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Biomedical subjects

H Lingeman

Publications and source records attributed to H Lingeman.

54 records · Page 3Linked to original sources
PubMed1991

On-line immunoaffinity sample pre-treatment for column liquid chromatography: evaluation of desorption techniques and operating conditions using an anti-estrogen immuno-precolumn as a model system.

An immunoaffinity precolumn (immuno-precolumn) containing an immobilized antibody directed against estrogen steroids, was used as a model system for the evaluation of different desorbing techniques, suitable for on-line coupling to column liquid chromatography (LC). Desorption of estrogen analytes from the immuno-precolumn proved to be impossible with the buffers and chaotropic solutions frequently used in affinity desorption. Micellar solutions are effective in obstructing the antibody-antigen reaction, but their use as desorbing solutions was not found to be practical because of the large interferences introduced into the chromatograms. Desorption with aqueous solutions at elevated temperature, created by microwave action or conventional heating, although effective is not practical in this instance, because the agarose used in this study as the stationary phase for the immuno-precolumn is prone to heat decomposition. The most effective and practical approach is desorption with a methanol-water mixture (95 + 5 v/v). On-line dilution of the eluate allows the concentration of the desorbed analytes using a reversed-phase LC system with subsequent separation and ultraviolet detection. The performance of the system with spiked urine and plasma samples, which were introduced directly into the system, was evaluated and the results were compared with immunoselective desorption.

Antibodies↗
PubMed1990

Liquid chromatographic determination of pentachlorophenol in serum, using pre-column phase-transfer catalysed dansylation and post-column photolysis with fluorescence detection.

Dansylation of pentachlorophenol was carried out after solid-phase extraction of acidified human serum and desorption with dichloromethane, in a dichloromethane-water two-phase system using tetrabutyl-ammonium bromide as the phase-transfer catalyst. Derivatisation was complete within 2 min at room temperature. After evaporation of an aliquot of the organic phase, the residue was dissolved in methanol and injected into a reversed-phase chromatographic system, equipped with a post-column photochemical reactor. In the reactor, dansylated pentachlorophenol is converted into highly fluorescent products. The recovery of the analyte from serum was 85 +/- 4%. Calibration graphs for horse and human serum were linear over two decades, with correlation coefficients ranging from 0.996 to 0.999. The detection limit of pentachlorophenol in horse and human serum was 400 pg ml-1. The reproducibility of the total procedure for a human serum sample containing 4 ng ml-1 was 4.5%.

Catalysis↗
PubMed1989

Post-column reactors for sensitive and selective detection in high-performance liquid chromatography: categorization and applications.

The increasing interest in the rapid trace analysis of large series of biomedical samples using column liquid chromatographic techniques requires the use of well balanced combinations of sample pretreatment, separation and detection techniques. In such work, selectivity, sensitivity and reproducibility are the key parameters. The application of automated or semi-automated on-line pre-column technology and/or post-column reaction detection are excellent ways to meet these requirements. A critical review is presented of the theoretical background of on-line post-column reactors with emphasis on their categorization, viz., open-tubular, packed-bed, segmented-stream and hollow-fibre membrane reactors. The evaluation of these reactor systems is performed by discussing selected applications of, for instance, systems based on electrochemical and redox, hydrolytic, photochemical, ion-pairing, true chemical derivatization, peroxyoxalate chemiluminescence and solid-phase reactions. As automation is becoming even more important, a number of labelling procedures, which can be performed in an on-line pre-column mode, are briefly discussed and a comparison is made between the potential of on-line pre- and post-column procedures.

Chemistry, Clinical↗
PubMed1989

Reversed-phase ion-pair analysis of 5-fluorouracil in pig bile, liver homogenate, plasma and urine after administration by isolated liver perfusion.

5-Fluorouracil is at present one of the most administered cytostatic drugs in cancer chemotherapy. However, due to its high toxicity, local administration of the drug, e.g. by isolated liver perfusion, may be advantageous. A bioanalytical procedure, suitable for the routine analysis of 5-fluorouracil in pig bile, liver homogenates, plasma and urine is described using reversed-phase ion-pair chromatography with absorbance detection at 268 nm. Using a protein precipitation procedure with acetonitrile, a determination limit of 3500 ng g-1 was achieved for liver samples, and 5 ng ml-1 for plasma samples using a liquid-liquid extraction step.

Animals↗
PubMed1988

Bioanalysis of (E)-5-(2-bromovinyl)-2'-deoxyuridine.

(E)-5-(2-Bromovinyl)-2'-deoxyuridine is an antiviral drug that is experimentally used for modulation of the antitumour effect of fluoropyrimidines, such as ftorafur and 5-fluorouracil. The isolation of the analyte, in the presence of 5-fluorouracil, from the matrix is performed either by means of a simple protein precipitation (plasma) or by means of a liquid-liquid extraction with ethyl acetate (urine). Following pretreatment, the analyte is analysed by reversed-phase chromatography and quantified by absorbance detection at 307 nm. The minimum detectable concentration in plasma and urine samples is ca. 6 ng/ml. The recovery after deproteination of plasma samples is 75%, while after liquid-liquid extraction of urine the recovery amounts 92%. The degree of protein binding of the analyte, measured by ultrafiltration, is found to be 97%. These data allow the bioanalysis of (E)-5-(2-bromovinyl)-2'-deoxyuridine for pharmacokinetic studies.

Antiviral Agents↗
PubMed1988

Conventional and laser induced fluorescence detection of glucuronic acid conjugates after derivatization and liquid chromatographic separation.

Pre-chromatographic derivatisation of the carboxylic acid function of glucuronic acid conjugates is a suitable method for the selective and ultra-sensitive analysis of these compounds in urine and plasma samples. This goal is achieved by applying an indirect derivatisation procedure and laser induced fluorescence detection with a homemade detection system equipped with a continuous-wave argon-ion laser. The minimum detectable amounts for the analytes, after derivatisation, are about 3 amol using the fluorescein fluorophore. In comparison with conventional induced fluorescence detection a gain in sensitivity of over four orders of magnitude is obtained.

Journal Article↗
PubMed1987

Automated analysis of mitomycin C in body fluids by high-performance liquid chromatography with on-line sample pre-treatment.

A fully automated liquid chromatographic system for the bioanalysis of mitomycin C has been described. The isolation of the analyte from the biological matrix (plasma, ascites and urine) is performed using a continuous-flow system equipped with a dialysis membrane in order to remove proteins. The samples are concentrated on a reversed-phase pre-column and subsequently introduced on to a reversed-phase analytical column by applying column-switching techniques. The drug is detected by absorbance measurements at 360 nm. Using the described system up to 100 samples a day can be analysed with determination limits of the order of 1 ng/ml, with a linear dynamic range of at least three decades for plasma and urine samples. The procedure was applied to pharmacokinetic studies of ovarian cancer patients treated intraperitoneally with mitomycin C.

Ascitic Fluid↗
PubMed1986

High-performance liquid chromatographic analysis of basic compounds on non-modified silica gel and aluminium oxide with aqueous solvent mixtures.

A comparison is made between the use of aluminium oxide and non-modified silica gel as cation-exchange materials for the separation of basic drugs (amines) with aqueous solvent mixtures. The retention behaviour of the amines is studied and appears to be controlled predominantly by the pH and the concentration and nature of the modifier; the nature and concentration of the competing ions and the buffer components of the mobile phase also exert some influence on the retention. Preparations with imidazoline and tetracycline derivatives have been analysed as examples of the application of these ion-exchange systems on non-modified silica gel and aluminium oxide in the analysis of pharmaceutical formulations.

Aluminum Oxide↗
PubMed1986

Mitomycin antitumour agents: a review of their physico-chemical and analytical properties and stability.

The review enumerates the physico-chemical and analytical properties of mitomycin antitumour antibiotics, of which mitomycin C is the most important representative. After a short overview of the position of the compounds in oncology the following subjects will be discussed: structural features, prototropic properties, spectroscopy (UV-VIS, ORD, CD, IR, NMR, MS), chromatography and electrochemistry. The chemical stability and aspects of the mechanism of action of the compounds are also discussed. The last part of the review surveys the analysis of mitomycin C in biological fluids.

Journal Article↗
PubMed1984

Rapid and selective derivatization method for the nitrogen-sensitive detection of carboxylic acids in biological fluids prior to gas chromatographic analysis.

A rapid and selective derivatization procedure is described for the pre-column labelling of carboxylic acids with a nitrogen-containing label. The carboxylic acid function is activated with 2-bromo-1-methylpyridinium iodide and the activated carboxylic acid function reacts with a primary or a secondary amine to yield an amide. With flurbiprofen as the test compound and dipropylamine as a label the acid was completely converted to the corresponding amide. The method was tested for several aliphatic, aromatic and for phenylacetic or phenylpropionic carboxylic acid derivatives, and was found to result in the complete derivatization of these compounds with a few exceptions only. The derivatization procedure is potentially useful for drug monitoring purposes, as is shown with the analysis of valproic acid and flurbiprofen in plasma.

Body Fluids↗
PubMed1984

Derivatization reactions in the gas-liquid chromatographic analysis of drugs in biological fluids.

Alkylation, acylation, silylation and other derivatization reactions applied to the gas chromatographic analysis of drugs in biological matrices are reviewed. Reaction conditions are discussed in relation to reaction mechanisms. Detector-oriented labelling of drugs, and derivatization with chiral reagents for the separation of enantiomers are surveyed. Data on the sample clean-up, derivatization and GLC analysis of more than 300 drugs and related compounds are listed.

Journal Article↗
PubMed1983

Aspects of the chemical stability of mitomycin and porfiromycin in acidic solution.

Aspects of the degradations of mitomycin and porfiromycin were studied. The initial degradation processes of the compounds in an acidic medium were investigated. Influences of pH, buffers, and other additives such as halogenides and dioctyl sodium sulfosuccinate [sodium 1,4-bis(2-ethylhexyl)sulfosuccinate] were studied. The hydrogen ion catalyzes the degradation of both the uncharged and the protonated species. Anions also promote the degradation of the compounds in an acidic medium. Rate constants for all of the catalytic reactions could be determined. From the pH profiles, after correction for buffer influences, accurate pKa values for the aziridine nitrogens could be obtained. The protective influence of the dioctyl sulfosuccinate ion could be explained. From the data obtained a plausible mechanism for the initial acidic degradation reactions was developed.

Drug Stability↗
PubMedDate not supplied

Capillary electrophoresis of the collagen crosslinks HP and LP utilizing absorbance, wavelength-resolved laser-induced fluorescence and conventional fluorescence detection.

A capillary electrophoretic (CE) method is presented for the determination of the collagen crosslinks hydroxylysylpyridinoline (HP) and lysylpyridinoline (LP). Various detection techniques are compared, i.e. UV-Vis diode-array absorbance detection (DAD) and fluorescence detection both in the laser-induced fluorescence (LIF) and the conventional fluorescence mode. LIF detection was performed using a frequency-doubled Rhodamine dye laser pumped by an excimer laser, for excitation at 290 and 325 nm. The emission was measured with an intensified diode-array detector mounted on a spectrograph to obtain wavelength-resolved spectra. Relevant concentration detection limits were achieved only by using LIF detection, i.e. 200 nM of HP and LP in a 30 mM phosphate buffer (pH 2.0). Linear calibration curves were obtained from the detection limits up to the maximum concentration available, 23 microM for HP and 4.2 microM for LP, respectively for both fluorescence modes. The identity of the migrating compounds was confirmed by on-line recording of both the absorption and the fluorescence spectra.

Buffers↗
PubMedDate not supplied

An acridinium sulphonylamide as a new chemiluminescent label for the determination of carboxylic acids in liquid chromatography.

The synthesis of a new acridinium sulphonylamide label for the liquid chromatographic determination of carboxylic acids is described. The label 10-methyl-N-(p-tolyl)-N-(p-iodoacetamidobenzenesulphonyl)-9-acr idi nium carboxamide iodide is synthesized from 9-acridine-carboxylic acid by a seven-step reaction. Ibuprofen, used as test compound, is coupled to the reactive iodoacetamide group of the label by means of an alkylation reaction in dry acetonitrile for 20 min at 50 degrees C in the presence of 18-crown-6 and potassium carbonate as base catalyst. The reaction mixture is injected into a liquid chromatographic system with chemiluminescence detection. Separation is performed on a Zorbax C18 column with acetonitrile-water-tetrahydrofuran (39:57:4, v/v/v) containing 10 mmol/L TBABr and 0.035% H2O2 as the mobile phase at a flow rate of 1.0 ml/min. Chemiluminescence detection is achieved by the post-column addition of 200 mmol/L potassium hydroxide dissolved in methanol-water (1:1, v/v) at a flow rate of 20 microL/min. The detection limit (S/N = 3) of derivatized ibuprofen is 60 pg (3 pg injected).

Acridines↗
PubMedDate not supplied

Dialysis as an on-line sample-pretreatment technique for column liquid chromatography: influence of experimental variables upon the determination of benzodiazepines in human plasma.

An evaluation is provided of dialysis, coupled on-line to column liquid chromatography, as a sample pretreatment procedure for macromolecule-containing biological samples. The influence of parameters such as acceptor phase flow rate, temperature, hydrophobicity of the analytes, pH, ionic strength and viscosity of the sample on the recovery and rate of dialysis is studied. In addition, methods to reduce the degree of drug-protein binding and thereby improve the recovery are reported. Diazepam, nitrazepam and oxazepam are used as model compounds. A method is reported for the fully automated determination of these compounds in human plasma using only 100 microliters of sample. Data on repeatability, linearity and detectability are given.

Anti-Anxiety Agents↗