Detection of methamphetamine, methylenedioxymethamphetamine, and 3,4-methylenedioxy-N-ethylamphetamine in spiked plasma by HPLC and TLC.

HPLC and TLC methods were developed for separation and detection of some amphetamine analogs: methamphetamine (MA); 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy"); and 3,4-methylenedioxy-N-ethylamphetamine (MDEA) in spiked plasma samples. The methods are based on purple chromogens formed by displacement reaction of these secondary aliphatic amine-bearing drugs with 7,7,8,8-tetracyanoquinodimethane at 80 degrees C for 25 min. For HPLC, both normal phase (silica gel) and RP (C18) columns were used. With the former, good detection limits in plasma were obtained with a 6 min run: 70, 100, and 500 ng/mL for MDMA, MA, and MDEA, respectively. For TLC, hexane-chloroform (1 + 9) and benzene-diethyl ether-petroleum ether (40-60 degrees)-acetonitrile-ethyl methyl ketone (2 + 3.5 + 3.5 + 0.5 + 0.5) were used as mobile phases for silica gel 60 TLC and cyano-bonded silica gel HPTLC plates, respectively. The former offered more sensitive results than the latter. Influence of evaporation steps on recovery and interferences for the HPLC and TLC methods were investigated. The developed methods are selective, simple, and easily applicable.

Determination of linezolid in human breast milk by high-performance liquid chromatography with ultraviolet detection.

A rapid and simple HPLC method was developed for the determination of linezolid (LNZ) in human breast milk after a simple protein precipitation with methanol. The chromatographic separation was achieved on a C18 column (5 microm, 250 x 4.6 mm id) using a mobile phase of acetonitrile-10 mM acetic acid (25:75, v/v) at a flow rate of 1 mL/min. The LNZ peak was measured by photodiode array detection at 250 nm. The calibration graph was linear over the range of 0.5-20.0 microg/mL. The limits of detection and quantitation were found to be 0.1 and 0.5 microg/mL, respectively. The precision of the assay and the recovery of LNZ from breast milk at three different concentrations were assessed. The intraday and interday RSD values were found to be < 5%. The mean absolute recovery was 85.33%. The developed method was successfully applied to the determination of LNZ in breast milk obtained from the breastfeeding mother after oral administration of LNZ.

A sensitive spectrophotometric method for the determination of desloratadine in tablets.

A simple, rapid, and sensitive visible spectrophotometric method was developed, for the first time, for analysis of desloratadine (DE) in tablets. The method is based on the deep-blue colored TCNQ*- radical anion formed by interaction of the drug (n-donor) with 7,7,8,8-tetracyanoquinodimethane (TCNQ, pi-acceptor) in acetonitrile at ambient temperature. Optimum conditions for the reaction were investigated, absorbances were read at 843 nm, and the linearity range for concentrations of DE was found to be 1.5-13 microg/mL. The reaction product remains stable up to 8 h when kept at room temperature in the dark. The developed method was validated and successfully applied to the determination of DE in tablets. The tablets were also analyzed with a column liquid chromatography method reported in literature. The results from both methods were statistically compared by t- and F-tests. No significant difference was found for the means and standard deviations at 95% confidence level. Accuracy was examined through recovery studies. Being very simple and reliable, the method can be recommended for routine quality control analysis of DE in tablets.

Determination of paroxetine in human plasma by high-performance liquid chromatography using 7,7,8,8-tetracyanoquinodimethane as the derivatization reagent.

A selective and sensitive reversed-phase HPLC method was developed for the determination of the antidepressant paroxetine in plasma. The method is based on the purple chromogen formed by a displacement reaction of paroxetine with 7,7,8,8-tetracyanoquinodimethane (TCNQ) in acetonitrile at 80 degrees C for 20 minutes. For the assay, the drug was extracted from 1 mL of plasma with chloroform and, after sample alkalinization, derivatized with TCNQ; then the reaction mixture was directly injected into a C18 column. Desipramine was used as internal standard. The mobile phase was acetonitrile-water (70:30) at a flow-rate of 1.0 mL/min, and the derivatives were eluted at 13.1 and 15.5 minutes for paroxetine and desipramine, respectively, and detected at 567 nm. Calibration curve was found linear over the range of 20-400 ng/mL, and the detection limit was 2 ng/mL at a signal-to-noise ratio of 3/1. Recoveries determined for 3 concentrations range between 81.3% and 88.1%. Intraday and interday relative standard deviation values were found to be within 3.8%-13.5% and 8.2%-14.6%, respectively. With this developed method, a pharmacokinetic study was performed for paroxetine.

Spectrophotometric methods for the determination of the antidepressant drug paroxetine hydrochloride in tablets.

Simple, sensitive, and accurate visible spectrophotometric methods are described for the determination of paroxetine hydrochloride (PA) in tablets. Among them, the first 3 methods are based on the ion-pair complexes of PA formed with bromothymol blue (BTB), bromophenol blue (BPB), and bromocresol green (BCG) in aqueous acidic buffers. The complex species extracted into chloroform were quantitatively measured at 414 nm with BTB and BCG and at 412 nm with BPB. Beer's law was obeyed over the concentration ranges of 2-20, 2-16, and 2-16 microg/mL, respectively. The fourth method described is based on a coupling reaction between PA and 7-chloro-4-nitrobenzofurazon (NBD-Cl) in borate buffer, pH 8.5, in which a yellow reaction product that was measured at 478 nm was formed. The Beer's law range for this method was 2-10 microg/mL. The last method developed describes the interaction of PA base, as an n-electron donor, with 7,7,8,8-tetracyanoquinodimethane (TCNQ), as a pi-acceptor, in acetonitrile to give blue-colored TCNQ- radical anion with absorption maxima at 750 and 845 nm. Measured at 845 nm, the absorbance-concentration plot was rectilinear over the range of 1.5-15 microg/mL. The new methods developed were successfully applied to the determination of PA in tablets without any interference from common tablet excipients. The results of the methods were in good agreement with those obtained with an official liquid chromatographic method. This report describes first colorimetric methods for the determination of PA.

7,7,8,8-Tetracyanoquinodimethane as a new derivatization reagent for high-performance liquid chromatography and thin-layer chromatography: rapid screening of plasma for some antidepressants.

Using 7,7,8,8-tetracyanoquinodimethane (TCNQ) as a new derivatization reagent for HPLC and TLC, novel methods are described to detect secondary amine-bearing antidepressants (paroxetine, desipramine, fluoxetine, nortriptyline, maprotiline). The HPLC method is sensitive enough to detect these drugs in plasma at therapeutic levels whereas the latter has potential to detect them in overdose or forensic cases. The methods are based on purple chromogens formed by the displacement reaction of the drugs with TCNQ. The resulting chromogens are directly separated by either reversed-phase HPLC on a C(18) column or TLC on silicagel plates. For HPLC, acetonitrile-water (60:40) was used as mobile phase, with detection at 567 nm and separation in 40 min. For TLC, three developing solvent systems were used. By HPLC, 36 ng ml(-1) spiked plasma concentration of the drugs gave easily detectable signals whereas by TLC, detection limits varied mostly between 240 and 480 ng ml(-1). The HPLC method was applied to real plasma samples. The methods described are simple and very selective; some metabolites of these antidepressants and a vast number of drugs do not interfere with detection.