Christoph Czerwenka

LC-MS/MS Analysis of Neonicotinoid Insecticides in Honey: Methodology and Residue Findings in Austrian Honeys

An analytical method for the simultaneous determination of residues of eight neonicotinoid insecticides and two metabolites in honey using LC-MS/MS was developed and validated. Two approaches of sample preparation were investigated, with the final method involving acetonitrile extraction and subsequent cleanup by dispersive solid-phase extraction (QuEChERS type). Validation was based on quintuplicate analysis at three fortification levels and showed satisfactory recoveries (60-114%) and high precision (RSDs between 2.7 and 12.8%). Low limits of detection and quantification could be achieved for all analytes ranging from 0.6 to 5 μg/kg and from 2 to 10 μg/kg, respectively. Investigations of Austrian honey samples revealed the presence of acetamiprid, thiacloprid, and thiamethoxam residues in honey; however, no sample exceeded the maximum residue limits. On average, flower honey samples contained neonicotinoid residues in higher quantities compared to forest honey samples.

Micro-HPLC and standard-size HPLC for the separation of peptide stereoisomers employing an ion-exchange principle.

Standard-size (4 mm ID) and micro-HPLC columns (0.5 mm ID) packed with a quinine-based ion-exchange type chiral stationary phase are comparatively evaluated for the separation of peptide enantiomers with up to six amino acid residues. The results show that downscaling the separation system in order to gain the advantages of miniaturized HPLC is possible without sacrificing separation power. Further, five different N-terminal protections (3,5-dinitrobenzoyl, 2,4-dinitrophenyl, 3,5-dinitrobenzyloxycarbonyl, carbazole-9-carbonyl, and 9-fluorenylmethoxycarbonyl) of the analytes are investigated regarding their effect on enantioselectivity. A comparison between a hydro-organic and a polar-organic mobile phase is also reported. The enantiomers of the peptides containing one to four amino acid residues were baseline resolved, while for the penta- and hexamers only partial separations were possible. In addition, all four stereoisomers of alanylalanine could be baseline separated.

Electrolyte and additive effects on enantiomer separation of peptides by nonaqueous ion-pair capillary electrophoresis using tert.-butylcarbamoylquinine as chiral counterion

Nonaqueous ion‐pair capillary electrophoresis separations of N‐protected (all‐R)/(all‐S) alanine peptide enantiomers with up to six amino acid residues using tert.‐butylcarbamoylquinine as selector and employing the partial filling technique are presented. The effects of various conditional parameters on separation were studied, namely chemical nature of the capillary wall, solvent composition of the background electrolyte (BGE), acid‐base‐ratio (equivalent to apparent pH), ionic strength and selector concentration. The influence of the solvent composition (methanol‐ethanol ratios) on resolution turned out to be rather complex. The separation of the peptide enantiomers was strongly altered by small changes in pH and ionic strength. An increase of the selector concentration was found to offer an easy way for enhancing enantioselectivity, although some drawbacks, e.g., elongation of run times, have to be considered. A method was developed that allowed the separation of N‐3,5‐dinitrobenzoyl oligoalanine enantiomers containing 1–6 amino acid residues in one run. Like in a recent high‐performance liquid chromatography (HPLC) study, separation selectivity thereby decreased from 1.541 (Ala), 1.340 (Ala2), 1.054 (Ala3), 1.029 (Ala4), 1.024 (Ala5) to 1.020 (Ala6). In addition, all four stereoisomers of N‐2,4‐dinitrophenyl‐ and N‐3,5‐dinitrobenzyloxycarbonyl‐protected alanylalanine could be baseline‐resolved.