Forensic classification of ballpoint pen inks using high performance liquid chromatography and infrared spectroscopy with principal components analysis and linear discriminant analysis

Several varieties of blue ballpoint pen inks were analyzed by high performance liquid chromatography (HPLC) and infrared spectroscopy (IR). The chromatographic data extracted at four wavelengths (254, 279, 370 and 400 nm) was analyzed individually and at a combination of these wavelengths by the soft independent modeling of class analogies (SIMCA) technique using principal components analysis (PCA) to estimate the separation between the pen samples. Linear discriminant analysis (LDA) measured the probability with which an observation could be assigned to a pen class. The best resolution was obtained by HPLC using data from all four wavelengths together, differentiating 96.4% pen pairs successfully using PCA and 97.9% pen samples by LDA. PCA separated 60.7% of the pen pairs and LDA provided a correct classification of 62.5% of the pens analyzed by IR. The results of this study indicate that HPLC coupled with chemometrics provided a better discrimination of ballpoint pen inks compared to IR. The need to develop a suitable IR method for analysing blue ballpoint pen inks has been emphasized and it is hoped that the development of such a method would indeed provide a valuable tool for the non-destructive analysis of blue ballpoint pen ink samples for forensic purposes.     

Cross-channel coupling in positron-atom scattering

Coupled-state calculations including positronium channels are reported for positron scattering by atomic hydrogen, lithium and sodium. Integrated cross sections and total cross sections are presented for all three atoms. For lithium differential cross sections are also given. Throughout, comparison is made between results calculated with and without inclusion of the positronium channels. S-wave cross sections for positron scattering by atomic hydrogen in the Ps(1s, 2s, 2p)+H(1s, 2s, 2p) approximation show the high energy resonance first observed by Higgins and Burke in the coupled-static approximation. This resonance has now moved up to 51.05 eV and narrowed in width to 2.92 eV. Other pronounced structure is seen in the S-wave cross sections between 10 and 20 eV; it is tentatively suggested that this structure may be due to the formation of a temporary pseudo-molecular collision complex. Results calculated in the Ps(1s, 2s, , 2p, ,+H(1s, 2s, , 2p, approximation show convergence towards accurate values in the energy region below and in the Ore gap. Contrary to previous work on lithium using only an atomic basis, it is found that coupling to the 3d state of lithium is not so important when positronium channels are included; this is because a mixed basis of atom and positronium states gives a more rapidly convergent approximation than an expansion based on atom states alone. The threshold behaviour of the elastic cross section and the Ps(1s) formation cross section for lithium is investigated. Results in the Ps(1s, 2s, 2p)+Na(3s, 3p) approximation for sodium show good agreement with the total cross section measurements of Kwan et al.     

The formation of cation-ligand complexes of tributylammonium cation with diethyl carbonate,ethylene carbonate,propylene carbonate, 4-butyrolactone,ethyl acetate,and cyclopentanone ino-dichlorobenzene at 25°C

The effects of adding millimolar quantities of a series of compounds containing the carbonyl function on the conductances of solutions (0.2 mM) of tri-n-butylammonium picrate ino-dichlorobenzene solvent at 25°C have been measured. Values of the complex formation constants K ₁ ⁺ for 1:1 cation-ligand complexes are derived from these data. The corresponding values of –G ₁ ⁰ at 25°C are (in kcal-mole ^–1 ): 4-butyrolactone, 4.29; propylene carbonate, 3.87; ethylene carbonate, 3.59; cyclopentanone, 3.42; ethyl acetate, 2.84; and diethyl carbonate, 2.78. These results together with earlier results from this laboratory are discussed in terms of the effects of structure on cation-ligand affinity.     

Synthesis and structure of [(Sn(mu-PCy))3(Na x PMDETA)2], containing an electron-deficient [(Sn(mu-PCy))3]2- dianion

The reaction of CyPHNa with Sn(NMe2)2 in the presence of PMDETA (= (Me2NCH2CH2)2NMe) gives the title compound [(Sn(mu-PCy))3(Na x PMDETA)2] (1), containing an electron-deficient [(Sn(mu-PCy))]3(2-) dianion with a novel two-electron, three centre (2e-3c) bonding arrangement.     

Characterisation of Sugar Cane Combustion Particles in the Araraquara Region, Southeast Brazil

Biomass burning is an important primary and secondary source of aerosol particles. The presence of carbonaceous particles in the respirable size range makes the study of this fraction important in view of possible health and climatic effects. The annual burning of sugar cane plantations causes emission of huge amounts of pyrogenic particles. Aerosol samples were collected in Araraquara city, São Paulo state, Brazil, during the harvest season for fine and coarse particles and bulk; they were analysed by electron-probe microanalysis, including facilities for low-Z element determination (low-Z EPMA) and by energy-dispersive X-ray fluorescence (EDXRF), in order to investigate the elemental composition of individual particles and bulk samples, respectively. Numerical analysis of the EPMA results by hierarchical clustering shows high contributions of carbonaceous particles that can be distinguished mainly in two different types: biogenic and carbon-rich. Additionally, two significant contributions of aluminosilicate particles were identified: as rather pure aluminosilicates or mixed with carbonaceous species. The EDXRF results are compatible with those of aerosol particles in Amazon, which is nowadays one of the main sources of biogenic particles in the world.     

Solubility of benzil in binary alkane + dibutyl ether solvent mixtures. Comparison of predictive expressions derived from the nearly ideal binary solvent model

Experimental solubilities are reported for benzil dissolved in six binary mixtures containing dibutyl ether with hexane, heptane, octane, cyclohexane, methylcyclohexane, and 2,2,4-trimethylpentane at 25°C. Results of these measurements are compared to the predictions of equations developed previously for solubility in systems of nonspecific interactions. The most successful equation in terms of goodness of fit involved a volume fraction average of the excess Gibbs energies relative to the Flory-Huggins model, and predicted the experimental solubilities in the six systems studied to within an overall average absolute deviation of 3.4% and with a maximum deviation of 6.0%.     

Dissociation behavior of doubly-charged tryptic peptides: correlation of gas-phase cleavage abundance with ramachandran plots

Analysis of fragmentation patterns from 5654 unique doubly charged tryptic peptides is obtained. Great variability of average relative abundance of bond cleavage is found between different amino acid combinations. There exist similarities as well as differences between b and y ions. Strong enhancement or suppression of cleavage gives insight into possible chemical interactions at reactive conformations formed by preferred phi-psi angles.     

Time evolution studies of the H2O/quartz interface using sum frequency generation, atomic force microscopy, and molecular dynamics

Many interfacial studies on solid surfaces, for example, quartz/water, assume that a standard cleaning procedure regenerates the surface reproducibly. In the reported work, the results of two surface specific techniques, sum frequency generation (SFG) spectroscopy and atomic force microscopy, show that the effects of prolonged exposure to Nanopure water and to pH 10 NaOH are distinctly different. In conjunction with the experimental data, molecular mechanics is used to correlate the SFG spectral frequencies to the hydrogen stretching vibrations of the surface-bound water molecules. It is found that after 17 days of soaking in water, water molecules penetrate into the SiO2 matrix to produce a swollen and amorphous layer; it is likely that broken Si-O bonds from the polishing process serve as nucleation sites for hydration and swelling. Disorder introduced in the interfacial water layer is detected by the rising intensity of the weakly hydrogen-bonded SFG peak at 3450 cm(-1). Dominance of the 3450 cm(-1) is absent in a pH 10, NaOH-soaked quartz disk, indicating that the strong hydrogen-bonded network in water remains intact.     

Spot tests for calcium sulphate, lead sulphate, silver, thallium, and formaldehyde based on reactions with selenosulphate

Summary Spot tests have been described for calcium sulphate, lead sulphate, silver, thallium and formaldehyde based on the reaction with selenosulphate. In these reactions either red elemental selenium (CaSO₄, CH₂O) or black metal selenide (PbSO₄ Tl, Ag) is formed. The limits of identification are: 0.2 mg of PbS04 or CaSO₄, 2 g of Ag, 10 g of Tl, 0.2 g of CH₂O.

---

Zusammenfassung Für Calciumsulfat, Bleisulfat, Silber, Thallium und Formaldehyd werden Tüpfelproben beschrieben, die auf Umsetzungen mit Selenosulfat beruhen. Hierbei -wird entweder rotes elementares Selen abgeschieden (CaSO₄ CH₂O) oder schwarze Selenide werden gebildet (PbSO₄, Tl, Ag). Die Nachweisgrenzen betragen: 0,2 mg PbSO₄ oder CaSO₄, 2 g Ag, 10 g Tl, 0,2 g CH₂O.

---

---

This paper has been dedicated to Prof. Dr.Fritz Wessely, Vienna, on the occasion of his 70th birthday.     

Extending the use of certified reference sediments for assessment of accuracy in determinations of trace metals

Straightforward analysis for components in a single certified reference sediment is of limited use for assessing the accuracy of environmental determinations. A systematic approach requires mixing of certified sediments, one with another and with environmental samples, and the preparation of secondary reference material by the laboratory. Use of Youden pairs, reference material embedded in samples and linear models should enable valid accuracy statements to be made based on well known statistical concepts. For assessing accuracy, reference sediments which are matched in particle size, and are end-members for components or sediment types are most useful.