Optimization of selectivity in micellar chromatographic procedures for the determination of drugs in urine by direct injection

Application of Micellar Mobile Phase for Quantification of Sulfonamides in Medicated Feeds by HPLC-DAD

Rapid chromatographic procedure for quantification of five sulfonamides in medicated feeds are proposed. Satisfactory separation of sulfonamides from medicated feeds was achieved using a Zorbax Eclipse XDB C18 column (4.6 × 150 mm, 5 µm particle size) with a micellar mobile phase consisting of 0.05 M sodium dodecyl sulphate, 0.02 M phosphate buffer, and 6% propan-2-ol (pH 3). UV quantitation was set at 260 nm. The proposed procedure allows the determination of sulfaguanidine, sulfadiazine, sulfamerazine, sulfamethazine, and sulfamethoxazole in medicated feeds for pigs and poultry. Application of the proposed method to the analysis of five pharmaceuticals gave recoveries between 72.7% to 94.7% and coefficients of variations for repeatability and reproducibility between 2.9% to 9.8% respectively, in the range of 200 to 2000 mg/kg sulfonamides in feeds. Limit of detection and limit of quantification were 32.7–56.3 and 54.8–98.4 mg/kg, respectively, depending on the analyte. The proposed procedure for the quantification of sulfonamides is simple, rapid, sensitive, free from interferences and suitable for the routine control of feeds. In the world literature, we did not find the described method of quantitative determination of sulfonamides in medicated feeds with the use of micellar liquid chromatography.

Comparative study of two different chromatographic approaches for quantitation of hydrocortisone acetate and pramoxine hydrochloride in presence of their impurities

In the present study, we compare the performance of two reversed-phase liquid chromatographic approaches using different eluents either conventional hydro-organic eluent or micellar one for simultaneous estimation of hydrocortisone acetate and pramoxine hydrochloride in presence of their degradants and process-related impurities; hydrocor-tisone and 4-butoxyphenol, respectively. For conventional reversed-phase liquid chromatography (RPLC), separation of the studied compounds was completed on an Inertsil ODS 3-C18 column (150 mm × 4.6 mm, 5 μm particle size) with a mobile phase consists of 50 mM phosphate buffer (pH 5.0): acetonitrile (50: 50, v/v). For micellar liquid chromatography (MLC), an Eclipse XDB-C8 column (150 mm × 4.6 mm, 5 μm particle size) was chosen for the separation with a green mobile phase consists of 0.15 M sodium dodecyl sulfate, 0.3% triethylamine and 10% n-butanol in 20 mM orthophosphoric acid (pH 5.0). Both methods were extended to analyze hydrocortisone acetate and pramoxine hydrochloride in their co-formulated cream. RPLC was superior to MLC with regard to sensitivity for the estimation of impurities. While, MLC represents an eco-friendly, less hazardous and biodegradable approach. Furthermore, the direct injection of the cream to the system without the need to laborious samples pretreatment, excessive amount of analysis time and/or use of large amount of toxic organic solvents is one of the outstanding advantages of MLC.

Micellar liquid chromatography in doping control

The issue of doping control in sport involves the development of reliable analytical procedures and efficient strategies to process a large number of samples in a short period of time. Reversed-phase LC techniques with aqueous-organic mobile phases and MS or diode-array detection yield satisfactory results for the identification of prohibited substances in sport. However, time-consuming sample pretreatment steps are required, which reduces sample throughput. Micellar LC (MLC) that uses hybrid mobile phases of surfactant above its critical micellar concentration and organic solvent has been revealed as an interesting alternative. The surfactant sodium dodecyl sulfate solubilizes the protein components of urine, serum and plasma, which permits their direct injection into the chromatographic system. Only dilution and filtering of the samples may be required. Most MLC analyses are performed in isocratic mode, with short retention times and good selectivity. The sensitivity of MLC allows the detection of a variety of doping substances at least 24-48 h after being administered.

Micellar liquid chromatographic analysis of benzyl alcohol and benzaldehyde in injectable formulations

An accurate, sensitive and selective reversed-phase micellar liquid chromatographic method was developed for simultaneous determination of benzyl alcohol and benzaldehyde. This method was applied in different injectable formulations containing diclofenac, piroxicam, lincomycin and clindamycin. The method showed excellent linearity in the range of 10-100 microg mL(-1) and 1-20 microg mL(-1) with the limit of detection (S/N = 3) 0.25 microg mL(-1) (2.3 x 10(-6) mol L(-1)) and 0.12 microg mL(-1) (1.13 x 10(-6) mol L(-1)) for benzyl alcohol and benzaldehyde, respectively. The suggested method was successfully applied to the analysis of the studied drugs in bulk with average recoveries of 100.1 +/- 1.0% for benzyl alcohol and 100.4 +/- 1.6% for benzaldehyde, and to the determination of benzyl alcohol and benzaldehyde in injectable formulations with the respective average recoveries of 99.8 +/- 0.3 and 100.0 +/- 0.4%.

Simultaneous high-performance liquid chromatographic assay of furosemide and propranolol HCL and its application in a pharmacokinetic study

A practical, sensitive, selective and efficient reversed-phase high-performance liquid chromatographic (HPLC) method is reported for the determination of two commonly used antihypertensive drugs, furosemide and propranolol hydrochloride. The drugs were eluted through a Nucleosil C(18) column with a mobile phase composed of 0.02 M potassium dihydrogen phosphate and acetonitrile (80:20, v/v) adjusted to pH 4.5 and the effluent from the column was monitored at 235 nm. The present method enabled simple and isocratic HPLC with UV detection of these drugs in raw materials and in pharmaceutical formulations. These procedures were also applied for the assay of furosemide in rabbits' plasma, using propranolol hydrochloride as an internal standard. The linear concentration range of the assay was 0.1-200 and 5-200 microg ml(-1) for furosemide and propranolol hydrochloride, respectively. The inter and intra-day assay precision and accuracy showed reproducibility and good linearity (r(2)>0.99). The method retained its accuracy and precision when applying the standard addition technique. The results obtained by applying the proposed method was statistically analysed and compared with those obtained by the reported methods.

Rapid analysis of furosemide in human urine by capillary electrophoresis with laser-induced fluorescence and electrospray ionization-ion trap mass spectrometric detection

Furosemide, a drug that promotes urine excretion, is used in the pharmacotherapy of various diseases and is considered as a doping agent in sports. Using alkaline electrolytes, analysis of furosemide by dodecyl sulfate based micellar electrokinetic capillary chromatography (MECC) and capillary zone electrophoresis (CZE) with laser-induced fluorescence detection (LIF, analyte excitation with the 325 nm line of a HeCd laser) is described. Data produced by injection of plain or diluted patient urines are confirmed with those obtained via analysis of urinary solid-phase extracts. CZE-LIF and MECC-LIF are thereby shown to permit unambiguous recognition of furosemide in urines collected after ingestion of therapeutic doses of this drug. This is in contrast to solute detection via UV absorbance for which the extraction of furosemide is required. MECC based electropherograms are somewhat more complex compared to those obtained by CZE-LIF, this suggesting that the latter approach is more suitable for rapid screening of urines with direct sample injection and LIF detection. Alternatively, capillary electrophoresis with negative electrospray ionization-ion-trap tandem mass spectrometry (CE-MS2) is shown to permit the direct confirmation of furosemide in human urine. This approach is based upon the monitoring of the m/z 329.3-->4m/z 285.2 precursor-product ion transition. CZE-LIF and CE-MS2 with injection of plain or diluted urine represent simple, rapid and attractive urinary screening and confirmation assays for furosemide in patient urines.

Micellar liquid chromatography: suitable technique for screening analysis

The screening capability of micellar liquid chromatography (MLC) is discussed using the reported chromatographic data of several sets of compounds (amino acids, beta-blockers, diuretics, phenethylamines, phenols, polynuclear aromatic hydrocarbons, steroids and sulfonamides) and new results (sulfonamides and steroids). The chromatographic data are treated with an interpretive optimisation resolution procedure to obtain the best separation conditions. Usually, the pH and the concentration of surfactant (sodium dodecyl sulfate, SDS, or cetyltrimethylammonium bromide) for the optimal mobile phase were 2.5-3 and < 0.12 M, respectively. The nature and concentration of organic solvent depended on the polarity of the eluted compounds: a low volume fraction of propanol (approximately 1%, v/v) was useful to separate the amino acids, with log P(o/w) < -1 (where P(o/w) is the octanol-water partition coefficient). A greater concentration of this solvent (approximately 5-7%) was needed for compounds in the range -1 < log P(o/w) < 2, as with the studied diuretics and sulfonamides, and a high concentration of propanol (approximately 15%) or a low concentration of butanol (< 10%) had to be used for less polar compounds with 1 < log P(o/w) < 3, such as the beta-blockers. Pentanol (< 6%) was more suitable for the even less polar compounds with log P(o/w) > 3, such as the steroids. For basic drugs such as the phenethylamines (0 < log P(o/w) < 1.7), eluted with a micellar eluent of anionic SDS, propanol was too weak. A study is also shown for mixtures of sulfonamides (log P(o/w) = -1.2 to 1.7) and steroids (log P(o/w) = 3.0-8.1) eluted from conventional C18 columns with SDS mobile phases containing acetonitrile and 1-pentanol, respectively, which are compared with classical acetonitrile-water and methanol-water mixtures. The results complement a previous study on beta-blockers (log P(o/w) = -0.03 to 2.8) and reveal that MLC is a very competitive technique for the screening of compounds against conventional RPLC, due to its peculiar behaviour with regard to the selectivity and elution strength. The concentration of organic solvent needed to obtain sufficiently low retention times (even for highly hydrophobic steroids with log P(o/w) = 7-8) is also appreciably smaller for MLC, which reduces the environmental impact of the mobile phases.

Liquid extraction and HPLC-DAD assay of hydrochlorothiazide from plasma for a bioequivalence study at the lowest therapeutic dose

The main parameters considered in optimizing the liquid extraction and quantitative assay were the yield, precision, limit of quantification, time required for extraction and concentration, and quantity of solvent. The influence on these parameters of the following factors was examined: nature of the extracting solvent, quantity of solvent, co-extraction solvent, and duration of stirring. Instead of equilibrium parameters of the involved thermodynamic system, a kinetic approach was preferred in terms of the effective partition 'constant', which is not really constant but a function of time and extraction conditions. The final selected method, considered to be rapid and simple, was applied to determine the pharmacokinetics of hydrochlorotiazide (HCT) after administration of Capozide (Bristol-Myers Squibb) tablets containing 50 mg Captopril and 25 mg HCT, to 4 healthy volunteers. The results obtained were in accordance with the pharmacokinetic parameters of HCT reported in the literature.

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.

Micellar liquid chromatography: a worthy technique for the determination of beta-antagonists in urine samples

Several beta-antagonists (acebutolol, atenolol, celiprolol, labetalol, metoprolol, nadolol, propranolol) were determined in urine samples with fluorometric detection after direct injection, in less than 15 min, with a micellar mobile phase of 0.1 M sodium dodecyl sulfate (SDS), 15% propanol, and 1% triethylamine at pH 3. The limits of detection (38 criterion) were usually between 3 and 30 ng/mL. The addition of propanol and triethylamine and the reduction of the pH of the mobile phase improved the efficiency of the chromatographic peaks that was rather low in pure micellar eluents. The selection of the composition of the mobile phase was easily performed through the use of an interpretive procedure which considered the retention times and peak shapes of the beta-antagonists in six chromatograms, obtained at varying concentrations of SDS (0.05-0.15 M) and propanol (5-15% v/v). The chromatograms of urine samples from healthy volunteers, which were administered atenolol, metoprolol, and propranolol, showed only one peak for the former drug and several peaks for the other two. These peaks corresponded to the parent drug and metabolites, which indicated the partial and the extensive degradation of metoprolol and propranolol, respectively.

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.

Comparison of two extraction methods for determination of propranolol and furosemide in human plasma by mixed-mode chromatography

An isocratic high performance liquid chromatographic method is described for the determination of the beta-adrenergic blocking drug, propranolol, and the diuretic, furosemide, in human plasma. The two compounds and the internal standard were extracted from plasma using a two-step extraction technique. Propranolol and pindolol (internal standard) were first extracted from alkaline plasma into diethyl ether; this was followed by extraction of furosemide into acidified ether: hexane (65:35). The two extracts were then combined and evaporated under nitrogen, and the reconstituted residues were analysed on a C18/SCX reversed-phase/cation exchange column with a mobile phase of acetonitrile: 0.1 M sodium acetate pH 4 (33:67). The drugs and the internal standard were detected by UV absorption at 230 nm. The drugs were also extracted from plasma by a column-switching technique utilizing a ten-port valve. The drug compounds were retained on a C18 pre-column. A comparison of RSD for within-batch (intra-assay) and between-batch (inter-assay) runs for both methods was carried out, the liquid/liquid extraction method giving better recovery values. The calibration graphs were linear from 25-300 ng ml-1 for furosemide and 50-400 ng ml-1 for propranolol. Recovery values were > 90.0% by liquid/liquid extraction and > 76.0% by column switching.

Determination of sulphonamides in human urine by azo dye precolumn derivatization and micellar liquid chromatography

A high-performance liquid chromatographic method for the determination of sulphonamides in urine is reported. The drugs (sulphadiazine, sulphaguanidine, sulphamethizole, sulphamethoxazole, and sulphathiazole) were diazotized with nitrite and coupled with N-(1-naphthyl)ethylenediamine dihydrochloride in a sodium dodecyl sulphate (SDS) micellar medium. Separation of the sulphonamide azo dyes was performed on a C18 column with a 0.05 M SDS-2.4% pentanol mobile phase, which permitted the direct injection of the urine samples. The limits of detection were in the 0.1-0.3 micrograms/ml range.

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.

A micellar liquid chromatographic procedure for the determination of amiloride, bendroflumethiazide, chlorthalidone, spironolactone and triamterene in pharmaceuticals

A procedure for the determination of amiloride, bendroflumethiazide, chlorthalidone, spironolactone and triamterene in pharmaceutical preparations (tablets) by micellar liquid chromatography, using a 0.07 M SDS-0.5% pentanol mobile phase, is proposed. Recoveries were found in the 100-108% range, with relative standard deviations of 0.4-3.1%. Elution of the most retained diuretics occurred in less than 18 min (at a 1 ml min-1 flow rate). The change in the values of the solute-micelle binding constants and the partition coefficients of the diuretics between the stationary phase and water, upon addition of pentanol, was also studied.

Separation of (R)- and (S)-naproxen using micellar chromatography and an alpha 1-acid-glycoprotein column: application for chiral monitoring in human liver microsomes by coupled-column chromatography

A column-switching system for fast determination of (R)- and (S)-naproxen in liver microsomes has been developed. The centrifuged sample was injected directly onto a pre-column with octadecylcoated silica. The retained analytes were then directed to an alpha 1-AGP column using a mobile phase composed of phosphate buffer (pH 6.5), dimethylocytylamine (30 mM) and the nonionic surfactant, Tween 20 (40 g/l). The method gave high absolute recoveries and good repeatabilities: 99.6% (1.7% relative standard deviation) and 94.9% (2.4% R.S.D.) for the (R)- and (S)-naproxen, respectively. The use of a surfactant in combination with an aliphatic amine in the mobile phase involves reduced retention times with retained enantioselectivity. Furthermore, the presence of the surfactant makes it possible to inject biological samples directly into the chromatographic system.

High-performance liquid chromatographic determination of diuretics in urine by micellar liquid chromatography

The use of micellar liquid chromatography for the determination of diuretics in urine by direct injection of the sample into the chromatographic system is discussed. The retention of the urine matrix at the beginning of the chromatograms was observed for different sodium dodecyl sulphate (SDS) mobile phases. The eluent strengths of a hybrid SDS-methanol micellar mobile phase for several diuretics were compared and related to the stationary phase/water partition coefficient with a purely micellar mobile phase. The urine band was appreciably narrower with a mobile phase of 0.05 M SDS-5% methanol (v/v) at 50 degrees C (pH 6.9). With this mobile phase the determination of bendroflumethiazide and chlorthalidone was adequate. Acetazolamide, ethacrynic acid, furosemide, hydrochlorothiazide and probenecid were overlapped by the urine matrix, and the retention of amiloride and triamterene was too long.

Determination of sun-screen agents in cosmetic products by micellar liquid chromatography

A micellar liquid chromatographic method was developed for the quantitative determination of sun-screen agents in cosmetic products. The qualitative analysis of parabens is also feasible. Excellent linearity was obtained (r = 0.999) and recoveries were generally greater than 98%. A variety of commercial formulations were analyzed.