Solid-Phase Extraction and GC-MS Analysis of THC-COOH Method Optimized for a High-Throughput Forensic Drug-Testing Laboratory*

Transcription

1 Solid-Phase Extraction and GC-MS Analysis of THC-COOH Method Optimized for a High-Throughput Forensic Drug-Testing Laboratory* Peter R. Stout, Carl K. Horn, and Kevin L. Kletle Navy Drug Screening Laboratory, P.O. Box 113, Bldg. H-2033, Naval Air Station, Jacksonville, Florida Abstract In order to facilitate the confirmation analysis of large numbers of urine samples previously screened positive for Ag-tetrahydrocannabinol (THC), an extraction, derivitization, and GC-MS analysis method was developed. This method utilized a positive pressure manifold anion-exchange polymer-based solidphase extraction followed by elution directly into the automated liquid sampling (ALS) vials. Rapid derivitization was accomplished using pentafluoropropionic anhydride/pentafluoropropanol (PFPA/PFPOH). Recoveries averaged 95% with a limit of detection of ng/ml with a 3-mL sample volume. Performance of 11-nor-Ag-tetrahydrocannabinol-9-carboxylic acid (THC-COOH)-d3 and THC-COOH-d9 internal standards were evaluated. The method was linear to 900 ng/ml THC-COOH using THC-COOH-d9 with negligible contribution from the internal standard to very weak samples. Excellent agreement was seen with previous quantitations of human urine samples. More than 1000 human urine samples were analyzed using the method with 300 samples analyzed using an alternate qualifier ion (m/z 622) after some interference was observed with a qualifier ion (m/z 489). The 622 ion did not exhibit any interference even in samples with interfering peaks present in the 489 ion. The method resulted in dramatic reductions in processing time, waste production, and exposure hazards to laboratory personnel. Introduction Urine drug testing has become a prevalent practice of employers in the United States and is a long-established policy in the Department of Defense (DOD). Confirmation of presumptive positive immunoassay results is a vital part of producing valid results that are forensically acceptable. However, this is an expensive process that involves significant input of personnel time and materials. As many commercial laboratories, the DOD laboratories are concerned with optimizing the process such * The opinions contained in the publication are not to be construed as official or as reflecting the views of the Department o[ Defense or the Department of the Navy. that accurate and reproducible results are produced with a minimum of expense. Reductions in labor have necessitated efficient processing to meet the needs of the customers. Many laboratories utilize a derivitization method with methyl iodide as a derivitizing reagent (1). This presents potential hazards for personnel exposed to the compound, as iodomethane is a nephrotoxin and neurotoxin as well as a suspected carcinogen (2). The method also utilizes tetramethylammonium hydroxide in dimethyl sulfoxide (DMSO) in the derivitization. Dermal exposure to DMSO has been associated with pruritis, urticaria, erythema, exfoliation, and pigmentation at the application site and peripheral neuropathies (3,4). Many liquid-liquid and solid-phase extraction methods have been developed utilizing various systems (1,5-8). In the forensic setting, ensuring that a sample is correctly identified throughout the process is of paramount importance. Many methods require samples and extracts to be transferred between containers multiple times throughout the process. Each transfer reduces efficiency because of glassware handling. Additionally, sample label materials may not perform well after multiple transfers and process steps, resulting in frustration for personnel. Multiple label transfers and glassware transfers also may also contribute to repetitive motion injuries. Methods optimized for a high-throughput laboratory not only need to meet the scientific acceptability of accuracy, precision, linearity, specificity, sensitivity, and reproducibility, but also production aspects related to process time, waste production, and personnel safety. The objective of this study was the development of a rapid, highly sensitive and accurate method for the analysis of 11-nor-Ag-tetrahydrocannabinol-9-carboxylic acid (THC- COOH) in urine minimizing processing steps, processing time, glassware transfers, waste production, and hazards to personnel. Methods Materials Extractions utilized a Speedisk 48 pressure processor positive pressure extraction manifold (SPEware, San Pedro, CA) and 550 Reproduction (photocopying) of editorial content of this journal is prohibited without publisher's permission.

2 polymer-based anion-exchange extraction columns (Cerex Polycrom THC, 50 mg, 3-mL capacity). The methanol, hexane, ethyl acetate, glacial acetic acid, and sodium hydroxide used were all ACS grade (Fischer, Pittsburgh, PA). Acetonitrile (Aldrich, St. Louis, MO) used was high-performance liquid chromatography (HPLC) grade. Pentafluropropionic anhydride (PFPA) and pentafluoropropanol (PFPOH) were purchased from United Chemical Technologies (Bristol, PA). Control materials were prepared in certified drug-free urine (Roche, Nutley, N J) using Ag-nor-11 carboxy THC in ethanol purchased from RTI (Research Triangle Park, NC). Deuterated internal standard stocks (THC-COOH-d3 and THC-COOH-dg) were purchased from Cerilliant, Inc. (formerly Radian, Austin, TX). Working solutions of internal standards were made up in methanol. All analyses were performed on Agilent (Palo Alto, CA) 489 F2 0~" OF K,.. / 2 H3C / "~ 459 F2C~CF3, o--/ II I H2 H2 ~ o ~ c / C ~ c / C ~ c H 3 H2 H2 CH3 THC-COOH/PFPA PFPOH Figure 1. Molecular justification of ions. Derivatization according to Knapp (9). Molecular weight of the parent ion was 622. Other fragments used in the method are indicated. Fil* c: \HFC=am\ ~ \ ~ T A \ ~ X mm\thc-std.d O~*r*tor i [~BII ~r : 30 J~ :0S u*ina Acqu*t~ T~C-~ InJt~t : r48os1 mmpl, mmm~ T~c st~dar~ Nlec ~n~o : ~ T Z ~ Vial ~ r ~ 2 a m ~ m/z Figure 2. Full spectrum scan of THCCOOH derivatized with PFPNPFPOL. Spectrum is a background subtracted scan from m/z 50 to 700 of a derivitized standard. A strong parent ion response is evident at rn/z 622. " 6890/5973 gas chromatograph-mass selective detectors (GC-MS) equipped with autoinjectors. All analyses were performed with HP-5ms 15-m columns. The injection port was maintained at 200~ and oven conditions started at ~ with a ramp of ~ to 295~ All injections were splitless with the injection port vented at 0.75 min. The transfer line was maintained at 280~ These conditions resulted in a retention time for the target analyte of approximately 4.1 min. All analyses were performed in single ion monitoring mode monitoring m/z 459, 468, 445, 454, 489, and 622. Quantitation used the ratio 459 to 468. Molecular justification of these ions is presented in Figure 1, and a full spectrum scan is presented in Figure 2. Hydrolysis To 3 ml of urine in a 13 x 100 tube, 0.1 ml of internal standard (THC-COOH-d9, mg/ml) and 0.25 ml of 10N KOH were added. Tubes were capped then incubated for 15 rain at 50-60~ and allowed to cool at room temperature. Extraction Hydrolyzed samples were poured into 3-mL solid-phase extraction columns and placed onto the Speedisk. Positive pressure was applied to the columns. Next, 1 ml of water/ ACN/NH4OH (85:15:1, v/v) was applied to the column followed by I ml methanol and then I ml ethyl acetate. Positive pressure was applied after each reagent addition. The THC-COOH was eluted directly into ALS vials with the addition 0.8 ml of hexane/ethyl acetate/glacial acetic acid (80:20:2, v/v). Samples were then evaporated to dryness under a stream of nitrogen. Derivatization Samples were derivatized in the ALS vials by the addition of ml PFPOH and ml of PFPA added to the ALS vials (9). Samples were capped, mixed, and incubated for 10 rain at 60-70~ Samples were removed from the heat block, allowed to cool, and then evaporated to dryness. Samples were then reconstituted with ml of ethyl acetate for GC-MS analysis. Results and Discussion Method recovery was assessed by analyzing two groups of five drug-free urine samples spiked with THC-COOH at 7 ng/ml as follows: the first set had internal standard added at the beginning of the extraction, and the second set had the internal standard added to the ALS vials after elution of the THC-COOH was complete. An average was taken of the THC-COOH/internal standard area results for the two groups of samples. Dividing these two numbers resulted in a measure of recovery. Evaluation of recovery samples indicated that recovery through the column and derivitization averaged 95%. The method was run using both heat and ambient temperature for the derivatiza- 551

3 tion. It was observed that samples derivatized with heat produced chromatographic results with somewhat greater peak areas. However, acceptable results were also obtained with samples derivitized at ambient temperature. The heating of samples was retained in the method to ensure complete derivitization and improved sensitivity. Control samples containing 15 ng/ml THC-COOH were also spiked with 50,000 ng/ml ibuprofen to determine if this would interfere with the assay. No measurable interference was evident from the addition of 50,000 ng/ml ibuprofen to samples. The limit of detection (LOD) and limit of quantitation (LOQ) of the method were determined by analyzing 13 levels of samples in quadruplicate spiked with THC-COOH ranging from to , :! Expected Concentration (gn/ml) Figure 3. Linearity of the assay from to 900 ng/ml. All replicates are plotted with a regression line. A slight increase in the variation between replicates is apparent for concentrations above 200 ng/ml. The data show excellent linearity and agreement with expected concentrations (R 2 = 0.993, F= 6938, df= 51)...J :1 Previous quantitation [IIJAX 1000 L~SD I ti 900 ng/ml. Extraction and GC-MS analysis were performed as previously described. The LOD was determined to be at the lowest concentration for which all replicates produced results with all analyte qualifying ion ratios within acceptable limits ( 20% of the calibrator ratios). The LOQ was determined to be at the lowest concentration at which the analyte qualifying ion ratios ratios were within the + 20% limit established by the calibrator and the determined concentration was within + 10% of the expected concentration. The LOD was determined to be ng/ml, and the LOQ was 1.75 ng/ml. The resulting %CV for the four replicates was within 5%, and the mean result was within 10% of the expected concentration. The limit of linearity was established by analyzing increasing concentrations of THC until one or more of the qualifying ion ratios failed or the determined concentration fell outside 10% of the expected concentration. The assay was linear from to 900 ng/ml with an r 2 of (F = 6938, df = 51) and the %CV for the four replicates was within 5% and the mean result was within 10% of the expected concentration. Some increase in variation was seen between replicates at concentration levels above 200 ng/ml with a maximum %CV of 4.14%. This increase in variation did not detract from the linearity of the assay above 200 ng/ml. This range of linearity provides wide coverage, such that few samples would fall above the linear range of the assay thereby requiring dilution. Both THC-COOH-d3 and THC-COOH-d9 were ' I000 evaluated as internal standards. The assay was linear to 450 ng/ml with both THC-COOH-d3 and THC-COOH-dg. However, the LOD was not as low using THC-COOH-d3 as with THC-COOH-d9 because of the contribution of the internal standard to the target analyte ions causing qualifying ion ratios to fall outside of acceptable ranges. Thus THC-COOH-d9 was determined to be the preferred internal standard for this method. The within run precision was accessed by analyzing 20 drug-free urine samples spiked with THC at the GC-MS cutoff concentration (15 ng/ml). Extraction and GC-MS analysis was performed as previously described. The precision samples yielded an average response of ng/ml and a %CV of 1.3%. Excellent correlation was seen between measured and expected results for control materials over a wide range of concentrations (Figure 3). Between-run precision, over the course of 40 separate batches prepared by 13 different technicians, produced a %CV for positive controls run with the batches of 5.0% Sample ID Figure 4. Comparison of analyses of one-year old samples. Both the Jacksonville Lab and the San Diego Lab analyzed samples over a range of 15 to 1500 ng/ml. These results are compared to the quantitation by a prior method. Comparative study Twenty 1-year-old human urine specimens previously reported positive for THC by GC-MS analysis (cutoff concentration 15.0 ng/ml) were extracted and analyzed as described previously. A duplicate set was also extracted and analyzed by the 552

4 o ~ E t~ ' E z 200.,oo,'R ~x.'r,'r 0 ~ ~ I ' I 0 50 loo Concentration (ng/ml) Figure 5. Distribution of 1100 human samples analyzed. Sample concentrations range between below detection to 245 ng/ml. Good chromatographic results were obtained over this range. 50O 4O Ion ( to ~68.70): THRQC.D i... J... i... ]... 9 =, , Ion (453,70 ~ ~ ): THRQC,D i... i... i... i ~... i... i, 3,95 4, , ,25 4,30 Ion 622,00 ( to 52!.70): THRQC,O v l... I... I... I... I... t... I... I... I' , , ,30 Time (rain) ; ~ i Ion 459,00 ( to 4 i9.70): THRQC.D 15~00~ ', ~ ~ 1200 to00 8OO 6OO 5OO 4OO 3OO 2OO Ior (44.4,70 to ): THRQC.D 0 i... i... i... i... i i... i... i , ): THRQC.D 0... i... i... i i... i... i... i, , , Time (mln) Figure 6. Example chromatography of a 7-ng/mL control for all ions examined. This result shows the interfering peak on the 489 ion that was observed. This result also demonstrated that the 622 ion was robust even when this interfering peak was present. Navy Drug Screening Laboratory in San Diego using the reported method. In addition to this set of 20, the Jacksonville lab analyzed an additional 17 previously reported positive samples. These results were compared against the quantitation obtained on these samples using the prior analytical method. The quantitation using the described method was performed using all controls and acceptance criteria standard in the laboratory. Figure 4 presents the results of the analyses from both the Jacksonville Laboratory and the San Diego Laboratory in comparison to the previous results from the Jacksonville Laboratory for these samples. By a student t-test, the results were not significantly different between the San Diego analysis and the Jacksonville analysis (at the 95% confidence level; df = 36, P = 0.555). Additionally, the results were not significantly different from the prior quantitation (at the 95% confidence level, df = 58, P = 0.652). The loss of THC-COOH between the original quantitation and the subsequent analyses is consistent with adsorptive loss to the plastic containers described in Stout et al. (10). Thus, the new assay is reproducible in comparison to previous methods used in our laboratory. Sample evaluation In all, 1100 human urine samples were analyzed by this method to evaluate the performance of the method in production. Approximately 300 of these samples were analyzed using an alternative m/z 622 qualifying ion. A wide range of THC-COOH concentrations was observed in the human urine samples evaluated, as seen in Figure 5. The majority of samples were at or below the 15- ng/ml DOD cutoff. Though clean chromatograph was observed for most samples as indicated in the chromatography of a 7-ng/mL control in Figure 6, an interfering peak on the 489 ion was observed in some samples (Figure 6). After evaluation of all reagents, the only remaining source of the contaminant was the column matrix. However the source of the interference could not be determined. As can also be seen in Figure 6, the m/z 622 ion did not exhibit any interference and shows no evidence of interference even when the interfering peak was present in the m/z 489 ion. Three hundred of the 1100 human urine samples were evaluated using the m/z 622 ion without observation of any interfering peaks. Thus, m/z 622 was determined to be the preferable ion to monitor. Conclusions The method developed provides a sensitive, accurate assay for THC-COOH in urine. Good 553

5 chromatographic performance was observed in controls as well as native samples. The use of the positive-pressure manifold and the polymer-based columns greatly reduced the waste production of the assay by eliminating the preconditioning steps and utilizing minimal solvent volumes. The waste production from this method was minimal per sample. The aqueous urine waste could be isolated from the organic solvent wastes further reducing disposal costs. This method produces 3 ml of organic solvent waste per sample without using any chlorinated solvents, thus simplifying disposal. Because of the high flow rates through the columns and minimal steps, the assay is very rapid. The small footprint and contained nature of the process reduces worker exposure to hazards, and derivatization with PFPA/PFPOL eliminates worker exposure to DMSO and methyl iodide. The elution of the samples and their derivatization directly into the ALS vials eliminates any glassware transfers, ensures the integrity of the samples, and simplifies labeling of the vials. References 1. B.D. Paul, L.D. Mell, Jr., J.M. Mitchell, and R.M. McKinley. Detection and quantitation of urinary 11-nor-delta-9-tetrahydrocannabinol-9-carboxylic acid, a metabolite of tetrahydro- cannabinol, by capillary gas chromatography and electron-impact mass fragmentography. J. Anal. ToxicoL 11:1-5 (1987). 2. M.J. Ellenhorn. Ellenhorn's Medical Toxicology, 2nd ed. Williams and Wi[kins, Baltimore, MD, 1997, pp A.M. Kligman. Topical pharmacology and toxicology of dimethyl sulfoxide-part II. J. Am. Med. Assoc. 193: (1965). 4. L. Reinstein, R. Mahon, Jr., and G.L. Russo. Peripheral neuropathy after concomitant dimethyl sulfoxide and sulidac therapy. Arch. Phys. Med. Rehabil. 63: (1982). 5. S.B. Needleman, K. Goodin, and W. Severino. Liquid-liquid extraction systems for THC-COOH and benzoylecgonine. J. Anal. Toxicol. 15: (1991). 6. A.H.B. Wu, N. Liu, Y. Cho, K.G. Johnson, and S.S. Wong. Extraction and simultaneous elution and derivitization of 11-nor-9-carboxydelta-9-tetrahydrocannabinol using Toxi-Lab SPEC prior to GO'MS analysis of urine. J. Anal ToxicoL 17: (1993). 7. R.C. Parry, L. Nolan, R.E. Shirley, G.D. Wachob, and D.J Gisch. Pretreatment of urine samples for the analysis of 11-nor-delta-9- tetrahydrocannabinol carboxylic acid using solid phase extraction. J. Anal ToxicoL 14:39-44 (1990). 8. D.K. Crockett, G. Nelson, P. Dimson, and F. Urry. Solid-phase extraction of 11-nor-Ag-tetrahydrocannabinol-9-carboxylic acid from urine drug testing specimens with the Cerex PolyCrom-THC column. J. Anal ToxicoL 24: (2000). 9. D.R. Knapp. Handbook of Analytical Derivitization Reactions. John Wiley and Sons, New York, NY, P.R. Stout, C.K. Horn, and D.R. Lesser. Loss of THCCOOH from urine specimens stored in polypropylene and polyethylene containers at different temperatures. J. Anal. Toxicol. 24: (2OOO). 554