Application of micellar mobile phases for the assay of drugs in biological fluids

Micellar liquid chromatographic green enantioseparation of racemic amino alcohols and determination of elution order

A micellar liquid chromatographic method was developed for the green enantioseparation of racemic amino alcohols using an aqueous solution of the mixed surfactants as an alternative for organic solvents. In this study, the derivatives of the amino alcohols were synthesized using highly reactive chiral esters of (S)-levofloxacin (Lfx) under microwave conditions, and an aqueous solution of the surfactants (Brij-35 and SDS) was used for the enantioseparation of the synthesized diastereomeric derivatives (DDs) of amino alcohols using reversed-phase HPLC. The activated ester of Lfx was synthesized by reacting with N-hydroxybenzotriazole and characterized using UV, IR, ¹ H NMR, high-resolution mass spectrometry, and elemental analysis. The DDs of racemic amino alcohols were separated on a C₁₈ column using micellar LC. Chromatographic conditions were optimized by varying the concentration of the surfactants in aqueous solution and by varying the concentration and pH of the buffer. The green assessment score was calculated for the developed method (score: 82, an excellent green method). In addition, the density functional theory calculations were performed to develop the lowest energy-optimized structures of DDs. The method was validated according to the International Conference of Harmonization guidelines, and the retention factor (k), selectivity factor (α), resolution factor (R_S ), limit of detection (0.198 ng mL^-1 or 0.291 pM mL^-1 ), and limit of quantification (0.594 ng mL^-1 or 0.873 pM mL^-1 ) were calculated.

An efficient method for the determination of enantiomeric purity of racemic amino acids using micellar chromatography, a green approach

A simple, sensitive and green micellar liquid chromatographic method (RP-HPLC) was developed for enantioseparation of four racemic amino acids, namely, (RS)-selenomethionine, (RS)-methionine, (RS)-cysteine and (RS)-penicillamine. An aqueous solution of sodium dodecyl sulfate and Brij-35 was prepared and used as mobile phase for HPLC analysis. Activated esters of (S)-ibuprofen, (S)-ketoprofen and (S)-levofloxacin were synthesized by reacting them with N-hydroxybenzotriazole. These esters were characterized by UV, IR, ¹ HNMR, HRMS and elemental analysis. These chiral reagents (activated esters) were used for the synthesis of diastereomeric derivatives of the chosen amino acids. The diastereomeric derivatives were separated on a C₁₈ column by micellar liquid chromatography. Chromatographic conditions were optimized by varying concentration of surfactant in aqueous solution, and by varying the concentration and pH of the buffer. The green assessment score was calculated for the developed method (78, an excellent green method score). In addition, density functional theory calculations were performed, using Gaussian 09 rev. A.02 and hybrid density functional B3LYP with a 6-31G* basis set program, in order to develop lowest energy optimized structures of diastereomeric derivatives. The method was validated according to International Conference on Harmonization guidelines and the retention factor (k), selectivity factor (α), resolution factor (R_S ) and limit of detection (0.295 ng ml^-1 ) and limit of quantification (0.896 ng ml^-1 ) were calculated.

Direct injection HPLC method for the determination of selected benzodiazepines in plasma using a Hisep column

A direct plasma injection HPLC method has been developed for the determination of selected benzodiazepines (nitrazepam, clobazam, oxazepam, lorazepam). The method uses an analytical hydrophobic shielded phase (Hisep) column equipped with a Hisep guard column, are easy to perform and requires 20 ul of a filtered plasma sample. The chromatographic run time is less than 15 min using a mobile phase of 15:85 v/v acetonitrile-0.18 M ammonium acetate pH 2.5. The method is good for 175 injections before replacement of the guard column. The method was linear in the range 0.5-18 ug ml(-1) (r>0.99, n=6) for the analytes with R.S.D. less than 10.82%. Interday and intraday variability were found to be less than 14%. The limits of detection and quantitation were 0.16 (s/n>3) and 0.5 ug ml(-1) (s/n>10), respectively, for each of the four benzodiazepines.

Direct injection HPLC method for the determination of selected phenothiazines in plasma using a Hisep column

A direct plasma injection HPLC method has been developed for the determination of selected phenothiazines (promethazine, promazine, chlorpromazine) using a Hisep column. The method is easy to perform and requires 20 microL of a filtered plasma sample. The chromatographic run time is less than 11 min using a mobile phase of 15:85 v/v acetonitrile-0.18 m ammonium acetate pH 5.0 and UV detection at 254 nm. The method is linear in the concentration range 0.1-25 microg mL(-1) (r > 0.99, n = 6) for each analyte with RSD less than 6%. Interday and intraday variability were found to be < or =14%. The limits of detection and quantitation were 0.1 (S/N > 3) and 0.25 microg mL(-1) (S/N > 10), respectively, for each of the three phenothiazines. We can also apply this method to separate three other phenothiazines (ethopromazine, trifluoroperazine, prochlorperazine), although it lacks the selectivity to determine the concentration of all six drugs concurrently. The separation is feasible using these drugs in certain combinations.

Determination of phenobarbital in plasma by micellar liquid chromatography

A new liquid chromatographic procedure for the determination of phenobarbital in plasma samples is described. The proposed system uses a Spherisorb octadecyl-silane ODS-2 C(18) analytical column, a guard column of similar characteristics, and a 0.03 M CTAB-3% 1-propanol at pH 7 mobile phase. The UV detector was set at 250 nm. Butabarbital was used as internal standard. Sample preparation only required the addition to the plasma samples of a 0.1 M SDS solution at pH 3 and centrifugation before injection into the chromatographic system. The limit of detection was 0.83 microg/mL of phenobarbital in plasma samples. The coefficients of variation were lower than 7. 5%.

Direct injection of physiological fluids in micellar liquid chromatography

Micellar liquid chromatography (MLC), which uses mobile phases of surfactants above the critical micellar concentration, provides a solution to the direct injection of physiological samples by solubilizing the protein components, and coating the analytical column with surfactant monomers to avoid clogging. A review showing the advantages and limitations of this technique over other chromatographic techniques used in drug analysis, working protocols, and examples of application is presented. The possibility of direct sample introduction simplifies and greatly expedites the treatments with reduced cost, improving the accuracy of the procedures. Surfactant monomers and micelles appear to displace drugs bound to proteins, releasing them for partitioning to the stationary phase. The versatility of MLC encompasses the wide range of drug classes normally monitored, such as analgesics, anticancer drugs, antidepressants, bacteriostats, beta-blockers, bronchodilators, catecholamines, diuretics and steroids, among others. Analytical procedures have been developed in urine, plasma, serum and cow milk samples. Most of them utilize sodium dodecyl sulphate as surfactant and a C18 column. UV detection is usual, but enhanced detection has been reported by measuring the absorbance in the visible region of drug derivatives formed precolumn, and with a variety of other techniques, such as fluorimetry, amperometry, inductively coupled plasma-mass spectrometry and immunoassay. Column-switching with on-line surfactant-mediated sample clean-up is shown as an attractive enrichment technique, which expands the practical use of MLC beyond the singular dimensional chromatographic process.

Determination of barbiturates in urine by micellar liquid chromatography and direct injection of sample

A liquid chromatographic procedure for the determination of six barbiturates (barbital, diallyl barbituric acid, phenobarbital, butabarbital, amobarbital and pentobarbital) in urine samples is described. The proposed system uses a Spherisorb octadecyl-silane ODS-2 C18 analytical column and a guard column of similar characteristics. The UV detector was set at 240 nm. A study to select adequate composition of the micellar mobile phase for the separation of these compounds in urine samples is performed. Maximum resolution was achieved with a 0.07 M sodium dodecylsulphate-0.3% propanol at pH 7.4 eluent. Limits of detection at 240 nm were ranged between 0.13 microg ml(-1) for diallyl barbituric acid and 2.7 microg ml(-1) for amobarbital. The procedure allows for the determination of these compounds in 20 minutes, it does not require prior a sample preparation step and it can be very useful to the investigation of intoxication.

Direct injection HPLC analysis of some non-steroidal anti-inflammatory drugs on restricted access media columns

Direct serum injection methods are described for the HPLC determination of selected non-steroidal anti-inflammatory drugs (NSAIDS) on restricted access media (RAM) columns, using either a Pinkerton (ISRP) or semi-permeable surface (SPS) column. Twenty microlitres of a filtered serum sample was injected directly onto each column. Calibration curves were prepared for ketoprofen (1-20 micrograms/mL), fenbufen (0.8-20 micrograms/mL), sulindac (0.8-20 micrograms/mL) and probenecid (1.5-40 micrograms/mL) on the SPS column, and nabumetone (1.5-40 micrograms/mL) and indomethacin (1.5-40 micrograms/mL) on the Pinkerton column. The percentage error and imprecision of the methods were found to be less than 10%. The inter- and intra-day variability for analytes were in the range of 0.15-10%. The limits of quantitation and detection were in the range of 800-1500 and 300-800 ng/mL, respectively, for the analytes studied. A hydrophobic shielded phase (Hisep) column was also investigated and was found to be generally too retentive (> 29 min) for assay of these analytes.

Method for the preparation of restricted access media by low-temperature plasma treatment

A new method for the preparation of restricted access media (RAM) was developed. A low-temperature plasma treatment removed octadecyl groups on the external surface of octadecylsilylated silica gel before those on the internal surface to produce silanol groups. The silanol groups produced were glycerylpropylsilylated to give RAM, DIOL-ODSs, consisting of internal octadecyl groups and external glycerylpropyl groups. DIOL-ODSs were inert to serum proteins and retained low-molecular-mass analytes adequately. Direct injection analysis of anticonvulsants in serum was accurately performed by column-switching high-performance liquid chromatography using a pre-column packed with DIOL-ODS.

Direct injection HPLC method for the determination of phenylbutazone and oxyphenylbutazone in serum using a semipermeable surface column

A direct injection HPLC method has been developed for the determination of phenylbutazone and its active metabolite oxyphenylbutazone in serum using a semipermeable surface (SPS) column. The method is easy to perform and requires 20 microliters of a filtered serum sample. The chromatographic time is less than 13 min using a mobile phase of 15:85 v/v acetonitrile-0.05M phosphate buffer pH 7.5. The method was linear in the range 0.5-20 micrograms ml-1 (r > 0.99, n = 6) with R.S.D. less than 6%. Interday and intraday variability were found to be less than 8.3%. The limit of quantitation and detection were 0.5 and 0.25 microgram ml-1 (s/n > 3), respectively, for both drug and metabolite.

Pharmaceutical applications of micelles in chromatography and electrophoresis

This review surveys the use of micelles as separation media in chromatography and electrophoresis. Applications to pharmaceuticals whose molecular masses are relatively small are focused on in this review. In high-performance liquid chromatography (HPLC), chromatography using micelles and reversed-phase stationary phases such as octadecylsilylized silica gel (ODS) columns is known as micellar liquid chromatography (MLC). The main application of MLC to pharmaceutical analysis is the same as in ion-pair chromatography using alkylsulfonate or tetraalkylammonium. In most cases, selectivity is much improved compared with other short alkyl chain ion-pairing agents such as pentanesulfonate or octanesulfonate. Direct plasma/serum injection can be successful in MLC. Separation of small ions is also successful by using gel filtration columns and micellar solutions. In electrophoresis, especially capillary electrophoresis (CE), micelles are used as pseudo-stationary phases in capillary zone electrophoresis (CZE). This mode is called micellar electrokinetic chromatography (MEKC). Most of the drug analysis can be performed by using the MEKC mode because of its wide applicability. Enantiomer separation, separation of amino acids and closely related peptides, separation of very complex mixtures, determination of drugs in biological samples etc. as well as separation of electrically neutral drugs can be successfully achieved by MEKC. Microemulsion electrokinetic chromatography (MEEKC), in which surfactants are also used in forming the microemulsion, is successful for the separation of electrically neutral drugs as in MEKC. This review mainly describes the typical applications of MLC and MEKC for the analysis of pharmaceuticals.

Capillary electrophoretic analyses of drugs in body fluids: sample pretreatment and methods for direct injection of biofluids

A variety of strategies for the analysis of biological samples by capillary electrophoresis (CE) are described, with particular emphasis on the determination of drugs and metabolites. Analytical methods involving extensive sample pretreatment before CE analysis are considered, as well as strategies for directly injecting untreated biofluids. The application in CE of techniques common in liquid chromatography is first described, e.g. protein precipitation, liquid-liquid extraction and solid-phase extraction. On-capillary methods of sample concentration are considered. Approaches to performing CE assays of urine and plasma, without prior sample treatment, are described. The use of both capillary zone electrophoresis and micellar electrokinetic chromatography for direct-injection assays is compared for both urine and plasma analyses, and capillary washing strategies are discussed. Finally, direct-injection microanalyses are mentioned.

Determination of peptide 520 in human plasma using post-column photolysis with electrochemical detection in liquid chromatography

A simple LC method for the determination of peptide 520 in human plasma was developed. Based on micellar chromatography, sodium octyl sulphate (SOS) was added into the mobile phase in order to separate the peptide from human plasma components. The procedure was fast and sensitive for the determination of the peptide in untreated human plasma. The electrochemical (EC) detection limit for peptide 520 in human plasma was 0.5 microgram ml-1. Linearity of the calibration plot for peptide 520 in human plasma was 0.999. This approach represents a direct injection technique for the potential detection and analysis of numerous peptides in biofluids, besides just plasma, with absolute quantification.

Column-switching techniques for high-performance liquid chromatography of drugs in biological samples

In recent years, an increasing number of publications have demonstrated the potential of column-switching techniques for the chromatographic separation, determination and preparative isolation of analytes from biological matrices. Column-switching systems greatly facilitate drug analysis, by on-line sample clean-up and trace enrichment, or by improving the analytical separative process. In this paper, the main applications of column-switching techniques to drug analysis in biological samples, are reviewed.

Strategies for the monitoring of drugs in body fluids by micellar electrokinetic capillary chromatography

Electrokinetic capillary techniques can exploit numerous separation principles, making them flexible and easily applicable to a variety of separation problems. In recent publications, this emerging technology has been shown to be well suited for monitoring drugs and metabolites in body fluids, including serum, saliva and urine. Most attention has been focused on micellar electrokinetic capillary chromatography (MECC) because it permits the separation and determination of drugs with discrimination being largely based on differences in hydrophobicity. An overview of literature data on the MECC of drugs in body fluids and recent data obtained with antiepileptics in serum and saliva, with model mixtures of illicit drugs, and with extracts from urine specimens that tested positively for opiates and cocaine metabolites are presented. Emphasis is focused on buffer selection and simple sample preparation procedures, including direct injection of body fluids, ultrafiltration and solid-phase extraction.

Direct analysis of whole blood by internal surface reversed-phase chromatography: an examination of the binding and metabolism of technetium dioxime complexes

We have developed a method using internal surface reversed-phase (ISRP) packing for rapid on-line separation of small hydrophobic compounds from cellular whole blood components. This is achieved by the use of 75-microns ISRP chromatographic material packed into a small high-performance liquid chromatographic (HPLC) column, in conjunction with column switching. We have applied this analytical method to study the in vitro metabolism of 99mTc-BATO (boronic acid adducts of technetium dioxime) cerebral and myocardial perfusion tracers in whole blood. The results from the ISRP procedure were compared with a conventional centrifugation method of analysis. This novel HPLC methods provides a rapid, convenient and reliable method for the analysis of radioactive and non-radioactive lipophilic components in whole blood.