CE of tricyclic antidepressant clomipramine and metabolites: Electromigration and wall adsorption

CE of tricyclic antidepressants clomipramine and its metabolites demethylclomipramine, didemethylclomipramine and 8-hydroxyclomipramine resulted in partly extremely tailing peaks in bare fused-silica capillaries. Especially at high pH of the BGE this behavior was not unexpected as adsorption of the cationic analytes onto the negatively charged wall due to electrostatic attraction can be supposed. Less expected was the observation that peak tailing could not be overcome neither by using a capillary with dynamic coating with cationic CTAB added to the BGE, nor by the usage of a capillary permanently coated with polyvinyl alcohol (PVA), both operated at acidic pH. As this tailing was even more pronounced than with bare fused silica, and was suppressed upon addition of MeCN to the BGE, another source of adsorption than pure ion-ion interaction seems plausible. In the bare silica capillary the mobility, mu, of the analytes followed roughly the pH dependence of a monoacidic base, but two deviations from the sigmoid theoretical curve were evident: (i) even at low pH the mobilities were not constant; they decreased in contrary with pH over the entire range; (ii) the apparent pK(a) values of two analytes, derived at the pH with halve the mobility at low pH, are significantly smaller than the thermodynamic pK(a). Upon modifying the expression for mu = f(pH), and considering the pH dependence of the negative charge density at the wall by an additional term which takes chromatographic retention into account, an equation was derived which enables the description of the observed electromigration of the analytes as function of pH, pK(a) of analytes and surface silanol groups, actual mobility of analytes, distribution coefficient (or retention factor) due to adsorption including its pH dependence. The interplay of electrophoretic movement and residual adsorptive retention allowed to resolve the analytes finally in an uncoated capillary, namely at pH 7.65 (30 mM ionic strength), whereas at the cost of the robustness of the separation system.

Sequestration of amitriptyline by liposomes

We study the uptake of amitriptyline, which is a common cause of overdose-related fatalities, in aqueous solutions by 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) liposomes and liposomes composed of a mixture of DMPC and 1,2-dioleoyl-sn-glycero-3-[phospho-rac(1-glycerol)] (DOPG) lipids. The effect of drug concentration, liposomal charge, pH, salt, and protein presence on the drug uptake is investigated using two different methodologies, a precipitation and a centrifugation method. Furthermore, the time scale of the drug uptake is studied through qualitative observations at high pH and through conductivity measurements at neutral pH and found to be <5 s. The results of the quantitative studies show that the fractional drug uptake decreases with increasing drug concentration, and for a given concentration it increases with the pH and decreases in the presence of salt. We find that a larger amount of drug is sequestered by negatively charged liposomes (those containing DOPG) than liposomes with no net charge (DMPC). We speculate that the mechanism of drug uptake is due to both electrostatic interactions as well as hydrophobic effects. The fractional uptake by DMPC:DOPG in a 70:30 ratio is as high as 95% in water and about 90% in physiological buffer. The fractional uptake is also measured in presence of 2% (w/w) bovine serum albumin (BSA), which is approximately the protein concentration in the intercellular fluid. In presence of protein the fractional uptakes by 70:30 DMPC:DOPG liposomes and 50:50 DMPC:DOPG liposomes are 82 and 90%, respectively, at 125 muM drug amitriptyline. In the absence of liposomes, 67% of the drug is taken up by the protein in a 2% (w/w) BSA, 125 muM amitriptyline solution. Thus, addition of 50:50 DMPC:DOPG liposomes reduces the free drug concentration by a factor of about 3.5, making them attractive candidates for drug detoxification.

Using of S-(-)-2-hydroxymethyl-1,1-dimethylpyrrolidinium tetrafluoroborate as additive to the background electrolyte in capillary electrophoresis

We synthesised and used new type of quaternary ammonium salt [S-(-)-2-hydroxymethyl-1,1-dimethylpyrrolidinium tetrafluoroborate] as effective additive to acidic background electrolytes. We used this quaternary ammonium salt as effective agent for capillary zone electrophoresis separation of model mixture of five tricyclic antidepressants (amitriptyline, nortriptyline, imipramine, desipramine and clomipramine) as model analytes. We observed that addition of S-(-)-2-hydroxymethyl-1,1-dimethylpyrrolidinium tetrafluoroborate ([HMDP](+) [BF(4)](-)) to acidic background electrolytes leads to suppression of magnitude of electroosmotic flow (EOF) and gradually change the direction of the EOF. Baseline separation of five TAs was achieved by using of 91.1 mmol L(-1) (20 gL(-1)) of [HMDP](+) [BF(4)](-) in 25 mmol L(-1) sodium phosphate pH 2.5, where electroosmotic mobility was -11.3 x 10(-9) m(2) V(-1) s(-1). We achieved baseline separation of five TAs with using of [HMDP](+) [BF(4)](-) as water solution too. We observed that [HMDP](+) [BF(4)](-) can be used as buffer additive, which offers relatively smaller anodic electroosmotic flow instead of cationic surfactants that are mostly used for genarating of anodic electroosmotic flow in capillary electrophoresis.

The effect of the process variables on the HPLC separation of tricyclic neuroleptics on a calixarene-bonded stationary phase

The chromatographic behavior of a new HPLC-stationary phase with supramolecular selectors on the basis of calixarenes is described for the separation of nine tricyclic neuroleptics. The effects of different chromatographic conditions (buffer system, pH-value, type and content of organic modifier, injection volume) on the separation of the analytes were studied. Additionally, the effect of structural differences of the neuroleptic analytes was studied. The chemical structure and pKa of the neuroleptics highly influenced their separation on the calix[8]arene phase. The separation of all analytes on the investigated calixarene-bonded stationary phase was possible with a mobile phase of acetonitrile with 30 mM ammonium acetate buffer (pH 3.5) 30:70(v/v) using 1 ml/min flow rate.

The use of the new SPE methods for isolation of some tricyclic antidepressant drugs from human serum

Solid-phase extraction (SPE) methods were applied to isolation of amitriptyline (AMI), imipramine (IMI) and chlorprothixene (CPX) from blood human serum. SPE was carried out using the octadecyl (C(18)) column for isolation of AMI and cyclohexyl (CH) columns in the case of IMI and CPX. The spiked serum samples were used to examine the recoveries of these drugs from C(18) and CH sorbent materials. The volume of serum sample was 500 microl. The recoveries of SPE method using CH cartridge were 100.3+/-1.63% (n=7), 99.7+/-2.3% (n=9) for IMI and CPX, respectively. The recovery of AMI from C(18) cartridge was 99.5+/-1.5% (n=8). Finally, after SPE sample clean-up step the antidepressant drugs were assayed by the own extractive-spectrophotometric methods.

Polar polymeric stationary phases for normal-phase HPLC based on monodisperse macroporous poly(2,3-dihydroxypropyl methacrylate-co-ethylene dimethacrylate) beads

The effect of variables such as shape template size, porogen composition and percentage, content of cross-linking monomer, and polymerization temperature on the properties of uniformly sized 3-microm porous poly(glycidyl methacrylate-co-ethylene dimethacrylate) beads prepared by the staged templated suspension polymerization technique has been studied. The porous properties of the beads including surface morphology, pore size distribution, and specific surface area have been optimized to obtain highly efficient stationary phases for normal-phase HPLC. A column packed with diol stationary phase obtained by hydrolysis of poly(glycidyl methacrylate-co-ethylene dimethacrylate) beads affords an efficiency of 67,000 plates/m for toluene using THF as the mobile phase. The retention properties and selectivity of the diol beads are easily modulated by changes in the composition of the mobile phase. The performance of these beads is demonstrated with the separations of a variety of polar compounds including positional isomers, aniline derivatives, and basic tricyclic antidepressant drugs.

Characterization of pharmaceutical drugs by a modified nonaqueous capillary electrophoresis--mass spectrometry method

A simple method for the separation and characterization of a group of nine basic compounds, comprising seven tricyclic antidepressant and two bronchodilator drugs, by nonaqueous capillary electrophoresis (NACE) employing ultraviolet and mass spectrometry detection is described. After optimization of the electrophoresis separation conditions, including the compositions of the electrolyte and the organic solvent, a reliable separation of all nine basic analytes was achieved in 80 mM ammonium formate dissolved in a methanol-acetonitrite (80:20 v/v) mixture, having an apparent pH of 8.7. The volatile nonaqueous electrolyte system used with a normal electroosmotic flow polarity also provided an optimal separation condition for the characterization of the analytes by mass spectrometry. When results were compared with reversed-phase gradient and isocratic high-performance liquid chromatography (HPLC) methods, the NACE method provided greater efficiency, achieving baseline resolution for all nine basic compounds in less than 30 min. The NACE method is suitable for use as a routine procedure for the rapid separation and characterization of basic compounds and is a viable alternative to HPLC for the separation of a wide range of pharmaceutical drugs.

Sample preparation with fiber-in-tube solid-phase microextraction for capillary electrophoretic separation of tricyclic antidepressant drugs in human urine

Solid-phase microextraction (SPME) is a solvent-free sample preparation technique using a thin coating attached to the surface of a fused silica-fiber as the extraction medium, which has been successfully applied to the analysis of a wide variety of compounds by coupling to gas chromatography (GC). In recent years, in-tube SPME using GC capillary column as the extraction medium has also been developed and coupled with liquid chromatography (LC) for the preconcentration of nonvolatile compounds. In this study, an on-line interface between the fiber-in-tube SPME and capillary electrophoresis (CE) has been developed, and the preconcentration and separation of four tricyclic antidepressant (TCA) drugs, amitriptyline, imipramine, nortriptyline, and desipramine, were performed with the hyphenated system. Under the optimized condition, a better extraction performance than conventional in-tube SPME was obtained, even the length of the extraction medium was much shorter. The results clearly indicated that the fiber was working effectively as an extraction medium. For the separation of these four TCAs, capillary electrophoretic separation with beta-cyclodextrin as the buffer additive has been employed and the application of the developed system to the analysis of complex sample mixtures in a biological matrix is also demonstrated.

Reversed-phase separation of basic tricyclic antidepressants using buffered and fluoroform-enhanced fluidity liquid mobile phases

In an effort to expand the range of applications of enhanced-fluidity liquid chromatography (EFLC) to strongly polar and basic analytes, fluoroform (CHF3) was investigated as a fluidity-enhancing agent. Fluoroform was chosen due to its high polarity, low viscosity and chemical inertness toward water and basic analytes. A group of representative basic compounds, tricyclic antidepressants, covering a wide range of polarity was chosen as model compounds. Their retention behavior on a C18 stationary phase in methanol/phosphate buffer and methanol/phosphate buffer/CHF3 mobile phases was characterized. The chromatographic performance with mobile phase conditions of different pH, with and without CHF3 addition and with addition of triethylamine was studied. The advantages of using CHF3 enhanced and buffered mobile phases were shown in the much improved chromatographic performance, such as shortened analysis time, increased efficiency, lower pressure drop and improved selectivity. Furthermore, this study demonstrated for the first time, that a commercial instrument could be readily utilized for EFLC separations which greatly expands the application range of the EFLC technique and chromatographic instrumentation.

Affinity screening by packed capillary high performance liquid chromatography using molecular imprinted sorbents. II. Covalent imprinted polymers

This study concentrates on the production of covalent molecular imprint polymers (MIPs) as highly selective sorbents for nortriptyline (NOR), a representative tricyclic antidepressant (TCA). The functionalized template contains a polymerizable 4-vinylphenyl carbamate moiety used to bind the template molecule to the polymer matrix. Polymerization with a cross-linker followed by hydrolytic cleavage of the labile carbamate functionality leaves an MIP with selective binding sites capable of binding template through hydrogen bonding interactions. Demonstrated chromatographically through a "selection index", these MIPs showed high selectivity for the template molecule (NOR) among a library of structurally similar compounds. The recognition was found to correlate with structural similarity to the template compound. A direct comparison between covalent and non-covalent molecular imprinting strategies reveals a great deal of improvement in the peak shape of the retained compound resulting from covalent imprinting (evidenced by peak asymmetry factors A.).

Normal-phase high-performance liquid chromatographic separations using ethoxynonafluorobutane as hexane alternative. I. Analytical and chiral applications

A novel, environmentally friendly, fluorinated solvent--ethoxynonafluorobutane--has been used to replace n-hexane in normal-phase HPLC applications. Fast gradients of methanol in ethoxynonafluorobutane on a cyano column have been successfully applied to the separation of steroids, benzodiazepines, NSAIDs, tricyclic antidepressants, beta-adrenergic blocking agents and mixtures of purines and pyrimidines. Small amounts of triethylamine and trifluoroacetic acid added to such gradients significantly improved peak shape and column performance for basic and acidic solutes. Ethoxynonafluorobutane and its mixtures with methanol have also been demonstrated to have a unique selectivity in chiral HPLC applications.

Capillary electrochromatography of hydrophobic amines on continuous beds

The capillary electrochromatographic separation performance of hydrophobic amines and a related quaternary ammonium compound on continuous beds based on polymers of acrylamide has been studied. The chromatographic bed is polymerized in situ and the character of the polymers with regard to hydrophobicity and charge has been systematically changed by regulating its content of isopropyl and sulfonate ligands, respectively. The best performance was obtained for columns with a molar ratio of 1:80 for the sulfonate and isopropyl groups, and resulted in efficiencies up to 200000 plates per meter. The effects on retention, resolution and elution order by ionic strength, pH, and content of acetonitrile in the mobile phase have been investigated. The quaternary ammonium compound was always the least retained irrespective of pH. By increasing the pH, a reversal of the migration order between the tertiary and secondary amine was obtained. The results indicate a complex migration/retention mechanism where ion-exchange, adsorption and electrophoretic mobilities play a role. The concentration limit of detection could be lowered from 1.3 microg/mL to 50 pg/mL by using a high content of 2-propanol (96%) in the sample compared to dissolving the analytes in the mobile phase.

Affinity screening by packed capillary high-performance liquid chromatography using molecular imprinted sorbents. I. Demonstration of feasibility

Molecular imprint polymers (MIPs) are synthetic polymers capable of selectively binding a template molecule. In this work, the potential utility of MIP-based chromatographic sorbents for affinity screening of structurally similar compounds was investigated as alternatives to in vitro bioassays and biological targets bound to chromatographic supports. A group of structurally similar tricyclic antidepressant drugs and related compounds were used to simulate a combinatorial library. One of the antidepressants, nortriptyline (NOR), was selected as the template species. Using capillary HPLC columns packed with NOR-imprinted MIP particles, the simulated library was screened and the degree of selective interaction of each compound was determined. This correlated with each compound's affinity for the NOR binding site in the polymer. The results of the study revealed that library species which possess the major structural features of the template, specifically the ring structure and pendant secondary amine, were best "recognized" by the MIP, while the most structurally dissimilar compounds exhibited the least selective interaction. An investigation of the retention mechanism on these MIPs provided evidence that hydrogen bonding between the pendant amine group on the antidepressants and a methacrylic acid moiety on the polymer surface was critical in the molecular recognition process.

Highly selective separations by capillary electrochromatography: molecular imprint polymer sorbents

Molecular imprint polymers (MIPs) are synthesized in the presence of a template, or 'imprint' molecule which results in the formation of specific recognition cavities complementary to the template in shape and chemical functionality. The resultant MIP then acts as a selective binding medium for the template molecule. The utility of MIPs lies in the selectivity of the rebinding process, which is based on molecular recognition. In many cases, the selectivity achieved with MIPs toward a particular molecule is comparable to that observed with antibodies. This has led to the application of MIPs to several areas of analytical chemistry including immunoassays, sensors and separations media. One of the most successful application areas of MIPs has been as chromatographic sorbents, where they have been utilized predominately in chiral separations. The use of MIP sorbents in CEC is attractive in that it combines the selectivity of a molecular recognition process with the enhanced flow dynamics of CEC, which can result in higher efficiency and shorter analysis times. This paper will review the use of molecular imprinted stationary phases in CEC. Following a brief introduction to molecular imprinting, various methodologies for preparation of MIP-CEC capillaries in addition to applications of the technique will be discussed.

The analysis of basic and acidic compounds using non-aqueous CE and non-aqueous CE-MS

It has been shown that non-aqueous capillary electrophoresis (NACE) can provide improved separations in comparison to those obtained using conventional CE under aqueous conditions (ACE). Previous work carried out in our laboratories involving initial investigations into the technique have been reported. Based on the findings of that work it was possible to separate a variety of basic pharmaceuticals from selected impurities and to obtain the successful separation of some hydrophobic sulphonic acids. The successful coupling of NACE to mass spectrometry (NACE-MS) has also been demonstrated.

Biotransformation of protriptyline by filamentous fungi and yeasts

1. The potential of various fungi to metabolize protriptyline (an extensively used antidepressant) was studied to investigate similarities between mammalian and microbial metabolism. 2. Metabolites produced by each organism were isolated by high-pressure liquid chromatography and identified by nuclear magnetic resonance and mass spectrometry. The metabolites identified in one or more fungi were 2-hydroxyprotriptyline, N-desmethylprotriptyline, N-acetylprotriptyline, N-acetoxyprotriptyline, 14-oxo-N-desmethylprotriptyline, 2-hydroxy-acetoxyprotriptyline and 3-(5-hydrodibenzo[bf][7]annulen-5-yl)propanoic acid. 3. Among 27 filamentous fungi and yeast species screened, Fusarium oxysporum f. sp. pini 2380 metabolized 97% of the protriptyline added. Several other fungi screened gave significant metabolism of protriptyline, including Cunninghamella echinulata ATCC 42616 (67%), C. elegans ATCC 9245 (17%), C. elegans ATCC 36112 (22%), C. phaeospora ATCC 22110 (50%), F. moniliforme MRC-826 (33%) and F. solani 3179 (12%). 4. F. oxysporum f. sp. pini produced phase I and phase II metabolites and thus is a suitable microbial model for protriptyline metabolism.

Prevention of tricyclic antidepressant adsorption loss with diethylamine during solvent evaporation

The authors evaluated the adsorption loss of tricyclic antidepressants in analytical procedures with solvent extraction and evaporation. In standard procedures with the use of triple solvent extraction between alkalinized and acidified samples before chromatographic analysis, the adsorption loss was more significant with the demethylated metabolites. As much as 50% adsorption loss can occur; this irreversible loss can be accounted for entirely during the solvent evaporation step. Because of differential adsorption loss among parent drugs, metabolites, and internal standards, the analytical methods usually had wide within-day and day-to-day variations. The authors found that the addition of as little as 0.05% diethylamine to the extract before evaporation completely eliminated the adsorption loss of amitriptyline-nortriptyline, imipramine-desipramine, and doxepin-desmethyldoxepin. with subsequent improvement in procedure performance. This simple modification can be adopted readily by all laboratories that use solvent extraction and subsequent chromatographic analysis of tricyclic antidepressants.

Capillary electrophoretic separation of tricyclic antidepressants using charged carboxymethyl-beta-cyclodextrin as a buffer additive

Charged carboxymethyl-beta-cyclodextrin was successful in the capillary electrophoretic separation of a series of tricyclic antidepressants. The cyclodextrin alone was successful in the separation of carbamazepine, protriptyline, desipramine, clomipramine, and opipramol using a 3-(trimethoxysilyl)propyl methacrylate capillary coating to reduce the electroosmotic flow. The ideal buffer pH was found to be in the range of 6-7 and the ideal cyclodextrin concentration to be 10 mM. All nine antidepressants were resolved using the charged cyclodextrin in the micellar electrokinetic chromatography (MEKC) mode with sodium dodecyl sulfate as the surfactant. Neither the cyclodextrin nor the surfactant alone were successful in resolving the whole series of compounds under investigation but a combination of both produced the separation. Separations were performed on a linear polyacrylamide coated capillary. The ideal pH of the buffer was in the range of 5-7.

Cerebral metabolism of imipramine and a purified flavin-containing monooxygenase from human brain

Flavin-containing monooxygenase (FMO), previously reported both from hepatic and extrahepatic tissues, including brain, catalyze the oxidation of certain xenobiotics and drugs that contain a nucleophilic heteroatom. Psychoactive drugs, including the antidepressant imipramine, are substrates for the brain FMO. Since FMO-mediated metabolism of these drugs might contribute to local pharmacodynamic modulation within the human brain, the metabolism of imipramine by human brain FMO was studied in further detail. In the present study, the FMO activity was determined in human brain microsomes by estimating the actual amount of imipramine N-oxide formed. It was then compared with the corresponding activity measured using substrate (imipramine)-stimulated rates of nicotinamide adenine dinucleotide phosphate (NADPH) oxidation, which was significantly higher than the activity estimated as the amount of N-oxide assayed using high-pressure liquid chromatography (HPLC). The brain FMO activity was measurable only in the presence of detergents (sodium cholate or Lubrol PX) or in microsomes that were freeze-thawed several times. The activity was inhibited by an antibody to rabbit pulmonary FMO, but an antiserum to the rat liver NADPH cytochrome P-450 reductase had no effect indicating that cytochrome P-450 was not involved in the above metabolic pathway. The optimum pH for N-oxidation of imipramine was found to be 8.5; thermolability experiments indicated that the FMO activity was completely lost only after the incubation of brain microsomes at 45 degrees C for 20 minutes. An FMO purified to apparent homogeneity from a human brain had a molecular weight of 71,000 Da. The purified enzyme cross-reacted with the antibody to rabbit pulmonary FMO and efficiently catalyzed the metabolism of imipramine to its N-oxide. The human brain clearly contains an active FMO system, and it is conceivable that such enzymes are significantly involved in the local metabolism and modulation of pharmacological and/or toxic effects of certain xenobiotics, including psychoactive drugs.

Application of a novel form of solid-phase sorbent (Empore membrane) to the isolation of tricyclic antidepressant drugs from blood

We employed a new form of solid-phase material, the Empore octyl (C8) extraction membrane (SPEM), for the efficient extraction of tricyclic drugs from patients' serum specimens. Both extraction and companion high-performance liquid chromatographic (HPLC) assay of doxepin (DOX), desmethyldoxepin (DDOX), imipramine (IMI), desmethylimipramine (DESI), amitriptyline (AMI), nortriptyline (NOR), clomipramine (CLO), and desmethylchlomipramine (DCLO) are presented here. Routinely, serum (1.0 mL or less) adjusted to pH 5.5 with phosphate buffer is passed through the SPEM secured in a MF-1 microfilter unit. Proteins and potential interferences retained on SPEM are removed with an acetonitrile-water wash. The tricyclic drugs are eluted with HPLC mobile phase and the eluate is injected directly on a Zorbax cyanopropyl (CN) HPLC column, thereby avoiding time consuming evaporation-concentration steps that can affect drug stability. Recovery for all drugs exceeds 90% and analytical responses are linear from a lower limit of sensitivity of 8 micrograms/L up to at least 1000 micrograms/L. Between-run coefficients of variation (CV) range from 2.9 to 8.3% through the concentration range of 75 to 300 micrograms/L. Performance characteristics of the SPEM are compared to those of conventional large particle silica- and polymeric-based sorbents. Within the requirements of this assay, the SPEM extraction requires less sample volume and reduces elution and solvent volumes.

[The detection of the presence of azafen in cadaveric material]

Possibility of isolating azaphen from the cadaveric material by acidified water and acetonitrile (as extractant) is shown. Isolation rate (75.6%) of azaphen (with 1 mg of preparation added to 25 g of the liver by acetonitrile is significantly higher than in isolation by acidified water (41.7%).

Comparison of methods for the analysis of tricyclic antidepressants in small whole blood samples

A variety of liquid-liquid and solid-phase extraction techniques have been compared for the extraction of tricyclic antidepressant drugs from small whole blood samples. Each of the procedures was evaluated with respect to extract cleanliness, extraction efficiency, and reproducibility. The three most efficient methods were compared on a variety of authentic whole blood case samples containing drugs at therapeutic and toxic levels. The results of the study indicated that a liquid-liquid extraction procedure involving the extraction of drugs by ether was the most suitable to use on poor quality forensic samples.

Stabilized analysis of antidepressant drugs by solvent-recycled liquid chromatography: procedure and proposed resolution mechanisms for chromatography

In this efficient extraction and isocratic liquid-chromatographic procedure for measuring eight antidepressant drugs in serum (amoxapine, 8-hydroxyamoxapine, doxepin, desmethyldoxepin, imipramine, desipramine, amitriptyline, and nortriptyline), they are extracted from serum as a group by use of disposable solid-phase cyanopropyl columns; the eluate is injected directly onto a Zorbax cyanopropyl analytical column. This sample preparation circumvents potential problems of drug instability associated with the usual evaporating/concentrating techniques. Recycling the acetic acid/acetonitrile/n-butylamine mobile phase not only maintains a stable, cost-effective system, it also prolongs column life. Standard curves for all eight drugs are linear to 1000 micrograms/L; the detection limit is 8-10 micrograms/L. For all drugs and metabolites, within-run CVs were 0.9 to 2.2%, between-run CVs 2.1 to 3.8%. Analytical recovery of the solid-phase extraction step was 85 to 100% (mean = 94.5%) for all analytes. Standards and controls, stored frozen in drug-free serum, are stable for at least six months. We also report a study of separation mechanisms.

Solvent extraction of tricyclic amines from blood plasma and liquid chromatographic determination

The extraction of seven tricyclic antidepressant amines from human plasma at different pH values was investigated for dichloromethane, diethyl ether and hexane--1-pentanol (95:5). The amines were extracted as bases and back-extracted to sulphuric acid, 0.10 mol/l, prior to the separation by bonded-phase liquid chromatography. Ether and hexane--1-pentanol (95:5) were most suitable, tertiary amines being best extracted at pH 8, and secondary amines at pH 10. Using ether, both while 15 min ws sufficient for hexane--1-pentanol (95:5). UV detection allowed concentrations down to 10 ng in 1 ml of plasma to be determined. Three ammonium ions--octylammonium, dimethylammonium, and trimethylammonium--were added as modifiers to the mobile phase containing acetonitrile in phosphoric acid, 0.10 mol/l. In the concentration interval 0.010--0.030 mol/l all of the amine modifiers gave on Polygosil C8 peak asymmetry factors of sufficiently low magnitude, while on Li-Chrosorb RP-18 this was so only for di- and trimethylammonium in a concentration of 0.030 mol/l.

Tricyclic antidepressants in serum by a Clin-ElutTM column extraction and high pressure liquid chromatographic analysis

We sought a method for routine therapeutic monitoring of serum tricyclic antidepressants (TCAs) which offered good reproducibility, detection limits, linearity, and specificity, and which was simple, rapid, and inexpensive to perform. The method described utilizes Clin-Elut columns (Analytichem International, Inc., Lawndale, CA 90206) to facilitate the extraction. The analysis is by high pressure liquid chromatography (HPLC) with a CN bonded phase column, a mobile phase of acetonitrile/pH 7.0 phosphate/methanol and detection at 210 nm. This chromatographic system gives short equilibration times, stable calibration curves, high sensitivity and resolution, short retention times, and long column life. The method is useful for determination of amitriptyline, doxepin, imipramine, nortriptyline, nordoxepin, desipramine, and protriptyline. Trimipramine is used as an internal standard for the tertiary amines and protriptyline for the secondary amines. Recovery is linear from 25 ato 1,000 ng/ml. Rubber stoppers of a new formulation in Vacutainer blood collection tubes (Becton-Dickinson, Rutherford, NJ 07070) do not affect serum TCA levels. Sera from 53 psychiatric patients suffering from endogenous depression were analyzed using the procedure presented. The mean serum level of four patients on amitriptyline therapy having complete remission was 201 ng/ml (range, 123-259). The mean serum level of four patients on imipramine therapy rated as having complete remission was 200 ng/ml (range, 145-258). These values compare well with recently published therapeutic ranges.