Certified reference materials for inorganic and organic contaminants in environmental matrices

Development of a Purity Certified Reference Material for Vinyl Acetate

Vinyl acetate is a restricted substance in food products. The quantification of the organic impurities in vinyl acetate is a major problem due to its activity, instability, and volatility. In this paper, while using the mass balance method to determine the purity of vinyl acetate, an improved method was established for the determination of the content of three impurities in vinyl acetate reference material, and the GC-FID peak area normalization for vinyl acetate was calibrated. The three trace organic impurities were identified by gas chromatography tandem high-resolution mass spectrometry to be methyl acetate, ethyl acetate, and vinyl propionate. The content and relative correction factors for the three organic impurities were measured. The purity of vinyl acetate determined by the mass balance method was 99.90% with an expanded uncertainty of 0.30%, and the total content of organic impurities was 0.08% with a relative correction factor of 1.23%. The vinyl acetate reference material has been approved as a national certified reference material in China as GBW (E) 062710.

What if using certified reference materials (CRMs) was a requirement to publish in analytical/bioanalytical chemistry journals?

Certified reference materials (CRMs) are routinely used by analytical chemists to validate new analytical methods and to demonstrate the quality of their quantitative measurements. Even though CRMs for trace element and trace organic analysis have been available and widely used for over 50 years, the majority of papers published in analytical chemistry journals do not mention the use of CRMs. What if analytical/bioanalytical chemistry journals required the use of CRMs to publish a paper? This feature article attempts to address this question by providing examples of recent papers that have made exceptional use of CRMs to validate new analytical methods and to describe novel, alternative uses of CRMs that provide new characterization of the CRM. The potential benefits of using a CRM even when it does not have certified values for the analytes of interest are presented.

Development, Optimization, and Validation of Forensic Analytical Method for Quantification of Anticholinesterase Pesticides in Biological Matrices from Suspected Cases of Animal Poisoning

Anticholinesterase pesticides are a main cause of the intentional or accidental poisoning of animals. Anticholinesterases include several substances that cause the overstimulation of both central and peripheral acetylcholine-dependent neurotransmission. Forensic analyses of poisoning cases require high levels of expertise, are costly, and often do not provide reliable quantitative information for unambiguous conclusions. The purpose of the present study was to develop and validate a method of high-performance liquid chromatography with diode array detector (HPLC−DAD) for the identification and quantitation of n-methyl carbamates, organophosphates and respective metabolites from biological samples of animals that were suspected of poisoning. HPLC−DAD is reliable, fast, simplistic and cost-effective. The method was validated for biological samples obtained from stomach contents, liver, vitreous humor and blood from four different animal species. The validation of the method was achieved using the following analytical parameters: linearity, precision, accuracy, selectivity, recovery, and matrix effect. The method showed linearity at the range of 25−500 μg/mL, and the correlation coefficient (r2) values were >0.99 for all matrices. Precision and accuracy were determined by the (a) coefficient of variation (CV), (b) relative standard deviation low-quality control (LQC), (c) medium-quality control (QCM), and (d) high-quality control (QCA). The indicated parameters were all less than 15%. The recovery of analytes ranged from 31 to 71%. The analysis of results showed no significant interfering peaks due to common xenobiotics or matrix effects. The abovementioned method was used to positively identify pesticide analytes in 44 of the 51 animal samples that were suspected of poisoning, demonstrating its usefulness as a forensic tool.

From urban dust and marine sediment to Ginkgo biloba and human serum-a top ten list of Standard Reference Materials (SRMs)

During the past 40 years, the National Institute of Standards and Technology (NIST) has developed over 180 natural matrix Standard Reference Materials® (SRMs) for the determination of trace organic constituents in environmental, clinical, food, and dietary supplement matrices. A list of the Top Ten SRMs intended for organic analysis was identified based on selection criteria including analytical challenge to assign certified values, challenges in material preparation, novel matrices, longevity, widespread use, and unique design concept or intended use. The environmental matrix SRMs include air particulate matter, marine sediment, mussel tissue, and human serum with the focus on contaminants such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), chlorinated pesticides, and polybrominated diphenyl ethers (PBDEs). Human serum and plasma SRMs for clinical diagnostic markers including vitamin D metabolites represent clinical analysis, whereas infant formula, multivitamin/multielement tablets, and Ginkgo biloba constitute the food and dietary supplement matrices on the list. Each of the SRMs on the Top Ten list is discussed relative to the selection criteria and significance of the material, and several overall lessons learned are summarized.

The Importance of Reference Materials and Method Validation for Advancing Research on the Health Effects of Dietary Supplements and Other Natural Products

Insufficient assessment of the identity and chemical composition of complex natural products, including botanicals, herbal remedies, and dietary supplements, hinders reproducible research and limits understanding mechanism(s) of action and health outcomes, which in turn impede improvements in clinical practice and advances in public health. This review describes available analytical resources and good methodological practices that support natural product characterization and strengthen the knowledge gained for designing and interpreting safety and efficacy investigations. The practice of validating analytical methods demonstrates that measurements of constituents of interest are reproducible and appropriate for the sample (e.g., plant material, phytochemical extract, and biological specimen). In particular, the utilization of matrix-based reference materials enables researchers to assess the accuracy, precision, and sensitivity of analytical measurements of natural product constituents, including dietary ingredients and their metabolites. Select case studies are presented where the careful application of these resources and practices has enhanced experimental rigor and benefited research on dietary supplement health effects.

Desarrollo de un material de referencia certificado para análisis elemental de agua potable

La producción de un material de referencia (MR) es un proceso en el que se realizan estudios relacionados con la preparación, envasado y caracterización (incluye homogeneidad y estabilidad). En este trabajo se presentan los resultados del desarrollo de un MR de agua potable. El envasado se realiza aplicando dos procedimientos (envasado convencional e inmersión). La caracterización se realizó por Absorción Atómica, ICPMS y Cromatografía iónica. La evaluación de homogeneidad del material se realizó para Na, Mg, Ca, Fe, K, Co, Pb, Mo, As, Ni, Se, Cu, Al, Cr Zn y aniones como NO3-y Cl-. La estabilidad se evaluó a corto (condiciones aceleradas) y largo plazo por ICPMS y CI, además se realizó seguimiento gravimétrico. La homogeneidad y estabilidad se evaluaron con base en su incertidumbre. La incertidumbre asociada a la homogeneidad y estabilidad MR evidenció resultados aceptables para la mayoría de los analitos. Los resultados del seguimiento gravimétrico permitieron detectar pérdidas de masa del material, por lo que se planteó un nuevo esquema para evaluar la estabilidad a través de métodos gravimétricos. Finalmente, se encontró que el MR presenta incertidumbres expandidas entre el 0,93% y el 4,38%, siendo apto para el uso previsto.

Stability of organochlorine pesticides during storage in water and loaded SPE disks containing sediment

With regard to the Water Framework Directive (WFD) and the required investigation of the whole water sample including suspended particulate matter (SPM), a storage stability study was conducted to determine the suitable storage time and conditions of 21 organochlorine pesticides (OCPs) spiked in water samples and pre-concentrated on solid-phase extraction disks (SPE disks). Furthermore, this work demonstrates the behaviour of three different certified sediment reference materials (CRMs) contaminated with OCPs in water samples as well as loaded on SPE disks under different temperature conditions and storage time periods. Extracts collected on SPE disks were stored for 3, 14 and 30 days at both 4 °C and -18 °C in darkness covered in (a) freezer bags and (b) aluminum foil. With few exceptions the results of these tests demonstrate stability of OCPs up to 30 days at -18 °C. The recoveries for most substances range between 84% and 133%. Furthermore, the stability of OCPs in water samples additionally spiked with CRM up to 500 mg and stored at a temperature of 4 °C in darkness up to 56 days was investigated. The addition of sodium azide enhanced the stability of some substances during storage, especially the endosulfans (I, II) but most substances were stable regardless of sodium azide addition over the entire storage period. An important conclusion of this study is that the storage of loaded SPE disks is an appropriate alternative to storing water samples.

Feasibility study of a candidate reference material for ions in PM2.5: does commutability matter also for inorganic matrices?

The existing Air Quality Directive 2008/50/EC establishes within the European Union (EU) member states limit values for fine air particulate matter (PM_2.5) including the possibility to discount natural sources of pollution when assessing compliance with the legislation. In proving this, EU member states shall determine, amongst others, the rural background concentration of some anions (Cl⁻, NO₃⁻ and SO₄²⁻) and cations (Na⁺, NH₄⁺, K⁺, Ca²⁺ and Mg²⁺). To deliver reliable data and to comply with the data quality objectives of the legislation, environmental control laboratories should use certified reference materials (CRMs) to validate or verify the performance of their analytical methods. Since no CRMs for anions and cations in PM_2.5 are presently available, we present the commutability issues encountered during the first attempt to develop such a material. We demonstrate that a dust, collected in a road tunnel and previously used for the production of two CRMs of a PM₁₀-like material, does not behave as an authentic fine particulate matter collected according to EN12341:2014 when measured by an established method proposed by the European Committee for Standardization (CEN/TR 16269:2011). The water-soluble fractions of SO₄²⁻, NH₄⁺, K⁺, Ca²⁺ and Mg²⁺ in a PM_2.5-like candidate CRM produced from that road tunnel dust are only fully extracted after 3 h of sonication and not after 30 min, as stated in the method. Moreover, we found that the particle size of the test material influenced the extraction yield of K⁺, Ca²⁺ and Mg²⁺, suggesting that these ionic species were incorporated in the core of the particles and inaccessible to the extraction procedure. These particular features make the material unsuitable for the measurements of ions with the CEN method. The difference in the extraction time can be seen as a commutability issue and the candidate CRM should be considered as not commutable with routine samples. This demonstrates that commutability studies should not only be considered for clinical CRMs, but also for inorganic CRMs when they are intended to be used to quantify operationally defined analytes.

Development of potential candidate reference materials for drugs in bottom sediment, cod and herring tissues

Regular use of a reference material and participation in a proficiency testing program can improve the reliability of analytical data. This paper presents the preparation of candidate reference materials for the drugs metoprolol, propranolol, carbamazepine, naproxen, and acenocoumarol in freshwater bottom sediment and cod and herring tissues. These reference materials are not available commercially. Drugs (between 7 ng/g and 32 ng/g) were added to the samples, and the spiked samples were freeze-dried, pulverized, sieved, homogenized, bottled, and sterilized by γ-irradiation to prepare the candidate materials. Procedures for extraction and liquid chromatography coupled with tandem mass spectrometry were developed to determine the drugs of interest in the studied material. Each target drug was quantified using two analytical procedures, and the results obtained from these two procedures were in good agreement with each other. Stability and homogeneity assessments were performed, and the relative uncertainties due to instability (for an expiration date of 12 months) and inhomogeneity were 10-25% and 4.0-6.8%, respectively. These procedures will be useful in the future production of reference materials.

Performance evaluation of polycyclic aromatic hydrocarbons analysis in sediment from proficiency testing with metrological reference values

This paper describes a metrological approach to evaluate the measurement capability of laboratories participating in two proficiency testing (PT) programmes involving the analysis of five polycyclic aromatic hydrocarbons (PAHs) in sediment samples. Reference values of PAHs in the programmes for performance assessment were obtained from an accurate isotope dilution gas chromatography mass spectrometry (ID-GCMS) method which was thoroughly validated and verified. Isotope dilution mass spectrometry (IDMS) technique usually has a well-defined measurement uncertainty budget and a traceability link to an International System of Units. Provision of the metrological reference values in PT enables the establishment of a technical platform to assess the actual competence of the participating laboratories in sediment PAHs analysis. Results of the PT programmes showed that about 80 % of the laboratories employed gas chromatography in their analyses and the remaining used liquid chromatography. Irrespective of the techniques being used, however, the majority of the participating laboratories were observed to underestimate values in which the mean values of the five reported PAHs were less than those of the ID-GCMS-derived reference values by 13-20 %. Only 41-44 % of the participating laboratories were able to achieve satisfactory z-scores. The present study revealed that the reinforcement of the capability for accurate measurement of PAHs in sediment samples in laboratories worldwide should be addressed.

The analysis of dioxins and related compounds

The analysis of polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, polychlorinated biphenyls, and other related compounds requires complex sample preparation and analytical procedures using highly sensitive and selective state-of-the-art instrumentation to meet very stringent data quality objectives. The analytical procedures (extraction, sample preparation), instrumentation (chromatographic separation and detection by mass spectrometry) and screening techniques for the determination of dioxins, furans, dioxin-like polychlorinated biphenyls and related compounds with a focus on new approaches and alternate techniques to standard regulatory methods are reviewed.

Preparation of reference material for organochlorine pesticides in a herbal matrix

The development of reference material for four organochlorine pesticides, namely hexachlorobenzene and three isomers of hexachlorocyclohexane (alpha-hexachlorocyclohexane, beta-hexachlorocyclohexane and gamma-hexachlorocyclohexane), in a ginseng root sample is presented. Raw materials (Panax ginseng) were purchased from a local market and confirmed to contain certain levels of incurred organochlorine pesticide residues by a validated gas chromatography-mass selective detection method. A total of more than 300 bottles each containing 25 g of samples were prepared after the materials had been freeze-dried, milled and thoroughly mixed. The homogeneity and stability of samples from randomly selected bottles were verified and the reference values were characterized using a highly precise isotope dilution gas chromatography-mass spectrometry (ID-GCMS) method that was recently developed by our laboratory. The purity of standard organochlorine chemicals was determined against certified reference materials to establish the accuracy of the ID-GCMS analysis. The concentrations (+/- expanded uncertainty) of hexachlorobenzene, alpha-hexachlorocyclohexane, beta-hexachlorocyclohexane and gamma-hexachlorocyclohexane in the reference material were 0.198 +/- 0.015, 0.450 +/- 0.022, 0.213 +/- 0.011 and 0.370 +/- 0.032 mg kg(-1), respectively. A portion (70 bottles) of the samples was also used in a proficiency testing (PT) scheme for assessing the testing capabilities of field laboratories. The consensus mean values of the PT obtained from the 70 participants were on the same order but deviated by -2.7 to -14.1% from those of the assigned reference values. Because of the wide spread of participants' data (relative standard deviation ranging from 44 to 56%), the PT results were not included in the calculation of the assigned values of the reference materials. The materials served as suitable reference materials to ascertain the quality control and validation processes for the determination of organochlorine pesticides in herbal matrices.