Simultaneous determination of tramadol and its major active metabolite O-demethyltramadol by high-performance liquid chromatography with electrochemical detection

Comprehensive overview of analytical and bioanalytical methodologies for the opioid analgesics - Tramadol and combinations

Synthetic opioids like Tramadol are used to treat mild to moderate pain. Its ability to relieve pain is about a tenth that of morphine. Furthermore, Tramadol shares similar effects on serotonin and norepinephrine to several antidepressants known as serotonin-norepinephrine reuptake inhibitors (SNRIs), such as venlafaxine and duloxetine. The present review paper discusses the recent developments in analytical methods for identifying drugs in pharmaceutical preparations and toxicological materials, such as blood, saliva, urine, and hair. In recent years, a wide variety of analytical instruments, including capillary electrophoresis, NMR, UV-visible spectroscopy, HPTLC, HPLC, LC-MS, GC, GC-MS, and electrochemical sensors, have been used for drug identification in pharmaceutical preparations and toxicological samples. The primary quantification techniques currently employed for its quantification in various matrices are highlighted in this research.

Solid-phase microextraction of ultra-trace amounts of tramadol from human urine by using a carbon nanotube/flower-shaped zinc oxide hollow fiber

A new method is successfully developed for the separation and determination of a very low amount of tramadol in urine using functionalized multiwalled carbon nanotubes/flower-shaped zinc oxide before solid-phase microextraction combined with gas chromatography. Under ultrasonic agitation, a sol of multiwalled carbon nanotubes and flower-shaped zinc oxide were forced into and trapped within the pore structure of the polypropylene and the sol solution immobilized into the hollow fiber. Flower-shaped zinc oxide was synthesized and characterized by Fourier transform infrared spectroscopy. The morphology of the fabricated solid-phase microextraction surface was investigated by scanning electron microscopy and X-ray diffraction. The parameters affecting the extraction efficiencies were investigated and optimized. Under the optimized conditions, the method shows linearity in a wide range of 0.12-7680 ng/mL, and a low detection limit (S/N = 3) of 0.03 ng/mL. The precision of the method was determined and a relative standard deviation of 3.87% was obtained. This method was successfully applied for the separation and determination of tramadol in urine samples. The relative recovery percentage obtained for the spiked urine sample at 1000 ng/mL was 94.2%.

Development of solid-phase microextraction coupled with liquid chromatography for analysis of tramadol in brain tissue using its molecularly imprinted polymer

In this work, performance of a molecularly imprinted polymer (MIP) as a selective solid-phase microextraction sorbent for the extraction and enrichment of tramadol in aqueous solution and rabbit brain tissue, is described. Binding properties of MIPs were studied in comparison with their nonimprinted polymer (NIP). Ten milligrams of the optimized MIP was then evaluated as a sorbent, for preconcentration, in molecularly imprinted solid-phase microextraction (MISPME) of tramadol from aqueous solution and rabbit brain tissue. The analytical method was calibrated in the range of 0.004 ppm (4 ng mL^-1 ) and 10 ppm (10 μg mL^-1 ) in aqueous media and in the ranges of 0.01 and 10 ppm in rabbit brain tissue, respectively. The results indicated significantly higher binding affinity of MIPs to tramadol, in comparison with NIP. The MISPME procedure was developed and optimized with a recovery of 81.12-107.54% in aqueous solution and 76.16-91.20% in rabbit brain tissue. The inter- and intra-day variation values were <8.24 and 5.06%, respectively. Finally the calibrated method was applied for determination of tramadol in real rabbit brain tissue samples after administration of a lethal dose. Our data demonstrated the potential of MISPME for rapid, sensitive and cost-effective sample analysis.

Simultaneous determination of tramadol and O-desmethyltramadol in human plasma using HPLC-DAD

A sensitive and accurate method for the extraction and quantification of tramadol (T) and its active metabolite, O-desmethyltramadol (ODT) in human plasma with high-performance liquid chromatography-diode array detection was developed and validated. The analytes were extracted from plasma samples by tert-butylmethyl ether in the presence of ammonium hydroxide as alkaline medium and back extraction with 1.0 M hydrochloric acid. Propranolol was used as internal standard. The extraction efficiencies of T and ODT were 83.51 and 78.72%, respectively. The calibration curves were linear (r(2) > 0.99) in the concentration range of 250-2000 ng/mL for T and ODT. Limits of detection and quantification were 125 and 250 ng/mL for both analytes. Intra- and interassay precision for T and ODT were ranged from 1.89 to 10.91% and 2.16 to 5.85%, respectively. Intra- and interassay accuracy for T and ODT were ranged from -13.07 to 4.99% and -2.03 to -6.98%, respectively. The method was successfully applied to quantify T and ODT from authentic plasma samples received from Hospital Sohag University. The method was completely validated and can be of interest to clinical and forensic laboratories.

Multivariate optimization of surfactant-assisted directly suspended droplet microextraction combined with GC for the preconcentration and determination of tramadol in biological samples

In this work, a novel procedure based on surfactant-assisted directly suspended droplet microextraction for the determination of tramadol prior to GC with flame ionization detection is proposed. In this technique, a free microdroplet of solvent is transferred to the surface of an immiscible aqueous sample containing Triton X-100 and tramadol while being agitated by a stirring bar placed on the bottom of the sample vial. After the predetermined time, the microdroplet of solvent is withdrawn by a syringe and analyzed. The effective parameters such as the type of organic solvent, extraction time, microdroplet volume, salt content of the donor phase, stirring speed, the source phase pH, concentration of Triton X-100, and extraction temperature were optimized. For this purpose, a multivariate strategy was applied based on an experimental design in order to screen and optimize the significant factors. This method requires minimal sample preparation, analysis time, solvent consumption, and represents significant advantages over customary analytical methods. The linearity ranged from 10 to 2000 μg/L with RSDs (n = 5) of 7.3-10. Preconcentration factors and the LODs were 391-466 and 2.5-6.5 μg/L, respectively. Finally, this method was applied to the analysis of biological samples and satisfactory results were obtained.

Tramadol hydrochloride

A profile of the analgesic tramadol hydrochloride ((1RS,2RS)-2-[(dimethylamino)methyl]-1-(3-methoxyphenyl)cyclohexanol hydrochloride) is provided in this chapter and includes a summary of the physical characteristics known for this drug substance (e.g., UV/vis, IR, NMR, and mass spectra). Details regarding the stability of tramadol hydrochloride in the solid state and solution-phase are presented and methods of analysis (compendial and literature) are summarized. Furthermore, an account of biological properties and a description of the chemical synthesis of tramadol hydrochloride are given.

Three-phase hollow fiber liquid-phase microextraction based on two immiscible organic solvents for determination of tramadol in urine and plasma samples

Recently, the new concept of three-phase liquid microextraction was introduced based on applying two immiscible organic solvents in lumen and wall pores of hollow fiber. In the present work, this novel microextraction technique combined with gas chromatography-mass spectrometry has been developed for determination of tramadol, an analgesic agent, in plasma and urine samples. A systematic investigation of the proposed method was applied to find optimal extraction conditions and evaluate the interaction effects between the factors by designing experiments according to the methodology of Box-Behnken response surface design. Analysis of variance (ANOVA) revealed that the important factors contributing to extraction efficiency are extraction time, stirring rate and hollow fiber length. Under the optimum conditions, the developed method provided a preconcentration factor of 546, good repeatability (RSD %=6.4), and good linearity (r(2)=0.995) for spiked plasma and urine real samples. The linear dynamic range from 0.1 to 400 μg L(-1) and limit of detection (LOD) of 0.08 μg L(-1) were obtained under selected ion monitoring mode. The results demonstrated that three-phase hollow fiber microextraction based on two immiscible solvents is a simple and accurate technique with very good preconcentration factor and clean-up for extraction of tramadol from biological samples.

Preparation and utilization of a molecularly imprinted polymer for solid phase extraction of tramadol

In this paper, a highly selective molecularly imprinted polymer (MIP) for tramadol hydrochloride, a drug used to treat moderate to severe pain, was prepared and its use as solid-phase extraction (SPE) sorbent was demonstrated. The molecularly imprinted solid-phase extraction procedure followed by high performance liquid chromatography with ultraviolet detector (MISPE-HPLC) was developed for selective extraction and determination of tramadol in human plasma and urine. The optimal conditions for molecularly imprinted solid-phase extraction (MISPE) consisted of conditioning with 1 mL methanol and 1 mL of deionized water at neutral pH, loading of tramadol sample (50 µg L−1) at pH 7.5, washing using 1 mL acetone and elution with 3 × 1 mL of 10% (v/v) acetic acid in methanol. The MIP selectivity was evaluated by checking several substances with similar molecular structures to that of tramadol. Results from the HPLC analyses showed that the calibration curve of tramadol (using MIP from human plasma and urine) is linear in the ranges of 6–100 and 3–120 µg L−1 with good precisions (1.9% and 2.9% for 5.0 µg L−1), respectively. The recoveries for plasma and urine samples were higher than 81%.

Evaluation of tramadol and its main metabolites in horse plasma by high-performance liquid chromatography/fluorescence and liquid chromatography/electrospray ionization tandem mass spectrometry techniques

Tramadol is a centrally acting analgesic drug that has been used clinically for the last two decades to treat pain in humans. The clinical response of tramadol is strictly correlated to its metabolism, because of the different analgesic activity of its metabolites. O-Desmethyltramadol (M1), its major active metabolite, is 200 times more potent at the micro-receptor than the parent drug. In recent years tramadol has been widely introduced in veterinary medicine but its use has been questioned in some species. The aim of the present study was to develop a new sensible method to detect the whole metabolic profile of the drug in horses, through plasma analyses by high-performance liquid chromatography (HPLC) coupled with fluorimetric (FL) and photodiode array electrospray ionization mass spectrometric (PDA-ESI-MS) detection, after its sustained release by oral administration (5 mg/kg). In HPLC/FL experiments the comparison of the horse plasma chromatogram profile with that of a standard mixture suggested the identification of the major peaks as tramadol and its metabolites M1 and N,O-desmethyltramadol (M5). LC/PDA-ESI-MS/MS analysis confirmed the results obtained by HPLC/FL and also provided the identification of two more metabolites, N-desmethyltramadol (M2), and N,N-didesmethyltramadol (M3). Another metabolite, M6, was also detected and identified. The present findings demonstrate the usefulness and the advantage of LC/ESI-MS/MS techniques in a search for tramadol metabolites in horse plasma samples.

Improved liquid chromatographic method for the simultaneous determination of tramadol and its three main metabolites in human plasma, urine and saliva

Tramadol, an analgesic agent, and its main metabolites O-desmethyltramadol (M1), N-desmethyltramadol (M2) and O,N-didesmethyltramadol (M5) were determined simultaneously in human plasma, saliva and urine by a rapid and specific HPLC method. The sample preparation was a simple, one-step, extraction with ethyl acetate. Chromatographic separation was achieved with a Chromolith Performance RP-18e 100 mm x 4.6 mm column, using a mixture of methanol:water (19:81, v/v) adjusted to pH 2.5 by phosphoric acid, in an isocratic mode at flow rate of 2 ml/min. Fluorescence detection (lambda(ex) 200 nm/lambda(em) 301 nm) was used. The calibration curves were linear (r(2)>0.996) in the concentration ranges in plasma, saliva and urine. The lower limit of quantification was 2.5 ng/ml for all compounds. The within- and between-day precisions in the measurement of QC samples at four tested concentrations were acceptable in all analyzed body fluids The developed procedure was applied to assess the pharmacokinetics of tramadol and its main metabolites following administration of 100mg single oral dose of tramadol to healthy volunteers.

Stereospecific high-performance liquid chromatographic analysis of tramadol and its O-demethylated (M1) and N,O-demethylated (M5) metabolites in human plasma

A stereospecific method for simultaneous quantitation of the enantiomers of tramadol (T) and its active metabolites O-demethyl tramadol (M1) and O-demethyl-N-demethyl tramadol (M5) in human plasma is reported. After the addition of penbutolol (IS), plasma (0.5 ml) samples were extracted into methyl tert-butyl ether, followed by back extraction into an acidic solution. The separation was achieved using a Chiralpak AD column with a mobile phase of hexanes:ethanol:diethylamine (94:6:0.2) and a flow rate of 1 ml/min. The fluorescence of analytes was then detected at excitation and emission wavelengths of 275 and 300 nm, respectively. All the six enantiomeric peaks of interest plus three unknown metabolite peaks and IS peak (a total of 10 peaks) eluted within 23 min, free from endogenous interference. The assay was validated in the plasma concentration range of 2.5-250 ng/ml, with a lower limit of quantitation of 2.5 ng/ml, for all the six analytes. The extraction efficiency (n=5) was close to 100% for both T and M1 enantiomers and 85% for M5 and IS enantiomers. The application of the assay was demonstrated by simultaneous measurement of plasma concentrations of T, M1, and M5 enantiomers in a healthy volunteer after the administration of 50 mg oral doses of racemic T.

Comparison of different stationary phases for bioanalytical studies of biologically active compounds

In this study, the chromatographic behaviour of four mixtures of compounds was tested on columns possessing various surface properties. Cocaine, dimefluron, nabumetone, and tramadol were chosen as the test compounds. Cocaine is a tropane alkaloid, which is relatively often abused as a drug. This is why many papers have already been written about its determination in human biological samples. Dimefluron, a derivative of benzo[c]fluorene, is a new perspective drug being investigated for its potential antineoplastic effects. Nabumetone is a non-steroidal anti-inflammatory prodrug used for treatment of inflammatory and degenerative rheumatic diseases. Tramadol, derived from an opioid structure is used as an anodyne for treatment of severe pain. As a medicament it is usually determined either in biological samples or in pharmaceuticals. The above-mentioned model drugs were separated using chromatographic columns with C18, C8, palmitamidopropyl, and pentafluorophenylpropyl chains. The best conditions for separation of the individual compounds and their metabolites were chosen on the basis of resolution, retention times, and peak symmetry.

Validation of a high-performance liquid chromatographic method for the simultaneous determination of tramadol and its impurities in oral drops as a pharmaceutical formulation

The novel, rapid high performance liquid chromatographic method for the determination of tramadol hydrochloride and its three impurities was developed and validated. The method can simultaneously assay potassium sorbate, used as preservative, and saccharin sodium, used as sweetener in tramadol pharmaceutical formulation. The separation was carried out on a C(18) XTerra (150 mm x 4.6 mm, 5 mm) column using acetonitrile-0.015 M Na(2)HPO(4) buffer (2:8, v/v) as mobile phase (pH value 3.0 was adjusted with orthophosphoric acid) at a flow rate 1.0 ml min(-1), temperature of the column 20 degrees C and UV detection at 218 nm. The method was found to be linear (r > 0.999) in the range of 0.05-0.8 mg ml(-1) for tramadol hydrochloride, 0.1-1.2 mg ml(-1) for impurities B and C and for impurity A (r > 0.995) in the range 0.15-2.4 mg ml(-1). The low RSD values indicate good precision and high recovery values indicate excellent accuracy of the HPLC method. Developed method was successfully applied to the determination of tramadol hydrochloride, its investigated impurities and potassium sorbate in commercial formulation. The recovery of tramadol hydrochloride was 98.25% and RSD was 1.80%. The method is rapid and sensitive enough to be used to analyse Trodon oral drops.

Development and validation of a rapid HPLC method for simultaneous determination of tramadol, and its two main metabolites in human plasma

Tramadol, an analgesic agent, and its two main metabolites O-desmethyltramadol (M1) and N-desmethyltramadol (M2) were determined simultaneously in human plasma by a rapid and specific HPLC method. The sample preparation was a simple extraction with ethyl acetate. Chromatographic separation was achieved with a Chromolith Performance RP-18e 50 mm x 4.6 mm column, using a mixture of methanol:water (13:87, v/v) adjusted to pH 2.5 by phosphoric acid, in an isocratic mode at flow rate of 2 ml/min. Fluorescence detection (lambda(ex)=200 nm/lambda(em)=301 nm) was used. The calibration curves were linear (r(2)>0.997) in the concentration range of 2.5-500 ng/ml, 1.25-500 ng/ml and 5-500 ng/ml for tramadol, M1 and M2, respectively. The lower limit of quantification was 2.5 ng/ml for tramadol, 1.25 ng/ml for M1 and 5 ng/ml for M2. The within- and between-day precisions in the measurement of QC samples at four tested concentrations were in the range of 2.5-9.7%, 2.5-9.9% and 5.9-11.3% for tramadol, M1 and M2, respectively. The developed procedure was applied to assess the pharmacokinetics of tramadol and its two main metabolites following administration of 100mg single oral dose of tramadol to healthy volunteers.

Determination of tramadol hydrochloride in ampoule dosage forms by using UV spectrophotometric and HPLC-DAD methods in methanol and water media

Two newly developed simple and sensitive methods for determination of tramadol hydrochloride in ampoule dosage forms were described and validated. Measurements for spectrophotometric method were performed using UV-Vis Spectrophotometer in ranges of 200-400 nm. The solutions of standard and the samples were prepared in methanol and water media and the UV absorption spectrums of tramadol were monitored with maximum absorptions at 275 and 271 nm for both mediums, respectively. The standard calibration curves of tramadol were constructed by plotting absorbance vs. concentration in the concentration range with the final dilution of 10-100 microg ml-1. Reversed phase chromatography for HPLC method was conducted using a Phenomenex Bondclone C18 column with an isocratic mobile phase consisting of 25% acetonitrile in 75% 0.01 M phosphate buffer (pH 3). The effluent was monitored on a DAD detector at 218 nm. Linear response (r>0.99) was observed over the range of 0.5-40 microg ml-1 for methanol and water and run on six different occasions. The methods were applied successfully to pharmaceutical ampoule forms, but also for comparison in two different solvent media. Besides, it was completely validated and proven to be rugged.

Investigation of the pharmacokinetics and determination of tramadol in rabbit plasma by a high-performance liquid chromatography–diode array detector method using liquid–liquid extraction

An HPLC system using a new, simple and rapid liquid-liquid extraction and high-performance liquid chromatography-diode array detector method (HPLC-DAD) detection was validated to determine tramadol concentration in rabbit plasma. The method described was applied to a pharmacokinetic study of intravenous tramadol injections in rabbits. The extraction with ethylacetate yielded good response. The recovery of tramadol from plasma averaged 90.40%. Serial plasma samples were obtained prior to, during and after completion of the infusion for determination of tramadol concentrations. Tramadol concentrations were measured using reverse-phase high-performance liquid chromatography and pharmacokinetic application with intravenous tramadol in rabbits revealed that tramadol followed one-compartment open model. Maximum plasma concentration (C(max)) and area under the plasma concentration-time curve (AUC) for tramadol were 14.3 microg mL(-1) and 42.2 microg h mL(-1), respectively. The method developed was successfully applied to a simple, rapid, specific, sensitive and accurate HPLC method for investigation of the pharmacokinetics of tramadol in rabbit plasma.

Migration behaviour and separation of tramadol metabolites and diastereomeric separation of tramadol glucuronides by capillary electrophoresis

Capillary electrophoresis with UV detection was used to separate tramadol (TR), a centrally acting analgesic, and its five phase I (M1, M2, M3, M4, M5) and three phase II metabolites (glucuronides of M1, M4 and M5). Several factors were evaluated in optimisation of the separation: pH and composition of the background electrolyte and the influence of a micellar modifier, sodium dodecyl sulfate. Baseline separation of TR and all the analytes was obtained with use of 65 mM tetraborate electrolyte solution at pH 10.65. The lowest concentrations of the analytes that could be detected were below 1 microM for the O-methylated, below 2 microM for the phenolic and ca. 7 microM for the glucuronide metabolites. The suitability of the method for screening of real samples was tested with an authentic urine sample collected after a single oral dose (50 mg) of TR. After purification and five-fold concentration of the sample (solid-phase extraction with Oasis MCX cartridges), the parent drug TR and its metabolites M1, M1G, M5 and M5G were easily detected, in comparison with standards, in an interference-free area of the electropherogram. Diastereomeric separation of TR glucuronides in in vitro samples was achieved with 10 mM ammonium acetate-100 mM formic acid electrolyte solution at pH 2.75 and with basic micellar 25 mM tetraborate-70 mM SDS electrolyte solution at pH 10.45. Both separations showed that glucuronidation in vitro produces glucuronide diastereomers in different amounts. The authentic TR urine sample was also analysed by micellar method, but unambiguous identification of the glucuronide diastereomers was not achieved owing to many interferences.

Synthesis of d1-N-ethyltramadol as an internal standard for the quantitative determination of tramadol in human plasma by gas chromatography–mass spectrometry

A gas chromatography-mass spectrometry (GC-MS) assay for the determination of tramadol in human plasma is presented. The synthesis of an N-ethyl analogue of the drug is described and its use as an internal standard for the quantitative measurement of tramadol in human plasma is described. The method involves extraction at plasma pH and analysis of the underivatized drug by gas chromatography-electron ionization mass spectrometry using m/z 58 and 73 for detection of tramadol and internal standard, respectively. The calibration curve was linear in the range of 5-640 ng/ml plasma (r=0.9999). The method was validated in the abovementioned calibration range. Data on solution stability, long- and short-term stability of tramadol in plasma samples, freeze-thaw-stability, as well as inter- and intra-day precision and accuracy have been evaluated and are presented. The application of the method to the pharmacokinetic profiling of the drug is demonstrated.

Development of electrochemical methods for determination of tramadol--analytical application to pharmaceutical dosage forms

A square-wave voltammetric (SWV) method and a flow injection analysis system with amperometric detection were developed for the determination of tramadol hydrochloride. The SWV method enables the determination of tramadol over the concentration range of 15-75 microM with a detection limit of 2.2 microM. Tramadol could be determined in concentrations between 9 and 50 microM at a sampling rate of 90 h(-1), with a detection limit of 1.7 microM using the flow injection system. The electrochemical methods developed were successfully applied to the determination of tramadol in pharmaceutical dosage forms, without any pre-treatment of the samples. Recovery trials were performed to assess the accuracy of the results; the values were between 97 and 102% for both methods.

High-performance liquid chromatographic determination of tramadol and its O-desmethylated metabolite in blood plasma. Application to a bioequivalence study in humans

Simultaneous HPLC determination of the analgetic agent tramadol, its major pharmacodynamically active metabolite (O-desmethyltramadol) in human plasma is described. Simple methods for the preparation of the standard of the above-mentioned tramadol metabolite and N1,N1-dimethylsulfanilamide (used as the internal standard) are also presented. The analytical procedure involved a simple liquid-liquid extraction of the analytes from the plasma under the conditions described previously. HPLC analysis was performed on a 250x4 mm chromatographic column with LiChrospher 60 RP-selectB 5-microm (Merck) and consists of an analytical period where the mobile phase acetonitrile-0.01 M phosphate buffer, pH 2.8 (3:7, v/v) was used, and of a subsequent wash-out period where the plasmatic ballast compounds were eluted from the column using acetonitrile-ultra-high-quality water (8:2, v/v). The whole analysis, including the equilibration preceding the initial analytical conditions lasted 19 min. Fluorescence detection (lambda(ex) 202 nm/lambda(em) 296 nm for tramadol and its metabolite, lambda(ex) 264 nm/lambda(em) 344 nm for N1,N1-dimethylsulfanilamide) was used. The validated analytical method was applied to pharmacokinetic studies of tramadol in human volunteers.

Enantiomeric determination of tramadol and its main metabolite O-desmethyltramadol in human plasma by liquid chromatography-tandem mass spectrometry

Pharmacokinetic studies require sensitive analytical methods to allow the determination of low concentrations of drugs and metabolites. When drugs present an asymmetric center, the enantiomeric determination of the compounds of interest should be performed. The method developed is based on on-line LC-MS-MS using atmospheric pressure chemical ionization as an interface determination of enantiomers of tramadol (T) and its active metabolite O-desmethyltramadol (ODT) in human plasma. This determination is preceded by an off-line solid-phase extraction (SPE) on disposable extraction cartridges (DECs), performed automatically by means of a sample processor equipped with a robotic arm (ASPEC system). The DEC filled with ethyl silica (50 mg) was first conditioned with methanol and water. The washing step was performed with water and the analytes were finally eluted by dispensing methanol. The collected eluate was then evaporated to dryness before being dissolved in the LC mobile phase and injected into the LC system. The enantiomeric separation of tramadol and ODT was achieved on a Chiralpak AD column containing amylose tris-(3,5-dimethylphenylcarbamate) as chiral selector. The mobile phase was isohexane-ethanol-diethylamine (97:3:0.1, v/v). The LC system was then coupled to a tandem mass spectrometry system with an APCI interface in the positive ion mode. The chromatographed analytes were detected in the selected reaction monitoring mode. The MS-MS ion transitions monitored were 264-->58 for tramadol, 250-->58 for ODT, and 278-->58 for ethyltramadol, used as internal standard. The method was validated. The recoveries were around 90% for both T and ODT. The method was found to be linear for each enantiomer of both compounds (r2>0.999). The mean RSD values for repeatability and intermediate precision were 3.5 and 6.4% for T enantiomers and 5.0 and 5.6% for ODT enantiomers, respectively. Moreover, the method was found to be selective towards other metabolites, N-desmethyltramadol and N,O-desmethyltramadol (NODT). The method developed was successfully used to investigate plasma concentration of enantiomers of T and ODT in a pharmacokinetic study.

Assay of tramadol in urine by capillary electrophoresis using laser-induced native fluorescence detection

Capillary electrophoresis (CE) with UV laser-induced native fluorescence detection was developed as a sensitive and selective assay for the direct determination of tramadol in human urine without extraction or preconcentration. The main problem in CE is the small inner diameter of the capillary which causes a low sensitivity with instruments equipped with a UV detector. Laser-induced native fluorescence with a frequency doubled argon ion laser at an excitation wavelength of 257 nm was used for the direct assay of tramadol in urine to enhance the limit of detection about 1,000-fold compared to UV absorption detection. The detection system consists of an imaging spectrograph and an intensified CCD camera, which views an illuminated 1.5 mm section of the capillary. This set-up is able to record the whole emission spectra of the analytes to achieve additionally wavelength-resolved electropherograms. In the concentration range of 20 ng/ml-5 microg/ml in human urine coefficients of correlation were better than 0.998. Within-day variation determined on four different concentrations showed accuracies ranging from 90.2 to 108.4%. The relative standard deviation (RSD) was determined to be less than 10%. Day-to-day variation presented accuracies ranging from 90.9 to 103.1% with an RSD less than 8%.

Simultaneous stereoselective analysis of tramadol and its main phase I metabolites by on-line capillary zone electrophoresis-electrospray ionization mass spectrometry

On-line combination of partial filling capillary electrophoresis and electrospray ionization mass spectrometry was demonstrated for the simultaneous enantioseparation of tramadol and its main phase I metabolites. The partial filling technique was efficient at avoiding MS contamination by the chiral selector. Different experimental factors were investigated, including the chiral selector nature and concentration, plug length as well as the separation temperature. The best enantioseparation of the investigated compounds was achieved with a coated polyvinyl alcohol capillary and a 40 mM ammonium acetate buffer, pH 4.0, adding sulfobutyl ether beta-cyclodextrin (2.5 mg/ml) as the chiral selector. The charged cyclodextrin not only allowed enantioseparation of tramadol and its metabolites, but also improved the selectivity of compounds with the same molecular mass. Finally, CE-electrospray ionisation-MS was successfully applied to the stereoselective analysis of tramadol and its main metabolites in plasma after a simple liquid-liquid extraction.