Georg Niessner - Academia.edu (original) (raw)
Papers by Georg Niessner
Rapid multiresidue screening method for the determination of pesticides in plant materials
Journal of Chromatography A, 1996
A multiresidue screening method for pesticides in plant materials is presented. Aliquots (10 g) o... more A multiresidue screening method for pesticides in plant materials is presented. Aliquots (10 g) of samples are extracted with acetone-water, the extract is concentrated by reversed-phase solid-phase extraction and cleaned up on Florisil. The pesticides are analyzed by gas chromatography in combination with electron-capture detection or mass spectrometry in the negative chemical ionization mode. The method has been tested for 23 pesticides in 19 different plant materials at a level of 0.02–3 ppm. The advantages of mass spectrometric detection with negative chemical ionization for the determination of pesticides are discussed.
Analytica Chimica Acta, 2000
Two sample preparation methods for the determination of dibenzylamine (DBA) in artificial saliva ... more Two sample preparation methods for the determination of dibenzylamine (DBA) in artificial saliva leachates from rubber baby bottle nipples have been developed, using either solid-phase extraction (SPE) with N-vinylpyrrolidone/divinylbenzene as the sorbent or solid-phase microextraction (SPME) with a polyacrylate coated fiber. The baby bottle nipples were immersed into artificial saliva for 6 h, a part of the solution was brought to pH 9 for SPE or pH 10 for SPME and the analyte was extracted by SPE or SPME. After elution with ethyl acetate (SPE) or thermal desorption (SPME) DBA was determined by gas chromatography with mass spectrometric detection. The main advantages of SPE were superior ruggedness and stability as well as the possibility of preparing several samples simultaneously. SPME offered a greater sensitivity and much smaller sample volumes were required. The results obtained for the investigated rubber baby bottle nipples were almost identical with both the methods showing deviations of less than 3%.
Multiresidue screening methods for the determination of pesticides in plant materials
Journal of Chromatography A, 1999
ABSTRACT
Monatshefte fuer Chemie/Chemical Monthly, 1998
The combination of capillary zone electrophoresis with potentiometric detection has been investig... more The combination of capillary zone electrophoresis with potentiometric detection has been investigated for the determination of chelating agents such as diethylenetriaminepentaacetic acid. The detector consists of a metallic copper electrode with a diameter of 100 mm arranged in an end-capillary con®guration. The electrode potential depends on the concentration of copper ions at the electrode surface and therefore decreases when chelating agents pass the electrode. In combination with UV detection, both free ligands and metal complexes could be detected.
Fresenius' Journal of Analytical Chemistry, 1998
A simple method for the determination of the urinary tract antibiotic nifuroxazide has been devel... more A simple method for the determination of the urinary tract antibiotic nifuroxazide has been developed. The electrochemical reduction of the nitro group at mercury and carbon paste electrodes can be used for the determination with and without adsorptive preconcentration. The influence of parameters like pH of the background electrolyte, preconcentration potential and preconcentration time on the sensitivity of the method has been studied. Modification of the carbon paste by addition of nonpolar polystyrene/divinylbenzene particles has been investigated to enhance the adsorption properties of the surface. Concentrations as low as 10 ng/mL could be determined in urine without interferences.
Moisture Sensor Arrangement
Anionenaustausch-Festphasenextraktion von Huminstoffen zur Bestimmung der komplexgebundenen Schwermetalle in natürlichen Gewässern mit hohem Gehalt an gelöstem organischem Kohlenstoff
Monatshefte fuer Chemie/Chemical Monthly
A solid phase extraction material based on a copolymer of styrene and divinylbenzene was develope... more A solid phase extraction material based on a copolymer of styrene and divinylbenzene was developed for the extraction of heavy metals complexed by humic and fulvic acids in water. The sorbent was synthesized by a modi®ed multistep activated swelling polymerization procedure; anion exchange functionalities were introduced by chemical modi®cation or by coating of the particle surface. These materials allowed the extraction of humic substances from water samples at their natural pH. The extract or the sorbent containing the humic substances was digested by dry ashing with sulfuric acid, and the metals Cu, Zn, Pb, and Cd were determined by differential pulse anodic stripping voltammetry. With this method, the four metals could be determined with recoveries between 87 and 99% at concentrations down to 50 ng/l.
Rapid multiresidue screening method for the determination of pesticides in plant materials
Journal of Chromatography A, 1996
A multiresidue screening method for pesticides in plant materials is presented. Aliquots (10 g) o... more A multiresidue screening method for pesticides in plant materials is presented. Aliquots (10 g) of samples are extracted with acetone-water, the extract is concentrated by reversed-phase solid-phase extraction and cleaned up on Florisil. The pesticides are analyzed by gas chromatography in combination with electron-capture detection or mass spectrometry in the negative chemical ionization mode. The method has been tested for 23 pesticides in 19 different plant materials at a level of 0.02–3 ppm. The advantages of mass spectrometric detection with negative chemical ionization for the determination of pesticides are discussed.
Analytica Chimica Acta, 2000
Two sample preparation methods for the determination of dibenzylamine (DBA) in artificial saliva ... more Two sample preparation methods for the determination of dibenzylamine (DBA) in artificial saliva leachates from rubber baby bottle nipples have been developed, using either solid-phase extraction (SPE) with N-vinylpyrrolidone/divinylbenzene as the sorbent or solid-phase microextraction (SPME) with a polyacrylate coated fiber. The baby bottle nipples were immersed into artificial saliva for 6 h, a part of the solution was brought to pH 9 for SPE or pH 10 for SPME and the analyte was extracted by SPE or SPME. After elution with ethyl acetate (SPE) or thermal desorption (SPME) DBA was determined by gas chromatography with mass spectrometric detection. The main advantages of SPE were superior ruggedness and stability as well as the possibility of preparing several samples simultaneously. SPME offered a greater sensitivity and much smaller sample volumes were required. The results obtained for the investigated rubber baby bottle nipples were almost identical with both the methods showing deviations of less than 3%.
Multiresidue screening methods for the determination of pesticides in plant materials
Journal of Chromatography A, 1999
ABSTRACT
Monatshefte fuer Chemie/Chemical Monthly, 1998
The combination of capillary zone electrophoresis with potentiometric detection has been investig... more The combination of capillary zone electrophoresis with potentiometric detection has been investigated for the determination of chelating agents such as diethylenetriaminepentaacetic acid. The detector consists of a metallic copper electrode with a diameter of 100 mm arranged in an end-capillary con®guration. The electrode potential depends on the concentration of copper ions at the electrode surface and therefore decreases when chelating agents pass the electrode. In combination with UV detection, both free ligands and metal complexes could be detected.
Fresenius' Journal of Analytical Chemistry, 1998
A simple method for the determination of the urinary tract antibiotic nifuroxazide has been devel... more A simple method for the determination of the urinary tract antibiotic nifuroxazide has been developed. The electrochemical reduction of the nitro group at mercury and carbon paste electrodes can be used for the determination with and without adsorptive preconcentration. The influence of parameters like pH of the background electrolyte, preconcentration potential and preconcentration time on the sensitivity of the method has been studied. Modification of the carbon paste by addition of nonpolar polystyrene/divinylbenzene particles has been investigated to enhance the adsorption properties of the surface. Concentrations as low as 10 ng/mL could be determined in urine without interferences.
Moisture Sensor Arrangement
Anionenaustausch-Festphasenextraktion von Huminstoffen zur Bestimmung der komplexgebundenen Schwermetalle in natürlichen Gewässern mit hohem Gehalt an gelöstem organischem Kohlenstoff
Monatshefte fuer Chemie/Chemical Monthly
A solid phase extraction material based on a copolymer of styrene and divinylbenzene was develope... more A solid phase extraction material based on a copolymer of styrene and divinylbenzene was developed for the extraction of heavy metals complexed by humic and fulvic acids in water. The sorbent was synthesized by a modi®ed multistep activated swelling polymerization procedure; anion exchange functionalities were introduced by chemical modi®cation or by coating of the particle surface. These materials allowed the extraction of humic substances from water samples at their natural pH. The extract or the sorbent containing the humic substances was digested by dry ashing with sulfuric acid, and the metals Cu, Zn, Pb, and Cd were determined by differential pulse anodic stripping voltammetry. With this method, the four metals could be determined with recoveries between 87 and 99% at concentrations down to 50 ng/l.