Percentage Of Organic Modifier Research Articles

Enantiomeric Resolution and Docking Studies of Chiral Xanthonic Derivatives on Chirobiotic Columns.

A systematic study of enantioresolution of a library of xanthonic derivatives, prepared “in-house”, was successfully carried out with four commercially available macrocyclic glycopeptide-based columns, namely ChirobioticTM T, ChirobioticTM R, ChirobioticTM V and ChirobioticTM TAG. Evaluation was conducted in multimodal elution conditions: normal-phase, polar organic, polar ionic and reversed-phase. The effects of the mobile phase composition, the percentage of organic modifier, the pH of the mobile phase, the nature and concentration of different mobile phase additives on the chromatographic parameters are discussed. ChirobioticTM T and ChirobioticTM V, under normal-phase and reversed-phase modes, respectively, presented the best chromatographic parameters. Considering the importance of understanding the chiral recognition mechanisms associated with the chromatographic enantioresolution, and the scarce data available for macrocyclic glycopeptide-based columns, computational studies by molecular docking were also carried out.

A Liquid Chromatography Method for Simultaneous Determination of Diphenhydramine, Promethazine, Chlorpheniramine and Ephedrine in Cold-Cough Syrups

Asimple, rapid isocratic liquid chromatography method was developed for the simultaneous determination of diphenhydramine, promethazine, chlorpheniramine, and ephedrine in cold-cough syrups commonly available in the Kenyan market. The influence of the percentage of organic modifier, ion pairing agent, buffer concentration as well as pH and column temperature on the selectivity with respect to analytes was investigated. Optimum chromatographic separation was achieved using a C18 Gemini® NX column (250 mm × 4.6 mm, 5 μm) maintained at 40°C and a mobile phase comprising methanol – triethylamine – 0.2 M ammonium acetate pH 5.0 – water mixture (50 : 0.15 : 40 : 9.85, v/v) delivered at a flow rate of 1.0 mL/min. Upon validation, the proposed liquid chromatography method satisfied the International Committee on Harmonization acceptance criteria for linearity, sensitivity, precision, and robustness. The method was applied in the analysis of commercial samples obtained from Nairobi County, Kenya. The method can be used in routine analysis of cold-cough syrups containing the specified compounds.

The influence of an aqueous-butanol plating bath on the microstructure and corrosion resistance of electrodeposited nickel coatings

The effects of higher concentrations (5 and 10%) of an organic modifier, butanol, added to an aqueous electroplating solution for nickel deposition have been studied. Nickel coatings were deposited on steel substrates from a modified all-sulfate bath with 5 and 10% additions of butanol under acidic conditions, while a modified pulse potential was applied. X-ray diffraction of the resulting nickel coatings showed a preferred (220) orientation for the crystal structure. The coatings were nanocrystalline with particle sizes between 16 and 35 nm as calculated from Williamson–Hall analysis. No cracking of the films was observed in the scanning electron microscopy images, even as the percentage of butanol increased, as typically is observed in other aqueous-organic baths. Corrosion resistance of the nickel coatings in a 3.5% sodium chloride solution was best for coatings deposited from plating solutions containing 5 and 10% butanol. E corr was shifted from −0.405 V for the nickel coating from the additive-free bath to −0.234 V for the nickel coating from the 5% butanol solution. EIS results indicated a twofold improvement in charge transfer resistance for nickel coatings deposited when butanol was used in the plating bath. The advantages of using higher percentages of organic modifiers like butanol to enable the use of non-electroactive particles for production of composite coatings are discussed.

Preparation of chiral oxazolinyl-functionalized β-cyclodextrin-bonded stationary phases and their enantioseparation performance in high-performance liquid chromatography.

A simple procedure for the synthesis of three new oxazolinyl-substituted β-cyclodextrins (6-deoxy-6-R-(-)-4-phenyl-4,5-dihydrooxazolinyl-β-cyclodextrin, 6-deoxy-6-S-(-)-4-phenyl-4,5-dihydrooxazolinyl-β-cyclodextrin, and 6-deoxy-6-S-(-)-(4-pyridin-1-ium-4-methyl-benzenesulphonate)-4,5-dihy-drooxazolinyl-β-cyclodextrin) and their covalent bonding to silica are reported. The ability of these chiral stationary phase columns for separating compounds is also presented and discussed. Twenty-eight compounds were examined in the polar-organic mobile phase mode, and 11 β-nitroethanols were tested in the reversed-phase mode. Excellent enantioseparations were achieved for most of the analytes, even for several challenging compounds. The rigid and flexible structures of mono-substituted chiral groups and the fragments around the rim of the β-cyclodextrin cavity played an important role in the separation process. Factors such as π-π stacking, dipole-dipole interactions, ion-pairing, and steric hindrance effects were found to affect the chromatographic performance. Moreover, the buffer composition, and percentages of organic modifiers in the mobile phase, were investigated and compared. The mechanisms involved in the separation were postulated based on the chromatographic data.

Separation behavior of basic compounds on unbonded silicon oxynitride and silica high-performance liquid chromatography stationary phases with reversed-phase eluents.

Unbonded silicon oxynitride and silica high-performance liquid chromatography stationary phases have been evaluated and compared for the separation of basic compounds of differing molecular weight, pKa , and log D using aqueous/organic mobile phases. The influences of percentage of organic modifier, buffer pH, and concentration in the mobile phase on base retention were investigated on unbonded silicon oxynitride and silica phases. The results confirmed that unbonded silicon oxynitride and silica phases demonstrated excellent separation performance for model basic compounds and both the unbonded phases examined possessed a hydrophobic/adsorption and ion-exchange character. The silicon oxynitride stationary phase exhibited high hydrophilicity compared with silica with a reversed-phase mobile phase. An ion-exclusion-type mechanism becomes predominant for the separation of three aimed bases on the silicon oxynitride column at pH 2.8. Different from silicon oxynitride stationary phase, no obvious change for the retention time of three model bases on silica stationary phase at pH 2.8 can be observed.

A novel and cost-effective method for the determination of fifteen polycyclic aromatic hydrocarbons in low volume rainwater samples

A novel single-step method was developed for the determination of 15 polycyclic aromatic hydrocarbons (PAHs) at ultratrace levels in rainwater by on-line in-tube solid-phase microextraction (IT-SPME) coupled to high-performance liquid chromatography-photodiode array-fluorescence detection. This paper is focused on a study of the IT-SPME coupling and optimization, its application to rainwater and other environmental waters and the stability of PAH rainwater solutions. In order to solve the different extractive behavior of PAHs, several IT-SPME parameters were optimized, with the type and percentage of organic modifier playing a decisive role. In the kinetic study on stability of PAH solutions, the organic modifier has proven to be effective as a preservative, avoiding the loss of the higher-molecular weight PAHs. The proposed method presents a wide interval of linearity (10–1500ngL−1) and a good relative standard deviation between 3.4% and 14.6% for the PAHs analyzed. Detection and quantification limits between 2.3 and 28ngL−1 and 5.7 and 65ngL−1 were obtained respectively, taking into account the values of the procedure blanks. Recoveries for different kinds of real water samples were within the range of 72–110%. Low and medium-molecular weight PAHs predominate in daily and monthly rainwater samples analyzed. In comparison with other methods reported, the proposed method achieves a significant reduction of the sample volume, the organic solvent consumption and time of sample treatment, allowing a cost-effective analysis of environmental waters. The method is especially suitable for samples from the precipitation events of low intensity or short duration for which sample volume is limiting.

One‐pot synthesis of a new high vinyl content hybrid silica monolith dedicated to nanoliquid chromatography

A new vinyltrimethoxysilane-based hybrid silica monolith was developed and used as a reversed-phase capillary column. The synthesis of this rich vinyl hybrid macroporous monolith, by cocondensation of vinyltrimethoxysilane with tetramethoxysilane, was investigated using an unconventional (formamide, nitric acid) porogen/catalyst system. A macroporous hybrid silica monolith with 80% in mass of vinyltrimethoxysilane in the feeding silane solution was obtained and compared to a more conventional low vinyl content hybrid monolith with only of 20% vinyltrimethoxysilane. Monoliths were characterized by scanning electron microscopy, (29) Si nuclear magnetic resonance spectroscopy and N2 adsorption-desorption. About 80% of the vinyl precursor was incorporated in the final materials, leading to 15.9 and 61.5% of Si atoms bonded to vinyl groups for 20% vinyltrimethoxysilane and 80% vinyltrimethoxysilane, respectively. The 80% vinyltrimethoxysilane monolith presents a lower surface area than 20% vinyltrimethoxysilane (159 versus 551 m(2) /g), which is nevertheless compensated by a higher vinyl surface density. Chromatographic properties were evaluated in reversed-phase mode. Plots of ln(k) versus percentage of organic modifier were used to assess the reversed-phase mechanism. Its high content of organic groups leads to high retention properties. Column efficiencies of 170 000 plates/m were measured for this 80% vinyltrimethoxysilane hybrid silica monolith. Long capillary monolithic columns (90 cm) were successfully synthesized (N = 120 000).

Chiral analysis of aromatic amino acids in food supplements using subcritical fluid chromatography and Chirobiotic T2 column

The enantiomeric recognition capability of the teicoplanin-based Chirobiotic T2 column for the analysis of amino acids using subcritical fluid chromatography is presented in this work. The chiral separation of the aromatic protein amino acids phenylalanine, tyrosine and tryptophan was studied employing an elevated percentage of organic modifier (ranging from 35 to 60% v/v), and a high percentage of water as additive (2–10%, v/v). Baseline enantioseparation of the individual amino acids was achieved in 7min (in 15min for their simultaneous separation by serially coupling of chiral/achiral columns) using 40% of modifier composed of a mixture methanol/water (90:10 v/v) without the necessity of other acidic or basic additives. The proposed method was validated obtaining suitable levels of recovery, precision and linearity. The detection and quantification limits ranged from 0.5 to 2.0μg/mL and from 1.7 to 6.7μg/mL, respectively, which allowed the determination of low amounts of d-amino acids (up to 0.2% for tryptophan) in the presence of a large excess of corresponding l-enantiomers. Finally, the method was applied to the determination of l-phenylalanine, l-tyrosine and l-tryptophan in five commercial food supplements, and the quality of these food supplements was confirmed through the absence of enantiomeric impurity in all of them.

Development and validation of reversed phase HPLC method for the determination of vildagliptin using an experimental design

A simple, robust and fast reversed phase HPLC method was developed and validated with UV detection (210 nm) for routine determination of vildagliptin. Chromatographic analysis was performed with mobile phase containing a mixture of 10 mM phosphate buffer (pH 4.6) and acetonitrile (85: 15, v/v) with flow rate of 1.0 mL/min. The procedure was validated as per International Conference on Harmonization (ICH) guidelines for linearity (correlation coefficient r2 = 0.999), accuracy, intermediate precision and robustness. Experimental design was used during validation to calculate method robustness and intermediate precision. For testing robustness three factors were considered: pH of buffer, flow rate and percentage (v/v) of acetonitrile. From the analysis it was observed that an increase in the flow rate results in a decrease of drug found concentration, while the pH of buffer and percentage of organic modifier have no significant effect on the response. To measure intermediate precision, the variables considered were: analyst, equipment and number of days. The relative standard deviation (RSD) value (2.25%, n = 24) indicated a good precision for analytical method. The proposed method was simple, accurate, precise, sensitive and cost effective for further determination of vildagliptin.

Investigation of the retention behavior of structurally diverse drugs on alpha1 acid glycoprotein column: Insight on the molecular factors involved and correlation with protein binding data

Retention of 49 structurally diverse drugs on alpha1 acid glycoprotein column was investigated under different chromatographic conditions. Acetonitrile and 2-propanol were used as organic modifiers at different percentages and the pH was adjusted at 7.0 using PBS. Analysis of extrapolated and isocratic retention in terms of lipophilicity and electrostatic interactions revealed significant effect of the nature and percentage of organic modifier, which was attributed to the different shielding degree of the charged sites on the stationary phase by the buffer constituents. AGP retention factors were compared to HSA retention factors analyzed previously. Application of LSER analysis, extended to incorporate fractions ionized, demonstrated hydrogen bond acidity, dipolarity/polarizability and excess molar refraction as the most significant parameters for all AGP chromatographic indices, elucidating the differentiation of AGP retention from octanol–water partitioning and HSA retention. An attempt to correlate AGP chromatographic indices to AGP association constants, available in literature, supported the importance of stationary shielding in retention mechanism. Thus, isocratic retention factors logk10(ACN)AGP show a moderate but still better performance than lipophilicity in the case of A variant and may be a useful tool for the estimation of relevant association constants. For F1/S binding simulation lower stationary phase shielding is needed to obtain a significant two term regression equation, where logk20(ACN)AGP exerts a secondary contribution next to the most important bulk effect expressed by molecular weight.

Implementation of design of experiments for optimization of forced degradation conditions and development of a stability-indicating method for furosemide

The study involved optimization of forced degradation conditions and development of a stability-indicating method (SIM) for furosemide employing the design of experiment (DoE) concept. The optimization of forced degradation conditions, especially hydrolytic and oxidative, was done by application of 2n full factorial designs, which helped to obtain the targeted 20–30% drug degradation and also enriched levels of degradation products (DPs). For the selective separation of the drug and its DPs for the development of SIM, DoE was applied in three different stages, i.e., primary parameter selection, secondary parameter screening and method optimization. For these three, IV-optimal, Taguchi orthogonal array and face-centred central composite designs were employed, respectively. The organic modifier, buffer pH, gradient time and initial hold time were selected as primary parameters. Initial and final organic modifier percentage, and flow rate came out as critical parameters during secondary parameter screening, which were further evaluated during method optimization. Based on DoE results, an optimized method was obtained wherein a total of twelve DPs were separated successfully. The study also exposed the degradation behaviour of the drug in different forced degradation conditions.

Micellar electrokinetic chromatography method development for simultaneous determination of thiabendazole, carbendazim, and fuberidazole

Thiabendazole (TBz), carbendazim (CBz), and fuberidazole (FBz) are systemic benzimidazole-type fungicides used for pre- and post-harvest treatment to control various types of fungal diseases on a variety of crops. Significant levels of these fungicides could alter the composition or flavour of crops, and being possible carcinogens, they could also pose risks for humans and the environment. A mode of capillary electrophoresis called micellar electrokinetic chromatography (MEKC) was investigated for the determination of these three benzimidazole fungicides. The study involved two kinds of surfactants in which several experimental conditions were optimized, i.e., buffer concentration, pH, micelle concentration, and percent organic modifier (methanol). Using the optimum experimental conditions, the fungicides were successfully separated by MEKC. The limits of detection and quantification were in the range of 0.6–0.7 and 2.1–2.5 mg L−1, respectively, and the calibration curves were linear over the range of 5–60 mg L−1 for the three fungicides. The potential of the proposed MEKC method was demonstrated by analyzing water samples which were fortified with the fungicides. The proposed method enabled simultaneous determination of the three benzimidazole fungicides and method validation with spiked water samples yielded satisfactory quantitative recoveries for all the three fungicides.

Ion-pair ultra-high performance liquid chromatographic analysis of monoamines: Peak-splitting at high flow rates

The use of ion-pair ultra-high performance liquid chromatography (UHPLC) coupled with electrochemical detection (ECD) is of great interest for the fast and sensitive determination of the monoamine neurotransmitters dopamine, noradrenaline and serotonin in microdialysis samples. However, when applying high flow rates in ion-pair UHPLC, other peaks than the initial compound peaks appear on the chromatogram. This peak-splitting phenomenon is caused by disturbed ion-pair retention mechanisms. The influence of several chromatographic parameters is investigated. Peak-splitting is delayed to higher flow rates when increasing the concentration of ion-pair reagent or buffering agent in the mobile phase, when decreasing the percentage of organic modifier in the mobile phase, when applying a stationary phase with a smaller amount of packing material or when increasing the separation temperature. One or a combination of these conditions can be applied to analyze the monoamine neurotransmitters using ion-pair UHPLC–ECD at high flow rates.

Development of a liquid chromatographic method for the simultaneous quantification of curcumin, β-arteether, tetrahydrocurcumin and dihydroartemisinin. Application to lipid-based formulations

A liquid chromatographic method was developed for the simultaneous separation of curcumin, β-arteether, tetrahydrocurcumin and dihydroartemisinin based on the design of experiments and the design space methodology. The influence of the percentage of organic modifier, flow rate of the mobile phase and column temperature on the analytes separation was investigated. The optimal chromatographic separation was achieved on a C18 column (125mm×4mm, 5μm) using an isocratic elution with a mobile phase consisting of methanol-ammonium acetate (pH 4; 10mM) (80:20, v/v) at a flow rate of 0.45ml/min and a column temperature of 32.5°C. This method was then validated for simultaneous quantification of curcumin and β-arteether contained in lipid-based formulations taking into account the β-expectation tolerance interval for the total error measurement. Finally, the suitability of the proposed liquid chromatographic method for routine analysis of curcumin and β-arteether loaded in lipid-based formulations has been proven.

Effect of Chromatographic Conditions on Enantioseparation of Bovine Serum Albumin Chiral Stationary Phase in HPLC and Thermodynamic Studies

Twelve chiral compounds were enantiomerically resolved on bovine serum albumin chiral stationary phase (BSA-CSP) by high-performance liquid chromatography (HPLC) in reversed-phase modes. Chromatographic conditions such as mobile phase pH, the percentage of organic modifier, and concentration of analyte were optimized for separation of enantiomers. For N-(2, 4-dinitrophenyl)-serine (DNP-ser), the retention factors (k) greatly increase from 0.81 to 6.23 as the pH decreasing from 7.21 to 5.14, and the resolution factor (R(s)) exhibited a similar increasing trend (from 0 to 1.34). More interestingly, the retention factors for N-(2, 4-dinitrophenyl)-proline (DNP-pro) decrease along with increasing 1-propanol in mobile phase (3%, 5%, 7% and 9% by volume), whereas the resolution factor shows an upward trend (from 0.96 to 2.04). Moreover, chiral recognition mechanisms for chiral analytes were further investigated through thermodynamic methods.

HPLC METHOD DEVELOPMENT FOR ESTIMATION OF RAMELTEON IN TABLET DOSAGE FORM

A simple, fast, accurate and precise reverse phase HPLC method is developed and described for the determination of ramelteon in tablet dosage form. Chromatography was carried on an ODS column using a mixture of acetonitrile and phosphate buffer pH 7.0 (35:65 V/V) as the mobile phase at a flow rate of 1.0 mL/min with detection at 286 nm. The retention time of the drug was 7.7 min. The procedure was validated for linearity, precision, accuracy, and robustness. The developed method was validated for linearity from 50 to 150% which shows the method is quite linear with a correlation coefficient of 0.999, for precision which includes system precision, method precision, intraday and by another analyst on another day, and accuracy. The %RSD for system precision was observed to be 1.1, whereas the method precision was observed to be 0.2. The % recovery from ‘accuracy’ studies yielded the recovery of 99.7-101.5% which indicates the capability of the method, and finally for robustness that includes studies w.r.t. change in flow rate, the percentage of organic modifier and pH. As per ICH guidelines, method validation results are in good agreement. The proposed method was simple, sensitive, precise and accurate.

Enantiomeric separations of chiral polychlorinated biphenyls on three polysaccharide-type chiral stationary phases by supercritical fluid chromatography

Enantiomeric separations of 18 chiral polychlorinated biphenyls (PCBs) were investigated on three polysaccharide-type chiral stationary phases (CSPs; Sino-Chiral OJ, Chiralpak IB, and Chiralcel OD) by supercritical fluid chromatography (SFC). With these commonly used polysaccharide CSPs, 17 PCBs except PCB 135 (R(S) = 0.81) were well resolved (R(S) > 1.5) under appropriate mobile phases and temperatures. Using Sino-Chiral OJ, 14 PCBs could be baseline-separated, while only one and nine PCBs could be completely separated using Chiralpak IB and Chiralcel OD, respectively. The influence of column temperature was studied for the optimization of resolution, as well as for the type and percentage of organic modifier in the mobile phase. The resolution decreased as the temperature increased in the range of 26-40 °C in which the enantiomeric separations were an enthalpy-driven process. The addition of modifiers in the mobile phase decreased the resolution of the PCB enantiomers, but it clearly shortened their retention time. These separation results indicate that SFC is a promising chromatographic technique for chiral separation and enantiopure standard preparation.

On the chromatographic efficiency of analytical scale column format porous polymer monoliths: Interplay of morphology and nanoscale gel porosity

Porous monolithic poly(styrene-co-divinylbenzene) stationary phases in 4.6mm I.D. analytical-scale column format with varying porosity, globule scale polymer morphology and flow-through pore structure have been investigated with respect to their transport properties toward small retained solutes in isocratic elution, reversed-phase liquid chromatography. The current study was performed under kinetically and thermodynamically relevant conditions comprising retention factors from close to zero up to the order of 50–100 under most extreme conditions, while a linear chromatographic flow velocity up to 4mm/s, in some instances up to 7mm/s, was realized. Carefully designed experiments aimed at resolving issues associated with the monoliths performance, while a particular focus is given on gel porosity, chromatographic retention and band dispersion. Elucidation of three important metric properties gave orthogonal insight. These are: (i) the columns dry-state morphology and surface area, (ii) the gel porosity with tetrahydrofuran as solvent determined by size exclusion chromatography using a range of small subnanometer-sized molecules and polystyrene standards, as well as (iii) the isocratic reversed-phase performance of small molecules at varying binary acetonitrile/water mobile phase solvent compositions, modulating gel porosity. Consistently throughout the study, the adjustable and general retention-factor-dependence of the performance of these monolithic materials is shown. It can also be correlated to the analytes molecular weight and consequently size. Isocratic performance strongly depends on the amount of gel porosity of the scaffold, which can be changed by varying the percentage of organic modifier in the mobile phase and indicates the adjustable chromatographic nature of porous polymer monoliths. This gel porosity which is absent in the dry-state of the polymer monoliths and is characterized by sub-nanometer to nanometer-sized pore space induces, additionally to permanent porosity, stagnant mass transfer zones. The displayed major reason for mass transfer resistance implied by the use of polymeric monolithic columns determines dispersion behavior of small molecules and its varying importance with respect to morphology and size of the globular features containing stagnant mass transfer zones is addressed. This leads to the conclusion, that a reduction in polymer feature size and increase in number of flow-through pores per unit cross-section of the monolith with an improved homogeneity may be an interesting option of tailoring column performance. It is further concluded that dry-state methods (such as nitrogen adsorption analysis and scanning electron microscopy) or solvated-state methods (such as size-exclusion chromatography in tetrahydrofuran) by itself are insufficient measures to explain the adjustable chromatographic performance of porous polymer monoliths.

Cyclodextrins as a chiral mobile phase additive in nano-liquid chromatography: comparison of reversed-phase silica monolithic and particulate capillary columns

Enantioseparations of racemic nonsteroidal anti-inflammatory drugs (naproxen, ibuprofen, ketoprofen, flurbiprofen, suprofen, indoprofen, cicloprofen, and carprofen) were performed by nano-liquid chromatography, employing achiral capillary columns and heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin (TM-β-CD) or hydroxylpropyl-β-cyclodextrin (HP-β-CD) as a chiral mobile phase additive (CMPA). Working under the same experimental conditions (in terms of mobile phase and linear velocity), the performance of a RP-C18 monolithic column was compared with that of a RP-C18 packed column of the same dimensions (100 μm i.d. × 10 cm). Utilizing a mobile phase composed of 30% ACN (v/v) buffered with 50 mM sodium acetate at pH 3, and containing 30 mM TM-β-CD, the monolithic column provided faster analysis but lower resolution than the packed column. This behavior was ascribed to the high permeability of the monolithic column, as well as to its minor selectivity. HP-β-CD was chosen as an alternative to TM-β-CD. Employing the monolithic column, the effects of different parameters such as HP-β-CD concentration, mobile phase composition, and pH on the retention factor and the chiral resolution of the analytes were studied. For the most of the analytes, enantioresolution (which ranged from R(s) = 1.80 for naproxen to R(s) = 0.86 for flurbiprofen) was obtained with a mobile phase consisting of sodium acetate buffer (25 mM, pH 3), 10% MeOH, and 15 mM HP-β-CD. When the same experimental conditions were used with the packed column, no compound eluted within 1 h. Upon increasing the percentage of organic modifier to favor analyte elution, only suprofen eluted within 30 min, with an R(s) value of 1.14 (20% MeOH). Replacing MeOH with ACN resulted in a loss of enantioresolution, except for naproxen (R(s) = 0.89).

Reversed-phase thin-layer chromatography behavior of aldopentose derivatives

Quantitative structure-retention relationships (QSRR) have been used to study the chromatographic behavior of some aldopentose. The behavior of aldopentose derivatives was investigated by means of the reversed-phase thin-layer chromatography (RP TLC) on the silica gel impregnated with paraffin oil stationary phases. Binary mixtures of methanol-water, acetone-water and dioxane-water were used as mobile phases. Retention factors, RM0, corresponding to zero percent organic modifier in the aqueous mobile phase was determined. Lipophilicity C0 was calculated as the ratio of the intercept and slope values. There was satisfactory correlation between them and log P values calculated using different theoretical procedures. Some of these correlations offer very good predicting models, which are important for a better understanding of the relationships between chemical structure and retention. The study showed that the hydrophobic parameters RM0 and C0 can be used as a measures of lipophilicity of investigated compounds.