The analytical limit of detection: Alternate calculation procedures and enhanced experimental techniques for the analysis of polychlorinated biphenyls

Trace levels of toxic contaminants present in the environment can be detrimental to human health and ecosystem stability. To better understand and manage the fate and transport of low levels of toxic compounds in important ecosystems, scientists need to measure contaminants with greater accuracy and at still lower levels. The detection of trace contaminants was improved by developing and evaluating alternate methods for calculating the limit of detection (and limit of quantification) that are more accurate and consistent than current methods, and by enhancing analysis techniques, using polychlorinated biphenyls (PCBs) as an example, to achieve lower detection limits.; Weighted least-squares regression has been used to calculate statistically exact limits of detection and quantification that can be applied to a limited number of future analyses (weighted prediction interval-based) or to a large and potentially unknown number of future analyses (weighted tolerance interval-based). Approximate methods have been evaluated that require much reduced statistical calculations yet provide results that compare well with the statistically exact methods.; Adding small amounts of oxygen to the electron capture detector (ECD) make-up gas ("oxygen doping") has been shown to moderately increase ECD sensitivity toward PCBs; however, response enhancements do not outweigh the increased noise. Thus, oxygen doping does not decrease detection and quantification limits for PCBs. Oxygen doping at high (6%) levels produces negative peaks for analytes with weak electron affinities, like PCB congeners 1, 3 and 4.; On-column supercritical fluid extraction-gas chromatography (SFE-GC) with ECD has been used to analyze picogram quantities of PCBs. The technique shows good reproducibility and good recovery of all but the lightest PCB congeners. Using an in-line carbon dioxide (CO{dollar}sb2){dollar} solvent purification system, previously prohibitive ECD responsive contamination has been reduced to nondetectable levels, thereby permitting lower detection and quantification limits.; The major ECD-responding contaminant in supercritical CO{dollar}sb2{dollar} used for SFE has been identified as chlorotrifluoroethylene (CTFE) grease, commonly used as a lubricant by the specialty gas industry. CTFE levels in three separate grades of CO{dollar}sb2{dollar} from two different manufacturers have been quantified. Moderate amounts of CTFE grease have been shown to cause overestimation of PCB concentrations.