Standard addition method

Standard Addition Method

The Standard Addition Method is a quantitative analytical technique used in Analytical Chemistry to determine the concentration of a substance (Analyte) in an unknown sample by comparison to a set of samples with known concentrations of the substance. This method is particularly useful when the sample matrix affects the analytical signal, making direct comparison with standard solutions inaccurate.

Overview

The principle of the standard addition method involves adding known quantities of the analyte to the unknown sample and measuring the analytical response for each addition. By plotting these responses against the known added concentrations, a calibration curve can be generated. Extrapolating this curve to the x-axis (where the analytical response is zero) gives the negative of the analyte concentration in the original sample.

Procedure

1. A series of aliquots of the unknown sample is prepared.
2. Known quantities of the analyte are added to each aliquot except for one, which serves as a blank.
3. The analytical response (e.g., absorbance, fluorescence) for each aliquot is measured.
4. The responses are plotted against the added concentrations, and a linear regression is performed.
5. The concentration of the analyte in the original sample is determined by extrapolating the linear regression to the point where the analytical response would be zero.

Applications

The standard addition method is widely used in situations where the sample matrix may interfere with the detection of the analyte. Common applications include:

• Environmental Chemistry for the analysis of water pollutants
• Pharmaceutical Chemistry for the determination of drug concentrations in biological matrices
• Food Chemistry for the quantification of additives or contaminants in food products

Advantages

• Minimizes matrix effects since the analyte is measured in the presence of the sample matrix.
• Does not require a calibration curve prepared from standards that are matrix-matched to the sample.
• Useful for complex matrices where it is difficult to prepare matrix-matched standards.

Limitations

• More time-consuming and requires more sample than direct calibration methods.
• Assumes that the matrix effect is constant across the range of analyte concentrations used.
• Linear response of the analytical method over the range of concentrations used is required.

See Also

• Analytical Chemistry
• Calibration Curve
• Matrix Effect