Standard Reference Material (SRM) 2378 fatty acids in frozen human serum. Certification of a clinical SRM based on endogenous supplementation of polyunsaturated fatty acids

Dietary fatty acids can be both beneficial and detrimental to human health depending on the degree and type of saturation. Healthcare providers and research scientists monitor the fatty acid content of human plasma and serum as an indicator of health status and diet. In addition, both the Centers for Disease Control & Prevention (CDC) and the National Institutes of Health - Office of Dietary Supplements are interested in circulating fatty acids (FAs) because they may be predictive of coronary heart disease. The National Institute of Standards and Technology (NIST) provides a wide variety of reference materials (RMs) and Standard Reference Materials® (SRM®s) including blood, serum, plasma, and urine with values assigned for analytes of clinical interest. NIST SRM 2378 Fatty Acids in Frozen Human Serum was introduced in 2015 to help validate methods used for the analysis of FAs in serum, and consists of three different pools of serum acquired from (1) healthy donors who had taken fish oil dietary supplements (at least 1000 mg per day) for at least one month (level 1 material), (2) healthy donors who had taken flaxseed oil dietary supplements (at least 1000 mg per day) for at least one month (level 2 material), and (3) healthy donors eating "normal" diets who had not taken dietary supplements containing fish or plant oils (level 3 material). The use of dietary supplements by donors provided SRMs with natural endogenous ranges of FAs at concentrations observed in human populations. Results from analyses using two methods at NIST, including one involving a novel microwave-assisted acid hydrolysis procedure, and one at the CDC are presented here. These results and their respective uncertainties were combined to yield certified values with expanded uncertainties for 12 FAs and reference values with expanded uncertainties for an additional 18 FAs.

Determination of nucleating agents in plastic materials by GC/MS after microwave-assisted extraction with in situ microwave-assisted derivatization

This work demonstrates the analysis of sorbitol-based nucleating and clarifying agents (NCAs) used as additives for polyolefin-based materials by gas chromatography/mass spectrometry (GC/MS), employing a highly reliable and efficient sample preparation methodology applying microwave irradiation. A derivatization by silylation of the analytes was done to improve the GC-suitability of the analytes. After successful optimization of the conditions for a microwave-assisted derivatization (MAD), the microwave-assisted extraction (MAE) of the analytes from polymer samples was investigated. Tetrahydrofuran (THF) turned out to be the best extraction solvent, as poorly soluble analytes show the highest solubility in this solvent and THF supports the silylation after extraction. This two-step approach and subsequent chromatographic determination resulted in reproducibilities from approximately 2% up to 6% and recoveries from 95.8% up to 104.2% in real samples. In order to reduce the number of sample preparation steps a one-step approach was investigated and optimized, in which MAE and MAD were carried out simultaneously. The developed procedure resulted in remarkably better repeatabilities ranging from 0.05% up to 4% and reproducibilities of up to 10%. The recoveries matched those obtained with the two-step process. Linearities could be achieved in both approaches with R(2) better than 0.99 for all selected analytes over two orders of magnitude. All data indicate the suitability of both presented methods for the reliable determination of sorbitol-based NCAs in polyolefin materials.