Elution Efficiency

The performance of a generator system is expressed by the elution efficiency, which is defined as the fraction of eluted Tc activity of the theoretically available radioactivity at the time of elution, usually given as a percentage. The yield varies with different generator systems, and is generally between 80 and 100% of the theoretical value however, daily elutions should represent a constant percentage, fluctuations as shown in the graph (Fig. 5.3) indicate poor performance. 

Generators produced with high specific activity fission molybdenum-99 may be eluted with a small volume of saline, showing a narrow elution profile, as indicated by the graphic presentation (Fig. 5.4). Still, there are differences in the elution pattern between generator systems from different producers. Therefore, it may be beneficial to know the elution profile of each generator used at a medical facility. 

The elution profile may be obtained from the manufacturer on request, or it may be determined by fractional elution using 1- to 2-ml fractions and measuring the eluted activity of each sample. Shown are elution efficiencies obtained with two generator systems manufactured by different producers. Generator I shows 61.6% of the eluted radioactivity in the first 3 ml shown in Fig. 5.5, whereas elution of generator II shows the major activity peak in the fractions between 3 and 5 ml (Fig. 5.6). Both generators are totally eluted with 5 mL of saline. 

Fractional elution may be indicated when small volumes of high activity are needed for bolus injection or for labeling. In the case of generator I, it will suffice to elute a total volume of 3 ml, while two 3-ml fractions should be obtained in the case of generator II, since the main activity peak is collected in the second fraction. 

After elution of the generator column, the Tc activity builds up until a maximum is reached after approximately four half-lives (22.89 h). Equilibrium between mother and daughter activity is established later, after 43.9 h. A schematic presentation depicts the growth of Tc activity after daily elution in relation to decreasing parent Mo, and the equilibrium state after day 5, when no elution is performed (Boyd 1982 Richards 1966 Fig. 5.7). 

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Phenyl (Cohesive Technologies), the polymer-based Oasis HLB (Waters), the Cyclone (Cohesive Technologies), and the porous graphitized carbon-based Hypercarb (ThermoHypersil, Cheshire, UK) Cohesive s 2300 system was the HTLC component. Merck s monolithic reversed-phased Chromolith Speed ROD (RP-C18 (50 x 4.6 mm) served as the analytical column. The Oasis HLB, Cyclone TFC, and Hypercarb yielded the best retention capacity and good elution efficiency and volume. Recovery was 42 to 94% with a sample volume of 10 mL. Run time was 14 min. LODs were 0.4 to 13 ng/L for most compounds. 

Kp can be changed by pH, ionic strength, temperature and other parameters. Therefore these parameters can be used to control the binding and elution efficiency of the reaction [1,4,22]... 

Column Performance. The only eluant found to elute Au-195m in any reasonable yield was NaCN, consequently the materials were investigated for variation in elution efficiency as a function of several variables, namely, concentration of cyanide, the volume of cyanide, and time/"specific activity" of Hg-195m on column. These parameters were of particular importance because of the over-riding requirement that the specific activity of Au-195m in solution should be greater than 20 mCi/ml. The parameter used to compare results was the % elution efficiency where ... 

Figure 1. Variation of elution efficiency with concentration of cyanide.

Figure 4. CPG Lipoamide Columns Time dependence of elution efficiency for different "specific activity" columns.

Often SDS can be omitted from the elution buffer. The eluted proteins can be injected then without necessity of Triton X-100 removal. However, depending on the batch and supplier of the membrane, elution efficiency with Triton X-100 alone may vary, and some proteins are eluted poorly with this eluent. 

Recovery from spiked samples is calculated by measuring the amount of analyte eluted from the sorbent and comparing the original concentration to the concentration remaining after SPE. Retention and elution are two separate phases of the SPE method. However, the value measured is the overall recovery, which depends on both the sorption and elution efficiencies. Therefore, protocol development is confounded by the interdependence of sorption and desorption processes ... 

Second, the elution step introduces a dilemma Removal of all the trace metal on the column theoretically requires an infinite volume of eluting solvent, yet the concept of preconcentration demands that eluent volume be kept to a minimum. In practice, a highly reproducible fraction of a trace metal is removed from a chelating column by the first several milliliters (21) thus, elution is carried out with this volume, the elution efficiency is factored into the final results, and a second portion of eluting solvent is passed to complete elution of the remaining tail into the waste container. 

Among the many potential eluants tested, only mineral acids and aqueous solutions of alkaline and ammonium carbonates yielded measurable elution efficiencies. While carbonates require higher concentrations and temperatures, dilute mineral acids turned out to be quite effective even at room temperature. Figure 8 shows six loading-elution cycles starting with a uranium content of the resin of 110 ppm. 

TABLE 6. Distribution Coefficients and Elution Efficiency of Fulvic Acid on XAD Resins... 

Elution efficiency. In flow systems with SPE involving derivatisation immediately after elution, it is possible to visually evaluate the efficiency of the elution process. In the ideal situation, a very abrupt colour formation is observed immediately after the inlet of the make-up stream. When elution is a limiting factor for optimum system performance, a slow fading of the colour is observed. 

Fig. 5.5. Elution of generator I (n = 67), using fractions of 1.6-3.0 ml, showing 61.6 8.3% in the first fractions and 16.2 5.9% in the second fractions, with an overall elution efficiency of 77.8 4.2%...

The effect of low elution efficiency on subsequent elutions has also been investigated, resulting in an increase of Tc carrier with each elution (Boyd et al. 1985). 

Table 5.6 presents the results obtained with 140 generators from two different manufacturers shown are the elution efficiencies and the Mo activity in the first eluate, expressed as 10 % of the " Tc activity and also as kilobecquerel per milliliter. 

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