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In this paper, the mass spectrometry (MS) detection has been applied for screening of fosinopril sodium impurities which arise during forced stress study. Before MS analysis, liquid chromatographic method with suitable mobile phase composition was developed. The separation was done on SunFire 100 turn x 4.6 mm 3.5 mu m particle size column. The mobile phases which consisted of methanol-ammonium acetate buffer-acetic acid, in different ratios, were used in a preliminary study. Flow rate was 0.3 mL min(-1). Under these conditions, percent of methanol, concentration of ammonium acetate buffer and acetic acid content were tested simultaneously applying central composite design (CCD) and artificial neural network (ANN). The combinations of experimental design (ED) and ANN present powerful technique in method optimization. Input and output variables from CCD were used for network training, verification and testing. Multiple layer perceptron (MLP) with back propagation (BP) algorithm was chosen for network training. When the optimal neural topology was selected, network was trained by adjusting strength of connections between neurons in order to adapt the outputs of whole network to be closer to the desired outputs, or to minimize the sum of the squared errors. From the method optimization the following mobile phase composition was selected as appropriate: methanol-10 mM ammonium acetate buffer-acidic acid (80:19.5:0.5 v/v/v). This mobile phase was used as inlet for MS. According to molecular structure and literature data, electrospray positive ion mode was applied for analysis of fosinopril sodium and its impurities. The proposed method could be used for screening of fosinopril sodium impurities in bulk and pharmaceuticals, as well as for tracking the degradation under stress conditions.

In this paper, the chromatographic characterization of fosinopril sodium and fosinoprilat is presented. The first stept was pK(a) determination for the active substance and its degradation product using RP-LC. It was followed by optimization employing the combination of experimental design and artificial neural networks. For the definition of input and output variables, the central composite design for three factors was built. Back propagation algorithm was applied to model the system, and then the optimization of the experimental conditions was carried out in the neural network with 3-8-2 structure, which confirmed to be able to provide the maximum performance. From the method optimization, the most appropriate experimental conditions for fosinopril sodium and fosinoprilat analysis were extracted. The optimized method was validated and applied in the quality control of tablets and for forced degradation studies.

Pramipexole is a dopamine D2-agonist/antiparkinsonian agent in which BI-II 546 CL, BI-II 751 xx and 2-amino benzothiazole are commonly found as impurities. Due to the lack of analytical data on pramipexole and its related substances in bulk drug and pharmaceuticals, we aim at the optimization and characterisation of the chromatographic behaviour of pramipexole and its related substances employing experimental design. The analysis was performed using a C18 column with mobile phases containing different ratios of acetonitrile and water phase (aqueous triethylamine/ortophosporic acid). The detection was performed at 262 nm for pramipexole, BI-II 751 xx and 2-aminobenzthiazole and at 326 nm for BI-II 546 CL. To define the influence of chromatographic parameters on separation, a central composite design was chosen. The content of acetonitrile, TEA and pH of the water phase were identified as the factors with important influences on retention. Using an appropriate mathematical model, we were able to predict retention under different conditions.

The main goal in this investigation was monocratic HPLC determination of dissociation constant values (pK(a)) of pramipexole and its impurities, BI-II 546 CL, BI-II 751 xx and 2-aminobenzothiazole. The chromatographic method is advantageous as a small amount of substance is needed and the degree of substance purity is less important. Analysis was carried out using stationary phases stable in a wide pH range. Triethylamonium phosphoric buffer was selected as appropriate pH controlling solution because it can cover a wide pH range. Detection was done on two different wavelengths, 262 nm for pramipexole, BI-II 751 xx and 2-aminobenzothiazole and at 326 nm for BI-II 546 CL. The constants were calculated from the typical sigmoidal curves of analyte obtained as retention factor versus the pH of the mobile phase.

Fosinopril sodium presents a prodrug for the active angiotensin converting enzyme (ACE) inhibitor, fosinoprilat. The dual elimination of fosinoprilat by the liver and the kidney distinguishes fosinopril from other angiotensin converting enzyme inhibitors. Such ways of elimination are important for antihypertensive therapy of patients on haemodialysis. The paper presents development and evaluation of a new and sensitive liquid chromatographic (LC) method for the analysis of fosinoprilat in plasma obtained from patients on haemodialysis. A microemulsion system mixture as mobile phase has been used for the separation and analysis of fosinoprilat in plasma samples. The plasma samples were injected directly onto the HPLC system (Waters Breeze) after appropriate sample dilution with mobile phase. Separations were performed on the Bakerbond ENV 4.6 mm x 150 mm, 5 mu m particle size column with UV detection at 220 nm. The flow rate was 1.00 mL min(-1). The mobile phase consisted of 1.0% (w/v) of diisopropyl ether, 2.0% (w/v) of sodium dodecyl sulphate (SDS), 6.0% (w/v) of n-propanol and 91 % (w/v) of aqueous 25 mM di-sodium hydrogen phosphate, pH adjusted to 2.8 with 85% orthophosphoric acid. The developed method was then subjected to method validation according to the criteria stated in the FDA bioanalytical method validation guidance. The results for specificity, linearity, low limit of quantification (LLOQ), precision, accuracy and stability were within the accepted criteria. The unique approach applied in this paper makes possible the determination of fosinoprilat even in the presence of metabolites of other drugs, so the method can be used for obtaining the reliable results in a fast and simple way.

The properties of the eluent are the essential factors governing the efficiency in the high-performance liquid chromatography (HPLC) method. A novel approach in retention modelling in the liquid chromatographic separation of fosinopril sodium and its degradation product, fosinoprilat, applying a microemulsion as the mobile phase, was used. The modifications of the mobile phase included the changes to the type of the lipophilic phase, the type and concentration of co-surfactant and surfactant, as well as the pH of the mobile phase. In this study, a full factorial 2(3) design, as the optimal method for screening of the experiment, was applied for selecting factors which had an influence on separation. Optimisation was done by a central composite design. An appropriate resolution with reasonable retention times was obtained with a microemulsion containing 0.9% w/w of cyclohexane, 2.2% w/w of sodium dodecyl sulphate (SDS), 8.0% w/w of n-butanol and 88.9% of aqueous 25 mM disodium phosphate, the pH of which was adjusted to 2.8 with 85% orthophosphoric acid. Separations were performed on an X-Terra 50-mmx4.6-mm, 3.5- mu m particle size column at 30 degrees C. UV detection was performed at 220 nm and with a flow rate of 0.3 mL min(-1). The established method was validated and applied for analysis of appropriate tablets. The proposed chromatographic procedure for the separation of fosinopril sodium and its degradation product is less expensive compared with the conventional reversed-phase HPLC method, as well as being simple and rapid. The optimised and validated method can be used for separation, identification and simultaneous determination of fosinopfil sodium and fosinoprilat in bulk drug and in pharmaceutical dose forms.

Indinavir, an antiviral drug, is a member of the novel hydroxyaminopentane amides class of HIV-1 protease inhibitors. It is the active substance in capsules which contain 400 mg indinavir as the sulfate salt and degradation products, a lactone and cis-aminoindanol, arising as a result of hydrolysis of its amide bond (at most 1.5% of the lactone and 0.5% cis-aminoindanol). RP HPLC has been evaluated as a method for qualitative and a quantitative analysis of indinavir and its degradation products in capsules. During method development the effects of several stationary and mobile phases on the separation were investigated. Separations were performed on an X Terra RP18, 150 mm x 4.6 mm, 5 mu m particle size, column at 20 degrees C. The mobile phase was 35:65 (v/v) mixture of acetonitrile and an aqueous solution of sodium lauryl sulfate and triethylamine. UV detection was performed at 214 nm. Important statistical data were determined for validation of the selectivity/specificity, linearity, precision, robustness, limit of detection, and limit of quantitation of the method. The validated method was then used for determination of amounts of indinavir (recovery between 100.6 and, 103.1%) and compounds resulting from hydrolysis of its amide bond (the lactone, 0.265%, and cis-aminoindanol, 0.07%). The method is suitable for simultaneous determination of indinavir and its degradation products in pharmaceuticals and the bulk drug.

The reversed-phase high-performance liquid chromatographic (RP-HPLC) method has been developed for the simultaneous determination of fosinopril-sodium and its degradation product in Monopril® tablets. The chromatographic system Hewlett Packard 1100 consisted era HP 1100 pump, HP 1100 UV-VIS detector and HP ChemStation integrator. Separations were performed on the X Terra™ 150 mm x 4.6 mm, 5 μm particle column at 45 °C. The samples were introduced through a Rheodyne injector valve with a 20 μL sample loop. Methanol-water (75:25 V/V) was used as a mobile phase, with flow rate 1 mL/min. pH was adjusted to 3.1 with ortophosphoric acid. UV detection was performed at 220 nm. Propylparaben was used as an internal standard. The results obtained showed a good agreement with the declared contents. Recovery values for fosinoprit-sodium were from 101.6% to 102.9%. Content of degradation product SQ 27519 was lower than 5%. The proposed method is rapid, accurate, selective and because of its sensitivity and reproducibility, it may be used for the quantitative analysis of fosinopril-sodium and its degradation product in Monopril® tablets.

The multi-component preparation Co -Diovan (R) 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 x 4.6 mm; 5 mm particle size) at 25 degrees 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 mu L, 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.

Perindopril tert-butylamine is a new member of angiotensin-converting enzyme inhibitors group used in the treatment of hypertension and heart failure. In this paper, the evaluation of reversed-phase high-performance liquid chromatographic method (RP-HPLC) for the determination of impurities level of perindopril tert-butylamine in tablets was done. The chromatograms were recorded using a Hewlett Packard 1100 chromatographic system with DAD detector. Separations were performed on a YMC-Pack C8 column (250 mm x 4.6 mm; 5 mu m particle size) at 50 degrees C column temperature. Mobile phase was a mixture of acetonitrile-potassium phosphate buffer (0.05 M) (37:63, v/v) (pH 2.5). pH of the mobile phase was adjusted with ortophosphoric acid. Mixture of acetonitrile-water (40:60, v/v) was used as a solvent. Injection volume was 50 mu l, flow rate 1.7 ml min(-1) and UV-detection was performed at 215 nm. The developed method subjected to method validation and parameters in terms of selectivity, linearity, precision, accuracy, limit of detection, limit of quantitation and robustness were defined. The validated method is suitable for the simultaneous determination of perindopril tert-butylamine as well as its impurities in pharmaceuticals.

The main objective of the work discussed in this paper was evaluation of a chromatographic method for simultaneous determination of hydrochlorothiazide (HCTZ), lisinopril (L), and their impurities in pharmaceuticals. Chlorothiazide (CTZ) and disulfonamide (DSA), as potential impurities in hydrochlorothiazide, and diketopiperazine (DKP), as an impurity of lisinopril, were analyzed. The chromatographic behaviour of these substances on different columns was studied using mobile phases of different polarity. The optimum separations were achieved by gradient elution on a 4.6 mm x 20 mm, 3.5 mu m particle size, C-18 column. The mobile phase was a gradient prepared by mixing 7:93 (v/v) acetonitrile-25 mm potassium dihydrogen phosphate, pH 5, and 50:50 (v/v) acetonitrile-25 mm potassium dihydrogen phosphate pH 5 in different ratios. The flow rate was 1.0 mL min(-1). UV detection was performed at 215 nm. Methylparaben was used as internal standard. The method was validated for selectivity, linearity, precision,. and accuracy. The limits of detection, LOD, and quantification, LOQ, were determined experimentally. Because of its speed and accuracy the method can be used for quality-control analysis.

The use of microemulsions as eluents in HPLC has shown excellent potential. We have developed a novel approach for the analysis of Simvastatin and its six impurities, applying microemulsions as mobile phase. The method was validated and applied to the analysis of commercially available tablets in order to confirm that the proposed approach is useful for the application of this technique to drug analysis. A microemulsion eluent containing 0.9% w/w of diisopropylether, 1.7% w/w of sodium dodecyl-sulphate (SDS), 7.0% w/w of co-surfactant such as n-butanol and 90.4% w/w of aqueous 25 mM di-sodium phosphate pH 7.0 was used for the analysis. Separations were performed on a 3.5 mu m X Terra(TM) 50 x 4.6 mm column at 30 degrees C. Detection was performed at 238 nm with an eluent flow rate of 0.3 mL min(-1). The optimized and validated method can be used for the identification and simultaneous determination of Simvastatin and its six impurities in bulk drug and in pharmaceutical dosage forms.

The simple and rapid RP-HPLC method, for the simultaneous determination of lidocaine and cetrimonium bromide in the presence of pellet color corrigent, was developed. Separations were performed on a Beckman Ultrasphere ODS 4.6 mm x 15 cm, 5 μm particle column at 40°C. The mobile phase consisted of water phase and acetonitrile (72:28:V/V), pH value of the mobile phase was adjusted to 2.0 with 85% ortophosphoric acid. Bisacodil was used as an internal standard. The flow rate was 1 ml/min and UV detection was performed at 208 nm. The proposed RP-HPLC method was validated and all the parameters for the validation of the method are given. According to the obtained results, the developed method was found to be suitable and accurate for the determination of these drugs in commercial formulations.

The successful analysis of drugs in complex pharmaceutical formulations by reversed-phase high performance liquid chromatography (RP-HPLC) relies upon the optimization of the chromatographic conditions, the sample preparation and post-column detection. HPLC separation of mixtures depends on a large number of factors. The optimization of RP-HPLC method defines the simultaneous influence of some important conditions, such as column type, mobile phase composition, pH of the mobile phase, column temperature and flow rate, to the separation and determination. In this paper the RP-HPLC method was applied for the optimal separation of lidocaine, cetrimonium bromide and color in the pharmaceutical pellets (Septalen(R) pellets). The selectivity factor values defined the optimal conditions, which were confirmed by analyzing the appropriate mathematical models. With the aid of the response surface methodology (RSM) it was possible to anticipate to a certain degree and precisely select optimal experimental conditions. Separations were performed on a Beckman Ultrasphere ODS 4.6 x 150 mm, 5 mum particle size column. Samples were introduced through a Rheodyne injector valve with a 20 muL sample loop. UV detection was performed at 208 nm. The optimization was performed within the pH range from 2.0 to 5.5; temperature range from 20 degrees C to 55 degrees C and composition of the mobile phase acetonitrile water from (15:85 V/V) to (35:65 V/V). The three-D graphs, constructed with sixty-four experimental points, confirmed the optimal conditions for the separation of lidocaine, cetrimonium bromide and color in analyzed pharmaceutical preparations.

A novel and unique approach was used for retention modelling in the separation of simvastatin and six impurities by liquid chromatographic using a microemulsion as mobile phase. A microemulsion is a modification of a micellar system where a lipophilic organic solvent is dissolved in the micelles; for that reason, microemulsions are usually treated as solvent-modified micellar solutions. When microemulsions are used as eluents in HPLC separations, solutes partition between the charged oil droplets and the aqueous buffer phase. The complexity of the composition of the microemulsion permits extensive manipulations to be made during method development in order to achieve acceptable resolution of such a complex mixture of substances. In order to avoid a laborious "trial and error" procedure, a 2(3) full factorial design was applied for choosing an optimal microemulsion composition to obtain good separation in a reasonable run time. Organic solvent, sodium dodecyl sulphate, and n-butanol content were varied within defined experimental domain. Optimal conditions for the separation of simvastatin and its six impurities were obtained using an X Terra(TM) 50 x 4.6 mm, 3.5 mum particle size column at 30degreesC. The mobile phase consisted of 0.9% w/w of diisopropyl ether, 2.2% w/w of sodium dodecylsulphate (SDS), 7.0% w/w of co-surfactant such as n-butanol, and 89.9% w/w of aqueous 25 mM disodium phosphate pH 7.0.

In this paper the experimental design has been applied to define the optimum chromatographic conditions for the separation of Fosinopril sodium and its degradation product, fosinoprilat. Fosinopril is a prodrug and after being hydrolysed, it becomes an active drug fosinoprilat. For experimental screening full factorial design 2 3 was applied. Methanol content, PH of the mobile phase and column temperature were independent variables or factors to be investigated in two levels - much greater thanlowmuch less than and much greater thanhighmuch less than. Capacity and selectivity factors were chosen as dependent variables and matrix was applied to estimate coefficients of the linear model. After experimental screening, RSM (response surface methodology) was applied for optimization. Optimum conditions were: X Terra(TM) 150 mm x 4.6 mm, 5 mum particle column at 45 degreesC; methanol-water (75 : 25 v/v) at pH 3.1 as a mobile Phase, with a flow rate of 1 mL min(-1). UV detection was performed at 220 nm. Propylparaben was used as an internal standard. The proposed method is rapid, accurate, selective and because of its sensitivity and reproducibility, it may be used for the quantitative analysis of fosinopril sodium and its degradation product in Monopril(R) tablets. Recovery values for fosinopril sodium were between 101.6% and 102.9% and content of degradation product fosinoprilat was lower than 5%. Applying the chemometrical approach enables a relatively limited number of experiments to define factors which affect the chromatographic behavior of investigated substances and obtain optimum conditions for their analysis.

A RP-HPLC method for quantification of allantoin in silk of fifteen maize hybrids (Zea mays L., Poaceae) was described. Following extraction of the plant material with an acetone-water (7:3, V/V) mixture, filtration and dilution, the extracts were analyzed without previous chemical derivatization. Separation and quantification were achieved using an Alltech Econosil C18 column under isocratic conditions at 40 degreesC. The mobile phase flow (20% methanol -80% water with 5 mM sodium laurylsulfate added at pH 2.5, adjusted with 85% orthophosphoric acid; pH of water phase was finally adjusted at 6.0 by addition of triethylamine) was maintained at 1.0 mL/min. Column effluent was monitored at 235 nm. This simple procedure afforded efficient separation and quantification of allantoin in plant material, without interference of polyphenols or other plant constituents of medium to high polarity, or similar UV absorption. Our study revealed that the silk of all investigated maize hybrids could be considered relatively rich in allantoin, covering the concentration range between 215 and 289 mg per 100 g of dry plant material.

The reversed-phase high-performance liquid chromatographic (RP-HPLC) method has been developed and validated for the simultaneous determination of imatinib mesylate and of the impurity product in Glivec(R) capsules (Novartis, Switzerland). Separations were performed on a X Terra(TM) 150 mm 4.6 mm, 5 mum particle size column at 25 degreesC. The mobile phase was a mixture of methanol-water-triethylamine (25:74: 1, v/v/v) with flow rate of 1.0 ml min(-1). pH value of water-triethylamine (TEA) was adjusted to 2.4 with orthophosphoric acid before adding of methanol. UV detection was performed at 267 nm. Acetaminophen was used as an internal standard. The method was validated statistically for its selectivity, linearity, precision, accuracy and robustness. Due to its speed and accuracy, the method may be used for quality control analyses.

For the determination of the optimal RP-HPLC chromatographic conditions for the separation of imatinib mesylate and its impurity STI 509-00 experimental design 2(4) was applied. All the factors that affect imatinib mesylate/STI 509-00 separation, as well as their mutial interations were investigated. Methanol and triethylamine content in the mobile phase, pH of the mobile phase and column temperature were independent variables or factors to be investigated in two levels: "low" and "high". Capacity factor was chosen as a dependent variable. From the experimentally determined capacity factor values, it was defined the factors that affect to chromatographic system the most. Applying response surface methodology the appropriate graphs were constructed from experimental points and optimal chromatographic conditions for the separation were defined. Optimal conditions for the separation of imatinib mesylate and STI 509-00 were obtained using X Terra 150 mm x 4.6 mm, particle size 5 mum column at 25 degreesC. Mobile phase consisted of 250 ml of methanol, 740 ml of water and 10 ml of triehylamine. pH of water phase was adjusted to 2.4 with 85% orthophosphoric acid and than methanol was added.

In this paper the second-derivative spectrophotometric method for the simultaneous determination of lidocaine (CAS 137-58-6) and hydrocortisone acetate (CAS 50-03-3) in suppositories is described. One suppository contains 60 mg of lidocaine and 5 mg of hydrocortisone acetate. Optimal conditions for the quantitative analysis were settled. The second-derivative spectra were recorded in the range from 210 to 380 nm against methanol. Determination of lidocaine was performed at 256.0 nm and hydrocortisone acetate at 260.5 nm, using the "zero crossing" method. The results obtained show that there was no interference of ingredients matrix under the mentioned experimental conditions. The method is simple, rapid and precise and can be used in a routine analysis of such pharmaceutical dosage forms.

A rapid and sensitive reverse-phase high performance liquid chromatography (RP-HPLC) method with ultra-violet (UV) detection for a routine control of hydrochlorothiazide and captopril in tablets was developed. The chromatographic system Hewlet Packard 1100 consisted of a HP 1100 pump, HP 1100 UV-VIS detector and HP ChemStation integrator. The samples were introduced through a Rheodyne injector valve with a 20-muL sample loop. The isocratic system consisted of a Beckman Ultrasphere ODS 4.6 mm x 15 cm, 5-mum-particle column and a mobile phase containing methanol/water (45:55 v/v). The pH of the mobile phase was adjusted to 3.8 with 85% ortophosphoric acid. Quantitation was accomplished using the internal standard method. At the selected conditions, the other excipients of the tablets did not interfere in the assay of active substances. The developed RP-HPLC method was validated, so linearity, precision, accuracy, robustness, limit of quantitation and limit of detection were investigated. For the robustness test, three factors were considered: the composition of the mobile phase, the pH of the mobile phase, and temperature. With the aid of response surface metodology (RSM), it was possible to precisely define the robustness of the method.

The optimization of RP-HPLC method defined the simultaneous influence of some important conditions, such as the mobile phase composition, pH of the mobile phase and temperature, on the separation and determination. The RP-HPLC method was done for the determination of paracetamol, caffeine and propyphenazone in a multicomponent pharmaceutical dosage form. The separation factor values define the optimal conditions, which were confirmed by analysing the appropriate mathematical models. The chromatographic system Hewlett Packard 1100 consisted of a HP 1100 pump, HP 1100 UV-VIS detector and HP integrator. Separations were performed on a Beckman Ultrasphere ODS 4.6 x 150 mm, 5 microns particle size column. Samples were introduced through a Rheodyne injector valve with a 20 microL sample loop. UV detection was performed at 265 nm and phenobarottons was used as an internal standard. The optimization was performed within the pH range from 2.5 to 6.0; temperature range from 20 degrees C to 55 degrees C and composition of the mobile phase methanol-water from (30:70 V/V) to (65:35 V/V). The three-D graphs, constructed with sixty-four experimental points, confirmed the optimal conditions for the determination of the investigated analgetic drugs.