Analytical Sciences

Detection Limit Estimated from Slope of Calibration Curve: An Application to Competitive ELISA

Yuzuru HAYASHI,* Rieko MATSUDA,* Katsutoshi ITO,** Waka NISHIMURA,** Kazuhiro IMAI,*** and Masako MAEDA*

*National Institute of Health Sciences, 1-18-1 Kami-Yoga, Setagaya, Tokyo 153-8501, Japan
**School of Pharmaceutical Sciences, Showa University, Tokyo 142-8555, Japan
***Research Institute of Pharmaceutical Sciences, Musashino University, Nishitokyo 202-8585, Japan

This paper theoretically derives a general rule that while the slope of the semi-logarithmic plot (Y vs. log X) of a calibration curve varies depending on analyte concentration, X, the slope takes a specific value at the detection limit (L_D). This rule holds good irrespective of the shape of the calibration curve (linear or non-linear) and in this paper, is applied to competitive ELISA (enzyme linked immunosorbent assay). The following relationship is deduced: slope of log-dose B/B₀ at L_D = [relative standard deviation (RSD) of blank responses] ÷ 0.13. The L_D obtained from the above-mentioned slope corresponds to the dose at which the RSD of dose estimates is 0.3 (= 30%). A commercial kit for 17α-hydroxyprogesterone is taken as an example.

J-STAGE: View this article in J-STAGE