A Method to Assess Radiochemical Purity of Compounds Measured by Radioimmunoassay

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Abstract
A method is described for assessing radiochemical purity of compounds measured by radioimmunoassay [RIA]. This method is applicable in cases when chromatography is used prior to the RIA proper. In individual fractions of the chromatographic zone containing the compound assayed, both radioactivity (e.g. in dpm) and mass (e.g. in pg) are measured. The measurement of mass is performed using RIA. Radiochemical purity is assumed, if the radioactivity/mass ratio (specific activity) in individual fractions of the zone is constant. The constancy of specific activity is tested statistically using a regression analysis. An RIA of progesterone [P] in a [human] blood plasma pool collected during the follicular phase of the menstrual cycle was used to demonstrate the practical features of the assessment of radiochemical purity. Radiochemically pure P could be obtained only after repeated chromatography. Purification to radiochemical purity resulted in a significantly decreased estimate of P contents in the plasma pool investigated. A value of 344 pg/ml was obtained, in contrast to the value of 422 pg/ml found prior to the repeated chromatography. The former value can be considered an accurate and valid estimate.

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