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The practical realisation of pH-measurements with Harned-cell type equipment used for the measurement of primary standards as recommended by IUPAC is shortly outlined. In contrast to the Harned-cell without transference, the glass electrode with a junction is preferred and more practical for field laboratories. The combined measurement uncertainty is evaluated step by step in a systematic way according to ISO-GUM for a sample pH-value measured using a glass type electrode system, that was calibrated with two certified pH-reference material solutions.

The influence of atmospheric pressure, air temperature, and relative air humidity on weighing results was determined in a long-term experiment. Two magnesium and three aluminium cylinders were weighed in a room without air conditioning over a period of more than three months. The climate parameters were automatically registered every 10 minutes. The climate data allow to calculate the masses from the weighing values which are subject to air buoyancy. It is then possible to check the validity of the empirical Schwartz equation for the calculation of the air density. The match between theory and experimental results is excellent for the influence of pressure and temperature and is weaker for the influence of humidity. The influence of this latter parameter on weight values is rather low and may be corrupted by water adsorption effects on the surfaces. It was found that the climate parameters can be looked at as triangular distributions rather than the previously proposed rectangular ones for the calculation of the weighing uncertainty budget

A short introduction of the general bottom-up uncertainty evaluation approach according to the ISO-GUM, JCGM 100 was presented [1, 3]. The Monte-Carlo Method (MCM) for the evaluation of the measurement uncertainty was outlined [2]. An application of the Monte-Carlo technique to the standard addition method using a simple excel-spreadsheet was explained in order to encourage the use of this important and powerful approach. A four and a five point standard addition method were compared for different sets of uncertainties of input variables and represented graphically.

Metrological comparability as well as reliability of ion activity results measured with ion-selective electrodes (ISE) was investigated within the framework of an interlaboratory comparison between eight partners from national metrology institutes and expert laboratories. Two electrolyte solutions containing the clinically most relevant ions sodium, potassium, magnesium, calcium and chloride having ion activities near the physiological range served as samples. The calibration of the measurement set-ups of the participants was carried out using gravimetrically prepared aqueous electrolyte solutions. The ion activities of these calibration standards were calculated by means of the semi-empirical Pitzer model. The measurement uncertainty of the measurement results was calculated according to the guide to the expression of uncertainty in measurement, GUM. Based on a new scale for ion activities traceable to the SI system of units, comparability and reliability of ISE measurement results of clinically relevant ions is realised.

In a chronoamperometric measurement the chemical activity of glucose is directly determined using a glucose sensitive biosensor based on glucose oxidase and an efficient mediator. Within the physiological range of 2 mmol kg−1 and 10 mmol kg−1 glucose in aqueous solutions behaves almost ideally and the chemical activity equals the glucose molality, the amount of glucose per unit mass of water, within the estimated measurement uncertainty. In physiological samples the equality between chemical activity and glucose molality is destroyed and has to be corrected for. Gravimetrically prepared mixtures of high purity glucose in buffered aqueous solutions are used as standards for calibration of the chronoamperometric measurement setup. Based on the model equation for the measurand aqueous or physiological sample, all significant sources of uncertainty are identified, their magnitude estimated from published and experimental data and finally combined to give the uncertainty in the reported value of the glucose molality. It is found, that the combined uncertainty of the glucose molality comprises mainly uncertainty contributions from the nonideal behavior, the chronoamperometric measurement setup, from the purity of glucose used and from the chemical composition of the test sample. The expanded uncertainty is below 2% rel., the glucose content determined by the bioelectrochemical measurements thus competes well with today's considered most accurate reference method Isotope Dilution Mass Spectrometry. Advantageous of the presented electroanalytical method is the direct measure of the glucose molality without prior sample preparation and dilution.

Based on the model equation for the measurand analyte activity, all significant sources of uncertainty are identified, their magnitude estimated from published and experimental data and finally combined to give the uncertainty in the reported value of the analyte activity. It is found that the combined uncertainty is dominated by the uncertainties in the diffusion potential EJ and the time-dependent response behavior κ of the sensor. Using Henderson's approach EJ is calculated not to vary more than 150 μV for physiological analytes in contact with a 3 M KCl reference solution. The stability of the reference electrode as well as the flow characteristics in the vicinity of the sensing element greatly influence the response time of the sensor. By minimizing the mentioned contributions of EJ and κ in the uncertainty budget, combined uncertainties for activity values in the range of 2% are feasible for univalent ions.

In order to evaluate alternative analytical methodologies to study the geographical origin of ciders, both multi-elemental analysis and Sr isotope abundance ratios in combination with multivariate statistical analysis were estimated in 67 samples from England, Switzerland, France and two Spanish regions (Asturias and the Basque Country). A methodology for the precise and accurate determination of the (87)Sr/(86)Sr isotope abundance ratio in ciders by multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) was developed. Major elements (Na, K, Ca and Mg) were measured by ICP-AES and minor and trace elements (Li, Be, B, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Se, Rb, Sr, Y, Mo, Cd, Sn, Sb, Cs, Ba, La, Ce, W, Tl, Pb, Bi, Th and U) were measured by ICP-MS using a collision cell instrument operated in multitune mode. An analysis of variance (ANOVA test) indicated that group means for B, Cr, Fe, Ni, Cu, Se, Cd, Cs, Ce, W, Pb, Bi and U did not show any significant differences at the 95% confidence level, so these elements were rejected for further statistical analysis. Another group of elements (Li, Be, Sc, Co, Ga, Y, Sn, Sb, La, Tl, Th) was removed from the data set because concentrations were close to the limits of detection for many samples. Therefore, the remaining elements (Na, Mg, Al, K, Ca, Ti, V, Mn, Zn, As, Rb, Sr, Mo, Ba) together with (87)Sr/(86)Sr isotope abundance ratio were considered for principal component analysis (PCA) and linear discriminant analysis (LDA). Finally, LDA was able to classify correctly 100% of cider samples coming from different Spanish regions, France, England and Switzerland when considering Na, Mg, Al, K, Ca, Ti, V, Mn, Zn, As, Rb, Sr, Mo, Ba and (87)Sr/(86)Sr isotope abundance ratio as original variables.

Gravimetric synthetic mixtures of seven enriched, purified cadmium isotope materials were used to determine the correction factors for mass fractionation (MC-TIMS) and mass discrimination (MC-ICP-MS). The isotope abundance ratios determined for various natural cadmium materials represents the isotope composition for natural cadmium materials. Correction of the isotope abundance ratios observed yielded isotope abundances of 106 Cd 0.012450(8), 108 Cd 0.008884(4), 110 Cd 0.124846(16), 111 Cd 0.127955(14), 112 Cd 0.241110(38), 113 Cd 0.122254(22), 114 Cd 0.287439(60) and 116 Cd 0.075183(32). The newly determined atomic weight of natural cadmium based on SI-traceable evaluation of the isotope abundance ratios is 112.41384(18). The cadmium material designated in the paper as Cd-2211 can be used as an isotope reference material with a δ ( 114 Cd/ 110 Cd)-value of 0‰. The results obtained show that the uncertainties for the isotope abundances and the atomic weight given as IUPAC values for cadmium are overestimated.

European Food Research and Technology, 226 (4), ISSN:1438-2377, ISSN:1438-2385

A first attempt was made to estimate an uncertainty budget for the multi-element analysis of glasses using LA-ICP-MS, in accordance with the ‘‘Bottom-up’’ approach of the EURACHEM/CITAC-Guide.1 Analyses of NIST SRM 612, 614 and USGS glasses BCR-2G and BIR-1G were carried out using a 193 nm excimer LA-ICP-MS under routine conditions. Calibration was performed using NIST 610 with internal standardisation using Ca. The uncertainty budgets for the analytes Co, La and Th were studied. Instrumental drift and uncertainties from working values of NIST 610, as reported by Pearce et al.,2 are the dominant sources of uncertainty for a typical individual analysis of NIST 612 and BCR-2G/BIR-1G with mass contents of Co, La and Th ranging from 6 to 52 μg g−1. In contrast, the uncertainty contributions from Poisson counting statistics prevail for those of NIST 614 and BIR-1G with the three elements having a lower range between 0.029 and 0.75 μg g−1. La was an exception. Its combined uncertainties were consistently dominated by its uncertainty from the working value of NIST 610 at all mass content ranges investigated, suggesting that more accurate reference values for the analyte in NIST 610, and for all analytes with large uncertainties, are needed. Additionally, a z-score assessment was carried out using procedures similar to those used in the International Proficiency Test for Analytical Microprobe Geochemistry Laboratories. The z-scores in this study were in the range −2 < z < 2, indicating that there were no significant unsuspected influences in the analytical system. This suggests that the uncertainty budget reported here contains all the significant parameters.

Weighing is a common task in any chemical laboratory and weighing data are associated with some uncertainty, as this is common with all other working procedures and their data. This paper presents the influence factors which are part of the combined measurement uncertainty of a mass determination and their interplay, namely the technical specifications of the balance (repeatability, nonlinearity, sensitivity tolerance, and temperature coefficient of the sensitivity) and the effect of air buoyancy. Depending on the net and gross weight, the densities involved (density of air and of the weighing object in relation to the density of the reference weights) and the uncertainties of these densities the relative uncertainty of weighing data is often in the 10−5 to 10−4 range (10 to 100 ppm). It must be kept in mind that such low values can only be obtained with simple weighing goods, i.e. in the absence of disturbances such as electrostatic charges, air drafts, evaporation, or water adsorption phenomena

The Istituto di Geoscienze e Georisorse (IGG), on behalf and with the support of the International Atomic Energy Agency (IAEA), prepared eight geological materials (three natural waters and five rocks and minerals), intended for a blind interlaboratory comparison of measurements of boron isotopic composition and concentration. The materials were distributed to twenty seven laboratories - virtually all those performing geochemical boron isotope analyses in the world -which agreed to participate in the intercomparison exercise. Only fifteen laboratories, however, ultimately submitted the isotopic and/or concentration results they obtained on the intercomparison materials. The results demonstrate that interlaboratory reproducibility is not well reflected by the precision values reported by the individual laboratories and this observation holds true for both boron concentration and isotopic composition. The reasons for the discrepancies include fractionations due to the chemical matrix of materials, relative shift of the zero position on the δ11B scale and a lack of well characterized materials for calibrating absolute boron content measurements. The intercomparison materials are now available at the IAEA (solid materials) and IGG (waters) for future distribution. L'Istituto di Geoscienze e Georisorse (IGG), pour le compte et avec le soutien de l'Agence Internationale de l'Energie Atomique (AIEA), a prepare huit materiaux geologiques (trois eaux naturelles et cinq roches et mineraux) destines a la conduite d'une comparaison en aveugle des mesures de composition isotopique et de concentration du bore entre differents laboratoires. Vingt-sept laboratoires -pratiquement tous ceux qui travaillent sur les isotopes du bore en geochimie - ont accepte de participer a cette intercomparaison, mais quinze seulement ont finalement envoye leurs donnees de composition isotopique et/ou de concentration du bore. Les resultats demontrent que la precision des valeurs indiquee par les laboratoires reflete mal la reproductibilite entre laboratoires des mesures de composition isotopique comme de concentration du bore. Les raisons de ces discordances peuvent comprendre l'existence de fractionnements isotopiques dus aux matrices chimiques des materiaux, un deplacement relatif du zero de l'echelle de δ11B, ainsi que le manque de materiaux bien caracterises pour calibrer les mesures de concentration du bore. Les materiaux utilises pour l'intercomparaison des mesures sont maintenant a disposition a l'AIEA (materiaux solides) et l'IGG (eaux) pour etre distribues.

The various assays in quantitative analytical chemistry always include mass determinations, along with other operations, and the same is true for the uncertainty budget of such a procedure. In order to obtain an accurate weighing result it is necessary to consider air buoyancy, which depends on, besides other parameters, atmospheric pressure. In contrast to air temperature and humidity, it is not possible to control the atmospheric pressure in a conventional laboratory. Therefore, it can be necessary to consider the uncertainty of pressure in uncertainty calculations of weighing operations, depending on the mass and density of the weighed object. The theoretical relationship between pressure variations and obtained weight value are derived. Experimental confirmation was obtained on the one hand by the mass determination of five Pyrex glass bottles over a period of 6 months; these are objects with a lower density than the reference weights of the balance, thus showing a negative dependence of weight value on atmospheric pressure. On the other hand, a tungsten cylinder was weighed over several weeks; this high-density object has a positive dependence. In both cases the experimental slopes agreed with the theoretical values. The consequences on the uncertainty budget of a weighing operation are remarkable: the total uncertainty of the mass determination of a 90 g glass bottle is 0.3 mg whereas it is 4 μg for a 4.6 g tungsten cylinder. The contributions originating from the pressure variation alone are 0.3 mg and 3.5 μg, respectively, i.e., the pressure uncertainty dominates and is much more important than the uncertainty contributions of balance repeatability and linearity.

Emission factors (EF) of volatile hydrocarbons, oxygenated organics, polycyclic aromatic hydrocarbons (PAH) and sulfur dioxide measured in a road tunnel study (Gubrist tunnel, close to Zurich, Switzerland) in September 1993 are reported, extending the previously published list. The speciation of organic exhaust emission of gasoline powered vehicles agreed generally well with recent tunnel studies from U.S.A.

The standard hydrogen electrode (SHE) acts as a primary reference in electrochemistry. The standard potentials of all other reference electrodes are linked to that of the SHE at the same temperature. The SHE contribution to the cell potential is by convention zero at all temperatures (see Chap. 1).

A single electrofilter ash sample from a municipal waste incinerator was analyzed for PCDD/PCDF. Different pretreatment procedures (chemical: sulfuric acid/no acid; mechanical: ground/not ground) were performed with two independent but identical samples each were subsequently Soxhlet extracted with toluene or subjected to SFE. It was shown, that an acid treatment subsequently combined with SFE gives the most favourable extraction efficiency. Consequently a severe underestimation of PCDD/PCDF concentrations can result from SFE extraction without preliminary acid treatment of the ash.

A new differential pulse polarographic method for the determination of W(VI) using a catalytic adsorption wave is described. W(VI) is first chelated by 7-iodo-8-hydroxyquinoline-5-sulfonic acid at pH 0.5. The complex ion formed is strongly adsorbed on the surface of a dropping mercury electrode. At a potential of −0.95 V versus the Ag/AgCl (3M KCl) reference electrode the adsorbed complex is reduced by the polarographic current and oxidized very fast by hydrated hydrogen ions providing the oxidized form of the complex ion for repeated redox cycles. As the redox process taking place in the electric double layer, the diffusion of the complex does not limit the polarographic current. Therefore, high currents occur, and consequently, a very high sensitivity is obtained. The practical detection limit (PDL) is 3.7 ng W/kg solution corresponding to 2 × 10−11M. The standard deviation of single values is 1.2 ng/kg at the concentration of 91 ng/kg lying in the middle of the linear part of the calibration curve. Because Mo (VI) gives a very similar catalytic adsorption wave, serious mutual interferences occur in the analysis of mixtures of both species. An effective separation of Mo(VI) was worked out. Using 1% (w/v) solution of trioctylphosphinoxide in kerosene, Mo(VI) can almost completely be extracted from 1.8M HCl with a threefold extraction resulting in a separation factor of 40000.

PCDD/PCDF were determined in solid samples from wood combustion. The samples included grate ashes, bottom ashes, furnace ashes as well as fly and cyclone ashes. The solid waste samples were classified into bottom and fly ash from native wood and bottom and fly ash from waste wood. For each of the four classes concentration distribution patterns from individual congeners, the sums of PCDD/PCDF and the international toxicity equivalents (I-TEQ) values are given. The I-TEQ levels of fly ash from waste wood burning can be approximately up to two thousand times higher than the values from fly ashes of natural wood. The I-TEQ levels in bottom ashes from waste wood combustion systems are as low as the corresponding ashes from the combustion of native wood. Grate ash samples from waste wood combustion systems with low carbon burnout show high levels of PCDD/PCDF.

Naturally occurring isotopes of such elements as strontium (Sr) have proved to be good tools for detecting trends in the soil-vegetation system and the tracing of a variety of objects. Multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) has been used for the precise determination of variations in the isotopic composition of Sr. The method described has been applied to the establishment of the potential and limits to determine the geographical origins of different Emmental-type cheese samples. The sample preparation consists of (i) a freeze-drying procedure to remove water, (ii) an extraction step to eliminate the fat components and to obtain the cheese casein fraction, (iii) a thermal decomposition of the latter, and (iv) a chromatographic matrix separation of the redissolved residue. The determination of the isotope abundance ratios 88Sr/86Sr, 87Sr/86Sr and 84Sr/86Sr resulted in precisions of 0.002–0.01%. Simultaneously, the ion currents for krypton (83Kr, 82Kr) and rubidium (85Rb) were measured to correct for interferences with the Sr isotopes 84, 86 and 87. These and further (argide) spectral interferences causing bias effects to the Sr isotope abundance ratios have been investigated and an adequate computational correction procedure has been assessed. The whole set of validation data has been used for the calculation of the combined standard measurement uncertainty of the isotopic abundance ratio, resulting in a value of 0.016%. Comparison of the measured 87Sr/86Sr data with thermal ionisation mass spectrometric (TIMS) results, determined on the same cheese samples, agreed within the stated measurement uncertainties, thus indicating that both the validation of the sample preparation procedures and the mass spectrometric measurements cause no evident bias effect with respect to the Sr isotope abundance values. The 87Sr/86Sr isotope abundance ratios in cheese originating from different regions (alpine, pre-alpine, Bretagne, Finland, Canada, Australia) accorded to local geological properties. No difference was found between “casein-bound” and “whole-cheese” Sr isotope abundance ratios within the stated measurement uncertainties.

Inductively coupled plasma mass spectrometry (ICP-MS) can be used as a screening test for chlorinated organic compounds such as polychlorinated biphenyls (PCBs) in oils. An upper limit for the PCB concentration can be deduced form the chlorine concentration. Owing to the contamination of oils with inorganic chlorine, a differentiation between ‘organic’ chlorine (PCB-chlorine) and inorganic chlorine is necessary. Electrothermal vaporization ICP-MS achieves this using a temperature programme having one step at 400 °C, for the vaporization of the PCBs, and a second at 2650 °C, for the vaporization of the inorganic chlorine compounds. The detection limits are between 0.5 and 10 µg of PCB per gram of oil depending on the nature of the oil and the degree of chlorination of the PCB.