Simultaneous determination of caffeine, theophylline and theobromine in human plasma by on-line solid-phase extraction coupled to reversed-phase chromatography

A reversed-phase liquid chromatographic column switching system was described for the determination of caffeine (CF), theophylline (TH) and theobromine (TB) in human plasma with a direct injection procedure. A short protein-coated mu Bondapak CN silica pre-column (20 x 3 mm, i.d.) was used for enrichment of the drugs and clean up from weakly retained plasma components using phosphate buffer saline pH 7.4. After washing step, the retained drugs were flushed into a reversed-phase column (5 microm TSK gel ODS-80 TM, 150 x 4.6 mm i.d.) with a mobile phase of methanol-0.01 M phosphate buffer, pH 3.5 (30:70, v/v) for the final separation. The eluent was monitored with a UV detector at 275 nm. The resulting chromatograms showed no interference from endogenous plasma components. A linear relationship between the concentration of drug and peak height was confirmed in the range of 0.5-20 microg/mL for all drugs. High extraction recoveries from plasma ranging from 96.12 to 100.32% were achieved. Validation of the method was examined performing intra- and inter-day accuracy and precision and was found to be satisfactory. The coefficients of variation of the three drugs were less than 3% for intra-day and less than 4% for inter-day run assays.     

Some characteristics of a protein-coated ODS column and its use for the determination of drugs by the direct injection analysis of plasma samples

Summary It was found that an ODS column of small pore (120?) which was coated with denatured plasma proteins (protein-coated ODS) no longer adsorbed plasma proteins from aqueous solution but retained the characteristics of native ODS for small hydrophobic molecules. Elemental analysis and nitrogen desorption (BET) analysis showed that the protein-coated ODS contained ca 25 mg proteing⁻¹ dry resin and that the pore diameter or pore volume was similar to that of native ODS. The coated denatured proteins, which seemed to be adsorbed on the external surface of the porous resin, were not eluted under usual reverse-phase elution conditions. Operating as either an analytical column or a pre-column, this protein-coated ODS column was used to analyse spiked-drugs in plasma. The recovery of all the spiked-drugs (such as doxorubicin, methotrexate) was almost quantitative (98–102%) with good reproducibilities (c.v., less than 2%). The present method was useful for the determination of total, that is, free + bound-to-plasma-proteins, hydrophobic drugs in plasma in view of its accuracy and simplicity. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984     

Simultaneous determination of free and bound adriamycin, adriamycinol, adriamycinone and duanorubicin in plasma using column-switching technique and protein-coated pre-columns

Adriamycin, adriamycinol, adriamycinone and duanorubicin were simultaneously determined by the development of an on-line plasma clean-up system. A short protein-coated Lichrosorb, RP-8, RP-2, CN and muBondapak phenyl as well as ODS silica have been examined for their performance as pre-columns. The drugs and metabolites were separated from weakly retained plasma components through two steps; phosphate buffer saline, pH 7.4 and 15% acetonitrile in 0.1 M sodium dihydrogen phosphate, pH 3. The chromatographic conditions were: ODS/TM column, flow rate 1 ml/min, 35% acctonitrile in 0.1 M sodium dihydrogen phosphate (pH 3) containing 0.3% heptafluorobutyric acid as mobile phase. The detection was carried out using fluorescence monitor operated at an emission 555 nm and excitation 460 nm. Good resolution was obtained within 13 min. This method is reproducible for analysis of drugs and metabolites (99.3-100.1%, CV < 2%) in plasma.     

硅胶基硝化苯硼酸亲和色谱材料的合成及应用

合成了硅胶基硝化苯硼酸亲和色谱材料,首先对间氨基苯硼酸进行硝基化,制得3-氨基-4-硝基苯硼酸功能基团,通过γ-缩水甘油醚氧丙基三甲氧基硅烷把功能基团键合到硅胶基体上,在20.7MPa压力下装成亲和色谱预柱(35mm×4.6mmi.d.)。用该预柱通过六通阀后接ODS分析柱(250mm×4.6mmi.d.),构成中心切割二维HPLC。该系统能对含有顺二羟基结构的化合物进行在线富集,实现生物复杂样品直接进样分离分析。使用该系统对尿中多种修饰核苷进行了分离分析,以pH值7.95的0.25mol/LNH4Ac碱性缓冲液把实际尿样(100μL)中核苷保留在预柱上,生物大分子无保留通过,再切换六通阀,以pH4.50的25mmol/LKH2PO4酸性洗脱液把保留在预柱上的核苷洗脱,进样到下一级ODS分析柱柱头上聚焦,然后用梯度洗脱法(pH4.50的25mmol/LKH2PO4缓冲液与体积比60∶40的甲醇-水梯度混合构成洗脱液)完成核苷在ODS分析柱上的分离(紫外检测260nm),11种目标核苷的分离分析取得了良好的定性定量结果。     

Development of an ultrasensitive stacking technique for 5‐nitroimidazole determination in untreated biological fluids by micellar electrokinetic chromatography

Cation‐selective exhaustive injection and sweeping followed by a MEKC separation is evaluated for the sensitive analysis of 5‐nitroimidazoles in untreated human serum and urine. Deproteinized serum and urine samples were diluted 76 and 143 times, respectively, in a low‐conductivity solvent (5.00 mM orthophosphoric acid containing 5.0% v/v methanol). Samples were electrokinetically injected at 9.8 kV for 632 s in a previously conditioned fused‐silica capillary (65.0 cm × 50 μm id). Separation was performed at –30 kV and 20°C using 44 mM phosphate buffer (pH 2.5), 123 mM SDS, and 8% v/v tetrahydrofurane as BGE. Signals were monitored at 276 nm and peak area was selected as analytical response. Good linearity (R² ≥ 0.988) and LODs lower than 1.5 and 1.8 μg/mL were achieved in serum and urine, respectively.     

金纳米粒子修饰的手性毛细管电色谱固定相的制备及性能表征

制备了粒径为15 nm的金纳米粒子(GNPs)并将其修饰到氨基衍生化的硅胶整体柱内,通过化学键合法将牛血清白蛋白(BSA)固载到GNPs的表面作为手性固定相。通过透射电子显微镜、扫描电子显微镜等方法进行表征,结果表明,GNPs分散性良好,并被成功地修饰到毛细管柱内,含量高达17.18%。优化了BSA手性柱的制备条件,最终确定了体积分数为10%的3-氨丙基三乙氧基硅烷(APTES)和15 g/L BSA为最佳反应条件。在毛细管电色谱分离模式下,对缓冲液pH值、电压等分离条件进行了考察,最终选择了10 mmol/L pH 7.4的磷酸缓冲液和15 kV运行电压作为最佳分离条件。手性柱对3种手性化合物(色氨酸、阿替洛尔和麻黄碱)有拆分效果,对色氨酸能实现基线分离。与物理吸附法相比,化学键合法制备的手性柱拆分效果好,分析物无需柱前衍生化,且色谱柱稳定性良好。该文的制备方法也为其他类型手性选择剂的引入提供了良好的思路。     

Fully automated method for the liquid chromatographic-tandem mass spectrometric determination of cyproterone acetate in human plasma using restricted access material for on-line sample clean-up

A new automated method for the quantitative analysis of cyproterone acetate (CPA) in human plasma has been developed using on-line solid phase extraction (SPE) prior to the LC-MS/MS determination. The method was based on the use of a pre-column packed with internal-surface reversed-phase material (LiChrospher RP-4 ADS, 25 mm x 2 mm) for sample clean-up coupled to LC separation on an octadecyl silica stationary phase by means of a column switching system. A 30 microl plasma sample volume was injected directly onto the pre-column using a mixture of water, acetonitrile and formic acid (90:10:0.1 (v/v/v)) adjusted to pH 4.0 with diluted ammonia as washing liquid. The analyte was then eluted in the back-flush mode with the LC mobile phase consisting of water, methanol and formic acid (10:90:0.1 (v/v/v)). The dispensing flow rates of the washing liquid and the LC mobile phase were 300 microl min(-1). Medroxyprogesterone acetate (MPA) was used as internal standard. The MS ionization of the analytes was achieved using electrospray (ESI) in the positive ion mode. The pseudomolecular ionic species of CPA and MPA (417.4 and 387.5) were selected to generate daughter ions at 357.4 and 327.5, respectively. Finally, the developed method was validated according to a new approach using accuracy profiles as a decision tool. Very good results with respect to accuracy, detectability, repeatability, intermediate precision and selectivity were obtained. The LOQ of cyproterone acetate was 300 pg ml(-1).     

Determination of nadolol in serum by high-performance liquid chromatography with fluorimetric detection.

A sensitive high-performance liquid chromatographic method for a routine assay of nadolol in serum is described. Serum samples spiked with atenolol (internal standard) were extracted with diethyl ether. After centrifugation, the organic layer was evaporated to dryness. The residue was redissolved in the mobile phase and injected onto an octadecyl silica column (150 mm x 4.6 mm I.D.). The mobile phase was 0.05 M ammonium acetate (pH 4.5)-acetonitrile (85:15, v/v). Fluorometric detection (excitation 230 nm, emission 300 nm) was used. The minimum detectable level of nadolol in serum was 1 ng/ml.     

Trace-level determination of 3'-azido-3'-deoxythymidine in human plasma by preconcentration on a silver (I)-thiol stationary phase with on-line reversed-phase high-performance liquid chromatography

A method was developed for the determination of 3'-azido-3'-deoxythymidine (AZT) in plasma. The method is based on the trace enrichment of AZT on a pre-column packed with a silver-loaded thiol stationary phase at pH 11.6. On-line desorption to the reversed-phase liquid chromatographic system is performed by injecting a plug of 50 microliters of 1 M perchloric acid on the silver (I)-thiol pre-column. Two different sample pretreatment methods - protein precipitation with perchloric acid and on-line clean-up via a polymeric PRP-1 pre-column - were applied for the determination of AZT in human plasma. The latter method allows the direct injection of plasma samples into the analytical system and can therefore easily be automated. With both methods detection limits in the order of 10(-8) M AZT were obtained after preconcentration of 1.0 ml of plasma, using UV detection at 267 nm.     

Dependence of cyano bonded phase hydrolytic stability on ligand structure and solution pH

As part of our program to develop more stable cyano (CN) high-performance liquid chromatography (HPLC) column packings, we have evaluated hydrolytic stability as a function of ligand connectivity, chain length, and side group steric protection and the pH of the mobile phase. Three accelerated tests were used to evaluate stability: (1) A non-HPLC screening test measuring carbon loss in refluxing MeOH-100 mM KH2PO4 pH 4.5 (1:1, v/v) solution; (2) a continuous flow HPLC test measuring capacity factor maintenance in 1% trifluoroacetic acid in water (pH 1.02) at 80 degrees C; and (3) a continuous flow HPLC test measuring column efficiency maintenance in 50 mM triethylamine in water (pH 10.00) at 50 degrees C. The stability of the CN phases was found to be dependent on both ligand chemical structure and the pH of the test conditions. The starting screen test of intermediate pH was least able to differentiate the CN phases based on structure, because two different degradation mechanisms appear to offset each other (acid induced siloxane bond cleavage vs. base induced silica dissolution). A trifunctional and a sterically protected CN phase were notably stable under the acidic test conditions, but had poor stability under basic conditions. Conversely, chain extension afforded poor stability under acidic conditions, but did afford improved stability at higher pH. In total, the data indicate that good CN column stability can be achieved by using a trifunctional or a sterically protected phase in acidic mobile phases. However, as mobile phases of intermediate or higher pH are employed, shorter column lifetimes can be expected due to an accelerated dissolution of the underlying silica substrate. Materials were also compared chromatographically using a mixture of non-polar, polar, and basic analytes under reversed-phase conditions.     

Liquid chromatographic determination of enrofloxacin in nasal secretions and plasma of healthy pigs using restricted access material for on-line sample clean-up

A new fully automated method was developed for the quantitative analysis of an antibacterial drug, enrofloxacin (ENRO), in both nasal secretions and plasma samples of healthy pigs. The method is based on the use of a pre-column packed with restricted access material (RAM), namely RP-18 ADS (alkyl diol silica), for on-line sample clean-up coupled to a liquid chromatographic (LC) column containing octadecyl silica. The only off-line sample preparation was the 50-fold dilution of nasal secretions and plasma samples in the washing liquid composed of 25 mM phosphate buffer of pH 7.4. A 10 microl diluted sample volume was injected directly onto the pre-column and washed for 7 min. By rotation of a switching valve, the analyte of interest was eluted in the back-flush mode with the LC mobile phase which consisted in a mixture of 25 mM phosphate buffer of pH 3.0 and acetonitrile according to a segmented gradient elution. By a new rotation of the switching valve, the pre-column and the analytical column were equilibrated for 3 min with the initial mobile phases. The flow-rate was 0.8 ml min(-1) for the washing liquid and 1.5 ml min(-1) for the LC mobile phase. ENRO was detected by fluorescence at excitation and emission wavelengths of 278 and 445 nm, respectively. Finally, the developed method was validated using an original strategy based on total measurement error and accuracy profiles as a decision tool. The limits of quantitation of ENRO in plasma and in nasal secretions were 30.5 and 91.6 ng/ml, respectively. The validated method was then applied successfully to the determination of ENRO in healthy pigs treated by intramuscular injection at different doses (2.5, 10 and 30 mg/kg bodyweight) for a pilot study. This method could be also used for the simultaneous analysis of ENRO and its main metabolite, ciprofloxacin (CIPRO).     

Simultaneous determination of ruthenium, osmium and palladium by reversed-phase HPLC using 4-(2'-thiazolylazo) resacetophenone oxime as chelating reagent

The chelates of Ru, Os and Pd with 4-(2'-thiazolylazo) resacetophenone oxime were separated simultaneously by HPLC using a pre-column derivatization method, at the wavelength 560 nm, on an octadecly-bonded silica stationary phase with a mobile phase methanol-water mixture (40-60 v/v) containing 40 mM of acetate buffer pH 5.0. The detection limits for Ru, Os and Pd were 2.0, 4.0 and 0.2 ng, respectively. The method has been applied successfully for the determination of metal ions in an anode slime.     

Determination of atrazine, its degradation products and metolachlor in runoff water and sediments using solid-phase extraction

In order to determine the fate of the herbicides atrazine (as well as some of its degradation products) and metolachlor in water and sediments, a method was developed to extract and analyse these compounds. The two matrices were separated completely by centrifugation followed by filtration using nylon filters (0.45 mum). Sediments were extracted with a mixture of methanol-0.1N hydrochloric acid (50:50, v/v) using a wrist-action shaker. Filtered water and extracts of sediments were adjusted to pH 4, then concentrated and purified onto two solid-phase extraction cartridges using in tandem C(18) bonded phase column atop sulfonic acid bonded column (SCX). Atrazine, deethylatrazine, deisopropylatrazine and metolachlor retained by the C(18) column were eluted with ethyl acetate. Chlorodiaminotriazine and hydroxyatrazine retained by the SCX column were eluted with a 50:50 (v/v) acetonitrile-0.1M Na(2) HPO(4) aqueous solution (pH 8.5). The extracts were quantified by high performance liquid chromatography with diode array detector (HPLC-DAD) and by gas chromatography with nitrogen-phosphorus detector (GC-NPD). Overall percent recoveries were about 75% and detection limits were between 0.05 and 0.15 microg/l., and 0.5 and 1.5 microg/kg for water and sediments, respectively.     

Optimization of chromatography to overcome matrix effect for reliable estimation of four small molecular drugs from biological fluids using LC–MS/MS

The article describes a systematic study to overcome the matrix effect during chromatographic analysis of gemfibrozil, rivastigmine, telmisartan and tacrolimus from biological fluids using LC–ESI–MS/MS. All four methods were thoroughly developed by the appropriate choice of analytical column, elution mode and pH of mobile phase for improved chromatography and overall method performance. Matrix effect was assessed by post-column analyte infusion, slope of calibration line approach and post-extraction spiking. The best chromatographic conditions established were: Acquity BEH C₁₈ (50 × 2.1 mm, 1.7 μm) column with 5.0 mm ammonium acetate, pH 6.0–methanol as the mobile phase under gradient program for gemfibrozil; Luna CN (50 × 2.0 mm, 3 μm) column with a mobile phase consisting of acetonitrile–10 mm ammonium acetate, pH 7.0 (90:10, v/v) for rivastigmine; Inertsustain C₁₈ (100 × 2.0 mm, 5 μm) column using methanol–2.0 mm ammonium formate, pH 5.5 (80: 20, v/v) as the mobile phase for isocratic elution of telmisartan; and Acquity BEH C₁₈ (50 × 2.1 mm, 1.7 μm) with methanol–10 mm ammonium acetate, pH 6.0 (95:5, v/v) as mobile phase for tacrolimus. The methods were thoroughly validated as per European Medicines Agency and US Food and Drug Administration guidance and were successfully applied for pharmacokinetic studies in healthy subjects.     

Determination of gliclazide in serum by high-performance liquid chromatography using solid-phase extraction.

A simple and sensitive high-performance liquid chromatographic method for a routine assay of gliclazide in serum is described. Serum samples spiked with glibenclamide (internal standard) were applied to Bond Elut C18 cartridges. After washing with phosphate buffer (pH 7.5) and water, the cartridge was eluted with 60% methanol. The eluate was evaporated to dryness. The residue was dissolved in methanol and injected onto an octadecyl silica column (5 microns, 150 mm x 4.6 mm I.D.). The mobile phase was 0.04 M potassium dihydrogenphosphate (pH 4.6)-acetonitrile-isopropyl alcohol (5:4:1, v/v). Ultraviolet detection at 227 nm was used. The minimum detectable level of gliclazide was 20 ng/ml.     

Determination of serum estradiol by normal-phase high-performance liquid chromatography with peroxyoxalate chemiluminescence detection

Estradiol extracted with an ODS minicolumn from serum (500 μl) is derivatized with 5-dimethylamino-1-naphthalenesulfonyl (dansyl) chloride at room temperature for 80 min, purified on the ODS minicolumn, separated on silica gel columns (150 × 1.9 mm i.d. and 100 × 1.9 mm i.d.) with n-hexane/chloroform/ethanol (70:30:0.1) as eluent at 3 ml min^?1 and detected by the chemiluminescence emission produced in a post-column reaction with bis-(2,4,6-trichlorophenyl) oxalate (8 mM in chloroform containing 100 mM triethylamine) and hydrogen peroxide (600 mM in methanol containing 6% (v/v) sodium acetate buffer at pH 4.0). The overall recovery of estradiol from serum is ca. 90% and the detection limit is ca. 50 pg.     

Simultaneous determination of olmesartan medoxomil and irbesartan and hydrochlorothiazide in pharmaceutical formulations and human serum using high performance liquid chromatography

 A simple, selective, sensitive, precise, simultaneous high performance liquid chromatographic analysis of serum samples and commercial tablet formulation containing hydrochlorothiazide, olmesartan medoxomil and irbesartan are reported. Good chromatographic separation was achieved using a μ-Bondapak, C18 column (15 cm×4.6 mm, 5 μm), and a mobile phase consisting of acetonitrile-0.2% acetic acid aqueous solution (50∶50, v/v) at a flow rate of 1.0 mL/min. The ultraviolet detector was set at a wavelength of 260 nm. Hydrochlorothiazide, olmesartan medoxomil, and irbesartan were eluted at 1.2, 3.8, and 4.4 min, respectively. No extraneous materials were found to interfere. The method uses protein precipitation with acetonitrile for the preparation of serum sample. The linear ranges for hydrochlorothiazide, olmesartan medoxomil, and irbesartan were 6.25-18.75, 20-60, and 75-225 ng/mL, respectively. The recoveries of hydrochlorothiazide, olmesartan medoxomil, and irbesartan in spiked samples were all greater than 98%, and their relative standard deviations were less than 2.0%. The limits of detection were 1, 2, and 2 ng/mL for hydrochlorothiazide, olmesartan medoxomil, and irbesartan, respectively, and the limits of quantification were 3 ng/mL, which allow their determination at the expected serum concentration levels.     

Determination of a new non-benzodiazepine anxiolytic and its O-demethyl metabolite in plasma by high-performance liquid chromatography using automated column-switching

An highly sensitive and fully automated high-performance liquid chromatographic assay was developed for the determination of a novel non-benzodiazepine anxiolytic (I) [(R)-2-(methoxymethyl)-1-[(7-oxo-8-phenyl-7H-thieno[2,3-a]quinolizin+ ++- 10-yl)carbonyl]pyrrolidine] and its O-demethyl metabolite (II) in plasma, using column-switching for direct injection of plasma samples. After dilution in internal standard solution, the sample was injected onto a pre-column (17 mm x 4.6 mm) dry-packed with pellicular C18 reversed-phase material. Polar plasma components were removed by flushing the pre-column with water-acetonitrile (90:10, v/v). Retained substances, including I and II, were backflushed onto an analytical column, separated by gradient elution and detected by means of fluorescence detection (excitation, 304 nm; emission, 475 nm). After washing the analytical column and re-equilibrating the pre-column, the system was ready for the next injection. The limit of quantification for I and II was 0.25 and 0.5 ng/ml, respectively, using a 350-microliter specimen of plasma. The practicability of the new method was demonstrated by analysis of more than 300 plasma samples from a tolerance study performed with human volunteers. Owing to its high sensitivity, the method can be used to calculate pharmacokinetic parameters of compounds I and II in man after a single oral dose of about 1 mg of I.     

柱前衍生高效液相色谱测定小儿复方氨基酸注射液中氨基酸

建立了高效液相色谱(HPLC)测定小儿复方氨基酸注射液中各种氨基酸含量的方法.采用Kromasil C18(250×4.6 mm,5 μm)色谱柱,以2,4-二硝基氟苯为衍生试剂,梯度洗脱.流动相A为乙腈∶水(50∶50,V/V),流动相B为0.04 mol/L的磷酸二氢钾溶液(pH=6.8);流速为1.0 mL/min;检测波长为360 nm.所测氨基酸的线性范围为0.008～0.2213 mg/mL,平均回收率在97.85%～102.86%之间.     

A reversed phase high performance liquid chromatography method for the determination of fumonisins B1 and B2 in food and feed using monolithic column and positive confirmation by liquid chromatography/tandem mass spectrometry

The development of a reversed phase high performance liquid chromatography fluorescence method for the determination of the mycotoxins fumonisin B(1) and fumonisin B(2) by using silica-based monolithic column is described. The samples were first extracted using acetonitrile:water (50:50, v/v) and purified by using a C(18) solid phase extraction-based clean-up column. Then, pre-column derivatization for the analyte using ortho-phthaldialdehyde in the presence of 2-mercaptoethanol was carried out. The developed method involved optimization of mobile phase composition using methanol and phosphate buffer, injection volume, temperature and flow rate. The liquid chromatographic separation was performed using a reversed phase Chromolith(?) RP-18e column (100 mm × 4.6 mm) at 30 °C and eluted with a mobile phase of a mixture of methanol and phosphate buffer pH 3.35 (78:22, v/v) at a flow rate of 1.0 mL min(-1). The fumonisins separation was achieved in about 4 min, compared to approximately 20 min by using a C(18) particle-packed column. The fluorescence excitation and emission were at 335 nm and 440 nm, respectively. The limits of detections were 0.01-0.04 μg g(-1) fumonisin B(1) and fumonisin B(2), respectively. Good recoveries were found for spiked samples (0.1, 0.5, 1.5 μg g(-1) fumonisins B(1) and B(2)), ranging from 84.0 to 106.0% for fumonisin B(1) and from 81.0 to 103.0% for fumonisin B(2). Fifty-three samples were analyzed including 39 food and feeds and 14 inoculated corn and rice. Results show that 12.8% of the food and feed samples were contaminated with fumonisin B(1) (range, 0.01-0.51 μg g(-1)) and fumonisin B(2) (0.05 μg g(-1)). The total fumonisins in these samples however, do not exceed the legal limits established by the European Union of 0.8 μg g(-1). Of the 14 inoculated samples, 57.1% contained fumonisin B(1) (0.16-41.0 μg g(-1)) and fumonisin B(2) (range, 0.22-50.0 μg g(-1)). Positive confirmation of selected samples was carried out using liquid chromatography-tandem mass spectrometry, using triple quadrupole analyzer and operated in the multiple reaction monitoring mode.