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1.
The measurement uncertainty of the result of chemical oxygen demand determination in wastewater was evaluated. The major
sources of uncertainty of the result of measurement were identified as the purity of reagents, volumetric operations, gravimetric
operations, bias, and the repeatability of the method. Identification and evaluation of uncertainty sources was followed by
combined uncertainty calculations. The combined uncertainty was compared to the experimentally determined variation and good
agreement was found, indicating that the major uncertainty sources had been identified. The results show that the major sources
of uncertainty arose from repeatability at high concentration level and volumetric steps at low concentration level, thus
revealing the target operations for reducing the measurement uncertainty of this determination.
Received: 5 August 2002 Accepted: 5 November 2002
Acknowledgements This research was supported by the Ministry of Education, Science and Sport of the Republic of Slovenia (Project Z2–3530).
Presented at CERMM-3, Central European Reference Materials and Measurements Conference: The function of reference materials
in the measurement process, May 30–June 1, 2002, Rogaška Slatina, Slovenia
Correspondence to A. Drolc 相似文献
2.
Summary An ion-chromatographic procedure is described for the determination of selenium (VI) at μg L−1 level in the presence of anions and heavy metal ions. Maximum permissible concentrations and effects from each interfering
substance were investigated for the Se concentration range 12.5–1,000 μg L−1. The method, optimized for the detection of SeO
4
2−
, gives results suitable for speciation analysis. Total selenium can be determined after complete conversion to selenate ion
by oxidation with KMnO4. The detection limit of selenium is 4.8 μg L−1 (0.96 ng for 200 μL sample).
Paper presented at the 41st Pittsburgh Conference, New York, March 5–9, 1990. 相似文献
3.
T. Drglin 《Accreditation and quality assurance》2003,8(3-4):130-133
A validation procedure based on the ISO/IEC 17025 standard was used to demonstrate the long-term stability of a calibration
process and to assess the measurement uncertainty of a standard test method for optical emission vacuum spectrometric analysis
of carbon and low-alloy steel (ASTM E 415–99a). The validation was used to provide documented evidence that the selected method
fulfils the requirements and that the method is ”fit for purpose”. A test for drift was applied to determine statistically
whether the analytical results vary systematically with time. The accuracy and traceability of the optimised method were tested
by an analysis of closely matched matrix certified reference materials (CRMs). The measurement uncertainty estimations took
account of the precision study, the bias and its uncertainty, and the qualification of uncertainties not considered in the
overall performance studies.
Received: 2 November 2002 Accepted: 2 January 2003
Acknowledgement The author expresses gratitude to Dr. Aleš Fajgelj for helpful discussions during the 3rd Central European Conference on Reference Materials and Measurements.
Presented at CERMM-3, Central European Reference Materials and Measurements Conference: The function of reference materials
in the measurement process, May 30–June 1, 2002, Rogaška Slatina, Slovenia
Correspondence to T. Drglin 相似文献
4.
N. Majcen 《Accreditation and quality assurance》2003,8(3-4):108-112
The fact that various definitions and terminology applied to measurements in analytical chemistry are not always consistent
and straightforward, by not only answering the question ”what”, but also ”how”, leads to their various interpretations. This
results in non-uniform implementation of very basic and essential metrological principles in chemistry. Such a diverse situation
is not conducive to the endorsement of harmonised measurements all across the world, to serve as a tool for improving the
quality of life in its broadest sense for all its citizens. The discussion in this paper is focused on problems associated
with terminology and definitions of ’reference material’ and ’validation’. The role of reference materials in measurement
processes for purposes other than calibration and validation principles in analytical chemistry are also discussed in this
paper. Where possible, potential solutions are proposed, but more often, questions of essential importance are raised in order
to initiate international discussion which will hopefully lead to equally understandable answers.
Received: 2 November 2002 Accepted: 3 February 2003
Acknowledgements
The author is grateful to Aleš Fajgelj for his comprehensive comments on the topic described in this paper. Sincere thanks
also to Philip Taylor, Ewa Bulska, Emilia Vassileva, Miloslav Suchanek and Margreet Lauwaars for their contribution during
fruitful discussions on validation.
Presented at the CERMM-3, Central European Reference Materials and Measurements Conference: The function of reference materials
in the measurement process, May 30–June 1, 2002, Rogaška Slatina, Slovenia
Correspondence to N. Majcen 相似文献
5.
Measurement uncertainties in the determination of 210Pb and 210Po in Reference Material IAEA-300 (Baltic Sea Sediment) were evaluated. 210Pb and 210Po were separated from the matrix using an Sr resin column. The chemical yield of 210Pb was determined gravimetrically in PbSO4 form. Precipitation was followed by beta proportional counting after 210Bi ingrowth. 210Po was determined by alpha spectrometry after its spontaneous deposition on a Cu planchet. The major source of uncertainty
was identified as the statistical counting uncertainty, which was also expected and is almost impossible to reduce without
extension of the time required for an analysis. The expanded uncertainties were determined as 7.4% and 12.2% for 210Pb and 210Po, respectively.
Received: 3 September 2002 Accepted: 3 December 2002
Acknowledgement This work was financially supported by Ministry of Education, Science and Sport, Republic of Slovenia (Project group PO-0106–0532).
Presented at CERMM-3, Central European Reference Materials and Measurements Conference: The function of reference materials
in the measurement process, May 30–June 1, 2002, Rogaška Slatina, Slovenia
Correspondence to P. Vreˇcek 相似文献
6.
Hosakere D. Revanasiddappa Banadahalli P. Dayananda 《Central European Journal of Chemistry》2006,4(4):592-603
Highly sensitive and simple spectrophotometric determination of selenium is described for the determination of selenium(IV)
using a new reagent leuco malachite green. The method is based on the reaction of selenium(IV) with potassium iodide in an
acidic condition to liberate iodine, the liberated iodine oxidizes leuco malachite green to malachite green dye. The green
coloration was developed in an acetate buffer (pH 4.2–4.9) on heating in a water bath (∼ 40 °C). The formed dye exhibits an
absorption maximum at 615 nm. The method obeys Beer’s law over a concentration range of 0.04–0.4 μg mL−1 selenium. The molar absorptivity and Sandell’s sensitivity of the color system were found to be 1.67 × 105 L mol−1 cm-1 and 0.5 ng cm−2, respectively. The optimum reaction conditions and other analytical parameters have been evaluated. The proposed procedure
has been successfully applied to the determination of selenium in real samples of water, soil, plant material, human hair,
and cosmetic samples. The results were compared to those obtained with the reference method. Statistical analysis of the results
confirms the precision and accuracy of the proposed method. In addition, the developed method is cost-effective and involves
easily accessible instrumentation technique which can be used by ordinary research laboratories. 相似文献
7.
Selenomethionine content of candidate reference materials 总被引:1,自引:0,他引:1
Selenium has been identified as an antioxidant of importance in the diet. Accurate determination of its chemical forms depends
on the availability of suitable reference materials (RMs). Two candidate reference materials for determination of selenomethionine
(Semet) in food-related materials, a standard wheat gluten sample (NIST RM 8418 Wheat Gluten) and a commercial selenium enriched
yeast, have been examined by use of a gas chromatography–isotope dilution mass spectrometry (IDMS) procedure, after treatment
of the matrix with 0.1 mol L–1 hydrochloric acid containing stannous chloride, addition of CNBr, and extraction with chloroform. This procedure results
in cleavage of the CH3Se group to form volatile CH3SeCN. Addition of isotopically enriched 74Semet to an analytical sample enables estimation of the naturally occurring protein-bound 80Semet by IDMS without a protein-digestion process.
We found that the Wheat Gluten RM contains a significant amount of Semet as a portion of its assigned value of 2.58 μg Setotal g–1. Commercial selenium yeast tablets are labeled as containing an elevated level of “organic selenium”, usually as Semet. The
sample we investigated contained 210 μg Setotal g–1 sample as determined separately by IDMS, measuring elemental selenium after digestion. 73% of this total (153±21 μg SeSemet g–1; n = 23) was present as Semet. Thus, these two materials contain significant amounts of their total selenium content as Semet
and would be good candidates for further study and characterization as reference materials for determining this important
food component.
The CNBr reaction used will also enable the determination of Se-(methyl)selenocysteine, the biological role of which is of
recent interest. In addition to matrix RMs for Semet, it is important to have standard materials of the pure substance. We
have examined a sample of a candidate standard material of selenomethionine being prepared by the USP. It was confirmed that
this material is pure selenomethionine.
Received: 13 December 2000 / Revised: 5 March 2001 / Accepted: 12 March 2001 相似文献
8.
Giovanni Calaresu Patrizia Piras Gavina Carta Roberta Galarini Giannina Chessa 《Accreditation and quality assurance》2006,11(1-2):10-16
A measurement uncertainty estimated for aflatoxin M1 determination in milk sample has been calculated using data generated from analytical method validation studies. The protocol
adopted is described in detail in document LGC/VAM/1998/088. The uncertainty budget was based on precision, trueness and ruggedness
data. The individual contributions are described in detail. The expanded uncertainty for aflatoxin M
1 at a concentration of 20 ng L−1 was estimated as 2.81 ng L−1. This was calculated using a coverage factor of two which gives a level of confidence of approximately 95%.
Presented at AOAC Europe / Eurachem Symposium March 2005, Brussels, Belgium 相似文献
9.
Ewelina Chajduk Halina Polkowska-Motrenko Rajmund S. Dybczyński 《Accreditation and quality assurance》2008,13(8):443-451
This article describes work on the development of a highly accurate RNAA method for determination of selenium in biological
samples. The analytical post-irradiation procedure is based on a combination of cation-exchange and extraction chromatography
with final selective and quantitative fixation of selenium on a column packed with 3,3′-diaminobenzidine (DAB) supported on
Amberlite XAD4, followed by gamma-ray spectrometric measurement. The suitability and accuracy of the method was demonstrated
by analysing CRMs with certified selenium content. The uncertainty budget for Se determination in standard reference material
Peach Leaves NBS 1547 was estimated; the combined standard uncertainty was calculated as 1.7%. The described method fulfils
all the criteria for definitive methods. It was subsequently used for determination of selenium in biological materials intended
as new CRMs and proficiency test samples. 相似文献
10.
Determination of selenium in soil by hydride generation AAS 总被引:2,自引:0,他引:2
Hydride generation AAS was applied for the determination of total selenium in soil. The influence of various anions and cations
present in the sample solution on the generation of selenium hydride was investigated. Special attention was paid to the wet
oxidation procedure for the sample dissolution. The proposed procedure involves microwave sample preparation by using a mixture
of H2O2/HNO3/H2SO4. The accuracy of the procedure was checked by the analysis of the standard reference material Buffalo River Sediment (SRM-2704,
NIST). Satisfactory agreement of the results obtained with the values reported was achieved. The detection limit of the procedure
was 25 ng Se/g of soil. The relative standard deviation of the measurements varied from 5.5% for SRM-2704 up to 10% for the
real soil samples.
Received: 20 January 1997 / Revised: 24 February 1997 / Accepted: 1 March 1997 相似文献
11.
P Smrkolj 《Analytica chimica acta》2004,512(1):11-17
A digestion mixture of H2SO4/HNO3/H2O2/HF/V2O5 was investigated for decomposition of plant samples and sensitive detection of selenium was achieved by hydride generation atomic fluorescence spectrometry (HG-AFS). The method was found to be accurate and reproducible, with a low detection limit (DL) (0.14 ng g−1 solution). The repeatability of the determination was mostly around 10%, the reproducibility over a period of 8 months for determination of selenium in the standard reference material Trace Elements in Spinach Leaves, NIST 1570a, was 9% and the relative measurement uncertainty was 7% using a coverage factor of 2.3 at 95% probability. The average recovery of the whole procedure was 90%. The characteristics of this method are simple and inexpensive equipment, low consumption of chemicals and the ability to analyse many samples in a short time. The whole procedure was carried out in the same PTFE tube, and in addition only a simple cleaning procedure is needed. As a consequence of all these advantages, the described method is suitable for environmental and nutritional studies. The selenium content was determined in 44 vegetable samples from different regions of Slovenia and the contents found were in the range 0.3-77 ng g−1 wet weight. 相似文献
12.
D. Kostova 《Journal of Analytical Chemistry》2011,66(4):384-388
Solvent extraction of molybdenum(VI) ion associate with triphenyltetrazolium chloride (TTC) has been studied. TTC was proposed as reagent for the spectrophotometric determination of micro amounts of molybdenum(VI)
at λmax 250 nm. The optimum conditions for extraction of molybdenum(VI) as an ionassociation complex with TTC has been determined.
Beer’s law is obeyed in the range of 0.5–10 μg/mL molybdenum(VI). The molar absorptivity of the ion-pair is 1 × 106 L/mol cm. The sensitivity of the method is 9.6 × 10−5 μg/cm2. The characteristic values for the extraction equilibrium and the equilibrium in the aqueous phase are: distribution constant
K
D = 32.64, extraction constant K
ex = 2.19 × 1010 association constant β = 6.71 × 108. The interferences of different cations, anions on molybdenum(VI) determination were also investigated. A sensitive and selective
method for the determination of microquantities of molybdenum(VI) has been developed. The determination was carried out without
preliminary separation of molybdenum. A novel procedure of molybdenum(VI) extraction and spectrophotometric determination
in different plant samples was examined. 相似文献
13.
Muñiz-Naveiro O Domínguez-González R Bermejo-Barrera A Bermejo-Barrera P Cocho JA Fraga JM 《Analytical and bioanalytical chemistry》2006,385(1):189-196
The purpose of the work described in this paper was to develop an easy and quick in-vitro method for comparing the bioavailability
of selenium in cows’ milk after different cow feed. The study focuses on bioavailability differences resulting from the use
of different selenium species (organic selenium as selenised yeast and sodium selenite) for supplementation of forage. A procedure
for determination of selenium in cows’ milk and dialysates, by hydride-generation atomic-fluorescence spectrometry (HG-AFS)
after microwave-assisted acid digestion, was optimised. The results show it is possible to obtain cows’ milk enriched with
selenium at different concentration without altering the original composition of the milk. The bioavailability was statistically
greater for cows’ milk obtained after supplementation of forage with organic selenium at levels of 0.4 and 0.5 μg Se g−1 than for that obtained after supplementation with inorganic and organic selenium at levels of 0.2 and 0.3 μg Se g−1. 相似文献
14.
Study of the uncertainty in gravimetric analysis of the Ba ion 总被引:3,自引:0,他引:3
The determination of barium by the gravimetric method, in which the precipitation of BaSO4 was formed and weighed, coupled with instrumental measurement of trace constituents was studied. The analyte’s remaining
in the filtrate and washes, mechanical loss, contaminants in the precipitate are the main influencing factors of uncertainty.
A series of condition tests have been done, to reduce the effect of the factors mentioned above and the optimum test condition
was found. The determination was carried out with a strictly defined operational procedure. The trace amounts of barium in
the filtrate, washes and mechanical loss were determined by ICP-AES, the chloride occluded in the precipitate was determined
by ion chromatography (IC), calculated as BaCl2 and barium, and sodium by FAAS, calculated as Na2SO4. The average mass of barium in the filtrate contributes about 0.06% relative to that of the total barium, in washes about
0.09%, mechanical loss about 0.06%, contaminants of BaCl2 about 0.08% and Na2SO4 about 0.05%. All the trace constituents were determined and corrected on a sample-by-sample basis. Sources of uncertainty
were assessed thoroughly. The uncertainty of this combined gravimetric-instrumental method was improved remarkably compared
with that of gravimetric method alone. The expanded uncertainty (k =2) is 0.08%.
Received: 15 June 2000 Accepted: 25 December 2001 相似文献
15.
The role of matrix reference materials in the process of demonstrating the degree of equivalence of measurement results obtained
from intercomparisons is outlined, reviewing exemplary selected experience gained at BAM regarding the determination of organic
contaminants in environmental matrices.
The specific characteristics of reference materials employed in the process of demonstrating equivalence between laboratories
in the course of proficiency testing as well as the development, comparison and validation of methods are elaborated. The
demand is for series of appropriately characterised samples which are fit for the purpose and it is seen from representative
examples that the utilisation of such tailor-made RM designed to tackle the specific need of an analytical problem dominates
over certified matrix reference materials in this context. Concluding, the role of certified matrix reference materials in
quality assurance is briefly looked at both from the user’s and providers’ points of view.
Received: 9 September 2002 Accepted: 16 December 2002
Presented at CERMM-3, Central European Reference Materials and Measurements Conference: The function of reference materials
in the measurement process, May 30–June 1, 2002, Rogaška Slatina, Slovenia
Correspondence to R. Becker 相似文献
16.
Wing-Chi Cheng Tsan-Sang Yau Wai-Nang Cheng Kok-Choi Cheng Della Wai-Mei Sin 《Accreditation and quality assurance》2007,12(9):483-490
An accurate and precise method for the determination of total 19-norandrosterone (19-NA), a major metabolite of nandrolone,
in human urine was developed based on isotope dilution gas chromatography-high resolution mass spectrometry (ID GC-HRMS).
The 19-NA glucuronide, together with deuterated 19-NA (d4-19-NA) (as the internal standard, IS), was subjected to enzymatic hydrolysis using β-glucuronidase, followed by solid phase
extraction (XtractT, mixed-mode column) and liquid–liquid extraction cleanup. The native and deuterated analogues of 19-NA
were then derivatised to the corresponding bis(trimethylsilyl) derivatives using N-methyl-N-trimethylsilyltrifluoroacteamide (MSTFA):NH4I:Dithiothretitol (1,000:2:3 w/w). Identification was achieved under selected ion monitoring of the respective trimethylsilyl
derivatives at ion masses m/z 405.26450 and 420.28800 for 19-NA and m/z 409.28920 and 424.31270 for d4-19-NA within the specific time windows (±1% of the relative retention time to the calibration standard). A linear calibration
curve (r
2 > 0.9995) was obtained based on seven calibration points (five replicates at each level) in the range 0.05–10 ng/g. The detection
limit for 19-NA was found to be 4 pg/g. The method has been applied for the determination of 19-NA by fortifying 19-NA glucuronide
at three concentrations (0.2, 2.1 and 7.2 ng/g) in blank urine samples with excellent accuracy and reproducibility. To circumvent
the iterative process of exacting matching, a single-point calibration procedure was adopted, where the acceptance criteria
for the isotopic ratio in the sample (RF
s) and calibration blends (RF
c) was set close to unity (0.95–1.05). This method was successfully applied in a pilot inter-comparison study, with results
in good agreement with the fortified value and other participants’ results (relative standard deviation, RSD < 2.0%) with
an expanded relative uncertainty (coverage factor of 2 at 95% confidence level) of 4.7%. It was found in our determination
that the main contributors to the uncertainty budget originated from the measurements of the purity of the reference material
and the response factor of the calibration standard. 相似文献
17.
Mahmure Ü. Özgür Güzin Alpdoğan Bürge Aşçi 《Monatshefte für Chemie / Chemical Monthly》2002,133(2):219-223
Summary. A simple and rapid derivative spectrophotometric assay procedure is described for the analysis of caffeine (1), acetaminophen (2), and propyphenazone (3) in tablet formulations. The concentration range of application is 5.0–25.0 μg·cm−3 for 2 and 3 and 1.0–5.0 μg·cm−3 for 1. The method involves the extraction of the drugs from tablets with 0.1 N H2SO4, filtration, appropriate dilution, and measurement of the fourth derivative absorbance values at zero crossing wavelengths
of 230.0, 263.2, and 256.6 nm for 1, 2, and 3. As a reference method, a reversed phase HPLC procedure was developed. Commercially available tablets were analyzed; statistical
comparison of the results with those obtained from the reference method showed good agreement. The derivative spectrophotometric
method has the advantage of being simple, rapid, inexpensive, and easy to perform.
Received April 18, 2001. Accepted (revised) June 5, 2001 相似文献
18.
《Monatshefte für Chemie / Chemical Monthly》2002,19(1):219-223
A simple and rapid derivative spectrophotometric assay procedure is described for the analysis of caffeine (1), acetaminophen (2), and propyphenazone (3) in tablet formulations. The concentration range of application is 5.0–25.0 μg·cm−3 for 2 and 3 and 1.0–5.0 μg·cm−3 for 1. The method involves the extraction of the drugs from tablets with 0.1 N H2SO4, filtration, appropriate dilution, and measurement of the fourth derivative absorbance values at zero crossing wavelengths of 230.0, 263.2, and 256.6 nm for 1, 2, and 3. As a reference method, a reversed phase HPLC procedure was developed. Commercially available tablets were analyzed; statistical comparison of the results with those obtained from the reference method showed good agreement. The derivative spectrophotometric method has the advantage of being simple, rapid, inexpensive, and easy to perform. 相似文献
19.
The possibility of determining selenium on the solid phase of polyacrylonitrile fibers impregnated by an AV-17 anion-exchanger
([PANV-AV-17]) were examined by virtue of diffuse reflectance spectroscopy. Reactions of a complex formation between selenium(IV) and
organic reagents on solid phase as well as the formation of an elemental selenium sol both on the solid phase and in solution
followed by absorption were studied. The best analytical parameters were achieved in the adsorption of selenium sol formed
in solution upon the addition of ascorbic acid. The comparison of the batch and dynamic adsorption modes revealed greater
advances of the dynamic one. The optimal conditions for determining selenium were proved as follows: the formation of a selenium
sol in a 1% ascorbic acid solution at pH 2 and dynamic adsorption at a flow rate of 5 mL/min. A procedure was developed for
determining selenium with a limit of detection of 0.1 mg/L. The procedure was validated by the added-found method in the analysis
of river and well natural waters and also the standard specimen OSO-200-90, which also contained As, Bi, Sb, and PO43−. The duration of analysis for 5–6 samples of the volume 100 mL was 30 min approximately, RSD < 20%. 相似文献
20.
The determination of palladium in a road dust sample taken close to the highway (w
Pd=450 ng g−1) was carried out by the ICP-MS method after sample decomposition by aqua-regia. Analyses were evaluated by two methods: external calibration accompanied with mathematical correction of spectral interferences (EC) and isotope dilution measurement after separation of Pd by extraction to dibutyl sulfide solution (ID). In both cases, the uncertainties and accuracy of results were investigated. Although in the case of ideally homogeneous sample the repeatability of EC results (11 ng g−1 Pd) was somewhat lower than those of ID results (16 ng g−1 Pd), the uncertainties of results of both techniques were almost the same and they reached the level of 19 ng g−1 Pd. The main uncertainty source of the EC method is represented by the correction of spectral interferences. In case of real non-homogeneous sample, the main uncertainty component represents the soil sampling. The uncertainty of results (approx. 75 ng g−1 Pd) only slightly exceeded the repeatability (approx. 70 ng g−1 Pd). The accuracy of results was proven by analyses of CRM TDB–1 Diabas Rock (in case of ID) and by the standard addition method (in case of EC). 相似文献