Search

Extraction, chromatographic separation, and quantification of low-concentration organic compounds in complex matrices are core challenges for reference material producers and providers of calibration services. Evidence of successful participation in formal, relevant international comparisons is needed to document measurement capability claims made by national metrology institutes (NMIs) and designated institutes (DIs). To enable NMIs and DIs to update or establish their claims, in 2014 the Organic Analysis Working Group (OAWG) initiated CCQM-K95.1 “Low-Polarity Analytes in a Botanical Matrix: Polycyclic Aromatic Hydrocarbons (PAHs) in Tea”. This was a follow-on comparison from CCQM-K95 which was completed in 2014. The polycyclic aromatic hydrocarbons (PAHs) benz[a]anthracene (BaA) and benzo[a]pyrene (BaP) are considered priority pollutants by U.S. Environmental Protection Agency and are regulated contaminants in food, pose chromatographic separation challenges, and for which exist well-characterized measurement procedures and standard materials. BaA and BaP in a smoked tea were therefore selected as representative target measurands for CCQM-K95.1. Ten NMIs participated in CCQM-K95.1. The consensus summary mass fractions for the two PAHs are in the range of (50 to 70) ng/g with relative standard deviations of (6 to 10) %. Successful participation in CCQM K95.1 demonstrates the following measurement capabilities in determining mass fraction of organic compounds, with molar mass of 100 g/mol to 500 g/mol and having polarity pKow −2, in a botanical matrix ranging in mass fraction from 10 ng/g to 1000 ng/g: (1) value assignment of primary reference standards (if in-house purity assessment carried out), (2) value assignment of single and/or multi-component organic solutions, (3) extraction of analytes of interest from the matrix, (4) cleanup and separation of analytes of interest from interfering matrix or extract components, and (5) separation and quantification using gas chromatography or liquid chromatography. KEY WORDS FOR SEARCH benz[a]anthracene (BaA), benzo[a]pyrene (BaP), gas chromatography(GC), isotope dilution (ID), liquid chromatography (LC), mass spectrometry (MS), polycyclic aromatic hydrocarbon (PAH), yerba mate tea Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Harmonized sample pre-treatment is an essential first step in ensuring quality of measurements as regards repeatability, inter-laboratory reproducibility and commutability. The development of standard preparation methods for single-wall carbon nanotube (SWCNT) samples is therefore essential to progress in their investigation and eventual commercialization. Here, descriptions of sample preparation and pre-treatment for the physicochemical characterization of SWCNTs are provided. Analytical methods of these protocols include: scanning electron microscopy (SEM; dry, wet), transmission electron microscopy (TEM; dry, wet), atomic force microscopy (AFM), inductively-coupled plasma mass spectrometry (ICP-MS), neutron activation analysis (NAA), Raman spectroscopy (dry, wet), UV-Vis-NIR absorption and photoluminescence spectroscopy, manometric isothermal gas adsorption and thermogravimetric analysis (TGA). Although sample preparation refers to these specific methods, application to other methods for measurement and characterization of SWCNTs can be envisioned.

At the October 2005 CCQM Organic Analysis Working Group Meeting (IRMM, Belgium), the decision was made to proceed with a Key Comparison study (CCQM-K47) addressing the calibration function for the determination of volatile organic compounds (VOCs) used for water quality monitoring. This was coordinated by CENAM and NIST. Benzene, o-xylene, m-xylene and p-xylene were chosen as representative VOCs. The solvent of choice was methanol. Key Comparison CCQM-K47 demonstrated the capabilities of participating NMIs to identify and measure the four target VOCs in a calibration solution using GC-based methods. The measurement challenges in CCQM-K47, such as avoiding volatility loss, achieving adequate chromatographic resolution and isolating potential interferences, are typical of those required for value-assigning volatile reference materials. Participants achieving comparable measurements for all four VOCs in this Key Comparison should be capable of providing reference materials and measurements for VOCs in solutions when present at concentration levels greater than 10 ?g/g. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Under the auspices of the Organic Analysis Working Group (OAWG) of the Comit? Consultatif pour la Quantit? de Mati?re (CCQM) a key comparison, CCQM K55.a, was coordinated by the Bureau International des Poids et Mesures (BIPM) in 2009/2010. Eleven national measurement institutes and the BIPM participated. Participants were required to assign the mass fraction of estradiol present as the main component in the comparison sample (CCQM-K55.a) which consisted of a bulk estradiol hemihydrate material obtained from a commercial supplier that had been extensively but not exhaustively dried prior to sub-division into the units supplied for the comparison. Estradiol was selected to be representative of the performance of a laboratory's measurement capability for the purity assignment of organic compounds of medium structural complexity [molar mass range 300?500 Da] and low polarity (pKOW??2) for which related structure impurities can be quantified by capillary gas phase chromatography (GC) or by high performance liquid chromatography (LC). The majority of participants used a mass balance approach to determine the estradiol content. The key comparison reference value (KCRV) for estradiol in CCQM-K55.a was assigned by combination of KCRVs assigned by consensus from participant results for each orthogonal impurity class. This allowed participants to demonstrate the efficacy (or otherwise) of their implementation of the mass balance approach and to demonstrate that their assigned value for the main component agreed with the KCRV through use of internally consistent contributing methods. The KCRV for the estradiol content of the material was 984.3 mg/g with a combined standard uncertainty of 0.42 mg/g. The individual participant results showed that a relative expanded uncertainty for the purity assignment of 0.2% is a reasonable estimate of the best achievable result by an individual laboratory for a material of this complexity available in this amount at this level of purity. The relative expanded uncertainties reported by laboratories having results consistent with the KCRV ranged from 0.2% to 0.8%. The review of results that were biased from the KCRV showed that two major analytical challenges are posed by the material: the measurement of its water content and controlling for related substance artefact formation during the analysis process. The results displaying a positive bias relative to the KCRV (overestimation of estradiol content) were due to underestimation of the water content of the material, while those with a negative bias (underestimation of estradiol) overestimated the total related substance impurities through a failure to detect and control for artefact formation arising from in situ oxidative dimerization of estradiol in neutral solution prior to analysis. There was however good agreement between all participants in the identification and the quantification of the individual related structure impurities actually present in the sample. The comparison also demonstrated the utility of high-field 1H NMR for both quantitative and qualitative analysis of high purity compounds. It is noted that all the participants who used qNMR as a major or contributing technique and included it as part of, combined it or confirmed it with a conventional 'mass balance' data estimate, obtained results consistent with the KCRV. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Key comparison CCQM-K62 was designed to enable demonstration of the equivalence in capabilities for measurement of vitamins in a food matrix. A milk-based fortified human infant/adult formula was selected as the matrix based upon material availability and relevance. Because vitamins were added to the CCQM-K62 study material in a single form and at levels significantly higher than those that would be naturally occurring in the milk base, the ability of a laboratory to measure the study vitamins is only indicative of a laboratory's ability to measure vitamins in fortified foods. Target analytes were selected for study because of the ready availability of suitable standard materials and the range of their chemical properties: folic acid (vitamin B9) is a single water-soluble molecular entity that typically occurs at low levels and can be unstable, niacin (vitamin B3) is a single stable molecular entity and is typically present at higher concentrations than the other water-soluble vitamins, vitamin A has multiple molecular forms (including retinol and retinyl palmitate), is fat-soluble and typically occurs at relatively high levels. Results for participants measuring only folic acid or niacin are only indicative of their ability to make that measurement; results for participants measuring both folic acid and niacin are indicative of a laboratory's ability to measure folic acid, thiamine, niacin, and riboflavin in fortified foods but not vitamin C or other water-soluble vitamins. The ability to measure vitamin A (reported as retinol equivalents) in this material is also indicative of the participant's ability to measure vitamin E (as alpha-tocopherol and alpha-tocopheryl acetate) but is not indicative of the ability to measure vitamins D and K, which typically occur at much lower concentrations. The relative degrees of equivalence of the reported measurements for all three analytes in CCQM-K62 were within 10%; however, since only two results were submitted for niacin and vitamin A and one of the three results for folic acid was withdrawn, no strong conclusions as to the expected comparability of higher-order vitamin measurements can be established. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Solutions of known mass fraction of organic analytes of interest are typically used to calibrate the measurement processes used in the determination of these analytes. Appropriate value assignments and uncertainty calculations for these calibration solutions are critical. For the Mutual Recognition Arrangement (MRA) developed by the CIPM, there are numerous Calibration and Measurement Capability Claims (CMCs) published in Category 3 Organic Solutions in the CIPM MRA Appendix C. Additional CMCs in this category are being proposed and reviewed. Evidence of successful participation in formal, relevant international comparisons is needed to support these claims. A CCQM pilot study conducted in 2004 was comprised of three parts: CCQM-P31a Organic Solution—Polycyclic Aromatic Hydrocarbons (PAHs), CCQM-P31b Organic Solution—Polychlorinated Biphenyl (PCB) Congeners, and CCQM-P31c Organic Solution—Chlorinated Pesticides. The results from the CCQM-P31a study are summarized below for the PAHs. After review of the P31a results at the April 2004 Organic Analytical Working Group (OAWG) meeting (Sevres 2004) and the October 2004 OAWG meeting (Beijing 2004), it was decided to proceed with a key comparison study for PAHs in solution (CCQM-K38) with a concurrent second pilot study for the PAHs in solution (CCQM-P31a.1). CCQM-K38 was conducted during the same time period as a PAHs in soil pilot study (CCQM-P69) coordinated by CENAM and BAM. This Key Comparison study demonstrated a high level of equivalence in capabilities of the participating NMIs to successfully identify and measure five PAHs (phenanthrene, fluoranthene, benz[a]anthracene, benzo[a]pyrene, and benzo[ghi]perylene) in a solution using GC/MS-based methods. The PAHs measured in CCQM-K38 were selected to be representative of PAHs typically used as calibrants in the determination of the PAHs found in environmental samples and to provide the typical analytical measurement challenges encountered in the value-assignment of these PAH calibration solutions, such as volatility losses and resolution from potential interferences and other PAHs present as components in the solution during chromatographic separation. The abilities demonstrated by the laboratories that provided comparable measurements for all five PAHs in this Key Comparison should be indicative of their ability to provide reference measurements for a suite of PAHs in solutions when present at levels greater than 3 µg/g provided the laboratory demonstrates an acceptable degree of separation of the PAHs in the specific solution being analyzed. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Polychlorinated biphenyls (PCBs) consist of 209 possible congeners depending on the substitution of the chlorine atoms around the biphenyl molecule. PCBs have been widely used as industrial fluids, flame retardants, diluents, hydraulic fluids, and dielectric fluids for capacitors and transformers. As a class of compounds, they are environmentally stable and tend to bioaccumulate. Of the 209 possible congeners, approximately 150 congeners have been reported in the environment. Congener-specific PCB methods, which are typically based on gas chromatography (GC) with electron capture detection (ECD) or mass spectrometric (MS) detection, are designed to measure selected priority congeners, but the congeners of interest change with the study and sponsoring agency. A pilot study (CCQM-P17) for the determination of PCB congeners in sediment was organized by NIST and NRC-Canada in 2000. Ten laboratories participated in the pilot study. After discussion and critical review of the data, there was agreement that the pilot study should be followed by a Key Comparison and that the Key Comparison Reference Value (KCRV) should be derived from isotope dilution GC/MS (ID-GC/MS) based methods that had been validated in the Pilot Study. The CCQM-K25 Key Comparison study utilized a sediment sample prepared by mixing known quantities of two sediment materials to simulate a moderately contaminated sample with respect to PCBs. Nine laboratories participated in CCQM-K25 and demonstrated a high level of equivalence in capabilities for determining five PCB congeners (congener numbers 28, 101, 105, 153, and 170) in a moderately contaminated sediment using GC/MS-based methods. The amount of substance concentration for the congeners measured ranged from ~10 ng/g to ~35 ng/g. The relative expanded uncertainties of the KCRVs ranged from 2% to 5%, indicating excellent agreement among the participants that used ID-GC/MS. Results from the one laboratory that used GC/MS with a non-labeled PCB congener as internal standard showed no systematic bias from the results of other laboratories. The five PCB congeners measured in CCQM-K25 were selected to be representative of the approximately 150 congeners found in environmental samples and to provide the typical analytical measurement challenges encountered in the measurement of individual congeners such as volatility losses during sample preparation and coelution during chromatographic separation. The abilities demonstrated by the laboratories that provided comparable measurements for all five congeners in this Key Comparison should be indicative of their ability to provide reference measurements for the typical suite of PCB congeners found in moderately contaminated sediments (individual congener amount of substance concentrations >5 ng/g dry basis). Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the Mutual Recognition Arrangement (MRA).