Question

Suppose that you carry out an analytical procedure to generate a linear calibration curve like that shown in Figure 4-13. Then you analyse an unknown and find an absorbance that gives a negative concentration for the analyte. What might this mean?

Short answer

When a negative concentration value is beyond an experimental error, there must be some errors in the analysis procedure. The reason is true for a value above 100% and it may be due to the extrapolation of the calibration curve.

Step-by-step solution

Linear Calibration Curve

The equation of a linear calibration line is$\mathbf{y}\left(\mp s_y\right)\mathbf{=}\left[m\left(\pm u_m\right)\right]\mathbf{x}\mathbf{+}\left[b\left(\pm u_b\right)\right]$, where y is the corrected absorbance.

Corrected absorbance =observed absorbance˗˗blank absorbance.

The reason for obtaining a negative concentration while analyzing an unknown analyte.

The reasons for obtaining a negative concentration are:

• A negative value implies zero experimental error. If a negative value is obtained, it says that no detectable analyte is present.

• When a negative concentration value is beyond an experimental error, there must be some errors in the analysis procedure.

• The above reason is true for a value above 100% and it may be due to the extrapolation of the calibration curve.