Mirjana Medenica

Reversed-phase ion-pair HPLC determination of some water-soluble vitamins in pharmaceuticals

A reversed-phase ion-pair high-performance liquid chromatografic method (RP-IPC) was developed to assay some water-soluble vitamins in solution dosage forms. Vitamins of the B-group B1, B2, B3, and B6, including vitamin C were determined in Oligovit coated tablets. In Beviplex coated tablets the vitamins B1, B2, B3, B6 and p-aminobenzoic acid were analysed. Hexanesulphonic acid sodium salt and triethanolamine in water methanol were used as mobile phase with adjusting pH to 2.8 with orthophosphoric acid. Phenol was used as an internal standard. For quantitative simultaneous analysis of vitamins in pharmaceutical formulations, the method of internal standard was used. All parameters for the validation of the method are given.

Effect of pH on the retention behaviour of some preservatives-antioxidants in reversed-phase high-performance liquid chromatography

SummaryIn this paper the dependence of eluent pH on the efficiency of separation in RP-HPLC is described. Preservatives-antioxidants, esters ofp-hydroxybenzoic acid (methyl, ethyl, propyl and butyl parabens), sorbic acid, butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), propyl gallate (PG) and L-ascorbic acid (Vitamine C) were investigated by reversed-phase high-performance liquid chromatography, utilising isocratic elution with UV detection. The mobile phase composition (methanol-water v/v containing 1% acetic acid), was varied in order to obtain the best separation. For all substances analysed the pH, pKa and the fitted pKa values were calculated in different mixtures of mobile phases using the graphical method of Charlot and Trémillon [1]. The retention factors (k) and the separation factors (α) were also calculated.

Chemometrical evaluation of ropinirole and its impurity's chromatographic behavior

The aim of this study was the chemometrical evaluation of ropinirole and its impuritys (4-[2-(dipropylamino)ethyl]-1H-indol-2,3-dione) chromatographic behavior in systematic and the most efficient way. For that purpose, as very descriptive, response surface designs are most preferable. Face-centered central composite design (CCD) with 2(3) full factorial design, +/-1 star design and four replication in central point was applied for a response surface study, in order to examine in depth the effects of the most important factors. Factors-independent variables (acetonitrile content, pH of the mobile phase and concentration of sodium heptane sulfonate in water phase) were extracted from the preliminary study and as dependent variables five responses (retention factor of ropinirole, retentin factor of its impurity, resolution, symmetry of ropinirole peak and symmetry of impurity peak) were selected. For the improvement of method development and optimization step, Derringers desirability function was applied to simultaneously optimize the five chosen responses. The procedure allowed deduction of optimal conditions and the predicted optimum was acetonitrile-5mM of sodium heptane sulfonate (21.6:78.4, v/v), pH of the mobile phase adjusted at 2.0 with ortho phosphoric acid. By calculating global desirabilitys determination coefficients (R(D)(2)), as well as by the visual inspection of 3D graphs for global desirability, robustness of the proposed method was also estimated.

Improved chromatographic response function in HILIC analysis: Application to mixture of antidepressants

This paper presents exploration of chromatographic behavior in HILIC system by experimental design and improved chromatographic response function denoted as N(CRF)*. As a model mixture six antidepressants were chosen: selegiline, mianserine, sertraline, moclobemide, fluoxetine and maprotiline. Due to complexity of retention mechanisms in HILIC system, detailed examination of experimental space assessing the influence of important factors (acetonitrile content in the mobile phase, buffer concentration and pH of the mobile phase) and their interactions was done by applying 3(3) experimental design. N(CRF)* is developed and designed to be the only output of the system which simultaneously measures the separation of all the examined substances, the chromatographic run duration and the quality of the obtained peaks shape. It allowed objective estimation of overall chromatogram quality and excluded the arbitrary judgment in ambiguous situations. The applied function highlighted the influence of investigated factors on entire mixture and enabled identification of experimental regions where the chromatographic behavior was satisfactory. Applied experimental design strategy combined with N(CRF)* proved to be valuable assistance in HILIC separation of complex mixtures.

Development of liquid chromatographic method for the analysis of dabigatran etexilate mesilate and its ten impurities supported by quality-by-design methodology.

In this paper, the development of reversed-phase liquid chromatographic method for the analysis of dabigatran etexilate mesilate and its ten impurities supported by quality by design (QbD) approach is presented. The defined analytical target profile (ATP) was the efficient baseline separation and the accurate determination of the investigated analytes. The selected critical quality attributes (CQAs) were the separation criterions between the critical peak pairs because the mixture complexity imposed a gradient elution mode. The critical process parameters (CPPs) studied in this research were acetonitrile content at the beginning of gradient program, acetonitrile content at the end of gradient program and the gradient time. Plan of experiments was defined by Box-Behnken design. The experimental domains of the three selected factors x1--content of the acetonitrile at the start of linear gradient, x2--content of the acetonitrile at the end of linear gradient and x3--gradient time (tG) were [10%, 30%], [48%, 60%] and [8 min, 15 min], respectively. In order to define the design space (DS) as a zone where the desired quality criteria is met providing also the quality assurance, Monte Carlo simulations were performed. The uniform error distribution equal to the calculated standard error was added to the model coefficient estimates. Monte Carlo simulation included 5000 iterations in each of 3969 defined grid points and the region having the probability π ≥ 95% to achieve satisfactory values of all defined CQAs was computed. As a working point, following chromatographic conditions suited in the middle of the DS were chosen: 22% acetonitrile at the start of gradient program, 55.5% acetonitrile at the end of gradient program end and the gradient time of 11.5 min. The developed method was validated in order to prove its reliability.

Advancement in optimization tactic achieved by newly developed chromatographic response function: application to LC separation of raloxifene and its impurities.

In this paper a new chromatographic response function (CRF) is designed and proposed for utilization in the optimization strategies. The function capability to represent the overall quality of a experimentally obtained chromatograms was compared to the other two objective functions and proved to give more accurate and reliable results. The new CRF has improved concept of separation and time term estimation. It reflects all important defects of the chromatogram such as the appearance of asymmetrical or overlapping peaks and prolonged elution time and allows the appropriate weighting of each of them. The LC separation of raloxifene and its four impurities was evaluated through the central composite design experimental plan choosing the new CRF to be the only output of the system. The function demonstrated the ability to judge the impact of the complex interactions of the selected chromatographic parameters (acetonitrile content in the mobile phase, sodium dodecyl sulfate concentration in the water phase, pH of the mobile phase and column temperature) on the mixture behavior and led to the determination of the optimal separation conditions. The newly developed CRF proved to have the advanced performances and it presents the important step forward in the optimization of the chromatographic separation.

Monitoring of Impurity Level of Valsartan and Hydrochlorothiazide Employing an RP–HPLC Gradient Mode

Abstract The multi‐component preparation Co–Diovan® is indicated for the hypertension treatment in patients whose blood pressure is not adequately controlled by monotherapy. Its active ingredients are valsartan and hydrochlorothiazide. The reversed–phase high performance liquid chromatographic method (RP–HPLC) for the determination of valsartan and hydrochlorothiazide, as well as their impurities level, was developed and described in this paper. As the investigated substances were structurally different with extremely different lipophilicity and polarity, isocratic elution was not possible, so an optimal gradient mode was settled on. The chromatograms were recorded using the Agilent 1100 Series chromatographic system with DAD detector. Separations were performed on a Hypersil 120–5 ODS column (250 mm×4.6 mm; 5 µm particle size) at 25°C column temperature. The gradient high performance liquid chromatographic system was developed, and the following mobile phases were used: A) mixture acetonitrile–water (10:90 V/V); pH of the mobile phase was adjusted to 2.5 with 85% orthophosphoric acid, and B) mixture acetonitrile–water (90:10 V/V); pH of the mobile phase was adjusted to 2.5 with 85% orthophosphoric acid. Injection volume was 50 µL, flow rate 1 mL min−1 and UV detection was performed at 256 nm. Methyl parahydroxybenzoate was used as an internal standard and acetonitrile–water (40:60 V/V) as a solvent. Afterwards, the developed method was subjected to the method validation. The investigated validation parameters (selectivity, linearity, precision, accuracy, LOQ, and LOD) proved the suitability of the method for the simultaneous determination of valsartan, hydrochlorothiazide, and their impurities in appropriate tablets.

Quantitation of pregabalin in dried blood spots and dried plasma spots by validated LC–MS/MS methods

In this paper, novel LC-MS/MS methods for the determination of antiepileptic drug pregabalin in dried matrix spots (DMS) are presented. This attractive technique of sample collection in micro amount was utilized in the form of dried blood spots (DBS) and dried plasma spots (DPS). Following a pre-column derivatization procedure, using n-propyl chloroformate in the presence of n-propanol, and consecutive liquid-liquid extraction, derivatized pregabalin and its internal standard, 4-aminocyclohexanecarboxylic acid, were detected in positive ion mode by applying two SRM transitions per analyte. A YMC-Pack Octyl column (50mm×4.0mm, 3μm particle size) maintained at 30°C, was utilized with running mobile phase composed of acetonitrile: 0.15% formic acid (85:15, v/v). Flow rate was 550μL/min and total run time 2min. Established methods were fully validated over the concentration range of 0.200-20.0μg/mL for DBS and 0.400-40.0μg/mL for DPS, respectively, while specificity, accuracy, precision, recovery, matrix-effect, stability, dilution integrity and spot homogeneity were found within acceptance criteria. Validated methods were applied for the determination of pregabalin levels in dried blood and plasma samples obtained from patients with epilepsy, after per os administration of commercial capsules. Comparison of drug level in blood and plasma, as well as correction steps undertaken in order to overcome hematocrit issue, when analyzing DBS, are also given.

Quality by Design in the development of hydrophilic interaction liquid chromatography method with gradient elution for the analysis of olanzapine

HIGHLIGHTSThe first gradient HILIC method developed in accordance with AQbD.For complex HILIC method well defined design space was created.Olanzapine and its seven impurities investigated in HILIC for the first time.Method was fully validated and applied for real sample analysis. ABSTRACT This paper deals with the development of hydrophilic interaction liquid chromatography (HILIC) method with gradient elution, in accordance with Analytical Quality by Design (AQbD) methodology, for the first time. The method is developed for olanzapine and its seven related substances. Following step by step AQbD methodology, firstly as critical process parameters (CPPs) temperature, starting content of aqueous phase and duration of linear gradient are recognized, and as critical quality attributes (CQAs) separation criterion S of critical pairs of substances are investigated. Rechtschaffen design is used for the creation of models that describe the dependence between CPPs and CQAs. The design space that is obtained at the end is used for choosing the optimal conditions (set point). The method is fully validated at the end to verify the adequacy of the chosen optimal conditions and applied to real samples.

The influence of inorganic salts with chaotropic properties on the chromatographic behavior of ropinirole and its two impurities.

Chaotropic agents recently gained popularity as interesting and useful mobile phase additives in liquid chromatography due to their effect on analytes retention, peak symmetry and separation efficiency. They mimic the role of classical ion-pairing agents, but with less drawbacks, so their use becomes attractive in the field of pharmaceutical analysis. In this paper, the influence of sodium trifluoroacetate and sodium perchlorate on the chromatographic behavior of ropinirole and its impurities is examined. By the extended thermodynamic approach, it was shown that the separation in the given system was predominantly governed by electrostatic interactions between the protonated analytes and the charged surface of the stationary phase, but the ion-pair complex formation in the eluent also proved to be significant. Further, the employment of face-centered central composite design enabled the understanding of the effect of chaotropic agent concentration and its interactions with other factors (acetonitrile content and pH of the water phase) that influence the given chromatographic system. Finally, the same data was used for multi-objective optimization based on the grid point search method. After the method validation, the adequacy of the suggested approach in development of methods for routine pharmaceutical analysis was proven.