Biomedical subjects

J L Bernal

Publications and source records attributed to J L Bernal.

At least 37 records · Page 2Linked to original sources

PubMed2002

Capillary gas chromatography with mass spectrometric and atomic emission detection for characterization and monitoring chlordimeform degradation in honey.

Capillary gas chromatography-mass spectrometry and capillary gas chromatography-atomic emission detection have been successfully used to identify and monitor the main degradation products of chlordimeform when this compound is initially present in honey. The analysis of laboratory-spiked honey samples over 28 weeks revealed the occurrence of two degradation products: 4-chloro-o-toluidine (I) and N-formyl-4-chloro-o-toluidine (III). During this period the concentration of chlordimeform decreased to 7.5% of its initial value; the concentration of compound I increased gradually whereas compound III was present in a larger proportion and reached a maximum around the 14th week.

Chlorphenamidine↗

PubMed2001

Applications of the Chiralpak AD and Chiralcel OD chiral columns in the enantiomeric separation of several dioxolane compounds by supercritical fluid chromatography.

Two chiral columns based on polysaccharide derivatives (Chiralpak AD and Chiralcel OD) have been tested for the chiral separation of several dioxolane compounds, using supercritical fluid chromatography. The compounds studied included ketoconazole and some of its precursors. The effect of the different modifiers and the pressure, on the chromatographic parameters was also evaluated. In general, the alcohol modifiers provided better results than acetonitrile, and all the compounds could be separated with these two columns, but the selection of the column depends on the kind of compound.

Chromatography, Supercritical Fluid↗

PubMed2001

Use of deactivated fused-silica capillary precolumns in pesticide analysis by gas chromatography with electron-capture detection.

The advantages and disadvantages of coupling a retention gap of fused-silica between the injection port and the chromatographic column are discussed. The influence on the peak width and height of several factors such as the solvent (n-hexane, acetone, ethyl acetate and methanol), the gap (length, inner diameter, deactivation mode), the injection volume and the pesticide concentration has been examined. Those factors have very different incidences so, it is not possible to extract a general recommendation about the use of gaps. For this reason, checking its viability in each particular case is more advisable.

Chromatography, Gas↗

PubMed2001

Analysis of pesticide residues in wine by solid-phase extraction and gas chromatography with electron capture and nitrogen-phosphorus detection.

A feasible and reproducible method for multiresidue analysis of several common pesticides, of different polarities, in wine samples is proposed. The method combines a solid-phase extraction on polymeric cartridges eluted with ethyl acetate and a gas chromatographic determination using electron capture and nitrogen-phosphorus detection. To avoid the matrix effect, previous washing of the cartridges with a mixture of water-2-propanol (90:10) and further clean-up of the extract on Florisil cartridges, together with a calibration using spiked extracts, are recommended.

Chromatography, Gas↗

PubMed2001

Validation of a liquid chromatographic method for the determination of ranitidine hydrochloride residues on surfaces in the manufacture of pharmaceuticals.

A liquid chromatographic method for determination of the residues of ranitidine hydrochloride on various surfaces employed in drug manufacture is described. Cotton swabs, moistened with a methanol-water (1:1, v/v) mixture were used to remove any residues of drugs from glass, vinyl, and stainless steel surfaces, and gave recoveries of 85%, 78% and 90%, respectively. Residues were determined by high-performance liquid chromatography on a C18 column at 25 degrees C with methanol-ammonium acetate (40:60 v/v) pH 6.7 as the mobile phase and detection at 320 nm. The method was validated over a concentration range of 20-10 000 ng/ml and had a detection limit of 2 ng/ml.

Chromatography, High Pressure Liquid↗

PubMed2001

High-performance liquid chromatographic determination of methyl anthranilate, hydroxymethylfurfural and related compounds in honey.

A high-performance liquid chromatographic method for determining 5-hydroxymethyl-2-furaldehyde (hydroxymethylfurfural), 2-furaldehyde (furfural), furan-2-carboxylic acid (2-furoic acid), furan-3-carboxylic acid (3-furoic acid), furan-3-carboxaldehyde (3-furaldehyde) and 2-aminobenzoic acid methyl ester (methyl anthranilate) in honey and honeydew samples is described. To prevent matrix interference and to isolate the compounds, a clean-up step which implies a solid-phase extraction on polymeric cartridges and an elution with 0.5 ml methanol is recommended. The compounds are separated on a reversed-phase column with a gradient of (A) 1% aqueous acetic acid-acetonitrile (97:3, v/v) and (B) acetonitrile-water (50:50, v/v), with UV detection at 250 nm. The method is applied to the analysis of samples from different botanical origin.

Calibration↗

PubMed2000

Determination of the 2-bromomethyl-2-(2,4-dichlorophenyl)-1, 3-dioxolan-4-yl)methyl benzoate diastereoisomers by supercritical fluid chromatography.

The study of the separation and determination of the two 2-bromomethyl-2-(2,4-dichlorophenyl)-1,3-dioxolan-4-yl-methyl benzoate diastereoisomers is presented in this work. The separation was achieved using packed column supercritical fluid chromatography. Three stationary phases were checked, the C(18) packing providing the best results. The influence of several parameters (nature and percentage of modifier, temperature and pressure) on the separation were also evaluated. The baseline separation (R(s)=1.78) of the compounds was obtained in only 2 min, using a C(18) column, a pressure of 100 bar, a temperature of 35 degrees C, a flow-rate of 2. 5 ml/min and 5% of 2-propanol as organic modifier. Under these conditions the unwanted diastereoisomer (trans) was eluted before the main compound (cis), so the determination of the purity was more accurate.

2-Propanol↗

PubMed2000

Separation of ketoconazole enantiomers by chiral subcritical-fluid chromatography.

The separation of ketoconazole enantiomers by subcritical-fluid chromatography using an amylose-based column is described. Drastic changes in the resolution have been obtained for the different organic modifiers evaluated, with ethanol providing the best results. Other chromatographic parameters such as temperature, pressure and flow-rate have also been studied. The best results in terms of resolution and analysis time were obtained using 30% ethanol (containing 0.1% triethylamine and 0.1% trifluoroacetic acid), a pressure of 300 bar, a temperature of 35 degrees C and a flow-rate of 3 ml/min. Under these conditions the ketoconazole enantiomers are resolved in a short time (less than 7 min) and with high resolution (4.29).

Amylose↗

PubMed2000

Gas chromatographic determination of acrinathrine and 3-phenoxybenzaldehyde residues in honey.

A procedure involving an extraction step and further gas chromatographic analysis with flame ionization detection to determine residues of acrinathrine and its main metabolite, 3-phenoxybenzaldehyde, in honey is proposed. Residues can be isolated from the matrix by means of liquid-liquid extraction with a mixture of benzene-isopropanol, by solid-phase extraction with octadecylsilane cartridges or Florisil packed columns, the latter method giving higher recoveries. Assays on spiked honey samples are carried out to test the procedures that are afterwards applied to honey samples from treated beehives.

Benzaldehydes↗

PubMed2000

Determination of oxalate, sulfate and nitrate in honey and honeydew by ion-chromatography.

An ion chromatographic method for determining the anions oxalate, sulfate and nitrate in honey and honeydew samples is described. To prevent matrix interference and to isolate the anions a clean-up step using solid-phase extraction on anionic cartridges and eluting with a 0.01 M chromate solution is recommended. The anions are separated on an anionic column with a mobile phase of borate-gluconate buffer and using conductimetric detection. The method is applied to the analysis of samples from different botanical origin.

Calibration↗

PubMed2000

Chiral separation of four 1,3-dioxolane derivatives by supercritical fluid chromatography on an amylose-based column.

The chiral separation of four 1,3-dioxolane derivatives by supercritical fluid chromatography on an amylose-based column is described. The effects of mobile phase composition, temperature and pressure have been investigated. The nature of the modifier is the parameter which has the highest impact on the chiral resolution and it is more important than the polarity of the mobile phase. The organic modifier used for the best enantiomeric separation was different for each compound, because it depends strongly on the molecular structure of the compound.

Amylose↗

PubMed2000

Determination of rotenone residues in raw honey by solid-phase extraction and high-performance liquid chromatography.

A method for determining residues of the insecticide rotenone in raw-honey by high-performance liquid chromatography (HPLC) is described. To extract the residues, organic solvents such as ethyl acetate, n-hexane/dichloromethane and solid-phase extraction with octadecylsilane cartridges or Florisil packed columns were tested. Determination was carried out by reversed-phase HPLC using acetonitrile-buffer phosphate (pH 7) (60:40, v/v) as mobile phase and detection at 210 nm. Although the data showed that the two extraction methods were able to isolate the pesticide residues, the extraction on octadecylsilane cartridges was preferred due to its simplicity and higher recovery. Recoveries depended strongly on the fortification level for the two extraction procedures. Practical determination limits of 0.015 mg/kg were obtained. In the analysis of honeys, from beehives treated with rotenone at therapeutical doses for 1 month, residual amounts below 0.2 mg/kg were found.

Chromatography, High Pressure Liquid↗

PubMed2000

Validation of the removal of acetylsalicylic acid. Recovery and determination of residues on various surfaces by high performance liquid chromatographic.

The validation of a procedure to clean glass, vinyl and stainless steel surfaces that have been exposed to acetylsalicylic acid during its manufacture is described. The cleaning procedure using two cotton swabs moistened with the mobile phase was validated using a wipe-test and a high-performance liquid chromatography (HPLC) method developed to determine low quantities of the acid. The HPLC method involves an octadecylsilane column at 55 degrees C, a mixture of water-acetonitrile-orthophosphoric acid (779:220:1, v/v) as mobile phase and detection at 226 nm. Recoveries of 86%, 90% and 94% were obtained from vinyl, glass and stainless steel plates respectively. The validation gave acceptable levels of sensitivity, recovery, precision and linearity.

Aspirin↗

PubMed2000

Behavior of monosaccharides, phenolic compounds, and color of red wines aged in used oak barrels and in the bottle.

A red wine with appropriate basic quality characteristics for aging was stored in oak barrels for 12 months and then bottled and aged for a further 6 months. The same ambient conditions of temperature and humidity were maintained throughout the entire aging process. The barrels used were made from three different species of oak by four different cooperages and had been used for at least two years. Analysis of variance and principal component analysis were run on the values for hexoses, pentoses, total anthocyanins, ortho-diphenols, low- and high-polymer polyphenols, and color parameters to study the behavior of the monosaccharides and polyphenols in response to the factors of aging time, the oak variety employed, and the source cooperage where the barrels had been made. Time trends for all the phenolic components were directly related to aging time, with low-polymeric polyphenols (LPPs) being the most affected by wood type and source cooperage. Wine color was defined by a basic red color which decreased with aging time in the barrel and was altered by yellowish pigment components differing for each of the barrels in which oxidative aging took place and by increased stability of the blue copigments. Principal component analysis showed that samples of the same source wine aged in different barrels tended to be grouped together according to each of the aging intervals considered.

Color↗

PubMed1998

Solid-phase microextraction applied to the analysis of pesticide residues in honey using gas chromatography with electron-capture detection.

The possibilities of using solid-phase microextraction to determine residues of pesticides in honey have been examined. For this purpose, three types of fiber have been assayed: polyacrylate of 85 microns thickness, and polydimethylsiloxane of 7 and 100 microns thickness. They have been applied to the extraction of 21 pesticides of different chemical families. The effects of the temperature, extraction time and ionic strength on the microextraction have been studied, proposing the most adequate for each fiber. Under optimized conditions, precision, intervals of linearity and detection limits were evaluated.

Chromatography, Gas↗

PubMed1998

Use of detergents and high contents of organic solvents for simultaneous quantitation of ionic and nonionic drugs by electrokinetic chromatography.

Buffers containing high percentages of organic solvents, typically 50% of acetonitrile and/or methanol, together with sodium dodecyl sulfate (SDS) are employed for the separation and quantitation by electrokinetic chromatography (EKC) of analytes found in a nasal spray. Solutes consist of benzalkonium chloride, a family of highly positive compounds, and 2-phenylethanol and beclomethasone dipropionate, which are electrically neutral and poorly soluble in aqueous buffers. It is observed that the effect of both concentration of SDS and temperature on the separation depends on the organic solvent used and the solute nature. It is also observed that SDS-solute interaction for neutral and cationic compounds are weaker in the presence of high contents of acetonitrile than in methanol. Concentration of SDS, temperature, and organic solvent nature and content, allow one to modify the selectivity of the separation when neutral and ionic species have to be simultaneously determined. The optimization of EKC conditions enables the analysis of compounds in less than 5 min. A one-step sample treatment consisting of centrifugation of the nasal spray solved in acetonitrile, together with the referenced optimum separation conditions enable the reproducible quantitation of the analytes. Relative standard deviation values of inter-day migration times lower than 2.45% are obtained (R.S.D.n = 12), while R.S.D.n = 12 values for inter-day peak areas were lower than 6.32%.

Administration, Intranasal↗

PubMed1998

Gas chromatography with electron-capture and nitrogen-phosphorus detection in the analysis of pesticides in honey after elution from a Florisil column. Influence of the honey matrix on the quantitative results.

A modified procedure to extract pesticides from honey samples that involves loading the honey onto a Florisil packed column and subsequently eluting it with an n-hexane-dichloromethane mixture is proposed. Anomalous high gas chromatographic responses and subsequently very high recoveries for the pesticides in the extracts were obtained by a conventional calibration with pesticide solutions in organic solvent. This effect was attributed to the honey matrix and can be circumvented by using spiked honey extracts as calibration standards.

Chromatography, Gas↗

PubMed1998

Packed-column supercritical fluid chromatography coupled with solid-phase extraction for the determination of organic microcontaminants in water.

A multiresidue method for the analysis of 35 common contaminants (including pesticides, polycyclic aromatic hydrocarbons and phenols) in lough and river waters from Castilla y León Spanish region, by using supercritical fluid chromatography (SFC) with five silica packed columns, is described. In order to decrease the detection limits, a preconcentration step by coupling solid-phase extraction to the SFC system was used. The different variables affecting the extraction procedure were studied and optimized, selecting the Isolute Env+ as the best sorbent. The detection limits achieved ranged from 0.4 to 2.6 micrograms l-1.

Chromatography↗