Simultaneous determination of the tobacco smoke uptake parameters nicotine,cotinine and thiocyanate in urine,saliva and hair,using gas chromatography-mass spectrometry for characterisation of smoking status of recently exposed subjects

A method using gas chromatography (GC)-mass spectrometry (MS) for the simultaneous determination of the smoke uptake parameters thiocyanate, nicotine and cotinine in human tissues is reported. Nicotine, cotinine and thiocyanate, in combination with a phase-transfer catalyst, were extracted from urine, saliva and hair into dichloromethane (DCM). Thiocyanate was alkylated in the DCM-layer to form a pentafluorobenzyl derivative. The biochemical markers in DCM were directly injected into the GC system and separated on a DB-1MS column using a 9.4 min temperature program. The method was validated in urine and saliva between the limits of quantitation (1.0-15 microg ml(-1) thiocyanate, 0.010-3.0 microg ml(-1) nicotine and cotinine in urine, 0.010-1.0 microg ml(-1) nicotine and cotinine in saliva). The calibration curves were found to be linear (r > 0.996), the within- and between-day accuracy's were 83-120%, the repeatability coefficients of variation were 3-20% and the limits of detection were 0.060 ng ml(-1) thiocyanate and 0.60 ng ml(-1) nicotine and cotinine. The results of the analysis of the biomarkers in the urine of 44 volunteers were used to develop a predictive model for smoking status, using discriminant analysis. The classification model correctly classified 93.2% of cross-validated grouped cases. Saliva samples were used to confirm the results of the classification method.     

Copper interference on the spectrophotometric determination of iron and their simultaneous determination using bathophenantroline-disulfonic acid disodium salt

The interference of copper on the spectrophotometric determination of iron with bathophenantroline-disulfonic acid disodium salt was studied using an experimental design. Copper interferes even below pH 5 [1], forming a yellow complex with bathophenantroline which turned to green after 5 min. This complex showed a maximum at 425 nm with a molar absorptivity of 7.5 × 10³ L mol^–1 cm^–1. Microgram quantities of iron and copper were determined simultaneously in water standard samples using bathophenantroline-disulfonic acid disodium salt at pH 4.8 and measuring the absorbances at two wavelengths. The interference of iron on the copper determination was also estimated. The RSDs of the method for both Cu and Fe were below 1.7%. Recoveries for Cu and Fe were within the ranges 97.2% to 98% and 99.7 to 100.5%, respectively. The method was applied to the determination of copper and iron in the waste water from a water treatment plant. The results obtained by spectrophotometry were compared with those obtained by flame AAS.     

Theoretical calculations of the ionic strength dependence of the ionic product of water based on a mean spherical approximation

A modified version of the restricted primitive model for electrolyte solutions based on the mean spherical approximation (MSA) is applied to estimate the ionic strength dependence of the ionic product of water in aqueous solutions containing different salts, which are commonly used as background electrolytes (NaCl, KCl, KNO₃, and NaC10₄). The modification involves the use of permittivity of the solvent as concentration-dependent parameter and a single average effective diameter. This is a way of including effects originated from the solvent which do not exist in the primitive model. In the case of potassium nitrate and sodium perchlorate, a complete methodology to calculate the effective diameter and density dependence of the dielectric constant has been proposed and developed. Fits between calculated and experimental pK_w values are possible over wide concentration ranges using a single adjustable parameter, namely, the average hard core diameter of water.     

Chromatographic behaviour of trace metal ions on a strong base anion exchange resin functionalized by azo ligands

A model which allows the evaluation of the elution volume V(E) and the central point V(C) of the breakthrough curve of a metal ion at trace level on a chromatographic column containing a chelating resin is presented. V(E) and V(C) mainly depend on the complexation properties of the active groups, and on the acidity and composition of the aqueous solution, according to the Gibbs-Donnan model for the resin. The model has been tested in the case of strong base anion exchange resins in chloride form functionalized with two different sulphonated azo ligands (T-azo-C, T-azo-R). The chromatographic behaviour of copper(II) and thorium(IV) is as expected from the formation of a complex with the azo dye in the resin, while that of zinc(II) and cadmium(II) is fully described by also taking into account the formation of anionic chloro complexes inside the resin.     

Au(I) extraction by LIX-79/n-heptane using the pseudo-emulsion-based hollow-fiber strip dispersion (PEHFSD) technique

The extraction of Au(I) from alkaline cyanide solutions through PEHFSD was conducted in a microporous hydrophobic polypropylene hollow-fiber membrane contactor. The organic extractant LIX-79 (N,N-bis(2-ethyl hexyl)guanidine) in n-heptane was used. The alkaline cyanide feed solution containing Au(I) was passed through the tube side, and pseudo-emulsions of LIX-79/n-heptane and NaOH were passed through the shell side in counter-current mode, using a single microporous hydrophobic polypropylene hollow-fiber contactor for extraction and stripping. In PEHFSD the aqueous strip (0.2 M NaOH) solution is dispersed in the organic (12% LIX-79/n-heptane) membrane solution in a container with a mixing arrangement (impeller stirrer) designed to form a strip dispersion. The strip dispersion is circulated from the mixer to the membrane module to provide a constant supply of the LIX-79/n-heptane solution to the membrane pores. Various hydrodynamic and chemical parameters, such as variation in feed pH; gold cyanide concentration in feed; variation in concentrations of NaOH, LIX-79/n-heptane and Au(I); variation in feed, strip and LIX-79/n-heptane volume ratios and variation in feed and strippant flow rates, were investigated. Mass transfer modeling was performed and the validity of the model was evaluated with experimental data and found to tie in well with theoretical values. It was possible to concentrate Au(I) in product (NaOH) using the PEHFSD technique.     

Computational study of 19F NMR spectra of double four ring-containing Si/Ge-zeolites.

(19)F NMR chemical shifts are calculated in order to study the F(-) environment in double four ring (D4R) containing Si/Ge-zeolites. The calculations with the DFT/CSGT/B3PW91 methodology yielded an agreement within 2 ppm with respect to the experimental peaks corresponding to the D4R units containing 8Si0Ge, 7Si1Ge and 0Si8Ge of the octadecasil zeolite. The optimisation of the 7Si1Ge-, 6Si2Ge-, 5Si3Ge- and 4Si4Ge-D4R units with DFT/B3LYP methodology shows that a covalent Ge-F bond is formed and therefore a Ge atom in the D4R is pentacoordinated. The displacement of the fluoride ion towards a Ge atom in the Ge-containing D4R units locates four Si/Ge atoms in the close vicinity of the F(-) and this makes possible a rationalization of the (19)F NMR signals in groups according to the number of Si (n) and Ge (m) atoms in the nearest F(-) environment, F-Si(n)Ge(m) (where n+m=4). Thus, the calculated chemical shifts show that higher values are observed when the number of Ge atoms in the nearest F(-) environment increases.     

Spectrophotometric study of complexation equilibria between HCrO4 and Cl ions

The complex equilibria between HCrO₄⁻ and Cl⁻ ions has been studied spectrophotometrically at a constant ionic strength of 3.0 mol dm⁻³ and the data have been analyzed both graphically and numerically by means of the program LETAGROP-SPEFO (L. G. Sillen and B. Warnquist, Arkiv. kemi. 1968, 31, 377). The experimental results can be explained on the basis of the following reaction: HCrO₄⁻+H⁺+Cl⁻ = CrO₃Cl⁻+H₂O (log β₁₁ = 1.37±0.08). Molar absorptivities of HCrO₄⁻ and CrO₃Cl⁻ were also reported.     

Protonation constants of α-alanine in electrolyte mixtures at constant ionic strength

The stoichiometric acid-base equilibrium constants for -alanine in tetraethylamonium iodide-potassium nitrate solutions were determined at a constant ionic strength of 1.4 m at 25°C. The results obtained are discussed on the basis of the Friedman and the Pitzer model for electrolyte mixtures.     

Ammonia IRMS-TPD measurements and DFT calculation on acidic hydroxyl groups in CHA-type zeolites

Br?nsted acidity of H-chabazite (CHA) zeolites (Si : Al(2) = 4.2) was investigated by means of ammonia infrared-mass spectrometry/temperature-programmed desorption (IRMS-TPD) methods and density functional calculations. Four IR bands were observed at 3644, 3616, 3575 and 3538 cm(-1), and they were ascribable to the acidic OH groups on four nonequivalent oxygen sites in the CHA structure. The absorption band at 3538 cm(-1) was attributed to the O(4)H in the 6-membered ring (MR), and ammonia adsorption energy (DeltaU) of this OH group was the lowest among the 4 kinds of OH groups. The other 3 bands were assigned to the acidic OH groups in 8MR. It was observed that the DeltaU in 8 and 6MR were 131 (+/-3) and 101 kJ mol(-1), respectively. On the other hand, the density functional theory (DFT) calculations within periodic boundary conditions yielded the adsorption energies on these OH groups in 8 and 6MR to be ca. 130 and 110 kJ mol(-1), respectively, in good agreement with the experimentally-observed values.     

Recent developments in capillary isoelectric focusing

The developments in capillary isoelectric focusing (cIEF) over the period 2003-2007 are reviewed. With the focus on technological aspects, cIEF papers published in the fields of methodology, new techniques, detection, multidimensional systems, miniaturization and applications are summarized. The methodology section covers recent research in ampholytes composition, detergents and other additives, carrier ampholyte free cIEF, coatings and other capillary modifications. In the section on new systems adjustments to the technique (e.g. dynamic IEF), different applications of cIEF (e.g. as injection system) and new devices are reported. Systems focusing on whole column imaging, fluorescence and chemiluminescence detection and coupling to mass spectrometers are discussed in the section on detection. Interfacing cIEF with MS via RPLC systems and hyphenation of cIEF with capillary electrochromatography and other capillary electrophoresis modes are also summarized. Papers focusing on miniaturization are reviewed in the section on microfluidic devices. The section on applications will show analysis of biopharmaceutical compounds and isolated proteins for metabolomic studies. For the analysis of complex biological matrices, generally multidimensional systems are needed, which are mentioned throughout this review.