Question

Describe how the solutions used in standard calibration curves differ from those used in a standard addition curve?

Describe how the concentration of an unknown analyte is found from a standard addition curve?

Why is distilled water used as a calibration blank?

Answer 1

standard calibration curve : In analytical chemistry, a calibration curve is a general method for determining the concentration of a substance in an unknown sample by comparing the unknown to a set of standard samples of known concentration.^[1] A calibration curve is one approach to the problem of instrument calibration; other approaches may mix the standard into the unknown, giving an internal standard.

standard addition curve: The method of standard addition is a type of quantitative analysis approach often used in analytical chemistry whereby the standard is added directly to the aliquots of analyzed sample. This method is used in situations where sample matrix also contributes to the analytical signal, a situation known as the matrix effect, thus making it impossible to compare the analytical signal between sample and standard using the traditional calibration curve approach.

Describing the concentration of an unknown analyte is found from a standard addition curve:

Example standard addition plot. This graph is an example of a standard addition plot used to determine the concentration of calcium in an unknown sample by atomic absorption spectroscopy. The point at zero concentration added Ca is the reading of the unknown, the other points are the readings after adding increasing amounts ('spikes') of standard solution. The absolute value of the x-intercept is the concentration of Ca in the unknown, in this case 1.69E-6 g/mL.

Why is distilled water used as a calibration blank?

Distilled water/deionised water is used in calibration blank for the preparation of standered solutions of known and unknown samples.