Dieter Freitag

Quantitative and qualitative precision improvements by effective mobility-scale data transformation in capillary electrophoresis analysis.

By transforming the time‐based x‐axis of electropherograms in capillary zone electrophoresis (CZE) into the corresponding effective mobility‐scale, we propose a simple and robust data representation for a better qualitative and quantitative capillary electrophoresis (CE) analysis. The time scale of the raw electrophoretic data (detection signal versus time) is transformed into an effective electrophoretic mobility scale (μeff‐scale) with account of the electroosmotic flow (EOF) peak or of an internal standard of known effective mobility. With the new scaling (detection signals versus effective mobility), the obtained electropherograms are more representative of the velocity‐based electrophoretic separation and the comparison of complete electropherograms is directly possible. This is of importance when tracking peaks in real samples where alteration in EOF stability can occur or when comparing electrophoretic runs from different experimental setups (independence in column length and voltage). Beside the qualitative possibilities, a quantitative improvement is achieved in the μeff‐scale with significant better peak area reproducibility and equal to more precision in quantitative analysis than with the primary time‐scale integration.*

Effect of dissolved humic material (DHM) on bioavailability of some organic xenobiotics to Daphnia magna

AbstractThe effects of dissolved humic material (DHM) on the bioconcentration of six organic xenobiotics—chlorobenzuron (CCU), diflubenzuron (DFB), terbutylazine (TBA), diazinon, 4-chloroaniline (4-CA) and pentachlorophenol (PCP)—to Daphnia magna (Straus) in laboratory experiments were investigated. Commercial Aldrich humic acids (A-DHM) were used as the sources of DHM. 24 h bioconcentrations (BC24) for these xenobiotics were determinated in the presence of 0, 0.5, 5.0, 10, 20 and 50 mg L−1TOC. With diazinon, 4-CA and PCP 48 h bioconcentrations (BC48) were determined as well.The bioconcentrations (BC) of CCU and diazinon, were significantly reduced, when DHM concentrations increased. The effect on the other chemicals was insignificant. With diazinon DHM exhibited a distinct time-dependency: BC48 lay significantly below BC24-values.The observed reduction of bioavailability to Daphnia magna was attributed to the binding of the organic chemicals to DHM, which was quantitatively measured for CCU by an equilib...

Capillary zone electrophoretic studies on Norwegian surface water natural organic matter

Abstract Capillary zone electrophoresis (CZE) is a useful tool for the analysis of the electrophoretic behavior of anionic polyelectrolytes like humic substances. CZE was used to compare natural organic matter (NOM) with high ash content obtained by reverse osmosis (RO) and low temperature, low pressure evaporation (Ev.) from different Norwegian surface water sources. The quantitative relation between the resulting electrophoretic signals (peak height and area) and the carbon amount of the injected NOM samples was found linear. The NOM gave homogeneous signals in CZE, with a distribution of the detection signals around an average electrophoretic mobility (AEM) corresponding to the charge density distribution of the NOM, governed by the distribution of their molecular sizes and acidities. Like humic substances, NOM only appears as anions in capillary electrophoresis (CE), but the high ash content of these samples and the presence of metals strongly influenced their mobilities at lower pH. CZE could be used as a tool for the rapid evaluation of the average net charge and the molecular radius of the NOM at pH 5.1.

Interactions of hydroxy-s-triazines with sodium dodecyl sulfate-micelles investigated by micellar capillary electrophoresis.

The electrophoretic behavior of fourteen 4,6‐diamino‐s‐triazines was investigated in the presence of an anionic surfactant (sodium dodecyl sulfate, SDS) using micellar capillary electrophoresis (MCE). The measurements were performed at the pH of zero charge of the hydroxytriazines and the existence of strong ionic and H‐bond interactions of hydroxy‐s‐triazine species with the anionic micelles could be shown. Their migration behavior was compared to the n‐octanol‐water partition coefficients (log Kow) measured with reverse‐phase HPLC and calculated with different fragment contribution methods. A partition model was proposed to understand the interactions of the three major hydroxy‐s‐triazine species: cationic, anionic and neutral (presenting enol and keto forms) with the charged SDS micelles taken as model for charged natural polyelectrolytes like humic substances. These results strongly indicate that hydroxy‐s‐triazines are polarized in the presence of the charged micelles and that they are essentially present in their keto form in the micellar phase (and enol form in the water phase), confirming previous studies suggesting the presence of zwitterionic resonance structures at a neutral pH around their isoelectric point.