Determination of trace-level vanadium in marine biological samples by

content of marine biological specimens, which have a tendency ... marine biological specimens and sediments for vanadium using pre-irradiation removal...
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178

ANALYTICAL CHEMISTRY, VOL. 51, NO. 2, FEBRUARY 1979

Determination of Trace-Level Vanadium in Marine Biological Samples by Chemical Neutron Activation Analysis Alan J. Blotcky, Carl Falcone, Victor A. Medina, and Edward P. R a c k * General Medical Research, Veterans Administration Hospital, Omaha, Nebraska 68 105, and Department of Chemistry, University of Nebraska Lincoln. Nebraska 68588

David W. Hobson Department of Biology, Texas A&M University, College Station, Texas 77840

A pre-irradiation chemistry neutron activation analysis procedure employing catlon-exchange chromatography is described for the determination of trace-level vanadium in marine biological specimens. The procedure, utilizing a low-power nuclear reactor ( 1 X ioi1 n/cm2-s), consists of wet diestion of the sample, cation-exchange chromatography employing nitric acid wash to remove the major radioactivatable contaminants (sodium and chloride ions), ammonium hydroxide elution to remove vanadium from the resin, and neutron irradiation and radioassay for ”V. The limit of detection of the method Is 30 ppb. The determinations of the vanadium content of NBS Standard Reference Material 1571 Orchard Leaves resulted in a value of 0.60 f 0.02 ppm. Determinations of the vanadium content in shrimp, crab, and oyster (RSD 5 5 % ) from four sites off and near Galveston Island, Texas, showed that the vanadium content is greater in samples taken in the industrialized areas as compared to a non-industrialized section.

the large amounts of sodium-24 and chlorine-38, almost always present in neutron-activated biological samples, cause a masking of the 1.434-MeV vanadium peak (52V). This means t h a t unless quantities of vanadium are very large, or t h e sodium and chlorine contributions are very small, vanadium cannot be accurately detected in a biological matrix. It then becomes necessary to devise means of sodium or vanadium separation from the sample, such as the pioneering method used by Meinke (21, involving post-irradiation chemistry. Unfortunately, post-irradiation chemical techniques have several drawbacks, especially in t h e case of a short-lived radioisotope such as ”V ( T I l r= 3.77 in), where appreciable quantities of activity are lost prior to radioassay. I n a recent study, Guinn and his co-workers (8) analyzed marine biological specimens and sediments for vanadium using pre-irradiation removal of sodium by hydrated antimony pentoxide (HAP). According to Guinn, the procedure worked fairly well but activation of antimony dissolved from the HAP made it difficult t o detect low vanadium levels in small biological samples. Guinn also proposed an alternate method involving co-precipitation of vanadium with ferric hydroxide, but found that the reproducibility of the method was not very good. At the present time, there is a n unavailability of certified standard samples, such as freeze-dried Bovine Liver (SRM 1577), Orchard Leaves (SRM 1571), or T u n a (SRM 1591), assayed for vanadium. However, Nadkarni and Morrison (9) quote a value for vanadium in Orchard Leaves (SRM 1571) of 0.61 ppm, as compared to Guinn‘s values of 0.52 0.02 ppm and 0.50 f 0.07 ppm, and that of 0.58 0.05 ppm, as obtained in six Japanese laboratories ( 8 ) . T h e main purpose of this study is to develop a sensitive neutron activation analysis procedure employing pre-irradiation chemistry to remove t h e major radioactivatable contaminants from marine biologicals such as oyster, crab, and shrimp, and to evaluate the procedure by analyzing NBS Orchard Leaves and comparing the values to those already reported. Rather than develop a procedure employing “shelf’ specimens, we obtained “real world” shrimp, blue crab, and oyster from four areas off or near Galveston Island, Texas. One area was in pristine waters and the other three were areas of varying degrees of industrial pollution. The areas selected for the collection of the “polluted” samples were near or adjacent to Texas City oil refineries and proximal to both the Gulf intra-coastal waterway and t h e Houston ship channel.

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Analytical methodology for the determination of petroleum hydrocarbons in sediment ( 1 ) is evolving a t a rapid rate. Unfortunately, there is no concomitant progress in developing highly sensitive techniques for measurement of the vanadium content of marine biological specimens, which have a tendency toward concentrating ( 2 , 3 ) vanadium from the environment, for reasons not yet understood. Environmental mobilization of vanadium and its compounds occurs by a number of means in the net transport of vanadium into the oceans. Some of these transport processes include terrestrial run off, industrial emissions, atmospheric wash out (vanadium in the air comes only from industry, as there are no significant natural sources), river transport, and oil spills, resulting in a complex ecological cycle ( 4 ) . There has been discussed ( 5 , 6) the possibility of vanadium deposition d u e t o oil spillage, b u t no evidence is yet available to confirm the release of vanadium from oil. Since crude oils are rather rich in vanadium (50-200 pprn), it is not inconceivable that some vanadium should be released upon the contact of oil with seawater ( 7 ) . While vanadium determinations may be accomplished in a variety of ways, including spectrophotometry, atomic absorption, X-ray fluorescence, and neutron activation (n,only a few of these methods are capable of detection limits which include natural concentrations of vanadium, without extensive pooling of samples. Because of favorable radioactivation properties of vanadium, neutron activation analysis, in theory, offers detection limits in the several parts per billion range. T h e reason why vanadium determination by neutron activation requires a rather elaborate procedure, when applied to biological samples, is t h a t the Compton contributions from 0003-2700/79/0351-0178$01 0010

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EXPERIMENTAL Sample Collection. All marine biological specimens were taken at four different sites on or around Galveston Island, Texas. One site was the rather non-industrialized or pristine San Luis Pass area off the westerly section of the island. The other three sites were in the industrialized area of Galveston. The Bolivar site is adjacent to the Texas City refineries and proximal to both

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1979 American Chemical Society

ANALYTICAL CHEMISTRY, VOL. 51, NO. 2, FEBRUARY 1979

the Gulf intra-coastal waterway and the Houston ship channel. The East Beach area is on the northeastern section of the island in the channel waterway. The Sportsman Road area is in the north central area of Galveston Island, south of the Texas City refineries. Blue crab (Callinectes sapidus) and white shrimp (Penaeus setiferous) were collected by seine. Oysters (Crassostrea uirginica) were pried off the rocks with a crowbar. All specimens were dried a t 95 "C in an oven to constant weight, and then crushed into a powder with a mortar and pestle. Samples analyzed weighed on the order of 0.25 g. Acid Digestion Procedure. All glassware was soaked in a 50% by volume aqueous (distilled water) solution of H N 0 3 for a t least 12 h, and then rinsed thoroughly with distilled deionized water to remove possible traces of vanadium prior to analysis. A wet-ashing procedure utilizing concentrated HNO, was employed to digest the specimens prior to the chemical separation of vanadium. We compared the vanadium contents of several commercial brands of reagent grade nitric acid for their suitability in the ashing procedure. Since there appeared little difference between Baker (0.006 wg/mL V) and Baker Ultrex (0.006 pg/mL V) "OB, we employed the Baker Reagent grade acid. It appears that vanadium is one of the least troublesome elements with respect to contamination. A comparison of 50 ppb undigested vanadium standards (as V,05) with 50 ppb digested standards showed that there was no measurable loss of vanadium due to the digestion process at the temperatures employed in the procedure. Samples weighing on the order of 0.25 g dry weight were placed in Vicor crucibles containing 10 mL of concentrated nitric acid. The crucibles were then placed in an ultrasonic bath for 30 niin to increase the surface area of the sample, which enhances its ability to dissolve in the digestion process. The crucibles were then placed on a sand bath and heated to 65 "C until absolutely dry (approximately 48 h). The low ashing temperature was used in order to prevent volatilization losses of any vanadium compound in the multielement biological matrix. T o effect an efficient digestion, 10 additional mL of concentrated HNOBwere added to the digested sample, after which it was again placed in the ultrasonic bath for 30 min and the sand bath digestion procedure repeated. After the sample was digested for t,he second time, 10 mL of 1 M HNO, was added to redissolve the sample, and the crucible was again placed in the ultrasonic bath for 30 min. The dissolved sample was then transferred to a centrifuge tube and centrifuged a t 2500 rpm for 10 niin to separate out the non-acid-soluble residue. Both the acid-soluble and the non-acid-soluble fractions were saved for analysis. Resin Columns. Cation-exchange columns were prepared by loading a 0.7 X 10 cm polypropylene column (Bio-Rad) with 2.5 g of Bio-Rad AG 50W-X8 cation resin (200-400 mesh, hydrogen form) in 3 mL distilled deionized water. The resin was then equilibrated with 10 mL of 1 M HN03. Vanadium Determination i n O r c h a r d Leaves. Two digestion procedures were evaluated, one involving concentrated H N 0 3 as previously described and the other a mixture of 20% solution. H 2 0 2by volume in a concentrated "0, The acid-soluble part of the sample was added to a previously prepared AG 50W-X8 resin column and allowed to elute through were then allowed the column. Two 3-mL aliquots of 4 M ",OH to elute through the resin and each 3-niL eluent was collected in an irradiation vial for activation. The non-acia-soluble residue was transferred to an irradiation vial using 3 mL distilled deionized water. D e t e r m i n a t i o n of V a n a d i u m in M a r i n e Biological Specimens. The acid-soluble part of the nitric acid-digested sample was added to the AG 50W-X8 resin column as described above. However, because of the large quantity of sodium and chlorine in the biological samples, i t was necessary to wash the column with 10 mL of 0.5 M H N 0 3 prior to eluting the vanadium off the resin with the 4 M NH40H. The two 3-mL aliquots of NHdOH were then collected for irradiation as described above. The non-acid-soluble residue was then transferred to an irradiation vial using 3 mL distilled deionized water. Instrumental neutron activation analysis of the residue showed minor quantities of sodium and chlorine; however, aluminum was a major radiocontaminant, probably the result of the 28Si(n,p)28A1 reaction, if the insoluble vanadium-containing residue was a silicate.

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Figure 1. ?-ray spectra following neutron irradiation of white shrimp from Bolivar area. Photo peaks with a Pr designation indicate escape peaks. (a) INAA procedure, (b) after pre-irradiation chemistry

Neutron Irradiation. All samples were irradiated in the Omaha Veterans Administration Hospital TRIGA Mark I reactor operating at a thermal-neutron flux of -1.1 X 10" n/cmz-s. The samples were irradiated in the rotary specimen rack of the facility for 10 min and allowed to decay for 2 min before counting. Radioassay. y counting was done using a 80-cm3 coaxial lithium-drifted germanium detector (Harshaw Chemical) and a Nuclear Data ND 600 2048-channel analyzer, with a system resolution of 2.3 keV (FWHM), a peak-to-Compton ratio of 26/1, and a relative peak efficiency of 12.7% for the 1.332-MeV y of 6OC 0 .

RESULTS AND DISCUSSION D e v e l o p m e n t of P r o c e d u r e P a r a m e t e r s in A q u e o u s S o l u t i o n . Shown in Figure l a is t h e instrumental neutron activation analysis (INAA) y-ray spectra following neutron irradiation of 0.25-g samples of white shrimp collected from the Bolivar area. It is obvious from inspection of this Figure t h a t INAA procedures cannot be employed, because of the large contribution of sodium, chlorine, and aluminum activities. Consequently, it is necessary t o employ either a pre-irradiation or post-irradiation wet chemistry procedure. '1Ve decided against the post-irradiation procedure developed by Fukai and Meinke (2) for various reasons. Because of the short half-life of 'q(TI,, = 3.77 m), any prolonged decay time after neutron irradiation will raise the limit of detection. Because vanadium exists in various oxidation states, neutron irradiation can result in Szilard-Chalmers reactions of vanadium with t h e medium, which can complicate any postirradiation procedure (10). We decided against the Guinn et al. ( 8 ) pre-irradiation use of hydrated antimony pentoxide (HAP) for the reasons discussed in t h e introduction. From our previous experience, for trace aluminum in urine and bone ( 1 1 , 121, we found t h a t a pre-irradiation cation-exchange chromatography procedure (employing HNO, elution) on digested biological samples resulted in a near 100% decontamination of sodium a n d chlorine. Vanadium is a n element t h a t can exist in multiple oxidation states; b u t while in t h e +5 oxidation state, it can exist as either a cation or anion species, depending on the p H of the system (13). T o study t h e feasibility of a cation-exchange chromatography procedure for vanadium in marine biologicals, it was first necessary t o study the interrelationships of vanadium retention on the resin a n d sodium a n d chlorine decontamination a t various HNO, concentrations. This was done with aqueous solutions of V205and NaC1. For the purpose of t h e cation-exchange experiments, we employed a 0.7 x 10 cm polypropylene columnpas compared to the 0.7 x 4 cm column in our aluminum studies ( 1 1 , 12). This resulted in a more efficient retention of vanadium on t h e cation column resin bed. Presented in Table I are the vanadium and sodium losses from t h e AG 5OW-X8 cation resin at various HNO, elution concentrations, and t h e number of washes employed. T h e

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ANALYTICAL CHEMISTRY, VOL. 51, NO. 2, FEBRUARY 1979

Table I. Vanadium and Sodium Loss from Resin a t Various HNO, Elution Concentrations and Number of Washes vanadium loss from resin resin loaded with 1 mL of 1 pg/mL V deionized water

+

1 0 mL distilled

% loss

HNO, wash 5mLlM 5 mL 0.5 M 5 mL 0.2 M

load 3.8 1.3 NDb

1st wash 1.7 3.9

total 3rd (2 wash washes)

2nd wash 64.0a 5.5 NDb

9.5 NDb

8.5 3.9

sodium decontamination from resin resin loaded with 1 mL of 1 mg/mL Na deionized water 5mLlM 5mL0.5M 5mL0.2M

24 39 38

+

Table 11. Elution Yield vs. Molarity of Ammonium Hydroxide molarity,(“M % yieldb 2 83.7 i 3.0 3 87.0 t 1 . 2 4 87.8 i 2.8 5 87.4 i 2.0 6 85.7 * 3.0 7 86.0 i 2.0 9 81.6 + 13.0 Each elution was with 5 mL Baker Reagent Grade “,OH. Resin loaded with 1 ppm V in 5 mL water. Table 111. Total Recovery of Vanadium in Marine Biological Specimens from the Bolivar Area

1 0 mL distilled

58 30 19

22 0 104 24 13 93 9 9 66 a The sum of the first two washes was 64.0% indicating 1M HNO, as a nonsuitable eluent. Nondetectable. ideal condition is to find an elution resulting in zero vanadium loss from the resin and 100% decontamination of sodium. As is generally known, and as we have found previously ( I I ) , the chloride ion readily passes through the resin. I t is apparent from inspection of the Table that greatest vanadium retention is with 0.2 M HNO,; however, a t this concentration of HNO,, the sodium decontamination is least efficient. I t is unfortunate that appreciable vanadium loss occurs as the number of H N 0 3 washes increases. We decided, for optimal results, t o use a 10-mL 0.5 M HNO, wash, which results in a 93% decontamination of sodium and a vanadium retention of >91% in an aqueous solution. Since the retention is not l o o % , there may be some question as t o actual reproducibility in biological samples. This question will be answered in the following section. T h e main vanadium species is probably V 0 2 +under these conditions (13). In the development of our cation-exchange chromatography procedure for aluminum in biological matrices (bone, urine) employing H N 0 3 elution, we radioassayed the aluminum on t h e resin. Employing the method of Currie ( 1 4 ) , the limit of detection using the vanadium captured on the resin is 0.006 Fg/mL. I t would seem that the ideal procedure would involve employing the resin. However, when we used actual marine biological samples, which contain significantly greater quantities of the radioactivatable contaminants sodium and chlorine, we found t h a t t h e level of sodium and chlorine contamination on the resin after a 10-mL 0.5 M HNOBwash was too great to allow accurate vanadium determinations. We evaluated the possibility of eluting the vanadium from the resin a n d performing a radioassay on the eluent. This procedure would have the added advantage in t h a t the resin radiocontamination would not be present in the assay. Since vanadium can exist as an anion a t pH values greater than 4 (13),we evaluated the use of N H 4 0 H as an eluting agent to remove vanadium. We loaded various columns with 1 p p m vanadium in 5 m L of water. T h e amount of vanadium retained on t h e resin under these conditions was 100%. Presented in Table I1 are the N H 4 0 H elution yields a t various N H 4 0 H molarities. I t would seem that the yields were rather insensitive t o the molarity a n d were generally > 8 l % . We chose t o use for our elutions 4 M N H 4 0 H . At this condition, the most probable vanadium species are anions such as VOd3or [V206(OH)]3-. In the procedure which we discussed in the Experimental section, we employed two 3-mL 4 M N H 4 0 H elutions for ease in sample handling in the radioassay steps.

marine biological samples load of resinC first 0.5 M HNO, washC second 0.5 M HNO, washC first 4 M “,OH elution second 4 M “,OH elution residue resin total vanadium in sample marine biological samples + 1 pg vanadium “ spike” load of resinC first 0.5 M HNO, washC second 0.5 M HNO, washC first 4 M “,OH elution second 4 M “,OH elution residue resin total vanadium in sample difference between “spike” and sample elution yield, %d

white blue shrimpa craba

oystera

N D ~ N D ~ N D ~ 0.06 N D ~ N D ~ 0.03 0.05 0.02 0.02 ND 0.05 0.11 0.06 0.12 0.22 0.13 0.02 0.00 ND ND 0.28 0.18 0.45 NDb 0.03 0.03 0.07 0.12 0.14 0.11 0.15 0.09 0.06 0.60 0.07 0.81 0.16 0.89 0.18 0.10 0.01 N D ~ N D ~ N D ~ 1.28 1.18 1.16 0.83 0.90 0.98

75 65 83 a p g vanadium per gram, dry weight. I , ND = nondetected. Approximate values. Because of the large sodium and chlorine radiocontamination, a computer matrix was used t o solve for the vanadium content. Calculated for the “,OH elution. Development of the P r o c e d u r e f o r Marine Biological Specimens. As can be seen in Table 111, employing “real world” marine biological samples, white shrimp, blue crab, and oyster specimens collected from the Bolivar area, we evaluated t h e vanadium procedure described in the Experimental section. We determined for these specimens and those containing a 1-pg vanadium “spike” as V 2 0 5the vanadium content of the various steps in the procedure. Because of the large sodium and chlorine contamination in the HNO, wash and the resin, these values can be considered only approximations. It is interesting to note t h a t even with these approximations, the accountability of the 1-pg “spike” for white shrimp, blue crab, and oyster is 0.83,0.90, and 0.98 pg. One interesting feature of this Table is that the vanadium content in the insoluble residue, probably a silicate, is constant within experimental error between the sample and the “spike”. Using the N H 4 0 H elutions for both the sample and the spike, by the method of standard additions, we calculated vanadium elution yields. As can be seen in Table I11 the major loss of vanadium appeared t o be in the HNO, washes. T h e total vanadium content in each sample is the “,OH elution fraction, corrected by employing an elution yield determined by the method of standard additions, and the vanadium content of the residue. In order for the procedure to be a viable one, it is important t h a t t h e vanadium elution yields with the NHIOH be reproducible. We determined relative standard deviations employing 16 different sets of marine

ANALYTICAL CHEMISTRY, VOL. 51, NO. 2, FEBRUARY 1979

Table IV. Analyses of Marine Biologicals in the Galveston Island Area for Vanadiuma ",OH elutions z 4 M ",OH eluentb yield, % residue white shrimpC Bolivar East Beach Sportsman Road San Luis Pass blue crab' Bolivar East Beach Sportsman Road San Luis Pass oysterf Bolivar East Beach Sportsman Road San Luis Pass The sum of the two 3 mL a n = 6. weight sample. e Collinectes sapidus.

total V content

0.78 i 0.61 i 1.64 f 0.12 i

0.13d 0.18 0.25 0.04

1.42 t O.lgd 2.67 i 0.18 3.05 i 0.34 0.40 i 0.09

0.47

i i i

0.05 0.18 0.12 0.07

1.09 f 0.09 1.76 I 0.26 1.84 i 0.14 1.31 i 0.09

0.18 i 0.65 i 0.11 81 0.26 i 0.43 i 0.13 90 0.80 t 0.62 i 0.02 76 94 0.07 t 0.46 i 0.05 Penaeus setiferous. 4M ",OH elutions. Crassostrea uirginica.

0.12 0.18 0.06

0.64 i 2.05 i 1.41i 0.28 i

0.06d 0.06 0.09 0.07

0.62 i 0.04 1.00 t 0.08 0.84 i 0.03 0.84 i 0.06

Table V . Vanadium Content of NBS Standard Reference Material 157 1 Orchard Leaves. Neutron Activation Analysis Procedures digestion vanadium destructive analyses procedure content, p g Vlg reported procedure C 0.60 i 0.02a modified reported d 0.44 i 0.04a procedure V . P. Guinn procedures, e 0.50 i 0.15b (8) HAP e 0.52 i 0.02 ( 8 ) WOW, 0.58 i 0.05a (8) f six independent Japanese laboratories (mean) instrumental neutron activation analyses this study 0.65 i 0.05 Nadkarni and Morrisor, 0.61 ( 9 ) a 1 standard deviation. 90% condifence limit. WetWet-ashed with ashed with 1 0 mL concentrated "0,. 8 m L concentrated HNO, + 2 mL H,O,. ' Wet-ashed ("0, + H,O,) ratio unknown. f Unknown. biological samples collected from all sites. Each set was composed of a t least six individual samples of t h e same specimen. T h e average relative standard deviations of the determinations was better than 5%. It is our contention that these elution yields are acceptably reproducible quantities.

Determination of Trace Levels of Vanadium in Marine Biological Specimens. Employing the procedure described in t h e Experimental section, we determined the vanadium content in white shrimp, blue crab, and oyster from the four sites off and near Galveston Island. Figure l b shows the combined spectra of the residue and the NHIOH elution for a typical analysis of Bolivar area shrimp. T h e major contribution of aluminum was from the residue, probably the result of t h e 28Si(n,p)2sA1reaction. T h e other radiocontaminants, 80Br, =Mn, 27Mg,and ,'Si, were mainly present in the residue. The total decontamination of radiocontaminants was greater than 90%. I t is important to realize that 52Vcan be produced from naturally occurring manganese. Since some of the samples contained manganese, we determined whether sufficient quantities of 52Vcould be produced by fast-neutron activation. A 50-pg manganese sample irradiated under identical conditions resulted in nondetectable quantities of 52V. Presented in Table IV are the vanadium results for the marine biological samples from the Galveston Island area. The

77 79 88

68 64 70 88 63

0.76

1.00 0.47 i

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0.83 i 0.02 0.69 i 0.24 1.42 i 0.05 0.53 i 0.03 0.05 All values expressed in pg V/g of dry-

vanadium contents in the N H 4 0 H elution and the residue were separately radioassayed for the 1.434-MeV 52Vy photopeak. T h e activity under the vanadium photopeak was determined by a computer procedure (15) utilizing a simplex method of linear programming. According t o the method of Currie (14), the lower limit of detection in the procedure is 30 ppb. Although it was not our intention in this paper to comment on the environmental or marine biological significance of vanadium differences in the various species collected in the non-industrialized and industrialized areas, it is apparent from inspection of Table IV t h a t the vanadium content of the species is greater in t h e industrialized areas as compared to the nonindustrialized San Luis Pass area.

Vanadium Content in NBS Standard Reference Material 1571 Orchard Leaves. Since there is no certified vanadium reference standard, it was of importance for us to determine the vanadium content in NBS Orchard Leaves SRM 1571. As can be seen in Table V, there are several reported values for the vanadium content of Orchard Leaves. Because of the low radiocontamination by other elements, vanadium can be readily determined by INAA. As discussed in the Experimental section, we employed two different experimental processes, the regular HNO, digestion procedure and one involving a mixture of NHO, and H 2 0 2similar to the Guinn digestion procedure (11). T h e remaining chemistry procedure was similar t o t h a t employed for t h e marine biological specimens. We note t h a t our "OB and H202digestion procedure resulted in a value 0.44 f 0.04, close to being within experimental error of the Guinn values of 0.52 0.02 and 0.50 0.07 pg V/g. These values were lower than the Japanese value of 0.58 0.05 pg V/g and our value employing HNO, digestion of 0.60 0.02 pg V/g. T h e Nadkarni and Morrison value of 0.61 pg V/g and our 0.65 f 0.05 by INAA are within experimental error of our 0.60 A 0.02 pg V/g value. We suggest t h a t the use of HNOB and H z 0 2 results in vanadium loss during digestion, and that the vanadium content in the Orchard Leaves is closer to the 0.60 pg V/g value.

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LITERATURE CITED (1) L. R . Hilpert. W. E. May, S. A. Wise, S. N. Chesler, and H. S. Hertzog. Anal. Chern.. 5 0 , 458 (1978). R . Fukai and W. W. Meinke, Lirnol. Oceanogr., 7 , 186 (1962) R. Soremark, J . Nurr., 92, 183 (1967). D. H. Klein. Water. Air. Soil Polluf.. 4. 89 11975). R . S. Barnes and W.R. Scheli, "Cycling'and Control of Metals", National Environmental Resource Center, Cincinnati, Ohio, 1973, p 45. (6) M. Zerner and M. Gouterman, Inorg. Chern., 5 , 1699 (1966). (7) National Academy of Sciences, "Medical and Biological Effects of Environmental Pollutants: Vanadium", Washington, D.C., 1974, 117 pp.

(2) (3) 14) (5j

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(8) V. P . Guinn, E. R. Christensen. K. delancey, W. W. Wadrnan 111, J. H, Reed, N. Hansen, A. Abu Samra, and V. J. Orphan, Roc. ThirdInf. Conf. Nucl. Meth. Environ. Res., in press. (9) R. A. Nadkarni and G. H. Morrison, J . Radioanal. Chem., 43, 347 (1978). (10) A. J. Blotcky, D. M. Duven, W. M. Grauer, and E. P. Rack, Anal. Chem.,

46, 838 (1974). (11) A. J. Blotcky, D. Hobson. J. A. Leffler, E. P. Rack, and R. R . Recker, Anal. Chem., 48, 1084 (1976). (12) A. J. Blotcky, E. P. Rack, R. R. Recker, J. A . Leffler, and S. Teitelbaum, J . Radioanal. Chem.. 43. 381 (1978). (13) 0. W. Howarth and R. G. Richards, J . Chem. SOC.,1965, 864. (14) L. A. Currie, Anal. Chem., 40, 586 (1968).

(15) F. J. Kerrigan, Anal. Chem., 38, 1677 (1966).

RECEIVED for review September 14, 1978. Accepted October 30, 1978. Research supported by t h e Omaha Veterans Administration Hospital (MRIS 7319) a n d t h e University of Nebraska Research Council ( N I H Biomedical Research Support Grant RR-07055). This is USDOE document number COO/1617-57.

Viscosity, Calorimetric, and Proton Magnetic Resonance Studies on Coal Liquid Fractions in Solution Krishna C. Tewari, Nan-sing Kan, David M. Susco, and Norman C. Li" Department of Chemistry, Duquesne University, Pittsburgh, Pennsylvania 152 19

Two coal liquid products derived from the same Kentucky hvAb coal have been separated into toluene-insoluble, asphaltene, and pentane-soluble heavy oil fractions. Viscosity and calorimetric studies are reported of the interaction between heavy oil and asphaltene (A) and its acidlneutral (AA) and base (BA) components in solvent benzene. The increase in viscosity and molar enthalpy of interaction, A H o , in the order BA > A > AA, correlates well with the proton magnetic resonance downfield chemical shift of the OH signal of o-phenylphenol, as a function of added asphaltene (A, AA, BA) concentration in solvent CS2. The results suggest that when asphaltene and heavy oil are present together, hydrogen-bonding involving largely phenolic OH, is one of the mechanisms by which asphaltene-heavy oil interactions are achieved and, in part, is responsible for the viscosity increase of coal liquids.

T h e high viscosity at ambient temperature of coal liquids, derived from hydrogenation processes, has been a major concern in t h e direct use of the coal liquids as a boiler fuel. The viscosity of these liquid products has been related t o the asphaltene (toluene-soluble, pentane-insoluble) and preasphaltene (toluene-insoluble, pyridine-soluble) fractions (1-5). Although t h e effect of preasphaltene concentration on t h e viscosity of coal liquids is dramatic, t h e increase caused by asphaltene materials has been suggested to be due to acid-base interactions ( 2 , 4 ) between hydroxyl or acidic nitrogen and basic nitrogen functions causing molecular aggregation and a corresponding trend toward highly viscous liquids. Recently. t h e effect of t h e heavy ends of coal liquids on viscosity has been studied by Schiller et al. (6). They, however, observe t h a t hydrogen bonding is more important in defining the effect of asphaltene on viscosity than are acid-base salt formation interactions. W e report here t h e effect of asphaltene concentration on t h e viscosity of benzene solutions containing pentane-soluble heavy oil (HO) fraction of t h e same coal liquid, and t h e observed correlation of viscosity change with calorimetric and proton magnetic resonance results. T h e d a t a suggest t h a t when asphaltene a n d HO are present together, hydrogenbonding involving largely phenolic OH, is one of t h e mechanisms by which asphalteneeheavy oil interactions are achieved, and in part is responsible for the viscosity increase of coal liquids. 0003-2700/79/0351-0182$01 OO/O

EXPERIMENTAL Centrifuged liquid product (CLP) samples, FB53-59 and FB57-42 were obtained from the 450 kg (1/2 ton) per-day Process Development Unit at the Pittsburgh Energy Research Center, after 236 and 168 h, respectively, and were prepared from the same feed coal, Kentucky hvAb, from Homestead Mine, a t 27.6 MPa (4000 psi) hydrogen pressure and 723 K reactor temperature. Run FB53-59 was made with the reactor packed with Harshaw 0402T CoMo catalyst, 11-min preheater and 3-min reactor residence time while run FB57-42 was made with the reactor charged with glass pellets, 17-min preheater and 6-min reactor residence time (residence time of coal slurry feed in preheater and reactor was calculated from Cold-Model studies). The isolation of toluene-insoluble (TI), asphaltene(A), and HO fractions from the two CLP samples was accomplished by solvent fractionation based upon solubility in toluene and pentane. The A fraction was further separated into acid/neutral (AA) and base (BA) components by bubbling dry hydrogen chloride gas through a stirred toluene solution. Details of these isolation methods have been previously described (7,8). Traces of residual solvent from dried asphaltene samples were removed by freeze-drying a dispersion of the isolated fraction in benzene. For the liquid HO fraction, dry nitrogen was passed for 8-10 h a t room temperature. o-Phenylphenol (OPP) was obtained from Eastman Kodak Co., purified by recrystallization from ether and stored in a vacuum desiccator a t 130 P a (1mm Hg) a t room temperature. Benzene was of Fisher pesticide grade dried over 4A molecular sieves. Carbon disulfide (CSJ was purified as described previously (9). The molecular weights were determined on a Mechrolab 301A vapor pressure osmometer a t 10-20 g/dm3 in toluene solutions. The solution viscosities were determined by Ostwald viscometer at 293 K. Viscosity data reported here are with respect to water whose viscosity (10) was taken as 1.002 CPa t 293 K. Proton magnetic resonance (PMR) spectra were obtained a t 220 and 60 MHz as CS2 solutions with tetramethylsilane (TMS) as an internal reference. Hydroxyl Silylation. Hexamethyldisilazane, 20 cm3, and 10 cm3 of N-trimethylsilyldiethylamine were added to 100 cm3 of benzene containing 2 g of asphaltene or HO sample. The mixture was slowly refluxed under nitrogen for 18 h. The solvent and unreacted reagents were removed on a Rotavap at 333 K. Nitrogen was then flushed to ensure dryness. The residue was repeatedly dissolved in benzene and dried as before. T o ensure nearly complete removal of reagents, the silylated asphaltene residue was finally freeze-dried from 10 cm3 of benzene over a 3-h period. In the case of the silylated HO fraction, dry nitrogen was bubbled through the solution for 8-10 h. The formation of HO or asphaltene trimethylsilyl ether was checked by infrared spectrometry for complete disappearance of the free phenolic or alcoholic hydroxyl group absorption a t 3600 cm *. Representative partial F 1979 American Chemical Society