Confidence interval for calibration curve. To use a calibration curve based on n points, we measure a new value of y and calculate the corresponding value of x. The one-standard deviation uncertainty in x, sx, is given by Equation 4-27. We express a confidence interval for x, using Student's t:
Confidence interval = x ± tsx
where t is taken from Table 4 - 2 for n - 2 degrees of freedom.
A calibration curve based on n = 10 known points was used to measure the protein in an unknown. The results were protein = 15.22 (± 0.46) μg, where sx = 0.46 μg. Find the 90% and 99% confidence intervals for protein in the unknown.