Potentiometric stripping analysis for lead in urine

Potentiometric stripping analysis is based on the preconcentration of analytes by means of potentiostatic reduction and amalgamation at a thin-film mercury electrode. After preconcentration, the potentiostatic circuitry is disconnected and the amalgamated metals are oxidized either by mercury(II) ions or by dissolved oxygen. Lead can be determined in acidified urine samples by potentiometric stripping analysis after the addition of Triton X-100. In deaerated samples the detection limit is 1 μg l^?1, and in non-deaerated samples 12 μg l^t-1, the preconcentration time being 16 min.     

Flow potentiometric stripping analysis for mercury(II)

The optimum experimental conditions, with respect to sample and stripping solution composition, in computerised flow potentiometric stripping analysis for mercury(II) with a gold working electrode are described. When pre-electrolysis -was done in a sample to which ammonia and iodide had been added and stripping was done in an acidified bromide solution containing chromium(VI), a detection limit of 2 nM (0.4 μg kg^-1) was obtained after 90 s of pre-electrolysis, the dynamic range being almost three decades. Copper(II) interfered when present in a 1000-fold excess and silver(I) when present in a 5-fold excess over mercury(II).     

Equilibrium and structural studies of silicon(IV) and aluminium(III) in aqueous solution—10. A potentiometric study of aluminium(III) pyrocatecholates and aluminium(III) hydroxo pyrocatecholates in 0.6 M Na(Cl)

Equilibria between aluminium(III), pyrocatechol (1,2-dihydroxybenzene, H₂L) and OH⁻ were studied in 0.6 M Na(Cl) medium at 25°C. The measurements were performed as emf titrations (glass electrode) within the limits 1.5 ≤ − log[H⁺] ≤ 9; 0.0005 ≤ B ≤ 0.015 M; 0.006 ≤ C ≤ 0.03 M and 2 ≤ C/B ≤ 30 (B and C stand for the total concentrations of aluminium(III) and pyrocatechol respectively). All data can be explained with a main series of complexes: A1L⁺, log β_−2,1,1 = − 6.337 ± 0.005; A1L₂⁻, log β_−4,1,2 = −15.44 ± 0.017 and A1L₃³⁻, log β_−6,1,3 = − 28.62 ± 0.024 together with two minor species: Al(OH)L₂²⁻, log β_−5,1,2 = − 23.45 ± 0.079 and Al₃(OH)₃L₃, log β_−9,3,3 = − 29.91 ± 0.066. Of the two, the latter probably is a type of average composition complex principally occurring at low C/B quotients. The first acidity constant for pyrocatechol as determined in separate experiments is log β_−1,0,1 = − 9.198 ± 0.001. The standard deviations given are 3σ(log β p,q,r). Data were analyzed with the least squares computer program LETAGROPVRID. In a model calculation using kaolinite as solid phase, we compared the complexation ability of this system with that of the system Al³⁺-OH⁻-salicylic acid, reported earlier in this series.     

Determination of enantiomeric purity of (S)-carboranylalanine using capillary column supercritical fluid chromatography

Carboranylalanine, the o-carborane analogue of phenylalanine, is a potential candidate for boron neutron capture therapy of cancer. In this paper a method is described for the determination of enantiomeric purity of (S)-carboranylalanine as the (N- trifluoroacetyl)propylester using open tubular column supercritical fluid chromatography with a chiral stationary phase consisting of permethyl-β-cyclodextrin methyloctylsiloxane.     

Determination of water by flow-injection analysis with the karl fischer reagent

A method for the determination of water in organic solvents by flow-injection analysis (f.i.a.) is described. The method, which is based on the reaction between water and the Karl Fischer reagent, is capable of 120 determinations per hour. The concentration range 0.01–5% (v/v) of water can be covered by using a single Karl Fischer reagent solution. The results obtained with a specially constructed potentiometric detector showed a relative standard deviation of less than 0.5% (v/v). This value was about 3 times less than that obtained with a spectrophotometric detector. The f.i.a. technique is shown to offer some unique possibilities in minimizing interferences associated with the standard Karl Fischer batch titration method.     

Quality Assessments of Recycled Plastics by Spectroscopy and Chromatography

Quality assessments will be important for improved use of recycled polymeric materials. Ongoing preparation of new standards in the area of recycled polymers needs an overview of which properties and thus which polymer characterisation methods that will be important for that purpose. We suggest three polymeric properties as important for this work; these are degree of mixing (composition), degree of degradation and number and amount of low molecular weight compounds (e.g. degradation products, additives, flavour compounds). DSC showed increased degradation as multi modality for LDPE materials obtained from three different sites in a recycling plant. IR demonstrated that the carbonyl index increased during the various steps going from collected material to new product. GC chromatograms obtained for collected film flakes, processed granules and ready-made bags were quite complex with a series of hydrocarbons among other compounds. The recycling process seems, however, to remove some of the low molecular weight compounds found in the incoming dirty material.     

Electrostatic potentials of strained systems: nitrocyclopropane

The presence of an NO₂ substituent is found to eliminate the negative electrostatic potentials associated with the “bent” CC bonds cyclopropane. This is presumably due in large part to a rearrangement of electronics charge caused by the nitro group, as is shown by electronic density difference plots. Bond path calculations reveal bent bonds in nitrocyclopropane that are very similar to those in cycloprophane.     

Hydrocarbon clusters from a foil diffusion source

Rydberg states and clusters of Rydberg states have been reported in several cases from high temperature sources, so-called diffusion sources. The present study uses the same technique as the one used for the study of excited Cs clusters (Åmanet al., 1990), and is aimed at highly excited Rydberg cluster formation from hydrogen containing molecules. Ionized clusters from a diffusion source with the graphite foil emitter at 1400 K are studied by time-of-flight mass spectrometry. The excited clusters are shown to be ionized by field ionization. The best results are found using ethylene in the source, and the flux from the source probably contains both hydrogen and hydrocarbon species. Typical clusters have a mass of 10,000–200,000 a.u., assuming singly charged clusters. The formation and stabilization (cooling) of such large clusters under the present conditions is only possible since excited states can form a condensed phase, of so called Rydberg matter (Manykinet al., 1981, 1982, Petterssonet al., 1992, Svenssonet al., 1991, 1992). The importance of excited hydrogen containing clusters for the chemistry and physics of interstellar space is pointed out.     

Analysis of 5-hydroxy-N-methyl-2-pyrrolidone and 2-hydroxy-N-methylsuccinimide in plasma

Summary A method for the determination of 5-hydroxy-N-methyl-2-pyrrolidone (5-HNMP) and 2-hydroxy-N-methylsuccinimide (2-HMSI) in plasma was developed. 5-HNMP and 2-HMSI are metabolites to the widely used organic solvent N-methyl-2pyrrolidone (NMP). The 5-HNMP and 2-HMSI were purified from plasma by C8 solid phase extraction, derivatised by bistrimethylsilyl trifluoroacetamid, and analysed by gas chromatography with mass spectrometric detection. For 5-HNMP, the precision was 2–7 % (120 and 780 ng mL⁻¹) and the detection limit was 6 ng mL⁻¹ (m/z 98). For 2-HMSI, the precision was 2–9 % (160 and 1000 ng mL⁻¹) and the detection limit was 4 ng mL⁻¹ (m/z 144). The method is applicable for analysis of plasma samples from workers exposed to NMP.     

Computer plots of HOH normal modes depending on time

The combination of the antisymmetric and symmetric stretching vibrations of water is a decoupled OH vibration. It means the X₁₃ anharmonicity constant of HOH must be related with the X₃₃ anharmonicity constant of HOD. It is found that $\text{1}\text{2}$X₁₃(HOH)= X₃₃(DOH) = X(OH). Instead of the usual condition X_ik = 0 for i > k a new definition will be given for the anharmonicity constants: $\text{X}$_ik = $\text{X}$_ki. The X values of other molecules were compared with each other and it follows the general rule for a symmetric molecule m-M-m with m ? M: $\text{X}$₁₃ (mMm) = $\text{X}$₃₁ (mMm) = X (Mm).Computer plots of normal modes of the ν₁ + ν₃ combination depending on time show the rotation of the dipole moment derivatives vector. It is strongly different for H₂O and HOD and explains the different band intensities. We expect higher band intensities and X₁₃ values using IR light with rotating electric field vector.