Determination of amoxycillin in human plasma by direct injection and coupled-column high-performance liquid chromatography

Angiotensin converting enzyme immobilized on magnetic beads as a tool for ligand fishing

Angiotensin converting enzyme (ACE) presents an important role in blood pressure regulation, since that converts angiotensin I to the vasoconstrictor angiotensin II. Some commercially available ACE inhibitors are captopril, lisinopril and enalapril; due to their side effects, naturally occurring inhibitors have been prospected. In order to endorse this research field we have developed a new tool for ACE ligand screening. To this end, ACE was extracted from bovine lung, purified and chemically immobilized in modified ferrite magnetic beads (ACE-MBs). The ACE-MBs have shown a Michaelian kinetic behavior towards hippuryl-histidyl-leucine. Moreover, as proof of concept, the ACE-MBs was inhibited by lisinopril with a half maximal inhibitory concentration (IC₅₀) of 10nM. At the fishing assay, ACE-MBs were able not only to fish out the reference inhibitor, but also one peptide from a pool of tryptic digested BSA. In conclusion, ACE-MBs emerge as new straightforward tool for ACE kinetics determination, inhibition and binder screening.

Direct bioanalytical sample injection with 2D LC–MS

New analytical platforms have been developed in response to the need for attaining increased peak capacity for multicomponent complex analysis with higher sensitivity and characterization of the analytes, and high-throughput capabilities. This review outlines the fundamental principles of target and comprehensive 2D LC method development and encompasses applications of LC–LC and LC × LC coupled to MS in bioanalysis using a variety of online analytical procedures. It also provides a rationale for the usage of the most employed mass analyzers and ionization sources on these platforms.

Simultaneous quantification of sulfamethoxazole and trimethoprim in whole egg samples by column-switching high-performance liquid chromatography using restricted access media column for on-line sample clean-up

This work reports the application of restricted access media (RAM) column, in a multidimensional configuration, for simultaneous analysis of sulfamethoxazole (SMX) and trimethoprim (TMP) in whole eggs with ultraviolet detection. The proteins were partially precipitated by adding 0.5 mL of acetonitrile into 1.0 mL of blended egg followed by centrifugation. The supernatant was injected (250 microL) directly into the multidimensional system. At the first dimension, a restricted access medium (RAM) bovine serum albumin (BSA) octadecyl column (100 mm x 46 mm I.D., Luna silica, 10 microm particle size and 100 A pore size), was used for extraction and concentration of the analytes and at second dimension, an octadecyl column (150 mm x 46 mm I.D., Luna silica, 10 microm particle size and 100 A pore size), for analysis. The developed method showed good selectivity, accuracy and precision for quantification of these different compounds in eggs, and the limits of quantification were 80 ng/mL, for both compounds. The validated method is reliable and sensitive for monitoring residues in whole eggs samples and thus, to determine withdraw period for laying hens using veterinary medicine having SMX-TMP combination.

Classification of commercial Catuaba samples by NMR, HPLC and chemometrics

For over a century, Catuaba has been used in Brazilian folk medicine as an aphrodisiac even though the identity of the plant material employed is often uncertain. The species recommended by the Brazilian Pharmacopeia is Anemopaegma arvense (Bignoniaceae), but many other plants, regionally known as Catuaba, are commercialised. Frequently, the quality control of such a complex system is based on chemical markers that do not supply a general idea of the system. With the advent of the metabolomics approach, a global analysis of samples becomes possible. It appears that (1)H-NMR is the most useful method for such application, since it can be used as a wide-spectrum chemical analysis technique. Unfortunately, the generated spectra is complex so a possible approach is to look at the metabolite profile as a whole using multivariate methods, for example, by application of principal component analysis (PCA). In the present paper, we describe for the first time a proton high-resolution magic angle spinning nuclear magnetic resonance ((1)H-HR-MAS NMR) method coupled with PCA for the metabolomic analysis of some commercial Catuaba samples, which provided a reduction in the time required for such analysis. A comparative study of HPLC, HR-MAS and liquid-NMR techniques is also reported.

Determination of interferon-gamma in Chinese hamster ovary cell culture supernatant by coupled-column liquid chromatography

A robust tandem HPLC method coupling size-exclusion (Shodex Asahipak GS-320HQ) and reversed phase (Vydac 218TP54) columns with ultraviolet detection was developed for quantitative determination of interferon-gamma (IFN-gamma) in Chinese hamster ovary cell culture supernatant. The 2D-HPLC system was linked up by a 6-port 2-position low hold-up volume switch valve. Compared to a commercial ELISA kit for IFN-gamma, the coupled column LC approach was able to detect and quantify soluble IFN-gamma, regardless of the glycoprotein's molecular/conformational variability and sample background. Each LC-LC analysis took 90 minutes inclusive of column regeneration. The relative standard deviation of measurements (n = 5) was less than 3%. The limit of detection (LOD) was determined to be 0.35 microg IFN-gamma.

Rapid method for the quantification of amoxicillin and its major metabolites in pig tissues by liquid chromatography-tandem mass spectrometry with emphasis on stability issues

A fast method for the quantitative determination of amoxicillin (AMO), amoxicilloic acid (AMA) and amoxicillin diketopiperazine-2',5'-dione (DIKETO) in pig edible tissues (kidney, liver, fat and muscle) with liquid chromatography-tandem mass spectrometry (LC-ESI-MS/MS) is presented. The method uses a simple liquid-liquid extraction of the tissue matrix with a 10 mM potassium dihydrogen phosphate buffer (pH 4.5) as extraction solvent. After deproteinisation by ultrafiltration, the tissue extract was directly injected onto the LC column. Chromatographic separation of the components was performed on a PLRP-S polymeric column using 0.1% of formic acid in water and acetonitrile. The mass spectrometer was operated in the positive electrospray MS/MS mode. The method was fully validated according to EU requirements (linearity, precision, trueness, quantification limit, detection limit and specificity). The stability of the components was evaluated over the pH range from 1.2 to 8.0. Biological samples of pigs medicated with AMO and AMO/clavulanic acid were analyzed using the developed method.

Simultaneous determination of amoxicillin and clavulanic acid in human plasma by isocratic reversed-phase HPLC using UV detection

A simple, rapid and sensitive isocratic reversed phase HPLC method with UV detection using internal standard has been developed and validated for simultaneous determination of amoxicillin and clavulanic acid in human plasma. The assay enables the measurement of amoxicillin and clavulanic acid for therapeutic drug monitoring with a minimum quantification limit of 15 and 30 ng ml(-1), respectively. The method involves simple, one-step extraction procedure and analytical recovery was complete. The separation was carried out in reversed-phase conditions using a Chromolith Performance (RP-18e, 100 mm x 4.6mm) column with an isocratic mobile phase consisting of 0.02 M disodium hydrogen phosphate buffer-methanol (96:4, v/v) adjusted to pH 3.0. The wavelength was set at 228 nm. The coefficients of variation for inter-day and intra-day assay were found to be less than 9.0%.

Development of a validated HPLC method for the determination of four penicillin antibiotics in pharmaceuticals and human biological fluids

A quantitative method for the determination of four penicillin antibiotics, amoxicillin (AMO), oxacillin (OXA), cloxacillin (CLO), and dicloxacillin (DICLO), has been developed. Separation was achieved on an Inertsil ODS-3 (250 x 4 mm, 5 microm) column after selective extraction of penicillin drugs from biological matrices by means of SPE. Gradient elution with a mobile phase consisting of 0.1% TFA (pH 1) and ACN, and PDA detection with monitoring at 240 nm was applied. Salicylic acid (5 ng/microL) was used as the internal standard. RP-8 Adsorbex Merck cartridges provided high absolute recoveries (98-101%). The developed method was fully validated in terms of selectivity, linearity, accuracy, precision, stability, and sensitivity. Repeatability (n = 8) and between-day precision (n = 8) revealed RSD <10%. Recoveries from biological samples ranged from 91 to 103%. The detection limits were estimated as 3.3 ng for AMO, OXA, and CLO, and 6.6 for DICLO in blood plasma. LOD in whole blood and urine was 6.6 ng. Injection volume was 20 microL. The method was applied to commercially available AMO containing pharmaceuticals and spiked biological matrices. The method was also applied to biological samples after AMO oral administration, where the drug was successfully identified and quantified.

Chromatographic analysis of penicillins in pharmaceutical formulations and biological fluids

Natural penicillin (benzylpenicillin) is the oldest antibiotic observed by Alexander Fleming in 1928. To broaden its spectrum of activity, natural penicillin was modified, giving rise to a group of antibiotics under the name 'penicillins'. Although an increasing number of bacteria appear to be resistant to them, penicillins are used to treat a variety of bacterial infections including Gram-positive, Gram-negative aerobic and anaerobic bacteria. Consequently, they are widely used in human and veterinary medicine to prevent and treat diseases. This review covers the analytical methodologies, mainly chromatographic, employed to the penicillins determination in pharmaceutical formulations, biological fluids and in production-scale fermentations reported in the literature. Results of published assays are comparatively presented focusing on sample preparation regarding isolation and purification, chromatographic conditions and method validation. Information on chemical structure, spectrum of activity and action mechanism of common penicillins has also been given.

Simultaneous determination of amoxicillin and ranitidine in rat plasma by high-performance liquid chromatography

A high-performance liquid chromatography method using ultraviolet detection at 230 nm for the simultaneous determination of amoxicillin and ranitidine in rat plasma has been validated. Plasma samples after pretreatment with acetonitrile to effect deproteinization were dried under N2 and reconstituted with water. The standard calibration curves for amoxicillin and ranitidine were linear (r2=0.9999) over the concentration range of 0.2-20 microg ml-1 and 0.03-6 microg ml-1 in rat plasma, respectively. The intra- and inter-day assay variability range for amoxicillin was 2.4-8.5% and 3.2-11.7%, and for ranitidine was 1.7-9.0% and 4.5-10.1%, respectively. This method has been successfully applied to a pharmacokinetic study after oral coadministration of amoxicillin and ranitidine to rats.

Development of restricted-access media supports and their application to the direct analysis of biological fluid samples via high-performance liquid chromatography

A quick overview of published methods for analyzing compounds in complex biological samples reveals that the most difficult step is the clean-up or extraction of a required compound from the matrix. The strategy required to analyze exogenous compounds in biological fluids depends greatly upon the nature of the compound and upon the biomatrix. Coupled-column separation using restricted-access media as the first dimension in order to exclude macromolecules and retain micromolecules has been successfully used for a number of biological fluids. This paper presents the history of the development of restricted-access media supports and of their application to the direct injection of biological fluid samples in high-performance liquid chromatography.

Automated microcolumn-switching system for drug analysis by direct injection of human plasma

This study presents the application of a system that joins the known advantages of capillary liquid chromatography (e.g., higher concentration of the analytes and lower consumption of mobile phase) with those of column-switching using restricted access material (RAM) (sample clean up and extraction) to the analysis of fluoxetine in plasma samples. Automatically, the system loads the biological sample, while a RAM-BSA-C18 column (50 mm x 520 microm) excludes the macromolecules and focuses the analytes; afterwards, a second mobile phase elutes the analytes, in backflush mode, and provides the separation in a C18 analytical column (100 mm x 520 microm). We optimized the procedure for a total analysis time of 25 min. Using this approach the calibration curve shows r=0.998 with a linearity range from 20 to 500 ng ml(-1). Precision, calculated as relative standard deviation (RSD), was<20%. The developed miniaturized system showed to be adequate and attractive, demonstrating a large potential for sample preparation.

Quantitative determination of 20-hydroxyecdysone in methanolic extract of twigs from Vitex polygama Cham

20-Hydroxyecdysone (20E) is effective in stimulating protein synthesis, therefore, it has been largely used as anabolic agent in several commercial formulas. Phytochemical study of methanolic extract of twigs from Vitex polygama, used in traditional Brazilian medicine as emenagogue, yielded a large quantity of 20E. This finding led us to developing and validating a simple and reliable method to determine 20E in the surveyed extract. Chromatographic separation of 20E was achieved on a phenyl-hexyl-based column using reversed elution mode. Extract was cleaned-up by solid phase extraction employing C(18) cartridge, and an absolute recovery of 97% was acquired. External standard and standard addition calibration graphs were obtained and good linearity was accomplished (r>0.999 for both curves). The limit of quantification and detection were determined. The results for accuracy fell within the -5 to +7% range.

A sensitive assay of amoxicillin in mouse serum and broncho-alveolar lavage fluid by liquid-liquid extraction and reversed-phase HPLC

A sensitive and simple high-performance liquid chromatography (HPLC) method was developed and validated for the analysis of amoxicillin in mouse serum and broncho-alveolar lavage (BAL) fluid. One hundred microlitres of sample were needed for the assay. Sample processing was carried out with liquid-liquid extraction. Cefadroxil was used as an internal standard. The chromatographic separation was achieved on a C18 reversed-phase column with a mobile phase consisting of phosphate buffer, 1-octanesulphonic acid sodium salt and acetonitrile. The detection was conducted at 210 nm. The ranges of the standard curves were 0.2-20 and 0.05-5 microg/ml for serum and BAL samples, respectively. The recoveries of amoxicillin from serum and normal saline were 87 and 88%, respectively. The coefficients of variation were 1.78-6.13% for intra-day and 0.82-6.42% for inter-day analyses. The accuracy was within 100+/-6%. This method was successfully applied to analyze amoxicillin in mouse serum and BAL samples from a pharmacokinetic study.

Determination of chlorpyrifos and its metabolites in rat brain tissue using coupled-column liquid chromatography/electrospray ionization tandem mass spectrometry

A method has been developed to quantify chlorpyrifos (O,O-diethyl-O-[3,5,6,-trichloro-2-pyridyl] phosphorothionate) and its metabolites chlorpyrifos-oxon (O,O-diethyl-O-[3,5,6,trichloro-2-pyridinyl] phosphate) and TCP (3,5,6,-trichloro-2-pyridinol) in rat brain tissue by coupled-column liquid chromatography/electrospray ionization tandem mass spectrometry (LC/LC/ESI-MS/MS). Rat brains were homogenized and treated by protein precipitation using ice-cold acetonitrile. The supernatant was directly injected onto the coupled-column system. Sample clean-up was achieved on a Zorbax Extend-C(18) column (2.1 x 50 mm, 5 microm) using a mobile phase of acetonitrile/water with 0.0025% formic acid (40:60, v/v). The compounds were separated isocratically on a Zorbax Eclipse XDB C(8) column (2.0 x 150 mm, 5 microm) using a mobile phase of acetonitrile/water with 0.0025% formic acid (75:25, v/v). Chlorpyrifos and chlorpyrifos-oxon were detected in positive ion mode using multiple reaction monitoring (MRM). TCP was detected in negative ion mode using precursor-to-precursor transition monitoring. The method was validated and the specificity, linearity, limit of quantitation (LOQ), precision, accuracy, stability, and recoveries were determined. Calibration curves for all three analytes yielded correlation coefficients of 0.993 or greater. The LOQs were 25.3 ng/g for chlorpyrifos and 6.3 ng/g for chlorpyrifos-oxon and TCP. All precision relative standard deviations (RSDs) were less than 16% for the LOQ and less than 11% for the other QC samples. This method was successfully applied to six rats that were injected subcutaneously with chlorpyrifos.

A validated higher-performance liquid chromatography method for quantification of cinchonain Ib in bark and phytopharmaceuticals of Trichilia catigua used as Catuaba

The hydroalcoholic extract, prepared from authentic chopped barks of Trichilia catigua, was evaluated by high-performance liquid chromatography using a diode array detector (200-400 mn). The crude extract was purified by rotation locular counter-current chromatography and the chloroform fraction obtained was clean-up by solid-phase extraction. With the aim of getting preliminary structure information on-line, the methanol fraction thus obtained was analyzed by gradient elution using the diode array detector coupled to a mass spectrometer. The presence of flavalignan in this extract was inferred by the chromatographic band, in the total ion current trace, that had an [M-H](-) = 451. With this information, cinchonain Ib was isolated as a pure compound from the crude hydroalcoholic extract using a solid-phase extraction procedure for the sample clean-up followed by a semi-preparative separation using the reverse mode of elution. The isolated compound, after complete characterization, was used as an external standard for the development and validation of a method for the analysis of this compound in herbal medicines using the ultraviolet as the detector. The validated method has been successfully applied for quantification of cinchonain Ib in commercialized herbal medicines sold as Catuaba in Brazil and also in standard chopped barks of T. catigua.

Development and Validation of a Solid-Phase Extraction-Liquid Chromatographic Method for Determination of Amoxicillin in Plasma

A bioanalytic method for the determination of amoxicillin in plasma by hydrophilic interaction solid-phase extraction and liquid chromatography has been developed and validated. Plasma was precipitated with acetonitrile before samples were loaded onto a zwitterionic hydrophilic interaction liquid chromatography (ZIC-HILIC) solid-phase extraction column. Amoxicillin was analyzed by liquid chromatography on an Aquasil (150 x 4.6 mm) LC column with mobile-phase acetonitrile: phosphate buffer (pH 2.5; 0.1 mol/L) (7:93, v/v) and UV detection at 230 nm. A regression model using 1/concentration weighting was found the most appropriate for quantification. The intraassay precision for plasma was 3.3% at 15.0 microg/mL and 10.9% at 0.200 microg/mL. The interassay precision for plasma was 1.8% at 15.0 microg/mL and 7.5% at 0.200 microg/mL. The total-assay precision for plasma over 4 days using a total of 20 replicates was 13.2%, 5.5%, and 3.8% at 0.200 microg/mL, 3.00 microg/mL, and 15.0 microg/mL, respectively. The lower limit of quantification and the limit of detection were 0.050 microg/mL and 0.025 microg/mL, respectively, for 100 microL plasma. Long-term storage stability studies of amoxicillin in plasma indicate that a temperature of -80 degrees C is necessary to prevent degradation of amoxicillin.

Supercritical fluid chromatography tandem-column method development in pharmaceutical sciences for a mixture of four stereoisomers

A tandem-column method using Chiralpak AD-H and Chiralcel OD-H columns was achieved for baseline separation of a mixture of chiral pharmaceutical compounds (i.e., four stereoisomers) via supercritical fluid chromatography (SFC) with a mobile phase consisting of 90% liquid carbon dioxide and 10% ethanol:isopropanol (50:50 v/v). On the contrary, this mixture (mixture A) could not be baseline separated by SFC conditions explored with individual Chiralpak AD-H and Chiralcel OD-H columns. The effects of various mobile phases on elution order, capacity factor, selectivity, and resolution were determined with mixture A on the individual aforementioned columns to develop the tandem-column method.

Flow injection-chemiluminescence determination of amoxycillin using potassium permanganate and formaldehyde system

It was found that amoxycillin can react with potassium permanganate in an acidic medium to produce chemiluminescence, which is greatly enhanced by formaldehyde. The optimum conditions for this chemiluminescent reaction were studied in detail using a flow-injection system. The experimental results indicate that, under optimum conditions, the chemiluminescence intensity is linearly related to the concentration of amoxycillin in the range 5.48 x 10(-8)-2.74 x 10(-6) mol/L, with a detection limit (3sigma) of 4.1 x 10(-8) mol/L. The relative standard deviation was 1.0% at 1.1 x 10(-6) mol/L amoxycillin (n = 11 measurements). This method has the advantages of high sensitivity, fast response and ease of operation. The method was successfully applied to the determination of amoxycillin in raw medicines and capsules.

A liquid chromatographic method for simultaneous determination of amoxicillin sodium and sulbactam sodium in a combination formulation

An isocratic liquid chromatographic method with UV detection at 210nm is described for simultaneous determination of amoxicillin sodium and sulbactam sodium in a new combination formulation. Chromatographic separation of the two drugs was achieved on a Hypersil C(18) column using a mobile phase consisting of a binary mixture of methanol and 0.01mol/l sodium acetate (5:95, v/v). The commonly used paired-ion aqueous mobile phase for the determination of penicillins was avoided in this study. The developed LC method offers symmetric peak shape, good resolution and reasonable retention time for both drugs. Linearity, accuracy and precision were found to be acceptable over the concentration ranges of 155.3-1553.0microg/ml for amoxicillin sodium and 45.0-450.0microg/ml for sulbactam sodium. The proposed LC method can be used for the quality control of formulated products containing these two drugs.

Enantiomeric determination of the plasma levels of omeprazole by direct plasma injection using high-performance liquid chromatography with achiral-chiral column-switching

A direct injection high-performance liquid chromatographic (HPLC) method, with column-switching, for the determination of omeprazole enantiomers in human plasma is described. A restricted access media (RAM) of bovine serum albumin (BSA) octyl column has been used in the first dimension for separation of the analyte from the biological matrix. The omeprazole enantiomers were eluted from the RAM column onto an amylose tris(3,5-dimethylphenylcarbamate) chiral column by the use of a column-switching valve and the enantioseparation was performed using acetonitrile-water (60:40 v/v) as eluent. The analytes were detected by their UV absorbance at 302 nm. The validated method was applied to the analysis of the plasma samples obtained from 10 Brazilian volunteers who received a 40 mg oral dose of racemic omeprazole and was able to quantify the enantiomers of omeprazole in the clinical samples analyzed. The assay was able to determine the cytochrome P450 2C19 phenotype of the subjects participating in this study.

Multidimensional separations in the pharmaceutical arena

The introduction of novel, powerful and rapid multidimensional separation and characterization methods has produced revolutionary global changes at the genome, proteome and metabolome level, bringing about a radical transition in our views of living systems, at the molecular level. The age of proteomics and metabolomics demands high-resolution multidimensional separation techniques. Multidimensional gas and liquid chromatography techniques, in addition to capillary and microchip electrophoresis methods, offer increased resolution and sensitivity, while also affording adequate throughput and reproducibility to meet the demands of the modern pharmaceutical industry. Coupled with MS, these techniques provide not only separation but also reliable identification of the sample components. The resolving power of these methods has proved to be superior over individual one-dimensional approaches, enabling the comprehensive separation of complex biological mixtures, with excellent resolution and reproducibility. High capacity computer systems that are capable of rigorous qualitative and quantitative analysis of the separation profiles allow the establishment and mining of large databases. Examples of various modern multidimensional separation techniques, and their integration with MS, are reviewed, here, with respect to pharmaceutical analysis.

Using analytical multidimensional isocratic HPLC methods of separation to isolate active constituents in natural products

Multidimensional reversed-phase HPLC was employed to isolate the active constituents from a crude extract of Clerodendrum floribundum R. Br. These active constituents were known to have bioactivity against the enzyme xanthine oxidase and potentially could be employed in the treatment of gout. Using a multidimensional separation approach, rapid isolation of the active constituents was achieved from a complex sample matrix. As each separation dimension was isocratic, no equilibration time was required and consequently the technique shows promise in the scale up to preparative levels where high throughput is important.