Chromatography of beta-adrenergic blocking agents

Determination of β-blocking receptor drugs in silica gel TLC systems with the mobile phase containing surfactant

Eight drugs blocking beta-adrenergic receptors activity (acebutolol, alprenolol, atenolol, oxprenolol, labetalol, metoprolol, propranolol and sotalol) were investigated through the use of the thin-layer technique with its mobile phase containing surfactant. Assessment of the effect of surfactant presence and 1-propanol concentration in the mobile phase on the retention and separation of investigated solutes was then carried out wherein the effect of the surfactant concentration on the zone shape properties (asymmetry and tailing coefficient) was investigated. The method was applied for the quantitative analysis of the chosen solutes, and the LOD and LOQ values of chosen were determined. These were as follows: acebutolol – 1.11 and 3.36 μg/spot, metoprolol 1.45 μg/spot, 4.4 μg/spot. The chosen system is environmentally friendly due to using silica gel plates and only 5% of propanol in water.

(+) or (-)-1-(9-fluorenyl)ethyl chloroformate as chiral derivatizing agent: A review

Over the last 30years, (±)-1-(9-fluorenyl)ethyl chloroformate ((±)-FLEC) was used as a chiral derivatizing agent in various analytical applications involving a wide range of endogenous, pharmaceutical and environmentally relevant molecules. This comprehensive review aims to present all the significant aspects related to the state of the art in FLEC labeling and subsequent chiral separation of the resulting diastereomers using LC, SFC and CE techniques.

Recent developments in HPLC analysis of β-blockers in biological samples

β-Adrenergic blockers represent a very important class of drugs that are used worldwide for treating various cardiac diseases. The present article describes the state-of-the art of analyses of β-adrenergic blockers using high-performance liquid chromatography (HPLC). Sample preparation techniques such as liquid-liquid extraction, solid-phase extraction and solid-phase microextraction have been discussed, which are essential prior to HPLC analysis. Additionally, applications of liquid chromatography coupled with tandem mass spectrometry are included. HPLC methods have been reported to include 0.6-26 min as the run times and 0.01 ng/mL to 25 µg/mL as detection limits. The most commonly used columns were C18 with various buffers as the mobile phases, along with various organic modifiers. The optimization of HPLC conditions has been discussed. It has been observed that the reported methods are quite satisfactory for the analyses of β-adrenergic blockers in biological samples. Future perspectives in the hyphenation of solid-phase microextraction-nano-liquid chromatography-tandem mass spectrometry have also been highlighted to achieve detections at nanogram and picogram levels. The present article is very useful for academicians, scientists, drug and pharmaceutical personnel and government regulatory authorities.

Enantioselective LC/ESI-MS/MS analysis and pharmacokinetic and tissue distribution study of (2RS)-1-(7-methoxy-1H-indol-4-yloxy)-3-(2-(2-methoxyphenoxy)ethylamino)-propan-2-ol in rats

A sensitive and stereospecific liquid chromatography-tandem mass spectrometry method for the quantitative determination of TWo8 enantiomers ((2RS)-1-(7-methoxy-1H-indol-4-yloxy)-3-(2-(2-methoxyphenoxy)ethylamino)-propan-2-ol) was developed and validated in rat serum and some tissues. Racemic TWo8 is a new chemical entity, and it has been shown to possess pharmacological activity in vivo. The assay involved the diastereomeric derivatization of racemic TWo8 with 2,3,4,6-tetra-O-acetyl-beta-glucopyranosyl isothiocyanate. The TWo8 diastereoisomers quantification was performed on a triple quadrupole mass spectrometer employing an electrospray ionization technique. The precursor to the product ion transition for TWo8 derivatives and for the internal standard (carbamazepine) was m/z 776.4 → 387.2 and 237.4 → 194.4, respectively. The assay was validated with a linear range of 10-2000 ng/ml of racemic TWo8. The inter-day precisions for (-)-(S)-TWo8 and (+)-(R)-TWo8 were 2.1% to 14.9% and 1.3% to 14.8%, respectively. The inter-day accuracy for (-)-(S)-TWo8 and (+)-(R)-TWo8 was within 86% to 114% and 91% to 114%, respectively. A pilot pharmacokinetic study of this new β-adrenolytic compound has shown that (-)-(S)-TWo8 is eliminated faster than its antipode. The terminal half-lives of (-)-(S)-TWo8 and (+)-(R)-TWo8 were 3.2 and 3.9 h, respectively. The compound distribution into different organs, evaluated in tissue homogenate samples following TWo8 intravenous administration, showed an enantioselective penetration of TWo8 enantiomers in the liver (p < 0.03), in the kidney (p < 0.001), and in the lungs (p < 0.05). The developed method using liquid chromatography-tandem mass spectrometry method with electrospray ionization could be employed for quantitative determination of compounds with similar structure.

Monitoring the effects of chiral pharmaceuticals on aquatic microorganisms by metabolic fingerprinting

The effects of the chiral pharmaceuticals atenolol and propranolol on Pseudomonas putida, Pseudomonas aeruginosa, Micrococcus luteus, and Blastomonas natatoria were investigated. The growth dynamics of exposed cultures were monitored using a Bioscreen instrument. In addition, Fourier-transform infrared (FT-IR) spectroscopy with appropriate chemometrics and high-performance liquid chromatography (HPLC) were employed in order to investigate the phenotypic changes and possible degradation of the drugs in exposed cultures. For the majority of the bacteria studied there was not a statistically significant difference in the organism's phenotype when it was exposed to the different enantiomers or mixtures of enantiomers. In contrast, the pseudomonads appeared to respond differently to propranolol, and the two enantiomers had different effects on the cellular phenotype. This implies that there were different metabolic responses in the organisms when they were exposed to the different enantiomers. We suggest that our findings may indicate that there are widespread effects on aquatic communities in which active pharmaceutical ingredients are present.

Stereoisomer quantification of the -blocker drugs atenolol, metoprolol, and propranolol in wastewaters by chiral high-performance liquid chromatography–tandem mass spectrometry

A chiral liquid chromatography-tandem mass spectrometry (HPLC-MS-MS) method was developed and validated for measuring individual enantiomers of three beta-blocker drugs (atenolol, metoprolol, and propranolol) in wastewater treatment plant (WWTP) influents and effluents. Mean recoveries of the pharmaceuticals ranged from 67 to 106%, and the limits of detection of the analytes were 2-17 ng/L in wastewater effluents. The method was demonstrated by measuring, for the first time, the stereoisomer composition of target analytes in raw and treated wastewaters of two Canadian WWTPs. In these trials, racemic amounts of the three drugs were observed in influent of one wastewater treatment plant, but nonracemic amounts were observed in another. Effluents of the two plants contained nonracemic amounts of the drugs. These results indicate that biologically-mediated stereoselective processes that differ among WWTPs had occurred to eliminate individual enantiomers of the target analytes.

Degradation and configurational changes of thioridazine 2-sulfoxide

Thioridazine (THD) is a phenothiazine neuroleptic drug used for the treatment of psychiatric disorders. After oral administration THD is extensively biotransformed to thioridazine 2-sulfone (THD 2-SO(2)), thioridazine 5-sulfoxide (THD 5-SO) and thioridazine 2-sulfoxide (THD 2-SO). THD 2-SO and THD 5-SO have two chiral centres and therefore exist as two diastereoisomeric pairs. The degradation and epimerization of THD 2-SO in human plasma, buffer and methanolic solutions were studied using an enantioselective HPLC method. The samples were prepared by liquid-liquid extraction with diethyl ether and the chiral resolution of the enantiomers was carried out on a Chiralpak AD column using a mobile phase consisting of hexane:ethanol:2-propanol (90:7:3, v/v/v) containing 0.2% diethylamine. The method was validated and used to study the degradation and epimerization under different conditions of incubation. Our results showed that both enantiomers were stable at varying temperatures, pH and ionic strengths; however, solubility problems were observed, mainly at pH 8.5. The influence of light on stability was studied using methanolic solutions and degradation and epimerization of the THD 2-SO enantiomers were observed under UV light of 366 and 254nm, respectively.

Combination of liquid-phase microextraction and on-column stacking for trace analysis of amino alcohols by capillary electrophoresis

We described a new method for the enrichment of basic drugs present in water samples via liquid-phase microextraction (LPME) combined with on-column stacking in capillary electrophoresis. Two steps were employed to enhance the detection sensitivity of four amino alcohols. The analytes were first extracted from aqueous sample (donor solution) that were adjusted to basic through a thin layer of 1-octanol entrapped within the pores of a polypropylene hollow fiber, and then into a 5-microl acidic acceptor solution inside the hollow fiber. The extract was then further enriched through on-column stacking in capillary electrophoresis. With this two-step enrichment procedure, the method provided 72-110-fold preconcentration of the target amino alcohols. The limits of detection were 0.08-0.5 microg/ml. Relative standard deviation (n=6) ranged between 4.3 and 6.9% for the studied drugs utilizing 2-amino-1-phenylethanol as internal standard. The extraction of amino alcohols in spiked urine samples was evaluated using the developed procedure.

High speed determination of beta-receptor blocking agents in human urine by liquid chromatography/tandem mass spectrometry

Beta-receptor blocking agents are present on the international market in a huge variety. The International Olympic Committee prohibits the use of these drugs in several sport sections and doping control laboratories analyse urine samples of high-performance athletes with different techniques. Therefore, fast and reliable methods are required to enable a sensitive detection of many drugs and a high throughput of samples. In the present study a screening procedure is described using high speed liquid chromatography and multiple reaction monitoring to identify 32 beta-receptor blocking agents extracted from human urine. Urine specimens (blank urine samples, spiked urine samples and specimens of excretion studies) were hydrolysed, extracted and analysed within 7 min. Quasi-molecular ions (M(+) + H) of the beta-blockers are generated by means of an atmospheric pressure chemical ionization interface followed by collision-induced dissociation in a triple quadrupole mass spectrometer and subsequent detection of daughter ions. Proposals for the origin of common and individual secondary ions are presented.

Determination of esmolol in serum by capillary zone electrophoresis and its monitoring in course of heart surgery

A new Capillary Zone Electrophoresis (CZE) procedure for determination of esmolol, an ultra-short-acting beta-blocker, in serum was developed. Dichloromethane was applied as a deproteination agent and it was used also for the inactivation of erythrocytal esterase and in the same time for the extraction of esmolol from blood. The re-extraction of esmolol from organic phase to water phase was performed by 0.01 M HCl. An aliquot of 200 ml of acid aqueous phase was used for the injection and analysis. CZE determination was done in 50 mM phosphate buffer (pH=8.0) with detection at 222 nm. The concentration detection limit of esmolol in serum was 0.051 microg/ml. This method was applied in an extensive heart surgery experiment on pigs (Sus scrofa).

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.

Liquid chromatographic enantioseparation of beta-blocking agents with (1R,2R)-1,3-diacetoxy-1-(4-nitrophenyl)-2-propyl isothiocyanate as chiral derivatizing agent

The applicability of (1R,2R)-1,3-diacetoxy-1-(4-nitrophenyl)-2-propyl isothiocyanate [(R,R)-DANI] as a recently developed chiral derivatizing agent for the enantioseparation of a series of beta-blockers is described. The thiourea diastereomers formed were analyzed by reversed-phase high-performance liquid chromatography, mixtures of water and methanol or acetonitrile being used for elution. Conditions of derivatizations (temperature, reagent excess and reaction time) were optimized, and the effects of organic modifiers on the retention and separation were investigated; the diastereomers could readily be baseline separated with methanol-containing mobile phases with resolutions between 1.58 and 2.72.

Detection of beta-blockers in human urine by GC-MS-MS-EI: perspectives for the antidoping control

We have developed a general method for the detection of beta-blockers and/or of their metabolites in human urine. The method comprises a pretreatment procedure (enzymatic hydrolysis, liquid/liquid extraction and derivatization by pentafluoropropionic anhydride, PFPA), carried out on an initial aliquot of 2.5-5.0 ml of urine, and the instrumental analysis of the derivatives, performed by GC-MS-MS (ion trap) with electronic impact ionization (EI). The GC-MS-MS analysis allows to isolate and to characterize specific fragments of the original molecular structure, and particularly the fragments originating from parent ion clusters specific for all beta blocking drugs, giving rise to m/z = 366 and 202 ions respectively. MS-MS analysis of the parent ion allows checking for the presence of the above-mentioned peaks in the GC-MS chromatogram. The proposed method is capable of detecting a great variety of known (and possibly also of newly synthesized) beta-blockers, with an average sensitivity limit of 20 ng/ml of drug/metabolite in urine. The method is presently being evaluated as a general screening protocol to be followed by an antidoping laboratory to detect illicit beta-blockers administration to the athletes.

Automated in-tube solid-phase microextraction coupled with liquid chromatography/electrospray ionization mass spectrometry for the determination of beta-blockers and metabolites in urine and serum samples

The technique of automated in-tube solid-phase microextraction (SPME) coupled with liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS) was evaluated for the determination of beta-blockers in urine and serum samples. In-tube SPME is an extraction technique for organic compounds in aqueous samples, in which analytes are extracted from the sample directly into an open tubular capillary by repeated draw/eject cycles of sample solution. LC/MS analyses of beta-blockers were initially performed by liquid injection onto a LC column. Nine beta-blockers tested in this study gave very simple ESI mass spectra, and strong signals corresponding to [M + H]+ were observed for all beta-blockers. The beta-blockers were separated with a Hypersil BDS C18 column using acetonitrile/methanol/water/acetic acid (15:15:70:1) as a mobile phase. To optimize the extraction of beta-blockers, several in-tube SPME parameters were examined. The optimum extraction conditions were 15 draw/eject cycles of 30 microL of sample in 100 mM Tris-HCl (pH 8.5) at a flow rate of 100 microL/min using an Omegawax 250 capillary (Supelco, Bellefonte, PA). The beta-blockers extracted by the capillary were easily desorbed by mobile-phase flow, and carryover of beta-blockers was not observed. Using in-tube SPME/LC/ESI-MS with selected ion monitoring, the calibration curves of beta-blockers were linear in the range from 2 to 100 ng/mL with correlation coefficients above 0.9982 (n = 18) and detection limits (S/N = 3) of 0.1-1.2 ng/mL. This method was successfully applied to the analysis of biological samples without interference peaks. The recoveries of beta-blockers spiked into human urine and serum samples were above 84 and 71%, respectively. A serum sample from a patient administrated propranolol was analyzed using this method and both propranolol and its metabolites were detected.

Introduction to the application of capillary gas chromatography of performance-enhancing drugs in doping control

Performance-enhancing drugs banned by antidoping rules are detected in doping control preferably by hyphenated chromatographic techniques, capillary gas chromatography in particular. Based on the prohibited classes of substances and on the general aspects of sample collection and preparation, a survey is given about the usual procedures of screening, identification and confirmation of the most important doping agents: stimulants, narcotics, anabolics, diuretics, beta-blockers. In addition to gas chromatography itself, the application of various MS techniques doping is outlined.

Determination of pindolol enantiomers in human plasma and urine by simple liquid-liquid extraction and high-performance liquid chromatography

A simple method for the measurement of pindolol enantiomers by HPLC is presented. Alkalinized serum or urine is extracted with ethyl acetate and the residue remaining after evaporation of the organic layer is then derivatised with (S)-(-)-alpha-methylbenzyl isocyanate. The diastereoisomers of derivatised pindolol and metoprolol (internal standard) are separated by high-performance liquid chromatography (HPLC) using a C18 silica column and detected using fluorescence (excitation gamma: 215 nm, emission gamma: 320 nm). The assay displays reproducible linearity for pindolol enantiomers with a correlation coefficient of r2> or =0.998 over the concentration range 8-100 ng ml(-1) for plasma and 0.1-2.5 microg ml(-1) for urine. The coefficient of variation for accuracy and precision of the quality control samples for both plasma and urine are consistently <10%. Assay parameters are similar to those of previously published assays for pindolol enantiomers, however this assay is significantly easier and cheaper to run. Clinically relevant concentrations of each pindolol enantiomer can readily be measured.

Stimulants, narcotics and beta-blockers: 25 years of development in analytical techniques for doping control

More than 25 years of developing doping control methods have led to comprehensive screening and confirmation procedures for stimulants, narcotics and beta-blockers. Much of this work has been initiated and/or improved by the late Prof. Dr. Manfred Donike. The methodological approach covered in this overview was applied to doping control procedures during the XXV Summer Olympics in Barcelona, Spain, in 1992 and the XVII Winter Olympics in Lillehammer, Norway, in 1994. Urine samples are screened through a combination of two analytical methods that are complementary: (a) gas chromatographic analysis of the parent compound and unconjugated metabolites, following single-step sample extraction and detection by a nitrogen-specific detector based on a retention index identification system and (b) gas chromatographic analysis including also conjugated drugs and metabolites after hydrolysis, solid-phase extraction, derivatisation and mass spectrometric detection. Confirmation and identification is always performed by gas chromatographic separation and full scan mass spectrometric detection. These methods facilitate the rapid screening and confirmation of more than 100 stimulants, narcotic analgesics and beta-blockers in urine for at least 24 h after the intake of a pharmaceutical dose. Application of the methods ensures high quality standards for the unequivocal identification of doping agents as well as a rapid turnaround time for sample analyses.

Determination of analytical error function for beta-blockers as a possible weighting method for the estimation of the regression parameters

Three analytical methods have been developed and validated for the quantification of beta-blockers (celiprolol, bisoprolol and oxprenolol) using high performance liquid chromatography (HPLC) with UV detection. The methods were determined to be linear, precise and accurate (RSDs were lower than 5%), which allowed the quantitation of beta-blockers assayed at concentrations in the range 25-0.78 micrograms ml-1. After validation of reversed-phase HPLC methods, their analytical error functions were established by a rapid, simple and economical procedure. The discrimination of the best function for each active principle was performed by an appropriate polynomial statistical analysis, yielding SD (microgram ml-1) = 0.0295 + 0.0124C - 3.88 x 10(-4)C2 for celiprolol, 0.0199 + 0.011C - 1.27 x 10(-5)C3 for bisoprolol; and 0.0183 + 0.0089C - 9.68 x 10(-6)C3 for oxprenolol. These analytical error functions are an alternative to the weighting methods used in parameter estimation of beta-blockers.

Solid-phase extraction on Styrosorb cartridges as a sample pretreatment method in the stereoselective analysis of propranolol in human serum

Sample pretreatment using solid-phase extraction (SPE) on cartridges filled with small-particle Styrosorb porous polystyrene-based sorbent has been used in the analysis of propranolol enantiomers in human serum by high-performance liquid chromatography (HPLC) with fluorescent detection. SPE on Sep-Pak C18 cartridges was used as a reference pretreatment method. The propranolol content of the samples was determined by achiral normal-phase HPLC and the enantiomeric ratio of propranolol (S/R) was then determined by chiral HPLC on a column with silica-bonded cellulose-tris(3,5-dimethylphenyl carbamate). Recoveries of propranolol from serum using SPE on Styrosorb and C18 phases were 97 +/- 5% and 96 +/- 5%, respectively. Detection and quantification limits for propranolol enantiomers were 4 and 7 ng/ml, respectively.

Ion-pair chromatography and micellar electrokinetic capillary chromatography in analyzing beta-adrenergic blocking agents from human biological fluids

Ion-pair chromatography (IPC) and micellar electrokinetic capillary chromatography (MECC) were used for the separation and determination of parent beta-blockers from human biological fluids. In both these techniques, N-cetyl-N,N,N-trimethylammonium bromide (CTAB) was used as a buffer additive. In IPC, CTAB was an ion-pair former, and in MECC it was a micelle-forming surfactant. The effectiveness of the IPC method using methanol-gradient elution and that of MECC were compared for drug-spiked serum and urine samples. Detection was performed with a diode-array detector in the IPC method and with a 214-nm filter in the MECC technique. In both methods a phosphate buffer (pH 7.0) was used. In MECC the buffer solution contained 10 mM CTAB, while in IPC the CTAB concentration was decreased from 7 to 4 mM during the separation when a methanol gradient was used. The study showed that the IPC technique performed better for bioanalyses than the high-performance MECC technique, since in MECC UV detection presented a problem because of the low sample concentration. However, in MECC sample preparation was less time-consuming, using hydrolyzation and protein precipitation and, unlike the IPC technique, it did not require any liquid-liquid extraction step.

The enantiomeric separation of metipranolol and desacetylmetipranolol on a cellulose tris-3,5-dimethylphenyl-carbamate chiral stationary phase

A high-performance liquid chromatographic (HPLC) method is described for direct separation of the enantiomers of metipranolol and its principal degradation product and main metabolite, desacetylmetipranolol. Separations are performed on a chiral stationary phase of cellulose tris-3,5-dimethylphenyl carbamate (Chiralcel OD), with hexane-propan-2-ol-diethylamine elution and UV detection at 278 nm. The method affords identification and determination of the optical purity of the bulk drug and its formulated ophthalmic products.

Methods for the analysis of enantiomers of racemic drugs application to pharmacological and pharmacokinetic studies

Although the existence and differences in biological behavior of optical isomers have long been appreciated, there has been an apparent reluctance to address these differences in pharmacology and the pharmaceutical sciences. At least part of this reluctance arises from the belief that the separation of enantiomers requires highly specialized analytical equipment and expertise. The purpose of this review is to present general principles that allow the separation of stereoisomers and demonstrate that these procedures can be accomplished using available and convenient chromatography techniques.

Systematic toxicological analysis of drugs and their metabolites by gas chromatography-mass spectrometry

Gas chromatographic-mass spectrometric (GC-MS) procedures for the systematic toxicological analysis of several categories of drugs relevant to clinical toxicology, forensic toxicology and doping control are reviewed. Papers from 1981 to 1991 are taken into consideration. They describe the detection of acute or chronic intoxication and the detection of drug abuse. Screening procedures are included for the following categories: barbiturates and other sedative-hypnotics, anticonvulsants, benzodiazepines, antidepressants, phenothiazine and butyrophenone neuroleptics, central stimulants (amphetamines, cocaine), hallucinogens (LSD, phencyclidine, tetrahydrocannabinol), opioid (narcotic) and other potent analgesics, non-opioid analgesics, antihistamines (histamine H1-receptor blockers), antiparkinsonian drugs, beta-blockers (beta-adrenoceptor blockers), antiarrhythmics (class I and IV), diuretics, laxatives and their metabolites. Methods for confirmation of results obtained by screening procedures using immunoassay or chromatographic techniques are also included. GC-MS procedures for the simultaneous detection of several categories of drugs, the so-called "general unknown analysis", are reviewed. The toxicological question to be answered and the consequence for the choice of an adequate method, the sample preparation and the chromatography itself are discussed. The basic information about the biosample assayed, work-up, GC column, mass spectral detection mode, reference data and sensitivity of each procedure are summarized in tables, arranged according to the category of drug. Examples of typical GC-MS applications are presented. Fragment ions that are suitable for mass spectral screening for particular categories of drugs and for general unknown are tabulated.

Stereospecific high-performance liquid chromatographic assay of metoprolol

A valid, sensitive high-performance liquid chromatographic technique is reported for the separation of the two enantiomers of metoprolol in human plasma. The procedure involves pre-column derivatization with the homochiral reagent S-(+)-1-(1-naphthyl)ethyl isocyanate. Once formed, the diastereomers are separated using normal-phase high-performance liquid chromatography. Fluorescence detection (220 nm excitation; no emission filter) was utilized, resulting in baseline resolution (Rs greater than 1.5). The peaks corresponding to metoprolol enantiomers were free from interference throughout the examined range of 5-500 ng/ml; accuracy and precision were within approximately 10%. Analysis of a plasma sample collected from a healthy volunteer demonstrated that the assay is applicable to clinical studies.

The chiral chromatographic separation of β-adrenoceptor blocking drugs

Over 100 chromatographic procedures for the separation of beta-blocker enantiomers are reviewed including a large number for the analysis of biological samples. All the principal chiral chromatographic procedures have found use, namely Chiral Mobile Phase Additives (CMPA), Chiral Derivatization Agents (CDA) and Chiral Stationary Phases (CSP). Chiral Mobile Phase Additives are less frequently employed than the other two procedures and many of the earlier methods were based on the use of CDAs. However, the recent development of sophisticated custom-made CSPs has allowed the separation of native (underivatized) analytes and this approach appears to be gaining in popularity. The beta-blockers are an extensive group of drugs and stereoselective separations have been reported for 40 different structures.

Chiral stationary phase designed for beta-blockers

A chiral stationary phase (CSP) derived from an N-3,5-dinitrobenzoyl-alpha-amino phosphonate was prepared for the direct separation of the enantiomers of underivatized beta-blockers. Structure-chromatographic activity relationships for beta-blockers and closely related analogues are reported for this CSP and are found to be consistent with the model used to design this CSP. The effect of temperature on the chromatographic behavior of beta-blocker enantiomers is unusual. A reduction in temperature reduces the retention of the less retained enantiomer and increases the retention of the more retained enantiomer without appreciable band broadening.