Development and validation of an HPLC method to be used for simultaneous detection and quantification of different statins after ex vivo skin diffusion studies.

A novel high performance liquid chromatography (HPLC) method was developed and validated to simultaneously analyse all statins currently available globally (atorvastatin, fluvastatin, lovastatin, mevastatin, pitavastatin, pravastatin, rosuvastatin, simvastatin). A Venusil XBP C18(2) reverse phase column (150 x 4.6 mm) with a 5 µm particle size was used. The gradient conditions started at 25% acetonitrile, which linearly increased to 90% after 1.0 min, held at 90% until 6.5 min, and lastly, re-equilibrated to starting conditions. The mobile phase consisted of acetonitrile/water and 0.005 M (0.2%) octane sulphonic acid-Na (pH 3.5). The flow rate was set at 1.0 ml/min with a 10 µl injection volume. The HPLC method indicated linearity (R² =0.9999) within the concentration range of 0.2-206.4 µg/ml. The limit of detection (LOD) and limit of quantification (LOQ) values were found to be within the permissible criteria of ≤15% and ≤20%, respectively. Following an appropriate investigation of all the parameters for method validation, it was confirmed that the HPLC method was successfully validated and proven to be accurate to simultaneously quantify statins even in combination with other excipients used during the formulation of nano-emulsions and nano-emulgels.

Determination of lovastatin, mevastatin, rosuvastatin and simvastatin with HPLC by means of gradient elution.

A novel HPLC method with UV detection was developed and validated in skin penetration (in vitro) studies to identify and quantify lovastatin, mevastatin, rosuvastatin and simvastatin. A Venusil XBP C18 (2), 150 x 4.6 mm, 5 µm column (Agela Technologies, Newark, DE) was used with gradient elution (start at 45 % acetonitrile and increase linearly to 90 % after 1 min; hold at 90 % until 6 min and then re-equilibrate at start conditions) and the mobile phase consisted of (A) Milli-Q ® water and 0.1% orthophosphoric acid, and (B) HPLC grade acetonitrile. The flow rate was set at 1 ml/min, 240 nm UV detection and an injection volume of 10 µl. Linearity was obtained over a range of 0.50-200.00 µg/ml and correlation coefficients ranging from 0.998-1.000 were obtained. Average recovery ranged from 95.9-100.6 %. The LOD and LOQ values obtained from the slope of a calibration curve and the standard deviation of the response ranged from 0.0138-0.0860 µg/ml and 0.0419-0.2615 µg/ml, respectively, where lovastatin and simvastatin could be detected at a concentration similar to the other statins, but could only be quantified at a higher concentration than the remaining statins. The specificity of the method was proved as accurate and quantification of statins was found, even within the incorporation of other compounds.

Estimation of simvastatin and cetirizine by RP-LC method: Application to freeze and thaw (FT) stability studies.

Sensitive, simple, reliable and rapid HPLC technique for the estimation of simvastatin (SMV) and cetirizine has been designed in this study. The chromatographic conditions were set using Shimadzu LC-10 AT VP pump, with UV detector (SPD-10 AV-VP). System integration was performed with CBM-102 (Bus Module). Partitioning of components was attained with pre-packed C-18 column of Purospher Star (5 µm, 250 x 4.6 mm) at ambient conditions. Injected volume of sample was 10 µl. Mobile phase was composed of 50:50 v/v ratio of Acetonitrile/water (pH 3.0 adjusted with ortho-phosphoric acid) having 2 ml/minutes rate of flow. Compounds were detected in UV region at 225 nm. Percent Recovery of simvastatin was observed in the range of 98-102%. All results were found in accept table range of specification. The projected method is consistent, specific, precise, and rapid, that can be employed to quantitate the SMV along with cetirizine HCl. It was estimated by 3 successive cycles of freeze and thaw stability. Results of FT samples were found within accept table limits the method was developed and validated in raw materials, bulk formulations and final drug products.

Expanding Transdermal Delivery with Lipid Nanoparticles: A New Drug-in-NLC-in-Adhesive Design.

A monolithic drug-in-NLC-in-adhesive transdermal patch, with a novel design, was developed for codelivery of olanzapine (OL) and simvastatin (SV). Nanostructured lipid carriers (NLC) and enhancers were used as passive strategies, while the pretreatment of the skin with Dermaroller was tested as an active approach. The formulation was optimized for composition in a quality by design basis, in terms of enhancer and adhesive, with focus on permeation behavior, adhesion properties, and cytotoxicity. Propylene glycol promoted the best permeation rate for both drugs, with enhancement ratios of 8.1 and 12.9 for OL and SV, respectively, relative to the corresponding Combo-NLC patch without enhancer. Molecular dynamics results provided a rationale for these observations. The adhesive type displayed an important role in skin permeation, reinforced by the presence of the enhancer. Finally, Dermaroller pretreatment did not promote a significant improvement in permeation, which highlights the role of the combination of NLC with chemical enhancer in the transdermal patch as the main driving force in the process. It is also observed that NLC are able to reduce cytotoxicity, especially that associated with SV. This work provides a promising in vitro-in silico basis for a future in vivo development.

Development and validation of a reversed-phase HPLC method for simultaneous analysis of butylhydroxyanisol, simvastatin and its impurities in tablet dosage forms.

A simple, rapid, and sensitive RP-HPLC method using photodiode array detection was developed and validated for the simultaneous determination of butylhydroxyanisol and simvastatin with its impurities in tablet forms. Chromatographic separation was achieved on a Phenomenex Hypersil (250×4.6 mm, 5 µm) column using the mobile phase acetonitrile-sodium acetate (12 mM) buffered to 4.2 with glacial acetic acid. The flow rate was 1.7 mL/min, and the UV detection were made at 238 nm for simvastatin and its impurities and at 290 nm for butylhydroxyanisol. The system suitability solution used for peak impurity identification was generated in-situ without use of any impurity reference standard. The method was validated according to ICH Q2(R1) guidelines, and the acceptance criteria for accuracy, precision, linearity, specificity, robustness, LOD, and LOQ, were met in all cases. Moreover, the reproducibility results obtained by 22 Official Medicines Control Laboratories (OMCL) of European Directorate were satisfactory. The compounds selected for impurity validation were based on those found during long term and accelerate stability studies carried out on several formulation tablets from Moroccan and other markets. The described method was robust and successfully applied in quality control laboratories for routine analysis to determine the butylhydroxyanisol and simvastatin with its impurities content in tablet dosage forms.

Simultaneous quantitation of aspirin, amlodipine and simvastatin in a fixed dose combination of encapsulated tablet formulation by HPLC-UV method.

A high-pressure liquid chromatography (HPLC-UV) based simple and specific method for simultaneous quantitative determination of aspirin, amlodipine besylate and simvastatin in a capsule formulation has been developed and validated according to ICH guidelines. Chromatographic separation of the three drugs was carried out by aSpherisorbODS2 reverse phase column (4.6 x 250 mm; 5 µm) using amobile phase, which consisted of 70: 30 (v/v) mixture of acetonitrile and triethylamine phosphate buffer (pH 3; 0.015 M) with final pH adjusted to 2.5 using dilute ortho-phosphoric acid, at a flow rate of 1mL/min. The eluents were detected at UV wavelength of 237 nm and the retention times for aspirin, amlodipine besylate and simvastatin were ~2.7 mins, ~6.1 mins and ~10.5mins, respectively. This method is suitable and specific for the three drugs and was found to be linear (R2>0.995), accurate, specific, reproducible and robust in the concentration range of 375 to 1125mcg/ml for aspirin, 25 to 75mcg/ml for amlodipine besylate and 50 to 150mcg/ml for simvastatin. This simple and convenient method could be easily utilized for the characterization and quantitation of the three drugs in a single formulation for combination therapy of cardiovascular diseases.

Generation of statin drug metabolites through electrochemical and enzymatic oxidations.

The generation of key drug metabolites for the purpose of their complete structural characterization, toxicity testing, as well as to serve as standards for quantitative studies, is a critical step in the pharmaceutical discovery and development cycle. Here, we utilized electrochemistry/mass spectrometry for the detection and subsequent generation of six phase I metabolites of simvastatin and lovastatin. Both simvastatin and lovastatin are widely used for the treatment of hypercholesterolemia. There are known drug-drug interaction issues of statin therapy, and it has been suggested that the oxidative metabolites may contribute to the cholesterol-lowering effect of both statins. Of the known phase I metabolites of simvastatin and lovastatin, none are commercially available, and chemical means for the synthesis of a very few of them have been previously reported. Here, we report that electrochemical oxidation of less than 1 mg each of simvastatin and lovastatin led to the generation of three oxidative metabolites of each parent to allow complete nuclear magnetic resonance characterization of all six metabolites. The yields obtained by the electrochemical approach were also compared with incubation of parent drug with commercially available bacterial mutant CYP102A1 enzymes, and it was found that the electrochemical approach gave higher yields than the enzymatic oxidations for the generation of most of the observed oxidative metabolites in this study.

Micellar liquid chromatography as a sustainable tool to quantify three statins in oral solid dosage forms.

A method based on micellar liquid chromatography has been developed to determine rosuvastatin, lovastatin and simvastatin in oral solid dosage forms. Samples were solved in mobile phase up to the target concentration, filtered and directly injected. The three statins were resolved in 30 min, using an aqueous solution of 0.10 M sodium dodecyl sulfate - 7.0% 1-butanol, buffered at pH 3 with 0.01 M phosphate salt as mobile phase, running under isocratic mode at 1 mL/min through a C18 column. Detection was at 240 nm. The effect of sodium dodecyl sulfate on elution strength was more important than that of the organic solvent. The procedure was successfully validated by the guidelines of the International Council for Harmonization in terms of: specificity, linearity (r2 > 0.990), calibration range (1.5 - 15 mg/L for rosuvastatin, 0.5-10 mg/L for lovastatin and simvastatin), limit of detection (0.4, 0.2 and 0.15 mg/L for rosuvastatin, lovastatin and simvastatin, respectively), trueness (98.8-101.7%), precision (<2.7%), carry-over effect, robustness, and stability. Values were inside the acceptance criteria of the Methods, Method Verification and Validation, Food and Drug Administration-Office of Regulatory Affairs, thus ensuring the reliability of the results. The main feature was the low proportion of organic solvent used, thus making the procedure sustainable and green. Besides, it was easy-to-conduct and with high sample-throughput, and then useful for routine analysis in pharmaceutical quality control. Finally, it was applied to commercial pharmaceutical preparations.

Simvastatin Coadministration Modulates the Electrostatically Driven Incorporation of Doxorubicin into Model Lipid and Cell Membranes.

Understanding the interactions between drugs and lipid membranes is a prerequisite for finding the optimal way to deliver drugs into cells. Coadministration of statins and anticancer agents has been reported to have a positive effect on anticancer therapy. In this study, we elucidate the mechanism by which simvastatin (SIM) improves the efficiency of biological membrane penetration by the chemotherapeutic agent doxorubicin (DOX) in neutral and slightly acidic solutions. The incorporation of DOX, SIM, or a combination of them (DOX:SIM) into selected single-component lipid membranes, zwitterionic unsaturated 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), neutral cholesterol, and negatively charged 1,2-dimyristoyl-sn-glycero-3-phospho-l-serine (DMPS) was assessed using the Langmuir method. The penetration of neutral lipid monolayers by the codelivery of SIM and DOX was clearly facilitated at pH 5.5, which resembles the pH conditions of the environment of cancer cells. This effect was ascribed to partial neutralization of the DOX positive charge as the result of intermolecular interactions between DOX and SIM. On the other hand, the penetration of the negatively charged DMPS monolayer was most efficient in the case of the positively charged DOX. The efficiency of the drug delivery to the cell membranes was evaluated under in vitro conditions using a panel of cancer-derived cell lines (A172, T98G, and HeLa). MTS and trypan blue exclusion assays were performed, followed by confocal microscopy and spheroid culture tests. Cells were exposed to either free drugs or drugs encapsulated in lipid carriers termed cubosomes. We demonstrated that the viability of cancer cells exposed to DOX was significantly impaired in the presence of SIM, and this phenomenon was greatly magnified when DOX and SIM were coencapsulated in cubosomes. Overall, our results confirmed the utility of the DOX:SIM combination delivery, which enhances the interactions between neutral components of cell membranes and positively charged chemotherapeutic agents.

Use of Entero-Test, a simple approach for non-invasive clinical evaluation of the biliary disposition of drugs.

AIM: To evaluate the non-invasive collection of bile from healthy human subjects for the qualitative characterization of the biliary disposition of a drug, using spectrometric techniques. METHODS: Twenty subjects underwent non-invasive bile capture using a peroral string test (Entero-Test) device prior to and following a single oral dose of simvastatin (80 mg). The device, consisting of a weighted gelatin capsule containing a highly absorbent nylon string, was swallowed by each subject with the proximal end of the string taped to the face. Once the weighted string was judged to have reached the duodenum, gallbladder contraction was stimulated in order to release bile. The string was then retrieved via the mouth, and bile samples were analysed for drug-related material using spectrometric and spectroscopic techniques following solvent extraction. RESULTS: Numerous metabolites of simvastatin were detected, and the major metabolites were consistent with those reported from studies where bile was collected using invasive techniques from patients dosed with [(14) C]-simvastatin. CONCLUSIONS: The results from this study demonstrate the utility of deploying the Entero-Test in human studies to provide structural information on biliary metabolites. This can be readily applied in drug development studies, including those in the target patient population and may eliminate the need for more invasive sampling techniques.

An Electrochemical Strategy for the Simultaneous Detection of Doxorubicin and Simvastatin for Their Potential Use in the Treatment of Cancer.

The aim of this study was to develop a disposable, simple, fast, and sensitive sensor for the simultaneous electrochemical detection of doxorubicin (DOX) and simvastatin (SMV), which could be used in preclinical studies for the development of new pharmaceutical formulations for drug delivery. Firstly, the electrochemical behavior of each molecule was analyzed regarding the influence of electrode material, electrolyte solution, and scan rate. After this, the proper electrode material, electrolyte solution, and scan rate for both active substances were chosen, and a linear sweep voltammetry procedure was optimized for simultaneous detection. Two chronoamperometry procedures were tested, one for the detection of DOX in the presence of SMV, and the other one for the detection of DOX and SMV together. Finally, calibration curves for DOX and SMV in the presence of each other were obtained using both electrochemical methods and the results were compared. The use of amperometry allowed for a better limit of detection (DOX: 0.1 µg/mL; SMV: 0.7 µg/mL) than the one obtained in voltammetry (1.5 µg/mL for both drugs). The limits of quantification using amperometry were 0.5 µg/mL for DOX (dynamic range: 0.5-65 µg/mL) and 2 µg/mL for SMV (dynamic range: 2-65 µg/mL), while using voltammetry 1 µg/mL was obtained for DOX (dynamic range: 1-100 µg/mL) and 5 µg/mL for SMV (dynamic range: 5-100 µg/mL). This detection strategy represents a promising tool for the analysis of new pharmaceutical formulations for targeted drug delivery containing both drugs, whose association was proven to bring benefits in the treatment of cancer.

Electrochemical Oxidation of Different Therapeutic Classes of Pharmaceuticals Using Graphite-PVC Composite Electrode.

This study reports electrochemical treatment of different therapeutic classes of pharmaceuticals (caffeine, prazosin, enalapril, carbamazepine, nifedipine, levonorgestrel, and simvastatin) in a mixture. The electrochemical process was investigated using graphite-PVC anode at different applied voltages (3, 5, and 12 V), initial concentrations of studied pharmaceuticals in aqueous solution (5 and 10 mg/L), and concentrations of sodium chloride (1 and 2 g/L). The % removal of pharmaceuticals increased with the applied voltage, and was found higher than 98% after 50 min of electrolysis at 5 V. Energy consumption ranged between 0.760 and 3.300 Wh/mg using 12 V being the highest value compared to 3 and 5 V. The formation of chlorinated by-products from four selected pharmaceuticals, simvastatin (C11H13Cl3O5, and C10H12Cl4O3), prazosin (C13H12Cl3N5O3 and C10H11Cl4N2O2), carbamazepine and caffeine (C15H11N2O2Cl and C8H9N4O2Cl) was identified and elucidated using liquid chromatography-time of flight mass spectrometry (LC-TOF/MS).

Use of the entero-test, a novel approach for the noninvasive capture of biliary metabolites in dogs.

Preclinical information on the biliary metabolites of a drug candidate is typically obtained through the collection of bile after surgical cannulation of the bile duct. In this study, we describe a novel approach using the Entero-Test, a simple device that facilitates the noninvasive sampling of duodenal bile. The Entero-Test was used to collect bile from six fasted dogs that had been dosed either orally with simvastatin (SV) or intravenously with simvastatin hydroxy acid (SVA), compounds that have been previously reported to undergo extensive metabolism and biliary secretion in the dog. The devices, consisting of a weighted gelatin capsule containing 90 cm of a highly absorbent nylon string, were swallowed by each dog with the proximal end of the string taped to the animal's face. Once the weighted string had reached the duodenum, gallbladder contraction was stimulated to release bile. Each bile-stained string was then retrieved via the mouth and, after solvent extraction, samples were analyzed for drug-related material by ultraperformance liquid chromatography-mass spectrometry and NMR spectroscopy. Numerous metabolites of SV and SVA were observed, and, in general, the major metabolites have been reported previously from studies with bile duct-cannulated animals dosed with [14C]SV or [14C]SVA. The results from this study demonstrate the utility of deploying the Entero-Test in absorption, distribution, metabolism, and elimination studies to provide information on the nature of biliary metabolites, which, on occasion, may be sufficient to negate the need for more invasive sampling techniques. The benefits and limitations of the technique are discussed.

Quantitative analysis of the cholesterol-lowering drugs ezetimibe and simvastatin in pure powder, binary mixtures, and a combined dosage form by spectrophotometry, chemometry, and high-performance column liquid chromatography.

Simple, accurate, sensitive, and precise UV spectrophotometric, chemometric, and HPLC methods were developed for simultaneous determination of a two-component drug mixture of ezetimibe (EZ) and simvastatin (SM) in laboratory-prepared mixtures and a combined tablet dosage form. Four spectrophotometric methods were developed, namely, ratio spectra derivative, ratio subtraction, isosbestic point, and mean centering of ratio spectra. The developed chemometric-assisted spectrophotometric method was the concentration residual augmented classical least-squares method; its prediction ability was assessed and compared to the conventional partial least-squares method. The developed HPLC method used an RP ZORBAX C18 column (5 microm particle size, 250 x 4.6 mm id) with isocratic elution. The mobile phase was acetonitrile-pH 3.5 phosphate buffer (40 + 60, v/v) at a flow rate of 1.0 mL/min, with UV detection at 230 nm. The accuracy, precision, and linearity ranges of the developed methods were determined. The developed methods were successfully applied for determination of EZ and SM in bulk powder, laboratory-prepared mixtures, and a combined dosage form. The results obtained were compared statistically with each other and to those of a reported HPLC method; there was no significant difference between the proposed methods and the reported method regarding both accuracy and precision.

Development and validation of spectrophotometeric method for simultaneous determination of simvastatin and ezetimibe in tablet formulations.

A versatile, accurate, precise and economic method for simultaneous determination of simvastatin and ezetimibe in fixed dose combination products was developed. The absorbance values at 236 nm and 234 nm of over line spectrum was used for the estimation of simvastatin and ezetimibe, respectively without mutual interference. This method obeyed Beer's law in the concentration range of 4-16 µg/ml for simvastatin and 4-16 µg/ml for ezetimibe. The results of analyses have been validated statistically for linearity, accuracy and precision of the proposed method.

Analysis of quinary therapy targeting multiple cardiovascular diseases using UV spectrophotometry and chemometric tools.

Herein, UV spectrophotometry assisted by multivariate chemometric analysis have been presented for quantitative determination of complex quinary therapy containing atenolol, ramipril, hydrochlorothiazide, simvastatin and aspirin without any prior separation. Such combination is very useful for treating various cardiovascular diseases (CVD) including high blood pressure, hypercholesterolemia in addition to its antiplatelet aggregating activity. Calibration (15 samples) and validation (10 samples) sets were prepared of different concentrations for these drugs via implementing partial factorial experimental design. The zero order UV spectra of these sets were recorded and then subjected for further chemometric analysis. Partial least square (PLS) with/without variable selection procedure i.e. genetic algorithm (GA) were employed to untangle the UV spectral overlapping of these mixtures. The performance of these chemometric techniques were compared in terms of accuracy and predictive abilities using cross-validation and external validation methods. It was found that PLS provides good recoveries with prompt predictive ability albeit GA-PLS exhibited better analytical performance owing to its capability to remove redundant variables i.e. the number of absorbance variables had been reduced to about 19-28%. The developed methods allowed reliable determination of such complex therapy in its laboratory prepared mixtures and pharmaceutical preparation within comparable results to those reported by HPLC method, posing these chemometric methods as valuable and indispensable analytical tools in in-process testing and quality control analysis of many pharmaceutical compounds targeting CVD.

Sustainable environment-friendly quantitative determination of three anti-hyperlipidemic statin drugs and ezetimibe in binary mixtures by first derivative Fourier transform infrared (FTIR) spectroscopy.

FTIR spectrometry is considered a sustainable green analytical chemistry procedure. Its use in quantitative analysis of pharmaceutical compounds in their raw resources and in their dosage forms is growing currently. The current research offers an environment-friendly, speedy, cost-effective, reliable and easy method for the simultaneous estimation of anti-hyperlipidemic drugs. No sample preparation was required except for grinding and mixing with KBr for making pellets used for acquisition of the FT-IR spectra. First-derivative FTIR spectroscopy is used to assess quantitatively atorvastatin (ATR), rosuvastatin (RSV) and simvastatin (SMV) in their binary mixtures with ezetimibe (EZT). For the first mixture, EZT and ATR were determined at 1733.18 cm-1 and 1647.74 cm-1, respectively. In the second mixture, the zero-crossing wave numbers selected for the determination of EZT and RSV were 1733.18 cm-1 and 955.69 cm-1, correspondingly. Whereas, the third mixture was quantified at the wavenumbers of 1520.93 and 3569.68 cm-1 for EZT and SMV, respectively. Validation of the procedure has been performed complying with recommendations of the International Conference of Harmonization (ICH) presenting linearity, accuracy, precision, robustness and selectivity. The linear range for all drugs was 2-30 mg/g. It was found that the LOD was 0.607, 0.311, 0.491 and 0.395 mg/g and the LOQ was found to be 1.839, 0.942, 1.490 and 1.190 mg/g for EZT, ATR, RSV, and SMV, correspondingly. The proposed technique was found to be accurate and precise in terms of percentage error and percentage relative standard deviation among intraday and interday measurements. It was also found selective through comparison of the results of standard drugs with results of binary mixtures and of pharmaceutical tablets. It was found robust through making slight variations in the working conditions and the results obtained remained statistically equivalent. The technique was applied effectively for the estimation of the binary mixtures under study in their tablets. Comparing the found outcomes to those of reference derivative UV spectrophotometric methods gave no significant difference between them. Analytical eco-scale and the scale of Green Analytical Procedure Index (GAPI) are the two scales utilized for evaluation of the greenness of the technique and it was found to be excellent green.

Ultrasound assisted ionic liquid dispersive liquid phase extraction of lovastatin and simvastatin: a new pretreatment procedure.

A fast and novel sample preparation procedure: ultrasound assisted ionic liquid (IL) dispersive liquid extraction for the concentration of lovastatin and simvastatin in aqueous samples was developed. An IL ([C(6)MIM][PF(6)]) was used as the extraction solvent, and the factors affecting the extraction efficiency such as initial temperature, the volume of IL, pH of water samples, cooling time, and salt concentration were optimized. In combination with HPLC-UV, both lovastatin and simvastatin exhibited a good linear range of 1-100 ng/mL. The limits of detection (LODs) of lovastatin and simvastatin were 0.17 and 0.29 ng/mL, respectively. Precisions of the proposed method (RSDs, n = 9) were 4.12 and 4.52%, respectively. This method has been successfully applied for the analysis of target compounds in three real water samples and good spiking recoveries were obtained in the range of 90.0-102.2% for lovastatin and 80.5-112.0% for simvastatin. These results indicated that ultrasound assisted IL dispersive liquid phase extraction would have good application prospect in the pretreatment of environmental samples.

Determination of 17alpha-ethynylestradiol, carbamazepine, diazepam, simvastatin, and oxybenzone in fish livers.

A method using liquid chromatography/tandem mass spectrometry (LC/MS/MS) was developed for the determination of 17alpha-ethynylestradiol in fish liver; a second method using LC/MS was developed for the determination of carbamazepine, diazepam, simvastatin, and oxybenzone in fish liver. The fish liver samples were extracted and cleaned up by using liquid-liquid extraction and solid-phase extraction before the extracts were analyzed by LC/MS or LC/MS/MS with electrospray negative and positive ionization. Recoveries of the 5 target compounds from spiked catfish liver ranged from 72 +/- 2 to 100 +/- 3%. Limits of quantification for the 5 compounds were between 4.2 and 12.3 ng/g (wet weight). Ten turbot (Pleuronichthys verticalis) liver samples were analyzed; levels of 17alpha-ethynylestradiol, carbamazepine, simvastatin, and oxybenzone were below the detection limits. Diazepam was detected in all 10 fish liver samples at concentrations ranging from 23 to 110 ng/g (wet weight).

Application of ion-trap mass spectrometry for identification and structural determination of an unknown impurity in simvastatin.

Anhydro-simvastatin and simvastatin dimer are the two main impurities in the fermentation broth as well as in the final product of simvastatin, which is a hypolipidemic drug. An unknown impurity with m/z 451 for [(M + H)(+)] was detected in the analysis of final simvastatin drug sample. By using reverse phase high performance liquid chromatography (HPLC)-mass spectrometry (MS) and MS/MS spectra, the unknown impurity was detected and identified. Separation was achieved on ACE-5 C18 (150 x 4.6 mm, 3 microm column) at the flow rate of 1.2 ml min(-1) applying gradient elution of mobile phase A consisting of Milli-Q water of pH 3.0 with formic acid and B consisting of acetonitrile. MS/MS spectrum of the unknown impurity was obtained using HPLC-MS equipped with positive electrosoray ionization (ESI). The unknown impurity is named as 7-[7-(2,2-dimethyl-butyryloxy)-2,6-dimethyl-1,2,6,7,8,8a-hexahydro-naphthalen-1 -yl]-3-hydroxy-5-hydroxymethyl-heptanoic acid.