Two-dimensional gas chromatography/electron-impact mass spectrometry with cryofocusing for simultaneous quantification of MDMA, MDA, HMMA, HMA, and MDEA in human plasma.
[FIGURE 1 OMITTED]
After oral administration, MDMA is enzymatically metabolized to 5 primary metabolites (9, 10). The major metabolic route involves conversion to 3,4-dihydroxymethamphetamine (HHMA), an unstable intermediate, and then to 4-hydroxy-3-methoxymethamphetamine (HMMA) and 4-hydroxy-3-methoxyamphetamine HMA. The minor pathway produces 3,4-methylenedioxyamphetamine (MDA), 3,4-dihydroxyamphetamine (HHA), and HMA. Whereas MDMA and MDA are in plasma primarily in free form, the 4 metabolites carrying one or more free hydroxyl groups are conjugated with both glucuronide and sulfate. Conjugated HMMA is the major metabolite in human plasma (9).
The majority of published methods for quantification of MDMA in human plasma focus on MDMA and its minor metabolite, MDA (11-14). 3,4-Methylenedioxy-N-ethylamphetamine (MDEA) has not been included previously in conjunction with MDMA, MDA, HMMA, and HMA in a human plasma analytical method. This analysis includes MDEA owing to its potential presence in illicit Ecstasy, known for its poor purity (15-18), and because toxicology applications frequently require testing for this drug.
Although 2-dimensional GC/MS was first developed nearly 50 years ago (19), forensic toxicology applications began only recently (20-24). The advantage of 2D-GC/MS is a high degree of chromatographic resolution (25). Components first are separated on a nonpolar primary column. "Cuts" are collected around peaks of interest and diverted to a secondary polar column through use of a pneumatic Deans switch (Fig. 1). Additional sensitivity due to peak sharpening is gained by cryofocusing analytes at the entrance to the second column. Increased sensitivity, selectivity, and resolution, as well as decreased routine maintenance and extended column life, are all advantages of 2D-GC/MS.
Materials and Methods
CHEMICALS AND REAGENTS
We obtained human plasma from the National Institutes of Health blood bank. Each lot was analyzed in this laboratory by 2D-GC/MS to ensure absence of MDEA, MDMA, and metabolites. Racemic mixtures of MDMA, MDA, MDEA, HMMA, MDMA-[d.sub.5], MDA-[d.sub.5], and MDEA-[d.sub.6] were obtained from Cerilliant Corp. ([+ or-]) HMA was purchased from Lipomed, Inc., phydroxymethamphetamine (pholedrine) from Sigma, and Styre Screen[TM] DBX solid-phase extraction (SPE) columns from United Chemical Technologies, Inc. ACS reagent-grade monobasic and dibasic potassium phosphate, hydrochloric acid (HCl), sodium hydroxide, acetic acid, isopropanol, ammonium hydroxide, and ethyl acetate (HPLC grade) were purchased from Mallinckrodt Baker. HPLC-grade methanol was obtained from Fisher Scientific and heptafluorobutyric acid anhydride (HFAA) from Pierce Chemical Co.
CALIBRATORS AND QUALITY CONTROL SOLUTIONS
We combined 1 mL of 1 g/L MDMA, MDA, MDEA, HMMA, and HMA standards in a 10-mL volumetric flask to obtain a 0.1 g/L stock solution. We prepared 10, 1.0, and 0.1 mg/L standard solutions by dilution in methanol. Appropriate amounts of standard solutions were added to plasma to produce 1.0, 2.5, 5.0, 10, 50, 100, and 400 [micro]g/L working calibrators.
We used stock solutions from a different lot to prepare MDMA, MDA, MDEA, and HMMA quality control (QC) solutions. As only a single lot of HMA was available from the vendor, we used a separate vial of the same lot to make QC solutions. Three QC concentrations were prepared: the low QC contained 3.0 [micro]g/L MDA and HMA and 7.5 [micro]g/L MDMA, HMMA, and MDEA; the medium QC, 15 [micro]g/L MDA and HMA and 40 [micro]g/L MDMA, HMMA, and MDEA; and the high QC, 75 [micro]g/L MDA and HMA and 200 [micro]g/L MDMA, HMMA, and MDEA. We prepared a working mixed internal standard solution (working IS) in methanol to deliver 25 ng MDMA-[d.sub.5], MDEA-d6, and pholedrine and 15 ng MDA-[d.sub.5] in a 25-[micro]L aliquot. Calibrator, control, and IS stock solutions were stored at-80[degrees]C and working solutions at-20[degrees]C.
SPECIMEN HYDROLYSIS AND EXTRACTION
We pipetted 1 mL blank or participant plasma into glass 16-by 100-mm screw-cap culture tubes. Calibrators and QCs were fortified as described above. We added 25 [micro]L working IS and 1mL 0.5 mol/L HCl; tubes were capped, vortex-mixed, and incubated at 100[degrees]C for 40 min. After cooling, we added 1 mL of 0.1 mol/L phosphate buffer [pH 6.0] and 50 [micro]L of 10 mol/L NaOH to adjust the pH to 6. Samples were centrifuged for 10 min at 1855g. Polymeric Styre Screen DBX SPE columns functionalized with benzenesulfonic acid and C18 were preconditioned with 1.5 mL methanol, 1.5 mL deionized [H.sub.2]O, and 0.5 mL 0.1 mol/L phosphate buffer, pH 6.0. We decanted the sample supernatants onto conditioned SPE columns and washed the columns sequentially with 1.5 mL deionized [H.sub.2]O, 0.5 mL 0.1 mol/L acetic acid and 1.5 mL methanol, followed by drying for 15 min. Elution of analytes was achieved with 2 750-[micro]L aliquots of freshly prepared ethyl acetate:isopropanol:ammonium hydroxide (90/6/4, vol/vol/vol).
Derivatization and back-extraction procedures were performed as described by Scheidweiler and Huestis (26). To reduce loss of analytes, we added 15 [micro]L of 0.12 mol/L methanolic HCl to the SPE eluates before evaporation under nitrogen at 35[degrees]C. Extract residues were reconstituted with 100 [micro]L 0.5 mol/L triethylamine in heptane, vortex-mixed, and derivatized with 10 [micro]L HFAA at 60[degrees]C for 20 min. After cooling, samples were back-extracted with 200 [micro]L Tris buffer, pH 7.4. Tubes were vortex-mixed and centrifuged at 1855g, and the top organic layers containing analytes were transferred into autosampler vials.
For specimen analysis, we used an Agilent 6890 gas chromatograph configured with a microfluidic Deans switch and flame ionization detector (FID) and interfaced to an Agilent 5973 mass selective detector (MSD). The GC also was equipped with a compressed air-cooled cryogenic focusing trap (Joint Analytical Systems). The microfluidic Deans switch enables 2D-GC with 2 capillary chromatographic columns in series. The pneumatic switch system directs output of the primary column to either the FID or the inlet of the secondary column. The inlet end of the secondary column was inserted through the cryogenic trap and the outlet directed to the MSD. The air-cooled cryogenic trap focuses time-programmed "cuts" from the primary capillary column at the head of the secondary capillary column, then revaporizes trapped eluent with rapid heating. Operating parameters are listed in Table 1.
We injected 3 [micro]L derivatized extract in splitless mode. Two-dimensional chromatographic separation (Fig. 2) was achieved with a primary DB-1MS capillary column (15 m length by 0.25 mm i.d. by 0.25 [micro]m film thickness; Agilent Technologies) and secondary ZB-50 capillary column (30 m length by 0. 32 mm i.d. by 0.25 [micro]m film thickness; Phenomenex).
The GC oven temperature was ramped, at 35[degrees]C/ min, from 70 to 150[degrees]C, held for 0.50 min, then increased at 10[degrees]C/min to 195[degrees]C and held for 0.11 min. At this point, analytes of interest were cut from the first column and cryogenically captured at the inlet of the second column. The GC oven temperature was decreased at 50[degrees]C/min to 100[degrees]C, the cryogenic trap was ramped at 800[degrees]C/min to 275[degrees]C to release analytes, and a final GC oven temperature ramp at 10[degrees]C/min to 190[degrees]C resolved analytes on the second column. A complete list of instrument parameters is presented in
The temperatures of the quadrupole, source, and MSD interface were 150, 230, and 280[degrees]C, respectively. One target ion and 2 qualifier ions were monitored for analytes, MDMA, MDA, MDEA, HMA, and HMMA. One qualifier was monitored for each internal standard, MDMA-[d.sub.5], MDA-[d.sub.5], and MDEA-d6. Specific ions were as follows (quantitative ion italicized): MDMA 254, 210, 162; MDMA-[d.sub.5] 258, 213; MDA 162, 135, 375; MDA-[d.sub.5] 167, 380; MDEA 268, 240, 162; MDEA-d6 274, 244; HMMA 210, 254, 360; HMA 240, 163, 360; and pholedrine 254, 210.
We identified analytes by comparing retention time ([+ or-]2%) and relative abundance of qualifier ions to corresponding average values ([+ or-]20%) of calibrators assayed in the same run. Concentrations of unknowns were calculated from the equation of the regression line using peak area ratios of analyte to internal standard vs concentration. A 1/x weighting scheme was used to account for heteroscedasticity or unequal variance across the linear range. Requirements for acceptable calibration curves were coefficient of determination ([r.sub.2]) >0.985 and individual calibrator concentrations within [+ or-]20% of target.
We evaluated acidic hydrolysis at 3 temperatures, 100, 120, and 140[degrees]C; 3 volumes of acid (0.5 mol/L HCl), 1, 1.5, and 2 mL; and 3 incubation times, 20, 40, and 60 min. Plasma from one participant dosed with MDMA as part of a controlled administration study was used to compare conditions. The clinical study was approved by the National Institute on Drug Abuse Institutional Review Board, and the participant provided written informed consent. We pooled plasma specimens from multiple time points following the MDMA dosing session and used 1-mL aliquots for evaluation of hydrolysis parameters. Each condition was tested in triplicate.
Method validation included determination of dynamic linear range of the assay, limit of detection (LOD), limit of quantification (LOQ), recovery, imprecision, specificity, extraction efficiency, dilution integrity, stability, and carryover. We used low, medium, and high QC samples for each analyte to evaluate each parameter.
We assayed 4 unique calibration curves. Linearity was evaluated by least-squares regression (1/x weighting) and expressed as [r.sub.2]. MDMA-[d.sub.5], MDA-[d.sub.5], and MDEA-d6 were used as internal standards for their respective nondeuterated analytes. Analytes with free hydroxyl groups were not commercially available in deuterated form; MDA-[d.sub.5] was evaluated for use as an internal standard for HMA, MDMA-[d.sub.5] for HMMA, and pholedrine for both.
We spiked blank plasma with decreasing concentrations of analytes in triplicate to determine LOD and LOQ. LOD was defined as the lowest concentration with a signal-to-noise ratio [greater than or equal to]3:1 for target and qualifier ions, ion ratios within 20% of average qualifier ion ratios of calibrators, retention time within [+ or-]2%, and shape of gaussian peaks. At the LOQ, all LOD criteria must be met, signal-to-noise ratio of the target ion is 10:1, and the calibrator must quantify within 20% of target concentration. With these definitions, it is possible for LOD to equal LOQ.
We evaluated imprecision and recovery over the dynamic range at low, medium, and high QC concentrations. Five replicates of each concentration were included in 4 separate analytical runs ([n.sub.total] = 20). We determined recovery by comparing mean measured concentration to target, expressed as mean percent of target; results were acceptable if [less than or equal to]20% of target. Interassay imprecision was expressed as percent coefficient of variation of 20 individual values, equally weighted over 4 batches. Intraassay imprecision was evaluated from 5 determinations per concentration over 4 batches. Coefficients of variation [less than or equal to]20% were required for a precise method. We used 1-way ANOVA to evaluate interassay variability at each QC concentration.
To test specificity of the analytical method, we added 1000 [micro]g/L of each potential interfering compound (n = 66, Supplementary Data Table 1) to low QC samples. If analytes met identification criteria and quantified within 20% of target, no interference was noted. Six different blank plasma pools were also evaluated for endogenous interference.
[FIGURE 2 OMITTED]
To assess extraction efficiency for each analyte, we added analyte control solution to blank matrix at low, medium, and high control concentrations before solid-phase extraction and to a second set after extraction, but before the derivatization step. We calculated relative extraction efficiency at each QC concentration by comparing mean analyte peak area of each compound in the first set with appropriate mean analyte peak area (n = 5) in the second.
To determine dilution integrity, we diluted plasma samples spiked at high QC concentrations with 0.1 mol/L phosphate buffer (pH 6.0). Samples (n = 5) were prepared, and a 75% dilution with buffer was performed. Measured concentrations were compared to one-fourth of mean undiluted QC concentration and percent difference calculated to evaluate dilution integrity. Sample integrity was unaffected by dilution if results were within 20% of target.
To investigate analyte stability, we stored 3 replicates of low, medium, and high QC samples in capped tubes at 3 different temperatures. Short-term stability was evaluated at room temperature for 12 h or at 4[degrees]C for 48 h. Freeze/thaw stability was determined by subjecting samples to 3 24-h freeze/thaw cycles before internal standard fortification and analysis. Concentrations of stability samples were compared to routinely prepared control samples; results were expressed as a percent difference from mean QC concentration.
We evaluated stability of derivatized extracts in triplicate experiments by reinjection of low, medium, and high controls 24 and 48 h after initial injection. To restore sufficient volume of solvent, 50 [micro]L heptane was added to each vial before the 48-h injection. Concentrations of all samples were quantified using the original calibration curve and compared to initial assay concentration. Percent differences between means of each group (n = 3/concentration) were calculated.
To investigate carryover, we assayed low QC samples after a plasma sample was spiked with 1000 [micro]g/L of each analyte. If low QC sample concentrations were within 20% of the mean of low QC samples and ion ratios were acceptable, no carryover occurred. A negative plasma sample was assayed following the highest calibrator to evaluate carryover in each assay run. Analyte abundance in the negative sample was required to be < LOD.
INTERNAL STANDARD EVALUATION
Structural similarities led to investigation of MDMA-[d.sub.5] as an internal standard for HMMA, MDA-[d.sub.5] for HMA, and pholedrine for both analytes. When pholedrine was used as internal standard for both HMMA and HMA in plasma, linearity improved, as evidenced by higher [r.sub.2] values and interpolated calibrator concentrations closer to target. Therefore, we selected pholedrine as internal standard for HMMA and HMA. It should be noted that, although pholedrine is appropriate for analysis of samples from controlled pharmacokinetic studies with MDMA, it presents a problem in other forensic applications. Pholedrine (p-hydroxymethamphetamine) is a metabolite of methamphetamine and the designer drug p-methoxymethamphetamine (PMMA).
Acidic hydrolysis was selected for its speed, low cost, and reported efficiency over basic and enzymatic hydrolysis (27, 28). No significant difference in recovery was observed between the 3 hydrolysis temperatures (results not shown). As a result, the lowest temperature of 100[degrees]C was selected as the working hydrolysis temperature. We chose an incubation time of 40 min and 1mL HCl (each tested independently) for routine analysis because these parameters provided higher, albeit nonsignificant, abundances for HMMA and HMA.
We constructed calibration curves (n = 4) with 6 concentrations, with the exception of HMA (5 concentrations). MDAwas linear from 1 to 100 [micro]g/L, HMA from 2.5 to 100 [micro]g/L, and MDMA, HMMA, and MDEA from 2.5 to 400 [micro]g/L. The LOQ of each analyte was the lowest concentration on the calibration curve. MDA and HMA are found in considerably lower concentrations than MDMA and HMMA; thus, an upper limit of quantification of 100 [micro]g/L was sufficient. Coefficients of determination were _0.997 for all analytes in each of 4 curves. Curve characteristics are listed in Table 2.
[FIGURE 3 OMITTED]
The highest CV for an intraassay batch was 8.4% (Table 3). CVs for interassay imprecision at all QC concentrations were [less than or equal to]6.7%. One-way ANOVA revealed significant interassay variation for low QC HMA and HMMA and medium and high QC MDMA, HMMA, and MDEA concentrations. However, differences in daily mean QC concentrations were [less than or equal to]8.2%, and therefore, although statistically significant, variation was clinically insignificant.
MDMA is often not the sole drug ingested, due to frequent abuse of cannabis and other drugs and the poor purity of illicit Ecstasy (16, 18, 29). As this method could be used in analysis of clinical and forensic toxicology cases, interference from other illicit and licit drugs was assessed to reduce risk of false-positive or-negative results. None of 66 tested exogenous interfering compounds caused the concentration of the 5 analytes to vary more than 20% from mean low QC concentration. No endogenous interference was noted from 6 different blank plasma pools.
Extraction efficiency and recovery were [greater than or equal to]85% at all tested concentrations (Table 3), which allowed attainment of low LOQs and provided assurance that the majority of each analyte was successfully extracted.
Although concentrations previously reported from controlled dosing studies have suggested that calibration curves in this method have sufficient upper limits of quantification, MDMA or HMMA may exceed 400 [micro]g/L. In addition, 1 mL plasma may not always be available. In both situations, dilution can be performed to produce quantifiable results. A 75% dilution with phosphate buffer (pH 6.0) resulted in mean concentrations within [+ or-]20% of target for all analytes.
All analytes were stable ([+ or-]20% of mean fresh QC) under short-term room-temperature and refrigeration conditions and 3 freeze/thaw cycles, except HMA at lower concentrations. HMA displayed instability at low and medium QC concentrations after storage at room temperature for 12 h and at low QC concentration after 3 freeze/thaw cycles. Lowered concentrations may be a result of analyte degradation or adhesion to the tube. An additional experiment, 1 freeze/thaw cycle at low QC concentration, was performed because 1 frozen storage cycle is often unavoidable. Mean HMA concentration after 1 freeze/thaw cycle was within 11% of mean fresh low QC concentration. These results demonstrate that to obtain accurate HMA concentrations, plasma specimens should be removed from the freezer and immediately analyzed after thawing and mixing or placed in the refrigerator for up to 48 h before analysis. Other conditions may result in inaccurate HMA quantification.
Mean concentrations of QCs reinjected 24 and 48 h after original injection were within 8.3 and 5.8% of the mean for original values, respectively. These results demonstrate accurate quantification up to 2 days after initial extract preparation.
No carryover was present in 2 low QC samples injected sequentially after a 1000 [micro]g/L sample. Concentrations of all analytes quantified [+ or-]20% of target, and ion ratios were within [+ or-]20% of the mean for calibrators assayed in the run. Carryover was not detected (<LOD) in negative samples assayed immediately after the high calibrator.
As proof of method, a plasma specimen was collected 7 h after a participant ingested 105.7 mg MDMA. Quantitative analysis of the plasma specimen yielded 80.9 [micro]g/L MDMA, 110.3 [micro]g/L HMMA, 6.7 [micro]g/L MDA, 4.1 [micro]g/L HMA, and no detectable MDEA. Merged ion chromatograms demonstrating 2D separation of analytes are shown in Fig. 3. Results met all identification and quantification criteria.
Two-dimensional GC/MS proved an excellent methodology for analysis of MDEA, MDMA, and metabolites in human plasma. Low LOQs were achieved, with stable ion ratios across extended linear dynamic ranges. Inlet liner changes were the only routine maintenance required.
2D-GC offers greater separation capability than standard 1-dimensional gas chromatography. The 2D capillary chromatography system, in combination with cryofocusing and mass spectrometry selectivity, proved to be an effective tool for selective analyte detection and quantification. Choice of column phases, column dimensions, linear velocity, and temperature parameters provides flexible opportunities for resolution of drug analyte from complex matrices such as plasma, blood, and oral fluid. This method should be applicable for quantification of MDMA analytes in matrices other than plasma. Additionally, the method uses relatively inexpensive upgrades to readily available GC/MS hardware and is cost-effective compared with tandem MS instrumentation.
The primary limitation of the method was the inability to include HHMA and HHA. Also, although run time was 18.8 min, resolution of 5 closely related analytes was achieved without interference from exogenous compounds.
To our knowledge, this is the first 2D-GC/MS method for analysis of amines and the first to combine these 5 analytes in 1 human plasma analytical method. Method applicability was demonstrated by analysis of a plasma specimen obtained during controlled MDMA administration. The 2D chromatographic system should be suitable for application to other analytes and to other complex matrices.
Grant/funding Support: This research was supported by the Intramural Research Program of the National Institute on Drug Abuse (NIDA/IRP).
Financial Disclosures: None declared.
Acknowledgments: The authors thank Robert Goodwin, David Gorelick, Robert Hayes, Elliot Stein, Thomas Ross, Loretta Spurgeon, and David Darwin.
Received August 24, 2007; accepted November 20, 2007.
Previously published online at DOI: 10.1373/clinchem.2007.096800
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 Nonstandard abbreviations: MDMA, 3,4-methylenedioxymethamphetamine (Ecstasy); LSD, lysergic acid diethylamide; HHMA, 3,4-dihydroxymethamphetamine; HMMA, 4-hydroxy-3-methoxymethamphetamine; HMA, 4-hydroxy-3-methoxyamphetamine; MDA, 3,4-methylenedioxyamphetamine; HHA, 3,4-dihydroxyamphetamine; MDEA, 3,4-methylenedioxy-N-ethylamphetamine; SPE, solid-phase extraction; QC, quality control; LOD, limit of detection; LOQ, limit of quantification.
Erin A. Kolbrich, Ross H. Lowe, and Marilyn A. Huestis *
Chemistry and Drug Metabolism, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Baltimore, MD.
* Address correspondence to this author at: Chemistry and Drug Metabolism, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, 5500 Nathan Shock Dr., Baltimore, MD 21224. Fax 410-550-2971; e-mail email@example.com.
Table 1. Gas chromatograph, Deans switch, flame ionization detector, and cryotrap parameters for the detection and simultaneous quantification of MDMA, MDA, HMMA, HMA, and MDEA in human plasma. Inlets Front inlet Mode Constant pressure/ splitless Inititial temperature 200 [degrees]C Pressure 21.63 psi (149 kPa) Purge flow 50.0 mL/min Purge time 0.80 min Total flow 56.7 mL/min Oven Initial temperature 70 [degrees]C Initial hold time 0.00 min Ramp #1: 35 [degrees]C/min Final temperature 150 [degrees]C Final time 0.50 min Ramp #2: 10 [degrees]C/min Final temperature 195 [degrees]C Final time 0.11 min Ramp #3:50 [degrees]C/min Final temperature: 100 [degrees]C Final time: 0.00 min Ramp #4:10 [degrees]C/min Final temperature: 190 [degrees]C Final Time: 0.50 min Run time 18.80 min Post run time 1.00 min Post temperature 300 [degrees]C Back Inlet (Cryotrap) Initial temperature 50 [degrees]C Initial time 8.90 min Ramp 800 [degrees]C/min Final temperature 275 [degrees]C Deans Switch FID restrictor length, i.d. 2.13 m, 0.18 mm Auxiliary 3 pressure 12.90 psi (89 kPa) Pholedrine, MDA cut Begin 5.58 min End 5.95 min HMA cut Begin 6.10 min End 6.30 min MDMA, HMMA, MDEA cut Begin 6.60 min End 7.30 min Flame Ionization Detector Temperature 275 [degrees]C Hydrogen flow 40 mL/min Air flow 450 mL/min Nitrogen makeup flow 20 mL/min Table 2. Simultaneous quantification of MDMA, MDA, HMMA, HMA, and MDEA in human plasma by 2D GC/MS with cryotrapping. Internal LOD, LOQ, Analyte standard [micro] g/L [micro] g/L MDMA MDMA-[d.sub.5] 0.5 2.5 MDA MDA-[d.sub.5] 1 1 HMMA Pholedrine 1 2.5 HMA Pholedrine 0.5 2.5 MDEA MDEA-[d.sub.6] 2.5 2.5 Slope, mean Intercept, Linear range, Analyte (SD) mean (SD) [micro] g/L MDMA 0.046 (0.002) -0.040 (0.013) 2.5-400 MDA 0.121 (0.003) -0.027 (0.008) 1.0-100 HMMA 0.007 (0.000) -0.011 (0.006) 2.5-400 HMA 0.018 (0.004) -0.012 (0.003) 2.5-100 MDEA 0.042 (0.003) -0.041 (0.013) 2.5-400 Table 3. Imprecision, recovery, and extraction efficiency results from a 2D GC/electron-impact MS method with cryotrapping developed for the simultaneous quantification of MDMA, MDEA, and metabolites in human plasma. Imprecision Intraassay mean % CV (n = 5 replicates/ Interassay Target, run, total % CV Analyte [micro] g/L of 4 runs) (n = 20) MDMA 7.5 2.0 2.8 40 1.2 2.4 200 2.3 3.5 MDA 3.0 3.5 3.5 15 1.5 1.8 75 2.6 2.8 HMMA 7.5 2.0 3.1 40 1.7 3.8 200 2.7 3.7 HMA 3.0 4.3 5.2 15 4.3 4.8 75 5.9 6.7 MDEA 7.5 1.5 1.6 40 1.0 3.1 200 2.5 3.6 Extraction Recovery efficiency, % Recovery, Extraction % of efficiency, target % Analyte (n = 20) (n = 5) (a) MDMA 91.5 88.9 85.8 88.9 94.0 91.3 MDA 93.7 96.1 87.2 85.2 87.9 94.9 HMMA 89.2 88.9 85.6 86.3 92.8 89.0 HMA 107.2 95.8 89.3 85.0 94.3 93.2 MDEA 88.0 86.9 86.6 89.3 91.8 89.6 (a) Blank plasma was spiked with quality control solution before hydrolysis/extraction or after solid-phase extraction. Results were expressed as the percent difference between analyte abundance in samples spiked before and after solid-phase extraction
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|Title Annotation:||Drug Monitoring and Toxicology|
|Author:||Kolbrich, Erin A.; Lowe, Ross H.; Huestis, Marilyn A.|
|Date:||Feb 1, 2008|
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