562
ANALYTICAL CHEMISTRY, VOL. 50, NO. 4, APRIL 1978
Determination of Ruthenium in Automobile Exhaust Emissions by Negative Ion Chemical Ionization Mass Spectrometry S. R. Prescott and T. H. Risby" Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 76802
An analytical procedure is presented for the determination of ruthenium on membrane filters. Also the preparation of platinum bis( l,l,l-trifluoro-2,4-pentanedlonate) is described and a discussion of the structure of this complex is included. The negative ion chemical ionlzation mass spectra of this chelate and the following complexes are reported: palladium bis( l , l ,l-trifluoro-2,4-pentanedionate) and ruthenium tris(l,l,l-trifluoro-2,4-pentanedionate).
As a result of the use of platinum and palladium metals in catalytic converters in mobile sources manufactured after 1973, and the proposed use of ruthenium metal in converters in automobiles to be manufactured in the future, accurate and sensitive methods of analysis for these elements are required to monitor possible increases in environmental baseline levels. The need for an effective method of analysis was demonstrated a t a Platinum Research Review Conference sponsored by the U.S. Environmental Protection Agency. At this conference it was reported that although the Los Angeles Catalyst Study has been on-line since June 1974, no measurements of the levels of platinum were possible since typical atmospheric ambient loadings were too low ( I ) . There are several methods of analysis which may be suitable for t h e monitoring of these elements in ambient air, water, or the biota although to this date only a few studies have been reported. Flameless atomic absorption spectrometry has been used to determine platinum and palladium in biological tissues and fluids a t levels of approximately 30 ppb (2,3). Neutron activation analysis has quantitatively detected platinum and palladium in a wide variety of environmental and biological matrices in the nanogram range ( 3 ) ,and low level concentrations of platinum and palladium (picograms per cubic meter of air) have been measured with isotope dilution spark source mass spectrometry ( 4 ) . To our knowledge, no investigations into the presence of ruthenium in water, air, or biota have been reported although a number of analytical chemistry techniques would appear to be suitable for such analyses (5). These elements are currently receiving extensive investigation for another reason: at this present time the only toxicological data on ruthenium, platinum, and palladium (3, 6-8) available are related to forms of these elements which are not potentially environmentally significant. Therefore, before their impact may be ascertained, environmental baselines and toxicology must be measured. Studies have shown that chemical ionization mass spectrometry is an attractive method of analysis for trace metals (9-11). A more recent study in our laboratory has demonstrated that P-diketonates which contain fluorine atoms have superior detection limits if negative ion chemical ionization mass spectrometry is used instead of the more conventional positive ion chemical ionization mass spectrometry (12). This increase in sensitivity toward negative ion formation is due to the increased electron capture cross section and/or electron affinity contributed by the fluorine atoms. This present paper reports an analytical procedure for the determination of ruthenium in doped automobile exhaust 0003-2700/78/0350-0562$0 1 OO/O
particle emissions trapped on membrane filters using a gas chromatography chemical ionization mass spectrometer system operated in the negative ion detection mode. T h e preparation of platinum bis( l,l,l-trifluoro-2,4-pentanedionate) together with a brief discussion of the structure of this complex will be reported. Finally, the negative ion chemical ionization mass spectra of this chelate and the following P-diketonates will be presented: palladium bis(l,l,l-trifluoro-2,4-pentanedionate) and ruthenium tris(l,l,l-trifluoro-2,4-pentanedionate).
EXPERIMENTAL Instrumentation. A gas chromatograph (Hewlett-Packard 402B) coupled to a chemical ionization mass spectrometer (Scientific Research Instruments Corporation Biospect System) which has been previously described (12) was used for the analyses. The initial mass spectra were obtained by placing solid samples directly onto the direct insertion probe; whereas for the analytical determinations of ruthenium, the samples were introduced through the gas chromatographic inlet. Methane served as both the reagent and carrier gas and spectra were recorded at a source pressure of 1.0 Torr. The gas chromatograph contained a 6-mm o.d., 3-mm i.d. glass column 55 cm long packed with 5% Dexil 300 on Supelcoport (100-120 mesh). The column was operated at 160 "C with a flow rate of 60 mL/min. The column effluent was split between atmosphere and the CI source in a ratio of 6:l. The gas chromatographic inlet consisted of a precision bore Pyrex capillary (0.2-mm id.) which was continuous from the column outlet to the source of the mass spectrometer. This interface was contained in an oven which was maintained at 180 "C. The mass to charge ratios of the various peaks were determined by the mass marker which had been calibrated with methyl stearate and lutetium tris(2,2,7,7-tetramethyl-3,5-heptanedionate) (12). The proton magnetic resonances were measured with a Varian A60 NMR spectrometer and the infrared spectra of the potassium bromide disks were obtained using a Perkin-Elmer 621 IR spectrometer. The melting point of Pt(tfa)zwas measured using a Thomas-Hoover melting point apparatus. Neutron activation analysis was performed on the membrane filters using a 5-min irradiation at 1 MW followed by a 30-min decay. The samples were then counted for either 200, 800, or 4000-s intervals with a 36-cm3 Ge(Li) detector. The 724.3 keV = 4.5 h) was used for the analysis. gamma ray of '05R~(tl12 Standards were prepared using known weights of RuOz (-0.001 g).
Chelate Preparation. Palladium bis(l,l,l-trifluoro-2,4pentanedionate) [Pd(tfa)J (13) and ruthenium tris(l,l,l-trifluoro-2,4-pentanedionate) [Ru(tfa),] (14) were prepared by methods which have been previously described. The chelates were purified by either recrystallization or reduced pressure sublimation. Platinum bis(l,l,l-trifluoro-2,4-pentanedionate) [Pt(tfa)*jwas prepared in the following manner: potassium tetrachloroplatinate was dissolved in water and the pH of the solution was adjusted to 8.5 by adding an aqueous solution of potassium hydroxide. The resulting solution was warmed to 60 "C and a slight excess of H(tfa) added. The solution was stirred for 2 h, after which time an equal volume of benzene was added, and the organic layer extracted. The solvent was evaporated and a yellowish residue remained which was washed with water and recrystallized from 2-methyl-2-propanoland water. Chemicals. Reagent grade chemicals were used throughout except where otherwise specified and were obtained from the 6 1978 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 50, NO. 4, APRIL 1978
following sources: l,l,l-trifluoro-2,4-pentanedione (Pierce Chemical Co.), palladium chloride (K and K Laboratories, Inc.), ruthenium chloride (Research Organic/Inorganic Chemicals Corp.), and potassium tetrachloroplatinate (Strem Chemicals Inc.). The nitric and hydrochloric acids were ultrapure (Ultrex, Baker Chemical Co.). Analytical Procedure. Prior to use, the heavy walled glass ampules were leached with aqua regia followed by washing with doubly distilled deionized water, acetone, and a solution of H(tfa) in toluene (10%). The fluoropore filters (Millipore Co 1pm) were rolled with Teflon coated forceps and placed into the ampules. A solution which consisted of 1.0 mL of HC1 (ll.OM) and a few drops of "OB (16.0 M) was added to the ampules and they were placed in an oven at 50 "C for 1 h. The ampules were removed from the oven and 0.5 mL of HC1 (1.1M) was added along with 0.5 mL of H(tfa). The contents of the ampules were then refluxed in a heating mantle for 1 h. The refluxing was maintained by passing water through copper tubing (3-mm 0.d.) coiled around the top of the ampule. After this time, the ampules were cooled and the resulting mixtures were neutralized to a pH of 6 with a solution of K,C03 (25% w/w) and 0.5 mL of toluene was added. The ampules were sealed and shaken for 30 min. The resulting toluene layers containing the Ku(tfa)3were transferred to sample vials, capped, and were ready for analysis. Blanks were prepared by following the same procedure with nontreated filters. Samples. The samples consisted of 47-mm fluoropore filters which had been obtained from the Mobile Source Laboratory of the U S . Environmental Protection Agency. The samples marked "Automobile Exhaust Only" were taken from the dynamometer warmup cycle using an uncontrolled (1972) vehicle operated on unleaded gasoline. The samples of "10.1 N g Ru Automobile Exaust" were collected by spotting the filters with RuC13and the automobile exhaust pulled through at the same time as the "Automobile Exhaust Only" samples. Other samples consisted of spotting filters with known volumes of RuC1, in 9 M HC1 and then wetting the filter with isopropanol t o disperse and infuse the material.
RESULTS AND DISCUSSION T h e furmation of a complex between platinum(I1) and 1,l,l-trifluciro-?.+pentanedione has been reported previously ( 1 5 ! . :-IC ' [ k i . Loir.plex was reported to be bonded ccj~ive~i:i;,i.a!l:,,:hruug:? the oxygen atoms on one ligand and through the methine carbon atom on the other. This complex is water soluble, but the Pt(tfa), which is reported in this study is water insoluble and readily dissolved in a variety of organic solvents. T h e proton magnetic resonance spectrum of this complex shows signals a t 2.1 and 6.0 ppm (8) with an integrated ratio of 31. These signals correspond to the presence of two identical methyl groups and methine proton resonances. Therefore, these data suggest the complex prepared contains two equivalent ligands. T h e infrared spectrum of this complex shows two strong absorptions a t 1590 and 1530 cm-'. H(tfa) exists as a mixture of keto and enol tautomers with the carbonyl stretches of the keto tautomer occuring a t 1775 and 1745 cm-l, whereas the carbonyl stretches of the enol form are observed around 1600 cm-'. T h u s it appears that the complex exists in the enolic form and is bonded through the oxygen. These observations are substantiated by the absorptions in the low frequency region of the infrared which consists of a broad band with a maximum a t 437 cm-'. This absorption corresponds to the frequency of the platinum-oxygen vibration and no evidence of platinum-carbon stretching was observed (26). Therefore, in conclusion we feel that the Pt(tfa), which is reported in this work is consistent with all other metal tfa complexes (13). A melting point of the complex was attempted, but the complex decomposed a t 210 "C without melting completely. CI M a s s Spectra. T h e negative ion chemical ionization mass spectra of Pt(tfa),, Pd(tfa),, and Ru(tfaIs showed that the molecular parent ion was the major ion observed which is formed by resonance capture of low energy electrons. This
583
Table I. Formation Efficiency Amount initially, Sample 13 14 15 16 17 18
pg
Ru
20 20 10 10
1.0 1.0
Formed, % 28 i 1.1 29 I 0.9 33 T 0.1 34 i. 0.2 30 i 0.3 32 3 0.2
Av 31 i 0.5 observation was expected from an earlier study carried out in our laboratory (12). Apart from the molecular parent ion a t 561 amu, the only other ion observed ( < 5 % parent ion intensity) occurred a t 153 amu and is attributed t o the ligand, H(tfa). Analysis of the M e m b r a n e Filters. Analytical procedures were investigated which were suitable for all these platinum group metals; however, after exhaustive studies it was found it was impossible to form a reproducible yield of Pt(tfa).?. Also it was found t h a t it was impossible t o form Ru(tfa)3 using a sealed tube reaction under any conditions which is a rather surprising result. In the initial btages of this work, the membrane filters were treated with a mixture of 1.0 mL of "0, and a few drops of HCl. When this procedure was used, very low amounts of Ru were extracted ( < 5 % ) . An important aspect of ruthenium chemistry is the formation of nitric oxide complexes. LJpon treatment with nitric acid, most ruthenium compounds will react preferentially with nitric oxide which will certainly inhibit the formation of Ru(tfa),. To prevent the formation of nitric oxide complexes, the dissolution of the sample was accomplished by using 1.0 mL of HCI and 1 or 2 drops of HNO,. However, the chloride is volatile, so care must be taken to maintain a temperature below 50 "C to prevent loss of the sample. Ruthenium was introduced into the source of the mass spectrometer from the gas chromatograph, whereas the palladium and platinum chelates were introduced on a capillary tube via the heated solids probe. Divalent transition metal @-diketonateshave problems associated with their gas chromatographic separation due to their tendencies toward oxidation, polymerization, or solvation (hydration) (17, 18). Therefore, it was decided to use the method of time resolved scans (19-23) for the analysis of divalent metals. Attempts t o obtain quantitative measurements for the chelates Pd(tfa), and Pt(tfa)zfailed because of loss of the chelate when the solvent was removed prior to introduction into t h e mass spectrometer source. T h e analysis of the Ru(tfa), was performed using the technique of single ion monitoring. Known concentrations of Ru(tfa), in toluene were injected into the gas chromatograph and mass chromatograms were obtained by scanning repeatedly across the mass window 555-565 amu which encompasses the molecular parent anion. T h e resulting areas of the mass chromatograms were measured and a calibration curve was plotted. T h e calibration curve for Ru(tfa), was found to be linear from 100 ppb to 100 ppm with the minimum detectable amount of ruthenium, after taking into account the splitting ratio, being 2.4 X lo-', g. This result represents the sensitivity of the CI technique and does not necessarily correspond t o the minimum detectable amount of R u in automobile exhaust. The results of the analyses of the various samples of ruthenium on membrane filters are shown in Tables I and 11. Table I summarizes the efficiency of formation of Ru(tfa), determined from a series of standards prepared in our laboratory. Knowing the amount of sample added to the filter, it was possible to calculate the efficiency of the formation of Ru(tfa)3 by comparison of the measured
ANALYTICAL CHEMISTRY, VOL. 50, NO. 4, APRIL 1978
564
ACKNOWLEDGMENT
Table 11. Determination of Ruthenium in Membrane Filters SamPle
Amt found, f i g Ru NAA CIMS
Amt. initially, wg Ru
1 1 2 (as 1,lO-phenan- -
throline) 2
1 2 (as 1,lO-phenan-
throline) 3
10
4 10 5 10 + Auto exhaust 6 10 + Auto exhaust 7 8 9
1.0 1.0
Auto exhaust only
10 Auto exhaust only 11 Blank filter 12
Blank filter
-
-
-
8.9 8.6 8.0
t t t
8.7
?:
0.09 0.1
0.08 0.1 1.0 i 0.1 1.1t 0.1 not detected not detected not detected not detected
9.2 i 0.15 9.5 t 0.26 8.2 i 0.47 9.1 0.29 0.97 i 0.08 1.0 i 0.1
*
not not not not
detected detected detected detected
signal to the calculated signal from the calibration curve. From these measurements, it was established that the efficiency of formation was 31% with a relative standard deviation of (*0.5%). Aliquots (0.8 fiL) of the real sample solutions were injected into the gas chromatograph, and the resulting areas were recorded and measured. Knowing the formation efficiency, the amount of ruthenium on the filters was determined and is listed in Table 11. Based on this developed methodology, the minimum detectable amount of ruthenium is on the order of 0.1 fig contained on the membrane filter. Also shown is the amount of ruthenium contained on the membrane filters determined by neutron activation analysis. The precision of the CI technique is comparable to the precision obtained with neutron activation analysis as evidenced by the relative standard deviations of the two methods. The loss of ruthenium(II1) as the 1,lO-phenanthroline chloro complex may be due to the decomposition of the complex with the concomitant formation of ruthenium chloride which is volatile (24). Currently further studies are being undertaken using other P-diketones in order to increase the extraction efficiency and thus increase the sensitivity of this technique. Also other ligand systems such as the tetradentate (?-keto amines are being investigated to attempt to develop similar analytical procedures for platinum and palladium.
We thank G. Wilkinson, R. E. Sievers, K. J. Eisentraut, P. C. Uden, and H. Veening for their advice on the analysis of ruthenium and J. E. Sigsby for supplying the samples.
LITERATURE CITED (1) C. E. Rodes, "Overview of the Los Angeles Catalyst Study", presented at the Phtinum Research Review Conference, Quail Roost, N.C., December 1975. (2) A. F. LeRoy, W. S. Friauf, C. L. Litterst, T. E. Gram, A. M. Guarino. and R. L. Dedrick, "Platinum analysis in animal tissues and fluids", in Ref 1. (3) A. H. Jones, Anal. Chern.. 48. 1472 (1976). (4) D. A. Becker, P. D. LaFleur, and A. F. LeRoy, "Spontaneous determination of platinum, palladium and gold in biologicaland environmental materials", in Ref. 1. (5) J. A. Carter and W. R. Musick, "Platinum metals in air particulates near a catawic converter test site as measured by isotope dilution spark sowce mass spectrometry", in Ref. 1. (6) J. J. Dulka, and T. H. Risby, Anal. Chern., 48, 640A (1976). (7) H. A. Schroeder, "The Poisons Around Us", Indiana University Press, Bloomington, Ind., 1974. (8) "Air Pollution ASDeCtS", Littone ReDOrtS. P. B. 188074-PB188091, September 1969.' (9) T. H. Risby, P. C. Jurs. F. W. Lampe, and A. L. Yergey. Anal. Chem., 46. 161 (1974). (10) Ref 9. D726. (1 1) S.R. Prescott, J. E. Campana, P. C. Jurs, T. H.Risby, and A. L. Yergey, Anal Chern., 48. 829 (1976). (12) J. E. Campana, S . R. Prescott, and T. H. Risby, Anal. Chern., 49, 1501 11977). (13) k. W. &shier and R. E. Severs, "Gas chromatography of metal chelates". Pergamon Press, Elmsford, N.Y., 1965; References cited therein. (14) H. Veening, W. E. Bachman, and D. M. Wilkinson, J . Ges Chrornatogr.. 5 , 248 1967). (15) D. Gibson, J. Lewis, and C. Oldham, J . Chem. SOC.A , 1453 (1966). (16) R. D. Gillard, H. G. Wilver, and J. L. Wood, Spectrochim. Acta, 2 0 , 63 (1964). (17) J. P. Fackier, Jr., Progr. Inorg. Chern., 7, 361 (1966). (18) D. F. Groddon, Coord. Chem. Rev., 4, l(1969). (19) A. E. Jenkins and J. R. Majer. Talanta, 14, 777 (1967). (20) A. E. Jenkins, J. R. Majer, and M. J. A. Reade, Talenta, 14, 1213 (1968). (21) J. R. Majer, M. J. A. Reade, and W. 1. Stephen, Talenta, 14, 373 (1968). (22) R. Belcher, J. R. Majer, R. Perry, and W. I. Stephen, Anal. Chim. Acta, 43, 451 (1968). (23) B. R Kowalski, T. L. Isenhour, and R. E. Sievers, Anal. Chern., 41, 998 (1969). (24) T. D. Avtokratova, "Analyticai Chemistry of Ruthenlum", Oldenbowg Press, Munich, 1963, pp 80-81.
RECEIVED for review September 14,1977. Accepted January 9, 1978. P a r t of this work was presented a t the Platinum Research Review Conference at Quail Roost, N.C., December 1975, sponsored by the U.S. Environmental Protection Agency. This work was supported by a grant sponsored by the U.S. Environmental Protection Agency (No. R803651010 and No. R803651020).
Determination of the Leachability of Solids 0. U. Anders," J. F. Bartel, and S. J. Altschuler The Dow Chemical Company, Midland, Michigan 48640
A novel method for measuring the leachability of homogeneous solids Is reported using as examples radioactive tracers incorporated In plastics and concrete. Theoretical treatment of the data using simple diffusion theory is able to reduce the experimental Information to a single "leachability constant'' for the material and permits the calculation of the leaching behavior as a function of time for any sire regular-shape object made of it.
T h e leachability of a material is frequently measured by experiments which either use Soxhlet extraction equipment 0003-2700/78/0350-0564$01.00/0
to ascertain zero concentration of the leachant at all times or involve immersion of the solid until an equilibrium concentration is reached in the liquid (1, 2 ) . Such experiments generally follow protocols specifying a certain specimen size and shape and are carried out at elevated temperatures to hasten the leaching process ( 3 ) . These test protocols and their results stand by themselves and serve as yes-no criteria for quality control and legislation etc. (4). They do not yield insight into the leaching process nor do they represent the real world. In particular, they do not answer the often most important question: what is the amount of noxious substance leached from an object made of the tested material during the object's use time. For example, it is not 1978 American Chemical Society
