An extraction procedure based on the Quick Easy Cheap Effective Rugged and Safe (QuEChERS) approach has been developed and used for analysis of particle-bound nitrated and oxygenated PAH derivatives (NPAH and OPAH, respectively). Several analytical conditions, for example GC injection temperature and MS detection settings, were optimized. This analytical procedure enabled simultaneous GC-NICIMS quantification of 32 NPAH and 32 OPAH (or other oxygenated compounds), including typical components of secondary organic aerosol (SOA) formed by photooxidation of PAH (e.g. 2-formyl-trans-cinnamaldehyde and 6H-dibenzo[b,d]pyran-6-one). The QuEChERS-like approach was optimized, including the nature of the extraction solvent, the sorbent used for clean-up, and extraction time. The final extraction procedure was based on brief mechanical agitation (vortex mixing for 1.5 min), with 7 mL acetonitrile as solvent. Because dispersive solid-phase extraction (d-SPE) did not provide satisfactory results, SPE using SiO2 was selected for sample purification. Identical results were obtained when the QuEChERS-like and traditional pressurised solvent extraction (PLE) procedures were compared for analysis of fortified ambient air particle samples. The procedure was validated by analysis of two aerosol standard reference materials (NIST SRM 1649b (urban dust) and SRM 2787 (fine particulate matter, <10 μm)). For numerous NPAH and OPAH, this is the first report of their quantification in both SRMs. Compared with other extraction methods, including PLE, the QuEChERS-like procedure resulted in increased productivity and reduced extraction cost. This paper shows that QuEChERS-like extraction procedures can be suitably adapted for molecular chemical characterization of aerosol samples and could be extended to other categories of compound.

Until recently, the Vitamin D External Quality Assessment Scheme (DEQAS) assessed the performance of various assays for the determination of serum total 25-hydroxyvitamin D [25(OH)D] by using a consensus mean based on the all-laboratory trimmed mean (ALTM) of the approximately 1000 participants' results. Since October 2012, the National Institute of Standards and Technology (NIST), as part of the Vitamin D Standardization Program, has participated in DEQAS by analyzing the quarterly serum sample sets using an isotope dilution LC-tandem MS (ID LC-MS/MS) reference measurement procedure to assign an accuracy-based target value for serum total 25(OH)D. NIST has analyzed 90 DEQAS samples (18 exercises × 5 samples/exercise) to assign target values. The NIST-assigned values are compared with the ALTM and the biases assessed for various assays used by the participants, e.g., LC-MS/MS, HPLC, and several ligand-binding assays. The NIST-value assignment process and the results of the analyses of the 90 DEQAS samples are summarized. The absolute mean bias between the NIST-assigned values and the ALTM was 5.6%, with 10% of the samples having biases >10%. Benefits of the accuracy-based target values are presented, including for sample sets with high concentrations of 25(OH)D2 and 3-epi-25(OH)D3.

Retention indices (I) for 45 polycyclic aromatic hydrocarbons (PAHs) and 63 methyl-substituted PAHs were determined by gas chromatography - mass spectrometry (GC-MS) using two different stationary phases: a Rxi-PAH phase (a "higher phenyl-content stationary phase") and a 50% (mole fraction) liquid crystalline dimethylpolysiloxane phase. Retention data were obtained for parent PAHs from molecular mass (MM) 128 g/mol (naphthalene) to 328 g/mol (benzo[c]picene) and for 12 sets of methyl-PAHs (methylfluorenes, methylanthracenes, methylphenanthrenes, methylfluoranthenes, methylpyrenes, methylbenz[a]anthracenes, methylbenzo[c]phenanthrenes, methylchrysenes, methyltriphenylenes, methylbenzo[a]pyrenes, methylperylenes, and methylpicenes). Molecular shape descriptors such as length-to-breath ratio (L/B) and thickness (T) were determined for all the PAHs studied. Correlation between I and L/B ratio was evaluated for both stationary phases with a better correlation observed for the 50% liquid crystalline phase (correlation coefficients ranging from 0.22 to 1.00). Graphical Abstract GC separation of six methylchrysene isomers (m/z 242) on two different stationary phases: 50 % phenyl-like methylpolysiloxane phase and 50 % liquid crystalline phase. Retention indices (I) are plotted as a function of L/B for both phases. The data marker numbers identify each isomer based on methyl-substitution position.

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