Question

A set of three replicate atomic absorption (AAS) measurements were made from the same standard to determine its limit of detection (LOD) for calcium analysis. The standard was prepared by dissolving 0.020 g of CaCO3 in 1.000 L. What is the LOD if, after blanking the instrument, the three absorbance readings from the standard were 0.101, 0.096, and 0.104?

Answer 1

Limit of detection - The Lowest quantity of a substance that can be distinguished from the blank solution with stated confidence.

or

Minimum concentration of your analyte that can be recognized by your instrument. It is estimated from the mean and standard deviation of the blank.

LoD is the lowest analyte concentration likely to be reliably distinguished from the blank at which detection is feasible.

It is of four types:

1 Instrument detection limit

2 Method detection limit

3 Practical quantification limit

4 Limit of quantification

Instruments give a signal when a blank is measured.

The formula for the Detection limit is as follows:

[[ Detection Limit of instrument = mean of blank values + 3 times of standard deviation of blank values ]]

Here we have three absorbance readings after blanking the instrument which is 0.101, 0.096, and 0.104.

Formula to calculate the mean is

Formula to calculate the standard deviation is:

	=	standard deviation
	=	number of terms
	=	each value
	=	mean value

The calculation part is in the attached image.

Our final answer is 0.110

Which is the limit of the detection of the instrument for the given analyte.