Lauri H. J. Lajunen

Guidelines for NMR measurements for determination of high and low pKa values (IUPAC Technical Report)

Factors affecting the NMR titration procedures for the determination of pKa values in strongly basic and strongly acidic aqueous solutions (2 > pH > 0 and 14 > pH > 12) are analyzed. Guidelines for experimental procedure and publication protocols are formulated. These include: calculation of the equilibrium H+ concentration in a sample; avoidance of measurement with glass electrode in highly acidic (basic) solutions; exclusion of D2O as a solvent; use of an individual sample isolated from air for each pH value; use of external reference and lock compounds; use of a medium of constant ionic strength with clear indication of the supporting electrolyte and of the way the contribution of any ligand to the ionic strength of the medium is accounted for; use of the NMR technique in a way that eliminates sample heating to facilitate better sample temperature control (e.g., 1H-coupled NMR for nuclei other than protons, GD-mode, CPD-mode, etc.); use of Me4NCl/Me4NOH or KCl/KOH as a supporting electrolyte in basic solution rather than sodium salts in order to eliminate errors arising from NaOH association; verification of the independence of the NMR chemical shift from background electrolyte composition and concentration; use of extrapolation procedures.

Critical evaluation of stability constants for alpha-hydroxycarboxylic acid complexes with protons and metal ions and the accompanying enthalpy changes. Part II. Aliphatic 2-hydroxycarboxylic acids (IUPAC Technical Report)

Stability constants for different aliphatic 2-hydroxycarboxylic acid complexes in aqueous solutions with protons and metal ions published between 1960 and the end of 1994 have been critically evaluated.

31 P NMR Study of organophosphonate protonation equilibrium at high pH

A 31P NMR technique was used to determine the protonation constants of the organophosphonates 1-hydroxyethane-1,1-diphosphonic acid (HEDPA, H4L), nitrilotri(methylenephosphonic acid) (NTPH, H6L) and 1,2-diaminoethane-N,N,N′,N′-tetra(methylenephosphonic acid) (EDTPH, H8L) at 24°C and I=3.4–3.5 mol dm-3 (CH3)4NCl over the range pH 11–14.5. For the dissociation of the aliphatic hydroxy group of HEDPA log K(H-1L+HL)14.6 while for NTPH and EDTPH log K(L+HHL) was found to be 14.2(0.1) and 13.8(0.1), respectively. The influence of (CH3)4NCl content on 31P NMR chemical shifts was demonstrated.

Determination of trace amounts of molybdenum in plant tissue by solvent extraction-atomic-absorption and direct-current plasma emission spectrometry.

Methods are presented for determination of molybdenum in plant tissue by flame and graphite-furnace atomic-absorption spectrometry and direct-current argon-plasma emission spectrometry. The samples are digested in HNO(3)-H(2)SO(4)-HC1O(4) mixture, and Mo is separated and concentrated by chelation and extraction. Three organic solvents (methyl isobutyl ketone, di-isobutyl ketone and isoamyl alcohol) and two ligands (8-hydroxyquinoline and toluene-3,4-dithiol) were studied. The procedure were tested on pine needle and birch leaf samples.

Influence of volatile hydride-forming elements on antimony determination by atomic-absorption spectrometry with hydride-generation

A study was undertaken to determine the interfering effects of arsenic, bismuth, germanium, lead, selenium, tin and tellurium on trace determination of antimony by atomic-absorption spectrometry with hydride-generation. A 1% NaBH(4) solution was used as reductant and a small amount of oxygen was added to the hydrogen produced, to support the combustion and atomization of SbH(3). The interference from selenium in the determination of antimony is removed if potassium iodide-ascorbic acid solution or copper sulphate is added to the sample solution. The interference of tin and tellurium can also be avoided by adding potassium iodide-ascorbic acid solution. A possible interference mechanism is discussed.

Determination of sulphur by tin, aluminium and indium monosulphide molecular absorption spectrometry using sharp line irradiation sources

Abstract Methods for the determination of sulphur by high-temperature molecular absorption spectrometry were investigated. Sulphur was determined via the molecular absorption of aluminium, indium and tin sulphides using hollow-cathode lamps of different elements as irradiation sources for the measurements. The best result was obtained when sulphur was measured as tin sulphide and was almost as good when measured as indium sulphide. The methods were tested for the determination of sulphur in some organic compounds and in rain-water samples.

High-performance liquid chromatographic method for simultaneous determination of clodronate and some clodronate esters

A quaternary alkylmethylamine-bonded stationary phase has been used for the liquid chromatographic resolution of bisphosphonates. Clodronate and three of its esters were separated by this technique. Nitric acid (30 mM) was used as the mobile phase. The effect of the pH of the mobile phase on the retention, resolution, capacity factor and theoretical plates of the column was examined. Thorium-ethylenediaminetetraacetic acid-xylenol orange mixed ligand complex was used as a postcolumn reagent for bisphosphonates. Bisphosphonates react quantitatively with this complex in slightly acidic solutions, and a change in the absorbance of postcolumn reagent is used as a measure of the bisphosphonate concentration. The relative standard deviation (R.S.D.) values for samples in aqueous solutions were in the range 2.3-15.5% (area) and 1.7-5.9% (height). The detection limits for different compounds, Cmin, varied from 0.3 to 1.4 mg/l (area) and from 0.3 to 0.5 mg/l (height). In urine samples the R.S.D. (%) varied from 3.1 to 18.9 (area) and from 1.1 to 6.3 (height). The linear dynamic range was from the detection limit up to 16 mg/l.

The r α-structure and anisotropy of the Hg-C indirect coupling constant of methylmercury nitrate dissolved in nematic and lyotropic liquid crystals

The 1H and 13C N.M.R. spectra of methylmercury nitrate in a nematic and lyotropic phase were recorded and analysed. The complete r α-structures were determined. The Hg-C distances and the HCH bond angles do not differ significantly in the two phases. In contrast, the relative anisotropies of the indirect Hg-C coupling constants are different, 18 per cent in the lyotropic phase and 34 per cent in the nematic phase. The results are discussed using a simple relativistic MO model.

Thermal decomposition of hydrated copper(II) 5-substituted salicylates

Abstract Trihydrates of copper(II) 5-chloro-, copper(II) 5-bromo-, and copper(II) 5-iodosalicylates and dihydrate of copper(II) 5-nitrosalicylate have been prepared and characterized on the basis of elemental analysis and IR studies. The thermal behaviour of these salicylate hydrates has been determined employing TG, DTG and DSC techniques. The decomposition reaction mechanism of these complexes was studied by analyzing the decomposition products with MS and IR spectroscopy. CuO has been detected as the final product in the decomposition processes.

Determination of chloride in drinking and ground water by AlCl molecular absorption spectrometry using graphite furnace atomic absorption spectrometer

The use of high temperature molecular absorption spectrometry for the determination of chloride in drinking and ground water samples is described. The chloride is measured by monitoring the absorbance of vaporised aluminium chloride molecule. The effect of various components commonly present in natural waters were studied and any serious interference was found. The accuracy was assessed by comparing the results obtained using the proposed method with those got by conventional titrimetric method.