High performance liquid chromatographic method for the determination and pharmacokinetic studies of oxyresveratrol and resveratrol in rat plasma after oral administration of Smilax china extract

A sensitive and simple HPLC method has been developed and validated for the determination of oxyresveratrol (trans-2,4,3',5'-tetrahydroxystilbene, OXY) and resveratrol (trans-3,5,4'-trihydroxystilbene, RES) in rat plasma. The plasma samples were extracted with ethyl acetate and analyzed using HPLC on an Aglient Zorbax SB-C(18) column (250 x 4.6 mm, 5 microm) at a wavelength 320 nm, with a linear gradient of (A) acetonitrile and (B) 0.5% aqueous acetic acid (v/v), at a flow rate of 1.0 mL/min. The method was linear over the range of 0.1265-25.3 microg/mL for OXY and 0.117-23.4 microg/mL for RES. The extraction recovery for OXY, RES and internal standard ranged from 71.1 to 88.3%. The intra- and inter-day precisions were better than 10%, and the accuracy ranged from 89 to 108%. The validated method was used to study the pharmacokinetic profiles of OXY and RES in rat plasma after oral administration of Smilax china root extract.     

Determination and pharmacokinetic study of nodakenin in rat plasma by RP-HPLC method

A simple, sensitive and selective RP-HPLC method has been developed for quantification of nodakenin in rat plasma. Nodakenin in rat plasma was extracted with acetonitrile, which also acted as a deproteinization agent. Chromatographic separation of nodakenin was performed on an analytical Diamonsil ODS C18 column, with a mobile phase of MeOH-H2O (1:1, v/v) at a flow-rate of 1.0 mL/min, and UV detection was set at 330 nm. The calibration curve was linear over the range 0.2-12.0 microg/mL (R2 = 0.9995) in rat plasma. The lower limit of detection and quantification were 0.01 and 0.1 microg/mL, respectively, using the rat plasma sample. The extraction recoveries were 77.36 +/- 4.56, 82.89 +/- 1.84 and 81.66 +/- 2.49% at concentrations of 1.0, 5.0 and 10.0 microg/mL, respectively. The intra- and inter-day precision and accuracy were validated by relative standard deviation and relative error, which were in the ranges 5.07-5.83 and 3.95-6.29%, respectively. After i.v. administration to rats at a single dose of 40 mg/kg, the plasma concentration-time curve of nodakenin was best conformed to a two-compartment open model. This assay method has been successfully applied to the study of the pharmacokinetics of nodakenin in rats.     

Determination of calycosin-7-O-beta-D-glucopyranoside in rat plasma and urine by HPLC

A reversed-phase high-performance liquid chromatographic (HPLC) assay for calycosin-7-O-beta-D-glucopyranoside in rat plasma and urine with solid-phase extraction (SPE) was developed. Rutin was employed as an internal standard. The mobile phase consisted of acetonitrile-water (16:84, v/v) at a flow rate of 1.0 mL/min. Detection was set at 280 nm. The limit of quantitation of calycosin-7-O-beta-D-glucopyranoside was 0.2 microg/mL in both plasma and urine. The standard curve was linear from 0.2 to 10.0 microg/mL in plasma, and 0.2 to 5.0 microg/mL in urine. Both intra- and inter-day precision of the calycosin-7-O-beta-d-glucopyranoside were determined and their RSD did not exceed 10%. The method was successfully applied to the analysis of samples obtained from a basic pharmacokinetic study, in which calycosin-7-O-beta-d-glucopyranoside was administered orally to rats.     

High-performance liquid chromatography analysis of curcumin in rat plasma: application to pharmacokinetics of polymeric micellar formulation of curcumin

A simple, rapid and reliable high-performance liquid chromatographic (HPLC) method was developed and validated for the determination of curcumin in rat plasma. Plasma was precipitated with acetonitrile after addition of the internal standard (IS), 4-hydroxybenzophenone. Separation was achieved on a Waters muBondapak C(18) column (3.9 x 300 mm, 5 microm) using acetonitrile (55%) and citric buffer, pH 3.0 (45%) as the mobile phase (flow rate = 1.0 mL/min). The UV detection wavelength was 300 and 428 nm for IS and curcumin, respectively. The extraction efficiencies were 97.08, 95.69 and 94.90% for 50, 200 and 1000 ng/mL of curcumin in rat plasma, respectively. The calibration curve was linear over the range 0.02-1 microg/mL with a correlation coefficient of r(2) > 0.999. The intra- and inter-day coefficients of variation were less than 13%, and mean intra- and inter-day errors were less than +/-6% at 50, 200 and 1000 ng/mL of curcumin. This assay was successfully applied to the pharmacokinetic studies of both solubilized curcumin and its polymeric micellar formulation in rats. It was found that polymeric micelles increased the half-life of curcumin 162-fold that of solubilized curcumin and increased the volume of distribution (Vd(ss)) by 70-fold.     

Head-column field-amplified sample stacking in capillary electrophoresis for the determination of cimetidine, famotidine, nizatidine, and ranitidine-HCl in plasma.

In this study, low concentrations of histamine2-receptor (H2-)antagonists were effected across a water plug, with separation taking place in a binary buffer comprising ethylene glycol and NaH2PO4 (pH 5.0), and detection at 214 nm. Liquid-liquid extraction with ethyl acetate- isopropanol is shown to provide extracts that are sufficiently clean. The calibration curves were linear over a concentration range of 0.1-2.00 microg/mL cimetidine, 0.2-5.0 microg/mL ranitidine-HCl, 0.3-5.0 microg/mL nizatidine, and 0.1-3.0 microg/mL famotidine. Mean recoveries were > 82%, while the intra- and interday relative standard deviations (RSDs) and relative errors (REs) were all < 13%. The method is sensitive with a detection limit of 3 ng/mL cimetidine, 30 ng/mL ranitidine HCl, 50 ng/mL nizatidine and 10 ng/mL famotidine (S/N = 3, electric-driven injection 90 s). This newly developed capillary electrophoresis (CE) method was applied for the determination of analytes extracted from plasma taken from a volunteer dosing a cimetidine, ranitidine, and nizatidine tablet simultaneously. These three H2-antagonists can be detected in real samples by this method, excluding the low dosing of famotidine tablet.     

Establishment of a HPLC method for preclinical pharmacokinetic study of the novel anti-Parkinson's disease candidate drug FLZ in rats

An HPLC method was established and validated for the determination of compound FLZ, a synthetic novel anti-Parkinson's disease candidate drug, in rat plasma. FLZ and the internal standard bicyclol were extracted from plasma by solid-phase extraction method and analyzed on a Restek C18 column (4.6 x 250 mm, 5 microm) with a mobile phase consisting of methanol and water (60:40, v/v) at a flow rate of 1.0 mL/min. The detection wavelength was set at 320 nm. The calibration curve was linear within the concentration range from 25 to 500 ng/mL (r2 > 0.999), the limit of quantitation was 25 ng/mL and the average recovery was 92.0% with the RSD less than 5.9%. The relative standard deviation for intra- and inter-day precision was less than 3.8 and 6.9%, respectively. The established HPLC method was validated to be a simple, rapid and reliable procedure and applied to study the preclinical pharmacokinetics of FLZ in rat plasma, and it was the first time that the pharmacokinetics of FLZ had been investigated.     

HPLC determination and pharmacokinetics of osthole in rat plasma after oral administration of Fructus Cnidii extract

A simple and sensitive high-performance liquid chromatographic (HPLC) method is developed for the determination of osthole in rat plasma and applied to a pharmacokinetic study in rats after administration of Fructus Cnidii extract. After addition of fluocinonide as an internal standard, plasma samples are extracted with diethyl ether. HPLC analysis of the extracts is performed on a Hypersil ODS2 analytical column, using methanol-0.4% acetic acid (65:35, v/v) as the mobile phase. The UV detector is set at 322 nm. The standard curve is linear over the range 0.0520-5.20 microg/mL (r = 0.9979). The mean extraction recoveries of osthole at three concentrations were 81.0%, 91.2%, and 90.7%, respectively. The intra- and interday precisions have relative standard deviations from 1.9% to 4.9%. The limit of quantitation is 0.0520 microg/mL. The HPLC method developed can easily be applied to the determination and pharmacokinetic study of osthole in rat plasma after the animals are given the Fructus Cnidii extract. The plasma concentration of osthole from six rats showed a Cmax of 0.776 +/- 0.069 microg/mL at Tmax of 1.0 +/- 0.3 h.     

Determination of 3',4',5',5,7-pentamethoxyflavone in the plasma and intestinal mucosa of mice by HPLC with UV detection

In a preliminary experiment 3',4',5',5,7-pentamethoxyflavone (PMF) inhibited adenoma development in Apc(Min) mice, a model of the human heritable condition familial adenomatous polyposis. An HPLC method for tricin was modified and validated to permit measurement of PMF in mouse plasma and intestinal mucosa. HPLC analysis was carried out on a Hypersil-BDS C(18) column with detection at 324 nm and tricin as internal standard. The assay was linear in the range of 100-2000 ng/mL plasma and 1.0-40 microg/mL mucosa. PMF in plasma was efficiently extracted using solid-phase columns. In the case of mucosa organic solvent protein precipitation displayed satisfactory accuracy and precision. The assay recovery at low, medium and high concentrations was between 85 and 103% for both biomatrices, with a relative standard deviation of <15%. The lower limits of quantitation for plasma and mucosa were 100 ng/mL and 1.0 microg/mL, respectively. This method allowed measurement of PMF steady-state median concentrations in plasma (1.08 nmol/mL, n = 11; 10th and 90th percentiles: 0.633 and 2.385 nmol/mL) and mucosa (108.5 nmol/g, n = 9; 10th and 90th percentiles: 38.9 and 164.4 nmol/g) in mice which had received PMF (0.2%, w/w) with their diet.     

HPLC method for preliminary analysis of constituents in rat blood after oral administration of the extract of Acanthopanax senticosus

An HPLC with SPE method has been developed for analysis of constituents in rat blood after oral administration of the extract of Acanthopanax senticosus (ASE). The plasma sample was prepared by SPE method equipped with Oasis HLB cartridge (3cc, 60 mg). The analysis was performed on a Dikma Diamonsil RP(18) column (4.6 mmx150 mm, 5 microm) with the gradient elution of solvent A (ACN) and solvent B (0.1% aqueous phosphoric acid, v/v) and the detection wavelength was set at 270 nm. The calibration curve was linear over the range of 0.156-15.625 microg/mL. The LOD was 60 ng/mL. The intraday precision was less than 5.80%, and the interday precision was less than 6.0%. The recovery was (87.30 +/- 1.73)%. As a result, 19 constituents were detected in rat plasma after oral administration of the ASE, including 11 original compounds in ASE and eight metabolites, and three of the metabolites originated from syringin in ASE. Six constituents were identified by comparing with the corresponding reference compounds.     

Quantitative determination of DRF-1042 in human plasma by HPLC: validation and application in clinical pharmacokinetics

A simple and sensitive high-performance liquid chromatography (HPLC) method has been developed and validated for the determination of DRF-1042, a novel orally active camptothecin (CPT) analog, in human plasma. The sample preparation was a simple deproteinization with acidified methanol yielding almost 100% recovery of DRF-1042. An isocratic reverse-phase HPLC separation was developed on a Supelcosil-LC318 column (250 x 4.6 mm, 5 microm) with mobile phase consisting of 1% v/v triethylamine acetate, pH 5.5 and acetonitrile (80:20, v/v) at a fl ow rate of 1.0 mL/min. The eluate was monitored with a fluorescence detector set at excitation and emission wavelengths of 370 and 430 nm, respectively. The standard curves were linear (r(2) > 0.999) in the concentration ranges 5.0-2004 ng/mL. The lower limit of quantification (LLQ) of the assay was 5 ng/mL. The mean measured quality control (QC) concentrations (range 5 ng/mL to 40 microg/mL) deviated from the nominal concentrations in the range of -10.5-0.08 and -14.5-7.97%, inter- and intra-day, respectively. The inter- and intra-day precisions in the measurement of QC samples at four tested concentrations, were in the range 0.64-5.89% relative standard deviation (RSD) and 0.33-14.7% RSD, respectively. The method was found to be suitable for measurement of plasma concentrations above the calibration curve after serial dilutions. Stability of DRF-1042 was confirmed in a battery of studies, viz., on bench-top, in the auto-sampler, in the stock solutions, after four quick freeze-thaw cycles, up to one month at -20 degree C in human plasma and up to 2 months in the ex vivo samples. The method is simple, sensitive and reliable and has been successfully implemented to investigate the clinical pharmacokinetics of DRF-1042 in cancer patients in a phase I clinical trial.     

Robust and sensitive high-performance liquid chromatographic-UV detection technique for the determination of tigecycline in rabbit plasma

An isocratic HPLC method with detection at 248 nm was developed and fully validated for the determination of tigecycline in rabbit plasma. Minocycline was used as an internal standard. A Hypersil BDS RP-C18 column (250 x 4.6 mm, 5 microm particle size) was used with the mobile phase phosphate buffer (pH 7.10, 0.070 M)-acetonitrile (76 + 24, v/v) at a flow rate of 1.0 mL/min. The elution time of tigecycline and minocycline was approximately 8.1 and 9.9 min, respectively. Calibration curves of tigecycline were linear in the concentration range of 0.021-3.15 microg/mL in plasma. The LOD and LOQ in plasma were estimated as 7 and 21 ng/mL, respectively. The intraday and interday precision values of the method were in the range of 5.0-7.1 and 5.6-9.1%, while the corresponding accuracy values were in the ranges of 92.8-111.1 and 97.6-102.3%, respectively. At the LOQ, the intraday precision was 18.7%, while intraday and interday accuracy values were 97.3 and 98.0%, respectively. Robustness of the proposed method was studied using a Plackett-Burman experimental design. A pharmacokinetic profile is presented for confirmation of the applicability of the method to pharmacokinetic studies.     

HPLC determination and pharmacokinetic study of tenatoprazole in dog plasma after oral administration of enteric-coated capsule

A simple, sensitive and selective high-performance liquid chromatographic (HPLC) method with UV detection (306 nm) was developed and validated for determination of tenatoprazole, a novel proton-pump inhibitor, in dog plasma. Tenatoprazole and internal standard (pantoprazole) were extracted into diethyl ether and separated using an isocratic mobile phase of 10 mm phosphate buffer (pH4.7)-acetonitrile (70:30, v/v) on a Diamonsil C(18) column (150 x 4.6 mm, 5 microm). The retention times for tenatoprazole and internal standard were 7.1 and 12.3 min, respectively. No endogenous interferences were observed. This HPLC method was fully validated. The lower limit of quantitation was 20 ng/mL, with a relative standard deviation of less than 20%. A linear range of 0.02-5.0 microg/mL was established. The interday and intraday precisions were within RSD 13.4-10.1 and 4.6-1.4%, respectively. This method developed can be easily applied to the pharmacokinetic study of tenatoprazole in dog plasma after oral administration of an enteric-coated capsule. The plasma concentration of tenatoprazole from six dogs showed a mean C(max) of 2.63 microg/mL at T(max) of 1.89 h. The bioavailability of tenatoprazole was improved by administration of enteric-coated capsule.     

Simultaneous determination of pantoprazole and its two metabolites in dog plasma by HPLC

A simple and sensitive high-performance liquid chromatography (HPLC) method is developed and validated for simultaneous determination of pantoprazole and its two metabolites (pantoprazole sulfone and pantoprazole thioether) in dog plasma and applied to a pharmacokinetic study in Beagle dogs. Following a protein precipitation procedure, the samples are separated using reversed-phase HPLC (C18) by a gradient of acetonitrile and ammonium acetate (pH 6.0) at a flow rate of 1.0 mL/min and quantitated using UV detection at 290 nm. Omeprazole is selected as the internal standard. The method has a lower limit of quantitation of 0.025 microg/mL for pantoprazole and its two metabolites, using 0.1-mL aliquots of plasma. The linear calibration curves are obtained in the concentration range of 0.025-10.0 microg/mL for three analytes. The intra- and interrun precision (relative standard deviation), calculated from quality control (QC) samples, is less than 13% for three analytes. The accuracy determined from QC samples is between -6.4% and 12%.     

Simultaneous estimation of acetylsalicylic acid and clopidogrel bisulfate in pure powder and tablet formulations by high-performance column liquid chromatography and high-performance thin-layer chromatography

This paper describes validated high-performance column liquid chromatographic (HPLC) and high-performance thin-layer chromatographic (HPTLC) methods for simultaneous estimation of acetylsalicylic acid (ASA) and clopidogrel bisulfate (CLP) in pure powder and formulations. The HPLC separation was achieved on a Nucleosil C8 column (150 mm length x 4.6 mm id, 5 microm particle size) using acetonitrile-phosphate buffer, pH 3.0 (55 + 45, v/v) mobile phase at a flow rate of 1.0 mL/min at ambient temperature. The HPTLC separation was achieved on an aluminum-backed layer of silica gel 60F254 using ethyl acetate-methanol-toluene-glacial acetic acid (5.0 + 1.0 + 4.0 + 0.1, v/v/v/v) mobile phase. Quantitation was achieved with UV detection at 235 nm over the concentration range 4-24 microg/mL for both drugs, with mean recoveries of 99.98 +/- 0.28 and 100.16 +/- 0.66% for ASA and CLP, respectively, using the HPLC method. Quantitation was achieved with UV detection at 235 nm over the concentration range of 400-1400 ng/spot for both drugs, with mean recoveries of 99.93 +/- 0.55 and 100.21 +/- 0.83% for ASA and CLP, respectively, using the HPTLC method. These methods are simple, precise, and sensitive, and they are applicable for the simultaneous determination of ASA and CLP in pure powder and formulations.     

HPLC method for determination of DRF-4367 in rat plasma: validation and its application to pharmacokinetics in Wistar rats

A specific, accurate, precise and reproducible high-performance liquid chromatography (HPLC) method was developed for the estimation of DRF-4367, a novel cyclooxygenase-2 inhibitor in rat plasma. The assay procedure involved simple liquid/liquid extraction of DRF-4367 and internal standard (IS, celecoxib) from plasma into dichloromethane. The organic layer was separated and evaporated under a gentle stream of nitrogen at 40 degrees C. The residue was reconstituted in the mobile phase and injected onto a Kromasil KR 100-5C(18) column (4.6 x 250 mm, 5 microm). The mobile phase consisting of 0.01 M potassium dihydrogen ortho-phosphate (pH 3.2) and acetonitrile (40:60, v/v) was used at a flow rate of 1.0 mL/min. The eluate was monitored using an UV detector set at 247 nm. The ratio of peak area of analyte to IS was used for quantification of plasma samples. Nominal retention times of DRF-4367 and IS were 6.6 and 11.2 min, respectively. The standard curve for DRF-4367 was linear (r(2) > 0.999) in the concentration range 0.1-20 micro g/mL. Absolute recovery was >86% from rat plasma for both analyte and IS. The lower limit of quantification of DRF-4367 was 0.1 micro g/mL. The inter- and intra-day precisions in the measurement of quality control samples, 0.1, 0.3, 8.0 and 15.0 microg/mL, were in the range 6.93-9.34% relative standard deviation (RSD) and 0.48-6.59% RSD, respectively. Accuracy in the measurement of QC samples was in the range 91.24-109.36% of the nominal values. Analyte and IS were stable in the battery of stability studies, viz. benchtop, autosampler and freeze-thaw cycles. Stability of DRF-4367 was established for 1 month at -80 degrees C. The application of the assay to a pharmacokinetic study in rats is described.     

A simple HPLC method for the determination of apigenin in mouse tissues

The flavone apigenin occurs in many leafy vegetables and fruits. It has been reported to have cancer chemopreventive efficacy in rodents. An HPLC method described previously for the determination of tricin, the dimethoxy cogener of apigenin, was modified and validated for measurement of apigenin in mouse tissues. Separation was carried out on a Hypersil-BDS C(18) column (4.6 x 250 mm) with an isocratic mobile phase of 55% methanol in 0.1 m ammonium acetate, pH 5.10, containing 0.27 mm disodium ethylenediamine tetraacetic acid. UV detection was at 336 nm, without interference from endogenous tissue compounds. The assay was linear in the range 25-400 ng/mL, 0.25-4 microg/mL and 2.5-40 microg/mL, with r(2) > 0.99 in all cases, for mouse plasma, liver and intestinal mucosa, respectively. Apigenin in mouse plasma, liver and intestinal mucosa was efficiently extracted with 0.1 m acetic acid in acetone. The assay recovery at low, medium and high concentrations was between 94.6 and 131.7% for all biomatrices, with a relative standard deviation of <10%. The lower limit of quantification for plasma was 25 ng/mL with a relative standard deviation of <15%. The method was used to measure the steady-phase apigenin levels in tissues of mice receiving apigenin in their diet.     

Determination of metoprolol in human plasma and urine by high‐performance liquid chromatography with fluorescence detection

A simple, specific and sensitive HPLC method has been developed for the determination of metoprolol in human plasma and urine. Separation of metoprolol and atenolol (internal standard) was achieved on an Ace C₁₈ column (5 μm, 250 mm×4.6 mm id) using fluorescence detection with λ_ex=276 nm and λ_em=296 nm. The mobile phase consists of methanol–water (50:50, v/v) containing 0.1% TFA. The analysis was performed in less than 10 min with a flow rate of 1 mL/min. The assay was linear over the concentration range of 3 – 200 and 5 – 300 ng/mL for plasma and urine, respectively. The LOD were 1.0 and 1.5 ng/mL for plasma and urine, respectively. The LOQ were 3.0 and 5.0 ng/mL for plasma and urine, respectively. The extraction recoveries were found to be 95.6 ± 1.53 and 96.4 ± 1.75% for plasma and urine, respectively. Also, the method was successfully applied to three patients with hypertension who had been given an oral tablet of 100 mg metoprolol.     

Determination of tanshinone I in rat plasma by high-performance liquid chromatography and its application to pharmacokinetic studies

This paper describes a rapid and sensitive high-performance liquid chromatographic (HPLC) method for the determination of the concentration of tanshinone I in rat plasma, and applies the method to pharmacokinetic study. The plasma is deproteinized with acetonitrile containing an internal standard (estradiolbenzoate). The HPLC assay is carried out using a Cosmosil C18 column. The mobile phase is acetonitrile, 0.05 mol/L(-1) ammonium acetate buffer with 1% acetic acid (66:34, v/v). The flow rate is 1.0 mL/min. The detection wavelength is set at 263 nm. The assay accuracy is better than 92%, and the precision of tanshinone I at low to high concentrations is better than 9% and 11% for intra-day and inter-day assays, respectively. The recovery of the method exceeds 88.3% for tanshinone I. The assay shows good linearity (r = 0.9998) over a relatively wide concentration range from 0.05 to 10.0 microg/mL. The method is used to determine the concentration-time profiles of tanshinone I in plasma following an intravenous injection of tanshinone I solution, and the pharmacokinetic parameters of tanshinone I are calculated for the first time by the Drug and Statistics 1.0 program. This assay is successfully applied to the determination of tanshinone I in rat plasma, and the developed method is applied to pharmacokinetic studies for the first time.     

High-performance liquid chromatographic assay of alpha-(4-fluorophenyl)-4-(5-fluoro-2-pyrimidinyl)-1-piperazine butanol (BMY 14802), a potential antipsychotic drug, in monkey and rat plasma

A high-performance liquid chromatographic-fluorescence method was developed for the quantitative analysis of BMY-14802 (I) in monkey and rat plasma. After the addition of the internal standard (BMY-14853 I.S.), 250 microliters of plasma were made basic by the addition of 2 ml of saturated sodium carbonate buffer. Compound I and the I.S. were then extracted into 5 ml of methyl tert.-butyl ether. The organic phase was evaporated and the resulting residue was reconstituted in mobile phase. Final separation and quantitation of I was achieved on an octadecyl column with a 0.05 M potassium phosphate-acetonitrile-triethylamine-85% phosphoric acid (650:350:0.1:0.05, v/v) mobile phase. Fluorescence detection was used to monitor the eluent at an excitation wavelength of 240 nm and an emission wavelength of 400 nm. The limit of detection was 0.5 ng/ml. The standard curve was linear over the range 5.0-1000 ng/ml. Intra-assay and inter-assay precision values were less than 4.0% relative standard deviation and accuracy was within 12% of nominal values. Compound I was shown to be stable in monkey and rat plasma for at least six months when stored at -20 degrees C.     

Determination of the flavone tricin in human plasma by high-performance liquid chromatography

Tricin is a flavone constituent of brown rice and rice bran, which interferes potently with the survival of human-derived breast and colon cancer cells in vitro. A specific and simple high-performance liquid chromatographic (HPLC) method was developed for the determination of tricin in human plasma with UV-visible detection. HPLC separation on Hypersil-BDS C(18) (4.6 x 250 mm) was carried out with an isocratic mobile phase of 52% methanol in 0.1 m ammonium acetate, pH 5.10, containing 0.27 mm disodium ethylenediamine tetraacetic acid and detection at 355 nm. The retention times of tricin and quercetin (internal standard) were 14.2 and 7.8 min, respectively. The assay was linear in the range 1-100 microg/mL (r(2 ) > or = 0.995). Tricin in plasma was efficiently extracted with 0.1 m acetic acid in acetone, and the recoveries were in the range 92.6-102.8% (n = 6) with relative standard deviation below 10% for three concentrations of tricin, 5, 10 and 100 microg/mL. The lower limit of quantitation (relative standard deviation <20%) was 1 microg/mL.