Question

What are the main reasons that will justify the utilization of standard addition (internal calibration) in quantitative analysis and, how is it done?

Answer 1

What are the main reasons that will justify the utilization of standard addition (internal calibration) in quantitative analysis and, how is it done?

Answer:

The principle of using an internal standard (IS) is that if the instrument (or sample introduction) affects the analyte response, it will affect the response of the IS by the same proportion. The method of Standard addion is a Qualatattive analysis.The method of internal standards is used to improve the precision of quantitative analysis.An internal standard is a known concentration of a substance that is present in every sample that is analyzed. Internal standards can be used with either the calibration curve or standard addition methods, although the former is probably more common.

The purpose of the internal standard is to behave similarly to the analyte but to provide a signal that can be distinguished from that of the analyte. Ideally, any factor that affects the analyte signal will also affect the signal of the internal standard to the same degree. Thus, the ratio of the two signals will exhibit less variability than the analyte signal.

Internal standards are often used in chromatography, mass spectroscopy and atomic emission spectroscopy. They can also be used to correct for variability due to analyte loss in sample storage and treatment.

Using the internal standard in the calculations

The principle of the internal standard is that, since it is all solutions at the concentration, any variation in its response must mean something has happened in the process (eg low injection volume) and this will have affected the analyte response as well. If the IS response is down by 10%, then so presumably is the analyte’s.

The simplest way to correct for these variations is not to scale up or down the analyte response based on the IS change, but simply to calculate the ratio of the response of the two.

Ratio = Analyte Respose/ Internal Standard Response.

CHOOSING A SUITABLE INTERNAL STANDARD

The internal standard is NOT the analyte, but a totally different species. It is not, however, a matter of simply grabbing whatever chemical happens to be at hand and throwing it in as the internal standard. The internal standard chose the following three category.

1. The chosen compound cannot be present in the sample.
2. The chosen compound should have similar physical and chemical properties to the analytes.
3. The chosen compound should be readily available