Simultaneous determination of arsenic, manganese, and selenium in biological materials by neutron-activation analysis

A new method was developed for the simultaneous determination of arsenic, manganese, and selenium in biological material by thermal-neutron activation analysis. The use of (81 m)Se as indicator for selenium permitted a reduction of activation time to 1 hr for a 1 g sample, and the possibility of loss of volatile compounds during irradiation could be dismissed. No pretreatment of the sample is required, and the radiochemical separation scheme is based on simple chemical operations, completed in less than 3 hr. A systematic experimental investigation of the performance characteristics of the method was carried out, including studies of the accuracy of the results. The actual precision achieved in routine application of the method in the analytical laboratory was in good agreement with the calculated precision, and the results are therefore well suited for statistical evaluation of differences at the ppM level in samples of biological tissue.     

THE USE OF SPIN LABEL OXIMETRY IN THE STUDY OF PHOTODYNAMIC INACTIVATION OF CHINESE HAMSTER OVARY CELLS

Spin label oximetry has been used to study the effects of photosensitizer hematoporphyrin on oxygen consumption in Chinese hamster ovary cells. These measurements demonstrate that, in the presence of the sensitizer, there occurs (i) an increase in total oxygen consumption during irradiation and (ii) a decrease in oxygen consumption following irradiation. These results are attributed to the effects of photosensitized oxygen consumption and decreased cellular respiration due to cell inactivation. Thus the inhibition of oxygen consumption after irradiation was shown to correlate with decreased cell survival measured in cell culture experiments. Possible mechanisms of inactivation and extensions of the oximetric approach are discussed.     

Electronic States of 1,5-Cyclooctadiyne Radical Cation and of Related Systems: The electronic structure of cis-bent carbon-carbon triple bonds

The photoelectron spectra of 1,5-cyclooctadiyne ( 2 ) and of 1,6-dithiacyclodeca-3,8-diyne ( 3 ) have been recorded. The first four ( 2 ) or six ( 3 ) PE. bands have been assigned as follows; in increasing order of ionization potentials: The relative sequence and the positions of the PE. bands are explained in terms of through-bond and through-space interactions between the basis π-orbitals and σ-orbitals of appropriate symmetry behaviour. An analysis of the PE. spectroscopic data for cyclooctyne ( 1 ) and for ( 2 ) indicates that a cis-bend of the acetylene moiety by θ < 20° leads to a split in energy of the in-plane and out-of-plane basis π-orbitals which is smaller than ∽ 0.2 eV. This is in agreement with the predictions derived from semiempirical models (MINDO/2, SPINDO) and qualitative orbital arguments. However, it is shown by using orbital localization procedures, that the rationales underlying the two semiempirical models differ significantly.     

Indirect determination of soluble trace elements in certified reference materials by neutron activation analysis

Since 1983 we have analyzedaqua regia extracts from environmental reference materials of 5 different soils and 4 different sludges by neutron activation analysis. Aqua regia as such is not accepted for irradiation in a nuclear reactor, and therefore the solution has to be evaporated to dryness, mixed and dried to constant weight before an aliquot can be taken and subjected to instrumental neutron activation analysis (INAA). Results for leachable Cr and Zn were found to display greater variability than results for total contents of these elements, and the reasons for this will be discussed.For the 1994 certification campaign for one soil and two sludges we have chosen to determine the total content of trace elements in these reference materials by INAA before and afteraqua regia leaching. The leachable contents are then found indirectly as a difference between the two results; in this way we eliminate the sources of uncertainty associated with the drying and handling of theaqua regia extracts, and we reduce the contributions from counting statistics.     

The development and validation of a novel LC–MS/MS method for the quantification of cenicriviroc in human plasma and cerebrospinal fluid

A high-performance liquid chromatography tandem mass spectrometric method was developed and validated for cenicriviroc (CVC) quantification in human plasma and cerebrospinal fluid (CSF). The method involved precipitation with acetonitrile and injecting supernatants onto the column. Separation was achieved on an XBridge C₁₈ column with a gradient elution of 0.1% formic acid in water and acetonitrile. Analyte detection was conducted in positive ion mode using selected reaction monitoring. The m/z transitions were: CVC (697.3 → 574.3) and CVC-d7 (704.4 → 574.3). Calibration curve ranged from 5 to 1000 ng/mL for plasma and from 0.241 to 15.0 ng/mL for CSF. The intra- and inter-day precision and accuracy were <15% for both plasma and CSF across four different concentrations. CVC recovery from plasma and artificial CSF was >90%. The method was utilized for the measurement of patients’ plasma and CSF samples taking a dose of 50, 150 and 300 mg q.d.     

Fe-contacts on InAs(100) and InP(100) characterised by conversion electron Mössbauer spectroscopy

We have grown 4 nm thin films of ⁵⁷Fe on InAs(100) and InP(100) surfaces by use of MBE and studied the samples by ⁵⁷Fe conversion electron Mössbauer spectroscopy. In the case of InAs, the Mössbauer spectrum showed a sextet due to α-Fe and a further magnetically split component with slightly smaller hyperfine field, which is attributed to interface components. This result indicates that there is a relatively sharp interface between Fe and InAs. On the contrary, the spectrum of the InP sample showed a sextet with very broad lines and a smaller average hyperfine field. This suggests a strong chemical reaction between iron and the substrate, which results in the formation of a poorly crystalline phase.