Question

Signals from analytical method give a mean blank of 0.203 mV and standard deviation of 0.052 mV. The quantitation limit of this method is: (1) 2.08 mV; (2) 0.72 mV; (3) 0.723 mV; (4) None of the above

Answer 1

Several approaches for determining the quantitation limit are possible, depending on whether the procedure is a non-instrumentalor instrumental. Approaches other than those listed below may be acceptable.

• Based on the Standard Deviation of the Response and the Slope

The quantitation limit (QL) may be expressed as:

QL =(10*σ)/S

where

σ= the standard deviation of the response

S = the slope of the calibration curve

• Based on Visual Evaluation

Visual evaluation may be used for non-instrumental methods but may also be used with instrumental methods. The quantitation limit is generally determined by the analysis of samples with known concentrations of analyte and by establishing the minimum level at which the analyte can be quantified with acceptable accuracy and precision.

--> As we don't know the slope of the calibration curve, we can use an aproximated approach to this method. Some collegues use LOQ (limit of quantification) as = mean blank value * 10 = ~ 2.03 mV. I would answer option (1) in this case.

Hope this helps!