Time-domain fluorescence lifetime imaging for intracellular pH sensing in living tissues

pH sensing in living cells represents one of the most prominent topics in biochemistry and physiology. In this study we performed one-photon and two-photon time-domain fluorescence lifetime imaging with a laser-scanning microscope using the time-correlated single-photon counting technique for imaging intracellular pH levels. The suitability of different commercial fluorescence dyes for lifetime-based pH sensing is discussed on the basis of in vitro as well of in situ measurements. Although the tested dyes are suitable for intensity-based ratiometric measurements, for lifetime-based techniques in the time-domain so far only BCECF seems to meet the requirements of reliable intracellular pH recordings in living cells.     

Microwave-assisted Kumada-type cross-coupling reactions of iodinated carba-closo-dodecaborate anions

The microwave-assisted Pd-catalyzed Kumada-type cross-coupling reaction of iodinated carba-closo-dodecaborate anions requires smaller amounts of Grignard reagent and catalyst and results in higher yields in much shorter reaction times in comparison to a reaction with conventional heat transfer. 12-Ph(3)P-closo-1-CB(11)H(11) was identified as the side product of the cross-coupling reactions that use [PdCl(2)(PPh(3))(2)]. The inner salt, which is the first example for a {closo-1-CB(11)} cluster with a B-P bond, was selectively synthesized via a related microwave-assisted cross-coupling protocol and characterized by NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction. In addition, the crystal structures of the tetraethyl ammonium salts of [12-Ph-closo-1-CB(11)H(11)](-), [12-(4-MeOC(6)H(4))-closo-1-CB(11)H(11)](-), and [12-(H(2)C═(Me)CC≡C)-closo-1-CB(11)H(11)](-) are described.     

Solid-phase dynamic extraction for the enrichment of polar volatile organic compounds from water

Headspace solid-phase dynamic extraction coupled to gas chromatography-mass spectrometry (HS-SPDE-GC/MS) was evaluated for the trace determination of polar volatile organic compounds (PVOC) from aqueous matrices. The target compounds included 3 ethers and 12 alcohols. Four SPDE needle coatings with different phase polarities and sorption properties (WAX, 1701, PDMS, PDMS/AC) were tested. The effects of extraction temperature, number of extraction cycles, and ionic strength on partitioning of the target compounds have been investigated in detail, including the determination of salting-out constants for the investigated compounds. Lowest method detection limits (MDLs) were obtained with the WAX and the PDMS/AC phase. The WAX phase showed MDLs for ethers in the range of 0.06 microg/L (MTBE) to 0.8 microg/L (1,4-dioxane) and for alcohols between 0.02 microg/L (3-methyl-1-pentanol) and 3.5 microg/L (1-propanol). The evaluated MDLs for ethers with the PDMS/AC were in the range 0.06 microg/L (MTBE) to 1.2 microg/L (1,4-dioxane) and for alcohols between 0.004 microg/L (1-hexanol) and 4.9 microg/L (ethanol). Using either of these two phases, SPDE provides comparable or better sensitivities for the investigated compounds than other enrichment techniques, high sample throughput because of full automation, and short extraction times as well as a high robustness of the extraction phase because of its protection inside the steel needle. SPDE applicability has been demonstrated for the determination of fusel oils in different alcoholic beverages.     

A new approach to determine method detection limits for compound-specific isotope analysis of volatile organic compounds

Compound-specific isotope analysis (CSIA) has been established as a useful tool in the field of environmental science, in particular in the assessment of contaminated sites. What limits the use of gas chromatography/isotope ratio mass spectrometry (GC/IRMS) is the low sensitivity of the method compared with GC/MS analysis; however, the development of suitable extraction and enrichment techniques for important groundwater contaminants will extend the fields of application for GC/IRMS. So far, purge and trap (P&T) is the most effective, known preconcentration technique for on-line CSIA with the lowest reported method detection limits (MDLs in the low microg/L range). With the goal of improving the sensitivity of a fully automated GC/IRMS analysis method, a commercially available P&T system was modified. The method was evaluated for ten monoaromatic compounds (benzene, toluene, para-xylene, ethylbenzene, propylbenzene, isopropylbenzene, 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, fluorobenzene) and ten halogenated volatile organic compounds (VOCs) (dichloromethane, cis-1,2-dichloroethene, trans-1,2-dichloroethene, carbon tetrachloride, chloroform, 1,2-dichloroethane, trichloroethene, tetrachlorethene, 1,2-dibromoethane, bromoform). The influence of method parameters, including purge gas flow rates and purge times, on delta13C values of target compounds was evaluated. The P&T method showed good reproducibility, high linearity and small isotopic fractionation. MDLs were determined by consecutive calculation of the delta13C mean values. The last concentration for which the delta13C value was within this iterative interval and for which the standard deviation was lower than +/-0.5 per thousand for triplicate measurements was defined as the MDL. MDLs for monoaromatic compounds between 0.07 and 0.35 microg/L are the lowest values reported so far for continuous-flow isotope ratio measurements using an automated system. MDLs for halogenated hydrocarbons were between 0.76 and 27 microg/L. The environmental applicability of the P&T-GC/IRMS method in the low-microg/L range was demonstrated in a case study on groundwater samples from a former military air field contaminated with VOCs.     

Determination of volatile organic compounds by solid-phase microextraction—gas chromatography-differential mobility spectrometry

Up to now the analysis of aqueous samples by ion mobility spectrometry is a challenge due to the lack of suitable sample introduction systems. But just the introduction of asymmetric field strengths leading to a higher selectivity and sensitivity, this technique is of growing interest for on-site analysis of contaminated water. In this work, first results for the preparation of a portable GC-DMS system are presented. A differential mobility spectrometer (DMS) with a ⁶³Ni ionization source has been used as a detector for the gaschromatographic separation of benzene, toluene, ethylbenzene m-, o-, and p-xylene (BTEX) in water. Separation from the matrix and pre-concentration of the analytes was achieved by solid-phase microextraction (SPME). The influence of the different chromatographic parameters, extraction conditions and differential mobility spectrometry settings on the sensitivity and signal shape were investigated. Results of the optimization of the analytical method as well as analytical validation parameters such as method detection limit, limit of quantification and the repeatability are discussed. Additionally, the applicability of the method was demonstrated by the analysis of a real surface water sample.     

Synergetic driving concepts for bundled miniature ultrasonic linear motors

Rotary ultrasonic motors have found broad industrial application in camera lens drives and other systems. Linear ultrasonic motors in contrast have only found limited applications. The main reason for the limited range of application of these very attractive devices seems to be their small force and power range. Attempts to build linear ultrasonic motors for high forces and high power applications have not been truly successful yet. To achieve larger force and higher power, multiple miniaturized motors can be combined. This approach, however, is not as simple as it appears at first glance. The electromechanical behaviour of the individual motors differs slightly due to manufacturing and assembly tolerances. The individual motor characteristics are strongly dependent on the driving parameters (frequency, voltage, temperature, pre-stress, etc.) and the driven load and the collective behaviour of the swarm of motors is not just the linear superposition of the individual drive's forces. Thus, the bundle of motors has to be synchronized and controlled appropriately in order to obtain an optimized drive that is not oversized and costly. We have investigated driving and control strategies of a set of linear ultrasonic motors. Our contribution will be divided into three main parts. In part I ultrasonic linear motors will be introduced. In part II driving strategies for a single motor as well as for a bundle of motors will be presented. These concepts will be verified by simulation results and experimental data. In part III a simplified model for the motor's electromechanical behaviour will be given.     

On the time transformation of mixed integer optimal control problems using a consistent fixed integer control function

Nonlinear control systems with instantly changing dynamical behavior can be modeled by introducing an additional control function that is integer valued in contrast to a control function that is allowed to have continuous values. The discretization of a mixed integer optimal control problem (MIOCP) leads to a non differentiable optimization problem and the non differentiability is caused by the integer values. The paper is about a time transformation method that is used to transform a MIOCP with integer dependent constraints into an ordinary optimal control problem. Differentiability is achieved by replacing a variable integer control function with a fixed integer control function and a variable time allows to change the sequence of active integer values. In contrast to other contributions, so called control consistent fixed integer control functions are taken into account here. It is shown that these control consistent fixed integer control functions allow a better accuracy in the resulting trajectories, in particular in the computed switching times. The method is verified on analytical and numerical examples.