Micellar liquid chromatography: suitable technique for screening analysis

Micellar enhanced chromatographic separation of selected hazardous chemical present in hair dye and their detection in formulations and swab, including assessment of damage caused to cuticle of hair shaft

Hydroquinone (HQ), resorcinol (RS), m-aminophenol (m-AMP) and p-phenylenediamine (p-PPD) are aromatic compounds which are generally used in hair dyes to provide different colours to hair. In European Union the concentrations of HQ, RS, m-AMP and p-PPD is regulated in hair dyes and other cosmetic products by EU commission regulation EU/2019/831. This legislation is generally exercised because all these compounds are toxic and may cause severe allergies when used regularly. However in India no such regulations exist to monitor these toxic compounds in hair dyes therefore in this study a simple, rapid, economical and ecofriendly micellar liquid chromatographic (MLC) technique has been developed which can monitor all the selected toxic compounds simultaneously. HQ and RS are positional isomers and are difficult to be separated by HPLC whereas with the developed MLC method it was well separated and detected. The developed MLC technique has been applied to detect and quantify selected analytes in oxidative and non-oxidative hair dyes and swab samples from the scalp. The simultaneous separation of selected analytes was performed in mobile phase 0.09 M SDS, 0.01 M NaH2PO4-2% v/v 1-butanol at pH 7 running through C18 column under isocratic mode at 1 mL/min. flow rate. All the analytes were eluted within 6 min. The present method has been validated following the EURCHEM Guideline, 2014 in terms of calibration range (0.08-15 µg/mL), limit of detection (0.01-0.09 µg/mL), limit of quantification (0.08-0.35 µg/mL), accuracy (<5.6%), precision (91-105%) and robustness (<5.8%). The selected compounds in hair dye formulation were found in the range of 0.06-12.2 µg/mL (when diluted 25 times). Hair dyes persistence study was conducted up to 10 days from the day of application on the scalp, suggesting that the dyes were not completely washed off and were retained on the scalp for more than one week. SEM analysis of dyed hair revealed that hair are severely damaged due to use of dyes. The advantage of the developed method is that it could easily be adopted by quality control and cosmetic laboratories for quality control and check for the simultaneous separation of positional isomers together with two other aromatic compounds.

Evaluating micellar liquid chromatographic methods on octadecyl particle-based and monolithic columns to predict the skin permeation of drug and cosmetic molecules

A micellar liquid chromatographic method was developed to assist in the modeling of the skin permeability of pharmaceutical and cosmetic compounds. The composition of the mobile phase was determined by means of a two-factor central composite design, after which it was tested on both a particle-based and monolithic column. The latter provided the opportunity to increase the flow rate from 1 to 8 mL/min without reaching too high backpressures. The micellar conditions allowed analyzing a large test set of compounds with diverse characteristics with just one mobile-phase composition. The obtained experimental chromatographic descriptors besides two sets of theoretical molecular descriptors were used to model the skin permeability coefficient log K_p, applying multiple linear regression and partial least squares regression approaches. The micellar method on the monolithic column provided useful models with similar or even slightly better performance parameters than the method on the particle-based column. Furthermore, a much faster analysis can be achieved when applying a flow rate of 8 mL/min, making the micellar monolithic method ideal to estimate skin permeability.

Enhanced spectrophotometric determination of Losartan potassium based on its physicochemical interaction with cationic surfactant

In this study, a simple and sensitive spectrophotometric method was developed for determination of Losartan potassium (LST K), an angiotensin-II receptor (type AT1) antagonist, in presence of cationic surfactant cetyltrimethylammonium bromide (CTAB). The physicochemical interaction of LST K with CTAB was investigated. The effect of cationic micelles on the spectroscopic and acid-base properties of LST K was studied at pH 7.4. The binding constant (Kb) and the partition coefficient (Kx) of LST K-CTAB were 1.62×10(5) M(-1) and 1.38×10(5); respectively. The binding of LST K to CTAB micelles implied a shift in drug acidity constant (ΔpKa=0.422). The developed method is linear over the range 0.5-28 μg mL(-1). The accuracy was evaluated and was found to be 99.79±0.509% and the relative standard deviation for intraday and interday precision was 0.821 and 0.963; respectively. The method was successfully applied to determine LST K in pharmaceutical formulations.

Measurement of the elution strength and peak shape enhancement at increasing modifier concentration and temperature in RPLC

Two approaches are proposed to measure the effect of different experimental factors (such as the modifier concentration and temperature) on the elution strength and peak shape in reversed-phase liquid chromatography, which quantify the percentage change in the retention factor and peak width (referred to the weakest conditions) per unit change in the experimental factor. The approaches were applied to the separation of a set of flavonoids with aqueous micellar mobile phases of the surfactant Brij-35 (polyoxyethylene(23)dodecanol), in comparison with acetonitrile-water mixtures, using an Eclipse XDB-C18 column. The particular interaction of each flavonoid with the oxyethylene chains of Brij-35 molecules (adsorbed on the stationary phase or forming micelles) changed the elution window, distribution of chromatographic peaks and partitioning kinetics, depending on the hydroxyl substitution in the aromatic rings of flavonoids. At 25 °C, peak shape with Brij-35 mobile phases was significantly poorer with regard to acetonitrile-water mixtures. At increasing temperature, the efficiency of Brij-35 increased, approaching at 80 °C the values obtained at equilibrium conditions, already reached with acetonitrile at 25 °C.

Recent theoretical and practical applications of micellar liquid chromatography (MLC) in pharmaceutical and biomedical analysis

Micellar liquid chromatography (MLC) is an analytical technique belonging to the wide range of reversed-phase liquid chromatographic (RP-LC) separation techniques. MLC with the use of surfactant solutions above its critical micellar concentration (CMC) and the addition of organic modifiers is currently an important analytical tool with still growing theoretical considerations and practical applications in pharmaceutical analysis of drugs and other biologically active compounds. The use of MLC as an alternative, relatively much faster in comparison to conventional chromatographic separation techniques has several advantages, especially as being suitable for screening pharmaceutical analysis. The analytical data received from MLC analysis are considered a useful source of information to predict passive drug absorption, drug transport and other pharmacokinetics and physicochemical measures of pharmaceutical substances. In the review several MLC assays for determination of drugs and other active compounds in biological samples were compared and critically discussed. The presented overview provides information on recent applications and achievements connected with the practical use of MLC. The review covers fields of interest related to theory and mechanism of MLC separation, direct applications of MLC in pharmaceutical analysis, including optimization and efficiency of separation with the use of modification of stationary phase and mobile phase compositions as well as the determination of physicochemical characteristics of drugs by MLC.

Basic Principles of MLC

Micellar liquid chromatography (MLC) is an efficient alternative to conventional reversed-phase liquid chromatography with hydro-organic mobile phases. Almost three decades of experience have resulted in an increasing production of analytical applications. Current concern about the environment also reveals MLC as an interesting technique for “green” chemistry because it uses mobile phases containing 90% or more water. These micellar mobile phases have a low toxicity and are not producing hazardous wastes. The stationary phase is modified with an approximately constant amount of surfactant monomers, and the solubilising capability of the mobile phase is altered by the presence of micelles, giving rise to a great variety of interactions (hydrophobic, ionic, and steric) with major implications in retention and selectivity. From its beginnings in 1980, the technique has evolved up to becoming in a real alternative in some instances (and a complement in others) to classical RPLC with aqueous-organic mixtures, owing to its peculiar features and unique advantages. The addition of an organic solvent to the mobile phase was, however, soon suggested in order to enhance the low efficiencies and weak elution strength associated with the mobile phases that contained only micelles.

Direct plasma metabolite analysis of positron emission tomography radioligands by micellar liquid chromatography with radiometric detection

Determination of radio-metabolites in plasma samples taken during a positron emission tomography (PET) study is an important component in the pharmacokinetic evaluation of PET radioligands. We have developed and validated a new analytical procedure for the plasma metabolite analysis of PET radioligands based on micellar liquid chromatography using an anionic surfactant mobile phase. Chromatographic separation was performed on an octadecyl semipreparative column (10 mm I.D. × 160 mm, 10 μm) using 100 mM sodium dodecyl sulfate (SDS) and 1-butanol in 10 mM sodium-phosphate (pH 7.2) at a flow rate of 5 mL/min. The samples taken from monkey or human plasma during PET measurements were directly injected into a liquid chromatographic (LC) system coupled to an online radiometric detector under micellar conditions using 1-2% (v/v) 1-butanol mobile phase to remove plasma proteins and concentrate the analytes at the column head. At 2 min, mobile phase was changed to elute and separate PET radioligand and its radiometabolites with high peak capacity under high submicellar conditions (10-25% 1-butanol). This procedure allowed direct plasma injection (up to 2 mL) into the LC column without any pretreatment with a short analysis-time of 8-10 min. Satisfactory reproducibility, linearity, sensitivity, accuracy and recovery were obtained in the validation study. The developed method was successfully applied to study the metabolism for diverse groups of PET radioligands and provided reliable determination of PET radioligands in human and monkey plasma. This method is advantageous in terms of simplifying and shortening the processes required to analyze short-lived radioligands as well as in providing a more accurate estimation of the metabolite corrected input function, especially for the radioligands with lower recoveries or degradation potential during the deproteination process in a conventional procedure.

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.

Interaction and micellar solubilization of diclofenac with cetyltrimethylammonium bromide: A spectrophotometric study

In this study, the interaction of diclofenac (Dic) with cationic surfactant cetyltrimethylammonium bromide (CTAB) was investigated. The effect of cationic micelles on solubilization of diclofenac in aqueous micellar solution was studied at pH 6.8, 29 °C and various drug concentrations. The binding of diclofenac to CTAB micelles was accompanied by a batochromic shift in the drug absorption spectra. The solubility of diclofenac increased with increasing surfactant concentration as a consequence of the association between the drug and micelles. From the results, the binding constants Kb, was obtained. By using the pseudo-phase model, the partition coefficient between the bulk water and CTAB micelles, Kx, and the Gibbs energy of binding were calculated. The value of binding constant and partition coefficient are increased by increasing of diclofenac concentration.

Retention mechanisms in micellar liquid chromatography

Micellar liquid chromatography (MLC) is a reversed-phase liquid chromatographic (RPLC) mode with mobile phases containing a surfactant (ionic or non-ionic) above its critical micellar concentration (CMC). In these conditions, the stationary phase is modified with an approximately constant amount of surfactant monomers, and the solubilising capability of the mobile phase is altered by the presence of micelles, giving rise to diverse interactions (hydrophobic, ionic and steric) with major implications in retention and selectivity. From its beginnings in 1980, the technique has evolved up to becoming a real alternative in some instances (and a complement in others) to classical RPLC with hydro-organic mixtures, owing to its peculiar features and unique advantages. This review is aimed to describe the retention mechanisms (i.e. solute interactions with both stationary and mobile phases) in an MLC system, revealed in diverse reports where the retention behaviour of solutes of different nature (ionic or neutral exhibiting a wide range of polarities) has been studied in a variety of conditions (with ionic and non-ionic surfactants, added salt and organic solvent, and varying pH). The theory is supported by several mechanistic models that describe satisfactorily the retention behaviour, and allow the measurement of the strength of solute-stationary phase and solute-micelle interactions. Suppression of silanol activity, steric effects in the packing pores, anti-binding behaviour, retention of ionisable compounds, compensating effect on polarity differences among solutes, and the contribution of the solvation parameter model to elucidate the interactions in MLC, are commented.

Determination of trazodone in urine and pharmaceuticals using micellar liquid chromatography with fluorescence detection

A simple and reliable liquid chromatographic procedure is described for the determination of trazodone in pharmaceutical formulations and urine samples. The optimized procedure uses fluorimetric detection, a C18 column and a micellar mobile phase of sodium dodecyl sulfate (SDS) and 1-butanol. The mobile phase selected for use was 0.2M SDS and 8% 1-butanol fixed at pH 3 with phosphate buffer. The total analysis time was 10 min. For the analysis of urine samples, one great advantage of the method is that no extraction step is required. The quantification limit was 9.5 ng mL(-1), ensuring the analysis of the drug in biological fluids. The procedure shows good accuracy, repeatability and selectivity. Repeatability and intermediate precision were tested for several concentrations of the drug. Good claim percentages were obtained in the analysis of pharmaceutical formulations. Calibration repeatability in urine matrix was also studied in the 0.06-22.4 microg mL(-1) range. Good recoveries were obtained from spiked urine samples. No interferences from common additives frequently administered with trazodone or from endogenous compounds in urine samples were found. The results show that the procedure is suitable for routine analysis of the drug.

Interaction of quinapril anion with cationic surfactant micelles of cetyltrimethylammonium bromide

In this study, the interaction of the anion of quinapril (QUIN), angiotensin converting enzyme (ACE) inhibitor, with cationic surfactant cetyltrimethylammonium bromide (CTAB) was investigated. The effect of cationic micelles on the spectroscopic and acid-base properties of QUIN was studied at pH 8. The binding of QUIN anion to CTAB micelles implied a shift in drug acidity constant (pK(a)(water)-pK(a)(micelle)=1.39) proving the great affinity of negatively charged QUIN ion for the positively charged CTAB micelle surface. The strong dependence of the partition coefficient K(x) on QUIN concentration, obtained by using pseudo-phase model, is consistent with an adsorption-like phenomenon. From the dependence of differential absorbance at lambda=272 nm on CTAB concentration, by using mathematical model that treats the solubilization of QUIN anion as its binding to specific sites in the micelles (Langmuir adsorption isotherm), the binding constant K(b)=(2.3+/-0.4)x10(3) mol(-1)dm(3) was obtained. QUIN-CTAB binding constant was also calculated from micellar liquid chromatography (MLC) and this method was found to be not accurate enough for its determination.

Counter-current chromatography using hexane/surfactant-containing water solvent systems

We developed a n-hexane/surfactant-containing water solvent system in counter-current chromatography (CCC) in order to separate hydrophobic compounds. By using the upper phase as the mobile phase, we have separated steroid samples. Retention times of steroids progesterone and delta4-androstene-3,17-dione increased slightly by increasing the concentration below the critical micellar concentration (CMC) of surfactant sodium 1-heptanesulfonate. However, the retention times increased drastically while the SHS concentrations were above the CMC. The partition of these two steroids in the two phases was significantly dependent on the interaction with micelles. Aromatic hydrocarbons were not retained by the lower phase no matter what the surfactant concentrations were. Their hydrophobic interaction with n-hexane greatly exceeded that with the micellar solution. The retention times of esters, however, were only slightly affected by the surfactant addition even above the CMC. The weaker interaction between esters and the micellar solution was probably due to their higher polarity. The micellar solvent systems provide an alternative way for hydrophobic sample separations in CCC, but the performance is limited.

Simultaneous optimization of resolution and analysis time in mixed micellar liquid chromatography of coumarins by use of a utility function

A chemometrics approach has been used to optimize the separation of eight coumarin compounds by mixed micellar liquid chromatography. A utility function, a multi-criterion decision-making (MCDM) method, was tested for evaluation of two different measures of chromatographic performance (resolution and analysis time). The effect of six experimental parameters on a chromatographic response function (CRF) was investigated. The factors studied were the concentrations of SDS and Brij-35, alkyl-chain length of the alcohol used as organic modifier, organic modifier concentration, mobile phase pH, and temperature. The experiments were performed according to a face-centered cube response-surface experimental design. For evaluation of the chromatograms a simple linear response function was used which expressed as a summation of two optimization criteria, resolution and analysis time. Then calculated CRF values were fitted to a polynomial model to correlate the CRF values with the variables and their interactions. The regression model obtained was characterized by both its descriptive and predictive ability (R=0.963 and R2cv=0.861) and used, by means of a grid-search algorithm, to optimize the chromatographic conditions. Experiments performed under the optimum conditions predicted by the model produced a chromatogram of high quality. The model was also verified by the good agreement observed between predicted and experimental values of the chromatographic response function under the optimum conditions.

Effect of ionization and the nature of the mobile phase in quantitative structure-retention relationship studies

The octanol-water distribution constant, commonly called partition coefficient, Po/w, is a parameter often retained as a measure of the hydrophobicity of a molecule. log Po/w, for a given molecule, can be conveniently evaluated constructing correlation lines between standard retention factor logarithms (log k) in reversed-phase liquid chromatography (RPLC) and standard log Po/w values. Many compounds of pharmaceutical interest can be quite hydrophobic and have, simultaneously, basic nitrogen atoms or acidic sulfur containing groups in their structure. This renders them ionizable. The hydrophobicity of the molecular drug form (Po/w value) is completely different from its ionic form (log Po/w(+ or -) value). The actual hydrophobicity of such ionizable molecule depends on the pH. It can be represented by an apparent Papp value that takes into account the amount of compound in its molecular and ionic state combining the Po/w and Po/w(+ or -) values. In this work, log k in RPLC for ionizable as well as non-ionizable pharmaceutical compounds with different therapeutic properties (10 beta-blockers, seven tricyclic antidepressants (TA), eight steroids and 12 sulfonamides) were correlated with log Po/w. Similar correlations were done between log k and the corrected log Papp values at pH 3. Aqueous-organic mobile phases containing acetonitrile (conventional RPLC) and micellar-organic mobile phases (micellar liquid chromatography, MLC), prepared with the anionic surfactant sodium dodecyl sulfate and the organic solvents acetonitrile, propanol or pentanol, were also used to elute the compounds. All mobile phases were buffered at pH 3. Using conventional retention RPLC data, the correlation of log k with log Po/w, was satisfactory for steroids because they cannot ionize. For ionizable beta-blockers and TAs, the use of log Papp values improved the quality of the correlations, but yielded similar results for sulfonamides. In MLC, since an electrostatic interaction is added to hydrophobic forces, poorer correlations were obtained in all cases. The retention data obtained in RPLC also seems to correlate better with the biological activity of the drugs.

Effects of pH and the presence of micelles on the resolution of diuretics by reversed-phase liquid chromatography

A comparative study on the performance of two RPLC modes on the separation of 18 diuretics with diverse acid-base behaviour (acetazolamide, althiazide, amiloride, bendroflumethiazide, benzthiazide, bumetanide, canrenoic acid, chlorothiazide, chlorthalidone, ethacrynic acid, furosemide, hydrochlorothiazide, piretanide, probenecid, spironolactone, triamterene, trichloromethiazide and xipamide) was carried out. A conventional octadecylsilane column and acidic acetonitrile-water mobile phases, in the absence and presence of micelles of the anionic surfactant sodium dodecyl sulphate (SDS), were used. The effects of pH and the modifiers acetonitrile and SDS on peak asymmetry, efficiency, selectivity, resolution and analysis time, were examined. The comparison of both RPLC modes (aqueous- and micellar-organics) was done using the same processing tools, applying several polynomial and mechanistic equations to describe the retention. The best separations were obtained by maximising the product of peak purities, considering a wide range of experimental conditions. The study illustrates that, despite the theoretical and practical complexity of the problem, the predicted optimal chromatograms can be reproduced experimentally with great accuracy. None of the examined RPLC modes was able to yield baseline separation of the 18 diuretics. However, their selectivity was complementary, being appropriate for different combinations of a smaller number of the assayed diuretics.

Recent Advances in the Analysis of Steroid Hormones and Related Drugs

The development during the last 15 years and the state-of-the-art in the analysis of bulk steroid hormone drugs and hormone-like structures and pharmaceutical formulations made thereof are summarized. Other steroids (sterols, bile acids, cardiac glycosides, vitamins D) as well as biological-clinical aspects and pharmacokinetic and metabolic studies are excluded from this review. The state-of-the-art is summarized based on comparisons of monographs in the latest editions of the European Pharmacopoeia, United States Pharmacopoeia and the Japanese Pharmacopoeia. This is followed by sections dealing with new developments in the methodology for the fields of spectroscopic and spectrophotometric, chromatographic, electrophoretic and hyphenated techniques as well electroanalytical methods. The review is terminated by two problem-oriented sections: examples on impurity and degradation profiling as well as enantiomeric analysis.

Synthesis and chromatographic purification of recombinant human pituitary hormones

Recombinant DNA-derived proteins and, in particular, human pituitary hormones, are increasingly used for research, diagnostic and therapeutic purposes. This trend has demanded new synthetic approaches and improved purification techniques. The type and sequence of the purification steps have to be selected in accordance with the cloning and protein expression strategy, the host organism and cellular localization of the protein of interest, with a view to producing the desired product at a required purity, biological activity and acceptable cost. This review article describes and analyzes the main synthetic and purification strategies that have been used for the production of recombinant human growth hormone, prolactin, thyrotropin, luteinizing hormone and follicle-stimulating hormone, giving special consideration to the few published downstream processes utilized by the biotechnology industry. Practically all types of prokaryotic and eukaryotic organisms utilized for this purpose are also reviewed.

Simultaneous determination of 16 estrogens, dehydroepiandrosterone and their glucuronide and sulfate conjugates in serum using sodium cholate micelle capillary electrophoresis

The simultaneous determination of 16 estrogens, dehydroepiandrosterone (DHEA) and their glucuronide and sulfate conjugates by micellar electrokinetic chromatography (MEKC) with sodium cholate micelle is reported. Sodium cholate, sodium dodecylsulfate (SDS) and alpha-, beta-, gamma-cyclodextrins were studied as micelle reagents in the pH range of 7.0-10.0. Estrogens, DHEA and their glucuronide and sulfate conjugates were separated using a 50 cm x 50 microm capillary with 10 mM borate-phosphate buffer (pH 8.0) containing 50 mM sodium cholate as carrier. The method could simultaneously determine 1.0-1000 microg/mL of steroids and metabolites in 100 microL of serum by photometric detection at 214 nm within 14 min and 80 ng/mL steroids could be determined by using 2.0 mL of serum. The relative standards deviations were 6.7-7.7% at 10 microg/mL in serum. The recoveries were 89.1-92.0% with 10 microg/mL serum samples.