共查询到20条相似文献,搜索用时 31 毫秒
1.
Petra Spitzer 《Accreditation and quality assurance》2001,6(2):55-60
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 相似文献
2.
P. Ya. Tishchenko 《Russian Chemical Bulletin》2000,49(4):680-684
The Pitzer method was used to calculate the pH values on the conventional and “true” scales for the TRIS—TRIS·HCl−NaCl−H2O buffer system in the 0–40 °C temperature region and 0–4 NaCl molality interval. This buffer can be used as a standard for
pH measurements in a wide range of ionic strengths. The conventional scale is used in cells without a salt bridge. The “true”
scale is recommended for pH measurements using cells with a salt bridge. At the same concentrations of the buffer solution,
the “true” scale is essentially transformed into the scale of the National Bureau of Standards (NBS) of the USA.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 676–680, April, 2000. 相似文献
3.
M. J. Guiomar H. M. Lito M. Filomena Camões Catarina M. Viçoso 《Accreditation and quality assurance》2007,12(9):447-453
Like all experimentally determined physical and chemical properties, pH measurements are affected by the limited precision
and accuracy of the measurement procedures. Fundamental studies of pH standards, based on measurement of the potential of
an electrochemical cell without transference, known as the Harned cell, containing a platinum–hydrogen electrode and a silver–silver
chloride reference electrode, indicate that vapour condensation phenomena on potentiometric cell walls not immersed in the
thermostatic bath are a major source of error in assessment of pH values. In this work a study was conducted on phthalate
buffer, 0.05 mol kg−1 KHPhth, and results are reported for the effect of this phenomenon on the assignment of pH values and on their corresponding
uncertainties. Identification and quantification of this effect constitute an original contribution to improvement of the
primary method of pH measurement and, therefore, more rigorous pH (PS) values. 相似文献
4.
Irina Ekeltchik Elena Kardash-Strochkova Orna Dreazen I. Kuselman 《Accreditation and quality assurance》2002,7(10):412-416
Dependence of the uncertainty of a pH measurement result on the quality of buffers (i.e. the uncertainty of their certified
pH values) at different levels of instrumental uncertainty (pH-meter, etc.) was simulated using the Monte Carlo method and
regression analysis. The contribution of the instrumental standard uncertainty (in the studied range from 0.1 to 1 mV) to
the uncertainty of the pH measurement result is negligible, if the standard uncertainties of the pH buffers exceed 0.04 pH
(e. g. for in-house buffers). It is shown how the choice of pH-meter and buffers should be correlated in order to meet the
required uncertainty of a pH measurement result in a sample under analysis. The results of the simulation were compared with
experimental data obtained from calibrations of a pH/ion-meter with a hydrogen working electrode (Radiometer PHM-240) and
with a glass electrode (Metrohm 744). Buffers of different quality (National Institute for Standards and Technology standard
reference materials, certified Radiometer buffers and Merck CertiPUR buffers) were used for the calibrations. The uncertainties
of the experimental results are close to the predicted ones obtained by the simulation.
Received: 16 June 2002 Accepted: 19 July 2002
Presented at the 14th International Conference of the Israel Society for Quality, 18–21 November 2002, Jerusalem, Israel
Correspondence to I. Kuselman 相似文献
5.
Charun Yafa Sirinapha Srithongtim Pranee Phukphatthanachai Araya Thiparuk Nittaya Sudsiri Laddawan Rojanapantip Mayuree Uraroongroj Panawan Kluengklangdon Preeyaporn Jaengkarnkit Kittipong Sirisuthanant Chamoy Thonglue Thanida Pimma Paramee Pengpreecha Tippaya Julwee Fortune Ratirot Zwicker Vorapot Permnamtip Sirinart Laoharojanaphnad Boonlert Suanmamuang Juwadee Shiowatana Weerawan Waiyawat Atitaya Siripinyanond Kunchit Judprasong Benjawan Boonsong Suwaluck Talaluck Chainarong Cherdchu 《Accreditation and quality assurance》2010,15(4):223-231
Reference materials play an important role for evaluating the accuracy of analytical results, and are essential parts of good laboratory practice. They represent a key tool for quality control of chemical analyses. In Thailand, the demand of food and environmental reference materials is constantly increasing, and the National Institute of Metrology (NIMT, Thailand) is responding to the urgent needs for affordable materials, which require collaborative efforts at the national level. This paper describes the preparation of a new glutinous rice reference material, along with homogeneity and stability studies and the analytical work carried out for the certification of the contents of inorganic elements. The incurred material was collected from an actual rice paddy field. Material preparation along with homogeneity and stability testing were carried out at the Environmental Research Training Centre (ERTC). The homogeneity study was designed to have three experimental conditions; (A) 10 bottles of candidate materials being analyzed each with 2 replicates, (B) 20 bottles with 2 replicates, (C) 10 bottles with 7 replicates, in order to study the suitable treatments for homogeneity testing in the reference material production. It was shown that a minimum number of 10 bottles with duplicate analyses are enough to demonstrate the homogeneity of candidate reference material. Certification of a candidate reference material in a single laboratory using reference method was confirmed with an interlaboratory comparison participated by a certain number of well recognized testing laboratories in Thailand. Further elaborative results will be discussed. 相似文献
6.
The IAEA conducted the IAEA-CU-2006-06 Proficiency Test (PT) on “The determination of major, minor and trace elements in ancient
Chinese ceramic” in 2006. The results of this PT showed that of the 21 analytes reported by our laboratory 9 failed the precision
criteria. Therefore the results reported by our laboratory along with the results of other laboratories which carried out
analysis using neutron activation analysis (NAA) were studied. It was found that the major factor contributing towards data
falling in the “Warning” category, failing the precision criteria was the high uncertainties cited in the certificates of
the reference materials (RMs) used for quantification of data. In this regard, it is recommended that synthetic standards
should be prepared and used on a routine basis especially for the measurement of the elements K, Eu, Lu, Ta, Tb and Yb. 相似文献
7.
Our understanding of metal ion adsorption to clay minerals has progressed significantly over the past several decades, and theories have been promulgated to describe and predict the impacts of pH, ionic strength, and background solution composition on the extent of adsorption. Studies evaluating the effects of ionic strength on adsorption typically employ a broad range of background electrolyte concentrations. Measurement of pH in these systems can be inaccurate when pH values are measured with liquid junction pH probes calibrated with standard buffers due to changes in the liquid junction potential between standard, low ionic strength (0.05 M) buffers and high ionic strength solutions (>0.1 M). The objective of this research is to determine the extent of the error in pH values measured at high ionic strength, and to develop an approach for accurately measuring pH over a range of ionic strengths using a combined pH electrode. To achieve this objective, the adsorption of cobalt (10(-5) M) onto gibbsite (10 g/L) from various electrolyte solutions (0.01-1 M) was studied. The pH measurements were determined from calibrations with standard buffers and ionic strength corrected buffer calibrations. The results show a significant effect of the aqueous solution background electrolyte anion and ionic strength on pH measurement. The 0.5 and 1 M ionic strength metal ion adsorption edges shifted to lower pH with increasing ionic strength when pH was calibrated with standard buffers whereas no shift in the adsorption edges was observed when calibrated with ionic strength corrected buffers. Therefore, to obtain an accurate pH measurement, pH calibration should contain the same electrolyte and ionic strength as the samples. 相似文献
8.
Marc Priel 《Accreditation and quality assurance》2009,14(5):235-241
Since the advent of the Guide to the expression of Uncertainty in Measurement (GUM) in 1995 laying the principles of uncertainty
evaluation numerous projects have been carried out to develop alternative practical methods that are easier to implement namely
when it is impossible to model the measurement process for technical or economical aspects. In this paper, the author presents
the recent evolution of measurement uncertainty evaluation methods. The evaluation of measurement uncertainty can be presented
according to two axes based on intralaboratory and interlaboratory approaches. The intralaboratory approach includes “the
modelling approach” (application of the procedure described in section 8 of the GUM, known as GUM uncertainty framework) and
“the single laboratory validation approach”. The interlaboratory approaches are based on collaborative studies and they are
respectively named “interlaboratory validation approach” and “proficiency testing approach”. 相似文献
9.
In order to verify the quality of biological measurements, the National Institute of Chemistry in Slovenia is regularly organizing
interlaboratory comparisons to estimate the analytical precision of different laboratories using the same test and to determine
if statistically significant differences exist between results. Several interlaboratory trials named “ILC-Waste Water” (ILC-WW)
were organized in the last 7 years. Acute toxicity testing with Daphnia magna mobility inhibition assay (ISO 6341) was included in eight successive rounds and about 20 laboratories from Slovenia and
a few adjacent countries took part in each study with two samples (T1 and T2) at two different concentration levels. Variation
coefficients of the mean 24 h
EC50s were determined for each exercise and the evaluation of the interlaboratory variability was analysed. Comparisons were also
made of the results and the variability laboratories using organisms taken from laboratory cultures versus those who used
daphnias hatched from dormant eggs (Daphtoxkits). 相似文献
10.
Target measurement uncertainties (TMUs), which should be achieved in chemical measurements, are proposed. Such TMUs are intended to set goals for measurement laboratories and could provide independent and objective criteria for laboratory assessors verifying the measurement capability of laboratories. A TMU is specified relative to a stated metrological reference for the measurand concerned. TMUs are common and objective, but are external criteria for both the measurement laboratories and their assessors. They are decided on the basis of the intended use of the measurement result, not evaluated as is the case for measurement uncertainty. The concept of TMU is illustrated by means of desirable applications in food measurements in Slovenia.P. De Bièvre is an Independent Consultant on Metrology in ChemistryPresented at the session Metrology in Chemistry of the XVII IMEKO World Congress, 26 June 2003, Dubrovnik-Cavtat, Croatia 相似文献
11.
Baibikov F. A. Vlasov G. A. Kozen A. L. Buravtseva G. I. Balduev M. E. 《Russian Journal of Applied Chemistry》2009,82(9):1721-1728
The Russian Federation in January 1993 signed the Parisian “Convention about the prohibition of development, production, accumulation
and application of chemical weaponry and about its destruction.” In 1996 Federal target program “The destruction of the reserves
of chemical weaponry in the Russian Federation” that has status of presidential was approuved for purposes of the realization
of the Convention. The convention came into force on April 29, 1997. 相似文献
12.
Iris Blankenhorn Dirk Meijer Robert J. Delft 《Fresenius' Journal of Analytical Chemistry》1992,343(6):497-504
Summary In view of the investigation of contaminated model sites in Baden-Württemberg an inter-laboratory comparison was organized for the methods used for analysing polycyclic aromatic hydrocarbons (PAHs). The laboratories performing chemical and physical analyses at the model sites participated at the request of the Landesanstalt für Umweltschutz, Baden-Württemberg. This inter-laboratory comparison was meant as a first laboratory evaluation, and not as the search for the best method available. Furthermore, it was to show the difficulties in comparing results from different laboratories, which have analysed identical samples. The results of the inter-laboratory comparison between the nine laboratories showed a reproducibility coefficient of variation, for the total of the 16 PAHs according to the EPA, between 48.8 and 61.1% in the concentration range of 5 to 55 mg/kg in the soil samples. One of the laboratories reported significantly lower values compared with the true value. This was probably due to an ill-suited (sample) preparation method. Although the results of the inter-laboratory comparison are, in general, satisfactory, the reproducibility can be improved by standardizing the analytical method for the determination of PAHs in solid environmental samples. 相似文献
13.
Prenesti E Fisicaro P Berto S Ferrara E Daniele PG 《Analytical and bioanalytical chemistry》2007,387(7):2595-2600
This paper reports evaluation of the behaviour of different combined glass electrodes applied to measurement of the pH of
a primary, 0.01 mol kg−1, tetraborate buffer. Measurements were first performed by use of a primary Harned cell (at 15, 25, and 37 °C); these results
were then compared with those obtained for the same solution by use of three combined glass electrodes (25 °C) with different
membranes and liquid-junction designs, calibrated by use of commercial pH-metric buffers. The pH of the same solution was
also measured in terms of the molal concentration of hydrogen ions, using acid–base titration to evaluate the formal potential
difference K of each cell at fixed ionic strength, I, adjusted by addition of KCl or Et4NI (tetraethylammonium iodide). The reference value from primary measurement, paH = 9.171, was slightly closer to the mean value obtained by determination of concentration, rather than that obtained by
direct measurement of activity; the differences were smaller than the extended uncertainty characteristics of the secondary
measurements. The importance of evaluation of the ionic strength of the solution under study is emphasised. We verified that
for tetraborate buffer slight modification of the value of I used to calculate γ
i
(the activity coefficient of a single ion) in the calculation of paH from the acidity function at zero molality of chloride can significantly affect the reference value of the calibrator tool.
This is true, in general, for low values of the ionic strength, such as those considered in this work; an approximate value
of I can then cause distortions along the pH traceability chain. Application of the concepts of thermodynamics to this traceability
chain is discussed. 相似文献
14.
The adsorption and migration behavior of a radionuclide in geological media heavily depends on its chemical forms in a given
chemical environment. In order to predict the temporal and spatial distribution of radionuclides around a disposal site when
its canister is damaged, it is necessary to develop coupled chemical speciation-solute transport models and relevant software.
For that reason, we wrote a new chemical speciation program CHEMSPEC. In this paper, the principles and structure of CHEMSPEC
are briefly described, and the strategy and algorithms that were used in this code are interpreted in some detail, such as
the measures adopted to prevent divergence in iteratively solving the mass balance equations, the “predictor-corrector” algorithm
for calculation of the number and quantities of solid species formed, and the alternate use of “freezing” and “defreezing”
oxidation states in handling of co-existent redox and precipitation equilibria. Four examples are given to illustrate CHEMSPEC’s
features and capabilities. 相似文献
15.
Matschat R Hassler J Traub H Dette A 《Analytical and bioanalytical chemistry》2005,383(7-8):1060-1074
The members of the committee NMP 264 “Chemical analysis of non-oxidic raw and basic materials” of the German Standards Institute
(DIN) have organized two interlaboratory comparisons for multielement determination of trace elements in silicon carbide (SiC)
powders via direct solid sampling methods. One of the interlaboratory comparisons was based on the application of inductively
coupled plasma optical emission spectrometry with electrothermal vaporization (ETV ICP OES), and the other on the application
of optical emission spectrometry with direct current arc (DC arc OES). The interlaboratory comparisons were organized and
performed in the framework of the development of two standards related to “the determination of mass fractions of metallic
impurities in powders and grain sizes of ceramic raw and basic materials” by both methods. SiC powders were used as typical
examples of this category of material. The aim of the interlaboratory comparisons was to determine the repeatability and reproducibility
of both analytical methods to be standardized. This was an important contribution to the practical applicability of both draft
standards. Eight laboratories participated in the interlaboratory comparison with ETV ICP OES and nine in the interlaboratory
comparison with DC arc OES. Ten analytes were investigated by ETV ICP OES and eleven by DC arc OES. Six different SiC powders
were used for the calibration. The mass fractions of their relevant trace elements were determined after wet chemical digestion.
All participants followed the analytical requirements described in the draft standards. In the calculation process, three
of the calibration materials were used successively as analytical samples. This was managed in the following manner: the material
that had just been used as the analytical sample was excluded from the calibration, so the five other materials were used
to establish the calibration plot. The results from the interlaboratory comparisons were summarized and used to determine
the repeatability and the reproducibility (expressed as standard deviations) of both methods. The calculation was carried
out according to the related standard. The results are specified and discussed in this paper, as are the optimized analytical
conditions determined and used by the authors of this paper. For both methods, the repeatability relative standard deviations
were <25%, usually ~10%, and the reproducibility relative standard deviations were <35%, usually ~15%. These results were
regarded as satifactory for both methods intended for rapid analysis of materials for which decomposition is difficult and
time-consuming. Also described are some results from an interlaboratory comparison used to certify one of the materials that
had been previously used for validation in both interlaboratory comparisons. Thirty laboratories (from eight countries) participated
in this interlaboratory comparison for certification. As examples, accepted results are shown from laboratories that used
ETV ICP OES or DC arc OES and had performed calibrations by using solutions or oxides, respectively. The certified mass fractions
of the certified reference materials were also compared with the mass fractions determined in the interlaboratory comparisons
performed within the framework of method standardization. Good agreement was found for most of the analytes. 相似文献
16.
Ricardo J. N. Bettencourt da Silva Maria Filomena G. F. C. Camões 《Accreditation and quality assurance》2010,15(12):691-704
The dispersion of results from proficiency tests for the analysis of pesticide residues in foodstuffs suggests that improvements
in the compatibility of measurement results are needed. Currently observed divergences can make the evaluation conclusion
on foodstuffs compliance with certain legislation dependent on the consulted laboratory. This work discusses the origin and
impact of this lack of compatibility, following the metrological concepts presented at the latest version of the “International
Vocabulary of Metrology” (VIM3), thus allowing for a clear diagnostic of the problem. The reporting of results from different
measurement methods uncorrected for the observed analyte recovery makes them traceable to different “operationally defined
measurement procedures” (VIM3) and, therefore, not comparable. When results from different measurement methods are reported
corrected for analyte recovery, R, and R is different for spiked and incurred residues, measurement results may be not compatible if this effect is not considered
on the uncertainty budget. This discussion is illustrated with metrological models for any possible combination of “measurement
performance” and “maximum residue level”. These models are complemented with experimental data of the analysis of pesticide
residues in a sample of ginseng powder from a proficiency test. The adopted experimental design allowed the identification
of additional threats to metrological compatibility in this field. Solutions to the faced problem are discussed for practicability
and impact on regulatory issues. The use of a universal “reference measurement procedure” proves to be the most feasible way
of ensuring comparability of measurements in this field. 相似文献
17.
David Lee Duewer 《Accreditation and quality assurance》2008,13(12):725-726
The distribution of interlaboratory results can often be successfully modeled as a mixture of distributions: a “majority”
population of results from laboratories of high and roughly equal competence and a (hopefully) minority “contaminant” population
from laboratories of lesser competence. Approximating the majority population as a normal distribution and the contaminant
as a uniform distribution can be and has been used to produce mixture populations that have realistically “heavy-tails” (i.e.,
leptokurtic).
Papers published in this section do not necessarily reflect the opinion of the Editors, the Editorial Board and the Publisher. 相似文献
18.
Characterization of groundwater humic and fulvic acids of different origin by GPC with UV/Vis and fluorescence detection 总被引:1,自引:0,他引:1
R. Artinger G. Buckau J. I. Kim S. Geyer 《Fresenius' Journal of Analytical Chemistry》1999,364(8):737-745
Gel permeation chromatography (GPC) was applied for recognizing the origin of groundwater humic and fulvic acids. GPC was
performed with Fraktogel TSK HW-50 in 0.1 M NaCl, pH 8.5 (0.05 M phosphate buffer), 1 mM EDTA, with 10% by volume methanol
added. Humic substances from groundwaters and sediments of four different aquifer systems in Germany were isolated, purified
and characterized. Both UV/Vis and fluorescence detection were applied. UV/Vis detection was found to be more powerful in
identifying differences between the various humic and fulvic acids. The four aquifer systems investigated (“Gorleben”, “Fuhrberg”,
“Franconian Albvorland” and “Munich”) differed from one another with respect to hydrological and geochemical conditions. The
results showed that the GPC-elution behavior reflects the geochemical environment and origin (source material and generation
process) of aquatic humic and fulvic acids.
Received: 17 November 1998 / Revised: 18 March 1999 / Accepted 23 March 1999 相似文献
19.
Subir K. Basak Ajoy Velayudhan Michael R. Ladisch 《Applied biochemistry and biotechnology》1994,44(3):243-261
Buffers used in electrophoresis and electrochromatography must have a relatively low ionic strength in order to minimize ohmic
heating in the presence of an applied potential. Calculation of pH, ionic strength, and the van Slyke buffer capacity, β,
is therefore important. This paper describes thea priori calculation of these parameters for tris buffer made up with either glycine (a zwitterion) or HCl. A quadratic expression
for pH, valid over wide ranges, is obtained for both buffer systems. The calculated values of pH, ionic strength, and buffer
capacity are shown to agree with experimental results as a function of tris, HCl, and glycine concentrations ranging from
1 to 50 mM. A new parameter, the electrokinetic buffer effectiveness factor, is introduced to characterize buffers being considered
for use in electrokinetic systems such as electrochromatography, and is used to determine the appropriate composition ranges
for the buffer components. 相似文献
20.
A statistical analysis of multi-point calibration procedure for practical measurement of pH under laboratory conditions is
given. The procedure is shown to provide the necessary elements for simple assignment of an uncertainty to a pH measurement
– an essential element of quality control. Performance of ordinary least squares regression for prediction of confidence limits
is compared to orthogonal regression, inverse regression and Monte Carlo simulations. In case of pH measurement by multi-point
calibration procedure, methods considering uncertainties in both axes are found to be statistically more satisfactory than
ordinary least squares regression. By analysis of 50 pH calibration data, randomly selected from 250 5-point glass electrode
calibrations, it is found that the practical differences, however, are of minor importance. The significance of uncertainty
in pH is demonstrated for an example from metal ion speciation in aqueous solution.
Received September 20, 1999. Revision April 19, 2000. 相似文献