1074
Anal. Chem. 1900, 52,
(19) McConnell, E. E.; Moore, J. A.; Haseman, J. K.; Harris, M. W. Toxicoi. Appl. Pharmacol. 1976, 3 7 , 146. (20) Poland, A.; Glover, E.; Kende, A. S. J . 6iol. Chem. 1976, 251, 4936. (21) Higginbotham, G. R.; Huang, A.; Firestone, D.; Verrett, J.; Ress, J.: Campbell. A. D. Nature (London) 1968, 220, 702. (22) Schwetz, 9. A.; Norris, J. M.; Sparschu, G. L.; Rowe, V. K.; Gehring, P. J.; Emerson, J. L.; Gerbig, C. G. EHP. Environ. Health Perspect. 1973,
_.
5 87
(23) Johnson, R. L.; Gehring, P. J.; Kociba, R. J.; Schwetz, B. J. EHP, Environ. Health Perspect. 1973, 5 , 171. (24) Cantrell, J. S.;Webb, N. C.; Mabis, A. J. Acta C~stallogr., Sect. 6 1969, 1325,150. (25) Schwetz, B. A.; Norris, J. M.; Sparschu, G. L.; Rowe, V. K.; Gehring. P. J.: Emerson, J. L.;Gerbig, C. G. Adw. Chem. Ser. 1973, No. 120, 55. (26) Matsumura, F.; Ward, C. T. Project No. OWRT A-058-Wis; Wisconsin University: Madison, WI, 1976. (27) Nestrick, T. J.; Lamparski, L. L.; Stehl, R. H. Anal. Chem. 1979, 51, 2273. (28) Poland, A. E.; Yang, G. C. J. Agric. Food Chem. 1972, 2 0 , 1093. (29) Kende, A. S.; Decamp, M. R. Tetrahedron Letf. 1975, 33, 2877.
1874-1877
(30) Boer, F. P.;van Remoortere, F.; Muelder, W. W. J . Am. Chem. Soc. 1972, 9 4 , 1006. (31) Aniline, 0. Adv. Chem. Ser. 1973, No. 120. 126. (32) Plimmer, J. R. Residue Rev. 1971, 3 3 , 47. (33) Plimmer, J. R.; Klingebiel, U. I.; Crosby, D. G.; Wong, A. S. Adv. Chem. Ser. 1973, No. 120, 44. (34) Crosby. D. G.; Wong, A. S.;Plimmer, J. R.; Woolson, E. A. Science 1971, 173, 748. (35) Plimmer, J. R.; Klingebiel. U. I. Science 1971, 174, 407. (36) Lamparski, L. L.;Stehl, R. H.; Johnson, R . L. Environ. Sci. Techno/. 1980, 14, 196. (37) Stehl, R. H.; Papenfuss, R. R.; Bredeweg, R. A,; Roberts, R. W. Adv. Chem. Ser. 1973, No. 120, 119. (38) Buser, H. R. J . Chromatogr. 1976, 129, 303. (39) Buser, H. R. Chemosphere 1979, 8 , 251. (40) Kearney, P. C.; Isensee, A. R.; Helling, C. S.;Woolson, E. A,; Plimmer, J. R. Adv. Chem. Ser. 1973, No. 120, 105.
RECEIVED for review April 30, 1980. Accepted June 27, 1980.
Separation of Chloride and Bromide from Complex Matrices Prior to Ion Chromatographic Determination Darryl D. Siemer Exxon Nuclear Idaho Company, Inc., P.O. Box 2800, Idaho Falls, Idaho 83407
The method involves a separation of the chloride and/or bromlde from the solution concomitants by passing the sample through a silver-loaded ion exchange system. The halide is then eluted from this column with ammonium hydroxide. The coeluted silver Is trapped In a Jones reductor leaving the halides in an ammoniacal soiutlon Ideally suited for an ion chromatographic finish analysis. The separation procedure is quantitative and effectively eliminates most of the interferences encountered In the direct analyses of the complex solutions encountered In the nuclear fuel reprocessing industry.
The determination of chloride in many of the process streams encountered in the nuclear fuel reprocessing industry is often complicated by rather exotic matrix concomitants. The analytical technique must contend with a host of metals (e.g., Al(III), Sn(IV), Zr(IV), Ca(II), U(IV), U(VI), B(III), CrUII), H(I), Hg(II)), with the fluoro complexes of many of those metals and with relatively overwhelming concentrations of fluoride, nitrate, and sulfate ions and lesser amounts of nitrite and phosphate ions. Modern ion chromatography utilizing conductometric detection with “suppressor-column” suppression of the eluant’s background signal is in this writer’s opinion as much an answer to anion analysis as the inductively coupled plasma (ICP) is to metal ion analyses ( I , 2). It permits the rapid quantitation of most anions a t sub-part-per-million levels with little more fuss than a n intelligent choice of eluent and dilution factor. However, it does suffer from “overloading” effects which occur when small amounts of an analyte anion are accompanied by overwhelming amounts of other anions. This tends to broaden the peaks and cause overlap. I t is also possible to “poison” the separator column by inadvertently precipitating a metal ion concomitant out on it. It is for these reasons that this writer decided to attempt to develop a simple, inexpensive, and rapid means to separate chloride from any or all of the matrix concomitants listed 0003-2700/80/0352-1874$01.OO/O
above. A successful method was developed utilizing a silver-loaded cationic exchange resin concentrator column with subsequent elution of the chloride from that column with ammonium hydroxide. The coeluted silver is removed by passing the ammoniacal solution through a miniature amalgamated zinc column, and the resultant solution is analyzed with a n ion chromatograph.
EXPERIMENTAL SECTION Apparatus. A Model 10 ion chromatograph, available from
Dionex Corp. was used for this work. A standard 3 by 150 mm anion column was used as a precolumn in series with a standard 3 by 150 mm anion separator column in order to protect the longer column from the deterious effects of metal salt retention. These columns have been described by Small ( I ) . A standard 6 by 250 mm anion suppressor column was used. All of these columns are available from Dionex. Disposable plastic-tippedmicropipets were used for measuring sample volumes. Silver-Loaded CoEumn. Figure 1shows the tiny column used for separating chloride from sample solutions. The actual column is a 30-mm length of 4 mm 0.d. borosilicate glass tubing with a medium-porosity glass frit sealed to its bottom end. The upper end is sealed to a length of 12 mm 0.d. tubing which serves as a sample aliquot reservoir. The column is prepared for use by pouring enough of a water slurry of BIO RAD, AG 50W-X8 hydrogen form, 200-400 mesh, cation exchange resin into it to fill the small diameter section. The column is inserted into a hole in a 00 rubber stopper and then mounted in a suction flask. After the water is drawn through, 1 mL of 5% silver nitrate solution is drawn through followed by another 1 mL of water. Jones Reductor. Figure 1 also depicts the Jones reductor column used to remove silver coeluted from the silver-loaded column when the chloride is eluted. This column is filled with 20 mesh zinc granules and is charged with mercury by drawing 10 mL of the acidified mercuric nitrate solution through it. The bottom section of this column is made from a 50-mm length of 4 mm 0.d. tubing and has two expanded sections above it. The lower of these sections (7 mm 0.d. tubing) is large enough to accommodate the end of the lower section of the silver-loaded column and the upper section (12-mm tubing) fits the 00 stopper fitted to the end of that column. A two-hole rubber stopper is fitted over the bottom section of the zinc-mercury column to 0 1980 American
Chemical Society
ANALYTICAL CHEMISTRY, VOL. 52, NO. 12, OCTOBER 1980 i I
/
1875
A
C/” A
-r
1m h o 4
C -5 min Figure 1. Silver-loaded column mounted over Jones reductor column: (A) 00 rubber stopper, (B) silver-loaded cation exchange resin column, (C)glass frit, (D) mercury-coated zinc granules, (E) to vacuum source, (F) neck of 100-mL volumetric flask.
+
Figure 2. Chromatogramsof complex solutions both with and without separation step: (A) no separation, (B) with the separation, (C) chloride alone-no concomitants and no separation steps. The solution tested has 200 pL each of the “Matrix mix”, U(V1) solution, and 1000 ppm chloride standard. It also contained 500 pL of the stock phosphate standard and 1000 pL of the sulfate standard.
Table I. “Matrix Mix” Composition H’
1.7 M
Zr( IV) Al( 111) Sn(1V) Cr( 111) Na(I1
0.44 M 0.7 M
3.39 M 2.55 M B( 111) 0.24 M the balance is water FNO,-
1.8 glL 1.3 g/L 0.16 a / L
permit the use of standard 100-mL volumetric flasks as suction flasks. Reagents. All reagents were prepared from reagent grade salts dissolved in water. The water used in this study was purified with a Milli Q System (Millipore Corp.). “Matrix Mix” is a solution representative of mixed dissolved aluminum and “Zircalloy 2” cladding alloys used for nuclear reactor fuel rods. It contains the analytical concentrations of the constituents listed in Table I. A solution of 30 g/L of uranium(V1) nitrate in water was also prepared for use in matrix interference studies. Stock solutions (1000 mg/L) of nitrate, chloride, nitrate, phosphate, sulfate, bromide, and iodide ions were prepared by dissolving stoichiometric quantities of the respective sodium salts in water. Other solutions used include 0.595 F sodium bicarbonate, 0.472 F sodium carbonate, 5% w/v silver nitrate, 0.3 F hydrofluoric acid, 1 F ammonium hydroxide, concentrated ammonium hydroxide (15 F), 8 F nitric acid, and a 1% w/v solution of mercuric nitrate monohydrate in 0.3 F nitric acid. These reagents were stored in plastic bottles equipped with calibrated eyedroppers to facilitate handling in the procedure. Column Regeneration. After a silver-loaded column has been used for an analysis, it is regenerated by drawing 1 mL each of 8 M nitric acid, 5% AgN03,and 1 mL of water through it in that order. The Jones reductor is rejuvenated periodically by drawing 2 mL of the 1% mercuric nitrate solution through it. It should have a shiny (silvery) appearance throughout at least the lower half of its length if it is to be used for an analysis. Separation Procedure. A miniature silver-loaded ion exchange column is placed onto the suction flask, and the sample is drawn through under vacuum. After the sample has passed through, the column is rinsed first with 0.5 mL of 0.3 F hydrofluoric acid and then with 0.5 mL of water. Then the column is placed over the tiny Jones reductor (Figure 1) mounted on a volumetric flask and 7 drops (0.3 mL) of concentrated ammonium hydroxide is added to the concentrator column. The vacuum is then applied and the chloride eluted into the 100-mL volumetric flask. The column is rinsed with two 10-drop (about 0.5 mL) aliquots of 1 M ammonium hydroxide solution. Then the column-reductor assembly is removed and 0.5 mL of each of the
Table 11. Ion Chromatographic Conditions eluent flow rate analytical column precolumn detector sensitivity injection volume suppressor column
0.003 M NaHC0,/0.0024 M Na,CO, 1 3 8 mL/h, 30% pump setting 3 by 500 mm ;standard anion separator 3 by 150 mm :standard anion separator 10 p full scale 100 pL 6 by 250 mm standard anion suppressor
stock bicarbonate (0.595 F) and carbonate (0.472 F) solutions are added to the flask before it is filled to the mark with distilled water. This bromide/chloride separation procedure was used for all of the work reported in this paper.
RESULTS AND DISCUSSION A typical direct ion chromatographic determination of chloride in a complex matrix is depicted in Figure 2A. T h e ion chromatograph was run with the conditions listed in Table 11. The sample was simply diluted with water and injected into the ion chromatograph. Several features of the chromatogram are of relevance t o the analyst. First it is obvious that the chloride response is not clearly separated from that of other species. I t rides on the trailing edge of the large fluoride peak and also appears t o overlap the leading edge of another unidentified peak (phosphate”). Second, it is obvious that with the eluent used, the total analysis time will be quite long-about 18 min for the last sizable peak (sulfate) t o completely elute and for the base line to be reestablished. A better separation of the chloride peak from those surrounding it can be achieved if a more dilute eluent is used. However, if this is done the analysis time becomes even longer. Another problem with the direct approach is t h a t much of the metal ion component of the sample precipitates out as the carbonate salt on the expensive separator column or onto the precolumn if one is used. Rejuvenation of these columns with strong acid a n d / o r base to remove the metals is not always totally effective in restoring column efficiency. Figure 2B shows the chromatogram obtained when the chloride in the sample solution is separated from the matrix with one of the miniature silver-loaded ion exchange columns. Figure 2C is the chromatogram of a solution obtained when the aliquot of chloride standard was pipeted directly into a
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ANALYTICAL CHEMISTRY, VOL. 5 2 , NO. 12, OCTOBER 1980
Table 111. Recovery of Chloride in Various Solutionsa
7
1mho A
A 4 min
I
Figure 3. Chromatogram of solution after chloride separation from mercury-containing matrix (A) and that of a sample standard (B).
100-mL flask, and amounts of ammonia and carbonate/bicarbonate solutions equivalent to those used when the column separation system was implemented were added before making up to volume with water. Adding the carbonate/bicarbonate mixture reduces the “water dip” interference on the chloride peak. A comparison of the first two chromatograms reveals that the silver-loaded column separation procedure effectively separates t h e chloride from the bulk of the other anionic species. The second chromatogram has a small fluoride peak due to incomplete washing of the silver-loaded column prior t o t h e ammonia elution. However, the small amount of fluoride left in no way interferes with the chloride determination. T h e comparison of the second and third chromatogram in Figure 2 shows t h a t t h e separation/elution efficiency of the system is very good-in this instance, 100.6% recovery of chloride from the complex original sample solution. Other species which were thought to be potential interferents include mercuric and nitrite ions. Mercury is used in the nuclear fuel rod dissolution process and often is present at formal concentrations as high or slightly higher than that of the chloride. Mercury forms a series of strong chloro complexes ( K , = 1.9 x IO7 ( 4 ) ) and it was feared that its presence might prevent the precipitation of the chloride as silver chloride in the silver-loaded ion exchange column. T o test this supposition, a 2.5 stoichiometric excess of mercuric ion was added to a “matrix mix” sample containing 200 pg of chloride and the solution subjected to the separationanalysis procedure. T h e chromatogram of this solution (3A) a n d a chloride-only standard (3B) are depicted in Figure 3. There is no mercury interference because the overwhelmingly high effective silver ion concentration on the separator column competes successfully with the much lower mercuric ion concentration present for the chloride in the sample solution. Nitrite was thought t o be a potential interferent both because its retention time in the ion chromatograph is similar enough to t h a t of chloride that the peaks usually overlap somewhat and because it forms a slightly soluble salt (Kgp.= 4.8 X ( 3 ) )with silver. However, in practice silver nitrite is sufficiently soluble t h a t t h e dilute hydrofluoric acid and then water rinsing steps are sufficient to wash it off of the column if it is indeed ever trapped there. Bromide behaves like chloride. T h a t is to say it is first efficiently trapped on the silver-loaded column when the sample is drawn through and can be then readily eluted with ammonium hydroxide. Of course, its behavior in the ion chromatographic instrument is not identical with that of chloride and it does give a well-separated, distinct peak. However, iodide cannot be eluted from the silver-loaded
matrix concomitantsa
% recoveriesblc
200 pL of “Matrix mix” 200 kL of “Matrix mix” + 200 pL of U( VI) soln 200 pL of “Matrix mix” + 400 p L of 1%Hg(NO,);H,O soln 200 pL of “Matrix mix” + 400 p L each of the phosphate, sulfate, and nitrate stock solutions 1000 p L of 8 F nitric acid
100.6
100.2 99.6 99.8 99.3
a Total solution volume was 2 mL which included 0.5 mL of the 0.3 M HF solution, the indicated volumes of matrix solutions, 200 pL of the 1000 pg/mL chloridestanRecoveries dard, and water to make up the difference. are based on relative peak height signals of these solutions after separation with the silver-loaded column and elution into a total volume of 100 mL with that of a standard prepared by adding the aliquot of chloride standard directly to a flask and diluting to volume with ion chromatograph eluent. Figures are based on the average of 3 determinations.
column with ammonia, and therefore it cannot be analyzed in the same manner as are both chloride and bromide. The recoveries of 200 pg of chloride from solutions of various compositions are listed in Table 111. In all cases the recoveries of the chloride were quantitative. The precision of the overall procedure is 1.1% on the basis of five repeated determinations of chloride in a “Matrix mix” matrix. Ammonium hydroxide is an ideal eluent for this separation procedure. It efficiently elutes the chloride (or bromide) from the silver-loaded column, it does not interfere with subsequent removal of the coeluted silver by the Jones reductor, and because it is a base, it gives essentially no background signal of its own when the final solution is injected into the ion chromatograph. Therefore, careful measurement of its volume is unnecessary. There appears to be no loss in overall separation efficiency occasioned when the silver-loaded column is inadvertently sucked dry after either the sample or any of the washing or eluent solutions were passed through it. The separation technique described herein has several important advantages for the analysis of complex samples. First, the only species likely to interfere with t h e overall determination are those with similar silver salt solubility characteristics to that of chloride and similar ion chromatographic behavior. No such species is present in normally encountered samples. However, negative errors would be expected with sample solutions containing sufficiently high concentrations of cations which are strongly retained by the resin because the silver ion would be eluted from the column before all of chloride was precipitated onto the column. In practice, however, this did not prove to be a problem with the complex samples investigated containing large amounts of aluminum, zirconium, uranium, and hydrogen ions (Table 11). Of course, the determination of chloride in concentrated ammonium hydroxide or in other concentrated solutions of ions t h a t strongly complex silver ion would also be subject to negative interferences because the silver would be washed from the column when the sample was run through. Strong reducing agents in quantities sufficient to reduce most of the silver on the column would also be expected to interfere if present in the sample solution. Another advantage to the separation is that the elimination prior to the actual ion chromatographic finish of the usually large sulfate and nitrate concentrations found in the original sample permits sample injections into the instrument at about 4 times the rate possible without the separation. This savings in instrument time more than compensates for the additional time required for the separation.
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Anal. Chem. 1980, 52, 1877-1881
A significant advantage peculiar to this industry is that practically all of the radiologically "hot" sample components are separated from the solution that is actually injected into the ion chromatograph. This means that the instrument does not become contaminated with radionuclides to the extent that it would with direct sample injection. This significantly reduces personnel exposure to radiation and in practice saves the trouble and expense of trying to clean up or replace (and correctly dispose of) the "hot" columns.
LITERATURE CITED (1) Small, H.; Stevens, T. S.;Bauman, W. C. Anal. Chem. 1975, 4 7 , 1801-1809. ( 2 ) Mulik, J. D.; Sawicki, E. Environ. Sci Techno/. 1979, 13, 804-809. (3) Nordman, Joseph "Qualitative Testing and Inorganic Chemistry"; Wiley: New York, 1957; p 376. (4) Drucker, K Z.Elektrochem. 1912, 78,236.
RECEIVED
for review May 15, 1980. Accepted July 11, 1980.
Determination of Molecular Weight Distributions of Polymerized Petroleum Pitch by Gel Permeation Chromatography with Quinoline Eluent R. A. Greinke" and L. H. O'Connor Union Carbide Corporation, Carbon Products Division, Parma Technical Center, P.O. Box 6 1 16, Cleveland, Ohio 44 10 1
The technique of gel permeation chromatography (GPC) using quinoline eluent has been applied to measure molecular weight distributions in thermally polymerized petroleum pitches. The molecules present In the toluene-soluble fraction of polymeric pitch eluted ideally in quinoline. A study of low molecular weight model pericondensed polynuclear aromatic hydrocarbons, which elute nonideally in most GPC eluents, revealed that the elutlon volume in quinoline was closely related to the maximum length of the molecule. The molecules present in the toluene-insoluble-quinoline-soluble fraction of polymerized pltch eluted nonideally, and the elution volume was a function of the concentration of these molecules. Ideal elution behavior was obtained for these molecules after reductive hydrogenatlon. A linear GPC polymerized pitch calibration curve was obtained for the 450-2000 molecular weight range. The technique is applicable for obtaining molecular weight distributions of petroleum pitch mesophases and semicokes which have quinoline-insoluble contents approaching 100 %
.
Pitch, defined as the solid fusible residue obtained from the pyrolysis of organic materials, generally has been produced from coal, petroleum, and pure compounds. Pitches are complex in constitution and are usually composed of mixtures of polynuclear aromatic hydrocarbons (PAHs) and heterocyclic compounds. Pyrolysis or carbonization of pitch leads to polymerization of these compounds resulting in polymeric pitches a n d finally infusible coke (1-3). T h e aromatic and heterocyclic components in pitch are quite similar in chemical structure but differ in molecular size and shape. The molecular weight of these components reflects the extent of polymerization and is, therefore, an important property of pitch materials. Quantitative characterization of pitches and polymeric pitches for molecular weight distribution by gel permeation chromatography has generally been plagued by nonideal elution behavior of the smaller molecular weight constituents (4-10) and by insufficient solubility of the higher molecular weight constituents (11). The nonideal elution behavior, particularly noticeable for the pericondensed polynuclear aromatics, has been observed in tetrahydrofuran (8),toluene 0003-2700/80/0352-187750 1.OO/O
( 9 ) , benzene (9, IO), and methylene chloride ( 4 , 5 ) . This
behavior, sometimes attributed to adsorption ( I O ) , generally results in a nonlinear calibration curve a t low molecular weights for petroleum residuals (12,13)and polymeric pitches (14). Bergmann et al. (9) have reported that the anomalous elution behavior of pitch molecules disappears when 1,2,4trichlorobenzene is used as the gel permeation chromatographic (GPC) solvent. However, interfering negative peaks were observed in 1,2,4-trichlorobenzenefor the GPC elution of pitch samples (14). Lewis and Petro (14) reported the first use of GPC to obtain molecular weight distributions of polymerized pitches. In their procedures the polymeric pitch was separated into pyridinesoluble (PS) and pyridine-insoluble (PI) fractions. After lithium reduction of the PI fraction, separate GPC curves were obtained on both fractions by using toluene eluent. The use of toluene, however, limited the GPC evaluation to no more than 70% by weight of a polymeric pitch containing 50% PI. T h e lithium-reduced P I fractions contained significant amounts of toluene insolubles (TI) and the T I portion of the PS fraction was also insoluble in toluene. In search for a better solvent, Tillmanns et al. (15) employed quinoline as a GPC eluent for pitches. In our present work, the application of quinoline as a GPC solvent for polymeric petroleum pitches is investigated. We have found that the low molecular weight pitch molecules, including the pericondensed molecules, elute ideally in quinoline, that a linear calibration curve of the logarithm of the molecular weight vs. elution count is obtained for pitch molecules with a molecular weight range from 450 to 2000, that polymeric pitches or semicokes with initial quinolineinsoluble (QI) contents near 100% now can be completely evaluated by GPC after chemical reduction of the samples, and that basic kinetic pitch polymerization data can be obtained directly from GPC curves since one chromatogram is now obtained on the entire sample rather than the two chromatograms previously obtained on the P I and PS fractions (14).
EXPERIMENTAL SECTION Instrumentation. Gel P e r m e a t i o n C h r o m a t o g r a p h y . The GPC experiments were performed with B Waters Associates Model 200 GPC instrument, equipped with a differential refractometer. 1980 American Chemical Society
