Unweighted linear regression, with errors

Quantitative analysis, A series of 5 aqueous standards, covering the concentration range of interest (10-100 ng ml was used to construct a calibration curve. A typical curve is shown in fig.4 in order to demonstrate the linearity and the precision. The curves were obtained by unweighted least squares linear regression based on previous research, which indicated that this type of statistical analysis can be employed with stable isotope labeled internal standards and for a 10-fold range of x-values because the errors associated with the y-values are approximately constant (16). Using the regression line(fig.4) in reverse, a standard error of 1. 2 ng ml could be... 

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