共查询到20条相似文献,搜索用时 78 毫秒
1.
Petronella Mathilda van Berkel 《Accreditation and quality assurance》2001,6(4-5):210-213
Proficiency testing by laboratories, national accreditation bodies, and other third parties is becoming more and more considered
as a standard and integral part of the quality control system. Therefore, it is of utmost importance that the quality of the
provided proficiency-testing (PT) service is outstanding. If PT-schemes are set up in order to help laboratories monitor and
improve their quality, PT-schemes need not only be of high quality themselves, but the organizer also needs to be able to
demonstrate this. In The Netherlands formal accreditation of the organization of proficiency testing schemes is used as a
tool to guarantee high quality schemes and also to enable organizers to demonstrate their competence. Since 1996, the Dutch
Council for Accreditation (RvA) has used the ISO-Guide 43–1 to assess PT-organizers in The Netherlands. From January 2000,
the ISO-guide 43–1 was replaced by the ILAC G13 document for assessing organizers. Up till now, four institutes have been
accredited by the RvA for the organization of PT-schemes. 相似文献
2.
For the determination of 16 PAHs in soils and sediment samples by GC/FID and GC/MS, the dynamic off-line supercritical fluid
extraction with both pure and modified carbon dioxide has been evaluated. The optimisation of extraction parameters was performed
for four individual groups of PAHs according to their number of aromatic rings (2–3 rings, 4 rings, 5 rings and 6 rings) by
varying pressure (200–510 bar), temperature (50–150 °C), extraction fluid volume (10–50 ml), and the methanol modifier concentration
(0–10%). Using a five level spherical factorial experimental design the number of experiments required for optimisation was
45. In spiked soil samples extraction efficiencies of 80–100% were achieved for the individual groups of PAHs. At the optimal
set of conditions 10–30% lower recoveries of PAHs were obtained for the standard reference material NIST SRM 1941a (marine
sediment). The largest differences between extraction recoveries of native and spiked PAHs occurred at high molecular weight
PAHs. Using SFE efficiency data for the standard reference material, cluster analysis proved that dividing the 16 PAHs into
four groups according to their number of aromatic rings was appropriate and correct.
Received: 2 February 1996/Revised: 26 November 1996/Accepted: 30 November 1996 相似文献
3.
The molecular and electronic structure of the ground state of peroxyacetyl nitrate (PAN) was calculated by the unrestricted
Hartree-Fock-Roothaan method with the use of the standard 3–21G and 6–31G basis set. The potential curve of the internal rotation
about the peroxide bond of PAN was calculated with the 6–31G basis set. The curve contains two maxima. The ground state of
PAN is characterized by a structure in which groups of atoms adjacent to the peroxide bond lie in planes that are perpendicular
to each other (the dihedral angle ϱ(COON) is 89.9°). The calculated barriers to rotation are 19.6 and 66.8 kJ mol−1.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 600–604, April, 1998. 相似文献
4.
A simple, rapid and reproducible HPLC method was developed and validated for the simultaneous determination of olmesartan
(OLM) medoxomil and hydrochlorothiazide (HCT) in combined tablets. Chromatography was carried out on a 4.6 mm I.D × 200 mm,
5 μm cyano column with methanol–10 mM phosphoric acid containing 0.1% triethylamine (pH 2.5, 50:50 v/v) at a flow rate of 1.0 mL min−1 and UV detector was set at 260 nm. Valsartan (VAL) was used as internal standard (IS). A linear response was observed in the
range of 0.2–6 μg mL−1 (r
2 = 0.9998) for OLM and 0.1–4 μg mL−1 (r
2 = 0.9999) for HCT, respectively. The method showed good recoveries (99.56% for OLM and 99.48% for HCT) and the relative standard
deviation (RSD) values for intra- and inter-day precision were 0.70–1.59 and 0.80–2.00% for OLM and 1.20–1.37 and 1.63–1.93%
for HCT, respectively. The developed method was applied successfully for quality control assay of OLM and HCT in combined
tablets and in vitro dissolution studies. 相似文献
5.
R. E. Jervis K. -L. Richard Ho B. Tiefenbach 《Journal of Radioanalytical and Nuclear Chemistry》1982,71(1-2):225-241
National energy programs for the next two decades entail increased total consumption of fossil fuels in general and, in particular
of portable fuels extracted from oil sands and shales and from lower quality coals. Improved fuel-upgrading and combustion
technologies are recognized to be vital for minimizing environmental degradation caused by continental and global acid-rain
precipitation from fossil-fuel impurities. A further consideration, however, is the fate of those trace-element co-contaminants
of acid-rain such as heavy metals, which are present at lower concentrations (10−4–10−7) but may also be of environmental significance when 107 to 109 tons·y−1 are utilized on several continents. In this laboratory, INAA procedures have been adapted for the determination of 25–30
trace impurities in a variety of fuels and extracts including: S, V and Al, As, Ba, Br, Ca, Ce, Cl, Co, Cr, Dy, Eu, Fe, Hf,
K, La, Mn, Na, Rb, Sb, Sc, Sm, Th, Ti, U. Samples were obtained of typical Canadian pumped crudes, and from several Canadian
oil-sands and coal deposits (mostly bituminous and subbituminous) both in their natural states and after stages of extraction
and upgrading. Also analyzed were fuels derived from them and the residues resulting from their refining and combustion. InAA
of all fossil fuel extracts including light oils, viscous bitumen and such organic fluids could be performed under the same
conditions as the parent substances: crude oils, oil-sands and coals, without any special sample preparation. Although no
standard samples are routinely required because of the 1–2% long-term flux stability of the reactor, accuracy checks were
performed periodically by reference to NBS-1632A standard coal and atomic absorption standard dilute solutions. Results obtained
for the NBS coal SRM and the BAM flyash sample (1978) are also given. A wide range of trace impurities determined in the Canadian
fossil fuels included some of those which are of particular significance in Canadian coals and their ashes (a STM standard
ashing method). The ‘inorganic’ traces can also be grouped according to their fate during static combustion at 750°C.
The research reported here was supported with funds from a Natural Sciences and Engineering Research Council of Canada Strategic
energy grant (G 0017), 1978–80, “Trace Contaminants of Environmental Importance in Present and Future Fossil Fuels”. 相似文献
6.
Aguilera-Luiz MM Plaza-Bolaños P Romero-González R Vidal JL Frenich AG 《Analytical and bioanalytical chemistry》2011,399(8):2863-2875
A rapid multi-analyte method has been developed for the simultaneous determination of pesticides and mycotoxins in milk by
ultra high-performance liquid chromatography coupled to triple quadrupole mass spectrometry (UHPLC–QqQ–MS/MS). A variety of
methodologies has been evaluated, including solid-phase extraction (SPE), “dilute-and-shoot” (liquid–liquid extraction-based
procedures), and QuEChERS (quick, easy, cheap, effective, rugged, and safe)-based methods. The optimization and development
process was carried out considering that the maximum residue level for aflatoxin M1 (AFM1) in milk in the European Union (EU)
is set at 0.05 μg kg−1, which is the lowest tolerance in the target compounds. The selected method consisted of an extraction by SPE using C18 as
sorbent and methanol as elution solvent. The final determination was performed by UHPLC–QqQ–MS/MS. Matrix-matched standard
calibration was used for quantification, obtaining recoveries in the range 60–120% with relative standard deviations <25%,
at three spiking levels: 0.5, 10, and 50 μg kg−1 (ten times lower for AFM1). Limits of quantification ranged from 0.20 to 0.67 μg kg−1, which were always below or equal to the established tolerance levels by the EU. Finally, the selected method was applied
to different types of milk. 相似文献
7.
8.
Dumont E Ogra Y Vanhaecke F Suzuki KT Cornelis R 《Analytical and bioanalytical chemistry》2006,384(5):1196-1206
Liquid chromatography (LC) hyphenated with both elemental and molecular mass spectrometry has been used for Se speciation
in Se-enriched garlic. Different species were separated by ion-pair liquid chromatography–inductively coupled plasma mass
spectrometry (LC–ICP–MS) after hot-water extraction. They were identified by on-line reversed-phase liquid chromatography–electrospray
ionization tandem mass spectrometry (RPLC–ESI–MS–MS). Se-methionine and Se-methylselenocysteine were determined by monitoring
their product ions. Another compound, γ-glutamyl-Se-methylselenocysteine, shown to be the most abundant form of Se in the
garlic, was determined without any additional sample pre-treatment after extraction and without the need for a synthesized
standard. Product ions for this dipeptide were detected by LC–ESI–MS–MS for three isotopes of Se—78
Se, 80Se: and 82Se. The method was extended to the species extracted during in-vitro gastrointestinal digestion. Because both Se-methylselenocysteine
and γ-glutamyl-Se-methylselenocysteine have anticarcinogenic properties, their extractability and stability during human digestion
are very important. Garlic was also treated with saliva, to enable detection and analysis of species extracted during mastication.
Detailed information on the extractability of selenium species by both simulated gastric and intestinal fluid are given, and
variation of the distribution of Se among the different species with time is discussed. Although the main species in garlic
is the dipeptide γ-glutamyl-Se-methylselenocysteine, Se-methylselenocysteine is the main compound present in the extracts
after treatment with gastrointestinal fluids. Two more, so far unknown compounds were observed in the chromatogram. The extracted
species and their transformations were analysed by combining LC–ICP–MS and LC–ESI–MS–MS. In both the simulated gastric and
intestinal digests, Se-methionine, Se-methylselenocysteine, and γ-glutamyl-Se-methylselenocysteine could be determined by
LC–ESI–MS–MS by measuring their typical product ions.
相似文献
9.
Muzaffer Özcan 《Journal of Solid State Electrochemistry》2008,12(12):1653-1661
Alternating current (AC) impedance measurements of mild steel/sulfuric acid interface in the absence and in the presence of
various concentrations of cystine (Cys–Cys) have been carried out in the 100 kHz–10 mHz frequency range. The results revealed
that Cys–Cys is a good and effective inhibitor for mild steel corrosion in 0.5 M H2SO4 and its percent inhibition efficiency changes with its concentration. Changes in impedance parameters indicated the adsorption
of Cys–Cys on the mild steel surface, which was verified by scanning electron microscope (SEM) and atomic force microscope
(AFM) photographs. Adsorption of Cys–Cys on mild steel surface was found to obey the Langmuir adsorption isotherm with a standard
free energy of adsorption of −33.2 kJ/mol. Energy gaps for the interactions between mild steel surface and Cys–Cys molecule were found to be close
to each other showing that Cys–Cys owns capacity to behave as both electron donor and electron acceptor. 相似文献
10.
Sturgeon RE Wahlen R Brandsch T Fairman B Wolf-Briche C Alonso JI González PR Encinar JR Sanz-Medel A Inagaki K Takatsu A Lalere B Monperrus M Zuloaga O Krupp E Amouroux D Donard OF Schimmel H Sejerøe-Olsen B Konieczka P Schultze P Taylor P Hearn R Mackay L Myors R Win T Liebich A Philipp R Yang L Willie S 《Analytical and bioanalytical chemistry》2003,376(6):780-787
The capabilities of National Metrology Institutes (NMIs—those which are members of the Comité Consultatif pour la Quantité de Matière (CCQM)of the CIPM) and selected outside "expert" laboratories to quantitate (C4H9)3Sn+ (TBT) in a prepared marine sediment were assessed. This exercise was sanctioned by the 7th CCQM meeting, April 4–6, 2001, as an activity of the Inorganic Analysis Working Group and was jointly piloted by the Institute for National Measurement Standards of the National Research Council of Canada (NRC) and the Laboratory of the Government Chemist (LGC), UK. A total of 11 laboratories submitted results (7 NMIs, and 4 external labs). Two external laboratories utilized a standard calibration approach based on a natural abundance TBT standard, whereas all NMIs relied upon isotope dilution mass spectrometry for quantitation. For this purpose, a species specific 117Sn-enriched TBT standard was supplied by the LGC. No sample preparation methodology was prescribed by the piloting laboratories and, by consequence, a variety of approaches was adopted by the participants, including mechanical shaking, sonication, accelerated solvent extraction, microwave assisted extraction and heating in combination with Grignard derivatization, ethylation and direct sampling. Detection techniques included ICP–MS (with GC and HPLC sample introduction), GC–MS, GC–AED and GC–FPD. Recovery of TBT from a control standard (NRCC CRM PACS-2 marine sediment) averaged 93.5±2.4% (n=14). Results for the pilot material averaged 0.680±0.015 µmol kg–1 (n=14; 80.7±1.8 µg kg–1) with a median value of 0.676 µmol kg–1. Overall, performance was substantially better than state-of-the-art expectations and the satisfactory agreement amongst participants permitted scheduling of a follow-up Key comparison for TBT (K-28), a Pilot intercomparison for DBT (P-43), and certification of the test sediment for TBT content and its release as a new Certified Reference Material (HIPA-1) with a TBT content of 0.679±0.089 µmol kg–1 (expanded uncertainty, k=2, as Sn) (80.5±10.6 µg kg–1).Electronic Supplementary Material Supplementary material is available in the online version of this article at . 相似文献
11.
Maria Brandl Klaus Lindauer Michael Meyer Jürgen Sühnel 《Theoretical chemistry accounts》1999,101(1-3):103-113
Small molecule studies indicate that C–H...X interactions (X: O,N) constitute weak H-bonds. We have performed a comprehensive
analysis of their occurrence and geometry in RNA structures. Here, we report on statistical properties of the total set of
interactions identified and discuss selected motifs. The distance/angle distribution of all interactions exhibits an excluded
region where the allowed C–H...X angle range increases with an increasing H...X distance. The preferred short C–H...X interactions
in RNA are backbone-backbone contacts between neighbour nucleotides. Distance/angle distributions generated for various interaction
types can be used for error recognition and modelling. The axial C2′(H)...O4′ and C5′(H)...O2′ interactions connect two backbone
segments and form a seven-membered ring that is specific for RNA. An AA base pair with one standard H-bond and one C–H...N
interaction has been identified in various structures. Despite the occurrence of short C–H...X contacts their free energy
contribution to RNA stability remains to be assessed.
Received: 17 May 1998 / Accepted: 4 August 1998 / Published online: 2 November 1998 相似文献
12.
Near-infrared spectroscopy offers the potential for direct in situ analysis in complex biological systems. Chemical selectivity
is a critical issue for such measurements given the extent of spectral overlap of overtone and combination spectra. In this
work, the chemical basis of selectivity is investigated for a set of multivariate calibration models designed to quantify
glucose, glucose-6-phosphate, and pyruvate independently in ternary mixtures. Near-infrared spectra are collected over the
combination region (4,000–5,000 cm−1) for a set of 60 standard solutions maintained at 37 °C. These standard solutions are composed of randomized concentrations
(0.5–30 mM) of glucose, glucose-6-phosphate, and pyruvate. Individual calibration models are constructed for each solute by
using the partial least-squares (PLS) algorithm with optimized spectral range and number of latent variables. The resulting
standard errors are 0.90, 0.72, and 0.32 mM for glucose, glucose-6-phosphate, and pyruvate, respectively. A pure component
selectivity analysis (PCSA) demonstrates selectivity for each solute in these ternary samples. The concentration of each solute
is also predicted for each sample by using a set of net analyte signal (NAS) calibration models. A comparison of the PLS and
NAS calibration vectors demonstrates the chemical basis of selectivity for these multivariate methods. Selectivity of each
PLS and NAS calibration model originates from the unique spectral features associated with the targeted analyte. Overall,
selectivity is demonstrated for each solute with an order of sensitivity of pyruvate > glucose-6-phosphate > glucose.
Figure Combination near-infrared spectroscopy allows selective analytical measurements for glucose, glucose-6-phosphate, and pyruvate
in ternary mixtures owing to the uniqueness of the individual absorption spectra for each solute 相似文献
13.
Jonathan Fang Jing C. Zhou Esther H. Lan Bruce Dunn Jeffrey I. Zink 《Journal of Sol-Gel Science and Technology》2009,50(2):176-183
Sol–gel encapsulation has been used as the basis for detecting cortisol by an immunoassay approach. Previous research showed
that antibodies immobilized in the pores of a sol–gel derived silica were able to bind cortisol and be used as an immunosensor.
However, this approach was not effective when measuring cortisol levels in human serum because of interference from other
fluorescence sources. The present paper describes a protocol which overcomes these limitations and enables sol–gel immunoassays
to effectively measure cortisol in human serum over the physiological range of cortisol blood concentrations in an adult (2–28 μg/dL).
The method involves a standard additions approach in which various amounts of cortisol are added to the serum. The cortisol
concentration values obtained with our sol–gel immunoassay were typically within 10% of the values obtained by traditional
analytical methods. The protocol presented here represents a significant contribution to sol–gel sensing and immunoassays
in particular, because of the ability to detect an analyte in human serum. In addition, this work reports the first comparison
between results from a sol–gel immunosensor and an alternative immuno-binding method for analyte detection. 相似文献
14.
Multiple headspace solid-phase microextraction (MHS-SPME) with gas chromatography–mass spectrometry is proposed for quantification of nine volatile oak compounds in aged wines. These compounds are formed and extracted by wine when it is matured in oak barrels and are responsible for particular organoleptic properties and the high quality of these wines. Some important variables of the extraction process, for example volume of sample and extraction time, were studied. Extraction of 50 μL wine was performed with a divinylbenzene–Carboxen–polydimethylsiloxane fibre at 55 °C for 60 min. For calibration the same conditions were used, except that the wine was substituted by 50 μL of a standard solution in synthetic wine. The linearity, detection limits, and repeatability of the method were determined by use of standard solutions in synthetic wine. Detection limits were between 0.01 and 10 μg L−1 (for eugenol and furfural, respectively) and repeatability, expressed as relative standard deviation, was from 2 to 6%. The method was used to analyse six red wines and the concentrations obtained were statistically compared with those obtained by the standard addition method for the same wines. 相似文献
15.
A supramolecular catalytic kinetic spectrofluorimetric method was developed for the determination of platinum(IV) and the
possible mechanism of catalytic reaction was discussed. The method was based on the fluorescence-enhancing reaction of salicylaldehyde
furfuralhydrazone (SAFH) with potassium bromate, which was catalysed by platinum(IV) in a water–ethanol medium. β–Cyclodextrin (β-CD) obviously sensitized the determination at pH 5.20 and 25°C. Under optimum conditions, the β-CD–platinum–KBrO3–SAFH supramolecular kinetic catalytic reaction system had excitation and emission maxima at 372 and 461 nm, respectively.
The linear range of this method was 0.60–180 ng ml−1 with a relative standard deviation of 1.2%, and the detection limit was 0.18 ng ml−1. Investigation of the mechanism and the effects of interferences is presented. The proposed method was applied successfully
to determine trace platinum(IV) in the chemotherapeutic drug cisplatin and serum from patients with satisfactory results.
相似文献
16.
Ralf Eiden Ralf Falter Barbara Augustin-Castro Heinz Friedrich Schöler 《Analytical and bioanalytical chemistry》1997,357(4):439-441
Distillation as a way of sample digestion has been combined with on-line RP C18 preconcentration and HPLC-UV-PCO-CVAAS (high
performance liquid chromatography – ultra violet – post column oxidation – cold vapour atomic absorption spectrometry) for
the determination of methylmercury at background levels in sediments, soils and fish tissue. To prove the accuracy of this
method, it was applied to sediment and fish tissue reference materials. The results correspond with the reference values within
their error ranges. Excellent recoveries (92–95%) were obtained for the sediment samples by means of the standard addition
method. The standard deviations of the sediment samples were within an acceptable range (7.2–12.5%), those of the fish samples
were substantially lower (3.4–5.0%). The detection limit is 0.04 ng/g for 1 g sample weight.
Received: 23 November 1995/Revised: 16 April 1996/Accepted: 20 April 1996 相似文献
17.
R. M. Dorizzi Michele Schinella Antonella Pupillo Luca Endrizzi 《Accreditation and quality assurance》2000,5(9):367-370
The estimation of reference limits represents quite a taxing task for laboratories which frequently adopt the limits suggested
by manufacturers or those reported in the literature. This practice does not meet the requirements of accreditation programs
(i.e. Essential Criteria, Clinical Pathology Accreditation) that require laboratories to produce or check all their reference
intervals. We collected 15 244 hematological results from females aged 0–99 years obtained by the Rovereto Hospital Laboratory
and calculated the reference intervals, or to be more precise the health-related intervals, using an indirect method (based
on all the inpatient and outpatient results). All the measurements were carried out using an automatic Coulter STK S analyzer,
and the results were transferred to Verona by e-mail. The results for hemoglobin were: <1 year (n=154)=90–171 g/l; 2–8 years
(n=619)=104–136 g/l; 9–14 years (n=322)=118–143 g/l; 15–44 years (n=6329)=106–144 g/l; 45–75 years (n=4893)=107–148 g/l; 75–99 years
(n=2927)=90–153 g/l. The results appear different from the results currently used by Rovereto Hospital (120–160 g/l) but comparable
to those reported in the literature with the exception of the subjects under 1 year and over 75 years, probably due to the
excess of "diseased" subjects in these classes. The indirect method allows even small laboratories to produce or check their
reference intervals for all age groups, increasing the clinical effectiveness of laboratory results and satisfying the accreditation
standards.
Received: 15 April 2000 · Accepted: 20 April 2000 相似文献
18.
The interaction of magnolol with bovine serum albumin(BSA) was studied using fluorescence spectroscopy under physiological conditions. The binding constants, K, and the ratio of quantum yields of protein fluorescence for complex and free protein, f, at 298 K, 304 K, and 310 K were obtained; the values were 6.799×105 L mol–1, 5.541×105 L mol–1, and 4.344×105 L mol–1 and 0.17, 0.30, and 0.34, respectively. The standard enthalpy change (H°) and the standard entropy change (S°) were calculated to be –28.53 kJ mol–1 and 15.88 J mol–1 K–1, which indicated that hydrophobic forces played major role in the interaction of magnolol and BSA. The binding average distance between magnolol and BSA (4.32 nm) was obtained on the basis of the theory of Förster energy transfer. 相似文献
19.
Pisonero J Kroslakova I Günther D Latkoczy C 《Analytical and bioanalytical chemistry》2006,386(1):12-20
The spatial distribution and concentration of impurities in metallurgical-grade silicon (MG-Si) samples (97–99% w/w Si) were investigated by use of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The spatial resolution
(120 μm) and low limits of detection (mg kg−1) for quality assurance of such materials were studied in detail. The volume-dependent precision and accuracy of non-matrix-matched
calibration for quantification of minor elements, using NIST SRM 610 (silicate standard), indicates that LA-ICP-MS is well
suited to rapid process control of such materials. Quantitative results from LA-ICP-MS were compared with previously reported
literature data obtained by use of ICP-OES and rf-GD-OES. In particular, the distribution of element impurities and their
relationship to their different segregation coefficients in silicon is demonstrated.
Dedicated to Professor Klaus G. Heumann 相似文献
20.
A novel method combining matrix solid phase dispersion (MSPD) with Soxhlet simultaneous extraction clean-up (SSEC) was developed.
Being a single-step extraction and clean-up procedure, it could be used instead of multistep solvent extraction and Florisol
column clean-up. It not only reduces sample contamination during the procedure, but it also decreases the amount of organic
solvent needed. The retention times of standards were used to qualitatively assess the method, and the external standard method
was used to quantitatively assess it. Residues of organochlorine pesticides (OCP) in tobaccos were determined by gas chromatography–electron
capture detection (GC–ECD), and their identities were confirmed by the standard addition method (SAM). The performance of
the method was evaluated and validated: the detection limit was 0.01–0.02 μg g−1, relative standard deviations were 5–26%, and recoveries were 72–99% at fortification levels of 0.10, 1.00 and 10.0 μg g−1. The analytical characteristics of MSPD–SSEC compared very favorably with the results from the classical multistep solvent
extraction and Florisol column clean-up method. 相似文献