausted larger suppressor, the water dip is separated from the C1- peak. Smaller columns naturally have less capacity than larger columns; in order to avoid delays due to frequent regeneration of these smaller columns, a dual suppressor system was used. One suppressor may be regenerated while the other is used for analysis. Figure 2 shows the flow system used for dual
Regeneration System
~
Concentration (ppb)
CI
f
l
-
l
Conditions Eluent: 0.003 NaHC03/0.0024 NazC03 Flow Rate: 138 ml/hr Columns: 3 x 500 m m Anion Separator 3 x 250 mm Anion Suppressor Sample Volume: 10 ml Meter Full Scale Setting: 3 pMHO
l
r
l
l
l
8101214 Minutes Figure 3. Trace anion analysis using a concentrator column 0
2
4
6
suppressor columns. Figure 3 shows a typical chromatogram obtained for a mixed ion standard using a 3 X 250 mm anion suppressor column. S t a n d a r d Solutions. Standard solutions of 1000 parts per million (ppm) were prepared for individual species (Cl-, Pod3-, NO (Aft? 0 Days
m
1
Peak Height' Afte; 7 Days (mm
1
RSD (%)
1535
1
Composite standard of 100 ml w a s Ioaaed on e a c h ConcenIralO A v e r a a e 0' l h r e e deternlnatlons l o r e a c h ion
be loaded and then stored for a t least 7 days a t room temperature before analysis without significantly affecting results. Table I shows the results of Experiment One which determined t h a t sample ions are quantitatively retained on concentrators, provided the resin capacity is not exceeded. Tables I1 through V show the data obtained from Experiment Two which determined linearity for the ions studied. Response for Po43-, NO3-, and SO4*-was linear over four orders of magnitude (%lo4 ppb). Response for C1- was linear over three orders of magnitude (2-103 ppb). Correlation coefficients for a linear least squares fit were the following: C1-: 0.9999, Pod3-:0,9991, NO3-: 0.9997, S042-:0.9887. The C1- deviation from linearity a t higher levels may be due to the NO3-, lower selectivity of the resin for C1- compared to Po43-, and S042-.During loading, C1- ions may wash through the concentrator a t lower levels than the other ions. Table VI lists the data obtained from Experiment Three
ACKNOWLEDGMENT The authors thank R. Chang and F. C. Smith, Jr. for their helpful consultation and the Westinghouse R&D Center for information regarding the use of concentrator columns when monitoring the purity of waters in power plants. LITERATURE CITED (1) Small. H.; Stevens, T. S.;Eauman, W. C. Anal. Chem. 1975, 47, 1801. (2) Sawicki, E.; Mulik, J. D.; Wittgenstein, E. "Ion Chromatographic Anaiysis of Environmental Pollutions"; Ann Arbor Science: Ann Arbor, Mich., 1978.
RECEIVED for review February 15, 1979. Accepted May 18, 1979.
Gas Chromatography/Infrared Matrix Isolation Spectrometry Gerald T. Reedy," Sidney Bourne, and Paul T. Cunningham
US. Department of
Energy, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439
A novel analytkal technique for the identtfkatlon of compounds separated by a gas chromatograph has been demonstrated. The compounds are collected individually In matrices of condensed inert gas using an apparatus of unique design. The matrices are examined using an infrared spectrometer. Under appropriate collection conditions, each matrix contains sample molecules fully Isolated from one another by inert gas atoms. The infrared spectra show sharp bands characteristic of the individual vibrational transitions of the matrix-Isolated sample molecules. Practical application of the technique is demonstrated by separating a mixture of chlorinated phenols and collecting the components lndividuaily under matrix-isolation conditions.
The technique of matrix-isolation spectroscopy involves the simultaneous condensation of a gaseous sample in an excess of inert gas to form a solid matrix in which sample molecules are isolated from one another. The technique is powerful with respect to both the large variety of species that can be studied and the quality of the spectra that can be obtained. Several books and reviews have been written which describe matrix-isolation spectroscopy in detail (1-3). The matrix-isolation method has been used extensively as a research tool. Its 0003-2700/79/0351-1535$01 .OO/O
application as a practical analytical technique for the identification of compounds separated by gas chromatography is the subject of this paper. Application of the matrix-isolation technique as a routine analytical method for the spectroscopic identification of unknown compounds has not been widely practiced. An early application of the matrix-isolation technique to the analysis of permanent gases was demonstrated by Rochkind ( 4 ) ;gases were collected in inert matrices by the rapid release of small quantities of premixed sample and argon onto a cold surface. The infrared bands of the trapped species in the resulting matrices were sufficiently sharp to allow the identification of several components deposited concurrently in a matrix. More recently, G. Mamantov et al. ( 5 ) reported the use of infrared matrix-isolation spectroscopy to differentiate between polycyclic aromatic compounds on the basis of sharp bands in the 800 cm-' region of the infrared spectrum. Samples were vaporized from Knudsen cells a t about 75 "C and co-condensed with nitrogen to obtain the matrices which were scanned with a Fourier transform infrared spectrometer to yield high-resolution spectra. T o successfully obtain matrix-isolation infrared spectra of the components eluted from a gas chromatograph, certain conditions must be met. First, provision must be made for collecting several components in rapid sequence. Second, the C 1979 American Chemical Society
