Determination of rifampicin in human plasma by high‐performance liquid chromatography coupled with ultraviolet detection after automatized solid–liquid extraction

A precise and accurate high‐performance liquid chromatography (HPLC) quantification method of rifampicin in human plasma was developed and validated using ultraviolet detection after an automatized solid‐phase extraction. The method was validated with respect to selectivity, extraction recovery, linearity, intra‐ and inter‐day precision, accuracy, lower limit of quantification and stability. Chromatographic separation was performed on a Chromolith RP₈ column using a mixture of 0.05 m acetate buffer pH 5.7–acetonitrile (35:65, v/v) as mobile phase. The compounds were detected at a wavelength of 335 nm with a lower limit of quantification of 0.05 mg/L in human plasma. Retention times for rifampicin and 6,7‐dimethyl‐2,3‐di(2‐pyridyl) quinoxaline used as internal standard were respectively 3.77 and 4.81 min. This robust and exact method was successfully applied in routine for therapeutic drug monitoring in patients treated with rifampicin.     

Surfactant‐assisted dispersive liquid–liquid microextraction of nitrazepam and lorazepam from plasma and urine samples followed by high‐performance liquid chromatography with UV analysis

Surfactant‐assisted liquid–liquid microextraction followed by high‐performance liquid chromatography with UV detection has been developed for the simultaneous preconcentration and determination of lorazepam and nitrazepam in biological fluids. In this study, an ionic surfactant (cetyltrimethyl ammonium bromide) was used as an emulsifier. The predominant parameters affecting extraction efficiency such as the type and volume of extraction solvent, the type and concentration of surfactant, sample pH, and the concentration of salt added to the sample were investigated and opted. Under the optimum conditions (extraction solvent and its volume, 1‐octanol, 70 μL; surfactant and its concentration, 1 mL of ultra‐pure water containing 2 mmol L^?1 cetyltrimethyl ammonium bromide; sample pH = 9 and salt content of 10% NaCl w/v), the preconcentration factors were obtained in the range of 202–241 and 246–265 for nitrazepam and lorazepam, respectively. The limits of quantification for both drugs were 5 μg L^?1 in water sample and 10 μg L^?1 in biological fluids with R² values higher than 0.993. The suitability of the proposed method was successfully confirmed by the extraction and determination of the target drugs in human urine and plasma samples in the range of microgram per liter.     

Optimized determination of polybrominated diphenyl ethers by ultrasound‐assisted liquid–liquid extraction and high‐performance liquid chromatography

A method based on ultrasound‐assisted liquid–liquid extraction and high‐performance liquid chromatography has been optimized for the determination of six polybrominated diphenyl ether congeners. The optimal condition relevant to the extraction was first investigated, more than 98.7 ± 0.7% recovery was achieved with dichloromethane as extractant, 5 min extraction time, and three cycles of ultrasound‐assisted liquid–liquid extraction. Then multiple function was employed to optimize polybrominated diphenyl ether detection conditions with overall resolution and chromatography signal area as the responses. The condition chosen in this experiment was methanol/water 93:7 v/v, flow rate 0.80 mL/min, column temperature 30.0°C. The optimized technique revealed good linearity (R² > 0.9962 over a concentration range of 1–100 μg/L) and repeatability (relative standard deviation < 6.3%). Furthermore, the detection limit (S/N = 3) of the method were ranged from 0.02 to 0.13 μg/L and the quantification limit (S/N = 10) ranged from 0.07 to 0.35 μg/L. Finally, the proposed method was applied to spiked samples and satisfactory results were achieved. These results indicate that ultrasound‐assisted liquid–liquid extraction coupled with high‐performance liquid chromatography was effective to identify and quantify the complex polybrominated diphenyl ethers in effluent samples.     

Determination of naproxen in human plasma by GC–MS

This paper describes a GC–MS method for the determination of naproxen in human plasma. Naproxen and internal standard ibuprofen were extracted from plasma using a liquid–liquid extraction method. Derivatization was carried out using N‐methyl‐N‐(trimethylsilyl)trifluoroacetamide. The calibration curve was linear between the concentration range of 0.10–5.0 μg/mL. Intra‐ and interday precision values for naproxen in plasma were <5.14, and accuracy (relative error) was better than 4.67%. The extraction recoveries of naproxen from human plasma were between 93.0 and 98.9%. The LOD and LOQ of naproxen were 0.03 and 0.10 μg/mL, respectively. Also, this assay was applied to determine the pharmacokinetic parameters of naproxen in six healthy Turkish volunteers who had been given 220 mg naproxen.     

Determination of cisapride in human plasma by high-performance liquid chromatography with fluorescence detection

Summary A new sensitive HPLC-FLD method has been developed and validated for the determination of cisapride in human plasma for a bioequivalence study. A gradient method was used to remove late-eluting plasma components of no interest. The separation was performed on a Li-ChroCART 250-4 Purospher RP-18 (5 μm particle) analytical column fitted with a LiChroCART 4-4 Purospher RP-18 endcapped (5 μm particle) guard column. The excitation and emission wavelengths were 295 and 350 nm during fluorescence detection. The calibration plot was linear in the range of 5–200 ng mL⁻¹. A demethoxy analogue of cisapride was used as internal standard.     

Vortex‐assisted liquid–liquid microextraction using a low‐toxicity solvent for the determination of five organophosphorus pesticides in water samples by high‐performance liquid chromatography

Vortex‐assisted liquid–liquid microextraction followed by high‐performance liquid chromatography with UV detection was applied to determine Isocarbophos, Parathion‐methyl, Triazophos, Phoxim and Chlorpyrifos‐methyl in water samples. 1‐Bromobutane was used as the extraction solvent, which has a higher density than water and low toxicity. Centrifugation and disperser solvent were not required in this microextraction procedure. The optimum extraction conditions for 15 mL water sample were: pH of the sample solution, 5; volume of the extraction solvent, 80 μL; vortex time, 2 min; salt addition, 0.5 g. Under the optimum conditions, enrichment factors ranging from 196 to 237 and limits of detection below 0.38 μg/L were obtained for the determination of target pesticides in water. Good linearities (r > 0.9992) were obtained within the range of 1–500 μg/L for all the compounds. The relative standard deviations were in the range of 1.62–2.86% and the recoveries of spiked samples ranged from 89.80 to 104.20%. The whole proposed methodology is simple, rapid, sensitive and environmentally friendly for determining traces of organophosphorus pesticides in the water samples.     

Development of a method for the determination of vardenafil in human plasma by high performance liquid chromatography with UV detection

A simple high‐performance liquid chromatographic (HPLC) method with photometric detection is described for the determination of vardenafil hydrochloride, a phosphodiesterase V inhibitor, in human plasma. Chromatographic separation of the analyte and internal standard was achieved on an analytical 250 × 4.6 mm i.d. reversed‐phase Kromasil KR 100 C₁₈ (5 µm particle size) column using a mobile phase of acetonitrile–potassium dihydrogen phosphate (30:70 v/v). The run time was less than 15 min. Column eluate was monitored at 230 nm. The linearity over the concentration range of 10–1500 ng/mL for vardenafil was obtained and the limit of quantification (LOQ) was 10 ng/mL. The method has been applied to analysis of the vardenafil concentrations for application in pharmacokinetic studies. Copyright © 2009 John Wiley & Sons, Ltd.     

Simple determination of some antidementia drugs in wastewater and human plasma samples by tandem dispersive liquid–liquid microextraction followed by high‐performance liquid chromatography

In this work, a simple method, namely, tandem dispersive liquid–liquid microextraction, with a high sample clean‐up is applied for the rapid determination of the antidementia drugs rivastigmine and donepezil in wastewater and human plasma samples. This method, which is based on two consecutive dispersive microextractions, is performed in 7 min. In the method, using a fast back‐extraction step, the applicability of the dispersive microextraction methods in complicated matrixes is conveniently improved. This step can be performed in less than 2 min, and very simple tools are required for this purpose. To achieve the best extraction efficiency, optimization of the variables affecting the method was carried out. Under the optimized experimental conditions, the relative standard deviations for the method were in the range of 6.9–8.7%. The calibration curves were obtained in the range of 2–1100 ng/mL with good correlation coefficients, higher than 0.995, and the limits of detection ranged between 0.5 and 1.0 ng/mL.     

Determination of meropenem levels in human serum by high‐performance liquid chromatography with ultraviolet detection

Meropenem is a β ‐lactam broad‐spectrum antibiotic and belongs to the subgroup of carbapenems. It is primarily used in intensive care units for intravenous treatment of severe infections. To avoid bacterial resistance or toxic side effects, the determination of serum meropenem concentration is highly advisable. A simple and fast method for the quantitative determination of meropenem in human serum using high‐performance liquid chromatography with ultraviolet detection (HPLC/UV) was developed and validated. Meropenem was determined by an isocratic HPLC using a tris(hydroxymethyl)aminomethane buffer (pH 8.5; 15% methanol) as a mobile phase and UV detection at 300 nm, with a flow rate of 1.0 mL/min and an analysis time of 10 min. Chromatographic separation was performed on a Kinetex C₁₈ column (5 μm, 150 × 4.6 mm). In order to remove undesired serum components, solid‐phase extraction was used for sample preparation. Since meropenem is not stable in solution, sample and stock solution were stored at −80°C. After preparation, samples were stable at room temperature for at least 6 h. The calibration curve was linear from 3.5 to 200 mg/L with a correlation coefficient r ² of 0.999. The method is accurate with an intra‐ and inter‐assay precision <18.5%.     

Monitoring the oleuropein content of olive leaves and fruits using ultrasound‐ and salt‐assisted liquid–liquid extraction optimized by response surface methodology and high‐performance liquid chromatography

A novel and rapid ultrasound‐ and salt‐assisted liquid–liquid extraction coupled with high‐performance liquid chromatography has been optimized by response surface methodology for the determination of oleuropein from olive leaves. Box–Behnken design was used for optimizing the main parameters including ultrasound time (A), pH (B), salt concentration (C), and volume of miscible organic solvent (D). In this technique, a mixture of plant sample and extraction solvent was subjected to ultrasound waves. After ultrasound‐assisted extraction, phase separation was performed by the addition of salt to the liquid phase. The optimal conditions for the highest extraction yield of oleuropein were ultrasound time, 30 min; volume of organic solvent, 2.5 mL; salt concentration, 25% w/v; and sample pH, 4. Experimental data were fitted with a quadratic model. Analysis of variance results show that BC interaction, A², B², C², and D² are significant model terms. Unlike the conventional extraction methods for plant extracts, no evaporation and reconstitution operations were needed in the proposed technique.     

Determination of Doxepin in human plasma using cloud‐point extraction with high‐performance liquid chromatography and ultraviolet detection

A new straightforward method based on cloud‐point extraction has been developed, optimized, and validated for the determination of doxepin in human plasma by high‐performance liquid chromatography separation and UV detection. The nonionic surfactant Triton X‐114 was chosen as the extraction solvent. Chromatography separation was performed on a μBondapak^R C₁₈ column (4.6 mm id × 300 mm, 3 μm particle size), which was used for isocratic elution at a detection wavelength of 289 nm. Under the optimum conditions, the linear range of doxepin in human plasma was 0.1–0.9 μg/mL. Also, the detection limit, preconcentration factor, and enrichment factor were 0.08 μg/mL, 50, and 49.0, respectively.     

柱前衍生高效液相色谱-荧光检测法测定血浆中同型半胱氨酸

建立了一种柱前衍生高效液相色谱-荧光检测法用于测定血浆中同型半胱氨酸(Hcy)。使用三(2-羧乙基)膦盐酸盐(TCEP)为还原剂,N-(1-芘)马来酰亚胺(NPM)为衍生剂进行样品预处理,Agilent Hypersil C-18柱(250 mm×4.0 mm, 5 μm)进行分离,流动相为15 mmol/L醋酸钠-乙腈-混合酸(300 mL水中含1 mL醋酸和1 mL磷酸)混合溶液,采用梯度洗脱,荧光检测激发波长为330 nm,发射波长为380 nm。Hcy的回收率为(102.08±4.94)%。线性范围为0.500～100 μmol/L,检出限（以信噪比为3计）为0.016 μmol/L。日内与日间相对标准偏差均小于5%。利用该方法对7例高血压患者和7例健康志愿者的血浆进行了测定,结果表明两组间的Hcy含量存在显著的差异(p＜0.05)。本方法简单、快速、灵敏、特异,适用于血浆Hcy的临床定量测定。     

Determination of sedative hypnotics in sewage sludge by pressurized liquid extraction with high‐performance liquid chromatography and tandem mass spectrometry

This paper describes a method for the determination of eight sedative hypnotics (benzodiazepines and barbiturates) in sewage sludge using pressurized liquid extraction and liquid chromatography with tandem mass spectrometry. Pressurized liquid extraction operating conditions were optimized and maximum recoveries were reached using methanol under the following operational conditions: 100ºC, 1500 psi, extraction time of 5 min, one extraction cycle, flush volume of 60% and purge time of 120 s. Pressurized liquid extraction recoveries were higher than 88% for all the compounds except for carbamazepine (55%). The repeatability and reproducibility between days, expressed as relative standard deviation (n = 5), were lower than 6 and 10%, respectively. The detection limits for all compounds were lower than 12.5 μg/kg of dry weight. The method was applied to determine benzodiazepines and barbiturates in sewage sludge from urban sewage treatment plants, and carbamazepine showed the highest concentration (7.9–18.9 μg/kg dry weight).     

Simultaneous determination of seven phthalic acid esters in beverages using ultrasound and vortex‐assisted dispersive liquid–liquid microextraction followed by high‐performance liquid chromatography

A sensitive, rapid, and simple high‐performance liquid chromatography with UV detection method was developed for the simultaneous determination of seven phthalic acid esters (dimethyl phthalate, dipropyl phthalate, di‐n‐butyl phthalate, benzyl butyl phthalate, dicyclohexyl phthalate, di‐(2‐ethylhexyl) phthalate, and di‐n‐octyl phthalate) in several kinds of beverage samples. Ultrasound and vortex‐assisted dispersive liquid–liquid microextraction method was used. The separation was performed using an Intersil ODS‐3 column (C₁₈, 250 × 4.6 mm, 5.0 μm) and a gradient elution with a mobile phase consisting of MeOH/ACN (50:50) and 0.2 M KH₂PO₄ buffer. Analytes were detected by a UV detector at 230 nm. The developed method was validated in terms of linearity, limit of detection, limit of quantification, repeatability, accuracy, and recovery. Calibration equations and correlation coefficients (> 0.99) were calculated by least squares method with weighting factor. The limit of detection and quantification were in the range of 0.019–0.208 and 0.072–0.483 μg/L. The repeatability and intermediate precision were determined in terms of relative standard deviation to be within 0.03–3.93 and 0.02–4.74%, respectively. The accuracy was found to be in the range of –14.55 to 15.57% in terms of relative error. Seventeen different beverage samples in plastic bottles were successfully analyzed, and ten of them were found to be contaminated by different phthalic acid esters.     

Sensitive and rapid high‐performance liquid chromatography tandem mass spectrometry method for estimation of fulvestrant in rabbit plasma

A rapid and sensitive high‐performance liquid chromatography and electrospray tandem mass spectrometry method was developed and validated for estimation of fulvestrant in rabbit plasma using liquid–liquid extraction. The separation and quantification of fulvestrant were achieved by reverse‐phase chromatography on a Sunfire C₁₈ column (50 × 2.1. i.d., 3.5 μm) with isocratic elution at a flow rate of 300 μL/min using norethistrone as an internal standard from 500 μL plasma sample. The method was validated over the concentration range from 0.092 to 16.937 ng/mL with a lower limit of detection of 0.023 ng/mL. The intra‐day and inter‐day accuracy and precision were within 10%. The recovery was 85 and 90% for fulvestrant and norethistrone respectively. The chromatographic run time was only 2.5 min. Copyright © 2009 John Wiley & Sons, Ltd.     

Determination of estrone and 17α‐ethinylestradiol in digested sludge by ultrasonic liquid extraction and high‐performance liquid chromatography with fluorescence detection

Estrone, 17β‐estradiol and 17α‐ethinylestradiol are increasingly recognised as important micropollutants to be monitored in wastewater treatment plants. These estrogens are retained onto sludge due to their high adsorption and since they are largely used in land applications, the monitoring of these chemicals in sludge samples is of great importance. This study describes a method for the determination of estrone and 17α‐ethinylestradiol in fresh sludge samples. After spiking fresh digested sludge with estrone and 17α‐ethinylestradiol and maintaining in contact during 5, 30 and 60 min, the freeze‐dried samples were subjected to ultrasonic liquid extraction, with methanol and acetone, and analysed by high‐performance liquid chromatography with fluorescence detection. The average recoveries obtained for estrone and 17α‐ethinylestradiol using the different contact times were 103 ± 3 and 97 ± 4%, respectively. Fresh sludge samples from one waste water treatment plant located in Portugal were analysed and estrone was detected in primary fresh sludge, anaerobic digested sludge and dehydrated sludge at a concentration in the range of 1–4.8 μg/g. The method here developed does not require any sample clean‐up, being fast and simple, reliable and inexpensive, making possible its application for monitoring the contamination of sludge with these estrogens.     

Determination of carboplatin in canine plasma by high‐performance liquid chromatography

Carboplatin is an antineoplastic drug administered to treat different tumoral conditions in canine oncology. The objective of this study was to validate a high‐performance chromatographic (HPLC) method which could be applied in canine pharmacokinetic studies. Following ultrafiltration using a Centrifree device, standards, quality controls and plasma samples were separated by isocratic reversed‐phase HPLC on an Inertsil ODS‐2 (250 × 4.6 mm i.d.) analytical column and quantified using UV detection at 220 nm. The mobile phase was potassium phosphate (pH 4.5), with a flow‐rate of 1.0 mL/min. The procedure produced a linear curve (r² > 0.999) over the concentration range 1–200 μg/mL. The lower limit of quantification was 1 μg/mL. The intra‐assay and inter‐assay precision was ～90%. The overall recovery was ～90%. The method was illustrated with a preliminary pharmacokinetic analysis on nine dogs treated with carboplatin at our hospital. Carboplatin disposition followed a monocompartmental structure in dogs and was characterized by a short half‐life (50 min). Copyright © 2009 John Wiley & Sons, Ltd.     

Determination of tryptophan in bee pollen and royal jelly by high‐performance liquid chromatography with fluorescence detection

A method for tryptophan analysis in bee pollen and royal jelly was developed using HPLC with fluorescence detection. To determine the free tryptophan in bee pollen and royal jelly, ultrasonic extraction was performed using water (pH 6.3)–acetonitrile (10:1, v/v) as extraction solvent. While determining the total tryptophan in these bee products, the method involves alkaline hydrolysis of the proteins with 4 mol/L sodium hydroxide at 110°C for 20 h under anaerobic conditions. The operating conditions for the HPLC analysis were: Symmetry C₁₈ column (4.6 × 250 mm, 5 µm), 0.1% trifluoroacetic acid–methanol (75:25, v/v) as the mobile phase at a flow rate of 1.0 mL/min at 30°C. The fluorescence detector was operated at an excitation wavelength of 280 nm and an emission wavelength of 340 nm. A linear response (r² > 0.9998) was obtained in the range 0.0625–5.0 µg/mL. The method was successfully applied to the determination of the free and total tryptophan contents in bee pollens, which were 0.069 ± 0.003 and 2.693 ± 0.476 mg/g, respectively, while only the total tryptophan was detected in royal jelly, with a content of 1.743 ± 0.066 mg/g. Copyright © 2009 John Wiley & Sons, Ltd.     

Fluorimetric determination of amphetamine in urine by flow injection with on-line liquid–liquid extraction

Determination of amphetamine in urine was performed by batch and flow injection methodologies. The suitable experimental conditions for fluorimetric measurements were established. The liquid–liquid extraction was carried out at pH 13 using diethyl ether as extracting reagent. The measurement conditions were 260 nm and 277 nm for excitation and emission wavelengths, respectively. The method requires standard addition calibration and Youden blank correction. The influence of the main metabolites of amphetamine and metamphetamine were studied. The accuracy and precision of the proposed method was tested and the method is adapted to the flow injection procedure with on-line extraction.