Comparability of retention indices of polar substances at elevated temperatures

Summary The non-linear dependency of the retention indices of drugs on temperature is demonstrated hence an indication of the actual working temperature is essential. Fixed temperatures for the determination of retention indices of drugs are proposed. Interlaboratory comparisons of the retention indices of 14 drugs frequently encountered in analytical practice are made for the first time on two stationary phases in three laboratories and on four GC apparatus. The data show that, in comparison with literature values, the interlaboratory deviation is reduced by 1/3 to 1/2 if same temperatures are used. Standardization of the temperature of determination of the retention indices of drugs and unknown substances in biological specimens on OV-1 and OV-17 is proposed.     

Considerations on the planned use of a scientific balance on Mars

The balance is the most widely used complex measuring instrument in science and techniques. To install a balance on Mars is a challenge for numerous aspects of in situ measurements in the next decade. By means of a balance useful parameters could be determined and a variety of investigations could be carried out there. Possible applications of a balance on Mars are reviewed. Choice of type and demands on the balance with regard to the conditions on Mars are discussed. The first step is to test a load cell with strain gauge deflection sensor.     

Morphology and oxygen sensor response of luminescent Ir-labeled poly(dimethylsiloxane)/polystyrene polymer blend films

Polymer films consisting of a linear poly(dimethylsiloxane) end-functionalized with a luminescent Ir(III) complex (Ir-PDMS), blended with polystyrene (PS), function as optical oxygen sensors. The sensor response arises by quenching of the luminescence from the Ir(III) chromophore by oxygen that permeates into the polymer film. The morphology and luminescence oxygen sensor properties of blend films consisting of Ir-PDMS and PS have been characterized by fluorescence microscopy, atomic force microscopy, and scanning electron microscopy. The investigations demonstrate that microscale phase segregation occurs in the films. In blends that contain a relatively small amount of Ir-PDMS in PS (ca. 10 wt %), the Ir-PDMS exists as circular domains, with diameters ranging from 2 to 5 mum, surrounded by the majority PS phase. For larger weight fractions of Ir-PDMS in the blends, the film morphology becomes bicontinuous. A novel epifluorescence microscopy method is applied that allows the construction of Stern-Volmer quenching images that quantify the oxygen sensor response of the blend films with micrometer spatial resolution. These images provide a map of the oxygen permeability of the polymer blend films with a spatial resolution of ca. 1 mum. The results of this investigation show that the micrometer-sized Ir-PMDS domains display a 2-3-fold higher oxygen sensor response compared to the surrounding PS matrix. This result is consistent with the fact that PDMS is considerably more gas permeable compared to PS. The relationship of the microscale morphology of the blends to their performance as macroscale optical oxygen sensors is discussed.     

Behavior and characteristics of biogenic amines, ornithine and lysine derivatized with the o-phthalaldehyde-ethanethiol-fluorenylmethyl chloroformate reagent

The stability and characteristics of the ornithine (Orn), lysine (Lys), putrescine (Put), cadaverine (Cad), 1,7-diaminoheptane (Diah), spermidine (Spd) and spermine (Spm) derivatives obtained with the o-phthalaldehyde (OPA)-ethanethiol (ET)-fluorenylmethyl chloroformate (FMOC) reagent has been investigated. The stoichiometry of the introduced, two-step derivatization process has been followed by photodiode array (DAD) and fluorescence (FL) detections, simultaneously, while the composition of derivatives was confirmed by on-line HPLC-electrospray ionization (ESI) MS measurements. Depending on the composition of the OPA reagents, in addition to the secondary amino group-containing Spd and Spm, under common aqueous conditions also Orn and Lys do react with FMOC resulting in derivatives of various compositions. Applying the OPA-ET reagent of increasing methanol (Met) content (38-80%, v/v) the formation of the FMOC group containing Orn and Lys derivatives could be considerably decreased. Optimum elution condition (18 min, including equilibration) was developed for the simultaneous quantitation of Orn, Lys, Put, Cad, Diah, Spd and Spm, in the presence of the rest of protein amino acids. The practical utility of the method was demonstrated by the analysis of mouse tissues. Average reproducibility of quantitations, characterized with the relative standard deviation percentages of fluorescence intensities and UV responses, in order of listing, proved to be 2.1% and 2.1%, respectively.     

In-source H/D exchange and ion-molecule reactions using matrix assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry with pulsed collision and reaction gases

Controlled in-source ion-molecule reactions are performed for the first time in an external matrix assisted laser desorption ionization (MALDI) source of a Fourier transform ion cyclotron resonance mass spectrometer. The MALDI source with a hexapole ion guide that was originally designed to incorporate pulsed gas to collisionally cool ions (Baykut, G.; Jertz, R.; Witt, M. Rapid Commun. Mass Spectrom. 2000, 14, 1238-1247) has been modified to allow the study of in-source ion-molecule reactions. Upon laser desorption, a reaction gas was introduced through a second inlet and allowed to interact with the MALDI-generated ions trapped in the hexapole ion guide. Performing ion-molecule reactions in the high pressure range of the ion source prior to analysis in the ion cyclotron resonance (ICR) cell allows to maintain the ultra high vacuum in the cell which is crucial for high mass resolution measurements. In addition, due to the reaction gas pressure in the hexapole product ion formation is much faster than would be otherwise possible in the ICR cell. H/D exchange reactions with different peptides are investigated, as are proton-bound complex formations. A typical experimental sequence would be ion accumulation in the hexapole ion guide from multiple laser shots, addition of cooling gas during ion formation, addition of reaction gas, varied time delays for the ion-molecule reactions, and transmission of the product ions into the ICR cell for mass analysis. In this MALDI source H/D exchange reactions for different protonated peptides are investigated, as well as proton-bound complex formations with the reaction gas triethylamine. Amino acid sequence, structural flexibility and folding state of the peptides can be seen to play a part in the reactivity of such ions.     

Optically and thermally induced electron transfer pathways in hexakis[4-(N,N-diarylamino)phenyl]benzene derivatives

The optically and thermally induced electron transfer pathways of highly symmetrical (D(3)) hexaarylbenzene systems with six triarylamine redox sites have been investigated. Owing to slightly different local redox potentials, the radical trication could be selectively generated by electrochemical methods. This trication shows a strong intervalence charge-transfer band in the near infrared (NIR) that was measured by spectroelectrochemistry and analysed using multi-dimensional Mulliken-Hush theory. Quantum chemical AM1 CI calculations indicate that there is no optically induced concerted three-electron transfer that transforms the ground state into a state in which all three positively charged triarylamine moieties change place with their neutral neighbours. The potential energy surface of the ground state was constructed by using quadratic potentials. From this potential surface it is apparent that there is also no thermally allowed concerted three-electron transfer pathway. Instead, three consecutive one-electron transfer steps are necessary for this process.     

Indirect determination of the sum of chelons in drinking- and ground-waters by anodic stripping voltammetry

The complexing ligand EDTA can be determined as its complex with bismuth by indirect anodic stripping voltammetry down to 0.1 μg/L without a concentration step. Interfering copper and excess bismuth have to be removed by cation exchange, although in presence of these metals EDTA can be determined down to 0.5 μg/L only. If NTA, EDTA, and DTPA are present simultaneously, the accumulation curves for the corresponding bismuth-complexes can overlap, preventing a separate determination of the three chelons. Due to the interaction of NTA and DTPA with soil normally only EDTA is present in ground-waters. Similarly, EDTA also dominates in surface-waters. Thus it seems to be sufficient to determine the sum of the three chelons as EDTA (index of bismuth-complexation) using suitable electrochemical conditions.     

Two-photon absorption of dissociating TLI in strong laser fields

In a strong laser field (I=2 GW/cm²) TlI is dissociated by a two-photon process and the Tl fragment is detected state specifically. The yield of Tl 6p ² P _3/2 (Tl*) is measured as a function of the dissociation wavelength (480 nm–540 nm). If the dissociation wavelength is close to two-photon transitions of the Tl atom from 6p ² P _3/2 to np² P _1/2,3/2 or mf² F _5/2,7/2,n=10 ... 15,m=7 ... 12 dips in the yield are observed. These dips show a significant asymmetric broadening, compared to a free atomic transition and the observation is interpreted as an absorption process of the transient state of dissociating TlI during the laser pulse. By applying the Landau-Zener approximation for the potential crossing of dressed molecular states, we are able to describe the broadening and the power density dependence of the observations. Simulations show that the asymmetry is determined by the difference potential of the electronic states which are coupled by the laser field.     

New SbS2 strings in the BaSb2S4 structure

The new compound BaSb₂S₄ crystallizes in the monoclinic system (space group: $\text{P2}{}_1\text{c}$, No. 14) with a = 8.985(2) Å, b = 8.203(3) Å, c = 20.602(5) Å, β = 101.36(3)°. SbS₃ ψ tetrahedra and ψ-trigonal SbS₄ bipyramids are connected by common corners and edgers to infinite strings. These are arraged cross-wise in sheets perpendicular to the c axis.     

Einfluß der thermischen Vorgeschichte auf die Phasenumwandlungen von Dipalmitoyllecithin/Wasser-Mischungen

1. The influence of the thermal pretreatment (first and second heating run, annealing process) on the phase transition temperaturesT _m, enthalpiesΔ¯H _m and the specific heatc _sp of 1,2-dipalmitoyllecithin-water-mixtures was studied by differential scanning calonmetry.
2. The differences in theT _m- andΔ¯H _m-data of the main transition of the first and second heating run were found in the concentration rangex ^w<0,75. In the concentration rangex _W>0.75 these differences disappear.
3. The annealing process of a 1,2-dipalmitoyllecithin-water-mixturex _W=0,89 leads to a splitting of the main transition peak in two separate peaks with a different shape. This behaviour may imply that 1,2-dipalmitoyllecithin coexists in two different hydration states.