This study examines the effect of bacterial metabolism on the adsorption of Cd onto Gram‐positive and Gram‐negative bacterial cells. Metabolically active Gram‐positive cells adsorbed significantly less Cd than non‐metabolizing cells. Gram‐negative cells, however, showed no systematic difference in Cd adsorption between metabolizing and non‐metabolizing cells. The effect of metabolism on Cd adsorption to Gram‐positive cells was likely due to an influx of protons in and around the cell wall from the metabolic proton motive force, promoting competition between Cd and protons for adsorption sites on the cell wall. The relative lack of a metabolic effect on Cd adsorption onto Gram‐negative compared to Gram‐positive cells suggests that Cd binding in Gram‐negative cells is focused in a region of the cell wall that is not reached, or is unaffected by this proton flux. Thermodynamic modeling was used to estimate that proton pumping causes the pH in the cell wall of metabolizing Gram‐positive bacteria to decrease from the bulk solution value of 7.0 to approximately 5.7.

A number of recent measurement series of nonmethane hydrocarbons (NMHCs) based on in situ analysis report very low alkene concentrations in the remote troposphere. It was speculated that during preconcentration or thermal desorption of the sample, atmospheric ozone may react with the reactive hydrocarbons, e.g., alkenes. Therefore the behavior of ozone in different inlet systems at different conditions was investigated, in order to indicate where O3 interferences may arise. The results for the inlet and preconcentration system used for our measurements show that up to 50% of the ambient ozone is lost during passage of a heated stainless steel inlet line. The remaining ozone is preconcentrated together with the hydrocarbons. During the process of thermal desorption the remaining ozone is lost within minutes leading to a loss of reactive hydrocarbons of the order of 2–10% which is usually less than the error of measurement. These results were confirmed when different amounts of ozone were added to samples of pressurized air with moderate and low NMHC concentrations. For ozone mixing ratios of up to 100 ppb no significant change in the concentration of light alkenes was observed. The results show that our system used for cryogenic preconcentration of NMHC with subsequent thermal desorption is suitable for quantitative measurements even of reactive light alkenes in the atmosphere without an additional ozone trap.

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