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A Sevillano-Cabeza

Publications and source records attributed to A Sevillano-Cabeza.

16 recordsLinked to original sources
PubMed2001

o-Phthalaldelhyde-N-acetylcysteine polyamine derivatives: formation and stability in solution and in C18 supports.

A comparative study of different derivatization procedures has been performed in order to improve the stability of the reaction products o-phthalaldehyde-N-acetylcysteine (OPA-NAC) polyamines. Procedures such as solution derivatization, solution derivatization followed by retention on a packing support, derivatization on different packing supports and on-column derivatization, have been optimized and compared. The degradation rate constant (k) of the derivative was dependent on the procedure used and on the analyte. For the spermine (the most unstable isoindol tested) k was 8 +/- 2 x 10(-2) min(-1) in solution versus 7.7 +/- 1.1 x 10(-4) min(-1) on the (C18) solid support. The results obtained showed that forming the derivative on the packing support (C18) gave the best results following this procedure: conditioning the cartridges with borate buffer (1 ml, 0.5 M, pH 8), retention of the analyte, addition of 0.8 ml of OPA-NAC reagent, 0.2 ml borate buffer 0.8 M (pH 8) and elution of the isoindol with 3 ml of MeOH-borate buffer (9:1). The different derivatization procedures have been used to study the stability of the reaction products OPA-NAC polyamines formed in urine matrix using spermine as model compound. Similar results were obtained for standard solutions and urine samples.

Acetylcysteine↗
PubMed1999

Urine polyamines determination using dansyl chloride derivatization in solid-phase extraction cartridges and HPLC.

The derivatization of biogenic amines such as putrescine, cadaverine, spermidine and spermine with dansyl chloride in solid phase extraction cartridges is described. Different types of filling materials were tested in order to have the highest retention of the different analytes. The best results were obtained by using C18 cartridges. The optimal conditions were: amine solution buffered at pH 12, 2 mM dansyl chloride (acetone-bicarbonate solution 20 mM (pH 9-9.5), 2 + 3 v/v) as reagent concentration, room temperature and 30 min reaction time. The developed procedure was applied to the determination of these polyamines in urine samples from healthy controls and cancer patients using HPLC with 1,7-diaminoheptane as internal standard. The concentrations ranged from 0.5 to 5 micrograms mL-1 and the detection limits were 10 ng mL-1 for all polyamines. By concentrating the urine extracts, the detection limits were improved down to 2 ng mL-1. The accuracy and the precision of the method were tested. The proposed dansylation method is advantageous with respect to solution dansylation. It improves the total analysis time, avoids high temperatures that can affect the thermal stability of the derivatives and could make possible the automation of the procedure.

Biogenic Polyamines↗
PubMed1998

New spectrophotometric procedure for determining cefotaxime based on derivatization with 1,2-naphthoquinone-4-sulphonate into solid-phase extraction cartridges--application to pharmaceutical and urine samples.

Cefotaxime was derivatised with 1,2-naphthoquinone-4-sulphonate (NQS), extracted into solid-phase cartridges (C18) and detected using a UV-visible detection system. Optimum conditions for this new procedure were: hydrogencarbonate-carbonate buffer, pH 10.5, 5-min reaction time at 25 degrees C and an NQS concentration of 7.1x10(-3) mol l(-1). The accuracy and the precision of the liquid-solid procedure were tested. The procedure was used to measure cefotaxime in pharmaceutical and urine samples. The results obtained were contrasted with those reported for a HPLC method for urine samples. The generalized H-point standard additions method was used to measure cefotaxime in urine samples.

Adult↗
PubMed1998

Automated pre-column derivatization of amines in biological samples with dansyl chloride and with or without post-column chemiluminescence formation by using TCPO-H2O2.

On-line automation of two different liquid chromatographic procedures, a pre-column derivatization system and a pre- and post-column system, in order to generate chemiluminescence is reported. Dansyl chloride (Dns-Cl) was used as a pre-column reagent to form fluorophores and bis(2,4,6-trichlorophenyl) oxalate (TCPO) and hydrogen peroxide (H2O2) as a post-column reagent to generate chemiluminescence. This procedure is based on the employment of a primary column packed with C18 material inserted in a multi-dimensional assembly for sample clean-up and derivatization with Dns-Cl. The dansyl derivatives formed are transferred and separated in a LiChrospher 100 RP18 analytical column (125 x 4 mm id, 5 microns film thickness) using acetonitrile-imidazole buffer (pH 6.8) (70 + 30) as eluent. The separated derivatives were transferred to the detector for fluorescence detection or to the post-column system where the chemiluminescence response was generated by using TCPO-H2O2 and the products were detected by chemiluminescence. The procedure was optimised for amphetamine and related compounds. A comparison between the on-line pre-column and pre- and post-column systems was performed. The results show that the sensitivity of chemiluminescence detection can be higher than that of fluorescence detection. The recoveries obtained ranged from 98 +/- 8 up to 108 +/- 8% for amphetamine and methamphetamine, respectively. The accuracy and precision of these methods were evaluated.

Amines↗
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

Amphetamine and methamphetamine determination in urine by reversed-phase high-performance liquid chromatography with simultaneous sample clean-up and derivatization with 1,2-naphthoquinone 4-sulphonate on solid-phase cartridges.

A liquid-solid procedure is proposed for sample clean-up and derivatization of amphetamine and methamphetamine in urine samples. The reagent was 1,2-naphthoquinone 4-sulphonate, and a commercial C18 packing cartridge was used. The samples derivatized at room temperature were chromatographed on a 5-microns Hypersil ODS (250 x 4 mm I.D.) with an elution gradient of acetonitrile-water containing propylamine. Under these conditions, the amines were eluted with short retention times. The procedure was used to determine amphetamine, or methamphetamine with its metabolite amphetamine, in spiked urine samples. The detection limit (at a signal-to-noise ratio of 3) for amphetamine (0.1 microgram/ml) was similar to that obtained with liquid-liquid derivatization and to those obtained with immobilized reagents on a polymeric solid support. The detection limit for methamphetamine (0.4 microgram/ml) was higher than with the liquid-liquid procedure because of the lower reactivity on the cartridge. The precision and accuracy of the method were also studied.

Amphetamine↗
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

On-line derivatization into precolumns for the determination of drugs by liquid chromatography and column switching: determination of amphetamines in urine.

A chromatographic system for the on-line derivatization of drugs using column switching is described. The system uses a 20 mm x 2.1 mm i.d. precolumn packed with a unmodified ODS stationary phase. This column is used for sample cleanup and enrichment of the analytes. Next, the trapped analytes are derivatized by injection of the derivatization reagent into the precolumn. Finally, the derivatives are transferred to the analytical column for their separation under reversed-phase conditions. The influence of several parameters such as the reaction time, the amount of derivatization reagents, or the system design has been studied some amphetamines as model compounds and three derivatization reagents: sodium 1, 2-naphthoquinone-4-sulfonate, o-phthaldialdehyde, and 9-fluorenylmethyl chloroformate. The potential of the described approach is illustrated by determining amphetamine and methamphetamine in untreated urine at ambient temperature.

Amphetamines↗
PubMed1994

Application of column-switching techniques to the determination of medium polarity drugs: determination of acetazolamide in urine.

A column-switching system for the determination of the medium polarity diuretic acetazolamide in urine, has been designed. An Hypersil ODS C18, 30 microns (20 x 2.1 mm I.D.) pre-column was used for the pre-concentration and separation of acetazolamide from the biological matrix. The most polar urinary compounds were removed by washing the pre-column with a phosphate buffer solution (pH 3), and the fraction of eluate containing the analyte was switched to a LiChrospher RP C18, 5 microns (125 x 4 mm I.D.) analytical column, where it was chromatographed using gradient elution with acetonitrile-water, and detected at 275 nm. The most apolar urinary compounds were directly discarded by means of a second switching valve. Under these conditions the recovery of drug was 96 +/- 5% in the 0.50-100.0 micrograms/ml concentration range. The limit of detection was 10 ng/ml, the total analysis time being less than 8 min.

Acetazolamide↗
PubMed1994

Column-switching techniques for screening of diuretics and probenecid in urine samples.

A method based on high-performance liquid chromatography using column-switching is described for the screening of diuretics and probenecid in urine samples. The system uses a 20- x 2.1-mm i.d. precolumn, packed with a Hypersil ODS-C18, 30-microns stationary phase, for the on-line sample cleanup and enrichment. Untreated urine samples are directly injected, and the precolumn is flushed for 1 min with water to eliminate polar matrix components. The retained analytes are then back-flushed by means of a six-port switching valve onto a Hypersil ODS-C18 analytical column (5 microns, 250- x 4-mm i.d.), where they are separated using an acetonitrile/phosphate buffer (pH = 3) gradient elution. Under these conditions, the separation and identification of diuretics and probenecid can be achieved with satisfactory selectivity and sensitivity. The described procedure is very simple and rapid since no off-line manipulation of the sample is required, the total analysis time being ca. 15 min.

Chromatography, High Pressure Liquid↗
PubMed1993

Column-switching techniques for high-performance liquid chromatography of drugs in biological samples.

In recent years, an increasing number of publications have demonstrated the potential of column-switching techniques for the chromatographic separation, determination and preparative isolation of analytes from biological matrices. Column-switching systems greatly facilitate drug analysis, by on-line sample clean-up and trace enrichment, or by improving the analytical separative process. In this paper, the main applications of column-switching techniques to drug analysis in biological samples, are reviewed.

Animals↗
PubMed1993

Improved detection limits for screening of diuretics by coupled liquid chromatography and ultraviolet-visible spectrophotometry.

Experimental conditions have been studied in order to improve the sensitivity for the analysis of diuretics and probenecid in urine samples by high-performance liquid chromatography with ultraviolet detection. Sample clean-up and chromatographic parameters have been optimized to obtain a suitable sensitivity for the detection or quantification of each diuretic using an HP-Hypersil ODS-C18 column (5 microns, 250 mm x 4 mm I.D.), taking into account the pharmacological properties of each compound. The reliability of this method was tested by analysing urine samples after a minimum single-dose administration of chlorthalidone and probenecid.

Chlorthalidone↗
PubMed1992

Determination of acetazolamide in human urine samples by reversed-phase high-performance liquid chromatography in the presence of xanthines.

A simple, rapid and selective high-performance liquid chromatographic assay for the determination of acetazolamide in urine samples is described. After extraction with ethyl acetate, the drug is chromatographed on an HP-Hypersil ODS-C18 column with a mobile phase of acetonitrile-phosphate buffer (pH 3) and ultraviolet detection at 275 nm. The efficiency of the extraction, the linearity and the reproducibility of the method permit the evaluation of acetazolamide urinary excretion a long time after its administration.

Acetazolamide↗
PubMed1989

Kinetic and chemometric studies of the determination of creatinine using the Jaffé reaction. Part I. Kinetics of the reaction: analytical conclusions.

A kinetic-spectrophotometric study of the Jaffé reaction was carried out and the kinetic behaviour, calibration step and interfering effect of albumin on creatinine standard solutions were studied. It was concluded that there is a variation in the kinetic behaviour of the system when higher concentrations of creatinine, picrate or sodium hydroxide are tested. The experimental conditions for quantifying creatinine must be chosen so that the kinetic behaviour is the same in the dynamic concentration range. Changes in the absorbance (delta A) versus concentration equations were chosen as the most suitable for calibration graphs. It was also shown that creatinine results will have a proportional bias error if the interfering effect of albumin is not taken into consideration.

Creatinine↗
PubMed1989

Kinetic and chemometric studies of the determination of creatinine using the Jaffé reaction. Part 2. Application to human serum samples: kinetic behaviour and chemometric evaluation of the determination.

The kinetic behaviour of the reaction of alkaline picrate with creatinine in human serum samples was found to be similar to that for standard creatinine solutions containing albumin. A chemometric evaluation of the kinetic determination of creatinine using the Jaffé reaction was carried out. The analysis of variance (ANOVA) method applied to the delta A45,180 values, obtained from two replicates of three different serum samples over a period of 10 d, showed that the between-day and between-replicate variations added a component to the total variability, the residual error (delta R2) being 5 X 10(-5). A study of the accuracy of the determination was carried out by means of percentage recovery experiments, Youden's method and the standard additions method. Percentage recovery experiments showed that albumin has a marked effect on the results obtained. The application of Youden's method to four serum samples indicated that the method does not have a constant bias error, but, by applying the standard additions method it was concluded that the method has a proportional bias error. The recovery factor, defined as the ratio of the slope of the standard additions graph to that of the standard response graph, was also calculated for the four serum samples. The best values were obtained with different standard response graphs (7.7, 15.4 and 25.6 g l-1 of albumin) for each sample. A modification of the routine procedure used in clinical laboratories is proposed. This modification is based on the principles of the standard additions method and gives better results for creatinine content than those obtained with the routine procedure.

Creatinine↗