Internal standards (Lecture 20)

Question 1

What is an internal standard?

Answer 1

An internal standard is a known amount of a compound different from the analyte that is added to the unknown.

Question 2

How do we determine how much analyte is present?

Answer 2

Signal from the analyte is compared to signal from the internal standard.

Question 3

Why is the internal standard chemically similar to the analyte?

Answer 3

so that uncontrolled effects of the matrix that increase or decrease the analyte signal might have a similar effect on the signal from the standard

Question 4

Where are internal standards useful?

Answer 4

Useful if uncontrolled loss of sample occurs during sample preparation. Useful for analyses in which the quantity of sample analysed or the instrument response varies slightly from run to run.

Question 5

What is the difference between internal standards and standard addition?

Answer 5

Standard addition corrects for systematic errors caused by the matrix.
Internal standards correct random errors caused by run-to-run variation. And the chemically similar internal standard also corrects systematic errors caused by the matrix.

Question 6

How do you calculate response factor (F)?

Answer 6

signal from analyte/conc of analyte = F ( signal from standard/conc of standard)

A(x)/[X]f = F (A(s)/[S]f)