842
Anal. Chem. 1984, 56, 642-646
(4) Kaizuma, H. Anal. Chem. 1982, 54, 732.
(11) Purnell, H. "Gas chromatography"; Wiley: New York, 1962; p 68. (12) Reference 11, p 63. (13) Kaizuma, H.; Ogawa, K.; Yamakita, I. J . Chem. SOC.Jpn. 1975, 935. Translated into English and kept at Los Alamos Science Laboratories, University of Callfornla, Code 51-7339-2. (14) Perry, J. H., Ed. "Chemical Engineering Handbook"; McGraw-Hill: Tokyo, 1963; pp 17-30.
(5) Kubo, T.; Suito, E.; Nakagawa, U.;Hayakawa, S. "Funtai"; Maruzen: Tokyo, 1962; p 208. (6) Kaizuma, H.; Yamakiata, I. Abstracts of the 20th Annual Meeting of the Chemical Soclety of Japan, 1972; 2103. (7) Reference 1, p 198. (8) Lange, N. D., Ed. "Handbook of Chemistry"; McGraw-Hili; New York, 1967: D 318. (9) Fuller; 'N.D.; Schettler, P. D.; Giddings, J. C. I n d . Eng. Chem. 1966, 58, 21. (10) James, A. T.; Martin, A. J. P. Biochem. J. 1950, 50, 679.
RECEIVED for review October 14,1982. Resubmitted October 24, 1983. Accepted December 6, 1983.
Determination of Manufacturing Impurities in Heroin by Capillary Gas Chromatography with Electron Capture Detection after Derivat.ization with Heptafluorobutyric Anhydride James M. Moore,* Andrew C. Allen, and Donald A. Cooper
Special Testing and Research Laboratory, Drug Enforcement Administration, 7704 Old Springhouse Road, McLean, Virginia 22102
A unique derlvatlzatlon reaction used In the gas chromatographlc-electron capture detection of selected manufacturlng lmpurltles In llllclt heroln Is described. The reaction involves the perfluoroacylatlon of A'6~1'-dehydroherolnlumchloride, A15*16-dldehydroheroIn, noscaplne, and related Impurities wlth heptafluorobutyrlc anhydride (HFBA) In the presence of 4(dlmethylamino)pyrldlne (4-DMAP). Thls reaction Is novel In that It Introduces a heptafluorobutyryl (HFB) group, In high yleld, at carbon sites, namely, at C-15 In A15*16-dldehydroheroln and C-4 In noscaplne. These electrophlles, along wlth the expected 0 - and Ill-HFB derlvatlves of other heroln Impurltles, are easily detected on-column at plcogram levels by using a fused slllca column In the splltless mode. The method Is also appllcable for the low-level detection of the Ill-oxides of alkaloids such as morphlne.
The characterization of manufacturing impurities in illicit drugs is important for forensic purposes, especially in sample comparison cases (1-9). We report here methodology suitable for the analyses of complex matrices of heroin manufacturing impurities at levels below 0.01 % by using capillary GC-ECD. The detection of manufacturing impurities in heroin, or other drugs, by GC-ECD usually requires prior derivatization with an electrophilic anhydride or acid chloride. The introduction of an electrophilic group in these impurities inevitably occurs a t 0 and N sites substituted with labile protons (10, 11). Although most heroin impurities in our study were amenable to these common acylation reactions, a select few reacted unexpectedly, in that in the presence of 4-DMAP, HFB groups were introduced in high yield a t carbon sites. Further investigations revealed that these reactions were also applicable for the sensitive detection of N-oxides of impurities such as morphine and codeine as C-HFB derivatives. We believe that this is the f i s t report of such reactions applied in the GC-ECD analyses of heroin and other drug manufacturing byproducts. Our derivatization procedure has been applied to unadulterated, illicit heroin samples as well as selected standards. The 0-,N - , and C-HFB derivatives of the heroin impurities were chromatographed in the splitless mode on a bonded, nonpolar, fused silica capillary column interfaced with a 63Ni ECD. Minimum on-column detectable quantities at low pi-
cogram (pg) or high femtogram (fg) levels for most HFB derivatives were easily achieved. The methodology was also shown to be reproducible, an important consideration in sample comparison cases.
EXPERIMENTAL SECTION Instrumentation. Nuclear magnetic resonance ('H NMR) spectra were obtained on a Nicolet (Fremont, CA) 200-MHz spectrometer interfaced with an 1180 data system and 293A pulser. Tetramethylsilane was used as an internal standard. All mass spectra (MS) were acquired on a Finnigan 4600 quadrupole mass spectrometer (Sunnyvale,CA). Electron impact (EI) mass spectra were collected at an ionizing potential of 50 eV and an ionizing current of 30 PA. Chemical ionization (CI) mass spectra and electron capture negative ion chemical ionization mass spectra (NICIMS)were obtained by using methane (0.5 torr uncorrected) as the reagent gas. The GC-MS was fitted with a 20 m X 0.20 mm i.d. fused silica capillary column coated with SE-54 (Hewlett-Packard, Avondale, PA). Hydrogen was used as the carrier gas. Infrared (IR) spectra were recorded in KBr on a Beckman 4240 spectrometer (Irvine, CA). Gas Chromatography-Electron Capture Detection. All standard and sample chromatograms were generated in the splitless mode on a Hewlett-Packard 5880A gas chromatograph fitted with a 15 m X 0.25 mm i.d. fused silica capillary column coated with DB-1 (J and W Scientific,Inc., Rancho Cordova, CA) at a film thickness of 0.25 wm. The GC was equipped with a 63Ni detector (15 mCi) and interfaced with a Hewlett-Packard Level IV data processor. Injector and detector temperatures were maintained at 300 "C and 275 "C, respectively. The oven temperature was multilevel programmed as follows: (level 1)initial temperature, 90 "C; initial hold, 1.8 min; temperature program rate, 25 OC/min; final temperature, 160 OC; final hold, 1.0 min; (level 2) temperature program rate, 4 OC/min; final temperature 275 "C. Helium ("Zero Grade") was used as the carrier gas at a flow rate of about 40 cm/s and measured at an oven temperature of 90 "C. An argon/methane (95/5) mixture was used as the detector makeup gas at a flow rate of 30 mL/min. The septa used were Thermogreen LB-1 (Supelco, Inc., Bellefonte, PA). All chromatogramswere recorded at an attenuation of 26 and a chart speed of 0.5 cm/min. During the splitless injection the solvent was vented after a 1.0 min hold. Reagents. The 4-DMAP was obtained from Alfa Products (Danvers, MA). Isooctane, acetonitrile, and diethyl ether were "Distilled in Glass" products of Burdick and Jackson Laboratories (Muskegon, MI). HFBA, supplied in 1-mL sealed ampules, was obtained from Pierce Chemical Co. (Rockford, IL). The pH 4 phthalate buffer was prepared according to the United States
This article not subJect to U.S. Copyright. Published 1984 by the American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 56, NO. 4, APRIL 1984
643
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Figure 1. Heroin Impurities and their HFB derivatives: (IV) R = R” = CH,, R’ = H, (IV’) R’ = HFB; (V) R = R’ = H, R” = CH,, (V’) R = R’ = HFB; (VI) R = H, R’ = Ac, R” = CH,, (VI’) R = HFB; ( V I I ) R = Ac, R’ = H, R” = CH3, (VII’) R’ = HFB; ( V I I I ) R = R” = H, R’ = Ac, (VIII’) R = R” = HFB; (IX) R = CHB,R’ = Ac, R” = H, (IX’) R“ = HFB; (X) R = R’ = Ac, R” = H, (X‘) R” = HFB; (XI) R = R‘ = R” = H, (XI‘) R = R’ = R“ = HFB.
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Figure 3. Splitless capillary GC-ECD chromatogram of a mixed standard. On-column quantities were as follows: p ,p’-DDT (A), 200 pg; XII’, 230 pg; XI’, 60 pg; V I I I ’ , 168 pg; dioctyl phthalate (B), 20 ng; IX’, 910 pg; X’ 420 pg; I’, 904 pg; III’,1.81 ng.
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Figure 2. Thebaol and Its 0-HFB derivative: (XII) R = H, (XII’) R = HFB.
Scheme I 0
1
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Scheme I1
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Pharmacopeia, Vol. XVIII. All other chemicals were of reagent grade quality. Standards. The structures for the following standards are illustrated in Figures 1 and 2 and Schemes I and 11. The hydrochlorides of normorphine (XI), 06-acetylnormorphine (VIII), were @,@-diacetylnormorphine(X), and 06-acetylnorcodeine (M) prepared by using the procedures of Rice et al. (12, 13). A16~17-Dehydroheroinium acetate (Ia) was obtained by the reaction of morphine N-oxide with acetyl chloride at 75 “C as described by Allen et al. (3). A1SJ6-Didehydroheroin(I) was prepared from Ia by precipitation of Ia from an aqueous solution with ammonium hydroxide. Thebaol (XII) was prepared according to Bentley (14). Noscapine (111) was obtained from Mallinkrodt (New York, NY). The internal standards l,l,l-trichloro-2,2-bis(p-chlorophenyl)ethane (p,p’-DDT) and dioctyl phthalate were products of Supelco, Inc., and Aldrich (Milwaukee, WI), respectively. Morphine N oxide (IT) was prepared by using the method of Craig et al. (15). Preparation and Derivatization of Standards. Individual methanolic solutions of XI1 (0.33 mg/mL), XI (0.098 mg/mL),
X (0.66 mg/mL), VI11 (0.27 mg/mL), IX (1.44 mg/mL), Ia (1.50 mg/mL), and I11 (2.58 mg/mL) were prepared. A 50-pL aliquot of each standard solution was carefully evaporated to dryness in a single 15-mLconical centrifuge tube. To the residue was added 1.0 mL of acetonitrile, 40 mg of 4-DMAP, and 50 pL of HFBA. After the components were mixed, the derivatization was allowed to proceed for 10 min at room temperature; to the acetonitrile was added 5.0 mL of isooctane:ethyl ether (85:15) (containing 100 pg/pL p,p’-DDT and 10 ng/pL of dioctyl phthalate) and 5 mL of a saturated aqueous solution of sodium bicarbonate. The tube was shaken vigorously for 5-10 s and then centrifuged. An appropriate volume of the upper layer was diluted with additional extraction solvent to give a thebaol concentration of 100 pg/pL. A 4-mL aliquot of this final dilution was placed in a centrifuge tube and back-extracted with 4 mL of pH 4 phthalate buffer. After centrifugation, about 2 pL of the upper layer was injected without delay into the GC-ECD under conditions described previously. The chromatogram of this mixed standard is illustrated in Figure 3. Sample Analysis. An amount of unadulterated sample equivalent to 15 mg of heroin was placed in a 15-mL conical glass-stoppered centrifuge tube. The sample was treated as above for standards, beginning with “To the residue was added 1.0 mL of acetonitrile...”(note: to significantly reduce chromatographic peaks due to 0-HFB derivatives of tertiary amines, e.g., IV’, the acid back-extraction was done with 0.5 N H2S04instead of pH 4 phthalate buffer; the final dilution prior to injection was dependent upon the level of refinement of the heroin, e.g., a 5 mL final dilution for highly refined heroin samples and a 10 mL or greater final dilution for crudely processed heroin samples). See Figures 4 and 5 for sample chromatograms.
RESULTS AND DISCUSSION Structural Requirements for C-Perfluoroacylation. A structural feature in some heroin impurities that promotes C-perfluoroacylation is the presence of an enamine moiety in ring D of the morphine-type molecule, e.g., I (see Scheme I). Thus, the product of the base influenced reaction of I with HFBA is 1’, a stable vinylogous amide which is easily isolated from the bulk heroin matrix. In the absence of base, the reaction of I with HFBA gave I’ in varying and usually lower yields. This was attributed to the presence of heptafluorobutyric acid in the HFBA. In the presence of this strong acid I is partially converted to its iminium form (Scheme I), a species not amenable to C-perfluoroacylation. In illicit heroin hydrochloride samples, the iminium form is the dominant species as A1eJ7-dehydroheroiniumchloride (Ib). The presence of base is necessary for proton abstraction a t C-15 in the iminium form, resulting in a shift of the equilibrium heavily
044
ANALYTICAL CHEMISTRY, VOL. 56, NO. 4, APRIL 1984
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Figure 4. Splitless capillary GC-ECD chromatogram of unadulterated Southeast Asian heroln: (a) using pH 4 back-extraction; (b) using 0.5 N H,S04 back-extraction.
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elimination of a (2-16 proton and the HFB-0 group (3). The resultant iminium species is transient in the presence of base, being converted to the enamine form which readily undergoes C-perfluoroacylation a t C-15 to yield 11’ in high yield. The C-perfluoroacylation of I11 at C-4 to yield 111’ is favored in part because the product is a stable vinylogous amide and exhibits extended aromatic conjugation. There is also evidence to suggest that the restricted geometry associated with rings A and B in I11 is a prerequisite for this reaction to occur (16). As with I and I1 the presence of a base is required for proton abstraction a t C-3 and C-4. Influence of Base on Yield of HFB Derivatives. Particular care must be exercised in the selection of an appropriate base to assist in the derivatization of certain heroin byproducts. Impurities such as IV-X did not require the presence of base for high-yield 0- and N-HFB formation. Conversely, the presence of pyridine, or 4-DMAP, was required for the complete 04-HFB derivatization of XI1 to yield XII’. As discussed previously, the presence of a base, such as pyridine or 4-DMAP, was necessary for the C-perfluoroacylation of I, Ia, Ib, and 11. For 111, however, the presence of pyridine or the strong base trimethylamine proved ineffective in assisting C-perfluoroacylation. For this reaction to occur in high yield, 4-DMAP was required. This suggested that the effective acylating species for I11 was the N-(heptafluorobutyryl)-4(dimethy1amino)pyridinium ion (17).For standard and sample analyses the amount of 4-DMAP used in the reaction was rather critical. Insufficient quantities of 4-DMAP can be scavenged by heptafluorobutyric acid, rendering derivatization of some impurities incomplete. Because 4-DMAP is a relatively strong base, its use in excessive amounts can promote the hydrolysis of 0-HFB groups. This hydrolysis was also noted when using trimethylamine. In this study, between 30 and 40 mg of 4-DMAP in the reaction solution was suitable. Reaction of I1 with HFBA. In the presence of pyridine, or 4-DMAP, the reaction of I1 with HFBA proceeded rapidly to give 11’in high yield. The reaction was also applicable for heroin N-oxide to give 1’. The important implications of this reaction are 2-fold. First, whereas the presence of A15J6-didehydro- impurities have been unequivocally established in heroin samples (3), little is known about the presence of N-oxides. The question is raised as to whether the chromatographic peaks in Figures 4 and 5 that represent 15-HFBA16J6-didehydro- derivatives, e.g., 1’, are due exclusively to A1b16-didehydro-impuities in the heroin sample or due in part to the presence of N-oxides. Secondly, this reaction has potential application for the low-level detection of N-oxides in botanical and biological matrices. Because of the charge separation associated with N-oxides, they are not amenable to direct gas chromatographic analysis. Our derivatization procedure not only converts the N-oxide to a species that can be chromatographed but also allows detection in some cases a t low picogram or high femtogram levels, e.g., 11’. Significance of Acid Back-Extraction Prior to Chromatography of HFB Derivatives. The acid back-extraction of the ethyl ether-isooctane extraction solvent prior to injection was important for several reasons. First, it effectively removed the bulk of the 4-DMAP, thus preventing possible column deterioration and injection port hydrolysis of 0-HFB derivatives. Second, it allowed for the quantitative removal of heroin, while retaining the bulk of the HFB derivatives in the organic phase. When microgram quantities of heroin were concomitantly injected with the HFB derivatives, overloading of the capillary column occurred, resulting in anomalous chromatographic behavior for some derivatized impurities. Finally, by manipulation of the pH of the acid back-extraction, certain HFB derivatives of tertiary amines were retained by or extracted from the organic phase. This is significant, be-
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Figure 5. Splitless capillary GC-ECD chromatogram of unadulterated Southwest Asian heroln using pH 4 back-extraction. favoring the enamine species. Thus, the reaction of Ia or Ib with HFBA in the presence of base proceeds through I to give I‘ in high yield. The reaction of I1 with HFBA in the presence of base is also believed to proceed via an enamine intermediate. The initial step in the reaction is probably coordination of an HFB group with the N-oxide oxygen followed by a trans-coplanar
ANALYTICAL CHEMISTRY, VOL. 56, NO. 4, APRIL 1984
645
Table 1. Retention Times of HFB Derivatives of Some Heroin Impurities retention time, compound min p,p'-DDT (internal standard A) 04-HFB-thebaol(XII') 06-HFB-codeine (IV')
17.12 17.50 17.87
03,06-di-HFB-morphine(V' ) 06-acetyl-03-HFB-morphine(VI') 03, 06,N-tri-HFB-normorphine(XI') 03-acetyl-06-HFB-morphine(VII') O6-acety1-O3,N-di-HFB-normorphine (VIII') dioctyl phthalate (internal standard B) 06-acetyl-N-HFB-norcodeine(IX') 03,06-diacetyl-N-HFB-normorphine( X ' ) 15-HFB-A15*'6-didehydroheroin (1') 4-HFB-~~,~-didehydronoscapine (111')
18.14
19.41 20.00 20.15 21.18 21.44 22.65 24.39 28.75 35.07 I
cause it allows one to ascertain with a high degree of probability which peaks in the chromatogram represent tertiary amines. Until this study we had been unable to effectively study the 0-HFB tertiary amine impurities along with other neutral and acidic HFB derivatives using capillary GC-ECD. With a pH 4 back-extraction, greater than 99% of the microgram quantities of heroin was removed from the isooctane-ethyl ether phase in a single extraction, whereas greater than 80% of the nanogram amounts of derivatized tertiary amine impurities such as 1V'-VII' were retained by the organic phase. This remarkable organic phase discrimination is probably related in part to the nonpolar character associated with the HFB group. More importantly, there is strong evidence to suggest that the HFB group(s), due to their strong electrophilicity, have a marked influence on the nitrogen lone pair, imparting to the molecule a partial neutral-like character. This evidence was found by back-extracting IV' from the isooctane-ethyl ether into increasingly acidic buffers (pH 6 to pH 1). When the percent of organic phase retention of IV' was plotted vs. pH, an S-shaped curve resulted. This curve indicated that at a p H of 4 or greater an organic phase retention of greater that 80% for IV' was realized. This value dropped to less than 10% below pH 1. Illustrated in Figure 4 are chromatograms of an HFB-derivatized, unadulterated Southeast Asian heroin sample that has been subjected to both pH 4 and 0.5 N sulfuric acid back-extractions. Chromatography, Response, and Reproducibility of HFB Derivatives. Figures 3-5 illustrate capillary chromatograms of HFB derivatives of the mixed standard and two illicit heroin hydrochloride samples, one of Southeast Asian origin and the other from Southwest Asia. Table I lists retention times for the major HFB derivatives. Most peaks in the first 8 min of all chromatograms were due to impurities associated with 4-DMAP. With the exception of 111', most HFB derivatives exhibited good chromatography. Attempts to improve the chromatography of 111' by changing chromatgraphic conditions, columns, etc. proved unsuccessful. Furthermore, the response of 111' was more sensitive to changes in injection port temperature than other HFB derivatives. In our studies, a temperature of 300 "C appeared optimum. Certain evidence suggested that the chromatography of 111' might be related to the splitless injection technique. Despite its chromatography, 111' was readily detected on-column at picogram levels. Most other derivatives could be detected at significantly lower picogram levels, and some, such as XI', at high femtogram levels under optimum conditions. In order to study the reproducibility of this method, we subjected selected heroin samples to replicate analyses. The results indicated that when the 0.5 N sulfuric acid back-extraction was used, the reproducibility was acceptable in terms
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Flgure 6. 'H NMR spectra: (a) 15-HFBh'5~'E-didehydroheroin (1'); (b)
A15~'Edldehydroheroin (I).
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Figure 7. 'H NMR spectra: (a) 4-HF&A3~4didehydronoscapine( I 11'); (b) noscapine (111).
of both retention times and responses for even the most peak-enriched chromatograms. Spectroscopic Characterizationof 1', 11', 111', and HFB Derivatives of Other Heroin Impurities. The IR spectrum of I' exhibited strong bands at 1770 and 1745 cm-' and were attributed to v(C=O) at O3and Ofi,respectively. Evidence for a perfluorinated vinylogous amide could be accounted for by bands at 1615 and 1580 cm-' (18). For 111', the v(C=O) due to the lactone moiety was present at 1770 cm-'. Strong bands at 1625 and 1585 cm-' were attributed to v(C=O) and v(C=C) in the vinylogous amide moiety. The lH NMR spectra of I, 1', 111,and 111' were recorded in CDC13and are illustrated in Figures 6 and 7. The chemical shifts and coupling constants were consistent with the structures assigned to I' and 111'. For 1', the assignment of the HFB group at C-15 is consistent with the fact that the resonance for H-15is absent and H-16has experienced a large downfield shift. To further confirm this assignment we exchanged I with deuterium at (2-15 to yield [15-2H]-A'6J6-didehydroheroin. This exchange was observed to completion by 'H NMR with the removal of the H-15 resonance and the resulting collapse of the H-16 resonance to a singlet. The deuterium exchange material was subjected to HFB derivatization to give the 15-HFB derivative. The 'H NMR of this derivative was identical with that illustrated in Figure 6a. This allowed for the conclusive assignment of the H-16 resonance
646
Anal. Chern. 1984, 56. 646-649
and the HFB group at C-15. The observation of the relatively large through-space anisotropic chemical shifts for H-5, H-7, H-1, H-2, and H-10 would indicate that in solution the conformation of the HFB group at (2-15 is freely rotating above the morphine system. The 'H NMR of 111' in Figure 7a showed the decided lack of high field multiple resonances of hydrogens at C-3 and C-4 which are prominent in I11 as illustrated in Figure 7b. This is readily justified by the introduction of the HFB group at C-4 and a double bond at C-3 to C-4. The isolated hydrogen at C-3 in 111' resonated at 7.276 ppm. Measured long range coupling of H-3 to H-1 (JS1= 1.0 Hz) established the validity of this chemical shift assignment. This also necessitated the HFB location at C-4. The substantial downfield shift of H-5 from 6.310 ppm in I11 to 7.859 ppm in 111' correlated well with the assigned C-4 location of the HFB group and the expected through-space anisotropic chemical shifts due to this group. Electron impact mass spectral analysis supported the structures assigned to I' and 111'. The structural characterization of 11' as well as the other HFB derivatives listed in Table I was confirmed by CINIMS.
481-81-2; HFBA, 336-59-4; heroin, 561-27-3.
LITERATURE CITED (1) Sobol, S. P.; Sperllng, A. R. ACS Symp. Ser. 1075, No. 73, 170. (2) Moore, J. M. I n "Instrumental Applicatlons in Forensic Drug Chemistry"; Klein, M., Kruegel, A. V., Sobol, S.P., Eds.; U.S. Government Printing Offlce, Washlngton, DC, 1978; pp 180-201. (3) Allen, A. C.; Moore, J. M.; Cooper, D. A. J . Org. Chem. 1083, 4 8 , 395 1. (4) Lurie, I.S.; Sottolano, S. M.; Blasof, S. J. J. Forenslc Scl. 1082, 27, 519. (5) Baker, P. B.; Gough, T. A. J. Chromatogr. Scl. 1081, 79, 483. (6) Neumann, H.; Gloger, M. Chromatographla 1082, 76,261. (7) Barron, R. P.; Kruegel, A. V.; Moore, J. M.; Kram, T. C. J. Assoc. Off. Anal. Chem. 1074, 57, 1147. (8) Stromberg, L. J. Chromatogr. 1075, 706,335. (9) Moore, J. M. J. Assoc. Off. Anal. Chem. 1073, 56,1199. (10) Drozd, J. J. Chromatogr. 1075, 773,303. (11) Ahuga, S. J . Pharm. Sci. 1078, 65,163. (12) Rice, K. C.; May, E. L. J . Heterocycl. Chem. 1077, 1 4 , 665. (13) Rice, K. C.; Jacobson, A. E. J . Med. Chem. 1075, 78, 1033. (14) Bentley, K. W. "The Chemistry of the Morphine Alkaloids", Oxford at the Clarendon Press: New York, 1954. (15) Craig, J. C.; Purushothaman, K. K. J. Org. Chem. 1070, 35, 1721. (16) Allen, A. C.; Moore, J. M.; Cooper, D. A., unpublished work, Drug Enforcement Agency, McLean, VA, 1983. (17) Hofmann, H.; Meyer, 8.; Hofmann, P. Angew. Chem., Int. Ed. Engl. 1072, 7 7 , 423. (18) Fraser, R. R.; Swlngle, R. B. Tetrahedron 1080, 25,3469.
Registry No. I, 86993-77-3;Ib, 86993-78-4; 11, 639-46-3; 111, 128-62-1;IV, 76-57-3; V, 57-27-2; VI, 2784-73-8; VII, 5140-28-3; VIII, 60223-55-4;IX, 7679-20-1;X, 58772-72-8;XI, 466-97-7;XII,
RECEIVED for review November 10, 1983. Accepted January 9, 1984.
Determination of Platinum and Palladium in Geologic Samples by Ion Exchange Chromatography with Inductively Coupled Plasma Atomic Emission Spectrometric Detection R. J. Brown* and W. R. Biggs Chevron Research Company, Richmond, California 94802-0627
An alternative procedure to the classical fire assay method for determining Pt and Pd in sulfide ores, concentrates, and furnace mattes is presented. A suitable amount of sample is digested with aqua regia and filtered and any remaining gangue is digested with a mixture of HF and HCi04. The solution is flitered and the residue fused with sodium peroxide granules. The fused salts are dissolved in a dilute HCI acid soiutlon and ail three solutions combined. The resultant solution ls passed through a Bio-Rad AG 50W-X8 cation exchange resin in the H+ form. The chlorocompiex anions of Pt and Pd are not retalned by the catlon exchange resin whlle the base metal cations are efficiently removed from the eluent. Pt and Pd concentrations are subsequently determined with an inductively coupled plasma (ICP). Preliminary experiments showlng the method's potential expandabllity to Au are included.
Today's economic climate has stimulated a renewed interest in platinum group metals (PGM). While determining PGM by spectroscopic methods does provide a rapid and accurate means of analysis, base metals (large concentrations of nonplatinum group elements) present in the sample can create spectroscopic interference effeds. To eliminate this problem, 0003-2700/84/0356-0646$01.50/0
spectroscopic analyses incorporate either empirical interference corrections or a separation step to free the PGM from their base metal burden. Several separation-spectroscopic methods have been reported (1-10). The classical fire assay procedure using Pb (1, 4) or other metals (5-10) as collectors is perhaps the most frequently used procedure in the PGM refining industry. Despite the overwhelming contribution made by the fire assay procedure, achieving success with this sample preparation procedure hinges on the experience and knowledge of the assayer. To minimize the dependence on the assayer, other methods have been explored. The use of solvent extraction procedures ( 1 , I I ) have been widely reported in the analysis of PGM. This method, however, typically requires several time-consuming steps in the preparation procedure. Numerous chromatographic approaches (11-16) exist for separation. Specifically, separation of Pt and Pd from complex sample matrices can be carried out most directly by eluting the chlorocomplex anion of these metals through a cation exchange resin while retaining the base metal cations on the resin. This work compares the results obtained for the analysis of sulfide ore, concentrate, and furnace matte samples by both traditional fire assay procedures with various spectrometric detectors and ion-exchange chromatography with inductively 0 1984 American Chemical Society
