Dilute-and-shoot enhances sensitivity of phthalate urinary concentrations for assessing the exposure in children.

Phthalates are not covalently bound to plastics. They can leach from experimental plastic devices. Due to the development of sensitive techniques, exogenous sources that interfere with the accuracy of phthalate monoester analysis can be easily detected. Here, we propose the simple and rapid dilute-and-shoot method to minimize sample handling and limit contact with laboratory apparatus, which efficiently reduced phthalate interferences mainly from experimental plasticware and improved the accuracy of analysis. Chemical additives in the mobile phase and modifiers in reconstituted solution were evaluated to improve peak shape and liquid chromatography separation. Under optimal conditions, the limit of detection ranged from 0.01 to 0.5 ng/mL. No phthalate monoesters were detected above the limit of detection in blank water while the leached concentrations of MMP, MEP, MiBP, MnBP and MEHP from the conventional solid phase extraction procedure were 1.9, 2.7, 0.9, 2.0 and 1.1 ng/mL, respectively. In 304 samples collected from primary school- children aged 9-10 years, we observed a positive association between body mass index (BMI) and urinary MMP and MiBP concentrations in boys, while MEOHP and MEHHP were inversely related to BMI in girls. Furthermore, detectable phthalate monoesters may be considered potential chemical obesogens related to BMI in children.

Conductance of tailored molecular segments: a rudimentary assessment by Landauer formulation.

One of the strengths of molecular electronics is the synthetic ability of tuning the electric properties by the derivatization and reshaping of the functional moieties. However, after the quantitative measurements of single-molecule resistance became available, it was soon apparent that the assumption of negligible influence of the headgroup-electrode contact on the molecular resistance was oversimplified. Due to the measurement scheme of the metal--molecule-metal configuration, the contact resistance is always involved in the reported values. Consequently the electrical behavior of the tailored molecular moiety can only be conceptually inferred by the tunneling decay constant (ßn in Rmeasured = R(n=0)e(ßnN), where N is the number of repeated units), available only for compounds with a homologous series. This limitation hampers the exploration of novel structures for molecular devices. Based on the Landauer formula, we propose that the single-molecule resistance of the molecular backbones can be extracted. This simplified evaluation scheme is cross-examined by electrode materials of Au, Pd, and Pt and by anchoring groups of thiol (-SH), nitrile (-CN), and isothiocyanate (-NCS). The resistance values of molecular backbones for polymethylenes (n = 4, 6, 8, and 10) and phenyl (-C6H4-) moieties are found independent of the anchoring groups and electrode materials. The finding justifies the proposed approach that the resistance of functional moieties can be quantitatively evaluated from the measured values even for compounds without repeated units.