Biomedical subjects

Demetrius G Themelis

Publications and source records attributed to Demetrius G Themelis.

10 recordsLinked to original sources

PubMed2006

Automated determination of flutamide by a validated flow-injection method: application to dissolution studies of pharmaceutical tablets.

The first flow-injection (FI) method for the determination of flutamide--a potent antiandrogen used for the treatment of prostate cancer--is reported. The method is based on the direct measurement of the absorbance of the analyte at 310 nm under flow conditions. Parameters affecting the determination such as detection wavelength, sample injection volume and flow rate were studied and optimized. The assay was validated (linearity, limits of detection and quantitation, accuracy, repeatability, reproducibility and selectivity) for the dissolution studies of flutamide-containing tablets during stability testing. The results were in good agreement with high performance liquid chromatography (HPLC) used as a reference method.

Androgen Antagonists↗

PubMed2006

High-throughput HPLC assay of acyclovir and its major impurity guanine using a monolithic column and a flow gradient approach.

Acyclovir and its major impurity guanine are determined rapidly by the incorporation of a monolithic column (100 mm x 4.6 mm i.d., Merck) to an automated HPLC system. A simple flow gradient protocol was adopted in order to accelerate the separation-detection cycle. Using 0.2% CH(3)COOH (pH 3.1) as the mobile phase and detection at 254 nm, guanine was effectively separated from the system peak (t(R)=1.25 min), while the retention time of acyclovir was 2.35 min. Linearity of the assay was validated in the range 0.1-1.0% guanine and 80-120% acyclovir (n=5). The accuracy and within- and day-to-day precision of the method were also validated, while the limits of detection and quantitation of both analytes were determined. The proposed method was successfully applied to the quality control of acyclovir raw material and the quality and stability control of acyclovir-containing pharmaceutical creams (Hagevir 5%, w/w, Cosmopharm Ltd., Korinthos, Greece).

Acyclovir↗

PubMed2006

Validated high-throughput HPLC assay for nimesulide using a short monolithic column.

High samples analysis rate is a key demand in modern pharmaceutical analysis, especially during new product development and validation of industrial-scale manufacturing process. The present study reports a validated HPLC assay for the dissolution studies of nimesulide-containing tablets (Lizepat 100 mg/tab, Cosmopharm Ltd., Korinthos, Greece). Using a 50 mm x 4.6 mm i.d. monolithic column (Chromolith, Merck) and acetonitrile-phosphate buffer (pH 7.0; 10 mM) (34:66, v/v) as the mobile phase, the separation cycle was completed in 60s at a flow rate of 4.0 ml min(-1). The assay was validated in terms of selectivity against potential impurities of the active ingredient, detection and quantification limits, linearity, accuracy and inter-/intra-day precision. Results from the application of the HPLC method to the accelerated and long-term dissolution stability control of Lizepat tablets (Lot 005) are reported.

Buffers↗

PubMed2006

Flow and sequential injection methods for the spectrofluorimetric determination of aluminium in pharmaceutical products using chromotropic acid as chromogenic reagent.

This work reports rapid and sensitive FI and SI spectrofluorimetric methods for the determination of aluminium in pharmaceutical formulations. The methods are based on the reaction of aluminium with chromotropic acid (CA) in acidic medium to form a water-soluble complex (lambdaex.=360 nm, lambdaem.=385 nm). The proposed methods were validated in terms of linearity, repeatability, detection limit, accuracy and selectivity. The calibration curves were linear over the range of 0.03-2.0 and 0.1-4.0mg/l of aluminium using the FI and SI assays, respectively. The repeatabilities (sr=0.8% and 1.1% at 1mg/l aluminium using the FI and the SI assay, respectively, n=12) were satisfactory. The FI and SI methods proved to be adequately selective and sensitive with respective 3sigma limits of detection equal to cL=0.01 and 0.03 mg/l Al(III). The sampling rates were 120 and 72 h(-1) with the FI and SI assay. The methods were applied successfully to the analysis of pharmaceutical formulations (tablets and suspensions). The results were in good agreement with those by an official reference method and the nominal values of the pharmaceutical products.

Aluminum↗

PubMed2005

Assay of the synthetic estrogen fosfestrol in pharmaceutical formulations using capillary electrophoresis.

This study reports--for the first time--a capillary electrophoretic method for the determination of fosfestrol, a synthetic estrogen used in the treatment of metastatic prostate cancer. The effects of the carrier ion concentration, injected volume and applied voltage were studied and optimized. A 10 mM sodium tetraborate solution was selected as the carrier electrolyte solution, while the sample was injected hydrodynamically by applying a 20 mmHg vacuum for 1 s. The driving voltage was 30 kV and the absorbance of the analyte (peak height) was monitored at 240 nm. Under the above-mentioned conditions, the migration time of fosfestrol was 6.6 min. Linearity was achieved in the analyte range 3-150 mgL(-1) with the detection limit being 1 mgL(-1). The proposed method is adequately precise (s(r)=2.8% at 100 mgL(-1) fosfestrol, n=10) without the use of an internal standard and was applied to the determination of fosfestrol in a pharmaceutical formulation. The results obtained by the proposed method were in good agreement with those derived from the USP reference method.

Antineoplastic Agents, Hormonal↗

PubMed2005

Development and validation of a flow-injection assay for dissolution studies of the anti-depressant drug venlafaxine.

The first flow-injection method has been developed, optimized and validated for the determination of venlafaxine, an antidepressant drug. The method is based on a direct measurement of the absorbance of the analyte in an acidic medium, at 274 nm. Flow-injection parameters, such as sample injection volume and flow rate, were studied and optimized. The proposed method was validated in terms of linearity, repeatability, detection limit, accuracy and selectivity. Linearity was obeyed in the range 30 - 150 mg L(-1) of venlafaxine, while the detection limit (1.5 mg L(-1)) and repeatability (sr < 1.0%, n = 12) were satisfactory. The sampling rate was 30 h(-1). The results of dissolution studies of venlafaxine tablets obtained by the proposed method were in good agreement with those by high-performance liquid chromatography.

Antidepressive Agents, Second-Generation↗

PubMed2004

Automated sample preparation based on the sequential injection principle. Solid-phase extraction on a molecularly imprinted polymer coupled on-line to high-performance liquid chromatography.

A molecularly imprinted polymer (MIP) prepared using caffeine, as a template, was validated as a selective sorbent for solid-phase extraction (SPE), within an automated on-line sample preparation method. The polymer produced was packed in a polypropylene cartridge, which was incorporated in a flow system prior to the HPLC analytical instrumentation. The principle of sequential injection was utilised for a rapid automated and efficient SPE procedure on the MIP. Samples, buffers, washing and elution solvents were introduced to the extraction cartridge via a peristaltic pump and a multi-position valve, both controlled by appropriate software developed in-house. The method was optimised in terms of flow rates, extraction time and volume. After extraction, the final eluent from the extraction cartridge was directed to the injection loop and was subsequently analysed on HPLC. The overall set-up facilitated unattended operation, operation and improved both mixing fluidics and method development flexibility. This system may be readily built in the laboratory and can be further used as an automated platform for on-line sample preparation.

Automation↗

PubMed2004

Rapid spectrofluorimetric determination of lisinopril in pharmaceutical tablets using sequential injection analysis.

The present work reports for the first time a simple and rapid method for the spectrofluorimetric determination of lisinopril (LSP) in pharmaceutical formulations using sequential injection analysis (SIA). The method is based on reaction of LSP with o-phthalaldehyde (OPA) in the presence of 2-mercaptoethanol (borate buffer medium, pH=10.6). The emission of the derivative is monitored at 455 nm upon excitation at 346 nm. The various chemical and physical conditions that affected the reaction were studied. The calibration curve was linear in the range 0.3-10.0 mg L(-1) LSP, at a sampling rate of 60 injections h(-1). Consumption of OPA reagent was significantly reduced compared with conventional flow injection (FI) systems, because only 50 microL of OPA was consumed per run. The method was found to be adequately precise ( s(r)=2% at 5 mg L(-1) LSP, n=10) and the 3 sigma detection limit was 0.1 mg L(-1). The method was successfully applied to the analysis of two pharmaceutical formulations containing LSP. The results obtained were in good agreement with those obtained by use of high-performance liquid chromatography (HPLC), because the mean relative error, e(r), was <1.8%.

Calibration↗

PubMed2002

Flow injection spectrophotometric determination of the antibiotic fosfomycin in pharmaceutical products and urine samples after on-line thermal-induced digestion.

A new flow injection (FI) method for the precise and rapid spectrophotometric determination of the antibiotic fosfomycin (FMC) in urine and pharmaceutical samples is described. The method is based on the on-line quantitative thermal-induced digestion of the analyte prior to injection into the FI system. Ammonium persulfate was used as the oxidation reagent. The resulting orthophosphate ions were determined spectrophotometrically (lambda(max) = 690 nm) using the molybdenum blue approach. Chemical and FI variables that affected on-line oxidation were studied and optimized. The proposed method is very precise (s(r) = 1.2% at 1.0 x 10(-4) mol L(-1) FMC, n = 12), offers a high sampling rate of 60 h(-1), and allows for the determination of the analyte in the range 3.0 x 10(-6) to 3.0 x 10(-4) mol L(-1) with a satisfactory 3sigma detection limit of 1.0 x 10(-6) mol L(-1). Application of the proposed method to urine and pharmaceutical samples yielded accurate results with percentage recoveries in the range 96.4-102.5%.

Ammonium Sulfate↗

PubMed2002

Determination of mineral content of active dry yeast used in pharmaceutical formulations.

The efficiency of seven common methods of digestion of active dry yeast (ADY), which is used in anticariogenic dental formulations, was evaluated for the analytical determination of Fe, Zn, Ca, Mg, Na and K. Four wet-acid digestion and three dry ashing methods are compared in consideration of their estimated reproducibility and metal concentrations obtained. HNO(3), HNO(3)+HCl, HNO(3)+H(2)SO(4) and HNO(3)+HClO(4) were applied for wet digestion of the samples in medium temperatures, while dry ashing at higher temperature with Mg(NO(3))(2) or SrCl(2) as ashing aid agents, were the alternative methods. The final solutions were subsequently analyzed for Fe, Zn, Ca and Mg by flame atomic absorption spectroscopy (FAAS) and for Na and K by atomic emission spectroscopy (AES). Two multivariate statistical methodologies, Analysis of variance (ANOVA) and the Kruskal-Wallis test were applied for the interpretation of the results. Seven additional statistical tests (least-significant difference, Bonferoni, Duncan multiple range, Student-Newman-Keuls, Tuckey significant difference, Tuckey b and Scheffe) were used and proved useful to estimate which of the decomposition methods are outliers. The ideographic approach enabled the comparison of the methods in terms of complexity and difficulty of their steps. Zn and Mg could be reliably determined by any one of the tested methods, while for the other elements, the most powerful method was found and the obtained recoveries were found (>95%).

Data Interpretation, Statistical↗