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Biomedical subjects

H Malissa

Publications and source records attributed to H Malissa.

11 recordsLinked to original sources
PubMed2006

Profiling preparations of recombinant birch pollen allergen Bet v 1a with capillary zone electrophoresis in pentamine modified fused-silica capillaries.

Three preparation batches of the recombinant birch pollen allergen Bet v 1a have been analyzed by capillary zone electrophoresis (CZE) using a separation electrolyte consisting of 100 mmol L(-1) phosphate at pH 6.50 with 2.0 mmol L(-1) tetraethylenepentamine (TEPA) added. TEPA improved the resolution by wall shielding and selective attachment to allergens, but reduced migration repeatability at concentrations >2.0 mmol L(-1). Heterogeneity of preparations determined by CZE and electrospray ionization-quadrupole-time-of flight-MS were in accordance and revealed chemically modified (carbamylated) allergens in one of the preparations. The method was validated according to the ICH-guidelines. Repeatability of effective electrophoretic mobility (mu(eff)) was <0.55% R.S.D. (n = 5). Migration time corrected peak areas were used for quantification. Limit of quantification (LOQ) was 25 microg mL(-1) for the major isoform Bet v 1a, based on a signal-to-noise ratio of 10, and detector response was linear between LOQ and 0.90 mg mL(-1). Purity of the different rBet v 1a preparations was determined to be between 40 and 92% depending on the manufacturing protocol.

Allergens↗
PubMed2001

Multiclass/multiresidue method for monitoring widely applied plant protecting agents in air during field dispersion work.

A multiclass/multiresidue method for surveying the uptake of plant protecting chemicals by inhalation during field spraying work is described. Eleven nowadays mainly dispersed compounds, which cover a wide range of chemical properties, are analysed in air with personal active sampling and in one single analytical run. This has the advantage, that one basic method only needs to be implemented, calibrated and validated in a laboratory to perform varying monitoring tasks without changing the method itself. Samples were taken with Tenax sorbent tubes operated to collect the active compounds simultaneously in the vapour state, in aerosol state or bound to particles. The procedure consists of four unit operations only: sampling, elution, dilution and HPLC measurement, and is described in SOP-format. The limits of quantification, calculated as method detection limits, were between 1 and 9 microg m(-3) based on 1 m3 air volume sampled (8 h). Method performance was characterised by way of generated test atmospheres and field spraying trials.

Air↗
PubMed2001

Determination of quaternary alkylammonium compounds by capillary zone electrophoresis and indirect UV detection as a real alternative to ion chromatography with suppressed conductivity detection.

A capillary electrophoretic (CE) method for the determination of residual mid-chain alkyltrimethylammonium compounds in the pharmaceutical product Welchol (an alkylated, crosslinked polyallylamine) was developed, validated and compared with the existing ion chromatographic (IC) method with suppressed conductivity detection. Excellent reproducibilities of migration times (RSD<0.5% within a series of 55 sample injections) and relative peak areas (RSD<2%) make the method suitable for quality control as a real alternative to IC. Limits of quantification of 0.01% w/w of each impurity in the active substance were achieved. Buffer systems for indirect UV detection based on creatinine as visualization reagent with different inorganic and organic acids (phosphoric, sulfuric, formic, acetic, oxalic and citric acid) and their effect on selectivity to ten quaternary ammonium compounds were studied. Selectivity changes were observed for the di- and trivalent analytes depending on the buffer applied. Also, the influence of acetonitrile, methanol, 1,4-dioxane and tetrahydrofuran on selectivity was investigated. In addition, CE-MS experiments were carried out in order to identify several impurities in the product.

Chromatography, Liquid↗
PubMed2001

Potential of microbore HPLC within a multiresidue method for the trace analysis of plant-protective substances in water.

The performance of microbore HPLC as a "measurement channel" within a true multiclass/multiresidue method for monitoring plant protectants in raw and potable water is demonstrated. The method has a modular design and consists of a non-selective sampling and preparation line generating 250 microL of an "extract" from a 100-mL water sample; this extract can be introduced to up to four measurement channels, as required by the analytical task. The microbore HPLC channel can be used to quantify 34 plant protectants in the 0.1 microg L(-1) concentration range by use of diode-array detection at seven different wavelengths. A solvent change is necessary to link sample preparation to microbore HPLC; this uses 50 microL of the "extract" and is accomplished directly in an autosampler vial. Performance characteristics were evaluated for tap water spiked at 0.2 microg L(-1). Average recoveries were between 65 and 100% and method detection limits were 0.07 microg L(-1) or better. The ability to provide comparable and accurate results was proven by participation in an interlaboratory comparison trial. The procedure for preparing microbore columns from 750 microm i.d. PEEK tubing is described in detail to enable the reader to prepare his own columns. The reproducibility of this preparation procedure was proven by an analysis-of-variance test.

Calibration↗
PubMed1992

Direct serum injection in ion chromatography on packing materials with a semi-permeable surface.

Reversed-phase packing materials with restricted access of proteins to the hydrophobic sites were tested for their applicability in the ion-interaction chromatography of anions. Especially C8-modified silica, which had been coated with a hydrophilic polymer acting as a semi-permeable barrier, could be used successfully for the separation of several anions in a proteinaceous matrix without removing the proteins prior to injection. In combination with UV or conductivity detection, this technique allows the determination of some physiologically important anions in serum samples.

Anions↗
PubMedDate not supplied

Determination of regularly distributed plant protectants in raw and drinking waters, using a multiresidue method with cyclodextrin-modified micellar electrokinetic chromatography.

Eighteen plant protectant compounds were separated and determined by cyclodextrin-modified micellar electrokinetic chromatography (MEKC) in a multiclass/multiresidue method. The pesticides included are those dispersed in the greatest amounts today over agricultural acreage, and they represent 8 different classes of compounds (azoles, benzoic acids, chloroacetanilides, phenoxy acids, phenylureas, sulfonylureas, thiocarbamates, and triazines) covering a wide range of chemical reactivities and physicochemical properties. A 500 mL sample of tap water is preconcentrated by solid-phase extraction (SPE) with 300 mg combined polystyrene-divinylbenzene and methacrylate macroporous resins. Trapped analytes are eluted collectively with diethyl ether. Concentration and solvent change yield 250 microL of an acetone "concentrate," which is further worked up and concentrated 1:10 to produce the MEKC injection solution containing 10 mmol/L sodium dodecyl sulfate (SDS) surfactant. For MEKC, 2 phosphate/SDS buffer systems were designed, each allowing complete separation of all pesticides in a single run. Sensitivity was enhanced by a self-etched bubble cell and an injection procedure which employs stacking at reversed polarity. The ability of MEKC to determine plant protectants in raw and drinking waters at the 0.1 microgram/L level, as demanded by the guidelines of the European Union, was demonstrated with spiked tap waters. Recoveries were between 75 and 110%, and limits of quantification, evaluated as method detection limits according to guidelines of the U.S. Environmental Protection Agency, ranged between 0.03 and 0.10 microgram/L. The precisions of the relative migration times were all below 0.5%.

Acetic Acid↗