Evaluation of the Use of Microtracers™ in a Proficiency Testing Program.

Background: An effective proficiency testing program must utilize accurate splitting procedures to ensure that customers receive equivalent (by some measure) test items. When test items are not equivalent, it becomes impossible to separate variation among laboratories from variation among test items, and the program cannot achieve its objectives. Therefore, there is a critical need to validate the splitting process used to manufacture test items. Objective: The incorporation of MicrotracersTM was investigated for validating the splitting process used in the Association of American Feed Control Officials Proficiency Testing Program and as a potential quality control event for a production run. Methods: Microtracers were incorporated into six production runs. From each run, 12 test items were randomly selected for evaluation. Proficiency test materials were prepared from commercially available feedstuffs using base animal feeds and feed additives. The tracers were incorporated into base feed with other additives, recovered, and counted from the randomly selected test items. Results: Uniformity of test items was evaluated with the following two statistical methods: (1) relative standard deviation (RSD) of particle counts according to a Poisson distribution and (2) a Pearson's Chi-square test. RSDs for counts (per mass basis) ranged from 2.49 to 4.13%, and Chi-square P values ranged from 0.0097 to 0.3740 over the six sets. Conclusions: Microtracers were determined to be a potential tool for validating the splitting process used to manufacture proficiency test items and a tool for incorporating quality control events into the manufacture of proficiency test items. Highlights: The authors offer suggestions for proficiency testing programs.

Arrays of giant octagonal and square cylinders by liquid crystalline self-assembly of X-shaped polyphilic molecules.

Nanopatterning by molecular self-assembly has been a topic of intense research in pursuit of 'bottom-up' methods of generating structures for use in nanotechnology. The systems most widely studied have been two- and three-dimensional morphologies of block copolymers. However, T- and X-shaped polyphilic liquid crystals have recently been shown to have great potential for generating soft honeycomb-like structures, surpassing those of polymers in both complexity and degree of order. The cell cross-section of the liquid crystals honeycombs has so far been limited by small molecular size. Here we overcome this limitation by exploiting the inability of the polyphiles to simultaneously achieve optimal packing and complete nanophase separation. This frustration results in a two-dimensional periodic honeycomb consisting of giant octagonal and square cylinders with circumferences of 12 and 8 molecules, respectively. In addition to forming large cells, the two-molecule-long bendy walls give this structure extra versatility and stability.