Field spikes Terms

B. Long-term potentiation in the dentate gyrus recorded in vivo. The graph plots the early rising slope of the field excitatory postsynaptic potential (EPSP) in response to low frequency stimulation (700 pA, 100 ms, 0.05 Hz). Four trains of high frequency stimulation (700 pA, 82.5 ms, 400 Hz) were dehvered at time 0. This produced an immediate increase in the EPSP slope (post-tetanic potentiation) and a sustained relatively constant enhancement that lasted for at least 60 minutes. Representative traces are included below the graph. Note the obvious increase in size of the superimposed population spike (downward deflection). 

There are several concepts and terms that are essential to discussions about QA, even the concept itself. While at a very detailed level any definition can be challenged as being too narrow or too broad, the definitions presented below are useful (20). It should be noted that these terms are quite recent in definition and are not usually given in statistics books. Other terms like pollution have evolved over hundreds of years (21). Some key terms used in the field like reproducibility, standard deviation, standard error, replicate analysis, blanks, spiked samples and blind samples are self-explanatory. 

Methods for determining the LOD that are based on the analysis of a field blank that does not contain the analyte of interest are problematic in many real-world applications because either such samples do not exist, or would be impossibly difficult to create. As such a circumstance is frequently encountered in environmental analysis, the USEPA adopted a detection limit procedure, termed the method detection limit (MDL), which focuses on an operational definition of detection limit. Specifically, the MDL is defined as the minimum concentration of a substance that can be measured and reported with 99% confidence that the analyte concentration is greater than zero. The MDL is determined from a replicate analysis of a sample of a specified matrix. Specifically, at least seven aliquots of sample, spiked to contain a concentration of from one to five times the method s estimated MDL, are analyzed. The MDL calculated from these results is statistically tested to determine its reasonableness. If the result fails the testing, this iterative process begins again with a new estimate of the MDL. 

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