Here is where the other LOD and LOQ techniques can be useful. If the results meet performance requirements, the LOD and LOQ have then been shown to be correct. The values calculated above should be considered estimates of the LOD and LOQ, and must be demonstrated by injecting multiple samples (e.g., n = 6) at the LOD and LOQ concentrations. In a similar manner, LOQ = 10 x 0.4328 / 1.9303 = 2.2 ng/mL. I would probably round these up to 1 ng/mL and 2.5-3.0 ng/mL. The slope of the calibration curve is listed at the bottom, labeled as the concentration coefficient. The 4 th item down, the standard error, is the standard deviation about the regression line for the entire data set, which I am using as σ for the ICH technique. On the upper right, I have listed some of the key data presented in the regression report. I’ve chosen to use the linear regression data that can be obtained in Microsoft Excel. These data can be analyzed by a linear regression algorithm, such as is included in most data system software. In Figure 1, I’ve listed a set of concentrations (ng/mL) and signal (area) for a calibration curve. I think the standard error (SE) method is the simplest, because it is easily obtained from a regression analysis of the calibration curve. Or (2) from the standard deviation of the calibration curve that contains samples in the range of the LOQ this can be measured as the standard error of the calibration curve or the standard deviation of the y-intercept. σ can be determined in one of two ways: (1) Based on the standard deviation of the blank, where blank samples are run and the standard deviation is determined this is equivalent to the standard deviation of the noise (or root-mean-square, RMS, of the noise). S is estimated from the slope of the calibration curve for the analyte. Here σ is the standard deviation of the response and S is the slope of the calibration curve. I’ve summarized some data in Figure 1 that will be useful for the present discussion. The ICH indicates that LOD (which they call DL, the detection limit) can be calculated as LOD = 3.3σ / S, and the limit of quantification (which they call QL, the quantitation limit) LOQ = 10σ / S. In HPLC Solutions #125 we looked at the first two techniques. Recall that a simple definition of the LOD is something like, “I’m sure there is a peak there for my compound, but I cannot tell you how much is there.” For the LOQ, we might say, “I’m sure there is a peak there for my compound, and I can tell you how much is there with this much certainty.” based on the standard deviation of the response and the slope.As we saw in HPLC Solutions #125, the International Committee on Harmonization (ICH, 1) lists three ways to determine the limit of detection (LOD) or limit of quantification (LOQ):

Elisa curve on graphpad prism