sildenafil-citrate and acetonitrile

A method which employed high-performance liquid chromatography coupled with electrochemical detection was developed for the simultaneous determination of sildenafil and its metabolite, N-desmethyl sildenafil, in human plasma has. The method was developed and validated for purposes of its application to a pharmacokinetic study in healthy volunteers after an oral dose of 50mg/tablet under fasting conditions. High precision and accuracy were demonstrated. A one-step liquid-liquid extraction further provides a simple and practical way to process plasma samples containing sildenafil with good quantitative recovery. Sampling lasted for 24h after dosing; consequently a limit of quantitation (LOQ) of 7.858 ng/mL was achieved for sildenafil whereas a LOQ of 8.675 ng/mL was obtained for N-desmethyl sildenafil. The mobile phase consisted of acetonitrile, methanol and phosphate buffer (0.05 M) (18.5:34.5:47.0, v/v/v) pH 7.68. The stationary phase was a C(8) (150 mm x 4.6 mm), 5 microm particle size operated at 27 degrees C. All analytes were stable at the pH of the supernatant, and during the analytical time window. At the applied potential of +1.20 V versus Ag/AgCl, no interferences from endogenous plasma compounds were recorded at the retention times of sildenafil, N-desmethyl sildenafil. High resolution was obtained between the analytes and the employed internal standards.

Topics: Acetonitriles; Administration, Oral; Buffers; Chromatography, High Pressure Liquid; Electrochemistry; Humans; Hydrogen-Ion Concentration; Linear Models; Male; Methanol; Phosphodiesterase Inhibitors; Piperazines; Purines; Reference Standards; Reference Values; Reproducibility of Results; Sensitivity and Specificity; Sildenafil Citrate; Solvents; Sulfones

We developed a method for the identification of 18 illegal adulterants in dietary supplements for erectile dysfunction by using high-performance liquid chromatography-mass spectrometry. The separation was achieved on a Cosmosil 3C18-EB column. The mobile phase consisted of 0.1% formic acid solution and 0.1% formic acid in acetonitrile, with gradient elution at a flow rate of 0.15 mL/min. The proposed method may be useful for the identification of illegal adulterants and for quality control of dietary supplements.

Topics: Acetonitriles; Benzodioxoles; Carbolines; Chromatography, High Pressure Liquid; Dietary Supplements; Food Contamination; Formates; Mass Spectrometry; Phosphodiesterase 5 Inhibitors; Piperazines; Purines; Quality Control; Sildenafil Citrate; Solutions; Sulfones; Tadalafil; Urological Agents; Vasodilator Agents

This work proposes a liquid chromatography-electrospray ionization ion trap mass spectrometry (LC-ESI-ITMS) method, for the quantification of sildenafil (SDF), tadalafil (TDF) and vardenafil (VDF) and their metabolites N-desmethylSDF, O-desethylSDF and N-desethylVDF, preceded by a sample preparation step based on protein and phospholipid elimination. A C8 column (150 mm × 4.6 mm, 5 μm) with ammonium formate (20mM) and acetonitrile as the mobile phase components have been used. This method has been validated, obtaining limits of quantification ranged from 1 to 2.5 ng/mL and 2 to 5 ng/g in serum and brain tissue respectively, while limits of detection ranged from 0.3 to 0.9 ng/mL in serum and 0.6 to 1.9 ng/g in brain tissue. Assay recoveries for low level QC samples were higher than 83% and the matrix effect ranged between 91% and 108% in serum and between 98% and 107% in brain tissue. The method has been applied to the quantification of these compounds in the serum and brain tissue of rats treated intraperitoneally with 10 mg/kg of SDF, TDF or VDF.

Topics: Acetonitriles; Animals; Biotransformation; Brain; Calibration; Carbolines; Chromatography, Liquid; Dealkylation; Formates; Imidazoles; Injections, Intraperitoneal; Limit of Detection; Male; Phosphodiesterase 5 Inhibitors; Piperazines; Purines; Rats; Rats, Sprague-Dawley; Reference Standards; Reproducibility of Results; Sensitivity and Specificity; Sildenafil Citrate; Spectrometry, Mass, Electrospray Ionization; Sulfones; Tadalafil; Tandem Mass Spectrometry; Triazines; Vardenafil Dihydrochloride

Pharmaceutical counterfeiting is a permanently growing problem. Control laboratories are constantly analysing counterfeit medicines. In industrialised countries, one of the main counterfeited class of medicines are erectile dysfunction drugs. This paper describes the development and validation of a fast method to detect and quantify the three authorised phosphodiesterase type 5 inhibitors and five analogues. The method is based on the use of a sub-2 microns polar-embedded column with a gradient using acetonitrile as organic modifier and 10mM ammonium formate buffer (pH 3.5) as aqueous component of the mobile phase. The separation was achieved in less than 4.5 min. The method has also been compared to the registered HPLC method for the assay of Viagra(®) which was considered as the reference method. The method is also compatible with on-line coupling mass spectrometry and will significantly reduce analysis times and solvent consumption.

Topics: Acetonitriles; Analysis of Variance; Chromatography, High Pressure Liquid; Counterfeit Drugs; Linear Models; Phosphodiesterase 5 Inhibitors; Piperazines; Purines; Reproducibility of Results; Sildenafil Citrate; Spectrophotometry, Ultraviolet; Sulfones

Novel sample preparation approaches for HPLC bioanalysis based on the phenomenon that acetonitrile can be separated from water by adding salts or cooling at subzero temperatures have been reported. These two methods are superior to conventional liquid-liquid extraction since the separated acetonitrile phase can be directly injected to the RP-LC system. However, the salting-out method suffers from a potential problem that the remained salt in the acetonitrile phase may harm the MS detector, while the subzero-temperature method is troublesome to operate. Here, we have reported a similar phase separation phenomenon that the acetonitrile aqueous mixture can be separated by adding a hydrophobic solvent; and capitalising on this phase transition phenomenon, we have proposed an alternative approach, named solvent induced phase transition extraction (SIPTE), to extract drug from plasma for HPLC-MS analysis. The proposed SIPTE method is much simpler and avoids contaminating the MS detector. Three structurally diverse drugs were selected as test compounds to design the SIPTE method and to validate the efficiency of this method. The four goals of plasma sample pretreatment for HPLC-MS analysis, i.e. removal of proteins, removal of other low-molecular interferences, preconcentration of the analytes of interest, and matching the sample solvent with the HPLC-MS system, can be rapidly performed in a very simple step by using the SIPTE method.

Topics: Acetonitriles; Chemical Fractionation; Chloroform; Chromatography, High Pressure Liquid; Diterpenes; Finasteride; Humans; Hydrophobic and Hydrophilic Interactions; Mass Spectrometry; Models, Molecular; Pharmaceutical Preparations; Piperazines; Purines; Reproducibility of Results; Sensitivity and Specificity; Sildenafil Citrate; Sulfones

HPLC method for the determination of sildenafil and its metabolite (N-demethylsildenafil) in rat serum has been developed. The technique included a solid phase extraction of the serum samples on a [poly(divinylbenzene-co-N-vinylpyrrolidone)] solid phase extraction sorbent. After conditioning, the cartridge was loaded with 0.5 mL of buffered serum containing internal standard. Elution was made with 1 mL of acetonitrile. After evaporation of the eluates to dryness and reconstitution with methanol, the samples were analyzed on Kromasil C18 column phase with phosphate buffer 0.05 M/acetonitrile: 54/46, pH 8. Detection was carried out using a photodiode array detector. For sildenafil and demethylsildenafil, full validation of the proposed method was provided (linearity range, calibration curves, average extraction efficiency; average intra-day and interday variabilities, limit of detection, limit of quantification, specificity). The proposed method was successfully utilised to quantify sildenafil and N-demethylsidenafil in rat serum for a pharmacokinetic study.

Topics: Acetonitriles; Animals; Buffers; Chromatography, High Pressure Liquid; Hydrogen-Ion Concentration; Phosphodiesterase Inhibitors; Piperazines; Purines; Pyrimidinones; Rats; Rats, Wistar; Reproducibility of Results; Sildenafil Citrate; Spectrophotometry, Ultraviolet; Sulfones

A simple, precise, sensitive and stability-indicating reverse-phase high performance liquid chromatographic (RP-HPLC) method has been developed for the quantitation of sildenafil citrate (SC) in pure form and its pharmaceutical formulations. Method employs water and acetonitrile (48:52 v/v) as mobile phase with flow rate of 1 ml min(-1), LiChrospher C18-5 microm (25 x 0.46 cm) column and UV detection set at 245 nm. The internal standard method using piroxicam (PX) as the internal standard is used. The linear dynamic range of SC was found to be 0.05-7.5 microg ml(-1). The proposed method is successfully employed for the determination of SC in the tablets. The excipients present in the formulations do not interfere with the assay procedure. Analytical parameters were calculated and full statistical evaluation is included.

Topics: Acetonitriles; Chromatography, High Pressure Liquid; Drug Stability; Excipients; Piperazines; Purines; Reproducibility of Results; Sildenafil Citrate; Sulfones; Water