Gas chromatography analysis: method validation and measurement uncertainty evaluation for volume fraction measurements of gases in simulated reformate gas stream

It is important to understand each analytical system and its limitations when performing any chromatographic measurements. In the present paper, a methodology for method validation and measurement uncertainty evaluation for the measurement of volume fractions of selected gases (CO₂, CO, CH₄, H₂) in simulated reformate gas streams by using gas chromatography was developed. A detailed procedure for in-house method validation based on a simple experimental design and consistent statistics is presented. The analytical protocol allowed us to quantify gases in volume fractions from 2.00 to 100.0 mL/(100 mL) with satisfactory recoveries. We proved that the method was selective for the measurement of gases in simulated reformate gas stream. In addition, a step-by-step illustration of modelling approach for measurement uncertainty evaluation of each component is also provided. Uncertainty arising from repeatability and trueness is relatively low, while the contribution from reproducibility is of higher level for all the analytes tested. The main reason for this is changes in atmospheric pressure that affect gas chromatographic measurements. Solution of this problem could be more frequent calibration of apparatus, yielding to higher costs and more time-consuming process, or by measuring the atmospheric pressure and using it to correct the response of the gas chromatograph for resulting variations in sample size. The obtained results confirm that it is imperative to fully characterize the analytical system before proceeding with an analysis.     

Kinetics and mechanism of the reduction of a macrocyclic Rh(III) complex by chromium(II) ions: pH-controlled selectivity to rhodium(II) vs. rhodium(III) hydride

Aqueous chromium(II) ions reduce a macrocyclic Rh(III) complex L(1)(H(2)O)(2)Rh(3+) (L(1) = 1,4,8,11-tetraazacyclotetradecane) to the hydride L(1)(H(2)O)RhH(2+) in two discrete, one-electron steps. The first step generates L(1)(H(2)O)Rh(2+) with kinetics that are first order in each rhodium(III) complex and Cr(H(2)O)(6)(2+), and inverse in [H(+)], k/M(-1) s(-1) = 0.065/(0.0031 + [H(+)]). Further reduction of L(1)(H(2)O)Rh(2+) to L(1)(H(2)O)RhH(2+) is kinetically independent of [H(+)], k/M(-1) s(-1) = 0.30. The difference in [H(+)] dependence allows relative rates of the two steps to be manipulated to generate either L(1)(H(2)O)Rh(2+) or L(1)(H(2)O)RhH(2+) as the final product.     

Principal/Two-Agent model with internal signal

Central European Journal of Operations Research - Our novel game-theoretic Principal/Two-Agent model ensures that the Principal has a reliable internal signal about the Agents’ invested work...     

Determination of Neonicotinoid Pesticides in Propolis with Liquid Chromatography Coupled to Tandem Mass Spectrometry

In this study, a method was developed for the determination of five neonicotinoid pesticides (acetamiprid, clothianidin, imidacloprid, thiacloprid, and thiamethoxam) in propolis. Two sample preparation methods were tested: solid-phase extraction and the quick, easy, cheap, effective, rugged, and safe (QuEChERS) method. The identities of analytes were confirmed using liquid chromatography–tandem mass spectrometry (LC-MS/MS) in the selected reaction monitoring mode. Solid-phase extraction resulted in cleaner extracts; therefore, the SPE-LC-MS/MS method was validated according to the SANTE protocol in triplicate at two spiking levels (10 ng/g and 50 ng/g). The average recoveries of analytes ranged from 61% to 101%, except for clothianidin (10–20%). The LOD ranged from 0.2 ng/g to 4.4 ng/g, whereas the LOQ was in the range of 0.8 ng/g–14.7 ng/g. In order to compensate for the matrix effect, matrix-matched calibration was used. Good accuracy (relative error: 1.9–10.4%) and good linearity (R² > 0.991) were obtained for all compounds. The optimised method was applied to 30 samples: 18 raw propolis and 12 ethanol tinctures. Acetamiprid, imidacloprid, and thiacloprid were detectable in seven samples but were still below the LOQ. This study is the first to report the determination of several neonicotinoid residues in propolis.     

Integration of metrological principles and performance evaluation in a proficiency testing scheme in support of the Council Directive 98/83/EC

Proficiency testing as a means of external quality assessment plays the role of independent evidence of laboratories’ performance. To enable laboratories to fulfil the requirements stated in legislation, methodology for evaluation of laboratories’ performance in proficiency testing schemes should incorporate principles of measurement results which are fit for intended use and incorporate evaluation of laboratories’ performances based on independent reference value. A proficiency testing scheme was designed to support Drinking Water Directive (98/83/EC) specifically. The methodology for performance evaluation, which takes into account a “fitness for purpose”-based standard deviation for proficiency assessment, is proposed and discussed in terms of requirements of the Drinking Water Directive. A ζ′-score, modified by application of target uncertainty was developed in a way that fulfils requirements defined in the legislation. As an illustration, results are reported for nitrate concentration in water. The approach presented can also be applied to other fields of measurements.     

Collection of Finite Lattices Generated by a Poset

It is proved that the collection of all finite lattices with the same partially ordered set of meet-irreducible elements can be ordered in a natural way so that the obtained poset is a lattice. Necessary and sufficient conditions under which this lattice is Boolean, distributive and modular are given.     

Kinetics and mechanism of the reaction of Cr(II) aqua ions with benzoylpyridine N-oxide

Aqueous chromium(II) ions, Cr(aq)(2+), react with benzoylpyridine oxide (BPO) much more rapidly than with other pyridine N-oxides previously explored. The kinetics were studied under pseudo-first order conditions with either reagent in excess. Under both sets of conditions, the major kinetic term exhibits first order dependence on limiting reagent, and second order dependence on excess reagent, i.e.k(Cr) = k2(Cr)[BPO][Cr(aq)(2+)]2 (excess Cr(aq)(2+)), and k(BPO) = k2(BPO)[Cr(aq)(2+)][BPO](2) (excess BPO), where k2(Cr) = (6.90 +/- 0.27) x 10(4) M(-2) s(-1) and k2(BPO) = (3.32 +/- 0.28) x 10(5) M(-2) s(-1) in 0.10 M HClO4. The rate constant k2(Cr) contains terms corresponding to [H+]-independent and [H+]-catalyzed paths. In the proposed mechanism, the initially formed Cr(aq)(BPO)(2+) engages in parallel oxidation of Cr(aq)(2+) and reduction of BPO. The latter reaction provides the basis for a convenient new preparative route for the BPO complex of Cr(III).     

(−)-Isocamphoric Acid Building Block for Chiral Liquid Crystals

The synthesis and liquid-crystal properties of the novel chiral (−)-isocamphoric acid ester 8 are reported. Although the new material is not itself mesogenic, it induces chirality in the nematic and smectic-C phase of an achiral host. A proposed mechanism for the chiral induction according to the `intercalated chirality' model opens the possibility for fine-tuning the chiroptical properties of the induced chiral mesophases.     

Size Measurement of Small Magnetic Particles

Many different methods for size measurement are known and since they differ in their physical principles, different results are also obtained. In the recent past, there were rapid developments in new measurement techniques and one can now quickly and routinely determine particle sizes in the very fine range. Smaller particle sizes, on the other hand, tend to increase the probability of agglomeration. The measurement of the particle sizes for magnetic materials is not well understood and this paper reports results regarding the size determination of very fine magnetic materials. Because of their dipole moment, these particles tend to agglomerate even more, which in turn causes certain difficulties during the measurements. Wet and dry laser measurement systems were compared and also magnetic materials with different permeabilities in order to establish the influence of individual factors on the measurement process and on the accuracy of the results obtained.     

Transition metal ion-assisted photochemical generation of alkyl halides and hydrocarbons from carboxylic acids

Near-UV photolysis of aqueous solutions of propionic acid and aqueous Fe(3+) in the absence of oxygen generates a mixture of hydrocarbons (ethane, ethylene and butane), carbon dioxide, and Fe(2+). The reaction becomes mildly catalytic (about five turnovers) in the presence of oxygen which converts a portion of alkyl radicals to oxidizing intermediates that reoxidize Fe(2+). The photochemistry in the presence of halide ions (X(-) = Cl(-), Br(-)) generates ethyl halides via halogen atom abstraction from FeX(n)(3-n) by ethyl radicals. Near-quantitative yields of C(2)H(5)X are obtained at ≥0.05 M X(-). Competition experiments with Co(NH(3))(5)Br(2+) provided kinetic data for the reaction of ethyl radicals with FeCl(2+) (k = (4.0 ± 0.5) × 10(6) M(-1) s(-1)) and with FeBr(2+) (k = (3.0 ± 0.5) × 10(7) M(-1) s(-1)). Photochemical decarboxylation of propionic acid in the presence of Cu(2+) generates ethylene and Cu(+). Longer-chain acids also yield alpha olefins as exclusive products. These reactions become catalytic under constant purge with oxygen which plays a dual role. It reoxidizes Cu(+) to Cu(2+), and removes gaseous olefins to prevent accumulation of Cu(+)(olefin) complexes and depletion of Cu(2+). The results underscore the profound effect that the choice of metal ions, the medium, and reaction conditions exert on the photochemistry of carboxylic acids.