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A procedure for estimation of measurement uncertainty of routine pH measurement (pH meter with two-point calibration, with
or without automatic temperature compensation, combination glass electrode) based on the ISO method is presented. It is based
on a mathematical model of pH measurement that involves nine input parameters. Altogether 14 components of uncertainty are
identified and quantified. No single uncertainty estimate can be ascribed to a pH measurement procedure: the uncertainty of
pH strongly depends on changes in experimental details and on the pH value itself. The uncertainty is the lowest near the
isopotential point and in the center of the calibration line and can increase by a factor of 2 (depending on the details of
the measurement procedure) when moving from around pH 7 to around pH 2 or 11. Therefore it is necessary to estimate the uncertainty
separately for each measurement. For routine pH measurement the uncertainty cannot be significantly reduced by using more
accurate standard solutions than ±0.02 pH units – the uncertainty improvement is small. A major problem in estimating the
uncertainty of pH is the residual junction potential, which is almost impossible to take rigorously into account in the framework
of a routine pH measurement.1
Received: 11 August 2001 Accepted: 22 February 2002 相似文献
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Kütt A Movchun V Rodima T Dansauer T Rusanov EB Leito I Kaljurand I Koppel J Pihl V Koppel I Ovsjannikov G Toom L Mishima M Medebielle M Lork E Röschenthaler GV Koppel IA Kolomeitsev AA 《The Journal of organic chemistry》2008,73(7):2607-2620
A general route to functionalized pentakis(trifluoromethyl)phenyl (C6(CF3)5) derivatives, promising building blocks for designing novel stable carbenes, radical species, superacids, weakly coordinating anions and other practically and theoretically useful species, is presented. This pertrifluoromethylation route proceeds via conveniently pregenerated (trifluoromethyl)copper (CF3Cu) species in DMF, stabilized by addition of 1,3-dimethyl-2-imidazolidinone (DMI). These species react with hexaiodobenzene at ambient temperature to give the potassium pentakis(trifluoromethyl)phenoxide along with hexakis(trifluoromethyl)benzene and pentakis(trifluoromethyl)benzene in a combined yield of 80%. A possible reaction pathway explaining the formation of pentakis(trifluoromethyl)phenoxide is proposed. Pentakis(trifluoromethyl)phenol gives rise to easily functionalized pentakis(trifluoromethyl)chlorobenzene and pentakis(trifluoromethyl)aniline. Pertrifluoromethylation of pentaiodochlorobenzene and pentaiodotoluene allows straightforward access to pentakis(trifluoromethyl)chlorobenzene and pentakis(trifluoromethyl)toluene, respectively. XRD structures of several C6(CF3)5 derivatives were determined and compared with the calculated structures. Due to the steric crowding the aromatic rings in all C6(CF3)5 derivatives are significantly distorted. The gas-phase acidities (Delta Gacid) and pKa values in different solvents (acetonitrile (AN), DMSO, water) for the title compounds and a number of related compounds have been measured. The origin of the acidifying effect of the C6(CF3)5 group has been explored using the isodesmic reactions approach. 相似文献
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Merike Lillenberg Sergei Yurchenko Karin Kipper Koit Herodes Viljar Pihl Kalev Sepp Rünno Lõhmus Lembit Nei 《Journal of chromatography. A》2009,1216(32):5949-5954
A new scheme for the quantitative determination of traces of fluoroquinolones (FQs), tetracyclines (TCs) and sulfonamides (SAs) in sewage sludge was developed. The compounds were simultaneously extracted from sewage sludge by pressurized liquid extraction (PLE). A novel and effective method for PLE was developed. Solid-phase extraction was used for cleaning up the extracts. Identification and quantification of the compounds was done using high-performance liquid chromatography with electrospray ionization mass spectrometry in selected reaction monitoring mode. The best recovery of FQs and TCs was obtained by using hydrophilic–lipophilic balance cartridges, recoveries ranged 59% for norfloxacin to 82% for ofloxacin and 95% for doxycycline; for SAs strong cation-exchange cartridges were more efficient, recoveries were 96% for sulfamethoxazole and 43% for sulfadimethoxine. Limit of quantification ranged from 0.1 ng/g for SAs to 160 ng/g for tetracycline. Method precision for TCs was 5.06% and 1.12%, and for SAs 0.43% and 2.01%. FQs precision ranged from 0.77% to 1.89%. 相似文献
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Kaljurand I Rodima T Pihl A Mäemets V Leito I Koppel IA Mishima M 《The Journal of organic chemistry》2003,68(26):9988-9993
Eleven new phenyl-substituted phosphazenes (P1-, P3-, and P4-bases) have been synthesized by the Staudinger or the Kirsanov reactions. The UV-vis spectrophotometric titration method was used to establish the relative basicity of them, and to extend the ion-pair basicity scale for THF medium. These measurements together with our previous work give a continuous basicity scale in THF ranging from 2.6 (2-MeO-pyridine) to 26.6 (2-Cl-C6H4P4(pyrr) phosphazene) in pKalpha units: that is for 24 orders of magnitude and containing 58 compounds (pyridines, anilines, amines, guanidines, amidines, phosphazenes). Ion-pair formation was taken into account by using the Fuoss equation. DeltapKip values of some phosphazene indicators estimated earlier by the 13C NMR method were revised. For some of the phosphazenes gas-phase basicities were measured. 相似文献
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Ako Rodima Martin Vilbaste Olev Saks Erko Jakobson Eve Koort Viljar Pihl Lilli Sooväli Lauri Jalukse Julia Traks Kristina Virro Heiki Annuk Kristjan Aruoja Aare Floren Ene Indermitte Monika Jürgenson Paavo Kaleva Kalle Kepler Ivo Leito 《Accreditation and quality assurance》2005,10(7):369-372
The experience of working under an ISO 17025 compliant quality system in a university environment is described in the example
of the Testing Centre of University of Tartu. University-specific features of the quality system include that the Testing
Centre acts as the “quality system server” for other units of the university and graduate students participate in the work
carried out under the quality system. The benefits for the university and the graduate students are discussed. It is concluded
that implementation of an ISO 17025 compatible quality system in a university is fully accomplishable and gives significant
added value to the university by helping to destroy the ivory tower perception about universities and by introducing real-world
flavour into the studies and broaden the minds (quality awareness) of the students. 相似文献
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The high-spin states of 125Te have been investigated using the 124Sn (α, 3nγ) reaction and the in-beam technique. Besides low-spin levels observed in the radioactive decay, the high-spin positive- and negative-parity bands have been established. As a possible explanation of the nature of the excited states in 125Te the idea of the odd-neutron(hole)-core coupling is discussed. 相似文献
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Maria Pihl Krzysztof Kolman Antiope Lotsari Marie Ivarsson Erich Schüster Niklas Lorén 《Journal of Dispersion Science and Technology》2019,40(4):555-562
Development of multi-purpose probes for mass transport measurements is of importance to gain knowledge in diffusional behaviour in heterogeneous structures such as food, hygiene or pharamceuticals. By combining different techniques, such as Fluorescence Recovery After Photobleaching (FRAP) and Nuclear Magnetic Resonance Diffusometry (NMR-d), information of both local and global diffusion can be collected and used to gain insights on for example material heterogeneities and probe-material interactions. To obtain a FRAP-responsive probe, fluorescent silica particles were produced using fluorescent preconjugates added in a modified Stöber process. A NMR-d responsive moiety was introduced by derivatizing the fluorescent silica particles with polyethylene glycol. The particle size distributions were determined by dynamic light scattering and transmission electron microscopy and these measurements were compared to value extrapolated from diffusion measurements using FRAP and NMR-d. The good agreement between the FRAP and NMR-d measurements demonstrates the potential of multi-purpose probes for future applications concerning mass transport at local and global scale simultaneously. 相似文献