A traceability protocol to the SI by gravimetric analysis

 An example is presented of a traceability protocol for the measurement of a single-element strontium reference material solution, executed by a "primary" method of measurement for certification. The method of measurement is briefly described together with the measurement equation and the associated calculations for the estimation of uncertainties. This is followed by a discussion and estimate of each component of uncertainty associated with the measurement, together with a final estimate of uncertainty. The final estimate of uncertainty compares well with observed uncertainties for two previous laboratory measurements of the reference material. Received: 21 February 1998 · Accepted: 17 August 1998     

Influence of relative humidity in sensing halogenated hydrocarbons with Reflectometric Interference Spectroscopy (RIfS)

For stand-alone sensor systems apart from defined laboratory circumstances sensors are required, which show a high stability against perturbing environmental influences like the relative humidity (r.h.). We present a portable sensor system, which is capable to quantify tetrachloroethene (TCE) in humid air. The system works highly reproducible and shows only negligible cross-sensitivity towards relative humidity. This allows a single calibration valid from 0 to 80% r.h.. Therefore, referencing with an extra sensor for humidity is not necessary. Binary mixtures of TCE and freone R113 were quantified for 0 and 40% r.h. with a root mean square error of prediction of approximately 3% with respect to the maximum concentration of TCE and R113. The sensitive elements used in the experiments consisted of thin polymer films on glass substrates. The measurements were performed with the optical measurement technique RIfS (Reflectometric Interference Spectroscopy). Received: 29 May 1998 / Revised: 4 August 1998 / Accepted: 8 August 1998     

Determination of cobalt by catalytic-adsorptive differential pulse voltammetry in the presence of 2-aminocyclopentene-1-dithiocarboxylic acid and nitrite

A novel method for the determination of cobalt(II) by stripping voltammetry is described. It involves an adsorptive accumulation of the cobalt(II)-2-aminocyclopentene-1-dithiocarboxylic acid complex on a hanging mercury drop electrode, followed by a stripping voltammetric measurement of the catalytic reduction current of the complex at –1.4 V at pH = 9 (vs. Ag/AgCl). The effects of various experimental parameters on the catalytic current were investigated. An accumulation time of 60 s results in a low experimental limit of detection of 0.1 ng/mL of Co(II), and 0.50 to 40.0 ng/mL of cobalt can be determined. The relative standard deviation at 0.50 ng/mL is 2.8%. Possible interferences from co-existing ions were also investigated. Received: 17 August 1998 / Revised: 16 November 1998 / Accepted: 20 November 1998     

Determination of cobalt by catalytic-adsorptive differential pulse voltammetry in the presence of 2-aminocyclopentene-1-dithiocarboxylic acid and nitrite

A novel method for the determination of cobalt(II) by stripping voltammetry is described. It involves an adsorptive accumulation of the cobalt(II)-2-aminocyclopentene-1-dithiocarboxylic acid complex on a hanging mercury drop electrode, followed by a stripping voltammetric measurement of the catalytic reduction current of the complex at –1.4 V at pH = 9 (vs. Ag/AgCl). The effects of various experimental parameters on the catalytic current were investigated. An accumulation time of 60 s results in a low experimental limit of detection of 0.1 ng/mL of Co(II), and 0.50 to 40.0 ng/mL of cobalt can be determined. The relative standard deviation at 0.50 ng/mL is 2.8%. Possible interferences from co-existing ions were also investigated. Received: 17 August 1998 / Revised: 16 November 1998 / Accepted: 20 November 1998     

The nature of corrosion products in lead pipes used to supply drinking water to the City of Glasgow, Scotland, UK

Corrosion products, obtained from lead service pipes carrying the public drinking water supply to the Glasgow area, have been characterised by FTIR spectrometry, powder x-ray diffraction spectrometry, flame atomic absorption spectrometry and ion chromatography. As expected, the products which formed in the presence of pH adjusted-water were mainly lead carbonate or basic lead carbonate. Products from areas where the water supply had been treated with orthophosphoric acid and pH adjustment for up to eight years also contained a variable proportion (up to ∼30% w/w) of a phosphate species. This has been identified as an apatite, most probably lead hydroxyapatite, Pb₅(PO₄)₃OH. Received: 3 August 1998 / Revised: 26 August 1998 / Accepted: 28 August 1998     

Some recent developments in reference methodology within the United Kingdom

 The UK Valid Analytical Measurement Programme has pump-primed developments in chemical metrology, through a major project on reference methodology and reference materials. This paper provides an overview of developments during 1994–1997 and covers work on primary methods for trace inorganic and trace organic analysis, including the use of isotope dilution mass spectrometry; studies of sample pre-treatment, including digestion, extraction, and separation aimed at improving this weak link in the traceability chain; prioritisation, production and marketing of both pure substance and matrix reference materials; and international collaboration concerned with interlaboratory comparisons and the development of concepts, terminology and systems to underpin the international chemical measurement system. References are given to a number of papers covering specific parts of the programme. Received: 5 August 1998 · Accepted: 12 September 1998     

FI spectrophotometric determination of Pd with DBOK-chlorophosphonazo

A flow injection method was developed for the determination of palladium, based on the reaction of palladium with DBOK-chlorophosphonazo with a detection limit of 0.07 μg/mL and a linear calibration range from 0.1 to 3.2 μg/mL of palladium. The reaction product has a maximum absorption at 630 nm. The method was applied to determine Pd²⁺ in catalysts and in anode mud samples. The relative error is less than 3% and the recovery of palladium is in the range 95% to 105% Received: 27 April 1998 / Revised: 24 August 1998 / Accepted: 26 August 1998     

FI spectrophotometric determination of Pd with DBOK-chlorophosphonazo

A flow injection method was developed for the determination of palladium, based on the reaction of palladium with DBOK-chlorophosphonazo with a detection limit of 0.07 μg/mL and a linear calibration range from 0.1 to 3.2 μg/mL of palladium. The reaction product has a maximum absorption at 630 nm. The method was applied to determine Pd²⁺ in catalysts and in anode mud samples. The relative error is less than 3% and the recovery of palladium is in the range 95% to 105% Received: 27 April 1998 / Revised: 24 August 1998 / Accepted: 26 August 1998     

Laboratory accreditation – where next?

 Laboratory accreditation is now well established and can justly claim to have had a beneficial impact on the quality of the services provided by accredited laboratories. However, the needs of laboratories and their customers are continually evolving. It is necessary for accreditation practices to keep abreast of these changing requirements if they are to continue to be of benefit to laboratories and their customers. This paper gives a brief review of current accreditation practice and suggests some changes that should be made to help laboratories meet the demands made on them by their customers. Received: 2 July 1998 · Accepted: 3 August 1998     

Statistical quality control of PCDD/PCDF analysis using a total measuring data set

 A random error and accuracy estimation approach for polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF) analysis is presented based on statistical treatment of all the data set registered in a run or in a bunch of uniform runs. Received: 18 August 1998 / Accepted: 21 October 1998     

Dissociative recombination of HeH+. I. Rovibrational spectrum of HeH Rydberg states

The repulsive ground electronic state X²Σ⁺ of HeH is strongly coupled to the Rydberg states at small interatomic distances. Such large couplings also occur between some of the Rydberg states. HeH⁺ ions that capture an electron in a Rydberg state end up in separated He and H atoms by indirect predissociation. This paper presents a study of potential functions and pertinent matrix elements involving the lowest electronic states: the ²Σ⁺ states, X, A, C, and D, and the ²Π states B and E. Individual transition rates as well as total radiative and non-radiative lifetimes have been computed for the lowest vibrational and rotational levels. Received: 22 June 1998 / Accepted: 21 August 1998 / Published online: 12 October 1998     

Calibration bias in the determination of polynuclear aromatic hydrocarbons in water

 We present the results of an investigative interlaboratory test to determine the reasons for poor agreement between data from different laboratories for the determination of polynuclear aromatic hydrocarbons in water. Received: 2 July 1998 · Accepted: 1 August 1998     

Chemical analysis as a specific class of measurements

 Specific features of the procedures involved in chemical analysis (sampling, sample preparation, matrix and impurities identification, quantitative analysis) are considered, and their effect on the uncertainty of the result of a quantitative determination of the component of interest is discussed. Received: 19 August 1998 / Accepted: 4 September 1998     

Means of checking for false compensation effects in liquid-phase reactions

A rapid method is presented for revealing a false compensation effect resulting from errors in measurement of the reaction rate constants. L. M. Litvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine, 70 Lyuksemburg ul., Donetsk 340114, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 34, No. 4, pp. 233–238, July–August, 1998.     

Traceable measurements of pH

 The primary method for pH is based on the measurement of the potential difference of an electrochemical cell containing a platinum hydrogen electrode and a silver/silver chloride reference electrode, often called a Harned cell. Assumptions must be made to relate the operation of this cell to the thermodynamic definition of pH. National metrology institutes use the primary method to assign pH values to a limited number of primary standards (PS). The required comparability of pH can be ensured only if the buffers used for the calibration of pH meter-electrode assemblies are traceable to these primary pH standards. To assess the degree of equivalence, comparisons of primary measurement procedures for pH were organized in co-operation with EUROMET. Typical results will be presented. In 1998, the Consultative Committee for Amount of Substance (CCQM) decided to include the field of pH in its working programme. The first key comparison for this quantity was recently carried out on two phosphate buffer solutions. Received: 14 June 2000 / Accepted: 22 August 2000     

Grid-free DFT implementation of local and gradient-corrected XC functionals

Following an approach to density functional theory calculations based on the matrix representation of operators, we implemented a scheme as an alternative to traditional grid-based methods. These techniques allow integrals over exchange-correlation operators to be evaluated through matrix manipulations. Both local and gradient-corrected functionals can be treated in a similar way. After deriving all the required expressions, selected examples with various functionals are given. Received: 7 March 1998 / Accepted: 21 May 1998 / Published on line: 6 August 1998     

Dioctyltin and tributyltin detection at trace levels in water and beverages by capillary gas chromatography with flame photometric detection

A simple chromatographic procedure has been developed for the sensitive determination of dioctyltin and tributyltin compounds in water and beverages. Dioctyltin and tributyltin react with NaBH₄ at pH 5 to produce volatile hydrides which can be quantitatively extracted into CH₂Cl₂. The corresponding dioctyltin hydride derivative is identified by HPLC-ES-MS and measured by flame photometric detection using the quartz surface-induced tin emission. Detection limits of less than 0.7 pg of tributyltin and 10 pg of dioctyltin were achieved. Results showed that up to 9.5 ng/mL levels of dioctyltin were present in beverages. Received: 20 July 1998 / Revised: 26 August 1998 / Accepted: 28 August1998     

Dioctyltin and tributyltin detection at trace levels in water and beverages by capillary gas chromatography with flame photometric detection

A simple chromatographic procedure has been developed for the sensitive determination of dioctyltin and tributyltin compounds in water and beverages. Dioctyltin and tributyltin react with NaBH₄ at pH 5 to produce volatile hydrides which can be quantitatively extracted into CH₂Cl₂. The corresponding dioctyltin hydride derivative is identified by HPLC-ES-MS and measured by flame photometric detection using the quartz surface-induced tin emission. Detection limits of less than 0.7 pg of tributyltin and 10 pg of dioctyltin were achieved. Results showed that up to 9.5 ng/mL levels of dioctyltin were present in beverages. Received: 20 July 1998 / Revised: 26 August 1998 / Accepted: 28 August1998     

Multireference perturbation CI III. Fast evaluation of the one-particle density matrix

Within the frame of multireference perturbation configuration interaction we have developed a fast algorithm, based on diagrammatic techniques, for the calculation of the first-order correction to the one-particle density matrix. As an example of an application we have chosen the evaluation of the dipole moment of the CO molecule, where utilization of the first-order density is shown to corroborate the variational calculation. Received: 4 August 1998 / Accepted: 21 September 1998 / Published online: 16 November 1998