Biomedical subjects

R Herráez-Hernández

Publications and source records attributed to R Herráez-Hernández.

At least 19 recordsLinked to original sources

PubMed2006

In-tube solid-phase microextraction-capillary liquid chromatography as a solution for the screening analysis of organophosphorus pesticides in untreated environmental water samples.

This paper describes a method for the selective screening of organophosphorus pesticides in water. In-tube solid-phase microextraction (SPME) in an open capillary column coupled to capillary liquid chromatography (LC) with UV detection has been used to effect preconcentration, separation and detection of the analytes in the same assembly. For in-tube SPME two capillary columns of the same length and different internal diameters and coating thicknesses have been tested and compared, a 30 cm x 0.25 mm I.D., 0.25 micro m thickness coating column, and a 30 cm x 0.1 mm I.D., 0.1 micro m of coating thickness column. In both columns the coating was 95% dimethylpolysiloxane (PDMS)-5% diphenylpolysiloxane. The proposed methodology provided limits of detections (LODs) for the tested organophosphorus pesticides in the 0.1-10 micro g/L range, whereas the direct injection of the samples onto the capillary LC system provided LODs in the 50-1000 micro g/L range. The sensitivity of the proposed in-tube SPME-capillary LC method is adequate to monitorize the analyte levels in drinking water. Several triazines, polycyclic aromatic hydrocarbons (PAHs), nonylphenol, organochloride pesticides or polybrominated diphenyl ethers (PBDEs) have been evaluated as possible interferents. The reliability of the described method is demonstrated by analysing different real water samples.

Chromatography, Liquid↗

PubMed2006

On-fibre solid-phase microextraction coupled to conventional liquid chromatography versus in-tube solid-phase microextraction coupled to capillary liquid chromatography for the screening analysis of triazines in water samples.

This paper compares the advantages and disadvantages of two different configurations for the extraction of triazines from water samples: (1) on-fibre solid-phase microextraction (SPME) coupled to conventional liquid chromatography (LC); and (2) in-tube SPME coupled to capillary LC. In-tube SPME has been effected either with a packed column or with an open capillary column. A critical evaluation of the main parameters affecting the performance of each method has been carried out in order to select the most suitable approach according to the requirements of the analysis. In the on-fibre SPME configuration the fibre coating was polydimethylsiloxane (PDMS)-divinylbenzene (DVB). The limits of detection (LODs) obtained with this approach under the optimized extraction and desorption conditions were between 25 and 125 microg/L. The in-tube SPME approach with a C18 packed column (35 mm x 0.5 mm I.D., 5 microm particle size) connected to a switching micro-valve provided the best sensitivity; under such configuration the LODs were between 0.025 and 0.5 microg/L. The in-tube SPME approach with an open capillary column coated with PDMS (30 cm x 0.25 mm I.D., 0.25 microm of thickness coating) connected to the injection valve provided LODs between 0.1 and 0.5 microg/L. In all configurations UV detection at 230 nm was used. Atrazine, simazine, propazine, ametryn, prometryn and terbutryn were selected as model compounds.

Chromatography, Liquid↗

PubMed2006

An evaluation of solid phase microextraction for aliphatic amines using derivatization with 9-fluorenylmethyl chloroformate and liquid chromatography.

The reliability of SPME combined with a chemical reaction for the analysis of short-chain aliphatic amines by liquid chromatography has been investigated. Different options to couple SPME and derivatization have been tested and compared: (i) derivatization of the analytes in solution followed by the extraction of the derivatives, (ii) extraction of the analytes and subsequent derivatization by immersing the SPME fibre onto a solution of the reagent, and (iii) extraction/derivatization of the analytes using fibres previously coated with the reagent. Methylamine (MA), dimethylamine (DMA) and trimethylamine (TMA) have been selected as a model of primary, secondary and tertiary amines, respectively. The analytes have been derivatized with the fluorogenic reagent 9-fluorenylmethyl chloroformate (FMOC), and the fibre coating was Carbowax-templated resin (CW-TR). The employment of fibres coated with FMOC to extract and derivatize the analytes was the best option, as compared with the other approaches tested the sensitivity was considerably improved. On the basis of these studies, a new procedure for the determination of MA, DMA and TMA in water is presented. To demonstrate the utility of the proposed conditions data on linearity, accuracy, repeatability and sensitivity are given. Results of the determination of the amines in tap, river and waste water are also presented.

Amines↗

PubMed2005

Application of solid-phase microextraction combined with derivatization to the enantiomeric determination of amphetamines.

The utility of combining chiral derivatization and solid-phase microextraction (SPME) for the enantiomeric analysis of primary amphetamines by liquid chromatography has been investigated. Different derivatization/extraction strategies have been evaluated and compared using the chiral reagent o-phthaldialdehyde (OPA)-N-acetyl-l-cysteine (NAC) and fibres with a Carbowax-templated resin coating. Amphetamine, norephedrine and 3,4-methylenedioxyamphetamine (MDA) were used as model compounds. On the basis of the results obtained, a new method is presented based on the derivatization of the analytes in solution followed by SPME of the OPA-NAC derivatives formed. The proposed conditions have been applied to determine the compounds of interest at low ppm levels (<or=10 microg/ml) in aqueous and urine samples. Data on the linearity, reproducibility, sensitivity and selectivity are given. The utility of the described procedure for the quantification of amphetamine, norephedrine and MDA enantiomers in different kind of samples is also discussed.

Amphetamines↗

PubMed2004

A method for the determination of dimethylamine in air by collection on solid support sorbent with subsequent derivatization and spectrophotometric analysis.

A new method for dimethylamine determination in air is reported. The proposed assay is based on the employment of C18-packed solid phase extraction cartridges for sampling. The retained amine is then derivatized inside the cartridges with the reagent 1,2-naphthoquinone-4-sulfonate. By observing the coloured area of the cartridge, a semiquantitative estimation of the amine can be made. It was also possible to distinguish between primary and secondary amines by visual inspection. Quantitative tests entailed desorption from the cartridges of the derivatives formed, and measurement of the absorbance of the collected extracts. The selected conditions were applied to quantify dimethylamine up to 100 microg, the quantification and detection limits being 6.7 and 2 microg, respectively. Satisfactory linearity and precision were obtained. Possible interferences by ammonia, primary amines and diethylamine were tested. The applicability of the procedure was demonstrated by estimating the concentration of dimethylamine in generated and real air samples. The procedure was useful for short-term exposure limit and threshold limit value estimations.

Air↗

PubMed2004

Application of solid-phase microextraction combined with derivatization to the determination of amphetamines by liquid chromatography.

This work evaluates the utility of solid-phase microextraction (SPME) in the analysis of amphetamines by liquid chromatography (LC) after chemical derivatization of the analytes. Two approaches have been tested and compared, SPME followed by on-fiber derivatization of the extracted amphetamines, and solution derivatization followed by SPME of the derivatives formed. Both methods have been applied to measure amphetamine (AP), methamphetamine (MA), and 3,4-methylenedioxymethamphetamine (MDMA), using the fluorogenic reagent 9-fluorenylmethyl chloroformate (FMOC) and carbowax-templated resin (CW-TR)-coated fibers. Data on the application of the proposed methods for the analysis of different kind of samples are presented. When analyzing aqueous solutions of the analytes, both approaches gave similar analytical performance, but the sensitivity attainable with the solution derivatization/SPME method was better. The efficiencies observed when processing spiked urine samples by the SPME/on-fiber derivatization approach were very low. This was because the extraction of matrix components into the fiber coating prevented the extraction of the reagent. In contrast, the efficiencies obtained for spiked urine samples by the solution derivatization/SPME approach were similar to those obtained for aqueous samples. Therefore, the later method would be the method of choice for the quantification of amphetamines in urine.

Amphetamines↗

PubMed2002

Strategies for the enantiomeric determination of amphetamine and related compounds by liquid chromatography.

This paper summarizes recent research on the stereospecific analysis of amphetamine, its analogs and metabolites, by liquid chromatography. The different methods proposed have been evaluated and compared in terms of resolution power, time of analysis, sensitivity, or potential for automation. Chiral derivatization, followed by separation of the diastereomers formed in achiral chromatographic systems, is still the method preferred for the analysis of amphetamines at trace levels, as derivatization also improves analyte detectability. This is the method of choice for the enantiomeric analysis of amphetamines at the low concentrations typically encountered in biological samples. In recent years, special attention has been devoted to the development of alternatives for the automation of the analytical process by integrating the derivatization step into the chromatographic scheme. A promising alternative is the employment of beta-cyclodextrins as chiral selectors, both immobilized on the stationary phase and added to the mobile phase. However, with a few exceptions, beta-cyclodextrins perform better for non-derivatized amphetamines. Therefore, the utility of these selectors in the analysis of biological samples is limited. The reliability of less-used chiral stationary phases (Pirkle type, cellulose based or protein based), as well as methods based on the mathematical treatment of the chromatographic signal, are also discussed.

Amphetamines↗

PubMed2001

Analysis of enantiomers giving partially overlapped peaks by using different treatments of the chromatographic ultraviolet signals: quantification of pseudoephedrine enantiomers.

Different strategies for the quantification of partially coeluting optical isomers have been investigated. The methods tested are based on the use of different features as the analytical UV signals: peak heights, perpendicular drop areas, first and second derivatives of the chromatograms, peak areas obtained by deconvolution of the overlapped peaks with data fitting optimization, and a multivariate model (principal component regression, PCR). The amphetamine-derivative drug pseudoephedrine was selected as a model compound. For chromatography, LiChrospher 100 RP18 and a mobile-phase consisting of methanol and a solution of carboxymethyl-beta-cyclodextrin (the chiral selector) were used. The UV detector was set at 215 nm. The accuracy obtained with the tested methods at different degrees of overlapping and at different concentration ratios between enantiomers was evaluated. The results of this study demonstrated that the best option for quantification of partially overlapped UV peaks of enantiomers and to obtain the enatiomeric excess is the use of a PCR model using peak heights, perpendicular drop peak areas and deconvoluted peak areas as the original variables. The predictive ability of the proposed calibration model is of about 2-8 times better (depending on the overlapping degree) than that achieved with the other models tested.

Ephedrine↗

PubMed2001

Sensitive determination of methylenedioxylated amphetamines by liquid chromatography.

Different strategies for the liquid chromatographic determination of methylenedioxylated amphetamines were evaluated: separation and detection of underivatized analytes by (i) UV or (ii) fluorescence, (iii) derivatization with 3,5-dinitrobenzoyl chloride followed by separation and UV detection of the derivatives formed and (iv) derivatization with 9-fluorenylmethyl chloroformate (FMOC) and subsequent separation and fluorimetric detection of the derivatives. The compounds tested were 3,4-methylenedioxyamphetamine (MDA), 3,4-methylenedioxymethamphetamine (MDMA) and 3,4-methylenedioxyethylamphetamine (MDE). On the basis of these studies, a new procedure for the chromatographic determination of MDA, MDMA and MDE is proposed, based on derivatization with FMOC. The described procedure allows the quantification of the tested compounds with adequate linearity, reproducibility and accuracy in the concentration interval 0.5-20.0 micrograms mL-1. The limits of detection were 0.01 microgram mL-1 for MDA and 0.025 microgram mL-1 for MDMA and MDE. The utility of the described assay was tested by determining methylenedioxylated amphetamines in plasma and urine.

3,4-Methylenedioxyamphetamine↗

PubMed2001

Determination of aliphatic amines in water by liquid chromatography using solid-phase extraction cartridges for preconcentration and derivatization.

Bond Elut C18 solid-phase extraction cartridges were used for preconcentration and pre-column derivatization with 3,5-dinitrobenzoyl chloride (DNB) of aliphatic amines in water. Conditions for analyte preconcentration and derivatization (including the volume of sample, concentration of reagent, time of reaction and pH) were investigated, using ethylamine, isopropylamine and dimethylamine as model compounds. On the basis of these studies, a rapid and sensitive method for the determination of aliphatic amines in water is presented. The analytes are retained and purified on the cartridges and then derivatized and desorbed by drawing in succession the DNB solution and acetonitrile. The collected extracts are subsequently chromatographed in a Hypersil ODS C18 column using acetonitrile-water for elution. The DNB derivatives are monitored at 230 nm. The method provides satisfactory reproducibility and linearity within the 0.050-1.0 mg l(-1) concentration interval, the limits of detection being 2-5 microg l(-1). Analyte recoveries were in the 70-102% range, whereas the conversion yields compared with those observed for the solution derivatization were in the 79-107% range. The total analysis time (sample treatment plus chromatography) was about 15 min. The method was applied to the determination of ethylamine, isopropylamine and dimethylamine in tap and river waters.

Amines↗

PubMed2000

H-point curve isolation method for coupled liquid chromatography and UV-visible spectrophotometry.

The H-point curve isolation method (HPCIM) for the detection of unknown interferences in chromatography is proposed. The method allows one to estimate the UV-vis spectra of interfering species in a sample as well as to test the purity of the chromatographic peaks. Besides the detection of the unknown interferences in a sample, this method allows one to calculate the concentration of an analyte in the presence of unknown compounds. To illustrate the reliability of the proposed method, samples of diuretics and amphetamines have been analyzed by normal- and reversed-phase high-performance chromatography.

Amphetamines↗

PubMed2000

Chromatographic separation of chlorthalidone enantiomers using beta-cyclodextrins as chiral additives.

Different beta-cyclodextrins have been tested as chiral additives in the mobile phase for the chromatographic analysis of chlorthalidone enantiomers in a C18 LiChrospher (125 x 4 mm I.D.) column. The effect on enantioresolution of different parameters was studied: composition of the mobile phase (percentage of organic solvent, type of buffer and pH), mobile phase flow-rate, and type and concentration of beta-cyclodextrin. A 25:75 mixture of methanol and 0.1 M phosphate buffer, pH 4, containing 2% triethylamine (v/v), and 12.5 mM beta-cyclodextrin, at a flow-rate of 0.8 ml/min, was found to be the best option for the resolution of chlorthalidone enantiomers. Under such conditions, linear calibration curves were obtained in the 0.5-20-microg/ml interval using UV detection at 230 nm. The limit of detection for both isomers was 50 ng/ml. The utility of the described assay has been tested by analyzing chlorthalidone in different pharmaceutical preparations. Examples of application to biological samples are also given.

Chlorthalidone↗

PubMed2000

Derivatization of tertiary amphetamines with 9-fluorenylmethyl chloroformate for liquid chromatography: determination of N-methylephedrine.

The fluorogenic reagent 9-fluorenylmethyl chloroformate (FMOC) was evaluated for the derivatization of tertiary amphetamines prior to liquid chromatographic analysis. Conditions for the derivatization were investigated, including the reaction time, the derivatization reagent concentration and the pH, using N-methylephedrine as a model compound. On the basis of these studies, a method for the quantification of N-methylephedrine is presented. The method involves derivatization with FMOC at ambient temperature and separation of the derivatives formed on a LiChrospher C18, 5 microns, 125 x 4 mm id column using acetonitrile-water gradient elution. The proposed procedure shows good linearity, accuracy and reproducibility in the 1.0-25.0 micrograms mL-1 concentration range. The limit of detection was 0.1 microgram mL-1 and the limit of quantification was 0.5 microgram mL-1. The utility of the assay was demonstrated by determining N-methylephedrine in water and urine samples.

Amphetamines↗

PubMed1999

Automated trace enrichment for screening and/or determination of primary, secondary and tertiary amphetamines in biological samples by liquid chromatography.

A rapid and simple liquid chromatographic method for the automated determination of amphetamines in biological fluids was developed. The proposed procedure is based on the injection of 250 microL of sample into a 20 x 2.1 mm id precolumn (packed with a 30 microns Hypersil C18 stationary phase) for enrichment and purification of the analytes. Next, the analytes are transferred to a 5 microns LiChrospher 100 RP18, 125 x 4 mm id analytical column for their separation under reversed-phase conditions. Water was used to eliminate the matrix components from the precolumn and a 0.2 M phosphate buffer (pH 3) containing 2% triethylamine was the mobile phase for the resolution of the amphetamines. The UV detector was set at 210 nm. The method was applied to the determination of different primary, secondary and tertiary amphetamines in plasma and urine: beta-phenylethylamine, norephedrine, ephedrine, N-methylpseudoephedrine, pseudoephedrine, N-methylephedrine, amphetamine, 3-phenylpropylamine and methamphetamine. The method provides satisfactory linearity and reproducibility within the tested concentration range (1.0-10.0 micrograms mL-1) and limits of detection of 50-500 ng/mL-1.

Amphetamines↗

PubMed1998

Chiral determination of amphetamine and related compounds using chloroformates for derivatization and high-performance liquid chromatography.

The enantiomeric determination of amphetamine and various amphetamine-type compounds by liquid chromatography after chiral derivatization with 9-fluorenylmethyl chloroformate-L-proline (FMOC-L-Pro) is reported. The results obtained were compared with those achieved after achiral derivatization with 9-fluorenylmethyl chloroformate and subsequent separation of the derivatives on a beta-cyclodextrin chiral stationary phase. Conditions for the derivatization of amphetamines with FMOC-L-Pro were investigated, including the effect of the derivatization reagent concentration, pH and reaction time, using amphetamine, ephedrine and pseudoephedrine as model compounds. On the basis of these studies, possible conditions for the determination of each amphetamine are indicated. To demonstrate the utility of the proposed procedures, data on linearity, repeatability and sensitivity are given. Results of the determination of ephedrine enantiomers in different pharmaceutical samples are also presented.

Amphetamines↗

PubMed1997

Liquid chromatographic analysis of amphetamine and related compounds in urine using solid-phase extraction and 3,5-dinitrobenzoyl chloride for derivatization.

A chromatographic method for the analysis of amphetamine and related compounds in urine using 3,5-dinitrobenzoyl chloride (3,5-DNB) as a labeling reagent is presented. This assay is based on the employment of solid-phase extraction (SPE) cartridges for sample cleanup and derivatization. Experimental conditions are optimized for the simultaneous derivatization of ephedrine, norephedrine, pseudoephedrine, beta-phenylethylamine, amphetamine, methamphetamine, and 3-phenylpropylamine. The derivatives formed are separated in a LiChrospher 1000 RP18 (125 x 4-mm i.d., 5-microns film thickness) analytical column using a water-acetonitrile gradient elution and detected at 254 nm. Derivatization in C18 SPE disks is found to be the best option for analysis of urine samples; this method provides analyte conversions that are about 85-102% of those obtained by the analogous solution derivatization. Because the 3,5-DNB reagent is a strong pi-acid, the described method can be used in combination with a Pirkle-type donor column for chiral analysis. The practicality of the described approach is illustrated by determining amphetamine enantiomers using a Supelcosil LC-(S)-naphtylurea (250 x 4.6-mm i.d., 5-microns film thickness) column and a mobile phase of n-hexane-acetonitrile-ethyl acetate. Under these conditions, good linearity and reproducibility are observed over the 0.5-10 micrograms/ml concentration range; the limit of detection is 50 ng/mL.

Amphetamines↗

PubMed1996

Determination of amphetamine and related compounds in urine using on-line derivatization in octadecyl silica columns with 9-fluorenylmethyl chloroformate and liquid chromatography.

A method for the determination of amphetamine and related compounds in urine based on on-line derivatization with 9-fluorenylmethyl chloroformate (FMOC) and high-performance liquid chromatography is described. Derivatization is performed in a 20 x 2.1 mm I.D. column packed with a Hypersil ODS C18, 30 micron stationary phase, which is also used for sample clean-up and enrichment of the analytes. Next, the derivatized analytes are transferred to a LiChrospher 100 RP-C18 (5 micron, 125 x 4 mm I.D.) analytical column for their separation and quantification, using reversed-phase conditions and fluorescence detection. The described assay was applied to the determination of norephedrine, ephedrine, pseudoephedrine, amphetamine, phenylpropylamine and methamphetamine at concentrations of 0.5-10.0 micrograms/ml. Analyte conversions were about 55-96% of those obtained by the off-line derivatization mode under similar conditions, resulting in limits of detection in the 5-25 ng/ml range.

Amphetamines↗

PubMed1996

Automated on-line dialysis for sample preparation for gas chromatography: determination of benzodiazepines in human plasma.

An on-line dialysis-solid-phase extraction-gas chromatographic (GC) approach has been developed for the determination of drugs in plasma, using some benzodiazepines as model compounds. Clean-up is based on performing the dialysis of 100 microliters samples for 7 min using water as acceptor phase and trapping the diffused analytes on a PLRP-S copolymer precolumn. After drying of the precolumn with nitrogen for 15 min, the analytes are desorbed with ethyl acetate (275 microliters) and injected on-line into the GC system via a loop-type interface. The system provides a very efficient clean-up, and offers the possibility of adding chemical agents which can help to reduce drug-protein binding and, thus, increase sensitivity. To demonstrate the potential of the described approach, the determination of benzodiazepines in plasma at their therapeutical levels is used as an example with flame ionization, thermionic and mass-selective detection.

Anti-Anxiety Agents↗