Enantioselective supercritical fluid chromatography using ristocetin A chiral stationary phases

Racemic mixtures of five acidic drugs have been successfully separated by supercritical fluid chromatography (SFC) using macrocyclic antibiotic chiral stationary phases (CSPs). A ristocetin A CSP has been prepared 'in-house' and effectively applied in packed capillary SFC to separate the enantiomers of dichlorprop (R(s) = 1.4), ketoprofen (R(s) = 0.9) and warfarin (R(s) = 0.9). The commercial ristocetin A CSP (Chirobiotic R) was subsequently studied in packed column SFC with similar results where the enantiomers of warfarin (R(s) = 2.2), coumachlor (R(s) = 2.5) and thalidomide (R(s) = 0.6) were separated. Interestingly, differences were observed between the two differently immobilised CSPs where the enantiomers of dichlorprop and ketoprofen, which were separated on the 'in-house' CSP, could not be separated on the commercial phase.

Determination of clenbuterol residues in bovine hair by using diphasic dialysis and gas chromatography-mass spectrometry

A method for the determination of clenbuterol (4-amino-3,5-dichloro-alpha[(tert.-butylamino)methyl]-benzyl alcohol hydrochloride) in hair of living cows has been developed. Hair samples were digested in an alkaline medium. The diphasic dialysis technique is a semi-permeable membrane technology developed for the direct extraction of relatively low-molecular-mass analytes such as clenbuterol. In this case, we used sodium citrate buffer to homogenize the digested hair, dichloromethane was used as the extraction solvent at 37 degrees C, and stirring was applied at 150 rpm for 4 h. The analysis was carried out using gas chromatography-mass spectrometry. The calibration curve for clenbuterol in hair was linear in the range from 12.5 to 400 ng g(-1). The detection limit of clenbuterol was 5 ng g(-1) and the quantification limit was 12.5 ng g(-1), in hair. A good inter-day reproducibility was obtained (R.S.D. = 7.08%). The repeatability and intra-day reproducibility (50 ng g(-1) of hair, n = 10) show R.S.D.s of 7.1 and 9.5%, respectively.

[The enantiomeric separation of aromatic alcohol amino drugs by thin-layer chromatography]

Two chiral aromatic alcohol amino drugs, Labarol and Bataroc, were resolved by thinlayer chromatography (TLC) on the silica gel GF254 plates (2.5 cm x 10 cm), by using the ammonium-D-10-camphorsulfonate (CSA) as chiral ion-pair interaction agent which was added to the mobile phase in the ammonium form. All developments were carried out at lower temperature (2-4 degrees C, in a refrigerator) in small glass jars of 250 mL volume. These two drugs were not resolved at room temperature (15-30 degrees C). Analytical reagent grade methanol and dichloromethane can be directly used as mobile phase without further drying. The chiral separation occured over a range from 40% to 70% (optimum 67%) dichloromethane in the mobile phase volume ratio and 55% to 80% (optimum 60%) dichloromethane in the mobile phase volume ratio. These separation conditions were easily obtained. This method is relatively inexpensive and attractive.

Error structure for the HPLC analysis for atenolol, metoprolol and propranolol: a useful weighting method in parameter estimation

Three reversed-phase high performance liquid chromatography (HPLC) methods with UV detection were developed and fully validated for the quantification of three beta-blockers: atenolol, metoprolol and propranolol. After validation, error structures for the HPLC analysis were established using a convenient and practical procedure. The mean percentage of relative standard deviation (RSD) of the experimental concentrations (C), were less than 4.29% for proportionality and less than 3.68% for precision for any of the drugs, which allowed the quantitation of beta-blockers assayed at concentrations in the range 25-0.78 micrograms.ml-1. The error structures for the HPLC analysis were: SD (micrograms.ml-1) = 5.02 x 10(-2) C for atenolol, SD (micrograms.ml-1) = 4.55 x 10(-2) + 0.63 x 10(-2) C - 7.58 x 10(-6) C3 for metoprolol and SD (micrograms.ml-1) = 2.73 x 10(-2) C - 3.49 x 10(-4) C2 for propranolol. The reciprocal of the square of the SD of the drug concentrations measured within the calibration curve could be used as weighting methods in parameter estimation by non-linear regression.

Evaluation of the immobilized artificial membrane phosphatidylcholine. Drug discovery column for high-performance liquid chromatographic screening of drug-membrane interactions

Chromatographic retention factors (k') of a series of eight beta-adrenoceptor antagonist compounds (beta-adrenolytic drugs) were determined employing an immobilized artificial membrane column (IAM.PC.DD). The influence of mobile phase pH, ionic strength, and organic modifier composition was studied in order to examine column performance. After the IAM.PC.DD columns were exposed to approximately 7000 column volumes of a 0.01 M PBS mobile phase, five out of six columns tested showed significant peak broadening and decreased k' values indicative of premature column failure. The data suggested that the immobilized phospholipids stationary phase was removed by the 0.01 M PBS mobile phase. The beta-adrenolytic drug's log k'IAM values obtained with an IAM.PC.DD column were compared to an esterIAM.PC.MG column for predicting drug membrane interactions. For the linear regression analysis between log k'IAM and the logarithm of the n-octanol-water partition coefficients (rIAM.PC.DD = 0.8710 vs. rIAM.PC.MG = 0.9538), the C18 HPLC retention factors (rIAM.PC.DD = 0.8408 vs. rIAM.PC.MG = 0.9380), the liposome partition coefficients (rIAM.PC.DD = 0.8887 vs. rIAM.PC.MG = 0.9187), and various pharmacokinetic parameters, significantly better correlations were obtained with the esterIAM.PC.MG column than the IAM.PC.DD column.

Enantiomeric separation and sensitive detection of propranolol, metoprolol and atenolol derivatized with a fluorogenic reagent, 4-(N-chloroformylmethyl-N-methyl)amino-7-N,N-dimethylaminosulf onyl-2,1, 3-benzoxadiazole (DBD-COCl), on cellulose chiral columns in the reversed-phase mode

An electrophilic fluorogenic reagent, 4-(N-chloroformylmethyl-N-methyl)amino-7-N,N-dimethylaminosulfo nyl-2,1,1,3-benzoxadiazole (DBD-COCl), was used to react with three beta-blockers, propranolol, metoprolol and atenolol, to yield the derivatives which were subsequently verified to be amide compounds (1:1 adducts) derived from the reaction with the secondary amino group of the beta-blockers. DBD-COCl exhibited high reactivity for the reaction completed within 5 min under mild conditions and without any need for a catalyst. The derivatives were well separated enantiomerically on cellulose CSPs (the derivative of propranolol on a Chiralcel OD-R column and those of metoprolol and atenolol on a Chiralcel OJ-R column) in the reversed-phase mode, with the S-configurations being eluted before the R-configurations. The derivatives were stable at 4 degrees C for 1 week. The detection limits (S/N = 3) were 50 fmol for both (S)- and (R)-propranolol, 12 and 17 fmol for (S)- and (R)-metoprolol, respectively, and 15 and 20 fmol for (S)- and (R)-atenolol, respectively.

A rapid and sensitive electron-capture gas chromatographic procedure for analysis of metoprolol in rat brain and heart

A procedure for analysis of metoprolol-utilizing extraction followed by derivatization with pentafluoropropionic anhydride and analysis on a gas chromatograph equipped with a fused silica capillary column, an electron-capture detector and a printer/integrator is described. Propranolol was carried through the procedure as internal standard. The pentafluoropropionyl derivative of metoprolol yields a sharp peak on the gas chromatograph, and the structure of the derivative was confirmed using combined gas chromatography-mass spectrometry. The analytical method is linear, sensitive and reproducible and has been applied to analysis of metoprolol in brain and heart from rats treated with metoprolol intraperitoneally. Pretreatment of the rats with the antidepressant desipramine prior to metoprolol administration resulted in a marked increase in levels of metoprolol in both brain and heart, indicating a pharmacokinetic drug-drug interaction between desipramine and metoprolol.

Densitometric determination of metoprolol tartrate in pharmaceutical dosage forms

This paper describes a simple densitometric method for the determination of metroprolol tartrate in tablets and ampoules. After separation on silica gel GF254 plates, using acetone-methanol-triethylamine as the mobile phase for the tablets and acetone-triethylamine for ampoules, the chromatographic zones corresponding to the spots of metoprolol were scanned. Quantitation was performed using a computer-controlled Camag TLC scanner and applying five-point calibration with polynomial regression. The calibration function was established in the ranges 1-28 micrograms for tablets and 1-9 micrograms for ampoules. The results obtained are precise and reproducible, with recovery values of 99.1-99.4%.

Vibrational spectrometry for the assessment of active substance in metoprolol tablets: a comparison between transmission and diffuse reflectance near-infrared spectrometry

Near-infrared spectrometry (NIR) was used to quantify metroprolol succinate in controlled release tablets. Metoprolol tablets were made according to an experimental design using different strengths around a central strength of 47.5 mg per tablet. A comparison was made between NIR in the diffuse reflectance mode and the transmission mode. This showed that, although a narrower wavelength range was available in the transmission mode, predictions were much better for models based on transmission spectra than for models based on diffuse reflectance spectra. The main reason for this is that in the reflectance mode NIR spectrometry is very sensitive to the inhomogeneity of the material, while in the transmission mode this problem is less severe. This is due to the larger volume of the material scanned in the transmission mode compared to that in diffuse reflectance. Spectra were taken before and after the tablets were stored under humid conditions. This allowed the final calibration models to be made more robust towards variations in the amount of water in the tablet. Different batches of metoprolol pellets and microcrystalline cellulose were used during the production of the tablets. this resulted in models that were more robust towards possible batch-to-batch differences in the main constituents.

Distribution of metoprolol enantiomers in a fatal overdose

The distribution of the racemic and the enantiomeric content of (+/-)-metoprolol was compared after ingestion of a massive fatal overdose of the racemic drug. Postmortem concentrations of the racemate in different tissues were assayed by gas chromatography after derivatization with trifluoroacetic acid anhydride. The distribution of the R- and S-enantiomers of metoprolol was analyzed by reversed-phase high-performance liquid chromatography. Metoprolol was extracted from postmortem specimens and derivatized with the chiral reagent 2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl isothiocyanate. The concentrations of active S(-)-isomer in blood, liver, and stomach contents were 33 mg/L, 224 mg/kg, and 56 mg/61 g, respectively. The concentrations of inactive R(-)-enantiomer in blood, liver, and stomach contents were 33 mg/L, 222 mg/kg, and 55 mg/61 g, respectively. These results indicate that half the total postmortem tissue concentration of metoprolol is the R-enantiomer, which is devoid of any beta-blocker activity.

Identification of a new by-product detected in metoprolol tartrate

A new impurity has been found in some batches of metoprolol tartrate. As the amount exceeded 0.1% it was of interest to deduce the structure. Techniques involved in solving the problem were LC, LC-MS and GC-MS. The LC systems showed that the impurity and metoprolol behaved differently to modifications of the mobile phase, indicating that there were differences in the functional groups. LC-MS was used to determine the molecular weight, which was 74 mass units higher than metoprolol. A hydrogen-deuterium shift technique using micro column LC-MS gave the information that three hydrogen atoms were bound to heteroatoms, i.e. one more than in metoprolol. This led to the conclusion that the impurity had three extra carbon and two extra oxygen atoms. It was supposedly a by-product in the synthesis. Knowledge of the synthesis steps for beta-receptor blocking drugs suggested three possible structures. Two were independently synthesized and one of these was found to be identical to the impurity.

Spectrophotometric investigation of metoprolol-benzyl orange reaction and its application to the assay in pharmaceutical dosage forms

A sensitive spectrophotometric method for the determination of metoprolol tartrate in tablets and ampoules is presented. Using spectrophotometric measurements, it was found that metoprolol tartrate and benzyl orange form a chloroform soluble ion-pair complex with an absorption maximum at 401 nm. The composition of the ion-pair complex was determined by applying Job's method to equimolar solutions of metoprolol tartrate: benzyl orange (1:2); molar absorptivity 7.39 x 10(3) mol-1 cm-1. Extraction of the ion-pair complex in chloroform was accomplished easily at a Britton-Robinson's buffered optimum pH = 5.2, mu = 0.1 mol/dm3. The relative stability constant, calculated according to the method of Sommer and Job's non-equimolar solutions, was log K = 9.72 (avg. value). Beer's law was obeyed up to 3.42 micrograms/ml of metoprolol tartrate (the detection limit was also 3.42 micrograms/ml). The precision of the method was checked at three different concentrations. The RSD (n = 7) varied from 0.51 to 2.03%. Reproducibility was examined by analysing Lopresor tablets and ampoules. Recoveries varied from 99-101%. The reported method, applied to the assay of metoprolol tartrate in tablets and ampoules, gives precise and reproducible results.

Simultaneous determination of metoprolol and alpha-hydroxymetoprolol in human plasma and urine by liquid chromatography with a preliminary observation on metoprolol oxidation in Japanese subjects

A simple, sensitive, and highly reliable liquid chromatographic method using fluorescence detection is described for the simultaneous determination of metoprolol and alpha-hydroxymetoprolol in plasma and urine. This method involves a single extraction of the compounds with the internal standard pindolol from alkalinized plasma or urine into dichloromethane. A reconstituted aliquot with a mobile phase is injected onto a reversed-phase, Zorbax ODS column, and the detection is achieved by the excitation and emission wavelengths at 230 and 300 nm, respectively. The assay is reproducible and precise for metoprolol and alpha-hydroxymetoprolol in both plasma and urine samples, as judged by a coefficient of variation of less than 9.2% at all concentrations examined. The standard curves for metoprolol and alpha-hydroxymetoprolol are linear over 10-200 ng/ml in plasma and over 0.5-10 micrograms/ml in urine. The lower detection limit is 2 ng/ml for each of the compounds in plasma using a 0.5-ml sample. Preliminary data on the oxidation polymorphism of metoprolol in Japanese subjects are reported using the current assay method. In 183 Japanese subjects no poor metabolizer of metoprolol has been identified so far.

Massive metoprolol ingestion associated with a fatality--a case report

An unusual fatality involving a 26-year-old male who intentionally ingested approximately 10 g of metoprolol is presented. Autopsy findings revealed foreign material in the gastric content with an acute thrombosis of the left anterior descending coronary artery. Microscopic studies showed evidence of an extremely early infarct. Metoprolol concentrations in the blood, liver, gastric content, and urine are reported by both capillary gas chromatography and ultraviolet spectrophotometric analysis. A review of the literature confirmed that little information has been published concerning intoxication with this drug.

Determination of metoprolol and two major metabolites in plasma and urine by column liquid chromatography and fluorometric detection

Metoprolol and its alpha-hydroxy metabolite were determined in plasma down to 2 nmol/l (S.D. 10-15%) after solvent extraction and bonded-phase liquid chromatography with fluorometric detection. The major metabolite with a carboxylic function was also measured in plasma when liquid-solid extraction on a column activated with dodecyl sulphate was applied. In urine the three components were assayed by direct injection of a diluted sample.

Verapamil tissue concentrations in fatal cases

Postmortem findings are presented for fourteen cases of Verapamil induced or related deaths. Liver, blood, and stomach concentrations of Verapamil alone or in combination with alcohol or other drugs are given with the age and sex of each victim and with the coroner's findings. The significance of these levels is discussed. Tissue homogenates were digested either by strong acid or enzymically by subtilisin and extracted with dichloromethane or 1-chlorobutane, respectively. Blood was buffered to pH 9 and extracted directly with 1-chlorobutane. Recoveries are reported. Verapamil was quantitated by gas chromatography on a 3% OV-17 column with a nitrogen-phosphorus detector.

Capillary gas chromatographic-mass spectrometric study of the effect of solvents on metoprolol and other aryloxypropanolamines

When metoprolol in methanol was analysed by capillary gas chromatography (GC), an additional peak was observed; mass spectrometry (MS) showed this additional peak to have a molecular weight 12 dalton higher than that of the parent compound. A similar phenomenon was observed with other beta-adrenergic blocking aryloxypropanolamines in methanol or dichloromethane. Capillary GC-MS using deuterated solvents as isotopic markers showed that a methylene group from the solvents was incorporated into the parent molecule. The structure of the observed products and the mechanism of their formation are proposed.

Influence of solute polarity in column-switching chromatography for the assay of drugs in plasma and urine

The polarity of a drug is one of the most important parameters for the elaboration of switching systems. If the polarity of the drug is low or medium, "reversed-phase" chromatography is well adapted. The plasma or urine sample is diluted with water, centrifuged and injected first into a column of medium polarity (C2, CN or diol bonded phases). The compounds of interest are stopped on the top of the column and rinsed with water, then eluted and chromatographed on a C8 or C18 analytical column. A third column of still lower polarity can be added to improve the specificity of the system. In each successive step, the polarities of the mobile phases and columns should be decreased to reconcentrate the sample and reduce the band broadening that occurred in the previous step. Compounds of high polarity show almost no retention on reversed-phase columns, and normal-phase chromatography should be used. Aqueous solutions cannot be injected into polar bonded-phase columns as they lead to excessive band broadening. This problem can be solved by diluting plasma or urine with a large volume of a water-miscible organic solvent and injecting the clear supernatant. The compounds to be assayed are first reconcentrated on a polar column (NH2 or N(CH3)2 bonded phase) and then eluted. The selected "heart cut" of the eluate is chromatographed on another, more polar column. The influence of the polarity of drugs on the choice of switching systems is exemplified by assay methods for drugs of low, medium and high polarity.

Fatal metoprolol overdose

Metoprolol, a beta 1-adrenergic blocking agent, has been found effective in the treatment of hypertension. A death due to deliberate ingestion of metoprolol is described, including the case history, postmortem toxicologic findings, and identification and quantitation of the drug by high pressure liquid chromatography and gas chromatography/mass spectrometry. Metoprolol levels were found to be 4.7 mg/L in blood, 194 mg/L in urine, 3.3 mg/L in vitreous humor, 3.9 mg/L in pleural fluid, 254 mg/L in bile, 7.1 mg/kg in kidney, and 6.3 mg/kg in liver.

Dissolution profile determination of a multicomponent product using a rapid liquid chromatographic analysis

A system was developed which is capable of monitoring the dissolution profiles of each of the active components in a two-component combination product. The UV spectra of the two drugs (metoprolol and hydrochlorothiazide) overlap considerably, making conventional UV analysis of either component unrealistic. By resolving the two drugs on a high-performance liquid chromatographic (HPLC) system both can be quantitated after separation. The analysis is sufficiently short to allow for the use of a six-station dissolution tester in tandem with an HPLC for determination of dissolution profiles. The HPLC system and equipment, can monitor six samples of this product at 5-min intervals in real analysis time.

Disposition of the adrenergic blocker metoprolol in the late pregnant women, the amniotic fluid, the cord blood and the neonate

Pharmacokinetic studies of the concentration of the beta 1-blocker metoprolol have been performed in maternal plasma, amniotic fluid, breast milk and the plasma of the newborn. The concentration of metoprolol in maternal plasma exceeds that in the amniotic fluid initially but not later on. The quotient between the metoprolol concentration in the venous maternal blood and the mixed cord blood at the time of delivery is at about 1. In the maternal plasma the metoprolol concentration will decline in a rapid way after the latest dose probably because of an increased clearance. Blood levels of metoprolol during the first postnatal hours will increase almost fourfold and are generally followed by a decrease over the next 15 hours. Active metabolites of metoprolol (alfa-OH-metoprolol and O-demethyl-metoprolol) are found in the urine of the newborn. The breast milk concentration of metoprolol is 3 times higher than in the maternal milk but the sucking newborn will only show very low or unmeasurable plasma levels between consecutive breast feeding periods in the majority of cases.

High-performance liquid chromatographic method for the quantitative analysis of the aryloxypropanolamines propranolol, metoprolol and atenolol in plasma and tissue

A simple and rapid high-performance liquid chromatographic method is described for the quantitative analysis of three beta-receptor blocking drugs of similar molecular structure (aryloxypropanolamines, AOPAs) but with different polarities. the method consists of extraction, reversed-phase ion-pair chromatography and fluorometric detection, whereby slight modifications in these parameters allow analysis of the different AOPAs in a similar way. The method was used to determine concentrations of propranolol, metoprolol and atenolol in plasma and various organs of the rat. In samples of 1 ml of plasma and 0.5--1.7 g of tissue, drug concentrations of at least 2 ng/ml and 5 ng/g, respectively, can be measured. Extension of the method to other AOPAs is possible.

Selected ion monitoring of metoprolol and two metabolites in plasma and urine using deuterated internal standards

A highly sensitive and specific quantitative assay for metoprolol and two of its metabolites, containing an unchanged 2-hydroxy-4-isopropylaminopropoxy sidechain, has been developed. The compounds are isolated from the alkalized sample (plasma or urine) by extraction with dichloromethane, and converted to trifluoroacetyl derivatives by reaction with methyl-bis-(trifluoroacetamide). The reaction mixture is gas chromatographed on an OV-17 column and each substance is assayed by electron impact mass spectrometry using selected ion monitoring, and quantified by comparing the intensity of fragment ion m/z 266 with the intensities of corresponding fragment ions from the deuterated internal standards (m/z 270 and 271). It is possible to determine concentrations as low as 1 nmol l-1 (0.3 ng ml-1) in 1 ml of sample with relative standard deviation of less than 10%.

Separation of enantiomeric amines by ion-pair chromatography

A high-performance liquid chromatographic method for the separation of optical isomers (enantiomers) of amines is described. It is based on ion-pair chromatography with a chiral counter ion in a system with an organic mobile phase and an adsorbing stationary phase. The method has been applied to enantiomers of 1-aryloxy-3-isopropylamine-2-propanol derivatives (alprenolol, metoprolol, propranolol) which are completely resolved with (+)-10-camphorsulphonate as the counter ion. Studies of the influence of the counter-ion structure and the mobile phase composition are presented.