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Articles |
1
Johns Hopkins Medical Institutions, 600 N. Wolfe St., Baltimore, MD 21287-7065.
2
Ansys, Inc., Irvine, CA 92718.
a Author for correspondence. Fax 410-955-0767; jnichols{at}pathlan.path.jhu.edu
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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The advantages of SPE have become even more pronounced in recent years with the advent of semiautomated and automated SPE instruments (2)(3)(7)(8)(9)(10). One study found that, in general, SPE was 12-fold less time-consuming and fivefold less expensive than LLE (11). Most semiautomated systems facilitate the aspiration of fluid through the columns by a vacuum system or vacuum box. These vacuum boxes often have some way to adjust and control the amount of vacuum. Today, most, if not all, laboratories that use SPE utilize some form of semiautomation but few utilize computer-controlled robot arms to fully automate some or all of the steps. The automated methods have been shown to offer higher drug recoveries and greater precision, usually because in manual procedures flow rates, sample application, and elution are much more variable (8). The automated systems also have the advantage of decreasing the amount of repetitive work done by laboratory staff. Overall, SPE has been shown to offer many advantages over traditional LLE, including automation, higher selectivity, improved reproducibility, and cleaner extracts (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17).
In our hospital laboratory we evaluated a prototype Toxi · Prep (TP) system for the screening of therapeutic drugs and drugs of abuse in urine. TP is a semiautomated processor that incorporates SPE with direct spotting onto a thin-layer chromatography (TLC) plate. In particular, TP automates labor-intensive extraction and TLC spotting, thereby minimizing operator hands-on time, reducing technical error, and improving reproducibility. TP is also a batch processor that can extract and spot up to seven samples in parallel.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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The following reagents, of analytical grade or better, were required for the TP system: ammonium metavanadate (Spectrum Chemical), glacial acetic acid, isopropanol, methanol, acetone, concentrated ammonium hydroxide, ethyl acetate, n-hexane, heptane, diethylamine, concentrated sulfuric acid, concentrated hydrochloric acid, 37% formaldehyde (Mallinckrodt Specialty Chemicals), deionized water, TL-A-3 reagent concentrate, Toxi · Dip (TD) THC-1 reagent vial (1 g/L fast blue BB salt), and THC hydrolysis reagent, which consists of 11.8 mol/L concentrated potassium hydroxide (Ansys).
The following equipment and other materials were loaned for the evaluation from Ansys: the TP system with the associated vacuum manifold and pump; Spec · Prep 6 mL C18AR/MP3 extraction columns; Toxi · Grams Prep A thin-layer chromatograms; Toxi · Discs A-1, A-2, A-3, A-4; disc handling needles; TL-A Plus dipping jars; TL-A Plus chromatography jar; test tubes (16 x 100 mm); and ultraviolet cabinet and light.
The following solutions were prepared for the extraction and spotting of basic drugs from urine according to manufacturer's recommendations: 1.0 mol/L acetic acid, wash reagent I (0.1 mol/L acetic acid), wash reagent II (100 mL of ethyl acetate, 100 µL of glacial acetic acid), acid elution reagent (140 mL of hexane, 60 mL of ethyl acetate, 200 µL of glacial acetic acid), and basic elution reagent (98 mL of ethyl acetate, 2 mL of concentrated ammonium hydroxide).
Solutions for TLC development of the basic drugs included TLC developing solution (30 mL of methanol, 15 mL of water, 870 mL of ethyl acetate), TD A-1 (25 mL of 37% formaldehyde), TD A-2 (250 mL of concentrated sulfuric acid), and TD A-3 (modified Dragendorff's reagent—add 10 mL of glacial acetic acid to Ansys-supplied proprietary vial of potassium iodide/iodine/bismuth subnitrate and dilute with deionized water to a volume of 250 mL).
Extraction and spotting solutions for THC metabolites in urine were also prepared according to manufacturer's recommendations: wash reagent I (20% acetic acid), wash reagent II (90 mL of heptane, 10 mL of dichloromethane), and acid elution reagent (70 mL of hexane, 30 mL of ethyl acetate, and 100 µL of glacial acetic acid).
Solutions for TLC development of THC metabolites included TLC developing solution (70 mL of heptane, 30 mL of acetone, 1 mL of glacial acetic acid), TD THC-1 (250 mg of 1 g/L fast blue BB salt, 250 mL of dichloromethane), TD THC-2 (15 mL of diethylamine), and TD THC-3 (150 mL of deionized water, 20 mL of concentrated hydrochloric acid).
Urine samples were discarded specimens from adults and children that were received in our hospital laboratory for clinical analysis. Specimens were frozen at -20 °C until analysis. Fifty-five urines, analyzed over 13 runs, were selected to represent the most commonly encountered basic drugs in our institution. The TLC results of basic drugs from TL-A and TP were compared directly with each other. In actual clinical practice, alternative identification methods were used to confirm TL's preliminary screening results. These results were not taken into account so that a more direct comparison could be made between the initial basic drug-screening results of TL-A and TP. Ten of the specimens, which contained 16 distinct drugs, were repeated to evaluate reproducibility. We further tested 20 urines over five runs for the presence of THC metabolites by the TP identification technique. Three of these specimens were repeated to evaluate reproducibility. All runs, including those for basic drug screening and THC metabolites, were timed with a stopwatch at the start of the extraction sequence and, from this data, time and motion studies were generated. TL-A and TP analyses were performed by different technologists. Specimens were coded and results were blinded to the participants until completion of the study.
procedures
TL
. The TL methods followed manufacturer's
recommendations for the evaluation of basic and neutral drugs (A-side)
and THC metabolites. TL is based on TLC and involves five major steps:
extraction, concentration, inoculation, development, and detection. The
procedure is a popular method in hospital laboratories for urine drug
screens.
In essence, for TL-A the drugs are extracted from 5 mL of urine with Toxi · Tubes, which contain a proprietary mixture of solvents and buffering salts at pH 9. When the solvent extracts are concentrated by heat and evaporation, the unknown drugs are deposited onto discs of chromatographic media. The dried discs are then fitted into the sample holes of the A chromatogram. The "loaded" chromatograms are developed by placing them in individual jars containing small volumes of solvents. Migration of unknown and calibrator drugs from the discs and the spacing of these drugs on the chromatograms occur during development.
Before development, TD calibrators (i.e., A-1, A-2, A-3, and A-4) are inoculated to appropriate areas of the chromatogram. The chromatogram is inserted into a developing tank that contains 12 mL of TLC developing solution and 80 µL of concentrated ammonium hydroxide. The tank is covered and the chromatogram is allowed to develop undisturbed for 12–17 min or until the solvent covers 95% of the chromatogram. The chromatogram is removed and dried for 60 s on a hot plate.
Detection of the known and calibrator drug spots is achieved when the chromatograms are dipped into chromogenic reagents. The chromatogram is placed into the A-1 jar and exposed to A-1 vapor for at least 10 min. The chromatogram is then dipped slowly in and out of the A-2 reagent and the color and position of any spots are recorded. The chromatogram is next dipped in and out of deionized water and the color and position of any spots are recorded. After blotting, the color and position of drugs are recorded under ultraviolet light. Finally, the chromatogram is dipped into the A-3 reagent for 30 s, removed, and the color and position of any drugs recorded. Identification is based on matching a drug spot with an adjacent calibrator drug spot having the same migration and color characteristics at each development stage.
The principles behind the identification of THC metabolites in urine (TL cannabinoid screen) are basically the same as that for the TL A-side. The steps include hydrolysis of conjugated THC metabolites in 10 mL of urine with 1.0 mL of THC hydrolysis reagent, extraction of free metabolite with 10 mL of THC extraction solvent (9 mL of hexane, 1 mL of ethyl acetate), concentration of the extract onto a disc, inoculation of a chromatogram with a disc, development of a chromatogram, and detection of a cannabinoid metabolite. A THC calibrator disc and positive and negative controls are included with each batch. For development, the chromatogram (disc end first) is inserted into a jar containing 3 mL of TLC developing solution. The chromatogram is removed after the solvent front has migrated ~5 cm (~15 min). For the detection of THC metabolites, the chromatogram is dipped once into the TD THC-1 jar and air dried for 1 min. The chromatogram is next placed into the TD THC-2 jar and the color reaction is observed after 15 s. THC metabolites will become visible as rose-red spots. The chromatogram is then dipped into the TD THC-3 jar. In this acidic pH, the rose-red spots will change to purple against a pale yellow background.
TP broad spectrum (basic drugs)
. The TP broad-spectrum
procedure for evaluating basic drugs is divided into four major steps:
sample extraction, spotting, TLC development, and drug detection. Up to
seven samples may be processed at once, unlike TL, which can only
accommodate one urine specimen at a time. During the procedure, six
buttons are used by the operator: vacuum on, vacuum off, dry on, dry
off, clamp up, and clamp down. Pushing the vacuum on button applies a
vacuum pressure, the amount of which can be manually adjusted. Pushing
the dry on button helps to maximize drying pressures and aid in
complete aspiration of reagents or sample when needed. The clamp down
control is used to hold the chromatography plates in place during
spotting. For sample preparation, 10 mL of patient urine is mixed with
1 mL of 1.0 mol/L acetic acid and vortex-mixed. The extraction sequence
is semiautomated. The columns are conditioned with 200 µL of
isopropanol to wet the extraction discs. After equilibrating with 500
µL of wash solution I, the urine sample is added. Vacuum pressure
aspirates the samples. Five-hundred microliters each of wash solution
I, acid elution reagent, and wash solution II are added and aspirated
in sequence. Unlike the TL procedure, no sample mixing or
centrifugation is required. To set up for spotting, an evaporation
screen is placed over the vacuum holes on the hot plate of the TP
processor. A TLC plate is placed over the evaporation screen, followed
by a second screen. The sandwich of screens and TLC plate is clamped
into place by pushing the clamp down button. Basic elution reagent (400
µL) is added and allowed to automatically spot directly onto the
chromatogram for 2 min. A second elution with another 400 µL of basic
elution reagent is then performed and allowed to spot for 3 min. Both
TP and TL-A follow the same procedure for TLC development, drug
detection, and identification.
TP THC metabolites
. The TP procedure for evaluating THC
metabolites in urine is divided into the same four major steps: sample
extraction, spotting, TLC development, and drug detection. As with the
broad-spectrum procedure, up to seven urines may be processed at once.
Six milliliters of urine is processed by mixing with 400 µL of THC
conjugate hydrolysis reagent. The columns are conditioned with 200 µL
of isopropanol and 500 µL of wash solution I. The urine sample is
added. Columns are washed with 500 µL of wash solution I, followed by
0.5 mL of hexane. Set up for spotting by placing a TLC plate between
two evaporation screens and clamping them into place. Acid elution
reagent (400 µL) is added to each SPE concentrator (SPEC) extraction
column and allowed to spot directly onto the chromatogram for 2 min.
Both the TP and TL cannabinoid screens follow the same procedure for
TLC development, drug-detection, and identification.
statistics
Comparisons between TL-A, TL, and TP for the time and motion
studies were performed with the Student's t-test.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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). The total number of drugs and metabolites identified with
TL-A (the reference method) was 205, whereas the total number of drugs
and metabolites identified by both TP and TL-A was 141. Therefore,
68.8% (141 of 205) of the drug occurrences were detected by both
methods. Drugs noted significantly more frequently on TP than TL-A
included quinidine and quinine (Q/Q), nortriptyline metabolites, and
diphenhydramine. We encountered five urines in which drugs were
identified by TP but not by the current laboratory method. These drugs
included Q/Q in three of the cases, and a high migrator,
diphenhydramine, and nortriptyline and metabolites in one case each.
Drugs noted significantly more frequently on TL-A than TP included
nicotine and metabolites, morphine, and methadone and metabolites.
These differences may be resolved through the use of alternative
extraction/detection reagents and migration solvents.
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Nicotine, acetaminophen, and meprobamate are lost during the acid elution wash of TP. Not being able to detect acetaminophen is clinically relevant. We recommend, therefore, that other analytical techniques be used to detect acetaminophen as part of acute-intoxication testing services. Assays used for acetaminophen testing should allow for accurate quantification as an aid in guiding antidotal therapy. Additionally, several of the assays available do not require chromatographic equipment or expertise. If nicotine and metabolites are eliminated from the calculations, then the percentage of all basic drugs seen by both TP and TL-A increases to 80.5% (124 of 154).
Reproducibility studies for TP demonstrated that the most consistently
reproducible drugs were Q/Q, tricyclic antidepressants, and methadone.
The least consistently reproducible drugs were nicotine and
diphenhydramine (Table 2
).
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Volume comparisons show that TP and TL-A require similar solvent volumes (~2 mL), but the recommended sample volume for TP is twice as much as for TL-A (10 vs 5 mL). Supplemental migrations (such as for morphine, sympathomimetic amines, or low migrators) would each require an additional 10 mL of urine for TP. This volume requirement is in contrast to TL-A, where one supplemental migration can be carried out with the same initial 5 mL of urine. Also, an additional 5 mL of urine is sufficient for two more supplemental migrations on TL-A.
Time and motion studies proved an overall labor reduction for
extraction and spotting of seven samples by ~40%: 55 min on TL-A
reduced to 33 min on TP (Table 3
). The overall procedure for TP often took slightly more time
than TL-A because of an increased time for the TLC development stage, a
stage that does not require a technologist to be continually present.
Since this evaluation, the manufacturers have altered the procedure to
reduce developing time from 35 to 15 min, a time comparable with the
current TL-A procedure. Nonetheless, the difference in time for the
overall procedure was statistically insignificant (P =
0.8).
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analysis of thc metabolites
Twenty specimens were analyzed for THC metabolites. All 16 of the
cases positive for THC metabolites were positive by both TP and TL
(sensitivity = 100%), whereas three of the four cases negative
for THC metabolites by TL were negative by TP (specificity =
75%). The one discrepant case may reflect enhanced sensitivity for THC
metabolites by TP. Three of the specimens were repeated, with 100%
reproducibility of results (Table 2
). Volume comparisons revealed that
TP used less extraction solvent than TL (1.7 vs 10 mL) and less urine
than TL (6 vs 10 mL). Time and motion studies indicate an overall labor
reduction for sample preparation, extraction, and spotting per patient
sample by ~39% (7.5 min on TL reduced to 4.6 min on TP) (Table 3
).
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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In previous reports on SPE, the method of detection was often gas chromatography with mass spectrometry (GC-MS) (1)(7)(13) or HPLC (14). Although relatively expensive, GC-MS, a highly sensitive and specific method, still remains the ideal analytical means for drug confirmation. There are a few reports of TLC detection after SPE (1)(3)(4). However, all of these procedures differ from TP in that none of them automated spotting of the extracts directly onto a chromatogram.
TLC offers advantages over other screening methods for detection of multiple drug classes. TLC can screen for many drugs simultaneously with a relatively high sensitivity and can handle several samples per plate. TLC is more selective in discriminating between representatives of a given class of drugs than when compared with various immunoassays that can only give simple qualitative answers for cross-reactive drugs within a class. Additionally, TLC is relatively simple conceptually, comes with low equipment costs, and has both a high efficiency and sensitivity (1)(3). Some disadvantages to TLC include only fair specificity and the requirement of technologist skill in accurately recognizing drug patterns by interpreting visualized color spots (1)(3).
Our study identified comparable advantages of TP over TL. TP provided a 40% labor reduction by automating the sample extraction, washing, and spotting steps, leading to cost savings; lowered control costs due to sample batching; and, for the analysis of THC metabolites, required less extraction solvent (1.7 mL vs 10 mL) and less urine (6 mL vs 10 mL) and produced cleaner chromatograms, leading to possible enhanced sensitivity.
Some disadvantages of TP were also noted. Nicotine, meprobamate, and acetaminophen, seen routinely on TL-A, were often not detected on the TP screen for basic drugs. In particular, acetaminophen, a weakly acidic compound, should not have been expected to be detected on TP because the procedure was specific for basic drugs. (Identification of acetaminophen on TL-A can be explained by the salting-out effect that is applied during that procedure.) Recommended sample volumes for TP were double those for TL-A (10 vs 5 mL). Although it may be possible to carry out the TP procedure with <10 mL of urine, we did not investigate this because we were examining applicability of the manufacturer's current recommendations. As could be expected, the increased urine volume over TL-A may have lent itself to offering higher sensitivity.
TL-A (basic and neutral drugs) requires 5 mL of urine, but TL-B (acidic drugs) requires an additional 4.5 mL of urine for a total of 9.5 mL. Recommendations (currently under investigation) for TP include use of only 10 mL of urine to evaluate basic, acidic, and neutral drugs. Another disadvantage to TP that we experienced was operational difficulty in reading and recording the results of seven samples on one chromatogram, especially when several drug spots were present in each sample. Some spots may have been missed because of fading or color change before the lanes were recorded. TP would also require a supplemental extraction and more sample to identify drugs such as benzoylecgonine.
Our data showed good correlation of results between TP and TL for basic drugs and THC metabolites in urine. However, there are some significant differences between the two extraction methods that prevent direct comparison of all drug classes. A sequential two-step extraction is applied in the TP procedure. First, acidic and neutral drugs are extracted; this extraction was not further analyzed in our investigation because that portion of the procedure was still under development. This extraction is followed by a second step in which the basic drugs are extracted and analyzed. In contrast, the TL procedure involves two separate extractions, one for basic and neutral drugs and another for acidic drugs. Thus, in the TP procedure basic drugs are not extracted alongside neutral drugs as they are in TL-A. Therefore, we report on the comparison of the basic drugs only. Additionally, we cannot accurately compare sensitivities between the two methods. In TP, the analyte(s) of 10 mL of urine end up in one spot; in TL-A, the analyte(s) of 5 mL of urine are subdivided over two wells, one containing a single A disc and another containing two A discs. With these volume and distribution differences, TP could be expected to offer an apparent higher sensitivity than TL-A for certain drugs. However, because of the built-in differences between the two techniques, we are unable to state whether the TP method is truly more sensitive than the TL-A method.
TP is a semiautomated batch processor that can reduce labor and increase productivity. At our fastest we were able to go from urine sample to spotted chromatography plate in 22 min, more than twice as fast as the current LLE method. TP is the first system to incorporate SPEC technology for SPE with direct spotting onto a TLC plate for detection of drugs in urine. The procedure has multiple uses, including, but not limited to, clinical drug screening, pharmaceutical drug testing, forensic drug profiles, environmental testing, and agricultural testing. In automating labor-intensive extraction and TLC spotting with a standardized operation, the TP system allows for minimal hands-on time, a reduction in technical error, and an improved reproducibility. TP would be most effective in high-volume laboratories where batching of specimens is commonplace.
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Acknowledgments |
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Footnotes |
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References |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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9-tetrahydrocannabinol-9-carboxylic acid from human urine with gas chromatographic–mass spectrometric confirmation. J Chromatogr 1991;567:81-91.
[Medline]
[Order article via Infotrieve]
9-tetrahydrocannabinol using TOXI-LAB SPEC prior to GC/MS analysis of urine. J Anal Toxicol 1993;17:215-217.
[Medline]
[Order article via Infotrieve]
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