Variability of procedural blanks leads to greater uncertainty in assessing detection limits for the measurement of polonium-210

Low-level measurements of ²¹⁰Po using alpha spectrometry with a ²⁰⁹Po tracer have been conducted at the Environmental Research Institute of the Supervising Scientist (eriss) for many years, on samples with a range of activity concentrations spanning several orders of magnitude. These samples originated from a wide range of research and monitoring projects, and included a wide variety of traditional foods consumed by the indigenous population in Australia’s Northern Territory. Assessment of instrument blank and analyte blank data from these measurements collected over a period of 8 years was conducted. Instrumental blank data for ²¹⁰Po and ²⁰⁹Po generally followed a normal distribution, whereas analyte blank data for ²¹⁰Po followed a lognormal distribution. Instrumental blank data for ²⁰⁹Po indicated an increasing trend, indicative of a low level of polonium volatilisation from prepared sources. Lower limits of detection, including the critical limit, detection limit and quantification limit have been calculated. The critical limit ranges from 12 to 37 counts per day. Detection and quantification limits range from 0.18 to 0.33 mBq and 2.3 to 3.6 mBq for a 4-day count, with an assumed mean chemical recovery of 53 %. These limits are relatively high for alpha spectrometric techniques due to the high variability of the analyte blank signal and non-normal distribution for ²¹⁰Po. Native plant species have relatively low activity concentrations of ²¹⁰Po in their edible fruits and the amount of sample that should be used for analysis to ensure 90 % of fruit samples analysed reach the specified quantification limit was 11 g.     

On the formation mechanism for electrically generated exciplexes in a carbazole–pyridine copolymer

Although carbazole‐containing copolymers are frequently used as hole‐transporting host materials for polymer organic light‐emitting diodes (OLEDs), they often suffer from the formation of undesired exciplexes when the OLED is operated. The reason why exciplexes sometimes form for electrical excitation, yet not for optical excitation is not well understood. Here, we use luminescence measurements and quantum chemical calculations to investigate the mechanism of such exciplex formation for electrical excitation (electroplex formation) in a carbazole–pyridine copolymer. Our results suggest that the exciplex is formed via a positively charged interchain precursor complex. This complex is stabilized by interactions that involve the nitrogen lone pairs on both chain segments. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012