Solid-phase extraction-high-performance liquid chromatography determination of verapamil and norverapamil enantiomers in urine

Enhancing verapamil trace determination from biological matrices by bar adsorptive microextraction

Verapamil is an L-type calcium channel blocker widely used in the treatment of cardiovascular diseases such as hypertension, angina and arrhythmias, requiring accurate therapeutic monitoring to maintain plasma, urine and saliva concentrations within a safe range. In this context, a novel analytical approach has been proposed to determine verapamil in biological samples, using bar adsorptive microextraction coated with reversed-phase polymers followed by high-performance liquid chromatography with diode array detection. Two adsorbents have been chosen, i.e. STRATA-CN and ENVI-18 polymers, showing recoveries from 56.01 ± 2.16% to 96.82 ± 0.61% under optimized experimental conditions, such as sample pH: 10.0 (STRATA-CN) and 8.0 (ENVI-18), 2 h of equilibrium time, stirring speed at 990 rpm, back-extraction solvent using methanol:acetonitrile (1 : 1 v/v), and 1 h under sonication. The analytical method showed linearity from 20 to 600 ng mL-1 (r ≥ 0.99), as well as adequate precision (with RSD% below 15%) and accuracy (with RE% within 15% of the nominal value). Finally, the analytical method was applied to plasma, urine and saliva samples and proved to be a promising alternative for the trace analysis of verapamil in biological matrices.

Rapid and sensitive LC-MS/MS method for the enantioanalysis of verapamil in rat plasma using superficially porous silica isopropyl-cyclofructan 6 chiral stationary phase after SPE: Application to a stereoselective pharmacokinetic study

A novel liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the rapid and sensitive enantioselective analysis of verapamil (VER) in rat plasma was developed and validated using new superficially porous silica isopropyl-cyclofructan 6 chiral column (LarihcShell-P, LSP). The isocratic mobile phase composed of acetonitrile: trifluoroacetic acid: 10 mM ammonium formate (100 : 0.1 : 0.1, v/v/v) at a flow rate of 0.3 mL/min was applied. Sulpride was utilized as the internal standard (IS). Positive multiple reaction monitoring (MRM) mode was used for mass spectrometry analysis, and the process of analysis was run for 5.2 min. The (S)-(-)- and (R)-(+)-VER enantiomers with the IS were extracted from plasma by using solid-phase extraction (SPE) procedure before the analysis. The C18 cartridge gave good recovery rates for both enantiomers without interference from plasma endogenous. The developed assay was successfully validated following the US-FDA guidelines. The method was linear over concentration ranges of 0.5-500 ng/mL (r² ≥ 0.997) for each enantiomer (plasma). The lower limits of quantification (LLOQ) for both isomers were 0.5 ng/mL. The intra- and inter-day relative standard deviations (RSD) were less than 8.7 % and the recoveries of (S)-(-)- and (R)-(+)-VER at three spiked levels of 1.5, 250.0 and 450.0 ranged from 92.0%-98.6%. The developed assay was effectively applied in monitoring the stereoselective pharmacokinetic study of VER enantiomers in rat plasma following oral administration of racemic VER. The pharmacokinetic parameters revealed that (S)-(-)-VER demonstrated prominently higher C_max and AUC values than (R)-(+)-enantiomer. The newly developed approach is the first chiral LC-MS/MS for the quantification of (S)-(-)- and (R)-(+)-VER utilizing superficially porous silica isopropyl-cyclofructan 6 chiral column in rat plasma after SPE.

Development and Validation of a Chiral Liquid Chromatographic Assay for Enantiomeric Separation and Quantification of Verapamil in Rat Plasma: Stereoselective Pharmacokinetic Application

A novel, fast and sensitive enantioselective HPLC assay with a new core-shell isopropyl carbamate cyclofructan 6 (superficially porous particle, SPP) chiral column (LarihcShell-P, LSP) was developed and validated for the enantiomeric separation and quantification of verapamil (VER) in rat plasma. The polar organic mobile phase composed of acetonitrile/methanol/trifluoroacetic acid/triethylamine (98:2:0.05: 0.025, v/v/v/v) and a flow rate of 0.5 mL/min was applied. Fluorescence detection set at excitation/emission wavelengths 280/313 nm was used and the whole analysis process was within 3.5 min, which is 10-fold lower than the previous reported HPLC methods in the literature. Propranolol was selected as the internal standard. The S-(-)- and R-(+)-VER enantiomers with the IS were extracted from rat plasma by utilizing Waters Oasis HLB C18 solid phase extraction cartridges without interference from endogenous compounds. The developed assay was validated following the US-FDA guidelines over the concentration range of 1-450 ng/mL (r2 ≥ 0.997) for each enantiomer (plasma) and the lower limit of quantification was 1 ng/mL for both isomers. The intra- and inter-day precisions were not more than 11.6% and the recoveries of S-(-)- and R-(+)-VER at all quality control levels ranged from 92.3% to 98.2%. The developed approach was successfully applied to the stereoselective pharmacokinetic study of VER enantiomers after oral administration of 10 mg/kg racemic VER to Wistar rats. It was found that S-(-)-VER established higher Cmax and area under the concentration-time curve (AUC) values than the R-(+)-enantiomer. The newly developed approach is the first chiral HPLC for the enantiomeric separation and quantification of verapamil utilizing a core-shell isopropyl carbamate cyclofructan 6 chiral column in rat plasma within 3.5 min after solid phase extraction (SPE).

Analytical techniques for the determination of verapamil in biological samples and dosage forms: an overview

Verapamil (VER) is a calcium channel blocker that is widely used to treat various cardiovascular diseases and is also effective in migraine prophylaxis. As the therapeutic range of VER is very narrow and toxicity can occur in patients after oral administration, therapeutic drug monitoring is recommended to optimize pharmacotherapy. The choice of an appropriate bioanalytical method for therapeutic drug monitoring of VER in the biological samples is a very important step in achieving fast and reliable results. This review focuses on the various analytical methods reported between 1976 and 2019 for the determination of VER in different biological samples and pharmaceutical dosage forms along with their methodological limitations. This review provides an overview for pharmaceutical industry researchers, clinicians and clinical chemists.

Determination of Verapamil in Exhaled Breath Condensate by Using Microextraction and Liquid Chromatography

Background:

Developing a simple analysis method for quantification of drug concentration is one of the essential issues in pharmacokinetic and therapeutic drug monitoring studies.

Objective:

A fast and reliable dispersive liquid-liquid microextraction procedure was employed for preconcentration of verapamil in exhaled breath condensate (EBC) samples and this was followed by the determination with high-performance liquid chromatography-ultraviolet detection.

Methods:

A reverse-phase high-performance liquid chromatography (RP-HPLC) combined with a dispersive liquid-liquid microextraction method (DLLME) was applied for quantification of verapamil in the EBC samples. The developed method was validated according to FDA guidelines.

Results:

Under the optimum conditions, the method provided a linear range between 0.07 and 0.8 µg.mL-1 with a coefficient of determination of 0.998. The intra- and inter-day relative standard deviation and relative error values of the method were below 15%, which indicated good precision and accuracy. The proposed method was successfully applied for the analysis of verapamil in two real samples with concentrations of 0.07 and 0.09 µg.mL-1.

Conclusion:

The established HPLC-UV-DLLME method could be applied for the analysis of verapamil in human EBC samples.

Enantiomeric separation of verapamil and its active metabolite, norverapamil, and simultaneous quantification in human plasma by LC-ESI-MS-MS

A simple, selective and high-throughput liquid chromatography-tandem mass spectrometry method has been developed and validated for the chromatographic separation and quantification of (R)- and (S)-enantiomers of verapamil and its active metabolite, norverapamil, in human plasma. All four analytes along with deuterated internal standards (D(6)-verapamil and D(6)-norverapamil) were extracted from 50 µL human plasma by liquid-liquid extraction. Separation was achieved on a Chiralcel OD-RH (150 × 4.6 mm, 5 µm) analytical column with resolution factors of 1.4 and 1.9 for (R)- and (S)-enantiomers of verapamil and norverapamil, respectively. A mobile phase consisting of 0.05% trifluoroacetic acid in water-acetonitrile (70:30, v/v) afforded capacity factors of 2.45, 3.05, 2.27 and 3.13 for (R)- and (S)-enantiomers of verapamil and norverapamil, respectively. Detection was carried out on a triple quadrupole mass spectrometer, operating in the multiple reaction monitoring and positive ion modes. The method was validated over the concentration range of 1.0-250.0 ng/mL for all four analytes. Absolute recovery for the analytes ranged from 91.1 to 108.1%. Matrix factors calculated at three quality control levels varied from 0.96-1.07. The method was successfully applied to a pharmacokinetic study in 18 healthy Indian males after oral administration of a 240-mg verapamil tablet formulation under fasting conditions.

Simultaneous analysis of the enantiomers of verapamil and norverapamil in rat plasma by liquid chromatography-tandem mass spectrometry

An enantioselective micromethod for the simultaneous analysis of verapamil (VER) and norverapamil (NOR) in plasma was developed, validated and applied to the study of the kinetic disposition of VER and NOR after the administration of a single oral dose of racemic-VER to rats. VER, NOR and the internal standard (paroxetine) were extracted from only 100-microL plasma samples using n-hexane and the enantiomers were resolved on a Chiralpak AD column using n-hexane:isopropanol:ethanol:diethylamine (88:6:6:0.1) as the mobile phase. The analyses were performed in the selected reaction monitoring mode. Transitions 456>166 for VER enantiomers, 441>166 for NOR enantiomers and 330>193 for the internal standard were monitored and the method had a total chromatographic run time of 12 min. The method allows the determination of VER and NOR enantiomers at plasma levels as low as 1.0 ng/mL. Racemic VER hydrochloride (10mg/kg) was given to male Wistar rats by gavage and blood samples were collected from 0 to 6.0 h (n=6 at each time point). The concentration of (-)-(S)-VER was three folds higher than (+)-(R)-VER, with an AUC ratio (-)/(+) of 2.66. Oral clearance values were 12.17 and 28.77 L/h/kg for (-)-(S)-VER and (+)-(R)-VER, respectively. The pharmacokinetic parameters of NOR were not shown to be enantioselective.

Thin-layer chromatography separation of enantiomers of verapamil using macrocyclic antibiotic as a chiral selector

Silica gel thin-layer chromatography plates impregnated with macrocyclic antibiotic, vancomycin, as chiral selector were prepared and used for the resolution of (+/-)-verapamil. A mobile phase system of acetonitrile-methanol-water (15:2.5:2.5, v/v) was worked out systematically. The effects of chiral selector, temperature and pH on resolution were also studied. The spots were detected with iodine vapors and the detection limit was found to be 0.074 microg of each enantiomers.

Simultaneous quantification of the enantiomers of verapamil and its N-demethylated metabolite in human plasma using liquid chromatography-tandem mass spectrometry

A stereoselective bioanalytical method for the simultaneous quantification of the enantiomers of verapamil and its active main metabolite norverapamil in human plasma has been developed and validated. The samples were analysed by liquid chromatography-electrospray-tandem mass spectrometry (LC-ESI-MS/MS) in the Selected Reaction Monitoring (SRM) mode using a deuterated internal standard. The stationary phase used for the chiral separation was a Chiral-AGP. The enantiomers of verapamil were selectively detected from those of norverapamil by the mass spectrometer due to different molecular masses, although there was a chromatographic co-elution. Thus, time-consuming procedures like achiral preseparation or chemical derivatisation could be avoided. Higher detection sensitivity than earlier published methods based on fluorescence detection was obtained, although a mobile phase of high water-content and high flow-rate was introduced into the electrospray interface (85% aqueous ammonium acetate pH 7.4 +15% acetonitrile at 0.6 ml/min). The enantiomers of verapamil and norverapamil could be quantified at levels down to 50 pg and 60 pg/500 microl plasma sample, respectively, with R.S.D. in the range of 3.6-7.8%. The presented method was successfully applied to an in vivo intestinal absorption and bioavailability study in humans, using the Loc-I-Gut method.

Multidimensional on-line sample preparation of verapamil and its metabolites by a molecularly imprinted polymer coupled to liquid chromatography–mass spectrometry

A new molecularly imprinted polymer (MIP) material was synthesized selective for verapamil and utilized for on-line metabolic screening of this common calcium antagonist in biological samples. Since some metabolites of verapamil have also shown pharmacological properties, a selective and sensitive sample preparation approach that provides a metabolic profile in biologically relevant samples is important. The MIP material was coupled on-line to a restricted access material (RAM) precolumn. The multidimensional nature of this set-up removed large matrix interferents such as proteins from the sample, while the selectivity of the MIP enabled further cleanup of the smaller analytes. The selectivity and extraction efficiency of the MIP for verapamil and its metabolites was evaluated in various biological matrices, such as cell cultures and urine. The experimental set-up with the developed method enabled the direct injection of biological samples for the selective isolation, preconcentration, identification and analysis of verapamil and its phase I metabolites by LC-MS(n). This multidimensional approach provided much qualitative information about the metabolic profile of verapamil in various biological matrices. An analytical method was developed for the quantification of verapamil and gallopamil in urine, plasma and cell culture. Acceptable linearity (R(2)=0.9996, 0.9982 and 0.9762) with an average injection repeatability (n=3) of 10, 25 and 15% R.S.D. was determined for urine, plasma and cell culture, respectively. This is the first application of the procedure for the selective metabolic screening of verapamil in biological samples.

Pharmacokinetic behavior and tissue distribution of verapamil and its enantiomers in rats by HPLC

The differences in pharmacokinetic behavior and tissue distribution of verapamil and its enantiomers were investigated in rats. In high-performance liquid chromatographic method, an achiral ODS column (150 mm x 4.6 mm i.d.) with the mobile phase consisting of methanol-water (73:30, v/v) was used for the determination of the concentration for racemic verapamil, and a Chiralcel OJ column (250 mmx4.6 mm i.d.) with the mixture of n-haxane-ethanol-triethylamine (85:15:0.2, v/v/v) as mobile phase was used to determine the concentrations of verapamil enantiomers. A fluorescence detector in the analytical system was set at excitation and emission wavelengths of 275 nm and 315 nm. The differences between enantiomers were apparent in the pharmacokinetics in rats. The area under the concentration-time curve (AUC) of S-(-) verapamil was higher than that of R-(+) verapamil. The half-distribution time (T 1/2(alpha)) of S-(-) verapamil which distributing to tissue from blood was shorter than that of R-(+) verapamil, but the elimination half-time (T 1/2(beta)) was longer in rat following oral administration of racemic verapamil. At 1.3 h after oral administration of racemic verapamil, however, there were no significant differences between enantiomers for the distributions in major tissues such as heart, cerebrum, cerebellum, liver, spleen and kidney.

Stereoselective determination of pyridoglutethimide enantiomers in serum with a chiral cellulose-based high-performance liquid chromatographic column using solid phase extraction and UV detection

A sensitive method for the separation and determination of R(+)- and S(-) enantiomers of pyridoglutehimide in serum by high performance liquid chromatography (HPLC) with UV detection was developed. The assay involves the use of a solid-phase extraction for serum sample clean-up prior to HPLC analysis using a C18 Bond-Elute column. Chromatographic resolution of the enantiomers was performed on a reversed-phase cellulose-based chiral column (Chiralcel OD-R, 250 x 4.6 mm I.D.) under isocratic conditions using a mobile phase of 25:75 v/v acetonitrile-0.3 M aqueous sodium perchlorate (pH 6.2 adjusted with perchloric acid) at a flow rate of 0.8 ml/min. Recoveries for R(+)- and S(-)-pyridoglutethimide enantiomers were in the range 86-91% at 300-900 ng/ml level. Intra-day and inter-day precision calculated as %R.S.D. were in the ranges of 2.9-3.9 and 1.5-4.7% for both enantiomers, respectively. Intra-day and inter-day accuracies calculated as percentage error were in the ranges of 1.9-3.3 and 1.5-3.9% for both enantiomers, respectively. Linear calibration curves in the concentration ranges of 100-1500 ng/ml for each enantiomer show correlation coefficient (r) of more than 0.9995. The limit of quantification (LOQ) of each enantiomer was 100 ng/ml using 1 ml of serum. The detection limit (LOD) for each enantiomer in serum using a UV detection set at 257 nm was 50 ng/ml (S/N = 2).

Stereoselective chromatography of cardiovascular drugs: an update

This review reports the latest achievements in chromatographic enantioseparations of various classes of cardiovascular drugs and selected applications of these methods in pharmaceutical and clinical analysis. The use of these drugs as test compounds for new chiral stationary phases and different parameters of chromatographic processes is also presented.

Determination of verapamil by adsorptive stripping voltammetry in urine and pharmaceutical formulations

A sensitive reduction peak of verapamil is obtained by adsorptive stripping voltammetry in 0.01 M phosphate (pH 7.4) at an accumulation time of 30 s. The peak potential is -1.81 V (vs. Ag/AgCl). The peak current is directly proportional to the concentration of verapamil (1x10(-8)-1x10(-6) M), with a 3sigma detection limit of 5x10(-10) M (0.246 ng/ml). The R.S.D. at the 1x10(-7) M level is 1.8%. The interference of some metal ions, and some amino acids, and the application of the method to analysis of urine, and pharmaceutical formulations are described. The method is simple (no extraction), rapid (30 s accumulation time), sensitive (the detection limit of verapamil is 0.491 ng/ml), reproducible(within day R.S.D. of 1.28-1.8%), and suitable for routine analysis of verapamil, urine, and pharmaceutical formulation.

Reversed-phase liquid chromatographic separation of enantiomers on polysaccharide type chiral stationary phases

The direct chiral separation by chiral stationary phases (CSPs) is one of the most important techniques to analyze enantiomeric purity as well as to get enantiomerically pure material quickly. Among various types of CSPs, polysaccharide type CSPs are well known by their versatility and durability. They are not only effective under normal-phase conditions, but also under reversed-phase conditions. In order to get a good separation under the reversed-phase conditions, it is the key to choose an appropriate mobile phase. For example, a simple mixture of water/acetonitrile or water/methanol are sufficient for a neutral analyte, while it is necessary to use an acidic solution instead of water for an acidic analyte and a solution of a chaotropic salt (or a basic solution) for a basic analyte, respectively. The paper also presents lists of more than 350 separation examples that include 22 validated methods for drug analyses from serum, plasma, or urine samples on polysaccharide type CSPs under reversed-phase conditions.

Reviewing mobile phases used on Chiralcel OD through an application of data mining tools to CHIRBASE database

During the past decade, thousands of compounds have been resolved on Chiralcel OD (a cellulose-based chiral stationary phase) under diverse eluting conditions. Many researches have documented the effects of mobile phase on enantioselectivity for a given family of samples but today no comprehensive study aimed at identifying the associations between the structural features present on solute and appropriate mobile phase conditions has yet been proposed. In this review of mobile phases used on Chiralcel OD, we try to go far beyond a simple enumeration of eluting conditions and an effort is made to explore the utility of data mining tools for assessing the knowledge contained in CHIRBASE database. We have extracted from CHIRBASE the chemical features of 2363 chiral compounds separated on Chiralcel OD and their corresponding mobile phases. This data set was submitted to data mining programs for molecular pattern recognition and mobile phase predictions for new cases. Some substructural characteristics of solutes were related to the efficient use of some specific mobile phases. For example, the application of CH3CN/salt buffer at pH 6-7 was found convenient for reversed-phase separation of compounds bearing a tertiary amine functional group. Furthermore, a cluster analysis allowed the arrangement of the mobile phases according to similarity found in molecular patterns of solutes. A decision tree, which may lead to a more rational choice of the mobile phase under reversed-phase conditions, is also proposed.