Method of Standard Addition

Panoramica

Source: Laboratory of Dr. Paul Bower - Purdue University

The method of standard additions is a quantitative analysis method, which is often used when the sample of interest has multiple components that result in matrix effects, where the additional components may either reduce or enhance the analyte absorbance signal. That results in significant errors in the analysis results.

Standard additions are commonly used to eliminate matrix effects from a measurement, since it is assumed that the matrix affects all of the solutions equally. Additionally, it is used to correct for the chemical phase separations performed in the extraction process.

The method is performed by reading the experimental (in this case fluorescent) intensity of the unknown solution and then by measuring the intensity of the unknown with varying amounts of known standard added. The data are plotted as fluorescence intensity vs. the amount of the standard added (the unknown itself, with no standard added, is plotted ON the y-axis). The least squares line intersects the x-axis at the negative of the concentration of the unknown, as shown in Figure 1.

Figure 1. Graphic representation of method of standard addition.

Procedura

1. Preparing the Reagents

100 ppm standard Al³⁺ solution: Dissolve 0.9151 g aluminum nitrate (Al(NO₃)₃•9H₂O) into a 1-L volumetric flask with DI water.
8HQ solution in 1 M acetic acid (2% wt/vol): Add 2.0 g of 8-hydroxyquinoline to a 100-mL volumetric flask.
Carefully add 5.74 mL glacial acetic acid to the 100-mL flask, then dilute to the mark with DI water. This allows the 8-hydroxyquinoline to dissolve in aqueous phase.
1 M NH
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Risultati

A scan of the excitation wavelength from 335–435 showed the highest absorption at 399 nm, so the excitation monochromator was set for that value. Then the emission scan was performed from 450–550 nm, and the strongest signal was found to be at 520 nm. These are the wavelengths that are used for all of the samples.

Sample

Applicazione e Riepilogo

The method of standard additions is often the technique utilized when accurate quantitative results are desired, used in analytical analysis such as atomic absorption, fluorescence spectroscopy, ICP-OES, and gas chromatography. This is often used when there are other components in the sample of interest that causes either a reduction or enhancement of the absorbance desired for quantitative results. When this is the case, one cannot simply compare the analytes signal to standards using the traditional calibration curve a

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