Ab Initio SCF Calculations Relating to the Cls Chemical Shifts for Some Alkanes

Ab initio calculatios have been made for a series of simple alkanes and the atomic charges have been estimated in two ways, using the Mulliken population analysis and also using an analysis due to Karlström where the charges are fitted to describe the electrical moments derived from the SCF wave function. Also the orbital energies were calculated. The results were used to interpret experimental data of the carbon core electron binding energies. It is found that the Karlström technique is best suited to describe the XPS data.     

Global calculations of ground-state axial shape asymmetry of nuclei

Important insight into the symmetry properties of the nuclear ground-state (gs) shape is obtained from the characteristics of low-lying collective energy-level spectra. In the 1950s, experimental and theoretical studies showed that in the gs many nuclei are spheroidal in shape rather than spherical. Later, a hexadecapole component of the gs shape was identified. In the 1970-1995 time frame, a consensus that reflection symmetry of the gs shape was broken for some nuclei emerged. Here we present the first calculation across the nuclear chart of axial symmetry breaking in the nuclear gs. We show that we fulfill a necessary condition: Where we calculate axial symmetry breaking, characteristic gamma bands are observed experimentally. Moreover, we find that, for those nuclei where axial asymmetry is found, a systematic deviation between calculated and measured masses is removed.     

Independent evaluation of a commercial deconvolution reporting software for gas chromatography mass spectrometry analysis of pesticide residues in fruits and vegetables

The gas chromatography mass spectrometry (GC–MS) deconvolution reporting software (DRS) from Agilent Technologies has been evaluated for its ability as a screening tool to detect a large number of pesticides in incurred and fortified samples extracted with acetone/dichloromethane/light petroleum (Mini-Luke method). The detection of pesticides is based on fixed retention times using retention time locking (RTL) and full scan mass spectral comparison with a partly customer built automated mass spectral deconvolution and identification system (AMDIS) database. The GC–MS was equipped with a programmable temperature vaporising (PTV) injector system which enables more sample to be injected. In a blind study of 52 real samples a total number of 158 incurred pesticides were found. In addition to the 85 pesticides found by manual interpretation of GC–NPD/ECD chromatograms, the DRS revealed 73 more pesticides (+46%). The DRS system also shows its potential to discover pesticides which are normally not searched for (EPN in long beans from Thailand). A spiking experiment was performed to blank matrices of apple, orange and lettuce with 177 different pesticides at concentration levels 0.02 and 0.1 mg/kg. The samples were analysed on GC–MS full scan and the AMDIS match factor was used as a mass spectral quality criterion. The threshold level of the AMDIS match factor was set at 20 to eliminate most of the false positives. AMDIS match factors from 20 up to 69 are regarded only as indication of a positive hit and must be followed by manual interpretation. Pesticides giving AMDIS match factors at ≥70 are regarded as identified. To simplify and decrease the large amount of data generated at each concentration level, the AMDIS match factors ≥20 was averaged (mean AMF) for each pesticide including the commodities and their replicates. Among 177 different pesticides spiked at 0.02 and 0.1 mg/kg level, the percentage of mean AMF values ≥70 were 23% and 80%, respectively. For 531 individual detections of pesticides (177 pesticides × 3 replicates) giving AMDIS match factor 20 in apple, orange and lettuce, the detection rates at 0.02 mg/kg were 71%, 63% and 72%, respectively. For the 0.1 mg/kg level the detection rates were 89%, 85% and 89%, respectively. In real samples some manual interpretation must be performed in addition. However, screening by GC–MS/DRS is about 5–10 times faster compared to screening with GC–NPD/ECD because the time used for manual interpretation is much shorter and there is no need for re-injection on GC–MS for the identification of suspect peaks found on GC–NPD/ECD.     

Preparation and in vitro evaluation of GdDOTA-(BOM)4; a novel angiographic MRI contrast agent

A novel Gd(III) complex, GdDOTA-(BOM)4, has been prepared by a simple three-step procedure. The complex showed high T1-relaxivity values in serum albumin solutions, blood and plasma, resulting from high affinity for serum albumin. The T1-relaxivity in plasma, 67.4 s-1 mM-1 (20 MHz, 37 degrees C), makes it a promising candidate for angiographic applications of MRI.     

Critical examination of some common reagents for reducing selenium species in chemical analysis

In an attempt to resolve apparently conflicting statements in the literature, a study has been made of the action of various reductants on selenium(VI) and selenium(IV). Chloride in hot non-oxidizing acid medium will reduce Se(VI) to Se(IV) but not further. Sulphur dioxide will reduce Se(IV) to Se, but has no effect on Se(VI). Hydrazinium salts reduce both Se(VI) and Se(VI) to Se, but hydroxylammonium salts reduce only Se(IV) to Se. Hydrogen peroxide partially reduces Se(VI) to Se(IV) but not further. If chloride is also present [to reduce Se(VI) to Se(IV)], sulphur dioxide or hydroxylammonium salts can then reduce the Se(IV) to Se, and this combined effect has led to some confusion in interpretation of experimental observations.     

Iron(III) as releasing agent for copper interference in the determination of selenium by hydride-generation atomic absorption spectrometry

Iron(III0 has a very effective releasing effect on the depressive interference from copper(II) on the determination of selenium by hydride-generation atomic absorption spectrometry. In solutionwith 100 mg 1^?1 Cu(II), 10 μg 1^?1 Se(IV) and 2.0 mol l^?1 HCl, the absorbance obtained was much higher when 8 g 1^?1 Fe(III) was added than for any earlier releasing agent.     

The mapping of charges in carbonyl complexes of some transition elements from XPS data

A method for internal calibration of ESCA (XPS ) spectra is described that permits the use of a simple relation between binding energy (E_b) and atomic charge (q) : E_b = kq + E_b0. This relation has been shown to hold for a large number of elements. In order to test these relations, a procedure is suggested that allows the calculation of the atomic charges in carbonyl complexes of chromium, iron and nickel from gas-phase and solid-state ESCA data. The agreement with theoretically calculated charge values is good.

The charge distribution in carbon monoxide has been estimated in a similar manner and the result is discussed in relation to other investigations.     

An examination of the hydride generation—atomic absorption spectrometric technique for the determination of selenium in technical sulphuric acid

Low recoveries of selenium(IV) added to technical sulphuric acid were obtained, although recoveries from the Suprapur acid were satisfactory. It is assumed that this is due to the different reactivity of the selenium present in the technical acid and the selenium added as standards.