Isolation and Simultaneous Determination of Coumarin Compounds in Radix Angelica dahurica

For the first time simple, rapid, and systematic methods have been established for preparative isolation and purification of coumarin compounds in an important traditional Chinese Medicine, Radix Angelica dahurica, and for simultaneous determination of several of the compounds in the medicine. Bergapten, imperatorin, and cnidilin, three of the biologically active coumarin compounds, were isolated from the chloroform-soluble fraction of the ethanol extract of Radix Angelica dahurica. After further purification by open column ODS chromatography the purified components were simultaneously determined, with two other coumarins (osthole and isoimperatorin), by reversed phase high-performance liquid chromatography (RP-HPLC) on a C₁₈ column, with methanol–water, 66:34 (v/v), as mobile phase at a flow rate of 0.8 mL min⁻¹. The compounds were detected by UV absorption at 310 nm. Calibration plots for all the coumarins had correlation coefficients close to unity. Limits of detection (S/N = 3) were <92 ng mL⁻¹ and limits of quantification (S/N = 10) were <259 ng mL⁻¹. Mean recovery of the coumarins was in the range 96.7–101.9% and the intra-day and inter-day precision, as relative standard deviation, was <2.3 and <2.9%, respectively. This simple, sensitive, and reproducible method can be used for quality control of Radix Angelica dahurica.     

Determination and Pharmacokinetic Study of 10-O-Dimethylaminoethylginkgolide B in Rat Plasma by LC–MS

To evaluate the pharmacokinetics of a novel analogue of ginkgolide B, 10-O-dimethylaminoethylginkgolide B (XQ-1) in rat plasma in pre-clinical studies, a sensitive and specific liquid chromatographic method with electrospray ionization mass spectrometry detection (LC–ESI–MS) was developed and validated. After a simple extraction with ethyl acetate, XQ-1 was analyzed on a Shim-pack C18 column with a mobile phase of a mixture of 1 μmol L⁻¹ ammonium acetate containing 0.02% formic acid and methanol (55:45, v/v) at a flowrate of 0.3 mL min⁻¹. Detection was performed in selected ion monitoring (SIM) mode using target ions at [M + H]⁺ m/z 496.05 for XQ-1 and m/z 432.10 for the internal standard (lafutidine). Linearity was established for the concentration range from 2 to 1,000 ng mL⁻¹ . The extraction recoveries ranged from 86.0 to 89.9% in plasma at concentrations of 5, 50, and 500 ng mL⁻¹. The lower limit of quantification was 2 ng mL⁻¹ with 100 μL plasma. The validated method was successfully applied to a pharmacokinetic study after intragastic administration of XQ-1 mesylate in rats at a dose of 20 mg kg⁻¹.     

Quantitative TLC Analysis of Sterol (24β-Ethylcholesta-5,22E,25-triene-3β-ol) in Agnimantha (Clerodendrum phlomidis Linn)

A quantitative method using silica gel 60F₂₅₄ high performance thin layer chromatography plates, automated bandwise sample application, and automated visible mode densitometric method has been developed for the determination of 24β-ethylcholesta-5,22E,25-triene-3β-ol (ECTO) in the aerial part of Clerodendrum phlomidis. ECTO was used as a chemical marker for the standardization of C. phlomidis plant extracts. The separation was performed on silica gel 60F₂₅₄ TLC plates using chloroform-methanol (98.5: 1.5, v/v) as mobile phase. The quantitation of ECTO was carried out using the densitometric reflection/absorption mode at 650 nm after post chromatographic derivatization with anisaldehyde reagent. A precise and accurate quantification can be performed in the linear working concentration range of 150–400 ng band⁻¹ with good correlation (r ² = 0.996). The method was validated for peak purities, precision, robustness, limit of detection (LOD) and quantitation (LOQ), etc. as per ICH guidelines.     

A Validated HPLC Method for Simultaneous Determination of 2-Hydroxy-4-methoxybenzaldehyde and 2-Hydroxy-4-methoxybenzoic Acid in Root Organs of Hemidesmus indicus

A reverse phase HPLC method was developed and validated for the simultaneous determination of 2-hydroxy-4-methoxybenzaldehyde and 2-hydroxy-4-methoxybenzoic acid in the root extracts of Hemidesmus indicus. A comprehensive validation of the method including sensitivity, linearity, reproducibility, accuracy, limit of detection (LOD) and limit of quantification (LOQ) was conducted using the optimized chromatographic conditions. The method was found to be linear (r > 0.998) in the range of 5–350 μg mL⁻¹ for 2-hydroxy-4-methoxybenzaldehyde and for 2-hydroxy-4-methoxybenzoic acid (r > 0.999) in the range 10–300 μg mL⁻¹. The method was found to be precise with inter-day precision values (% RSD) in the ranges of 0.61–1.76% for 2-hydroxy-4-methoxybenzaldehyde and 1.3–2.8% for 2-hydroxy-4-ethoxybenzoic acid while intra-day precisions (% RSD) of two analytes were in the range of 0.41–1.07 and 0.95–2.5%. The limits of detection (LODs) for 2-hydroxy-4-methoxybenzaldehyde and 2-hydroxy-4-methoxybenzoic acid were 0.84 and 2.34 μg mL⁻¹. The described method was fast, sensitive and reproducible, and thus well suited for routine analysis of these two compounds from root extracts of H. indicus and other plants.     

Simultaneous Determination of Six Major Constituents in the Stems of Kadsura heteroclita by LC-DAD

The stem of Kadsura heteroclita is a traditional Chinese medicine with a variety of biological activities. For efficient monitoring of the quality of the herb, a simple, rapid, and accurate HPLC method has been developed for simultaneous determination of five cyclolanostane triterpenoid compounds (schisanlactone E, nigranoic acid, schisandronic acid, and heteroclitalactones A and D) and one tetrahydrofuran lignan (d-epigalbacin) in the stems of K. heteroclita. These six compounds were separated on a C₁₈ column by elution with a mobile-phase gradient prepared from acetonitrile and 0.05% (v/v) aqueous phosphoric acid. The flow rate was 1.0 mL min⁻¹ and the detection wavelength was 210 nm. The recovery of the method was in the range 95.03–102.19% and a good linear relationship (r ² > 0.9999) was obtained between response and compound concentration over a relatively wide range. The method was successfully applied to analysis of the herb collected at different stages of growth.     

Characterization of catechol 1,2-dioxygenase from cell extracts of <Emphasis Type="Italic">Sphingomonas xenophaga</Emphasis> QYY

Sphingomonas xenophaga QYY, capable of growing significantly on more than ten kinds of aromatic compounds as sole carbon source, was used to study characterization of catechol 1,2-dioxygenase (C12O) in cell extracts. Characterization of the crude C12O showed that the maximum activity was obtained at 40–70°C and pH 7.8–8.8. Metal ions had different influences on the activity of crude C12O. It was suggested that strain QYY possessed an inducible and ferric-dependent C12O. Kinetic studies showed that the value of V _max and K _m was 0.25 μmol catechol/L/mg protein/min and 52.85 μmol/L, respectively. In addition, the partial purification of C12O was achieved by a HiTrap Q Sepharose column chromatography. Supported by the National Natural Science Foundation of China (Grant No. 50608011) and the 39th Postdoctoral Funds of China (Grant No. 20060390983)     

Determination of hypericin and pseudohypericin in extracts fromHypericum Perforatum L. and pharmaceutical preparations by liquid chromatography-fluorescence detection

Summary An isocratic reversed-phase liquid chromatographic method for the simultaneous determination of hypericin and pseudohypericin, two of the main constituents ofHypericum Perforatum L., has been developed. The compounds were eluted from an Inertsil ODS-3, column by triethylammonium acetate-methanol-acetonirile (5:15:80) eluent and detected fluorimetrically, excitation 478, emission 598 nm. Hypericin and pseudohypericin were extracted from flowring tops by Soxhlet and pseudohypericin was isolated from the extract by collecting its chromatographic peak from the eluent flow. Identification of peaks was by HPLC coupled to a diode array detector and electrospray MS. The method was applied to the determination of hypericin and pseudohypericin in plant extract and in pharmaceutical tablets. For the latter a solid-phase extraction procedure was adopted. Riboflavin (0.1 ng.μL⁻¹) was used as internal standard. The linear working range of the method is 0.025–4 ng.μL⁻¹ and limit of detection 0.2 ng injected on-column. A comparative SPE study for hypericin is presented.     

Simple LC Method with Chemiluminescence Detection for Simultaneous Determination of Arbutin and l-Ascorbic Acid in Whitening Cosmetics

Simultaneous determination of arbutin (ART) and l-ascorbic acid (AA) by HPLC with chemiluminescence detection is proposed for the first time. This method is based on the CL reaction of acidic potassium permanganate with ART and AA in the presence of formaldehyde as enhancer. The separation was performed on a C₁₈ column with a 90:10 (v/v) mixture of 0.02 M phosphate buffer and methanol as mobile phase. The effects of several conditions on HPLC resolution and CL emission were studied systematically. The linear ranges were 0.5–50 and 1–200 μg mL⁻¹ for ART and AA, respectively. The detection limits were 0.2 and 0.3 μg mL⁻¹, respectively. The method was successfully applied to the determination of ART and AA in whitening cosmetics.     

Isomerism in OBe3F3 + cation: anab initio study

Ab initio MP2/6-31G^*//HF/6-31G^*+ZPE(HF/6-31G^*) calculations of the potential energy surface in the vicinity of stationary points and the pathways of intramolecular rearrangements between low-lying structures of the OBe₃F₃ ⁺ cation detected in the mass spectra of μ₄-Be₄O(CF₃COO)₆ were carried out. Ten stable isomers with di- and tricoordinate oxygen atoms were localized. The relative energies of six structures lie in the range 0–8 kcal mol⁻¹ and those of the remaining four structures lie in the range 20–40 kcal mol⁻¹. Two most favorable isomers, aC _2v isomer with a dicoordinate oxygen atom, planar six-membered cycle, and one terminal fluorine atom and a pyramidalC _3v isomer with a tricoordinate oxygen atom and three bridging fluorine atoms, are almost degenerate in energy. The barriers to rearrangements with the breaking of one fluorine bridge are no higher than 4 kcal mol⁻¹, except for the pyramidalC _3v isomer (∼16 kcal mol⁻¹). On the contrary, rearrangements with the breaking of the O−Be bond occur with overcoming of a high energy barrier (∼24 kcal mol⁻¹). A planarD _3h isomer with a tricoordinate oxygen atom and linear O−Be−H fragments was found to be the most favorable for the OBe₃H₃ ⁺ cation, a hydride analog of the OBe₃F₃ ⁺ ion; the energies of the remaining five isomers are more than 25 kcal mol⁻¹ higher. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 420–430, March, 1999.     

LC–MS for Identification and Elucidation of the Structure of In-Vivo and In-Vitro Metabolites of Atropine

In-vivo and in-vitro metabolism of atropine has been investigated by use of a highly specific and sensitive LC–MS ⁿ method. Feces, urine, and plasma samples were collected separately after ingestion of 25 mg kg⁻¹ atropine by healthy rats. Rat feces and urine samples were cleaned by liquid–liquid extraction and by solid-phase extraction (on C₁₈ cartridges), respectively. Methanol was added to rat plasma samples to precipitate plasma proteins. Atropine was incubated, in vitro, with homogenized liver and with intestinal flora from rats. The metabolites in the incubation solution were extracted with ethyl acetate. These pretreated samples were then analyzed by reversed-phase high-performance liquid chromatography on a C₁₈ column with methanol–ammonium acetate (2 mm, adjusted to pH 3.5 with formic acid), 70:30 (v/v), as mobile phase. Detection was by on-line MS ⁿ . Identification and elucidation of the structure of the metabolites were achieved by comparing molecular mass (ΔM), retention-times, and full-scan MS ⁿ spectra with those of the parent drug. Ten new metabolites (aponoratropine, apoatropine, hydroxymethoxyatropine, trihydroxyatropine, dimethoxyatropine, dihydroxymethoxyatropine, hydroxydimethoxyatropine, trihydroxymethoxyatropine, dihydroxydimethoxyatropine, and tropic acid) were identified in rat urine after ingestion of atropine. Nine metabolites (nortropine, tropine, aponoratropine, apoatropine, noratropine, hydroxyatropine, hydroxyatropine N-oxide, hydroxymethoxyatropine, and tropic acid) and the parent drug were detected in rat feces. Five metabolites (nortropine, tropine, tropic acid, apoatropine, and hydroxyatropine) and the parent drug were detected in rat plasma. Only two metabolites (apoatropine and noratropine) were detected in the homogenized liver incubation mixture. The hydrolyzed metabolites (tropine and tropic acid) and dehydrated metabolite apoatropine were found in the rat intestinal flora incubation mixture.     

Development and Validation of a Stability-Indicating LC Method for Determination of Ebastine in Tablet and Syrup

A simple stability-indicating reversed-phase liquid chromatographic method with diode-array detection was developed and validated for the quantitative determination of ebastine in tablets and syrup. The LC method was carried out on a C₁₈ column with acetonitrile:phosphoric acid 0.1% pH 3.0 (55:45, v/v) as mobile phase, at a flow rate of 1.2 mL min⁻¹. Ultraviolet detection of ebastine was at 254 nm. A linear response (r = 0.9999) was observed in the range of 10–80 μg mL⁻¹. The RSD values for intra- and inter-day precision studies showed good results (RSD < 2%) and accuracy was greater than 98%. Validation parameters such as specificity and robustness were also determined. The method was found to be stability-indicating and can be applied to quantitative determination of ebastine in tablets and syrup.     

Quantitative Determination of Four Water-Soluble Compounds in Herbal Drugs from Lamiaceae Using Different Chromatographic Techniques

HPTLC-densitometric and HPLC–UV techniques were used for qualitative and quantitative determination of luteolin-7-O-glucuronide, lithospermic acid, rosmarinic acid and caffeic acid in several herbal drugs from the Lamiaceae family: Thymi herba, Serpylli herba, Majoranae herba and Menthae piperitae folium. Unmodified silica gel (HPTLC Si60) and silica gel chemically modified with aminopropyl groups (HPTLC NH₂) were used during the investigation process. Among HPTLC methods the best resolution and selectivity was achieved with mobile phases: diisopropyl ether–acetone–formic acid–water (50:30:10:10, v/v/v/v) and acetone–formic acid (85:15, v/v), respectively. Plates were densitometrically evaluated. Contents of analyzed compounds in the studied aqueous extracts prepared from herbal drugs were established using both techniques. The results from the HPTLC-densitometric analysis have been compared with those from HPLC–UV on a C18 column with acetonitrile–water–formic acid as a mobile phase. The chromatographic methods were validated for linearity, LOD, LOQ, repeatability, intermediate precision and recovery. An analysis of variance showed that the HPTLC-densitometric and HPLC–UV methods are equivalent and sufficiently precise for the estimation of polyphenolic compounds mentioned above, in investigated herbal drugs. All of the suggested methods (HPTLC NH₂, HPTLC Si60 and HPLC RP18) give results with good agreement.     

Development and Validation of an HPLC Method for Determination of Ceftiofur Sodium

An isocratic high-performance liquid chromatographic method has been developed for assay of ceftiofur sodium in drug substance and in sterile powder for injection. Chromatography was performed on a 250 mm × 4.6 mm, 5 μm particle, C₁₈ column with a 78:22 (v/v) mixture of 0.02 m disodium hydrogen phosphate buffer (pH adjusted to 6.0 with 85% orthophosphoric acid) and acetonitrile as mobile phase, at a flow rate of 1.0 mL min⁻¹. The separation was monitored by UV detection at 292 nm. Validation of the method for linearity and range, intra- and inter-day precision, accuracy, specificity, recovery, robustness, and limits of quantification and detection yielded good results. The calibration plot was linear from 20.0–120.0 μg mL⁻¹ and the correlation coefficient was 0.9999. It was shown that ceftiofur was degraded under acidic, alkaline, oxidative, and photolytic conditions. The method was found to be stability-indicating and could be used for routine analysis of ceftiofur sodium for injection.     

Determination and Pharmacokinetic Study of Calycosin-7-O-β-d-glucoside in Rat Plasma After Intravenous Administration of Aidi Lyophilizer

Aidi injection is a clinical medicine used in China for the treatment of cancer. Calycosin-7-O-β-d-glucoside is the main effective components of the formulas. In this study, a high performance liquid chromatographic (LC) method was developed to quantify calycosin-7-O-β-d-glucoside in rat plasma using a liquid–liquid extraction and ultraviolet (UV) absorbance detection. LC analysis was performed on a Diamonsil C₁₈ column (200 × 4.6 mm i.d., 5 μm particle size) with isocratic mobile phase consisting of acetonitrile–0.05% phosphoric acid (19.5:80.5, v/v) of a flow rate of 1.0 mL min⁻¹. The linear range was 0.11–17.6 μg mL⁻¹ and the low quantification limit was 0.11 μg mL⁻¹ (S/N = 10). The intra- and inter-day relative standard deviations (RSD) in the measurement of quality control (QC) samples 0.11, 0.22, 1.32 and 8.80 μg mL⁻¹ ranged from 4.1 to 6.3 and 4.3 to 6.2%, respectively. The accuracy was from −6.7 to 4.3% in terms of relative error (RE). Calycosin-7-O-β-d-glucoside was stable in storage at −20 °C for 2 weeks and stable after three freeze–thaw cycles in rat plasma. This method was validated for specificity, accuracy, precision and was successfully applied to pharmacokinetic study of calycosin-7-O-β-d-glucoside in rat plasma after intravenous administration of Aidi lyophilizer.     

Simultaneous HPLC Determination of Five Flavonoids in Flos Inulae

A simple and accurate reversed-phase high-performance liquid chromatographic (RP-HPLC) method has been developed for simultaneous determination of five flavonoids, spinacetin, quercetin, luteolin, 6-methoxyluteolin, and isorhamnetin, in an extract of the flowers of Inula britannica L., an important Traditional Chinese Medicine (TCM). Samples were extracted with 80% ethanol. Optimum separation and detection were achieved on an ODS-3 column with a methanol–acetonitrile gradient containing 0.49% (v/v) citric acid as mobile phase. The flow rate was 1.0 mL min⁻¹ and detection was at 360 nm. All calibration plots revealed linearity was good (r ² = 0.999) within the concentration ranges tested. Repeatability was evaluated by performing intra-day and inter-day assays; relative standards deviations (RSD) were less than 2.8%. Recovery of the five flavonoids was between 91.5 and 103.6%, with RSD less than 6.5%. The method was successfully used for analysis of seven samples of Flos Inulae from different parts of China and was found to be simple and efficient.     

High-performance liquid chromatographic determination of diltiazem in human plasma after solid-phase and liquid–liquid extraction

A selective, sensitive, and accurate high-performance liquid chromatographic method for determination of diltiazem in plasma samples has been developed and validated. The effects of mobile phase composition, buffer concentration, mobile phase pH, and concentration of organic modifiers on retention of diltiazem and internal standard were investigated. Solid-phase and liquid–liquid extraction were examined and proposed for isolation of the drug and elimination of endogenous plasma interferences. A 5 m Lichrocart Lichrospher 60 RP-select B chromatographic column was used; the mobile phase was acetonitrile–0.025 mol L^–1 KH₂PO₄ (pH 5.5), 35:65 ( v / v) at a flow-rate of 1.5 mL min^–1. The detection wavelength was 215 nm. The calibration plots were linear in the concentration range 20.0–500.0 ng mL^–1. The method has been implemented to monitor diltiazem levels in patient samples.     

Simultaneous Determination of Olanzapine and Fluoxetine by HPLC

A rapid, specific reversed phase HPLC method has been developed for simultaneous determination of olanzapine and fluoxetine in their formulations. Chromatographic separation of these two pharmaceuticals was carried out on an Inertsil C₁₈ reversed phase column (150 mm × 4.6 mm, 5 μm) with a 40:30:30 (v/v/v) mixture of 9.5 mM sodium dihydrogen phosphate (pH adjusted to 6.8 ± 0.1 with triethylamine), acetonitrile and methanol as mobile phase. The flow rate 1.2 mL min⁻¹ and the analytes are monitored at 225 nm. Paroxetine was used as internal standard. The assay results were linear from 25 to 75 μg mL⁻¹ for olanzapine (r ² ≥ 0.995) and 100–300 μg mL⁻¹ for fluoxetine (r ² ≥ 0.995), showed intra- and inter-day precision less than 1.0%, and accuracy of 97.7–99.1% and 97.9–99.0%. LOQ was 0.005 and 0.001 μg mL⁻¹ for olanzapine and fluoxetine, respectively. Separation was complete in less than 10 min. Validation of the method showed it to be robust, precise, accurate and linear over the range of analysis.     

Determination of Carbamazepine in Parenteral Nanoemulsions: Development and Validation of an HPLC Method

A high performance liquid chromatographic method was developed and validated for the quantitative determination of carbamazepine in intravenous nanoemulsions. The method validation yielded good results with respect to linearity, specificity, precision and accuracy. The method was carried out on a RP-18 column with a mobile phase composed of methanol–water (70:30 v/v) subjected to a gradient of acetonitrile after drug elution, and detection at 286 nm. The linearity in the range of 10.0–50.0 μg mL⁻¹ presented a determination coefficient (r ²) of 0.9996, calculated by least-squares regression; the RSD values for intra-day and inter-day precision for % recovered were <0.44 and <1.21%, respectively; and the recovery of carbamazepine from the sample matrix ranged from 94.3 to 104.9%.     

Quantitative Determination of Acyclovir in Aqueous Humor by LC-MS

A specific, sensitive and precise liquid chromatographic assay method was established using LC-MS for the determination of acyclovir (ACV) in aqueous humor (AH), which was directly injected onto an Inertsil ODS-3 C₁₈ column without any pretreatment. The Agilent 1100 series LC–MS system was operated under the electrospray ionization mode (ESI). The analyte was separated from endogenous substances with a mobile phase of methanol: water: acetic acid (5:95:0.1, v/v) at a flow-rate of 0.3mL min⁻¹. A linear response was observed over the concentration range from 5 to 50ng mL⁻¹ (r=0.9993). Intra- and inter-day coefficients of variation were in the ranges 5.2–9.0% and 5.8–8.2%, respectively. The recovery was > 91.0%, and the limit of detection was approximate 1ng mL⁻¹. The pharmacokinetics of topically applied eye-drop and thermosetting gel were compared in rabbits utilizing the present method, the results demonstrated that LC-MS was a powerful tool for the detection of ACV in AH.     

Determination of clozapine in human plasma by solid-phase extraction and liquid chromatography with amperometric detection

Summary A sensitive and selective high-performance liquid chromatographic method has been developed for monitoring clozapine levels in human plasma. Chromatography was performed on a reversed-phase column (C₈, 150 mm×4.6 mm i.d., 5 μm) with acetonitrile-aqueous sodium acetate solution, 88∶12 (v/v), as mobile phase; the flow rate was 1 mL min⁻¹. Clozapine oxidation at +800 mV was detected amperometrically. Response was linearly dependent on concentration over the range 50–1500 ng mL⁻¹ clozapine in plasma. Sample preparation by solid-phase extraction before HPLC analysis gave high extraction yield (94%). The accuracy and precision of the method were both very good (recovery: 97%;RSD<3.3%).