Minimum detectable activity MDA

Taking into consideration the method of °Sr analysis, the activity equilibrium state between °Sr and its decay product °Y is very important. This state is attained 12 days after the separation of radiostrontium [62]. The reliability of the received results of °Sr determination depends on the minimum detectable activity (MDA) [5]. The MDA should be calculated for each analysis sample. Generally, the separation of °Sr with the use of fuming HNO3, and subsequent co-precipitation of radium, lead, and barium as chromates, is used for the analysis of flora, soil, ash filters, and water samples. The fusion products (e.g., Cs) are removed by co-precipitation of the hydroxides, then transformed into yttrium oxalate, and the activity of °Y measured in a low-level proportional counter. The yield is controlled by measuring the activity of Sr (gamma emitter) added to each sample before analysis as an internal tracer [1, 46]. The accuracy of the analytical results obtained should be verified in a validation process with the use of certified reference materials (CRMs). 

The minimum detectable activity (MDA), which is analogous to the minimum detectable concentration, is given by... 

The minimum amount of radioactivity that can be detected by a flow-through radiochemical detector is a subject of continuing debate. It is generally accepted that a fairly sharp peak that contains counts that are at least twice background can be detected. One formula for calculating the minimum detectable activity (MDA) is given by... 

The minimum detectable activity (MDA) is the smallest net count that can be reported with a certain degree of confidence that represents a true activity from a sample and is not a statistical variation of the background. The term MDA is not universally acceptable. In the general case, in measurements not necessarily involving radioactivity, other terms such as lowest detection limit have been used. Here, the notation and applications will be presented with the measurement of a radioactive sample in mind. 

Figure 2.12 The meaning of the critical detection limit (CDL) and minimum detectable activity (MDA) in terms of the confidence limits defined by a and /3.

Beads packed in microcolumns is the most reported in literature, since users can customize the quantity of resin according to the capacity of it, to the volume of sample to be loaded, and to the minimum detectable activity (MDA) of the detector used. In general, packing is manually replaced in flow systems based on flow injection analysis G A), sequential injection analysis (SIA), multisyringe flow injection analysis (MSFIA) and multipumping flow systems (MPFS). By the contrary, lab on valve (LOV) allows the manipulation of heterogeneous solutions, i.e. bead injection, achieving the automated replacement of the resin. In Chapter 3 are described in detail the parts of the microcolumns and the way to fill them. Table 8.1 summarizes the variety of available resins from TrisKem International [4]. 

In Section 5.6, I discussed the principles underlying the concepts of Critical Limit, Limit of Detection and its activity equivalent, the dubious Minimum Detectable Activity (MDA), which you will recall is not the minimum activity detectable. In that section, I pointed out that the common use of MDA as an indication of the upper limit of activity within a measured sample is not justifiable. However, it is the correct parameter to consider when discussing what if in the context of evaluation of... 

Measurement methods have limits of detection arising from the presence of naturally occurring radioactive materials, from statistical fluctuations in counting rates, and from factors related to sample preparation and analysis. Appendix II describes the concepts of minimum significant activity (MSA) and minimum detectable activity (MDA), which are used to characterize the limits of detection of any measurement method. 

The minimum detectable activity (MDA), often termed the detection limit L ), corresponds to the level of activity which is needed to ensure, with some chosen level of confidence P, that the net signal will be detected, according to the criterion that it exceed the MSA. The mathematical treatment is simplified, as in the following section, if P = a, and by common convention 0.05 is adopted for both. 

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