高效液相色谱-串联质谱法测定动物源食品中3-甲基喹喔啉-2-羧酸和喹喔啉-2-羧酸残留

建立了动物源食品中喹喔啉类药物代谢残留标识物3-甲基喹喔啉-2-羧酸和喹喔啉-2-羧酸的高效液相色谱-串联质谱检测方法。样品在酸性环境水解,经乙酸乙酯、磷酸盐缓冲液依次提取,Oasis MAX固相萃取小柱净化,用Waters Xterra MS C18柱(150 mm×2.1 mm, 5 μm)分离,以甲醇-0.2%甲酸为流动相梯度洗脱,采用多反应监测(MRM)正离子模式检测,内标法定量。各物质在1.0～20.0 μg/L范围内线性关系良好,相关系数均不低于0.9996; 3-甲基喹喔啉-2-羧酸和喹喔啉-2-羧酸在0.1、0.2、1.0 μg/kg加标水平的回收率为62.4%～118%,相对标准偏差为1.48%～28.1%;定量限(以信噪比≥10计)为0.1 μg/kg。该方法简单、灵敏、稳定,可满足猪肉、猪肝、鸡肉、鸡肝、鱼、虾等动物源食品中3-甲基喹喔啉-2-羧酸和喹喔啉-2-羧酸残留的检测与确证需要。     

液相色谱-串联质谱测定鸡肉中喹乙醇残留标示物3-甲基喹恶啉-2-羧酸

建立了简便、灵敏、科学和可靠的液相色谱-串联质谱测定鸡肉中喹乙醇残留标示物3-甲基喹恶啉-2-羧酸（MQCA）的分析方法。采用给鸡灌服喹乙醇的方式,获得含MQCA的鸡肉试样,比较了酶解、酸解和碱解等方法水解鸡肉中MQCA的效率,实验表明,碱水解鸡肉组织得到最高含量的MQCA。样品经1.0 mol/L氢氧化钠溶液水解,正己烷除脂,MAX混合型阴离子交换固相萃取柱直接净化,采用C₁₈反相色谱柱分离,质谱选择反应监测模式检测。结果表明：MQCA在1.0~100 μg/L范围内线性关系良好,相关系数（r²）大于0.99;方法检出限为0.4 μg/kg。在1.0、5.0和50.0 μg/kg 3个添加水平下,采用外标法定量,MQCA的平均回收率为71.7%~82.4%,采用内标法定量,其回收率为96.3%~103.7%,相对标准偏差均小于6.0%。该方法适用于动物性食品中3-甲基喹恶啉-2-羧酸残留的日常监测。     

高效液相色谱-串联质谱法检测猪肉中3-甲基喹喔啉-2-羧酸残留

建立了高效液相色谱-串联质谱同时定量和确证猪肉中3-甲基喹喔啉-2-羧酸（MQCA）残留量的检测方法。试样用0.3 mol/L盐酸溶液水解提取，加入乙腈和乙酸乙酯萃取，再用0.1 mol/L氢氧化钠溶液反萃取，阴离子交换固相萃取柱净化，经Agilent Eclipse Plus C₁₈柱（50 mm×3.0 mm，1.8 μm）分离，采用液相色谱-串联质谱仪检测，基质匹配添加标准曲线定量。MQCA在1.0~50 μg/L范围内线性相关系数大于0.99，在0.5、1.0、5.0 μg/kg加标水平下其回收率为90.5%~119.6%，相对标准偏差为3.14%~4.22%。方法可用于猪肉中MQCA残留量的快速定量和确证检测。     

Development of a high-performance liquid chromatography method for the simultaneous quantification of quinoxaline-2-carboxylic acid and methyl-3-quinoxaline-2-carboxylic acid in animal tissues

A method of high-performance liquid chromatography with UV detection has been established for simultaneous quantitative determination of quinoxaline-2-carboxylic acid (QCA) and methyl-3-quinoxaline-2-carboxylic acid (MQCA), the marker residues for carbadox (CBX) and olaquindox (OLA), respectively, in the muscles and livers of porcine and chicken and in the muscle of fish. Tissue samples were subject to acid hydrolysis followed by liquid-liquid extraction and Oasis MAX solid-phase extraction clean-up. The method was validated according to the EU Commission Decision 2002/657/EC. The decision limits (CCalpha) were 0.7-2.6microg/kg and the detection capabilities (CCbeta) were 1.3-5.6microg/kg for QCA and MQCA in tissues. The recoveries of QCA and MQCA, spiked at levels of 2-100microg/kg, were from 70 to 110%; the relative standard deviation values were <20%. This simple, fast and economic method could be applied to the monitoring for the possible misuse of CBX and OLA in animal edible tissue samples.     

超高效液相色谱-串联质谱测定水产品中的卡巴氧、喹烯酮、乙酰甲喹及其代谢物

建立了超高效液相色谱-串联质谱法测定水产品中卡巴氧(CBX),喹烯酮(QCT)、乙酰甲喹(MEQ)、哇噁啉-2-羟酸(QCA),3-甲基喹噁啉-2-羧酸(MQCA) 5种化合物残留的分析方法.样品分别采用乙酸乙酯-乙腈(50:50)混合溶液、磷酸盐缓冲液分步提取,正己烷净化,以甲醇-乙腈(11:3)混合溶液和0.1%甲...     

A reversed phase high-performance liquid chromatography method for determination of cephalexin in human plasma

A reversed-phase HPLC method for the analysis of cephalexin (7-[(aminophenylacetyl)amino]-3-methyl-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid) by isocratic separation is described. A comparison is made between the ultrafiltration land the extraction procedure developed in our laboratory. The extraction procedure, based on the deproteinization of plasma with perchloric acid followed by the extraction with dichloroethane and separation of cephalexin on a reversed phase column, gave better recovery. Quantitative validation of our method has been performed by an external standard technique. The relative standard deviations were between 1.1 and 1.9% in the within-day assay and between 1.2 and 2.2% in the inter-day assay. The limit of detection was 0.14ug/ml and the limit of quantification was 0.28ug/ml. This method is rapid, sensitive, simple, and reproducible. The LC MS/MS technique was successfully used for identification and quantification of cephalexin in human plasma samples.     

A simple method of isolation of chloramphenicol in honey and its estimation by liquid chromatography coupled to electrospray ionization tandem mass spectrometry

To detect sub-ppb levels of the antibiotic chloramphenicol in honey matrix, a convenient method of extraction and measurement using liquid chromatography with detection by tandem mass spectrometry (LC/MS/MS) was developed. Honey samples fortified with chloramphenicol and isotopically labeled chloramphenicol were extracted using diatomaceous-based supported liquid-liquid extraction cartridges to generate a standard calibration curve. Four MS/MS transitions were used for quantification and four other transitions for confirmation of chloramphenicol. The limit of detection for chloramphenicol was 0.05 ng/g and the lower limit of quantification was 0.1 ng/g. Several commercial honey samples were analyzed for chloramphenicol content using this method.     

Quantitative determination of cetirizine enantiomers in guinea pig plasma, brain tissue and microdialysis samples using liquid chromatography/tandem mass spectrometry

Sensitive enantioselective liquid chromatographic assays using tandem mass spectrometric detection were developed and validated for the determination of S-cetirizine (S-CZE) and R-cetirizine (R-CZE) in guinea pig plasma, brain tissue, and microdialysis samples. Enantioselective separation was achieved on an alpha1-acid glycoprotein column within 14 min for all methods. A cetirizine analog, ucb 20028, was used as internal standard. Cetirizine and the internal standard were detected by multiple reaction monitoring using transitions m/z 389.1 --> 200.9 and 396.1 --> 276.1, respectively. The samples were prepared using protein precipitation with acetonitrile. For guinea pig plasma, the assay was linear over the range 0.25-5000 ng/mL for both S-CZE and R-CZE, with a lower limit of quantification (LLOQ) of 0.25 ng/mL. For the brain tissue and microdialysis samples, the assays were linear over the range 2.5-250 ng/g and 0.25-50 ng/mL, respectively, and the LLOQ values were 2.5 ng/g and 0.25 ng/mL, respectively. The intra- and inter-day precision values were < or =7.1% and < or =12.6%, respectively, and the intra- and inter-day accuracy varied by less than +/-8.0% and +/-6.0% of the nominal value, respectively, for both enantiomers in all the matrices investigated.     

超高效液相色谱-串联质谱法检测动物源性食品中残留的9种β-受体激动剂

建立了动物源性食品中特布他林、西马特罗、沙丁胺醇、非诺特罗、氯丙那林、莱克多巴胺、克仑特罗、妥布特罗和喷布特罗等9种β-受体激动剂残留检测的超高效液相色谱-串联质谱方法。样品经酶解后,用高氯酸去除蛋白质等杂质,调节上清液的pH值后,分别用乙酸乙酯和叔丁基甲醚进行萃取,再用MCX固相萃取柱净化,然后用Waters Acquity UPLC BEH C18色谱柱(50 mm×2.1 mm,1.7 μm)分离,以0.1%甲酸乙腈溶液和0.1%甲酸水溶液为流动相进行梯度洗脱,外标法定量。结果表明:9种β-受体激动剂在0.25～5 μg/kg的空白添加浓度范围内呈良好的线性关系,相关系数(r)均大于0.990;特布他林等8种药物的检出限为0.1 μg/kg,定量限为0.25 μg/kg;喷布特罗的检出限为0.25 μg/kg,定量限为0.5 μg/kg。从0.5,1和2 μg/kg共3个添加浓度的检测结果可以看出,9种药物的平均回收率为87.1%～108.6%,批内、批间相对标准偏差(RSD)均小于20%。该方法具有简便快捷、灵敏度高、定性准确等特点。     

超高效液相色谱-串联质谱法检测畜产品和水产品中3-甲基喹恶啉-2-羧酸残留

以猪肉、猪肝、猪肾、胖头鱼、对虾和蟹为试验材料,建立了喹乙醇(OLA)的残留标示物3-甲基喹恶啉-2-羧酸(MQCA)残留的超高效液相色谱-串联质谱(UPLC-MS/MS)检测方法。采用0.2 mol/L盐酸提取可食性组织中的分析物,经C18固相萃取小柱净化、35 ℃氮气吹干及含0.1%(v/v)甲酸的乙腈溶解后,采用超高效液相色谱分离,串联质谱法确证和定量分析。质谱检测采取正离子多反应监测模式,外标法定量。结果表明: MQCA在2～500 μg/L范围内呈良好的线性关系,各组织中的相关系数(r2)均大于0.990;猪肉、猪肝、猪肾、鱼、对虾和蟹中MQCA的检出限依次为0.90、1.51、0.94、1.04、1.62和1.80 μg/kg,定量限依次为3.00、5.02、3.13、3.46、5.40、6.00 μg/kg。从3～100 μg/kg的添加浓度的检测结果可以看出,MQCA的平均回收率均在73.6%与89.0%之间,日内相对标准偏差(RSD, n=5)在15%以下,日间RSD(n=3)为20%以下。该方法的灵敏度、准确度和精密度均符合兽药残留分析技术的要求,适用于动物组织中MQCA残留的定量分析和确证检测。     

Simultaneous quantification of ten cytotoxic drugs by a validated LC–ESI–MS/MS method

A liquid chromatography separation with electrospray ionisation and tandem mass spectrometry detection method was developed for the simultaneous quantification of ten commonly handled cytotoxic drugs in a hospital pharmacy. These cytotoxic drugs are cytarabine, gemcitabine, methotrexate, etoposide phosphate, cyclophosphamide, ifosfamide, irinotecan, doxorubicin, epirubicin and vincristine. The chromatographic separation was carried out by RPLC in less than 21 min, applying a gradient elution of water and acetonitrile in the presence of 0.1% formic acid. MS/MS was performed on a triple quadrupole in selected reaction monitoring mode. The analytical method was validated to determine the limit of quantification (LOQ) and quantitative performance: lowest LOQs were between 0.25 and 2 ng mL(-1) for the ten investigated cytotoxic drugs; trueness values (i.e. recovery) were between 85% and 110%, and relative standard deviations for both repeatability and intermediate precision were always inferior to 15%. The multi-compound method was successfully applied for the quality control of pharmaceutical formulations and for analyses of spiked samples on potentially contaminated surfaces.     

A rapid UPLC‐MS/MS method for the determination of oleanolic acid in rat plasma and liver tissue: application to plasma and liver pharmacokinetics

A reliable high‐throughput ultra‐high performance liquid chromatography–tandem mass spectrometry (UPLC‐MS/MS) method was developed and validated for oleanolic acid (OA) determination in rat plasma and liver tissue using glycyrrhetic acid as the internal standard (IS). Plasma and liver homogenate samples were prepared using solid‐phase extraction. Chromatographic separation was achieved on a C₁₈ column using an isocratic mobile phase system. The detection was performed by multiple reaction monitoring mode via positive electrospray ionization interface. The calibration curves showed good linearity (R² > 0.9997) within the tested concentration ranges. The lower limit of quantification for plasma and liver tissue was ≤0.75 ng/mL. The intra‐ and inter‐day precision and accuracy deviations were within ±15% in plasma and liver tissue. The mean extraction recoveries ranged from 80.8 to 87.0%. In addition, the carryover, matrix effect, stability and robustness involved in the method were also validated. The method was successfully applied to the plasma and hepatic pharmacokinetics of OA after oral administration to rats. Copyright © 2015 John Wiley & Sons, Ltd.     

液相色谱-串联质谱法测定牛奶和奶粉中卡巴氧和喹乙醇代谢物的残留量

建立了牛奶和奶粉中卡巴氧代谢物喹喔啉-2-羧酸(QCA)和喹乙醇代谢物3-甲基喹喔啉-2-羧酸(MQCA)残留量的液相色谱-串联质谱测定方法。将样品经0.6%(体积分数)的甲酸溶液进行消化,用Tris缓冲溶液调节pH后,加入Protease蛋白酶进行酶解,样品溶液用0.3 mol/L HCl溶液酸化后,采用阴离子交换固相萃取柱Oasis MAX进行净化和富集。分析样品以0.1%(体积分数)的甲酸溶液-甲醇-乙腈为流动相,经Inertsil ODS-3色谱柱分离,采用负离子扫描,在LC-MS/MS多反应监测模式下进行定性及定量分析。喹口恶啉-2-羧酸和3-甲基喹口恶啉-2-羧酸的方法测定下限牛奶为0.5μg/kg,奶粉为4.0μg/kg。对牛奶在0.5~5.0μg/kg,奶粉在4.0~40.0μg/kg添加水平的平均回收率为68.2%~82.5%,RSD为3.4%~12%。     

A sensitive and specific ELISA for determining a residue marker of three quinoxaline antibiotics in swine liver

Methyl-3-quinoxaline-2-carboxylic acid (MQCA) is a possible residue marker for three quinoxaline veterinary medicines (olaquindox, mequindox, and quinocetone). The wide application of mequindox/quinocetone or the illegal use of olaquindox leads to MQCA residue in animal’s original food, thereby threatening the safety of human food. The indirect competitive enzyme-linked immunosorbent assay (IC-ELISA) with a specific coating antigen and monoclonal antibody (MAB) was established and optimized for detecting MQCA in swine liver. Samples were acidified with 2 mol?l^?1 hydrochloric acid, extracted with ethyl acetate–hexane–isopropanol (8?+?1?+?1, v/v/v) and then detected by IC-ELISA. The logarithm correlation of standards to OD values ranged from 0.2 to 200 μg?l^?1, with IC₅₀ of 6.46 μg?l^?1. Negligible cross-reactivity happened to five quinoxaline antibiotics (olaquindox, mequindox, quinocetone, carbadox, and cyadox) and the metabolite of carbadox and cyadox (quinoxaline-2-carboxylic acid). When spiked with 1 to 100 μg?kg^?1 of MQCA, the recoveries ranged from 85.44 to 100.02 %, with the intra-assay coefficient of variation (CV) of 6.64–10.57 % and inter-assay CV of 7.29–10.88 %. The limit of detection for MQCA was 1.0 μg?kg^?1 in swine liver. Furthermore, incurred samples were detected by the IC-ELISA and then conformed by a reported LC/MS/MS method, it shown that there was good correlation between the two methods. All these results indicated that the IC-ELISA method is appropriate for surveillance MQCA residue in animal tissues.

Development of liquid chromatographic methods for determination of quinocetone and its main metabolites in edible tissues of swine and chicken

Quinocetone (QCT), a new antimicrobial growth promotant of quinoxalines, can effectively improve the growth and feed efficiency of food animals with more safety than is provided by olaquindox and carbadox. To clarify its metabolism and residue levels in animals, a liquid chromatographic method with UV-Vis detection was developed for the determination of QCT and its main metabolites, desoxyquinocetone (DQCT) and 3-methylquinoxaline-2-carboxylic acid (MQCA), in muscle, liver, kidney, and fat of swine and chicken. For sample pretreatment, QCT and DQCT were extracted with ethyl acetate and purified with iso-octane; after alkaline hydrolysis of the tissue, MQCA was extracted with ethyl acetate and citric acid buffer (pH 6.0), and the extract was purified over a cation-exchange column (AG MP-50 resin). Detection was at 312 and 320 nm for QCT and DQCT, respectively, and at 320 nm for MQCA. The observed limit of detection for the 3 compounds was 0.025 microg/g in various tissues. The methods were linear over the concentrations range of 0.01-0.64 microg/mL with mean recoveries of approximately 71-86% and relative standard deviations of about 4-12% at the levels of 0.05, 0.10, and 0.20 microg/g. The method is highly selective and can be applied to the determination of QCT and its main metabolites in animal tissues, which would accelerate the pharmacokinetic and residue study of QCT in food animals.     

Determination of gentamicin in swine and calf tissues by high-performance liquid chromatography combined with electrospray ionization mass spectrometry

Gentamicin is a broad-spectrum aminoglycoside antibiotic widely used in veterinary medicine for the treatment of serious infections. The purpose of this study was to develop and validate a method to determine gentamicin residues in edible tissues of swine and calf. Extraction of gentamicin was performed using a liquid extraction with phosphate buffer containing trichloroacetic acid, followed by a solid-phase clean-up procedure on a CBA weak cation-exchange column. Tobramycin was used as the internal standard. After drying of the eluate, the residue was redissolved and further analyzed by reversed-phase liquid chromatography/electrospray ionization tandem mass spectrometry (MS/MS). Chromatographic separation of the internal standard tobramycin and the gentamicin components was achieved on a Nucleosil (5 microm) column using a mixture of 10 mM pentafluoropropionic acid in water and acetonitrile as the mobile phase. The gentamicin components C1a, C2 + C2a and C1 could be identified with the MS/MS detection, and subsequently quantified. The method was validated according to the requirements of the EC at the maximum residue limit (MRL) (100 ng g(-1) for muscle and fat, 200 ng g(-1) for liver and 1000 ng g(-1) for kidney), half the MRL and double the MRL levels. Calibration graphs were prepared for all tissues and good linearity was achieved over the concentration ranges tested (r > 0.99 and goodness of fit <10%). Limits of quantification of 25.0 ng g(-1) were obtained for the determination of gentamicin in muscle, fat, liver and kidney tissues of swine and calf, which correspond in all cases to at least half the MRLs. Limits of detection ranged between 0.5 and 2.5 ng g(-1) for the tissues. The within-day and between-day precisions (RSD) and the results for accuracy fell within the ranges specified. The method was successfully used for the determination of gentamicin in tissue samples of swines and calves medicated with gentamicin by intramuscular injection.     

Novel surface molecularly imprinted sol-gel polymer applied to the online solid phase extraction of methyl-3-quinoxaline-2-carboxylic acid and quinoxaline-2-carboxylic acid from pork muscle

A new molecularly imprinted polymer (MIP), selective for major metabolites of quinoxaline-1,4-dioxides was firstly prepared by combining surface molecular imprinting technique with the sol–gel process. Methyl-3-quinoxaline-2-carboxylic acid (MQCA) was used as template, 3-aminopropyltriethoxysilane as functional monomer, and tetraethoxysilicane as cross-linker. The MIP was characterized by Fourier transform infrared and evaluated through static adsorption experiments. The results indicated that MIP had high adsorption capacity, fast binding kinetics for MQCA, and the polymer showed a high degree of cross-reactivity for quinoxaline-2-carboxylic acid (QCA). The MIP was then applied as a selective sorbent in an online solid phase extraction (SPE) coupled with high-performance liquid chromatography (HPLC). For a 50-mL sample solution, enrichment factors of 1,349 and 1,046 for QCA and MQCA, respectively, and limits of detection (S/N = 3) of 0.8 and 2 ng L⁻¹ for QCA and MQCA, respectively, were obtained (corresponding to 0.02 and 0.04 ng g⁻¹ in solid samples for final 100 mL of sample solutions of 5 g of pork). The sample preparation protocol was simplified and only included one step extraction with acetonitrile (MeCN) after the release of target analytes through acidic hydrolysis without further sample cleanup. The new MIP-SPE-HPLC method was successfully applied to the quantification of trace QCA and MQCA in pork muscle with good recoveries ranging from 67% to 80% and RSD below 8%.     

Development and validation of high-performance liquid chromatography/electrospray ionization mass spectrometry for assay of madecassoside in rat plasma and its application to pharmacokinetic study

A rapid, sensitive and specific high-performance liquid chromatography/electrospray ionization mass spectrometric (LC-ESI-MS) method was developed and validated for the quantification of madecassoside, a major active constituent of Centella asiatica (L.) Urb. herbs, in rat plasma. With paeoniflorin as an internal standard (IS), a simple liquid-liquid extraction process was employed for the plasma sample preparation. Chromatographic separation was achieved within 6 min on a Shim-pack CLC-ODS column using acetonitrile and water (60:40, v/v) containing 0.1% (v/v) formic acid as the mobile phase. The detection was performed by MS with electrospray ionization interface in negative selected ion monitoring (SIM) mode. The linear range was 11-5500 ng/mL with the square regression coefficient (r(2) ) of 0.9995. The lower limit of quantification was 11 ng/mL. The intra- and inter- day precision ranged from 4.99 to 9.03%, and the accuracy was between 95.82 and 111.80%. The average recoveries of madecassoside and IS from spiked plasma samples were >92%. The developed method was successfully applied to the pharmacokinetic study of madecassoside in rats after an oral administration.     

Quantification of clenbuterol in equine plasma,urine and tissue by liquid chromatography coupled on-line with quadrupole time-of-flight mass spectrometry

Clenbuterol (CBL) is a potent beta(2)-adrenoceptor agonist used for the management of respiratory disorders in the horse. The detection and quantification of CBL can pose a problem due to its potency, the relatively low dose administered to the horse, its slow clearance and low plasma concentrations. Thus, a sensitive method for the quantification and confirmation of CBL in racehorses is required to study its distribution and elimination. A sensitive and fast method was developed for quantification and confirmation of the presence of CBL in equine plasma, urine and tissue samples. The method involved liquid-liquid extraction (LLE), separation by liquid chromatography (LC) on a short cyano column, and pseudo multiple reaction monitoring (pseudo-MRM) by electrospray ionization quadrupole time-of-flight tandem mass spectrometry (ESI-QTOF-MS/MS). At very low concentrations (picograms of CBL/mL), LLE produced better extraction efficiency and calibration curves than solid-phase extraction (SPE). The operating parameters for electrospray QTOF and yield of the product ion in MRM were optimized to enhance sensitivity for the detection and quantification of CBL. The quantification range of the method was 0.013-10 ng of CBL/mL plasma, 0.05-20 ng/0.1 mL of urine, and 0.025-10 ng/g tissue. The detection limit of the method was 13 pg/mL of plasma, 50 pg/0.1 mL of urine, and 25 pg/g of tissue. The method was successfully applied to the analysis of CBL in plasma, urine and various tissue samples, and in pharmacokinetic (PK) studies of CBL in the horse. CBL was quantified for 96 h in plasma and 288 h in urine post-administration of CLB (1.6 micro g/kg, 2 x daily x 7 days). This method is useful for the detection and quantification of very low concentrations of CBL in urine, plasma and tissue samples.     

A rapid and specific approach for direct measurement of donepezil concentration in human plasma by LC-MS/MS employing solid-phase extraction

A selective, rapid and simple liquid chromatography-tandem mass spectrometry (LC-MS/MS) method is described for assay of donepezil in human plasma using escitalopram as an internal standard. Chromatographic separation was achieved on a Betabasic-C(8), 5 microm, 100 x 4.6 mm column using methanol:water:formic acid (90:9.97:0.03, v/v/v) as mobile phase. Detection of donepezil and internal standard was achieved by ESI MS/MS in positive ion mode using 380.20/91.10 and 325.13/262.00 transitions, respectively. The linearity over the concentration range of 0.15-50 ng/mL for donepezil was obtained and the lower limit of quantification was 0.15 ng/mL. For each level of quality control samples, inter-day and intra-day precisions (RSD) were < or =8.92 and 10.35% and accuracy (%RE) were < or =7.33% and 9.33%, respectively. The recovery was more than 88.50% for both donepezil and internal standard by solid-phase extraction, eliminating evaporation and reconstitution steps.