2164
Anal. Chem. 1980,
The solubilities determined by the chromatography method are compared to the solubilities determined by the UV method for the aromatic liquids. In the chromatography method, all the correlation coefficients with the exception of the 0.975 value for m-dichlorobenzene a t 20.0 "C were from 0.985 to 1.OOO for the least-squares fits to eq 1. Fifteen of the nineteen aromatic liquid solubilities determined by the chromatography method agree within experimental error with the solubilities determined by the UV method. For toluene at 30.0 "C, diethyl phthalate at 20.0 "C, and ethylbenzene a t 10.0 "C the minimum solubilities (average solubility minus one standard deviation) determined by the chromatography method are respectively 6%, 7%, and 10% higher than their maximum UV determined solubilities (average solubility plus one standard deviation). For rn-dichlorobenzene at 20.0 "C, the maximum solubility determined by chromatography is, however, 15% lower than its minimum UV determined value. This nonagreement between the two methods appears to be random experimental error since the nonagreement does not depend on temperature or chemical structure. The average experimental error of both methods is 4% and, with the exception of toluene at 10.0 and 20.0 "C, there is good agreement between the experimental and literature solubilities in Tables 1-111. With the exception of the ethylbenzene experimental solubility at 10.0 "C and that of m-dichlorobenzene at 20.0 "C, the chromatography-determined solubilities are in closer agreement with their literature values than their UV determined solubilities. In Tables 1-111, the solubilities of l,l,l-trichlorethane and l,l,Z,Z-tetrachloroethanewere determined by the elution chromatography method. The UV absorption method could not be applied t o these compounds since they do no exhibit absorption spectra above the lower wavelength measurement limit of 2000 A. T h e average experimental error of the chloroethane solubilities is 2 % . At 20.0 "C, the elution chromatography determined solubilities are 3&40% higher than their literature values. Low solubility values would result from incomplete solubilization of the solute in the water during the solubility determination. Unfortunately, Arkel and Vles
52. 2164-2168
did not described the method they used (14). There are two types of solubility with temperature variation apparent in Tables 1-111. All the benzene derivatives exhibit a minimum solubility a t 20.0 "C. This behavior has been observed for the alkyl benzenes and has been ascribed to a transition in the structure of water near this temperature (5). The chloroethanes, however, tend to remain fairly invariant with respect to temperature. I t is difficult to be more definitive about these behavior patterns since measurements were taken a t only three temperatures. For the study of this property in more detail, solubility measurements will have to be performed at smaller temperature intervals in this range.
LITERATURE CITED (1) (2) (3) (4) (5) (6) (7) (8) (9)
(IO) (1 1) (12) (13) (14)
Rex, A. Z.Phys. Chem. 1908, 55,355-370. Klemenc, A.; Low, M. Red. Paw. Chim. Pays-Bas 1930, 49, 629-640. Gross, P. M.; Taylor, J. H. J . Am. Chem. SOC.1931, 53,1745-1751. Bohon. R . L.; Claussen. W. F. J . A m . Chem. SOC. 1951, 73, 1571-1578. Arnold, D.; Plank, C.; Erickson, E. Chem. Eng. Data Ser. 1958, 3, 253-256. Wauchope, P.; Getzen, F. J . Chem. Eng. Data 1972, 77, 38-41. Franks, F.; Gent, M.; Johnson, H. H. J . Chem. SOC.1983, 2716-2723. Ben-Naim, A.; Wilf. J.; Yaacobi, M. J . Phys. Chem. 1973. 77,95-102. Schwarz, F. P. J . Chem. Eng. Data 1977, 22, 273-277. May, W. E.; Wasik, S. P.; Freeman, D. H . Anal. Chem. 1978, 50, 997- 1000. Brown, R.; Wasik, S.P. J. Res. Natl. Bur. Stand., Sect. A 1974, 78 (45), 453-460. Schwarz, F. P.; Wasik, S. P. J . Chem. Eng. Data 1977, 22, 270-273. Schwarz, F. P. Anal. Chem. 1980, 52, 10-15. van Arkel, A. E.; Vles, S. E. Red. Paw. Chirn. Pays-Bas 1938. 55, 407-4 11.
RECEIVED for review May 19,1980. Accepted August 11,1980. This work has been supported by the Office of Environmental Measurements at the National Bureau of Standards. Certain commercial equipment, instruments, and materials are identified in this paper in order to specify adequately the experimental procedure. In no case does such identification imply recommendation or endorsement by the National Bureau of Standards, nor does it imply that the material, instruments, or equipment identified are necessarily the best available for the purpose.
Size Exclusion Chromatographic Analysis of Refuse-Derived Fuel for Mycotoxins Merlin K. Bicking and Richard N. Kniseley" Ames Laboratory-USDOE,
Iowa State University, Ames, Iowa 500 1 1
A Styragel packing material is characterized in several solvent systems by using a series of test solutes and mycotoxins. Differences in interpretation with other work are discussed. Three different separation modes are generated on one stationary phase. An improved separation of mycotoxlns from a complicated matrix results by simultaneously using size exclusion and liquld-liquid partitioning.
Refuse-derived fuel (RDF) is becoming increasingly important as an energy source. Since this fuel is derived from urban waste, i t is of interest to analyze the fuel for fungal metabolites known as mycotoxins ( I ) . Some of these mycotoxins are toxic or even oncogenic and, if present, could be 0003-2700/80/0352-2 164$0 1.OO/O
hazardous to personnel who work with the wastes. In samples from an RDF processing plant, it was found that the accepted "official methods" for determining mycotoxins, employing conventional column or thin-layer chromatography or various precipitation reagents (2),were unsatisfactory. The RDF matrix is a very complex mixture of organic compounds and conventional clean-up methods are not very effective. This results in an unacceptable level of background streaking when thin-layer chromatography (TLC) is used for analysis. The search for an alternative method for cleaning up samples has led to a consideration of size exclusion chromatography (SEC). The reported use of an SEC resin for mycotoxin analysis is limited ( 3 ) . Size exclusion is not the only mechanism operating in these resins. Nonexclusion effects in SEC have been reviewed ( 4 ) . Several interpretations have been 0 1980 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 52, NO. 13, NOVEMBER 1980
proposed, but there is still some disagreement in the literature. T h e Hildebrand solubility parameter, 6, has been employed t o explain solvent-gel and solvent-solute interactions (5-7). Recently, Mori (8, 9) has proposed t h a t t h e separation mechanism is a function of t h e polarity of t h e solvent. By varying t h e solvent polarity, one can change the elution behavior from a reversed-phase to a normal-phase system. Solubility parameters were employed t o indicate solvent “polarity”, relative to t h a t of t h e stationary gel phase. Separate adsorption a n d partition mechanisms were described. With few exceptions (ref 8, for example), most workers have ignored a fundamental interaction between solvent a n d polymer molecule. Any cross-linked polymer will be most soluble and show the greatest swelling (10) in a solvent which has a n identical 6 value. Under these conditions, a cross-linked polymer swells so as to form a kind of stationary phase “sponge” of solvent a n d gel. If t h e “polarity” (6 value) of the mobile phase is changed by adding a modifier, on t h e basis of thermodynamic considerations t h e stationary phase will still retain the original solvent. Now, if true liquid-liquid partitioning exists between t h e original stationary phase and a modified mobile phase, t h e nature of the modifier would determine the type of partitioning. For polystyrene-divinylbenzene (PS-DVB) copolymers 6 is equal t o 9.1 (10). T h u s chloroform (6 = 9.31, benzene (6 = 9.2), and tetrahydrofuran (THF) (6 = 9.1) should function well for SEC. Tetrahydrofuran has been shown to be very reactive toward hydrogen-bonding molecules (11) and was not studied here. This paper considers the change in retention of a series of mycotoxins and test solutes as a function of the total solubility parameter. For verification of this retention change, the specific solubility parameters (12),dispersion (6J, orientation (&), induction (Sin), proton donor (6a), and proton acceptor (6b), must not change drastically as 6 changes. This can be accomplished by a judicious choice of solvent modifiers. However, strongly hydrogen-bonding solvents should be avoided (13). T h u s t h e solvent binary systems chosen are chloroform/n-propyl chloride, chloroform/acetonitrile, benzene/cyclohexane, and benzene/acetonitrile. Nine mycotoxins and a series of test solutes were chosen t o provide a wide variety of functional groups. Suitable absorption at 254 nm was also considered. T h e packing chosen was designed for analysis of low molecular weight materials.
EXPERIMENTAL SECTION Liquid Chromatograph. The system employed a peristaltic pump (Gilson Minipuls 11) with 1.42 mm i.d. Viton tubing, a Rheodyne Type 50 Teflon rotary valve equipped with a 100-pL sample loop, and a Gilson Model 260 UV detector with a 2-mm, 8-pL semipreparative flow cell. The columns were borosilicate glass, 12.7 mm i.d., obtained from Laboratory Data Control. Each column included a movable bed support at each end for adjusting bed height. Each bed support was fitted with 10-pm and 40-pm Teflon filters. The packing used was Styragel (SO-A pore size, 37-75-pm particle size) (Waters Associates, Inc.). The exclusion limit was near 500. Solvents. Chloroform as received contained approximately 0.7% (v/v) ethanol to prevent air oxidation to phosgene. This was unacceptable for chromatographic purposes. The ethanol was removed by passing reagent grade chloroform through a column of neutral alumina (Activity Grade I) (25 g/500 mL of CHC1,) ( 1 4 ) . Gas chromatographic analysis showed no ethanol present. Acetonitrile was dried by refluxing over CaHz and distilling through a Vigreaux column under N2. 1-Chloropropane was distilled through a Vigreaux column under N2. Other solvents were reagent grade and used as received. All solvents were filtered through a 4-pm glass frit before use.
2165
Table I. Bed Height (cm) as a Function of Solvent Composition % modifier
base chloroform benzene
nonpolar 50 30 10 21.8
22.0
21.8 23.0 22.0 22.4
0
10
polar 30
23.0 22.4
23.0 22.4
20.4 22.4
50
20.3 20.8
Mycotoxins. The mycotoxins selected were aflatoxins B1, B2, G1, G2, sterigmatocystin, ochratoxin A, penicillic acid, patulin, and citrinin. Citrinin was a gift from Eivind Lillihoj (USDA Regional Research Laboratory, Peoria, IL). All others were obtained from the Aldrich Chemical Co. Mycotoxins were dissolved in an appropriate solvent for UV standardization, injected as 10-100 ppm solutions, and monitored near wavelengths of maximum absorbance. Solutes. The test solutes used were all reagent grade distilled in glass: benzene, toluene, phenol, nitrobenzene, acetone, methyl ethyl ketone, and pyridine. All were diluted to provide satisfactory detector responses. The stationary phase (10.0 g) was packed in each column. For the CHC13-based series, the gel was allowed to swell and was packed as a balanced density slurry in toluene/chloroform. The packing was compressed to form a 12.7 mm X 23.0 cm column. The gel was also slurried in benzene and packed into a 12.7 mm X 22.4 cm column. Agreement of capacity factors, k’, calculated for identically packed columns, was within 10.03. System Operation. At least two injections were made for each compound and the results averaged. Retention times were reproducible to 10.1 min. Flow rate was adjusted to 1.00 1 0.02 mL/min and monitored periodically. For the test solutes, detection was at 254 nm for CHC13-based solvent systems and 280 nm for benzene-based solvent systems. Peak shapes of eluting mycotoxins were symmetrical with little or no tailing. Plate counts were somewhat lower for the benzene series though. The capacity factor, k’, was calculated by using eq 1, where
V, is the retention volume of the solute and Vo is the void volume, represented by the retention of a polystyrene standard (50 000 nominal mol wt, Waters Associates). The equation for k’normally used in SEC has pore volume, Vi, in the denominator rather than Vo. Equation 1 is used here for two reasons. First, the system is operating in a non-SEC mode for much of this work and eq 1 is valid for these conditions. Second, it is unlikely that any solute can achieve total permeation without interacting with the gel and thus measurement of Vi is often a subjective experiment (15). After the solutes were chromatographed in chloroform (or benzene), the composition of the mobile phase was changed to include 10% modifier, and the experiments were repeated. Additional data were taken for 30% and 50% modifier concentrations. AU variations in modifier concentrations were made in 10% increments to prevent changes in the column packing.
RESULTS AND DISCUSSION Table I gives the bed height as a function of solvent composition. It was found that when the difference between t h e 6 value of the solvent and the gel became greater, the gel would tend to shrink. As a result, column performance deteriorated and void volume increased unless the bed height was shortened. T h e movable bed supports allowed the bed height t o be changed to correct for shrinking of the gel. Thus the mobile phase could be changed without repacking the column each time, as was suggested by Mori (9). Figure 1presents the data for the chloroform-based systems. T h e benzene-based system offers no advantage for the separation of t h e mycotoxins and is of less interest for routine procedures because of the possible health problems associated with the use of benzene.
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ANALYTICAL CHEMISTRY, VOL. 52, NO. 13, NOVEMBER 1980
Table 11. Capacity Factors (k’ ) for Mycotoxins in Chloroform-Based Solvent Systems 1-chloropropane 50% 30% 10% chloroform 10% penicillic acid patulin sterigmatocystin citrinin ochratoxin A aflatoxins
0.533
1.00 0.756 0.622
0.711 0.567
0.651 1.02 0.735 0.590 0.590 0.566
0.556 0.778 0.485 0.475 0.505 0.515
ace tonitrile
0.495 0.544 0.485 0.456 0.359 0.466
0.518 0.846 0.477 0.462 0.452 0.508
30%
50%
0.522 0.500 0.633 0.522 0.322 0.544
0.538 0.538 0.9 56 0.736 0.615
Table 111. Capacity Factors ( k ’ ) for Mycotoxins in Benzene-Based Solvent Systems cyclohexane penicillic acid patulin sterigmatocystin citrinin ochratoxin A aflatoxins
acetonitrile
50%
30%
10%
benzene
10%
30%
50%
0.272 0.636 1.44 0.882 0.982 0.300
0.531 0.802 1.21
0.53 7 1.44 0.874 0.884 0.916 0.389
0.416 1.21 0.78 2 0.782 0.851 0.386
0.400 0.690 0.700 0.600 0.480 0.460
0.480 0.598 0.706 0.627 0.480 0.608
0.358 0.435 0.747 0.674 0.474 0.578
1.00 1.02 0.448
The solvent systems to the right of the base solvent represent a reverse-phase separation 6mobile > 6stationary. T o the left is the normal-phase separation, hrnobile < 6stationary. In general, the solutes follow the trends expected, with more polar compounds eluting fasting in reverse phase and vice versa. However, it is clear t h a t there is no simple explanation and there are exceptions. Of particular interest is the tendency for the retention a t 0% modifer to increase relative to the adjacent data points. This is not apparent from the data reported by Mori (8)since he only presented data for 0% and 50% modifier concentrations. The increased retention a t 0% modifier could be the result of a size exclusion process. Perhaps the absence of other solvent effects allows greater permeation through the pores and therefore greater retention when no modifier is present. If one ignores the 0% modifier data points, there is a smooth relationship throughout the range of polarity. This is indicative of the expected liquidliquid partitioning system. Note that polar compounds such as phenol show minimum retention in the more polar mobile phase. Many SEC calibration curves obtained for a homologous series may include such polarity effects, since molecular weight and polarity are generally related in a homologous series. It should be emphasized t h a t such calibration curves are still useful because despite whatever functional group interactions are occuring, they are the same for each member of the series. However, systems of this type should not be considered strictly noninteractive chromatography (SEC). It appears that the partitioning process is occurring inside the pores of the gel rather than on the surface. The polystyrene standard elutes in the void volume and shows no signs of other effects, except in 50% cyclohexanefbenzene, where the standard is retained somewhat. Void volume is determined by other components in t h a t solvent system. If the separation mechanism is indeed partitioning, it should follow trends predicted by solubility parameter theory (16) or an expanded solubility parameter theory (17). The stationary phase is assumed to be the chloroform layer distributed interstitially among the polymer strands. A good approximation for the experimental data is obtained with the expanded treatment, when one includes a roughly 25% contribution from the polymer itself (7). Another inconsistency illustrated in Figure 1 involves the extremes of polarity, i.e., with 50% modifier. On the nonpolar side, all solutes show a decrease in retention. Partition theory predicts an increase in retention under these conditions. These retention volumes are indicative of a sorption process. The
s toe0
1
-020
I1
x, %
v
i
1
I
I
I
30% 10% CHC13 10% CHLOROPFOPANE
I
30% ACETONITRILE
I 50 %
Figure 1. Experimental log k’vs. % modifier, chloroformbased mobile methyl phase: (0)phenol, ( + ) benzene, ( X ) toluene, (0)pyridine, (a) ethyl ketone, (A)nitrobenzene, (0)acetone.
distinct CHC1, stationary phase can no longer exist under these conditions (50% modifer). Citrinin in 50% CH3CN/ CHC13 shows pronounced tailing, similar to its performance in normal adsorption chromatography. When the modifier concentration is then reduced, citrinin still shows more tailing than in the original solvent system. In addition, the original retention times for various solutes could not be reproduced. Futhermore, the original bed height could not be regenerated, even after passing CHC1, through the column for several hours. These trends are indicative of irreversible sorption on the polystyrene gel. This is not consistent with published work involving other SEC resins, where column performance was regenerated after exposure to 50% modifier (9). In that study, it was suggested t h a t partitioning occurred over a wide range of modifier concentrations. The data presented here indicate t h a t partitioning probably occurs a t modifier concentrations of less
ANALYTICAL CHEMISTRY, VOL. 52, NO. 13,NOVEMBER 1980
2167
y----+-+-
W 0
z
m a Lz
In 0
m
a W
> -
+ a
-I
W (L
LLL IO L”
0
IO
TIME (minl
Flgure 2. Elution behavior of citrinin in chloroform-base mobile phase: (a) 100% CHCI,, (b) 10% CH,CN/CHCI,, (c) 30% CH,CN/CHCI,, (d) 30 % CH,CN/CHC13 after preequilibration with 50 % CH,CN, (e) 100% CHCI, after preequilibration with 50% CH,CN.
I30 -
I20 I10
-
100 z
090
-
080 -
070 060
-
050
-
Flgure 3. Experimental k’ vs. % chloroform for chloroform/tetrahydrofuran mixtures (12.7mm X 17.6cm column): ( e ) benzene, ( X ) toluene, (m) aniline, (0)acetone, (0)phenol, (+) aflatoxins, (A)penicillic acid.
than 40%. A t high concentrations the mechanism is more likely sorption. Two good SEC solvents, chloroform and T H F , were mixed in varying ratios as shown in Figure 3. In this supposedly noninteractive mode, other effects must be considered. Hydrogen bonding is particularly important in the elution of phenol when T H F is present in the mobile phase (11). Even nonpolar solutes such as benzene and toluene show some variation. In some cases, these effects might be used to advantage. A useful separation scheme has evolved as a result of the preceding discussion. T h e mycotoxins are, in general, polar molecules and show the expected behavior in a liquid-liquid partitioning system. Such polar compounds should be more soluble in the “polar” mobile phase of a reverse-phase system and thus should show a decrease in retention relative to nonpolar solutes. These should be preferably retained by the nonpolar stationary phase. T h e opposite would be true for a normal-phase system. T h e effect of the polarity of the mobile phase is shown in Figure 4 for a chloroform extract of refuse-derived fuel. As the acetonitrile content of the mobile phase is increased (becoming more polar), the less polar components spend more time in the stationary phase and elute after the mycotoxins. The brackets indicate the elution volumes of the mycotoxins. T h e optimum separation appears to occur with 30% acetonitrile. Apparently, a large portion of the material is less polar than the mycotoxins. This technique has thus produced a “class separation” based roughly on polarity. Elution occurs
TIME (mir 1
Figure 4. Chloroform extract of an RDF sample eiuted with varying concentrations of CH3CN in the moble phase. The brackets indicate the elution times of the mycotoxins: (a) 100% CHC13,(b), 10% CH,CN, (c) 30% CH,CN, (d) 50% CH3CN. The elution time for citrinin is
indeterminate for this mobile phase.
in order of decreasing polarity when acetonitrile is present in the mobile phase. Note that for 50% CH,CN, some material elutes very slowly from the column. In fact, some colored components could not be removed from the column with this solvent system. Sorption, not partitioning, must be the mechanism operating in this case. This is further evidence that liquid-liquid partitioning may not occur over a wide range of solvent modifier concentrations as is claimed by some workers (8,9). In all solvent systems, the stationary phase shows evidence that a size exclusion process is still operating. The first components elute in a volume identical with that of the polystyrene standard used to determine void volume. This high molecular weight fraction includes the most highly colored material in the extract. It is this dual mode of operation that makes this technique useful. Styragel can be used in such a manner that one can generate three different separation modes on one stationary phase by choice of solvent alone. Since the stationary phase is relatively nonpolar, it will be most useful in the reverse-phase mode. The packing is relatively inexpensive and reusable, even on a semipreparative scale, if suitable precautions are taken. This procedure should be useful for many difficult separation problems, especially when natural products are being separated. The intelligent use of specific interactions (hydrogen bonding, dipole, etc.) should increase the versatility of the technique.
ACKNOWLEDGMENT The authors wish to express their appreciation to H. J. Svec (Ames Laboratory-USDOE, Iowa State University) for his helpful consultation during the term of this project and to Christina Barnes (Ames Laboratory Summer Student Trainee from Mount Holyoke College) for ably performing much of the tedious technical work.
LITERATURE CITED (1) Rcdricks, J. V.; Hesseltine, C. W. In “Mycotoxins in Human and Animal Health”; Mehlman, M. A., Ed.; Pathotox Publishers: Park Fails South, IL, 1977; Chapter 1. (2) “Official Methods of Analysis of the A.O.A.C.”; Horwitz, W., Ed.; Association of Official Anaivticai Chemists: Washinaton DC. 1980: D 418. section 26.030. (3) Josefsson. B. G.E.; Mailer, T. E. J . Assoc. O f f .Anal. Chem. 1977, 6 0 , 1369. (4) Gaylor, V. F.; James, H. L. Anal. Chem. 1978, 50, 29R. ( 5 ) Yamamoto. Y; Yamamoto, M.; Ebisui, S.: Takagi, T.; Hashirnoto, T.; Izuhara. M. Anal. Len. 1973, 6 , 45. (6) Saitoh, K.: Ozawa, T.; Suzuki, N. J. Chromatogr. 1978, 724, 231. D. H.; Kiiiion, D. J. Polyrn. Sci.. Polym. phys. Ed. 1977, 75, (7) Freedman, 31147
-
h%:’S.
(8) Anal. Chern. 1978. 5 0 , 745. (9) Mori, S . ; Yamakawa, A. Anal. Chem. 1979, 57,382. (10) Burreil, H.; Immergut, B. I n ”Polymer Handbook”; Brandrup, J., Immergut, E. H., Eds.; Interscience: New York, 1986; pp IV-344, IV-366.
Anal. Chem. 1980, 52, 2168-2173
2168
(11) Klimish, H. J.; Reese. D. J . Chromatogr., 1972, 67, 299. (12) Karger. B. L.; Snyder, L. R.; Eon, C. J . Chromatogr. 1976, 125, 71. (13)Karger, B. L.; Snyder, L. R.; Horvarth, C. "An Introduction to Separation Science"; Wiley-Interscience: New York, 1973; p 50. (14) Gordon, A. J.; Ford, R. A. "The Chemist's Companion"; Wiley-Inter-
science: New York, 1972; p 432. Hansler, D. W.; Hellgeth, J. W.; McNair, H.
M.; Taylor, L. T. J. Chromatogr. Sci. 1979, 17, 617. (16) Snyder. L. R. In "Modern Practice of Liquid Chromatography"; Kirkland, J. J., Ed.; Why-Interscience: New York, 1971; p 138.
(15)
(17) Karger, B. L.; Snyder, L. R.; Eon, C. Anal. Chem. 1978, 50,2126.
RECEIVEDfor review May 7,1980. Accepted August 11,1980. This research was supported by U.S. Department of Energy, Contract No. W-7405-Eng-82, Office of Health and EnvironResearch* Pouutant Characterization and Safety Research Division (GK-01-02-04-3).
Computer-Controlled Scanning Monochromator for the Determination of 50 Elements in Geochemical and Environmental Samples by Inductively Coupled Plasma-Atomic Emission Spectrometry M. A. Floyd, V. A. Fassei,' and A. P. D'Silva Ames Laboratory and Department of Chemistty, Iowa State University, Ames, Iowa 500 1 1
The application of a computer-controlled, scanning monochromator to the determination of 50 elements in geachemlcal and environmental matrices is described. The monochromator Is combined wlth an Inductively coupled plasma excitation source so that elements at major, minor, and trace levels may be determined in sequence without changlng experimental parameters other than the spectral line observed. A single set of spectral lines was found to be applicable to a broad range of sample compositions and to show negllglble spectral Interferences regardless of the sample matrlx.
In years past, elemental determinations at the major, minor, a n d sometimes at the trace level in ores, minerals, soils, manufactured products, e.g., glass and pigments, and sediments and ashes have been performed by classical gravimetric, titrimetric, and spectrophotometric techniques. During the past several decades, the classical approaches have been largely replaced by a variety of instrumental techniques, which include X-ray fluorescence, atomic absorption spectrometry, arc emission spectroscopy, neutron activation analysis, and proton-induced X-ray emission analysis. I n recent reviews ( I - @ , several authors have adequately documented that inductively coupled plasma-atomic emission spectroscopy (ICP-AES) offered several advantages as an alternative approach for the analysis of the sample types discussed above. I n view of these advantages, i t is not surprising that ICP-AES has been applied, to a rapidly increasing extent, to the analysis of the sample types discussed above (7-21). Most of the applications discussed to date have involved t h e use of a polychromator for the multielement determination of selected elements of interest in matrices of closely similar composition. When the analyst is faced with the determination of a broader range of elements a t various concentration levels in samples of widely varying composition, the fixed array of exit slits used for isolating the spectral lines in a polychromator becomes restrictive. We have recently described (22) a computer-controlled, scanning monochromator system that provides the capability for the rapid sequential determination of the elements a t the major to ultratrace levels without changing the experimental 0003-2700/80/0352-2168$01.OO/O
conditions, other than the elemental lines that are observed. In this communication, we describe the application of this instrument to the rapid determination of major, minor, and trace constituents in sample types as diverse as ores and minerals, coal and fly ash, urban particulates, and sediments. A single sample dissolution procedure is used, a n d a single set of analytical calibrations apply to the broad range of sample compositions examined. EXPERIMENTAL SECTION Instrumentation. The programmable scanning monochomator utilized in this investigation and the operating conditions for the ICP have been previously described (22). Sample Dissolution. A 0.20-g sample was accurately weighed into a 15-mL graphite crucible (Vitrecarb, Anaheim, CA) after which 2 g of NaOH pellets was added to the crucible. The crucible was gently heated with a Fisher blast burner to melt the contents, care being taken to assure that no spattering occurred. After the moisture was evaporated from the NaOH, which usually required 2 to 3 min, the sample was brought to red heat until a clear melt was obtained. The red hot fused melt was carefully and quickly poured into a 150-mL platinum dish. The upright crucible was also set into the dish. After the sample cooled, 5.0 mL of concentrated HCl was added to both the fused sample and the graphite crucible. Heat was gently applied on a hot plate to dissolve the melt, including the portions adhering to the crucible. The crucible was then thoroughly washed with deionized water and the contents were added to the platinum dish. The sample was then diluted to approximately 40 mL with deionized water and heat applied gently until the solution was clear. Samples containing high silicon content were filtered or centrifuged to remove flocculent hydrated silicon oxide. The sample solution was then transferred to a 100-mL polypropylene volumetric flask and diluted to volume with deionized water. The time required for dissolution of a sample was approximately 30 min. Prior to sample fusion, the graphite crucibles were processed by the fusion-dissolution procedure described above to minimize contamination. Crucibles preprocessed in such a manner were reusable for several fusions. During the analysis of samples, a blank solution prepared from the NaOH pellets and HC1 utilized in the fusion-dissolution procedure was analyzed, and the appropriate blank corrections were stored in memory and were automatically subtracted, if significant,from the determined total concentrations. Reference Solutions. Stock solutions were prepared by dissolution of pure metals or reagent grade salts in dilute (1% ) 0 1980 American Chemical Society
