Enantioselective binding analysis of verapamil to plasma lipoproteins by capillary electrophoresis-frontal analysis.

Capillary electrophoresis coupled with frontal analysis was applied to the study of enantioselective binding of verapamil (VER) to plasma lipoproteins. The drug-lipoprotein mixed solution, which had been in the binding equilibrium, was hydrodynamically introduced into a non-coated fused-silica capillary. Since VER is positively charged in the neutral run buffer (pH 7.4), the unbound VER enantiomers migrated toward the cathodic end much faster than negatively charged lipoproteins and their bound forms. Once unbound VER migrated apart from lipoprotein, the bound VER was quickly released from the protein to maintain the binding equilibrium. Thus, VER migrated as a zone through the capillary and gave a trapezoidal peak with a plateau region on the electropherogram. The VER concentration in this plateau region was equal to the unbound VER concentration in the initial sample solution. It was found that the bindings of VER to high-density lipoprotein (HDL), low-density lipoprotein (LDL) and oxidized LDL were not site-specific and not enantioselective. Partition-like binding to lipid part of these lipoproteins seemed to be dominant. The total binding affinities of LDL to VER were about seven-times stronger than those of HDL, and the oxidation of LDL by copper ion enhanced the binding affinities significantly.

Binding analysis of nilvadipine to plasma lipoproteins by capillary electrophoresis-frontal analysis.

Capillary electrophoresis coupled with frontal analysis (HPCE/FA) was applied to the ultramicro analysis of enantioselective binding of nilvadipine (NV), a calcium channel blocker, to plasma lipoproteins. The drug lipoprotein mixed solution was hydrodynamically introduced into a non-coated fused silica capillary for capillary electrophoresis. Since NV has no electric charge in the run buffer (pH 7.4), the unbound NV moved towards the cathodic end by electroosmotic flow, which was faster than the electrophoretic migrations of negatively charged lipoproteins and the bound NV. Once unbound NV migrated apart from lipoprotein, and bound NV was quickly released from the protein to maintain the binding equilibrium. Thus, NV migrated as a zone with a plateau region. The concentration of NV in this plateau region appearing on the electrophorogram was the same as the unbound NV concentration in the initial sample solution. It was found that the binding of NV to high-density lipoprotein (HDL), low-density lipoprotein (LDL) and oxidized LDL was non-specific and not enantioselective. Partition-like binding to the lipid part of these lipoproteins seemed to occur dominantly. The total binding affinities of NV to LDL were about seven times stronger than those to HDL, and the oxidation of LDL enhanced the binding affinity significantly.

HPLC Determination of some antibilharzial antimonials by extraction of antimony.

The antimonial drug (antimony potassium tartrate, antimony piperazine tartrate or antimony lithium thiomaleate) in aqueous solution or biological fluid is treated with sodium diethyldithiocarbamate in the presence of a suitable masking reagent, the pH is adjusted to 9 +/- 0.5. and the antimony complex extracted with n-hexane and determined by reversed-phase HPLC with an ODS column and detection at 254 nm. The limits of detection are 20 ng (for antimony potassium tartrate and antimony lithium thiomaleate) and 16 ng (for antimony piperazine tartrate).

Spectrophotometric determination of some catecholamine drugs using metaperiodate.

A rapid spectrophotometric procedure for the determination of isoprenaline salts, levodopa, dopamine hydrochloride, and dobutamine hydrochloride, either in the drug substances or in pharmaceutical formulations, is described. The method is based on the development of orange, red, or violet products with sodium metaperiodate in an aqueous alcoholic medium. The reaction is suggested to proceed via oxidative cyclization of the catecholamine to form an aminochrome. The wavelengths of maximum absorption range from 465 to 520 nm. The structure of the cyclization product was confirmed by ultraviolet, infrared, and nuclear magnetic resonance spectroscopy and microanalysis data.

Spectrophotometric determination of epinephrine and norepinephrine with sodium periodate.

A simple and accurate spectrophotometric method is described for the determination of epinephrine (EP), norepinephrine (NE) and their bitartrate salts. The method is based on the development of a red colour (lambda(max) 490 nm) with sodium periodate in aqueous alcoholic medium. The colour is stable for at least 1 hr. The molar reacting ratio of EP or NE to periodate is 1:2. The proposed method is particularly suitable for routine analysis of EP and NE injections. The interference due to the sodium metabisulphite normally used as antioxidant can be overcome by addition of acetone. Results for analysis of bulk drugs and injections agree well with those of official methods.

HPLC determination of niridazole.

A high-performance liquid chromatographic method has been developed for the determination of niridazole in bulk form and in pharmaceutical dosage form. A reversed-phase system, based on an octadecylsilane-bonded stationary phase and a 60:40 v/v methanol/water mobile phase, is used. The detector response at 370 nm is linearly related to the amount injected, over a wide range. The method is sensitive, simple, rapid and precise.

Spectrophotometric determination of some dibenzazepine drugs by electrophilic coupling.

Two sensitive spectrophotometric methods for the determination of imipramine hydrochloride, clomipramine hydrochloride, desipramine hydrochloride, and trimipramine maleate in bulk and in dosage forms are described. The first method is based on the interaction of diazotized p-nitroaniline (DPNA) with the dibenzazepine drug in 5M hydrochloric acid. The second is based on the oxidative coupling of the dibenzazepine drug with 3-methylbenzothiazolin-2-one hydrazone (MBTH) in the presence of ammonium iron(III) sulphate in 0.1M hydrochloric acid. The resulting chromophores are measured at 575 nm (for the DPNA method) or at 620-630 nm (for the MBTH method), and are stable for at least 24 hr. The commonly encountered excipients and additives do not interfere with the determinations. Results from the analysis of pure drugs, commercial tablets and laboratory-prepared tablets by these methods agree well with those of official methods.

Determination of phenyltoloxamine salicylamide, caffeine, paracetamol, codeine and phenacetin by HPLC.

A reversed-phase high-performance liquid chromatographic method for the determination of six common analgesics (phenyltoloxamine dihydrogen citrate, salicylamide, caffeine, paracetamol, codeine phosphate and phenacetin) is presented. The method is specific for detection and determination of each of these compounds in a complex mixture, without pretreatment. A 10-mum C(18) silica gel stationary phase is used with a methanol-acetonitrile-water-tetrahydrofuran mixture (20:20:55:5 v/v) and spectrophotometric detection at 254 nm. All six components are eluted within 7 min. The method has given good results for three commercial products containing two, three and five active ingredients respectively. Phenacetin, a common analgesic which might be found in other formulations, is used as an internal standard.

Spectrophotometric determination of isocarboxazid bulk drug and tablets by reaction with p-dimethylaminocinnamaldehyde.

A spectrophotometric method is described for the determination of isocarboxazid. The method is based on the reaction of the drug with p-dimethylaminocinnamaldehyde in the presence of trichloroacetic acid in a methanolic medium to produce a very intense red chromophore (lambda max = 500 nm, Emax = 1.05 x 10(5]. The reaction is proposed to proceed via electrophilic attack at the C-4 position of the isoxazole nucleus. Job's plot indicated a 1:1 drug-to-reagent ratio. Regression analysis of Beer's plot showed excellent correlation (r = 0.9996) in the concentration range 0.25-2.10 micrograms isocarboxazid/mL. The developed color is stable for at least 12 h. Results of analyses of bulk drug and tablets by the proposed method are comparable to those for USP XXI methods.