Characterization of water content in biodiesel fuel certified reference material (NMIJ CRM 8302-a)

The National Metrology Institute of Japan has issued a certified reference material of biodiesel fuel derived from palm oil (NMIJ CRM 8302-a) for the measurement and quality control of water, methanol, six elements (sulfur, phosphorus, sodium, potassium, magnesium, and calcium), density, and kinematic viscosity. This paper presents the technical details for the characterization of the water content in NMIJ CRM 8302-a. Because the water content in biodiesel is easily affected by ambient humidity, sample handling is extremely difficult. Thus, a sample handling technique that overcomes this limitation was established, and optimized coulometric and volumetric Karl Fischer titrations were performed in order to accurately determine the water content with traceability to the International System of Units. The certified water content and its expanded uncertainty with a coverage factor k = 2 were 393 mg kg^?1 and 25 mg kg^?1, respectively.     

加替沙星纯度标准物质研制

研制加替沙星纯度标准物质。采用质量平衡法和氢谱定量核磁法对加替沙星纯度标准物质候选物进行纯度定值,采用卡尔费休法和热重分析法准确测量了影响主成分纯度的水分含量,并考察了水分含量的稳定性。开展了加替沙星纯度定值、均匀性检验、稳定性考察以及不确定度评估。结果表明,加替沙星纯度标准物质的纯度值为93.1%,扩展不确定度为0.6%(k=2),水分含量为6.6%,特性量值均匀性良好,6个月稳定性可靠,被认定为国家二级标准物质,编号为GBW(E) 100476。研制的加替沙星纯度标准物质填补了国内空白,同时也为吸湿性较强的药物纯度标准物质研制过程中水分测定提供了参考与借鉴。     

Determination of Ultra-Trace Platinum,Palladium, Ruthenium,Rhodium, and Iridium in Rocks and Minerals by Inductively Coupled–Plasma Mass Spectrometry Following Nickel Sulfide Fire Assay Preconcentration and Open Mixed Acid Digestion

Platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), iridium (Ir), and osmiun (Os) are platinum-group elements with similar physic-chemical properties, and have important applications in geochemistry and environmental chemistry. However, due to their low abundance and inhomogeneous distribution in natural ores as well as the nugget effect, the accurate determination of the platinum-group elements has been a challenge for geological analysis. In this work, self-prepared and purified sodium carbonate (NiCO₃) instead of commercial nickel oxide (NiO) was used as the fire assay collector in order to greatly reduce the reagent blank and method detection limits. In addition, the fuming time of HClO₄ was strictly controlled at 10?min and a high sensitive method was developed for the simultaneous determination of ultra-trace Pt, Pd, Ru, Rh, and Ir in minerals by inductively coupled plasma-mass spectrometry (ICP-MS) following preconcentration with the nickel sulfide fire assay. Under the optimized conditions, the linear ranges of Pt, Pd, Ru, Rh, and Ir were between 0 and 100?ng mL^?1, with correlation coefficients exceeding 0.9997. The detection limits were 0.015, 0.056, 0.014, 0.004, 0.012?ng mL^?1 (for 10?g sample) for Pt, Pd, Ru, Rh and Ir, respectively. The developed method was successfully applied to analyze Chinese Certified Reference Materials (CRMs) GBW07288, GBW07289, GBW07290, GBW07291, GBW07292, GBW07293, GBW07294, GBW07101, GBW07102 and GBW07201 and the determined values were in good agreement with the certified values. The relative standard deviations (n?=?5) of Pt, Pd, Ru, Rh and Ir were between 3.42% and 6.87% for the determination of GBW07291.     

Evaluation of certified reference materials for oxidation-reduction titration by precise coulometric titration and volumetric analysis

The accuracy and uncertainty of coulometric titration of Japanese certified reference materials (CRMs) for oxidation-reduction titration were examined in this study. The results for potassium dichromate, sodium oxalate, and potassium iodate are presented. Potassium dichromate was directly determined by coulometric titration, and sodium oxalate and potassium iodate were determined by volumetric analysis using potassium dichromate assigned by coulometry.The uncertainty of the method was investigated by examining the dependency on the sample size and on the electrolysis current. Changes in the titration parameters did not result in any significant effects on the titration results. The coulometric system used primarily consists of a constant current source, timer, switching circuit, indicator unit, and voltmeter. They were controlled using the coulometry software by a PC/AT compatible computer. A highly automated coulometric system achieves repeatabilities of less than one part in 30,000 (k = 2) and uncertainties of less than one part in 15,000 (k = 2). In addition, using volumetric method, SI units traceable sodium oxalate and potassium iodate (purity standards for redox reaction) CRMs were developed.Reference materials for volumetric analysis are the most basic substances used in analytical chemistry. These materials are analyzed by several analytical methods and are produced globally; however, their purities have not been compared at the international level. Therefore, the relationship between the purity and reliability of these materials has not yet been established. In this paper, we determine the relationship between these parameters by titrating each material obtained from different laboratories.     

Traceability of measurement results in chemistry: a case study of certification of three new pharmaceutical reference materials

This paper compares the results of the studies carried out with three new candidate certified reference materials (CRM) of captopril, metronidazole, and sodium diclofenac, which are the first CRMs of these active pharmaceutical ingredients (APIs) reported in the literature. The studies were carried out according to the ISO Guides 34: 2009 and 35: 2006 and included the determination of organic, inorganic, and volatile impurities mass fractions, evaluation of homogeneity and stability under transport and storage conditions, calculation of API mass fractions by mass balance, cross-checking of obtained results, and estimation of measurement uncertainties. The certified property values and corresponding expanded uncertainties, obtained from the combined standard uncertainties multiplied by the coverage factor (k?=?2), for a confidence level of 95?%, were (995.65?±?0.93) mg/g for captopril, (998.87?±?0.15) mg/g for metronidazole, and (999.76?±?0.10) mg/g for sodium diclofenac. These new CRMs are intended to be used in assay and tests methods, including equipment calibration, method validation, as well as assignment of traceable property values and corresponding uncertainties to non-certified reference materials, with the objective to ensure metrological traceability of measurement results to the International System of Units, as well as results accuracy and comparability.     

Preparation and certification of two freshwater sediments certified reference materials for polycyclic aromatic hydrocarbons

Two freshwater sediments certified reference materials (CRMs) for 16 polycyclic aromatic hydrocarbons (PAHs) have been developed by the Institute for Environmental Reference Materials (IERM) of Ministry of Environmental Protection (MEP) in China. The methodology for preparing the CRMs of PAHs in sediments is described in this paper. The collected natural sediment samples were air-dried, ground, homogenised, packed, sterilised and tested on stability and homogeneity. Homogeneity results showed that the between-unit variation was confirmed to be below 4.5% for each compound. Stability was assessed after storage of samples for 16 months at temperature less than 30°C and in shade. The certification of the natural sediment matrix CRMs for PAHs was based on the agreement of results using different analytical techniques including gas chromatography/mass spectrometry (GC/MS) and reversed-phase liquid chromatography (LC) by no less than eight collaborating laboratories including IERM. Results of the homogeneity showed that the calculated u_bb′ was 0.9–2.5% for environmental river standard-4 (ERS-4) and 9–2.3% for environmental lake standard-1 (ELS-1), whereas stability results of total 16 PAHs indicated that the calculated u_rel,lts was 4.2% for ERS-4 and 2.2% for ELS-1. Certified values of 16 PAHs in ERS-4 varied from 8.5 to 167 μg/kg and ranged from 0.036 to 2.8 mg/kg in ELS-1.The good comparability, together with the independent confirmation of the assigned mass fraction by using different methods, confirmed that the CRMs are suitable for the method validation and quality control in soil or sediments analysis.     

Certification by the Karl Fischer method of the water content in SRM 2890, Water Saturated 1-Octanol, and the analysis of associated interlaboratory bias in the measurement process

The calibration of Karl Fischer instruments and reagents and the compensation for instrumental bias are essential to the accurate measurement of trace levels of water in organic and inorganic chemicals. A stable, non-hygroscopic standard, Water Saturated Octanol, which is compatible with the Karl Fischer reagents, has been prepared. This material, Standard Reference Material (SRM) 2890, is homogeneous and is certified to contain 39.24 ± 0.85 mg water/mL (expanded uncertainty) of solution (47.3 ± 1.0 mg water/g solution, expanded uncertainty) at 21.5?°C. The solubility of water in 1-octanol has been shown to be nearly constant between 10?°C and 30?°C (i.e., within 1% of the value at 21.5?°C). The results of an interlaboratory comparison exercise illustrate the utility of SRM 2890 in assessing the accuracy and bias of Karl Fischer instruments and measurements.     

Certification of reference materials for Cd, Cr, Hg and Pb in polypropylene

Two reference materials, at relatively low and high concentrations (GBW08404 and GBW08405), for analysis of the mass fractions of Cd, Cr, Hg and Pb in polypropylene were developed. The reference materials were prepared by doping blank polypropylene base material with Cd, Cr, Hg and Pb in the form of oxides, salts or pigments. Homogeneity and stability studies were performed by inductively coupled plasma mass spectrometry. The certification of the four analytes was carried out by isotope-dilution mass spectrometry (IDMS) with microwave-assisted digestion. Combined uncertainties were calculated from the IDMS uncertainty evaluation budget and the uncertainty of the homogeneity. The mass fractions of Cd, Cr, Hg and Pb of the two certified reference materials (CRMs) were from 8 to 1,000 mg kg⁻¹. The two samples were also used in an interlaboratory comparison scheme in which National Institute of Metrology, China, National Metrological Institute of Japan and Korea Research Institute of Standards and Science participated. The agreement of the comparison results proved that the certification procedure of the CRMs is valid and that the certified values of Cd, Cr, Hg and Pb are accurate and reliable.     

Assessment and assurance of quality in water measurement by coulometric Karl Fischer titration of petroleum products

The precise and accurate determination of water in petroleum products—gasoline, diesel oil and aromatic hydrocarbons—is of significant importance for their normal functional and operational characteristics for economics as well as in meeting international requirements. The standard method ISO 12937 for the measurement of water by the coulometric Karl Fischer titration method was subject to within-laboratory assessment. Thereby it was established that the analytical procedure could not always be relied upon, especially when low levels of water were determined. The aim of this work is to assess each stage of the test procedure depending on the particular problems defined by the samples, using high-reactive Karl Fischer reagents and coulometric cells with and without a diaphragm, and to indicate the major factors causing the uncertainty. A reduced combined uncertainty was achieved by modifying the sample preparation step, the administration of the moisture in the coulometric cell, and sample injection manipulation. Experiments showed that the cell without the diaphragm ensures lower and uniform uncertainty of the measurements in the range of 0.01 to 10 mg H₂O in comparison to the cell with a diaphragm and therefore is more appropriate for the determination of low water levels in the petroleum products. A procedure that utilized a mixture of the reagent and toluene (10:6) was able to resolve the problem of two phases of formation and reduced conductivity of the reagent in direct titration of diesel oils. The results suggest that the modified procedure ensures relative expanded uncertainty equal to or less than 2.0% (n=5, confidence interval close to 95%) and 99.4% recovery for petroleum products investigated in repeatability conditions.     

Homogeneity studies of reference materials by solid sampling – AAS and INAA

The necessity to quantify a natural material's homogeneity with respect to its elemental distribution prior to chemical analysis of a given aliquot is emphasised. The instruments and methods which are currently available are described. Additionally, the calculation of element specific, relative homogeneity factors, H _E and the minimum sample mass, M _5%, to achieve 5% precision on a 95% confidence level is given. Especially, in the production and certification of certified reference materials (CRMs) this characteristic information should be determined in order to provide the user with additional inherent properties of the CRM, to enable more economic use of the expensive material and to evaluate further systematic bias of the applied analytical technique.     

HPLC direct purity assay using ultra-purified materials as primary standards

Reference materials certified for purity are essential to ensure harmonization of analytical measurements. LGC is currently certifying these materials using an indirect multi-method approach quantifying impurities: Related substances using high-performance liquid chromatography, gas chromatography (GC), differential scanning calorimetry; Residual solvents using headspace GC coupled to mass spectrometry; Inorganic content using ashing, acid digest ion couple plasma mass spectrometry or thermogravimetric analysis; Water using oven coulometric Karl Fischer/direct addition coulometric Karl Fischer. Related substances are not straightforward to quantify without an appropriate standard due to possible difference in response factor for the impurity relative to the main compound. In this article, existing LGC RMs certified for purity were purified further using semi-preparative HPLC. These ultra-purified organic substances were virtually free of related substances making their purity assessment faster and more straightforward, i.e., no need to identify impurities and subsequently quantify them. After characterization, these ultra-purified standards were used as calibrants to determine directly the mass fraction of the analyte in the original CRM using exact matching single-point HPLC calibration. This new approach opens the possibility of certifying the purity of low purity substances with a relative small uncertainty without the need of identifying the impurities present in the sample.     

Determination of trace moisture in hydrogen chloride gas by Karl Fischer titration

Moisture of several ppm in hydrogen chloride gas has been accurately determined by a new method using the Karl Fischer reagent, which hitherto had a limitation in accuracy because of a partial reaction with hydrogen chloride when direct titration was employed.The moisture in the sample gas was collected in a cold trap kept at about ?80 °C while the hydrogen chloride gas passed through and the frozen moisture was dissolved by pyridine-methanol (1:1) solvent. a KF Reagent of factoe: 0.35 mg H₂O/ml.Titration by the Karl Fischer reagent having the equivalency factor of, e.g., 0.5 mg H₂O/ml was carried out and the concentration of the moisture was calculated from the sample volume used.     

Use of multivariate statistical analysis to evaluate experimental results for certification of two pharmaceutical reference materials

This paper demonstrates the use of the multivariate analysis for the quick and easy evaluation of the experimental results from the homogeneity test of two new certified reference materials (CRM) of active pharmaceutical ingredients (API): metronidazole and captopril. The principal component analysis (PCA) and the hierarchical cluster analysis (HCA) indicated that some results from the homogeneity test were statistically different when the concentrations of all API impurities were considered simultaneously. Through the use of these statistical tools, it was possible to reduce the standard uncertainty due to between-bottle (in)homogeneity (u _bb) and consequently the combined standard uncertainty of the certified reference materials (u _CRM) with 95% confidence level.     

Wasserbestimmung in Phenolen durch Karl-Fischer-Titration

Summary Karl Fischer titration can be applied to many phenols without any interference, though some are oxidized during titration. One-component reagents are to be preferred because they are less sensitive to interferences. Only pyrogallol and aminophenols are oxidized in this case. With two-component reagents dihydroxybenzenes and naphthols are oxidized, too. With coulometric titration interferences are more frequent. The oxidation rate depends on the pH and can be suppressed or minimised by adding salicylic acid to the Karl Fischer reagent.     

Determination of the water content of amphiphilic liquid crystals by coulometric Karl Fischer titration

An apparatus is described, which allows the precise determination of the water content of amphiphilic liquid crystals by means of coulometric Karl Fischer titration. The scope and limitations of this method are described.     

Determination of water by controlled-potential coulometry

Summary A new electroanalytical approach, utilizing controlled-potential coulometry, for the determination of water has been devised. The proposed method involves the coulometric measurement of iodide produced by the stoichiometric reaction of water with Karl Fischer reagent and shows promise of providing a selective means of water estimation without prior chemical calibration.

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Zusammenfassung Zur Bestimmung von Wasser wird die Coulometrie bei kontrolliertem Potential vorgeschlagen. Das beschriebene Verfahren beruht auf der coulometrischen Bestimmung des Jodids, das bei der Reaktion von Wasser mit Karl-Fischer-Reagens entsteht. Die Methode ermöglicht eine selektive Wasserbestimmung ohne vorhergehende chemische Eichung.

     

Determination of trace water in gas samples by an improved Karl Fischer coulometer.

The determination of trace water in gas samples, such as isobutene, chloromethane (polymeric staple gases) and SF6 by a conventional Karl Fischer coulometer is very difficult, because of the adsorption of trace water on the surface of sample pipe, the gasification of the liquefied samples, and the migration of moisture into the measuring cell from the surroundings. To solve these problems, we improved a device for coulometric determination of water by Karl Fischer method. The improved coulometer was used to determine the trace water in isobutene, chloromethane and SF6; RSD was less than 5%, and recoveries ranged from 94.1 to 109.1%, which is adequate for the analysis of industry.     

Cyclic neutron activation analysis for determination of selenium in food samples using <Superscript>77m</Superscript>Se

Cyclic neutron activation analysis method was conducted for determination of Se in food samples. High accuracy and good precision were proved by analyzing certified reference materials (CRMs) of chicken (GBW10018), rice (GBW10010) and cabbage (GBW10014). The detection limits for the three CRMs reached 0.16, 0.66 and 1.2 ng after 6 cycles at the 161.9 keV γ-peak from ^77mSe, under a neutron flux of 9.0 × 10¹¹ n cm⁻² s⁻¹ and the conditions of 30 s irradiation, 2 s decay, 30 s counting and 2 s waiting, significantly lower than those of conventional neutron activation analysis without any cycles, which were 0.94, 3.6 and 4.3 ng, respectively.     

Solid-phase extraction of trace metal ions with magnetic nanoparticles modified with 2,6-diaminopyridine

We have modified silica-coated Fe₃O₄ nanoparticles with 2,6-diaminopyridine and used these for selective magnetic solid-phase extraction of trace amounts of metal ions. The nanoparticles were characterized by transmission electron microscopy and Fourier transform infrared spectroscopy. Quantitative extraction of trace amounts of Cu(II) and Zn(II) from mixed-ion solutions was accomplished at an optimal pH value of 6 within less than 10?min. The metal ions were eluted from the sorbent with hydrochloric acid. Common electrolytes and chemically related metal ions do not interfere. The relative standard deviations of the method are <4?%. It was successfully applied to the separation and preconcentration of trace metal ions from the certified reference materials GBW 08301 (river sediment) and GBW 08607 (water solution), in natural water, and in samples of vegetable with satisfying results.     

Determination of the rare earth elements La, Eu, and Yb using solidified floating organic drop microextraction and electrothermal vaporization ICP-MS

We have developed a method for the determination of trace levels of the rare earth elements La, Eu, and Yb in biological and environmental samples. It is based on solidified floating organic drop microextraction using 1-(2-pyridylazo)-2-naphthol (PAN) as a chelator, followed by electrothermal vaporization (ETV) and quantification by inductively coupled plasma mass spectrometry. PAN also acts as a modifier in ETV. The effects of pH, amount of PAN, extraction time, stirring rate, volume of sample solution, and temperature program were examined. Under optimized conditions, the detection limits are 2.1, 0.65 and 0.91 pg mL^?1 for the elements La, Eu and Yb, respectively. The relative standard deviations are <6.0 % (c?=?0.1 ng mL^?1, n?=?9). When applied to the analysis of (spiked) natural water samples, the recoveries range from 92 to 105 %. The accuracy was validated with certified reference materials (combined sample of branch and leaf of shrub: GBW 07603 and human hair: GBW 07601), and the results were in good agreement with the certified values.