Elution yield

Band broadening is also affected by the gradient steepness. This effect is expressed in Table 16-14 by a band compression factor C, which is a fnuctiou of the gradient steepness and of equilibrium parameters. Since C < 1, gradient elution yields peaks that are sharper than those that would be obtained in isocratic elution at

[Pg.1536]

Eluate Obtained in low volume 2 ml With high elution yield Minimum breakthrough of parent isotope in large number of elutions Sterile Pyrogen-free... 

From the interpretation of the values with respect to "elution yield" can be derived that for a good "elution yield ( 70%) a combination with 0.1-5 would be needed. Complexing agents meeting this criterion, namely THI0, TRIS, PAH, GTT, MPG and TM were further tested in column experiments. 

Table V. Overview of Column "Elution yield" of Experiments Simulating the Au-198-complexes. 

Figure 1. Simulated elution yield vs. molarity of the eluent. System Si02 ZnS/Au-198-THI0.

Eluent. When evaluating the various concentrations of THIO solutions as an eluent, we found that the yield of Au-195m depends on the THIO concentration similarly as shown in Figure 1. However, for the real parent/daughter pair, 91% "elution yield" is not reached, but, depending on the generator loading, only 25-45 ... 

Figure 3. Elution yield of Au-195m vs. mercury activity (mCi) adsorbed on the column. Key 1, generators produced 36 h or later after EOB and 2, generators produced within 10 h after EOB.

Figure U. Elution yield of Au-195m. Generators autoclaved in nitrate solution. Dashed line not autoclaved generators washed with THIO immediately after loading.

The elution yield and iron breakthrough were measured as a function of time and number of elutions. Six elutions were performed over a period of 26 hours and gave essentially constant Mn-52m recovery, averaging 93% of the available radioactivity. 

Production of Sr-82. An important consideration in the development of radioisotope generators is the availability, cost, and radionuclidic purity of the long-lived parent. In the case of Sr-82, the 25 day radionuclide is needed in 100-200 mCi amounts in order to provide adequate elution yields of Rb-82 from one loading of Sr-82 every three months. Initially the Sr-82 for the generator was produced at the Lawrence Berkeley Laboratory (LBL) 88-inch cyclotron by the Rb-85 (p,4n) Sr-82 nuclear reaction (12). However, because of the long irradiation time required to produce... 

Elution and Breakthrough Characteristics of the Generator. The fractional elution yield and cumulative yield of Rb-82 are shown in Figure 5a,b for 2% saline bolus elutions at a flow rate of 1 ml/sec. Nine 3 ml fractions were collected over 27 sec. Each value is the mean of 3 determinations. Fractions 3-5 contain 70% of the Rb-82 available from the Sr-82 on the alumina column. The total elution yield is about 95% in nine fractions. 

Column 10c contained an unusually large amount of Sr-85 activity of about 2 Ci. To compensate for this heavy loading, a small trapping column of 1.5 ml of alumina was placed down-stream from the main column and the breakthrough was maintained in the 30-40 nCi range. Because of the increased total volume from the addition of the second alumina column, the elution yield of Rb-82 decreased from 78% to 61% in column 10c. 

Figure 5. Fractional elution yield of Rb-82 from an alumina column at a flow rate of 1 mL/s and accumulative yield for nine 3-mL fractions, mean of 3 determinations, (Reproduced with permission from Ref. 21. Copyright 1981, J. Nucl. Med.)...

Elution Yield Measurement. The elution yield is defined as the ratio of the total eluted activity (TEA) measured under the defined experimental conditions described below to the maximum available activity, which is equivalent (taking into account the branching ratio) to the total parent activity (Q) present on the column at the time of elution. Different methods were... 

Figure 3. Typical curve of Au-195m elution yield versus elution flow rate.

A most important characteristic of a generator other than the elution yield of the daughter is the extent of contamination of the eluate by the parent nuclide. This contamination is defined as breakthrough which can be calculated as shown in equation (14). Breakthrough is dependent on the distribution... 

Y (D) is a function of the flow rate D and involves the elution yield and the decay rate of the daughter in the transfer tubing. 

The fundamental conclusion of this study is that the optimal clinical elution flow rate in the case of continuous elution of a short-lived radionuclide from a perfusion generator does not necessarily correspond to the conditions for maximum elution yield. This conclusion was confirmed by experimental studies with various short-lived radionuclide generators such as the Hg-195m/Au-195m and Sr-82/Rb-82 systems. 

Further elution of MSC-1 after standard elution yielded fraction F2. e One-tenth scale standard parfait column using 14C-glycine. Eluates and drying-conditioning washes from individual ion-exchange resins were pooled Teflon, MSC-1, and A-162 denote radioactivity on these beds after elution (see text). 

---