Polycapillary‐optics‐based micro‐XANES and micro‐EXAFS at a third‐generation bending‐magnet beamline

A focusing system based on a polycapillary half‐lens optic has been successfully tested for transmission and fluorescence µ‐X‐ray absorption spectroscopy at a third‐generation bending‐magnet beamline equipped with a non‐fixed‐exit Si(111) monochromator. The vertical positional variations of the X‐ray beam owing to the use of a non‐fixed‐exit monochromator were shown to pose only a limited problem by using the polycapillary optic. The expected height variation for an EXAFS scan around the Fe K‐edge is approximately 200 µm on the lens input side and this was reduced to ～1 µm for the focused beam. Beam sizes (FWHM) of 12–16 µm, transmission efficiencies of 25–45% and intensity gain factors, compared with the non‐focused beam, of about 2000 were obtained in the 7–14 keV energy range for an incoming beam of 0.5 × 2 mm (vertical × horizontal). As a practical application, an As K‐edge µ‐XANES study of cucumber root and hypocotyl was performed to determine the As oxidation state in the different plant parts and to identify a possible metabolic conversion by the plant.     

Study of the Influence of Different Diphenol Compounds on Soil Microbial Activity by Microcalorimetry

Microcalorimetry was applied to follow the toxic effects caused by different diphenol compounds on microbial activity of Chinese fir soil. The activity of the microorganisms in soil was stimulated by adding 0.3 mL of a nutrient solution containing 2.5 mg of glucose and 2.5 mg of ammonium sulfate and the measurements were performed under a 35% controlled humidity at 28°C. Power‐time curves recorded on a microcalorimeter were followed by increasing the amount of diphenol compounds, which affected directly the total thermal effects evolved by the microorganisms. The curves showed a synergism on total thermal effect obtained by the addition of 2000 mg·kg^?1 of resorcinol, causing a consumption of resorcinol by the microorganisms as a new source of nutrients. Above this dose, the total thermal effect decreased exponentially. However, the addition of catechol and hydroquinone caused the total thermal effects to decrease directly. It was concluded that the increase in the diphenol concentration strongly affected the microbial life in this ecosystem. Microcalorimetry appears as a suitable technique to carry out both qualitative and quantitative comparative studies of microbial activity in soil.     

Comparative study of analytical inductively-coupled argon-plasma discharges using different outer gases

The analytical capabilities of high power (2-4 kW) ICPs with argon as inner and intermediate gas and different outer gases (argon, nitrogen, oxygen and air) were studied under optimum and compromise operating conditions. Under the optimum conditions, the lowest detection limits for elements with sensitive atom lines (C, B, Zn) or ion lines (Mg, Mn, Fe, Cr, Ti, V) were achieved with argon as outer gas and an observation height of 13 mm. Under compromise conditions (3 kW, aerosol gas gauge-pressure 3 bar) the lowest detection limits for the atom lines were also found with a pure argon plasma at an observation height of 13 mm. For ion lines, however, the argon/oxygen and argon/nitrogen plasmas and an observation height of 8 mm were better. The detection limits were poorer in the presence of an aluminium matrix; under the optimum operating conditions, the relative increase in detection limit was smaller with the argon/oxygen and argon/air ICPs than with the pure argon or argon/nitrogen ICPs. It was found that the interferences arising from an easily ionizable matrix are lower with a diatomic gas than with argon as outer gas. The interferences when the argon/nitrogen, argon/oxygen and argon/air plasmas are used are similar and practically independent of the nebulizer-gas pressure applied.     

Studying the toxic effect of cadmium and hexavalent chromium on microbial activity of a soil and pure microbe

Using TAM III multi-channel calorimetry combined with direct microorganism counting (bacteria, actinomycetes and fungi) under laboratory conditions, we determined the microbial population count, resistance and activity toward cadmium (Cd(II)) and hexavalent chromium (Cr(VI)) toxicity in soil. The thermokinetic parameters, which can represent soil microbial activity, were calculated from power-time curves of soil microbial activity obtained by microcalorimetric measurement. Simultaneous application of the two methods showed that growth rate constant (k), peak-heat output power (P _max) and the number of living microorganisms decreased with increasing concentration of Cd and Cr. The accumulation of Cr on E. coli was conducted by HPLC-ICP-MS. Cr⁶⁺ accumulation by Escherichia coli was increased steadily with increasing Cr⁶⁺ concentration. The results revealed that the change in some thermo-kinetic parameters could have good corresponding relationship with metal accumulation. Our work also suggests that microcalorimetry is a fast, simple, more sensitive, on-line and in vitro method that can be easily performed to study the toxicity of different species of heavy metals on microorganism compared to other biological methods, and can combine with other analytic methods to study the interaction mechanism between environmental toxicants and microbes.